Path-Following Control With Obstacle Avoidance of Autonomous Surface Vehicles Subject to Actuator Faults

This paper investigates the path-following control problem with obstacle avoidance of autonomous surface vehicles in the presence of actuator faults,uncertainty and external disturbances.Autonomous surface vehicles inevitably suffer from actuator faults in complex sea environments,which may cause existing obstacle avoidance strategies to fail.To reduce the influence of actuator faults,an improved artificial potential function is constructed by introducing the lower bound of actuator efficiency factors.The nonlinear state observer,which only depends on measurable position information of the autonomous surface vehicle,is used to address uncertainties and external disturbances.By using a backstepping technique and adaptive mechanism,a path-following control strategy with obstacle avoidance and fault tolerance is designed which can ensure that the tracking errors converge to a small neighborhood of zero.Compared with existing results,the proposed control strategy has the capability of obstacle avoidance and fault tolerance simultaneously.Finally,the comparison results through simulations are given to verify the effectiveness of the proposed method.

Experimental study on surface arc plasma actuation-based hypersonic boundary layer transition flow control

Effective control of hypersonic transition is essential.In order to avoid affecting the structural proflle of the aircraft,as well as reducing power consumption and electromagnetic interference,a low-frequency surface arc plasma disturbance experiment to promote hypersonic transition was carried out in theΦ0.25 m double-throat Ludwieg tube wind tunnel at Huazhong University of Science and Technology.Contacting printed circuit board sensors and non-contact focused laser differential interferometry testing technology were used in combination.Experimental results showed that the low-frequency surface arc plasma actuation had obvious stimulation effects on the second-mode unstable wave and could promote boundary layer transition by changing the spectral characteristics of the second-mode unstable wave.At the same time,the plasma actuation could promote energy exchange between the second-mode unstable wave and other unstable waves.Finally,the corresponding control mechanism is discussed.

Carnivorous plants inspired shape-morphing slippery surfaces

Carnivorous plants,for instance,Dionaea muscipula and Nepenthes pitcher plant,inspired the innovation of advanced stimuli-responsive actuators and lubricant-infused slippery surfaces,respectively.However,hybrid bionic devices that combine the active and passive prey trapping capabilities of the two kinds of carnivorous plants remain a challenge.Herein,we report a moisture responsive shape-morphing slippery surface that enables both moisture responsive shapemorphing and oil-lubricated water repellency for simultaneous active-and passive-droplet manipulation.The moisture deformable slippery surface is prepared by creating biomimetic microstructures on graphene oxide(GO)membrane via femtosecond laser direct writing and subsequent lubricating with a thin layer of oil on the laser structured reduced GO(LRGO)surface.The integration of a lubricant-infused slippery surface with an LRGO/GO bilayer actuator endows the actuator with droplet sliding ability and promotes the moisture deformation performance due to oil-enhanced water repellency of the inert layer(LRGO).Based on the shape-morphing slippery surface,we prepared a series of proof-of-concept actuators,including a moisture-response Dionaea muscipula actuator,a smart frog tongue,and a smart flower,demonstrating their versatility for active/passive trapping,droplet manipulation,and sensing.

Influence of low ambient pressure on the performance of a high-energy array surface arc plasma actuator

In order to solve the problem of single arc plasma actuator's failure to suppress the boundary layer separation, the effectiveness of the array surface arc plasma actuator to enhance the excitation intensity is verified by experiment. In this study, an electrical parameter measurement system and high-speed schlieren technology were adopted to delve into the electrical, flow field, and excitation characteristics of the high-energy array surface arc plasma actuator under low ambient pressure. The high-energy array surface arc discharge released considerable heat rapidly;as a result, two characteristic structures were generated, i.e., the precursor shock wave and thermal deposition area. The duration increased with the increase in environmental pressure. The lower the pressure, the wider the thermal deposition area's influence range. The precursor shock wave exhibited a higher propagation speed at the initial phase of discharge;it tended to decay over time and finally remained at 340 m/s. The lower the environmental pressure, the higher the speed would be at the initial phase. High-energy array surface arc plasma actuator can be employed to achieve effective high-speed aircraft flow control.

