On the Projection of a Flexible Bodies Modal Coordinates Onto Another Finite Element Model With Local Modifications

2019 ◽  
Vol 14 (7) ◽  
Author(s):  
Wolfgang Witteveen ◽  
Pöchacker Stefan ◽  
Florian Pichler
Keyword(s):  
Finite Element ◽  
Multibody System ◽  
Time Integration ◽  
Fe Model ◽  
Processing Unit ◽  
Multibody Simulation ◽  
Notch Radius ◽  
Simple Method ◽  
Central Processing ◽  
Flexible Component

The time integration of a complex multibody system is a time consuming part of the entire evaluation process of a flexible component. A multibody simulation of a flexible crankshaft, for instance, interacting with pistons, con rods, fly wheel, hydrodynamic bearings and further takes several hours of central processing unit (CPU) time and may dominate the entire simulation chain. Small, local changes in the involved finite element (FE) models, for example, another notch radius, normally require a new time integration of the entire multibody system. In this publication, a remarkably simple method is presented, so that the multibody simulation of such a variant can be skipped entirely. Instead, a simple and cheap projection of the original results to the modified FE model is proposed. One simple and one elaborate example demonstrate the extraordinary resulting quality for minor design changes like notch radius variations.

Accuracy of large eddy simulation for turbulent flow by the finite element method

1998 ◽  
Vol 212 (7) ◽  
pp. 643-650
Author(s):  
T Uchiyama
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Large Eddy Simulation ◽  
Processing Unit ◽  
The Finite Element Method ◽  
Central Processing ◽  
Eddy Simulation ◽  
Advection Term ◽  
Large Eddy ◽  
Element Method

This paper investigates the computational accuracy and CPU (central processing unit) time of large eddy simulation (LES) for turbulent flows performed by the finite element method. The investigations are accomplished by simulating a fully developed turbulent channel flow, which was analysed by Kim et al. using the direct numerical simulation (DNS) technique. When the advection term is discretized in gradient form, the turbulence decays and disappears with the passage of time. In using a multipass algorithm to solve the velocity field, the numerical result obtained by discretizing the advection term in divergent form agrees very well with that of the DNS. The multipass algorithm with the number of iterations k = 2 and 3 predict almost the same results. Thus, the algorithm with k = 2, allowing calculation with less CPU time, is successfully applicable to LES.

scholarly journals Finite Element Multibody Simulation of a Breathing Crack in a Rotor with a Cohesive Zone Model

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Rugerri Toni Liong ◽  
Carsten Proppe
Keyword(s):  
Finite Element ◽  
Crack Closure ◽  
Cohesive Zone ◽  
Cohesive Zone Model ◽  
Zone Model ◽  
Fe Model ◽  
Multibody Simulation ◽  
Closure Model ◽  
Breathing Mechanism ◽  
Cracked Shaft

The breathing mechanism of a transversely cracked shaft and its influence on a rotor system that appears due to shaft weight and inertia forces is studied. The presence of a crack reduces the stiffness of the rotor system and introduces a stiffness variation during the revolution of the shaft. Here, 3D finite element (FE) model and multibody simulation (MBS) are introduced to predict and to analyse the breathing mechanism on a transverse cracked shaft. It is based on a cohesive zone model (CZM) instead of linear-elastic fracture mechanics (LEFM). First, the elastic cracked shaft is modelled by 3D FE. As a second step, the 3D FE model of the shaft is transferred into an MBS model in order to analyze the dynamic loads, due to the crack, and the inertia force acting during rotation at different rotating speeds. Finally, the vibration responses in the centroid of the shaft obtained from MBS have been exported into FE model in order to observe the breathing mechanism. A bilinear crack closure model is proposed. The accuracy of the bilinear crack closure model and the solution techniques have been demonstrated by a comparison with the corresponding results of previous publications.

