Switched-model-based compound control of hypersonic vehicles with input nonlinearities

Nonlinear Dynamics - Focusing on the large-envelope control problem of air-breathing hypersonic vehicles (AHVs), this paper employs a switched control-oriented model (SCOM) to describe vehicle...     

Robust adaptive dynamic surface control design for a flexible air-breathing hypersonic vehicle with input constraints and uncertainty

The flight control problem of a flexible air-breathing hypersonic vehicle is presented in the presence of input constraint and aerodynamic uncertainty. A control-oriented model, where aerodynamic uncertainty and the strong couplings between the engine and flight dynamics are included, is derived to reduce the complexity of controller design. The flexible dynamics are viewed as perturbations of the model. They are not taken into consideration at the level of control design, the influence of which is evaluated through simulation. The control-oriented model is decomposed into velocity subsystem and altitude subsystem, which are controlled separately. Then robust adaptive controller is developed for the velocity subsystem, while the controller which combines dynamic surface control and radial basis function neural network is designed for the altitude subsystem. The unknown nonlinear function is approximated by the radial basis function neural network. Minimal-learning parameter technique is utilized to estimate the maximum norm of ideal weight vectors instead of their elements to reduce the computational burden. To handle input constraints, additional systems are constructed to analyze their impact, and the states of the additional systems are employed at the level of control design and stability analysis. Besides, “explosion of terms” problem in the traditional backstepping control is circumvented using a first-order filter at each step. By means of Lyapunov stability theory, it is proved theoretically that the designed control law can assure that tracking error converges to an arbitrarily small neighborhood around zero. Simulations are performed to demonstrate the effectiveness of the presented control scheme in coping with input constraint and aerodynamic uncertainty.     

Input-and-measurement event-triggered control for flexible air-breathing hypersonic vehicles with asymmetric partial-state constraints

In this paper, an input-and-measurement event-triggered control scheme considering asymmetric partial-state constraints is proposed for flexible air-breathing hypersonic vehicles (FAHV) subject to lumped disturbances and limited resources. To realize a precise disturbance rejection with decreased communication burden in sensor-to-control channels, intermittent measurement-based extended state observers using switching threshold samplers are developed in altitude and velocity subsystems, while the quantitative relationship between the upper bounds of observation errors and the design parameters of switching triggering mechanism is derived. Subsequently, to ensure the angle of attack (AoA) well within the allowable operational region and simultaneously achieve a reference tracking with expected characteristic, asymmetric constraints imposed on partial states including AoA, velocity, and altitude are embedded in design process, while a one-to-one nonlinear mapping is designed to avoid the violation of state constraint of AoA without enforcing feasibility conditions on virtual control laws, and a modified prescribed performance control is constructed to govern the output constraints of velocity and altitude, releasing the demand on the precise knowledge of initial states. Next, to maintain the resources occupation (energy and communication in controller-to-actuator channel) at low levels and ensure a desirable tracking precision, robust control laws based on switching event-triggered mechanisms are designed for FAHV to circumvent Zeno phenomena and compensate for the sampling error induced by event-triggered conditions. The simulation results and comparisons validate the effectiveness of the proposed scheme.

     

热喷干扰气体模型对飞行器气动特性影响分析

针对不同气体模型对高超声速飞行器喷流反作用控制系统(RCS)热喷干扰流场模拟的计算效率和准确性问题, 基于喷流燃气物理化学模型, 通过数值求解含化学反应源项的三维N-S方程, 建立了飞行器RCS热喷干扰流场数值模拟方法, 分别采用化学反应流、反应冻结流、二元异质流以及空气喷流四种气体模型开展了典型外形热喷干扰流场的数值模拟, 研究了不同气体模型对热喷干扰流场结构、飞行器气动力热特性的影响, 分析了不同马赫数、飞行高度下的变化规律. 研究表明: 化学反应流模型计算精度较高, 计算与风洞试验数据的吻合程度优于其他三种简化模型; 在本文的低空条件下, 采用简化模型进行热喷干扰流场数值模拟, 会低估分离区大小, 使飞行器气动力特性预测出现偏差, 同时也会低估表面热环境, 对防热系统设计不利, 随着马赫数增加, 简化模型对气动力热特性预估的误差进一步增大, 同时不同简化模型之间的差异也进一步增大; 飞行高度较高时, 模型之间的差异减小, 此时可采用简化模型进行计算以提高计算效率. 本文的研究结果可为飞行器热喷干扰流场数值模拟及喷流反作用控制系统设计提供参考.      

