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  1. 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
  2. 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!
  3. 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
  4. 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!
  5. 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!
  6. 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!
  7. 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!
  8. Thanks for your feedback, I will check it!
  9. 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!
  10. It's really hard to say if you did not upload a model to show how you build the model.
  11. Thanks Rahul, I will take a look on this! Meanwhile, I am modeling a FR simulation in Optistruct, then I will compare with the old results!
  12. Dear all, In my company, we are using Nastran and Patran to do frequency response simulation and random response simulation, but I see that Optistruct could do the same, did any one have a comparison between the two software? I mean whether the response stress/acc/dis is same in a more complex situation. Looking forward to your answers. Thanks!
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