HS Orthogrid Panel Smeared Stiffened Analysis

[mjlafrenier]

Analysis approach: HS Orthogrid smeared stiffened panel
FE Modeling: Webs (CQUADS), Outer Cap (BAR elements)

1) Panel stiffener spacing and relationship with FE modeling:
- Example: Orthogrid (S_0&90 = 5", t_skin = 0.1", t_stiff_0&90 = 0.1", h_stiff_0&90 = 1", X_span = Y_span = 15"), Minimum unit for Geometry Rule 40 (3S)
- The panel is modeled with outer caps (outer flange, etc) using bar elements.
- Option 1: 3 stiffeners (Spacing: 1/2S,S,S,1/2S). If the smeared stiffened approach leaves a 0.5*S skin segment on either side, then I'm left with a row of half bay webs next to the outer cap. This is not ideal for fastener installation and may require us to carry extra weight as those 1/2*S bays are the same thickness as full sized interior bays, but are also supported by the outer caps.
- Option 2: 4 stiffeners (Spacing: S,S,S). The other alternative is to assume full bays and then the outer smeared stiffeners are coincident with the location of the bar element outer caps. This bay sizing is more ideal for design.
- See attachment. Do you have any experience or guidance with this scenario?


2) Panels with cutouts
- If a larger cutout is modeled in the FEM, is HyperSizer able to accommodate the cutout for global panel buckling, or would the procedure need to be to follow the smeared approach for a uniform panel and then analyze the cutout detail for stability using other methods (NASTRAN SOL105, etc.)?

3) High Aspect Ratio Panels:
- Since the geometry rule 40 requires width/spacing >= 3, is there a HS method to analyze an orthogrid panel with less than 3 stiffener widths in only one direction?
- Currently it seems as though one would have to either discretely model it and deviate from the smeared (type 1) approach, or analyze it as uniaxial stiffened panel along the long dimension.

[James]

The smeared sizing in HyperSizer assumes scenario 1 (0.5*S,S,S,0.5*S).
I understand that you'd prefer not to have 1/2 bay on each side.
I recommend to update the FEM with the stringers meshed-in, with bar elements, using the same spacing that HyperSizer determined as optimal. So model it as (SSSS). Then you can use the stringer segment (tech2) approach to size each skin pocket and stringer.

What is the size and shape of the cutout?
Is it within a pocket, bounded on all sides by stringers ?

Geometry rule 40 is a suggestion, to ensure that the smeared approach is more valid. If the panel is bounded on all sides by supporting structure, e.g. other panels, then I think it's okay to turn that rule off and size the smeared panel with fewer than 3 stringers.

[mjlafrenier]

Thanks James,

The cutouts would be bound by stiffeners and integrated into the orthogrid, but would be larger and span at least several bays. The shape will likely be a large slotted shape or circular.

Best,
Mike

[James]

In that case, I'd recommend modeling them in and using HyperSizer + Nastran Sol15 to size for buckling.

-James