I am trying to solve for the modes of this plate using the SmitcSolver.
On all the boundaries I wish to have a simply supported boundary condition, that is, I want the displacement in the z axis direction to be 0 along all boundaries. To my understanding this should do it, given that Deflection 1 should be normal (to surface?) displacement:
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Boundary Condition 1 Target Boundaries(4) = 1 2 3 4 Name = "SimplySupported" Deflection 1 = 0 End
As a consequence, the Eigenfunctions are wrong and Eigenfrequencies larger than 10 kHz are significantly shifted. I have the gut feeling that instead to constrain the displacement along z the displacement along another direction was constrained.
Why is this happening? Is there any way to fix it? (I have prepared the simple geometry with FreeCAD and I meshed it both with Salome and Gmsh having the same results).
Whole sif file:
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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.vtu Coordinate Scaling = 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 = "Panel" Equation = 1 Material = 2 End Solver 1 Equation = Elastic Plates Eigen System Values = 10 Eigen System Select = Smallest magnitude Procedure = "Smitc" "SmitcSolver" Variable = -dofs 3 Deflection Eigen Analysis = True 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 = 5000 Nonlinear System Newton After Iterations = 3 Nonlinear System Newton After Tolerance = 1.0e-3 Nonlinear System Relaxation Factor = 1 Linear System Solver = Direct Linear System Direct Method = Umfpack End Equation 1 Name = "DML" Active Solvers(1) = 1 End Material 1 Name = "Fibre" Damping = 4e-2 Tension = 0.0 Poisson ratio = 0.3 Youngs modulus = 1.4e9 Thickness = 3.25e-3 Youngs modulus = 1.4e9 Poisson ratio = 0.3 Porosity Model = Always saturated Density = 265 End Material 2 Name = "Aluminium (generic)" Electric Conductivity = 37.73e6 Damping = 4e-4 Tension = 0.0 Relative Permeability = 1.000022 Youngs modulus = 70.0e9 Heat Conductivity = 237.0 Electric Conductivity = 37.73e6 Electric Conductivity = 37.73e6 Poisson ratio = 0.35 Youngs modulus = 70.0e9 Thickness = 8.1e-4 Heat Capacity = 897.0 Youngs modulus = 70.0e9 Relative Permeability = 1.000022 Sound speed = 5000.0 Poisson ratio = 0.35 Heat expansion Coefficient = 23.1e-6 Poisson ratio = 0.35 Porosity Model = Always saturated Mesh Poisson ratio = 0.35 Electric Conductivity = 37.73e6 Density = 2700.0 Relative Permeability = 1.000022 End Boundary Condition 1 Target Boundaries(4) = 1 2 3 4 Name = "SimplySupported" Deflection 1 = 0 End