Thermal Characteristics Of Marine Meteorological Monitoring Airship

Nowadays,the Chinese marine economic is developing rapidly,but people's production and living safety is seriously threatened by the complex marine environment and frequent marine disasters such as sea fog,typhoons and severe convection,causing huge economic losses.The stratospheric airship used in marine meteorological monitoring has its unique advantages:work continuously at 15-30 km,high regional and temporal resolution,strong loading capacity.The application of stratospheric meteorological airship is of great significance for further improving the monitoring and forecasting ability of marine meteorology and accelerating the process of marine meteorological service.As a weather monitoring platform,the airship must be stable and reliable.The thermal characteristics of airship are closely related to the hovering altitude,structure and equipment performance,and the characteristics of envelope materials.In this paper,the stratospheric meteorological airship with overpressure helium bag is taken as the research object,and the influence of environmental factors and airship internal factors on the thermal characteristics of airship is calculated by the finite element simulation C++program.The main research contents and achievements are as follows:(1)The thermal environment mathematical model of airship is established,including:solar radiation,the sky and the ground long wave radiation,infrared radiation inside and outside the translucent envelope,convective heat transfer inside and outside the airship.The thermodynamic equilibrium equations of envelope,photovoltaic cells and helium gasbag are established.Based on the above mathematical model,the program is compiled,and the reliability of the program is verified by the experimental data.(2)The effect of different seasons,latitudes,wind speed,gasbag distribution,envelope emissivity,absorptivity,photovoltaic cells emissivity,absorptivity,photovoltaic cells conversion efficiency and photovoltaic cells thermal resistance on stantaneous airship temperature was investigated.Investigation results show that:airships operating in summer or at low latitudes have poor thermal stability.At the same time,the empirical formula of external forced convection which is applicable to the airship geometry and the Reynolds number range has a large error,and the maximum swings of helium temperature calculated by different formulas is about 15K.The Nusselt number calculated by Fluent was used in the program and compared to the error of the above empirical formula calculation.The results show that Dai's formula(2.51)is more applicable to this topic.The left-right distribution of the main and additional helium gasbags is more conducive to reducing the daily-temperature swings than upper-lower distribution.The influence of envelope solar radiation absorptivity on airship temperature is greater than long wave radiation emissivity.Photovoltaic cells with large absorptivity have higher output power even though the Photovoltaic cells temperature is higher.The increase of battery emissivity is beneficial to reduce the working temperature and improve the working performance.The increase of photoelectric conversion efficiency and thermal resistance can alleviate the“superheat”to a certain extent.(3)Based on the DOE(Design of Experiments)method,Minitab software was used for multi factor sensitivity analysis.The results show that,10 factors were screened and sorted according to the influence degree of helium daily-temperature swings:envelope solar radiation absorptivity>wind speed>gasbag distribution>seasons>latitudes>envelope long wave emissivity>photovoltaic cells solar radiation absorptivity>photovoltaic cells long wave emissivity>photovoltaic cells conversion efficiency.After removing the factors beyond control and insignificant,the experiment is designed again and the equation is fitted,the optimal factor level combination obtained is:envelope absorptivity 0.1,envelope emissivity 0.9,photovoltaic cells absorptivity 0.5,photovoltaic cells emissivity 0.9,photovoltaic cells thermal resistance 0.8 m~2?K/W.The helium daily-temperature swings of this combination under the extreme summer conditions is17.40K,and the error between the fitted equation and the program is 1.77%.