Learning Forum

[eric.smith]

Everyone,

I am performing a random vibration analysis of a simple two block system to obtain a better understanding of the reaction forces and moments. The random vibration analysis utilizes the result of a modal analysis. The random vibration analysis is conducted with a PSD acceleration applied at the fixed support locations (base excitation). I am attempting to create APDL command snippets to determine the reactionary forces for 1 sigma and 3 sigma results in the nodal coordinate system of excitation plane.

To obtain the reactionary forces I am utilizing the FSUM command and *get command. As noted in the ANSYS help file... When using FSUM in spectrum analysis, "...the summation of the element nodal forces is performed prior to the combination of those forces. In this case, RSYS does not apply. The forces are in the nodal coordinate systems, and the vector sum is always printed in the global coordinate system." 

However, since the *get command utilizes the results of the FSUM command, which is printing the vector sum in the global coordinate sytem, I do not get the results I desire. Instead, I like them in the local coordinate system to the base support (eventually used to determine bolt loads or transmission forces for example). Due to the nature of spectral analysis and the lack of implementation of RSYS, I suspect I cannot simply transform the printed out results into another coordinate system (if that is possible please tell me so).

Another question I have, what is the APDL command to obtain the FSUM results for 2 sigma and 3 sigma scaling factors (since 1 sigma is the default)?

Thank you for your time and assistance,

-Smith

[Ashish Khemka]

Hi Eric,

 

Please see if the following link helps you:

 

Estimating Structural Response to Random Vibration in ANSYS Mechanical: Reaction Forces - PADT (padtinc.com)

 

Regards,

Ashish Khemka