SIMULATION OF INCOMPRESSIBLE FLOWS ACROSS MOVING BODIES USING MESHLESS FINITE DIFFRERENCING

Multiphysics numerical modelling of backward flow forming process of AISI 5140 steel

Fluid–structure interaction with ALE formulation and skeleton-based structural models

Abstract. This work proposes a new FE model to predict dynamic crack propagation mechanisms in quasi-brittle materials. The numerical strategy uses a Moving Mesh (MM) technique consistent with the Arbitrary Lagrangian-Eulerian (ALE) formulation to reproduce the variation of the geometry of the computational domain caused by dynamically growing cracks. Specifically, the motion of the mesh nodes takes place consistently with conditions dictated by classic Fracture Mechanics, which provide conditions concerning the direction of propagation and the velocity of advancing cracks. As a remarkable key novelty, the proposed method introduces the ALE formulation of the M-integral for extracting Dynamic Stress Intensity Factors (DSIFs) at a moving crack front. This formulation allows extracting fracture variables on deforming elements without losing accuracy. Comparisons with analytical and numerical data are proposed to assess the validity and efficiency of the proposed strategy.

An adaptive mesh rezoning scheme for moving boundary flows and fluid–structure interaction

This paper presents a complete derivation and implementation of the Arbitrary Lagrangian Eulerian (ALE) formulation for the simulation of large deformation quasi-static and dynamic problems. While most of the previous work done on ALE for dynamic applications was mainly based on operator split and explicit calculations, this work derives the quasi-static and dynamic ALE equations using a fully coupled implicit approach. Full expression for the ALE virtual work equations and finite element matrices are given. Time integration relations for the dynamic equations are also derived. Several quasi-static and dynamic large deformation applications are solved and presented.

Due to the significant health and economic impact of blood vessel diseases on modern society, its analysis is becoming of increasing importance for the medical sciences. The complexity of the vascular system, its dynamics and material characteristics all make it an ideal candidate for analysis through fluid structure interaction (FSI) simulations. FSI is a relatively new approach in numerical analysis and enables the multi-physical analysis of problems, yielding a higher accuracy of results than could be possible when using a single physics code to analyse the same category of problems. This paper introduces the concepts behind the Arbitrary Lagrangian Eulerian (ALE) formulation using the penalty coupling method. It moves on to present a validation case and compares it to available simulation results from the literature using a different FSI method. Results were found to correspond well to the comparison case as well as basic theory.

An arbitrary Lagrangian-Eulerian (ALE) approach is used to model the orthogonal metal cutting in a steady state situation. The thermomechanical model includes the effects of elasticity, plasticity, strain rate, large strains and friction with heat generated between the tool and the chip. The ALE formulation can combine the advantages of both the Eulerian and Lagrangian approaches in a single description. Particularly, problems linked to the free surface in a Eulerian description and those linked to severe mesh distortions in a Lagrangian one can be solved by this formulation. The ALE governing equations are briefly reviewed in this paper; finite element and finite volume methods are used for the discretization of the conservation equations and an explicit time integration is adopted. Only the steady state solution is required; the ALE formulation is exploited to update the free and the contact surfaces. The model predicts the thermomechanical quantities, the chip geometry and the cutting forces from the cutting data and the material and friction parameters. Cutting experiments were performed with 42CD4 steel and comparisons of experimental tool forces and chip geometry with the numerical results are presented.

Our objective is to develop a finite element model for studying fluid-structure interaction. The geometrically non-linear structural behaviour is considered and based on large rotations and large displacements. An arbitrary Lagrangian-Eulerian (ALE) formulation is used to represent the compressible inviscid flow with moving boundaries. The structural response is obtained using Newmark-type time integration and fluid response employs the Lax-Wendroff scheme. A number of numerical examples are presented to validate the structural model, moving mesh implantation of the ALE model and complete fluid-structure interaction

The need for Out-Of-Position (OOP) simulation capabilities in crash safety software has risen in importance in the automotive industry after the final ruling of FMVSS 208 by the National Highway Transportation Safety Administration (NHTSA) in 2000. However, because of current technical challenges, the thermodynamics airbag models are not capable of either accurately simulating the flow-bag interactions under OOP conditions, or differentiating the effect of some important design changes, such as vent locations, inflator configuration, and flow diverging devices. The development of these capabilities entails overcoming tremendous technical challenges and numerical difficulties in computational fluid dynamics (CFD) and crash simulations due to the complexity and extreme conditions of OOP. This paper summarizes the developments of algorithms used in the context of an Arbitrary Lagrangian-Eulerian (ALE) formulation. The main developments of this study include the gas dynamic model for mixing gases, the special treatment of inflator gas flows, a penalty based fluid-structure coupling algorithm, and a permeability algorithm for porous fabrics. To expedite the developments and resolve the technical difficulties, a set of benchmark problems was used in this study. Each of the benchmark problems addresses specific technical difficulties of airbag OOP simulations by comparing simulation results to analytical solutions, well-known numerical solutions, or test results. The benchmark set was designed to start from simple CFD problems and progress to the most complicated OOP applications such that the weakness and algorithmic errors of the simulation code can be easily identified. Simulation results of the benchmark problems and the issues addressed by them are discussed in this paper. The simulation results have demonstrated that LS-DYNA now has the capabilities to simulate certain OOP problems.

