1,721,007 research outputs found
Asymptotic stability estimates for some evolution problems with singular convection field
No full textWe establish asymptotic stability estimates for solutions to evolution problems with singular convection term. Such quantitative estimates provide a measure with respect to the time variable of the distance between the solution to a parabolic problem from the one of the its elliptic stationary counterpart
Tire multiphysical modeling for the analysis of thermal and wear sensitivity on vehicle objective dynamics and racing performances
No full textThe handling behavior of a vehicle is one of its most important properties because of its relation to performance and safety and to its deep link with concepts such as “over-steer” or “under-steer”. Tire–road interaction models play a fundamental role in the vehicle system modeling, since tires are responsible for the generation of forces arising within contact patches, fundamental for both handling and ride/comfort. Among the models used to reproduce such forces, Pacejka's Magic Formula (MF) is undoubtedly one of the most used ones in real-time automotive simulation environments because of its ability to fit quite easily a large amount of experimental data, but its original formulation did not take into account of the tire thermodynamics and wear conditions, which clearly affect tire and vehicle dynamics and are not negligible, especially for high level applications, such as motorsport competitions. Exploiting a multiphysical tire model, which consists in an evolved version of the standard MF model (MF-evo), and a vehicle model properly validated throughout experimental data acquired in outdoor testing sessions carried out with an industrial partner, the current work presents a study on vehicle behavior variation induced by thermodynamic and wear parameters, defining a series of metrics to analyze and show results. One of the elements of interest on which the focus is placed is the possibility to highlight how under-over-steering behavior of a car changes according to different thermodynamic states of tires; to do this, a commercial software VI CarRealTime has been used to perform a series of objective steady-state maneuvers and long runs, exploiting the logic of a lap time optimizer
Regularity results for solutions to elliptic obstacle problems in limit cases
No full textWe prove the Lewy–Stampacchia’s inequality for elliptic variational inequalities with obstacle involving Leray–Lions type operator whose simpler model case is given by the following (Formula presented.) where Ω is a smooth bounded domain of RN with N⩾2, ΔNu denotes the classical N–Laplacian operator and the coefficient B:Ω→RN belongs to a suitable Lorentz–Zygmund space. For this kind of obstacle problems, we also provide regularity results and amongst them we give sufficient conditions to get boundedness of solutions
A real-time thermal model for the analysis of tire/road interaction in motorcycle applications
No full textWhile in the automotive field the relationship between road adherence and tire temperature is mainly investigated with the aim to enhance the vehicle performance in motorsport, the motorcycle sector is highly sensitive to such theme also from less extreme applications. The small extension of the footprint, along with the need to guarantee driver stability and safety in the widest possible range of riding conditions, requires that tires work as most as possible at a temperature able to let the viscoelastic compounds-constituting the tread and the composite materials of the whole carcass structure-provide the highest interaction force with road. Moreover, both for tire manufacturing companies and for single track vehicles designers and racing teams, a deep knowledge of the thermodynamic phenomena involved at the ground level is a key factor for the development of optimal solutions and setup. This paper proposes a physical model based on the application of the Fourier thermodynamic equations to a three-dimensional domain, accounting for all the sources of heating like friction power at the road interface and the cyclic generation of heat because of rolling and to asphalt indentation, and for the cooling effects because of the air forced convection, to road conduction and to turbulences in the inflation chamber. The complex heat exchanges in the system are fully described and modeled, with particular reference to the management of contact patch position, correlated to camber angle and requiring the adoption of an innovative multi-ribbed and multi-layered tire structure. The completely physical approach induces the need of a proper parameterization of the model, whose main stages are described, both from the experimental and identification points of view, with particular reference to non-destructive procedures for thermal parameters definition. One of the most peculiar and challenging features of the model is linked with its topological and analytical structure, allowing to run in real-time, usefully for the application in co-simulation vehicle dynamics platforms, for performance prediction and setup optimization applications
