Decreasing the radiated acoustic and vibration noise of a mid-size AUV

An Odyssey IIb autonomous underwater vehicle (AUV) made by Bluefin Robotics, Inc., was acquired by the Marine Physical Laboratory, Scripps Institution of Oceanography, to conduct research in underwater acoustics as well as provide a platform for other scientific studies. The original Odyssey IIb tail cone was replaced with a ducted fan, vectored thrust system installed on vehicles currently sold by Bluefin. In initial sea tests with the new thrust system, the acoustic self noise levels of the vehicle while underway were 20 to 50 dB higher than typical ocean background noise levels, preventing the vehicle's use as a receiver of low level sounds. Controlled tests were performed to characterize the radiated and vibration noise of the AUV propulsion and actuators. Once this baseline was established, changes were made, mostly to the tail cone propulsion, to decrease the vehicle's self noise. The resulting self noise levels of the AUV from 10 Hz up to 10 kHz measured while underway by a hydrophone mounted on the AUV's inner shroud now are at or below typical shallow water background noise levels except in three bands; below 250 Hz, around 500 Hz, and from 0.9 to 2.0 kHz. The goal of this paper is to describe these changes and their effects in lowering vehicle noise levels.     

Maneuvering modeling and simulation of AUV dynamic systems with Euler-Rodriguez quaternion method

The purpose of this study is to develop maneuvering models and systems of a simulator to improve the motion performance of autonomous underwater vehicles (AUVs) at the preliminary design stages in advance. The AUVs simulation systems based on the standard submarine equations of motion in six-degree-of-freedom (6-DOF) integrated with the Euler-Rodriguez quaternion method for representing singularity-free AUV attitude and time-saving calculation, and with a nonlinear control model for maneuvering and depth control simulations, time-marching in the fourth-order Runge-Kutta scheme. For validation of the simulation codes, results of the ISiMI AUV open-loop tests including turning test and zigzag test as well as an AUV simulator on the basis of Euler-angle method were used to compare with the quaternion-based AUV simulator. The computational results from the proposed simulator agree well with those from both the ISiMI AUV experiments and the Euler-angle based simulations. Additionally, a new maneuvering procedure, namely "put-out" was implemented to test directional stability for a large-scale AUV in the proposed AUV simulator that can be considered for vehicles in space as well as in constrained planes.     

小型水下自航行器自沉浮装置设计与研究

文中对水下自航行器(Autonomous Underwater Vehicle,简称AUV)的自沉浮装置进行了详细设计与研究。通过对已有的自沉浮装置方案进行对比研究,设计了以高压气体吹除压载水舱的新型自沉浮装置,该装置具有结构简单、可靠性高和可维护性好的特点,并可实现模块化设计。最后,对装置的主要设计参数进行了计算与优化。     

The optimum control of thruster system for dynamically positioned vessels

An offshore vessel with a dynamic positioning system (DP system) needs fast response to produce thrust to counteract the environmental forces acting on it for the purpose of maintaining its position and heading as close as possible to the working position. Therefore, quick and effective modulation of the thrust is the problem to determine the thrust and the rotation angle of the thruster devices of the ship. This paper presents an effective optimum control for a thruster system, using the sequential quadratic method to achieve economical and effective modulation of the thrust and the direction of the thruster. An optimum control study of a 2280 tons DP coring vessel with five rotary azimuth thruster marine positioning is studied in detail, which can quickly and exactly estimate the thrusts and angles of direction of all the thrusters. The results can provide a valuable thruster system for a dynamically positioned vessel.     

自治水下机器人机械手系统协调运动研究

简单描述了自治水下机器人搭载的三功能水下电动机械手的设计,鉴于自治水下机器人-机械手系统运动学冗余、内部可能干涉以及载体圆筒式外形等特点,将惩罚调节因子引入系统运动学伪逆矩阵,保证了关节在允许范围内运动,避免载体大幅度姿态变化及载体与机械手之间的干涉,同时采用梯度投影法优化海流作用下的系统推力。仿真表明,该算法在解决系统冗余度的同时,有效地协调多任务下的系统动作。     

