Multi-objective characterization of an inflatable space structure with a quasi-static experimental deflation and finite element analysis

Abstract

We propose a methodology for the multi-objective characterization of a light, single layer orthotropic fabric inflatable space structure. The presented approach focuses on a custom in-situ experimental quasi-static deflation, semi-empirical development of flow coefficients and structural integrity loss parameters as well as process validation with finite element analysis. The experiments are designed to investigate a collapse of a thin, deployable, one segmented inflatable structure caused by a simulated single leak and passive porous leakage through the fabric material. The acquisition of real time data with a custom designed standalone ambient conditions sensing platform and the wireless internal sensing unit furnishes pressures, temperatures, mass flow rates, dynamic strains and accelerations. Synchronously, geometric changes in the shape of the structure's representative area are recorded utilizing photogrammetry. The non-wireless and wireless outputs are treated with a series of smoothing, best-fitting and refining operations and combined with the corresponding sequence of active surface area photogrammetric results. The formulation of inflatable characterization parameters and a single leak/passive porous leakage structural integrity loss ratios allows for an in depth description of the inflatable structure behavior. A closer examination of the experimental data shows that the majority of the structural integrity loss ~97% is attributed to the sudden and relatively short leak due to puncture and the remaining ~3% to the slow and prolonged pressure loss caused by the passive porous areal leakage through the membrane. A semi-empirical framework based on a thermodynamic equilibrium produces sets of single leak, passive porous leakage and active area coefficients to be validated with the Ls-DYNA® finite element simulation of a polyurethane coated nylon fabric inflatable structure model. We use implicit and explicit fea of a control volume deflation to validate the aforementioned coefficient curves and constants. The subsequent comparison with the experimental internal temperature, internal pressure and mass flow rates results in a 1.83%, 0.61% and 1.19% difference respectively for the single leak events. The successive contrasting with the experimental internal temperature, internal pressure and active area produces 2.04%, 1.26% and 1.68% difference for the passive porous leakage respectively. We demonstrated that the multi-objective, structural integrity loss characterization techniques for the space structures have promising capabilities for the application in inflatable structures of diverse shapes and sizes.