Guidance and control strategies for aerospace vehicles

A simplified method of matched asymptotic expansions was developed where the common part in composite solution is generated as a polynomial in stretched variable instead of actually evaluating the same from the outer solution. This methodology was applied to the solution of the exact equations for three dimensional atmospheric entry problems. Compared to previous works, the present simplified methodology yields explicit analytical expressions for various components of the composite solution without resorting to any type of transcendental equations to be solved only by numerical methods. The optimal control problem arising in the noncoplanar orbital transfer employing aeroassist was also addressed

Guidance and control strategies for aerospace vehicles

The optimal control problem arising in coplanar orbital transfer employing aeroassist technology and the fuel-optimal control problem arising in orbital transfer vehicles employing aeroassist technology are addressed

On Becoming an African-Asian English Academic at Rhodes University

No Abstrac

Guidance and Control strategies for aerospace vehicles

A neighboring optimal guidance scheme was devised for a nonlinear dynamic system with stochastic inputs and perfect measurements as applicable to fuel optimal control of an aeroassisted orbital transfer vehicle. For the deterministic nonlinear dynamic system describing the atmospheric maneuver, a nominal trajectory was determined. Then, a neighboring, optimal guidance scheme was obtained for open loop and closed loop control configurations. Taking modelling uncertainties into account, a linear, stochastic, neighboring optimal guidance scheme was devised. Finally, the optimal trajectory was approximated as the sum of the deterministic nominal trajectory and the stochastic neighboring optimal solution. Numerical results are presented for a typical vehicle. A fuel-optimal control problem in aeroassisted noncoplanar orbital transfer is also addressed. The equations of motion for the atmospheric maneuver are nonlinear and the optimal (nominal) trajectory and control are obtained. In order to follow the nominal trajectory under actual conditions, a neighboring optimum guidance scheme is designed using linear quadratic regulator theory for onboard real-time implementation. One of the state variables is used as the independent variable in reference to the time. The weighting matrices in the performance index are chosen by a combination of a heuristic method and an optimal modal approach. The necessary feedback control law is obtained in order to minimize the deviations from the nominal conditions

Modification of silicon carbide fibers for use in SiC/Ti composites

The degradation of silicon carbide fibers during exposure to conditions typical of composite fabrication was investigated. The tensile strength of pristine fibers and fibers sputtered with thin metal coatings were determined before and after treatment at 870 C for one hour in vacuum. Each fiber strength distribution was related by an analytical procedure to a projected composite ultimate tensile strength (PC UTS). The results indicate that a thin aluminum diffusion barrier can yield a 150 percent increase in PC UTS over the baseline SiC/Ti system

Vrou is Gif: The representation of violence against women in Margie Orford’s Clare Hart novels

This article takes as its starting point that crime fiction is a public and political response to gender-based violence. Using the methods of both discourse analysis and literary analysis of the crime fiction genre, the novels of Margie Orford, internationally acclaimed crime author and patron of Rape Crisis, are examined for their representations of violence against women, and the role played by these representations in Orford’s overall feminist project in the Clare Hart series. The article also considers theories about gender-based violence which link male violence to a purported crisis in the established gender order of South Africa. An attempt is made to understand the relationship between fictionalised representations of violence and the ‘banality’ of real-life violence. Finally, Hart, Orford’s hard-boiled female detective figure, is assessed to determine whether this character constitutes a significant feminist achievement that contributes to discourses which counter gender-based violence.Keywords: South Africa; crime fiction; gender-based violence; representation; feminist detectiv

Inflaton Decay in an Alpha Vacuum

We study the alpha vacua of de Sitter space by considering the decay rate of the inflaton field coupled to a scalar field placed in an alpha vacuum. We find an {\em alpha dependent} Bose enhancement relative to the Bunch-Davies vacuum and, surprisingly, no non-renormalizable divergences. We also consider a modified alpha dependent time ordering prescription for the Feynman propagator and show that it leads to an alpha independent result. This result suggests that it may be possible to calculate in any alpha vacuum if we employ the appropriate causality preserving prescription.Comment: 16 pages, 1 figure, Revtex 4 preprin

Gearbox Health Condition Monitoring: A brief exposition

Gearbox is a mechanical power transmission device, most commonly used to get the mechanical benefits in terms of speed and torque. The gearbox is made up of different types of gears assembled in a cascading order to perform the intended task. Failure of any rotating component inside the gearbox will terminate the working condition of the mechanical system associated with it. This causes interrupted services to the industries, which lead to expensive compensation. Especially, in an aircraft engine, it is used as an accessory drive, which provides power for hydraulic,pneumatic and electrical systems. This motivated to monitor the gearbox health condition. This paper presents a brief review of GHCM (gearbox health condition monitoring), gearbox faults, overview of time-domain features, frequency-domain features, time-frequency domain; feature extraction techniques, and fault classification techniques.The outcome of this study is to provide brief information regarding gearbox health condition monitoring