水下自主机器人水动力预报方法研究

针对水下机器人操纵性优化设计中水动力系数预报问题,在水下机器人水动力预报中引入艇体肥瘦指数概念,确定了水下机器人艇体几何描述的五参数模型。提出采用小波神经网络方法预报水下机器人水动力,确定了神经网络的结构,利用均匀试验设计方法,设计了神经网络的学习样本。研究结果表明,只要确定适当的输入参数,选择适当的学习样本和网络结构,利用小波神经网络方法对水下机器人水动力进行预报可以达到较好的精度。     

Toward an improved understanding of thruster dynamics forunderwater vehicles

This paper proposes a novel approach to modeling the four quadrant dynamic response of thrusters as used for the motion control of ROV and AUV underwater vehicles. The significance is that these vehicles are small in size and respond quickly to commands. Precision in motion control will require further understanding of thruster performance than is currently available. The model includes a four quadrant mapping of the propeller blades lift and drag forces and is coupled with motor and fluid system dynamics. A series of experiments is described for both long and short period triangular, as well as square wave inputs. The model is compared favorably with experimental data for a variety of differing conditions and predicts that force overshoots are observed under conditions of rapid command changes. Use of the model will improve the control of dynamic thrust on these vehicles     

A Numerical and Experimental Study on the Hull-Propeller Interaction of A Long Range Autonomous Underwater Vehicle

Range is an important factor to the design of autonomous underwater vehicles(AUVs), while drag reduction efforts are pursued, the investigation of body-propeller interaction is another vital consideration. We present a numerical and experimental study of the hull-propeller interaction for deeply submerged underwater vehicles, using a proportionalintegral-derivative(PID) controller method to estimate self-propulsion point in CFD environment. The hydrodynamic performance of hull and propeller at the balance state when the AUV sails at a fixed depth is investigated, using steady RANS solver of Star-CCM+. The proposed steady RANS solver takes only hours to reach a reasonable solution. It is more time efficient than unsteady simulations which takes days or weeks, as well as huge consumption of computing resources. Explorer 1000, a long range AUV developed by Shenyang Institute of Automation, Chinese Academy of Sciences, was studied as an object, and self-propulsion point, thrust deduction,wake fraction and hull efficiency were analyzed by using the proposed RANS method. Behind-hull performance of the selected propeller MAU4-40, as well as the hull-propeller interaction, was obtained from the computed hydrodynamic forces. The numerical results are in good qualitative and quantitative agreement with the experimental results obtained in the Qiandao Lake of Zhejiang province, China.     

An on-line adaptation method in a neural network based controlsystem for AUVs

A neural network based control system “Self-Organizing Neural-Net-Controller System: SONCS” has been developed as an adaptive control system for Autonomous Underwater Vehicles (AUVs). In this paper, an on-line adaptation method “Imaginary Training” is proposed to improve the time-consuming adaptation process of the original SONCS. The Imaginary Training can be realized by a parallel structure which enables the SONCS to adjust the controller network independently of actual operation of the controlled object. The SONCS is divided into two separate parts: the Real-World Part where the controlled object is operated according to the objective, and the Imaginary-World Part where the Imaginary Training is carried out. In order to adjust the controller network by the Imaginary Training, it is necessary to introduce a forward model network which can generate simulated state variables without involving actual data. A neural network “Identification Network” which has a specific structure to simulate the behavior of dynamical systems is proposed as the forward model network. The effectiveness of the Imaginary Training is demonstrated by applying to the heading keeping control of an AUV “Twin-Burger”. It is shown that the SONCS adjusts the controller network-through on-line processes in parallel with the actual operation     

可着陆式水下机器人的多体动力学建模与仿真

可着陆式水下机器人由于变浮力机构的设计要求,其外形与结构较之传统的水下航行器更为复杂。在设计阶段对可着陆式水下机器人进行仿真和操纵性分析具有重要意义。文中采用多体系统动力学方法分析可着陆式水下机器人动力学特性,将作用在系统各组成部分上的流体动力、推进力以及其它作用力分别计算和考虑,建立了多体动力学模型,并进行了三维空间运动仿真。该方法为具有较复杂附体结构的水下机器人设计和动力学仿真提供了有效途径。     

