I am new member of this community. Firstly I would like to thank whole Elmer team for distribution of manuals and tutorials online. They have already helped me to better understand FEM. These papers are really clear and easy to understand. I cannot thank enough for including parts of .sif file which gave me basis to start.
I am turning to you with a problem refering to tutorial 16. I have implemented example file hole.grd. I have generated case.sif file according to instructions from Elmer Tutorial (Solution procedure). My intention is to calculate acoustic impedance of a single hole in microperforation used in MEMS microphones. I plan to modify dimensions of initial model in hole.grd and observe how they would affect the results. I have read that in such case I should use equation:
Z = (Pin - Pout)/vin
where:
Pin - inlet pressure
Pout - outlet pressure
vin - inlet velocity
I have tried to conduct time-domain analysis (with parameters given in Simulation section of case.sif) and to plot the results in Paraview. To my concern, values of both velocity and pressure are suspiciously huge (regardless negative sign). Besides I am not sure about distribution of these values. What should I anticipate?
Am I using proper equation for analysis at all? Is this a matter of boundary conditions? And what is the most important - is there any approximately minimum value of time period after which Pout is taken?
Thank to anyone that would be willing to help.
Here is code of my case.sif:
Code: Select all
Header
CHECK KEYWORDS Warn
Mesh DB "." "."
Include Path ""
Results Directory ""
End
Simulation
Max Output Level = 5
Coordinate System = Cartesian 3D
Coordinate Mapping(3) = 1 2 3
Simulation Type = Transient
Timestep Intervals = 10
Timestep Sizes = 0.00001
Steady State Max Iterations = 1
Output Intervals = 1
Timestepping Method = BDF
BDF Order = 1
Solver Input File = case.sif
Post File = flow.vtu
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 1"
Equation = 1
Material = 1
End
Solver 1
Equation = Navier-Stokes
Variable = Flow Solution[Velocity:3 Pressure:1]
Procedure = "FlowSolve" "FlowSolver"
Variable DOFs = 4
Exec Solver = After Timestep
Stabilize = True
Bubbles = False
Lumped Mass Matrix = False
Optimize Bandwidth = True
Steady State Convergence Tolerance = 1.0e-5
Nonlinear System Convergence Tolerance = 1.0e-5
Nonlinear System Max Iterations = 1
Nonlinear System Newton After Iterations = 3
Nonlinear System Newton After Tolerance = 1.0e-8
Nonlinear System Relaxation Factor = 1
Linear System Solver = Iterative
Linear System Iterative Method = BiCGStab
Linear System Max Iterations = 200
Linear System Convergence Tolerance = 1.0e-8
BiCGstabl polynomial degree = 2
Linear System Preconditioning = ILU0
Linear System ILUT Tolerance = 1.0e-3
Linear System Abort Not Converged = False
Linear System Residual Output = 10
Linear System Precondition Recompute = 1
End
Solver 2
Exec Solver = After Timestep
Equation = Fluidic Force
Procedure ="FluidicForce" "ForceCompute"
Calculate Viscous Force = True
End
Solver 3
Exec Solver = After Timestep
Equation = SaveScalars
Procedure = "SaveData" "SaveScalars"
Filename = "flowdata.dat"
Save Variable 1 = Velocity 3
Save Coordinates(1,2) = 0.0 0.0
End
Equation 1
Name = "Equation 1"
NS Convect = True
Active Solvers(3) = 1 2 3
End
Material 1
Name = "Air (room temperature)"
Density = 1.205
Sound speed = 343.0
Heat Capacity = 1005.0
Viscosity = 1.983e-5
Heat expansion Coefficient = 3.43e-3
Heat Conductivity = 0.0257
Relative Permittivity = 1.00059
End
Boundary Condition 1
Target Boundaries(1) = 4
Flow Force BC = True
Name = "BoundaryCondition 1"
Velocity 3 = 2.0e3
Slip Coefficient 1 = 2e-4
Normal-Tangential Velocity = True
Slip Coefficient 2 = 2e-4
Calculate Fluidic Force = True
End
Boundary Condition 2
Target Boundaries(2) = 8 10
Name = "BoundaryCondition 2"
Normal-Tangential Velocity = True
Velocity 2 = 0.0
End
Boundary Condition 3
Target Boundaries(2) = 2 3
Flow Force BC = True
Name = "BoundaryCondition 3"
Normal-Tangential Velocity = True
Slip Coefficient 1 = 2e-4
Velocity 3 = 0.0
Slip Coefficient 2 = 2e-4
End
Boundary Condition 4
Target Boundaries(2) = 6 9
Name = "BoundaryCondition 4"
Normal-Tangential Velocity = True
Velocity 1 = 0.0
End
Boundary Condition 5
Target Boundaries(1) = 5
Name = "BoundaryCondition 5"
Pressure = 0.0
Normal-Tangential Velocity = True
End
Boundary Condition 6
Target Boundaries(1) = 1
Flow Force BC = True
Name = "BoundaryCondition 6"
Slip Coefficient 2 = 2e-4
Normal-Tangential Velocity = True
Velocity 1 = 0.0
Slip Coefficient 3 = 2e-4
End
Boundary Condition 7
Target Boundaries(1) = 7
Flow Force BC = True
Name = "BoundaryCondition 7"
Normal-Tangential Velocity = True
Slip Coefficient 3 = 2e-4
Slip Coefficient 1 = 2e-4
Velocity 2 = 0.0
End