WaveSolver and Eigen Analysis

Numerical methods and mathematical models of Elmer
CrocoDuck
Posts: 79
Joined: 12 May 2016, 13:15
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WaveSolver and Eigen Analysis

Post by CrocoDuck »

Hello!

I am trying to solve for the acoustic eigenmodes of a 3D rectangular room by using the WaveSolver. I am using this as a guide.

See below my sif file:

Code: Select all

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 = 10
  Output Intervals = 1
  Timestepping Method = BDF
  BDF Order = 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 = 5.67e-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
  Initial Condition = 1
End

Initial Condition 1
  Pressure Velocity = Real 1
End

Equation 1
  Name = "Wave Equation"
  Active Solvers(1) = 1
End

Solver 1

  ! Equation
  Equation = "Wave Equation"
  Procedure = "WaveSolver" "WaveSolver"
  Variable = "Pressure"
  Variable DOFs = 1
  
  ! Solver
  
  ! Steady State
  Steady State Convergence Tolerance = 1e-09
  
  ! Nonlinear
  !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
  !Linear System Scaling = Logical True
  !Linear System Symmetric = Logical True
  Linear System Solver = string "Iterative"
  Linear System Direct Method = Umfpack
  Linear System Iterative Method = BiCGStab
  Linear System Max Iterations = integer 10000
  Linear System Convergence Tolerance = real 1e-8
  BiCGstabl polynomial degree = 4
  Linear System Preconditioning = ILU0
  Linear System ILUT Tolerance = 1.0e-3
  Linear System Abort Not Converged = True
  Linear System Residual Output = 50
  Linear System Precondition Recompute = 1
  
  ! Special
  Eigen Analysis = True
  Eigen System Values = 10
  Eigen System Convergence Tolerance = Real 1.0e-6
  Eigen System Max Iterations = 10000
  Eigen System Select = smallest magnitude
  !Eigen System Shift = Real 1000
  Eigen System Normalize To Unity = Logical True
  
End

Material 1
  Name = "Air (room temperature)"
  Heat expansion Coefficient = 3.43e-3
  Heat Capacity = 1005.0
  Heat Conductivity = 0.0257
  Sound speed = 343.0
  Viscosity = 1.983e-5
  Relative Permittivity = 1.00059
  Viscosity = 1.983e-5
  Porosity Model = Always saturated
  Turbulent Prandtl Number = 0.713
  Relative Permittivity = 1.00059
  Density = 1.205
  Relative Permeability = 1.00000037
  Sound Speed = Real 343.0
  Sound Damping = Real 0.0
  Sound Reaction Damping = Real 0.0
End

Boundary Condition 1
  Target Boundaries(6) = 2 3 4 5 6 7
  !Pressure = Real 0
  !Source Acceleration = Real 0
  Pressure Velocity = Real 0
End

My issue is that I always get an infinite norm:

