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QUESTIONS on MULTI RUN MODAL ANALYSIS on TEST LAB

Good morning,
I would like to submit some questions about the multi-run modal analysis tool of Test Lab. My problem is the following: starting from the averaged FRF derived from n points of acquisition, I have to analyze the mode shapes in the frequency range [5-40] Hz and to do this I create a first processing with all frequencies of interest (target) and subsequently I want to isolate in individual processings each mode in order to obtain a better mode shape. Then I proceed in merging the individual processings through the multi-run tool to get one that contains all frequencies and I would like to know how the software uses the upper and lower residuals for each processing and therefore how those of the final processing final are calculated, as the synthesized FRF. What I would like is that the upper and lower residuals out of the range [5-40] Hz were those of the process containing the target frequencies. Moreover I need a clarification on scaling mode of ways, in particular which of the two between Unity modal A and Driving Point scaling is best suited to my stuation, having two driving point.

Thanks for your support. 

Agnese Caprara

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Accepted by topic author AgneseCaprara
‎06-08-2017 05:19 PM

Re: QUESTIONS on MULTI RUN MODAL ANALYSIS on TEST LAB

Hello,

 

Are you creating partial mode shapes in each of your processings?  i.e. For each run which includes only some of your measurements you are creating a partial mode shape and after all processing you wish to merge the partial measurements from each run.  That is the intent of Multi Run Modal to compensate for run to run variations due to mass loading, temperature shifts, boundary conditions changing, etc.

 

From your description, it sounds like you are isolation modes in each processing and each mode is a complete mode shape.  Is that the case?  If so, you don't need to use Multi Run Modal.  Instead, use Modal Validation and the Data Handling minor worksheet.

 

For each processing set, add the mode(s) and the Residuals to the workspace and when all of them are added you can then create a new Processing set that includes all modes and correctly uses the Lower Residual from the lowest frequency and the Upper Residual from the highest frequency.  This will give you a processing set with all the modes which you can use on Modal Synthesis and Modal Validation.