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[Andre Massing <question143963@xxxxxxxxxxxxxxxxxxxxx>]

Question #143963 on DOLFIN changed:
https://answers.launchpad.net/dolfin/+question/143963

    Status: Open => Answered

Andre Massing proposed the following answer:
Den 03.02.11 17.37, skrev Till B:
> New question #143963 on DOLFIN:
> https://answers.launchpad.net/dolfin/+question/143963
>
> Hi,
>
> I recently installed the Fenics package and now I try to solve some problems with it. I want to simulate the flow of air around an obstacle. Eventually I want to include the temperature and see how a hot obstacle cools down in a colder air flow. However I encounter several problems, already with my baby example which does not even include the temperature. I am new in the CFD business. To begin, I adapted a few examples for Navier-Stokes solvers that I found in the Dolfin examples or on launchpad.net/nsbench (I tried both steady state and transient flow examples). I use a 3d mesh.
>
> My main problem occurs with mesh size. Unless I use a rather coarse mesh, I run out of memory, sometimes with a std::bad_alloc error, sometimes with the message that UMFPACK has run out of memory. It works with a mesh that has 7828 cells, but for example not, if I refine this mesh with the refine function of Dolfin.
> Is there anything I can do about this? I could get more RAM, but I do not think that this will ultimately solve my problem. In the end I want to use much larger meshes.
>
> With this coarse mesh I do not get realistic results. Now matter how I set my inflow velocity, the speed of the fluid in the bulk is very low. When I use a 2d version of my example with a finer mesh, I get results that make sense.
>
> Is there a way to circumvent the memory issue?
>
> Thank you!
>
> Till
>

To remedy the issues with a direct solver you can change to an iterative 
solver which is by far less memory consuming.
Have a look at the parameter demos or the stokes-iterative demos
in the undocumented demo section in your dolfin installation.

Cheers,
Andre


-- 
André Massing       		email: massing@xxxxxxxxx
Ph.D. student			mobile: +47 469 57 401
Simula Research Laboratory
NO-1367 Fornebu, Norway

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