Pre-Stressed Modal analysis

Altair Forum User
Altair Forum User
Altair Employee
edited November 2020 in Community Q&A

Hello,

 

I would like to perform a modal analysis of a helicopter blade while it is rotating at a constant RPM.

 

I have created two steps in hyper-mesh, first is a linear static with boundary conditions and applied a centrifugal force with the RFORCE card.

Second step is a normal modes step with the previous step linked through the STATSUB card and no boundary conditions or forces selected (free-free) modal analysis.

 

Whenever i run this, the first step works, however i get an error:

 

*** ERROR #  15 ***
 CTETRA element 252760 is distorted (zero or negative Jacobian).
  

I checked my mesh and i have no issues with the Jacobian or mesh at those indicated elements.

As a check, i've run both steps separately and both work and give good results. 

 

I don't know if this is the right way to perform such an analysis where the blade stiffness is changed by the centrifugal loading due to rotation.

 

Your help is appreciated.

 

Kind Regards,

Mohamed

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Answers

  • Altair Forum User
    Altair Forum User
    Altair Employee
    edited January 2017

    Hi Mohamed,

     

    Which version of HyperWorks are you using?

     

    I don't see the error you posted when I used the model file you shared in HyperWorks 14.0. Instead I see a different error and that is because your laminate has only one ply which is very thin. 

     

    Kindly update to HW 14.0 and try again :)/emoticons/default_smile.png' srcset='/emoticons/smile@2x.png 2x' title=':)' width='20'>

     

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