Adaptive sliding mode backstepping control for near space vehicles considering engine faults

A fault tolerant control methodology based adaptive sliding mode(ASM) backstepping is proposed for near space vehicle(NSV) attitude control system under engine faults. The proposed scheme combined adaptive backstepping with the sliding mode control strategy could guarantee the system’s stability and track desired signals under external disturbances and engine faults. Firstly, attitude mode description and the engine faulty model are given. Secondly, a nominal control law is designed.Thirdly, a sliding mode observer is given later in order to estimate both the information of engine faults and external disturbances. An adaptive sliding mode technology based on the previous nominal control law is developed via updating faulty parameters. Finally,analyze the system’s fault-tolerant performance and reliability through experiment simulation, which verifies the proposed design of fault-tolerant control can tolerate engine faults, as well as the strong robustness for external disturbance.

Communication Resource-Efficient Vehicle Platooning Control With Various Spacing Policies

Platooning represents one of the key features that connected automated vehicles may possess as it allows multiple automated vehicles to be maneuvered cooperatively with small headways on roads. However, a critical challenge in accomplishing automated vehicle platoons is to deal with the effects of intermittent and sporadic vehicle-to-vehicle data transmissions caused by limited wireless communication resources. This paper addresses the co-design problem of dynamic event-triggered communication scheduling and cooperative adaptive cruise control for a convoy of automated vehicles with diverse spacing policies. The central aim is to achieve automated vehicle platooning under various gap references with desired platoon stability and spacing performance requirements, while simultaneously improving communication efficiency. Toward this aim, a dynamic event-triggered scheduling mechanism is developed such that the intervehicle data transmissions are scheduled dynamically and efficiently over time. Then, a tractable co-design criterion on the existence of both the admissible event-driven cooperative adaptive cruise control law and the desired scheduling mechanism is derived. Finally, comparative simulation results are presented to substantiate the effectiveness and merits of the obtained results.

Fault tolerant control for near space vehicle:a survey and some new results

A review on fault-tolerant control（FTC） for near space vehicle（NSV） is presented.First,the concept of near space is introduced,the background of NSV is emphasized,and the model characteristics of NSV in faulty case are investigated.Then,a comparison of different existing approaches is briefly carried out,and achievements on the current research in this field are also presented in the view of the practical application.Furthermore,several existing advanced FTC results for nonlinear flight control systems are given.Finally,the recent literature of NSV are presented to provide an overall view of future developments in this area.

Switching disturbance rejection attitude control of near space vehicles with variable structure

A switching disturbance rejection attitude control law is proposed for a near space vehicle(NSV) with variable structure.The multiple flight modes, system uncertainties and disturbances of the NSV are taken into account based on switched nonlinear systems. Compared with traditional backstepping design methods,the proposed method utilizes the added integrals of attitude angle and angular rate tracking errors to further decrease the tracking errors. Moreover, to reduce the computation complexity, a rapid convergent differentiator is employed to obtain the derivative of the virtual control command. Finally, for disturbance rejection, based on the idea from the extended state observer(ESO), two disturbance observers are designed by using non-smooth functions to estimate the disturbances in the switched nonlinear systems. All signals of the closed-loop system are proven to be uniformly ultimately bounded under the Lyapunov function framework. Simulation results demonstrate the effectiveness of the proposed control scheme.

Prescribed performance neural control to guarantee tracking quality for near space kinetic kill vehicle

A prescribed performance neural controller to guarantee tracking quality is addressed for the near space kinetic kill vehicle (NSKKV) to meet the state constraints caused by side window detection. Different from the traditional prescribed performance control in which the shape of the performance function is constant, this paper exploits new performance functions which can change the shape of their function according to different symbols of initial errors and can ensure the error convergence with a small overshoot. The neural backstepping control and the minimal learning parameters (MLP) technology are employed for exploring a prescribed performance controller (PPC) that provides robust tracking attitude reference trajectories. The highlight is that the transient performance of tracking errors is satisfactory and the computational load of neural approximation is low. The pseudo rate (PSR) modulator is used to shape the continuous control command to pulse or on-off signals to meet the requirements of the thruster. Numerical simulations show that the proposed method can achieve state constraints, pseudo-linear operation and high accuracy.

Adaptive functional link network control of near-space vehicles with dynamical uncertainties

The control law design for a near-space hypersonic vehicle（NHV） is highly challenging due to its inherent nonlinearity,plant uncertainties and sensitivity to disturbances.This paper presents a novel functional link network（FLN） control method for an NHV with dynamical thrust and parameter uncertainties.The approach devises a new partially-feedback-functional-link-network（PFFLN） adaptive law and combines it with the nonlinear generalized predictive control（NGPC） algorithm.The PFFLN is employed for approximating uncertainties in flight.Its weights are online tuned based on Lyapunov stability theorem for the first time.The learning process does not need any offline training phase.Additionally,a robust controller with an adaptive gain is designed to offset the approximation error.Finally,simulation results show a satisfactory performance for the NHV attitude tracking,and also illustrate the controller＇s robustness.

