Development of a dual-shaft propeller thruster equipped with rotational speed sensor for UVMS control

Majority of underwater robots utilize single propeller thrusters for navigation. A disadvantage of using a single-shaft propeller thruster is that the thrust force generated from a single propeller for reverse and forward thrust is asymmetric due to the disturbed flow caused by the thruster’s body which may reduce thruster efficiency. Moreover, measurement procedures to precisely calculate propeller’s rotation speed were also not available. To address these problems, this paper proposes a dual-shaft magnetic coupling-driven propeller thruster for underwater robot, equipped with sensors for measuring propeller’s rotational speed. Numerical studies and experimental results on the position and orientation control of the proposed thruster are presented. Detail comparison of the rotational speed, thrust force and duty ratio between numerical calculation and actual experimental measurement results show the effectiveness of the proposed thruster. This paper also demonstrated that by using the proposed thruster, the control performance of an underwater robot can be improved significantly compared to commercially available thruster. The ability to determine propeller rotation directions is also a major advantage of this work.     

Development of dam inspection robot with negative pressure effect plate

This paper describes the development of an underwater robot that performs visual inspection while making mechanical contact with a dam surface by a pulling force generated from thrusters with negative pressure effect plates. In general, small and lightweight remotely operated vehicles (ROVs) have low‐power thrusters. Their positioning performance is inferior with respect to external disturbances. Moreover, it is difficult for untrained operators to control the ROV position to check and inspect dams visually. A negative pressure effect plate attached to a thruster produces negative pressure that maintains mechanical contact between the robot and a dam wall surface and ensures stable robot motion on a dam surface to acquire clear continuous images. As described herein, we theoretically investigate the negative pressure effect plate characteristics and experimentally measure the force generated by the pressure difference. Results show that the force of a thruster with the effect plate is five times greater than the nominal thrust force provided by the thruster alone. Based on those results, we designed and developed the underwater robot with the negative pressure effect plates for dam inspection. Moreover, we conducted an experiment in a water tank and a field test at Shorenji Dam, Mie‐prefecture, Japan. The experimentally obtained results indicated that the negative pressure effective plate is effective at generating sufficient force and at realizing stable robot motion on the dam surface. Results demonstrate that the developed robot acquired clear images of the dam surface continuously with no sophisticated operator or controller.     

NiTi形状记忆合金驱动的仿生鱼鳍的研究

为了提高仿鱼型推进器在水中运动的灵活性,选择了典型的依靠腹部绸带状鱼鳍波动运动产生推进力的黑色魔鬼刀鱼进行研究,对此绸带状鱼鳍的形态和运动机理进行了分析,同时对鱼鳍的结构进行简化．基于绸带状鱼鳍的这种简化模型设计了形状记忆合金驱动的仿生鱼鳍．介绍了鱼鳍的机械结构和相应的控制电路．重点推导了仿生鱼鳍波状运动时理论上能到达的推进速度和产生的推进力;并采用数值仿真给出了波动推进时仿生鱼鳍表面的压力分布以及推进力随时间的周期变化规律．将数值仿真结论和先前的实验结果进行了比较,验证了数值仿真的合理性和正确性．通过上述分析,说明基于形状记忆合金驱动的仿生鱼鳍的研究是很有意义而且可行的．     

船用螺旋桨敞水性能数值分析

为预测某船用螺旋桨在不同螺距下的敞水性能,对标准螺旋桨DTMB 4119的敞水性能进行数值模拟,得到的推力因数和扭矩因数计算值与试验值的对比表明通过求解RANS方程模拟螺旋桨黏性流场是可行的.用该方法预测某船用螺旋桨的敞水性能:模拟得到不同螺距下螺旋桨推力因数、扭矩因数和表面压力因数的变化以及尾流情况.通过RANS方法...     

两关节仿生水下航行器SPC-III 的推进与机动性

为评估尾鳍推进机构的实用性,以SPC-III 机器鱼作为研究平台,在同等排水量下分别使用尾鳍推进 器和螺旋桨推进器,比较两者的功率和机动能力．在海试条件下,对尾鳍推进器和螺旋桨推进器的功率及机动性进 行了测试,表明前者的转弯半径约为后者的2/5,在2.2 kn 速度下,前者的功率比后者低约7%．SPC-III 仿生水下航 行器携带多参数水质探测仪在太湖完成了航程为49 km 的水质探测实验,得到了太湖水域的蓝绿藻浓度分布数据．     

舵桨联合操纵水下机器人运动控制研究

水下机器人空间运动具有耦合性和非线性等特点,具有良好品质的运动控制器是水下机器人完成各种作业的前提.针对某舵桨联合操纵小型自主式水下机器人运动控制问题进行了研究.对速度,深度和艏向控制系统进行了介绍,根据控制需求,建立了水下机器人动力学模型,对执行机构进行了描述,设计了水下机器人滑模控制方案,采用变速趋近项代替一般指数...     

