# Harmonic Analysis

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• Last Post 10 December 2018
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harishnarayanan7 posted this 06 December 2018

Hello!

I am currently modelling  a rail with Enclosure and I wanted to know if it is possible to apply a time step load in Harmonic Acoustics over a constant frequency. I tried the Transient analysis with acoustics act but I cannot upload a imported velocity there and only upload a displacement.

peteroznewman posted this 07 December 2018

Hello, I recently made a video of building an acoustics model of a Tuning Fork, where I imported the velocity from a Harmonic Response Analysis. You might find something useful there.

harishnarayanan7 posted this 08 December 2018

Thanks for the video!

But this is something which I already have done with my model and I am looking to see if I can do time step analysis besides frequency based analysis in Harmonic acoustics. Is there any way to use any script for analysis or any other way?

Thanks

peteroznewman posted this 08 December 2018

I don't know what you mean by time step analysis.  If you want time-history results from a time-history input of any kind of load, you do that in a Transient analysis. Please explain in detail, using screen shots of the geometry and screen shots of a load in Transient Dynamics that would explain what you want to do.

harishnarayanan7 posted this 08 December 2018

So in Transient Analysis you can apply load with respect to change in time for each step. I wanted to know if we can perform the same thing in Harmonic acoustics. Since in harmonic acoustics we can only get the result based on frequency ie it is a frequency based rather than time based. In harmonic it provides a result at a particular velocity and frequency. I want to know if we can apply 5 different loads at a same time( different time steps as in Transient) for one particular frequency.

This is the harmonic one where there are 5 solution intervals in range of 0-491Hz, and results are for one imported velocity.

This is load transfer to rail from external data where only vel 2 is imported to the rail @491Hz

Is it possible to test all the velocities at same time (Different time steps) with a common frequency domain of 491Hz.

I hope this explains my issue

I could get more pictures if you need

Thanks

Regards

Harish

peteroznewman posted this 09 December 2018

Dear Harish,

Several loads can be applied to a Harmonic Response analysis. They are all present simultaneously. All the loads oscillate at the same frequency. The loads can have a phase relationship. That means if you have a force at the left end of the part pointing up, and another force at the right end of the part pointing up, if both forces have a phase of 0 degrees, then they are both going up together and down together, but if you put a phase of 180 degrees on the force at the right, then that force is going down at the time the force at the left is going up, and when the force at the left is going down, the force at the right is going up.

Once you have defined the number of locations on your structure where you want a sinusoidal load and defined its magnitude, direction and phase, then you define the range of frequencies that you want to observe the response.

If you are really interested in the response at 491 Hz, you can request just one result.  What is more typical is to select a range, such as 400 Hz to 600 Hz and calculate results at a 10 Hz interval for a total of 21 result sets.  In your example above, you only asked for 5 result sets, but at about a 100 Hz interval.

I hope this clarifies for you what is possible in a Harmonic Response.

What you can't do in a Harmonic Response is have two loads at different frequencies. That would require a Transient Dynamics solution.

Kind regards,
Peter

harishnarayanan7 posted this 09 December 2018

Hello! Yes, this explains my issue. My intent is to get moving dynamic load so I would try the same in transient dynamics. Thanks

peteroznewman posted this 10 December 2018

Dear Harish,

Great!  Please click Like below the posts that were helpful and click Is Solution below the post that best answered your question.  Open a new discussion if you need more help.

Regards,
Peter

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