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Ricercatore t.d. art. 24 c. 3 lett. B
Dipartimento di Scienze e Metodi dell'Ingegneria

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2021 - A Heat Pump-Based Multi-source Renewable Energy System for the Building Air Conditioning: The IDEAS Project Experience [Articolo su rivista]
Cesari, Silvia; Natali, Alessia; Larwa, Barbara; Baccega, Eleonora; Boschetti, Micol; Mainardi, Elena; Cavazzuti, Marco; Piazzi, Agostino; Mangherini, Giulio; Vincenzi, Donato; Bottarelli, Michele

2021 - An integrated approach for the analysis and modeling of road tunnel ventilation. Part II: Numerical model and its calibration [Articolo su rivista]
Cingi, P.; Angeli, D.; Cavazzuti, M.; Levoni, P.; Stalio, E.; Cipollone, M.

The present work represents the second and final part of a twofold study aiming at the definition and validation of an integrated methodology for the analysis and modeling of road tunnel ventilation systems. A numerical approach is presented, based on the Finite Volume integration of the 1D mechanical and thermal energy conservation equations on a network of ducts, representing the ventilation system of the 11.6 km long Mont Blanc Tunnel. The set of distributed and concentrated loss coefficients, representing dissipation of mechanical energy by friction in each part of the ventilation system, is calibrated against a rich experimental dataset, collected throughout a dedicated set of in situ tests and presented in the first part of the work. The calibration of the model is carried out by means of genetic optimization algorithms. Predictions of the flow field using the calibrated parameters are in remarkable agreement with the experimental data, with an overall RMS error of ± 0.27 m/s, i.e. of the same order of the accuracy of the measurement probes. Further validation against a selection of field data recorded by the tunnel monitoring and control system is brought forward, highlighting the robustness and potential general applicability of the proposed approach.

2021 - The association of peak systolic velocity in the carotid artery with coronary heart disease: A study based on portable ultrasound [Articolo su rivista]
Konig, C. S.; Atherton, M.; Cavazzuti, M.; Gomm, C.; Ramachandran, S.

Cardiovascular disease (CVD) is the highest cause of death globally with more people dying annually from it than from any other cause. CVD is associated with modifiable risk factors (dyslipidaemia, hypertension and diabetes) and treating each of these factors lowers the risk of CVD. It is impossible to estimate the benefit of risk factor modification in the individual patient and extrapolating data from multiple trials is difficult. It would be useful to have a marker of risk that accurately estimates real time risk by measuring blood flow factors associated with the pathogenesis of atheroma. The aim of this preliminary study was to validate a low-cost measurement technique for obtaining blood flow velocity profiles and assess whether any of the measured and calculated factors, based on computational fluid dynamics (CFD) simulation, known to be associated with atheroma was associated with coronary heart disease (CHD), thus establishing its feasibility and acceptability as a clinical tool and suggesting areas for future research. Our study identified (i) that mean peak systolic (PS) velocity being associated with CHD; individuals without CHD: mean (SD) = 62.8 (16.1) cm/s, with CHD: mean (SD) = 53.6 (17.3) cm/s, p = 0.042; and (ii) that low-cost, portable ultrasound, which is routinely available in general practice, is a suitable assessment tool.

2020 - Compressible Fanno flows in micro-channels: An enhanced quasi-2D numerical model for turbulent flows [Articolo su rivista]
Cavazzuti, M.; Corticelli, M. A.; Karayiannis, T. G.

Fanno theory provides an analytical model for one-dimensional confined viscous compressible flows. The model holds under the assumptions of adiabatic flow and constant cross-section channel. From theory, the differential of every flow-related quantity is expressed as a function of Mach number and friction factor. One-dimensional flow numerical models can be derived by discretizing Fanno equations. However, theory does not assess how to evaluate friction, while the model works properly only if friction is estimated correctly. Compressibility and turbulence act by deforming the velocity profile making it flatter. Assuming the friction factor function of the Reynolds number alone, in line with incompressible flow theory, is thus not correct. Better correlations should include the Mach number to address compressibility effects. Here, the impact of turbulence and compressibility on the velocity profiles in a micro-channel is analysed by means of CFD simulations. Friction factor correlations are deduced for turbulent micro-flows. The impact of the velocity profile on other quantities, such as dynamic pressure and bulk temperature, needed for the numerical model operation, is also evaluated. Additional correlations for these quantities overcome the instrinsic limits of the one-dimensional model, necessarily unaware of local velocity profiles, in a quasi-2D fashion significantly improving its predicting capabilities.

2020 - Development and calibration of a 1D thermo-fluid dynamic model of ventilation in tunnels [Relazione in Atti di Convegno]
Cingi, P.; Angeli, D.; Cavazzuti, M.; Levoni, P.; Cipollone, M.

In complex, large civil infrastructures where ventilation has a crucial role for the safety of users in both normal operation and hazardous scenarios, the correct prediction of flow and heat transfer parameters is of fundamental importance. While full 3D simulation is applicable only to a limited extent, and the resort to 1D modeling is a common practice in both design and evaluation phases, the limitation of such models lies in the choice of transfer parameters, such as friction loss coefficients and heat transfer coefficients. In this work, an original approach based on the Finite Volume integration of the 1D flow and energy equations is presented. Such equations are to be solved on a network of ducts, representing the ventilation system in the 11.6 km long Mont Blanc Tunnel with a spatial resolution of 10 m. A preliminary calibration of a set of friction loss coefficients against a rich experimental dataset collected throughout a dedicated set of in situ tests is of particular concern here, as it is carried out by means of genetic optimization algorithms. Predictions of the flow field are in remarkable agreement with the experimental data, with an overall RMS error of - 0.42 m/s. Further refinements and possible parameter choices are also discussed.

