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Matteo GIACOPINI

Professore Ordinario
Dipartimento di Ingegneria "Enzo Ferrari"

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Pubblicazioni

2024 - Investigation on the Low Cycle Thermal Fatigue of a Hybrid Power Unit Transmission Clutch [Relazione in Atti di Convegno]
Barbieri, Saverio Giulio; Mangeruga, Valerio; Piergiacomi, Andrea; Giacopini, Matteo
abstract

A numerical methodology for the thermal-structural assessment of a clutch for a high-performance hybrid power unit is proposed. Clutches are commonly adopted in internal combustion engines to connect the crankshaft to the gearbox. However, the specific clutch under investigation is employed for the coupling between the electric motor and the engine transmission primary shaft in a P2 hybrid architecture. In this specific configuration, the clutch may be activated and deactivated frequently to maximise the efficiency of the power unit depending on the required output torque and on the particular control strategy developed. As a consequence, the thermal loads insisting on the clutch may differ with respect to the ones encountered in a typical full combustion architecture. The results of the presented research show the great influence of the thermal deformation on the stress state of this component, and the onset of possible failure due to low cycle fatigue phenomena is detected. In addition, the influence of different modelling strategies is considered.

2024 - Numerical modelling of the cavitation damage in the conrod big end bearing of a high-performance internal combustion engine [Relazione in Atti di Convegno]
Renso, Fabio; Giacopini, Matteo; Bertocchi, Enrico; Dini, Daniele
abstract

In this contribution a complementarity formulation for the solution of the elastohydrodynamic problem in the presence of cavitation is employed to investigate the tribological behaviour of the conrod big end bearing in a high-performance internal combustion engine. The continuous effort towards higher engine efficiencies, poses new challenges related to the increased specific loads to which engine components are subjected. In particular, the connecting rod big end bearing is subjected to both high loads and high relative velocity of the mating surfaces. Therefore, its tribological behaviour plays a crucial role. In fact, on one side, possible asperity contact pressures can produce wear of the interested components, and on the other side, a parallel possible cavitation of the lubricant can additionally damage the mating interfaces. Unfortunately for quantifying the cavitation damage, a universally established theory does not exist, even if it is well accepted that it is related to the sudden rapid implosion of the vapour bubbles near the surface. The precise investigation of this damage mechanism is usually neglected in big end bearing analysis since the implosion of the bubbles is difficult to quantify and it is not a standard output of any commercial software. Thus, in this work, a quantitative index previously proposed is reviewed and adopted to quantify the cavitation damage in a connecting rod big end bearing.

2023 - A numerical algorithm to model wall slip and cavitation in two-dimensional hydrodynamically lubricated contacts [Articolo su rivista]
Cam, M. Y.; Giacopini, M.; Dini, D.; Biancofiore, L.
abstract

Hydrodynamic lubrication takes a fundamental role in mechanical systems to reduce energy losses and prevent mechanical breakdown. The analytic instrument usually adopted to describe hydrodynamic lubrication is the Reynolds equation, which in its simplest statement for monophase lubricants and with assuming no fluid slip at the walls, is a linear equation in the hydrodynamic pressure. However, this classical linear Reynolds equation cannot reflect all the lubricant characteristics in engineered surfaces (e.g. superhydro(oleo)phobic surfaces and textured surfaces). In these cases, the effect of two critical factors, such as wall slip and cavitation, need to be considered, introducing non-linearities in the system. In order to tackle this issue, a modified two-dimensional Reynolds equation is introduced, able to capture both the cavitation presence, via a complementary mass-conserving model, and wall slippage, starting from the multi-linearity description introduced by Ma et al. (2007). In addition, an alternative model for the slippage at the wall is proposed by modifying the multi-linearity wall slip model to improve accuracy and computational cost. In this new model, the possible slip directions are limited to three, separated by equal angles, with the slip occurring only along the first direction, and the other directions, then, used to iteratively adjust the direction of slippage, until a suitable convergence criterion is satisfied. The proposed mathematical model is validated versus results available in literature with tests performed on (i) journal bearings, (ii) slider bearings, (iii) squeeze dampers, and (iv) surface textured bearings. By conducting these tests, the proposed alternative wall slip model is proved to be up to one order of magnitude more computational efficient than the original multi-linearity wall slip model.

2023 - Development of an Experimental/Numerical Validation Methodology for the Design of Exhaust Manifolds of High Performance Internal Combustion Engines [Articolo su rivista]
Lorenzini, Mariano; Giulio Barbieri, Saverio; Mangeruga, Valerio; Giacopini, Matteo
abstract

Several typical failure modes in the exhaust manifold of an internal combustion engine are commented on. In particular, thermal loading and the related thermal fatigue damage mechanism are addressed. The component under investigation is a cast exhaust manifold including the turbine involute. Finite Element simulations are performed, and a numerical methodology is presented to interpret and understand the observed failures, with the aim of developing a useful tool to virtually validate the component, before the manufacturing phase. The Finite Element analysis closely mimics the experimental validation procedure that considers several heating and rapid cooling cycles to simulate typical engine operating conditions. A static mechanical characterization at high temperatures of the materials involved is carried out, aimed at identifying a suitable alloy and its mechanical characteristics useful for feeding the numerical models. The developed design methodology proposes a damage criterion for thermal fatigue investigation, considering the elastoplastic behaviour of the material when subjected to high temperature cycles. In particular, the accumulated equivalent plastic strain range for a single thermal cycle (ΔPEEQ) is used, following the Ferrari expertise. The methodology appears to be well correlated with the experimental evidence, thus limiting the number of tests necessary for the approval of the component.

2023 - Effect of the Thermal Mean Stress Value on the Vibration Fatigue Assessment of the Exhaust System of a Motorcycle Engine [Articolo su rivista]
Barbieri, Saverio Giulio; Mangeruga, Valerio; Giacopini, Matteo; Callegari, Marco Severino; Bagnoli, Leonardo
abstract

The exhaust manifold of a high-performance motorcycle engine is subjected to combined thermal and vibrational loadings. In this research, the whole fatigue assessment of an exhaust manifold is addressed. First, a classic low-cycle fatigue analysis is performed. Then, a specific methodology for determining the fatigue cycle of components subjected to thermal and vibration loadings is developed and presented in a way that possible damages can be evaluated. The results are post-processed and the damage caused by fatigue cycles is computed referring to the Wöhler curve of the material using the Dirlik approach.

2023 - Finite Element Analysis of the Influence of the Assembly Parameters on the Fretting Phenomena at the Bearing/Big End Interface in High-Performance Connecting Rods [Articolo su rivista]
Renso, Fabio; Barbieri, Saverio Giulio; Mangeruga, Valerio; Giacopini, Matteo
abstract

Fretting fatigue is a well-known and dangerous damage mode that occurs on the mating surfaces of mechanical components, mainly promoted by a combination of stress distribution, contact pressure distribution, and relative sliding (micro)motion between the surfaces. However, predicting this mechanism is challenging, necessitating specific studies for each assembly due to variable influences. This article presents a methodology for evaluating fretting fatigue damage at the contact between a titanium connecting rod big end and the bearing, adopting the Ruiz parameter as a quantifying damage index. For this purpose, a thermal-structural finite element model is prepared. In particular, the machining and assembly of the split conrod big end are simulated, considering thermal effects. A full engine cycle is first simulated, and results are used for identifying critical instants to be considered for accurate yet computationally efficient calculations. The dependence of fretting fatigue on three factors is studied: bearing crush, bolts tightening torque, and friction coefficient between the big end and the bearing. In summary, the damage increases with a higher crush and friction, while tightening torque has marginal effects. Following a 20% increase in crush height, a corresponding 10% rise in the Ruiz parameter is observed. Conversely, reducing the crush height by 20% leads to an approximately 8% decrease in the Ruiz parameter. When the influence of the bolt preload is taken into account, only a marginal 1% increase of the Ruiz parameter is recorded despite a 30% rise in preload. Evaluating the impact of the friction coefficient on the Ruiz parameter reveals an almost linear relationship. These findings suggest that adjusting the screw preload can enhance the hydrodynamic behavior of the bearing without exacerbating fretting. Furthermore, exploiting the linear correlation between Ruiz and the friction coefficient allows for the generalization of results obtained with specific coefficient values. This methodology can, therefore, serve as a valuable reference for adjusting different variables during the initial design phases of a four-stroke internal combustion engine’s dismountable connecting rod.

2023 - Influence of the crankshaft dynamic phenomena on the fatigue behaviour of a transmission chain in a hybrid power unit [Relazione in Atti di Convegno]
Mangeruga, Valerio; Renso, Fabio; Raimondi, Francesco; Barbieri, Saverio Giulio; Giacopini, Matteo
abstract

This paper is part of an activity related to a specific hybridization process for an existing and commercialized motorcycle engine. The electric motor is mechanically connected to the engine using the original valvetrain transmission chain leading to a P0 hybrid architecture. The aim of this work is to analyse the structural behaviour of the chain now used as torque transmission device. Although on one side the maximum torque of the electric motor determines a stress state on the chain below its fatigue limit, on the other side, the dynamic behaviour of the system strongly influences the maximum stress on the chain. In fact, the main source of load on the chain derives from the torsional oscillation of the system. Engines rotational speed irregularity can be easily estimated through common analytical approaches which consider the contribution of combustion and inertial forces on the instantaneous torque produced by the crank mechanism and the overall inertia of the moving parts. However, more detailed lumped-parameters and Multibody dynamic models are here developed in order to estimate the actual instantaneous engine speed taking into account the arising of possible high order vibration phenomena. Specifically, the influence of the torsional vibration behaviour of the internal combustion engine isinvestigated on the resulting stress on the chain. Finally, the structural chain integrity is assessed by performing a fatigue analysis considering the actual operating conditions.

2023 - Influence of the pressure gradient during combustion on the fatigue behaviour of an internal combustion engine piston [Relazione in Atti di Convegno]
Bianco, Luigi; Barbieri, Saverio Giulio; Mangeruga, Valerio; Giacopini, Matteo; Perez, Fabrizio Fontana
abstract

In recent years, increasing demands for higher power density, lower emission and lower fuel consumption drive the research on internal combustion engines towards the adoption of innovative types of combustion like Homogeneous Charge Compression Ignition, Spark Controlled Compression Ignition and Gasoline Direct Injection Compression Ignition. All these systems exhibit aggressive combustion strategies and, as a consequence, a high-pressure gradient can be encountered in the combustion chamber at the early beginning of the combustion process. On one hand, the specific value of the pressure gradient marginally affects the kinematic analysis of the engine piston and its primary axial translational motion. On the other hand, it can possibly affect its secondary motions, namely piston transversal motion and piston tilting. Therefore, to investigate the influence of the pressure gradient, a numerical approach capable to capture the whole piston dynamic behaviour is mandatory. In this contribution, different pressure profiles are taken into account and then employed in different Multibody analyses to understand the influence of the pressure gradient on the piston secondary motions. In particular, three different pressure profiles exhibiting an increasing gradient, but with the same total heat released, are considered. In addition, three different radial clearances between the piston and the cylinder liner are simulated for each pressure profile. So that, a total of nine Multibody analyses are performed. The results are then post-processed and the Dang Van high cycle fatigue safety factor contour plot on the piston is obtained for each configuration. The results show a dependency of the fatigue life of the piston on the pressure gradient, albeit no detrimental structural issues are detected for the different configurations analysed. The presented methodology represents a useful tool for the structural assessment of pistons when a first original safe combustion strategy is modified towards more efficient ones characterized by pressure profiles presenting a higher gradient.

2023 - Investigation via Finite Element Analysis of the Influence of Boiling on the Thermo-Structural Behavior of the Engine Head of a High-Performance Combustion Engine [Relazione in Atti di Convegno]
Piergiacomi, Andrea; Barbieri, Saverio Giulio; Renso, Fabio; Mangeruga, Valerio; Giacopini, Matteo
abstract

This paper presents a numerical methodology for studying the effect of boiling on the structural behavior of high-performance internal combustion engines. Boiling occurs when the portion of engine coolant in contact with hot walls reaches high temperatures and vapor bubbles form. While incipient vaporization of the coolant can promote additional cooling, excessive vapor can act as an insulator and lead to potentially dangerous high temperatures in the engine. Boiling is typically analyzed using Computational Fluid Dynamic Analyses, which are usually computationally intensive. In this study, the authors propose a Finite Element methodology that combines semi-empirical formulations, less demanding than Computational Fluid Dynamic models, with thermal Finite Element simulations to detect and manage boiling. Two different empirical formulations for boiling were employed, proposed by Garro and Chen respectively, and their results were compared. Three thermal analyses were conducted: the first neglected the effect of boiling, which leads to results inconsistent with the assumption of single-phase fluid, while in the second and third simulations, the occurrence of boiling and its effects were managed using the Garro and Chen formulations. The results showed a significant decrease in wall temperatures around the regions where boiling was detected and a parallel reduction of the thermal gradients inside the component. The two semi-empirical approaches for boiling estimation produced similar results, suggesting their substantial equivalence. Then, the temperature fields obtained were employed in structural Finite Element Analyses to evaluate the effects of boiling on the fatigue life of the engine head. In the structural analyses, the more uniform thermal field leads to a reduction of thermal deformations and to a different stress state, affecting the safety factor distribution. This methodology has the potential to be a suitable tool for detecting boiling and its effect during the early stages of engine design.

