FEM-Newbie: finding out "elment equations" in Elmer

[teobo]

in simple example /tests/savescalars (simplest heat conduction case) the governing equation are described in gui tutorial 1. That is Ok.

In order to study FEM in general terms and especially interested where the values at the node stem from
I now want to know (how to find out to get it in in math notation)

-which is the so called element equation (see 3. paragraph) in this elmer case?
-How is it generated, with what math methode?
-and how might it be defaultly parametrized in Elmer?

It is that I have never/no where seen a so called element equations, therefoer I use Elmer to learn them.

All hints welcome.
Thanks in advance

[raback]

Hi

I suggest that you study the Model PDE. The equations for it can be found in the Elmer Programmers Tutorial and the test case is available with the source as ModelPDE. The heat equation has some historical layers and is not the best presentation of the current way to implement the equations.

-Peter

[annier]

Hi Teobo,
Also, I am a newbie like you and i mostly have similar queries in my mind. And, Peter always provides some hints to study for.

Let me describe you a layman way of Elmer structure,

1. What does the elmerfem/fem/tests/any_test/ directory contain?

• (a) output from preprocessor (example: mesh directory containing .mesh.* files or simply mesh files)

• (b) solver input file (SIF) that contains some inputs to the elmer solver, for example--materials,BCs,initial condiitions, path to input mesh directory, desirable output format for postprocessing, materials and other simulation conditions such as time, iteration etc. (Solvers are not inside the sif, they are in Elmer installation directory-- ~/elmerinst/share/elmersolver/lib/ . So, the sif file communicates with the solvers of solver n listed in it.The ElmerSolver utilizes the ELMERSOLVER_STARTINFO to execute sif file.

• (c) output files (.ep or elmer post files, .vtu files, .dat files, .dat.names files) after we run the ElmerSolver. These are the output from elmersolver and are ready to be postprocessed.

2. Where can we observe the source files of ElmerSolver (i.e. where finite element method is being implemented)?

• We can peep into ~/elmerfem/fem/src/modules/ directory.Then we copy a .src files anywhere else. Let me illustrate with AdvectionDiffusion.src. Change .src to .f90 and view AdvectionDiffusion.f90 in fortran 90 format. There you can see the finite element formulation of a partial differential equation namely, Advection Diffusion Equation.

3. Types / Ways of Working in Elmer

• Type A: >> Using Elmer by creating a geometry and SIF for already existing Elmer solvers.The existing Elmer solvers (.src) files implementing Finite Element Method(FEM) for solving Partial Differential Equation (PDE) are used in their default way.

• Type B:>>Type A+ SIF(with MATC code and/or linked to UDF). Using Elmer by creating a geometry and SIF (with MATC code within a SIF file and linking a User Defined Function (UDF) to the SiF) . In this context, elmerf90 compiler has to be used to compile the UDF. The existing Elmer solvers (.src) files implementing Finite Element Method(FEM) for solving Partial Differential Equation (PDE) are used in their default way.

• Type C:>> (Type A or Type B) + Writing an elmer solver for a PDE (need to write an Elmer module in fortran 90 format and compile it with a elmerf90 compiler). This is like writing an entirely new module in Elmer. Also, this module can be used in combination with the existing Elmer solvers (.src) files.

4. When can one feel implementing Full Scale finite element method in Elmer?

• One can feel like that when he/she becomes user of Type C (i.e. when she/he writes an Elmer module for solving a PDE).

The description about ModelPDE (as referred by Peter) is given in Chapter 7 (entitled Partial Differential Equations) in
http://www.nic.funet.fi/pub/sci/physics ... torial.pdf. Similarly, ModelPDE.src is located in ~/elmerfem/fem/src/modules/ directory(you can copy this file into your homework project directory,rename it as ModelPDE.f90 and observe for relating with the description in ElmerProgrammersTutorial).

Yours
Anil Kunwar

[teobo]

Thanks for both pointing me the way. Need to go for it later. But anyway great work, annier.