Code: Select all

ELMER SOLVER (v 8.4) STARTED AT: 2020/08/18 16:15:10
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: 8.4 (Rev: unknown, Compiled: 2020-08-17)
MAIN:  Running one task without MPI parallelization.
MAIN:  Running with just one thread per task.
MAIN:  HYPRE library linked in.
MAIN:  MUMPS library linked in.
MAIN: =============================================================
LoadInputFile: Reading only "Run Control" section
MAIN: 
MAIN: 
MAIN: -------------------------------------
MAIN: Reading Model: case.sif
LoadInputFile: Scanning input file: case.sif
LoadInputFile: Scanning only size info
LoadInputFile: First time visiting
LoadInputFile: Reading base load of sif file
LoadInputFile: Loading input file: case.sif
LoadInputFile: Reading base load of sif file
Model Input:  Unlisted keyword: [pressure velocity] in section: [initial condition 1]
Model Input:  Unlisted keyword: [pressure velocity] in section: [boundary condition 1]
LoadInputFile: Number of BCs: 1
LoadInputFile: Number of Body Forces: 0
LoadInputFile: Number of Initial Conditions: 1
LoadInputFile: Number of Materials: 1
LoadInputFile: Number of Equations: 1
LoadInputFile: Number of Solvers: 1
LoadInputFile: Number of Bodies: 1
Loading user function library: [WaveSolver]...[WaveSolver_Init0]
LoadMesh: Base mesh name: ./.
LoadMesh: Scaling coordinates: 1.000E-03 1.000E-03 1.000E-03
LoadMesh: Elapsed REAL time:     0.0863 (s)
MAIN: -------------------------------------
AddVtuOutputSolverHack: Adding ResultOutputSolver to write VTU output in file: case
Loading user function library: [WaveSolver]...[WaveSolver_Init]
Loading user function library: [WaveSolver]...[WaveSolver_bulk]
Loading user function library: [WaveSolver]...[WaveSolver]
OptimizeBandwidth: ---------------------------------------------------------
OptimizeBandwidth: Computing matrix structure for: wave equation...done.
OptimizeBandwidth: Half bandwidth without optimization: 15311
OptimizeBandwidth: 
OptimizeBandwidth: Bandwidth Optimization ...done.
OptimizeBandwidth: Half bandwidth after optimization: 1064
OptimizeBandwidth: ---------------------------------------------------------
Loading user function library: [ResultOutputSolve]...[ResultOutputSolver_Init]
Loading user function library: [ResultOutputSolve]...[ResultOutputSolver_bulk]
Loading user function library: [ResultOutputSolve]...[ResultOutputSolver]
WARNING:: InitCond: We can only set timederivative for transients
ElmerSolver: Number of timesteps to be saved: 10
MAIN: 
MAIN: -------------------------------------
MAIN:  Steady state iteration:            1
MAIN: -------------------------------------
MAIN: 
SingleSolver: Attempting to call solver
SingleSolver: Solver Equation string is: wave equation
DefUtils::DefaultDirichletBCs: Setting Dirichlet boundary conditions
DefUtils::DefaultDirichletBCs: Dirichlet boundary conditions set
CRS_IncompleteLU: ILU(0) (Real), Starting Factorization:
CRS_IncompleteLU: ILU(0) (Real), NOF nonzeros:    241600
CRS_IncompleteLU: ILU(0) (Real), filling (%) :       100
CRS_IncompleteLU: ILU(0) (Real), Factorization ready at (s):     0.01
       1   Infinity
ERROR:: IterSolve: Numerical Error: System diverged over maximum tolerance.
Note: The following floating-point exceptions are signalling: IEEE_DIVIDE_BY_ZERO
STOP 1

Or, if I try a direct solver:

Code: Select all

ELMER SOLVER (v 8.4) STARTED AT: 2020/08/18 16:20:29
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: 8.4 (Rev: unknown, Compiled: 2020-08-17)
MAIN:  Running one task without MPI parallelization.
MAIN:  Running with just one thread per task.
MAIN:  HYPRE library linked in.
MAIN:  MUMPS library linked in.
MAIN: =============================================================
LoadInputFile: Reading only "Run Control" section
MAIN: 
MAIN: 
MAIN: -------------------------------------
MAIN: Reading Model: case.sif
LoadInputFile: Scanning input file: case.sif
LoadInputFile: Scanning only size info
LoadInputFile: First time visiting
LoadInputFile: Reading base load of sif file
LoadInputFile: Loading input file: case.sif
LoadInputFile: Reading base load of sif file
Model Input:  Unlisted keyword: [pressure velocity] in section: [initial condition 1]
Model Input:  Unlisted keyword: [pressure velocity] in section: [boundary condition 1]
LoadInputFile: Number of BCs: 1
LoadInputFile: Number of Body Forces: 0
LoadInputFile: Number of Initial Conditions: 1
LoadInputFile: Number of Materials: 1
LoadInputFile: Number of Equations: 1
LoadInputFile: Number of Solvers: 1
LoadInputFile: Number of Bodies: 1
Loading user function library: [WaveSolver]...[WaveSolver_Init0]
LoadMesh: Base mesh name: ./.
LoadMesh: Scaling coordinates: 1.000E-03 1.000E-03 1.000E-03
LoadMesh: Elapsed REAL time:     0.0840 (s)
MAIN: -------------------------------------
AddVtuOutputSolverHack: Adding ResultOutputSolver to write VTU output in file: case
Loading user function library: [WaveSolver]...[WaveSolver_Init]
Loading user function library: [WaveSolver]...[WaveSolver_bulk]
Loading user function library: [WaveSolver]...[WaveSolver]
OptimizeBandwidth: ---------------------------------------------------------
OptimizeBandwidth: Computing matrix structure for: wave equation...done.
OptimizeBandwidth: Half bandwidth without optimization: 15311
OptimizeBandwidth: 
OptimizeBandwidth: Bandwidth Optimization ...done.
OptimizeBandwidth: Half bandwidth after optimization: 1064
OptimizeBandwidth: ---------------------------------------------------------
Loading user function library: [ResultOutputSolve]...[ResultOutputSolver_Init]
Loading user function library: [ResultOutputSolve]...[ResultOutputSolver_bulk]
Loading user function library: [ResultOutputSolve]...[ResultOutputSolver]
WARNING:: InitCond: We can only set timederivative for transients
ElmerSolver: Number of timesteps to be saved: 10
MAIN: 
MAIN: -------------------------------------
MAIN:  Steady state iteration:            1
MAIN: -------------------------------------
MAIN: 
SingleSolver: Attempting to call solver
SingleSolver: Solver Equation string is: wave equation
DefUtils::DefaultDirichletBCs: Setting Dirichlet boundary conditions
DefUtils::DefaultDirichletBCs: Dirichlet boundary conditions set
ERROR:: EigenSolve:  Error with DNAUPD, info =           -9
STOP 1

