HYDRODYNAMIC ANALYSIS AND SIMULATION OF A SWIMMING BIONIC ROBOT TUNA

A dynamic model for undulatory locomotion was proposed to study the swimming mechanism of a developed bionic robot tuna. On the basis of inviscid hydrodynamics and rigid-body dynamics, the momentum and propulsive force required for propelling the swimming robot tuna’s flexible body was calculated. By solving the established dynamic equations and efficiency formula, the swimming velocity and propulsive efficiency of the bionic robot tuna were obtained. The relationship between the kinematic parameters of the robot tuna’s body curve and the hydrodynamic performances was established and discussed after hydrodynamic simulations. The results presented in this article can be used to increase the swimming speed, propulsive thrust, and the efficiency of underwater vehicles effectively.     

HYDRODYNAMIC STUDY ON A PECTORAL FIN ROWING MODEL OF A FISH

Fish pectoral fin movement involves primarily a drag-based and a lift-based mechanisms to produce thrust. A numerical study on a pectoral fin rowing propulsion model based on the drag-based mechanism is presented in this article. The propulsive mechanism of the pectoral fin rowing model is related with the voriticity and pressure in the flow field. The relationship between the thrust and kinematic parameters and the wake-captured problem are analyzed. It is shown that a high thrust is produced in the power stroke, mainly due to the backward translation acceleration, the anticlockwise angular acceleration and the absence of stall in the uniform translation. Moreover, the flow control mechanism and the effect of dynamic flexible deformation are further analyzed. To properly choose controllable factors and adopt an appropriate dynamic deformation can improve the propulsive performance.     

对称双翼沉浮振动推进性能研究

该文利用非定常双时间NS方程的预处理方法对摆翼地效推进器进行了推力和推进性能的分析,结果显示沉浮振动的推力和效率与速度的变化关系表现出一致性;固定频率,改变速度,发现推力和效率存在极大值点;随着频率增大,极大值点右移.最大推力和效率的动力攻角为 6o-9o,利用速度矢量图和压力云图显示了分离涡的输运和扩散,再一次展示了地效的存在.     

静水中长鳍扭波推进的水动力数值研究

长鳍扭波推进是一种典型的鱼类游动方式,具有高效、低噪、机动灵活等一系列优点。该文以"尼罗河魔鬼"鱼为仿生研究对象,采用弹性光顺法和局部网格重划法的动网格技术对大摆幅的长鳍扭波推进运动流场进行了数值计算研究,鳍条最大摆幅高达85°,对长鳍扭波推进在系泊状态下的水动力进行了研究,并与试验结果进行了比较验证。数值分析了鳍面压力分布及其随相位的变化,以及与推力产生的关联,并分析了长鳍扭波推力随扭波频率的变化,研究表明,系泊状态下,推力系数不随频率而改变。     

Energy saving by using asymmetric aftbodies for merchant ships–design methodology,numerical simulation and validation

The methodology and procedures are discussed on designing merchant ships to achieve fully-integrated and optimized hull-propulsion systems by using asymmetric aftbodies. Computational fluid dynamics(CFD) has been used to evaluate the powering performance through massive calculations with automatic deformation algorisms for the hull forms and the propeller blades. Comparative model tests of the designs to the optimized symmetric hull forms have been carried out to verify the efficiency gain. More than 6% improvement on the propulsive efficiency of an oil tanker has been measured during the model tests. Dedicated sea-trials show good agreement with the predicted performance from the test results.     