2020 - Viscous heating effects on heat transfer characteristics of laminar compressible channel flow [Articolo su rivista]
Cavazzuti, M.

The present paper investigates viscous heating effects on heat transfer characteristics of laminar Newtonian compressible channel flow. At first, incompressible Poiseuille flow case is addressed analytically by including viscous dissipation term in energy conservation equation. Temperature distributions in the channel cross-section and local Nusselt numbers are derived as functions of the Brinkman number, highlighting the role of the viscous term. The analysis is numerically supported by a set of CFD simulations. Additional CFD results are employed to extend the analysis to compressible flow case resulting in dedicated local Nusselt number correlations, function of Brinkman and Mach numbers, and expansion-altered temperature profiles. The study assumes no-slip flow and no temperature-jump boundary conditions at the channel wall (Knudsen number Kn<10−3), and addresses both fluid heating and cooling, both uniform heat flux (UHF) and uniform wall temperature (UWT) boundary condition (BC), and both circular (CR) and parallel-plate (PP) channel cross-section.

2019 - Compressible Fanno flows in micro-channels: An enhanced quasi-2D numerical model for laminar flows [Articolo su rivista]
Cavazzuti, Marco; Corticelli, Mauro A.; Karayiannis, Tassos G.

Micro-scale fluid systems are becoming common in many applications ranging from electronic cooling to refrigeration systems and more. One-dimensional numerical models represent a simple and fast tool for the design of such devices, yet they struggle to accurately predict the flow characteristics in compressible micro-flows. Under the adiabatic assumption, the elegant theory developed by Fanno allows models for the viscous compressible flow in constant cross-section channels to be easily built. Although reasonably accurate, these models suffer from drawbacks inherent to their being one-dimensional, as such they cannot take into account the local profiles of quantities like the velocity and the temperature. In cascade, this results into incorrect evaluations of other dependent quantities, such as the dynamic pressure and the fluid thermophysical properties. The mismatch turns large when the fluid compressibility becomes important. As the Mach number grows, the velocity profile changes, and so the friction factor, even though a reliable model for predicting this change is still missing. In fact, a constant friction factor throughout the channel is generally assumed, following the incompressible flow theory. Here, a set of correlations is proposed improving the 1D theory accuracy by taking into account the effects of the non-uniform velocity and temperature profiles in a quasi-2D fashion. A detailed analysis of the velocity profiles at different Mach numbers coming from a large set of CFD simulations results in a model for assessing the impact of compressibility on friction and other quantities. The numerical model proposed, being able to properly account for the compressibility effects, offers an improved tool for the design of micro-scale fluid systems. Extending the analysis to include heat transfer is not difficult as the effect of heat flux will be analogous to the effect of pressure drop due to friction.

2019 - Compressible flows in micro-channels: an enhanced quasi-2D Fanno-based numerical model [Relazione in Atti di Convegno]
Cavazzuti, Marco; Corticelli, Mauro A.; Karayiannis, Tassos G.

Fanno theory provides an analytical model for the prediction of confined viscous compressible flows under the hypotheses of constant cross-section channel and adiabatic flow. From theory, differentials of flow characteristic quantities can be expressed in function of Mach number and friction factor. Yet, the theory does not assess how to evaluate friction, whereas classical formulas for friction prediction in channels are derived under the hypothesis of incompressible flow and are no longer valid in case of compressible flows. Compressibility deforms the velocity profiles in the channel by making them more flat. As a consequence friction is increased compared to the incompressible case. At the same time, the change in the velocity profiles affects the average dynamic pressure and the bulk temperature along the channel. Correlations, function of Mach and Reynolds numbers, are required for quantifying these changes and improve the prediction of the Fanno model. In the present paper, the impact of compressibility on laminar and turbulent flows in micro-channels is assessed on the basis of a series of CFD simulations, and correlations are presented for friction, average dynamic pressure, and bulk temperature. The correlations are proven to enhance the accuracy of the Fanno model predictions.

2019 - Friction factor evaluation of compressible microflows using 1D Fanno flow-based numerical model [Relazione in Atti di Convegno]
Rehman, Danish; Cavazzuti, Marco; Hong, Chungpyo; Morini, GIAN LUCA

A numerical model based on the conventional Fanno flow theory for the friction factor evaluation of the gas flows inside microchannels has recently been developed by Cavazzuti et al. [1]. The current work aims to compare this numerical model with experimental results of microchannels. Pressure drop experiments are performed for a circular cross sectional microtube and a rectangular microchannel with Nitrogen gas as working fluid. The hydraulic diameters of microtube and microchannel are 100 μm and 69.4 μm respectively. Rectangular microchannel with an aspect ratio (height to width) of 0.036 is chosen for the comparison. This allows to treat the rectangular microchannel as parallel plate in the numerical Fanno model. During experiments stagnation pressure at the inlet is increased such that maximum Reynolds number is 3000 in the case of microchannel and 7600 for microtube. Results show that for the evaluation of average friction factor in both considered geometries, there exists a good match between Fanno-based 1D numerical model and experimental results in the laminar regime whereas comparison worsens as the flow approaches choking. Limitations as well as the potential reasons for the discrepancies between the developed model and experiments will be discussed.

