Shear Panel Modeling in NASTRAN

Question

Shear Panel Modeling in NASTRAN

kilbchoi (Aeronautics)

(OP)

17 May 02 11:12

Hi guys!
Anybody who let me know the modeling way using CSHEAR element? As u know, spar web can be modeled with that element very often for simplicity based on conservatism in aerospace industry. I tried it comparing with the other elements, membrane and plate, but I got a strange result for CSHEAR element in deflection!.

Hope to get valuable comments.

Thanks

zuardy (Aeronautics) · Answer 1 · 2002-05-18 02:29:37

CSHEAR is used in the region, where the bending or axial membrane stress is negligible compared to in-plane shear stress, because it supports shear stress in its interior. It can be seen from the "shear stress diagram" of any wing box, that the spar web is mainly loaded by shear stress, so it SHOULD be modelled with CSHEAR in stead of CQUAD. Of course, it CAN be modelled with CQUAD (plate/membrane) but, it may result in an overly stiff model, like what you got.

cheers.

kilbchoi (Aeronautics) · Answer 2 · 2002-05-21 14:52:05

Hi zuardy,

Thank you for your reply.

The more detail explanation about my question is

  - On the data sheet of PSHEAR,
  - Effectiveness factor for extensional stiffness along edges,
    F1, F2
  - Varying the above two factors, from 1.0 to 0.0,
     the lower value is the more flexible as we expected. But the
     thing is the singularity is occured at 0.0 which is default one.
     As u know, the modified Nastran introducted additional axial
     stiffness term in CSHEAR element with those factors.

I am not sure of that factors, shall I minimize the magnitude of
the factors, 0.001, to return to purely shear element property?

Expect to get your experince.

Thanks,

zuardy (Aeronautics) · Answer 3 · 2002-05-22 06:11:18

oic,
you mean, you didn't variate the element types but only the shear element property, right?
Yes, MSC/NASTRAN has introduced F1 and F2 in representing an effective siffness of the panel by means of equivalent rods (bars) on the perimeter of CSHEAR element. You are right, that for F1 and/or F2 equal 1.0, the panel is fully effective. So if you set the value 0.0, then this axial stiffness would be ignored. The singularity of course depends on the loading conditiion of the wing. If there exist extensional loads (e.g manouvering or flaps/aeleron deployed) then this axial stiffness should be activated.
I have got wing models from static people. They have build this shear panels with two methodes, 1. By setting F1 or F2 to 1.0 or 2. Ignoring the value of F1 and F2, but building CROD or CONROD on the perimeter of the CSHEAR.
I would prefer this last methode to setting the F1 or F2 with value 0.001.
Hope this would help you.

regards

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Shear Panel Modeling in NASTRAN