蝌蚪模型并列游动的数值研究

该文通过数值求解雷诺平均N-S方程,对高雷诺数下蝌蚪模型同相位和反相位并排游动进行了数值研究,揭示了并列蝌蚪群游的流动机制。研究表明,非流线型的蝌蚪并列群游与流线型的鱼体不同。蝌蚪同相位并列游动时,总推力比单独游动时低,尽管能量消耗有所增加但推进效率更高;蝌蚪反相位并列游动时,总推力比单独游动时低,但比同相位并列游动时高,间距很近时消耗的能量会显著增加,而推进效率依然提高。蝌蚪的钝体头部产生的涡在群游时有利于增加推力。     

Effect of head swing motion on hydrodynamic performance of fishlike robot propulsion

This paper studies the effect of the head swing motion on the fishlike robot swimming performance numerically.Two critical parameters are employed in describing the kinematics of the head swing: the leading edge amplitude of the head and the trailing edge amplitude of the head.Three-dimensional Navier-Stokes equations are used to compute the viscous flow over the robot.The user-defined functions and the dynamic mesh technology are used to simulate the fishlike swimming with the head swing motion.The results reveal that it is of great benefit for the fish to improve the thrust and also the propulsive efficiency by increasing the two amplitudes properly.Superior hydrodynamic performance can be achieved at the leading edge amplitudes of 0.05L( L is the fish length) and the trailing edge amplitudes of 0.08 L.The unsteady flow fields clearly indicate the evolution process of the flow structures along the swimming fish.Thrust-indicative flow structures with two pairs of pressure cores in a uniform mode are generated in the superior performance case with an appropriate head swing,rather than with one pair of pressure cores in the case of no head swing.The findings suggest that the swimming biological device design may improve its hydrodynamic performance through the head swing motion.     

An overview of simulation-based hydrodynamic design of ship hull forms

This review paper presents an overview of simulation-based hydrodynamic design optimization of ship hull forms. A computational tool that is aimed to accomplishing early-stage simulation-based design in terms of hydrodynamic performance is discussed in detail. The main components of this computational tool consist of a hydrodynamic module, a hull surface modeling module, and an optimization module. The hydrodynamic module includes both design-oriented simple CFD tools and high-fidelity CFD tools. These integrated CFD tools are used for evaluating hydrodynamic performances at different design stages. The hull surface modeling module includes various techniques for ship hull surface representation and modification. This module is used to automatically produce hull forms or modify existing hull forms in terms of hydrodynamic performance and design constraints. The optimization module includes various optimization algorithms and surrogate models, which are used to determine optimal designs in terms of given hydrodynamic performance. As an illustration of the computational tool, a Series 60 hull is optimized for reduced drag using three different modification strategies to outline the specific procedure for conducting simulation-based hydrodynamic design of ship hull forms using the present tool. Numerical results show that the present tool is well suited for the hull form design optimization at early design stage because it can produce effective optimal designs within a short period of time.     

Numerical and experimental studies of hydrodynamics of flapping foils

The flapping foil based on bionics is a sort of simplified models which imitate the motion of wings or fins of fish or birds. In this paper, a universal kinematic model with three degrees of freedom is adopted and the motion parallel to the flow direction is considered. The force coefficients, the torque coefficient, and the flow field characteristics are extracted and analyzed. Then the propulsive efficiency is calculated. The influence of the motion parameters on the hydrodynamic performance of the bionic foil is studied. The results show that the motion parameters play important roles in the hydrodynamic performance of the flapping foil. To validate the reliability of the numerical method used in this paper, an experiment platform is designed and verification experiments are carried out. Through the comparison, it is found that the numerical results compare well with the experimental results, to show that the adopted numerical method is reliable. The results of this paper provide a theoretical reference for the design of underwater vehicles based on the flapping propulsion.     

