So, I am trying to set up a simple model using the AcousticsSolver. As a first step, since I never used the solver, I am trying to use the simplest possible parameters. However, I can only get trivially 0 solutions. Maybe you can help me understand what I am doing wrong.

The model is just a sort of 3D pipeline. I would like all the walls to be rigid, a part for one termination of the pipeline that I would like to have constant velocity along the axis of the pipeline (z axis). The model was created with FreeCAD and the I prepared an unv mesh with Salome, which I converted to Elmer format with:

Code: Select all

```
ElmerGrid 8 2 FineGeometryMesh.unv
```

Code: Select all

```
! Steady State Linearized Navier-Stokes solver
Header
CHECK KEYWORDS Warn
Mesh DB "." "FineGeometryMesh"
Include Path ""
Results Directory ""
$ f = 110 5 20 27.5 55 60 100 105 110 140 180 205 220 220 260 300 305 340 380 405 420 440 460 500 505 540 580 605 620 660 700 705 740 780 805 820 860 880 900 905 940 980 1005 1105 1205 1305 1405 1505 1605 1705 1760 1805 1905 2005 2105 2205 2305 2405 2505 2605 2705 2805 2905 3005 3105 3205 3305 3405 3505 3520 3605 3705 3805 3905 4005 4105 4205 4305 4405 4505 4605 4705 4805 4905 7040
$ v = 1
End
Simulation
Max Output Level = 5
Coordinate System = Cartesian
Coordinate Mapping(3) = 1 2 3
Simulation Type = Scanning
Steady State Max Iterations = 1
Output Intervals = 1
Timestepping Method = BDF
BDF Order = 1
Timestep intervals = 1 !84
Solver Input File = case.sif
Post File = case.ep
Coordinate Scaling = 0.001
Frequency = Variable time; Real MATC "f(tx - 1)"
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 2
Equation = Linearized Navier–Stokes
Procedure = "Acoustics" "AcousticsSolver"
Variable = Flow
Variable Dofs = 10
!Element = p:1 b:5
Bubbles in Global System = False
Utilize Previous Solution = False
Block Preconditioning = False
Max Outer Iterations = 500
!Max Inner GCR Iterations = 10
Ratio of Convergence Tolerances = 0.001
!Residual Reduction Ratio = 0.01
Linear System Convergence Tolerance = 1.0e-10
!Velocity Convergence Tolerance =
!Schur Complement Convergence Tolerance =
Linear System Max Iterations = 500
!Velocity Assembly = True
ILU Order for Schur Complement = 1
!ILU Order for Velocities =
!!Linear System Solver = Iterative
!!Linear System Iterative Method = BiCGStab
!!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 = 1
!!Linear System Precondition Recompute = 1
!!Nonlinear System Convergence Tolerance = 1.0e-7
!!Nonlinear System Max Iterations = 500
!!Nonlinear System Newton After Iterations = 3
!!Nonlinear System Newton After Tolerance = 1.0e-3
!!Nonlinear System Relaxation Factor = 1
Exec Solver = Always
!!Stabilize = True
!!Lumped Mass Matrix = False
!!Optimize Bandwidth = True
!!Steady State Convergence Tolerance = 1.0e-5
End
Solver 1
Equation = Result Output
Output File Name = case
Save Geometry Ids = False
Output Format = Vtu
Procedure = "ResultOutputSolve" "ResultOutputSolver"
Exec Solver = After Timestep
End
Equation 1
Name = "airModel"
Active Solvers(1) = 2
End
Equation 2
Name = "paraviewExport"
Active Solvers(1) = 1
End
Material 1
Name = "Air (room temperature)"
Relative Permeability = 1.00000037
Heat Conductivity = 0.0257
!Turbulent Prandtl Number = 0.713
Heat Capacity = 1005.0
Relative Permittivity = 1.00059
Relative Permeability = 1.00000037
Viscosity = 1.983e-5
Viscosity = 1.983e-5
Sound speed = 343.0
Heat expansion Coefficient = 3.43e-3
Relative Permittivity = 1.00059
Porosity Model = Always saturated
Relative Permittivity = 1.00059
Relative Permittivity = 1.00059
Density = 1.205
Relative Permeability = 1.00000037
Specific Heat = 0.718
Specific Heat Ratio = 1.39972144846797
Equilibrium Density = 1.205
Equilibrium Temperature = 20
! Heat Conductivity =
! Viscosity =
! Bulk Viscosity =
! Re Heat Source =
! Im Heat Source =
! Re Body Force i =
! Im Body Force i =
End
Boundary Condition 1
Target Boundaries(1) = 11
Name = "airRadiator"
Re Velocity 1 = 0
Im Velocity 1 = 0
Re Velocity 2 = 0
Im Velocity 2 = 0
Re Velocity 3 = Real MATC "v"
Im Velocity 3 = 0
End
Boundary Condition 2
Target Boundaries(10) = 2 3 4 5 6 7 8 9 10 12
Name = "airRigid"
Re Velocity 1 = 0
Im Velocity 1 = 0
Re Velocity 2 = 0
Im Velocity 2 = 0
Re Velocity 3 = 0
Im Velocity 3 = 0
End
```

