Stress in voice coil actuated system. What type of analysis?

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  • Last Post 05 September 2018
Yannick posted this 03 September 2018

Hello,

I have a flexure mechanism that contains a voice coil actuator, very similar to a speaker. Some parts of the mechanism are grounded by a fixed support, others are moved by the actuator. I want to calculate the stress in the system during the applied dynamic load. The force input is available in the time domain 4kHz (10sec) and can easily be converted into a spectrum (FFT) or PSD curve. What type of analysis do I need to perform? Spectrum analysis only allows the load to be applied at the boundary conditions as a,v,d. But I have a force and don't want to apply the load into my fixed supports. Transient would work but my model is complex and has many elements so that a transient is not appropriate even when only analyzing a second of my 4kHz signal. A harmonic analysis allows to apply a force, however I'm not looking for the stress at a specific frequency but the stress caused by the whole spectrum. What type of analysis do you recommend?

Thanks

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peteroznewman posted this 03 September 2018

Hello Yannick,

If you want to apply a force to the coil structure in the model, then you have to go with Transient Structural.

When you say the force input is available in the time domain, I assume the 4 kHz refers to the sampling frequency. A minimum of 10 samples per cycle are required for transient time history loads, so you should not see frequencies in the data above 400 Hz. An FFT on the signal will show you how much frequency content is above 400 Hz.

If the moving mass is easily calculated, then you could convert the force to an acceleration and apply an acceleration load to the mass and reap the benefits of using a linear analysis method called Random Vibration where you could take the PSD of the acceleration load and apply that to the model. I have some experience converting a time-history signal into a PSD so if you want to attach a zip file to your reply with a spreadsheet or text file of the force time history, I will take a look at it.

Though you say "I'm not looking for the stress at a specific frequency", once you have that linear system, it may be worth looking at a Harmonic Response, since it quick to do and you may learn something useful.

Regards,

Peter

sk_cheah posted this 05 September 2018

Hi Yannick,

Spectrum analysis only allows the load to be applied at the boundary conditions as a,v,d.

Perhaps PSD which allows F for nodal excitation would work for you. This may possibly be pursued as an interim step to identify high stress area for the CMS described next. 

Transient would work but my model is complex and has many elements so that a transient is not appropriate even when only analyzing a second of my 4kHz signal. 

I agree Mode-Superposition Transient Dynamic Analysis is the right path. Perhaps look into Component Mode Synthesis to represent all parts except for the high stress areas. 


Kind regards,
Jason

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