Setting parameters for forward simulation

On the Forward tab you can select the solver for the forward simulation and specify the parameters for the solving process.

A detailed description of parameters is given in Forward section.

Linear system equations solvers

The numerical parameters determine the way the linear system equations are solved by CrysMAS.

CrysMAS uses several linear system equations solvers. The user can optionally select which of them to be used in simulation.

Iterative solvers:

  • BiCG: Biconjugate gradient iteration.

  • STABBiCG: Biconjugate gradient iteration stabilized.

  • CGS: Conjugate gradient squared iteration.

  • IR: Richardson iteration.

Direct solver:

  • GSSV

Two pre-conditioners can be used for an iterative solver:

  • DIAG

  • ILU (default)

A default solver is selected for any type of computation. For temperature calculation the direct GSSV solver is in some cases more stable than the conjugated gradients, also it is the only solver incorporated which can use multiple threads. The GSSV solver is advised for direct thermal computation always if the hybrid mesh is used. Credit for GSSV goes to Demmel et al. (see bibliography). If you are interested in the meaning of the details of the GSSV parameters, please consult the SuperLU documentation available on the web, usually the default parameters are sufficient.

In case of hybrid mesh the stacked iteration procedure is running, whereby the solver of the global thermal problem from the list above on both types of the meshes is running alternately with the other solver which is running only on the block-structured mesh. The solver for the block-structured mesh is the SIP solver (Strongly Implicit Procedure), see the paper of Stone in Bibliography .

The setting of numerical parameters for the SIP solver takes place not in the Forward dialog button but in the dialog buttons created automatically after the structured mesh was generated. In case if no convection is computed on the structured mesh the SIP solver is not used. The enthalpy transport equation is discretized on the structured mesh in the same manner as in case of the SIP solver. The matrix resulted from the discretization is passed to the selected solver from the above list for the solution of the global heat transfer problem.

The SIP solver is extremely quick but is applicable only for rigorously diagonally occupied matrix equations which are resulted from the Finite Volume discretization on the block structured mesh. Another drawback of the SIP solver is, it works in the sequential mode, therefore its parallelization is possible only by domain decomposition and partitioning of the computational weights attached to each block.

  1. Select Computation > Numerical parameter > Forward tab.

    The Forward dialog opens:

    Forward tab in Numerical parameters dialog 

    Figure 16. Forward tab in Numerical parameters dialog

  2. The default values were gained from experience and produce satisfactory results. Change the defaults only if inevitable.

    If necessary change the defaults for the forward solver, the preconditioner, the numbers of allowed inner and outer iterations, the desired residuum, the residuum improvement factor and the forward relaxation factor.

  3. Click on Apply and Close.

    or

    Click on OK to apply the changes and to close the dialog.

The front tracking section allows to enable fronttracking and to set corresponding parameters:

Related Dialogs

Forward