scholarly journals An accurate and efficient three‐dimensional high‐order finite element methodology for the simulation of magneto‐mechanical coupling in MRI scanners

2019 ◽  
Vol 119 (12) ◽  
pp. 1185-1215 ◽  
Author(s):  
M. Seoane ◽  
P.D. Ledger ◽  
A.J. Gil ◽  
M. Mallett
Keyword(s):  
Finite Element ◽  
Three Dimensional ◽  
High Order ◽  
Mechanical Coupling ◽  
Finite Element Methodology

scholarly journals 3D simulation of magneto-mechanical coupling in MRI scanners using high order FEM and POD

2020 ◽  
Author(s):  
◽  
Marcos Choucino
Keyword(s):  
Finite Element ◽  
Magnetic Fields ◽  
Eddy Currents ◽  
High Order ◽  
Design Stage ◽  
Model Parameters ◽  
Mechanical Problem ◽  
Mechanical Coupling ◽  
Coupled Problem ◽  
Finite Element Methodology

Magnetic Resonance Imaging (MRI) scanners have become an essential tool in the medi-cal industry due to their ability to produce high resolution images of the human body. To generate an image of the body, MRI scanners combine strong static magnetic fields with transient gradient magnetic fields. The interaction of these magnetic fields with the con-ducting components present in superconducting MRI scanners gives rise to an important problem in the design of new MRI scanners. The transient magnetic fields give rise to the appearance of eddy currents in conducting components. These eddy currents, in turn, result in electromagnetic stresses, which cause the conducting components to deform and vibrate. The vibrations are undesirable as they lead to a deterioration in image quality (with image artefacts) and to the generation of noise, which can cause patient discomfort. The eddy currents, in addition, lead to heat being dissipated and deposited into the cryo-stat, which is filled with helium in order to maintain the coils in a superconducting state. This deposition of heat can cause helium boil off and potentially result in a costly magnet quench. Understanding the mechanisms involved in the generation of these vibrations and the heat being deposited into the cryostat are, therefore, key for a successful MRI scanner design. This involves the solution of a coupled magneto-mechanical problem, which is the focus of this work.In this thesis, a new computational methodology for the solution of three-dimensional (3D) magneto-mechanical coupled problems with application to MRI scanner design is presented. To achieve this, first an accurate mathematical description of the magneto-mechanical coupling is presented, which is based on a Lagrangian formulation and the assumption of small displacements. Then, the problem is linearised using an AC-DC splitting of the fields, and a variational formulation for the solution of the linearised prob-lem in a time-harmonic setting is presented. The problem is then discretised using high order finite elements, where a combination of hierarchical H1 and H(curl) basis func-tions is used. An efficient staggered algorithm for the solution of the coupled system is proposed, which combines the DC and AC stages and makes use of preconditioned iter-ative solvers when appropriate. This finite element methodology is then applied to a set of challenging academic and industrially relevant problems in order to demonstrate its accuracy and efficiency.This finite element methodology results in the accurate and efficient solution of the magneto-mechanical problem of interest. However, in the design stage of a new MRI scanner, this coupled problem must be solved repeatedly for varying model parameters such as frequency or material properties. Thus, even if an efficient finite element solver is available for the solution of the coupled problem, the need for these repeated simulations result in a bottleneck in terms of computational cost, which leads to an increase in design time and its associated financial implications. Therefore, in order to optimise this process, the application of Reduced Order Modelling (ROM) techniques is considered. A ROM based on the Proper Orthogonal Decomposition (POD) method is presented and applied to a series of challenging MRI configurations. The accuracy and efficiency of this ROM is demonstrated by performing comparisons against the full order or high fidelity finite element software, showing great performance in terms of computational speed-up, which has major benefits in the optimisation of the design process of new MRI scanners.

Influence of temperature and strain rate on the longitudinal compressive crashworthiness of 3D braided composite tubes and finite element analysis

2016 ◽  
Vol 26 (7) ◽  
pp. 1003-1027 ◽  
Author(s):  
Xianyan Wu ◽  
Qian Zhang ◽  
Bohong Gu ◽  
Baozhong Sun
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Strain Rate ◽  
Coupling Effect ◽  
Three Dimensional ◽  
Composite Tubes ◽  
Element Analysis ◽  
Impact Compression ◽  
Mechanical Coupling ◽  
The Impact

This article reports the longitudinal compressive crashworthiness of three-dimensional four-step circular braided carbon/epoxy composite tubes at temperatures of 23, −50, and −100℃ under strain rate ranging from 340 to 760/s both experimentally and finite element analysis. The experimental results showed that the compression strength, stiffness, and specific energy absorption increased with the decrease in temperature and with the increase in strain rate. It also showed that, the compressive damage morphologies were sensitive to the change in temperature and strain rate. A coupled thermal-mechanical numerical analysis was conducted to find the thermo/mechanical coupling effect on the compressive crashworthiness of the three-dimensional composite tube. The temperature distributions in the braided preform and the resin during the impact compression were also calculated through finite element analysis. From the finite element analysis results, the inelastic heat generation was seen to be more in the preform than the matrix and its distribution and accumulation led to the damage progress along the loading direction.

