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