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Solar array is essential for converting sunlight energy to electricity and ensure normal operation of propellers, payloads and avionics of stratospheric airship. Apart from electrical energy, excess solar irradiation is transformed to heat load on the airship, seriously affecting the pressure balance and structural integrity. However, the investigation of insulation layers between solar cells and airship film are rare. This paper aims to maximize the output energy of solar array through optimizing the configuration of insulation layers. The energy model and heat transfer model are established. Based on the theoretical model, the influence of insulation parameters on the output energy of solar array and differential pressure are studied. The energy acquirement and differential pressure have negligible change when increasing the thermal conductivity and thickness of insulation substrate in the same proportion. The thermal impedance as the ratio of thickness to thermal conductivity is firstly adopted to describe the configuration of insulation structure. The optimal thermal impedance can be obtained based on flight missions considering airspeeds, latitudes and dates. The output energy can be maximized while keeping the differential pressure within limited range with the optimal thermal impedance. The result provides a conducive reference for the preparation of solar powered airship. [ABSTRACT FROM AUTHOR]

Station-keeping endurance of high altitude balloon is the foundation of the assignments of environmental monitoring and communicational relaying. Exploiting the natural wind-field that varies with altitude by the altitude control system to extend the station-keeping endurance is proposed in this paper. A Matlab program is developed based on the theoretical model to simulate the station-keeping performance of the balloon in the real wind field. The trajectories of the balloon in different wind fields and the states of the balloon caused by the venting and pumping processes are discussed in detail. The results show that with the altitude control system it is possible to retain the balloon within the designated district for few days to a week. This can serve as a guideline for the design and initial flight tests of the serviceable high altitude balloon. [ABSTRACT FROM AUTHOR]

Abstract For the absence of the propeller system to resist wind load, the balloon will float everywhere with unstable position. In order to fix the balloon within a specific district and extend the station-keeping endurance, an effective approach that utilizes the wind from different directions by altering the float altitude was proposed. A program was developed to simulate the flight performance and the station-keeping endurance of the stratospheric super-pressure balloon in the real wind field. The influences of the initial Helium volume ratio and the float altitude on the traveled horizontal distance of the balloon were analyzed. The results indicate that the altitude of the balloon fluctuates with the change of the volume of the balloon during the day-night cycle, providing the possibility to catch the wind from different directions. By choosing the appropriate Helium volume ratio and float altitude, the traveled horizontal distance of the balloon can be shortened greatly. Our study can provide guidance for investigation on active control algorithm for station-keeping of the balloon that can fix the balloon within the desired district for months and years. [ABSTRACT FROM AUTHOR]

The thermal performance of stratospheric airship is closely related to the superheat/overpressure of airship, the thermal stress of the hull, the mechanics property of the envelope, as well as the airship reliability and lifetime. A comprehensive understanding of the thermal performance of the airship is important for the increase of airship applications. For the improved airship with rotatable photovoltaic array, the location of the photovoltaic array changes with time to utilize the solar radiation maximally, which decrease the mass of photovoltaic array greatly. The thermal performance may be different with the traditional airship with fixed photovoltaic array. In this paper, a thermal model of stratospheric airship with rotatable photovoltaic array was proposed to investigate the thermal performance and compare with traditional stratospheric airship with fixed photovoltaic array. A user define function program in computational fluid dynamic software was developed based on the model. The temperature distribution of surface and flow field of inner lifting gas of the airship with rotatable/fixed photovoltaic array were simulated and compared. The result shows that the temperatures of photovoltaic array and envelope of the improved airship are slight higher than that of traditional airship. The temperature fields of the Helium are also various and the uneven temperature distribution leads to the formation of eddies and chaotic state of the flow field. It is helpful in guiding the design of novel stratospheric airship with low-weight power system, especially the design of thermal control system and inner pressure regulation system of the airship. [ABSTRACT FROM AUTHOR]

