A general calculation method to specify center-of-buoyancy for the stratospheric airship with multiple gas cells

As the lighter-than-air (LTA) flight vehicle, the stratospheric airship is a desirable platform to provide communication and surveillance services. During the ascent from sea-level to the mission altitude, the volume of the lifting gas may change significantly, which will result in the change of the center-of-buoyancy (CB). A general calculation method is developed to specify CB for the stratospheric airship with a double-ellipsoid hull and an arbitrary number of the gas cells. The cross-section-integral (CSI) method is used as a basic calculation scenario to specify CB. Considering the complexity in determining the boundary between the helium and air in the gas cell, a searching algorithm is put forward and the specification of CB can be conducted by the iterative calculation. As an important application, the stable condition of the pitch angle is analyzed when the change of CB is involved. Under different initial configurations, the stable pitch angle of the stratospheric airship during the ascent is specified and compared, which shows the advantages of the multi-gas-cell configuration. The results of this paper may provide an important reference for the engineering application of the stratospheric airship.     

平流层飞艇热力学验证温度测量方法研究

平流层飞艇的热力学分析是平流层飞艇关键技术之一。针对热力学分析的工程验证及模型完善,提出了适合于平流层飞艇的艇囊内气体及囊体表面的温度测量方法,包括采集点的分布,传感器的选型,数据传输和处理及数据准确性评价等。经过两次平流层飞艇的缩比飞行试验,对比同艇发放的探空仪采集的温度数据,验证了该方法测量到的数据的准确性。     

Modeling and analysis of floating performances of stratospheric semi-rigid airships

In recent years, the study of semi-rigid airship has revived with the development of airships. Semi-rigid airships have some characteristics of rigid airships and non-rigid airships. Due to the flexibility of the envelope of the non-rigid airship, the variation of the temperature of the inner gas will lead to its structure deformation and affect its flight altitude. This paper develops the structural mechanics model, thermodynamic model and dynamic model of the semi-rigid airship, based on which nonlinear finite element analysis is employed for geometrically nonlinear deformation of the airship upper film in consideration of thermodynamics and structural mechanics coupling. Based on the thermal-structural interaction, the thermal characteristics and flight performances of the airship during floating flight are investigated. The 3-D solar radiation and temperature distribution of the airship skin and the temperature variation of the inner gas are presented to investigate the thermal performance of the airship, flight velocity, acceleration and flight altitude are simulated to investigate the flight performance, and the variations of the volume and pressure difference of the inner gas are calculated to provide a basis for structure design. The results of the simulation can be referenced for the design of the semi-rigid airship, and can be used for the further study on the attitude control of the airship during its floating flight.     

Experimental investigation of transient thermal behavior of an airship under different solar radiation and airflow conditions

Knowledge of the thermal behavior of airships is crucial to the development of airship technology. An experiment apparatus is constructed to investigate the thermal response characteristics of airships, and the transient temperature distributions of both hull and inner gas are obtained under the irradiation of a solar simulator and various airflow conditions. In the course of the research, the transient temperature change of the experimental airship is measured for four airflow speeds of 0 m/s (natural convection), 3.26 m/s, 5.5 m/s and 7.0 m/s, and two incident solar radiation values of 842.4 W/m² and 972.0 W/m². The results show that solar irradiation has significant influence on the airship hull and inner gas temperatures even if the airship stays in a ground airflow environment where the heat transfer is dominated by radiation and convection. The airflow around the airship is conducive to reduce the hull temperature and temperature nonuniformity. Transient thermal response of airships rapidly varies with time under solar radiation conditions and the hull temperature remains approximately constant in ∼5–10 min. Finally, a transient thermal model of airship is developed and the model is validated through comparison with the experimental data.     

