Finite Mass Simulation Techniques in LS-DYNA®

This paper describes the development and results of numerical models describing parachute inflation behavior. The models were developed using Fluid Structure Interaction (FSI) techniques in the commercially available transient dynamic finite element code LSDYNA. Prior to 2009, FSI simulation methodologies developed at Airborne Systems had restricted analysis to the steady-descent phase of parachute operations. That is to say the modeling was performed in an infinite mass scenario, where the parachute does not influence the freestream air velocity; such models can be compared to tests conducted in a wind tunnel or during the steady descent phase of operation. Funding provided by NSRDEC in 2009/10 enabled Airborne Systems to develop a simulation methodology that is capable of assessing parachute performance in a finite mass scenario. Such a scenario enables the more complex inflation phase of a parachute to be investigated. In addition, the availability of experimental data, describing parachute inflation, has until recently proved limiting in quantifying the accuracy of simulation techniques. The availability of test data from a series of indoor vertical parachute tests conducted at the Space Power Facility at NASA Glenn Research Center Plum Brook Station provided an excellent means of code result validation. The experimental test set-up produced a sufficiently controlled and instrumented environment specifically developed for basic parachute performance data collection. The results of the modeling, discussed herein, compare favorably with the indoor vertical parachute tests, with good prediction of both inflation force and post inflation breathing frequency. The models were developed prior to test data reduction and analysis, and as such acted as a true prediction.