The solar array is one of the major components of long-endurance stratospheric airship which converts the solar energy to electric energy. Exact calculation of the output performance of solar array is significant to the operation of the airship. The move of the sun and the curve surface of the airship lead to the dramatic change of the incidence angle of solar radiation. Therefore, the angular losses, caused by the change of incidence angle, decreasing the efficiency of solar cell and then reducing the output energy of solar array, should be taken into account. But the relevant investigations are rare. In this paper, a simplified numerical model including solar radiation model, thermal model and angular losses model was established. A MATLAB computer program was developed based on the model to research the deviation of output energy of solar array with/without angular losses. The effects of date, airship’s attitude and latitude on the deviation were also discussed in detail. The result indicates that the output energy of solar array on stratospheric airship was overestimated without considering the angular losses and the angular losses should be taken into account for an accurate calculation. It is believed that the present models and program will lead to a better design for the energy management system of stratospheric airship. [ABSTRACT FROM AUTHOR]

The capacity of station-keeping and long endurance of renewable energy system have great impact on the application of the high altitude balloon. In this paper, the station-keeping mechanism based on an altitude control system is proposed to ride the natural wind field with diverse directions and speeds at different altitudes and then retain the balloon within the desired district. Combined with the energy harvesting/consuming model and the dynamic model, the energy management strategy is designed to extend the energy endurance of the balloon. The station-keeping strategy (the pumping/venting states of the air ballonet) based on the energy management strategy is optimized by the genetic algorithm. The optimization result shows that the air ballonet needs to be pumped 6 times and vented 5 times in one day. By pumping and venting the air ballonet, the balloon can be restricted within the district with a radius of 30 km and the maximum horizontal distance between the center of the district and the location of the balloon is about 28 km. In addition, the payload and the altitude control system can be powered by the PV array and the lithium battery sustainably. These results can assist in the design and initial flight tests of the serviceable high altitude balloon. [ABSTRACT FROM AUTHOR]

Abstract High-altitude solar powered scientific balloon can be powered by thin-film solar panel mounted on the balloon. The temperature change of solar panel might have significant influence on the thermal performance of the balloon, which is closely related to the superheat and overpressure of balloon. The thermal model of solar powered scientific balloon was presented to investigate the thermal performance and compare with unpowered balloon. A user define function program in computational fluid dynamic software was developed based on the model. The effects of layout parameter and area of solar panel on the thermal performance of solar powered balloon were also analyzed. The results show that the temperature of envelope and internal helium of solar powered balloon is much higher than that of unpowered balloon during the daylight, and the maximum velocity of internal helium is decreased with the existence of solar panel. Moreover, the increase of the height and area of solar panel would result the raise of temperature and pressure of internal Helium, but the helium velocity and the flow distribution were hardly changed. The present work may be used to guide the design of solar energy system and the thermal control of scientific balloon. Highlights • The thermal performance of high-altitude solar powered scientific balloon is initially analyzed. • The effects of the layout parameter and area of solar panel on the thermal performance of balloon are studied. • A UDF program in CFD software is developed based on the thermal model of scientific balloon. • The superheat/overpressure of high-altitude balloon may be exacerbated with the existence of solar panel. [ABSTRACT FROM AUTHOR]

The efficiency of solar cell is a critical problem to the energy management of high-altitude airship. Excessive temperature and solar radiation intensity of solar cell will reduce the cell efficiency. The main purpose of this study is to increase the energy output of solar array through optimizing transmittance of solar array encapsulant. The thermal and heat transfer models of solar array were considered during the investigation of the effect of transmittance on output performance of solar array. And the optimization model of transmittance is presented to obtain the optimum transmittance in different working conditions for the first time. The feasibility of the numerical model is verified by comparison with experimental data of the temperature of solar array during a day. The results indicate that the output performance of solar array is variable under different transmittances and the optimum transmittance of solar array is changing with the working latitude and date. The simulation results show that the maximum increase of output energy can reach up to 0.5 MJ on summer solstice. The optimization study provides both theoretical and practical support for choosing optimal encapsulant materials in the preparation stage of high-altitude airship. [ABSTRACT FROM AUTHOR]

