
[Sponsors] 
January 22, 2013, 08:08 
Second equation uses wrong state variables boundary condition

#1 
New Member
Fabian Wein
Join Date: Jan 2013
Posts: 13
Rep Power: 4 
Hello,
this is my first post, so I introduce myself quickly. I am Fabian, a Postdoc in Germany. I do topology optimization and now work on an OF based project. Someone else wrote most of the solver and other stuff, my task is to change the code in such a way, that a second problem is solved afterwards. I do it in the same code. I have good C++ knowledge but am totally new to OpenFOAM. The forward problem is solved for h with dynamic boundary conditions defined based on the time in 0/h as inlet code. The forward problem is nonlinear with implicit time stepping. I need to solve a so called adjoint problem which is linear, needs to be solved with explicit time stepping and goes backwards in time. I do the backwards in time by going forward in time (resetting my time object) but have for the solution variable the boundary conditions with other times in the dynamic 0/lambda code. I have fvScalarMatrix lambda_eqn( phi * C * fvm::ddt(lambda) == fvc::laplacian(k, lambda) ); lambda_eqn.solve(); and hope, this solves my problem with an explicit time stepping. in fvSolution I have solvers { h { solver PCG; preconditioner DIC; // tolerance 1e06; tolerance 1e14; relTol 0.1; } lambda { solver PCG; preconditioner DIC; // tolerance 1e06; tolerance 1e14; relTol 0.1; } hFinal { $h; relTol 0.0; } } In fvSchemes I have laplacianSchemes { default none; laplacian(k,lambda) Gauss linear uncorrected; laplacian(k,h) Gauss linear uncorrected; } For the forward problem the inlet code of 0/h is executed (I do a command line output) and then it is written "DICPCG: Solving for h, Initial residual ..." For the adjoint problem again the code from 0/h is executed and then it is written " diagonal: Solving for lambda, Initial residual = 0, Final residual = 0, No Iterations 0" My problem is, that the inlet code from h is executed but not from lambda ?! Any help or hint is very much appreciated! Thank you very much, Fabian 

January 22, 2013, 19:18 

#2 
Senior Member
Daniel P. Combest
Join Date: Mar 2009
Location: St. Louis, USA
Posts: 546
Rep Power: 18 
Fabian,
there are a number of things that could be the issue. You could... * Have a zero values for your constants that zero out your field * Illposed boundary conditions (e.g. all are set to zeroGradient) that essentially do nothing * Mean to use fvm::laplacian(k,lambda) instead of fvc::laplacian( * Have an issue somewhere else in your algorithm that is causing your problem. is there more code that you have changed that we can see and track down the problem? 

January 23, 2013, 05:00 

#3  
New Member
Fabian Wein
Join Date: Jan 2013
Posts: 13
Rep Power: 4 
Chegdan,
thank you very much for reply. Please note, that I am really new to OF and have much more guessing about how it works than knowledge. From you points I can see that they are issues, but I do not see, how they could cause my problem, that the boundary conditions from the state variable of the first problem are used for the second problem with another state variable. Quote:
Here is some of the code Foam::Time time(Foam::Time::controlDictName, args); Foam::fvMesh mesh(Foam::IOobject(Foam::fvMesh::defaultRegion, time.timeName(), time, Foam::IOobject::MUST_READ)); // h is state variable for first problem volScalarField h(IOobject("h",time.timeName(),mesh,IOobject::MUST _READ,IOobject::AUTO_WRITE),mesh); // state variable for second problem (adjoint problem) adjoint solution  counterpart of h. Reversed time scheme in 0/lambda volScalarField lambda(IOobject("lambda",time.timeName(),mesh,IOob ject::MUST_READ,IOobject::AUTO_WRITE),mesh); volVectorField rho(IOobject("rho",time.timeName(),mesh,IOobject:: MUST_READ_IF_MODIFIED,IOobject::AUTO_WRITE),mesh); volScalarField phi(IOobject("phi",time.timeName(),mesh,IOobject:: READ_IF_PRESENT,IOobject::NO_WRITE),mesh); volScalarField s(IOobject("s",time.timeName(),mesh,IOobject::MUST _READ,IOobject::AUTO_WRITE),mesh); volScalarField k(IOobject("k",time.timeName(),mesh,IOobject::MUST _READ,IOobject::AUTO_WRITE),mesh); volScalarField C(IOobject("C",time.timeName(),mesh,IOobject::MUST _READ,IOobject::AUTO_WRITE),mesh); while(time.run()) { .... fvScalarMatrix hEqn ( phi*C*(fvm::ddt(h)  fvc::ddt(h)) == fvm::laplacian(k,h)  phi*fvc::ddt(s) ); hEqn.solve(); } // now adjoint problem time.setTime(0.0, 0); // reset to start again from 0 // history saves h for every timestep in the forward problem for (int i = history.size()  1; i >= 0; i) { const TimeStep& step = history[i]; time.setDeltaT(step.dt); time++; // set C and K fvScalarMatrix lambda_eqn( 1.0 * phi * C * fvm::ddt(lambda) == fvc::laplacian(k, lamba) ); lambda_eqn.solve(); } Now the problem is, that during solving the first and second problem, the dynamic boundary conditions from the inlet code 0/h are used but not from 0/lambda. But 0/lambda is compiled (easy to check with a syntax error)! Why is OF touching h in the second problem? Thanks for any help! 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Radiation interface  hinca  CFX  15  January 26, 2014 18:11 
Noslip condition for nonresolved boundary layer in open channel banks  AlbertoVe  Main CFD Forum  1  January 17, 2013 04:11 
RPM in Wind Turbine  Pankaj  CFX  9  November 23, 2009 05:05 
Boundary condition in pressure equation  Paolo Lampitella  FLUENT  0  February 21, 2008 07:30 
Boundary Conditions  Jan Ramboer  Main CFD Forum  11  August 16, 1999 08:59 