I want to create a plane wave at the x=0 boundary and apply a far-field condition on the other side at x=0.1 to ensure there are no reflected waves.
The far-field conditions were set appropriately thanks to Mika's help.
viewtopic.php?t=8275
But the analysis results still seem strange to me.
From the analysis, the characteristic impedance of air was calculated as (p / ||v||) and the results in the graph below were obtained.
I expected the characteristic impedance (per mass) of air to be the same value 343+0i at all locations. However, the analysis results showed that the characteristic impedance of air varies depending on the x position.
I think it's probably because I gave the plane wave condition incorrectly. The current plane wave boundary conditions are as follows.
Boundary Condition 1
Name = "Radiator"
Target Boundaries(1) = 1
Im Surface Traction 1 = Real 1
Calculate Acoustic Impedance = Logical True
End
The full sif is as follows.
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 = Steady state
Steady State Max Iterations = 1
Steady State Min Iterations = 1
Output Intervals(1) = 1
Solver Input File = case.sif
Post File = case.vtu
Frequency = Real MATC "f"
$ f = 1000.0
$ U = 4.530183E-2
$ c = 343.0
$ p = 1.205
$ r = 1
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 = Linearized NavierStokes
Variable = "Flow"
Variable DOFs = 10
Procedure = "Acoustics" "AcousticsSolver"
Element = "p:1 b:1"
Bubbles in Global System = False
Linear System Solver = Iterative
Linear System Iterative Method = BiCGStabl
BiCGstabl polynomial degree = 2
Linear System Preconditioning = ILUT
Linear System ILUT Tolerance = 1.0e-3
Linear System Max Iterations = 2000
Linear System Convergence Tolerance = 1e-13
Linear System Scaling = Logical False
Linear System Row Equilibration = Logical True
Linear System Abort Not Converged = Logical True
Linear System Residual Output = 10
End
Equation 1
Name = "Equation 1"
Active Solvers(1) = 1
End
Material 1
Specific Heat = Real 1005.0
Specific Heat Ratio = Real 1.401
Equilibrium Density = Real MATC "p"
Equilibrium Temperature = Real 293.15
Heat Conductivity = Real 0.0257
Viscosity = Real 1.983e-5
Bulk Viscosity = Real 5.98e-06
End
Boundary Condition 1
Name = "Radiator"
Target Boundaries(1) = 1
Im Surface Traction 1 = Real MATC "2 * pi * f * p * U / c"
Calculate Acoustic Impedance = Logical True
End
Boundary Condition 2
Name = "Absorber"
Target Boundaries(1) = 6
Re Specific Acoustic Impedance = Real MATC "-r * c"
Im Specific Thermal Impedance = Real MATC "-2 * pi * f / (c * p)"
Calculate Acoustic Impedance = Logical True
End
Boundary Condition 3
Target Boundaries(4) = 2 3 4 5
Name = "Symmetry"
Re Velocity 2 = 0
Im Velocity 2 = 0
Re Velocity 3 = 0
Im Velocity 3 = 0
Re Surface Traction 2 = 0
Im Surface Traction 2 = 0
Re Surface Traction 3 = 0
Im Surface Traction 3 = 0
End
In the Helmholtz solver, it was possible to create a plane wave by setting the imaginary part of the flux as shown below.
Wave Flux 2 = Real 18.3183
What is the correct way to apply plane wave boundary condition in the acoustics solver?