26. SIMULATION_CONTROL Namelist (Experimental)
26.1. Overview
There may be points in time during a simulation when something changes abruptly; a boundary condition or source turns on/off, or a physics model is enabled/disabled, for example. In such circumstances it is best to hit these times precisely with a time step and then continue from that point with a reduced step size appropriate to resolving the time transients that result from the impulsive forcing of the model—in essence, to split the simulation seamlessly into a sequence of phases where each phase is a new simulation whose initial state is the final state of the preceding phase. This experimental namelist provides a means for achieving this. The start time of each additional phase subsequent to the initial phase is specified using the Phase_Start_Times array, and the initial step size using either the Phase_Init_Dt or Phase_Init_Dt_Factor variables. Truchas will hit those times precisely with a time step, smoothly adjusting the step size in advance to avoid abrupt step size changes, and then effectively restart the timestepping. Currently this only effects the second-order diffusion solver which maintains a (smooth) history of states at recent time steps. When restarting that history is deleted and time stepping begins fresh using only the current state.