Inputting PSD Curve

[Stringmaker]

I'm inputting a PSD curve that Ansys is not liking very well and I'd like to know if my workout is proper. Here is a segment of the initial:

Hz G^2/Hz
5 0.047
7 0.047
7 0.18
9 0.18
9 0.026
13 0.026
13 0.16
27 0.16

This is the first 8 points given on the PSD curve. When I input as shown above Ansys prompts me with a message for each duplicate frequency and when I issue the psdgraph command it shows nothing like the actual. As a work around I've been inputting the above as this for instance:

Hz G^2/Hz
5 0.047
7 0.047
7.1 0.18
9 0.18
9.1 0.026
13 0.026
13.1 0.16
27 0.16

I notice that when I issue PSDGRAPH for the above the G^2/Hz value will occasionally fall to a zero value for the small range which the function is not defined for since it is not continuous.

My question is: Is my workaround an acceptable way of entering the PSD curve without affecting results? Or would a better way be to keep a continuous function but omit the second data point at any given frequency. For instance:

Hz G^2/Hz
5 0.047
7 0.047
9 0.18
13 0.026
27 0.16

As I understand dynamics this very closely approximates the original PSD. I'm just concerned that Ansys may not properly input the curve the way I have entered it now. Thankyou for reading and any help on this matter is much appreciated!

Best,
-Brian Craig

 

[Drej]

Brian,

Your initial PSD curve is:

Hz G^2/Hz
5 0.047
7 0.047
7 0.18
9 0.18
9 0.026
13 0.026
13 0.16
27 0.16

i.e. two values of acceleration for 7, 9 and 13 hz? Are you sure this is what you want to do? You cannot have more than one magnitude for a single frequency for PSD. If you have two PSD curves you can input these separately using PSDFRQ and PSDVAL.


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