PhD Thesis - staffweb - University of Greenwich

PhD Thesis by John Ewer.When Inactive regions occupy a greater proportion of the mesh savings in computational timecan be improved significantly.In the second example, the second door is opened after 40 seconds but rather than opening tothe outside it opens into an otherwise sealed compartment. The solution domain again consistsof three distinct regions, the external region outside of the open door, the fire compartment andthe second, initially sealed, compartment. The computational mesh in each region comprises of8 x 22 cells, 22 x 22 cells and 30 x 22 cells respectively i.e. a total of 1320 cells. Using standardCFD solution techniques the solver operates equally in all the cells throughout the solutiondomain, even the cells in the second sealed and isolated compartment.Once again, the initially dormant region is marked as Inactive resulting in the numerical solverspending the minimum amount of effort in this region. When the second door opens after 40seconds, the Inactive region changes to Active and the solution domain extends to cover thesecond compartment. As in the previous case both solution techniques result in identicalsolutions prior to the opening of the second door. When both doors are opened, both methodsconverge to the steady state solution depicted in the figure (See Figure 7.2.3-3). However, usingthe conventional solver, the run time up to the point where the second door opens wasapproximately 4.40 hours while using the group solver this was reduced to 3.06 hours, a savingof 31%. Thus, by effectively reducing the computational domain by 50%, a saving incomputational time of 31% is achieved. This saving is less than might have been expected butit is explained by the need for initialisation and property updates that occur in all cells regardlessof their group membership.More work is needed in this area to determine if there are benefits for the dynamic control ofeach group's solution controls.7.2.4 Investigation of dynamic groupsThe case used to investigate the use of dynamic group solvers is a preliminary investigation into7-109