Learning Forum

[Davide_P]

Hi all!

I'm trying an harmonic analysis with displacements boundary conditions (BC) coming from a table.

Frequency Hz	Amplitude mm
0	0
5	0
5	10
20	10
20	20
30	20

In the first colum of the table there is the frequency while in the second the amplitude to a given frequency. BC are applied to few nodes of the structure using the following command:

Solution -> Define Load -> Apply -> Structural -> Displacement -> On Node -> Existing Table

I cannot understand how to effectively perform the analysis because the solver seems to ignore the input value on the table in terms of amplitude at a given frequency. Basically the solver performs an harmonic analysis with a flat input.

I really appreciate your support.

Davide

[peteroznewman]

A Harmonic Response analysis takes the amplitude of a sinusoidal load and computes the response of the structure from a start frequency to an end frequency.

Displacements are less common than forces or accelerations for applied loads.  Are you trying to do a MSUP or a Full Harmonic Response analysis?  If you are doing MSUP, are you trying to do Base Excitation?  

You can run two analyses to get the results for your table, one with an amplitude of 10 mm and sweep from 5 Hz to 20 Hz, while the second analysis would have an amplitude of 20 mm and would sweep from 20 Hz to 30 Hz.  You don’t have to run an analysis for the first two rows in your table. The answer is zero.

[Davide_P]

Dear @peteroznewman, I perfectly agree with you in performing two different analysis as you suggested.

Honestly, i tried a base excitation with a prescribed flat acceleration and with a tabular input, but i was not able. To approach the problem in a simpler way, I started approch the problem from a tabular input displacement with a full response analysis.

So, If you kindly suggest and explain in details how to perform a base excitation analysis as well as how to use a tabular input within the analysis, i will really appreciate.

I'm quite new in performing such analyses in Ansys APDL.

Thanks,

Davide