Loads

This project uses the HyperSizer Free Body Diagram (FBD) tab for direct input of design-to loads. This is contrast to most other projects which obtain internal loads from FEA. In this example, simple equations were defined to calculate the design-to internal loads on the cylindrical Outer Mold Line (OML) panels of launch vehicle structure. For this type of structure, a design-space exploration was performed very rapidly without needing to build a FEM and applying corresponding aerodynamic pressures. 

There were two loadings considered. The ascent thrust load case causes pure uniaxial compression on the cylindrical shell. A wind gust causes shear and a bending moment in the stack, resulting in peak compression forces and in-plane shear. If the cylindrical structure also contained ringframes, then the Poisson’s coupling effect of the ringframes generate a small component of compression force transverse to the panels. This compressive transverse (–Ny) loading component was included with the primary axial compression (-Nx) load.

Excel spreadsheet load input

Instead, of using FEA, these two loadings were calculated in an Excel spreadsheet as a function of geometry input, then automatically fed into the FBD tab through HyperSizer’s Object Model.

The use of a spreadsheet also provided a convenient way to manage data and to generate unit weights and corresponding graphs automatically.