平流层飞艇总体设计的基础问题

平流层飞艇是一种新型的长航时临近空间飞行器，具有驻空高度高、驻空时间长、承载能力大、使用效费比高等特点，在对地观测及通信中继等领域具有广泛应用前景。但是该飞行器系统十分复杂，技术与设计实现难度大，总体设计需要考虑的基础问题及解决方案尚不完全明晰。根据平流层大气风场、温度和压力的基础特征，考虑平流层环境对平流层飞艇总体设计的影响，根据空气动力学与热力学基本理论，分析平流层飞艇的显著特征及与常规低空飞艇的区别，研究这些基础问题对平流层飞艇总体设计的影响，为平流层飞艇技术发展提供建议和参考。      

Robust three-dimensional path-following control for an under-actuated stratospheric airship

This paper proposes a robust three-dimensional (3-D) path-following controller for an under-actuated stratospheric airship in the presence of uncertainties. The resultant control system exhibits an inner-outer loop control structure. In the outer control loop, the path-following error dynamics is constructed in a moving Serret-Frenet frame and a new guidance law with the sideslip and attack angle compensation is designed, which decreases the path-following steady-state error. In the inner control loop, a disturbance observer based backstepping control law is proposed to achieve the desired dynamic behavior on the path. Furthermore, a new velocity tracking control strategy is developed which aligns the resultant velocity tangent to the path. Finally, numerical simulation results are shown to verify the effectiveness of the proposed controller.     

Effect of vapor condensation on ascending performance of stratospheric airship

This paper reports a numerical investigation on the effects of water vapor condensing inside the air bag of a stratospheric airship on its ascending performance. The kinetic and thermal model considering vapor condensation was established, based on which a computer program was written in Fortran. The simulation results show that the vapor condensation remarkably affects the kinetic and thermal characteristics of the stratospheric airship in the ascent process. During the ascent process below 11 km, a large amount of latent heat is released when the water vapor in the air inside the air bag of the stratospheric airship condenses, which results in the increase of the temperature and the reduction of the weight of the air in the air bag, causing the airship to speed up, the accelerated expansion of the helium, and the decrease of the helium temperature in the helium bag. When the flight altitude is higher than 11 km, the effect of vapor condensation on the kinetic and thermal characteristics of the stratospheric airship is negligible because vapor is virtually nonexistent in the air.     

欠驱动变质心飞行器的滚偏耦合自抗扰控制

针对单滑块滚控式变质心飞行器的欠驱动问题，提出基于自抗扰思想的控制器，利用横向配置单滑块实现指令滚转角跟踪和侧滑角镇定控制。应用质点系动量矩定理建立了系统姿态动力学模型，分析表明，滚转和偏航通道拥有同一控制输入，且存在滑块惯性和运动耦合，滑块横向偏移会影响偏航通道。为此，设计自抗扰控制（ADRC）器进行滚偏耦合控制，将模型误差、滑块耦合和不确定干扰视作总和扰动，对滚转角跟踪子系统和侧滑角镇定子系统同时进行状态观测和总和扰动动态补偿，该控制器能够较好地抵抗系统内外干扰，且结构简单、易于实现。摄动仿真结果验证了所提控制器的有效性和鲁棒性。      

Influence of processing and external storage conditions on the performance of envelope materials for stratospheric airships

Envelope materials are extremely vital for stratospheric airships, which are widely used in numerous applications. The influence of processing as well as the storage and utilization conditions on the performance of envelope materials has been studied systematically for the first time. Results show that the performance of envelope materials depends largely on the hot-pressing temperature and the flexing during processing. The tensile strength of samples dropped to 289.1 ± 8.0 MPa from 346.6 ± 9.3 MPa when pressed at temperature above 180 °C and helium leakage appeared. The outer layers would be worn off when flexed no matter by manual or machine, resulting in dramatic increase of helium permeability and even leakage as well as varying decrease of mechanical properties. Hence, suitable hot-pressing temperature and limitation of flexing as little as possible during processing are essential to obtain products with suitable properties. Besides, the storage and utilization conditions are also critical to the properties of envelope materials. Both naturally aged samples in outdoor storage on ground and samples recovered from actual flight on stratospheric airship exhibited reduced mechanical properties and even helium leakage due to excess solar irradiation, ozone concentration and energetic particles interaction compared with those stored indoors. The weatherability of envelope materials should be further strengthened in the next few years. This research could provide a theoretical guidance for actual practice.     