2023 - Numerical Investigation of the Dynamic Effects on the Fatigue Behaviour of a Transmission Chain in a Hybrid Power Unit [Articolo su rivista]
Mangeruga, Valerio; Renso, Fabio; Barbieri, Saverio Giulio; Giacopini, Matteo; Raimondi, Franceco
abstract

2023 - Oil jets piston cooling: A numerical methodology for the estimation of heat transfer coefficients and optimization of the piston temperature field through a genetic algorithm [Articolo su rivista]
Renso, Fabio; Giacopini, Matteo; Barbieri, Saverio Giulio; Mangeruga, Valerio
abstract

High-efficiency internal combustion engines need specific methodologies to be developed for the design improvement of the components. Predicting and reducing the thermal loadings on the parts are critical tasks to be addressed. This contribution focuses on the thermal management of the piston through oil jets. The operating temperature of the piston deeply affects its thermo-mechanical behavior, thus possibly jeopardizing the structural integrity of the component. The design of piston cooling jets is usually addressed through Computational Fluid Dynamics, which can guarantee accurate results, usually at a high computational cost. In this contribution, a faster tool is derived to grasp the effect of the cooling jets on the temperature of the piston. Empirical correlations are applied to predict the instantaneous heat transfer coefficients on the piston. The reciprocating motion of the piston is considered since it affects the interaction between the surface and the oil jets. Instantaneous coefficients are cycle-averaged and used to estimate the temperature of the piston through a Finite Element thermal analysis. Finally, an optimization code is developed to find the best jet configuration capable to minimize the temperature of the piston. This methodology is a powerful tool to select the optimal oil jet nozzles for piston cooling.

2022 - Influence of the thermal deformation on the lubricating performance of the piston-gudgeon pin interface in an internal combustion engine [Articolo su rivista]
Bianco, L.; Barbieri, S. G.; Mangeruga, V.; Giacopini, M.; Capoccia, G.
abstract

This contribution describes a methodology to evaluate the influence of bellmouth profiles on the elastohydrodynamic behaviour of the contact interface between the gudgeon pin and the piston of a high-performance internal combustion engine. First, a thermo-mechanical simulation is performed to evaluate the piston bosses thermal strains. Consequently, a Multibody elastohydrodynamic model is set up to evaluate the tribological behaviour of this lubricated interface considering a perfectly cylindrical shape of the piston bosses and their thermal deformation. Then, a preliminary bellmouth profile is adopted and a second Multibody model is performed. Nevertheless, the results, together with issues encountered analysing some tested pistons, suggest that modifications of piston bosses have to be introduced. Finally, an optimised bellmouth geometry is proposed and analysed.

2022 - Structural Analysis of the Forming Process for Hairpin Windings for Electric Motor Applications: Torsional-Flexural Instability Issues [Relazione in Atti di Convegno]
Barbieri, S. G.; Mangeruga, V.; Giacopini, M.; Mantovani, S.
abstract

Electric motor manufacturing technology is evolving due to automotive transport development. Besides, environmental issues and the need of CO2 emission reduction have led to an increasing demand for electric drives efficiency. Permanent magnet synchronous machines are widely employed for traction systems and distributed windings produced by using insert techniques are growing in popularity. These methods require preformed wires such as the well-known hairpin shape. The advantages of hairpins are discussed in the pertinent literature. In the present paper, the manufacturing process of a hairpin is investigated by analysing its mechanical behaviour via Finite Element simulations. In fact, many problems might occur during the forming of a hairpin, depending on the shape required. In particular, this study aims at describing the influence of the geometry of the wire cross-section on the resulting final shape of the formed hairpin. Suitable ranges of geometrical and manufacturing parameters are identified to avoid torsionalflexural instabilities.

2022 - Towards an analytical model of a pin-lug connection [Articolo su rivista]
Strozzi, A.; Giacopini, M.; Bertocchi, E.; Mantovani, S.; Baldini, A.
abstract

A preliminary analytical model of a pinned connection is carried out. The lug is idealized in terms of a curved beam, and the presence of an initial clearance between the pin and the lug is accounted for. This model rationalizes the nonlinear and linear mechanical responses of the structure; a coefficient summarizing the effect of the load, Young’s modulus, and initial clearance, is derived; this coefficient is kindred to that computed according to the theory of elasticity. An enhanced load factor that accounts for the lug geometry is proposed. Two loci of local maximum stress occur. One point is the stress at the centre of the pin-lug contact, whereas the other point falls laterally along the lug bore border. While the central stress is forecast by the analytical model with reasonable accuracy, the analytical stress computed laterally is too approximate to be employed in engineering applications. Despite this drawback, a better understanding of the load transfer mechanism within the pinned connection is achieved, by particularly rationalizing the nonlinear, progressive character of the pin-lug contact, and the usefulness of the load factor.

2021 - Synergy between topology optimization and additive manufacturing in the automotive field [Articolo su rivista]
Mantovani, Sara; Barbieri, SAVERIO GIULIO; Giacopini, Matteo; Croce, Alessandro; Sola, Antonella; Bassoli, Elena
abstract

This article purposes on developing and on re-interpreting the numerical results of a topology optimization for a structural component built via additive manufacturing. A critical appraisal of the optimization results is presented by modeling the feasible component with a holistic approach that merges structural and manufacturing requirements. The procedure is expected to provide a design guideline for similar applications of practical relevance, toward an increase of the right-first-time parts that is required to bring additive manufacturing to its full competitiveness. Topology optimization of a steering upright for a Formula SAE racing car was performed by targeting weight minimization while complying with severe structural constraints, like global and local stiffness performance. Cornering, bumping and braking vehicle conditions were considered. The optimization constraints were evaluated via finite element analysis on a reference component, where the loading conditions were retrieved from telemetry data. The reference part was manufactured by computer numerical control machining from a solid aluminum block. Spurred by the interpretation of the topology optimization predictions, a new upright geometry was designed and validated by calculating its stress field and the possible occurrence of Euler buckling. The new upright was 9% lighter than the reference component. The new geometry was analyzed according to Design for Additive Manufacturing principles to choose the orientation on the build platform and the supports’ location and geometry. The part was successfully manufactured and proved consistent with the application.

2021 - The Effects of the Specific Material Selection on the Structural Behaviour of the Piston-Liner Coupling of a High Performance Engine [Relazione in Atti di Convegno]
Barbieri, Saverio Giulio; Mangeruga, Valerio; Giacopini, Matteo
abstract

The materials commonly employed in the automotive industry are various and depend on the specific application field. For what concern the internal combustion engines the choice is guided by the thermomechanical performance required, technological constraints and production costs. Actually, for high-performance engines, steel and aluminium are the most common materials selected for the piston and the cylinder liner manufacturing. This study analyses the effect of possible material choice on the interaction between piston and cylinder liner, via Finite Element analyses. A motorcycle engine is investigated considering two possible pistons: one (standard) made of aluminium and one made of steel. Similarly, two possible cylinder liners are considered, the original one made of aluminium and a different version made of steel obtained by simply thinning the aluminium component in order to obtain two structurally equivalent components. In particular, four possible combinations of coupling between piston and cylinder liner are identified, derived from the two variants of applied materials. The components theoretically necessary for the Finite Element model are the engine head, the engine block, the bolts, the gasket, the upper part of the crank mechanism and the cylinder liner. Nevertheless, a simplified methodology is employed to reduce the computational effort. This analysis makes it possible to evaluate gap and interference with respect to the material choice. A first proposal of the barrel shape and ovality of the steel piston is obtained starting from the original aluminium piston and the thermal field involved in the analysis. Besides, the presented methodology consists of a useful tool to estimate the stress field and the fatigue safety factor of the components involved. The results obtained with this methodology can guide the definition of the correct piston profile, temperature field and stress distribution estimation, as a function of the specific materials employed for piston-liner coupling.

2020 - A simplified finite element methodology for the structural assessment of an engine piston under dynamic loadings [Relazione in Atti di Convegno]
Barbieri, Saverio Giulio; Bianco, Luigi; Mangeruga, Valerio; Giacopini, Matteo
abstract

The piston slap strongly affects the structural integrity of engine pistons. This phenomenon is caused by the dynamic effects of the piston secondary motions, both horizontal translation and tilting. This occurrence amplifies the contact forces between the piston and the cylinder liner if compared to the ones calculated by using simple kinematic analysis. A numerical approach is therefore mandatory. This paper presents a numerical methodology to predict the influences of piston secondary motions on the piston fatigue life. A combined Multy-Body/FEM strategy is developed to obtain truthful forecasts saving computational effort. First, Multi-Body simulations are performed to evaluate the piston secondary motions and the loadings involved. The most critical instants are retrieved and equivalent lateral accelerations are derived in order to prepare simplified quasi-static Finite Element models. Then, the stress field and the resulting fatigue safety factor distribution of the piston are obtained. The methodology reveals itself to be a useful tool to predict the fatigue life of pistons capable of limiting the computational effort and supporting the dimensioning of engine components during the early stages of the design process.

2020 - Experimental Measurement of Roughness Data and Evaluation of Greenwood/Tripp Parameters for the Elastohydrodynamic Analysis of a Conrod Small-End/Piston Pin Coupling [Articolo su rivista]
Ferretti, Andrea; Giacopini, Matteo; Dini, Daniele; Fantoni, Stefano
abstract

For the investigation of the tribological behavior of lubricated contacts, the choice and the calibration of the adopted asperity contact model is fundamental, in order to properly mimic the mixed lubrication conditions. The Greenwood/Tripp model is extensively adopted by the commercial software commonly employed to simulate lubricated contacts. This model, based on a statistic evaluation of the number of asperities in contact and on the Hertzian contact theory, has the advantage of introducing a simple relationship between oil film thickness and asperity contact pressure, considerably reducing the simulation time. However, in order to calibrate the model, some non-standard roughness parameters are required, that are not available from commercial roughness measuring equipment. Standard values, based on some limited experiences, are typically used, and a limited literature can be found focusing on how to evaluate them, thus reducing the predictivity of the model. In this contribution, the roughness profile of the surfaces of the conrod small-end and the piston pin of a high performance motorbike engine are measured, adopting an optical measurement equipment. An algorithm is developed in order to properly evaluate the Greenwood/Tripp non-standard roughness parameters and set an elastohydrodynamic analysis of the lubricated coupling. A complementarity form of the Reynolds equation capable of handling the cavitation problem is coupled with both Greenwood/Tripp theory and with an alternative complementarity formulation of the asperity contact problem. The results obtained adopting the two different models are critically discussed, comparing them with empirical evidences provided by small-end/piston pin coupling failures, occurred in a severe running condition test at an early stage of the design process of the engine.

2020 - Investigation on the Dynamic Behaviour of a Torque Transmission Chain for an Innovative Hybrid Power Unit Architecture [Articolo su rivista]
Mangeruga, V.; Giacopini, M.; Barbieri, S.; Russo, M.
abstract

In this contribution, the mechanical torque transmission between the Electric Motor (EM) and the Internal Combustion Engine (ICE) of a P0 architecture hybrid power unit is analysed. In particular, the system is made up of a brand new, single-cylinder 480cc engine developed on the basis of the Ducati 959 Panigale V90 2-cylinders engine. The thermal engine is assisted by a custom electric motor (30 kW), powered by a Li-Ion battery pack. The Ducati 959 Panigale engine is chosen because of its high power-to-weight ratio, and for taking advantage of its V90 2-cylinders layout. In fact, the proposed hybridization process considers to remove the vertical engine head and to replace it by the electric motor directly engaged to the crankshaft using the original valvetrain transmission chain, thus achieving a very compact package. This solution could be suitable for many V-type engines and it aims to obtain a small hybrid power unit for possible motorcycle/small vehicle applications. The original timing chain object of this study is a silent chain, which is commonly employed as a transmission component in hybrid power units because it can operate at high speeds transmitting high loads and ensuring noise reduction. For this reason, the aim of this study is to assess the possibility of using the original chain to couple the EM and the ICE. This investigation allows the replacing of the minimum number of components during the hybridization process leading to a real plug&go solution. Therefore, the mechanical behaviour of the chain is investigated performing a dynamic analysis of the whole crank mechanism. In particular, the original twin cylinders model considering the original valvetrain system is compared with the single cylinder model engaged with the EM. The dynamic analysis provides the maximum load on the single chain link in both configurations, allowing the evaluation of a relative fatigue safety factor.

