Frequently Asked Questions

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Below is a list of some of the most frequently asked questions. You can suggest new FAQs on the forum.

Technical Questions

  • Q: How do I create geometries with Elmer?
    A: Elmer suite does not include proper geometry generation tools. You should use other geometry and proposal software mesh generations tools and import the files into Elmer. Gmsh and GiD (mesh) and SALOME (CAD) are the most commonly used ones. Some simple geometries may be defined directly in ascii-format using the .grd (ElmerGrid) and .in2d (netgen) formats, for example.

  • Q: I edit the .sif file manually but modifications are erased by ElmerGUI
    Q: How can I import my .sif file into ElmerGUI?
    A: The state of ElmerGUI is defined by the project file which is used to generate the sif file. Therefore the modifications in the .sif file are not communicated to the ElmerGUI and a .sif file cannot be used as a starting point for ElmerGUI work.

  • Q: I try to set a "keyword" value in the .sif file but ElmerSolver gives an error "Unknown speficier" for property name:"keyword". What's wrong?
    A: The list of known keywords is defined in the SOLVER.KEYWORDS file. The list can never be complete since the code is all the time developing and the user may also invent new variable names. If the type of the keyword is not known the user must provide it from one of the following: Logical, Integer, Real, String and File. Also Equals defines the type implicitely to be of type Real.

  • Q: Where can I find examples on how to use a specific solver?
    A: The are a few walk-through cases in Elmer Tutorials. In addition there are more than 130 minimalistic tests in the Elmer distribution. Among the .sif files you can try to find the ones that include the the solver of interest. By increasing the "Max Output Level" and link building defining a "Post File" in the "Simulation" section its easier to get aquinted to the solver.

  • Q: What unit system should I use in Elmer?
    A: Elmer does not assume any specific units so you can use any unit system that is consistant. The natural choice is SI units. By default the equations are scaled to an optimal range so usually there is no need for altering the unit system for the sake of numerical accuracy. However, If you choose, for example, your mesh to be in mm remember that it reflects to the units of velocity, density, force, viscosity etc. as well.

  • Q: I want to restart using the .ep file, how do I do that?
    A: Unfortunately Elmer uses the "Post File", with the usual suffix .ep, only for visualization. If you want to restart you need to save the data in a "Result File" which has some additional information required.

  • Q: I want to vizualize my results using graphs, how should I proceed?
    A: There are auxiliary solvers SaveLine and SaveScalars that may be used to generate appropriate data in ascii format. See the Models manual or search the discussion forum for more information.

  • Q: I want to use Paraview (or other VTK based visualizatio software). How should I proceed?
    A: You can utilize the ResultOutputSolve with vtu (or vtk) output format. See Models manual for details.

    Generic Questions

  • Q: How large is the Elmer community?
    A: Based on different web & download statistics, a rough estimate would be hundreds of active users and thousands of test users each year.

  • Q: There have been quite few official releases of Elmer. Has the development stopped?
    A: No. Elmer is actively developed and each major commit is run against a large number of tests cases. Therefore we consider the trunk version to be stable and recommend it as starting point for any compilation. However, we plan to give more regularly official releases in the future.

  • Q: Are you trying to make money with Elmer?
    A: No. Elmer is maintained by CSC - IT Center for Science which is a governmental non-profit organization in Finland. However, in order to fund the development of the code we do have to put a price tag on the labour when we're not serving the Finnish universities.

  • Q: Can I use Elmer for commercial consultation or other non-academic work?
    A: Yes. GPL license does not limit commercial use in any way.

  • Q: Can I use parts of Elmer in my own code?
    A: Yes, with the condition that if you publish the code it must be published under the same license i.e. GPL.

  • Q: Can I copy the documentation freely?
    A: Yes. They have been published under Creative Commons licence. However, no derivative works are allowed i.e. the copies must not include any modifications to the originals.

  • Q: I would like to write a solver for my own problem. Is it difficult?
    A: It depends. Most solvers can be written as dynamically linked modules utilizing high level library functions. A simple Poisson equation ready for all dimensions and all massively parallel simulations will takes just 30 lines of code, or so. Using some special elementtypes for complicated vector valued equations is more laborious and requires some knowhow of finite elements.

  • Q: I would like to contribute but I can't program, is there anything I could do?
    A: Yes. Often in the development defining what equations to solve, setting up appropriate test cases and creating the computational mesh is easily 80% of the work load. If you can help in these aspects then the actual coding work will be much more attractive to the developers. Also sharing your simulation work will benefit the project by attrackting new users.

  • Q: How are the new features of Elmer decided?
    A: In large, Elmer development is guided by a number of externally funded projects which result to new features in different application areas. For minor issues a good idea is often a sufficient starting point and therefore feature wishes and bug reports are always welcome.
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