[Svensen]

I'm trying to simulate FSI on simple elastic pipe. I've create both meshes for fluid and solid. checkMesh found no erros. But when I started icoFsiElasticNonLinULSolidFoam I've got a lot of warning about "complex eigenvalues detected for tensor". And after this the program crashes.

The output:

/*---------------------------------------------------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | foam-extend: Open Source CFD                    |
|  \\    /   O peration     | Version:     3.1                                |
|   \\  /    A nd           | Web:         http://www.extend-project.de       |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
Build    : 3.1-7d8e040bf53d
Exec     : /opt/foam/foam-extend-3.1/applications/bin/linux64GccDPOpt/icoFsiElasticNonLinULSolidFoam
Date     : Mar 21 2015
Time     : 15:00:44
Host     : sergey-Notebook-PC
PID      : 12838
CtrlDict : /opt/foam/foam-extend-3.1/etc/controlDict
Case     : /home/sergey/tmp/elastic_pipe/fluid
nProcs   : 1
SigFpe   : Enabling floating point exception trapping (FOAM_SIGFPE).

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
Create time

Create dynamic mesh for time = 0

Selecting dynamicFvMesh dynamicMotionSolverFvMesh
Selecting motion solver: laplace
Selecting motion diffusivity: quadratic

Reading transportProperties

Reading field p

Reading field U

Reading/calculating face flux field phi

Reading incremental displacement field DU

Patch vessel    Traction boundary field: DU
        nonLinear set to updated Lagrangian
Reading incremental displacement field DV
Reading accumulated velocity field V

Reading accumulated stress field sigma

Reading incremental stress field DSigma

Selecting rheology model linearElastic
Creating constitutive model

Reading coupling properties
Create fluid-to-solid and solid-to-fluid interpolators
Check fluid-to-solid and solid-to-fluid interpolators
Fluid-to-solid face interpolation error: 0.20018
Solid-to-fluid face interpolation error: 1.11023e-16

Starting time loop

Time = 0.001

Selecting coupling scheme Aitken

Time = 0.001, iteration: 1
Current fsi under-relaxation factor: 0.01
Maximal accumulated displacement of interface points: 0
Courant Number mean: 0 max: 0.765854 velocity magnitude: 0.8
DILUPBiCG:  Solving for Ux, Initial residual = 0.661236, Final residual = 9.87969e-12, No Iterations 2
DILUPBiCG:  Solving for Uy, Initial residual = 0.657091, Final residual = 9.85265e-12, No Iterations 2
DILUPBiCG:  Solving for Uz, Initial residual = 1, Final residual = 1.05188e-11, No Iterations 2
GAMG:  Solving for p, Initial residual = 1, Final residual = 4.06804e-07, No Iterations 16
GAMG:  Solving for p, Initial residual = 0.00154278, Final residual = 4.60129e-07, No Iterations 4
time step continuity errors : sum local = 3.54272e-07, global = 1.16647e-07, cumulative = 1.16647e-07
GAMG:  Solving for p, Initial residual = 0.000170456, Final residual = 7.44231e-07, No Iterations 5
GAMG:  Solving for p, Initial residual = 1.77539e-05, Final residual = 9.98566e-07, No Iterations 1
time step continuity errors : sum local = 7.65403e-07, global = 1.52512e-07, cumulative = 2.69159e-07
Setting traction on solid patch
Total traction force = (-4.63054e-08 -2.6171e-07 0.159168)
--> FOAM Warning : 
    From function eigenValues(const tensor&)
    in file primitives/Tensor/tensor/tensor.C at line 170
    complex eigenvalues detected for tensor: (-1.15174 0.689561 0.0389201 -0.64029 0.373721 0.0277594 -64.1658 28.6624 -0.601871)
--> FOAM Warning : 
    From function eigenValues(const tensor&)
    in file primitives/Tensor/tensor/tensor.C at line 170
    complex eigenvalues detected for tensor: (-1.15174 0.689561 0.0389201 -0.64029 0.373721 0.0277594 -64.1658 28.6624 -0.601871)
--> FOAM Warning : 
    From function eigenValues(const tensor&)
    in file primitives/Tensor/tensor/tensor.C at line 170
    complex eigenvalues detected for tensor: (-2.7914 1.59273 0.0193284 -2.34685 2.0507 -0.000694244 -81.644 36.6711 1.82105)

and so on. Any ideas ?

[D_LEE]

Could you post your solid/constant/rheologyProperties and solid/system files? Maybe its

 planeStress     no;

[Svensen]

Yes, planeStress was no, but when I changes it to "yes" it doesn't help me...
I attach the case files for fluid and solid, maybe it will be useful..

The file size is bigger than 100k, so I upload it to cloud storage: https://yadi.sk/d/wsPFmLZifYBbr

[stephie]

Hey,

did one of you find a solution?
I run the case with one processor and now I have got the same mistake.

I would be verx grateful for anyones help .
best regards,
Stephie

[Svensen]

Yes, I solved this problem. In my case the problem was in incorrect mesh definition, which leads to wrong solid-mesh interpolation like:
"Reading coupling properties Create fluid-to-solid and solid-to-fluid interpolators Check fluid-to-solid and solid-to-fluid interpolators Fluid-to-solid face interpolation error: 0.20018 Solid-to-fluid face interpolation error: 1.11023e-16Do you also have THIS problem ?

[stephie]

Hey,
yes I had a look into my log file and there I found the same mistake:

Reading coupling properties
Create fluid-to-solid and solid-to-fluid interpolators
Check fluid-to-solid and solid-to-fluid interpolators
Fluid-to-solid face interpolation error: 1.24127e-16
Solid-to-fluid face interpolation error: 1.24127e-16

How did you solved this problem?

