From 3847f71337332ff199bc5b3a17b7de0f1db9b99e Mon Sep 17 00:00:00 2001 From: Ann Almgren Date: Fri, 10 May 2019 10:52:54 -0700 Subject: [PATCH] Update info on time stepping --- docs/source/InputsTimeStepping.rst | 27 +++++++++++++++++++++------ 1 file changed, 21 insertions(+), 6 deletions(-) diff --git a/docs/source/InputsTimeStepping.rst b/docs/source/InputsTimeStepping.rst index 6d82138..71f14d5 100644 --- a/docs/source/InputsTimeStepping.rst +++ b/docs/source/InputsTimeStepping.rst @@ -69,18 +69,33 @@ That is determined by the following calculation: 2) In a pure fluid case, there are two options: * If you want to fix the dt, simply set :cpp:`mfix.fixed_dt = XXX` and the fluid time - step will always be that number. [SHOULD WE ABORT IF YOU ALSO SET CFL? OR SPECIFY - THAT FIXED_DT OVERRIDES CFL?] + step will always be that number. * If you want to let the code determine the appropriate time step using the advective CFL - condition, then set :cpp:`mfix.cfl = 0.5` for example, and the fluid time step will + condition, then set :cpp:`mfix.cfl = 0.7` for example, and the fluid time step will be computed to be dt = 0.5 * dx / max(vel). -Note that these choices apply to steady state calculations as well as unsteady runs. + * If dt as computed in the compute_dt routine is smaller than the user-specified + ```mfix.dt_min``` then the code will abort: +.. highlight:: c++ + +:: + + amrex::Abort::0::"Current dt is smaller than dt_min !!! + + * If dt as computed in the compute_dt routine is larger than the user-specified + ```mfix.dt_max``` then dt will be set to the minimum of its computed value and dt_max + + * If dt as computed in the compute_dt routine is larger than the user-specified + + * Note that the cfl defaults to 0.5 so it does not have to be set in the inputs file. If neither + :cpp:`mfix.cfl` nor :cpp:`fixed_dt` is set, then the default will be the second option here. + If :cpp:`mfix.fixed_dt` is set, then it will override the cfl option whether + :cpp:`mfix.cfl` is set or not in the inputs file. + +These options apply to steady state calculations as well as unsteady runs. 3) In a coupled particle-fluid case, dt is set as in the pure-fluid case. In this case the particle time step is first computed as in the particle-only case, then is adjusted so that an integral number of particle steps fit into a single fluid time step. - -[HOW ARE DT_MIN AND DT_MAX USED???] -- GitLab