基于主动控制策略的机翼颤振特性模拟

航空航天飞行器舵翼类结构的气动颤振是一种灾难性的动力学行为.在基于偶极子理论的气动弹性动力学模型中,气动载荷可表达为基于结构动力学响应的一种状态反馈的闭环控制力,控制律取决于翼型的几何参数、材料参数、结构动力学特性以及来流速度等多种条件,通常需通过实际飞行或风洞实验进行辨识与检验.在实验室条件下,以系统动力学响应的模态特征等效为前提,提出了一种基于人工主动控制的方式进行气动载荷下舵翼类结构自激颤振的特征值跟踪策略.建立并讨论了等效系统的非自伴随动力学微分方程及其特征方程的求解过程,并与通用软件的计算结果进行了对比,二者具有较好的一致性.通过优化搜索分别获得了位移和速度的最优反馈点、最优作动点位置及最优反馈增益系数,经对比计算拟合得到风速-位移增益曲线和风速-速度增益曲线,从而实现了由单点反馈、单点作动的集中力的闭环控制等效系统的真实气动力分布控制.仿真算例表明,由此预示的实验过程无需辨识和重构非定常气动力的时域波形,无需其他干预即可实现地面模拟实验,主动控制的效果满足预期,初步实现了自激颤振的特征值跟踪,为进一步推动主动控制模拟实验及颤振参数辨识提供了基础.      

高超声速飞行流场中的最大氧离解度分析简

针对大气层内高超声速飞行时的化学非平衡现象,建立了沿驻点线流动的空气中氧离解度的计算模型. 模型假设氮气在氧气未充分离解时不发生离解,并且不涉及边界层内的复合反应. 理论计算发现,空气中氧的离解度随飞行高度的增加呈先增后减的非单调变化规律,其原因是由于化学反应平衡移动与非平衡效应相互作用的结果. 这一结论得到了数值模拟结果的验证,同时也解释了文献中当飞行高度较高时真实气体效应减弱的现象. 基于驻点线的近似理论模型,计算得到了轴对称钝头体绕流流场中的最大氧离解度及边界层外缘温度随飞行速度和高度变化的等值线图谱,相关结果可以为工程设计所用.     

高超声速飞行流场中的最大氧离解度分析

针对大气层内高超声速飞行时的化学非平衡现象,建立了沿驻点线流动的空气中氧离解度的计算模型. 模型假设氮气在氧气未充分离解时不发生离解,并且不涉及边界层内的复合反应. 理论计算发现,空气中氧的离解度随飞行高度的增加呈先增后减的非单调变化规律,其原因是由于化学反应平衡移动与非平衡效应相互作用的结果. 这一结论得到了数值模拟结果的验证,同时也解释了文献中当飞行高度较高时真实气体效应减弱的现象. 基于驻点线的近似理论模型,计算得到了轴对称钝头体绕流流场中的最大氧离解度及边界层外缘温度随飞行速度和高度变化的等值线图谱,相关结果可以为工程设计所用.      