My feeling is that something is not OK with the boundary conditions. I tried zero and non-zero values for the boundary conditions without any success. I also played with all the Linear System options still without success.

I am using Elmer on Ubuntu 18.04, installed through the PPA.

Any idea?
raback
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Re: WaveSolver and Eigen Analysis

Post by raback »

Hi,

Try with the same keywords as the example. Now you switched at least material parameters to something different. The default is zero if the parameters are not found.

-Peter
CrocoDuck
Posts: 79
Joined: 12 May 2016, 13:15
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Re: WaveSolver and Eigen Analysis

Post by CrocoDuck »

Hi Peter,

Thank you very much for your help. I tried to change the material parameters to this (as in the example):

Code: Select all

Material 1
  Name = "Ideal"
  Wave Speed = Real 1.0
End 
But I will get this error:

Code: Select all

ERROR:: ListInitElementKeywords: Keyword required but not present: Sound speed
Wave Speed is not a correct keyword according to the manual. The available material parameters appear to be:
  • Sound Speed
  • Sound Damping
  • Sound Reaction Damping
CrocoDuck
Posts: 79
Joined: 12 May 2016, 13:15
Antispam: Yes

Re: WaveSolver and Eigen Analysis

Post by CrocoDuck »

Also, this line:

Code: Select all

Procedure = "WaveEq" "WaveSolver"
Needs to be this instead:

Code: Select all

Procedure = "WaveSolver" "WaveSolver"
I tried the same sif as in the example, a part the few changes mentioned above:

Code: Select all

Check Keywords "Warn"

Header
  Mesh DB "." "."
  Include Path ""
  Results Directory ""
End

Simulation
  Coordinate System = "Cartesian"
  Simulation Type = Steady State
  Steady State Max Iterations = 1
  Coordinate Scaling = 0.001
  Max Output Level = 5
End

Body 1
  Equation = 1
  Material = 1
  Initial Condition = 1
End

Initial Condition 1
  Potential Velocity = Real 1
End

Material 1
  Name = "Ideal"
  Sound Speed = Real 1.0
End 

Equation 1
  Active Solvers(1) = 1
End

Solver 1
  Equation = "Poisson"

  Variable = "Potential"
  Variable DOFs = 1
  Procedure = "WaveSolver" "WaveSolver"

  Steady State Convergence Tolerance = 1e-09

!  Linear System Solver = "Direct"
  Linear System Direct Method = Umfpack

  Linear System Scaling = Logical True
!  Linear System Symmetric = Logical True
  Linear System Solver = string "Iterative"
  Linear System Convergence Tolerance = real 1e-8
  Linear System Iterative Method = BiCGStabl
  BiCGStabl Polynomial Degree = 4
  Linear System Residual Output = integer 1
  Linear System Max Iterations = integer 2000
  Linear System Preconditioning = ILU2
  Linear System Residual Output = 50

