Robust linear output feedback controller for autonomous landing of a quadrotor on a ship deck

Ship deck landing control of a quadrotor requires certain robustness with respect to ship heave motion. Typical systems only provide relative height, therefore do not have relative heave rate information. In this paper, a linear output feedback control consisting of a full state feedback controller and a Luenberger observer is formulated. Invariant ellipsoid method is used to formulate an estimation of a bound on the response of a linear output feedback-controlled system subjected to external disturbances and measurement noise. The gains that result in a minimum bound are optimized using a gradient descent iterative approach proposed in this paper where the invariant ellipsoid condition is linearized into a tractable LMI condition. This approach is applied to a simulation of a quadrotor landing on a ship deck and results are compared with other gains. The gains selected using the proposed approach exhibits improved robustness to external disturbances and measurement noise.     

基于Hausdorff距离的反舰导弹预定目标选择方法

超视距反舰导弹(Anti-ship missile,ASM)在选择预定目标时,目前普遍采用的瞄准点选择方法受自控终点散布和目标机动影响较大.为此提出了一种基于Hausdorff距离的预定目标选择方法,该方法不受自控终点散布和编队目标整体机动的影响.原理是将火控雷达探测到的编队和末制导雷达探测到的编队都用平面点集表示,然...     

污染源位置对圆柱形水工建筑下游污染物浓度分布的影响

利用雷诺方程和RNG k-ε紊流模型,对排放源在圆柱形水工建筑上游和下游两种工况下的尾流浓度场进行数值模拟,从污染物时均浓度、浓度脉动强度和浓度半宽度3个方面比较了污染源位置对圆柱形水工建筑下游污染物浓度分布特性的影响。结果表明:随流程的增大,两种工况下污染物时均浓度横向断面分布先后经历双峰结构、过渡阶段和高斯分布3个阶段;排放源在上游时,浓度脉动强度先增大后减小;排放源在下游时,浓度脉动强度一直减小;两种工况的浓度半宽度变化规律一致,当1≤x/D15时浓度半宽度呈非线性增长,当15≤x/D≤30时呈线性增长。     

船舶横摇运动的非线性振动与混沌

本文针对船舶非线性横摇运动模型，以波浪尺度为变参数，运用平均化方法和范德坡变换，一系统的振动解随参数变化的定性情况，然后通过数值积分和胞映射相结合的方法，确定系统的多种开熙熙攘攘夺动解。可以看到胞映地能灵活地处理各种不同形式的上子，如周期解，各阶亚谐解乃至混沌吸引子并能方便快速地求解。横摇运动的大量非线性现象，如吸引子工存，对称性碳缺，倍周期分岔等现象都被观察到，文中还给出了由一系列倍周期分岔导致     

UHMWPE板在自卸货船上的应用

介绍超高分子量聚乙烯板在自卸货船上的应用,研究了其用作货舱内衬板的安装方式、加工方法及胶粘剂的选取,应用获得满意结果。     

An experimental study on aerodynamic sound generated from wake interaction of circular cylinder and airfoil with attack angle in tandem

In our previous study, the effects of the interval between the cylinder and the airfoil on the aerodynamic sound were investigated and compared with the cases of single circular and single airfoil. In this study, the effects of the attack angle of the airfoil located downstream on the characteristics of aerodynamic sound and the wake structure are investigated at a given interval between the cylinder and the airfoil. It is found that the sound pressure level of DFN and the peak frequency decrease with increasing attack angle of airfoil because of the diffusive wake structure due to the increased back pressure of circular cylinder, which is caused by the blocking effect of airfoil. It is shown that the sound sources are corresponded to the attack points of shedding vortex form the upstream circular cylinder to the downstream airfoil. We conclude that the pressure fluctuation at the airfoil surface effects on the sound pressure level, from the flow visualizations and the exploration test of sound source.     

A general momentum theory applied to an energy‐extracting actuator disc

A general momentum theory for an energy‐extracting actuator disc modelling a rotor with a multiplicity of blades having radially uniform circulation is presented that includes the effects of wake rotation and expansion. A parallel theory directed at the propeller has been published elsewhere, but not one intended for the wind turbine. The rotation of the wake is shown to be accompanied by a fall in static pressure that is additional to that which occurs across the actuator disc and accounts for the energy extraction from the wind. Energy extraction is recognized in the fully developed wake by the flow regaining the static pressure of the undisturbed wind at the expense of the kinetic energy in the wake. Because the wake is still rotating in the fully developed wake, the additional fall in static pressure appears there also and so does not augment the energy extraction. However, the additional fall in pressure would cause a discontinuity in pressure across the fully developed wake but is prevented by a further slowing down of the wake. The additional slowing down extracts a little more energy from the flow than that predicted by the simple momentum theory, which does not include wake rotation. The overall effect of wake rotation on energy extraction is very small for wind turbines operating at high tip speed ratios but can significantly increase the predicted power output for turbines operating at low tip speed ratios. Copyright © 2004 John Wiley & Sons, Ltd.     

Fatigue life prediction at a ship deck/superstructure intersection

Difficulties arise in identifying an appropriate method to predict fatigue life for the weld joint at the intersection of a ship's deck and superstructure. The problem relates to the gross stress concentration and rapidly changing stress at this location. Variations on the 'hot spot' stress approach to fatigue life analysis are reviewed, and applied to results from an experimental programme of fatigue tests on welded joints. Finally tentative recommendations are made for a procedure to predict fatigue life of the structure.     

利用改进单分类支持向量机提升舰船尾流目标的检测准确率

舰船在航行过程中会在尾部产生一段包含大量气泡的湍流区域,通过对尾流的声学检测可以有效地跟踪船舶。基于一种改进单分类支持向量机（OCSVM）算法,利用无尾流情况下回波信号作为训练集的一个最优分类器,用于尾流回波信号模式判断。对回波信号进行降噪处理,进而提出一种自适应特征提取方法对回波信号进行处理;将特征提取作为输入,使用两层决策边界的双阈值OCSVM算法进行尾流检测。仿真结果表明,与常规OCSVM算法相比,改进算法在不同信噪比下的检测准确率均有提升,检测准确率最高可达96.27%,具有较好的工程应用价值。     

An energy‐efficient asynchronous wake‐up scheme for underwater acoustic sensor networks

In addition to the requirements of the terrestrial sensor network where performance metrics such as throughput and packet delivery delay are often emphasized, energy efficiency becomes an even more significant and challenging issue in underwater acoustic sensor networks, especially when long‐term deployment is required. In this paper, we tackle the problem of energy conservation in underwater acoustic sensor networks for long‐term marine monitoring applications. We propose an asynchronous wake‐up scheme based on combinatorial designs to minimize the working duty cycle of sensor nodes. We prove that network connectivity can be properly maintained using such a design even with a reduced duty cycle. We study the utilization ratio of the sink node and the scalability of the network using multiple sink nodes. Simulation results show that the proposed asynchronous wake‐up scheme can effectively reduce the energy consumption for idle listening and can outperform other cyclic difference set‐based wake‐up schemes. More significantly, high performance is achieved without sacrificing network connectivity. Copyright © 2015 John Wiley & Sons, Ltd.