Identification of Free-Free Modes From Constrained Vibration Data for Flexible Multibody Models

1999 ◽  
Author(s):  
Tong Y. Yi ◽  
Parviz E. Nikravesh
Keyword(s):  
Finite Element ◽  
Boundary Conditions ◽  
Finite Element Model ◽  
Degrees Of Freedom ◽  
Multibody System ◽  
Element Model ◽  
Flexible Body ◽  
Fe Model ◽  
Modal Data ◽  
Vibration Data

Abstract This paper presents a method for identifying the free-free modes of a structure by utilizing the vibration data of the same structure with boundary conditions. In modal formulations for flexible body dynamics, modal data are primary known quantities that are obtained either experimentally or analytically. The vibration measurements may be obtained for a flexible body that is constrained differently than its boundary conditions in a multibody system. For a flexible body model in a multibody system, depending upon the formulation used, we may need a set of free-free modal data or a set of constrained modal data. If a finite element model of the flexible body is available, its vibration data can be obtained analytically under any desired boundary conditions. However, if a finite element model is not available, the vibration data may be determined experimentally. Since experimentally measured vibration data are obtained for a flexible body supported by some form of boundary conditions, we may need to determine its free-free vibration data. The aim of this study is to extract, based on experimentally obtained vibration data, the necessary free-free frequencies and the associated modes for flexible bodies to be used in multibody formulations. The available vibration data may be obtained for a structure supported either by springs or by fixed boundary conditions. Furthermore, the available modes may be either a complete set; i.e., as many modes as the number of degrees of freedom of the associated FE model is available, or it can be an incomplete set.

Crack Propagation Calculation for Axial Cracks in Hollow Cylinders Subjected to Thermal Shock

2021 ◽  
Author(s):  
Diego F. Mora M. ◽  
Markus Niffenegger
Keyword(s):  
Fracture Toughness ◽  
Finite Element ◽  
Crack Propagation ◽  
Weight Function ◽  
Thermal Shock ◽  
Initial Crack ◽  
Fe Model ◽  
Simple Method ◽  
Hollow Cylinders ◽  
Fracture Arrest

Abstract The core region of the RPV can be considered a hollow circular cylinder disregarding the geometrical details due to nozzles. This contribution investigates the prediction capabilities for crack initiation, crack growth and arrest by means of a rather simple method based on the closed-weight function formula for the stress intensity factor (SIF) for axial cracks in hollow cylinders subjected to thermal shock. The method is explained together with some illustrative examples for real low allow steel used in nuclear applications. In order to obtain the temperature and stress distribution in the cylinder during the thermal shock, a finite element (FE) model is defined to obtain the uncoupled solution of these two fields needed for the closed-weight function. Since the material exhibits a ductile-brittle transition fracture behavior, the temperature-dependent fracture toughness for initiation and for arrest are described using the ASME model. The solution for the SIF is based on linear elastic fracture mechanics (LEFM) and therefore only elastic material is assumed and the crack can propagate in brittle manner. The crack initiates propagation if the SIF value at the crack tip reaches the fracture toughness (for initiation) and propagates unstably in mode I unless the fracture arrest toughness is reached. The quality of the solution is checked by comparing the obtained solution for a “stationary” crack with the calculated extended finite element method (XFEM) solution for the same loading transient. The results show that for some geometries of the cylinder, the crack stops and in some other cases the crack propagates until the cylinder fails. The combined closed-weight function-initiation-growth-arrest (WFF-IGA) algorithm does not require expensive computational resources and gives fast reliable results. The WFF-IGA method provides a powerful and economical way to predict the crack propagation and arrest of the initial crack. This is an advantage when an optimization of the structure is needed.

Extraction of Free-Free Modes from Constrained Vibration Data for Flexible Multibody Models

2001 ◽  
Vol 123 (3) ◽  
pp. 383-389 ◽  
Author(s):  
Tong Y. Yi, ◽  
Parviz E. Nikravesh
Keyword(s):  
Finite Element ◽  
Boundary Conditions ◽  
Finite Element Model ◽  
Degrees Of Freedom ◽  
Multibody System ◽  
Element Model ◽  
Flexible Body ◽  
Fe Model ◽  
Modal Data ◽  
Vibration Data

This paper presents a method for identifying the free-free modes of a structure by utilizing the vibration data of the same structure with boundary conditions. In modal formulations for flexible body dynamics, modal data are primary known quantities that are obtained either experimentally or analytically. The vibration measurements may be obtained for a flexible body that is constrained differently than its boundary conditions in a multibody system. For a flexible body model in a multibody system, depending upon the formulation used, we may need a set of free-free modal data or a set of constrained modal data. If a finite element model of the flexible body is available, its vibration data can be obtained analytically under any desired boundary conditions. However, if a finite element model is not available, the vibration data may be determined experimentally. Since experimentally measured vibration data are obtained for a flexible body supported by some form of boundary conditions, we may need to determine its free-free vibration data. The aim of this study is to extract, based on experimentally obtained vibration data, the necessary free-free frequencies and the associated modes for flexible bodies to be used in multibody formulations. The available vibration data may be obtained for a structure supported either by springs or by fixed boundary conditions. Furthermore, the available modes may be either a complete set, having as many modes as the number of degrees of freedom of the associated FE model, or an incomplete set.

