Criteria

Text:
Affiliation:
Display:

Results

Viewing 1 to 30 of 106
2015-04-14
Technical Paper
2015-01-1510
Edoardo Sabbioni, Davide Ivone, Francesco Braghin, Federico Cheli
Estimation of friction coefficient and sideslip angle represents a key-point for improving control systems for vehicle safety, e.g. ESP (Electronic Stability Control), VDC (Vehicle Dynamics Control), etc. A model-based approach (state observer or Kalman filter) is generally used on purpose. Benefits induced by in-tyre sensors on sideslip angle and friction coefficient estimation are investigated in this paper. Thus tyre cornering force measurements are added to the ones usually present on-board vehicle (steer angle, lateral acceleration and yaw rate) and used to implement an Extended Kalman Filter (EKF) based on a single-track vehicle model. Tyre-road contact forces are assumed to be provided once per wheel turn by a smart tyre constituted of two tri-axial accelerometers glued on the tyre inner liner. Performance of the proposed observer is evaluated on a series of handling maneuvers and its robustness to road bank angle and tyre/vehicle parameters variation is discussed.
2015-04-14
Technical Paper
2015-01-0315
Francesco Braghin, Andrea Fuso, Edoardo Sabbioni, Nicola De Val
Abstract The Linear Time Varying (LTV) Model Predictive Control (MPC) is a linear model predictive control based on linearization of the nonlinear vehicle model. The linearization is carried out consideing each vehicle state. The developed model is able to steer to avoid obstacles and follow a given path. Once the optimal parameters are found, both in terms of trajectory following and real-time performances, the LTV-MPC is used for assessing the limit vehicle conditions as a function of the vehicle forward target speed, the obstacle shape as well as the road conditions (both dry and wet road conditions were taken into account). It is shown that, to avoid collisions, given performances of the vehicle brakes and of the mounted sensors are required.
2015-04-14
Technical Paper
2015-01-0228
Francesco Braghin, Francesco Salis
Abstract The objective of this study is to demonstrate the design and construction of an innovative active gear-shift and clutch for racecars, applied to a Formula Student car, based on the use of DC gear-motors. Racecars require extremely quick gear-shifts and every system to be as light as possible. The proposed solution is designed to reduce energy consumption, weight and improve gear-shift precision compared to traditionally employed electro-hydraulic solutions, although maintaining state of the art performances.
2015-04-14
Technical Paper
2015-01-0376
Tommaso Lucchini, Augusto Della Torre, Gianluca D'Errico, Gianluca Montenegro, Marco Fiocco, Amin Maghbouli
Prediction of in-cylinder flows and fuel-air mixing are two fundamental pre-requisites for a successful simulation of direct-injection engines. Over the years, many efforts were carried out in order to improve available turbulence and spray models. However, enhancements in physical modeling can be drastically affected by mesh structure and quality which can negatively influence the predicted structure of organized charge motions, turbulence generation and interaction between in-cylinder flows and injected sprays. This is even more relevant for modern direct injection engines where multiple injections and control of charge motions are employed in a large portion of the operating map. Currently, two different approaches for mesh generation exist: manual and automatic. The first makes generally possible to generate high-quality meshes but, at the same time, it is very time consuming and not completely free from user errors.
2015-04-14
Technical Paper
2015-01-0384
Andrea Montorfano, Federico Piscaglia, Angelo Onorati
The paper focuses on the development of a mesh moving method based on non-conformal topologically changing grids applied to the simulation of IC engines, where the prescribed motion of piston and valves is accomplished by rigidly translating the sub-domain representing the moving component. With respect to authors’ previous work, a more robust and efficient algorithm to handle the connectivity of non-conformal interfaces and a mesh-motion solver supporting multiple layer addition/removal of cells, to decouple the time-step constraints of the mesh motion and of the fluid dynamics, has been implemented as a C++ library to extend the already existing classes for dynamic mesh handling of the finite-volume, open-source CFD code OpenFOAM(R), in the version released by OpenCFD(R).
