Browsing by Author "Thomasson, P. G."
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Item Open Access Application of nonlinear control theory in weapon guidance and control(2001-03) Brundle, D.; Thomasson, P. G.This thesis considers the application of nonlinear control theory in two subjects pertinent to weapon applications. Initially, Section 2 considers the development of a simple nonlinear autopilot for a Laser Guided Bomb (LGB). Later a nonlinear autopilot design is developed using a Pulse-Width Modulated (PWM) controller derived from the method developed by Bemelli-Zazzera et al4. This is applied to an LGB utilising a “bang-bang” actuator, enabling the control surfaces to achieve a pseudo-proportional response. The PWM design stems from an equivalent Pulse Amplitude Modulated controller, which required a design technique to be developed for a linear autopilot and, in addition, simulation of an electro-mechanical actuator. Simulation demonstrated that the PWM controller can achieve the desired response but the design must incorporate actuator dynamics. Section 3 considers the use of nonlinear control theory to examine the nonlinear intercept equations using a Proportional Navigation (PN) guidance law. Using a simple heuristic example, PN is introduced and vector algebra used to develop a simple model of the intercept. The model is then used to illustrate the importance of the kinematic gain. Using the method pioneered by Ha et al16, Lyapunov theory is used to demonstrate that PN is a robust guidance law. Although generally derived assuming the target maintains rectilinear flight, Lyapunov theory is used to demonstrate interception is always possible provided the pursuer has sufficient manoeuvre advantage over the target. Noting that many missiles incorporate a 1 directional warhead, Lyapunov theory is used to design a time-varying rate bias that controls the direction of approach to the target. Simulation demonstrates that the guidance requirements are indeed achieved by this law but additional effort is required by the control system. In Section 3 it is demonstrated that the PN guidance law will always ensure an intercept, i.e. it does not by itself generate miss-distance. In the final part of Section 3, using adjoint software designed by Zarchan42, it is demonstrated that miss-distance develops in practical systems as the result of sub-system dynamicsItem Open Access A combined design and trajectory optimisation algorithm for an orbiter vehicle(Cranfield University, 1995-04) McGregor , Andrew. E.; Thomasson, P. G.This thesis describes the development of a computer program to optimise the design of a rocket powered orbiter vehicle, by combining a design synthesis with consideration of both the ascent and re-entry trajectories. This work is a extension of an existing trajectory optimisation program. Firstly the background to the problem is examined and a summary of previous work is presented. The objectives of this research program are examined and there follows a discussion of the mission requirements for such a vehicle and a description of the baseline design. The development of this problem as a integrated optimal control problem is discussed and is followed by a description of the mathematical models which are used to evaluate the vehicle. These include the geometry and packing model, the estimation of the orbiter's mass properties, the evaluation of the aerodynamics and the simulation of the trajectories. The mathematical details of these models are presented in detail i the appendices. The architecture and philosophy behind the writing of the program are then discussed. A user's guide is also presented as an appendix. Results are given for the solutions to a variety of orbiter design problems. These problems include a variety of separation conditions for air-launched vehicles, various re-entry cross-range conditions and a number of differing objective functions. A investigation into the optimality of the solutions and their sensitivity to changes in the optimisable parameters is also considered. The difficulty in obtaining optimal solutions is discussed in full.Item Open Access Development of a simulation tool for flight dynamics and control investigations of articulated vtol unmanned aircraft(Cranfield University, 1996-06) Saghafi, F.; Thomasson, P. G.A simulation tool for flight dynamics and control investigations of three different Vertical Take Off and Landing (VTOL) unmanned aircraft configurations has been developed. A control concept has been proposed in order to take advantage of the fast response characteristics of the ordinary small engine/propeller propulsion systems in such aircraft, as well as replacing the complex rotors used previously in VTOL concepts for small unmanned aircraft. The simulation model has been established on the basis of the proposed concept so that it can also be used to study the feasibility of this idea. An Object-based methodology has been introduced so as to reduce the amount of