2019 - A Simplified Methodology for the Analysis of the Cylinder Liner Bore Distortion: Finite Element Analyses and Experimental Validations [Relazione in Atti di Convegno]
Barbieri, Saverio Giulio; Giacopini, Matteo; Mangeruga, Valerio; Bianco, Luigi; Mastrandrea, Luca Nicolò
abstract

Advances in modern engines are becoming more and more challenging. The intense increase of thermal and mechanical loads, as a consequence of a higher power density, requires the improvement of the main couplings encountered between moving engine components. In this scenario, the cylinder liner/piston coupling plays a crucial role in terms of engine performance and durability, especially with regards to pollution emission and friction reduction. In this paper a numerical methodology is proposed, which aims at simplifying the Finite Element evaluation of the cylinder liner bore distortion in an eight-cylinder V-type four stroke turbocharged engine. Finite Element simulations are performed to obtain a virtual approval of the component geometry, in advance with respect to the component manufacturing. In particular, preliminary Finite Element analyses are developed which accurately follow the experimental procedure, where a single engine bank is coupled with a simplified test engine head. The Finite Element model is properly tuned in order to obtain the same cylinder liner distortion registered by experimental measurements. Further Finite Element analyses, both thermal and thermo-mechanical, are then performed to evaluate the cylinder liner distortion considering the actual engine head. In order to speed up the analyses, the engine head, the gasket, and the bolt tightening are subsequently substituted by pressure distributions mimicking the actual contact interactions. The methodology reveals itself to be well correlated with the experimental evidences and with the complete Finite Element model of the engine bank thus consisting in a useful tool for reducing the time necessary for the component approval. © 2019 SAE International and © 2019 SAE Naples Section. All rights reserved.

2019 - A finite element numerical methodology for the fatigue analysis of cylinder liners of a high performance internal combustion engine [Relazione in Atti di Convegno]
Barbieri, S. G.; Mangeruga, V.; Giacopini, M.; Laurino, C.; Lorenzini, M.
abstract

In this paper a numerical methodology is proposed, which aims at predicting the fatigue behaviour of engine cylinder liners in an eight-cylinder V-type four-stroke turbocharged engine. A preliminary kinematic and dynamic study of the crank mechanism is fulfilled in order to properly identify the load cycle that involves the cylinder liner. Finite Element analyses, both thermal and thermo-mechanical, are performed to evaluate the stress and the strain of the component. In particular, non-linear models are developed to mimic the piston-liner interaction when subjected to different loading conditions. A simplified approach is proposed in order to reduce the computational effort of the simulations. FEM results are then processed employing the multiaxial Dang Van fatigue criterion.

2019 - Design of a Hybrid Power Unit for Formula SAE Application: Packaging Optimization and Thermomechanical Design of the Electric Motor Case [Articolo su rivista]
Mangeruga, V.; Giacopini, M.; Barbieri, S. G.; Berni, F.; Mattarelli, E.; Rinaldini, C.
abstract

This paper presents the development of a parallel hybrid power unit for Formula SAE application. In particular, the system is made up of a brand new, single-cylinder 480 cc internal combustion engine developed on the basis of the Ducati "959 Superquadro" V90 2-cylinders engine. The thermal engine is assisted by a custom electric motor (30 kW), powered by a Li-Ion battery pack. The performance of the ICE has been optimized through CFD-1D simulation (a review of this activity is reported in a parallel paper). The main design goal is to get the maximum amount of mechanical energy from the fuel, considering the car typical usage: racing on a windy track. The Ducati "959 Superquadro" engine is chosen because of its high power-to-weight ratio, as well as for its V90 2-cylinder layout. In fact, the vertical engine head is removed and it is subsequently replaced by the electric motor directly engaged to the crankshaft using the original valvetrain transmission chain, thus achieving a very compact package. The mechanical behaviour of the original chain is investigated for this purpose. A specific electric motor case is then designed and manufactured via Additive Manufacturing technology, in order to include the chain housing, the electric motor cooling system and the lubrication system. Furthermore, the case flange is designed to perfectly fit to the original engine deck in order to allow the engine cooling circuit to match with the electric motor cooling circuit. Several types of circuit layout - around the stator - are analysed via CFD simulations comparing pressure drop and heat transfer coefficients. Finally, a thermo-structural analysis is performed in order to assess the mechanical strength of the electric motor case.

2019 - Interplay between wall slip and cavitation: A complementary variable approach [Articolo su rivista]
Biancofiore, L.; Giacopini, M.; Dini, D.
abstract

In this work a stable and reliable numerical model based on complementary variables is developed to study lubricated contacts characterised by slip at one or both surfaces and in the presence of cavitation. This model can be used to predict surface behaviour when cavitation induced by e.g. the presence of surface texture, slip, or a combination of the two is encountered, with varying surface parameters. For this purpose, two different algorithms are coupled to predict the formation of cavitation, through a mass-conserving formulation, and the presence of slip at the wall. The possible slippage is described by a limiting shear criterion formulated using a Tresca model. To show the flexibility of our model, several bearing geometries have been analysed, such as a twin parabolic slider, a cosine profile used to mimic a bearing, and a pocketed slider bearing employed to study the effect of surface texture. We observe that the lubrication performance (i.e. low friction coefficient) can be improved by using materials that promote slippage at the moving wall. The location of the slippage region can be optimised to find the lowest value of friction coefficient. Our theoretical developments and numerical implementation are shown to produce useful guidelines to improve and optimise the design of textured superoleophobic surfaces in the presence of lubricated contacts.

2018 - A repertoire of failures in gudgeon pins for internal combustion engines, and a critical assessment of the design formulae [Articolo su rivista]
Strozzi, A.; Baldini, A.; Giacopini, M.; Bertocchi, E.; Mantovani, S.
abstract

The geometries commonly employed in gudgeon pins for internal combustion engines are examined. In particular, various methods for reducing the pin weight are considered. The selection of the appropriate clearance is addressed. The most typical failure modes are classified and interpreted in the light of stress analysis. The available approximate design formulae are assessed versus selected Finite Element forecasts. The fatigue cycles of stress and displacement related parameters are examined. The effect of the initial clearance on the contact pressure and on the pin ovalization is explored for selected clearance values. A typical Y-shaped fatigue crack is interpreted with the aid of Mohr circle. An error in a classical design approach based upon the containment of the pin ovalization is hypothesized.

2018 - Design of an Additive Manufactured Steel Piston for a High Performance Engine: Developing of a Numerical Methodology Based on Topology Optimization Techniques [Articolo su rivista]
Barbieri, SAVERIO GIULIO; Giacopini, Matteo; Mangeruga, Valerio; Mantovani, Sara
abstract

Modern high performance engines are usually characterized by high power densities, which lead to high mechanical and thermal loadings acting on engine components. In this scenario, aluminum may not represent the best choice for piston manufacturing and steel may be considered as a valid alternative. In this article, a methodology involving optimization techniques is presented for the design of an internal combustion engine piston. In particular, a design strategy is preliminary investigated aiming at replacing the standard aluminum piston, usually manufactured by forging or casting, with an alternative one made of steel and manufactured via an Additive Manufacturing process. Three different loading conditions are employed for the topology optimizations setup. Optimization results are then interpreted and the various structural features of the steel piston are designed starting from the density distribution contour plots. Different Finite Element thermomechanical models are finally prepared in order to correct and validate the designed geometry.

2018 - Design of an Additive Manufactured Steel Piston for a High Performance Engine: Developing of a Numerical Methodology Based on Topology Optimization Techniques [Articolo su rivista]
Barbieri, S. G.; Giacopini, M.; Mangeruga, V.; Mantovani, S.
abstract

Modern high performance engines are usually characterized by high power densities, which lead to high mechanical and thermal loadings acting on engine components. In this scenario, aluminium may not represent the best choice for piston manufacturing and steel may be considered as a valid alternative. In this paper, a methodology involving optimization techniques is presented for the design of an internal combustion engine piston. In particular, a design strategy is preliminary investigated aiming at replacing the standard aluminium piston, usually manufactured by forging or casting, with an alternative one made of steel and manufactured via an Additive Manufacturing process. Three different loading conditions are employed for the topology optimizations set up. Optimization results are then interpreted and the various structural features of the steel piston are designed starting from the density distribution contour plots. Different Finite Element thermo-mechanical models are finally prepared in order to correct and validate the designed geometry.

2018 - Investigation of the Influence of Different Asperity Contact Models on the Elastohydrodynamic Analysis of a Conrod Small-End/Piston Pin Coupling [Articolo su rivista]
Ferretti, A.; Giacopini, M.; Mastrandrea, L.; Dini, D.
abstract

Bearings represent one of the main responsible of friction losses in internal combustion engines and their lubrication performance has a crucial influence on the operating condition of the engine. In particular, the conrod small-end bearing is one of the most critical engine parts from a tribological point of view since limited contact surfaces have to sustain high inertial and combustion forces. In this contribution an analysis is performed of the tribological behaviour of the lubricated contact between the piston pin and the conrod small-end of a high performance motorbike engine. An algorithm is employed based on a complementarity formulation of the cavitation problem. A comparison between two different approaches to simulate the asperity contact problem is performed, the former based on the standard Greenwood-Tripp theory and the latter based on a complementarity formulation of the asperity contact problem. A model validation is performed by comparing the results with those obtained adopting the commercial software AVL Excite Power Unit. Similar results are obtained from both the approaches, if a proper calibration of the model input data is performed. However, a remarkable sensitivity is highlighted of the results obtained using the Greenwood/Tripp model to the adjustment parameters. The realistic (engineering) difficulty in defining and identifying the roughness data and their purely statistical nature returns results that may be afflicted by a dose of uncertainty. Considering that results of such simulations usually offer guidelines for a correct design of the coupling, further investigations are suggested to identify a relationship between simply available roughness data and model input, starting from a direct experimental measurements of real roughness profiles.

2018 - Investigation of the Influence of Different Asperity Contact Models on the Elastohydrodynamic Analysis of a Conrod Small-End/Piston Pin Coupling [Articolo su rivista]
Ferretti, Andrea; Giacopini, Matteo; Mastrandrea, Luca; Dini, Daniele
abstract

Bearings represent one of the main responsible of friction losses in internal combustion engines and their lubrication performance has a crucial influence on the operating condition of the engine. In particular, the conrod small-end bearing is one of the most critical engine parts from a tribological point of view since limited contact surfaces have to sustain high inertial and combustion forces. In this contribution an analysis is performed of the tribological behaviour of the lubricated contact between the piston pin and the conrod small-end of a high performance motorbike engine. An algorithm is employed based on a complementarity formulation of the cavitation problem. A comparison between two different approaches to simulate the asperity contact problem is performed, the former based on the standard Greenwood-Tripp theory and the latter based on a complementarity formulation of the asperity contact problem. A model validation is performed by comparing the results with those obtained adopting the commercial software AVL Excite Power Unit. Similar results are obtained from both the approaches, if a proper calibration of the model input data is performed. However, a remarkable sensitivity is highlighted of the results obtained using the Greenwood/Tripp model to the adjustment parameters. The realistic (engineering) difficulty in defining and identifying the roughness data and their purely statistical nature returns results that may be afflicted by a dose of uncertainty. Considering that results of such simulations usually offer guidelines for a correct design of the coupling, further investigations are suggested to identify a relationship between simply available roughness data and model input, starting from a direct experimental measurements of real roughness profiles.

2018 - Thermo-mechanical analysis of the exhaust manifold of a high performance turbocharged engine [Relazione in Atti di Convegno]
Lorenzini, Mariano; Giacopini, Matteo; Barbieri, SAVERIO GIULIO
abstract

This contribution presents a methodology for the structural analysis of the exhaust manifold of an internal combustion engine. In particular, the thermal loading and the related thermal fatigue damage mechanism are addressed. The component investigated is a melted exhaust manifold which includes the turbine involute. The complex geometry of the component derives from the project constrains in terms of engine performance and sound targets. Finite Element simulations are performed to obtain a virtual approval of the component geometry, in advance with respect to the component manufacturing. The Finite Element analysis accurately follow the experimental approval procedure which considers different warming and rapid cooling cycles to mimic typical engine operating conditions. Two particular aspects of the developed numerical methodology are described in details: a) the elasto-plastic behaviour of the material at high temperatures; b) a damage criterion for thermal fatigue. Following the Ferrari expertise derived by previous experimental and numerical analysis of other exhaust manifolds, the increase of the equivalent plastic strain registered for a single thermal cycle (delta PEEQ) is firstly adopted as a damage criterion. The methodology reveals itself to be well correlated with the experimental evidences thus limiting the number of tests necessary for the component approval.