2015-04-14
Technical Paper
2015-01-1472
Roberto Arienti, Carlo Cantoni, Massimiliano Gobbi, Giampiero Mastinu, Mario Pennati, Giorgio Previati
Abstract The lightweight seat of a high performance car is designed taking into account a rear impact, i.e. the crash due to an impulse applied from the rear. The basic parameters of the seat structure are derived resorting to simulations of a crash with a test dummy positioned on the seat. The simulations provide the forces acting at the seat structure, in particular the forces applied at the joint between the seat cushion and the seat backrest are taken into account. Such a joint is simulated as a plastic hinge and dissipates some of the crash energy. The simulations are validated by means of indoor tests with satisfactory results. A tool has been developed for the preliminary design of lightweight seats for high performance cars.
2015-04-14
Journal Article
2015-01-1520
Massimiliano Gobbi, Giampiero Mastinu, Federico Ballo, Giorgio Previati
A wheel able to measure the generalized forces at the hub of a race motorcycle has been developed and used. The wheel has a very limited weight (about 2 kg). It is made from magnesium with a special structure to sense the forces and provide the required level of stiffness. The wheel has been tested both indoor for preliminary approval according to internal standards and on the track. The three forces and the three moments at the hub can be measured with a resolution of respectively 1N and 0.3Nm. Twelve strain gauges are positioned at relevant locations to sense the generalized forces. Utilizing an encoder (angle resolution 0.06°), a simultaneous ADC sampling is performed on the six strain gauges bridges outputs while coupling the force/torque output with the absolute wheel angular position. The sincronous sampling allows seamless real-time measurements at vehicle speed up to 400 km/h.
2015-04-14
Journal Article
2015-01-0395
Federico Piscaglia, Andrea Montorfano, Angelo Onorati
Abstract Swirling flows are very dominant in applied technical problems, especially in IC engines, and their prediction requires rather sophisticated modeling. An adaptive low-pass filtering procedure for the modeled turbulent length and time scales is derived and applied to Menter' original k - ω SST turbulence model. The modeled length and time scales are compared to what can potentially be resolved by the computational grid and time step. If the modeled scales are larger than the resolvable scales, the resolvable scales will replace the modeled scales in the formulation of the eddy viscosity; therefore, the filtering technique helps the turbulence model to adapt in accordance with the mesh resolution and the scales to capture.
2015-04-14
Journal Article
2015-01-1594
Johannes Edelmann, Massimiliano Gobbi, Giampiero Mastinu, Manfred Ploechl, Giorgio Previati
The friction estimation at the tyre-ground contact is crucial for the active safety of vehicles. Friction estimation is a key problem of vehicle dynamics and the ultimate solution is still unknown. However the proposed approach, based on a simple idea and on a simple hardware, provides an actual solution. The idea is to compare the tyre characteristic at a given friction (nominal characteristic) with the actual characteristic that the tyre has while running. The comparison among these two characteristics (the nominal one and the actual one) gives the estimate of the actual friction coefficient. The mentioned comparison is an efficient but complex algorithm based on a mathematical formulation of the tyre characteristic. The estimation method is based on force and torque measurements in real time by a relatively simple smart wheel which is able to detect the three forces and the three moments acting at the hub. Both the theoretical and experimental issues are discussed in the paper.
2015-04-14
Technical Paper
2015-01-0375
Gianluca D'Errico, Tommaso Lucchini, Gilles Hardy, Ferry Tap, Giel Ramaekers
Abstract Diesel combustion is a very complex process, involving a reacting, turbulent and multi-phase flow. Furthermore, heavy duty engines operate mainly at medium and high loads, where injection durations are very long and cylinder pressure is high. Within such context, proper CFD tools are necessary to predict mixing controlled combustion, heat transfer and, eventually, flame wall interaction which might result from long injection durations and high injection pressures. In particular, detailed chemistry seems to be necessary to estimate correctly ignition under a wide range of operating conditions and formation of rich combustion products which might lead to soot formation. This work is dedicated to the identification of suitable methodologies to predict combustion in heavy-duty diesel engines using detailed chemistry.
2015-04-14
Journal Article
2015-01-0313
Ugo Rosolia, Francesco Braghin, Andrew Alleyne, Edoardo Sabbioni
Abstract This paper presents a nonlinear control approach to achieve good performances in vehicle path following and collision avoidance when the vehicle is driving under cruise highway conditions. Nonlinear model predictive control (NLMPC) is adopted to achieve online trajectory control based on a simplified vehicle model. GMRES/Continuation algorithm is used to solve the online optimization problem. Simulations show that the proposed controller is capable of tracking the desired path as well as avoiding the obstacles.