2019 - Thermal management of a Formula E electric motor: Analysis and optimization [Articolo su rivista]
Cavazzuti, Marco; Gaspari, Gloria; Pasquale, Stefano; Stalio, Enrico

The thermal analysis of a high performance brushless synchronous electric motor with permanent magnets and water jacket cooling is presented. The analysis is carried out following a lumped parameter thermal network approach which allows to identify the most important thermal paths in the motor and the main parameters influencing them. Thanks to its simplicity, the solution of such a thermal network model is very fast, allowing a large number of what-if scenarios to be computed over a short amount of time. For this reason, the model is coupled with external tools for performing systematic sensitivity analyses and optimizations. Goal of the investigation is the reduction of the windings temperature being this temperature inversely proportional to the efficiency and the power delivered by the motor. The sensitivity analysis, performed over a series of material, geometric, and operational factors, leads to the identification of the most relevant parameters influencing the thermal behaviour of the motor. A series of optimizations, focusing on these parameters and including suitable constraints granting the well-posedness of the problem and the feasibility of the solution, bring to the definition of an optimum layout of the water jacket and of the stator geometries. The optimized geometry allows a significant reduction of the windings temperature to be achieved.

2019 - Velocity profile development and friction in compressible micro-flows [Relazione in Atti di Convegno]
Cavazzuti, Marco; Corticelli, Mauro A.; Karayiannis, Tassos G.

rom Poiseuille theory, it is known that incompressible laminar fully-developed flow of a Newtonian fluid in a constant cross-section channel is characterised by steady parabolic velocity profiles after a fully-developed flow condition is attained. In turbulent fully-developed flow the velocity profiles are non-parabolic and become more flat for higher Reynolds numbers. When the incompressible hypothesis does not hold, as in the case of high velocity ideal gas flow, the velocity profile becomes flatter, as if more turbulent, due to the superposition of compressibility and turbulence effects, if applicable. This is typical in micro-channel flows, where pressure gradients are high and the gas is rapidly accelerating, eventually up to the sound velocity. As the flow accelerates the effects of compressibility grow stronger and the velocity profile keeps changing shape. The radial velocity component does not zero as in fully-developed flow but reverses after the entrance effects have damped out and grows with the Mach number. A net mass transfer toward the walls is thus generated making the velocity profile more flat. This affects the friction factor which is no longer constant, being proportional to the normal-to-wall velocity gradient, and needs to be evaluated. In the present work, the compressible friction factor is numerically investigated and correlations are proposed based on the velocity profile shape evolution as a function of the Mach number. This, together with other considerations on the velocity profile shape change, is shown to enhance the predictive capability of the Fanno theory for compressible flows.

2018 - Optimization methodology for automotive chassis design by truss frame: A preliminary investigation using the lattice approach [Relazione in Atti di Convegno]
Mantovani, Sara; Campo, GIUSEPPE ALESSIO; Ferrari, Andrea; Cavazzuti, Marco

The present paper investigates the application of optimization methodologies to vehicle chassis in view of an integrated and transdisciplinary vehicle design. A detailed sizing optimization in cascade to Topology Optimization (TO) for the design of automotive chassis is investigated. This approach is also known as lattice optimization. The TO is employed to find a coarse optimum chassis lay-out under linear elastic conditions. The second stage of the methodology converts into a truss frame the edges of the FE cells, including only the elements that remained above a certain density threshold after TO. The diameter of each truss is then optimized in view of chassis weight reduction while meeting a set of given design requirements, such as maximum stress and minimum size. Various tubular frame architectures for lightweight solutions are considered complying with different sets of constraints over different design spaces. Finally, the balance between the computational cost and the feasibility of the lattice solution is discussed in comparison to TO.

2017 - A pilot study to assess peak systolic velocity as possible marker of atherosclerotic burden using ultrasound [Abstract in Atti di Convegno]
Koenig, Carola; Atherton, Mark A.; Cavazzuti, Marco; Ramachandran, Sud; Gomm, Corinna; Strange, Richard; Halliday, Ian; Schenkel, Torsten

Introduction: Ischemic heart disease (IHD) has been associated with lower peak systolic velocity (PSV) on penile Doppler measurements [1]. This study establishes whether carotid ultrasound (US) PSV was associated with computational fluid dynamics (CFD) outputs, which in turn may contribute to IHD pathogenesis. Methods: A sample of 57 subjects (with IHD: 27, without IHD: 30) had US velocity profiles (left- common carotid artery) determined between 10e12 equispaced points. Bezier curve fitting was used to fit the profile through the measured velocity points for a normalised diameter. PSV was correlated against CFD results such as wall shear stress (WSS) [2]. Difference in PSV between individuals with/without IHD was studied via t-test. Linear regression was carried out to see if peak systolic velocity was associated with CFD outputs. Any significant associations were analysed within stratified groups (with/without IHD). Results: PSV was significantly lower (p Z 0.042) in subjects with IHD (with IHD: 53.6 17.3 cm/s, without IHD: 62.8 16.1 cm/s). PSV was associated with carotid bulb average pressure drop (p < 0.001), area of average bulb WSS (<1 Pa: p Z 0.016, <2 Pa: p Z 0.006, <3 Pa: p Z 0.001). All the above associations remained significant in individuals with IHD (average bulb pressure drop: p Z 0.001, average bulb WSS (<1 Pa: p Z 0.013, <2 Pa: p Z 0.008, <3 Pa: p Z 0.003). In subjects without IHD, PSV was associated with only average bulb pressure drop (p Z 0.016). Conclusions: This study suggests that further work on PSV and its associations with CFD outputs is required in individuals with and without IHD in various vascular beds.

