Journal of Aerospace Science and Technology
Volume:4 Issue: 4, Winter 2007

This paper investigates the dynamical behavior of an assembled beam like structure with tip masses modeling a two stage space rocket structure. The beam like structure is composed of two beams connected together carrying two masses at the free ends to model the payload, and the stabilizing fins mass properties. The effect of non-homogeneity of the structure due to different cross section properties at each stages of the rocket and the tip masses, heavily affects the dynamical behavior and stability regions of the structure if excited using a follower force. The rocket thrust is considered in this study as follower force as in flexible space structures the thrust direction is affected by the lateral vibrations of the structure. As demonstrated in this study the primarily mode of instability in such a structure, i.e. divergence or flutter, depends on the stiffness and mass distributions of the structure. This would enable the designer to alter the mode of instability by modifying these distributions. In inspecting the instability regions of the structure under follower force, and establishing an analytical solution, the Galerkin method is employed and the stability regions of the structure are determined.

To formulate a single-leg seat inventory control problem in an airline ticket sales system, the concept and techniques of revenue management are applied in this research. In this model, it is assumed the cabin capacity is stochastic and hence its exact size cannot be forecasted in advance, at the time of planning. There are two groups of early-reserving and late-purchasing customers demanding this capacity. The price rate as well as the penalty for booking cancellation caused by overbooking is different for each group. The model is developed mathematically and we propose an analytical solution method. The properties of the optimal solution as well as the behavior of objective function are also analyzed. The objective function is neither concave nor convex in general. However, we prove it is a unimodal function and by taking advantage of this property, the optimal solution is determined.

A Space Free-Flying Robot (SFFR) includes an actuated base equipped with one or more manipulators to perform on-orbit missions. Distinct from fixed-based manipulators, the spacecraft (base) of a SFFR responds to dynamic reaction forces due to manipulator motions. In order to control such a system, it is essential to consider the dynamic coupling between the manipulators and the base. Explicit dynamics modeling of such systems with flexible appendages is developed in this paper. The SFFR is divided into two parts, the manipulator(s), and the main base body (spacecraft) that consists of flexible appendages. The recursive Lagrangian approach is used to describe dynamics model of the flexible base system. For modeling the multi-manipulator system, a Recursive Newton-Euler approach is followed. The obtained dynamics model can be employed either numerically or symbolically. Interacting forces and torques acting between the manipulators and the main body are also modeled that could be used for simulation studies of controller design.

In this research, an automatic control system is designed for landing of a small helicopter on a 4 DOF moving platform. The platform has three translational and one directional degree of freedom. The controller design approach is based on development of helicopter nonlinear dynamic model into the SDC (State Dependent Coefficient) form and real time solving of state dependent Riccati equation (SDRE). To compensate the simplifications and term eliminations done to make the SDC form, a nonlinear compensator is added. The performance of the control system in automatic landing is evaluated by computer simulation in different scenarios. The results show a satisfactory tracking performance of the controller during landing on a moving platform.