  # Rex

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2. Hi Rahul, Where I can find all these interesting presentations you attached above? I am really interested with these! Let me know, thanks!
3. I also faced similar problem, but I just fixed, I know what is the problem you want to solve! In Optistruct help document, the format for the stress outputs is not given, so we will confuse with all these stress tensors, it also took me long time to understand the stress tensor during FRF simulation, below is my solution. 1) First of all, you need have the .pch file for desired element, all the stress tensors is shown in it, I already saw it in you picture 2) Then you can load the .h3d file in Hyperview, and hide all the element except the desired element. 3) Now you can plot the stress of this element (please keep the averaging method as none), then compare this contour plot result with your .pch file, by using this way you can understand the format of the stress tensors Hope this can help u!
4. oops, the attachment is failed to load in previous..... pch_calculation.xlsx
5. I already found the way to calculate the Von Mises Stress by using the Real & Imaginary stress tensor, if anyone is interested on this topic, you can find the attachment below. I am still working on the cycles counting in Optistruct!
6. Hi Rahul, Thanks for your answer, but I did not get your point! you only show me how to calculate the magnitude displacement in time domain, but how the Hyperview uses the 12 stress tensors to find the response Von Mises stress in time domain? To your 2nd answer, I know what you mean, you need calculate the time to increased to the top frequency, but how the software deal with the bottom frequency? and how will the software use the time to calculate the cycles? I mean the software will count all the time to the top frequency or 50% on the bottom frequency & 50% on the top frequency? For example: sweep rate 5Hz/min, bottom frequency is 5Hz, top frequency is 10Hz, so it takes 60 seconds to reach 10Hz. Then how will the software use this time to count the cycles? 10Hz*60s at 10Hz? or how? Thanks again!
7. Dear, I did a sweep calculation for a Degas Bottle, the frequency range is from 15Hz to 100Hz, acceleration level is 3g, when I got the response stress after the model frequency simulation, I outputted the stress tensor of the most critical element, but I found there are 12 stress tensor in the pch file, so how the hyperview use these tensor to get the plot stress? I could not find the way. Meanwhile, how the Optistruct calculate the damage based on the response stress, I mean how to calculate the cycles at interested frequency, I know the help document, but it doesn't tell too much. Thanks a lot! 20191202_GWM_B30_Degas_Bottle_LT_V5_Opt.pch
8. Hi Tommy, thanks for your answer if this is to my question. I will try on Monday, the MFLUID only supports for shell element, if I model the tank in solid, then it will be a problem apply the MFLUID on the mesh, I do not care about the eigenvalue of fluid, I just want to know the fluid influence on the tank. Thanks again
9. Hi Rahul, Always finding good feedback from you, one question from my side, may I use tet10 instead of 2D mesh then use MFUILD in it? or I must use shell element for the container? If the MFUID can only use on the shell element, may I put a very thin layer on the solid elements, then use MFUID on this thin layer? Thanks in advance!
10. I made a PSD fatigue model based on my understanding to Optistruct, but I do not know whether this is the right setting, I see the stress PSD and RMS stress is similar with Patran, but I am not sure about the fatigue damage results, is there someone who can help me to check? Thanks a lot! Notes: In my model, a simple beam is built, on the tip of this beam, a 0.2kg mass is added. Then the other end of this beam is fixed, and the PSD loads in here is 0.475G^2/Hz from 20Hz to 200Hz, this random test keeps for 4 hours. 20191028_Beam_PSD_FATIGUE.fem
11. 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!
12. 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!
13. 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!
14. 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!
15. Thanks for your feedback, I will check it!
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