Spent fuel pool and storage racks are important nuclear security structures and components. In order to prevent it from structural failure, which includes the loss of the structural integrity of the spent fuel pool and stability of the spent fuel storage racks, also includes the possibility of fallen down of storage racks under seismic loading. Besides the necessary static analysis of structures, the influence of seismic loading on the interaction between water and structure should be fully considered, Especially concerned the analysis of the shaking effect of water sloshing on the storage racks, the displacement and the possibility of fallen down of the storage racks. The present paper is concerned with the problem of modeling the fluid-structure interaction (FSI) in filled liquid and filled with spent fuel pool. The study focuses on the sloshing phenomena and on the coupling computational fluid dynamic (CFD) analysis with the finite element stress analysis (FEA) code LS-DYNA. By the results of the response of seismic, such as the displacement of the storage racks, pressure exerted on the plate of racks and the walls of the pool. This paper also evaluates the seismic performance of the structure and the safety margin. Various numerical methods can be used for analysis of liquid storage pools, among these we mention explicit finite element, implicit Lagrangian-Eulerian, hybrid finite element, Smoothed Particle Hydrodynamics volume of fluid. In this article the coupled sloshing dynamics in a rectangle pool were studied using a model developed in LS-DYNA environment. The main solution methodology is based on explicit time integration. In order to demonstrate the FSI results of the FEA models of the spent fuel pool on seismic analysis, a 3D FEA models were developed. The Finite element model composed of the spent fuel pool (steel plate concrete), spent fuel storage racks, cushion block, water and air. Solid element modeling is used in concrete, cushion block, water and air. Steel plate and storage racks employ the shell element. The constitutive model of solid element is linear elastic. And the constitutive model of fluid element is described by the Gruneisen equation. Arbitrary Lagrangian-Eulerian (ALE) formulation is thought of as algorithms that perform automatic rezoning. It realized the advection of water and air in the ALE multi-material group.

Meshless method is a new numerical analysis scheme and researches for many analysis models have been conducted in recent years. We have applied the element free Galerkin method (EFGM), the meshless method presented by T. Belytschko et al. in 1994, to analyze membrane structure with cable reinforcement. To model the sliding cable on membrane, the arbitrary Lagrangian-Eulerian (ALE) method is adopted. By using ALE formulation, deformation of membrane and sliding between cable and membrane can be represented as different displacement components. In this paper, an ALE-EFGM formulation using the convected coordinate system for geometrically non-linear analysis is presented. Finally, the proposed method is applied to a simple analysis of membrane structure with sliding cable and its validity is demonstrated.

Unmanned surface vehicles (USVs) have great application prospects in defense, environmental surveillance and offshore energy due to their cost-effectiveness and long-duration mission ability. The structural safety issues induced by the prolonged cyclic wave loading on such small-sized marine structures, such as fatigue failure mechanism, represent an important research topic. In order to characterize the loading process, a piston-type numerical wave flume with wave absorption setting is constructed using the Arbitrary Lagrangian Eulerian (ALE) formulation, and the fluid–structure interaction (FSI) simulations are performed. Simulated wave profiles are measured and compared with corresponding analytical wave solutions to verify the accuracy of target waves. The wave absorption effect is verified by comparing the velocities of water particles in different water regions. Then, different impact scenarios are performed by applying a range of the applicable target waves. Simulated wave forms, impact scenes along with the computed wave load data are presented, and the impact process is analyzed. As a result, the FSI simulations demonstrate cyclic loading characteristics of small-sized floating structures subjected to wave impacts, and the constructed ALE numerical wave flume possesses the extensibility for the simulation of nonlinear water wave impact scenarios.

This paper reports a follow-up feasibility study on different approaches for numerical modeling of blast loads, implemented recently in a few commercial programs based on finite element method and explicit time integration. Four approaches have been considered including: explicit blast wave representation using fluid-structure interaction (FSI) with 2D and 3D multi-material arbitrary Lagrangian-Eulerian (ALE) formulations, direct application of empirical explosive blast loads on structures, and the most recent, combined method, in which direct empirical loading is applied to a reduced ALE domain. Each of these approaches has its own strengths and weaknesses, although the last one seems to be the most universal. Based on the published experimental data, a benchmark problem was selected, which considers a pressure loading exerted by explosion of near field hemispherical charges on a rigid steel plate. The comparison is done in terms of pressure peaks (overpressure) and time histories of reflected pressure, and reflected specific impulses.

We are interested in the numerical solution of a two-dimensional fluid-structure interaction problem.A special attention is paid to the choice of physically relevant inlet boundary conditions for the case of channel closing.Three types of the inlet boundary conditions are considered.Beside the classical Dirichlet and the do-nothing boundary conditions also a generalized boundary condition motivated by the penalization prescription of the Dirichlet boundary condition is applied.The fluid flow is described by the incompressible Navier-Stokes equations in the arbitrary Lagrangian-Eulerian (ALE) form and the elastic body creating a part of the channel wall is modelled with the aid of linear elasticity.Both models are coupled with the boundary conditions prescribed at the common interface.The elastic and the fluid flow problems are approximated by the finite element method.The detailed derivation of the weak formulation including the boundary conditions is presented.The pseudo-elastic approach for construction of the ALE mapping is used.Results of numerical simulations for three considered inlet boundary conditions are compared.The flutter velocity is determined for a specific model problem and it is shown that the boundary condition with the penalization approach is suitable for the case of the fluid flow in a channel with vibrating walls.

Fluid–structure interaction study of the start-up of a rocket engine nozzle