LSTM-based lane change prediction using Waymo open motion dataset: The role of vehicle operating space

Lane change prediction is critical for crash avoidance but challenging as it requires the understanding of the instantaneous driving environment.With cutting-edge artificial intelligence and sensing technologies,autonomous vehicles(AVs)are expected to have exceptional perception systems to capture instantaneously their driving environments for predicting lane changes.By exploring the Waymo open motion dataset,this study proposes a framework to explore autonomous driving data and investigate lane change behaviors.In the framework,this study develops a Long Short-Term Memory(LSTM)model to predict lane changing behaviors.The concept of Vehicle Operating Space(VOS)is introduced to quantify a vehicle's instantaneous driving environment as an important indicator used to predict vehicle lane changes.To examine the robustness of the model,a series of sensitivity analysis are conducted by varying the feature selection,prediction horizon,and training data balancing ratios.The test results show that including VOS into modeling can speed up the loss decay in the training process and lead to higher accuracy and recall for predicting lane-change behaviors.This study offers an example along with a methodological framework for transportation researchers to use emerging autonomous driving data to investigate driving behaviors and traffic environments.

Vehicle Planar Motion Stability Study for Tyres Working in Extremely Nonlinear Region

Many researches on vehicle planar motion stability focus on two degrees of freedom（2DOF） vehicle model, and only the lateral velocity （or side slip angle） and yaw rate are considered as the state variables. The stability analysis methods, such as phase plane analysis, equilibriums analysis and bifurcation analysis, are all used to draw many classical conclusions. It is concluded from these researches that unbounded growth of the vehicle motion during unstable operation is untrue in reality thus one limitation of the 2DOF model. The fundamental assumption of the 2DOF model is that the longitudinal velocity is treated as a constant, but this is intrinsically incorrect. When tyres work in extremely nonlinear region, the coupling between the vehicle longitudinal and lateral motion becomes significant. For the purpose of solving the above problem, the effect of vehicle longitudinal velocity on the stability of the vehicle planar motion when tyres work in extremely nonlinear region is investigated. To this end, a 3DOF model which introducing the vehicular longitudinal dynamics is proposed and the 3D phase space portrait method is employed for visualization of vehicle dynamics. Through the comparisons of the 2DOF and 3DOF models, it is discovered that the vehicle longitudinal velocity greatly affects the vehicle planar motion, and the vehicle dynamics represented in phase space portrait are fundamentally different from that of the 2DOF model. The vehicle planar motion with different front wheel steering angles is further represented by the corresponding vehicle route, yaw rate and yaw angle. These research results enhance the understanding of the stability of the vehicle system particularly during nonlinear region, and provide the insight into analyzing the attractive region and designing the vehicle stability controller, which will be the topics of future works.

Adaptive Sampling for Near Space Hypersonic Gliding Target Tracking

For modern phased array radar systems,the adaptive control of the target revisiting time is important for efficient radar resource allocation,especially in maneuvering target tracking applications.This paper presents a novel interactive multiple model(IMM)algorithm optimized for tracking maneuvering near space hypersonic gliding vehicles(NSHGV)with a fast adaptive sam-pling control logic.The algorithm utilizes the model probabilities to dynamically adjust the revisit time corresponding to NSHGV maneuvers,thus achieving a balance between tracking accuracy and resource consumption.Simulation results on typical NSHGV targets show that the proposed algo-rithm improves tracking accuracy and resource allocation efficiency compared to other conventional multiple model algorithms.

The Orbital Error Analysis and Study of Space Vehicle Active Phase

In this paper we solve the three-dimensional coordinate that the satellite is relative to the geocentric coordinate under certain conditions, making use of the satellite orbit standard trajectory differential equations. By means of the method of tri-parametric equation fitting, we confirm the three-dimensional trajectory function of target flying object to geocentric coordinate in double satellites observation conditions, and analyze theoretical errors.

Research Progress in Aerospace Vehicles Propelled by Rocket-Based Combined Cycle Engines

The research status on the development of RBCC engines and corresponding aerospace vehicles around the world was overviewed,and the technical and application characteristics of RBCC technology were summarized.New development trends of combined cycle engines as well as space transportation were analyzed,and lastly,some suggestions on the development of RBCC and the relative aerospace vehicles were proposed.