  Eigen System Select = smallest magnitude
!  Eigen System Shift = Real 1.0e3

! For visualization purposes make amplitude one for all
  Eigen System Normalize To Unity = Logical True

  Eigen Analysis = True
  Eigen System Values = 10
  Eigen System Convergence Tolerance = Real 1.0e-6
  Eigen System Max Iterations = 1
End

Solver 2
!  Exec Solver = never
  Equation = "result output"
  Procedure = "ResultOutputSolve" "ResultOutputSolver"
  Output File Name = case
  Vtu Format = Logical True
  Single Precision = Logical True 

  Eigen Analysis = True
End


Solver 3
  Equation = "SaveScalars"
!  Filename = f.dat

  Procedure = "SaveData" "SaveScalars"
  Save EigenValues = True

! Compare the norm of the 10th eigenvalue
  Show Norm Index = 10 
End


Boundary Condition 1
  Target Boundaries(6) = 2 3 4 5 6 7
  Potential = Real 0
!  Potential Velocity = Real 0
End

Solver 3 :: Reference Norm = 1.730641551602E+002

Same results:

Code: Select all

ERROR:: IterSolve: Numerical Error: System diverged over maximum tolerance.
Note: The following floating-point exceptions are signalling: IEEE_DIVIDE_BY_ZERO
STOP 1
I see the example was last updated in 2017. Perhaps it is not up to date?
raback
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Re: WaveSolver and Eigen Analysis

Post by raback »

Hi

It turned out that the updated WaveSolver under modules didn't assemble MASS for harmonic/eigen systems. So it could not have worked. I fixed it and removed the older WaveEq.f90 from the test case.

https://github.com/ElmerCSC/elmerfem/co ... 2f0ed93dd1

-Peter
CrocoDuck
Posts: 79
Joined: 12 May 2016, 13:15
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Re: WaveSolver and Eigen Analysis

Post by CrocoDuck »

I see, thanks for looking into this! I will maybe look into building the devel branch to test it out.
raback
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Re: WaveSolver and Eigen Analysis

Post by raback »

Hi,

You can just compile the updated solver:

Code: Select all

elmerf90 -o WaveSolver.so WaveSolver.F90 
(or .dll in Windows).

-Peter
CrocoDuck
Posts: 79
Joined: 12 May 2016, 13:15
Antispam: Yes

Re: WaveSolver and Eigen Analysis

Post by CrocoDuck »

raback wrote: 20 Aug 2020, 10:06 Hi,

You can just compile the updated solver:

Code: Select all

elmerf90 -o WaveSolver.so WaveSolver.F90 
(or .dll in Windows).

-Peter
Ha! Nice one. That works! I finally got a solution.

