Impose a free surface condition

[L29430]

Hello everybody,

I'm working on a fluid dynamics case, with two-phase flow. Fluids are separated by a free surface. With an interface capturing method, I can find the position of the free surface at any time t. I would like to know if it's possible to impose a Dirichlet condition on this free surface, which is not a boundary of the domain?

Regards,

[vladotomov]

Hi @L29430,

If the surface is aligned with the mesh, you can probably impose Dirichlet BC to the linear system.

If the surface is not aligned, you should consider approximate/weak enforcement as in this paper. Related MFEM code can be found in #2043, however, the correct weak form depends on the equations you're solving.

Other approaches to do this are CutFEM and XFEM, but MFEM does not have these capabilities.

Best,
Vladimir

[v-dobrev]

Just to add to @vladotomov's answer: when the interface is aligned with the mesh, you can impose a Dirichlet b.c. on the interface the same way as on an external boundary. You need to make sure that the interface in described in the input mesh file as a set of "boundary" elements with some corresponding "boundary" attribute that identifies the interface. With that, setting up Dirichlet b.c. on the interface can be done as in example 1/1p except that you only mark the interface attribute with 1 in the array ess_bdr -- note that attribute attr (which is assumed to be >= 1 in MFEM) is marked by setting the entry ess_bdr[attr-1] to 1.

[L29430]

Hi @L29430,

If the surface is aligned with the mesh, you can probably impose Dirichlet BC to the linear system.

If the surface is not aligned, you should consider approximate/weak enforcement as in this paper. Related MFEM code can be found in #2043, however, the correct weak form depends on the equations you're solving.

Other approaches to do this are CutFEM and XFEM, but MFEM does not have these capabilities.

Best,
Vladimir

Hello Vladimir,

I'm solving a Laplace equation, so I would be very interested to understand the Shifted Diffusion Miniapp :)
How can I download the shifted files at the following link : https://github.com/mfem/mfem/tree/master/miniapps/shifted. Uploads are disabled.

Best,

@L29430

[vladotomov]

I'm not sure if Github supports downloading individual files.
The best way is to clone the Github repository. This way you can also build the code and run the miniapp.

Best,
Vladimir

[L29430]

I'm not sure if Github supports downloading individual files.
The best way is to clone the Github repository. This way you can also build the code and run the miniapp.

Best,
Vladimir

Hello Vladimir,

I copied the shifted repository in miniapps, in the library. But it didn't run... I don't know why.

[L29430]

Hello,

I copied the shifted repository in miniapps, in mfem-4.2. When I'm in this new repository, the "make" command doesn't work, I cannot get the .exe files. Is there a particular step to know to run this miniapp ?

Best,

[vladotomov]

Hi @L29430,

Are you working on a Linux or a Windows machine? What is the error you're getting?
Please also look at the INSTALL file.

Best,
Vladimir

[L29430]

Hi @L29430,

Are you working on a Linux or a Windows machine? What is the error you're getting?
Please also look at the INSTALL file.

Best,
Vladimir

Hello,

I'm working on a linux machine, my error is :

make: nothing to do with "all".

I have already looked at the INSTALL file, it doesn't say anything about the installation of this miniapp.

[L29430]

Hello Vladimir,

Can you tell me where I can find the document needed to install the shifted miniapp ?

Best.

[vladotomov]

Hi @L29430,

First you should build the MFEM library in parallel and run some of the parallel examples to make sure everything works as expected. Then you can build the shifted diffusion miniapp in /miniapps/shifted.

Vladimir

[stale]

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