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Matteo GIACOPINI

Professore Associato presso: Dipartimento di Ingegneria "Enzo Ferrari"


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Pubblicazioni

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, 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, 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 Nicolò; 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, M.; Sissa, S.; Rosi, R.; 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, A.; Bertocchi, E.; Baldini, A.; Giacopini, M.
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, A.; Giacopini, M.; Bertocchi, E.; 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 [Abstract in Atti di Convegno]
Dini, Daniele; Mastrandrea, Luca N.; 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]
Matteo Giacopini; Luca Bertocchi; Andrea Baldini; 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]
Antonio Strozzi; Matteo Giacopini; Enrico Bertocchi; 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, L.; Giacopini, M.; Strozzi, A.
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 [Relazione in Atti di Convegno]
Oliva, E.; Strozzi, A.; Baldini, A.; Giacopini, M.; Bertocchi, E.
abstract

The achievement is examined of a uniform elastic contact pressure in a frictionless, keyless, shaft-hub interference fit, obtained by properly shaping the mating profiles. 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 (polar) model, whereas only the shaft radial deflection requires a more complex analysis in cylindrical coordinates. Explic it 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 - Achievement of a uniform contact pressure in a shaft–hub press-fit [Articolo su rivista]
A Strozzi; A Baldini; M Giacopini; E Bertocchi; L Bertocchi
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;Matteo Giacopini;Mark T. Fowell;Andrea Baldini
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;Antonio Strozzi;Matteo Giacopini;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]
A. Strozzi; A. Baldini; M. Giacopini; E. Bertocchi; E. Campioni; S. Mantovani
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;Matteo Giacopini;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]
M. Giacopini; S. Sissa; R. Rosi
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 - 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]
A. Strozzi; A. Baldini; M. Giacopini; E. Bertocchi; L. Bertocchi
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]
A. Strozzi; A. Baldini; M. Giacopini; E. Bertocchi; L. Bertocchi
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]
M. Giacopini; S. Fontanesi; 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]
A. Strozzi; A. Baldini; M. Giacopini; E. Bertocchi; L. Bertocchi; E. Campioni; S. Mantovani; 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]
G. Cantore; M. Giacopini; R. Rosi; A. Strozzi; 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]
G. Cantore; S. Fontanesi; G. Cicalese; A. Strozzi; M. Giacopini
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]
A. O. Andrisano; A. Baldini; E. Bertocchi; M. Giacopini; F. Leali; S. Mantovani; M. Pellicciari; F. Pini; A. Strozzi; A. Vergnano
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]
A. Strozzi; E. Radi; A. Baldini; M. Giacopini; E. Campioni
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]
G. Cantore; S. Fontanesi; G. Cicalese; A. Strozzi; M. Giacopini
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]
A Strozzi; A Baldini; M Giacopini; R Rosi; E Bertocchi
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; A Strozzi; A Baldini; M Giacopini; R Rosi
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]
A. Strozzi; A. Baldini; M. Giacopini; R. Rosi
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]
A. Baldini; M. Giacopini; R. Rosi; 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]
A. BALDINI; E. BERTOCCHI; M. GIACOPINI; S. MARGINI; S. RIVASI; R. ROSI; A. STROZZI
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.


2008 - Potenziamento e sviluppo dell'industria motoristica incluse le due ruote con motori a basso consumo e a basso impatto ambientale: Definizione di una piattaforma integrata per la progettazione di componenti motore di motoveicoli a basso rapporto peso/potenza e ridotto impatto ambientale attraverso metodi di modellazione d’avanguardia e ricerca su nuovi materiali e nuove tecnologie di processo, anche trasferibili ad altre componenti veicolo. [Partecipazione a progetti di ricerca]
Strozzi, Antonio; Cantore, Giuseppe; Mattarelli, Enrico; Paltrinieri, Fabrizio; Baldini, Andrea; Giacopini, Matteo; Fontanesi, Stefano; Rosi, Roberto; Rinaldini, Carlo Alberto
abstract

Realizzazione di una piattaforma integrata basata su metodi di modellazione e simulazione innovativi e ricerca su nuovi materiali e tecnologie di processo per la progettazione di componenti di motoveicolo. Tale metodologia costituirà lo strumento cardine per la progettazione preliminare di un motoveicolo a basso rapporto peso-potenza e ridotto impatto ambientale. Sviluppo di nuovi materiali e tecnologie di processo innovative per la realizzazione di componenti di motoveicoli a prestazioni migliorate. In particolare individuazione di nuove soluzioni per l’utilizzo di materiali più leggeri e nuovi sistemi di industrializzazione e processo che consentiranno la riprogettazione di tali componenti nelle forme più efficienti e con tecniche realizzative atte a ridurne il peso. Definizione di metodologie di modellazione e simulazione del processo di combustione, dei fenomeni di riempimento motore, dei fenomeni di scambio termico e del comportamento statico e dinamico di componenti motoveicolo finalizzate a: a) miglioramento dell’efficienza di combustione, b) incremento della potenza, c) ottimizzazione termo-strutturale dei componenti, d) ottimizzazione del comportamento dinamico-strutturale di parti in movimento.


2008 - Sviluppo di metodologie di base per l'applicazione ditecnologie innovative per riduzione consumi ed aumentoprestazioni specifiche per motori ad alte prestazioni [Partecipazione a progetti di ricerca]
Franceso Vattaneo; Mauro Rioli; Giuseppe Cantore; Davide Moro; Bianca Maria Vaglieco; Stefano Fontanesi; Simone Malaguti; Matteo Giacopini; Andrea Baldini; Antonio Strozzi
abstract

1. Metodologie avanzate per l'analisi delle mutue influenze dei parametri motor e vettura2. Metodologie avanzate di calcolo per la definizione fluidoidinamica del motore mediante codici 1De 3D3. Algoritmi di controllo, validati al simulatore, per il trattamento del segnale delle bobine aionizzazione4. Metodologie di indagine sperimentale, su motori ad accesso ottico, finalizzate alla conoscenzaapprofondita dei fenomeni di combustione e formazione degli inquinanti5. Linee guida per la definizione delle geometrie del sistema di combustione e delle strategie diiniezione, basate su analisi su motore con accesso ottico6. Metodologie avanzate per la simulazione dinamica e termo-strutturale dei componenti delmotore


2007 - Maximum Stresses in a Taper-shanked Round-ended Lug Loaded by an Oblique Concentrated Force [Articolo su rivista]
A. STROZZI; A. BALDINI; M. GIACOPINI; S. RIVASI; R. ROSI
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; A. STROZZI; A. BALDINI; M. GIACOPINI
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 [Articolo su rivista]
S. FONTANESI; D. CARPENTIERO; V. GAGLIARDI; S. MALAGUTI; S. MARGINI; M. GIACOPINI; A. STROZZI; 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 [Capitolo/Saggio]
CIAVARELLA M; STROZZI A; BALDINI A; M. GIACOPINI; RIVASI S; ROSI R
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.