Modeling and Parameter Estimation of Spacecraft Lateral Fuel Slosh
Author: Yadira Rodriguez Chatman Title: Modeling and Parameter Estimation of Spacecraft Lateral Fuel Slosh Institution: Embry-Riddle Aeronautical University Degree: Master of Science in Aerospace Engineering Year: 2008 Predicting the effect of fuel slosh on spacecraft and launch vehicle attitude control systems has been a very important and challenging task and has been the subject of considerable research over the past years. Analytic determination of the slosh analog parameters has been met with mixed success and is made more difficult by the introduction of propellant management devices such as elastomeric diaphragms. The experimental set-up in this research incorporates a diaphragm in a simulated spacecraft fuel tank subjected to lateral slosh behavior. This research focuses on the parameter estimation of a SimMechanics model of the simulated spacecraft propellant tank with diaphragms using lateral fuel slosh experiment data. An experimental investigation was conducted to determine and measure the slosh forces response of free surface slosh and diaphragms in an eight inch diameter spherical tank. The lateral slosh testing consisted of the tank assembly partially filled with different liquids, for other tests, diaphragms were incorporated into the tank. The experiment results from different testing conditions were compared for estimation of unknown parameter characteristics that include the pendulum model stiffness constants and damping coefficients.
Experimental Investigation and CFD Simulation of Active Damping Mechanisms for Propellant Slosh in Spacecraft and Launch Vehicles
Violent motion of propellant in the tank due to inertial forces transferred from actions like stage separation and trajectory correction is termed as propellant slosh. If unchecked, propellant slosh can reach resonance and lead to complete loss of the stability of spacecraft, change the trajectory or increase consumption of propellant from the calculated requirements, thereby causing starvation of the latter stages. A spherical tank modeled for CFD simulation in ANSYS CFX software package considers free surface of the propellant exposed to atmospheric pressure. The propellant is hydrazine. Hydrazine being toxic and its properties being close to that of water, water is used as propellant for experimental study. For close comparison of the data, water is chosen as propellant in CFD simulation. The research is done in three phases. First phase is modeling of CFD simulation and validation of model by comparison to previous experimental results. Second phase is developing a damping mechanism and simulating the behavior by FSI model. Third phase is experimental development of damping mechanism and comparing the FSI simulation and experimental results. Various passive damping devices (diaphragm and baffles) and active damping device (frequency control) are compared in terms of their effectiveness in damping of fuel slosh.
Stereoselective interaction between the R enantiomer of warfarin and cimetidine.
The stereoselectivity of the pharmacokinetic interaction between warfarin and cimetidine was investigated in eight healthy volunteers. The warfarin enantiomers were given separately as single doses (15 mg) alone and during chronic administration of cimetidine (1 g day-1). Cimetidine did not interact with S warfarin but there was an interaction with the R enantiomer of warfarin. Cimetidine caused a significant increase in the mean plasma half-life of R warfarin (from 47.8 h to 57.8 h) and a significant decrease in its mean plasma clearance (from 2.3 to 1.7 ml h-1 kg-1) (P less than 0.02). Administration of a pharmacological dose of vitamin K1 together with the enantiomers of warfarin was necessary clinically and resulted in elevation of vitamin K1 2,3-epoxide concentrations, which were similar in each case.