As part of a project, I have performed an eigenmode analysis of a stator and have also compared the results with those generated by ANSYS. Even though I've had to implement a coarse mesh, the eigenmodes and displacement values are very close to eachother. However, I have noticed that when calculating the eigenfrequencies with : lambda = (2*pi*f)^2 , these turn out to be very small, e.g.:
Eigenmode 7: lambda = 14.34 => f = 0.603
Compared to the results in ANSYS, the eigenfrequencies in Elmer should all be bigger by a factor of 10^3 in order to be reasonable. Do you have any idea why this may be happenning? Have I overseen something? I'll attach relevant documents.
Kind Regards
Marc
Code: Select all
$
shift = (2*pi*0)^2
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) = 1
Coordinate Scaling = 0.001
Solver Input File = case.sif
Post File = case.vtu
End
Constants
End
Body 1
Target Bodies(1) = 1
Name = "Body 1"
Equation = 1
Material = 1
End
Solver 1
Equation = Linear elasticity
Procedure = "StressSolve" "StressSolver"
Variable = -dofs 3 Displacement
Displace mesh = Logical False
Eigen System Select = Smallest magnitude
Eigen Analysis = Logical True
Eigen System Values = Integer 50
Exec Solver = Always
Stabilize = Logical True
Bubbles = Logical False
Lumped Mass Matrix = Logical False
Optimize Bandwidth = Logical True
Steady State Convergence Tolerance = 1.0e-5
Nonlinear System Convergence Tolerance = 1.0e-7
Linear System Solver = Direct
Linear System Iterative Method = BiCGStabl
Linear System Max Iterations = 5000
Linear System Convergence Tolerance = 1.0e-8
BiCGstabl polynomial degree = 2
Linear System Preconditioning = ILUT
Linear System ILUT Tolerance = 1.0e-3
Linear System Abort Not Converged = True
Linear System Residual Output = 10
Linear System Precondition Recompute = 1
Eigen System Shift = $ shift
Element = "P:2"
End
Solver 2
Equation = "Result Output"
Procedure = "ResultOutputSolve" "ResultOutputSolver"
Exec Solver = After Saving
Show Variables = Logical true
Output Directory = "results"
Output File Name = "results_1"
Output Format = VTU
Eigen Analysis = Logical True
End
Equation 1
Name = "Equation 1"
Active Solvers(2) = 1 2
End
Material 1
Name = "Material 1"
Youngs modulus = 2e5
Poisson ratio = 0.35
Density = 7680
End