Training Module #10: Stiffened Panels

The word "smeared" refers to a modeling technique applied to stiffened panels in which the representative stiffnesses of each stiffener is "smeared" into the overall panel stiffness formulation (ABD Matrix). This is done by extending the assumptions of Classic Lamination Theory (CLT), namely: plane sections remain in-plane after bending. For more information, see Panel Stiffness Formulation.

Smeared Stiffened Panels are particularly useful for preliminary trade studies and Sizing. Compared to discretely modeling stiffeners in the FEM, smeared models are much easier to construct. There is less labor involved in meshing because the grids do not have to be aligned with the stiffener spacing. These models are typically a lot more coarse, and therefore also see benefits when it comes to FEA Solve and HyperX Size times.

There's also no change in the HyperX Sizing and Analysis workflow between Smeared Stiffened Panels and simple panel designs. That means you can easily swap all designs and dimensions on the fly, even allowing multiple panel designs to be considered at once, without remeshing.

To discretely model a Stiffened Panel is to represent stiffeners with finite elements. The primary advantage of discrete models is that unique stiffener buckling, crippling, strength, and local buckling margins of safety may be reported for each skin and stringer segment component. In HyperX, Panel Segments are used to correspond to these components during analysis.

The Panel Segment Analysis Entity allows HyperX to properly recognize discretely modeled skins and stiffeners as part of a collective system, rather than individual Zones. This allows Design Results and Margins of Safety to be calculated per object within the Segment (left skin, right skin, and stiffener).

In order to be combined into a Panel Segment, the Zones corresponding to the related panels and beams must be in the same Structure. As with traditional Zones, Panel Segments require Design, Load, and Analysis Properties in order to define the Sizing/Analysis. But, since a single Panel Segment consists of 3+ different entities (left skin, stiffener, right skin), that assignment process looks a little different. An example is shown below - taken from the Tech 2 Blade Sample Project.

The loads processing for Panel Segments works a little differently as well - since the loads-sharing between skin and stiffener elements must be properly applied over the cross-section. The image below summarizes this process. Note the skin element orientations, as it is important to have those consistent with the stiffener axial direction.

The HyperX install contains 4 different Sample Projects to serve as reference for setting up a stiffened-panel analysis – technique and concept dependent. These Sample Projects can be opened from the initial ‘Start’ window as indicated.