A Multiblock Mesh Manager

The aim of this subtask has been to develop a manager for structured multiblock grids. The focus of the development has been on the block topology, of which the manager should have full control. The manager should also be easy to expand, in particular with new ways to describe the geometry of blocks in the grid. Typically grid generation involves a good deal of trial and error. Consequently the mesh manager should be exible, and allow the user to freely edit, add and delete blocks and grids on diierent levels. One can distinguish several diierent aspects of the multiblock grid that the user should be able to modify. First, there must be operations to edit a block's geometry, i.e. its (continuous) distribution in space. This could mean for instance changing the shape of an edge or a surface. Since blocks stick together, changing the geometry of one block, usually means that some of its adjacent blocks' geometry must change too. Moreover, it should be possible to change the topology of the multiblock grid. By \topology" we mean how the diierent blocks are connected to each other. The topology is a property of the whole grid, not of the individual blocks. It changes when for instance a block is split into two, when new blocks are added or old ones deleted, etc. The mesh should also be controlled by the user through appropriate operations. The mesh is considered to be the evaluation of the geometry at a discrete set of points. Some typical mesh characteristics that could be modiied, are the mesh size (number of points) and the mesh density (stretching parameters). Because of the common constraint that grid lines should be continuous across block boundaries, changes in one block generally propagate to other blocks as well. In addition, the user should be permitted to change the geometry representation of a block. The geometry representation is the set of parameters and the mathematical expression which describe the geometry. Sometimes edges are best described by B-splines, sometimes with straight lines or arcs. The user should have the choice. In particular this is important for the physical boundaries where a precise geometry description is often necessary. Finally, it is very important that the grid generator allows one block to meet with multiple other blocks along one boundary. This may seem obvious, but in principle it is not necessary; one can always manage without …