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MAURO GIACALONE

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Pubblicazioni

2024 - A methodology to reduce the computational effort in 3D-CFD simulations of plate-fin heat exchangers [Articolo su rivista]
Torri, Federico; Berni, Fabio; Giacalone, Mauro; Mantovani, Sara; Defanti, Silvio; Colombini, Giulia; Bassoli, Elena; Merulla, Andrea; Fontanesi, Stefano
abstract

The analysis of a plate-fin heat exchanger performance requires the evaluation of key parameters such as heat transfer and pressure drop. In this regard, computational Fluid Dynamics (CFD) can be proficiently adopted, at the design stage, to predict the performance of plate-fin heat exchangers. However, these last are often characterized by a complex geometry, such as in the case of plate exchangers with turbulators, leading to a huge computational effort, which often exceeds the available resources. In this study, a numerical methodology for the simulation of plate heat exchangers is proposed, to bypass the limits imposed by the computational cost. The methodology relies on the simulation of a minimal portion of the exchanger (two plates, one per fluid) characterized by periodic boundary conditions (that mimic the presence of several layers). The total heat exchanged is obtained simply multiplying the calculated heat transfer by the number of plate couples composing the device. Moreover, the two plates allow to calibrate porous media which are adopted to rebuild (in a simplified version) the two fluid circuits of the whole exchanger and obtain the overall pressure drop across the device for both the hot and cold fluids. The proposed approach is validated against experimental data of an oil cooler for automotive application, that is a plate-fin heat exchanger characterized by the presence of turbulators. The numerical outcomes are compared to the experiments in terms of pressure drop and heat transfer for a wide range of volumetric flow rates. Particular attention is devoted to the mesh sensitivity and the adopted computational grid minimizes the number of cells (and, thus, the computational cost), without compromising the accuracy. Moreover, the Reynolds-Stress-Transport turbulence model is accurately selected among the most diffused ones, in order to properly match the test bench data. The proposed methodology allows to reduce of nearly one order of magnitude the total number of cells required for the simulation of the heat exchanger performance. The heat transfer is predicted with high accuracy, i.e. error is always lower than 4%. As for the pressure loss, the deviation compared to the experiments increases up to nearly 15% (for one of the simulated conditions) but it is considered still acceptable.

2024 - Dimensional and Mechanical Assessment of Gyroid Lattices Produced in Aluminum by Laser Powder Bed Fusion [Relazione in Atti di Convegno]
Defanti, Silvio; Giacalone, Mauro; Mantovani, Sara; Tognoli, Emanuele
abstract

The study investigates the use of aluminum gyroid lattices for structural purposes, with a particular focus on feasibility, dimensional accuracy, and compressive load performance. Gyroid lattice samples were built using laser powder bed fusion technology with AlSi10Mg, utilizing cell sizes of 6, 8, and 12 mm and a wall thickness of 0.5 mm. The compression performance of the samples was tested. The study revealed differences in dimensional accuracy in different directions, which was attributed to the fabrication process. All samples were heavier than expected, with additional materials being proportional to cell size. However, the samples exhibited high compressive strength and stiffness, indicating their potential use in load-bearing applications.

2023 - Evaluation of TPMS Structures for the Design of High Performance Heat Exchangers [Relazione in Atti di Convegno]
Torri, F.; Berni, F.; Fontanesi, S.; Mantovani, S.; Giacalone, M.; Defanti, S.; Bassoli, E.; Colombini, G.
abstract

