In a previous post, I have presented how to apply a harmonic base excitation in ANSYS Mechanical 15.0 using three different techniques. Among those techniques, we had the great ACT extension that has received a great attention due to its ease of use and practicality.
ANSYS 16.0 offers the capability of applying a harmonic base excitation natively, and without the need for the ACT. Acceleration applied as a base excitation uses the Enforced Motion Method.
Base excitation using Enforced Motion Method is performed in a Mode-Superposition harmonic analysis. The first step is to create a linked harmonic analysis as shown below.
You would then follow the normal procedure to set-up the modal analysis and the harmonic analysis, etc.
When it comes to applying the acceleration, the default “Inertial Acceleration” is the Global Support Acceleration Method “GSAM” presented in the previous blog. In this method, the entire structure is subject to acceleration as a global excitation. Although this is the most straight forward method to apply a base acceleration, the output does not resemble the actual testing environment since it only reports the relative motion between the base and the rest of the structure (i.e., the base is already fixed). Also, phase information is lost in this case. This global acceleration is applied using the ACEL command, which does not support frequency dependent acceleration.
You can then change this default method by changing the “Base Excitation” under definition to “Yes”. This will allow you to pick the support to excite, the direction of excitation (global x, y, or z), and the magnitude of excitation. Note that the supports must be defined in the modal analysis system.
Also, the excitation can be either constant or frequency dependent.
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