[petsc-users] Removing rigid body motion using Null Space

[Hom Nath Gharti]

Thanks for the suggestion. I will try.

On Tue, Jul 28, 2015 at 1:23 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
>
>> On Jul 28, 2015, at 11:51 AM, Hom Nath Gharti <hng.email at gmail.com> wrote:
>>
>> Dear all,
>>
>> After searching old mailing lists, it appears that the rigid body
>> motion can be removed using Null Space features in PETSc.
>> Unfortunately, I could not successfully implement this to a simple
>> elastostatic problem. I have an unconstrained sphere and I need to
>> compute displacement field due to a point load on the surface.
>>
>> I tried:
>> call MatNullSpaceCreate(PETSC_COMM_WORLD,PETSC_TRUE,0,0,nullspace,ierr)
>> call MatSetNullSpace(Kmat,nullspace,ierr)
>> call MatNullSpaceRemove(nullspace,bvec,PETSC_NULL_OBJECT,ierr)
>
>
>     This won't provide the rigid body motions (translations and rotations) this only provides a constant null space. Perhaps you need MatNullSpaceCreateRigidBody()
>
>    Barry
>
>> call MatNullSpaceDestroy(nullspace,ierr)
>>
>> But the solution did not converge! Any help/hint would be greatly appreciated.
>>
>> Best,
>> Hom Nath
>