Anders Logg wrote:
> On Wed, Feb 13, 2008 at 08:52:29PM +0100, Dag Lindbo wrote:
>>>> On Tue, Feb 12, 2008 at 10:23:09AM +0100, Dag Lindbo wrote:
>>>>> Hello all!
>>>>>
>>>>> In the stokes demo (taylor-hood), I notice spurious pressure spikes
>>>>> near
>>>>> the corners. What is causing these?
>>>>>
>>>>> I changed to a paraboloc inflow profile (consistent with the no-slip
>>>>> BCs),
>>>>> but the problem remains. Further, I ran the same problem on a
>>>>> unitsquare
>>>>> mesh (see plot attached). The pressure spikes are large. Is the demo
>>>>> problem ill posed?
>>>>>
>>>>> Thanks!
>>>>> Dag Lindbo, KTH
>>>> I would also suspect the boundary conditions for the velocity
>>>> to be the problem, but if you still see the spikes with a parabolic
>>>> inflow profile (which is zero at the no-slip boundaries) then I have
>>>> no idea.
>>>>
>>> Is this in all corners? Could you send a plot?
>>>
>>> /Johan
>> Problem solved. Thanks for the help! The error is that the facets adjacent
>> to the corners no get properly marked for noslip BC.
>>
>> Fix to get the correct subdomain markers, in demo/mesh/subdomain/main.cpp:
>>
>> class Noslip : public SubDomain
>> {
>> bool inside(const real* x, bool on_boundary) const
>> {
>> return (x[1] > 1.0 - DOLFIN_EPS || x[1] < DOLFIN_EPS) && on_boundary;
>> }
>> };
>>
>> /Dag & Shilpa
>
> Then you don't get no-slip on the dolphin which makes the solution
> look pretty dull, don't you think?
>
Right. For the dolfin you can put
return ((x[1] > 1.0 - DOLFIN_EPS || x[1] < DOLFIN_EPS) ||
(x[0] > DOLFIN_EPS && x[0] < 1.0 - DOLFIN_EPS) ) && on_boundary;
Dag
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