Abstract

This paper shows the recent work of the authors in the development of a time-domain FEM model for evaluation of the seal dynamics of a surface effect ship. The fluid solver developed for this purpose, uses a potential flow approach along with a stream-line integration of the free surface. The paper focuses on the free surface-structure algorithm that has been developed to allow the simulation of the complex and highly dynamic behavior of the seals in the interface between the air cushion, and the water.

The developed fluid-structure interaction solver is based, on one side, on an implicit iteration algorithm, communicating pressure forces and displacements of the seals at memory level and, on the other side, on an innovative wetting and drying scheme able to predict the water action on the seals. The stability of the iterative scheme is improved by means of relaxation, and the convergence is accelerated using Aitken’s method.

Several validations against experimental results have been carried out to demonstrate the developed algorithm.

Abstract

Unified formulation to solve fluid-structure interaction and multi-fluids problems are gaining popularity in many engineering applications, in particular for material forming processes. Indeed, it simplifies different issues related to mesh generation and boundary conditions and increases the flexibility to deal with multiscale problems.

We propose in this work a monolithic formulation where the complete problem is written in a fully Eulerian framework and the phases (fluid, solid,…) are separated by a level set function. The obtained system is solved using stabilized finite element methods. We combine this approximation with time-dependent anisotropic mesh adaptation to ensure accurate capturing of the discontinuities at the interfaces.

Different use of the levelset function ranging from, grain growth models for the evolutions of microstructure or void disclosure induced by forming operations, to the heat treatment of immersed metallic-alloys inside three-dimensional industrial furnaces will be presented. The advantages and the encountered numerical issues as well as the ongoing investigations related to these formulations will be discussed. 

Abstract

The necessity to provide physically reasonable and mathematically sound descriptions of mechanical behaviour at different scales is without discussion. Nevertheless, for engineering design quick estimations of important quantities such as stresses and strain are needed. This is not even enough. At a larger scale, information about the overall behaviour of complex systems has to be supplied. For this reason, we need to develop computational methods which on the one hand enable a detailed material description, on the other hand allow the bridging to coarser scales without losing too much information. In the present contribution, methods such as the phase field method are combined with FE technology, and, FE technology is combined with model reduction in order to reach this goal.

Abstract

En esta tesis se describe el desarrollo e implementación de un sistema informático para el tratamiento de toda la información necesaria para un análisis por el Método de los Elementos Finitos o por otros métodos numéricos (diferencias finitas, volúmenes finitos, métodos de contorno, métodos de puntos, etc.).Algunas de sus partes se refieren principalmente al diseño y organización de un sistema de estas características. En otras, se describen los nuevos algoritmos que ha sido necesario desarrollar para cumplir los objetivos propuestos.Las diversas disciplinas que se describen a lo largo de la tesis se pueden diferenciar en:* Organización del sistema. Consiste en definir el tratamiento de todos los datos de un análisis genérico de manera uniforme. También se dan criterios sobre el ordenamiento interno de los datos.* Modelación geométrica. Se presenta una serie de algoritmos que se han desarrollado para tratar y modificar la geometría del modelo.* Generación de malla. Se describen diferentes técnicas y algoritmos para poder realizar la generación de la malla.* Adaptabilidad del sistema a diferentes análisis. Se describe como se ha diseñado y como se realiza la adaptación del sistema a un código de análisis cualquiera.La implementación del conjunto de criterios y algoritmos descritos a lo largo de esta tesis, ha permitido la creación de un sistema que da soporte al proceso de análisis mediante métodos numéricos de modelos, tanto a nivel académico como industrial.

Abstract

We present a general formulation for analysis of fluid-structure interaction problems using the particle finite element method (PFEM). The key feature of the PFEM is the use of a Lagrangian description to model the motion of nodes (particles) in both the fluid and the structure domains. Nodes are thus viewed as particles which can freely move and even separate from the main analysis domain representing, for instance, the effect of water drops. A mesh connects the nodes defining the discretized domain where the governing equations, expressed in an integral from, are solved as in the standard FEM. The necessary stabilization for dealing with the incompressibility condition in the fluid is introduced via the finite calculus (FIC) method. A fractional step scheme for the transient coupled fluid-structure solution is described. Examples of application of the PFEM method to solve a number of fluid-structure interaction problems involving large motions of the free surface and splashing of waves are presented.

