Gabriele Virzi' Mariotti | Università degli Studi di Palermo (original) (raw)

Papers by Gabriele Virzi' Mariotti

This paper presents the experimental tests for the thermomechanical characterization of biopolyme... more This paper presents the experimental tests for the thermomechanical characterization of biopolymer polylactic acid, and its composites with beech flour or with nanoreiforcement of modified montmorillonite, with the purpose of applicability in the automotive sector. Tests of torque and traction are executed for the mechanical characterization and the results comparison; dynamical tests are executed for the thermomechanical characterization, determining the elastic modulus and loss factor versus the actual temperature

After an initial study of the characteristics of magnetorheological fluids base d on a thorough s... more After an initial study of the characteristics of magnetorheological fluids base d on a thorough search in literature, a preliminary configuration of MR brake is proposed. It comes from the evaluation of the main factors influencing the design of an appropriate magnetic circuit, and then the performance obtained in terms of brake torque. The analytical study of the brake has allowed a first preliminary sizing. T hrough the subsequent execution of an electromagnetic finite element model, created in ANSYS, it was possible to assess more accurately the distribution of the magnetic field inside the MR fluid and hence the resistance to relative motion between rotor and stator. T he work needs an accurate optimization due to insufficient value of the braking torque and high mass of the device. ). The use of MR fluid dampers for motor vehicles allows the construction of suspension at variable calibration with obvious advantages for the vehicle's dynamic behavior Gillespie, 1992), it seems that the use of MR suspension (Barbaraci and Virzì Mariotti, 2009) is better than electrorheological suspension , the features are still under investigation. Besides, MR fluids oppose certain resistance to sliding, and have the ability to control the amount of shear stress, which suggests their application in a brake, which represents the objective of this work. In the literature many papers are found . Paper contains the design of a MR brake with FEM analysis and experimental tests that that prove a hysteretic behaviour; paper reports the design, the optimization and experimental tests of a MR brake, with the conclusion that the brake is not sufficient to stop the vehicle , paper shows the results of the experimental test on a MR brake, concluding that the torque increase with the increase of the magnetic field until the saturation, designing the electromagnet at high efficiency by FEM. The main advantages of MR brakes are a more rapid response in operation and reduction of the number of braking system components. Their disadvantages are high mass of the device and the lack of sensitivity in braking; the papers containing a survey on the disadvantages are very few. The development of brake begins looking at the main brake operation factors by which MR brake could achieve performance comparable to that of a conventional automotive brake [f.e. Aleksendric, Duboka and Virzi' Mariotti, 2008). Particular attention is put to the choice of an appropriate configuration of the magnetic circuit to obtain the magnetization of the fluid and to generate the required braking torque. In particular a system with four active surfaces is designed in order to reduce the mass and the radial size and increase the braking torque. The possibilities offered by this type of system are assessed by the implementation of a preliminary analytical model and the subsequent execution of an electromagnetic Finite Element (FE) calculation that simulates the operation of the device. This paper shows that the preliminary design is not able to implement a brake able to stop the vehicle and that the brake has a too high mass for a practical application; the second part shows that an accurate optimization can eliminate the disadvantages, and also that the thermal problem (Wiehe, Noack and Maas, 2009) has high importance.

This work studies the teenage pedestrian–sport utility vehicle (SUV) crash; injury to the vital p... more This work studies the teenage pedestrian–sport utility vehicle (SUV) crash; injury to the vital parts of the body, such as the head and chest, and to the femur is evaluated. More advanced injury criteria are applied, as provided in the rules. The multibody technique is applied by making use of SimWise software and of the teenager anthropomorphic model, the use of which is now consolidated. Head injury criterion (HIC) is used for the head, thoracic trauma index (TTI) criterion for the thorax in the case of side impact and 3 ms criterion in the case of frontal impact, while the force criterion is used for the femur. Both the TTI and femur load evaluation require non-substantial modifications of the dummy, by insertion of sensors for the measurement of the acceleration of the 4th rib and the 12th vertebra and two very thin plates at the knees for the correct individuation of the contact point with the vehicle bumper. Particular attention is paid
to the front shape of the vehicle, concluding that the SUV examined in this paper is less dangerous than the sedan studied in a previous work, since its frontal dimensions (bonnet angle, bumper height and bonnet height) are more advantageous. However the teenage pedestrian in a lateral position is less prone to injuries in the head and chest, with respect to the frontal position; the pedestrian’s position has little influence on femur damage. Furthermore, the braking of the vehicle reduces the possibility of crash fatality. In conclusion, a theoretical approach is shown, to highlight the influence
of the vehicle mass on the pedestrian speed after the impact.