仿生魟鱼环形胸鳍波动推进的流场仿真

针对自主设计的仿生魟鱼水下机器人环形胸鳍波动推进过程进行了流场仿真研究。基于魟鱼前进运动时的胸鳍波动特征,建立了仿生环形胸鳍三维波动运动模型。利用CFD对胸鳍波动推进过程进行数值计算,分析了波动胸鳍产生的拉力以及前向运动的速度等推进性能。研究了周期波动过程中鳍面的周向压力分布,进行鳍面附近核心涡以及切面二维涡分量的计算,分析了涡的产生、发展以及尾迹涡的相关特性。结果表明,稳定后的拉力系数以近似正弦波形式进行波动,鳍面波动前后缘分布的高压和低压区域随波动沿周向从前往后传播,环形波动长鳍最终在尾迹处形成卡门涡,流场分析为仿生魟鱼水下机器人的运动控制及性能优化提供理论基础。     

A Computational Fluid Dynamics （CFD） Analysis of an Undulatory Mechanical Fin Driven by Shape Memory Alloy

Many fishes use undulatory fin to propel themselves in the underwater environment. These locomotor mechanisms have a popular interest to many researchers. In the present study, we perform a three-dimensional unsteady computation of an undulatory mechanical fin that is driven by Shape Memory Alloy (SMA). The objective of the computation is to investigate the fluid dynamics of force production associated with the undulatory mechanical fin. An unstructured, grid-based, unsteady Navier-Stokes solver with automatic adaptive remeshing is used to compute the unsteady flow around the fin through five complete cycles. The pressure distribution on fin surface is computed and integrated to provide fin forces which are decomposed into lift and thrust. The velocity field is also computed throughout the swimming cycle. Finally,a comparison is conducted to reveal the dynamics of force generation according to the kinematic parameters of the undulatory fin (amplitude, frequency and wavelength).     

Adaptive multi-mode switching strategy for the spherical underwater robot with hybrid thrusters

The conventional autonomous cruise and tracking system cannot transition and change its motion mode according to the underwater environment during operation, so it is of great significance to study the multi-mode switching of cruise control for Autonomous Underwater Vehicles (AUVs). In this paper, a Multi-Mode Adaptive Switching (MMAS) strategy for the Spherical Underwater Robot with Hybrid Thruster (HPSUR) was proposed, which provided the possibility for the robot to choose optimal control mode according to the unpredictable operating environment. Then, the dynamic and force of the hybrid thruster are analyzed to improve the accuracy of multi-mode switching, and the MMAS strategy is developed linking the attitude adjustment and switching problems. Furthermore, a series of multi-mode switching experiments were conducted using water-jet mode, propeller mode and hybrid mode. Finally, the experimental result was discussed, which verified the effectiveness and accuracy of the proposed MMAS strategy. The proposed control strategy has a certain reference value for the multi-mode switching of propulsion devices.     

7000米载人潜水器推进器故障容错控制分配研究

介绍了7000米载人潜水器推进系统的组成和推进器布置,描述了潜水器控制分配问题,对推进器推力和期望控制量进行了归一化处理．根据载人潜水器的推进器布置,建立了系统的控制分配模型,设计了推进器故障容错处理策略,研究了基于推力最小二范数的载人潜水器控制分配求解方法．采用基于伪逆矩阵与定点分配的混合控制分配求解算法,在半物理仿真平台上实验验证了控制分配求解算法的正确性和有效性．     

A contribution to the problem of vortex breakdown

Associated with the breakdown process is the formation of a stagnation point on the axis of the vortex. This requires the deceleration of the axial velocity component, which must be enforced by a positive axial pressure gradient. The analysis presented here shows, how the pressure gradient along the axis of the vortex is influenced by the radial and azimuthal velocity components. An explicit expression for $\text{?p/?x (x, 0)}$ can be obtained by integration of the momentum equation for the radial velocity component with respect to the radial and subsequent differentiation of the integral with respect to the axial direction. In an order of magnitude analysis it is then demonstrated that for large Reynolds numbers one component of the frictional force in the azimuthal direction cannot be neglected. In order to obtain an estimate for the pressure gradient rigid body rotation is assumed for the vortex core, and a distribution similar to that of a potential vortex $\text{w = kr}{}^{\mathrm{?n}}$, for the outer portion. The estimate shows that a positive axial pressure gradient can exist only, if the radial velocity component is positive and if the exponent $\text{n}$ is less than unity. It is also verified that a potential vortex cannot support an axial pressure gradient, that the pressure gradient in magnitude is directly proportional to the square of the maximum of the azimuthal velocity, referenced to the freestream velocity.     

开架水下机器人生物启发离散轨迹跟踪控制

针对水下机器人常规反步跟踪控制的速度跳变问题,提出了基于生物启发模型的反步滑模混合控制方法.应用生物启发模型的平滑、有界输出特性,产生渐变的参考跟踪速度,克服了速度跳变问题,也满足了推进器推力约束.同时自适应滑模控制算法产生跟踪控制律,对于水下干扰及模型不确定影响具有鲁棒性,能够实现水下机器人稳定、准确的轨迹跟踪控制.所提方法的稳定性通过Lyapunov理论进行了证明,并将该方法对FALCON开架水下机器人进行水平面离散轨迹跟踪控制的仿真研究,实验结果表明了提出控制方法的有效性.     