Experimental investigation of hydrodynamic force coefficients over AUV hull form

Extensive use of autonomous underwater vehicles (AUVs) in oceanographic applications necessitates investigation into the hydrodynamic forces acting over an AUV hull form operating under deeply submerged condition. This paper presents a towing tank-based experimental study on forces and moment on AUV hull form in the vertical plane. The AUV hull form considered in the present program is a 1:2 model of the standard hull form Afterbody1. The present measurements were carried out at typical speeds of autonomous underwater vehicles (0.4-1.4 m/s) by varying pitch angles (0-15°). The hydrodynamic forces and moment are measured by an internally mounted multi-component strain gauge type balance. The measurements were used to study variation of axial, normal, drag, lift and pitching moment coefficients with Reynolds number (Re) and angle of attack. The measurements have also been used to validate results obtained from a CFD code that uses Reynolds Average Navier-Stokes equations (ANSYS™ Fluent). The axial and normal force coefficients are increased by 18% and 195%; drag, lift and pitching moment coefficients are increased by 90%, 182% and 297% on AUV hull form at α=15° and Re_v=3.65×10⁵. These results can give better idea for the efficient design of guidance and control systems for AUV.     

Development of a deep ocean electric autonomous manipulator

This paper describes an underwater 3500 m electric manipulator (named Huahai-4E,stands for four functions deep ocean electric manipulator in China),which has been developed at underwater manipulation technology lab in Huazhong University of Science and Technology (HUST) for a test bed of studying of deep ocean manipulation technologies.The manipulator features modular integration joints,and layered architecture control system.The oil-filled,pressure-compensated joint is compactly designed and integrated of a permanent magnet (PM) brushless motor,a drive circuit,a harmonic gear and an angular feedback potentiometer.The underwater control system is based on a network and consisted of three embedded PC/104 computers which are used for servo control,task plan and target sensor respectively.They communicate through User Datagram Protocol (UDP) multicast communication in Vxworks OS.A supervisor PC with a virtual 3D GUI is fiber linked to underwater control system.Furthermore,the manipulator is equipped with a sensor system including a unique ultra-sonic probe array and an underwater camera.Autonomous grasp strategy based multi-sensor is studied.The results of watertight test in 40 MPa,joint’s efficiency test and autonomous grasp experiments in tank are also presented.     

Transformed equations of motion for underwater vehicles

A method for dynamics investigation and coupling detection between velocities of autonomous underwater vehicles (AUVs) is presented in this paper. The method is based on transformation of equations of motion, which are usually used for an underwater vehicle, into equations with a diagonal mass matrix. The obtained equations contain quasi-velocities and allow one to give a further insight into the AUV dynamics especially for an underactuated system. Some advantages of the proposed approach are discussed, too. An analytical example for a 3-DOF AUV shows possible application of the transformed equations. Moreover, the given approach is validated via simulation on a 6-DOF vehicle.     

Bistatic synthetic aperture imaging of proud and buried targets from an AUV

The use of autonomous underwater vehicles (AUVs) for the detection of buried mines is an area of current interest to the Mine CounterMeasures (MCM) community. AUVs offer the advantages of lower cost, stealth, reduced operator risk, and potentially improved coverage rates over more traditional mine hunters. However, AUVs also come with their own set of difficulties, including significant error in navigation and low communication rates with the mother platform and each other. In the case of bistatic detection scenarios, AUVs will therefore have difficulty knowing where exactly in space they are and the trigger time of sources on other platforms, be they ships or other AUVs. However, the potential improvement in detection and coverage rates offered by bistatic sonar concepts makes resolution of these issues a high priority. In this paper, the problems of inaccurate navigation and source timing information are addressed for the Generic Oceanographic Array Technology data set. In this experiment, conducted off Marciana Marina during June 1998, a MIT AUV with a SACLANTCEN acoustic array and acquisition system was used together with a TOPAS parametric sonar to explore issues of buried target detection using AUVs. In this paper, solutions to the navigation and timing problems are proposed which enable the effective use of bistatic synthetic aperture sonar (SAS) concepts for the detection of buried objects in the mid-frequency regime of 2-20 kHz.     

