An Adaptive Obstacle Avoidance Algorithm for Unmanned Surface Vehicle in Complicated Marine Environments

Unmanned surface vehicles(USVs) are important autonomous marine robots that have been studied and gradually applied into practice. However, the autonomous navigation of USVs, especially the issue of obstacle avoidance in complicated marine environment, is still a fundamental problem. After studying the characteristics of the complicated marine environment, we propose a novel adaptive obstacle avoidance algorithm for USVs,based on the Sarsa on-policy reinforcement learning algorithm.The proposed algorithm is composed of local avoidance module and adaptive learning module, which are organized by the “divide and conquer” strategy-based architecture. The course angle compensation strategy is proposed to offset the disturbances from sea wind and currents. In the design of payoff value function of the learning strategy, the course deviation angle and its tendency are introduced into action rewards and penalty policies. The validity of the proposed algorithm is verified by comparative experiments of simulations and sea trials in three sea-state marine environments. The results show that the algorithm can enhance the autonomous navigation capacity of USVs in complicated marine environments.

Numerical Simulation of a Planing Vessel at High Speed

计划容器处于民用、军事的状况广泛地被使用。由于他们的高速度，计划容器的运动是复杂的。以便预言计划容器的运动，分析以高速度计划容器的水动力学表演是重要的。计算液体动态方法(CFD ) 被建议了计算计划容器的水动力学性能。在很传统的 CFD 途径，然而，模型测试或实验公式被需要在计算前获得计划容器的跑的态度。这份报纸论述一个新 CFD 方法计算计划容器的水动力学力量。数字方法基于平均 Reynolds 的海军司烧(RANS ) 方程。液体(VOF ) 的体积方法和 six-degrees-of-freedom 方程被使用。一个有效过程被介绍在数字模拟解决数字分叉问题。与试验性的结果相比，数字模拟结果显示跑的态度和水动力学性能能以高速度被预言很好。

Numerical Study of Propulsion Mechanism for Oscillating Rigid and Flexible Tuna-Tails

Numerical study on the unsteady hydrodynamic characteristics of oscillating rigid and flexible tuna-tails in viscous flow-field is performed. Investigations are conducted using Reynolds-Averaged Navier-Stokes （RANS） equations with a moving adaptive mesh. The effect of swimming speed, flapping amplitude, frequency and flexure amplitude on the propulsion performance of the rigid and flexible tuna-tails are investigated. Computational results reveal that a pair of leading edge vortices develop along the tail surface as it undergoes an oscillating motion. The propulsive efficiency has a strong correlation with various locomotive parameters. Peak propulsive efficiency can be obtained by adjusting these parameters. Particularly, when input power coeffcient is less than 2.8, the rigid tail generates larger thrust force and higher propulsive efficiency than flexible tail. However, when input power coefficient is larger than 2.8, flexible tail is superior to rigid tail.

RANSE Simulation of High-speed Planning Craft in Regular Waves

这份报纸在计划航行在常规波浪的手艺的数字模拟上论述研究。这允许保留高速度手艺的性能的海的精确估计。模拟集合在自由运动六度基于雷纳兹平均 Navier 司烧液体(RANSE VOF ) 的方程体积解答者。整修网孔技术和不可分的动态网孔方法被用来保证水动力学力量的好精确性和数字模拟的高效率。事件头波浪，倾斜的波浪和横梁波浪与三不同速度在模拟被产生(Fn =1.0， 1.5， 2.0 ) 。与波浪让计划手艺的性能来自不同方向的运动和海在流动解答者被显示。轮船设计者在驾驶在造高速度手艺的配置计划手艺的振幅和压力分发上把一个重音放在波浪的效果上。

Experimental Study on Hydrodynamics of L-type Podded Propulsor in Straight-ahead Motion and Off-Design Conditions

试验性的测试被进行评估 L 类型 podded propulsor 的水动力学性能在直向前，用一台开水的测量仪器的运动和离开设计条件为 podded propulsors 由作者发展了，拖引坦克的一个轮船模型，并且在水粒子图象 velocimetry (PIV ) 下面测量系统。在条件的三种类型下面， L 类型 podded propulsor 的主要参数被测量，包括推进器戳和转矩，以及整个豆荚单位的戳，方面力量，和时刻。另外，在推进器和神气之间的节上的流动领域被分析。试验性的结果证明动态 azimuthing 率和方向和转弯的方向在推进器和整个豆荚单位上影响力量。因为推进器旋转的效果，力量不均匀地在左、正确的 azimuthing 方向之间被散布。这研究的调查结果为关于 L 类型 podded propulsors 的进一步的研究提供一个基础。

Study on Unsteady Hydrodynamic Performance of Propeller in Waves

The speed of a ship sailing in waves always slows down due to the decrease in efficiency of the propeller. So it is necessary and essential to analyze the unsteady hydrodynamic performance of propeller in waves. This paper is based on the numerical simulation and experimental research of hydrodynamics performance when the propeller is under wave conditions. Open-water propeller performance in calm water is calculated by commercial codes and the results are compared to experimental values to evaluate the accuracy of the numerical simulation method. The first-order Volume of Fluid(VOF) wave method in STAR CCM+ is utilized to simulate the three-dimensional numerical wave. According to the above prerequisite, the numerical calculation of hydrodynamic performance of the propeller under wave conditions is conducted, and the results reveal that both thrust and torque of the propeller under wave conditions reveal intense unsteady behavior. With the periodic variation of waves, ventilation, and even an effluent phenomenon appears on the propeller. Calculation results indicate, when ventilation or effluent appears, the numerical calculation model can capture the dynamic characteristics of the propeller accurately, thus providing a significant theory foundation forfurther studying the hydrodynamic performance of a propeller in waves.

Fluid dynamics of a self-propelled biomimetic underwater vehicle with pectoral fins

Fluid dynamics of a self-propelled biomimetic underwater vehicle(BUV)with pectoral fins is investigated by an immersed boundary(IB)method.Typically,the BUV with a pair of pectoral fins starts from rest and attains a constant mean velocity as the mean longitudinal force is zero.The capability and accuracy of the IB method to deal with the interaction between the fluid and complex moving body are firstly validated.Then we carry out a parametric study to understand the effect of key governing parameters on the dynamic response of the BUV.It is found that with the increase of motion frequency or rolling amplitude,the pectoral fin propulsors can induce larger forward velocity so that the BUV takes less time to attain its stable periodic swimming state.Although the pectoral fin is a very complicated lifting surface,a linear relationship between forward Reynolds number(final swimming velocity is used as velocity scale)and frequency Reynolds number(product of motion frequency and fin chord length is used as velocity scale)can be established when the frequency Reynolds number is above a critical value.A linear relationship between forward Reynolds number and rolling amplitude is also found within the studied range of rolling amplitude.Furthermore,a small-density-ratio BUV is sensitive to the surrounding flow with more rapid evolution process of self-propulsion.Whereas,BUV with a large density ratio is more stable.The implications of the hydrodynamic analysis on the bio-inspired engineering design of BUV with pectoral fins are also discussed.