The Application of a New Material Porosity Algorithm for Parachute Analysis

This paper documents the simulation of parachute performance and the role of LS-DYNA in the design of parachutes at Irvin Aerospace Inc. It has long been known that fabric permeability is an important weapon in the arsenal of a parachute designer. In the careful balance of payload rate of descent and parachute stability, the permeability of the parachute material often plays a vital role. The substitution of an impervious material with a highly permeable fabric can turn a parachute from a wandering sloth into a plummeting stabilizer. An accurate consideration of fabric permeability has long eluded the parachute designer. The implementation of a penalty coupling method to describe the interaction of components defined by Eulerian and Lagrangian formulations permits the effect of fabric permeability to be accounted for within the coupling definition. The majority of this paper discusses the implementation of a new porosity algorithm that allows the effect of fabric permeability to be accurately assessed. Correct consideration of material permeability has existed within LS-DYNA for many years, however, these methods were only accurate for the applications originally conceived, namely the airbag. Although both parachute and airbag analyses investigate fabric structures, they differ in many respects, perhaps most significant is that the parachute designer is as concerned about the air that has passed through the parachute as he is with that remaining inside the parachute. Whereas the air that has passed through the airbag is of minimal concern to the automotive engineer. The influence of the air once it has passed through the structural medium can now be assessed within LS-DYNA. This paper provides a level of validation for the technique when considering parachute applications and discusses the importance of this breakthrough to the parachute designer.