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.
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. The GSSV solver is advised for direct thermal computation always if the hybrid mesh is used.
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.
Select Computation > Numerical parameter > Forward tab.
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.
Click on Apply and Close.
or
Click on OK to apply the changes and to close the dialog.
In the Other section some special parameters can be set by the user:
Track interface
If this option is activated, in case of the unstructured mesh the enthalpy method will be used for the phase transition. The mesh will be adjusted to the phase boundary in a two phase material when calculating temperature. The vertices next to the phase boundary are moved in order to match with the melting isothermal with a given accuracy. This approach is analogous to the interface tracking in case of multiphase convection calculations. The parameters for the interface tracking can be found in the multiphase tab of convection parameters menu. This option is only needed if the Write interface option is used or point defects calculation shall be performed. There is no influence on the behavior of the interface tracking for convection or stress calculations by this checkbox.
See Multiphase for information of the parameters to set.
If the phase transition is modeled by means of the hybrid mesh, then the button Track interface activates the phase tracking procedure. The region boundary and the meshes inside are deformed so that vertices of the region boundary between the crystal and the melt regions will coincide with the isotherm line crossing the triple point in the converged solution. The phase tracking method works in both Czochralski (crystal over the melt) and Bridgmann (crystal under the melt) configurations.
Related tasks: Setting multiphase parameters
Underrelaxation: This parameter works only in conjunction with the phase tracking procedure on the hybrid mesh. The computed shift of the vertices at the region boundary is reduced typically by factor equal or small than 0.01. The deceleration of the phase boundary movement is necessary in order to stabilize the computation. To quick interface movement may lead to the degraded numerical mesh.
Start Residual: This parameter works only in conjunction with the phase tracking procedure on the hybrid mesh. The phase tracking is activated only if the normed residual of the enthalpy equation becomes less than the prescribed value.
Point defects ramp:
Turns on the coupling between interstitial and vacancy concentration smoothly in order to improve the numerical stability. This option can be used if convergence problems during point defect calculations occur.