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How to verify correctness of static analysis run with inertia relief (INREL,-2)?

Hello,
 
I run a static analysis (SOL101) using the parameter INREL,-2.
My structure has 6 rigid body modes + 1 mechanism mode in dof 6 (mode at 0.06 Hz with modal effective masses = 0 in all dof)​.
On the Natsran QRG I see that if the structure has more then 6 rigid body degrees of freedom, the analysis with INREL,-2 will give incorrect results.
 
So how do I verify that my mode at 0.06 Hz is not causing any trouble? (Of course I could run the same analysis blocking the mechanism dof and comparing the results, but since the run takes a while I would prefer to try first some other verification approach, if any).
 
What I tried up to now is checking the OLOAD Resultant.
If I apply a pressure of 1000 Pa to a surface (only in X direction for example), in the OLOAD I should see the total force applied (so Pressure*Area) in the direction of application (X --> T1), right?
What I see however are also components in R2 and R3 (R2 has the same order of magnitude as T1, R3 one order of magnitude lower).
 
Any help will be really appreciated.
Thank you!
Parents
  • The Inertia Relief capability is described in the Linear Static Analysis User Guide... this can be found here:
     
     
    In the Guidelines portion of the Inertia Relief section, it has item 4 listed below:
     
    "Inertia relief is not recommended on models with extra mechanisms or unconnected parts with mass,
    with > 6 zero Hz modes. INREL = -1 will fatal with suports > 6, and INREL = -2 with auto-suport
    will fatal or give unreliable results."
     
    So, it is our position that you should not do this with mechanisms in the model.
     
    Please review the appropriate section of the documentation for additional details.
     
     
     
     
Reply
  • The Inertia Relief capability is described in the Linear Static Analysis User Guide... this can be found here:
     
     
    In the Guidelines portion of the Inertia Relief section, it has item 4 listed below:
     
    "Inertia relief is not recommended on models with extra mechanisms or unconnected parts with mass,
    with > 6 zero Hz modes. INREL = -1 will fatal with suports > 6, and INREL = -2 with auto-suport
    will fatal or give unreliable results."
     
    So, it is our position that you should not do this with mechanisms in the model.
     
    Please review the appropriate section of the documentation for additional details.
     
     
     
     
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