Large Scale Finite Element Analysis Via Assembly-Free Deflated Conjugate Gradient

2014 ◽  
Vol 14 (4) ◽  
Author(s):  
Praveen Yadav ◽  
Krishnan Suresh
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Conjugate Gradient ◽  
Degrees Of Freedom ◽  
Large Scale ◽  
Solid Mechanics ◽  
Processing Unit ◽  
Element Analysis ◽  
Central Processing ◽  
Computational Bottleneck

Large-scale finite element analysis (FEA) with millions of degrees of freedom (DOF) is becoming commonplace in solid mechanics. The primary computational bottleneck in such problems is the solution of large linear systems of equations. In this paper, we propose an assembly-free version of the deflated conjugate gradient (DCG) for solving such equations, where neither the stiffness matrix nor the deflation matrix is assembled. While assembly-free FEA is a well-known concept, the novelty pursued in this paper is the use of assembly-free deflation. The resulting implementation is particularly well suited for large-scale problems and can be easily ported to multicore central processing unit (CPU) and graphics-programmable unit (GPU) architectures. For demonstration, we show that one can solve a 50 × 106 degree of freedom system on a single GPU card, equipped with 3 GB of memory. The second contribution is an extension of the “rigid-body agglomeration” concept used in DCG to a “curvature-sensitive agglomeration.” The latter exploits classic plate and beam theories for efficient deflation of highly ill-conditioned problems arising from thin structures.

Semihyper-Reduction for Finite Element Structures With Nonlinear Surface Loads on the Basis of Stress Modes

2020 ◽  
Vol 15 (8) ◽  
Author(s):  
Lukas Koller ◽  
Wolfgang Witteveen ◽  
Florian Pichler ◽  
Peter Fischer
Keyword(s):  
Finite Element ◽  
Degrees Of Freedom ◽  
Hydrodynamic Lubrication ◽  
A Priori ◽  
Time Integration ◽  
Practical Implementation ◽  
Fe Model ◽  
Lubrication Film ◽  
Nonlinear Surface ◽  
Surface Loads

Abstract Model reduction via projection is a common method to accelerate time integration of finite element (FE) structures by reducing the number of degrees-of-freedom (DOFs). However, nonlinear state-dependent surface loads are usually computed based on the nonreduced DOFs of the FE model. When a considerably high number of DOFs are involved in the nonlinear surface loads, their computation becomes a bottleneck. This paper presents a general approach for reduced time integration and reduced force computation for FE models. The required force trial vectors can be computed easily and systematically out of deformation trial vectors, commonly called “modes.” Those force trial vectors, which we call “stress modes,” can be determined a priori so that a nonlinear computation of the full system is not necessary. The new idea in this contribution is that stress recovery is used to decrease the number of equations for the force computation. A general framework for semihyper-reduction (SHR) is developed and its practical implementation is discussed. The term SHR is introduced because it is an intermediate approach between the straight-forward method of using the FE DOFs and pure hyper-reduction (HR) where the FE DOFs are omitted for computing state-depended surface loads. In order to demonstrate the proposed SHR approach practically, a numerical example of a planar crank drive is given, where a hydrodynamic lubrication film separates piston and cylinder. Thereby, very good result quality has been observed in comparison to a finite difference reference solution.

Object-Oriented Environment for Dynamic Finite Element Modeling of Tires and Suspension Systems

2006 ◽  
Author(s):  
Tamer M. Wasfy ◽  
Hatem Wasfy
Keyword(s):  
Finite Element ◽  
Time Integration ◽  
Time History ◽  
Object Oriented ◽  
Rigid Bodies ◽  
Leaf Spring ◽  
Fe Model ◽  
Suspension Systems ◽  
Preliminary Model ◽  
Time Histories