2017 - An algorithm for solving steady-state heat conduction in arbitrarily complex composite planar walls with temperature-dependent thermal conductivities [Articolo su rivista]
Cavazzuti, Marco; Corticelli, Mauro Alessandro

An algorithm for solving steady-state heat conduction problems in arbitrarily complex composite walls is presented. Per se, steady-state heat conduction across a wall can easily be solved by hand. Yet, in practical applications the wall structure is often complex enough to deter such an approach if a finer yet simple analysis of the thermal bridges is of interest. Moreover, if high-temperature applications are involved, the additional complexity of including time-dependent thermal conductivity must be considered. Thus, a general methodology for solving arbitrary topology walls, involving any kind of thermal resistances in series and in parallel is discussed. While such a problem is formally simple to solve for a given wall following the theory, its algorithmic generalization is not. A method is provided, involving a program written in python language. The focus of the work is mainly on the algorithmic point of view: a simple way for the assessment of the wall topology and for the resolution of the heat conduction problem originating is sought. Temperature-dependent thermal conductivity of the materials is addressed, resulting in the need of evaluating the heat fluxes and the average temperature at each thermal resistance.

2017 - Convective heat transfer of turbulent decaying swirled flows in concentric annular pipes [Articolo su rivista]
Cavazzuti, Marco; Corticelli, Mauro Alessandro

The heat transfer characteristics of turbulent decaying swirled flows in concentric annular pipes is investigated numerically by means of CFD simulations using the OpenFOAM package. The simulations are performed for different Reynolds numbers and swirl angles at the duct inlet. By including cases with large temperature differences between the fluid and the wall, also the effects of radial temperature gradients on the velocity distribution are accounted for. A novel correlation, holding locally, is proposed and is presented in a form similar to the classical Sieder-Tate correlation, including an additional term to address the influence of the swirled flow. In a similar fashion, a correlation for the friction factor is given in the form of the Petukhov formula, yet with an additional swirl-related term. Also a formula assessing the swirl decay rate is presented. This allows global correlations to be extracted by solving the local ones over the pipe length in a system and integrating.

2017 - Numerical modelling of Fanno flows in micro channels: a quasi-static application to air vents for plastic moulding [Articolo su rivista]
Cavazzuti, Marco; Corticelli, Mauro Alessandro

The flow in micro air vents, as those used in the plastic moulding industry, can be assimilated to a Fanno flow. Even though Fanno theory is well-established, its outcome strongly depends on the correct assessment of the friction factor term. Yet, friction factor evaluation is not straightforward since traditional fluid-dynamics formulas fail to account for the compressibility effects and are only valid when low Mach numbers are attained, which is often not the case. A numerical model implementing the non-isoentropic compressible Fanno flow theory is presented. A friction factor correlation is proposed, based on the results of a large set of CFD simulations used for calibrating the numerical model. The model is then used for characterizing micro air vent geometries under different operating stagnation pressures and temperatures. The vents characterization is finally employed for the quasi-static assessment of the mass flow rate through the vents, and of the air pressure in the mould during a typical moulding process.

2015 - Optimization of a finned concentric pipes heat exchanger for industrial recuperative burners [Articolo su rivista]
Cavazzuti, Marco; Agnani, Elia; Corticelli, Mauro Alessandro

A numerical application is presented in which a finned concentric pipes heat exchanger is simulated by means of CFD, and optimized by the Nelder and Mead simplex downhill optimization algorithm. The heat exchanger parameterization takes into consideration the main geometrical aspects of the exchanger under different operating conditions. The work originates from an industrial problem related to heat recovery issues in recuperative burners, in which air is pre-heated by the exhaust gas before entering the combustion chamber. Such a device allows for an in situ and more efficient heat recovery from exhaust gases, also reducing both the sizing of the heat recovery system downstream to the furnace, and the burner fuel consumption. It is found that the fine tuning of just a few geometrical parameters can result in a sensible enhancement of the exchanger efficiency.

2015 - Optimization of recuperative burners for industrial kilns through CFD simulation [Relazione in Atti di Convegno]
Agnani, Elia; Cavazzuti, Marco; Corticelli, Mauro Alessandro

An optimization of the shape of a recuperative burner for industrial furnaces for tiles production is presented. The aim of the study is the maximization of the energy recovery from exhaust gas across a heat exchanger in order to pre-heat the combustion air. The study is carried out by means of CFD simulations. Eleven geometric parameters have been chosen and varied individually in an introductory sensitivity analysis. Useful information on the parameters influence have been thus obtained. Due to the large grid size and computing times, a direct optimization has been deemed unfeasible for our purpose. In its place, a fine tuning of the solution has been achieved by investigating the parameters interactions and finding a rather linear superposition of the effects. A reduction of the burner fuel consumption of almost 5% has been attained without affecting the markers of the product firing quality, such as the temperature profile on the tiles floor along the kiln room.

