Underwater glider design based on dynamic model analysis and prototype development

Underwater gliders are efficient mobile sensor platforms that can be deployed for months at a time, traveling thousands of kilometers. Here, we describe our development of a coastal 200 m deep underwater glider, which can serve as an ocean observatory platform operating in the East China Sea. Our glider is developed based on dynamic model analysis: steady flight equilibrium analysis gives the varied range of moving mass location for pitch control and the varied vehicle volume for buoyancy control; a stability analysis is made to discuss the relationship between the stability of glider motion and the location of glider wings and rudder by root locus investigation of glider longitudinal- and lateral-directional dynamics, respectively. There is a tradeoff between glider motion stability and control authority according to the specific glider mission requirements. The theoretical analysis provides guidelines for vehicle design, based on which we present the development progress of the Zhejiang University (ZJU) glider. The mechanical, electrical, and software design of the glider is discussed in detail. The performances of glider key functional modules are validated by pressure tests individually; preliminary pool trials of the ZJU glider are also introduced, indicating that our glider functions well in water and can serve as a sensor platform for ocean sampling.     

Passive and active acoustics using an autonomous wave glider

The recently developed wave glider has the potential to be an effective unmanned platform for acoustic applications. We present the results of a variety of experiments that quantify this potential. The radiated self‐noise of the autonomous platform is evaluated using an integrated passive acoustic recorder during a set of field trials off the coast of Hawaii. We present the radiated noise spectra from these trials to illustrate the dependence on hydrophone location and sea state. Using the same instrumentation, we demonstrate the ability of a modified wave glider to detect marine mammals using passive acoustic monitoring techniques. We also evaluate the performance of the wave glider operating as an active acoustic gateway, highlighting the potential of this platform to serve as a navigation reference and communications relay for scientific, industrial, and military subsea assets. To demonstrate the potential of the wave glider platform to support acoustic navigation, we assess the performance of time‐of‐flight range estimation and seafloor transponder localization. These tests were performed using commercial off‐the‐shelf acoustic positioning hardware integrated with the wave glider to illustrate that the low self‐noise of the wave glider makes it possible to achieve acoustic positioning performance similar to previously reported results. Finally, we show that the glider can operate as a station‐keeping surface communications gateway and provide recommendations for its use. © 2012 Wiley Periodicals, Inc.     

水下滑翔机垂直面运动优化控制

水下滑翔机是一种依靠水动力和净浮力驱动的新型水下机器人. 本文分析了滑翔机在垂直面滑翔时, 浮力变化和内置可动质量块位置变化对滑翔机运动状态的影响．针对滑翔机在潜浮切换时, 由于机翼受力不对称产生的无升力现象而导致的切换过程不稳定的问题, 采用两点边值的优化控制方法, 规划了内置质量块的位量, 以消除滑翔机在潜浮切换过程中各个时刻产生的不对称无升力现象．最后给出了滑翔机实际机械系统可接受的最优控制 方案. 仿真表明了这种优化方法的有效性.     

水下滑翔机海洋环境深平均流估计方法

提出了水下滑翔机海洋环境深平均流估计方法．首先,基于水下滑翔机稳态运动模型,研究海水密度差异和耐压舱体压缩变形对水下滑翔机运动速度的影响,建立水下滑翔机运动速度快速计算模型,并证明了该模型的正确性及有效性．然后,利用得到的水下滑翔机运动速度和船位推算方法结合,给出了海洋环境深平均流估算方法．利用该深平均流估算方法对3台水下滑翔机海上试验过程中的深平均流进行估算,并分析了估算结果的有效性．实验结果证明利用本文得到的深平均流可以提高水下滑翔机船位推算中的定位精度．     

Adaptive heading control of unmanned wave glider with heading information fusion

The unmanned wave glider (UWG) is a new kind of wave powered unmanned marine vehicle for persistent marine environment monitoring. However, the heading control of UWG is unusual, mainly about the heading control of the surface float body (Float), since it is indirectly actuated and with a large lag of the control response. The adaptive heading control method for the Float with heading information fusion is discussed. The basic and improved arrangement methods of the desired heading of Glider are proposed. Via direct heading control of Glider, the heading control of Float is realized indirectly. Simulation and sea trial results demonstrate that the proposed adaptive heading control method improves the heading control performance of UWG significantly.     

