PeriodicXPIC Custom Task

A custom task to use XPIC(m) method on selected time steps

Introduction

The XPIC(m) method is an advanced damping method that filters out unwanted noise (in the null space) without damping out useful information. Its drawback is that it adds calculation time as m in XPIC(m) increases. In some simulations, it may not be necessary to use XPIC(m) update methods on every time step. This custom tasks lets you convert such simulations to use XPIC(m) periodically instead of on every time step. Note that both the XPIC(m) method and this custom tasks are only available in OSParticulas.

Task Scheduling

The first step is to select default update method. Normally, the default method would be a standard FLIP method selected by using Damping commands and picking (fractionPIC) to 1. Next, you schedule this task and use it to select an XPIC order (the m in XPIC(m)) and frequency to run the XPIC(m) calculations. In scripted files, a PeriodicXPIC custom task is scheduled with

CustomTask PeriodicXPIC
Parameter XPICOrder,(order)
Parameter fractionPIC,(fractionPIC)
Parameter periodicSteps,(stepInterval)
Parameter periodicTime,(timeInterval)
Parameter periodicCFL,(CFLfactor)
Parameter verbose,{verbose}

In XML files, this task is scheduled using a <Schedule> element, which must be within the single <CustomTasks> block:

<Schedule name='PeriodicXPIC'>
   <Parameter name='XPICOrder'>(order)</Parameter>
   <Parameter name='fractionPIC'>(fractionPIC)</Parameter>
   <Parameter name='periodicSteps'>(stepInterval)</Parameter>
   <Parameter name='periodicTime'>(timeInterval)</Parameter>
   <Parameter name='periodicCFL'>(CFLfactor)</Parameter>
   <Parameter name='verbose'>(verbose)</Parameter>
</Schedule>

where the parameters are:

• (XPICOrder) and (fractionPIC) - Enter XPIC order (the m in XPIC(m)) and fraction XPIC(m) (0 to 1) to use when doing periodic XPIC(m) calculations. See Damping Options for details on these settings. The defaults are(XPICOrder)=5 with (fractionPIC)=1.
• (stepInterval), (timeInterval), and (CFLfactor) - sets the frequency for running periodic XPIC(m) calculations for mechanics. The (stepInterval) option sets number of time steps between each XPIC(m) calculation, (timeInterval) sets frequency in alt time units, and (CFLfactor) sets frequency relative to the basic time step for the momentum equation. If (stepInterval) is used, it is used and the other two are ignored. If (stepInterval) is not used, the time step is found from the (CFLfactor) (if provided) or from (timeInterval). One of these three parameters is required to enable periodic XPIC calculations.
• (verbose) - If a non-zero integer, a comment line is printed in the output file every time XPIC(m) calculations are done. The default is 0.