2017 - A Design Strategy Based on Topology Optimization Techniques for an Additive Manufactured High Performance Engine Piston [Articolo su rivista]
Barbieri, Saverio Giulio; Giacopini, Matteo; Mangeruga, Valerio; Mantovani, Sara
abstract

In this paper, a methodology for the design of a motorcycle piston is presented, based on topology optimization techniques. In particular, a design strategy is preliminary investigated aiming at replacing the standard aluminum piston, usually manufactured by forging or casting, with an alternative one made of steel and manufactured via an Additive Manufacturing process. In this methodology, the minimum mass of the component is considered as the objective function and a target stiffness of important parts of the piston is employed as a design constraint. The results demonstrate the general applicability of the methodology presented for obtaining the geometrical layout and thickness distribution of the structure.

2016 - A complete 3-D description of the elastic behavior of a piston ring and its influence on the tribological behavior of the piston ring-cylinder liner interface [Relazione in Atti di Convegno]
Mastrandrea, LUCA NICOLO'; Giacopini, Matteo; Bertocchi, Enrico; Strozzi, Antonio; Dini, D.
abstract

Advances in modern engine development are becoming more and more challenging. The intense increase of thermal and mechanical loads as a result of higher power density requires perfecting the function of all engine components especially with regard to emission and friction reduction. In particular, piston rings pack represent one of the most important cause of mechanical friction loss in internal combustion engine [1], and inadequate ring-liner lubrication leads to high fuel/oil consumption and increased engine emissions with dramatic impact over the entire system efficiency. A desirable piston ring-pack set has to provide efficient sealing performance with both the cylinder wall in a radial direction and the top or bottom sides of the piston ring housing in an axial direction, leading to minimal gas blow-by, oil consumption and friction loss. Moreover piston ring other requirement are low friction, low wear and good resistance against mechanical/thermal fatigue. This is a challenging task due to the nature of the phenomena and interactions associated with piston rings. For example, increasing the installed ring tension, which is a method to control oil consumption, also tends to increase ring friction. Hence, any attempt to optimize ring-pack performance output parameters requires a good understanding of the dynamics of all the involved components. Different key elements have to be considered: the ring shape in its free state (namely free shape), the ring crossing-section geometry and the contact surface profile, which play important roles in determining the ring behavior. In order to achieve sealing, the piston rings are first held against the cylinder liner in its front face by their tension after being installed into the cylinder bore. The contact pressure on the cylinder wall is achieved by the inherent spring force of the ring in conjunction with the gas pressure behind the ring. During different engine operating conditions, the piston rings experience dynamically changing forces and axial as well as radial movements of the rings can occur. The contact on the side of the piston housing is achieved by the axial forces acting on the ring. The axial forces are composed of the gas pressure above and under the ring, the mass forces (inertia), and the friction forces. These forces change their direction during the cycle, and, as a result, the piston ring moves from one side of the groove to the other during the engine cycle. This is known as ring fluttering when the axial movement becomes excessive. This behavior open an additional gas flow path: gas can flow around the inner diameter of the ring which results in very high engine blow-by loss. In addition the ring pack design should also consider other factors, including gas blowback and, as said before, ring pack friction. The blowback is the reverse process of blowby and is highly related to engine emission and oil consumption while ring friction can cause severe ring and cylinder wall wear, which results in the ring losing its sealing capability. These factors are related to the ring circumferential pressure distribution, which is defined by the ring free shape and the ring cross section geometry. The understanding of the piston ring behavior is an hard challenge for automotive engineer. Firstly, in 1936 Castleman [2] investigated and proposed the concept of hydrodynamic lubrication for the piston ring. Thereafter, more and more research has been done in this field. Dowson et al. [3] predicted the behavior of a piston ring using the EHL theory. Sun [4] conducted his study for ring-bore conformability, in which the ring was modeled as a curved beam under in-plane loads. Liu and Tian [5, 6] developed an FEA tool for piston ring design. Ejakov et al. [7] modeled ring twist behavior predicting ring axial, radial displacements, bending and twisting angles along the ring periphery over an engine cycle. In this contributions a complete 3D model of the piston ring is propose

2016 - A repertoire of failures in connecting rods for internal combustion engines, and indications on traditional and advanced design methods [Articolo su rivista]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Bertocchi, Enrico; Mantovani, Sara
abstract

Several typical and uncommon failure modes in con-rods for internal combustion engines are commented from the stress level viewpoint. The interpretation of the fractures is supported with traditional calculations, with more advanced analytical models, and with Finite Element (FE) predictions. The repertoire of failures in a con-rod is presented by separately addressing the parts composing the con-rod itself, namely the shank, and the small and big ends.

2016 - Analytical evaluation of the peak contact pressure in a rectangular elastomeric seal with rounded edges [Articolo su rivista]
Strozzi, Antonio; Bertocchi, Enrico; Mantovani, Sara; Giacopini, Matteo; Baldini, Andrea
abstract

The contact pressure is considered for an elastomeric rectangular seal with rounded edges. An asymptotic matching is performed between an available analytical expression of the contact pressure that neglects the finiteness of the seal dimensions and a fracture mechanics solution describing a periodically laterally cracked strip of finite width. This matching provides a corrected formula for the peak contact pressure that accounts for the finiteness of the seal dimensions. The analytical expression for the peak contact pressure is validated versus finite element predictions for a large family of seal geometries and, in particular, for a seal reference shape extracted from the pertinent literature. An appraisal of the finite deformation effect has been carried out numerically.

2015 - A General Finite Volume Method for the Solution of the Reynolds Lubrication Equation with a Mass-Conserving Cavitation Model [Articolo su rivista]
Profito, Francisco J.; Giacopini, Matteo; Zachariadis, Demetrio C.; Dini, Daniele
abstract

This contribution presents the development of a general discretization scheme for the solution of Reynolds equation with a mass-conserving cavitation model and its application for the numerical simulation of lubricated contacts to be discretized using irregular grids. Such scheme is based on a hybrid-type formulation, here named as element-based finite volume method that combines the flexibility of the FEM to deal with unstructured grids, while preserving the local and global fluid-flow conservation aspect of the FVM throughout the discretized domain. The accuracy and robustness of the method are successfully tested using several benchmark cases proposed in the recent literature. Simulations of fully or partially textured sliding bearings are finally employed to show the advantages of being able to adopt irregular meshes both in terms of flexibility for the discretization of complex surface features and computational speed.

2015 - Analytical evaluation of the peak contact pressure in a rectangular elastomeric seal with rounded edges [Abstract in Atti di Convegno]
Baldini, Andrea; Bertocchi, Enrico; Giacopini, Matteo; Mantovani, Sara; Strozzi, Antonio
abstract

Rectangular seals constitute an alternative design to O-rings. Rectangular seals are employed in demanding applications such as aircraft actuators, e.g. ref. [1]. The seal edges are generally rounded, ref. [2]. As a consequence of the presence of filleted edges, the contact pressure exhibits Hertzian-type local bumps in its lateral zones; it remains almost flat in the central zone of the contact. The lateral bumps and the central flattish zone confer to the contact pressure distribution a camel-backed profile, see ref. [2], and ref. [3] for a similar axisymmetric problem. It is difficult to derive a rigorous, analytical expression of the contact pressure curve for the title problem. In fact, the analytical solution available for a rectangular punch with rounded edges indenting a half plane, e.g. ref. [4] and related bibliography, is exact only in the situation of a rigid punch indenting a deformable half plane, ref. [5], whereas in the title problem the punch (i.e., the seal) is flexible and the half plane (i.e., the counterface) is rigid. It has recently been shown in refs [5-7] that the unrealities of the above analytical solution may be corrected by combining the analytical solution with Fracture Mechanics (FM) results dealing with the stress singularities at the tip of a transverse crack in a strip of finite width. In this paper, an extension of formula (20) of ref. [5] is developed, that accounts for the combined effects of a) the presence of a filleted edge, and b) a finite seal width and height.

2015 - Elastohydrodynamic analysis of the conrod small-end of a high performance motorbike engine via a mass conserving cavitation algorithm [Relazione in Atti di Convegno]
Mastrandrea, LUCA NICOLO'; Giacopini, Matteo; Dini, Daniele; Bertocchi, Enrico
abstract

In this contribution a complementarity formulation for the solution of EHL problem in presence of cavitation is employed in order to investigate the tribological behavior of the conrod small-end of a high performance motorbike engine. The influence of different physical and geometrical parameters is discussed. In particular, the clearance between the conrod small-end and the piston pin, the lubricant physical properties, the surface roughness and the stiffness of the piston pin are investigated, thus providing preliminary guidelines for the correct design of the coupling. Due to the negligible influence of the transversal forces acting on the conrod small-end and of the relative sliding speed between the mating surfaces, a two symmetrical model of the assembly is prepared and results are compared with those obtained adopting a simply symmetrical model.

2015 - Influence of different temperature distributions on the fatigue life of a motorcycle piston [Articolo su rivista]
Giacopini, Matteo; Sissa, Simone; Rosi, Roberto; Fantoni, S.
abstract

In this paper, finite element analyses are performed to evaluate the stresses and the strains in a motorcycle piston. Non-linear finite element models are employed to mimic the piston behaviour when subjected to different loading conditions. In particular, the gas forces, the inertial forces and the piston-to-cylinder contact forces are considered. Appropriate temperature distributions are applied to the model to include the thermal stresses and strains in the analyses. Two different thermal configurations are considered: the first has a standard design of the oil jet hitting the underside zone of the piston crown, while the second presents modified parameters able to increase the heat transfer coefficient appreciably. The different operating temperature distributions related to the two thermal configurations considered strongly influence the pistons thermomechanical behaviour. This paper aims to perform high-cycle fatigue analyses to show how the fatigue life and fatigue-critical points of the component change when moving from the standard configuration to the modified configuration.

2015 - On the applicability of the Boussinesq influence function in modelling the frictionless elastic contact between a rectangular indenter with rounded edges and a half-plane [Articolo su rivista]
Strozzi, Antonio; Bertocchi, Enrico; Baldini, Andrea; Giacopini, Matteo
abstract

The applicability of the Boussinesq influence function in modelling the frictionless elastic contact between a rectangular indenter with rounded edges and a half-plane is numerically explored. The potential of the asymptotic matching method combined with classical fracture mechanics results is investigated. Manageable design formulae for evaluating the maximum equivalent stress are analytically derived with the aid of the asymptotic matching method.

2015 - Preliminary investigation of the cavitation damage in the conrod big end bearing of a high performance engine via a mass-conserving complementarity algorithm [Abstract in Atti di Convegno]
Giacopini, Matteo; Bertocchi, Enrico; Baldini, Andrea; Strozzi, Antonio
abstract

The conrod big end bearing is one of the most critical components of internal combustion engines; it is usually subjected to high dynamic loads and high sliding velocities between contacting surfaces are often involved. Therefore, the tribological behaviour of the conrod big end bearing is often one of the key elements to engine reliability, and it has been investigated both theoretically and experimentally in several contributions in the pertinent literature [1]. With the ever-increasing quest to improve engine performance, and the consequent increase of the rotational speed and combustion/inertial loads, the cavitation of the lubricant used in conrod big end bearings may play a crucial role in the assessment of bearing durability. To overcome problems related to film cavitation, palliatives such as the reduction of the clearance between the components, the increase of the oil supply pressure and/or the use of harder coating materials have been commonly adopted. However, such simple adjustments do not always represent a valid solution; further investigations are required in order to avoid cavitation damage occurrence. The cavitation damage has been studied for more than a century both theoretically [2-5] and experimentally [6,7], and many attempts have been made to predict or measure the pressure spikes developing in the cavitated areas due to bubble collapse. Although a universally accepted theory seems not to exist, it is clear that the cavitation damage occurs due to the rapid and violent collapse of the vapour bubbles in the proximity of a solid boundary. The aim of the present work is the preliminary evaluation of the damaging effect of the cavitation in a conrod big end bearing via elasto-hydrodinamic numerical analyses.