An object-oriented graphical modeling environment, which includes integrated pre-processor, post-processor, and explicit time-integration finite element solver, for predicting the dynamic response of tires mounted on suspension systems is described. The pre-processor allows creating a hierarchical preliminary model of the system including the tire, suspension system, and terrain. The pre-processor includes an automatic mesh generator for generating the finite element (FE) model from the preliminary model. A tire preliminary object allows defining the tire cross-section, specifying the number of elements along the tire circumference, and defining beam elements along the circumference and meridian direction to model the various tire structural components such as the bead, ply, and belt. Other preliminary model objects include rigid body, linear spring-damper, leaf-spring, spherical joint, revolute joint, prismatic joint, and polygonal terrain. The user can also include support objects such as physical materials, and scalar graphs (for time-histories of known quantities). The preprocessor includes a model tree-editor which allows adding objects and changing their properties. The FE model is submitted to the solver which generates the system's motion time-history. The FE model consists of solid elements (including brick, beam, and truss), rigid bodies, and joints. The post-processor is used to display the analysis results, which include an animation of the motion of the system, coloring/contouring the tire using various scalar response quantities, and various types of graphs of response quantities (such as time-history, frequency and time-averaged graphs). The graphical output of the pre-processor and the post-processor can be displayed either on the computer screen or in immersive stereoscopic virtual-reality facilities. Users can control the visualization using the tree-editor.

scholarly journals Investigation of Mesh Size Effect on Dynamic Behaviour of an Assembled Structure with Bolted Joints using Finite Element Method

2018 ◽  
Vol 15 (3) ◽  
pp. 5695-5709 ◽  
Author(s):  
R. Omar ◽  
M.N Abdul Rani ◽  
M. A. Yunus ◽  
A. A. Mat Isa ◽  
W. I. I. Wan Iskandar Mirza ◽  
...  
Keyword(s):  
Finite Element ◽  
Modal Analysis ◽  
Total Error ◽  
Mesh Size ◽  
Bolted Joints ◽  
Fe Model ◽  
Processing Unit ◽  
Memory Usage ◽  
Fe Modelling ◽  
Selection Of

The predicted results of the finite element (FE) model of an assembled structure with different types of joints are highly dependent on the mesh size of the FE model. The complexity of the FE model has forced engineers to seek the most efficient techniques for the selection of the appropriate mesh size specifically in obtaining accurate predicted results in normal modes analysis. This paper concerns the investigation into the effects of the mesh sizes and selection technique of the appropriate mesh size in the FE modelling and analysis of the assembled structure with bolted joints. The investigation was carried out by predicting the modal parameters of the FE models with the predefined range of mesh sizes. The predicted results of the FE models were compared with the measured counterparts obtained from the experimental modal analysis (EMA). The total error obtained from the comparison between FE and EMA was recorded. Evaluations were made by comparing the number of nodes and elements of the FE models, percentage of total error, computer processing unit (CPU) elapsed time and memory usage. The outcomes of the evaluations showed that there are significant effects of the mesh sizes on the accuracy, computing time and memory usage of the FE modal analysis of the assembled structure with bolted joints. This work also demonstrated an efficient technique for the selection of the appropriate mesh size in achieving a reliable, efficient and economic FE modelling and analysis of the assembled structure with bolted joints.

Dynamic Analysis and Fatigue Life Prediction of a Very Flexible Component in Multibody System

2006 ◽  
Vol 321-323 ◽  
pp. 1597-1600
Author(s):  
Ji Won Yoon ◽  
Kab Jin Jun ◽  
Tae Won Park
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Multibody System ◽  
Beam Theory ◽  
Computational Method ◽  
Deformation Analysis ◽  
Flexible Beam ◽  
Combined System ◽  
Absolute Nodal Coordinates ◽  
Flexible Component

Recently, the finite element absolute nodal coordinate formulation(ANCF) was developed for large deformation analysis of flexible bodies in multi-body dynamics. This formulation is based on finite element procedures and the general continuum mechanics theory to represent elastic forces. In this paper, a computational method, which predicts the dynamic and structural properties of a very flexible beam in a multibody system, is presented based on Euler-Bernoulli beam theory and ANCF. In order to consider the dynamic interaction between a continuous large deformable beam and a rigid multibody system, a combined system equations of motion was derived by adopting absolute nodal coordinates and rigid body coordinates. The efficiency and reliability of the computational results are verified by comparison with a commercial program. These methods can be applied for predicting the dynamic stress and fatigue life of the wire harness used in a robot system. The process of predicting the fatigue life using the proposed method in this paper may be applied to continuous mechanical parts of various dynamic systems.

Sign in / Sign up

Export Citation Format

Share Document