The development of the additive manufacturing tech nology has enabled the design of components with complex structures that were previously unfeasible with conventional techniques. Among them, the Triply Periodic Minimal Surface (TPMS) structures are gaining scientific interest in several applications. Thanks to their high surface-to-volume ratio, lightweight construction, and excep tional mechanical properties, TPMS structures are being investigated for the production of high-performance heat exchangers to be adopted in different industrial fields, such as automotive and aerospace. Another significant advantage of the TPMS structures is their high degree of design flexibility. Each structure is created by replicating a characteristic unit cell in the three spatial dimensions. The three key parameters, namely cell type, cell dimension and wall thickness can be adjusted to provide considerable versatility in the design process. As for the heat exchangers, the variation of these parameters results in different values of heat transfer and pressure drop. If, on the one and, this flexibility leads to a wide range of design possibilities, on the other hand it generates uncertainty when the most suitable cell (with the best set of parameters) has to be selected. Therefore, the aim of the paper is to address the initial challenge in the design process of an innovative heat exchanger that incorporates a TPMS structure, which is the selection of the unit cell. Based on a literature review, four TPMS structures are selected as the most promising ones for the purpose, namely Gyroid, I-WP, Primitive and Diamond. Small prototypes of the selected structures are numerically tested at laminar and turbulent flow conditions to compare their performances in terms of heat transfer and pressure drop against a more traditional solution. In order to ensure an unbiased comparison between the structures, they are compared on equal volume of the specimen, wall thickness and unit cell dimension. Finally, a compact plate heat exchanger based on turbulators is added to the comparison, to investigate the capabilities of the TPMS structures compared to a more conventional solution.

2023 - Fatigue and failure analysis of aluminium and composite automotive wheel rims: Experimental and numerical investigation [Articolo su rivista]
Zanchini, Michele; Longhi, Daniel; Mantovani, Sara; Puglisi, Francesco; Giacalone, Mauro
abstract

This paper deals with the adoption of composites in the design of the wheel rims of a sports car. With particular reference to cornering structural performance, the design of a composite wheel rim, produced via Resin Transfer Moulding (RTM) led to a reduction in mass and to an increase in bending stiffness. The adoption of alternatives to aluminium alloys allows the unsprung masses, as well as the total mass of vehicle to be contained. This paper provides a comprehensive view of the fatigue tests used for the wheel rim type-approval, followed by a rundown of wheel rims designed by Ferrari S.p.A from 2009 to present. These wheel rims have been classified in terms of mass and stiffness, and manufacturing process like casting, forging, or RTM. The failure modes of the reference Ferrari 488 GTB wheel rim were compared to those of the new composite wheel. In addition, the interpretation of the failures is supported by the results of Finite Element analyses. Though some initial defects led to a loss of stiffness of the wheel throughout the cornering fatigue test, the experimental results show that composite wheel rims are considered safe and they comply with the homologation targets and the Ferrari S.p.A. regulations.

2023 - On the Technological Feasibility of additively manufactured self-supporting AlSi10Mg lattice structures [Articolo su rivista]
Bassoli, Elena; Mantovani, Sara; Giacalone, Mauro; Merulla, Andrea; Defanti, Silvio
abstract

The capability to design and manufacture metal lattice structures is today one of the most promising targets of Powder Bed Fusion technologies. Not only additively manufactured lattices offer great lightweighting possibilities, but they open the way to tailored and graded mechanical response. To best capitalize on this opportunity, research effort is first needed to assess the feasibility of reticular structures and to quantify the expected deviations from the nominal geometry, as a function of the cell topology and dimensions. Notwithstanding the inherent suitability of additive processes to complex shapes, this paper proposes a more exact definition of the technological boundaries for body-centred cubic lattices, showing to what extent specific dimensional ratios, as well as a self-supporting cell structure, can be favourable to minimize thedeviation from the nominal reticulum in terms of dimensions, density and presence of defects.

2023 - Rare Earth Materials Reduction in a Hypercar Propulsion System [Relazione in Atti di Convegno]
Devito, G.; Puglisi, F.; Barater, D.; Nuzzo, S.; Giacalone, M.; Franceschini, G.
abstract

Low-usage and rare earth free high-performance machines are in high demand, pushed by increasing costs and supply issues of rare earth materials. High torque density and high efficiency are key requirements in traction field. The challenge is designing propulsion systems which achieve such objectives while pursuing a global optimization logic in costs. This paper fits into this context by proposing a solution in which the same interior permanent magnet motor design is used for a four-wheel drive of a hypercar. A proper adaptation in axial length and magnets arrangement of the rear axle motor makes it suitable for the front axle requirements. Electromagnetic finite element analyses are performed to test different solutions with and without ferrite magnets. Torque, torque ripple, base speed, efficiency and rare earth reduction are the outputs under investigation. The best configurations are further studied via finite element structural analyses, as well as they are subjected to vibrational considerations. Different eligible solutions are found out with good performance while achieving a reduction in rare earth usage by 45.5%.