2015 - The influence of textured surfaces on the tribological behaviour of hip replacements employing a mass conserving complementarity algorithm [Relazione in Atti di Convegno]
Dini, Daniele; Giacopini, Matteo; Giuseppe, Mulas Antonio; Bertocchi, Enrico
abstract

The tribological behaviour of Metal-on-Metal (MoM) hip prostheses is a key factor for their success. In particular, wear is recognized to have a crucial role in the failure of a prosthesis and can have severe consequences on the patient’s health, e.g. pseudo-tumors in MoM implants, [1,2]. The lubrication of the coupling between the prosthetic head and the acetabular cup can affect both the contact behaviour and the wear of the prosthesis [3]. Different contributions exist in the pertinent literature addressing the elastohydrodynamic analysis of the head-acetabulum coupling, but rarely these analysis are performed taking into account the possible fluid cavitation in the contact area between the mating surfaces [4]. In order to improve the tribological performance of hip implants, the use of textured surfaces has been proposed in recent studies [5]. The present contribution focuses on the possible improvement that textured surfaces could give to the hip joint replacement tribological behaviour. Textured surfaces are widely used in mechanics in order to increase the carrying capacity of various kind of joints working in elastohydrodynamic condition [6-8]. Textured surfaces typically show a path of cavitated zones due to the presence of dimples in the contact surfaces. The effect of these cavitated zones can result in a global decreasing of friction and wear [9]. This preliminary contribution aims at studying, by means of preliminary simplified one-dimensional models, the influence of the geometrical parameters of the textures on the tribological behavior of a hip joint coupling. The analysis have been carried out employing a linear complementarity mass-conserving algorithm originally proposed in [10], capable of properly capturing the phenomenon of cavitation.

2014 - ANALISI PRELIMINARE DELL’INFLUENZA DI SUPERFICI TEXTURIZZATE SUL COMPORTAMENTO DEL FILM FLUIDO IN PROTESI D’ANCA ATTRAVERSO UN ALGORITMO COMPLEMENTARE CON CONSERVAZIONE DELLA MASSA [Relazione in Atti di Convegno]
Mulas, Giuseppe Antonio; Giacopini, Matteo; Strozzi, Antonio; Baldini, Andrea; Bertocchi, Enrico
abstract

Il comportamento tribologico e in particolare l’usura gioca un ruolo cruciale nel fallimento di una protesi d’anca. La lubrificazione dell’accoppiamento tra testa protesica e coppa acetabolare può influenzare sia la dinamica del contatto sia l’usura della protesi. Il regime di lubrificazione che governa l’accoppiamento testa-acetabolo è elastoidrodinamico. Nei diversi studi presenti nella bibliografia pertinente, raramente le analisi sono effettuate considerando la possibile cavitazione del fluido nella zona di contatto, o al più applicando una modellistica di cavitazione che si è dimostrata imperfetta in termini di conservazione della massa. Al fine di incrementare le prestazioni tribologiche di protesi d’anca, recenti studi hanno proposto l’impiego di superfici texturizzate. Attraverso l’utilizzo di un preliminare modello semplificato, viene studiata l’influenza, sul comportamento dell’accoppiamento, dei parametri geometrici che descrivono le texture. Si è utilizzato un recente algoritmo di complementarietà lineare capace di simulare il fenomeno della cavitazione conservando la massa di fluido.

2014 - Formulation of the tangential velocity slip problem in terms of variational inequalities [Articolo su rivista]
Strozzi, Antonio; Giacopini, Matteo; Bertocchi, Enrico; Dini, D.
abstract

This contribution deals with a modelling of the tangential velocity slip problem in terms of variational inequalities. In particular, various technical situations for which the slippage problem appears to play an important role are first reviewed. Then, a mathematical formulation in terms of variational inequalities is developed where the critical shear stress criterion is considered. The theoretical conditions under which a unique solution exists are also discussed and an algebraic description based upon a complementarity approach is presented. Preliminary numerical results end the paper and a validation versus an analytical solution is proposed.

2014 - Low-cycle Thermal Fatigue and High-cycle Vibration Fatigue Life Estimation of a Diesel Engine Exhaust Manifold [Relazione in Atti di Convegno]
Sissa, Simone; Giacopini, Matteo; Rosi, Roberto
abstract

This paper aims at estimating the low-cycle and high-cycle fatigue life of a turbocharged Diesel engine exhaust manifold. First, a decoupled thermo-structural Finite Element analysis has been performed to investigate low-cycle fatigue phenomena due to the thermal loadings applied to the exhaust manifold. High/low temperature cycles causes stress-strain hysteresis loops in the manifold material whose related dissipated energy can be directly correlated to low-cycle thermal fatigue. Afterwards, a dynamic harmonic analysis has been performed aiming at investigating the existence of high-cycle fatigue phenomena due to vibrational loading applied to the exhaust manifold during the duty cycle. Three direction acceleration experimental loadings have been applied to the model. An ad-hoc methodology has been developed to superimpose thermo-structural results to dynamic harmonic analysis results. In particular, quasi-static thermo-structural results have been employed to identify the mean stress values of vibration fatigue cycles, while alternate stress values have been derived from harmonic analysis. Different combinations of frequencies and phases of the acceleration input signals have been considered to create different high-cycle fatigue loadings. Each cyclic load case has been processed employing the multiaxial Dang Van fatigue criterion.

2014 - Numerical investigation of the cavitation damage in a high performance engine conrod big end bearing via a mass-conserving complementarity algorithm [Relazione in Atti di Convegno]
Dini, Daniele; Mastrandrea, LUCA NICOLO'; Giacopini, Matteo; Bertocchi, Enrico
abstract

The object of the study is the conrod big end bearing of an high performance motorbike engine. Comparative analyses involving different geometrical configurations of the crankpin/conrod assemblies, and in particular of different shapes of the inner profile of the bearing, are presented. The influence of the properties of the lubricant is also discussed. A preliminary cavitation damage index is proposed based on the variation in time of the void fraction at a certain location. The results obtained show a strong influence of the geometry of the bearing on the cavitation phenomenon. Experimental evidence qualitatively agrees with numerical forecasts, thus corroborating the use of both the methodology and the cavitation damage index proposed in this contribution.

2014 - Numerical investigation of the cavitation damage in the wet cylinder liner of a high performance motorbike engine [Articolo su rivista]
Fontanesi, Stefano; Giacopini, Matteo; Cicalese, Giuseppe; Sissa, Simone; S., Fantoni
abstract

In this paper a numerical methodology is proposed which aims at understanding the origin of a particular failure occurred in a two-cylinder high performance spark ignition engine for motorbike applications. A relevant cavitation damage/erosion has been detected at the water side of the engine cylinder liner during severe reliability bench tests, performed at the early stage of the engine design process. On the contrary, no damages have been registered during parallel high-load long runs of the motorbike. This contribution investigates in detail the differences between the bench test cooling circuit layout and the actual motorbike cooling circuit layout in order to find an explanation of the engine critical behaviour. In particular, CFD-CHT analyses of the water cooling jacket are performed, the computational domain covering both the coolant galleries and the surrounding metal components (head, block, gasket, valves, valve seats, valve guides, cylinder liner, spark plug). The contribution of a two-phase approach which takes into account the effect of a phase transition within the engine coolant is considered. Different engine operating conditions are investigated and a detailed analysis of different thermo-mechanical parameters influencing the engine behaviour is carried out. Results of the CFD simulations asses the methodology capability to correctly capture and understand the origin of the engine failure, thus providing a useful design tool for a faster and more effective design modification.

2013 - A Complementarity Formulation for the EHL Analysis of a Connecting Rod Big End Bearing [Relazione in Atti di Convegno]
Giacopini, Matteo; Luca, Bertocchi; Baldini, Andrea; Daniele, Dini
abstract

In this paper, the mass-conserving formulation first proposed by Giacopini et al. in [12] and then extended in [13] to include compressibility and to study non-Newtonian fluids is further improved to consider the elastic deflection of the solid surfaces. This formulation is essentially based on a manipulation of the Reynolds equation that allows the lubrication problem in the presence of cavitation to be described as a simple Linear Complementarity Problem (LCP). In particular, this algorithm is here applied to the EHL analysis of the lubrication performance of one of the connecting rods big-end bearing of a spark ignition motorsport engine under dynamic loadings.

2013 - A Complementarity Formulation of the Tangential Velocity Slip Problem in Lubricant Films [Relazione in Atti di Convegno]
Strozzi, Antonio; Giacopini, Matteo; Bertocchi, Enrico; Daniele, Dini
abstract

This contribution deals with a modelling of the tangential velocity slip problem in terms of variational inequalities. In particular, the critical shear stress criterion is considered. The theoretical conditions under which a unique solution exists are discussed and an algebraic description based upon a complementarity approach is presented, similar to the one adopted in [7]. Finally, preliminary numerical results are presented and discussed.

2013 - A complementarity formulation to study lubricated contact problems in the presence of cavitation [Relazione in Atti di Convegno]
Bertocchi, Luca; Giacopini, Matteo; Strozzi, Antonio
abstract

A mass-conserving formulation of the Reynolds equation has been recently developed using the concept of complementarity [1]. The mathematical derivation of the Linear Complementarity Problem (LCP) implemented in the solver favoured in [1] overcomes the drawbacks previously associated with the use of such complementarity formulations for the solution of cavitation problems in which reformation of the liquid film occurs. In the present paper, the proposed methodology, already successfully applied to solve textured bearing and squeeze problems in the presence of cavitation in a one dimensional domain and for incompressible fluids [1], has been extend to a two dimensional domain and the fluid compressibility has been included in the formulation. The evolution of the cavitated region and the contact pressure distribution are studied for a number of different configurations. Some of the results obtained with the proposed scheme are critically analysed and compared with the predictions obtained using alternative formulations (including full CFD calculations). The stability of the proposed algorithm and its flexibility in terms of the implementation of different compressibility laws is highlighted.

2013 - Achievement of a uniform contact pressure in a shaft–hub press-fit [Articolo su rivista]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Bertocchi, Enrico; Bertocchi, Luca
abstract

In this article, the achievement of a uniform elastic contact pressure in a frictionless, keyless, shaft-hub interference fit obtained by properly shaping the mating profiles is examined. The peculiarity of the hub mechanical response according to which, under the effect of a uniform pressure applied to the hub bore, the bore axial profile moves radially without any distortion, is exploited to simplify the determination of the mating profiles that return a uniform pressure. In particular, the hub radial deflection may be computed with a simple plane model, whereas only the shaft radial deflection requires a more complex analysis in cylindrical coordinates. Explicit approximate expressions are reported for the shapes to be conferred to the mating profiles to achieve a uniform pressure. Selected examples are presented to clarify the proposed design procedure and to preliminarily explore the effect on the pressure profile of simple shape errors.

2013 - Fluid film lubrication in the presence of cavitation: a mass-conserving two-dimensional formulation for compressible, piezoviscous and non-Newtonian fluids [Articolo su rivista]
Luca, Bertocchi; Daniele, Dini; Giacopini, Matteo; Mark T., Fowell; Baldini, Andrea
abstract

A mass-conserving formulation of the Reynolds equation has been recently proposed by some of the authors to deal with cavitation in lubricated contacts [1]. This formulation, based on the mathematical derivation of a linear complementarity problem (LCP), overcomes the drawbacks previously associated with the use of such complementarity formulations for the solution of cavitation problems in which reformation of the liquid film occurs. In the present paper, the methodology favoured in [1], already successfully applied to solve textured bearing and squeeze problems in the presence of cavitation in a one dimensional domain for incompressible fluids, has been extended to include the effects of fluid compressibility, piezoviscosity and the non-Newtonian fluid behaviour and it has been also applied to the analysis of two dimensional problems. The evolution of the cavitated region and the contact pressure distribution are studied for a number of different configurations which can be considered as relevant benchmarks. In particular, some of the results obtained with the proposed scheme are critically analysed and compared with the predictions obtained using alternative formulations, including full CFD calculations. The stability of the proposed algorithm and its flexibility in terms of implementation of different models for compressibility, piezoviscosity and non-Newtonian behaviour are highlighted.

2013 - Multiphase CFD–CHT optimization of the cooling jacket and FEM analysis of the engine head of a V6 diesel engine [Articolo su rivista]
Fontanesi, Stefano; Giacopini, Matteo
abstract

The present paper proposes a numerical methodology aiming at analyzing and optimizing an internal combustion engine water cooling jacket, with particular emphasis on the assessment of the fatigue strength of the engine head. Full three-dimensional CFD and FEM analyses of the conjugate heat transfer and of the thermo-mechanical loading cycles are presented for a single bank of a currently made V6 turbocharged Diesel engine under actual operating conditions. A detailed model of the engine, consisting of both the coolant galleries and the surrounding metal components is employed in both fluid-dynamic and structural analyses to accurately mimic the influence of the cooling system layout on the thermo-mechanical behavior of the engine. In order to assess a proper CFD setup useful for the optimization of the thermal behavior of the engine, the experimentally measured temperature distribution within the engine head is compared to the CFD forecasts. Particular attention is paid to the modeling of the phase transition and of the vapor nuclei formation within the coolant galleries. Thermo-mechanical analyses are then carried out aiming at addressing the design optimization of the engine in terms of fatigue strength. Because of the wide range of thermal and mechanical loadings acting on the engine head, both high-cycle and low-cycle fatigue are considered. An energy-based multi-axial criterion specifically suited for thermal fatigue is employed in the low-cycle fatigue region (i.e. the combustion dome) while well-established multi-axial stress/strain-based criteria are adopted to investigate the high-cycle fatigue regions of the engine head (i.e. the coolant galleries). The proposed methodology shows very promising results in terms of point-wise detection of possible engine failures and proves to be an effective tool for the accurate thermo-mechanical characterization of internal combustion engines under actual life-cycle operating conditions.