[Svensen]

It's not an error. In my case the patches were not correctly defined so the interpolation error Fluid-to-solid face interpolation was very big (0.20018). I simply redefine the patches, so the solid and fluid patches become closer to each other. This fix my problem. But you don't have to solve it, because in your case all is OK with interpolation.

[stephie]

Okay, good news.
Unfortunately, every time I restart the case the interpolation error becommes bigger and bigger.

Reading coupling properties
Reading accumulated fluid interface displacement
Create fluid-to-solid and solid-to-fluid interpolators
Check fluid-to-solid and solid-to-fluid interpolators
Fluid-to-solid face interpolation error: 0.167309
Solid-to-fluid face interpolation error: 0.312902

This was an extract of the log file after I restarted the case.

[Svensen]

Very interesting... I can't restart the computation from latestTime. I always have to start my computation from zero time...
How do you find the way to continue simulation from last step ?

[stephie]

If i want to restart the case i change into Fluid and type in icoFsiElasticNonLinULFoam >> log.icoFsiElasticNonLinULFoam
It continues to write the residuals in the log file But be careful it overrides the last log File. So you have to modify the name of the log File. If you run the case in parallel you have to use mpirun. And you have to use startfrom latesttime. I hope i could help you.

[Harak]

Originally Posted by Svensen

It's not an error. In my case the patches were not correctly defined so the interpolation error Fluid-to-solid face interpolation was very big (0.20018). I simply redefine the patches, so the solid and fluid patches become closer to each other. This fix my problem. But you don't have to solve it, because in your case all is OK with interpolation.

In my case I got:
Fluid-to-solid face interpolation error: -1e+300
Solid-to-fluid face interpolation error: 0.010357179

I created my mesh with ICEM and the patches actually should be fine because with the exact same geometry my simulation works pretty well with very small interpolation errors.

What can I do to solve this error?

[sfmoabdu]

Dear all

has anyone faced the problem of interface separation? , in which the solid interface moves away from fluid interface (as in the attached snapshot) ... it happens very slowly without any crash of solution and at some time step the gap becomes very big and the solver gives "Floating point exception (core dumped) " or "complex eingenvalues in the matrix ... " !!

has anyone of you the solution of that?

it happens in both fsiFoam and icoFsiElasticNonLinULSolidfoam.

by the way i have used the HronTurek tutorial but i just changed the material and thickness of the plate. Furthermore, the fluid domain is perfectly solved as only CFD.

[Horst]

Originally Posted by sfmoabdu

Dear all

has anyone faced the problem of interface separation? , in which the solid interface moves away from fluid interface (as in the attached snapshot) ... it happens very slowly without any crash of solution and at some time step the gap becomes very big and the solver gives "Floating point exception (core dumped) " or "complex eingenvalues in the matrix ... " !!

has anyone of you the solution of that?

it happens in both fsiFoam and icoFsiElasticNonLinULSolidfoam.

by the way i have used the HronTurek tutorial but i just changed the material and thickness of the plate. Furthermore, the fluid domain is perfectly solved as only CFD.

Hello sfmoabdu,

i experience the same problem on my cases. I am running a 2D-kind of beamInCrossflow case with a solid density of 4000. First i was using fluid density around 1 and it worked perfectly on a a broad selection of meshes. Then i increased to 4000 an the interfaces seperate. I increased the outer iterations of the interaction and of the deformation solver. Both didn't show any remarkable positive effect.
Did you find any solution for the problem?

[Aliiiii]

Originally Posted by Horst

Hello sfmoabdu,

i experience the same problem on my cases. I am running a 2D-kind of beamInCrossflow case with a solid density of 4000. First i was using fluid density around 1 and it worked perfectly on a a broad selection of meshes. Then i increased to 4000 an the interfaces seperate. I increased the outer iterations of the interaction and of the deformation solver. Both didn't show any remarkable positive effect.
Did you find any solution for the problem?

Hi Georg,


I know it's been a while since you posted this but did you figure out how to resolve the problem of separation of fluid/solid interface? I have the exact same problem with beamincrossflow!

[Horst]

Dear Aliiiii,
first of all, i would recommend a switch to a newer version. The FSI package for extent4.1 (you can get it from the extent bazar) is so much better then the older versions. In my eyes, there is actually no reason for mesh-seperation any more, because of the use of the ALE-method.



There is even a newer package (solids4foam) in the pipelines that is available on demand, but i think that it will be released in the near future.


Good luck
Horst

[popa]

Originally Posted by sfmoabdu

Dear all

has anyone faced the problem of interface separation? , in which the solid interface moves away from fluid interface (as in the attached snapshot) ... it happens very slowly without any crash of solution and at some time step the gap becomes very big and the solver gives "Floating point exception (core dumped) " or "complex eingenvalues in the matrix ... " !!

has anyone of you the solution of that?

it happens in both fsiFoam and icoFsiElasticNonLinULSolidfoam.

by the way i have used the HronTurek tutorial but i just changed the material and thickness of the plate. Furthermore, the fluid domain is perfectly solved as only CFD.

i also run the provided case,but i can't get the result which it can Swing up and down，instead,it stay still;i didn't change any parameter,could you tell me how die you operate? 3Q

[popa]

Originally Posted by popa

i also run the provided case,but i can't get the result which it can Swing up and down，instead,it stay still;i didn't change any parameter,could you tell me how die you operate? 3Q

I run the case on foam-extend 4.1