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Hi,

I am currently performing random vibrartion analysis, where I have sweep up PSD data for muffler.

I have some query mention below:

1)From testing, I got PSD data  (G^2/Hz  vs  Freq) . Do I have to change it into { (mm/sec2)^2  vs freq}.

2)when I am giving the input in (G^2/Hz  vs  Freq) and FRF excitation as 1 , then PSD stress is very very less e-7.

3)Plz suggest the appropriate methodology step by step for providing -  input (in which form) and post-processing method to interpret results (which stress is useful).

 

Thanks in Advance

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Since all the results are complex you cant use standard calculation for vonmises stress because it is phase dependent. So at any loading frequency at any element you have 360 degree sweep of the vonmises stress. So you have to calculate the maximum value of that 360 degree sweep and there is method called segalman method to do that in HyperView.

Set the global output request "STRESS(H3D,BOTH,CORNER,RMS) = YES"

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Hi Rahul,

 

I am simulating random vibration in optistruct. I have input psd in (m/s^2)/Hz, model content in mm, output required is stress in MPa. I submitted 1 run and  i am getting high stress(RMS stress over frequencies) which are not realistic. Unit excitation is 9810 (SPCD) and I have submitted another run with unit excitation 1 (SPCD), here i am getting very low stress which is not realistic. Can you suggest me the right procedure. I guess i have mistake in unit conversion. If anyone having dummy procedure file please share me. 

and one more my stresses should not be higher than endurance limit (criteria). Stresses whatever i am checking is the right one to compare with endurance limit ?? 

 

Note: Earlier i used to do in abaqus. recently we purchased altair software and trying to simulate in optistruct. Please help me. Your suggestion is very valuable to us.

Please call me if possible. here is my number 9019717355

 

Thanks you in advance

Capture_2.PNG

Aux_Converter_RV_4.fem

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On ‎10‎/‎3‎/‎2019 at 5:03 PM, Rahul R said:

Please refer to the best practices for random response analysis from Resource Library.

Random Vibration Best Practices.pdf 719.31 kB · 25 downloads

Hi Rahul,

 

Where I can find all these interesting presentations you attached above?

 

I am really interested with these!

 

Let me know, thanks! 

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15 hours ago, Rahul R said:

You can refer to below Altair Resource Library with keyword as random.

https://altairhyperworks.com/ResourceLibrary.aspx?keywords=random

oops, it's really difficult to download the presentations, I mean the download speed, is there a way to download all the Optistruct presentations in a more efficiency way?

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Hello everyone,

now I am facing with the problem of setting up an random response analysis. Therefore I have some questions…

1. The input data from testing is in acceleration [mm/s²] vs. time and my fe-model is in units of [mm], [tonne]. I have created in HyperGraph a curve for my frequency resonse analyse by using FFT --> Hamming. But how can I create the PSD-signal for my RRA in HyperGraph?

2. Further I want to achieve my results for stress in [MPa] and displacements in [mm]. So the unit of my PSD should be in [(mm/s²)²/Hz], I am right?

3. I have read that the TABRND in my RRA must have the LOG - LOG. Can someone please explain this?

 

Best regards Tommy

 

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On 3/11/2020 at 4:24 AM, Tommy said:

Hello everyone,

now I am facing with the problem of setting up an random response analysis. Therefore I have some questions…

1. The input data from testing is in acceleration [mm/s²] vs. time and my fe-model is in units of [mm], [tonne]. I have created in HyperGraph a curve for my frequency resonse analyse by using FFT --> Hamming. But how can I create the PSD-signal for my RRA in HyperGraph?

2. Further I want to achieve my results for stress in [MPa] and displacements in [mm]. So the unit of my PSD should be in [(mm/s²)²/Hz], I am right?

3. I have read that the TABRND in my RRA must have the LOG - LOG. Can someone please explain this?

 

Best regards Tommy

 

@Tommy

Hello, I try to answer you based on my knowledge, if I am wrong, please correct me!

1. I did not use the HyperGraph to do this, so I do not know, but I know there is a free software can do this convert, usually I will use Scilab or Smath to do this work, but you can use the vibrationdata made by Tom Irvine

2. Usually, the PSD used in the vibration test is log-log format, then we should use the same in the simulation, the log-log makes the PSD looks like linear, but they are not a straight line in the real, if you use linear-linear, the vibration energy will be reduced.

 

Hope it helps, keep in touch!

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