2012 - A Mass-Conserving Complementarity Formulation to Study Fluid Film Lubrication in the Presence of Cavitation for Non-Newtonian and Compressible Fluids [Relazione in Atti di Convegno]
Daniele, Dini; Mark T., Fowell; Strozzi, Antonio; Giacopini, Matteo; Luca, Bertocchi
abstract

A mass-conserving formulation of the Reynolds equation has been recently developed using the concept of complementarity [1]. The mathematical derivation of the Linear Complementarity Problem (LCP) implemented in the solver favoured in [1] overcomes the drawbacks previously associated with the use of such complementarity formulations for the solution of cavitation problems in which reformation of the liquid film occurs. In the present paper, the proposed methodology, already successfully applied to solve textured bearing and squeeze problems in the presence of cavitation in a one dimensional domain and for incompressible fluids [1], has been extend to a two dimensional domain and the fluid compressibility has been included in the formulation. The evolution of the cavitated region and the contact pressure distribution are studied for a number of different configurations. Some of the results obtained with the proposed scheme are critically analysed and compared with the predictions obtained using alternative formulations (including full CFD calculations). The stability of the proposed algorithm and its flexibility in terms of the implementation of different compressibility laws is highlighted.

2012 - A contribution to the Legendre series solution of the mechanical analysis of cylindrical problems [Relazione in Atti di Convegno]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Bertocchi, Enrico; Campioni, Eleonora; Mantovani, Sara
abstract

A series solution in terms of Legendre polynomials of the stress function suitable for modelling the mechanical response of a cylindrical component is revisited, and some contributions to the definition of the series terms are given. In particular, the correction to be imparted to a logarithmically singular series solution is considered, and a recursive approach for its determination is developed. A preliminary example dealing with an elastic, deformable cylindrical hub forced onto a rigid shaft is presented.

2012 - Analysis of the Lubrication Regimes at the Small End and Big End of a Connecting Rod of a High Performance Motorbike Engine [Relazione in Atti di Convegno]
Daniele, Dini; Giacopini, Matteo; Luca, Bertocchi
abstract

In the present paper, the algorithm proposed by Giacopini et. al. [1], based on a mass-conserving formulation of the Reynolds equation using the concept of complementarity is suitably extended to include the effects of compressibility, piezoviscosity and shear-thinning on the lubricant properties. This improved algorithm is employed to analyse the performance of the lubricated small end and big end bearings of a connecting rod of a high performance motorbike engine. The application of the algorithm proposed to both the small end and the big end of a con-rod is challenging because of the different causes that sustain the hydrodynamic lubrication in the two cases. In the con-rod big end, the fluid film is mainly generated by the relative high speed rotation between the rod and the crankshaft. The relative speed between the two races forms a wedge of fluid that assures appropriate lubrication and avoids undesired direct contacts. On the contrary, at the con-rod small end the relative rotational speed is low and a complete rotation between the mating surfaces does not occurs since the con-rod only oscillates around its vertical axis. Thus, at every revolution of the crankshaft, there are two different moments in which the relative rotational speed between the con-rod and the piston pin is null. Therefore, the dominant effect in the lubrication is the squeeze caused by the high loads transmitted through the piston pin. In particular both combustion forces and inertial forces contribute to the squeeze effect. This work shows how the formulation developed by the authors is capable of predicting the performance of journal bearings in the unsteady regime, where cavitation and reformation occur several times. Moreover, the effects of the pressure and the shear rate on the density and on the viscosity of the lubricant are taken into account.

2012 - Influence of the temperature distribution on both high-cycle and low-cycle fatigue life of a motorbike piston [Relazione in Atti di Convegno]
Giacopini, Matteo; Sissa, Simone; Rosi, Roberto
abstract

Finite Element analyses are performed to evaluate stresses and strains in a motorbike piston. Non-linear Finite Element models are employed to mimic the piston behaviour when subjected to different loading conditions. In particular, gas forces, inertial forces, and piston-tocylinder contact forces are considered. Temperature distributions formally evaluated and validated against experimental evidences [1] are applied to the model to include thermal stresses and strains into the analysis. Two different thermal configurations are considered: the first has a no-optimized design of the oil jet hitting the underside zone of the piston crown, while the second presents modified parameters able to appreciably increase the heat transfer coefficient. This aspect causes different operating temperature distributions that strongly influence the piston behaviour. This paper aims at performing both low-cycle and high-cycle fatigue analysis to show how the fatigue life and fatigue-critical points change in the two considered thermal configurations

2012 - On the loosening mechanism of a bush press-fitted in the small end of a connecting rod [Articolo su rivista]
L., Marmorini; Baldini, Andrea; Bertocchi, Enrico; Giacopini, Matteo; Rosi, Roberto; Strozzi, Antonio
abstract

The loosening mechanism is explored of a bush press-fitted into the small end bore of a con-rod. A modelling of the bush loosening mechanism is proposed. Numerical and analytical forecasts of the tensile inertial force responsible for the bush loosening are presented for a purely elastic model. Proper design charts are compiled that allow (a) the initial interference precluding any bush loosening to be determined within the respect of an imposed safety factor and (b) the maximum elastic stress within the small end to be computed for a general inertial load.

2012 - Stress Concentrations at the Rounded Edges of a Shaft-Hub Interference Fit Expressed in Terms of a Coefficient Normalizing the Coupling Geometry and the Young’s Modulus Effects [Relazione in Atti di Convegno]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Bertocchi, Enrico; Bertocchi, Luca
abstract

The elastic stress concentrations developed from the keyless, frictionless, static press-fit of a solid shaft into a hub with bore rounded edges are addressed. Derived from an analytical approach, a normalising parameter Φ is employed that accounts for the combined effects on the hub stress concentration of the fillet radius of the hub bore, the shaft radius, the interference, and the Young’s modulus. Compiled with the aid of Finite Elements, several design charts are presented that report the elastic stress concentrations within the hub versus the normalising parameter Φ. Each curve is valid for prescribed ratios of a) the hub inner radius to the outer radius, and b) the fillet radius to the shaft radius. An approximating expression of ample validity is also presented for a prompt evaluation of the hub stress concentration factor.

2011 - Maximum equivalent stress in a pin-loaded lug in the presence of initial clearance [Articolo su rivista]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Bertocchi, Enrico; Bertocchi, Luca
abstract

Various design charts of ample validity and prompt access are presented, which permit the contact stresses within the lug of a pinned connection to be forecast in the presence of an initial clearance between the pin periphery and the lug bore. To cover the range of the practically encountered geometries and loadings, round-ended lugs of various widths and with a variously tapered shank are considered, and several inclinations of the applied load are addressed. The charts are compiled with the aid of finite elements. The employment of the recently proposed load factor Φ allows the combined effects on the peak contact stresses of the load intensity and of the initial clearance to be predicted.

2011 - Normalization of the stress concentrations at the rounded edges of a shaft–hub interference fit [Articolo su rivista]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Bertocchi, Enrico; Bertocchi, Luca
abstract

The elastic stress concentrations developed from the keyless frictionless static press-fit of a shaft into a hub are addressed. Two configurations are examined, namely (a) an infinitely long solid shaft press-fitted into a hollow hub with bore rounded edges, and (b) a shaft with filleted extremity, partially inserted into a hub. Derived from an analytical approach, a normalizing parameter is proposed that accounts for the combined effects on the stress concentrations of the fillet radius, the shaft radius, the interference, and Young’s modulus. With the aid of finite elements, various design charts are compiled that report the elastic stress concentrations within the hub versus the proposed normalizing parameter. Each curve is valid for a fixed ratio of inner to outer hub radii.

2011 - Rilevanza delle proprietà termofisiche di materiali e interfacce di accoppiamento nell’analisi termomeccanica di componenti motore [Relazione in Atti di Convegno]
Giacopini, Matteo; Fontanesi, Stefano; C., Forte; A., Morri
abstract

All’interno del presente contributo verrà descritta una metodologia di calcolo integrata CFD/FEM che consente il calcolo del campo di temperatura in diversi componenti motore. Al fine di impostare correttamente le singole simulazioni sarà necessario considerare diversi parametri termofisici in termini di conducibilità termica dei materiali e resistenze di contatto tra i vari componenti, alcuni dei quali sono di incerta reperibilità.Verranno poi presentate opportune analisi di sensibilità a questi parametri al fine di evidenziare l’influenza che ognuno di questi ha sul campo di temperatura calcolato all’interno del componente. Infine, saranno presentate opportune tecniche di validazione sperimentale della metodologia proposta, necessarie a causa delle inevitabili incertezze che permangono all’atto del settaggio delle diverse analisi.

2011 - Torque Transmission by Friction in a Keyed Shaft-Hub Press-Fits [Relazione in Atti di Convegno]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Bertocchi, Enrico; Bertocchi, Luca; Campioni, Eleonora; Mantovani, Sara; O., Quareshi
abstract

Interference fits are widely employed to semi-permanently connect gears, pulleys, flanges, wheels, disks, rotors, and similar mechanical components, to a shaft. The stress state along the hub central portion may be thoroughly predicted by modelling the press-fit problem as plane and by employing the Lamé equations for thick-walled cylinders, and the transmissible torque may be confidently estimated by relying on the Lamé predictions, since they are valid along most of the contact axial length. Often a key is added to the press-fit, to secure the torque transmission and to prevent any relative rotation between the shaft and the hub. Both parallel and tapered keys are employed in practical applications. With respect to their tapered counterparts, parallel keys possess the advantage that they do not cause any eccentricity. This study considers parallel keys only. The presence of the keyseat increases the compliance of the hub and the shaft, thus producing a diminution of the contact pressure between the hub and the shaft, which results in a similar diminution of the transmissible torque. In this paper, a preliminary Finite Element analysis is carried out to quantify the above diminution of the contact pressure in the assumption of frictionless contact. The analysis is carried out for a solid shaft and for a practically relevant selection of ratios between the hub inner and outer radii. A preliminary development is presented of an analytical approach based upon the classical Michell polar solution, which is particularly suitable to mimic rings. The diminution of the transmissible torque with respect to a keyless shaft-hub press-fit is quantified, and the results are presented in a design diagram.

2011 - Validation of a combined CFD/FEM methodology for the evaluation of thermal load acting on aluminum alloy pistons through hardness measurements in internal combustion engines [Articolo su rivista]
Cantore, Giuseppe; Giacopini, Matteo; Rosi, Roberto; Strozzi, Antonio; P., Pelloni; C., Forte; M., Achiluzzi; G. M., Bianchi; L., Ceschini; A., Morri
abstract

This work presents the results of a multidisciplinary research project, carried out in close collaboration with Ducati Motor Holding S.p.A., for the development of an integrated methodology to design engine components in aluminum alloy under high thermal loads. The results refer to the study of an AA2618 (Al-Cu-Mg) alloy piston for high performance motorcycle engines. The piston has been selected as the pilot component for the development and validation of an advanced Fluid Dynamics (CFD) and Finite Element (FE) simulation methodology for the prediction of the inner thermal diffusion. The subsequent validation has been achieved through both the mechanical and microstructural characterization of the component. The methodology here presented consists of close interaction between fluiddynamics (CFD) simulations of the combustion process and Finite Element (FEM) simulations of the thermal diffusion inside the components. Combustion is the main engine heat source and is simulated by means of a threedimensional CFD code for reactive flows (FIRE v2008-AVL), with the use of advanced combustion (ECFM) and wall interaction models. The temperature map on the surfaces is based on the results of the iteration with FEM simulation of thermal diffusion. The FEM model used for the diffusion analysis receives the results of combustion analysis as input. Two different methods have been tested for the transfer of the CFD thermal load to the FEM models: a) imposition on the piston crown of a spatial distribution of heat flux averaged over the mean engine cycle; b) imposition on the piston crown of both heat flux coefficients and temperatures. The latter option allows the reduction of the number of iterations for the convergence of the thermal map inside the piston. The dissipation of the thermal load is accomplished by applying heat coefficients and temperatures, on the remaining parts of the piston surface. The validation of the CFD/FEM methodology is carried out through hardness measurements in different piston locations after bench tests. The identification of the hardness curves, as a function of temperature and time, for the T6 heat-treated AA2618 allowed the assessment of the local temperature reached by the component from the knowledge of the operating time of the engine and local hardness.