aerodynamic required data for the simulation model. The equations of motion associated with the aircraft multibody system with ten degrees of freedom have been derived using the Newton-Euler method. The modelling of various subsystems including the propeller model, the airframe aerodynamics and the engine model has been carried out. A method for calculating the propellers' slipstream effects on the other components has been presented. Input data for the simulation model have been estimated, using different sources. The Advanced Continuous Simulation Language (ACSL) has been used for the programming of the mathematical model. A series of comprehensive tests have been carried out in order to demonstrate the validity of the simulation model. The ability of the simulation model to explain the aircraft modes of motion as well as to discover unknown nonlinear behaviours and to describe them has been demonstrated.Item Open Access The development of the mathematical model of an RPV and an investigation on the use of an EKF for the identification of its aerodynamic derivatives(Cranfield University, 1987-05) Milonidis, E.; Thomasson, P. G.A six-degrees of freedom mathematical model of an experimental Remotely Piloted Vehicle (RPV) and the linearised longitudinal and lateral models at 30m/sec are developed. The longitudinal and lateral dynamics are analysed and the equivalent discrete systems are used to provide baseline data for the identification of the aerodynamic derivatives of the RPV. An advanced aircraft parameter estimation method - the Extended Kalman Filter - is implemented for the estimation of the aerodynamic characteristics of the RPV. Conclusions are drawn about the identifiability of the stability and control derivatives from pitch, roll and yaw rate measurements.Item Open Access The development of the mathematical model of an RPV and an investigation on the use of an EKF for the identification of its aerodynamic derivatives(1987-05) Milonidis, E.; Thomasson, P. G.A six-degrees of freedom mathematical model of an experimental Remotely Piloted Vehicle (RPV) and the linearised longitudinal and lateral models at 30 m/sec are developed. The longitudinal and lateral dynamics are analysed and the equivalent discrete systems are used to provide baseline data for the identification of the aerodynamic derivatives of the RPV. An advanced aircraft parameter estimation method - the Extended Kalman F ilte r - is implemented for the estimation of the aerodynamic characteristics of the RPV. Conclusions are drawn about the id e n tifi- a b ility of the s tab ility and control derivatives from pitch, roll and yaw rate measurements.Item Open Access Integration of global positioning and inertial reference system data inside a flight management computer(1992-01) Richards, N. P.; Thomasson, P. G.A Kalman filter is used to integrate the outputs from a Global Positioning System and an Inertial Reference System inside a Flight Management Computer. To initialise the Kalman filter, account is taken of the 1RS errors that get set up during alignment. Algorithms are developed that allow the Kalman filter to be initialised to several 1RS specific alignment conditions.Item Open Access Motion of a rigid body in an unsteady non-uniform heavy fluid(1995) Thomasson, P. G.The Lagrangian formulation of the equations of motion of a body immersed in a steady but heavy perfect fluid is outline in Lamb [1] and a resulting set of equations for the unsteady fluid case, is given in Lewis et al [2] in a form suitable for the flight dynamics of underwater vehicles. These equations have also been used to model the motion of airships in a steady uniform atmosphere, Cook et al [4]. Recently however the author has had some difficulty in applying these equations to the motion of other vehicles. In principle they should be applicable to not only underwater vehicles but also to airships, parafoils and aircraft. Two major problems of the equations in [2] is that they do not reduce to the small perturbation equations that are used for aircraft in gusts [3],[13], plus as will be seen later, the fluids inertial velocity causes difficulty. This paper identifies the source of the problems as being the conventional approach of lumping together the inertial and added masses. It provides an alternative formulation that keeps them separate and so avoids the difficulties.Item Open Access Motion of a rigid body in an unsteady non-uniform heavy fluid :(1996) Thomasson, P. G.Difficulties with an earlier set of equations are explained by deriving the equations of motion of a rigid body moving in a perfect fluid that is itself accelerating and contains velocity gradients. The equations are derived on the assumption that changes in the fluid velocity over the vehicles length are small compared to the velocity of the stream in its neighbourhood. It is shown how the resultant perfect fluid equations can be augmented to include viscous forces and moments derived from other theoretical or experimental sources.