GGU-3D-SSFLOW: "Optimise" menu item

You first select in a dialog box whether the diagonals or the topology should be optimised.

"Diagonals" button

Optimisation of diagonals is implemented in order to create a numerically favourable FEM mesh, i.e. where possible, equilateral triangles. The effect of the optimisation of diagonals can best be seen using an example:

If an existing unfavourable diagonal cuts two different soil areas, no optimisation takes place, because this would alter the system.

"Topology" button

This program routine displaces the triangular element nodes so that, where possible, equilateral triangles are created. Equilateral triangles have especially favourable numerical properties. Because the displacement of system boundaries and element boundaries with neighbouring elements consisting of different soils does not make much sense, these element boundaries are fixed from the outset. Nodes with defined water level boundary conditions also remain unaltered. Optimisation of the FEM mesh can be followed on the screen by setting the "With graphics" check box. The optimisation routine can be aborted at any time by pressing the right mouse button.

In principle, it is always a good idea to optimise the element topology before commencing modelling. However, this leads to a problem; after individual nodes are displaced, the z-values cannot be adapted to the new position. The program therefore displays a warning message beforehand. It is possible to assign the precise values via an interpolation mesh following the optimisation (see "I mesh" menu pp.).