## General Mechanical

#### Impulse Harmonic Analysis

• ItalicBike
Subscriber

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
Subscriber

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
Subscriber

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

• peteroznewman
Subscriber

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
Subscriber

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
Subscriber

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
Subscriber

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

• peteroznewman
Subscriber

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.

• ItalicBike
Subscriber

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

• peteroznewman
Subscriber

You're welcome.