Solver parameter (dialog)

The Solver Parameter Dialog provides ability to adjust control parameters controlling directly the process of solving the equation system. Values offered by default have been preset in such manner, that for most usual cases none of them needs to be adjusted.

Provided the VAPOUR-Option and/or HARMONIC / TRANSIENT-Option are available the decision will be made here if solving Vapour Transfer and/or Transient problems shall be executed.

The most important setting is given by the Termination Condition which defines the targeted precision of the solution. This parameter is directly connected to the resulting relative close-up error describing the quality and precision of results.
Further parameters are used to optimize the efficiency (computational time) of the calculation process.

Within the Advanced -tab you can edit details of solver parameters or, for a very special case, adjust further advanced parameters.

Remark: The decision if the solver shall run in parallel on multiple processors has to be done within application settings.

Control parameters of solution iterations (Iteration control)
Termination condition (Delta)	If the largest change of temperature (normalized onto value interval 0.0 - 1.0) is continuously below the value entered here then the iterations are assumed as being precise. Reducing this value leads to more precise results at cost of longer computational time. Within the application settings: Delta Value range: [5.0*10-14 , 1.0]
Maximum number of iterations	If the current number of iterations reaches the value entered here the solution process will be aborted without creating the solution. Remark: At each new run counting of iterations starts at 0. Since AnTherm Version 8 this value is fixed to 1 billion and cannot be changed by the user.
Minimum number of iterations below Delta	Defines the number of iterations at which the termination condition (delta) must be continuously satisfied prior to the assumption of precise solution and its final generation. Within the application settings: MinItNoBelowDelta Value range: [1 , 10000]
Relaxation factor for initial iterations	Defines the value of the relaxation factor ω which is used during initial "StartItNo" of iterations. Within the application settings: StartOmega Value range: [1.0 , 2.0]
Number of initial iterations	Defines the number of initial iterations with constant relaxation factor "StartOmega" (executed prior to further iterations with varying relaxation factor). Within the application settings: StartItNo Value range: [0 , 1000000]
Relaxation factor for final iterations	Defines the value of the relaxation factor ω which is used during final "FinalItNo" of iterations. Within the application settings: FinalOmega Value range: [1.0 , 2.0]
Number of final iterations	Defines the number of final iterations with constant relaxation factor "FinalOmega" (executed after "MinItNoBelowDelta" iterations with varying relaxation factor continuously satisfied the termination criteria - i.e. result variation was continuously below termination delta). This smoothes the final temperature distribution in the solution. Within the application settings: FinalItNo Value range: [0 , 1000000]
Number of Iterations for tracing the Delta	Number of latest iteration steps to monitor the delta value changes. Within the application settings: DeltaTraceItNo Value range: [2 , 99], currently shall not be changed (read only) = 10.

Control parameter of the dynamic adjustment of the relaxation factor (ω) (Releaxtion factor control)
Factor determining the largest relaxation factor ωmax	Weighting factor used for calculation of largest relaxation factor ωmax which is larger than the optimal relaxation factor ωopt . ωmax =  ωopt - l * (ωopt - 1) * (ωopt - 2) Within the application settings: OmegaMaxFactor Value range: ≥ 0.0
Factor determining the smallest relaxation factor ωmin	Weighting factor used for calculation of smallest relaxation factor ωmin which is smaller than the optimal relaxation factor ωopt . ωmin =  ωopt + k * (ωopt - 1) * (ωopt - 2) Within the application settings: OmegaMinFaktor Value range: ≥ 0.0
Number of iterations between ωmin and ωopt	Defines the speed at which the relaxation factor is increased between iterations. Within the application settings: OmegaMinOptItNo Value range: [2 , 1000]
Delta Trace ItNo	Number of latest iteration steps to monitor the delta value changes. Within the application settings: DeltaTraceItNo Value range: [2 , 99]
Number of iterations prior to reset (ω Veto)	Even if the over-relaxation starts to be divergent (instead of converting to stable solution) the relaxation factor ω will be reset to its minimum value ωmin after at least that defined number of iterations between consecutive resets. Within the application settings: OmegaVetoItNo Value range: [2 , 1000]

Control parameters of vapour transfer calculation
Compute Vapour Transfer Solution	If checked the application will create the solution of vapour transfer problem also (if applicable). Usually used to suppress vapour calculation even if all data required for such is available but that specific solution is not required. Within the application settings: "Compute vapour transfer solution" Remark: This setting requires a valid license feature DAMPF2DIM or DAMPF3DIM.

Force Recalculation of Solution	The existing solution (if available for loading) will be marked as "not solved" and calculation will be started. The calculation will restart with already available results. This setting will not be saved and is reset on each run. Remark: Usually the calculation step is skipped if valid results are already available. This setting provides the means to force calculation to start at any case to, for example, repeat the final "smoothing" iterations.
Restore Default	Resets all solver parameters to the values define within application settings
Set As Default	Current solver settings are set as default and stored as application settings
Pick from Project...	Solver parameters are loaded from another project file.
Always show this dialog automatically when required	If checked the application will automatically reveal this dialog on each solution run (in preparation of each calculation).

Solver parameters are saved to the project file.

Remark: Proper estimation of the optimal relaxation factor ω_opt becomes very important for large and possibly converging slowly calculations. It is advised to adjust parameters used for controlling the estimation of optimal omega in such a way, that better estimation ω_opt of  is provided - reduce the termination condition of omega estimation (e.g. 10^-7) and enlarge the maximum number of iterations used in this process (e.g. 5000). The preset value of only 250 iterations provides vary coarse estimation. Especially calculations of large cases with many spaces shall be run with well estimated omega because the process of solving by over-relaxation is executed repeatedly for each separate space! By using optimal relaxation factor the convergence behaviour of the solver will be sped up significantly!

VAPOUR-option: Analysis of multidimensional vapour diffusion is only possible with an active VAPOUR-Option of the program..

Running Solver on multiple CPUs

Running the solver on multiple CPUs enhances the calculation performance and thus (in most cases) reduces significantly the calculation time. Multi CPU (or Multicore) behaviour of the solver is controlled by respective application settings separately.

MULTICORE-option: Speeding up computationally intensive jobs by distributing them on multiple processors or processor cores for parallel execution is only possible with an active MULTICORE-Option of the program.

Advanced Solver parameters

Within the tab Advanced you can edit details of solver parameters.

Parameter settings composed of several parameters are shown pre-pended with a small plus sign. A click onto the plus sign will expand the detailed list of these parameters and offer them for editing.

The bottom part of the window shows explanations related to the parameter currently marked for editing. You can change the height of this description area by dragging the separator line shown above it.

Important: Transient (harmonic) solver parameters are grouped together within the section "Transient Problem Solver". Parameters offered by default shall not be changed. Ability to modify these settings is provided for testing and diagnostics purposes only.

Remarks:

• The highest number of periods the solver can process is limited to 2000.
• Period lengths (also of the higher harmonics) are kept as integers (seconds, 1..99999999).
• The "Periods" Array will contain more then only the fist 6 harmonics exclusively if TRANSIENT option is in place.
  Additional periods will be appended only if TRANSIENT is available.

See also: Application settings, Fine Grid parameter, The over-relaxation, Solver window