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.
Modeling, Simulation, and Parameter Estimation of Lateral Spacecraft Fuel Slosh
Predicting the effect of fuel slosh on a spacecraft and/or launch vehicle attitude control system is a very important and a challenging task. Whether the spacecraft is under spinning or lateral moving conditions, the dynamic effect of the fuel slosh will help determine whether the spacecraft will remain on its chosen trajectory. There are three categories of slosh that can be caused by launch vehicle and/or spacecraft maneuvers when the fuel is in the presence of an acceleration field. These include bulk fluid motion, subsurface wave motion, and free surface slosh. Each of these slosh types have a periodic component that is defined by either a spinning or lateral motion. For spinning spacecraft, all three types of slosh can play a major role in determining stability. Bulk fluid motion and free surface slosh can affect the lateral slosh characteristics. For either condition, the possibility for an unpredicted coupled resonance between the spacecraft and its on board fuel can have mission threatening affects. This on-going research effort aims at improving the accuracy and efficiency of modeling techniques used to predict these types of lateral fluid motions. In particular, efforts will focus on analyzing the effects of viscoelastic diaphragms on slosh dynamics.
Liquid motions in nonaxisymmetric, partially filled containers rotating at zero gravity
Sloshing and internal wave motions of liquid in rotating wedge-shaped tanks are studied. The tank cross section is composed of a cylindrical annulus with sidewalls that are radial rays. The axis of rotation is the axis of the cylinder. The liquid is inviscid and incompressible. Closed-form solutions are obtained for the full three-dimensional flowfield, as well as for the limiting cases of axisymmetric and two-dimensional cylindrical containers. Two kinds of oscillating motions are found. For motions that are completely internal (i.e., have no oscillation of the free surface), infinite families of discrete frequencies were predicted, with all frequencies being less than twice the rotation frequency. For oscillations with frequencies greater than twice the rotation frequency, each harmonic supplied one or two characteristic sloshing modes (i.e., having an oscillation of the free surface), depending upon the geometrical parameters. These solutions should prove useful in validating approximate theories for situations in which an exact analysis is not possible.