Aerodynamic actuation characteristics of radio-frequency discharge plasma and control of supersonic flow

In this paper, aerodynamic actuation characteristics of radio-frequency(RF) discharge plasma are studied and a method is proposed for shock wave control based on RF discharge. Under the static condition, a RF diffuse glow discharge can be observed; under the supersonic inflow, the plasma is blown downstream but remains continuous and stable.Time-resolved schlieren is used for flow field visualization. It is found that RF discharge not only leads to continuous energy deposition on the electrode surface but also induces a compression wave. Under the supersonic inflow condition, a weak oblique shock wave is induced by discharge. Experimental results of the shock wave control indicate that the applied actuation can disperse the bottom structure of the ramp-induced oblique shock wave, which is also observed in the extracted shock wave structure after image processing. More importantly, this control effect can be maintained steadily due to the continuous high-frequency(MHz) discharge. Finally, correlations for schlieren images and numerical simulations are employed to further explore the flow control mechanism. It is observed that the vortex in the boundary layer increases after the application of actuation, meaning that the boundary layer in the downstream of the actuation position is thickened. This is equivalent to covering a layer of low-density smooth wall around the compression corner and on the ramp surface, thereby weakening the compressibility at the compression corner. Our results demonstrate the ability of RF plasma aerodynamic actuation to control the supersonic airflow.

Modeling and Experiment of a Morphing Wing Integrated with a Trailing Edge Control Actuation System

Morphing wing has attracted many research attention and effort in aircraft technology development because of its advantage in lift to draft ratio and flight performance.Morphing wing technology combines the lift and control surfaces into a seamless wing and integrates the primary structure together with the internal control system.It makes use of the wing aeroelastic deformation induced by the control surface to gain direct force control through desirable redistribution of aerodynamic forces.However some unknown mechanical parameters of the control system and complexity of the integrated structure become a main challenge for dynamic modeling of morphing wing.To solve the problem,a method of test data based modal sensitivity analysis is presented to improve the morphing wing FE model by evaluating the unknown parameters and identifying the modeling boundary conditions.An innovative seamless morphing wing with the structure integrated with a flexible trailing edge control system is presented for the investigation.An experimental model of actuation system driven by a servo motor for the morphing wing is designed and established.By performing a vibration test and the proposed modal sensitivity analysis,the unknown torsional stiffness of the servo motor and the boundary condition of the actuation mechanism model is identified and evaluated.Comparing with the test data,the average error of the first four modal frequency of the improved FE model is reduced significantly to less than 4%.To further investigate the morphing wing modeling,a wing box and then a whole morphing wing model including the skin and integrated with the trailing edge actuation system are established and tested.By using the proposed method,the FE model is improved by relaxing the constraint between the skin and actuation mechanism.The results show that the average error of the first three modal frequency of the improved FE model is reduced to less than 6%.The research results demonstrate that the presented seamless morphing wing integrated with a flexible trailing edge control surface can improve aerodynamic characteristics.By using the test data based modal sensitivity analysis method,the unknown parameter and boundary condition of the actuation model can be determined to improve the FE model.The problem in dynamic modeling of high accuracy for a morphing wing can be solved in an effective manner.

TEOS-GO掺杂的银基离子聚合物金属复合材料的制备及其致动性能

离子聚合物金属复合材料(IPMC)是一种新型的电驱动软材料,具有质量轻、驱动电压低的优点,但也存在输出力较小、驱动时间短的缺点,限制了其应用前景。提出了一种在基膜内掺杂硅酸乙酯-氧化石墨烯(TEOS-GO)以提高保水性和驱动能力的银基IPMC,通过对纯Nafion IPMC与TEOS-GO/Nafion IPMC致动器的含水量、尖端位移、输出力和稳定性等参数的测试,证实优化后IPMC的驱动性能有明显的提升。实验结果表明,掺杂质量分数1.5%TEOS-GO的IPMC在3 V直流电压下,尖端位移达到16.579 mm,相当于纯Nafion IPMC的3.37倍;输出力最高达到0.439 gf(1 gf=9.8 mN),是纯Nafion IPMC的5倍。这种改进方式弥补了IPMC用于致动器的缺点,为今后的发展开拓了前景。