Code: Select all

```
case.sif
1
```

Code: Select all

```
ElmerSolver >solver.log 2>&1
```

Code: Select all

```
ELMER SOLVER (v 8.3) STARTED AT: 2018/03/09 13:45:31
ParCommInit: Initialize #PEs: 1
MAIN:
MAIN: =============================================================
MAIN: ElmerSolver finite element software, Welcome!
MAIN: This program is free software licensed under (L)GPL
MAIN: Copyright 1st April 1995 - , CSC - IT Center for Science Ltd.
MAIN: Webpage http://www.csc.fi/elmer, Email elmeradm@csc.fi
MAIN: Version: 8.3 (Rev: unknown, Compiled: 2018-03-08)
MAIN: HYPRE library linked in.
MAIN: MUMPS library linked in.
MAIN: =============================================================
MAIN:
MAIN:
MAIN: -------------------------------------
MAIN: Reading Model: case.sif
LoadInputFile: Scanning input file: case.sif
LoadInputFile: Loading input file: case.sif
WARNING:: LoadInputFile: > Equation 2 < not used in any Body!
Loading user function library: [ResultOutputSolve]...[ResultOutputSolver_Init0]
Loading user function library: [Acoustics]...[AcousticsSolver_Init0]
LoadMesh: Base mesh name: ./FineGeometryMesh
LoadMesh: Scaling coordinates: 1.000E-03 1.000E-03 1.000E-03
LoadMesh: Elapsed REAL time: 0.2475 (s)
MAIN: -------------------------------------
Loading user function library: [ResultOutputSolve]...[ResultOutputSolver_Init]
Loading user function library: [ResultOutputSolve]...[ResultOutputSolver_bulk]
Loading user function library: [ResultOutputSolve]...[ResultOutputSolver]
Loading user function library: [Acoustics]...[AcousticsSolver_Init]
Loading user function library: [Acoustics]...[AcousticsSolver_bulk]
Loading user function library: [Acoustics]...[AcousticsSolver]
OptimizeBandwidth: ---------------------------------------------------------
OptimizeBandwidth: Computing matrix structure for: linearized navier–stokes...done.
OptimizeBandwidth: Half bandwidth without optimization: 67066
OptimizeBandwidth:
OptimizeBandwidth: Bandwidth Optimization ...done.
OptimizeBandwidth: Half bandwidth after optimization: 3646
OptimizeBandwidth: ---------------------------------------------------------
MAIN:
MAIN: -------------------------------------
MAIN: Time: 1/1 1.0000000000000000
MAIN: -------------------------------------
MAIN:
SingleSolver: Attempting to call solver
SingleSolver: Solver Equation string is: linearized navier–stokes
AcousticsSolver: Helmholtz solution is not available
AcousticsSolver: Acoustic interface boundary conditions cannot be applied
AcousticsSolver:
AcousticsSolver: -------------------------------------
AcousticsSolver: Frequency (Hz): 110.00000000000000
AcousticsSolver: -------------------------------------
AcousticsSolver:
AcousticsSolver: Starting Assembly
AcousticsSolver: Estimated assembly time (s): 128.67
AcousticsSolver: Assembly: 8 % done
AcousticsSolver: Assembly: 16 % done
AcousticsSolver: Assembly: 24 % done
AcousticsSolver: Assembly: 33 % done
AcousticsSolver: Assembly: 41 % done
AcousticsSolver: Assembly: 49 % done
AcousticsSolver: Assembly: 58 % done
AcousticsSolver: Assembly: 66 % done
AcousticsSolver: Assembly: 74 % done
AcousticsSolver: Assembly: 83 % done
AcousticsSolver: Assembly: 91 % done
AcousticsSolver: Assembly: 99 % done
WARNING:: Acoustics: Could not find variable U for FSI simulation
DefUtils::DefaultDirichletBCs: Setting Dirichlet boundary conditions
DefUtils::DefaultDirichletBCs: Dirichlet boundary conditions set
AcousticsSolver: Assembly done
SolveSystem: Solution trivially zero!
AcousticsSolver:
AcousticsSolver: Result Norm : 0.0000000000000000
AcousticsSolver: Relative Change: 0.0000000000000000
AcousticsSolver: Assembly: (s) 110.98
AcousticsSolver: Solve: (s) 0.00
AcousticsSolver: Exiting the solver...
SingleSolver: Attempting to call solver
SingleSolver: Solver Equation string is: result output
ResultOutputSolver: -------------------------------------
ResultOutputSolve: Saving with prefix: case
ResultOutputSolver: Creating list for saving - if not present
CreateListForSaving: Field Variables for Saving
ResultOutputSolver: Saving in unstructured VTK XML (.vtu) format
VtuOutputSolver: Saving results in VTK XML format with prefix: case
VtuOutputSolver: Saving number of partitions: 1
ResultOutputSolver: -------------------------------------
WritePostFile: Saving results in ElmerPost format to file FineGeometryMesh/case.ep
ElmerSolver: *** Elmer Solver: ALL DONE ***
ElmerSolver: The end
SOLVER TOTAL TIME(CPU,REAL): 124.78 126.10
ELMER SOLVER FINISHED AT: 2018/03/09 13:47:38
```

Code: Select all

```
AcousticsSolver: Helmholtz solution is not available
AcousticsSolver: Acoustic interface boundary conditions cannot be applied
```