Differential evolution and underwater glider path planning applied to the short-term opportunistic sampling of dynamic mesoscale ocean structures

This paper presents an approach where differential evolution is applied to underwater glider path planning. The objective of a glider is to reach a target location and gather research data along its path by propelling itself underwater and returning periodically to the surface. The main hypothesis of this work is that gliders operational capabilities will benefit from improved path planning, especially when dealing with opportunistic short-term missions focused on the sampling of dynamic structures. To model a glider trajectory, we evolve a global underwater glider path based on the local kinematic simulation of an underwater glider, considering the daily and hourly sea currents predictions. The global path is represented by control points where the glider is expected to resurface for communication with a satellite and to receive further navigation instructions. Some well known differential evolution instance algorithms are then assessed and compared on 12 test scenarios using the proposed approach. Finally, a real case glider vessel mission was commanded using this approach.     

Steering control for underwater gliders

Steering control for an autonomous underwater glider (AUG) is very challenging due to its changing dynamic characteristics such as payload and shape. A good choice to solve this problem is online system identification via in-field trials to capture current dynamic characteristics for control law reconfiguration. Hence, an online polynomial estimator is designed to update the yaw dynamic model of the AUG, and an adaptive model predictive control (MPC) controller is used to calculate the optimal control command based on updated estimated parameters. The MPC controller uses a quadratic program (QP) to compute the optimal control command based on a user-defined cost function. The cost function has two terms, focusing on output reference tracking and move suppression of input, respectively. Move-suppression performance can, at some level, represent energy-saving performance of the MPC controller. Users can balance these two competitive control performances by tuning weights. We have compared the control performance using the second-order polynomial model to that using the fifth-order polynomial model, and found that the former cannot capture the main characteristics of yaw dynamics and may result in vibration during the flight. Both processor-in-loop (PIL) simulations and in-lake tests are presented to validate our steering control performance.     

基于多传感器的波浪能滑翔器导航策略研究

以LPC2478为核心的嵌入式控制系统通过对多路传感器的数据采集,实现了波浪能滑翔器在海洋中的自主巡航监测环境。基于高斯大地线算法,计算出当前位置与预设位置的大地线距离和航向角偏差值;同时基于PID控制算法,计算出尾舵系统需要偏转的角度。2种算法构成了导航策略的算法体系,实现了波浪能滑翔器的视向跟踪和虚拟锚泊。同时,为保证导航信息的精准度,增加2组传感器:波高仪和流速仪,作为辅助导航传感器,从而建构了一个完整的控制波浪能滑翔器自主运行的导航系统结,在实际海洋试验中,取得了良好效果。     

基于改进Xmodem协议的水下滑翔机通信系统设计

水下滑翔机是一种依靠重心和自身净浮力变化驱动航行的新型水下机器人。为满足其长时间大尺度海洋调查的要求,设计了一种无线电和铱星卫星通信相结合的通信系统,并根据通信系统在海洋环境下通信链路不稳定的特点,设计了一种改进Xmodem通信协议,以保证水下滑翔机在海洋调查过程中通信的有效性和可靠性。通过海上实验表明:该通信系统和改进Xmodem协议可以满足水下滑翔机上传实验数据的应用需求。     

大深度无动力运载器上浮弹道特性研究

研究无动力大深度布放导弹运载器出水动态优化问题,在姿态角、速度和角速度等参数满足一定性能指标要求时,能使导弹和运载器成功安全分离。由于无控制上浮弹道受几何外形、海流、海浪及发射速度等因素影响,使上浮特性不清。为此利用运载器流体动力参数,建立运动数学模型,研究运载器弹道,并在CFD软件上进行仿真,重点分析了运载器壳体长细比、鳍板展弦比和发射速度对弹道参数影响规律。结果表明,出水俯仰角随长细比和发射速度减小而增大,展弦比和发射速度对出水合速度影响较小。研究结果可以为导弹运载器外形和弹道设计提供一定参考。     

Persistent ocean monitoring with underwater gliders: Adapting sampling resolution