Abstract

In this paper a simple iterative method is presented for finite element solution of incompressible plane strain problems using linear elements. Instead of using a mixed formulation approach, we use an equivalent displacement/velocity approach in an iterative manner. Control volumes are taken for regions where are to exhibit incompressible behavior. For triangular elements the control volume is chosen as the area built on the parts of each pair of elements at the sides of an edge. In this case, elements are let to exchange volume. It is shown that the proposed edge based approach removes the deficiency of the linear triangular elements i.e. locking effect.Similar edge based approach is applied to the linear quadrilateral elements. However, if the control volume is chosen as the element volume the formulation gives similar results as the discontinuous mixed formulation using one pressure point without exhibiting instability behavior. The formulation is based on decomposition of the displacement/velocity field into deviatoric and volumetric parts. The volumetric part is iteratively eliminated without confronting locking or instability phenomenon. The iterative procedure is very cheap and simple to be implemented in any FEM code. Several examples are given to demonstrate the performance of the procedure.

Abstract

The paper presents an overview of the advances in recent years on the finite element method (FEM) and on particle-based methods for the simulation of industrial metal forming processes. More specifically, we present the evolution of the FEM in the field from the early plastic/viscoplastic flow approaches to the new stabilized FEM for analysis of multiphysics bulk forming processes. Also the paper describes the state of the art in the new rotation-free shell elements for simulation of sheet stamping processes. Finally, we present the so-called Particle Finite Element Method (PFEM), as a component of a family of new computational techniques integrating particle-based methods and mesh-based procedures. The PFEM is particularly suited for large deformation problems in solids and fluids involving nonlinear mechanical and geometrical effects, fluid-structure interactions and frictional contact situations. Applications of the FEM and the PFEM to several metal and material forming processes are presented.

Abstract

We present a generalized Lagrangian formulation for analysis of industrial forming processes involving thermally coupled interactions between deformable continua. The governing equations for the deformable bodies are written in a unified manner that holds both for fluids and solids. The success of the formulation lays on  a  residual-based  expression of the mass conservation equation obtained using the Finite Calculus (FIC) method that provides the necessary stability for quasi/fully incompressible situations. The  governing equations are discretized with the FEM via a mixed formulation using simplicial elements with equal linear interpolation for the velocities, the pressure and the temperature. The merits of the formulation  are demonstrated in the solution of 2D and 3D thermally-coupled forming processes using the Particle Finite Element Method (PFEM).

Abstract

Several residential, commercial and industrial applications have their efficiency increased when a thermal energy storage system is incorporated. The PCMs (Phase Change Materials), due to their high latent heat of fusion, are materials that represent a viable alternative to the implementation of thermal energy storage systems. This paper presents a numerical study of RT (Rubitherm Technologies GmbH) PCMs family fusion process in cylindrical cavities. The study was conducted through a CFD ''(''Computational Fluid Dynamics) numerical simulation, with ANSYS Fluent software. The numeric model adopted is two-dimensional and has been validated with numerical and experimental results of literature, achieving a good approximation. For PCMs here studied, increasing the temperature from 10 ''^oC'' to 20 ''^oC'' and 10 ''^oC'' to 30 ''^oC'', above the phase change temperature, for liquid fractions between 0.4 and 0.8, the average reduction of fusion time is approximately 55.8% and 71.8 %, respectively.

Abstract

The steady and careful checking process of the test examples is almost impossible for developers and users of Kratos, and needs to be automated. This has been the inspiration of development of an Automated Benchmarking module. During the nightly builds of Kratos, which will be done on the upcoming Kratos server, this module automatically runs all test examples and verifies the results against a reference data set. It will send an email containing the status of each test example to a list of recipients. This can be useful in several ways. First, it will be clear when a conflict has occurred. This will help greatly to find the user committed the changes, ask him / her to correct / undo it. Also, it will let other users to be aware of a conflict in the latest code base, and avoid updating their own local code base, before it has been corrected. This can save them a lot of time and effort.