Code: Select all

ELMER SOLVER (v 8.4) STARTED AT: 2020/08/21 11:59:36
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: 8.4 (Rev: unknown, Compiled: 2020-08-17)
MAIN:  Running one task without MPI parallelization.
MAIN:  Running with just one thread per task.
MAIN:  HYPRE library linked in.
MAIN:  MUMPS library linked in.
MAIN: =============================================================
LoadInputFile: Reading only "Run Control" section
MAIN: 
MAIN: 
MAIN: -------------------------------------
MAIN: Reading Model: case.sif
LoadInputFile: Scanning input file: case.sif
LoadInputFile: Scanning only size info
LoadInputFile: First time visiting
LoadInputFile: Reading base load of sif file
LoadInputFile: Loading input file: case.sif
LoadInputFile: Reading base load of sif file
Model Input:  Unlisted keyword: [pressure velocity] in section: [initial condition 1]
Model Input:  Unlisted keyword: [pressure velocity] in section: [boundary condition 1]
LoadInputFile: Number of BCs: 1
LoadInputFile: Number of Body Forces: 0
LoadInputFile: Number of Initial Conditions: 1
LoadInputFile: Number of Materials: 1
LoadInputFile: Number of Equations: 1
LoadInputFile: Number of Solvers: 1
LoadInputFile: Number of Bodies: 1
Loading user function library: [WaveSolver]...[WaveSolver_Init0]
LoadMesh: Base mesh name: ./.
LoadMesh: Scaling coordinates: 1.000E-03 1.000E-03 1.000E-03
LoadMesh: Elapsed REAL time:     0.0841 (s)
MAIN: -------------------------------------
AddVtuOutputSolverHack: Adding ResultOutputSolver to write VTU output in file: case
Loading user function library: [WaveSolver]...[WaveSolver_Init]
Loading user function library: [WaveSolver]...[WaveSolver_bulk]
Loading user function library: [WaveSolver]...[WaveSolver]
OptimizeBandwidth: ---------------------------------------------------------
OptimizeBandwidth: Computing matrix structure for: wave equation...done.
OptimizeBandwidth: Half bandwidth without optimization: 15311
OptimizeBandwidth: 
OptimizeBandwidth: Bandwidth Optimization ...done.
OptimizeBandwidth: Half bandwidth after optimization: 1064
OptimizeBandwidth: ---------------------------------------------------------
Loading user function library: [ResultOutputSolve]...[ResultOutputSolver_Init]
Loading user function library: [ResultOutputSolve]...[ResultOutputSolver_bulk]
Loading user function library: [ResultOutputSolve]...[ResultOutputSolver]
WARNING:: InitCond: We can only set timederivative for transients
ElmerSolver: Number of timesteps to be saved: 10
MAIN: 
MAIN: -------------------------------------
MAIN:  Steady state iteration:            1
MAIN: -------------------------------------
MAIN: 
SingleSolver: Attempting to call solver
SingleSolver: Solver Equation string is: wave equation
WaveSolver: Solving the divergence pressure wave
WaveSolver: We have a harmonic or eigenmode system
DefUtils::DefaultDirichletBCs: Setting Dirichlet boundary conditions
DefUtils::DefaultDirichletBCs: Dirichlet boundary conditions set
CRS_IncompleteLU: ILU(2) (Real), Starting Factorization:
CRS_IncompleLU: Recursive round: 1
CRS_IncompleteLU: ILU(2) (Real), NOF nonzeros:   1102560
CRS_IncompleteLU: ILU(2) (Real), filling (%) :       456
CRS_IncompleteLU: ILU(2) (Real), Factorization ready at (s):     0.17
      12 0.1228E-14 0.9235E-09
      22 0.7611E-12 0.3690E-08
       5 0.5304E-12 0.2564E-08
       4 0.1043E-11 0.5115E-08
       4 0.1915E-12 0.9567E-09
       4 0.1027E-11 0.5092E-08
       4 0.6112E-13 0.2997E-09
       4 0.1125E-12 0.5514E-09
       4 0.3809E-13 0.1910E-09
       4 0.4597E-12 0.2274E-08
       4 0.1939E-11 0.9609E-08
       4 0.1317E-11 0.6608E-08
       4 0.1958E-11 0.9892E-08
       4 0.4634E-13 0.2300E-09
       4 0.7754E-12 0.3925E-08
       4 0.5258E-13 0.2682E-09
       4 0.4891E-13 0.2444E-09
       4 0.3098E-12 0.1575E-08
       4 0.5467E-12 0.2729E-08
       4 0.1925E-11 0.9782E-08
       4 0.1083E-11 0.5455E-08
       4 0.1909E-11 0.9570E-08
       4 0.1098E-11 0.5615E-08
       4 0.1266E-11 0.6381E-08
       4 0.1625E-11 0.8228E-08
       4 0.1846E-11 0.9409E-08
       4 0.3496E-13 0.1789E-09
       4 0.1573E-11 0.8068E-08
       4 0.5069E-12 0.2593E-08
       4 0.1596E-11 0.8240E-08
       4 0.1605E-11 0.8212E-08
       4 0.9570E-12 0.4932E-08
EigenSolve: 
EigenSolve: Eigen system solution complete:
EigenSolve: 
EigenSolve: Convergence criterion is:    1.000E-06
EigenSolve: Number of converged Ritz values is: 10
EigenSolve: Number of update iterations taken: 1
EigenSolve: 
EigenSolve: Computed 10 Eigen Values
EigenSolve: --------------------------------
EigenSolve: 1:   -4.206542E-10   0.000000E+00
EigenSolve: 2:    4.648218E+04   0.000000E+00
EigenSolve: 3:    7.265766E+04   0.000000E+00
EigenSolve: 4:    1.192635E+05   0.000000E+00
EigenSolve: 5:    1.293377E+05   0.000000E+00
EigenSolve: 6:    1.760333E+05   0.000000E+00
EigenSolve: 7:    1.863612E+05   0.000000E+00
EigenSolve: 8:    2.023335E+05   0.000000E+00
EigenSolve: 9:    2.491492E+05   0.000000E+00
EigenSolve: 10:    2.595073E+05   0.000000E+00
EigenSolve: --------------------------------
Loading user function library: [WaveSolver]...[WaveSolver_post]
ComputeChange: SS (ITER=1) (NRM,RELC): (  0.0000000      0.0000000     ) :: wave equation
SingleSolver: Attempting to call solver
SingleSolver: Solver Equation string is: internalvtuoutputsolver
ResultOutputSolver: -------------------------------------
ResultOutputSolver: 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: -------------------------------------
Loading user function library: [ResultOutputSolve]...[ResultOutputSolver_post]
ElmerSolver: *** Elmer Solver: ALL DONE ***
ElmerSolver: The end
SOLVER TOTAL TIME(CPU,REAL):        11.13        7.39
ELMER SOLVER FINISHED AT: 2020/08/21 11:59:44
I will play with it some more and maybe be back with some questions.