2014-10-13
Technical Paper
2014-01-2565
Harun Mohamed Ismail, Hoon Kiat Ng, Suyin Gan, Tommaso Lucchini
Abstract Modeling the combustion process of a diesel-biodiesel fuel spray in a 3-dimensional (3D) computational fluid dynamics (CFD) domain remains challenging and time-consuming despite the recent advancement in computing technologies. Accurate representation of the in-cylinder processes is essential for CFD studies to provide invaluable insights into these events, which are typically limited when using conventional experimental measurement techniques. This is especially true for emerging new fuels such as biodiesels since fundamental understanding of these fuels under combusting environment is still largely unknown. The reported work here is dedicated to evaluating the Adaptive Local Mesh Refinement (ALMR) approach in OpenFOAM® for improved simulation of reacting biodiesel fuel spray. An in-house model for thermo-physical and transport properties is integrated to the code, along with a chemical mechanism comprising 113 species and 399 reactions.
2014-04-01
Technical Paper
2014-01-1428
Federico Brusiani, Gian Marco Bianchi, Stefania Falfari, Angelo Onorati, Tommaso Lucchini, Rita Di Gioia
Abstract Today, multi-hole Diesel injectors can be mainly characterized by three different nozzle hole shapes: cylindrical, k-hole, and ks-hole. The nozzle hole layout plays a direct influence on the injector internal flow field characteristics and, in particular, on the cavitation and turbulence evolution over the hole length. In turn, the changes on the injector internal flow correlated to the nozzle shape produce immediate effects on the emerging spray. In the present paper, the fluid dynamic performance of three different Diesel nozzle hole shapes are evaluated: cylindrical, k-hole, and ks-hole. The ks-hole geometry was experimentally characterized in order to find out its real internal shape. First, the three nozzle shapes were studied by a fully transient CFD multiphase simulation to understand their differences in the internal flow field evolutions. In detail, the attention was focused on the turbulence and cavitation levels at hole exit.
2014-04-01
Technical Paper
2014-01-0645
Gianluca Montenegro, Augusto Della Torre, Angelo Onorati, Dalia Broggi, Gerd Schlager, Christian Benatzky
Abstract This work proposes a focus on the simulation of a rotative volumetric expander via a CFD code. A customized application of OpenFOAM® has been developed to handle the particular motion of the calculation grid. The model uses a mesh to mesh interpolation technique, switching from a calculation grid to the new one on the basis of mesh quality considerations performed on the fly. This particular approach allows to account for the presence of leakages occurring between the stator and blade tips and also occurring at the top and bottom of the vanes. The fluid considered is the refrigerant R245fa, whose particular properties have been determined resorting to the NIST database. Experimental data, measured at different conditions of mass flow and fluid temperature, are compared to calculation results. Moreover, the CFD analysis has allowed the estimation of the influence of the leakage mass flow occurring at the tip of the vanes on the overall machine performances.
2014-04-01
Technical Paper
2014-01-1121
Thuong Nguyen, Peter Janas, Tommaso Lucchini, Gianluca D'Errico, Sebastian Kaiser, Andreas Kempf
Abstract In this study two different simulation approaches to large eddy simulation of spark-ignition engines are compared. Additionally, some of the simulation results are compared to experimentally obtained in-cylinder velocity measurements. The first approach applies unstructured grids with an automated meshing procedure, using OpenFoam and Lib-ICE with a mapping approach. The second approach applies the efficient in-house code PsiPhi on equidistant, Cartesian grids, representing walls by immersed boundaries, where the moving piston and valves are described as topologically connected groups of Lagrangian particles. In the experiments, two-dimensional two-component particle image velocimetry is applied in the central tumble plane of the cylinder of an optically accessible engine. Good agreement between numerical results and experiment are obtained by both approaches.