Analysis of long-endurance station-keeping flight scenarios for stratospheric airships in the presence of thermal effects

The ability to achieve long-endurance station-keeping flights makes stratospheric airships desirable platforms for the provision of communication and surveillance services. To maintain long-endurance flights, it is necessary to consider the problem of energy consumption. In this paper, we discuss long-endurance flight scenarios of stratospheric airships in the presence of thermal effects. The balance between buoyancy and gravity is influenced by thermal effects during the diurnal cycle. We perform a theoretical analysis based on the helium’s mass, pressure differential, and altitude as the main factors. To verify the effectiveness of the control over the pressure differential and the altitude, three long-endurance flight scenarios are proposed and compared. Then, the corresponding optimization problems are constructed to determine the energy-minimum flight. Finally, further efforts are made to reduce energy consumption. The realization and limitations of two strategies for improvement are analyzed. A comparison with other scenarios shows the effectiveness of energy conservation. The study in this paper thus provides a reference for station-keeping applications of stratospheric airships.     

综合热力学模型的平流层飞艇上升轨迹优化

针对平流层飞艇的上升轨迹优化问题,综合热力学模型进行了研究.主要分析了飞艇基本热力学行为,研究了蒙皮及内部气体的能量方程并建立了详细的飞艇动力学和运动学模型.在热力学、动力学和运动学分析的基础上,建立了以飞行时间为优化目标的平流层飞艇的轨迹优化模型.利用直接配点法将轨迹优化问题转化为非线性优化问题,再通过非线性求解器SNOPT(Sparse Nonlinear Optimizer)对不同场景的问题进行最优化轨迹求解.优化结果表明:热力学效应对优化轨迹有较大影响,在上升过程中,太阳能辐射为主要影响因素,另外风场也对换热量有一定影响.     

Trajectory tracking control for underactuated stratospheric airship

Stratospheric airship is a new kind of aerospace system which has attracted worldwide developing interests for its broad application prospects. Based on the trajectory linearization control (TLC) theory, a novel trajectory tracking control method for an underactuated stratospheric airship is presented in this paper. Firstly, the TLC theory is described sketchily, and the dynamic model of the stratospheric airship is introduced with kinematics and dynamics equations. Then, the trajectory tracking control strategy is deduced in detail. The designed control system possesses a cascaded structure which consists of desired attitude calculation, position control loop and attitude control loop. Two sub-loops are designed for the position and attitude control loops, respectively, including the kinematics control loop and dynamics control loop. Stability analysis shows that the controlled closed-loop system is exponentially stable. Finally, simulation results for the stratospheric airship to track typical trajectories are illustrated to verify effectiveness of the proposed approach.     

Matching trajectory optimization and nonlinear tracking control for HALE

This paper concerns optimal trajectory generation and nonlinear tracking control for stratospheric airship platform of VIA-200. To compensate for the mismatch between the point-mass model of optimal trajectory and the 6-DOF model of the nonlinear tracking problem, a new matching trajectory optimization approach is proposed. The proposed idea reduces the dissimilarity of both problems and reduces the uncertainties in the nonlinear equations of motion for stratospheric airship. In addition, its refined optimal trajectories yield better results under jet stream conditions during flight. The resultant optimal trajectories of VIA-200 are full three-dimensional ascent flight trajectories reflecting the realistic constraints of flight conditions and airship performance with and without a jet stream. Finally, 6-DOF nonlinear equations of motion are derived, including a moving wind field, and the vectorial backstepping approach is applied. The desirable tracking performance is demonstrated that application of the proposed matching optimization method enables the smooth linkage of trajectory optimization to tracking control problems.     

