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.
Dynamic Modeling and Controller Design for a Space Vehicle with Fuel Sloshing
This paper is dedicated to modeling of fuel sloshing dynamics and its effect on the stability and control of the space vehicle. Sloshing due to the liquid movement in the fuel tank of a space vehicle's propulsion system can be effective on the vehicle’s control and stability. Force and moment interaction between fuel sloshing and space vehicle’s control system will be appeared as a feedback in the control system. Analyzing of a rigid body's equations of motion is simpler in comparison with a fluid dynamics equations which can be led to reduction in computational efforts. Consequently, it is possible to apply a mechanical model instead. So in this paper fuel sloshing is modelled as a linear mechanical system to investigate its effect on the stability and control of the vehicle. For this purpose, two mechanical models, mass-spring and pendulum systems, are applied to model dynamics of a space vehicle with fuel sloshing and each system’s parameters are evaluated for simulation of dominant sloshing modes. Nonlinear dynamic equations of both systems are simplified and linearized in MAPLE and then an LQR controller is applied for the state space equations of the systems in MATLAB. Finally time response of states and control inputs demonstrate the stability of the system.
Probabilistic system identification of two flexible joint models
The flexibility of welded joints is an important issue in structural analysis and design of car bodies. Two three-dimensional, design-oriented models (uncoupled and coupled) are developed to represent the complaint behavior of multibranch flexible joints. The uncoupled model consists of torsional springs restraining the relative rotation of the joint branches in the three planes, while all branches are assumed to be rigidly connected in translation. Coupling between motions in different planes is neglected. The coupled model accounts for such coupling. A statistical system identification method is proposed for inferring the model parameters from the static response of the structure. The method is demonstrated by applying it to a simple cube frame structure and a car body. Finally, the two models are compared in terms of their ability to predict static response.