Poor mesh convergence 3D linear elasticity
Posted: 25 Mar 2019, 13:59
Hi!
I started using Elmer a few weeks ago, and I'm trying to incorporate it in a parameter optimization program, to evaluate different designs of springs automatically. I use GMSH for meshing a STEP file from Autodesk Inventor, which then is converted to Elmer format with ElmerGrid, and finally ElmerSolver is used to solve a static linear elastic analysis with a force applied to this spring, to determine the spring's stiffness and stresses in it.
It seems, however, that my results conform poorly to FEM simulations in other software (namely the built in FEM functionality in Autodesk Inventor) with the same type of mesh, using similarly sized elements. I've also done experiments which show that the other FEM software are within 10 % from reality, stiffness-wise. Using a mesh size that I would find reasonable, my results from Elmer are around 5 times stiffer than reality and other FEM results. Refining the mesh shows rapid changes in results, but even with a ridiculously fine mesh I am around 30 % off from reality. A picture of different mesh sizes and the results is attached, and also a picture showing the deformation to illustrate what the simulation is doing.
I've tried using second order elements (adding Element = "p:2" to the equation section in the .sif), but the results don't get any better for the same computation time. Am I doing something stupid that is causing this? It feels like my simulation should be a fairly simple one. Any pointers or help would be greatly appreciated.
I wish you all a good day,
Felix Eriksson
I started using Elmer a few weeks ago, and I'm trying to incorporate it in a parameter optimization program, to evaluate different designs of springs automatically. I use GMSH for meshing a STEP file from Autodesk Inventor, which then is converted to Elmer format with ElmerGrid, and finally ElmerSolver is used to solve a static linear elastic analysis with a force applied to this spring, to determine the spring's stiffness and stresses in it.
It seems, however, that my results conform poorly to FEM simulations in other software (namely the built in FEM functionality in Autodesk Inventor) with the same type of mesh, using similarly sized elements. I've also done experiments which show that the other FEM software are within 10 % from reality, stiffness-wise. Using a mesh size that I would find reasonable, my results from Elmer are around 5 times stiffer than reality and other FEM results. Refining the mesh shows rapid changes in results, but even with a ridiculously fine mesh I am around 30 % off from reality. A picture of different mesh sizes and the results is attached, and also a picture showing the deformation to illustrate what the simulation is doing.
I've tried using second order elements (adding Element = "p:2" to the equation section in the .sif), but the results don't get any better for the same computation time. Am I doing something stupid that is causing this? It feels like my simulation should be a fairly simple one. Any pointers or help would be greatly appreciated.
I wish you all a good day,
Felix Eriksson