dolfin team mailing list archive

["Johan Hoffman" <jhoffman@xxxxxxxxxx>]

> On Jan 14, 2008 8:56 PM, Gideon Simpson <grs2103@xxxxxxxxxxxx> wrote:
>>  Related question for both incompressible flow and elasticity problems.
>> Suppose I have a plane of symmetry that will allow me to reduce my
>> computational domain.  If
>>
>> \sigma_ij
>>
>> is the relevant stress tensor, then I will have that
>>
>> t^k_i \sigma_ij n_j = 0
>>
>> where t^k is the k-th tangential vector of the local geometry.
>> Physically,
>> this is vanishing shear stress.  This is in addition to the condition
>>
>> u_i n_i = 0
>>
>> for no normal flow (the slip condition).
>>
>>
>> Any thoughts on implementing the vanishing shear stress condition?
>
> If we discretize with primitive variables and have Newtonian stress, this
> just amounts to a Neumann condition on the velocity. At bottom, Neumann
> conditions are just extra weak forms, so I think for more complicated
> constitutive relations, you just add the relevant weak form for the
> condition.
>
>    Matt

Yes that is right. And for the vanishing shear stress condition you
mention you actually do nothing (the "do nothng bc"). The relevant weak
form you are supposed to add should be zero.

/Johan

>> -gideon
>>
>> On Jan 14, 2008, at 2:57 PM, Murtazo Nazarov wrote:
>>
>>
>> Is there an obvious high level way to implement normal flow type
>> boundary conditions or symmetry type boundary conditions?
>>
>> -gideon
>>
>>
>>
>> If you mean slip boundary condition which for normal velocity, it is
>> already implemented and soon will be available with UNICORN.
>>
>> The slip with friction is also implemented.
>>
>> /murtazo
>>
>>
>>
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>
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