Setting abortion parameters

The parameters in this window give some control over the strategy to be used when solving convection. The interruption criteria here are common for computation on unstructured and structured mesh.

For the unstructured mesh the buoyancy driven convection is the default, but you can turn it off by clicking on the box in front of with buoyancy. This button doesn't affect the behavior on the structured mesh. For switching off of the buoyancy effect the gravity parameter in the General tab of the Process Parameters dialog can be set equal to zero,

The defaults were gained from experience and should only be changed, if necessary. In practice, the only parameters frequently adapted are the underrelaxation velocity factors.

  1. Select Computation > Convection parameters.

    The Convection parameters dialog opens with the Abortion tab:

    Abortion tab in Convection parameters dialog 

    Figure 20. Abortion tab in Convection parameters dialog

  2. The Inner iteration limits are available only for the computation on the unstructured mesh. They define the solving process: First the equations for pressure and momentum are solved and as soon as the momentum norm has reached the value specified in Momentum1, the temperature equation is solved. When the result is close to Temperature 1, the next iteration will be started. The number of iteration loops is limited to 5.

    For the structured mesh the momentum and enthalpy equations are solved each iteration together.

    Set the convergence criteria Momentum 1 and Temperature 1.

  3. The computation will stop in two cases: Either both final values, Momentum 2 and Temperature 2, are reached or the solution does not change anymore (max. solution change), although the values for momentum and temperature have not been reached.

    Set the criteria for stopping the computation.

  4. For the unstructured mesh a linear dependency of the underrelaxation factors for the velocity equation can be specified. For the structured mesh the underrelaxation parameters are fixed and are entered in the automatically created dialog tabs after the structured mesh is generated.

    Example: inc. from 0.1 to 0.75 between 1 and 0.01 will result in an underrelaxation factor of 0.1 (0.75), if the residuum is higher (lower) than 1 (0.01), and in a linearly increasing factor from 0.1 to 0.75 between 1 and 0.01.

    For constant underrelaxation factors set upper and lower limits to the same value.

    Set the Underrelaxation velocity factors.

  5. Click on Apply and Close.

    or

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

Related Dialogs

Abortion