A chattering-free sliding-mode controller for underwater vehicles with fault-tolerant infinity-norm thrust allocation

There are two objectives to this paper. First, a chattering-free sliding-mode controller is proposed for the trajectory control of remotely operated vehicles (ROVs). Second, a new approach for thrust allocation is proposed that is based on minimizing the largest individual component of the thrust manifold. With regards to the former, a new adaptive term is developed that eliminates the high-frequency control action inherent in a conventional sliding-mode controller. As opposed to the common adaptive approach, the new adaptive term does not require the linearity condition on the dynamic parameters and the creation of a regressor matrix. In addition, it removes the need for a priori knowledge of upper bounds on uncertainties in the dynamic parameters of the ROV. With regards to the latter, it is demonstrated that minimizing the l_∞ norm (infinity-norm) of the thrust manifold ensures low individual thruster forces. The new control and thrust allocation concepts are implemented in numerical simulations of a work class ROV, and the chattering-free nature of the controller is demonstrated during typical ROV manoeuvres. In the simulation studies, the l_∞ norm-based thrust allocation problem is cast as a linear programming problem that allows direct incorporation of the thruster saturation limits and a fault-tolerant property. To achieve real-time solution rates for the l_∞ norm-based thrust allocation problem, a recurrent neural network is designed. In the simulation studies, the l_∞ norm-based thrust allocation provides smaller maximum absolute value of the largest component of the thrust manifold than that of a conventional l₂ norm (2-norm) minimization, satisfies the saturation limits of each thruster, and accommodates faults that are introduced arbitrarily during the manoeuvre.     

Power systems for autonomous underwater vehicles

In this paper, we examine the issues involved in designing battery systems and power-transfer (charging) techniques for Autonomous Underwater Vehicles (AUVs) operating within an Autonomous Ocean Sampling Network (AOSN). We focus on three different aspects of the problem, battery chemistry, pack management and in situ charging. We look at a number of choices for battery chemistry and evaluate these based on the requirements of maximizing power density and low temperature operation particular to AUVs. We look at the issues involved in combining individual cells into large battery packs and at the problems associated with battery monitoring, and the charging and discharging of packs in a typical AUV application. Finally, we present a methodology for charging an AUV battery pack in situ in support of long term deployments at remote sites     

Modeling and simulation of autonomous underwater vehicles: design and implementation

Autonomous underwater vehicles (AUVs) have many scientific, military, and commercial applications because of their potential capabilities and significant cost-performance improvements over traditional means for performing search and survey. The development of a reliable sampling platform requires a thorough system design and many costly at-sea trials during which systems specifications can be validated. Modeling and simulation provides a cost-effective measure to carry out preliminary component, system (hardware and software), and mission testing and verification, thereby reducing the number of potential failures in at-sea trials. An accurate simulation can help engineers to find hidden errors in the AUV embedded software and gain insights into the AUV operations and dynamics. This paper reviews our research work on real-time physics-based modeling and simulation for our AUVs. The modeling component includes vehicle dynamics, environment and sensor characteristics. The simulation component consists of stand-alone versus hardware-in-the-loop (HIL) implementation, for both single as well as multiple vehicles. In particular, implementation issues with regard to multitasking system resources will be addressed. The main contribution of this paper is to present the rationale for our simulation architecture and the lessons learned.     

自主水下航行器离散反馈避碰设计及仿真

为了使自主水下航行器(AUV)避碰仿真更接近实际情况,在离散时间系统中考虑海流作用,设计了AUV反馈避碰算法.针对海底探测AUV的运行特点,考虑海流作用,建立AUV垂直平面的状态空间方程.在每一个离散时间节点.利用障碍物高度信息,计算下一时刻AUV的深度目标值.然后利用反馈控制方法对其响应,在仿真时间内不断循环完成避碰仿真.对不同流场下不同高度的矩形障碍物,进行了避碰仿真.仿真结果证明了系统的可行性和合理性.     

水下机器人推力器布置及控制仿真研究

针对自治水下机器人(Autonomous underwater vehicle,AUV)推力器布置和控制仿真的困难性及以往电机仿真难以进行的缺点,提出1种进行多推力器运动仿真的方法,该方法建立的模型克服了推力器推力控制系统不能与电机结合的问题,能较好地反映推力器布置和电机的响应情况,可为AUV的运动控制、布置设计及控制系统开发等提供验证模型.针对流线型AUV CRanger-2的推力器布置情况,在对其建立推力器模型的基础上,利用模型对设定推力下的推力器控制进行仿真.仿真结果表明:该方法能够有效地模拟推力器布置既定情况下的电机运动与推力控制,可为水下机器人控制策略优化提供仿真平台.