Over the past year, the Structural Dynamics and Loads Branch of Marshall Space Flight Center has been calculating prelaunch ground winds for several different launch-vehicle configurations. Engineers developed a computer programming system to streamline the analysis cycle.
This documented procedure, known as Automated PreLaunch Loads Estimation (APLLE), uses a spreadsheet, word processor, and FORTRAN computer programs to provide quick and accurate load estimations. APLLE can easily be adapted for structures other than launch vehicles.
APLLE combines the input of structure geometry (width and height), a reference peak-wind value, a reference altitude and density, and an estimated drag-coefficient value based upon the shape of the structure. With these inputs, APLLE calculates a concentrated load, cumulative shear, and bending-moment values for a set of discrete points. The spreadsheet macro provides rapid diagrams of shear and moment. Additionally, pressures are extrapolated from the concentrated loads to form a pressure field that can be applied to a finite-element code.
For a free-standing structure, wind loading is the only forcing function other than gravity acting on the vehicle. Calculation of these wind loads assumes the wind load acts as a steady-state load.
Wind loading is divided into two parts: the drag load and the vortex-shedding load. The drag load is assumed to act parallel to the wind vector, and the vortex shedding acts normal to the wind vector. An uncertainty factor of 1.5 is applied to the wind loads to account for vortex shedding and gusts.
This work was done by Samuel B. Fowler and Joseph Brunty of the Marshall Space Flight Center. MFS-31149