Figure 1.6: The PDS Method Determination Wizard

Based on the information you provide, the wizard will tell you the fastest method for solving your probabilistic design problem. The wizard will issue the PDMETH command and either the PDLHS or the PDDOEL command. You will still need to run the analysis, then fit the results to a response surface, etc. to evaluate your results.

1.3.9. Execute Probabilistic Analysis Simulation Loops

You can execute your analysis on your computer alone (serial execution), or using other computers in your network to save running time and speed processing (parallel execution).

If you want to use serial processing only, select the serial option from the Run menu.

If you want to run parallel analyses on multiple CPUs, you must first set the parallel options before performing the analysis. (See PDS Parallel Analysis Runs (p. 27) for more details).

Command(s): PDEXE

GUI: Main Menu> Prob Design> Run> Exec Serial> Run Serial Main Menu> Prob Design> Run> Exec Parallel> Run Parallel

Caution

For security reasons, ANSYS, Inc. recommends that you use parallel processing only within the firewall of your local area network.

If you use serial processing to perform a probabilistic analysis, you will use only the CPU of the computer you are working on. If you have access to only one product license, or if you have access to only one computer, then this is the only way in which you can run a probabilistic analysis. While the simulation loops are running in serial mode, your session is locked (you cannot perform other tasks in the same session). If you are running your session in interactive mode, the simulation loops are also performed

in interactive mode. If you are running your session in batch mode, the simulation loops are performed in batch mode.

If you select the PDS parallel-processing option, you can use other CPUs that you have access to for running the probabilistic analysis. PDS parallel processing can distribute the necessary jobs in a local area network. With this option, the simulation loops are sent to CPUs that you can specify, where they are executed in "server mode." This looks the same as a batch run (in other words, there is no interactive visualization during the execution of a simulation loop). While the simulation loops are running in parallel mode, your session is locked; however, you can instruct the session to start postprocessing the

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probabilistic results as they are calculated so you can review and visualize the results before all simulation loops are finished.

In parallel processing, you can monitor the running jobs and the completed results.

When using parallel-processing, for n available licenses, n - 1 will be available for PDS solutions, as one license is used as a PDS administrator. For example, if you have 8 licenses available, you will be able to run 7 PDS solutions concurrently.

1.3.9.1. Probabilistic Design Looping

Regardless of whether you opt for serial or parallel processing, the program controls the analysis looping. You cannot modify this process, which does the following:

•Always reads the analysis file from the beginning.

•Always ignores the RV settings and replaces their value with the derived value that the probabilistic method has assigned to an RV for a particular loop.

•Always reads the PDS database after each loop.

For the execution of the simulation loops you must specify a solution label (Slab on the PDEXE command). The solution label is used for several purposes:

•The results are stored in an ASCII readable file under the name "jobname_Slab.pdrs". Here, Slab is the user-specified solution label.

•If you want to fit response surfaces to the results of the random output parameters then you need to specify the solution label to indicate which set of results you want to use for the fitting procedure.

•If you want to postprocess the results generated with the PDEXE command then you must specify the solution label to indicate which results you want to postprocess.

When you execute the probabilistic analysis (PDEXE), the program creates a probabilistic design loop file (Jobname.LOOP) from the analysis file. This loop file is used to perform analysis loops. Looping continues until all parameters have been evaluated.

If a loop is interrupted due to an error in the execution run (for example, a meshing failure, a nonconverged nonlinear solution, etc.), PDS aborts that loop. Further processing depends if you are in serial or parallel processing mode. If you are using:

•Serial interactive processing: you can terminate when you receive the error, or continue processing.

•Serial batch processing: processing terminates at the first error.

•Parallel processing: processing terminates if the allowed number of failed loops is exceeded (set in PDEXE), otherwise it continues.

Note that for all failed loops (loops with errors), the results for that loop are discarded, no data from that loop is used for post processing.

After the PDEXE command is issued, the PDS generates a file containing the input sample values. The file is called jobname.samp. An example of the content of the file is given below: