I used the Helmholtz Solver for acoustics a bunch of times for 3D meshes. Typically, the vtu file Elmer saves has two scalar fields inside, "pressure wave 1" and "pressure wave 2". Today I produced a simulation on a 2D mesh instead, on the XY plane. After I solved the study, I was surprised to find that inside the final vtu there is a single vector field "pressure wave" with 3 components, "pressure wave_X", "pressure wave_Y" and"pressure wave_Z". The _Z component seems to be 0 all over, and to me it looks like _X and _Y are the real and imaginary parts of the actual scalar field.
I could not find information in the Models Manual about how the mesh dimensionality affects the resulting vtu. Do you guys think my interpretation of the result above is correct?
My sif is file below, I now realise that I used a 3D cartesian system. Any chance this is the reason why I got a vector field instead of a scalar one?
Code: Select all
Header
CHECK KEYWORDS Warn
Mesh DB "." "."
Include Path ""
Results Directory ""
$ f = 40000
$ p = 1.205
$ U = 0.34
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
Coordinate Scaling = 0.001
Solver Input File = case.sif
Post File = case.vtu
End
Constants
Gravity(4) = 0 -1 0 9.82
Stefan Boltzmann = 5.670374419e-08
Permittivity of Vacuum = 8.85418781e-12
Permeability of Vacuum = 1.25663706e-6
Boltzmann Constant = 1.380649e-23
Unit Charge = 1.6021766e-19
End
Body 1
Target Bodies(1) = 1
Name = "Body 1"
Equation = 1
Material = 1
End
Solver 1
Equation = Helmholtz Equation
Variable = -dofs 2 Pressure Wave
Element = "p:2"
Procedure = "HelmholtzSolve" "HelmholtzSolver"
Exec Solver = Always
Stabilize = True
Optimize Bandwidth = True
Steady State Convergence Tolerance = 1.0e-5
Nonlinear System Convergence Tolerance = 1.0e-7
Nonlinear System Max Iterations = 1
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 = BiCGStabl
Linear System Max Iterations = 10000
Linear System Convergence Tolerance = 1.0e-10
BiCGstabl polynomial degree = 2
Linear System Preconditioning = ILUT
Linear System ILUT Tolerance = 1.0e-3
Linear System Abort Not Converged = False
Linear System Residual Output = 10
Linear System Precondition Recompute = 1
End
Equation 1
Name = "Helmholtz"
Frequency = Real MATC "f"
Active Solvers(1) = 1
End
Material 1
Name = "Air (room temperature)"
Turbulent Prandtl Number = 0.713
Relative Permeability = 1.00000037
Sound speed = 343.0
Heat Capacity = 1005.0
Viscosity = 1.983e-5
Relative Permittivity = 1.00059
Heat expansion Coefficient = 3.43e-3
Heat Conductivity = 0.0257
Porosity Model = Always saturated
Density = Real MATC "p"
End
Boundary Condition 1
Target Boundaries(7) = 1 3 4 5 6 7 8
Name = "Rigid"
Wave Flux 1 = 0
Wave Flux 2 = 0
End
Boundary Condition 2
Target Boundaries(1) = 2
Name = "Radiator"
Wave Flux 2 = Real MATC "2 * pi * f * p * U"
Wave Flux 1 = 0
End
Boundary Condition 3
Target Boundaries(1) = 9
Name = "Outlet"
Plane Wave BC = True
End