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How to simulate two harmonic loads with different starting phases

Posted 3 lug 2021, 03:20 GMT-4 Structural & Acoustics, Acoustics & Vibrations Version 5.6 2 Replies

Zhaochong Cai
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Hi,

I want to study the vibration of a metal solid structure actuated by two harmonic vibrations. The two harmonic vibrations, which is the excitation source, are of the same frequency, but a temporal phase shift to each other.

To do this, I build the geometry of my structure, and set two bounday loads with each of them locating on where the excitation source is, and study in Frequency Domain. The subnode of Phase 1 under Node Boundary Load 1 was set as pi/3, so that the two loads have a temporal phase shift of pi/3.

But I didn't get what I expected, it turned out that the the two loads were of the same phase, but one load got the amplitude of A*cos(pi/3).

So my question is: Obviouly for COMSOL the load phase is NOT equal to starting phase of the harmonic load (when studying in Frequency Domain). But I am curious to know how can I do to simulate my case: solid structure excited with two harmonic source of different starting phases?

Thanks!

2 Replies Last Post 9 lug 2021, 03:53 GMT-4
Henrik Sönnerlind COMSOL Employee

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Posted: 3 years ago 5 lug 2021, 02:33 GMT-4

You did the right thing, you just had problems with the result interpretation.

The default is that the results are shown at the 'zero' phase. You can shift the phase for output through a setting in the dataset. Since the results from a harmonic analysis are complex valued, you can also work with the operators real(), imag(), abs(), and arg().

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Henrik Sönnerlind
COMSOL
You did the right thing, you just had problems with the result interpretation. The default is that the results are shown at the 'zero' phase. You can shift the phase for output through a setting in the dataset. Since the results from a harmonic analysis are complex valued, you can also work with the operators real(), imag(), abs(), and arg().
Zhaochong Cai
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Posted: 3 years ago 9 lug 2021, 03:53 GMT-4
Updated: 3 years ago 9 lug 2021, 03:55 GMT-4

Hi Henrik,

Thank you so much for your answer. It works well and finally solve my issues.

For any other Comsol learners who may have the similar problems, I summize the key issues I got when making it working:

In frequency domain study,

  1. The subnode Phase under Boundary load acts as the stating phase of the periodic load (e.g. Boundary load F and Phase Φ works as F cos (ωt+Φ))
  2. Results (e.g. mode shape, stress) are displayed at "zero" phase as default, and can be shifted in Datasets setting.
  3. To display the full harmonic behaviour of the results, use Animation and on its setting select Sequence type as Dynamic data extention (which means Frames vs phases) instead of the default Stored solutions.

Kind regards, Zhaochong

Hi Henrik, Thank you so much for your answer. It works well and finally solve my issues. For any other Comsol learners who may have the similar problems, I summize the key issues I got when making it working: In frequency domain study, 1. The subnode Phase under Boundary load acts as the stating phase of the periodic load (e.g. Boundary load F and Phase Φ works as F cos (ωt+Φ)) 2. Results (e.g. mode shape, stress) are displayed at "zero" phase as default, and can be shifted in *Datasets* setting. 3. To display the full harmonic behaviour of the results, use *Animation* and on its setting select *Sequence type* as *Dynamic data extention* (which means Frames vs phases) instead of the default *Stored solutions*. Kind regards, Zhaochong

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