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Rex

Fatigue simulation in frequency domain

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Dear,

I am trying to use Optistruct to run random response simulation in frequency domain, then to run the fatigue simulation by using the stress PSD, but I noticed that the fatigue in Optistruct only supports in time history, am I right?

 

Thanks in advance! 

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You can also run fatigue in frequency domain.Currently sine sweep and random response fatigue is available with OptiStruct 2017.2.2 or higher version.

Please search with keyword sine sweep and random fatigue, you would get many relevant material for this topic in Support forum.

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10 hours ago, Rex said:

Dear,

I am trying to use Optistruct to run random response simulation in frequency domain, then to run the fatigue simulation by using the stress PSD, but I noticed that the fatigue in Optistruct only supports in time history, am I right?

 

Thanks in advance! 

 

Hi Rex, 

 

For curiosity, why you want to perform fatigue simulation in frequency domain ?

 

Best regards, 

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On ‎10‎/‎21‎/‎2019 at 11:22 PM, Rahul R said:

You can also run fatigue in frequency domain.Currently sine sweep and random response fatigue is available with OptiStruct 2017.2.2 or higher version.

Please search with keyword sine sweep and random fatigue, you would get many relevant material for this topic in Support forum.

Thanks for your feedback, I will check it!

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On ‎10‎/‎22‎/‎2019 at 1:41 AM, Farouk Maaboudallah said:

 

Hi Rex, 

 

For curiosity, why you want to perform fatigue simulation in frequency domain ?

 

Best regards, 

Hi Farouk,

Sorry for late replying, just came back from a business trip.

To you question:

I want to do the fatigue simulation in frequency domain because that usually the OEM will ask you to use the ASD&test time in different direction to check whether the parts will be survived, in this case, it makes no sense to change the input to time history.

In other side, fatigue simulation in time domain takes much long time than frequency domain.

If I am wrong, let me know. thanks!

 

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On ‎10‎/‎21‎/‎2019 at 11:22 PM, Rahul R said:

You can also run fatigue in frequency domain.Currently sine sweep and random response fatigue is available with OptiStruct 2017.2.2 or higher version.

Please search with keyword sine sweep and random fatigue, you would get many relevant material for this topic in Support forum.

Sorry Rahul, I did not find something about random fatigue simulation in frequency domain.

I know that Optistrut can run random response simulation, then we can get the Stress PSD in frequency and RMS, but how can we use this information to calculate the damage factor in optistruct?

The theory will be use the 1 sigma stress(RMS), 2 sigma stress & 3 sigma stress and the cycles at different stress level to calculate the damage, then sum the sub-damage at these levels to get the total damage in all the elements.

Hope you can give me more information, thanks!

 

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Refer below video for fatigue in Frequency domain using OptiStruct.

https://www.altair.com/resource/extending-the-life-of-products-with-simulation-playlist?weight=4

 

Attached fem file for Sine sweep and Random response fatigue.Refer OptiStruct online help for more details.

sine_seep_fatigue_spring_link_done.fem frame_frf_PSD.fem

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12 hours ago, Rex said:

Hi Farouk,

Sorry for late replying, just came back from a business trip.

To you question:

Thank you for your answer :) 

 

12 hours ago, Rex said:

the ASD&test time

What do you mean by ASD* ? 

 

12 hours ago, Rex said:

In other side, fatigue simulation in time domain takes much long time than frequency domain.

Yeah sure.

 

12 hours ago, Rex said:

If I am wrong, let me know. thanks!

Im just asking in order to learn from you. Thank you again ;) 

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On ‎10‎/‎25‎/‎2019 at 5:26 PM, Rahul R said:

Refer below video for fatigue in Frequency domain using OptiStruct.

https://www.altair.com/resource/extending-the-life-of-products-with-simulation-playlist?weight=4

 

Attached fem file for Sine sweep and Random response fatigue.Refer OptiStruct online help for more details.

sine_seep_fatigue_spring_link_done.fem 1.93 MB · 3 downloads frame_frf_PSD.fem 3.51 MB · 2 downloads

Hi Rahul,

Thanks for your model, now I know Optistruct can deal with fatigue in frequency domain, it will take me sometime to check the cards, meanwhile the PSD model you attached in here is not a fatigue model. I will try to find out how to do random fatigue by myself!

Have nice day!

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On ‎10‎/‎26‎/‎2019 at 3:13 AM, Farouk Maaboudallah said:

Thank you for your answer :) 

 

What do you mean by ASD* ? 

 

Yeah sure.

 

Im just asking in order to learn from you. Thank you again ;) 

1) ASD is Acceleration spectrum density, it always with the unit (G^2/Hz) in X direction and Hz in X direction, and it tells how much the acceleration will be in 1sigma level.

2) If you want to know why I want to run the random fatigue in frequency domain, you can search on google, they explain it better than me. For me, I would say do the random fatigue in time history is a very time-consuming work, and usually if you want to know the random input in a better way, you need enough acceleration data in time domain. Meanwhile, if you see the acceleration input on time history, sometime it does not help you too much, but in the frequency you could find which frequency is more important.... oh, by the way,by using Miner rules, we can even get the total damage considering different acceleration inputs(like the acceleration on the air intake manifold can be caused by engine and road together, it's difficult for us to consider the fatigue in time history...)

Please learn more on this topic by using google or here, all these answers are based on my understanding, if I am wrong, just let me know!

Thanks!

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