直升机尾桨完全失效后自转着陆轨迹优化

为了研究直升机尾桨完全失效后自转着陆的最优轨迹和操纵过程,建立相应的飞行动力学模型并采用最优控制方法进行计算分析。建立直升机6自由度刚体飞行动力学模型,在模型中加入可以描述尾桨完全失效和自转着陆阶段发动机出轴功率以及旋翼转速变化的相关方程,并将直升机尾桨完全失效后的自转着陆问题转换为非线性最优控制问题进行求解。以某型号单旋翼带尾桨直升机为样机,计算空中停车自转着陆过程,并与飞行试验数据进行对比,验证了所建模型和最优控制方法的准确性。计算分析该型号直升机在以巡航速度下前飞时,尾桨完全失效后自转着陆的最优轨迹和操纵过程。从结果可以看出:尾桨完全失效时,直升机在旋翼反扭矩的作用下会产生较大的偏航角速度和侧滑角变化,进而产生复杂的耦合运动,驾驶员在关闭发动机进行自转着陆操作的同时,还需要通过操纵横向周期变距稳定滚转角,并以侧滑的方式来稳定横航向的姿态角,最后安全着陆。计算得到的最优轨迹和操纵过程,与工程试飞得出的定性的结论和建议相符。      

考虑倍率的平流层飞艇储能电池建模与分析

准确掌握储能电池的实际电量是确保平流层飞艇实现长航时飞行的关键因素之一。首先，建立了平流层飞艇能源系统仿真模型，对能量输入和消耗进行动态分析。随后，对储能电池进行不同电流倍率的充放电测试，采用多项式拟合的方法，根据测试数据建立了储能电池充放电过程中荷电状态(SOC)、剩余放电时间(RDT)、剩余充电时间(RCT)的分析模型。最后，结合能源系统能量输入、消耗模型和储能电池模型进行飞行模拟仿真，获取各部分变化数据，与已有试验数据进行量化对比分析。结果表明:所构建储能电池模型在SOC、RDT、RCT的计算误差分别小于3%、1.5%、1.5%，能够准确反映电池工作过程中SOC、RDT、RCT的变化，可为平流层飞艇平台制定优化的飞行策略提供量化支撑。      

基于压差梯度的平流层飞艇艇囊应力计算和仿真

平流层飞艇体积庞大,艇囊表面曲率小,因而蒙皮材料的局部应力集中极易导致飞艇艇囊蒙皮发生过大变形而迅速超压损伤破坏.基于飞艇艇囊内外压力压差梯度载荷条件,建立飞艇艇囊蒙皮受内外压差真实工况下环向与轴向应力的理论计算模型,构建飞艇蒙皮应力分析的Von Mises强度准则.并采用ABAQUS有限元软件非线性仿真艇囊蒙皮分别在超压300,500,800 Pa载荷下的各点环向的Von Mises应力状况.仿真结果与理论模型计算的应力值基本保持一致,飞艇艇囊蒙皮环向Von Mises应力呈现随压差梯度增大而递增的规律,而轴向Von Mises应力大小由环向Von Mises应力、蒙皮局部经纬向曲率共同决定,且两方向的Von Mises应力均与超压载荷大小成正相关关系,为飞艇艇囊蒙皮超压应力评估和强度计算提供基础性研究.     

Station-keeping control for a stratospheric airship platform via fuzzy adaptive backstepping approach

This paper presents a novel approach for station-keeping control of a stratospheric airship platform in the presence of parametric uncertainty and external disturbance. First, conceptual design of the stratospheric airship platform is introduced, including the target mission, configuration, energy sources, propeller and payload. Second, the dynamics model of the airship platform is presented, and the mathematical model of its horizontal motion is derived. Third, a fuzzy adaptive backstepping control approach is proposed to develop the station-keeping control system for the simplified horizontal motion. The backstepping controller is designed assuming that the airship model is accurately known, and a fuzzy adaptive algorithm is used to approximate the uncertainty of the airship model. The stability of the closed-loop control system is proven via the Lyapunov theorem. Finally, simulation results illustrate the effectiveness and robustness of the proposed control approach.     

一类平流层飞艇质量和惯量特性的计算方法与分析

针对一类具有双拼椭球体外形的平流层飞艇,根据适当假设,给出该类飞艇质量和惯量特性的解析计算方法.以飞艇上升过程为例,通过仿真计算给出该过程飞艇质量、质心位置和转动惯量的变化曲线,结合理论分析,验证该计算方法的合理性.最后,简要分析了质量和惯量特性变化对飞艇运动稳定性和能控性的影响.