NUMERICAL PREDICTION OF PROPELLER EXCITED ACOUSTIC RESPONSE OF SUBMARINE STRUCTURE BASED ON CFD,FEM AND BEM

A mesh-less Refined Integral Algorithm (RIA) of Boundary Element Method (BEM) is proposed to accurately solve the Helmholtz Integral Equation (HIE).The convergence behavior and the practicability of the method are validated.Computational Fluid Dynamics (CFD),Finite Element Method (FEM) and RIA are used to predict the propeller excited underwater noise of the submarine hull structure.Firstly the propeller and submarine’s flows are independently validated,then the self propulsion of the "submarine+propeller" system is simulated via CFD and the balanced point of the system is determined as well as the self propulsion factors.Secondly,the transient response of the "submarine+ propeller" system is analyzed at the balanced point,and the propeller thrust and torque excitations are calculated.Thirdly the thrust and the torque excitations of the propeller are loaded on the submarine,respectively,to calculate the acoustic response,and the sound power and the main peak frequencies are obtained.Results show that:(1) the thrust mainly excites the submarine axial mode and the high frequency area appears at the two conical-type ends,while the torque mainly excites the circumferential mode and the high frequency area appears at the broadside of the cylindrical section,but with rather smaller sound power and radiation efficiency than the former,(2) the main sound source appears at BPF and 2BPF and comes from the harmonic propeller excitations.So,the main attention should be paid on the thrust excitation control for the sound reduction of the propeller excited submarine structure.     

Marine propellers performance and flow-field prediction by a free-wake panel method

A Boundary Element Method （BEM） hydrodynamics combined with a flow-alignment technique to evaluate blades shed vorticity is presented and applied to a marine propeller in open water. Potentialities and drawbacks of this approach in capturing propeller performance, slipstream velocities, blade pressure distribution and pressure disturbance in the flow-field are highlighted by comparisons with available experiments and RANSE results. In particular, correlations between the shape of the convected vortex- sheet and the accuracy of BEM results are discussed throughout the paper. To this aim, the analysis of propeller thrust and torque is the starting point towards a detailed discussion on the capability of a 3-D free-wake BEM hydrodynamic approach to describe the local features of the flow-field behind the propeller disk, in view of applications to propulsive configurations where the shed wake plays a dominant role.     

Numerical simulation of hull/propeller interaction of submarine in submergence and near surface conditions简

Hull/propeller interaction is of great importance for powering performance prediction. The features of hull/propeller interaction of a submarine model with a high-skew five blade propeller in submergence and near surface conditions are numerically simulated. The effect of propeller rotation is simulated by the sliding mesh technique. Free surface is captured by the volume of fluid （VOF） method. Computed results including resistance, thrust, torque and self-propulsion factor are compared with experimental data. It shows fairly good agreement. The resistance and wave pattern of the model at different depths of submergence are computed. And the thrust, torque and self-propulsion factor of the model in submergence and near surface condition are compared to analyze the effect of free surface on self-propulsion performance. The results indicate that free surface has more influence on resistance than that on self-propulsion factors.     

水下高速航行体艏部水动力自噪声预报方法及低噪声线型设计

针对水下高速航行体水动力自噪声特征,采用过渡区声辐射理论,建立了航行体艏部水动力自噪声预报方法。经模型试验考核偏差小于3dB,故该方法可以用于可用于航行体艏部水动力自噪声预报及低噪声线型设计。理论研究表明,航行体艏部水动力自噪声与边界层层流向湍流过渡转捩点位置有关,转捩点越往后,水动力自噪声越低。在此基础上,针对通用鱼雷外形,给出雷头低噪声设计拟合曲线。进一步分析发现,鱼雷艏部水动力自噪声随着平头端面直径的增大而增加,端面直径增加一倍,水动力自噪声增加约5dB,因此可以采用小的端面直径,来降低鱼雷艏部水动力自噪声。     

THE NUMERICAL CALCULATION FOR THE STERN FLOW OF THREE DIMENSIONAL SURFACE SHIP WITH MULTI-PRO-PELLERS IN OPERATION

In this paper the complex structure and pattern of ship stern flow driven by multi-propellers is simulated numerically by using RANS equations with K-ε turbulence model and propeller lifting surface theory as essential research tool and coupling the computer code of ship stern flow to the computer code of propeller performance prediction through the medium of body force.A ship model with four propellers is selected as the numerical example.Detailed computational results are presented graphically and the qualitative and quantitative analysis is made. Finally,the comparison between the calculated result and the available experimental data is made.The agreement between them is satisfactory.     

