The Mathmatic Modeling And Simulation Of Pressure Control Of Stratospheric Airship

This article focuses on the research of pressure control system of airship, with the background of stratospheric communication platform.Unlike the traditional aircraft, the buoyancy of airship mainly comes from lifting gas (Helium) which is packed in the airbag. Meanwhile, some typical applications of airship also focus on the control and multi-demonstration of airbag. A good control method can reduce the burden of engine and enhance the fight velocity. On the contrary, a bad control method not only impacts the fight character, but also transforms the airbag, even endanger the airship. Thus, the control method of airbag is vitally important to airship.Pressure Control includes safety control, lifting control and pitch control, and has a close relationship with atmospheric environment. The complexity and instability of atmosphere influence the airship flight dramatically. Thus the modeling and simulation of control system are undoubtedly difficult.The function of pressure control includes: (1) Shape maintenance. The airship is a non-rigid gasbag which is filled with gas. So, it is necessary to restrain the pressure difference between the interior gas and the atmosphere by pressure control so as to maintain the shape of the airship. When the airship is rising, the atmosphere pressure is decreasing, so the deflate valve should be opened to discharged the gas so as to maintain the pressure difference. When the airship is declining, the atmosphere pressure is increasing, so the blowing machine should be on, so as to charge the airship.(2) Lift control. The main lifting force of airship is the buoyancy which depends on the density of the atmosphere. The density of the atmosphere is changed with the height. In order to adjust the net lift, we should control the proportion of the Helium and air in the airship. The general approach is charge or discharge the front and rear assistant ballonet, so as to implement the lift control.The control system is based on the atmosphere model, pressure model, pitch model and buoyancy model. As the lack of experimental data, this thesis develops a mathematical model for the airship pressure control system. Based on the physical principles of the airship operation, the buoyancy model, the pressure difference model and the pitch model are presented. This thesis divides the purpose of pressure control into two aspects: safety control and balance control. The safety control is corresponding to the pressure difference model and the balance control is corresponding to the buoyancy model. This paper analyzes the stability of safety control and the balance control. Then illustrate the feasibility of pressure control by simulation.On the base of analyzing the pressure control model, this paper suggests 2 control methods, respectively, based on altitude and pressure self-adjustment. And we also include the heat flow and temperature discrepancy into the airship model based on the mathematic model and control method. Besides the standard atmospheric model, we emphasize on the influence of Solar Radiation and daily temperature change because of some practical problems and phenomenon. Then this paper suggests what we should pay attention to in different situation based on the analysis of simulation result.Finally, this paper list the actual factors need to consider in the practice, such as the temperature and the pressure of atmosphere, the super hot, the purity of Helium, the weather, and the length of airship. And then it analyzes the effects of these factors.