I'm trying to get valid results from the linear elastic solver and failing. I think I'm misunderstanding the boundary conditions.
I have a 100mmx20mmx4mm aluminum beam, fixed at one end, with a load of 100N applied in the thin direction on the other end. I expect about 4.3mm of deflection.
I'm using ElmerGUI (nglib) to load a STEP file and create a mesh. I have 2 different meshes (2 different projects), one of 264 elements and one of 933 elements.
I'm using Coordinate Scaling = Real 0.001 as a Simulation parameter to deal with the STEP import scaling problem.
After some initial confusion, I expect that the boundary condition "Force" should be Desired_Force/Boundary_Area or 100N/8e-5m^2, or "Displacement i Load" could be Desired_Force/Nodes_in_boundary, when using Boundaries as a Target.
However, the results are not near to what I expect. Moreover, the two different meshes produce different results. I'm getting 0.7mm deflection for the 264 element simulation and 0.99mm for the 933 element mesh.
Does anyone know what boundary conditions I should be using to get more accurate results? Why are the 2 simulations giving such different results?
An example sif file:
Code: Select all
Header CHECK KEYWORDS Warn Mesh DB "." "." Include Path "" Results Directory "" End Simulation Max Output Level = 5 Coordinate System = Cartesian Coordinate Mapping(3) = 1 2 3 Simulation Type = Steady state Steady State Max Iterations = 1 Output Intervals = 1 Timestepping Method = BDF BDF Order = 1 Solver Input File = case.sif Post File = case.ep Coordinate Scaling = Real 0.001 End Constants Gravity(4) = 0 -1 0 9.82 Stefan Boltzmann = 5.67e-08 Permittivity of Vacuum = 8.8542e-12 Boltzmann Constant = 1.3807e-23 Unit Charge = 1.602e-19 End Body 1 Target Bodies(1) = 1 Name = "Body Property 1" Equation = 1 Material = 1 End Solver 2 Equation = Linear elasticity Procedure = "StressSolve" "StressSolver" Variable = -dofs 3 Displacement Exec Solver = Always Stabilize = True Bubbles = False Lumped Mass Matrix = False Optimize Bandwidth = True Steady State Convergence Tolerance = 1.0e-5 Nonlinear System Convergence Tolerance = 1.0e-7 Nonlinear System Max Iterations = 20 Nonlinear System Newton After Iterations = 3 Nonlinear System Newton After Tolerance = 1.0e-3 Nonlinear System Relaxation Factor = 1 Linear System Solver = Iterative Linear System Iterative Method = BiCGStab Linear System Max Iterations = 500 Linear System Convergence Tolerance = 1.0e-10 BiCGstabl polynomial degree = 2 Linear System Preconditioning = Diagonal Linear System ILUT Tolerance = 1.0e-3 Linear System Abort Not Converged = False Linear System Residual Output = 1 Linear System Precondition Recompute = 1 End Solver 1 Equation = Result Output Procedure = "ResultOutputSolve" "ResultOutputSolver" Output File Name = case Output Format = Vtu Exec Solver = After Timestep End Equation 1 Name = "strain" Calculate Stresses = True Active Solvers(1) = 2 End Equation 2 Name = "paravu" Active Solvers(1) = 1 End Material 1 Name = "Aluminium (generic)" Heat expansion Coefficient = 23.1e-6 Heat Conductivity = 237.0 Sound speed = 5000.0 Heat Capacity = 897.0 Mesh Poisson ratio = 0.35 Density = 2700.0 Poisson ratio = 0.33 Youngs modulus = 72.0e9 End Boundary Condition 1 Target Boundaries(1) = 1 Name = "Fixed" Displacement 3 = 0 Displacement 2 = 0 Displacement 1 = 0 End Boundary Condition 2 Target Boundaries(1) = 3 Name = "Force" Force 2 = $100/8e-5 !Displacement 2 Load = Real $100/8 End
Thanks in advance