SOMMARIO È proposta una carena innovativa di tipo a catamarano, costituita da due scafi simmetric... more SOMMARIO È proposta una carena innovativa di tipo a catamarano, costituita da due scafi simmetrici affiancati con superfici tali da formare un canale convergente-divergente: l'energia ceduta è convogliata attraverso il canale con aumento della velocità nel tratto convergente, ed è in parte recuperata nel tratto divergente. Sono state condotte una serie di simulazioni fluidodinamiche utilizzando un software commerciale, l'attendibilità delle quali è convalidata da prove sperimentali eseguite in vasca. L'ottimizzazione della forma della carena proposta avviene minimizzando la resistenza totale (attrito+onda) valutata attraverso simulazione numerica. Si è messa a punto una procedura che applica un loop chiuso: partendo da una data configurazione iniziale si ottiene la geometria della carena che minimizza la resistenza totale attraverso la modifica della superficie b-spline che definisce la carena stessa. La superficie ottenuta viene salvata nel formato neutro IGES al fine di poter essere utilizzata dai più diffusi software commerciali sia di CAD che di CFD. ABSTRACT A new shape for a catamaran hull is investigated. It is constituted by two symmetric hulls, having the interior surfaces forming a convergent – divergent canal: the yielded energy is conveyed across the canal with speed increasing in the convergent side and it is partially recovered in the divergent side. Series of fluid dynamic simulations have been executed with a commercial software, reliability of which it is confirmed by experimental results obtained from towing tank test. The shape optimization of the proposed hull happens minimizing the total resistance (friction + wave) evaluated by numerical simulations. A procedure is set up applying a closed loop: starting from a given initial configuration, the optimal hull geometry is obtained by means of a minimization process. The surface is defined by means of a B–spline surface in IGES neutral format which is the adopted standard for many CAD and CFD software applications.

Data obtained in teenage cyclist impact against three vehicles (sedan, SUV and Pick Up), tested i... more Data obtained in teenage cyclist impact against three vehicles (sedan, SUV and Pick Up), tested in previous works, are analyzed to verify the theoretical results by the coupling of momentum conservation principle and energy conservation principle. The speed of vehicle and thorax are compared with theoretical ones, obtaining an excellent agreement. Following the results found in the literature, particular emphasis is done on teenager cyclist thorax and head speeds, indicating that the cyclist speed can be theoretically until 1,41 times the impact speed, while greater values, until 2, are obtained in the simulations. A small slowing of the vehicle is found theoretically and in the simulations, due to kinetic energy transfer. A small component of the vehicle speed exists in the orthogonal plane to the motion, due, for example, to the compression of the rider body on the bonnet. A parameter is determined using all the data in term of thorax speed, in all the impact speeds and in all the relative positions; its value does not appear depending on the vehicle mass. It allows the subsequent determination of the best values of three geometric actual parameters identified in front of the vehicle: bumper height, bonnet height and bonnet inclination angle, by interpolation with a second order curve, by making the conclusion that the frontal part of the vehicle may be designed in order to reduce the injury.

In this work the data, obtained for the three vehicles (sedan, SUV and Pick Up), tested in previo... more In this work the data, obtained for the three vehicles (sedan, SUV and Pick Up), tested in previous works, are compared. Following the results found in the literature, particular emphasis is done on the speed of the teenager cyclist head at the instant of impact and the diagrams of the head speed and the chest obtained in the simulations are shown. The speed of the head is that absolute, and this is used for processing the data and the subsequent determination of the best values of the three geometric actual parameters identified in front of the vehicle. Absolute speed is preferred because using the relative speed respect to vehicle, some amounts that cannot be disregarded are omitted from the evaluation. The chosen speed is 30 km/h because higher values appear too dependent on the mass of the vehicle, while lower values may not result in serious injury and are therefore less attractive. The procedure, to obtain the optimal values of the height of the bumper, the height of the bonnet and of the inclination angle of the bonnet is illustrated in the case the side impact vehicle-teenager cyclist. The conclusion is made that analogous procedure can be applied to HIC values.

