Stratospheric Autonomous Airship: Model, Dynamics And Control

Based on the motion characteristics and extensive untapped potential of stratospheric autonomous airship in information, space exploration, military and monitoring areas, the research and exploitation of which have become a hot spot again at home and abroad from the nineties of the last century. It's also a new area of the international competition in space resources, especially for the developed countries.The development of the stratospheric autonomous airship system, as a class of nonlinear system with highly complex and multi-degree of freedom, demands a workable dynamical model characterizing its intrinsic physical properties. And based on this mode, the different performances and control strategies of airship can be researched. This thesis is mainly focused on studying the model, dynamics, motion characteristics and optimal control of the airship.1. Based on the survey of airship research at home and abroad, the breakthrough direction about modeling airship for this thesis is found out. The airship six-degree freedom model equipped with ballast and ballonets is derived from defining mass of airship, Kirchhoff equation, Newton-Euler theory, continuity equation, Navier-Stokes equation, body motion equations, ballast and ballonets motion equations. The derived methods and expression equations of airship model have extensive different in essence between in this thesis and the "traditional" model presented in other papers. Meanwhile, not only the general items such as buoyancy, gravity, aerodynamic effects, added mass and inertial but also the independent equations of ballast and ballonets are included in this model. It facilitates to study the ballast and ballonets respectively. Secondly, in order to make the model more matched with the moving mass system and suspension system, the nonlinear feedback transformation is implemented technically to the airship model. Finally, in order to facilitate the study of motion performance, control strategies and dynamics of airship. Some reasonable assumptions are set up to simplify the airship model under ensuring the accuracy of the model.2. Dynamics is a branch of theoretical mechanics, it major focus on the relationships between force and motion of objects. The mainly purpose of study airship dynamics is to find out the relationships among force, velocity and acceleration of the ballast, ballonets and body. All of these relationships can reveal the intrinsic nature of airship systems. The study airship dynamics performance will be of benefit to systematically understand the structure and function of airship, and it can provide supports for the structural and control strategy design of airship in theoretical and empirical. This thesis have studied the airship dynamics and the effects of the flow to the dynamics performance through designing linear quadratic regulator, motion styles of ballast and ballonets, nonlinear feedback controller, feedback-linearized dynamics system and equilibrium paths. The simulation results in longitudinal plane and in three-dimensional space are verified the correctness of theoretical analysis.3. Based on the airship linearized model, the airship motion stability and dynamic performance are discussed. The stability study focuses on the airship's response to small perturbation at trimmed and non-inputed conditions and cares whether the motion can return or not. Based on the eigenvalue analysis, some conclusions of airship motion stability at different base motion are given and the characteristic modes of the perturbation motion are also summarized. For the dynamic performance analysis, the study mainly focuses on the airship's response characteristics to the various control inputs, and it verifies the correctness of the airship model.4. The stratospheric autonomous airship must have capability for autonomous flight. Trajectory planning is a key technology for airship automatic navigation. Solving the airship optimal trajectory is also to solve the airship optimal control history of the time. In this thesis, the direct collocation with nonlinear programming method is presented to convert the optimal control problem into a nonlinear programming problem, then using the search function of clone selection algorithm to find out the optimal trajectory from one point to another point. This optimal trajectory should be satisfied the guidance principles, constraint conditions, external environment, optimal flight effects, achievable in practice and objective function optimized. The simulation results in different conditions are concluded and the effectiveness of this method is verified.