PhD Thesis - staffweb - University of Greenwich

PhD Thesis by John Ewer.specified. Suitable monitoring was applied to give an assessment of the appropriateness of eachset of initial control parameters. A base set of "safe" control parameters was also used as acomparison for the expert specified cases. This "safe" set of relaxation parameters was arrivedat from the Software Developer's experiences of validation and testing of the prototypeinteractive system when used on similar simulation scenarios.The CFD users who answered the questionnaire gave the following recommended controlspecifications for the partitioned room fire simulation.TABLE 6.2.1-2 : Control regimes taken from questionnaires.Control ItemSafe Set#1.1Expert#1.2Expert#1.3Expert#1.4Expert#1.5Number of sweeps 100 200 100 200 30Pressure relaxation 0.4 0.6 0.6 0.1 0.8Momentum linear relax 1.0 1.0 0.2 0.1 1.0Momentum false time relax 0.1 0.1 0.5 0.01 0.05Turbulence linear relax 1.0 1.0 0.2 0.1 1.0Turbulence false time relax 0.01 0.05 0.1 0.01 0.05Enthalpy linear relax 1.0 1.0 0.2 1.0 0.5Enthalpy false time relax 1.0 0.1 0.5 0.1 0.05Temperature relaxation 1.0 1.0 0.5 1.0 1.0Buoyancy relaxation 1.0 1.0 0.6 1.0 1.0Density relaxation 0.5 0.8 1.0 0.1 0.8The simulations where run as specified by the various experts and the run-times and convergencebehaviours are shown in the table (See Table 6.2.1-3).At first glance it appears, from the timings, that the user specified set #1.5 returned the optimalperformance because of its shorter run-time, however the simulation results were very poor forthat set of initial control parameters because none of the time steps actually converged to a6-93