A Parallel Computational Model for Three-Dimensional, Thermo-Mechanical Stokes Flow Simulations of Glaciers and Ice Sheets

2014 ◽  
Vol 16 (4) ◽  
pp. 1056-1080 ◽  
Author(s):  
Wei Leng ◽  
Lili Ju ◽  
Max Gunzburger ◽  
Stephen Price
Keyword(s):  
Finite Element ◽  
Computational Model ◽  
Stokes Flow ◽  
Stokes Problem ◽  
Three Dimensional ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Iterative Solution ◽  
Element Model ◽  
High Order

AbstractThis paper focuses on the development of an efficient, three-dimensional, thermo-mechanical, nonlinear-Stokes flow computational model for ice sheet simulation. The model is based on the parallel finite element model developed in [14] which features high-order accurate finite element discretizations on variable resolution grids. Here, we add an improved iterative solution method for treating the nonlinearity of the Stokes problem, a new high-order accurate finite element solver for the temperature equation, and a new conservative finite volume solver for handling mass conservation. The result is an accurate and efficient numerical model for thermo-mechanical glacier and ice-sheet simulations. We demonstrate the improved efficiency of the Stokes solver using the ISMIP-HOM Benchmark experiments and a realistic test case for the Greenland ice-sheet. We also apply our model to the EISMINT-II benchmark experiments and demonstrate stable thermo-mechanical ice sheet evolution on both structured and unstructured meshes. Notably, we find no evidence for the “cold spoke” instabilities observed for these same experiments when using finite difference, shallow-ice approximation models on structured grids.

scholarly journals Thermo-mechanical coupling–based finite element analysis of the load distribution of planetary roller screw mechanism

2018 ◽  
Vol 10 (6) ◽  
pp. 168781401877525 ◽  
Author(s):  
Shangjun Ma ◽  
Chenhui Zhang ◽  
Tao Zhang ◽  
Geng Liu ◽  
Shumin Liu
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Load Distribution ◽  
Three Dimensional ◽  
Theoretical Models ◽  
Element Model ◽  
Element Analysis ◽  
Mechanical Coupling ◽  
Roller Screw ◽  
Screw Mechanism

In this article, 3D or three-dimensional finite element analysis is used to simulate and evaluate the load distribution characteristics of a planetary roller screw mechanism under thermo-mechanical coupling. The finite element model takes into account the installation modes of the planetary roller screw mechanism, which is verified by comparison with theoretical models for a certain load magnitude in four installation modes. In addition, the effects of the installation mode, load magnitude, and temperature condition on the load distribution are also systematically analyzed. The numerical results reveal a phenomenon of threads separating from the meshing, which indicates that the influence of thermo-mechanical coupling on the load distribution cannot be ignored. Furthermore, the influence of the installation mode on the screw–roller interface is larger than that on the nut–roller interface. Compared with the screw–roller interface, the temperature difference is one of the main conditions affecting the load distribution of the planetary roller screw mechanism and has a significant effect on the nut–roller interface. In addition, the influences of the screw rotational speed and the load magnitude on the load distribution on the screw–roller interface are larger than those on the nut–roller interface for the four installation modes.

3-D Finite Element Simulation of the Vertical-Horizontal Rolling Process

2010 ◽  
Vol 145 ◽  
pp. 187-192 ◽  
Author(s):  
Jin Hua Ruan ◽  
Li Wen Zhang ◽  
Chong Xiang Yue ◽  
Sen Dong Gu ◽  
Wen Bin He ◽  
...  
Keyword(s):  
Finite Element ◽  
Deformation Behavior ◽  
Metal Flow ◽  
Three Dimensional ◽  
Rolling Process ◽  
Shape Evolution ◽  
Rigid Plastic ◽  
Coupling Analysis ◽  
Mechanical Coupling ◽  
Element Simulation

In order to investigate the deformation behavior of a plate during a vertical-horizontal rolling process, a thermo-mechanical coupling analysis is carried out by three-dimensional (3-D) rigid-plastic FEM to simulate the process. The metal flow and the shape evolution of the plate are focused during this investigation. The thickness and the width of the plate agree well with the measured values.

Analysis on Thermal Mechanical Coupling of Buried Thermal Pipeline Based on ADINA

2013 ◽  
Vol 694-697 ◽  
pp. 751-754
Author(s):  
Mei Yang ◽  
Xiao Liu ◽  
Yan Hua Chen
Keyword(s):  
Finite Element ◽  
Axial Strain ◽  
Three Dimensional ◽  
Mechanical Coupling ◽  
Geometry Model ◽  
Earthquake Force ◽  
Single Temperature ◽  
Temperature Load ◽  
Earthquake Load ◽  
Earthquake Action

High temperature medium in the thermal pipeline will affect distortion and stress distribution of the pipe wall, so its very important to analyze the thermal mechanical coupling in thermal pipeline. Numerical simulation of buried thermal pipeline damage under the earthquake action is carried by finite element method-ADINA. Three-dimensional finite element modeling considered site condition is investigated; geometry model is constructed with native and parasolid method in ADINA. Gravity and earthquake force are defined in structure model, and temperature load in thermal model. According to the results of thermal mechanical coupling, the damage of buried thermal pipeline is analyzed. Influence of single temperature load on the stress and strain of buried thermal pipeline is very small, but the stress and circumferential strain increase rapidly under earthquake action. Also, the axial strain is very complex. The temperature load mainly affects axial strain under gravity and earthquake load; the increasing temperature enables to reduce axial strain, which makes axial destruction reduced. Finally, some advice is proposed.

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