Numerical Simulation Of Thermal-structure Coupling For Near Space Airship

As a high-altitude platform, the near space airship has a great range of performance capabilityavailable to be exploited for commercial and military sectors. The main benefits of near space airshipare extended durations, low cost, and recycling. Currently, many developed countries, such as theUnited States, South Korea and Japan, have carried out intensive investigations of the research anddevelopment of near space airship. As is well known in the field of airship design, it is very importantto predict the inner gas temperature for the design and operation of an airship because its buoyancydepends strongly on the temperature difference between the inner gas and surrounding air. For thenear space airship skin, membrane structure is adopted. The membrane with the characteristic of lowrigid is taken as a flexible structure. The temperature variations of the inner gas may cause themembrane structure to deform, while the deformation alse influence the temperature of inner gas. Theinteraction between the temperature of the inner gas and the nonlinear large deformation is acomplicated thermal-structure coupling problem.In the paper, a series of studies on the thermal-structure coupling problem of near space airship isdone. The main contents are as follow:(1) The thermodynamic model of the stratospheric airship is developed, based on which thecalculation program is implemented and verified by comparing the calculated values with theexperimental results. By numerical simulation, the thermal characteristics of the airship is explored,and the transient temperature variations of the skin and inner gas are presented. The effects ofradiative properties of the skin, wind velocity and attitude angle of the airship on the temperturevariations of buoyancy gas and the non-uniform temperture distribution of the skin have beenanalysed.(2) The three-layer heat conduction model of the photovoltaic array is developed and coupled withthe thermaldynamic model of the stratospheric airship, and then the photovoltaic array and airshipcoupling analysis model is developed. According the coupling model, the calculation programprogram of thermal characterics of the ship updates to estimate the thermal performances and outputpower of the array, the effects of the latitude, wind velocity and insulation on the power output of thePV array are analyzed and the effect of the PV array on the thermal characteristics of the airship isinvestigated.(3) The mathematical model of membrane structure is developed, the computational program ofmembrane deformation is implemented, and the validity and the accuracy of the computationalprogram are evaluated. Based on coupling the membrane strucuture model with thermodynamicmodel of the airship, the program of numerical simulation about thermal-structure coupling problemof the stratospheric airship is designed. By using the program, the structure analysis of thestratospheric airship is studied on, the effects of the differential pressure and elastic modulus andPoisson ratio of the skin on the structural deformation and the stress of the stratospheric airship areanalyzed, which offer references for structure design of the stratospheric airship. The steadythermal-structure analysis to the stratospheric airship in spot hover at night and noon is discussed. Theeffects of elastic modulus and radiative properties of the skin to the temperature of the inner gas,differential pressure, and the volume and flight altitude of the airship are analyzed. The transient thermal-structure analysis to the stratospheric airship is carried on during spot hover and floatingflight. the variation of inner gas temperature and pressure can be predicted precisely. The maximummain stress of the skin can be obtained, which is used to discern whether the stratospheric airship maybrust during floating flight.(4) The thermal-structure model of super pressure balloon is developed, the structure analysis of theballoon is done, and the effects of the number of the tendons, subtended angle at equator, elasticmodulus and Poisson ratio of the skin, elastic modulus of the tendons on the super pressure balloonare investigated. The structure behavior of Pumpkin-shaped and spherical balloons are compared andanalyzed. The study and analysis would offer references and experiences for structure design of thesuper pressure balloon. The transient thermal-structure analysis to the super pressure balloon is given.The maximum main stress of the skin and the maximum tension of the tendon can be accuratelypredicted to examine whether the balloon may brust, when the temperature and pressure of inner gasvaries from day to night. At last, the paper proposes a new way to design “Constant Angle”pumpkin-shaped balloon which could be good fundamentals for the design of the super pressureballoon.