2014 - A review on artificial intelligence applications to the optimal design of dedicated and reconfigurable manufacturing systems [Articolo su rivista]
Renzi, Cristina; Leali, Francesco; Cavazzuti, Marco; Andrisano, Angelo Oreste

Reconfigurable manufacturing systems (RMS) are considered the future of manufacturing, being able to overcome both dedicated (DMS) and flexible manufacturing systems (FMS). In fact, they provide significant cost and time reductions in the launch of new products, and in the integration of new manufacturing processes into existing systems. The goals of RMS design are the extension of the production variety, the adaption to rapid changes in the market demand, and the minimization of the investment costs. Despite the interest of many authors, the debate on RMS is still open due to the lack of practical applications. This work is a review of the state-of-the-art on the design of cellular RMS, compared to DMS, by means of optimization. The problem addressed belongs to the NP-Hard family of combinatorial problem. The focus is on non-exact meta-heuristic and artificial intelligence methods, since these have been proven to be effective and robust in solving complex manufacturing design problems. A wide investigation on the most recurrent techniques in DMS and RMS literature is performed at first. A critical analysis over these techniques is given in the end.

2014 - Mesh morphing and fatigue analysis integration: A way to increase the industrial productivity and performance with shape optimization [Relazione in Atti di Convegno]
Cenni, Riccardo; Cova, M.; Baldini, Andrea; Cavazzuti, Marco

A methodology is developed for fatigue driven shape optimization of industrial mechanical components by means of mesh morphing. The methodology is integrated in commercial software platforms to increase its productivity and performance in industrial applications. It is well known that shape optimization is a way to improve the structural performance of components, yet it is mostly applied to linear elastic load cases. The idea of including fatigue analysis into the optimization process is of great interest for mechanical components design. Tools based on parametric geometries are becoming standard for fine-tuning optimization processes in industry. These tools can handle multiaxial fatigue analysis, but they are limited by difficulties in maintaining geometry coherence. The use of finite element models in place of parametric geometries results in a faster and more flexible methodology. In fact, mesh morphing avoids geometry coherence problems and the need of re-meshing. The aim of this work is the integration of mesh morphing and multiaxial fatigue in the context of shape optimization. A tool for achieving this was created and is presented here together with its application to part of a cast iron component subject to multi-axial high-cycle fatigue. The results obtained with the proposed methodology are closer to the industrial needs than those that can be obtained from shape optimization based on structure stiffness alone.

2013 - CFD analyses of Syngas-fired industrial tiles kiln module [Articolo su rivista]
Cavazzuti, Marco; Corticelli, Mauro Alessandro; Gianluca, Masina; Roberto, Saponelli

Industrial kilns for ceramic tiles production demand thorough control of the firing parameters to ensure uniform product quality. A given temperature profile must be imposed along the kiln length, while spanwise temperature profile should be as uniform as possible at the tiles level at any location. Due to special needs in emerging markets, interest is growing towards the use of gases produced by gasification processes as an alternative to methane. This requires specific burner design and proper re-calibration of the firing parameters. In the present work, computational fluid dynamics is used to analyse an industrial kiln section for different fuels, nominal burner powers, and burner nozzle diameters. The results are given in terms of temperature and velocity fields in the kiln room, and temperature distributions over the tiles floor. It is shown that a sensible combination of the three parameters investigated can lead to satisfactory results, even with gases having poor heating value.

2013 - CFD analysis of a syngas-fired burner for ceramic industrial roller kiln [Articolo su rivista]
Cavazzuti, Marco; Corticelli, Mauro Alessandro; A., Nuccio; B., Zauli

Kiln burners for industrial tile production are usually fuelled by methane gas. However, the interest towards the use of coal or synthesis gases is rapidly increasing, mainly due to the opening of important markets in developing countries. The widely variable chemical composition of these fuels demands the gas burner to be adapted on case-by-case basis, since the firing parameters are strictly fixed, to guarantee the required temperature distribution within the kiln. In this context, computational fluid dynamics analysis represents a very convenient alternative to the traditional design based on experiments. In this article three-dimensional numerical predictions are presented for a syngas-fired burner. Three different fuels, two burner layouts and two burner nominal power are considered. Temperature, velocity and oxygen mass fraction distributions are discussed, and general design lines for low lower heating value gas burners are extracted.

2013 - Optimization Methods: from theory to design Scientific and technological aspects in mechanics [Monografia/Trattato scientifico]
Cavazzuti, Marco

Many words are spent on optimization nowadays, since it is a powerful instrument to be applied in design. However, there is the feeling that it is not always well understood and the focus still remains on creating new algorithms more than on understanding the way these can be applied to real-life problems. This book is about optimization techniques and is subdivided into two parts. In the first part a wide overview on optimization theory is presented. This is needed for the fact that having knowledge on how the algorithms work is important in order to understand the way they should be applied, since it is not always straightforward to setup an optimization problem correctly. Moreover, a better knowledge of the theory allows the designer to understand which are the pros and cons of the algorithms, so that he will be able to choose the better ones depending on the problem at hand. The optimization theory is introduced and the main ideas in optimization theory are discussed. Optimization is presented as being composed of five topics, namely: design of experiments, response surface modelling, deterministic optimization, stochastic optimization, and robust engineering design. Each chapter, after presenting the main techniques for each part, draws application-oriented conclusions including didactic examples. In the second part, some applications are presented to guide the reader through the process of setting up a few optimization exercises, analyzing critically the choices which are made step-by-step, and showing how the different topics that constitute the optimization theory can be used jointly in an optimization process. The applications which are presented are mainly in the field of thermodynamics and fluid dynamics due to the author’s background. In particular, we deal with applications related to heat and mass transfer in natural and in forced convection, and to Stirling engines. Notwithstanding this, it must be reminded that optimization is an inherently interdisciplinary and multidisciplinary topic and the discussion which is made is still valid for other kind of applications. Summarizing, the idea of the book is to guide the reader towards applications in the optimization field because looking at the literature and at industry there is a clear feeling that a link is missing and optimization risks to remain a nice theory but with not many chances for application after all, while instead it would be a very powerful instrument in industrial design. This is probably enhanced by the fact that the literature in the field is clearly divided into various sub-fields of interest (e.g. gradient-based optimization or stochastic optimization) that are treated as worlds apart and no book or paper has been found trying to put the things together and give a wider overview over the topic. This is limiting optimization application to often ineffective one-shot applications of an algorithm. It could be argued that the book also discusses many techniques that are not properly optimization methods in themselves, such as design of experiments and response surface modelling. However, in the author’s opinion, it is important to include also these methods since in practice they are very helpful in the optimization of real-life industrial application. A practical and effective approach in solving an optimization problem should be an integrated process involving techniques from different subfields. Every technique has its particular features to be exploited knowledgeably, and no technique can be self-sufficient.

