PhD Thesis - staffweb - University of Greenwich

PhD Thesis by John Ewer.This corresponds to the diagram (See Figure 3.7.7-2) of the equivalent C++ classes. Some ofthe arrays in the legacy CFD code (See Figure 3.7.7-1) contain actual data values (e.g. P,OLDP, AREA and XYZCRD) whilst others contain index values (e.g. CELFAC and FACPTS)that are used to reference data items in other arrays. It should be noted, at this point, that thelinks between the identified class objects could have been implemented using pointers and arraysof pointers instead of integer indices and arrays of indices. The major problem with usingpointers extensively is that this would necessarily introduce pointer de-referencing to accessvalues. This would almost certainly be unfamiliar to many numerical CFD developers. It wasdecided that the object links be implemented in a form not too dissimilar from the legacy code.Whilst this was often less elegant, than some other techniques, it did have the benefits ofconsistency and ease of implementation.Cell PropertiesPPoint PropertiesOLDPLASTPxyz12nCELFACXYZCRDIndex linksFace Properties123nFACPTSAREASKINFRFIGURE 3.7.7-1 : Legacy FORTRAN data storage in simple arrays.There was a potential problem for the storage of cell properties because of the need to maintainup to four different historical versions of some variables. For example a transient flow simulationneeds old time-step, last sweep, previous inner iteration and newest values of pressure and3-62