Hi David, The two attached figures show the simulation of pressing an
incompressible cube. A constant pressure was applied uniformly on the
side y=y_min. Its opposite side, y=y_max, is the Dirichlet BC side,
which is fixed in the y and z directions. That is, this side deforms
only along the x axis. Both figures confirm this. The yellow frame
depicts the undeformed object, whereas the colored cube depicts the
deformed object. What is odd are two things:
1. I ran the same simulation code with a debug version of Libmesh and a
release version, respectively. However, as the two figures show, the
results are different: With the debug mode, the Dirichlet boundary
side (y=y_max) is stretched toward the positive-x direction; With
the release mode, this side is stretched toward the negative-x
direction.
2. The Dirichlet boundary side (y=y_max) is supposed to deform evenly
along both directions of the x-axis. However, in both figures, the
deformation occurs mainly in one direction.
Thanks very much for your help. Cheers, Dafang Date: Tue, 4 Mar 2014
18:47:51 -0500 From: David Knezevic <[email protected]>
Subject: Re: [Libmesh-users] Dirichlet Boundary Condition on Part of the
Variables To: <[email protected]> Message-ID:
<[email protected]> Content-Type: text/plain;
charset="ISO-8859-1"; format=flowed Hi Dafang, I've done this a lot for
elasticity problems, and haven't had any problems with it. If you can
send through an example that illustrates what is happening (e.g. a
modified version of systems_of_equations_ex6), I'd be happy to have a
look. David On 03/04/2014 06:08 PM, Dafang Wang wrote:
Hi,
The Libmesh Examples tell how to use the DirichletBoundary class to
constrain all the variables in a system, but I am not sure how to apply
zero Dirichlet BC to PART of the field variables in a system. I am
solving a simple 3D elastic problem and I want to fix a boundary in the
y direction while allowing it to move in the x-z plane.
I did the following way but the results did not seem correct:
My system has 3 displacement variables: ux (id=0), uy (id=1), and uz
(id=2).
std::vector<int> variables(1);
variables[0] = uy; //the vector contains uy only
DirichletBoundary bc(boundary_ids, variables, &ZeroFunction);
The result I got showed that ux and uz were somewhat fixed with respect
to one edge on the Dirichlet boundary side, which made no sense since ux
and uz are supposed to evenly spread.
Any suggestions will be greatly appreciated.
Cheers,
Dafang
--
Dafang Wang, Ph.D
Postdoctoral Fellow
Institute of Computational Medicine
Department of Biomedical Engineering
Johns Hopkins University
Hackerman Hall Room 218
Baltimore, MD, 21218
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