2012 - Numerical simulations of turbulent heat transfer in a channel with one wavy wall [Relazione in Atti di Convegno]
Errico, Orsola; Cavazzuti, Marco; Angeli, Diego; Stalio, Enrico

Wavy surfaces are encountered in a large variety of applications, and are well-known for enhancing heat and mass transfer mechanisms. The present study numerically investigates the flow dynamics and heat transfer for turbulent flow in a channel with one flat and one wavy wall. Investigations have been conducted for a Prandtl number Pr = 0.71 and Reynolds numbers Re = 13840 and Re = 19 000, based on the bulk velocity and the hydraulic diameter. Direct Numerical Simulations (DNSs) have been performed for a deep understanding of the dynamic effects on the heat transfer mechanisms for the case of turbulent flow in the channel with one wavy wall. The performance of two different Reynolds-Averaged Navier Stokes (RANS) turbulence models, namely the k-omega SST and the q-zeta, selected for their favorable characteristics, is assessed against the DNSs results. The applicability of the two selected RANS model is ascertained from a qualitative point of view.

2012 - Structural optimization of automotive chassis: theory, set up, design [Relazione in Atti di Convegno]
Cavazzuti, Marco; Splendi, Luca; D'Agostino, Luca; Torricelli, Enrico; Costi, Dario; Baldini, Andrea

Improvements in structural components design are often achieved on a trial-and-error basis guided by the designer know-how. Despite the designer experience must remain a fundamental aspect in design, such an approach is likely to allow only marginal product enhancements. A different turn of mind that could boost structural design is needed and could be given by structural optimization methods linked with finite elements analyses. These methods are here briefly introduced, and some applications are presented and discussed with the aim of showing their potential. A particular focus is given to weight reduction in automotive chassis design applications following the experience matured at MilleChili Lab.

2011 - Automotive Chassis Topology Optimization:a Comparison Between Spider and Coup´e Designs [Relazione in Atti di Convegno]
Cavazzuti, Marco; Costi, Dario; Baldini, Andrea; P., Moruzzi

Weight reduction is a major issue for carmakercompanies due the need to comply with the emission regulationswithout reducing the vehicle safety. A classic trial-and-errorapproach to design in the automotive industry is becominginadequate and new means are needed to enhance the designprocess. A major improvement on the end product can beachieved by adopting suitable optimization techniques fromthe early design stage. In the present paper the problem ofautomotive chassis design in view of weight reduction is tackledby means of topology optimization. The design methodologyproposed is applied twice: at first addressing a chassis for spidervehicles, then for coup´e vehicles. The two chassis, togetherwith some intermediate result are discussed and compared.The methodology has been proven to be successful in findinginnovative and efficient layouts for automotive chassis.

2011 - High performance automotive chassis design: a topology optimization based approach [Articolo su rivista]
Cavazzuti, Marco; Baldini, Andrea; Bertocchi, Enrico; Costi, Dario; Torricelli, Enrico; P., Moruzzi

Automotive chassis design in view of car weight reduction is a challenging task due to the many performance targets that must be satisfied, in particular in terms of vehicle safety. In this paper a methodology for automotive chassis design in involving optimization techniques is presented. In particular, topology, topometry and size optimizations are coupled with fem analyses and adopted in cascade for reaching an optimum chassis configuration. The methodology is applied to the design process of a rear-central engine high performance vehicle chassis. The objective of the optimization process is the chassis weight reduction, yet in fulfilment of structural performance constraints as required by Ferrari standards. The results demonstrate the general applicability of the methodology presented for obtaining the general trusses layout and thicknesses distribution of the structure. The numerical model at this stage shows a significant weight reduction when compared to the chassis of the Ferrari F458 Italia.

2011 - Lightweight crash energy absorber design using composite materials [Relazione in Atti di Convegno]
Mantovani, Sara; Cavazzuti, Marco

In an ongoing effort to increase the effectiveness of crash energy absorbers, thus improving the safety performance of cars, the interest in automotive industry in exploring lightweight alternatives to aluminum is deepening. In view of weight reduction, the research on composite materials has grown quickly because of their higher energy absorption-to-weight ratio. In the present work fiberglass composites with different shapes, types of fiber and stacking sequence are considered and analyzed by means of experiments and numerical simulations. At first, tension, compression, and shear properties of the materials are evaluated. Their dynamic properties are also investigated by drop testing according to ASTM D7136 standard. At a later stage, drop-tests are performed on cylindrical composite specimens in order to simulate the crash absorbers dynamic behaviour. Although the cylindrical specimens are not adhering to the standard, the drop tests allow to correlate the experimental data with the numerical simulations. Finally, in the light of the previous dynamic results, the stacking sequence of the composite crash absorbers is numerically optimized by means of design of experiments and optimization techniques for different geometrical shapes. Those considered are simple regular shapes, namely: circular, hexagonal, and octagonal.

