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.     

Ascent trajectory optimization for stratospheric airship with thermal effects

Ascent trajectory optimization with thermal effects is addressed for a stratospheric airship. Basic thermal characteristics of the stratospheric airship are introduced. Besides, the airship’s equations of motion are constructed by including the factors about aerodynamic force, added mass and wind profiles which are developed based on horizontal-wind model. For both minimum-time and minimum-energy flights during ascent, the trajectory optimization problem is described with the path and terminal constraints in different scenarios and then, is converted into a parameter optimization problem by a direct collocation method. Sparse Nonlinear OPTimizer(SNOPT) is employed as a nonlinear programming solver and two scenarios are adopted. The solutions obtained illustrate that the trajectories are greatly affected by the thermal behaviors which prolong the daytime minimum-time flights of about 20.8% compared with that of nighttime in scenario 1 and of about 10.5% in scenario 2. And there is the same trend for minimum-energy flights. For the energy consumption of minimum-time flights, 6% decrease is abstained in scenario 1 and 5% decrease in scenario 2. However, a few energy consumption reduction is achieved for minimum-energy flights. Solar radiation is the principal component and the natural wind also affects the thermal behaviors of stratospheric airship during ascent. The relationship between take-off time and performance of airship during ascent is discussed. it is found that the take-off time at dusk is best choice for stratospheric airship. And in addition, for saving energy, airship prefers to fly downwind.     

末端制导飞行轨迹的仿真与试飞

提出了战斗机完成制导装置末端制导阶段飞行轨迹的仿真和试飞方法.末端制导阶段的飞行轨迹要求进入段尽可能减小高度损失,并在俯冲段满足精确的轨迹跟踪.采用6自由度全量非线性方程,考虑纵向和横航向运动的相互耦合关系,通过对飞机的高速度、大俯冲角、大落差飞行全过程进行仿真研究,分析了3种利用滚转操纵进入俯冲的情况,获得了满足高精度飞行轨迹的操纵方案,即在进入段,先操纵副翼使滚转角接近180°,拉杆使俯冲角满足轨迹要求后,再反向操纵副翼使飞机正飞进入俯冲.通过飞行试验验证了方案的合理性和有效性.研究表明:该方法在保证飞行安全的前提下,提高了飞行轨迹精度和试飞效率.     

Backstepping sliding-mode control of stratospheric airships using disturbance-observer

In the presence of unknown disturbances and model parameter uncertainties, this paper develop a nonlinear backstepping sliding-mode controller (BSMC) for trajectory tracking control of a stratospheric airship using a disturbance-observer (DO). Compared with the conventional sliding mode surface (SMS) constructed by a linear combination of the errors, the new SMS manifold is selected as the last back-step error to improve independence of the adjustment of the controller gains. Furthermore, a nonlinear disturbance-observer is designed to process unknown disturbance inputs and improve the BSMC performances. The closed-loop system of trajectory tracking control plant is proved to be globally asymptotically stable by using Lyapunov theory. By comparing with traditional backstepping control and SMC design, the results obtained demonstrate the capacity of the airship to execute a realistic trajectory tracking mission, even in the presence of unknown disturbances, and aerodynamic coefficient uncertainties.     

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。      

一种非线性航迹自适应跟踪控制方法

针对小型无人飞行器航迹跟踪精度和飞行品质问题,提出了一种基于非线性航迹的自适应跟踪控制方法.应用五阶B样条拟合航点,构建非线性期望航迹;建立基于非线性期望航迹Serret-Frenet坐标系下的位置和运动航向误差方程;根据误差方程设计渐近稳定收敛的自适应运动航向控制律.并应用此方法进行了外场飞行实验,实验结果表明自适应航迹跟踪控制方法有效且能保证航迹跟踪精度.     

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.     

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。      

可重复使用运载器再入轨迹次实时优化

新一代可重复使用运载器RLV(Reusable Launch Vehicle)再入时应具备自主导航的能力,其实现的关键是用机载计算机近实时或实时地生成一条满足各种约束条件的再入轨迹.根据RLV再入的特点,引入了新的假设,对再入轨迹方程进行简化处理,优化难度降低,工作量减少.另外引入次优化轨迹的概念,对控制量(迎角和滚转角)的优化分两步进行,每步只对当中一个控制量进行优化.这样处理能在很大程度上加快算法的收敛速度.仿真结果表明,只需10s左右的时间就能产生一条满足终端约束条件、控制量约束条件和加热率约束条件的次优化轨迹.其结果具有较好的工程应用价值.      

