# Impulse Harmonic Analysis

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• Last Post 13 June 2018
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ItalicBike posted this 08 June 2018

Hi everybody,

I'm new on the forum. I use ansys 18.2. I've some question for my job.

I've to model a experimental test, in particular the FRF of an aluminium panel subject to a impulsive load (like an hammer test). So the take-away question is:

It's possible to model an impulse load without carry out a transient analysis? Could you say me which block i'have to use?

Best Regards

peteroznewman posted this 08 June 2018

Use a Harmonic Response system block. That can either be on its own, or linked from a Modal analysis. Here is an example on a Bridge.

Select a face to be a Fixed Support and apply a unit Force at the point where the hammer would impart an impulse load. The system will treat this as a harmonic forcing function. In Analysis Settings, select the frequency range of interest and how many points to plot over that range. Request a Frequency Response output at the point where you would put the accelerometer. The output will be like an FRF.

ItalicBike posted this 11 June 2018

it's possible to apply a damping coefficient function frequency?

peteroznewman posted this 11 June 2018

Yes, there are several ways to add damping.  Either as a constant damping ratio or as coefficients to the Mass and Stiffness matrices (Rayleigh Damping) or both. You can also add damping to the material, which will add to these values.

ItalicBike posted this 12 June 2018

Thank you Peteroznewman, but i have to define frequency dependent structural damping. Does it is possible in Workbench o I need to write an APDL command?

If yes, could you help me to understand the variuos command TBDATA, TBFIELD, TB, SDAMP?

Thanks

Best Regards

peteroznewman posted this 12 June 2018

If you click on the pull down menu on the Stiffness Coefficient line where it says Direct Input, you will see you can input frequency dependent structural damping.

ItalicBike posted this 12 June 2018

Sorry peteroznewman, but only 1 value? I need to input 16 values. Thanks

peteroznewman posted this 12 June 2018

Damping is frequency dependent when you use Mass and Stiffness coefficients. Here is the equation that shows how the frequency is combined with the coefficient to calculate a damping ratio.

Take the table of 16 frequency and damping ratio pairs and fit the three coefficients to your data. I can help with the fitting if you don't get a good fit.

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ItalicBike posted this 12 June 2018

Thank you so much, very very very useful. And also thank for you patience.

peteroznewman posted this 13 June 2018

You're welcome.

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