2011 - Non-Newtonian and flow pulsatility effects in simulation models of a stented intracranial aneurysm [Articolo su rivista]
Cavazzuti, Marco; Atherton, M. A.; Collins, M. W.; Barozzi, Giovanni Sebastiano

Three models of different stent designs implanted in a cerebral aneurysm, originating from the virtual intracranial stenting challenge, are meshed and the flow characteristics simulated using commercial computational fluid dynamics (CFD) software in order to investigate the effects of non-Newtonian viscosity and pulsatile flow. Conventional mass inflow and wall shear stress (WSS) output are used as a means of comparing the CFD simulations. In addition, a WSS distribution is presented, which clearly discriminates in favour of the stent design identified byother groups. It is concluded that non-Newtonian and pulsatile effects are important to include in order to avoid underestimating WSS, understand dynamic flow effects, and to discriminatemore effectively between stent designs.

2010 - Advanced high performance vehicle frame design by means of topology optimization [Relazione in Atti di Convegno]
Cavazzuti, Marco; A., Merulla; Bertocchi, Enrico; Strozzi, Antonio; M., Pettazzoni

Automotive chassis design, often based on the company know-how and the designer experience, usually leads to consolidated solutions that are poorly innovative and not necessarily altogether efficient. Optimization techniques are powerful means for systematic design that can make it possible to avoid this drawback. The present study proposes a methodology for automotive chassis design based on topology, topometry and size optimizations coupled with fem analyses. In particular, the methodology is applied to the design of a chassis suitable for a rear-central engine high performance car. A massive 3d fem model is conceived, in order to respect the geometrical requirements yet leaving maximum freedom to the topology optimization algorithm. Shell mod- els are employed for the subsequent topometry and size optimizations. The objective is the minimization of the chassis mass in fulfillment of a given set of structural performance constraints. The results demonstrate the general applicability of the method proposed.

2010 - Beyond the Virtual Intracranial Stenting Challenge 2007: non-Newtonian and flow pulsatility effects [Articolo su rivista]
Cavazzuti, Marco; M. A., Atherton; M. W., Collins; Barozzi, Giovanni Sebastiano

Three models of stented cerebral aneurysms, originating from the VirtualIntracranial Stenting Challenge 2007 (visc'07), are meshed and the owcharacteristics simulated using commercial Computational Fluid Dynamics(cfd) software. Following views expressed in the literature and consistentwith the recommendations of a report, the eects of non-Newtonian viscos-ity and pulsatile ow are implemented. Conventional graphical Wall ShearStress (wss) output and basic summary measures of wss are normally usedas a qualitative means of comparing the cfd simulations. Herein a quan-titative measure of stent performance using wss distribution is presented,which clearly discriminates in favour of the stent design identied by theother groups in the report and provides a more informative comparison. Weconclude that non-Newtonian and pulsatile eects are important to includein order to avoid underestimating wss and to discriminate more eectivelybetween stent designs.

2009 - Numerical simulation of forced convection over steps at low Prandtl number [Relazione in Atti di Convegno]
Angeli, Diego; Cavazzuti, Marco; Stalio, Enrico

Convective heat transfer in laminar conditions is investigated numerically for a Prandtl number Pr = 0.025, representative of liquid lead-bismuth eutectic (LBE). The geometry selected is a periodic channel with a set of backward and forward steps. Finite-volume simulations are carried out on structured orthogonal curvilinear grids, for ten values of the Reynolds number up to the transitional range. It is shown how flow can undergo separation and reattachment also at very low-Re. The influence of flow separation mechanisms on local and global heat transfer rates is discussed, also considering the effect of different thermal boundary conditions imposed at the channel walls.

2009 - Optimization of heat exchanger enhanced surfaces under turbulent conditions [Relazione in Atti di Convegno]
Cavazzuti, Marco; Angeli, Diego; Corticelli, Mauro Alessandro; Barozzi, Giovanni Sebastiano

The optimization of heat transfer enhancing surfaces for compact heat exchangers is discussed.The heat transfer passages are parameterized through Bézier curves, and the optimum choice of the parameters is sought using both multi-objective and single objective optimization techniques. The objectives of the optimization are the maximization of the heat transfer rate and the minimization of the pressure drop encountered by the fluid crossing the passage. The objectives are evaluated in nondimensional form in terms of the Nusselt number and the friction factor. The investigation is carried out by means of CFD analyses, the fluid flowing in the passages is air, and turbulent flow is assumed. Two different turbulence models (namely, k- and k-!) are adopted in the optimization processes and the effect of the choice of the turbulence model on the optimization outcome is discussed.

2008 - Optimization of a buoyancy chimney with a heated ribbed wall [Articolo su rivista]
Cavazzuti, Marco; Corticelli, Mauro Alessandro

Heat and mass transfer in natural convection vertical channels was investigated by means of two-dimensional CFD simulations aided by optimization algorithms. The channel was immersed in air, enclosed between an adiabatic smooth wall and an isothermally heated ribbed wall. The ribs were perpendicular to the fluid flow and their height, width, pitch, thermal conductivity and lateral wall inclination were variable. Also the smooth heated wall channel was studied and compared with the ribbed one. The existence of an optimal channel width for a given channel height and rib geometry was shown. A sensitivity analysis was carried out for the ribbed and the smooth channels. Optimization was applied to the ribbed channel problem in order to maximize the heat and the mass transfer through a multi-objective genetic algorithm. It was found that the presence of the ribs penalizes the channel performance so that no ribbed channel over-performed the smooth one.

