Swept sine dynamic response
Swept sine dynamic response
(OP)
To assess the dynamic response of a structure in a particular direction and to determine the participation of each mode in the response it was suggested that a swept sine method be used for frequencies within a certain range.
What force/displacement function is input to get this response from a FE model?
What force/displacement function is input to get this response from a FE model?





RE: Swept sine dynamic response
You will probably have to generate the forcing function based on the frequency content desired...We used to do this from specified shock spectra....essentially generated a time history (usually velocity) that had the same frequency content as the specified spectra...
Next question is how.....I don't remember (its been much too long since I did this) so can't help much with that....maybe check a vibrations book
I think the forcing function could be either a force time history or a velocity time history...
Maybe that will point you in some direction...
Ed.R.
RE: Swept sine dynamic response
It depends on what the physical test is. I admit that my understanding of swept sine is fairly limited, but my understanding of it is that simply devolves to a steady state dynamics analysis. The critical question is how the test was run (applied force, applied acceleration, etc).
For a given applied force in test, my understanding is that the equivalent approach in FEA would be to do a constant-force Steady State Dynamics run, and extract the relevant output.
Don't take my response as authoritative, as it is based on a loose understanding of "swept sine testing". If I know the physical test that you are performing, I can probably give a more informed response as to the FEA equivalent.
Cheers,
Brad
RE: Swept sine dynamic response
What I have done in the past is to do a frequency response analysis with constant acceleration (1 - unity) in one direction over a frequency range (1-3000Hz). This mimics a transmissibility test (A out/A in). From the results I will have a better understanding what to adjust to reduce resonance. You could also use force, displacement or velocity.
BJP
RE: Swept sine dynamic response
bjpil's comment sounds good in that it sounds like a spectrum response analysis with acceleration against frequency, and is a steady state analysis. I'm not sure if that is what brad is referring to by a steady state constant force dynamics analysis. Presumably a constant force implies a constant acceleration as bjpil suggests?
Either way this sounds the easiest way of obtaining the required results.
Many thanks
corus
http://www.corusresearch.com