2022 - Effective Mechanical Properties of AlSi7Mg Additively Manufactured Cubic Lattice Structures [Articolo su rivista]
Mantovani, Sara; Giacalone, Mauro; Merulla, Andrea; Bassoli, Elena; Defanti, Silvio
abstract

Lattice structures, whose manufacturing has been enabled by additive technologies, are gaining growing popularity in all the fields where lightweighting is imperative. Since the complexity of the lattice geometries stretches the technological boundaries even of additive processes, the manufactured structures can be significantly different from the nominal ones, in terms of expected dimensions but also of defects. Therefore, the successful use of lattices needs the combined optimization of their design, structural modeling, build orientation, and setup. The article reports the results of quasi-static compression tests performed on BCCxyz lattices manufactured in a AlSi7Mg alloy using additive manufacturing. The results are compared with numerical simulations using two different approaches. The findings show the influence of the relative density on stiffness, strength, and on the energy absorption properties of the lattice. The correlation with the technological feasibility points out credible improvements in the choice of a unit cell with fewer manufacturing issues, lower density, and possibly equal mechanical properties.

2022 - Shafts with U-shaped circumferential grooves: design charts for stress concentration factors, radial displacement and Poisson’s ratio influence [Articolo su rivista]
Mantovani, Sara; Chiari, Alessandro; Giacalone, Mauro; Strozzi, Antonio
abstract

Shafts with U-shaped circumferential grooves subjected to internal normal force and bending moment are investigated on the basis of finite element analysis. The classical problem of the Stress Concentration Factors (SCFs) identification is addressed. SCF charts are provided, adopting the maximum equivalent von Mises stress in the SCF definition. The discrepancy between the uniaxial SCFs extracted from the standard reference books and the multiaxial SCF obtained by finite element increases from 5% up to 20%. The intersections between the SCF curves are studied, which reveal a non-monotonic profile of the SCFs with respect to the outer and inner diameter ratio of the notched shaft. The radial displacement at the notch root is examined and design charts of ample validity and prompt access are compiled. It is found that the radial displacement sign and magnitude are largely dependent on the geometry of the notch. Furthermore, the strain and stress state of extremely shallow grooves are analysed and a critical discussion on their SCFs using the von Mises criterion is presented. The influence of the Poisson’s ratio is considered. A simplified method for the evaluation of a multiaxial SCF is proposed to account for the Poisson’s ratio effect. Thanks to the employment of few dedicated diagrams, the present method allows an accurate evaluation of the SCF for U-grooved shafts, when the Poisson’s ratio differs from the common 0.3 value.

2022 - Steering column support topology optimization including lattice structure for metal additive manufacturing [Articolo su rivista]
Mantovani, S.; Campo, G. A.; Giacalone, M.
abstract

Structural engineering in the automotive industry has moved towards weight reduction and passive safety whilst maintaining a good structural performance. The development of Additive Manufacturing (AM) technologies has boosted design freedom, leading to a wide range of geometries and integrating functionally-graded lattice structures. This paper presents three AM-oriented numerical optimization methods, aimed at optimizing components made of: i) bulk material, ii) a combination of bulk material and graded lattice structures; iii) an integration of solid, lattice and thin-walled structures. The optimization methods were validated by considering the steering column support of a mid-rear engine sports car, involving complex loading conditions and shape. The results of the three methods are compared, and the advantages and disadvantages of the solutions are discussed. The integration between solid, lattice thin-walled structures produced the best results, with a mass reduction of 49.7% with respect to the existing component.

2020 - Numerical-experimental correlation of dynamic test of a honeycomb impact attenuator for a formula sae vehicle [Articolo su rivista]
Vettorello, A.; Campo, G. A.; Goldoni, G.; Giacalone, M.
abstract

A honeycomb impact attenuator for a Formula SAE (FSAE) prototype vehicle is examined using both experimental and numerical analyses. Two common FSAE impact attenuators were compared to a new design concept, combining four layers of hexagonal honeycomb. The comparison aimed to obtain the combination of the lowest mass and highest energy absorption. The attenuator must comply with both the FSAE championship rules and further internally-defined design constraints. The work continues addressing the numerical-experimental correlation of the applied materials. Finally, the finite element models for virtual crash testing are presented and were validated through the experimental tests.