From 39dc6c6e78b5f06a82382700e440f9420d449efa Mon Sep 17 00:00:00 2001 From: Ann Almgren Date: Fri, 10 May 2019 11:05:02 -0700 Subject: [PATCH] How particle dt is determined --- docs/source/InputsTimeStepping.rst | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/docs/source/InputsTimeStepping.rst b/docs/source/InputsTimeStepping.rst index 38a783e..f38e173 100644 --- a/docs/source/InputsTimeStepping.rst +++ b/docs/source/InputsTimeStepping.rst @@ -53,9 +53,9 @@ Setting the Time Step There are several ways that the inputs are used to determine what time step is used in the evolution of the fluid-particle system in MFiX-Exa. -1) In a pure particle case, the "mfix.fixed_dt", if specified, is only used to determine the frequency -of outputs, it has no effect on the dt used in the particle evaluation. If you do not specify a positive -value of "mfix.fixed_dt" then the code will abort. +1) In a pure particle case, the :cpp:`mfix.fixed_dt`, if specified, is only used to determine the frequency +of outputs, it has no effect on the "subdt" used in the particle evaluation. If you do not specify a positive +value of :cpp:`mfix.fixed_dt` then the code will abort. .. highlight:: c++ @@ -63,8 +63,8 @@ value of "mfix.fixed_dt" then the code will abort. amrex::Abort::0::If running particle-only must specify fixed_dt in the inputs file !!! - -That is determined by the following calculation: +The particle time step "subdt" is determined by computing the collision time "tcoll" from particle properties, +then setting "dtsolid" to be "tcoll / 50". 2) In a pure fluid case, there are two options: @@ -94,6 +94,6 @@ That is determined by the following calculation: 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. +3) In a coupled particle-fluid case, dt is determined as in the pure-fluid case. In this case + the particle time step "subdt" is first computed as in the particle-only case ("dtsolid"), + then is adjusted so that an integral number of particle steps fit into a single fluid time step. -- GitLab