FRA analysis
hello again,
we made a FRA for a system (attached picture) with enforced displacement of 1mm. The first plot shows the displacement of the mass without damping. The results are the same as we expected. The second plot shows the results for the same system with damping. we did not expect these results and can not understand them. we expected the maximum displacement at the eigenfrequency. is the second plot right and how can we understand it?
Thanks
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we changed the viscous damping to a structural damping with a value of 0.1768, and we got this plot. We got maximum displacement (5.7478mm) at the eigenfrequency 1.125 s^(-1). We expected the maximum at a lower frequency, because of damping. Our calculated displacement is only 3.037mm.
Why are there these differences?
Hi,
the value of 0.1768 is the damping ratio (C/Co). We multiplied it with 2, changed it in HyperWorks and got the same plot as you. Do you know why we have to multiply with 2? You can see our calculation in the picture. For the frequence 1.125 s^(-1) we calculate the same value as Radioss.
Our problem is, that if you calculate a maximum of V, it has to be at a frequence of 1.093 s^(-1). You can see the calculation in the second picture. Are our thoughts correct?
Thanks a lot
No information yet.Did you check the script which we have asked you to refer in other post?(That should give some basic idea)
You can also refer below pdf & script id screenshot.
https://fenix.tecnico.ulisboa.pt/downloadFile/395143173426/MSc Thesis HFonseca [Last Version].pdf
Hi RAHUL,
I have done modelling and setup the model has you said but i am not getting any movement. Can you please check once so that it will easy for to check it i am attaching the model.
Hi Ajay,
You can try the same with RADIOSS. I just tried the same in RADIOSS and the files are attached along for your reference.
You can also try a similar approach.
We don't have a direct output for TL. But, certainly for radiated power (ERP).Since TL is a logarithmic measure of Incident power to the radiated power, you can measure/output the radiated power from OptiStruct and then manually calculate the TL.I have attached a sample tutorial which walks you through the steps to output ERP using OptiStruct.
For ERP refer online help for detailed information.
Hi,
with no damping the maximum displacement is expected at or near the natural frequency of the component, this is what the first graph says.
but this is the not case in when you have damping.
Please run the same analysis with Structural damping instead of viscous damping and you will notice, the peaks reduces as the damping increases.