分析两端扭转弹簧约束下简支输流管道的动力特性

研究了两端受扭转弹簧约束的简支输流管道的固有频率特性和静态失稳临界流速.根据梁模型横向弯曲振动模态函数,由端部支承和约束边界条件得到了其模态函数的一般表达式.根据动力方程的特征方程,具体分析了约束弹性刚度、流体压强、流速和管截面轴向力等参数对管道固有频率特性和静态失稳临界流速的影响.数值分析表明,约束弹性刚度的增大使管道的固有频率和失稳临界流速明显提高;流体流速、压强和管截面受到的轴向压力的增加使管道的固有频率和失稳临界流速降低.当管道的固有频率和失稳临界流速较低时,可以通过增加端部约束的方法来提高.     

优化排水直管段流量测量准确性的研究

研究排水直管段流量的测量精度问题。由于目前传统的测量方法不能有效地减小直管段安装角度造成的误差,导致流量测量的准确度较低。为了优化流量测量的准确性,流体力学湍流双方程理论,建立直管段湍流模型,采用计算流体力学软件Fluent仿真孔板前后压差随着排水直管段安装角度所产生的变化,并得出消除静压差后的流量定量值。仿真结果表明,随着流速增大,角度变化对流量测量准确性的影响越小。仿真结果证明,角接取压在整体测量方法中较为准确,是一种处理流量测量精度问题的有效方法。     

微腔体内射流特性的研究

采用数值模拟的方法对微射流结构中的射流特性进行了分析研究,研究了射流管的长度、射流管截面形状、驱动振幅、驱动频率、气体介质及环境压强等对射流中心最大流速和流速轴向衰减指数的影响,为微射流结构的改进优化提供了依据.     

万米级水下机器人浮力实时测量方法

提出了一种适用于万米级水下机器人的实时浮力测量方法,主要解决大于一万米水深环境下密度变化、新材料力学参数不确定等因素造成浮力计算困难的问题．该方法基于推进器和加速度计进行浮力测量．为了减少相关动力学参数不确定性对测量结果的影响,水下机器人需要在海底执行特殊的运动动作．文中讨论了该方法的特点和适用情况,并使用“海斗”号自主遥控水下机器人（“海斗”ARV）在近10900 m深的海底中进行了实验验证．实验结果表明,该方法测量得到的结果与参考值的平均误差为0.3 N,满足预期要求．     

新型推力式流速传感器的测量原理与结构设计研究

提出了一种基于颗粒相特性进行流速检测的新型推力式流速传感器的实验装置结构.该流速传感器实验装置通过测量牵引线对置于流体中刚性浮球产生的拉力,再根据刚性浮球在流体中受力情况,计算得到流体对浮球的推力.最终利用推力和流体流速之间的经验公式得到流体流速.新型流速传感器结构简单,成本低,不仅可以测量一般河流、输水渠道、湖泊、海...     

Fluid–structure interaction study on the performance of flexible articulated caudal fin

In this paper, the propulsive performance of a flexible articulated caudal fin is investigated by fluid–structure interaction. The caudal fin is composed of two links which are connected by a hinge. One link is driven by pitching motion while the other one moves passively. Five cases of link flexibility are investigated, namely, the rigid–rigid case, the medium flexible–medium flexible case, the flexible–flexible case, the rigid–flexible case and the flexible–rigid case. Their fluid field and structure deformations are analysed and hydrodynamic forces are compared. It is found that the rigid–rigid caudal fin produces larger thrust force than other cases with a low-pitching frequency, while the rigid–flexible case performs better with a higher frequency. The mean thrust force increases with the frequency in our experiments, however, for the medium flexible–medium flexible case, an optimal frequency exists. Besides, the effect of the hinge stiffness is studied. It is seen that the medium flexible–medium flexible case exhibits a striking performance. When the hinge stiffness decreases, its mean thrust force increases and possesses larger amplitude while the forces of other cases decrease. These results can guide the design of flexible propeller with links and will be useful for the development of flexible underwater robots.     

Two-dimensional simulation of unsteady marine propulsor blade flow using dynamic meshing techniques

The unsteady flow around a marine propeller blade section embedded in a traveling wave field is simulated and the results are validated against the well-known experimental data. Unstructured dynamic meshing techniques based on smoothing and remeshing are implemented and applied. The Massachusetts Institute of Technology Flapping Foil Experiment is selected for the validation, as it reveals the complex unsteady flow physics on a typical marine propeller blade section. The comparison with experimental data is good in terms of the first harmonic amplitudes and phases of the surface pressure coefficient and streamwise velocity component around and in the boundary layer of the blade section. The validation results suggest that the present computational approach with the unstructured dynamic meshing techniques, which are also available for three-dimensional problems, is both easy to apply and accurate enough for more realistic problems.     

Spacecraft thruster control allocation problems

We consider the control allocation problem in a spacecraft thruster configuration. It consists on the determination of the force command to be sent to each thruster in order to point the total torque and/or thrust vectors. Here, we state four possible practical problems and propose a control allocation algorithm based on a subgradient optimization, which is shown to be faster than existing allocators.