2014-04-01
Technical Paper
2014-01-1161
Donald Selmanaj, Harald Waschl, Michael Schinnerl, Sergio Savaresi, Luigi del Re
Abstract Especially in view of more and more stringent emission legislation in passenger cars it is required to reduce the amount of pollutants. In the case of Diesel engines mainly NOx and PM are emitted during engine operation. The main influence factors for these pollutants are the in-cylinder oxygen concentration and the injected fuel amount. Typically the engine control task can be divided into two separate main parts, the fuel and the air system. Commonly air system control, consisting of a turbocharger and exhaust gas recirculation control, is used to provide the required amount of oxygen and address the emission targets, whereas the fuel is used to provide the desired torque. Especially in transient maneuvers the different time scales of both systems can lead to emission peaks which are not desired. Against this background in this work instead of the common way to address the air system, the fuel system is considered to reduce emission peaks during transients.
2014-04-01
Technical Paper
2014-01-1977
Robert Golimbioschi, Giampiero Mastinu, Luca Cordioli, Massimiliano Gobbi, Davide Tagliabue, Giorgio Previati, Francesco Braga
Abstract A new electric powertrain and axle for light/medium trucks is presented. The indoor testing and the simulation of the dynamic behavior are performed. The powertrain and axle has been produced by Streparava and tested at the Laboratory for the Safety of Transport of the Politecnico di Milano. The tests were aimed at defining the multi-physics perfomance of the powertrain and axle (efficiency, acceleration and braking, temperature and NVH). The whole system for indoor tests was composed by the powertrain and axle (electric motor, driveline, suspensions, wheels) and by the test rig (drums, driveline and electric motor). The (driving) axle was positioned on a couple of drums, and the drums provided the proper torques to the wheels to reproduce acceleration and braking. Additionally a cleat fixed on one drum excited the vibration of the suspensions and allowed assessing NVH performance. The simulations were based on a special co-simulation between 1D-AMESIM and VIRTUAL.LAB.
2014-04-01
Technical Paper
2014-01-0134
Isabel Ramirez Ruiz, F. Cheli
Abstract In the last years the number of electronic controllers of vehicle dynamics applied to chassis components has increased dramatically. They use lookup table of the primary order vehicle global parameters as yaw rate, lateral acceleration, steering angle, car velocity, that define the ideal behavior of the vehicle. They are usually based on PID controllers which compare the actual behavior of every measured real vehicle data to the desired behavior, from look up table. The controller attempts to keep the measured quantities the same as the tabled quantities by using ESP, TC (brakes and throttle), CDC (control shocks absorbers), EDIFF(active differential) and 4WS (rear wheels active toe). The performances of these controls are good but not perfect. The improvement can be achieved by replacement of the lookup tables with a fast vehicle model running in parallel to the real vehicle.
2014-04-01
Technical Paper
2014-01-1147
Andrea Montorfano, Federico Piscaglia, Angelo Onorati
Abstract The dynamics and evolution of turbulent structures inside an engine-like geometry are investigated by means of Large Eddy Simulation. A simplified configuration consisting of a flat-top cylinder head with a fixed, axis-centered valve and low-speed piston has been simulated by the finite volume CFD code OpenFOAM®; the standard version of the software has been extended to include the compressible WALE subgrid-scale model, models for the generation of synthetic turbulence, some improvements to the mesh motion strategy and algorithms for LES data post-processing. In order to study both the initial transient and the quasi- steady operating conditions, ten complete engine cycles have been simulated. Phase and spatial averages have been performed over cycles three to ten in order to extract first and second moment of velocity; these quantities have then been used to validate the numerical procedure by comparison against experimental data.
2014-04-01
Technical Paper
2014-01-1131
Tommaso Lucchini, Marco Fiocco, Roberto Torelli, Gianluca D'Errico
The definition of a robust methodology to perform a full-cycle CFD simulation of IC engines requires as first step the availability of a reliable grid generation tool, which does not only have to guarantee a high quality mesh but also has to prove to be efficient in terms of required time. In this work the authors discuss a novel approach entirely based on the OpenFOAM technology, in which the available 3D grid generator was employed to automatically create meshes containing hexahedra and split-hexahedra from triangulated surface geometries in Stereolithography (STL) format. The possibility to introduce local refinements and boundary layers makes this tool suitable for IC engine simulations. Grids are sequentially generated at target crank angles which are automatically determined depending on user specified settings such as maximum mesh validity interval and quality parameters like non-orthogonality, skewness and aspect ratio.