Earth–Moon low energy trajectory optimization in the real system

The problem of the Earth–Moon low energy trajectory optimization in the real system (the model defined by the JPL ephemeris DE405) is considered in this paper. First, this problem is investigated in the model of circular restricted three-body problem, since the fuel consumption is closely related to the Jacobi integral of the transfer trajectory, a method based on Jacobi integral is proposed and eight optimal trajectories are obtained. These optimal trajectories provide initial information (the flight time and the braking velocity impulse) to search the optimal low energy trajectories in the real system through optimization techniques. Considering the merit and drawback of particle swarm optimization and differential evolution algorithm in solving the space trajectory problem, an improved cooperative evolutionary algorithm is put forward. Result shows that the low energy trajectories in the real system are more fuel-efficient than the corresponding ones under the circular restricted three-body problem.     

微小型无人直升机避障最优轨迹规划

针对无人直升机在低空复杂环境下避障飞行问题,提出了一种基于非线性最优控制理论的求解策略.以避障机动飞行时间为优化目标,无人直升机六自由度非线性动力学方程为等式约束,直升机飞行性能限制以及三维空间中障碍物限制等因素为不等式约束,建立了避障机动飞行的最优控制模型.然后利用高斯伪谱法（GPM,Gauss Pseudospectral Method）将轨迹规划问题转化为非线性规划（NLP,Non-Linear Programming）问题,并采用序列二次规划算法进行求解.在此基础上研究了障碍物尺寸对最优轨迹的影响.计算结果表明,该方法能够以较高的精度生成真实可行的避障飞行轨迹,最优机动动作取决于障碍物纵横向尺寸比.      

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。     

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.     

无人机高机动抗扰轨迹跟踪控制方法

针对传统的四旋翼控制方法在高机动飞行时控制效果不佳,难以跟踪机动性较强的轨迹且控制精度较低的问题,设计了基于增量非线性动态逆控制(INDI)方法和微分平坦前馈的轨迹跟踪控制器,不仅提高了高机动轨迹的跟踪精度,也增强了抗扰能力。由于角加速度无法直接获得,该方法对其非常敏感,设计了多种角加速度估计方法进行对比,通过飞行试验选择了效果最佳的互补滤波方法。试验结果证明:设计的基于互补滤波的前馈INDI方法可以控制飞行器快速、准确地跟踪高机动轨迹,且具有较强的抗扰能力。      

The yaw stability analysis for stratospheric airships in float situation

When a stratospheric airship free floats at pressure altitude, the sideslip angle of the airship is neither random nor against the wind, but is stable on certain values. According to classical potential flow theory, a simplified two-dimensional ellipse and three-dimensional ellipsoid are firstly analyzed respectively, which implied that the airship could present crosswind orientation. The numerical investigations (CFD) on the yaw stability based on a bare hull and a finned airship are employed for verifying the theory conclusion. It is found that the finned airships can remain stable when its sideslip Angle is 55–70°, which is less than 90° of the stable angle of the ellipsoid and bare hull, but statically unstable at low sideslip angles, its static instability is similar to that of dynamic flight. Then the fight data of three stratospheric airships is analyzed. The yaw stability in flight data generally agrees with expectations drawn of theoretical and numerical simulation. These investigations serve to provide references for yaw control and configuration design of airships.     

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.     

Optimal tracking and formation keeping near a general Keplerian orbit under nonlinear perturbations

This study presents a semi-analytic approach for optimal tracking and formation keeping with high precision. For a continuous-thrust propulsion system, optimal formation keeping problems near a general Keplerian orbit are formulated with respect to a reference trajectory which is an explicit function of time. A nonlinear optimal tracking control law is then derived in generic form as a function of the states by employing generating functions in the theory of Hamiltonian systems. The applicability of the overall process is not affected by the complexity of dynamics and the selection of coordinates. As it allows us to design a nonlinear optimal feedback controller in the Earth-centered inertial frame, a variety of nonlinear perturbations can be incorporated easily without complicated coordinate transformations. Numerical experiments demonstrate that the nonlinear tracking control logic achieves superior tracking accuracy and cost reduction by accommodating higher-order nonlinearities.     

基于backstepping/RHO的变体飞机控制器设计

为了确保变体飞机在变体过程中的飞行稳定性,提出了一种并行修正控制器设计方案.采用backstepping方法进行标称控制器设计,提供基本的飞行稳定性和跟踪性能.使用雅可比线性化方法对变体飞机非线性方程进行线性化得到线性化模型,采用基于指令滤波器的滚动时域优化（RHO,Receding Horizon Optimal）方法进行修正控制器设计.在有限时域区间内实时解算修正控制量,对标称控制器进行补偿.从航迹角控制系统仿真结果可以看出,航迹角能够较好地跟踪指令信号,基本不受变体过程的影响,飞行控制系统满足实时性和鲁棒性的要求.