7: Processing the Model

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PRCS Command

Before running the model, you should always issue the prcs command. In preparation for processing the time-step information, it computes the model time step for stability and opens the necessary arrays for field-data storage.

prcs

Although the prcs command is automatically entered with the first exec command if it has not already been so, it is good practice to enter it before beginning. Once it is entered, no alterations to model geometry, material properties, and so on are permitted.

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Although 80% is default, it can be on the conservative side for some models. Users can adjust this upwards using the time command (must be issued before the prcs command) to help:

  1. Reduce simulation time (larger timestep means less steps for a set simulation time)
  2. Increase accuracy (reducing the amount of sampling in the time domain)

However, it is important to note than increasing it too much will eventually cause the model to become unstable, and care should be taken. A good value to try initially is 0.95:

time * * 0.95 

Increasing the TSF is also useful if you are running a model that propagates over longer distances (>25 wavelengths). By reducing the effect of sampling in the time domain, the solution at each timestep is more accurate, and therefore the cumulative effects of numerical dispersion can be lessened somewhat.

Tutorial Tasks

Within the Wave_Prop.flxinp file:

  1. Issue the time command with a time stability factor of 0.95
  2. Issue the prcs command

Progress to tutorial section: Model Execution

Tutorial Code

time * * 0.95 

prcs
/* check models, sets up required data arrays, calculates stable timestep for solver to run model grph nvew 2 1 line on /* turn on mesh lines arrow pole /* turn on poling arrows plot piez /* plot created electrode plot matr piez /* plot created electrode on top of model end term /* pause model to allow check
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