2010 - A Mass-Conserving Complementarity Formulation to Study Lubricant Films in the Presence of Cavitation [Articolo su rivista]
Giacopini, Matteo; M. T., Fowell; D., Dini; Strozzi, Antonio
abstract

A new mass-conserving formulation of the Reynolds equation is developed using the concept of complementarity. This new method overcomes the drawbacks previously associated with the use of such complementarity formulations for the solution of cavitation problems in which reformation of the liquid film occurs. Validation against a number of analytical and semi-analytical formulations, for a variety of problems including textured bearings and squeeze film dampers, is performed. The current formulation is shown to be in very good agreement with existing analytical and numerical mass-conserving solutions.

2010 - Analisi Termo-Meccanica a Fatica di un Motore Diesel Automobilistico [Relazione in Atti di Convegno]
Cantore, Giuseppe; Fontanesi, Stefano; Cicalese, Giuseppe; Strozzi, Antonio; Giacopini, Matteo
abstract

L’articolo presenta alcuni risultati relativi all’analisi termo-meccanica di un motore Diesel automobilistico. Lo studio è condotto utilizzando simulazioni disaccoppiate CFD e FEM allo scopo di valutare la resistenza a fatica del motore. Una metodologia semplificata per stimare la caratteristica termo-meccanica di testate motore soggette alle reali condizioni operative è stata proposta dagli autori in precedenti pubblicazioni [1,2], ed è ora affinata apportando rilevanti miglioramenti su entrambi i fronti di simulazione.Dal lato CFD, l’analisi CHT (conjugate heat transfer) include nel dominio di calcolo anche il metallo del basamento, dei componenti forzati della testa, nonché della guarnizione. Particolare cura è rivolta alla rappresentazione dello strato limite e all’applicazione delle condizioni al contorno termiche, in particolare alla distribuzione dei flussi termici tra i vari componenti motore. Al fine di massimizzare l’accuratezza delle previsioni CFD, sono valutati criticamente gli effetti dell’ebollizione del refrigerante sulla previsione dello scambio termico.L’accuratezza della previsione numerica viene valutata mediante confronto con misure sperimentali di temperatura in alcuni punti della testa per condizioni stazionarie di funzionamento del motore. I risultati delle simulazioni CFD, ed in particolare la distribuzione puntuale del flusso di calore all’interfaccia fluido/solido, sono trasferiti come condizione al contorno all’analisi termo-strutturale tramite una routine appositamente realizzata. Dal lato termo-meccanico, la principale novità introdotta è l’implementazione di un criterio di tipo energetico per la stima della resistenza a fatica a basso numero di cicli; tale criterio, utilizzato congiuntamente ai più classici criteri tensionali o deformativi, consente di disporre di uno strumento di progettazione capace di predire la resistenza delle singole parti del motore soggette ai differenti carichi agenti. Sono infatti analizzati carichi affaticanti sia ad alto sia a basso numero di cicli, e la metodologia proposta è applicata con successo per predire i possibili punti di innesco di fratture sulla testa e migliorare le caratteristiche del circuito di raffreddamento.

2010 - Automazione e Verifica del Processo di Incollaggio in Linee Produttive di Telai per Vetture d’Alta Gamma [Abstract in Atti di Convegno]
Andrisano, Angelo Oreste; Baldini, Andrea; Bertocchi, Enrico; Giacopini, Matteo; Leali, Francesco; Mantovani, Sara; Pellicciari, Marcello; Pini, Fabio; Strozzi, Antonio; Vergnano, Alberto
abstract

Sommario. La produzione industriale dei telai auto ha registrato, nel tempo, una grande evoluzione progettuale e tecnologica, spinta dalla necessità di garantire alte prestazioni e comfort elevato, nel rispetto della sicurezza dei passeggeri e della sostenibilità ambientale. Le linee produttive di assemblaggio sono, soprattutto in segmenti di fascia alta, progettate per l‟esecuzione, su telai diversi, di articolati processi ibridi di giunzione, basati, cioè, sull‟adozione di tecnologie di saldatura, rivettatura ed incollaggio. I sistemi che ne derivano sono, dunque, caratterizzati da elevata complessità e richiedono lo sviluppo di dispositivi automatici dedicati e l‟impiego simultaneo di robot industriali e risorse umane. La soluzione di tali problematiche richiede l‟intervento sinergico di vari settori dell‟Ingegneria Meccanica poiché coinvolge competenze metallurgiche, progettuali e tecnologiche. A queste si aggiungono le competenze necessarie alla progettazione di sistemi produttivi ad alta flessibilità che, secondo la visione proposta dagli autori, siano caratterizzati da elevata modularità strutturale ed operativa, parametricità e standardizzazione delle soluzioni progettuali e dei componenti, autonomia esecutiva, e che assicurino una rapida ed efficace riconfigurazione, garantendo, parallelamente, l‟alto livello qualitativo dei prodotti ed il completo controllo dei processi realizzati. Il presente articolo tratta lo sviluppo e la progettazione integrata del modulo robotizzato di incollaggio per linee di assemblaggio ibride di telai in alluminio, svolta in collaborazione con il gruppo ALCOA e con SIR SpA. Successivamente vengono presentati i risultati sperimentali ottenuti dalla verifica strutturale a lap shear e peeling di alcuni provini ricavati da assemblati del tunnel, effettuata secondo normative interne Ferrari SpA. Abstract. In the last years, industrial production of automotive chassis has gained a great evolution in design and technology, spurred by the need to achieve high performance and comfort, while ensuring both the safety of passengers and the environmental sustainability. State-of-the-art assembly lines, especially in top class segments, are designed to employ hybrid junctions on different chassis. Such complex process is based on the simultaneous adoption of welding, riveting and adhesive bonding technologies. The production systems design engages the development of specific automated devices and the cooperation of industrial robots and human resources. The solution of these issues involves the synergic action of various sectors of mechanical engineering, as metallurgy, design, and mechanical technology. Design of high flexibility production systems is another important issue: according to the viewpoint proposed by the authors, such systems are characterized by high structural and operational modularity, by parametric and standard design of solutions and components, by executive autonomy and rapid reconfiguration capability, thus simultaneously ensuring high quality of products and the complete control of processes. The present paper deals with the development and integrated design of the robotic adhesive bonding module in hybrid assembly lines for aluminum chassis, carried out in collaboration with the ALCOA group and SIR SpA. Experimental results are also presented, that refer to lap shear and peeling tests, carried out on specimens extracted from the chassis tunnel, according to Ferrari SpA internal standards.

2010 - Multiphase CFD-CHT Analysis and Optimization of the Cooling Jacket in a V6 Diesel Engine [Relazione in Atti di Convegno]
Fontanesi, Stefano; Cicalese, Giuseppe; Giacopini, Matteo
abstract

The paper presents a numerical activity directed at the analysis and optimization of internal combustion engine water cooling jackets, with particular emphasis on the fatigue-strength assessment and improvement.In the paper, full 3D-CFD and FEM analyses of conjugate heat transfer and load cycle under actual engine operation of a single bank of a current production V6 turbocharged Diesel engine are reported.A highly detailed model of the engine, made up of both the coolant galleries and the surrounding metal components, i.e. the engine head, the engine block, the gasket, the valve guides and valve seats, is used on both sides of the simulation process to accurately capture the influence of the cooling system layout under thermal and load conditions as close as possible to actual engine operations.Concerning the CFD side, a 50-50 binary mixture of ethylene-glycol and water is used in order to correctly reproduce the coolant behavior, while boundary conditions are derived from a combination of experimental measurements and a CFD-1D model of the whole engine.In order to find a proper CFD setup for the optimization of the thermal behavior of the engine, a preliminary comparison between experimental temperature distribution within the engine head and CFD forecasts is carried out. Eight thermocouples are used to measure the engine head local temperature at some critical locations.Among the many competing numerical sub-models involved in the CFD simulations, particular attention is devoted to the modeling of phase transition and vapor nuclei formation within the coolant galleries.Concerning the FEM side, thermo-mechanical analyses are carried out aiming at addressing the design optimization of the engine in terms of fatigue strength. In view of the wide range of thermal and load conditions, both high-cycle and low-cycle fatigue must be properly characterized by means of ad-hoc criteria. An energy-based criterion specifically suited for low-cycle fatigue regions is therefore superimposed to well-established S-N o ε-N criteria for the high cycle fatigue regions.The proposed methodology shows very promising results in terms of point-wise detection of possible engine failures ans proves to be an effective tool for the accurate thermo-mechanical characterization of internal combustion engines under actual life-cycle operations.

2010 - Preliminary plane mechanical modeling of hexagonal contact [Relazione in Atti di Convegno]
Strozzi, Antonio; Radi, Enrico; Baldini, Andrea; Giacopini, Matteo; Campioni, Eleonora
abstract

A hexagonal joint is mechanically analysed. A cross section of the contact between male and female components is modelled as a plane strain problem, and the contact and detachment zones are investigated with two approaches, a) an analytical study formulated in terms of an integral equation; b) a FE analysis. Preliminary results refer to the situation of null initial clearance and coefficient of friction. For each side of the hexagonal contact, the contact zone constitutes a small portion of the length of the hexagonal side, since separation occurs along a sizeable side length.

2010 - Sviluppo di una metodologia CFD e FEM per l’analisi a fatica di componenti motoristici [Relazione in Atti di Convegno]
Cantore, Giuseppe; Fontanesi, Stefano; Cicalese, Giuseppe; Strozzi, Antonio; Giacopini, Matteo
abstract

L’articolo presenta alcuni risultati relativi all’analisi termo-meccanica di un motore Diesel automobilistico 6 cilindri a V di cilindrata complessiva 2900cc. Lo studio è condotto utilizzando simulazioni disaccoppiate CFD e FEM allo scopo di valutare la resistenza a fatica dei componenti. La distribuzione di fluido nel circuito di raffreddamento è stata in precedenza oggetto di approfondite analisi e ottimizzazioni al fine di migliorare le caratteristiche dei passaggi del refrigerante. Una metodologia semplificata al fine di stimare la caratteristica termo-meccanica di testate motore soggette alle reali condizioni operative è stata proposta dagli autori in precedenti pubblicazioni. Come conseguenza dell’elevata complessità dei vari fenomeni coinvolti, in questo articolo si introducono alcune importanti migliorie, che consentono un’analisi più accurata della resistenza a fatica del motore, soggetto a carichi affaticanti ad alta frequenza e a bassa frequenza. La metodologia oggetto del presente articolo si basa ancora una volta sull’analisi disaccoppiata CFD e FEM, con rilevanti miglioramenti apportati su entrambi i fronti di simulazione. Dal lato CFD, si utilizza una nuova tipologia di griglia poliedrica, che riesce a combinare l’elevata risoluzione spaziale della mesh con una richiesta computazionale accettabile e un’elevata stabilità numerica della simulazione; particolare attenzione viene dedicata alla rappresentazione del flusso in parete. Mediante l’analisi CFD – CHT (conjugate heat transfer) è valutata la distribuzione puntuale del flusso di calore al refrigerante, includendo nel dominio di calcolo anche il metallo del basamento, della testa completa dei componenti forzati, nonché della guarnizione. Al fine di valutare e incrementare l’accuratezza della previsione numerica, sono stati effettuati e vengono mostrati alcuni confronti con misure sperimentali di temperatura in alcuni punti della testa per condizioni stazionarie di funzionamento del motore. Particolare cura è rivolta alla rappresentazione dello strato limite, fluidodinamico e termico. Allo stesso tempo, grande attenzione è data all’applicazione delle condizioni al contorno termiche, in particolare alla distribuzione dei flussi termici tra i vari componenti affacciati alla camera di combustione. Al fine di massimizzare l’accuratezza delle previsioni CFD, sono valutati criticamente gli effetti dell’ebollizione del refrigerante sulla previsione dello scambio termico tra refrigerante e metallo. I risultati delle simulazioni CFD, ed in particolare la distribuzione puntuale del flusso di calore sulla superficie di contatto fluido/solido, sono successivamente trasferiti come condizione al contorno all’analisi termo-strutturale per la valutazione della resistenza a fatica del componente. A tal fine, si utilizza una routine appositamente realizzata, in grado di mappare la distribuzione puntuale dei flussi termici calcolata tramite le simulazioni CFD su una griglia di calcolo ottimizzata per le analisi FEM. Dal lato termo-meccanico, la principale novità introdotta è l’implementazione di un criterio di tipo energetico per la stima della resistenza a fatica a basso numero di cicli; tale criterio, utilizzato in congiunzione con i più classici criteri tensionali o deformativi, consente di disporre di uno strumento di progettazione capace di predire la resistenza delle singole parti del motore soggette ai differenti carichi agenti. Sono infatti analizzati carichi affaticanti sia ad alto sia a basso numero di cicli, e la metodologia proposta è applicata con successo al fine di predire i possibili punti di innesco di fratture sulla testa e di migliorare le caratteristiche del circuito di raffreddamento.