2014-04-01
Journal Article
2014-01-1144
Tommaso Lucchini, Gianluca D'Errico, Francesco Contino, Mehdi Jangi
Detailed chemistry and turbulence-chemistry interaction need to be properly taken into account for a realistic combustion simulation of IC engines where advanced combustion modes, multiple injections and stratified combustion involve a wide range of combustion regimes and require a proper description of several phenomena such as auto-ignition, flame stabilization, diffusive combustion and lean premixed flame propagation. To this end, different approaches are applied and the most used ones rely on the well-stirred reactor or flamelet assumption. However, well-mixed models do not describe correctly flame structure, while unsteady flamelet models cannot easily predict premixed flame propagation and triple flames. A possible alternative for them is represented by transported probability density functions (PDF) methods, which have been applied widely and effectively for modeling turbulent reacting flows under a wide range of combustion regimes.
2014-04-01
Technical Paper
2014-01-0874
Edoardo Sabbioni, Federico Cheli, Matteo Riva, Andrea Zorzutti
Abstract For passenger cars, individual tyre model parameters, used in vehicle models able to simulate vehicle handling behavior, are traditionally derived from expensive component indoor laboratory tests as a result of an identification procedure minimizing the error with respect to force and slip measurements. Indoor experiments on agricultural tyres are instead more challenging and thus generally not performed due to tyre size and applied forces. However, the knowledge of their handling characteristics is becoming more and more important since in the next few years, all agricultural vehicles are expected to run on ordinary asphalt roads at a speed of 80km/h.
2014-04-01
Journal Article
2014-01-0860
Edoardo Sabbioni, Federico Cheli, Michele Vignati, Stefano Melzi
In recent years, concerns for environmental pollution and oil price stimulated the demand for vehicles based on technologies alternative to traditional IC engines. Nowadays several carmakers include hybrid vehicles among their offer and first full electric vehicles appear on the market. Among the different layout of the electric power-train, four in-wheel motors appear to be one of the most attractive. Besides increasing the inner room, this architecture offers the interesting opportunity of easily and efficiently distribute the driving/braking torque on the four wheels. This characteristic can be exploited to generate a yaw moment (torque vectoring) able to increase lateral stability and to improve the handling of a vehicle. The present paper presents and compares two different torque vectoring control strategies for an electric vehicle with four in-wheel motors. Performances of the control strategies are evaluated by means of numerical simulations of open and closed loop maneuvers.
2013-09-08
Technical Paper
2013-24-0014
Gianluca D'Errico, Tommaso Lucchini, Alessandro Stagni, Alessio Frassoldati, Tiziano Faravelli, Eliseo Ranzi
Detailed chemistry represents a fundamental pre-requisite for a realistic simulation of combustion process in Diesel engines to properly reproduce ignition delay and flame structure (lift-off and soot precursors) in a wide range of operating conditions. In this work, the authors developed reduced mechanisms for n-dodecane starting from the comprehensive kinetic mechanism developed at Politecnico di Milano, well validated and tested in a wide range of operating conditions [1]. An algorithm combining Sensitivity and Flux Analysis was employed for the present skeletal reduction. The size of the mechanisms can be limited to less than 100 species and incorporates the most important details of low-temperature kinetics for a proper prediction of the ignition delay. Furthermore, the high-temperature chemistry is also properly described both in terms of reactivity and species formation, including unsaturated compounds such as acetylene, whose concentration controls soot formation.
2013-09-08
Technical Paper
2013-24-0027
Federico Piscaglia, Andrea Montorfano, Angelo Onorati
The current development to set up an automatic procedure for automatic mesh generation and automatic mesh motion for internal combustion engine simulation in OpenFOAM®-2.2.x is here described. In order to automatically generate high-quality meshes of cylinder geometries, some technical issues need to be addressed: 1) automatic mesh generation should be able to control anisotropy and directionality of the grid; 2) during piston and valve motion, cells and faces must be introduced and removed without varying the overall area and volume of the cells, to avoid conservation errors. In particular, interpolation between discrete fields is frequent in computational physics: the use of adaptive and non-conformal meshes necessitates the interpolation of fields between different mesh regions. Interpolation problems also arise in areas such as model coupling, model initialization and visualisation.
