16 research outputs found
An Enhanced Tire Model for Dynamic Simulation based on Geometrically Exact Shells
In the present work, a tire model is derived based on geometrically exact shells. The discretization is done with the help of isoparametric quadrilateral finite elements. The interpolation is performed with bilinear Lagrangian polynomials for the midsurface as well as for the director field. As time stepping method for the resulting differential algebraic equation a backward differentiation formula is chosen. A multilayer material model for geometrically exact shells is introduced, to describe the anisotropic behavior of the tire material. To handle the interaction with a rigid road surface, a unilateral frictional contact formulation is introduced. Therein a special surface to surface contact element is developed, which rebuilds the shape of the tire
The cellular modifier MOAG-4/SERF drives amyloid formation through charge complementation.
While aggregation-prone proteins are known to accelerate aging and cause age-related diseases, the cellular mechanisms that drive their cytotoxicity remain unresolved. The orthologous proteins MOAG-4, SERF1A, and SERF2 have recently been identified as cellular modifiers of such proteotoxicity. Using a peptide array screening approach on human amyloidogenic proteins, we found that SERF2 interacted with protein segments enriched in negatively charged and hydrophobic, aromatic amino acids. The absence of such segments, or the neutralization of the positive charge in SERF2, prevented these interactions and abolished the amyloid-promoting activity of SERF2. In protein aggregation models in the nematode worm Caenorhabditis elegans, protein aggregation and toxicity were suppressed by mutating the endogenous locus of MOAG-4 to neutralize charge. Our data indicate that MOAG-4 and SERF2 drive protein aggregation and toxicity by interactions with negatively charged segments in aggregation-prone proteins. Such charge interactions might accelerate primary nucleation of amyloid by initiating structural changes and by decreasing colloidal stability. Our study points at charge interactions between cellular modifiers and amyloidogenic proteins as potential targets for interventions to reduce age-related protein toxicity
Noise, vibration, harshness model of a rotating tyre
The tyre plays a fundamental role in the generation of acoustically perceptible driving noise and vibrations inside the vehicle. An essential part of these vibrations is induced by the road excitation and transferred via the tyre into the vehicle. There are two basic ways to study noise, vibration, harshness (NVH) behaviour: Simulations in time and frequency domains. Modelling the tyre transfer behaviour in frequency domain requires special attention to the rotation of the tyre. This paper shows the approach taken by the authors to include the transfer behaviour in the frequency range up to 250 Hz from geometric road excitations to resulting spindle forces in frequency domain. This paper validates the derived NVH tyre model by comparison with appropriate transient simulations of the base transient model
Simulation of Dynamic Gas Cavity Effects of a Tire under Operational Conditions
The authors are responsible for the development of a structural 3D shell based bead-to-bead model with sidewalls and belt that separately models all functional layers of a modern tire [4]. In this model, the inflation pressure is modeled as a uniform stress acting normal to the shell’s inner face. The pressure can vary depending on the application: prescribed by the MBS-tool to align to a constant pressure specified for a vehicle or scenario, but it can also be modified dynamically to simulate e.g. a sudden pressure loss in a tire [1]. For many applications, this description of the inflation pressure as a time dependent quantity is sufficient. However, there are applications where it is needed to describe the inflation gas using a dynamic gas equation (Euler or Navier-Stokes). One such example is when the tire model is used in NVH (Noise-Vibration-Harshness) applications where the frequency range extends the 200 Hz range. For passenger car tires, a first mode of the inflation gas is at around 200-250. This mode couples with the tire structure and yields significant peaks in the spindle force spectrum, which have to be considered in the NVH assessment of a car. In this paper, we show the effect of modeling the inflation gas of a tire by an isentropic compressible Euler equation and couple it to the tire dynamics in the nonlinear transient application range. After motivation and validation of the overall model by comparison with respective measurements, we also describe how to derive a linear model from the overall transient tire model, that can then be used in linear FEM based NVH-tools. It can be observed that the tire rotation will yield a split in the cavity mode which increases with rotational velocity, an effect that can also be correctly predicted by the linearized model
Dynamic simulation of the inflation gas of a tire under operational conditions
In this work, we are describing the coupling of an already existing tire model with a quasi-1D flow model to describe the inflation gas cavity fluctuations in a simple physical way. Since the gas cavity fluctuations are due to excitations - produced by transient tire deformations based on the interaction with the road surface - the gas model must be built to fully account for the tire shape variation. Thus, we derive the 1D Euler equations in a torus having a time and spatial dependent cross section area. The equations are discretized with a finite difference spatial discretization and integrated by an extended Lax-Wendroff scheme, which can handle source terms. The coupling between the mechanical response and the inflation gas model is done in the following way: The transient shape of the tire appears as a source term in the Euler equations. The local gas cavity fluctuations on the other act on the tire structure and on the rim, both of which produce entries into the resulting spindle forces. We are showing results for the overall non-linear model for transient simulations (cleat runs) and are comparing the results with and without dynamic gas cavity model and with measurements. Finally, we are showing how the overall model can be linearized around a steady state. With the resulting linear model, a modal analysis can be performed and we identify the so called ‘cavity mode’ and its dependence on rotational velocity
Managing the variety of potential tire / wheel sizes in the early vehicle development process
Virtual Tire Design/Assessment in the Early Vehicle Development Process
The choice of the optimal tire setup for a given vehicle is not a trivial task. Nowadays car manufacturers often collaborate with the tire manufacturers during the development phase of new vehicles in order to improve the quality of their final products. At the beginning of a new development project, vehicle engineers define the so called vehicle key performance indicators (KPIs) and respective targets that the vehicle has to achieve