Ocean processes are dynamic and complex and occur on multiple spatial and temporal scales. To obtain a synoptic view of such processes, ocean scientists collect data over long time periods. Historically, measurements were continually provided by fixed sensors, e.g., moorings, or gathered from ships. Recently, an increase in the utilization of autonomous underwater vehicles has enabled a more dynamic data acquisition approach. However, we still do not utilize the full capabilities of these vehicles. Here we present algorithms that produce persistent monitoring missions for underwater vehicles by balancing path following accuracy and sampling resolution for a given region of interest, which addresses a pressing need among ocean scientists to efficiently and effectively collect high‐value data. More specifically, this paper proposes a path planning algorithm and a speed control algorithm for underwater gliders, which together give informative trajectories for the glider to persistently monitor a patch of ocean. We optimize a cost function that blends two competing factors: maximize the information value along the path while minimizing deviation from the planned path due to ocean currents. Speed is controlled along the planned path by adjusting the pitch angle of the underwater glider, so that higher resolution samples are collected in areas of higher information value. The resulting paths are closed circuits that can be repeatedly traversed to collect long‐term ocean data in dynamic environments. The algorithms were tested during sea trials on an underwater glider operating off the coast of southern California, as well as in Monterey Bay, California. The experimental results show improvements in both data resolution and path reliability compared to previously executed sampling paths used in the respective regions. © 2011 Wiley Periodicals, Inc.     

Autonomous maritime collision avoidance: Field verification of autonomous surface vehicle behavior in challenging scenarios

We present results from sea trials for an autonomous surface vehicle (ASV) equipped with a collision avoidance system based on model predictive control (MPC). The sea trials were performed in the North Sea as part of an ASV Challenge posed by Deltares through a Dutch initiative involving different authorities, including the Ministry of Infrastructure and Water Management, the Netherlands Coastguard, and the Royal Netherlands Navy. To allow an ASV to operate in a maritime environment governed by the International Regulations for Preventing Collisions at Sea (COLREGs), the ASV must be capable of complying with COLREGs. Therefore, the sea trials focused on verifying COLREGs‐compliant behavior of the ASV in different challenging scenarios using automatic identification system (AIS) data from other vessels. The scenarios cover situations where some obstacle vessels obey COLREGs and emergency situations where some obstacles make decisions that increase the risk of collision. The MPC‐based collision avoidance method evaluates a combined predicted collision and COLREGs‐compliance risk associated with each obstacle and chooses the ‘best’ way out of dangerous situations. The results from the verification exercise in the North Sea show that the MPC approach is capable of finding safe solutions in challenging situations, and in most cases demonstrates behaviors that are close to the expectations of an experienced mariner. According to Deltares’ report, the sea trials have shown in practice that the technical maturity of autonomous vessels is already more than expected.     

无人机低空滑翔抗攻击突防控制律优化设计

为了提高无人机的低空滑翔抗攻击突防和控制能力,提出一种基于快速模型预测的无人机低空滑翔抗攻击突防控制技术。采用融合传感识别技术进行无人机的姿态和位置参数信息采集,分析无人机的低空滑翔控制的物理环境参数模型,构建无人机飞行轨迹地图模型,使用标准卡尔曼滤波器进行无人机低空滑翔抗攻击突防控制信息的融合处理,根据信息融合结果进行控制指令设计。采用动态基元轨迹跟踪方法,得到无人机低空突防控制的滑模面,在有限Morrey空间内采用串联弹性驱动控制方法求得在控制约束参量分布模型的最优解。根据无人机低空突防段的初始位姿参数进行快速模型预测和飞行轨迹跟踪,实现低空滑翔抗攻击突防控制。仿真结果表明,采用该方法进行无人机低空滑翔抗攻击突防控制的精度较高,无人机的姿态参数的自适应调节性能较好。     

Stability Analysis of an Underactuated Autonomous Underwater Vehicle Using Extended-Routh’s Stability Method

In this paper, a new approach to stability analysis of nonlinear dynamics of an underactuated autonomous underwater vehicle (AUV) is presented. AUV is a highly nonlinear robotic system whose dynamic model includes coupled terms due to the hydrodynamic damping factors. It is difficult to analyze the stability of a nonlinear dynamical system through Routh’s stability approach because it contains nonlinear dynamic parameters owing to hydrodynamic damping coefficients. It is also difficult to analyze the stability of AUVs using Lyapunov’s criterion and LaSalle’s invariance principle. In this paper, we proposed the extended-Routh’s stability approach to verify the stability of such nonlinear dynamic systems. This extended-Routh’s stability approach is much easier as compared to the other existing methods. Numerical simulations are presented to demonstrate the efficacy of the proposed stability verification of the nonlinear dynamic systems, e.g., an AUV system dynamics.     