不同粗糙度下织构处理前后端面密封表面的接触压力与摩擦性能分析

端面密封表面摩擦性能对叶片式液压摆动油缸的稳定运行有重大影响。对端面密封在不同粗糙度下、织构处理前后的接触压力与摩擦性能展开研究,综合分析粗糙度、织构化处理与端面密封摩擦性能的关系。将MATLAB与COMSOL相结合,建立端面密封有限元模型,仿真分析不同粗糙度、是否织构化处理等不同条件下的接触压力分布;结合对应摩擦实验获得端面密封摩擦力分布,并考虑叶片密封润滑模型,建立摆动油缸总摩擦力计算模型;最后通过摆动油缸实验,验证理论分析的准确性。结果表明:一定预压缩量下,接触压力随粗糙度的增大而增大;油润滑状态下,织构化表面摩擦性能优于未处理表面;所建立的总摩擦力计算模型可用于分析摆动油缸在不同粗糙度等条件下的摩擦性能。

基于全驱系统方法的高阶严反馈系统时变输出约束控制

针对输出受不对称时变约束的不确定高阶严反馈系统,提出一种基于全驱系统方法的高阶自适应动态面输出约束控制方法.所研究的高阶严反馈系统,每个子系统都是高阶形式,通过非线性转换函数将原输出约束系统转换为新的无约束系统,从而将原系统输出约束问题转化为新系统输出有界的问题.进一步结合全驱系统方法和自适应动态面控制,直接将每个高阶子系统作为一个整体进行控制器设计,而不需要将其转化为一阶系统形式,有效简化了设计步骤;同时通过引入一系列低通滤波器来获得虚拟控制律的高阶导数,以代替复杂的微分运算.基于Lyapunov稳定性理论证明闭环系统所有信号是一致最终有界的,系统输出在满足约束的条件下能有效跟踪期望的参考信号,且可通过调整参数使得系统跟踪误差收敛到零附近的足够小的邻域内.最后,通过对柔性关节机械臂系统进行仿真,验证了所提出控制方法的有效性.

表面电弧放电等离子体激励调控稳焰器的流动与燃烧

针对表面电弧放电等离子体激励对稳焰器的调控问题,对表面电弧放电唯象模型的适用性进行了验证,并分析了不同激励位置和激励强度对稳焰器流场结构、燃料雾化、点火延迟以及火焰稳定性的影响。研究结果显示,不同激励位置对流场结构产生显著影响,尤其在激励能量有效集中时,形成强烈的激励区域,导致回流区膨胀,进而促进燃料雾化,减缓点火延迟及提高平均火焰温度。同时,随着激励强度的增加,回流区长度、混合效率和燃烧效率呈线性增加。

基于命令滤波反推方法的水面无人艇容错编队跟踪控制

研究了具有模型不确定性和执行器故障的多水面无人艇系统的编队跟踪控制问题。通过在线信息交互,为跟随无人艇设计完全分布式观测器以估计期望的位置、航向和速度,并提出命令滤波反推控制协议。该控制协议实现了闭环误差系统的实用指数稳定性及多无人艇系统的编队跟踪。该控制方法的一个优点是不依赖于通信拓扑图Laplacian矩阵的谱信息,使得提出的控制协议能在完全分布式架构下实施。仿真实验验证了该控制协议的有效性。

某型起落架主起开锁作动筒堵盖开裂分析

为准确定位外场某型起落架开裂原因,采用技术归零的“定位准确、机理清楚、问题复现、措施有效、举一反三”五步分析方法。对3件堵盖故障件进行了外观目视检查、微观观察、断口成分分析及显微组织检测等多角度故障分析,并随机选取了2件开锁作动筒组件,按照图样和设计要求进行了盐雾试验。通过试验,成功复现了故障现象,发现了堵盖开裂的失效机制:主起开锁作动筒堵盖的外筒螺纹部位积存腐蚀介质后,一旦螺纹表面的保护膜受损、装配时径向应力过大,便易导致堵盖分模面处流线露头,暴露的晶界成为腐蚀通道,最终引起沿晶界的应力腐蚀破坏。为解决堵盖应力腐蚀开裂问题,改进了端盖模压成型过程中分模面的角度,并在开锁作动筒装配环节采用定力矩方法,以此控制装配应力,防止类似问题的再次发生。