The solar array layout is one of the critical factors affecting the output performance of a solar array on a stratospheric airship. Optimizing the layout to improve output energy per day is very important for a long endurance vehicle, but the research about this subject is rare. This paper outlines a numerical method based on a rotating model of a stratospheric airship to optimize the solar array layout. Combined with the solar radiation model, the solar array layout optimization model applying genetic algorithm is developed using a MATLAB computer program in this paper. Compared with the design parameters of three stratospheric solar-powered airships, the theoretical model is proved to be feasible. In the course of the study, the effects of the starting point and the central angle of solar array are discussed in detail. In addition, the optimal results of the solar array layout for four common situations are investigated using the method. The results indicate that this method is helpful in the preparation stage for installing large area flexible solar arrays. [ABSTRACT FROM AUTHOR]

Solar energy is a key factor for high altitude airships to achieve long endurance flight. In order to receive more solar energy and improve the endurance performance of airships, this paper presents a multidisciplinary design methodology to obtain an optimal configuration of the high altitude airship considering the energy optimization. First, a parameterized shape of the airship is proposed and the aerodynamic characteristics are obtained and integrated through a kriging model. Then the solar radiation and photovoltaic (PV) array models are introduced and validated by a ground experiment. After elaborating the structure, propulsion and energy subsystems, an external-internal loop optimization process is carried out to minimize the total weight considering the maximum solar power from PV array. The result of the multidisciplinary design shows an obvious increase on the received solar energy to 3.36 GJ compared with 0.45 GJ for the traditional design, which has a great potential to save the weight of the PV array laid on the airship surface. Further, the effects of the latitudes, dates and wind conditions on airship endurance performance are analyzed and in order to achieve long endurance flight, an adaptability discussion is carried out through a multi-objective optimization process. The result indicates that the improved design has a higher adaptability ratio in different environments compared with the single input design. It suggests that an adaptability design of high altitude airships might be an effective approach in airship engineering applications. [ABSTRACT FROM AUTHOR]

Highlights • A multidisciplinary model of solar-powered hybrid airship is carried out. • A mission-based flight strategy of the hybrid airship is presented. • Multi-objective optimization is conducted to obtain the optimal design set. Abstract This paper presented a multidisciplinary optimization methodology of a high altitude solar-powered hybrid airship. A multidisciplinary model of the hybrid airship is proposed including the geometry, aerodynamics, structures, propulsions and energy consisting of the photovoltaic array and energy stored system (ESS). To achieve a continuous flight and reduce the total mass and energy cost, a multi-phase strategy including the climb, daytime cruise, glide and nighttime cruise is proposed. The mission-based optimization is achieved through an enhanced collaborative optimization and the result shows a large decrease in the total mass compared with a baseline design. Since the flight altitude has a great influence on the hybrid airship with the multi-phase strategy, a multi-objective optimization achieved by NSGA-II (Non-dominated Sort Genetic Algorithm-II), is carried out to discuss the design tradeoffs in different altitudes. The result also indicates that the multi-objective optimization provides a solution set so that the optimal design of the hybrid airship in different flight altitudes could be obtained. [ABSTRACT FROM AUTHOR]

