[CIG-SHORT] Plane strain test problem

[Birendra jha]

Dear Brad,

I am running this plane strain test case (files attached) with equal compression on two y faces, zero tractions on x faces, and zero normal displacement on z faces. (Does this replicate Plane Strain?)

I don't understand why the y-displacements are not uniform along the length i.e. along x. Why does the grid rotate counterclockwise when the compressions are equal on opposite sides?

Any help will be greatly appreciated.

Thanks and best regards
Birendra

--- On Thu, 5/10/12, Brad Aagaard <baagaard at usgs.gov> wrote:

> From: Brad Aagaard <baagaard at usgs.gov>
> Subject: Re: Linear system solve
> To: "Birendra jha" <bjha7333 at yahoo.com>
> Cc: cig-short at geodynamics.org
> Date: Thursday, May 10, 2012, 2:22 AM
> On 05/09/2012 01:23 PM, Birendra jha
> wrote:
> > Dear developers,
> > 
> > I have a question about KSPSolve in,
> > 
> > err = KSPSolve(_ksp, residualVec, solutionVec);
> > CHECK_PETSC_ERROR(err);
> > 
> > called inside,
> > 
> > pylith::problems::SolverLinear::solve(
> > topology::Field<topology::Mesh>* solution,
> topology::Jacobian*
> > jacobian, const
> topology::Field<topology::Mesh>&  residual)
> > 
> > I find that for same residualVec and jacobian matrix,
> my solutionVec
> > (i.e. dispIncr) changes. What could be the reason? Does
> KSPSolve do
> > anything other than solving Ax=b system, after it's
> provided with A
> > and b?
> > I checked the jacobian in Implicit.py:step() using
> > self.jacobian.view(), before the call to solve() is
> made. I checked
> > residualVec and solutionVec using
> > VecView(solutionVec,PETSC_VIEWER_STDOUT_WORLD) inside
> the
> > SolverLinear::solve().
> >
> 
> What do you mean solutionVec changes? Do you mean the
> address of solutionVec changes or values inside the
> solutionVec change? When do they change?
> 
> KSPSolve is a PETSc routine. The documentation is here http://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/KSP/KSPSolve.html
> 
> Within SolverLinear::Solve() we do have to transfer values
> between Sieve sections and PETSc vectors via
> scatterSectionToVector() and scatterVectorToSection(). These
> calls will change values of the corresponding Sieve sections
> or PETSc vectors.
> 
> > Boundary conditions are independent of time.
> Compression on two side
> > boundaries, and nothing specified for other two sides
> which means
> > traction-free surface, is that correct?
> 
> If not BC is specified on a surface, it will be traction
> free as in nearly all finite-element implementations.
> 
> Brad
> 
>
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