基于水射流的水轮机转轮室混凝土拆除执行机构研制

针对水电站水轮机转轮室改造修复工程中存在的混凝土拆除作业强度高、施工效率低、环境影响大等问题,探索研制了一种基于水射流的超大型水轮机转轮室混凝土拆除执行机构。经工程应用表明,该高压水射流执行机构能够利用压力大于130 MPa、流量大于60 L/min的射流水高效拆除超大型转轮室混凝土结构,其效率是传统人工机械的2.7倍,实现了施工半自动化,且具备修复质量高、安全、环保等特性,在同类型结构工程的改造中具有很好的应用前景。

Improvement of Aircraft Rolling Power by Use of Piezoelectric Actuators

Piezoelectric actuators are distributed on both side of a rectangular wing model,and the possibility of improvement of aircraft rolling power is investigated. The difference between the model with aileron deflection and the model without aileron (fictitious control surface, FCS) is studied. The analytical results show that these two cases are substantial different. In aileron deflection case, the aeroelastic effect is disadvantageous, so the structural stiffness should be high until the electrical voltage is not necessary. But in the case of FCS,the aeroelastic effect is advantageous and it means that lower structural stiffness can lead to lower voltage. Compared with aileron project, the FCS project can save structure weight.

Dynamics of Droplets of Biological Fluids on Smooth Superhydrophobic Surfaces under Electrostatic Actuation

This study describes the dynamic behaviour of droplets of biological liquids on hydrophobic surfaces under electrostatic actuation, to devise sample handling in lab-on-chip diagnostic tools. Bovine Serum Albumin （BSA） is taken as a representative biomolecule, since it is often used in adsorption studies. Green Fluorescence Protein （GFP） is also considered, given its natural fluorescence. Several effects such as sample concentration and pH are discussed. The results show negligible effects of proteins concentration in electrowetting, although increased concentrations endorse passive adsorption mechanisms, which alter the local wettability of the substrates precluding droplet motion. Bioinspired surfaces promote the largest spreading diameter, which is beneficial for droplet motion. However, surface roughness promotes energy dissipation limiting the receding droplet motion. Hence, the most effective approach is altering the surface chemistry. The coating is applied to a surface with a mean roughness smaller than 20 nm and does not alter significantly the topography, thus leading to the so-called smooth superhydrophobic surface. This coating also reduces passive proteins adsorption, as confirmed by Confocal Microscopy （CM）, which is beneficial for droplet motion. Evaluating absorption spectra of protein solutions evidences an increase in protein concentration ascribed to droplet evaporation as confirmed by theoretical analysis and time resolved infrared visualization.

Validation of actuator disc circulation distribution for unsteady virtual blades model

The actuator disc method is an engineering approach to reduce computer resources in computational fluid dynamics(CFD)simulations of helicopter rotors or aeroplane propellers.Implementation of an actuator disc based on rotor circulation distribution allows for approximations to be made while reproducing the blade tip vortices.Radial circulation distributions can be formulated according to the nonuniform Heyson-Katzoff“typical load”in hover.In forward flight,the nonuniform disk models include“azimuthal”sin and cos terms to reproduce the blade cyclic motion.The azimuthal circulation distribution for a forward flight mode corresponds to trimmed conditions for the disk rolling and pitching moments.The amplitude of the cos harmonic is analysed and compared here with presented in references data and CFD simulations results.