2008 - Optimization of heat exchanger enhanced surfaces through multi-objective genetic algorithms [Articolo su rivista]
Cavazzuti, Marco; Corticelli, Mauro Alessandro

Heat transfer enhancing surfaces are of interest for a wide range of industrial applications. Theaim of this paper is to provide a robust automated method for the design of two-dimensionalenhanced surfaces. Multi-objective optimization algorithms are employed: the competing objectivesaddressed are the maximization of the heat transfer and the minimization of the pressuredrop for Re = 1000 and Pr = 0:74. The surfaces are parameterized with Bézier curves anda finite volume solver is used for the cfd analysis. The optimization is based on different algorithmsused sequentially. Finally, a robust design assessment analysis is carried out on twoconfigurations.

2008 - Turbulence Models comparison in heat exchanger enhanced surfaces optimization [Relazione in Atti di Convegno]
Cavazzuti, Marco; Corticelli, Mauro Alessandro; Barozzi, Giovanni Sebastiano

In this paper the problem of the optimization of heat transfer enhancing surfaces is faced. The surfaces are parameterized usingBezier curves and solved with a finite volumes CFD code. The optimization is based on three different algorithms used in cascade:MOGT, MOGA-II and simplex for non-linear optimization. The Reynolds number is based on the average velocity and hydraulicdiameter of the channels and is set to 1000, the Prandtl number is 0:744. The same optimization process is carried out twice usingtwo different turbulence models: k-e RNG with enhanced wall treatment and k-w SST with low Reynolds number correction to theturbulent viscosity. It is found that the differences in the optimum channel shapes are significant and even that the same channelcan give quite different results being solved with a turbulence model or another. Though, from the results of the two optimizationprocesses, the rules of thumb we can infer on which elements a channel needs in order to have a certain performance, are almostthe same.

2008 - Vascular device interaction with the endothelium [Abstract in Atti di Convegno]
M. A., Atherton; A. W., Khir; Cavazzuti, Marco; Barozzi, Giovanni Sebastiano; M. W., Collins

The interaction between cerebral stents and endothelium, as well as the interaction between intra aortic balloon pumps, temporary cardiac assist devices, with aortic tissues are described in view of the numerical modelling of the above vascular devices.

2007 - Radiation heat transfer effect on natural convection in asymmetrically heated vertical channels [Relazione in Atti di Convegno]
Cavazzuti, Marco; F., Pinto; Corticelli, Mauro Alessandro; E., Nobile

Heat and mass transfer in vertical channels with a heated ribbed wall is investigated numerically and the results coming from two different CFD codes are compared. The codes are based on finite volume (Fluent 6.2) and on finite element approach (COMSOL Multiphysics) respectively. The channel is two dimensional, is set in vertical position and it is bounded by a heated ribbed wall facing an adiabatic smooth wall. The effects of the aspect ratio, the temperature difference between the heated wall and the ambient, the thermal conductivity of the ribs and the emissivity of the heated wall are considered. The results show that small aspect ratios and low thermal conductivity ribs have a negative effect on heat and mass transfer. High temperature differences and high emission coefficients for the heated wall, on the contrary, lead to a strong enhancement of the channel heat and mass transfer.

2006 - Optimization of a natural convection vertical channel with a heated ribbed wall [Relazione in Atti di Convegno]
Cavazzuti, Marco; Corticelli, Mauro Alessandro; E., Nobile; G., Tanda

Heat transfer and mass flow rate in a natural convection vertical channel was investigated using a CFD code coupled with anoptimization dedicated software. The channel was considered bidimensional and set in vertical position, immersed in air, witha heated wall at uniform temperature condition, the other wall being adiabatic. The channel was open at the bottom and at thetop to allow the natural circulation of the ambient air. The heated wall was filled with ribs whose height, width, pitch, thermal conductivity and side wall inclination were variable. The analysis proceeded through the following steps: a) results validation versus schlieren experiments [1]; b) performance comparison: ribbed versus smooth configuration; c) smooth channel sensitivity analysis; d) ribbed channel sensitivity analysis; e) ribbed channel DOE sampling; f) ribbed channel optimization through genetic and simplex algorithms, aiming at average heat transfer and mass flow maximization. In the first steps the existence of an optimal channel width was investigated; the results coming from the latter steps clearly show the importance of the rib height: higher ribs strongly disturb the air stream leading to a performance drop.

2003 - Un modello numerico per l’analisi termodinamica di motori Stirling–Beale [Relazione in Atti di Convegno]
Borghi, Massimo; M., Bonnici; Cavazzuti, Marco; Barozzi, Giovanni Sebastiano

Si presenta un modello simulativo applicabile ai motori lineari a pistoni liberi a ciclo Stirling, secondo lo schema proposto da Beale. Il modello si basa sulla discretizzazione temporale delle equazioni del moto dei pistoni e delle equazioni di bilancio di massa e di energia per il volume di lavoro della macchina. Il modello è destinato all’esecuzione di analisi di stabilità e di efficienza di soluzioni progettuali alternative, in sede di dimensionamento dei dispositivi