2013-09-08
Journal Article
2013-24-0021
Mattia Bissoli, Alberto Cuoci, Alessio Frassoldati, Tiziano Faravelli, Eliseo Ranzi, Tommaso Lucchini, Gianluca D'Errico, Francesco Contino
A new multi-zone model for the simulation of HCCI engine is here presented. The model includes laminar and turbulent diffusion and conduction exchange between the zones and the last improvements on the numerical aspects. Furthermore, a new strategy for the zone discretization is presented, which allows a better description of the near-wall zones. The aim of the work is to provide a fast and reliable model for carrying out chemical analysis with detailed kinetic schemes. A preliminary sensitivity analysis allows to verify that 10 zones are a convenient number for a good compromise between the computational effort and the description accuracy. The multi-zone predictions are then compared with the CFD ones to find the effective turbulence parameters, with the aim to describe the near-wall phenomena, both in a reactive and non-reactive cases.
2013-09-08
Journal Article
2013-24-0024
Tommaso Lucchini, Marco Fiocco, Angelo Onorati, Alessandro Montanaro, Luigi Allocca, Paolo Sementa, Bianca Maria Vaglieco, Francesco Catapano
This paper is focused on the development and application of a CFD methodology that can be applied to predict the fuel-air mixing process in stratified charge, sparkignition engines. The Eulerian-Lagrangian approach was used to model the spray evolution together with a liquid film model that properly takes into account its effects on the fuel-air mixing process into account. However, numerical simulation of stratified combustion in SI engines is a very challenging task for CFD modeling, due to the complex interaction of different physical phenomena involving turbulent, reacting and multiphase flows evolving inside a moving geometry. Hence, for a proper assessment of the different sub-models involved a detailed set of experimental optical data is required. To this end, a large experimental database was built by the authors.
2013-09-08
Journal Article
2013-24-0070
Gianluca Montenegro, Augusto Della Torre, Tarcisio Cerri, Giulio Lenzi, Andrea Fioravanti, Paolo Badalassi, Francesco Maiani
In this work a multilevel CFD analysis have been applied for the design of an intake air-box with improved characteristics of noise reduction and fluid dynamic response. The approaches developed and applied for the optimization process range from the 1D to fully 3D CFD simulation, exploring hybrid approaches based on the integration of a 1D model with quasi-3D and 3D tools. In particular, the quasi-3D strategy is exploited to investigate several configurations, tailoring the best trade-off between noise abatement at frequencies below 1000 Hz and optimization of engine performances. Once the best configuration has been defined, the 1D-3D approach has been adopted to confirm the prediction carried out by means of the simplified approach, studying also the impact of the new configuration on the engine performances.
2013-09-08
Technical Paper
2013-24-0139
Stephanie Stockar, Marcello Canova, Yann Guezennec, Augusto Della Torre, Gianluca Montenegro, Angelo Onorati
The automotive industry is striving to adopt model-based engine design and optimization procedures to reduce development time and costs. In this scenario, first-principles gas dynamic models predicting the mass, energy and momentum transport in the engine air path system with high accuracy and low computation effort are extremely important today for performance prediction, optimization and cylinder charge estimation and control. This paper presents a comparative study of two different modeling approaches to predict the one-dimensional unsteady compressible flow in the engine air path system. The first approach is based on a quasi-3D finite volume method, which relies on a geometrical reconstruction of the calculation domain using networks of zero-dimensional elements. The second approach is based on a model-order reduction procedure that projects the nonlinear hyperbolic partial differential equations describing the 1D unsteady flow in engine manifolds onto a predefined basis.
2013-04-08
Technical Paper
2013-01-1087
Tommaso Lucchini, Luca Cornolti, Gianluca Montenegro, Gianluca D'Errico, Marco Fiocco, Atsushi Teraji, Taisuke Shiraishi
A correct prediction of the initial stages of the combustion process in SI engines is of great importance to understand how local flow conditions, fuel properties, mixture stratification and ignition affect the in-cylinder pressure development and pollutant formation. However, flame kernel growth is governed by many interacting processes including energy transfer from the electrical circuit to the gas phase, interaction between the plasma channel and the flow field, transition between different combustion regimes and gas expansion at very high temperatures. In this work, the authors intend to present a comprehensive, multi-dimensional model that can be used to predict the initial combustion stages in SI engines. In particular, the spark channel is represented by a set of Lagrangian particles where each one of them acts as a single flame kernel.
Viewing 1 to 30 of 106

Filter

  • Range:
    to:
  • Year: