[JBUNSW]

Dear all,

I implemented SUNDIALS CVODE 2.7 in OpenFOAM 2.0.x. I pretty much followed the instructions given here. I am using BDF with Newton linear solver. I tested my implementation with OpenFOAM's native "test-ode.C" solver and it works fine.

However, when I use it to integrate the ODE system in a 58 species chemistry mechanism which is highly stiff, the cpu-time dramatically increases. It becomes even slower than OpenFOAM's native ODE-solver "RK" which is an explicit ODE solver.

The problem, I guess, is the jacobian. The chemistry mechanism I am using is in the form of a Fortran subroutine that outputs the derivatives "only". I don't have any information on the jacobian. That's why I can not provide the jacobian function as input to CVODE, and consequently CVODE calculates the jacobian by its internal "difference-quotient" jacobian estimator.

Any help is highly appreciated.

Jalal

[luiscardona]

@JBUNSW

After several tests I reached similar conclusions about CVODE. So in my case I had to use SIBS.

In order to speed up a bit my simulation, which also involved a chemical mechanism, I ended using a tabulation technique (ISAT) and got a faster simulation by a factor of 2 or more (28 species mechanism). Perhaps it wouldn't be possible to use in your case, because your mechanism comes from a FORTRAN routine...

[JBUNSW]

Thanks Luis for your feedback.

Anyone else has anything to share, please? Any tips are highly appreciated.

[adhiraj]

I have also noticed it. For mechanisms that are important for my work,
(~100-200 species), CVODE slows to a crawl, or cannot solve the system at all.
On the other hand for the large mechanisms, SIBS seems to run.

[randolph]

Originally Posted by adhiraj

I have also noticed it. For mechanisms that are important for my work,
(~100-200 species), CVODE slows to a crawl, or cannot solve the system at all.
On the other hand for the large mechanisms, SIBS seems to run.

Adhiraj,

I am planning to follow your path to use CVODE with OpenFOAM. Before I put in the effort (and after your observation of performance of CVODE), I would like to consult you, if possible.

I am trying to solve ODE with fraction orders such as dy/dx = -1*sqrt(y). I tried the ODE solver in OpenFOAM. The explicit solver RK family and Euler require an extreme small time step to integrate. And all the other ODE solvers complain about singular matrix. After some google, I realize the ODE that I try to solve is a type of fractional ODE and is difficult to solve (I may be wrong).

Here is the definition of the ODE in the ODE-test that I use to solve dy/dx = -1*sqrt(y). Did I made some mistakes? Do you think I can benefit from CVODE?

    void derivatives
    (
        const scalar x,
        const scalarField& y,
        scalarField& dydx
    ) const
    {
        dydx[0] = -1*Foam::pow(y[0],0.5);
    }

    void jacobian
    (
        const scalar x,
        const scalarField& y,
        scalarField& dfdx,
        scalarSquareMatrix& dfdy
    ) const
    {
        dfdx[0] = 0.0;
        dfdy(0, 0) = -1*0.5*Foam::pow(y[0],0.5-1.0);
    }

Thanks,
Rdf

[adhiraj]

It has been some time since I have used CVODE, and there have been newer versions of the code. If you need help with CVODE, I would ask you to read the documentation of the code, and ask questions on their mailing list.

[bany]

Originally Posted by JBUNSW

Dear all,

I implemented SUNDIALS CVODE 2.7 in OpenFOAM 2.0.x. I pretty much followed the instructions given here. I am using BDF with Newton linear solver. I tested my implementation with OpenFOAM's native "test-ode.C" solver and it works fine.

However, when I use it to integrate the ODE system in a 58 species chemistry mechanism which is highly stiff, the cpu-time dramatically increases. It becomes even slower than OpenFOAM's native ODE-solver "RK" which is an explicit ODE solver.

The problem, I guess, is the jacobian. The chemistry mechanism I am using is in the form of a Fortran subroutine that outputs the derivatives "only". I don't have any information on the jacobian. That's why I can not provide the jacobian function as input to CVODE, and consequently CVODE calculates the jacobian by its internal "difference-quotient" jacobian estimator.

Any help is highly appreciated.

Jalal

Dear JBUNSW, i like follow your work implementing CVODE into OpenFOAM. Sorry to recall this post. Are you solve the problem that slower calculation when used CVODE?

Thanks a lot

[dlahaye]

https://github.com/blttkgl/DLBFoam-1.0