General Mechanical

General Mechanical

Analysis settings in mode superposition transient analysis of a turboexpander model

    • shantashreejena97
      Subscriber

      Hii Everyone, 


      I am doing Transient analysis of a turboexpander model. But I couldn't know what will be the exact analysis settings for this analysis. Below is my model, analysis settings(which I have given randomly), graph and mode shapes(which I got from modal analysis) . can anyone tell me what will be the correct settings for the rotational velocity of 240000 rpm? I have also taken displacement about y-axis in the sleeve as zero.


      Model



      Analysis Settings



      Graph



      Mode Shapes


    • jj77
      Subscriber

      You do not have a force (except of grav.) in your transient?


      (In your graph you are seeing the first mode excited perhaps by gravity).


       


      What is the purpose of the transient analysis, that is, what are you trying to do?


       


       

    • shantashreejena97
      Subscriber

      Thanks for your reply jj77. I have only rotational velocity and grav as parameter. I want to know the total deformation wrt time. In harmonic I gave remote force but this cant be applied here and except these, I don't have other force parameters. Is any other force necessary to do transient analysis? 

    • jj77
      Subscriber

      I am not an expert in rotor dyn., but I am not sure what you want to study.


       


      Neither rotation or gravity are transient loads.


      Look in the the link I sent you, for rot. dyn. because as far as I understand rotational velocity is there to generate the Campbell diagrams and to introduce all the gyroscopic effects that come in the damping and stiffness matrices (used in the modal analysis), but it is not a load.


       


      To see examples  of transient rotor dynamic analysis see the same link in your previous post, under examples, there are more than 5 there.

    • shantashreejena97
      Subscriber

      Sorry for the late response. I have made a little change. I have added a sinusoidal time-dependent force of magnitude 1000sin25132.7*t where 25132.7rad/s is my rot vel. I got 2 peaks within the range of 6s but these two are of same amplitude rather than decreasing amplitude. To get a stable system I need the amplitude should be is in decreasing order. What will I do to get the desired result? below is my analysis settings, force graph, and the graph of total deformation.


      graphical representation of force:



      graph of total deformation wrt time:


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