Aeroelastic stability analysis considering a continuous flight envelope

This paper presents a new methodology to analyze aeroelastic stability in a continuous range of flight envelope with varying parameter of velocity and altitude. The focus of the paper is to demonstrate that linear matrix inequalities can be used to evaluate the aeroelastic stability in a region of flight envelope instead of a single point, like classical methods. The proposed methodology can also be used to study if a system remains stable during an arbitrary motion from one point to another in the flight envelope, i.e., when the problem becomes time-variant. The main idea is to represent the system as a polytopic differential inclusion system using rational function approximation to write the model in time domain. The theory is outlined and simulations are carried out on the benchmark AGARD 445.6 wing to demonstrate the method. The classical pk-method is used for comparing results and validating the approach. It is shown that this method is efficient to identify stability regions in the flight envelope.     

Finite time integral sliding mode control of hypersonic vehicles

This study investigates the tracking control problem for the longitudinal model of an airbreathing hypersonic vehicle (AHV) with external disturbances. By introducing finite time integral sliding mode manifolds, a novel finite time control method is designed for the longitudinal model of an AHV. This control method makes the velocity and altitude track the reference signals in finite time. Meanwhile, considering the large chattering phenomenon caused by high switching gains, an improved sliding mode control method based on nonlinear disturbance observer is proposed to reduce chattering. Through disturbance estimation for feedforward compensation, the improved sliding mode controller may take a smaller value for the switching gain without sacrificing disturbance rejection performance. Simulation results are provided to confirm the effectiveness of the proposed approach.     

Airship horizontal trajectory tracking control based on Active Disturbance Rejection Control (ADRC)

Aiming at flight property of airship, a trajectory tracking controller of airship horizontal model is designed based on active disturbance rejection control (ADRC). The six Degree of Freedom (DOF) dynamic model of airship is simplified at a horizontal plane. ADRC is used to realize the decoupling control for the multivariable system. The uncertain items of the model and external disturbances are estimated by the extended state observer (ESO) and dynamic feedback compensation is carried on at real time. The disturbance of wind is added to the simulation environment. The simulation results show that the designed tracking controller can overcome the influences of uncertain items of the model and external disturbances, and track the desired trajectory rapidly and steadily, and possess good robustness and control performances.     

Certain optimum forms of radiating bodies in supersonic gas flow

We solve two variational problems on determining the optimum form of a radiating body of given dimensions in a gas flow at high supersonic velocity with a laminar flow regime in the boundary layer. We consider the case in which two heat transfer processes are significant: convective heat transfer from the gas to the body and radiation from the body surface. The first problem involves finding the contour of the body which receives the minimal thermal flux. In the solution of the second problem we seek that form of the thermally isolated body for which its surface temperature will be minimal for given parameters of the approaching stream or for which the motion velocity will be maximal for a given wall temperature and flight altitude.     

Inner-outer feedback linearization for quadrotor control: two-step design and validation

This paper proposes a novel control architecture for quadrotors that relies twice on the Feedback Linearization technique. The solution comprises a tracking inner-loop resulting from applying the mentioned method to the attitude and altitude dynamics. The horizontal movement, and, thereby, the zero dynamics, are stabilized without linearizing nor simplifying it by resorting to the same nonlinear technique. Linear quadratic controllers with integral action are implemented to the resulting chain of integrators of the inner and outer loops. As a result, the inner-loop dynamics asymptotically track the desired attitude and altitude over a broad region of the state-space, and the outer-loop yields a tracking system that is input-to-state stable and exponentially stable in the absence of external inputs. The stability of the proposed inner-outer loop control architecture is studied, leading to the proof of asymptotic stability in an extensive region of the state-space. Trajectory tracking, the capacity to overcome significant deviations on the mass and inertia values, and the robustness to external disturbances are evaluated using a simulation model, in which measurement noise and saturation limits are considered. In addition, comparisons regarding the performance in trajectory tracking of the proposed strategy and the results obtained with similar solutions from the literature are established. Experimental tests were conducted using a commercially available drone, equipped with an Inertial Measurement Unit, a compass, and an altimeter. A motion capture system gives the inertial position of the drone. The results obtained allow the validation of the modeling and control system solution.