基于物理模型的舰艏浪三维可视化

针对以往舰艏浪三维可视化中仅从实际观察出发建立动态模型,不能反映舰艏浪物理运动规律的问题,提出一种基于物理模型的舰艏浪三维可视化方法。该方法将舰艏浪物理模型应用到三维可视化中,采用边界元方法计算得到舰艏浪外形数据,利用粒子系统技术建立了三维动态模型,基于OpenSceneGraph粒子系统,在VS2010平台上实现了舰艏浪的三维可视化。实验结果表明该方法更符合物理运动规律,能较好地模拟舰船航行时的艏浪。     

Stochastic automated search methods in cellular automata: the discovery of tens of thousands of glider guns

This paper deals with the spontaneous emergence of glider guns in cellular automata. An evolutionary search for glider guns with different parameters is described and other search techniques are also presented to provide a benchmark. We demonstrate the spontaneous emergence of an important number of novel glider guns discovered by an evolutionary algorithm. An automatic process to identify guns leads to a classification of glider guns that takes into account the number of emitted gliders of a specific type. We also show it is possible to discover guns for many other types of gliders. Significantly, all the found automata can be candidate to an automatic search for collision-based universal cellular automata simulating Turing machines in their space-time dynamics using gliders and glider guns.     

基于现场观测数据的卫星雷达高度计海面风速和有效波高真实性检验方法研究

卫星遥感产品定量化应用前需通过真实性检验。卫星雷达高度计可观测海面风速大小和有效波高等海洋动力环境参数,而对其进行真实性检验存在不同的时空匹配方法。使用3种不同的时空匹配方法,利用美国国家浮标数据中心(NDBC)现场观测数据对2011年的Jason2海面风速和有效波高产品进行了检验。Jason2海面风速大小和有效波高的均方根误差分别为1.28 m/s和0.28 m,同时结果表明:采用卫星高度计海面风速大小(有效波高)和同步的现场观测数据在一定时间(1 h)和空间(50 km)限制条件下进行对比检验,可以得到合理的高度计海面风速大小和有效波高精度评价结果。 Jason2卫星高度计海面风速大小和有效波高的精度与探测海域有关,其精度在墨西哥湾与西大西洋海域相对较高。     

Swing Suppression and Accurate Positioning Control for Underactuated Offshore Crane Systems Suffering From Disturbances

Offshore cranes are widely applied to transfer large-scale cargoes and it is challenging to develop effective control for them with sea wave disturbances. However, most existing controllers can only yield ultimate uniform boundedness or asymptotical stability results for the system’s equilibrium point, and the state variables’ convergence time cannot be theoretically guaranteed. To address these problems, a nonlinear sliding mode-based controller is suggested to accurately drive the boom/rope to their desired positions. Simultaneously, payload swing can be eliminated rapidly with sea waves. As we know, this paper firstly presents a controller by introducing error-related bounded functions into a sliding surface, which can realize boom/rope positioning within a finite time, and both controller design and analysis based on the nonlinear dynamics are implemented without any linearization manipulations. Moreover, the stability analysis is theoretically ensured with the Lyapunov method. Finally, we employ some experiments to validate the effectiveness of the proposed controller.      

基于GPRS的水下滑翔机器人监控系统设计

水下滑翔机器人具有续航能力强、作业时间长等特点，适合于大范围海洋环境监测应用，可用于构建近海海洋环境立体监测网络。利用近海较好的GPRS网络覆盖条件，设计了基于GPRS网络的近海水下滑翔机器人监控系统。该监控系统不仅实现了在现场监控中心对水下滑翔机器人的监控，还可以通过Internet网络对水下滑翔机器人进行远程监控。文章详细介绍了监控系统的总体架构、GPRS终端硬件设计和系统软件设计。     

Dependence of mean square slope on wave state and its application in altimeter wind speed retrieval

Mean square slope (MSS) of sea surface is a parameter describing the sea surface roughness and plays a key role in understanding the sea surface dynamics. Although MSS is influenced by many factors such as wind speed and sea surface waves, it has been traditionally parameterized by wind speed only. In this study, the surface wave impact on MSS is investigated using a collocated data set of altimeter and buoy measurements. It is found that the MSS detected by Ku-band altimeter is closely related to the wind wave components and increases with the degree of wind wave development; however, it is almost independent of the swell. The wave effect on MSS is mainly ascribed to the contribution of longer waves rather than shorter waves. An analytical spectral MSS model is proposed, and it is shown that the MSS calculated from the model agrees well with the altimeter-measured MSS when the pseudo-wave age is adjusted to the wave age corresponding to wind waves. This model is applied to derive wind speeds from altimeter data including the normalized radar cross section and the significant wave height of sea surface waves. With the collocated data set, it is shown that this new algorithm performs better than previous empirical algorithms.