xPSDA long, long, time ago PADT wrote a protoype for an external tool that used ANSYS Mechanical APDL results to do PSD analysis on very large models. We still use it today when we need to go beyond what the standard program can do. We share it here with the user community on an as-is basis.

One of the most important types of mechanical simulation is the prediction of a system’s behavior due to random vibration. Almost every type of machinery, from computer circuit cards to satellite sub-assemblies,PSD Collage undergoes some type of random vibration, and it is the job of the analyst to determine if the system can stand up to this loading. xPSD is a tool from PADT that allows a user to take the results of a standard modal analysis and conduct fast, flexible studies on the behavior of the structure under just such loading.

xPSD uses the “large mass method” to capture the modal response of a system to random vibration, expressed in terms of a Power Spectral Density (PSD) input. The user can quickly specify many different PSD input curves and extract the response of the system. The goal of the tool is to provide a simple—but fast and accurate—way for users to carry out PSD analyses. In fact, on a typical model (300,000 DOFs, 200+ modes), nodal response and 1-sigma values can be calculated in a matter of just minutes.

The first version of this tool, xPSD for ANSYS, works with version 8.0 of the ANSYS general-purpose Finite Element code. It has the following features. Instructions are provided to modify it for more recent versions.

Features include:

  • Supports single base excitation
  • Utilizes a standard modal analysis (with large mass) as input
  • Stores modal information in efficient binary file that is an order of magnitude smaller than the equivalent *.RST modal result file
  • Solves in minutes, or even seconds
  • User can request displacement, velocity, acceleration, or component stress response at any node
  • User can request “1-sigma” displacement, velocity, acceleration, or component stress information for the entire model, or for sub-components of the model
  • Response curves can be output for display in ANSYS or a spreadsheet
  • “1-sigma” results can be output for contour display in ANSYS
  • Entire process can be run from within ANSYS, interactively or in batch mode
  • Input PSD and output request controlled by simple text file

This initial release was developed specifically to address the immediate needs of one of PADT’s large aerospace customers. It is aimed at delivering the above capabilities to the user community as quickly as possible, and hence does not have a lot of “bells and whistles”.


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NOTE: PADT provides this software free of charge on an “as is” basis. No support for this software will be provided.

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