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    • Rahul Ponginan

      Please click here for a short but important announcement   03/26/17

      Dear Users Our Commercial and Academic users around the world can use these same forums here as before i.e. the Altair Support Forum , Commercial users from India with solver queries can go to the Solver Forum for India Commercial Users , Academic Users from India and AOC India Participants are requested to go to the Forum for India Academic Users and AOC India Participants , We will be tending to all queries in all the forums promptly as before, thank you for your understanding. 


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  1. FRF direct/modal - variable acceleration

    Thank you for the answer LKZ, yes it works like you said.
  2. Hi guys, I am reading the book "OptiStruct for Linear Dynamics" from Altair and trying to run direct and modal FRF analysis. If I apply a variable load all is good but I don't understand how to apply a variable displacement, velocity or acceleration. I defined the unit load as SPCD but I don't really understand the sentence on page 51 (see picture attached). It seems that I have to put a constraint on the node and direction that I want to excite. Can you help me?
  3. Pretension manager

    Hi all, I am exploring the Optistruct pretension manager capabilities instead of preloading the bolts in a "manual" way. Do you know if Optistruct iterates to find the right preload values starting from my input? Example: I need to apply a bolt preload of 20000N. Once applied, I calculate the sum of the gpforces on a section of the bolt and I find the total force to be 18000N. So I have to increase the input preload to 22000N to obtain an actual preload of 20000N. This is because of the elasticity of the components connected. Does Optistruct iterate starting from the input value to find the right preload value? As an additional question, is there a faster way in Hyperview to measure the gpforces on the section of the bolt? It is time-consuming exporting the value to excel to sum them all. Thank and Regards
  4. Plot eigenvectors

    Hi Raul, Thank you for the answer. I can't dowload the .fem you uploaded (I don't know why) but I would like to do something like in the picture that I am attaching (I took it from an old Nastran output). I want to see if my hand calculations are right on a few dof system.
  5. Plot eigenvectors

    Hi all, How can I plot the eigenvectors of a mass-spring system? I have a system like this: constraint ----spring-----mass-----spring-----mass-----spring-----constraint A 2 degrees of freedom system, in a modal analysis will output 2 eigenvectors. I would like to see the vectors in the output file along with the eigenvalues (it is only for educational purposes). How can I do it?
  6. Apply nodal displacement from saved eigevectors

    Hi Prakash, There is a technique to evaluate the stress on a component at its natural frequency without running a frequency response analysis. Clearly, it is an approximation since it does not take into account the damping effect. I want to investigate what the error is in terms of percentage. In order to do so, I need evaluate the normal modes of the component (it can be done by running a modal analysis). For each natural frequency (eigenvalue) there is a modal shape associated (eigenvector). I need to apply as "displacement load" one of the modal shapes found in the modal analysis. The eigenvector that I need to apply to the part should be normalized to the largest displacement of the eigenvector. Namely, the largest nodal displacement should be 1 and the other displacements between 0 and 1. There are 2 things that I am not able to do yet: 1) save the modal shape for a natural frequency (NORM=MAX may normalize the vector the way I need) 2) apply the shape vector obtained in point 1 to the structure Sorry if I didn't make myself clear in the first post. I can also make a little presentation to explain it better.
  7. Apply nodal displacement from saved eigevectors

    In few words I need to apply a static displacement to the nodes of the model. The displacement should be the normalized eigenvector a the first modal frequency. But I am still trying to understand how. The only thing that I have understood so far is that with RESVEC i can output the normalized eigenvector (see picture).
  8. Hi all, I need to apply a nodal displacement X to my model and evaluate the stress. The displacement X should be the nodal amplitude at a natural frequency normalized to the largest displacement (I can use NORM=MAX in the eigrl card) What I can't understand is how I can apply the nodal normalized displacements to the model to evaluate the stress. Maybe using EIGVRETRIEVE as input in "post>apply results" in Hypermesh?
  9. expression builder doesn't open

    I was just wondering if, like hyperview does, there is a function in the expression builder that I can use to extract the maximum VM stress between the 2 layers. Writing 2 distinct responses (for z1 and z2) would increase the computation time.
  10. expression builder doesn't open

    Hi Rahul, thank you for the prompt response. The problem is that 6.051e8 is greater than 4.55e8 and I need to extract the maximum stress. I understand that with 2D elements we have to check the stress at the top and bottom face. Why Hyperview, when plotting the VonMises, decides to pick the z2 one? I am tempted to say because it is the highest between the ones computed in z1, z2 and mid. But if in Hyperstudy I need the maximum VonMises stress, I need to input not one but 3 responses: 1) Resvect for vonmises Z1 2) Resvect for vonmises Z2 3) Resvect for vonmises mid because I can't know from start, during the design exploration, which one of the 3 will be the highest. Can you clarify that for me?
  11. expression builder doesn't open

    Hi Rahul, thanks for the video. I am using the same resvec function to extract the max stress value but there is a significant discrepancy with the value read in the .h3d file from hyperview (see picture attached). I also tried to compare the value using all the averaging methods but none of them match with the stress extracted.
  12. solid face offset

    Yes, it works! I had to set continuous offest (picture attached) Thank you.
  13. solid face offset

    Hi Q.Nguyen, Thank you for the answer. So it is not possible to offset a face without extracting it from a solid right?
  14. solid face offset

    Hi all, Can you suggest me what is the fastest way to offset a solid face in Hypermesh? In the picture attached I want to reduce the shank diameter for example.
  15. expression builder doesn't open

    Hi Rahul, Thank you for the video, i was able to create the DVs but I am still stuck on the same tutorial. I created the responses but I can't select all the nodes for the max_displacement response. It seems easy usiing the file assistant but I am on hyperstudy13.0 and I have to go through the expression builder. Maybe there is a sintax to use in the filter on the side of the request? (see picture attached) Something like N1000--N2000?