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[chiheb ben abdallah]

hello, i performed a transient structural anlysis  where i applied a vertical force with a random variation over time on a semi trailer axles, i want to get the deformation and stress results vs frequency not vs time to investigate the effects of resonance on the structure. can anyone help me .

N.B: i used a MSUP method

thanks in advance.

 

 

[peteroznewman]

Hello,

You did not apply a random vibration, but a specific force-time history. This force-time history data has a time step of 0.1 seconds or a sampling frequency of 10 Hz. This is too slow/low of a sampling rate to be useful. Where did this force-time history come from?

I have mounted accelerometers onto a structure and recorded acceleration-time history. If I am interested in using this data to simulate vibrations in a Transient Structural model where the highest frequency of interest in the structure was 400 Hz, I should use a sampling frequency 20 times higher or 8000 Hz to have good input data for Transient Structural simulations.

With data sampled at 8000 Hz that has a random vibration characteristic, I can convert the acceleration-time history data into Power Spectral Density (PSD) vs Frequency.  I can then use that as input data in a Random Vibration analysis.

A Random Vibration analysis block needs an upstream Modal analysis block and the Solution cell of the Modal is linked to the Setup cell of the Random Vibration analysis.  The requirement is that you include enough modes in the Modal to reach at least 1.5 times higher than the highest vibration of interest. There are other requirements too.

I recommend you take the dynamics courses on Modal and Random Vibration that are in the Learning section of this site.

/courses/index.php/courses/intro-to-modal-based-methods/

/courses/index.php/courses/random-vibration-analysis/

[chiheb ben abdallah]

Thanks Peteroznewman, 

The time history force are simulation results extracted from a software called trucksim where an event of a semi trailer vehicle traversing a bumpy road has been simulated, this was done because an experimental test procedure could not be done. 

Can you please explain to me how to convert the time history force data into psd vs frquency

Thank you 

[chiheb ben abdallah]

Thanks Peteroznewman,

the time history force time history are simulation results extracted form a software called trucksim where an event  of a semi trailer vehicle traversing a bumpy road has been simulated, this was done because an experimental test procedure could not be done to get the required data

Can you please explain to me how to convert a force time history  data can be converted into a psd vs frquency.

Thank you 

[peteroznewman]

Tom Irvine provides free matlab scripts at Vibrationdata that will do many things including converting a time history into a PSD. If you don't have matlab, he also provides a stand alone program.

[chiheb ben abdallah]

Thanks Peter, 

One last question, I don't have the acceleration time history, I have only the force time history, can I use that in a random vibration analysis or should I use another dynamic analysis system, the goal is always to investigate the effect of the resonance phenomen.

 

[chiheb ben abdallah]

can you help me with that ?

[peteroznewman]

The PSD type can be displacement, velocity, force, pressure, or acceleration.  However, only acceleration and displacement input are supported in the Workbench interface. To use a force PSD input to a Random Vibration analysis, you will need to use some APDL code.  I can't help you with that, someone else will have to help with that.

If the only data you have is what you show in your original post, the time interval of that data is inadequate to use in a Random Vibration analysis.

[chiheb ben abdallah]

thank you,

but i want to investigate the resonance effects and i only have this data.is there a way to do that? 

[chiheb ben abdallah]

hello peter, 

i'm using the vibration data standalone system to convert an acceleration time history to psd. 

is there an easy way to convert excel worksheet to an ascii file ? 

[peteroznewman]

The trucksim data is inadequate to generate a useful psd because the sampling frequency is much lower than required.  Have you done a Modal analysis of your structure?  What is the frequency of the first mode?

Instead of trucksim data, use a published psd table for truck transport on a rough road. I expect you could find that on the internet.

The easy way to convert an excel worksheet to an ascii file is to Save As a Comma Separated Values (.csv) file type.