飞机主动式余度作动舵面铰链力矩飞行测量方法

现代飞机舵面大多采用主动式余度作动系统。这种系统固有的力纷争现象,导致传统的基于原位载荷校准试验的飞机结构载荷测量方法,不再适用于现代飞机操纵舵面铰链力矩飞行测量。提出了一种基于离位载荷校准试验和原位载荷验证试验的飞机舵面铰链力矩测量方法,建立了相应的载荷测量模型,分析确定了铰链力矩测量精准度的影响因素,给出了可能引起的系统误差的验证和修正方法,形成了主动式余度作动舵面铰链力矩飞行测量流程。通过多型飞机舵面铰链力矩测量试飞,验证了该方法的可行性和有效性;提高了飞机舵面铰链力矩测量的精准度,为飞机舵面设计载荷验证与优化提供了可靠的实测载荷;得到了飞机舵面各作动机构的载荷分配,实现了飞机舵面作动系统力纷争的飞行监测,确保了飞行安全。

基于自适应阈值与扩张状态滑模观测器的AUV执行机构故障检测与估计

作为自主式水下机器人(AUV)的重要组成部分,执行机构的可靠性对系统的安全运行具有重要意义.本文以AUV六自由度模型为基础,提出了一种基于自适应阈值与扩张状态滑模观测器相结合的故障检测与估计机制.首先,本文将模型中除去控制输入的部分扩张成新的系统状态,得到估计值和实际值之间的残差;其次,针对执行机构的未知扰动,文章设计了一种改进的自适应阈值以监测残差的变化,进一步降低了误诊率与漏诊率;随后,文章在扩张状态的结构基础上设计滑模观测器,将观测器的增益求解转化为线性矩阵不等式(LMI)约束优化问题;最后,通过动态滑模面的设计实现了抖振的抑制并论证了该动态滑模面的收敛性,同时引入等效控制输出误差注入原理,实现了AUV执行机构的故障重构.仿真结果表明,本文所提方法对AUV执行机构的故障具有较好的检测灵敏度和估计精度.

压电陶瓷在精密超精密领域的应用及发展

论述压电陶瓷在高精度领域的不同应用,包括压电陶瓷对物体微小形变测量、压电陶瓷作为传感元件与谐振器结合应用、压电传感技术在应力测量领域应用、压电陶瓷作为驱动器在纳米定位领域应用、压电陶瓷对材料构件损伤识别、压电陶瓷在无损检测领域应用、基于相移干涉法对三维表面微观轮廓检测等;描述压电材料分类以及特性;深度剖析压电陶瓷在当前科技发展阶段不同工业领域的应用,分析目前研究中的难点,展望未来的研发方向。

十二烷基硫酸钠水溶液液滴在微凹槽阵列PDMS表面上的电润湿行为实验研究

目的研究十二烷基硫酸钠(Sodium dodecyl sulfate,SDS)水溶液液滴在微凹槽阵列聚二甲基硅氧烷(Polydimethylsiloxane,PDMS)表面的电润湿行为特征。方法采用注入析出法,测量含KCl的SDS水溶液液滴在微凹槽阵列非浸润表面的接触角滞后。通过施加直流电压,研究SDS浓度和表面粗糙度对含KCl的SDS水溶液液滴的电润湿行为的影响。结果微凹槽阵列非浸润表面表现出较强的润湿各向异性,与平行于微凹槽方向上的表观接触角(110°≤θe≤141°)、前进角(116°≤θa≤144°)和后退角(99°≤θr≤137°)相比,垂直于微凹槽方向上的表观接触角(142°≤θe≤165°)、前进角(159°≤θa≤177°)和后退角(118°≤θr≤140°)普遍更大。当表面固定时,水溶液液滴电润湿的启动电压和饱和电压,以及发生润湿状态转变所需的电压均随着SDS浓度的增加而减小。当水溶液中SDS的浓度固定时,沿垂直于凹槽方向的启动电压随着固相分数的减小而减小,沿平行于凹槽方向的启动电压随着固相分数的减小而增大,而饱和电压均随着固相分数的减小而减小。结论添加十二烷基硫酸钠可以有效降低SDS水溶液液滴电润湿的启动电压和电润湿过程中水溶液液滴在微凹槽PDMS表面润湿状态转变所需的电压,使得SDS水溶液液滴在微凹槽阵列PDMS表面的电润湿行为发生了改变。