2009 - Contact stresses within a split ring inserted into acircular housing [Articolo su rivista]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Rosi, Roberto; Bertocchi, Enrico
abstract

The contact problem between a split ring and a circular housing is mechanicallyexamined. This contact is revisited in terms of receding contact, the zones along which the ringbeds over the housing are investigated, and normalizing design parameters are evidenced. Thesplit ring is modelled in terms of a straight, purely flexural beam as well as of a curved, shearelasticbeam; for both models, analytical solutions are obtained. Various easy accessible designdiagrams, useful for estimating the maximum elastic stresses within the split ring and the axialinsertion force, have been prepared with the aid of these two beam models and using finiteelements. The mechanical response of the split ring when its angular width is appreciably lowerthan p is clarified.

2009 - Influence of the initial clearance on the peak stress in connecting-rod small ends [Articolo su rivista]
A., Pioli; Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Rosi, Roberto
abstract

The stress increase that is caused by the presence of an initial clearance within thesmall end of connecting rods for motorbike and car engines is investigated. Plane analyticaland numerical modellings of the dry contact between the small-end and piston pin areadopted. Based upon a recent analytical result, a normalizing parameter is introduced, whichallows the stress concentration factor at the small-end bore sides to be expressed as a functionof a proper combination of the initial clearance between the small end and gudgeon pin, theapplied load, and Young’s modulus, for prescribed aspect ratios of the small end and hollowpin. Design diagrams summarizing the consequences of an initial clearance between the smallendbore and gudgeon pin on the eye peak stress are reported, which cover a wide range ofgeometries, clearances, and loadings. Selected comparisons between two-dimensional andthree-dimensional models are carried out.

2009 - Three examples of inadequacy of the Williams asymptotic method in predicting the singularity strength in elastic problems [Relazione in Atti di Convegno]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Rosi, Roberto
abstract

Three examples are presented for which the Williams asymptotic method appears to be inadequate in forecasting the strengh of the singularity encountered in elastic problems. The first case addresses a Kirchhoff plate resting on an irregular linear support; the second example revisits a classical plane elasticity contact problem; the third case considers an infinite sheet with a square hole. The reasons of the inadequacy of the Williams asymptotic method in treating the above situations are discussed.

2008 - A new decoupled CFD and FEM methodology for the fatigue strength assessment of an engine head [Relazione in Atti di Convegno]
Fontanesi, Stefano; Carpentiero, Davide; Malaguti, Simone; Giacopini, Matteo; Margini, Stefano; L., Arnone
abstract

A 2200 cc engine head for marine applications has been analysed and optimized by means of decoupled CFD and FEM simulations in order to assess the fatigue strength of the component. The fluid distribution within the cooling jacket was extensively analysed and improved in previous works, in order to enhance the performance of the coolant galleries.As a consequence of the many complex phenomena involved, an improved approach is presented in this paper, capable of a better characterization of the fatigue strength of the engine head under both high-cycle and low-cycle fatigue loadings. The improved methodology is once again based on a decoupled CFD and FEM analysis, with relevant improvements added to both simulation realms.From the CFD side, a new generation polyhedral grid is employed to combine high resolution surface spacing, computational demand, and numerical stability of the CFD simulations, with particular emphasis on the boundary layer representation. The local heat flux distribution is calculated by means of CFD analyses of the coolant galleries, now including the engine block portion, plus the engine head metal cast. In order to tune and improve the accuracy of the numerical forecasts, comparisons are carried out with experiments in terms of local metal cast temperature distribution for steady operation of the cooling circuit. Once again, particular care is devoted to the CFD representation of the boundary layer, both fluid and thermal. At the same time, great attention is paid to the thermal boundary conditions, i.e. the distribution of the heat fluxes among the many components facing the combustion process. In order to improve the accuracy of the CFD forecasts, effects of coolant boiling on the heat transfer forecast are investigated and included in the procedure.As a result, a pointwise heat transfer distribution on the fluid/solid interface is transferred as a boundary condition to a thermo-structural analysis for the evaluation of the fatigue strength of the component. An ad-hoc routine is used to map the CFD computed pointwise distribution of the heat flux on a FEM-optimized grid.From the FEM side, an energy based fatigue strength criterion is now implemented in order to create a design tool capable of predicting the fatigue strength of automotive parts subjected to different thermo-mechanical loadings. Both high-cycle fatigue and low-cycle fatigue regions are analysed, and the proposed methodology is successfully applied to predict the site of crack nucleation on an actual engine head and to improve the cooling jacket behaviour.

2008 - Astra Research [Spin Off]
Baldini, Andrea; Giacopini, Matteo; Rosi, Roberto; A., Salsi
abstract

2008 - Biomechanical aspects in dental replacements [Capitolo/Saggio]
Baldini, Andrea; Bruzzesi, G.; Zaffe, Davide; Giacopini, Matteo; Strozzi, Antonio; DE POL, Anto
abstract

This chapter deals with biomechanical aspects in dental replacements. The state of the art is critically reviewed taking into account the body of the literature results. The initial section is devoted to the mechanical properties of bone and to a description of the jaw geometry and of its loading and constraining. The following section presents a classifi cation of the various tooth replacement confi gurations and of the various materials adopted, where single and multiple replacements are considered. A specifi c section is devoted to the solid modelling of the jaw as input to numerical analyses, where the aid offered by reverse engineering and tomography is underlined. The fi nite element method as well as alternative numerical and experimental approaches are reviewed in a dedicated section. The stress analysis forecasts and measurements are biomechanically interpreted in the light of the current literature results. The chapter ends with a section devoted to biological aspects.

2008 - ON TORSIONAL VIBRATIONS IN CONROD ASSEMBLIES FOR HIGH PERFORMANCE ENGINES [Relazione in Atti di Convegno]
Baldini, Andrea; Bertocchi, Enrico; Giacopini, Matteo; Margini, Stefano; Rivasi, Stefano; Rosi, Roberto; Strozzi, Antonio
abstract

In the paper, the authors discuss possible causes of conrod torsional vibrations. Several simplified models are laid out for prediction, evaluation and future research. Some critical remarks about these prospective models are presented. Comparisons with a limited number of experimental cases is finally provided.

2007 - Maximum Stresses in a Taper-shanked Round-ended Lug Loaded by an Oblique Concentrated Force [Articolo su rivista]
Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Rivasi, Stefano; Rosi, Roberto
abstract

In this study, the stress state in a round-ended, taper-shanked lug loaded by an oblique point force is investigated. Numerical, analytical and, partially, photoelastic studies were carried out. In the analytical model, the lug is modelled as a plane problem, and it is partially likened to a ring examined with a Michell-type series solution; the differences in shape between lug and ring are overcome by endowing the series solution with degrees of freedom suitable for adapting the ring solution to the lug actual geometry. Three prompt access design charts are presented, which report the normalised stress concentration for three lug shank taper angles, for selection of five aspect ratios between bore radius and radius of the rounded extremity, and for load inclinations ranging from longitudinal to transverse directions

2007 - NORMALIZATION OF LOAD AND CLEARANCE EFFECTS IN BALL-IN-SOCKET-LIKE REPLACEMENTS [Articolo su rivista]
M., Ciavarella; Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo
abstract

A normalizing loading parameter useful in summarising the mechanical response ofplane pin-in-plate-like contacts is extended to axisymmetric ball-in-socket-like contacts. Anexample addressing a compliant layered artificial hip joint is presented, and the usefulness ofthe normalizing loading parameter is evidenced.

2007 - Thermo-mechanical analysis of an engine head by means of integrated CFD and FEM [Relazione in Atti di Convegno]
Fontanesi, Stefano; Carpentiero, Davide; Gagliardi, Vincenzo; Malaguti, Simone; Margini, Stefano; Giacopini, Matteo; Strozzi, Antonio; L., Arnone; M., Bonanni; D., Franceschini
abstract

A 2200 cc engine head for marine applications has been analysed and optimized by means of both fluid-dynamic and thermo-structural simulations. First, the fluid distribution within the cooling jacket has been deeply investigated, in order to point out critical aspects of the current jacket layout and propose modified gaskets aiming at modifying the coolant path and increasing the cooling performance. A new generation polyhedral grid has been employed to combine high resolution surface spacing, computational demand, and numerical stability of the CFD simulations. Different turbulence models and near-wall approaches have been tested in order to accurately predict the boundary layer behaviour, which is fundamental for the subsequent thermal analysis. Comparisons have been carried out between the different gasket layouts in terms of both cylinder to cylinder flow balancing and cooling effectiveness in the critical regions of the engine head.At a second stage, the CFD model has been extended to the whole engine head, i.e. covering both the cooling jacket and the metal cast, and heat flux distribution on the fluid/solid interface has been computed and transferred as a boundary condition to a structural finite elements code for the analysis of the fatigue strength of the component. To this aim, an ad-hoc developed routine has been created to map the computed punctual distribution of the heat transfer coefficient on a FEM-optimized grid. Particular attention has been paid to the thermal boundary conditions, i.e. the distribution of the heat losses among the combustion chamber and pre-chamber components.Along with this coherent approach of thermo-mechanical loading, the mechanical constitutive law of the material, the damage parameters and an energy based fatigue strength criterion have been considered in order to create a design strategy capable of performing predictive calculations of automotive parts subjected to thermo-mechanical loading. The methodology favoured in this study has been successfully applied to predict the site of incipient crack on an actual engine head.

2006 - On the Applicability of the Loading Parameter PHI in Pinned Connections with Relevant Initial Clearance [Relazione in Atti di Convegno]
Ciavarella, M; Strozzi, Antonio; Baldini, Andrea; Giacopini, Matteo; Rivasi, Stefano; Rosi, Roberto
abstract

In pinned connections, the presence of an initial clearance increases the lug stress concentration with respect to a neat fit configuration. By employing a recently proposed loading parameter Φ valid for plane models, the applied load and initial clearance effects on the stress concentration are normalised for a straight-shanked, round-ended, longitudinally loaded pin-lug connection of fixed outer to inner radius ratio. Results are obtained with a Mitchell-type, Fourier series solution and with commercial Finite Elements. The applicability of the loading parameter Φ to pinned connections with small to relevant initial clearances is explored. Two preliminary design charts are presented, which quantify the lug stress concentration factor versus the loading parameter Φ for two lug geometries defined by inner to outer radii ratios of 0.376 and 0.77.

2005 - Coating photoelasticity applied to a rapid prototyping model of a hub for high performance cars [Capitolo/Saggio]
Baldini, A.; Cevolini, F.; Giacopini, M.; Piraccini, M.; Ronco, V.; Strozzi, A.
abstract

A photoelastic technique is presented that is based on a photoelastic coating applied along the surface of a model of a mechanical component made with rapid prototyping. The proposed procedure allows more flexible models to be obtained in comparison to metal parts, thus favouring the outset of a higher number of photoelastic fringes. In addition, the proposed approach permits enlarged models to be easily constructed, thus easing the photoelastic readings. The preliminary study here presented addresses a wheel hub for high performance cars, with particular regard to the stress concentrations by the fin fillets.

2005 - Optimization of a Cooling Circuit in an Internal Combustion Engine for Marine Applications [Relazione in Atti di Convegno]
Cantore, G.; Fontanesi, S.; Gagliardi, V.; Malaguti, S.; Baldini, A.; Giacopini, M.; Strozzi, A.; Rosi, R.
abstract

An optimization study involving both fluid-dynamic and thermostructural aspects has been carried out for a 2200 cc turbocharged engine head for marine applications. In this cross-disciplinary problem, the structural and thermodynamic aspects have been decoupled. A preliminary set of CFD numerical analyses of the cooling jacket layout has been performed, in order to investigate critical aspects of the present configuration and improve the cooling performance, by means of local flow patterns and flow distribution analysis. At a second stage, temperature distributions within the metal cast parts have been derived from CFD in order to assess the fatigue strength of the component with structural finite elements. A proper choice of both CFD methodology and boundary conditions is carried out in order to determine a trade-off between computational effort and actual engine behavior representation. The proposed modelling procedure allows a sensitivity study to be carried out of the engine head to variations of the leading geometric parameters, thus devising an optimized component. The methodology favored in this study is finally applied to carry out a comparison between the basic configuration and a fluid-dynamic improved solution, in order to estimate the effectiveness of the design optimization on the fatigue strength of the component.