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START Time Flow Mechanism Simulation Time SCAN A Phase Time Flow Mechanism Iteration Time SCAN A' Phase EXECUTE ALL CELLS' TRANSITION FUNCTION B phase Does all cells' state converge ? Terminate Simulation ? END Yes No SCAN ALL CELLS C phase ACTIVITY 1 CellSpreadState == 'inTest' and CellState == spreadCondition Add neighbouring cells to the active set No Yes ACTIVITY 2 CellPhase == 'quiescent' Remove the cell from the active set Figure 12: Three-phase approach modification for implicit model simulation Figure 12 depicts an adaptation of the three-phase approach for the simulation of implicit models. A principal time scanning loop is in charge of the simulation time (A phase). However, the A phase has been doubled by a smaller loop in charge of the iteration time base (A’ phase). As long as the states of all cells do not converge, the transition function of a cell is executed. Once the state of a cell converges it is added or removed from the calculation domain (C phase). 26
7 RESULTS OF FIRE SPREAD SIMULATION For the PSM we chose to program our implemented model in C++ for efficiency reasons. We used three techniques for the simulation phase (Balci and Sargent, 1989; Youngblood and Pace, 1995; Hill et al., 1996) (1) comparison validation: comparison of simulation results with an experiment; (2) confrontation validation: asking physicists if the results and behaviour of the simulation model were consistent; (3) graphic validation: using visualisation and animation to make use of the human ability to apprehend spa- tial relationships. Figure 13 shows a comparison of the simulated and experimental fire fronts obtained for a point- ignition. Black squares represent the experimental fire fronts. Figure 14 represents the evolution of the active cells around the fire fronts. Finally, Figures 15 and 16 depict the execution time gain (on a 500 MHz Pentium III processor) obtained focusing on the active cells of the propagation domain. We can remark that this gain is more important for a three-phase simulation. Indeed, for the implicit method if the time step is greater than the explicit one (of ten times), the number of iteration per time step is lower than ten. Moreover, the number of active cells is approximately equivalent at each time step. Hence, if at the end of the simulation the three-phase method will execute 10 million of cell transition functions, the pure discrete event one corresponding to the explicit model necessitates 56 millions of cell transition functions. 27
Page 1 and 2: OBJECT-ORIENTED FRAMEWORK FOR MODEL
Page 3 and 4: 1 INTRODUCTION Ecosystems show a hi
Page 5 and 6: Among the disturbing propagation pr
Page 7 and 8: Multimodel attributes methods conta
Page 9 and 10: on large-scale (Wu et al., 1996; Ha
Page 11 and 12: PHENOMENON Problem definition Probl
Page 13 and 14: 2. The Environmental Conditions pac
Page 15 and 16: Statistical Model statisticalDescri
Page 17 and 18: we have developed a strategy based
Page 19 and 20: Where Tij is the grid node temperat
Page 21 and 22: low level (Local Rule), rules can b
Page 23 and 24: mentation. However, the computer ti
Page 25: In the case of fire spread, two gri
Page 29 and 30: Execution time (log. scale in min.)
Page 31 and 32: ACKNOWLEDGMENTS The authors gratefu
Page 33 and 34: Campos, A., Hill, D.R.C., 1998. An
Page 35 and 36: Hill, D., 1996. Object-oriented ana
Page 37 and 38: Miller, J.D., Yool, S.R., 2002. Mod
Page 39 and 40: Veach, M.S., Coddington, P.D., Fox,

Object-oriented framework for modelling and ... - ResearchGate

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