On some non-local approximation of nonisotropic Griffith-type functionals
Full text linkThe approximation in the sense of Γ-convergence of nonisotropic Griffith-type functionals, with p−growth (p > 1) in the symmetrized gradient, by means of a suitable sequence of non-local convolution type functionals defined on Sobolev spaces, is analysed
Ultraviolet Light Radiation Effects on Viscoelastic Property Variation in Polymers
No full textViscoelastic materials exhibit a variable mechanical behavior generally investigated through Dynamic Mechanical Analysis (DMA). Such kind of test is carried out on standardized specimens, which have to be specifically produced or extracted from the component to be characterized, causing its destruction. This work, taking advantage of an innovative non-invasive testing procedure, based on an instrumented evaluation of indentation, aims to experimentally study the viscoelastic properties changes in polymer compounds, caused by exposure to UV rays. The analysis has been executed on two different polymer compounds designed for tire tread. An extensive use of UV radiation is performed to generate changes in rubber compound properties, but as concerns tire compounds application, there are only a few studies in literature and the same can be stated regarding the monitoring of properties over time using non-destructive procedures. In order to evaluate the viscoelastic properties variation, a proper test bench has been developed employing an UV lamp coupled with an innovative testing device. A test campaign has been carried out on the different tire compound specimens, tested in different conditions in terms of exposure time, exposure face and after various time ranges from the exposition. The tested compound samples exhibit a different chemical composition in terms of polymer blend ratio. The overall results highlight: the ability of the proposed technique to measure the variation in the mechanical behavior of the materials induced by exposure to UV rays and significant variations in viscoelastic properties induced on the compounds as a function of the time of exposure to UV rays and of the chemical composition
Virtual 7-Post Rig: A 7 DoF Vehicle Model for Suspensions Parameters Optimization
No full textVehicle testing is a key factor in motorsport field, always oriented towards maximizing performance. In last decades, testing procedures have evolved, going from classic outdoor tests to indoor test benches capable of stressing the vehicle in different ways, up to complex virtual simulation environments. In this scenario, this work presents a virtual 7-post rig, based on a seven degree of freedom vehicle model developed with a Lagrangian approach, able to reproduce the vertical behaviour of sprung and unsprung masses. This model could represent a valid alternative to the real test bench, allowing a significant reduction in the testing phase time and costs. The model performance has been assessed by means of a comparison with a much more complex simulation environment and from the comparison of the results it is clear that the developed model can be actually used for the evaluation of the optimal conditions of stiffness and damping of the suspension
An Enhanced Greenwood-Williamson Contact Model for the Evaluation of Local Tire/Road Contact Area
No full textContact modeling plays a crucial role in tire road interaction, impacting several fields, including vehicle dynamics, road safety, and transportation efficiency. As the tire is in contact with the road, the real contact area is smaller than the nominal area due to the indentation of the rubber over the road profile, influenced by the distribution of road texture. This paper introduces a novel approach to contact modeling, focusing on the evaluation of the ratio between the real contact area and the nominal one (AcA0), considering the Greenwood-Williamson formulation. This ratio is fundamental for characterizing the tire-road contact behavior, as it depends on tire viscoelastic properties, road roughness characterization and tire operating conditions. The paper presents some simulations conducted in MATLAB to assess the AcA0 ratio for various road specimens. These simulations were conducted considering a specific compound, while varying parameters such as contact pressure and compound temperature, with a fixed sliding velocity. This research, thus, enhances the understanding of how the road texture, combined with the tire properties and operating conditions, affects tire indentation over the road profile which is strictly related to the perceived friction values
Quasiconformal mappings and sharp estimates for the distance to L^\infty in some function spaces
No full textWe provide several estimates which involve the distance to L∞ in some function spaces, the composition operator induced by a quasiconformal mapping and the logarithm of the Jacobian of a quasiconformal mapping. Our results are sharp in the two dimensional case
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