The study of the injury caused by vehicle-teenage cyclist crash is presented in this paper. The r... more The study of the injury caused by vehicle-teenage cyclist crash is presented in this paper. The results of the crash with three vehicles: sedan, SUV and Pick up are compared. Three different positions are analyzed: front, rear and lateral position. The injury on the cyclist head is examined by HIC criterion, in the way indicated by the rules. A comparison is done between the results of the simulations for Pick up, SUV and sedan, concluding that the injury of the head is more dangerous for Pickup impact than SUV or the sedan, but only at greater speed than 40 km/h. Teenage cyclist is more likely to suffer an injury to the chest in rear impacts with the sedan, because 3 ms values remain above the values obtained with the SUV and Pick up. Unlike Pick up could cause greater injury to the chest in the front and side impact because of greater height from the ground. The vehicle mass has not great importance, but only to low speed. Consideration is made that teenage cyclist has a better chance of surviving in the front impact collision than adult pedestrian, because HIC values remain consistently below the determined values. A further comparison is done between the impact points of the three vehicles concluding that both the shape of the bonnet and the height of the front part must be studied carefully in order to reduce the damage to cyclists and pedestrians. At last the throwing distance are calculated and compared with the literature data, concluding that they are strongly dependent on the relative position.

The purpose of this paper is the study of the shape of catamaran with asymmetrical hulls by both ... more The purpose of this paper is the study of the shape of catamaran with asymmetrical hulls by both experimental and numerical viewpoint. The experimental study is based on the towing tank tests on a catamaran hulls shape obtained from previous works, showing that the wave resistance is very low produces a lower energy loss and a greater effectiveness. The hulls shape is optimized by the CFD application by force of commercial software, which shows that the reduction of wasted energy is very sensitive to make some changes; in particular three different width of the catamaran are tested and their performances are compared.

This paper presents the optimization process of MR – magnetorheological brake in order to define ... more This paper presents the optimization process of MR – magnetorheological brake in order to define its configuration, and to reach the requested vehicle braking torque. FEM analysis previously carried out, concerning structural sizing of such a brake, showed that both braking torque and brake mass did not satisfy the requirements. Due to the necessity of limitation on the suspended mass of a motor vehicle, the optimization of the form of MR brake stator has been executed, including determination of its contribution to the total mass of the brake. Thus a percentage reduction of approximately 40% was obtained. In order to estimate the brake temperature which results from the transformation into heat of a vehicle kinetic energy during brake application, a thermal Finite Element Analysis is carried out. In particular a fade braking test composed of snub braking, i.e. repeated cycles of acceleration and consecutive braking applications is performed.

Sommario Questo lavoro ha come obiettivo principale lo studio teorico e con supporto di software ... more Sommario Questo lavoro ha come obiettivo principale lo studio teorico e con supporto di software F.E.M. di un dispositivo che consenta recupero energetico da una sospensione automobilistica. In sostituzione allo smorzatore viscoso, che dissipa l'energia cinetica del veicolo a seguito dell'attraversamento di strade sconnesse o ostacoli più marcati, si è usato uno smorzatore elettromagnetico che svolga le funzioni dello smorzatore viscoso consentendo un recupero di energia elettrica. Lo smorzatore elettromagnetico è di tipo a magneti permanenti e il suo funzionamento si basa sul fenomeno dell'induzione elettromagnetica. Il modello matematico descrive il funzionamento dello smorzatore, restituendo i valori delle grandezze elettriche e meccaniche in funzione della velocità relativa tra stelo e statore. Si è valutato il recupero energetico considerando una minicar elettrica che transita su una strada mediamente sconnessa. La potenza elettrica recuperata ha un valore complessivo di circa 250 W. Abstract Main objective of this work is the theoretical study and support of FEM software of a device that allows for energy recovery from an automotive suspension. In replacing the viscous damper, which dissipates the kinetic energy of the vehicle due to rough roads or obstacles more marked, an electromagnetic damper is used that performs the functions of the viscous damper allowing a recovery of electricity. The damper is of the electromagnetic type with permanent magnets and its operation is based on the phenomenon of electromagnetic induction. The mathematical model describes the operation of the damper, restoring the values of the electrical and mechanical magnitudes as a function of the relative speed between the rod and the stator. Energy recovery has been estimated considering an electric minicar that transits on a bumpy road. The recovered power has a total value of about 250W.

The strain field on the surface of a steel SEC specimen has been investigated using the contact m... more The strain field on the surface of a steel SEC specimen has been investigated using the contact moirè technique. The results agree with those of other Authors and, at least in a limited region near the crack tip, also with Hutchinson relations. The J1c parameter is therefore considered to be suitable for the description of the strain state in presence of extended palsticitation.

Sommario Le vele di una imbarcazione sono sottoposte a grandi spostamenti a causa della loro natu... more Sommario Le vele di una imbarcazione sono sottoposte a grandi spostamenti a causa della loro natura altamente flessibile, per tale motivo, la forma che assumono quando sono sottoposte alla forza del vento è differente da quella di progetto stabilita dal velaio. Nel lavoro gli autori propongono un metodo basato sull'utilizzo della tecnica fotogrammetrica per il rilievo in navigazione di vele in vera grandezza. L'utilizzo di tecniche ottiche di Reverse Engineering consente, infatti, la ricostruzione tridimensionale del modello dell'intera vela. Vengono costruiti i modelli CAD delle vele di un'imbarcazione di classe Meteor in condizioni di navigazione (flying shape) e in condizioni di progetto (design shape) che sono analizzati con metodi CFD. Abstract The sails of a vessel are subjected to large displacements due to their highly flexible nature; therefore, the form they take when they are subjected to the force of the wind project is different from that established by the sailmaker. In the work the authors propose a method based on the use of photogrammetric techniques for the relief of sails in navigation in real size. The use of optical techniques of Reverse Engineering allows, in fact, three-dimensional reconstruction model of the entire wing. CAD models of the sails of a boat in the Meteor-class are built in surfing conditions (flying shape) and in design conditions (design, shape) and are analyzed by CFD methods. Parole chiave: fotogrammetria, vele, flying shape, design shape, CFD. 1. INTRODUZIONE La vela è una superficie di tela o di sottile e robusto materiale sintetico di forma tale che, utilizzando la forza del vento, genera propulsione. Al fine di realizzare geometrie che ottimizzino le performance dell'imbarcazione, esistono particolari software che consentono al velaio di disegnare la vela con una corretta curvatura, originando la sua design shape cioè la sua forma di progetto. Per ottenere una valutazione del comportamento aerodinamico delle vele progettate, queste possono essere sottoposte ad una analisi CFD, la quale, tuttavia, può fornire previsioni di prestazioni inesatte a causa di una differenza non sempre trascurabile tra la forma a riposo delle vele e quella sotto carico o flying shape, poiché le superfici veliche sono sottoposte a grandi spostamenti a causa della loro natura altamente flessibile.

The study of the injury caused by Pickup vehicle-teenage cyclist crash is presented in this paper... more The study of the injury caused by Pickup vehicle-teenage cyclist crash is presented in this paper. The vehicle has high frontal part, in order to compare the results with those obtained previously in the sedan and SUV-teenage cyclist crash. No variation is executed on the model of the teenage cyclist and the bike. Three different positions are analyzed: front, rear and lateral position. The injury on the cyclist head is examined by HIC criterion, in the way indicated in the rules. Correlation HIC – AIS is used to calculate the lethality of the injuries. A comparison is made between the results of the simulations for Pick up, SUV and sedan, concluding that the injury of the head is more dangerous for Pickup impact than SUV and the sedan, but only at the maximum speed (50 km/h). This value of the speed can be considered critical, since HIC values are very high for all the three vehicles. The more dangerous injury is the side impact. A further comparison is done between the impact points of the three vehicles concluding that both the shape of the bonnet that the height of the front part must be studied carefully in order to reduce the damage to cyclists and pedestrians.

In this paper we consider the problem of disc brake noise, an unstable behaviour that occurs in d... more In this paper we consider the problem of disc brake noise, an unstable behaviour that occurs in disc brakes due to particular vibratory phenomena. The most obvious phenomenology is the product wheezing during braking. The numerous researches carried out have not yet reached satisfactory results for knowledge. There was a total of high frequency squeal, which depends only on the characteristics of the disc and not by brake complete. Finite element method is applied to achieve modal analysis; a linear model was developed noting that to eliminate or reduce brake noise it is necessary that the ranges of calliper-disc frequencies modes do not overlap. The modal analysis of the runway braking is a good starting point but is not the only approach possible because the phenomenon of brake squeal depends on many other factors that make it quite complex.

