Wing deflection analysis. Having issue with load distribution

[Ash_w1]

Hello!
I am conducting a wing deflection analysis on an aircraft wing. the wing skin and spar were modelled in abaqus as separate parts. they were then assembled together using tie constraints. The ribs for the wing were defined as MPC beam constraints.

I applied a pressure load on the bottom surface of the wing skin between reference point 11 and 13 which are ribs 18 and 17. both the spar and the wing skin have been defined as shells.

The major problem I am facing is that the pressure load is acting on one concentrated part of the applied surface instead of spreading out throughout the whole wing. this is causing the wing skin to fold in like a blanket. I believe this is to do with how the wing skin is constrained to the rest of the assembly but I'm not too sure. I am working in SI units (mm, tonne/mm^3, etc).

I have included an image of what's happening. If anyone can shed light on what is happening I would greatly appreciate it. Thank you!

 

[FEA way]

Indeed, it can be a problem with connections. Try running modal analysis to check them.

 

[Ash_w1]

I believe it's an error with how i've defined the skin. in the property section, i have defined an area of the model to be a skin. I have applied a shell homogenous section property to it. however, when i go to run the job, ABAQUS says there is no section assigned to the skin area. Do you know anyway to fix this? Thanks!

 

[FEA way]

Do you mean that you used the Create Skin option ? Is it really necessary in your case ? It’s used to model an additional reinforcing layer on the surface of a part. When assigning a section to it, one should set the selection mode (drop-down list next to the cursor symbol) to Skins.

 

[Ash_w1]

I did use the create skin option. I managed to add a section to it however I realize now that it just added more stiffness to the wing.

Im afraid the modal analysis didn't help either. I've got no clue on how to proceed with this.

Surely there is a way to ensure that the pressure force does not concentrate on that one area and cause the shell section to bend like that. If the force were to rather push the wing up and bend the whole thing upwards rather than fold the skin inwards the analysis would be realistic.

I'm not certain how to constrain the skin section to not deform the way it does but rather ensure the force applied is completely utilized in bending the wing in the y-axis. If you have any suggestions it would be of great help. thank you for your time so far.

 

[FEA way]

If you check the mode shapes from modal analysis, is there no indication that something becomes separated from the model or that some region has much lower stiffness and thus its deformation dominates in some modes ?

What if you remove the skins or apply the pressure to a different region ?

 

[SWComposites]

Well, what actual airplane wing only has pressure over a short section of the span??

Of course, the applied pressure is just flexing the local skin. Nothing wrong with the FEM. The loading is wrong.

And using MPCs for rib is likely to result in very incorrect internal loading. Model them properly with shell elements.

And why would you not model the skin and spar with common nodes rather than messing with tie constraints?