Characterization of Sinusoidal Vibration Induced Fluid Motion in Spherical Elastomeric Diaphragm Tanks
Elastomeric diaphragm tanks are commonly used in spacecraft applications to incite positive expulsion of hydrazine monopropellant. The diaphragm exhibits low flexural rigidity, causing it to easily fold under its own weight at low fill levels. If the tank is sinusoidally oscillated under standard gravity, such as during ground transportation or launch pad winding, these folds will result in rubbing, eventually wearing down the thin material to the point of failure. The ability to accurately predict the presence of folds, rubs, and center of gravity shifts for a given tank design and frequency excitation is thus of critical importance to mission reliability, safety, and success. It is the objective of this thesis to determine the controlling aspects and parameters of the tank assembly which contribute to deformations and their functional relationship to the deformations, to validate this model, and to create a design evaluation method to ensure that the risk of diaphragm rubbing is mitigated. The current work proposes and implements an analytic technique to determine the governing parameters of the fluid-tank assembly as well as a computational scheme based on the inextensibility of the diaphragm and dominant parameters of the fluid phase to provide a highly efficient simulation of the fluid-structure interaction for the purposes of iterative design. Additionally, the current work develops an experimental framework for the validation of computational models and future tank designs, allowing for the complete characterization of the fluid distribution via analytic, computational, and experimental means. The computational model shows strong correlation with experimental data and is limited in generality only by the required spherical shape of the tank. This work can be expanded to allow other tank and diaphragm geometries to encompass all elastomeric diaphragm tank designs by developing abstract structured meshing techniques. This will serve to reduce development costs and increase confidence in mission success for al diaphragm tank-based spacecraft.