Abstract Energy management system is very critical for solving the energy problem of a long endurance stratospheric airship. But the researches about the energy management system and energy management strategy for a stratospheric airship are rare. This paper presents the hybrid energy system consisting of one renewable energy system and two energy storage systems. Combined with the models of energy harvesting, balance and storage, and the thermal model of the PV (Photovoltaic) panel, the details of the rule-based energy management strategy to cooperate the three energy sources or storage devices: photovoltaic, lithium battery and fuel cell are obtained. Furthermore, the energy management strategy in the situation of a storage system failure is proposed to ensure the operation of the airborne equipment. In the course of the investigation, the power curves and the state of charge of the energy storage systems are reported in detail to prove the validity and applicability of the management strategies. It indicates that the energy system of the airship can provide uninterrupted energy to control system and payload system, but can not resist the wind drag after LB failure, which will increase the difficulty of the trajectory planning. The results indicate that the strategy is helpful for planning energy management. Highlights • A suitable hybrid energy system is designed for stratospheric airship. • The models of energy harvesting, balance and storage are investigated. • A rule-based energy management strategy for this system is presented. • An effective way to deal with the battery failure in airship is proposed. • The thermal effects on output performance of PV is researched. [ABSTRACT FROM AUTHOR]

The increasing application of hybrid airships which have been recently proposed as high altitude platforms, makes it necessary for research into the thermal performance of such airships that possess a photovoltaic module array(PVMA). In this study, a simplified thermal model of a high-altitude hybrid airship with a PVMA, was proposed that included direct solar, infrared, reflected, and scattered radiation and convective heat transfer. Based on computational fluid dynamics(CFD), a simulation methodology, using a user defined function(UDF) program, was introduced to investigate the PVMA's thermal effects on the hybrid airship. A ground experiment was also performed to validate this numerical method's effectiveness. Further simulations and discussion of temperature and velocity distributions of the hybrid airship's internal helium were conducted. The results showed that the PVMA atop the hull had large effects on the hybrid airship's thermal performance. The temperature distribution of the envelope varied greatly during the day and night because of the PVMA's influence as well as the internal helium flow. In addition, forced convection had little influence on the PVMA's output performance, which was analyzed in detail. [ABSTRACT FROM AUTHOR]

The output performance of solar array on near-space airship can be effectively improved by the layout optimization of solar array. This paper studied the effect of layout parameters on output energy of solar array on the airship with and without thermal effect, and particularly the optimization of solar array layout under the thermal effect. Based on the thermal model of solar array and the layout optimization model, a Matlab numerical program is adopted to calculate the output power or energy of solar array and latitudes and the change trend of optimum layout parameters for whole year and different latitude. The theoretical model is clearly verified comparing with the experimental result of temperature distribution of solar array. The effect of layout parameter on the thermal performance of airship was then analyzed by CFD simulation. The results show that the output performance of solar array is significantly improved through optimized layout and the output power or energy is decreased when considering thermal effect. The optimization of layout parameter may increase average temperature of airship and the velocity of internal helium of airship. Therefore, it is valuable to investigate the thermal effect of solar array in practical engineering of solar power system. [ABSTRACT FROM AUTHOR]

The high altitude solar-powered airships have been proposed for use as long endurance platforms, for a variety of military and civilian applications. The challenges of perpetual endurance flight require the airship to generate sufficient power over a wide range of operational latitudes so that the aerial vehicle can keep station through high wind events and maintain persistence. This paper provides a theoretical approach to analyzing the perpetual endurance performance of a high altitude solar-powered airship. According to the features of stratospheric airship and the theoretical model, a custom tool is developed using MATLAB computer program when the airship operates in the cruise condition. The effects of the operational latitudes, wind velocities and solar array areas on the energy ratio are numerically investigated in detail, and the required areas of solar array under the conditions of different minimum energy ratio were discussed. The results showed that the solar-powered airships faced severe operational limitations at high latitudes in the winter, especially in the high wind. In addition, a case study was analyzed to demonstrate the effectiveness of this approach to predicting the perpetual endurance region. The results demonstrated that the theoretical approach suggested a pathway towards planning the flight date and location for an airship. [ABSTRACT FROM AUTHOR]

