Modifying stressedFoam for geometric non-linearity
 

Hello fellow foamers,

My name is Craig and this is my first time posting to the forum, so I hope that I am following the Forum rules correctly.

To provide background and context to my post, I am currently working on a research project which I am using foam-extend v4.0 to model cartilage and conduct a stress analysis. I am developing both my model and solver in an incremental fashion, starting with infinitesimal strain moving to finite strain.

I am trying to modify the stressedFoam solver to account for finite strains. I am aware that foam-extend already offers solvers which can handle this task, however I am required to develop my own solver and therefore have started with a solver I feel comfortable using and can take the steps of modifying.

My model is a simple column shape; 250 mm in height and with a 400 mm^2 cross sectional area.

I have fixed one end (the bottom) and applied a load to other (the top). the walls are free to deform in a uniaxial direction.

I have used the traction boundary condition on the walls and top of the column and everything works as expected for the linear-elastic case.

When I try to now implement non linearity to the model I am receiving an error which I do not understand which I have included below. I have also attached both the .C of the solver and traction displacement boundary for those who wish to see how I have implemented the nonlinearity.

/*---------------------------------------------------------------------------*\
| ========= | |
| \\ / F ield | foam-extend: Open Source CFD |
| \\ / O peration | Version: 4.0 |
| \\ / A nd | Web: http://www.foam-extend.org |
| \\/ M anipulation | For copyright notice see file Copyright |
\*---------------------------------------------------------------------------*/
Build : 4.0-268bb07d15d8
Exec : NLStressedFoam
Date : May 25 2020
Time : 15:41:49
Host : mn14cat-XPS-13-7390
PID : 17826
CtrlDict : "/home/mn14cat/foam/mn14cat-4.0/run/exercise/NonLinStressedFoam/NonlinColumn/system/controlDict"
Case : /home/mn14cat/foam/mn14cat-4.0/run/exercise/NonLinStressedFoam/NonlinColumn
nProcs : 1
SigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).

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

Create mesh for time = 0

Reading mechanical properties

Normalising E : E/rho

Calculating Lame's coefficients

Plane Strain

mu = 500000 Pa/rho
lambda = 4.66668e+06 Pa/rho
threeK = 1.5e+07 Pa/rho
Reading thermal properties

Reading field U


Calculating displacement field

Iteration: 1



--> FOAM FATAL ERROR:

request for volTensorField grad(U).T() & grad(U) from objectRegistry region0 failed
available objects of type volTensorField are

2
(
grad(U)
(grad(U).T()&grad(U))
)


From function objectRegistry::lookupObject<Type>(const word&) const
in file /home/mn14cat/foam/foam-extend-4.0/src/foam/lnInclude/objectRegistryTemplates.C at line 139.

FOAM aborting

Aborted (core dumped)

I would be extremely grateful for any help understanding where I have gone wrong in modifying the solver, and hope that I have provided enough detail for anyone who is willing to help.

Thanks in advance,
Craig