During the calculation, the diagram of the residuals is shown (see the image Diagram of Iterations and Residuals ). It is a logarithmic chart that is also available for inspection after the calculation.
The graph illustrates the progress of the applied residual quantity during the iterative simulation process. Starting from an initial value of the residual quantity, the simulation refines the residuals with every iteration, trying to reduce the imbalance of the residual in the finite volume. The lower the residuals become, the more accurate the solution will be. The simulation terminates when the convergence criterion or the maximum number of iterations has been reached (note that no less than 300 iterations are always carried out). Thus, the residuals represents an important tool to judge the convergence of the simulation.
You can control the iterative calculation with the settings in the "Simulation Parameters" dialog box (see Chapter Simulation Parameters).
To resize the "Graph of residuals and iterations," move the window frames accordingly.
Use the
button to print the diagram. The "Windows Print" dialog box appears where you can
specify the printer and its settings.
When you click the
button, the "Graph Settings" dialog box is opened. There, you can adjust the
layout of the "Curves," for example.
If the "Residuals" diagram reveals any problems concerning convergence, you should review Simulation Parameters (mesh density, convergence criterion) and Wind Tunnel. For the latter, the default size is set as small as possible to obtain short calculating times. If its length in the X-direction is too short (especially the area behind the object), effects of divergence and, thus, oscillating values of residual pressure may arise. In that case, extend the wind tunnel accordingly. For more details, see Chapter Troubleshooting. In specific cases, however, oscillating results are correct when they are within a consistent bandwidth without increasing. This effect is illustrated in the simulation of a cylinder model at YouTube and explained in FAQ 4731 .