Forces due to exterior singularities upon 2- and 3-dimensional bodies

Thrust deduction, or the resistance increase, is not fully investigated probably because of the complexity of the flow pattern in the stern region. In this work, it is assumed that the theory of potential flows may represent the most significant portion of the physics of the phenomena. Hence the propulsor and other devices in the stern region are represented by exterior singularities and their effects upon the resistance increase are estimated by taking a circular cylinder and a sphere as the 2- and 3-dimensional body, respectively. Results for a circular cylinder are summarized, and those for a sphere are given more attention.

     

PROPULSIVE PERFORMANCE AND VORTEX SHEDDING OF A FOIL IN FLAPPING MOTION

1 .　INTRODUCTIONInsectsandfishhaveexperiencedabillions yearprocessofevolutionwithnaturalselectionfortheirsurvivalandhavedevelopedtheirsuperiorandcomplete performanceofflightandswim ming .Usually ,aflappingmotionisabasicmodeoflocomotionforinsects ,birds ,andfish .Thrustandliftaregeneratedwhentheflappingwingsortailsinteractwiththesurroundingfluids .Becauseofthehighlyunsteadynatureofviscousflowaroundaflappingwing ,itisfarfromsatisfactorytounderstandthephysicalmechanismandvortexsheddinginuns…     

两种手姿态在不同攻角下划水的数值模拟

该文旨在用计算流体力学（CFD）的方法研究游泳推进问题,建立了手掌和前臂的联接模型,并生成3D非结构网格，计算了两种不同手姿态：并拢和张开在不同来流速度和攻角下的推进阻力和推进升力，并结合计算结果进行了流场分析，研究了两种手姿态对推进效率的影响。结果表明，在各个攻角状态下，手并拢划水均能获得更高的推进效率。     

COMPUTATION OF HYDRODYNAMIC INTERACTION FORCES BETWEEN SHIPS BASED ON B-SPLINES

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Using spanwise flexibility of caudal fin to improve swimming performance for small fishlike robots

This paper examines the beneficial effects of the spanwise flexibility of the caudal fin for the improvement of the swimming performance for small fishlike robots. A virtual swimmer is adopted for controlled numerical experiments by varying the spanwise flexible trajectories and the spanwise flexible size of the caudal fin while keeping the body kinematics fixed. 3-D Navier-Stokes equations are used to compute the viscous flow over the robot. Elliptical, parabolic and hyperbola trajectories are chosen to describe the spanwise flexible profile of the caudal fin. According to the sign(positive or negative) of the phase difference of the swinging motion, the spanwise flexibility can be divided into the fin surface of "bow" and the fin surface of "scoop". It is observed that for both the fin surface of "bow" and the fin surface of "scoop", the spanwise elliptical trajectory has the optimal swimming velocity, thrust, lateral force, and efficiency. With comparisons, using the flexible caudal fin with the fin surface of "bow", the lateral force and the power consumption can be reduced effectively and the swimming stability can be increased while reducing little the swimming velocity and thrust. Meanwhile, using the flexible caudal fin with the fin surface of "scoop" can greatly improve the swimming velocity, thrust, and efficiency while increasing part of the lateral force and the power consumption. Three-dimensional flow structures clearly indicate the evolution process around the swimming robot. It is suggested that the fish, the dolphin, and other aquatic animals may benefit their hydrodynamic performance by the spanwise flexibility of the caudal fin.     

基于直接内力法的拱坝建基面稳定分析

提出适合分析拱坝建基面等效正应力的直接内力法，结合小湾高拱坝三维弹塑性有限元整体分析成果，研究分析了超载过程中拱端推力、推力角和抗滑安全系数的分布规律。研究结果表明，建基面抗滑安全系数衰减速度低于超载速度，高拱坝超载过程中各高程段的推力角均有所增加，这反映了拱坝具有较高超载能力的内在机制，也说明基于刚体极限平衡法对拱坝坝肩稳定分析成果偏于安全。