Sommario In questa memoria si considera il problema del disc brake noise, un comportamento instab... more Sommario In questa memoria si considera il problema del disc brake noise, un comportamento instabile che si verifica nei freni a disco a causa di particolari fenomeni vibratori. La fenomenologia più evidente è il sibilo prodotto durante la frenata. Nonostante le numerose ricerche svolte non si è ancora arrivati a risultati soddisfacenti per la conoscenza. Ci si è occupati del high frequency squeal, che dipende solamente dalle caratteristiche del disco e non dall' impianto frenante completo. Si è applicato il metodo agli elementi finiti per realizzare un'analisi modale. È stato sviluppato il modello lineare osservando che per eliminare o ridurre i fenomeni di rumorosità del freno è necessario che gli intervalli di frequenze modali di disco e pinza non si sovrappongano. L'analisi modale della pista frenante è un ottimo punto di partenza ma non è l'unico approccio possibile in quanto il fenomeno del brake squeal dipende da molti altri fattori che lo rendono parecchio complesso. Abstract In this memory we consider the problem of disc brake noise, an unstable behaviour that occurs in disc brakes due to particular phenomena vibrators. The most obvious phenomenology is the product wheezing during braking. The numerous research carried out has not yet reached satisfactory results for knowledge. There was a total of high frequency squeal, which depends only on the characteristics of the disc and not by brakes complete. The finite element method is applied to achieve modal analysis. It was developed linear model noting that to eliminate or reduce the phenomena of noise brake is necessary that the ranges of calliper-disc frequencies modal do not overlap. The modal analysis of the runway braking is a good starting point but is not the only approach possible because the phenomenon of brake squeal depends on many other factors that make it quite complex. Parole chiave: disc brake noise, high frequency squeal, analisi modale, FEM.

The research is carried out to improve passenger’s comfort to increase the vehicles stability in ... more The research is carried out to improve passenger’s comfort to increase the vehicles stability in dynamic
conditions. The literature available in the automotive engineering considers different topics for studying suspensions. An
example represents mechanisms structure and analysis (synthesis, kinematics, and dynamics) under various operating
conditions. These aspects have been approached before analytically, numerical. The current paper studies the influence of the
lateral force on the contact patch of the wheel and the corresponding variations of vehicle stability parameters, such as cambe
r
angle and wheel rear track. The study is performed for a newer innovative rear suspensions mechanism which does not have
a wheel track and camber angle variation, relative to the chassis, when the suspension components was considered rigid. A
numerical solution is obtained through a virtual model on several commercial codes: MSC Adams, Patran, Nastran.
Concerning the analysed parametes, their variation increases as the applied force is increased. Moreover, the largest variation
corresponds to the case were elastic bushings and deformable links are considered.

Sommario Il lavoro ha come oggetto lo studio numerico di un freno a fluido magnetoreologico (MR) ... more Sommario Il lavoro ha come oggetto lo studio numerico di un freno a fluido magnetoreologico (MR) per uso automobilistico tramite il codice agli elementi fin iti ANSYS. In seguito ad un dimensionamento analitico preliminare del freno la realizzazione di un modello FEM magnetico permette un&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;accurata valutazione della distribuzione del campo magnetico nel fluido MR e la valutazione del momento frenante

Sommario Nel lavoro è valutato il comportamento di carrelli per serramenti in condizioni di caric... more Sommario Nel lavoro è valutato il comportamento di carrelli per serramenti in condizioni di carico variabile al fine di valutarne l'usura. Le prove di fatica sono state condotte su una macchina di semplice concezione appositamente realizzata e adatta a gara ntire un moto alterno sotto carico. Per la valutazione dell'usura è stata eseguita una scansio ne molto accurata della geometria

Engineering Analysis with Boundary Elements

In this paper are calculated stress concentration factors in collar and shouldered shafts subject... more In this paper are calculated stress concentration factors in collar and shouldered shafts subjected to axial or bending load, using both the boundary element (BEM) and finite element (FEM) methods. The values obtained by the two methods are in good agreement; for shouldered shafts in bending they are also very close to the available data in the literature obtained by the photoelastic technique. For shouldered shafts in traction, the values obtained are close to some experimental data of the literature and higher than others. Additionally, BEM and FEM values are interpolated in order to give useful plots and formulae.

Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering

The research reported in this paper aims to simulate the road-holding of a virtual vehicle using ... more The research reported in this paper aims to simulate the road-holding of a virtual vehicle using multi-body simulation to estimate both the contact forces between the tyre and ground and the roll motion when cornering. Furthermore, the effect of the characteristic angles on the variation in the forces of the tyre in contact with the ground is studied to determine optimal values for these angles. Emphasis is placed on an average-class vehicle, of which both the external dimensions and mass are chosen appropriately, with a McPherson suspension mounted on both the front and the rear. The characteristic values of the camber and toe-in angles, in both the front and the rear, are optimized for motion in the curve under constant traction. The results of numerical simulation are compared with results from the theory of stability in the curve (given the vertical configuration of the vehicle).

Engineering Analysis with Boundary Elements

Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering