NASA Tech Briefs, December 1991

Topics include: Electronic Components and Circuits. Electronic Systems, Physical Sciences, Materials, Computer Programs, Mechanics, Machinery, Fabrication Technology, Mathematics and Information Sciences

Fuzzy-Model-Based (FMB) Control of a Spacecraft with Fuel Sloshing Dynamics

During the upper-stage separation and orbit injection, orbital control, and attitude maneuver, propellant slosh in partially-filled fuel tanks can cause dynamical instability or pointing errors. The spacecraft dynamics combined with propellant sloshing results in a highly nonlinear and coupled dynamic system that requires a complicated control law. This problem has been a long-standing concern for space missions. The purpose of this research is two fold. The first part is to investigate and develop nonlinear Takagi-Sugeno (T-S) fuzzy model-based controllers for a spacecraft with fuel sloshing considering the input constraints on the actuators. It includes i) a fuzzy controller/observer with a minimum upper-bound control input based on the parallel-distributed compensation (PDC) technique, ii) a fuzzy controller/observer based on the linear quadratic regulator (LQR) that uses the premises of the T-S model, and iii) a robust-optimal fuzzy-model-based controller/observer. The designed controllers are globally asymptotically stable and have a satisfactory performance and robustness. The second part of the research is to develop a mathematical model of a spinning spacecraft with fuel sloshing during high-g maneuvers. The equations of motion of a spacecraft with partially-filled multiple-tanks are derived using the Kane’s method. To do this, two spherical pendulums as an equivalent mechanical model of the fuel sloshing are adopted. The effect of the slosh model parameters on the spacecraft nutation angle is studied. The developed model is validated via several numerical simulations

Mathematical and fuzzy modelling of high-speed interconnections in integrated circuits.

Microstrip line are the most popular interconnection type mainly due to its planar geometry. The mode of propagation is almost a transverse electromagnetic mode of wave propagation (TEM) and can be described by the Telegrapher's equations. These facts make mathematical and fuzzy modelling of microstrip lines possible.Two types of nonuniformly coupled microstrip lines, namely, nonuniformly spaced and strictly nonuniform, are presented in this study. A new model of capacitance matrix was developed for nonuniformly spaced coupled microstrip lines. The model obtained was then translated into a Mathematica program in order to be utilised in real systems. Furthermore, a new matrix; mutual capacitance ratio matrix, was deduced from the previous model. A few valuable properties were then established from this matrix. Novel concepts were introduced to approximate capacitance of strictly nonuniform coupled microstrip lines and Mathematica programs were coded to implement these methods. The study then continued with the development of new algorithms to calculate the time delay and characteristic impedance using capacitance matrices of both types of nonuniform lines. These algorithms finally became a generalised algorithm which could be used in any type of coupled microstrip lines, uniform and nonuniform. The time delay and characteristic impedance were later used as parameters to simulate crosstalk using SPICE. Analysis of geometrical and electrical parameters of microstrip lines was performed mathematically and simulations modelled using the Mathematica package. Experimental work was also carried out to investigate the characteristic of crosstalk. All information obtained from these analyses were then fed into the developed novel fuzzy model. The model was designed to minimise crosstalk and to optimise the geometrical and electrical parameters of coupled microstrip lines simultaneously. These models have the potential to become 'multi purpose on board designing tools' for a designer before the system is finally fabricated

NASA Tech Briefs, December 1997

Topics: Design and Analysis Software; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Software; Mechanics; Manufacturing/Fabrication; Mathematics and Information Sciences; Books and Reports

NASA Tech Briefs, January 1999

Topics include: special coverage sections on sensors and data acquisition and sections on electronic components and circuits, electronic software, materials, mechanics, bio-medical physical sciences, book and reports, and a special section of Photonics Tech Briefs

NASA Tech Briefs, August 1993

Topics include: Computer Graphics; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery; Fabrication Technology; Mathematics and Information Sciences; Life Sciences; Books and Reports

NASA Tech Briefs, November 1994

Topics: Advanced Manufacturing; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery/Automation; Manufacturing/Fabrication; Mathematics and Information Sciences; Life Sciences; Books and Reports

Neural Network Models And Sensitivity Analysis For The Production Of Isopropyl Myristate In Semibatch Reactive Distillation

Isopropyl myristate (IPM) is an important chemical in the cosmetic and pharmaceutical industries. The IPM can be produced either through esterification or the transesterification process in semibatch reactive distillation (BRD). However, the latter process is not widely explored. The transesterification process in BRD can be represented by a mathematical model, however, this model will end with a large number of differential equations and be very expensive to solve and will also be time consuming. Hence, the empirical model such as the artificial neural network (ANN) model provides better solution as it can deal with highly nonlinear and complex structures. In this work, the production of industrial scaled IPM in BRD through the transesterification process is simulated using Aspen Plus and the simulation result achieved shows a comparable result as reported in the literature. The validated model is then used for sensitivity analysis to determine the relationship between the process input-output variables. The nonparametric test is used and the selected inputs are ranked according to their mean overall sensitivity. From the results, the reboiler duty, the initial mole of isopropanol, methyl mysistate, the reflux ratio, the feed flowrate and the temperature at stage 32 are considered as the input variables in the ANN model development to predict the bottom and distillate composition

Mapa de la recerca del Campus de Vilanova i la Geltrú

Postprint (author’s final draft