This paper presents a discussion of “Dynamic modeling and simulation of a heat engine aerobot for atmospheric energy utilization” Wei Yao et al. Energy 79 (2015) 439–446. In the discussed paper, a novel design called a heat engine aerobot was proposed to utilize the atmospheric low grade heat. Then a dynamic theoretical model was established to analyze the thermodynamic performance and conversion efficiency. However, some discrepancies in the basic principle and dynamic model of the heat engine aerobot were identified. It seemed that several main influencing factors are not considered and the solutions due to violation of constraints were not feasible. In this discussion, clarification regarding above-mentioned problem was presented. [ABSTRACT FROM AUTHOR]

This paper aims to develop a high-altitude solar-powered hybrid airship, which combines aerodynamic lift and buoyancy with buoyancy force and cruises continuously. A multi-lobed configuration is employed and the solar irradiance and photovoltaic array model are proposed. After introducing all the parts mass of the hybrid airship and design procedure, an optimal problem with the constraint of energy and the equilibrium between buoyancy and weight are proposed. Through a hybrid optimization search method, the solution is obtained and the sensitivities of geographical location and seasons are discussed. The results show a comprehensive influence of the constraint both in latitude and wind field environment. [ABSTRACT FROM AUTHOR]

Renewable energy system is very critical for solving the energy problem of a long endurance stratospheric airship. Output performance of the traditional solar array fixed on the upper surface of the airship remains to be improved to reduce the area and weight of renewable energy system. Inspired by the solar tracking system and kirigami, a rotatable renewable energy system (mainly including solar array) is designed to improve the current status of the energy system. The advantages of the rotatable solar array are studied using a MATLAB computer program based on the theoretical model established in this paper. The improvements in output energy and required area of the solar array were compared between the traditional airship and improved one. Studies had shown that the rotatable renewable energy system made the total weight of energy system decreased by 1000 kg when the maximum design speed of the airship was greater than 22 m/s. The results demonstrate that the rotatable renewable energy system for the airship can be a good way to improve the output performance of solar array, and the conceptual design and theoretical model suggest a pathway towards solving the energy problem of a stratospheric airship. [ABSTRACT FROM AUTHOR]

Energy requirement is a key factor influencing the station-keeping mission of stratospheric airships. This study proposes an energy strategy for airships to improve the endurance performance. Firstly, an airship energy model including propulsion, energy stored system (ESS) and photovoltaic (PV) array is introduced. To improve the duration time of airships, an energy optimization strategy based on the position potential is established and a case study is conducted to validate this strategy. The result shows that the proposed approach has a 119.9 hour duration of ESS until the on-board energy is exhausted, which is an obvious improvement compared with traditional wind resistance modes (32.4 hour). Further discussions are carried out focused on its improvement on the energy condition of a baseline airship. The result shows that the approach is effective to resolve the energy deficit during nighttime and provide a potential endurance performance in a shortly strong wind field. Moreover, possible weight savings for airships through this strategy are also obtained. The results and conclusions of this study would provide a valuable reference for engineering applications of stratospheric airships. [ABSTRACT FROM AUTHOR]

The wind field that is suitable for scientific balloon realizing horizontal regional residence is related to altitude. In order to help scientific balloon flight in the expected 3-D region, a scientific balloon 3-D region control system consisting of altitude control, vertical velocity control and horizontal distance control was proposed. The theoretical model was established based on the control system. A MATLAB computer program was developed to simulate the scientific balloon performance in the real wind field. Venting and pumping gas effects, the differences between control systems, as well as 3-D region control performances are investigated in detail. The results indicate that the control system adjusts the scientific balloon vertical velocity by venting and pumping gas, the balloon horizontal trajectory deviations are below 1.6%. In addition, the 3-D region control system adjusts the scientific balloon in certain altitude range and vertical velocity range to make a better use of wind field, which helps the balloon flight in a expected region for a long period to accomplish the desired 3-D region residence purposes. This work may provide a valuable reference for improving the long-endurance flight of scientific balloon. [ABSTRACT FROM AUTHOR]