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Found 33 results

  1. Hello Everyone! I am doing a response spectrum analysis an like to retrieve a eigenvalues and vectors from normal modes analysis which has already done. I hav saved the eigen value using EIGVNAME = modes and EIGVSAVE = 100. The file is has saved as modes.100.eigv. While doing RSPEC, I retreived the eigv using EIGVRETRIEVE = 100 and same EIGVNAME. But Solving throws an error as, *** ERROR # 372 *** Number of MPC constraints in file modes.100.eigv 474 does not match current value 0. Can Someone figure it out . Thanks in Advance -RathinaVel
  2. A propeller shaft experiences opposing torques on its ends, while rotating. What types of analyses are generally carried out on a propeller shaft, apart from static, modal, fatigue? What are the reversing loads to be given in a fatigue analysis? (The only reversing force that comes to my mind is the shaft's self weight, acting sinusoidally. Are there any other reversing loads in a rotating shaft?)
  3. Guest

    Modal Analysis

    Hi Mr prakash, i'm student that doing my project on modal analysis, my situation now are it possible that I used the result from bending simulation from hyperform for modal analysis in hyperworks? hope hear your reply soon. warm regards syam sazani. MY.
  4. How to conduct Non-linear Modal analysis ?
  5. Is it possible to conduct Operational Modal Analysis (OMA) in Optistruct ?
  6. Hello, i want to reduce the dynamic stiffness of a rubber bearing by changing the geometry. I have an approximate idea of the "optimized" geometry of this rubber bearing therefore I created morphvolumes and changed the specified area (solid elements) by translating the handles. I saved these changes as shapes which are my design variables. I know that the optimum is between the initial model and the changed model. I want to do an optimization with optistruct to find the optimum. To reduce the dynamic Stiffness i need 3 responses and an equation (dont know another way so far). The calculation of the dynamic Stiffness is simple: Cdyn = Force/Displacement. First i defined an equation with the dequation-panel: F(x,y)=x/y --> where x is the "frf force (ELFORCE)" and y the displacement (frf displacement) which are two of the three responses. The Last response is "function" which includes the dequation and the other two responses defined before. I would like to minimize the response "function" (which is the dynamic stiffness). But it's not possible to create an objective which minimizes my response "function", i get following error: *** ERROR # 1812 *** Multiple responses are assigned to the DESOBJ objective function. A MINMAX/MAXMIN objective function definition with DOBJREF should be used instead. Number of responses = 1000 1) Do you know what the maximum number of responses is? (It's an frequency response analyis from 0 Hz to 3000 Hz with an increment of 3, thats why its 1000 responses (i guess)) . I created an obj reference "dobjref" which includes the response "function", then i created MINMAX objective.This works, and i can start the optimization but here i have some questions: 2) When i define the obj reference i can choose neg and pos reference. What can i do with these references? 3) I don't really know what this minmax function does. Does it minimize the maximum value of the equation? It is not my goal to minimize only the maximum value of the equation, it's rather minimizing the area of the function. 4) Is it normal that optistruct finds a solution after 2 iterations? I have two different shapes and i would expect that it takes a lot of time and iterations to find the optimum. I guess i did something wrong or forgot sth. Sry for asking so many questions and sry for my bad english. I thank you so much in advance. Regards, Fatih Uysal
  7. How to perform simulation (Nastran) on a system by applying a sinusoidal load of 0.1g which swept from 10-50 Hz which varies at rate of 1Hz/min ??? How to use the Time domain in solver deck? In Modal Frequency Response i don't use varying rate (1 Hz/min) . So please let me know how to apply the time here.....!!!
  8. Can we use symmetry in modal analysis? When I did with symmetry and without symmetry, I noticed huge difference in the first modal frequency. And this forum, advices against using symmetry for modal analysis http://www.eng-tips.com/viewthread.cfm?qid=333936 But my part is a simple plate where even the constraints are also symmetric. Can anyone adivce me on this. Thanks.
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