Guus Segal

Solving conformal wheel–rail rolling contact problems

The stresses between railway wheels and rails can be computed using different types of contact models: simplified methods, half-space-based boundary element approaches and finite element models. For conformal contact situations, particularly the contact between flange root and rail gauge corner, none of these models work satisfactorily. Finite element methods are too slow, half-space approaches ignore the effects of conformality, and simplified approaches schematise the elasticity of the material even further. This paper presents a thorough investigation of the conformal wheel–rail rolling contact problem. We use CONTACTs boundary element approach together with numerical influence coefficients, that are computed using the finite element approach. The resulting method is fast and detailed and can be embedded into vehicle system dynamics simulation. The results indicate that the contact area is longer and narrower, with smaller area and reduced stiffness, than is predicted by the half-space approach. The predicted maximum pressures are increased by 30%. Finally the longitudinal and lateral forces changed up to 15% of the Coulomb maximum.

Hydrodynamic and Thermal Behavior of Journal Bearings using Upwind Petrov-Galerkin FEM

A novel approach to modeling plain journal bearings is presented. The journal is assumed to be cut open at the oil supply groove and modeled in Cartesian coordinates. The streamline upwind Petrov-Galerkin (SUPG) finite element method is used to develop the three-dimensional model. The model is validated using Boncompain, Costa, and Dowsons experimental data and compared to Khonsaris analytical method. The maximum deviation from the measured temperatures is 10 per cent for Costas data and the predictions of 51.2°C from the model are 0.3°C lower than Dowsons experimentally measured peak temperature. The model shows rapid convergence, stabilizing in only three iterations. The cavitation interface thermal boundary conditions need not be specified. Side leakage predictions are within 2.8 percent of the measured value whereas Martins analytical method achieves an accuracy of 11.2 percent.

Three-Dimensional Modeling of Thermohydrodynamic Lubrication in Slider Bearings Using Streamline Upwind Petrov-Galerkin Method

A three-dimensional thermohydrodynamic lubrication model which couples the Reynolds and energy equations is developed in the finite-element program Sepran. The model uses the streamline upwind Petrov-Galerkin method. Model results indicate the peak temperature is not on the mid-plane surface. This position shifts toward the mid-plane as the width-to-length ratio is reduced from 10 to 1 as well as when pressure boundary conditions are altered in such a way that the inlet/outlet pressure is higher than the side pressure. The adiabatic temperature profiles of an infinite slider and a square slider are compared. The wider slider shows a higher peak temperature. The side flow plays a major role in determining the value and position of the peak temperature. Model results also indicate peak side flow at a width-to-length ratio of 2.

SEPRAN: A versatile finite-element package for a wide variety of problems in geosciences

Numerical modelling of geological processes, such as mantle convection, flow in porous media, and geothermal heat transfer, has become quite common with the increase in computing and the availability of usable software. Today modelling these dynamical processes entails the solving of the governing equations involving the mass, momentum, energy and chemical transport. These equations represent partial differential equations and must be solved on powerful enough computers because they require sufficient spatial and temporal resolution to be useful. We describe here the salient and outstanding features of the SEPRAN software package, developed in the Netherlands, as a case study for a robust and user-friendly software, which the geological community can utilize in handling many thermal-mechanical-chemical problems found in geology, which will include geothermal situations, where many types of partial differential equations must be solved at the same time with thermodynamical input parameters.

Numerical results of falling film absorption with water/ammonia

Abstract A model was set up for the heat, mass and momentum transport in a falling film absorber with a binary gas phase. Results are given for water/ammonia and countercurrent gas flow. If the ratio of diffusion to convection is not negligible (here for a gas channel smaller than 5 mm) absorption is higher with countercurrent gas flow than with cocurrent flow. For larger gas channels the outcomes from a simpler one-component gas phase model are, if the interface boundary conditions are formulated correctly, almost equal to the outcomes from the present model.

Block preconditioners for the incompressible stokes problem

This paper discusses the solution of the Stokes problem using block preconditioned iterative methods Block preconditioners are based on the block factorization of the discretized problem We focus on two specific types: SIMPLE-type preconditioners and the LSC preconditioner Both methods use scaling to improve their performance We test convergence of GCR in combination with these preconditioners both for a constant and a non-constant viscosity Stokes problem.

Deflation Accelerated Parallel Preconditioned Conjugate Gradient Method in Finite Element Problems

We describe the algorithm to implement a deflation acceleration in a preconditioned Conjugate Gradient method to solve the system of linear equations from a Finite Element discretization. We focus on a parallel implementation in this paper. Subsequently we describe the data-structure. This is followed by some numerical experiments. The experiments indicate that our method is scalable.

THREE-DIMENSIONAL THERMAL FIELD IN SLIDER BEARINGS

A three dimensional thermohydrodynamic lubrication model which couples the Reynolds and energy equations is developed. The model uses the streamline upwind Petrov-Galerkin (SUPG) method to solve the non-symmetric stiffness matrix that results from the convective-dominated flow. Model results indicate that the peak temperature is not on the mid-plane surface, a fact that cannot be predicted with two dimensional models. This position shifts towards the mid-plane as the width to length ratio is reduced from ten to one (square slider) as well as when pressure boundary conditions are altered in such a way that the inlet/outlet pressure is higher than the side pressure. The square slider has a peak temperature 4°K less than the wider slider. This is due to the higher side flow in the square slider.Copyright

An unstructured staggered scheme for the Navier—Stokes equations

A novel scheme for viscous incompressible flows on unstructured grids is introduced. A staggered positioning of the variables is used: the pressure is located in the centroids of the triangles while the normal velocity components are placed at the midpoints of the faces of the triangles. The pressure-correction approach is employed to deal with the divergence-freedom constraint of the velocity. Spatial discretization is discussed. For the lid-driven cavity problem, good results are obtained.