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Converting Time domain data to Frequency domain.

Converting Time domain data to Frequency domain.

(OP)
I am doing a shock analysis of a pump with shock load of 48g in 40ms(Full sine wave).I have solved using Solidworks Time history analysis. As i searched more,i got to know that it can solved using Response spectrum method also by converting time domain data to Frequency domain. How to convert the data from time domain to frequency domain? any links showing examples or materials please share.

Thanks

RE: Converting Time domain data to Frequency domain.

A couple of words of caution. Excel's FFT function has a rather odd syntax and is a bit of a pain. When you are using a new FFT algorithm always check with a known signal, for example a synthesised sine wave at say 20% of the sampling frequency. Be aware that you'll get a complex number in each frequency bin, again not an Excel strongpoint. If you have access to Matlab, Octave,Mathcad, or any mathematical package they will undoubtedly be more straightforward than Excel.

Cheers

Greg Locock

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RE: Converting Time domain data to Frequency domain.

A shock repsonse spectrum is not the same as an FFT. A shock response spectrum can be thought of as the maximum absolute response of a series of single degree of freedom oscillators to a given base motion. Try doing a google search on shock response spectrum calculation. Another thing to keep in mind with SRS analysis is that while it is less computationally intensive than a transient analysis, the results of a shock spectrum analysis are statistical estimates of the structural response and not the actual response. This is due to the way shock spectrum analysis works. For linear systems, the complete response to a transient input can be described as the linear combination of responses of each mode of vibration. The individual modal responses are solved for and then combined to get the total response. All modes are assumed to act in phase, hence the predicted stresses may be higher than actual stresses. Direct linear combination and square root sum of the squares are two methods used to combine the modal responses, with direct combination being the most conservative. Also, if you are interested in anything other than the peak response, you can't get that from the SRS analysis either.

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