考虑负荷空间均衡和充电站合作博弈的快速充电定价机制

为了平衡快速充电负荷空间分布,提高电动汽车用户充电满意度,提出考虑负荷空间均衡和充电站合作博弈的快速充电动态定价机制。首先,通过实际订单数据逆地理编码得到出行概率转移矩阵,结合路网模型和速度-流量模型建立电动汽车充电负荷时空分布模型;然后,考虑用户主观意愿,建立计及用户偏好的充电站选择决策模型,模拟用户对于充电站选择的理性决策行为;最后,以充电站节点负荷均衡性为目标,建立区域内快速充电站合作模式下的动态定价博弈模型,通过迭代算法求解均衡值,并利用Shapley值法对合作联盟所得剩余收益进行分配。仿真实例表明,所提快速充电站动态定价策略能有效降低充电站节点的负荷方差,提高充电桩利用率和充电站收益,并减小用户排队时间,提高用户满意度。

轨道车辆垂向轮轨力时域识别对比及其机器学习修正

为了尽可能减小轨道车辆垂向轮轨力时域识别中存在的误差,以时域法为基础,开展了基于机器学习修正的轨道车辆垂向轮轨力识别研究.首先建立了车辆动力学仿真模型,获取了车辆在随机轨道激励下以250km/h速度行驶时的轴箱加速度响应和垂向轮轨力.其次,建立了Green函数法、状态空间法这2种时域法对应的动载荷识别模型,对状态空间法的初值误差进行了分析,并引入多项式拟合法修正其趋势项误差,进而对比分析了2种方法的计算精度和计算效率.然后,针对时域法存在的识别误差,提出采用NARX(nonlinear autoregressive models with exogenous inputs)模型对识别误差进行训练和预测,用于消减模型中存在的如响应观测不全与观测噪声等因素造成的影响,进而对时域法识别结果进行修正,提高识别精度.最后,通过一个10自由度轨道车辆垂向动力学模型,对方法的正确性进行了验证.研究结果表明:2种方法对轨道车辆垂向轮轨力均具有较高的识别精度,对于各轮对的识别精度各有优劣;在计算效率方面,状态空间法比Green函数法更优;经NARX模型修正的2种时域法对轨道车辆垂向轮轨力均具有很好的识别效果,识别值与正演值的Pearson相关系数大于0.99,为极强相关.基于NARX模型的机器学习误差修正方法可有效提高时域识别精度,可以为后续轨道车辆轮轨力预测提供参考,具有较强的工程运用价值.

基于空间目标定向观测的飞行器导航方法研究

本文主要研究基于定向观测星相机和惯性测量单元(inertial measurement unit, IMU)信息融合的飞行器高精度导航方法.在已有导航方式中,惯性导航系统(inertial navigation system, INS)/全球导航卫星系统(global navigation satellite system, GNSS)组合导航在无线电信号拒止环境中存在性能下降的风险,传统INS/天文导航系统(celestial navigation system, CNS)组合导航能够抑制惯性测量单元中的陀螺漂移,但不能有效消除加速度计零偏的影响.针对上述问题,提出一种基于空间目标定向观测的飞行器自主导航新方法,在飞行器上配置星相机对星历已知的空间目标和背景恒星的视线方向(line-of-sight, LOS)进行观测,利用IMU进行状态预测,通过扩展卡尔曼滤波器(extended Kalman filter, EKF)获得载体位置、速度和姿态的估计值,同时,对惯性器件测量偏差进行校准.设计了基于克拉美劳下界(Cramer-Rao lower bound, CRLB)的观测目标优化选取策略,通过空间目标可见性分析、导航系统可观度分析以及导航滤波器数学仿真验证了所提方法的有效性.

气体引射对临近空间升力体飞行器气动力热影响

针对临近空间高速飞行器的降热减阻需求,采用三维数值模拟手段研究了临近空间典型升力体飞行器气动力/热特性,分析了壁面气体质量引射对气动力/热特性的影响规律和作用机理。结果表明:壁面质量引射会略微增大激波脱体距离,对激波层和速度边界层有增厚作用,降低了边界层内的速度梯度,使得表面剪切力减小,从而具有较好的减阻效果。对于典型的升力体构型,在高度为60~70 km时,壁面质量引射减阻效率均不低于47.5%;在高度为80 km时,壁面质量引射减阻效率不低于10.2%;且壁面质量引射减阻效果随攻角增大而增强,随飞行高度升高而减弱。同时,壁面引射排出的低温气体对飞行器具有隔热保护作用,因此壁面质量引射能显著降低迎风面的热流,具有较好的降热效果。