Thanks!
CrocoDuck
Posts: 79
Joined: 12 May 2016, 13:15
Antispam: Yes

Re: WaveSolver and Eigen Analysis

Post by CrocoDuck »

So, the eigenvalues appear to be angular frequency squared. If I calculate the associated frequency in Hz I get these values (omitting the first small negative value clearly associated with the 0 order mode, a constant pressure field with 0 eigenvalue):

Code: Select all

 34.313370192521894
 42.900349974920196
 54.96344008822581 
 57.237769116156144
 66.77556124149527 
 68.70650873280937 
 71.59027467208264 
 79.44194711791363 
 81.0764867267743
They really agree well with what I expect:

Code: Select all

 34.3
 42.87500000000001
 54.90679033598667
 57.16666666666666
 66.66721666439793
 68.6
 71.45833333333333
 79.26401076641136
 80.89638820738537
I guess I will be able to raise the agreement even further with finer and/or higher order mesh.

I had a cursory look at the the associated eigenmodes and they look reasonable, but I still have to do a proper accuracy analysis like this one. I would say that everything is looking good so far.

I was wondering though why the manual does not mention the Eigen Analysis keywords. Is it maybe because the feature is still experimental?

Also, the manual does not mention the possibility of defining boundary conditions of this kind (which I used to get the solution above):

Code: Select all

Boundary Condition 1
  Target Boundaries(6) = 2 3 4 5 6 7
  Pressure Velocity = Real 0
End
Where Pressure is the name I gave to the solver variable:

Code: Select all

Solver 1

  ! Equation
  Equation = "Wave Equation"
  Procedure = "WaveSolver" "WaveSolver"
  Variable = "Pressure"
  
  ...
I assume that the Pressure Velocity boundary condition is used to specify the particle velocity associated with the pressure field, and the results seems consistent with this interpretation. Is this correct?
raback
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Re: WaveSolver and Eigen Analysis

Post by raback »

Hi

Great that you found success.

Now the Models Manual does not mention this possibility because it is a library feature mainly. As long as we take care that the time derivative multiplier matrix is registered even though the case is not transient, any time-dependent equation may become eigenvalue or harmonic system in this way. I would guess the "Eigen Analysis" will be found on the SolverManual side.

The same applies to "Pressure Velocity". That being said, I don't really recall what it would do in harmonic case. Does it play a role whether you have it or not? This is also taken care by the library.

From documentation point of view the challenge is that there are N modules and M library features and we don't really feel like documenting each of NxM combinations but try to get by with N+M.

-Peter
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