     

近空间高超声速飞行器气动特性研究的若干关键问题

在30$\sim$70km空域机动飞行的高超声速飞行器的优点是可以耦合利用所处空域的空气产生的升力和高速飞行的离心力进行远距离机动滑翔飞行,具有重要的实用价值.尽管过去数十年在高超声速流动研究方面取得显著进展,但在设计研究近空间远程滑翔的高超声速飞行器方面仍然存在许多挑战,特别是对特定飞行条件下的流动机理了解不清楚.本文介绍了作者研究团队在开展近空间高超声速飞行器有关的关键气动问题方面的研究进展,主要包括:建立了近空间高超声速飞行的流动模型,发展了系统的相关计算空气动力学方法,针对高空高速飞行条件下稀薄气体效应和真实气体效应的耦合作用影响研究了合适的滑移边界条件,考虑了不同组分存在条件下的温度、速度和压力的滑移效应影响;提出了飞行器气动外形的动态优化方法,获得了可工程实用化的高升阻比飞行器气动外形;建立了高速飞行器动稳定性理论,在实现高超声速飞行器动态稳定飞行方面取得重大进展;最后讨论了高超声速飞行器设计中进一步需要关注的若干关键技术和科学问题、可能解决的途径及其所涉及的学科发展方向.      

Nonlinear adaptive control for quadrotor flying vehicle

In this work, we deal with autonomous tracking and disturbance rejection problem of quadrotor vehicle flying in uncertain environment. The vehicles kinematic and modeling error uncertainties are associated with external disturbance, inertia, mass, and nonlinear aerodynamic forces and moments. The proposed method integrate the techniques from adaptive control and robust control theory. Robust and adaptive control algorithms for translational and orientation tracking are derived using Lyapunov method. It is shown in our analysis that the altitude, position, and attitude tracking errors are bounded and their bounds asymptotically converge to zero in Lyapunov sense. Simulation results on a commercial quadrotor flying vehicle are given to demonstrate the effectiveness of theoretical arguments for real world application.     

四旋翼飞行器建模及位置跟踪控制(英文)

相对其他无人飞行器平台,四旋翼飞行器有其独特的优势,因而受到广泛的关注。位置跟踪控制对四旋翼飞行器的应用非常重要。在阐述四旋翼飞行器的飞行原理和操控机制的基础上,研究了其动力学模型,并提出了一种简化的数学模型。四旋翼飞行器是欠驱动耦合系统,为了实现系统解耦并得到清晰的控制回路,设计了多回路PID控制方案,其控制目标是位置和偏航角,而姿态角和横滚角由位置误差调节。最后,通过仿真验证了控制方法的有效性。     

Tracking control of uncertain switched nonlinear cascade systems: a nonlinear H ∞ sliding mode control method

This paper considers the tracking control problem for a class of uncertain switched nonlinear cascade systems via the multiple Lyapunov functions (MLFs) method. Each subsystem under consideration is composed of two cascade-connected parts: the null space dynamics part and the range space dynamics part. The two main robust control strategies, nonlinear H _∞ control (NHC) and the sliding mode control (SMC), are integrated to function in a complementary manner for tracking control tasks. Furthermore, sufficient conditions for the solvability of the tracking control problem of the switched system and design of both switching laws and controllers are presented. Finally, a simulation example is provided to demonstrate the feasibility of the developed method.     