融入智能网联汽车的混行交通流混沌特性

为了研究混行交通流混沌特性、辨析影响混行车队混沌程度的因素,在传统交通流理论基础上,利用Cao方法和改进的Cao方法确定混行交通流延迟时间和嵌入维数,对混行交通流序列进行相空间重构并通过计算最大Lyapunov指数判定其混沌特性.对混行交通流中智能网联汽车(intelligent connected vehicle,ICV)协同自适应巡航(cooperative adaptive cruise control,CACC)车辆比例及延迟时间关键参数进行影响分析.结果表明:在跟驰过程中车头间距序列的最大Lyapunov指数小于0时,混行交通流存在混沌;CACC车辆比例增加能够减弱混沌的时间区域,比如当CACC车辆比例达到0.6时,跟驰系统趋于稳定;CACC车辆的延迟时间对混沌的影响显著,保持低通信延迟才能发挥CACC车辆的作用,从而有效抑制混沌.

面向“总师型”人才培养的航天飞行器设计课程创新建设

航天飞行器设计是航空宇航科学与技术相关专业本科生的专业核心课程,以培养“总师型”后备人才基本能力和素养为教学目标。航天飞行器设计涉及要素多、概念多、学科耦合强,强调综合性、系统性和创造性。该文讨论航天飞行器设计课程的四个主要教学难点,结合西北工业大学办学目标,详尽地阐述课程创新建设思路。课程在知识体系、教学方法、教学资源方面持续改革,构建“国防战略牵引-航天思政引入-工程案例分析-虚拟仿真强化”的创新教学模式,论述课程创新建设具体实施过程。通过多维度评价与反馈,课程创新建设效果良好,有力支撑总体专业骨干和总师后备人选培养。

自适应地平线约束下的车辆三维检测

目前较为常用的基于单目视觉的车辆三维检测方法是目标检测结合几何约束的方法,但是几何约束中消失点的位置对结果影响很大。为了获取更加准确的约束条件,提出一种基于地平线检测的车辆三维检测算法。首先,利用车辆图片获取消失点的相对位置,将车辆图片预处理至合适大小;然后,将经过预处理的车辆图片送入消失点检测网络,获得消失点信息热力图组,回归出消失点信息,并计算得出地平线信息;最后,根据地平线信息构建几何约束,在约束空间内对车辆初始尺寸迭代优化计算精确的车辆三维信息。实验结果表明,所述地平线求解算法能够获得更准确的地平线,与随机森林的方法相比,曲线下面积(AUC)提升1.730个百分点;同时,所提地平线约束能够有效地限制车辆三维信息,与使用对角线和消失点约束的算法相比,车辆三维信息的平均精度提升2.201个百分点。可见地平线可以作为几何约束在路侧单目相机的场景下求解车辆三维信息。

考虑通行方向利用率的交叉口感应式控制

为缓解城市出行延误中交叉口延误占比较大的问题,提高交叉口的通行效率,以标准的四相位交叉口为研究对象,提出了基于交叉口实时路况信息的感应式通行方向利用率信号控制方法。根据车辆空间占用率、交叉口通行效率、车头间距阈值于Python中建立了交叉口相位决策优化模型。以长沙市某交通需求变化大的交叉口为例,通过Vissim 8.0建模,将感应式控制方法与传统的基于车流量的Webster控制方法在多种交通需求下进行仿真对比。结果表明:交叉口平均车辆延误在平峰、PHF15、拥堵交通需求下降低了3.21%、13.1%、4.17%;交叉口的车均延误降低率随着交通需求的增大呈先增后降的趋势。研究成果证实了感应式控制能适应较为广泛的交通环境,能有效降低交叉口车辆延误。

复杂环境下DWA与RRT算法融合的AUV局部路径规划

针对复杂水下环境下的自主水下航行器(autonomous underwater vehicle,AUV)局部路径规划问题,传统动态窗口法(dynamic window approach,DWA)存在复杂障碍物中陷入局部停滞,动态避障性能不佳等问题,本文提出了一种基于DWA与快速随机搜索树(rapid-exploration random tree,RRT)算法融合的路径规划算法。改进的DWA算法速度空间根据整个动态窗口的周期生成,重设了评价函数并结合AUV任务环境引入洋流能耗评价函数;改进的RRT算法在局部已知空间内规划导引点,帮助DWA脱离局部停滞状态并实现更安全的动态避障。将2种算法融合,实现了AUV在复杂水下环境中的局部路径规划。仿真表明,该融合算法能够降低AUV在洋流中的能耗代价,解决了DWA在复杂障碍物中陷入局部停滞的问题,能够安全有效地躲避动态避障物。