Evaluation of stochastic particle dispersion modeling in turbulent round jets

ODT (one-dimensional turbulence) simulations of particle-carrier gas interactions are performed in the jet flow configuration. Particles with different diameters are injected onto the centerline of a turbulent air jet. The particles are passive and do not impact the fluid phase. Their radial dispersion and axial velocities are obtained as functions of axial position. The time and length scales of the jet are varied through control of the jet exit velocity and nozzle diameter. Dispersion data at long times of flight for the nozzle diameter (7 mm), particle diameters (60 and 90 µm), and Reynolds numbers (10, 000–30, 000) are analyzed to obtain the Lagrangian particle dispersivity. Flow statistics of the ODT particle model are compared to experimental measurements. It is shown that the particle tracking method is capable of yielding Lagrangian prediction of the dispersive transport of particles in a round jet. In this paper, three particle-eddy interaction models (Type-I, -C, and -IC) are presented to examine the details of particle dispersion and particle-eddy interaction in jet flow.     

Modeling of thermally activated dislocation glide and plastic flow through local obstacles

A unified phenomenological model is developed to study the dislocation glide through weak obstacles during the first stage of plastic deformation in metals. This model takes into account both the dynamical responses of dislocations during the flight process and thermal activations while dislocations are bound by obstacle arrays. The average thermal activation rate is estimated using an analytical model based on the generalized Friedel relations. Then, the average flight velocity after an activation event is obtained numerically by discrete dislocation dynamics (DD). To simulate the dynamical dislocation behavior, the inertia term is implemented into the equation of dislocation motion within the DD code. The results from the DD simulations, coupled with the analytical model, determine the total dislocation velocity as a function of the stress and temperatures. By choosing parameters typical of the face centered cubic metals, the model reproduces both obstacle control and drag control motion in low and high velocity regimes, respectively. As expected by other string models, dislocation overshoots of obstacles caused by the dislocation inertia at the collisions are enhanced as temperature goes down.     

On the need of nonlinear control for efficient model-based wake stabilization

The mitigation of oscillatory vortex shedding behind a cylinder is chosen as a well-investigated benchmark problem to compare model-based feedback flow control approaches. The flow is sensed by a single velocity signal in the wake and is manipulated via a single volume force actuator. A low-dimensional proper orthogonal decomposition Galerkin model is adopted as a control-oriented fluid flow representation. An extended Kalman filter is used as an effective means for online dynamic state estimation. Investigated strategies of linear and nonlinear controller design include pole placement, linear parameter-varying, input–output linearization, Lyapunov-based backstepping, and nonlinear model predictive control. These strategies are applicable to a large class of flows with oscillatory dynamics and to experimental conditions, where variants have already been used. Controllers are evaluated and compared based on their application to the full plant, that is, to the direct numerical simulation of the wake, emulating an experiment with a single hot-wire sensor. Overall, nonlinear closed-loop control is shown to be distinctly superior to linear approaches. As is often the case, physics dictates a similarity of successful control commands, irrespective of the design approach, and differentiates these controllers, as a group, from less successful approaches.     

临近空间大气密度时空扰动规律及建模研究

大气密度是飞行器能源动力设计、飞行控制中的重要输入参数. 近年来, 多项研究发现, 对于临近空间高层大气, 常用经验模型如USSA-76, NRLMSISE-00的密度预示值偏大. 另外, 随着飞行器精细化设计趋势, 要求经验模型可预示不同纬度、昼夜和季节条件下的密度特性. 基于此, 本文利用卫星观测数据全面分析了临近空间大气密度随纬度、地方时、日期的变化规律, 包括变化模式和变化幅度. 纬度、日期引起的变化幅度大于地方时引起的变化幅度. 纬度、日期引起的密度变化在不同高度范围表现出不同模式; 变化幅度在78 km附近达最大值, 在22 km和92 km附近达局部极小值. 地方时引起的密度变化随高度递增. 根据大气密度的时空变化特性, 本文提出了临近空间大气密度的时空扰动模型, 该模型能描述临近空间大气密度及其随纬度、地方时、日期的变化规律. 与以往经验模型相比, 时空扰动模型可更好地描述不同高度下密度的时空变化规律. 在相同误差带条件下, 本文模型的置信度明显优于NRLMSISE-00. 本文建模方法合理, 模型结果对临近空间飞行器设计有应用价值.