Hydrodynamic interaction.among hull,rudder and bank for a ship sailing along a bank in restricted waters

By applying a CFD tool to solve the RANS equations, the viscous flow around a model of hull-rudder system towed along a bank in shallow water is numerically simulated. Hydrodynamic forces and moments acting on the ship are calculated for different ship-bank distances and rudder angles. A container ship, KCS, is taken as an example for the numerical study. Under the assumption of low ship speed, the influences of free surface elevation and ship squat are assumed to be negligible. Based on the calculation results, the hydrodynamic interaction among the hull, rudder and bank is analyzed.     

EXPERIMENTAL STUDY AND NUMERICAL CALCULATION OF HYDRODYNAMIC FORCES AND MOMENTS ACTING ON A HIGH-SPEED TRANSOMSTERN SHIP RUNNING OBLIQUE TO THE COURSE

On the basis of oblique towing tests and flow visualizations of ship models, the flow" pattern around a high-speed transom-stern ship, its motion attitudes (sinkage and trim) and the characteristics of hydrodynamic forcesare analysed. It is concluded that the variation of ship motion attitudes, caused by ship speed, has a great influenceover the coefficients of hydrodynamic forces and moments acting on the oblique running ship. Ship attitudes relatedto different speed and drift angles are calculated by Hess-Smith method. By distributing complex singularities overthe surface of a double model and by considering separated vortex sheets in the wake at the lee side of the model,pressures and velocities of the fluid around the model may be calculated directly by solving a three-dimensionalbody with lift problem. The transom stern stream-lines are extended to form a virtual length. In this way, thehydrodynamic lateral forces, yaw moments and pressure distribution are calculated. The results show good agree-ment with those measured from model tests.     

CALCULATION OF VISCOUS HYDRODYNAMIC FORCES ON A SHIP HULL IN OBLIQUE MOTION

This paper focuses on computations of viscous hydrodynamic forces acting on a ship in oblique motion by solving the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations. The standard κ-ε turbulence model with wall function was applied. The conservation equations were discretized by a cell-centered second-order Finite Volume Method (FVM) in a block-structured body-fitted grid and the coupling of velocity and pressure was resolved with the SIMPLE method. Computations were performed for a Wigley hull model to investigate the viscous flows around it. The results show good agreement with experimental data and more reasonable prediction of hydrodynamic forces and moments than other numerical results available.     

SECOND-ORDER DRIFT FORCES AND MOMENTS BETWEEN TWO SUBMERGED BODIES IN WAVES ON 3D METHOD

Two near field methods, namely the integral method and differential method, were presented for giving second-order mean drift forces and moments between two fixed submerged bodies in regular waves. For the integral method, with a series of mathematical manipulations, second order drift forces and moments could be easily expressed by distributed sources which could be calculated by source distribution techniques with the assumption that the amplitude of ship motions are small on the basis of the linear 3D frequency theory. For the differential method, drift forces and moments could be expressed by the derivative of velocity potential with respect to space coordinate. Because two bodies would behaveas a single body while the clearance is very large, the numerical results of one sphere in such case were given and compared with analytical results of a single sphere which does not involve the effect of free surface. When submerged depth becomes enough large, a good agreement can be reached. Then the integral method was used to predict the second order drift forces and moments of two submerged spheres and spheroids with a small lateral separation distance in waves compared with the numerical results obtained by the differential method and they agree well. By comparison, it indicates the interaction effects between two submerged bodies have a profound influence on the drift forces and moments. In this paper, the forward speed effect on submerged spheres was also considered.     

CALCULATION OF MANOEUVERING HYDRODYNAMIC FORCE INCLUDING THE EFFECT OF VISCOSITY

Based on the method of Chapman and Yamasaki, this paper calculates the wave making hydrodynamic forces acting on a yawed ship. In order to study the effect of viscosity, this paper calculates the wave making resistance of a new ship model whose boundary is formed by adding the displacement thickness on real ship body. The comparisons between the calculated results of a Wigley model and experimental values verify the validity of the new model and the numerical methods.     

SIMULATION OF TANK SLOSHING BASED ON OPENFOAM AND COUPLING WITH SHIP MOTIONS IN TIME DOMAIN

Tank sloshing in ship cargo is excited by ship motions, which induces impact load on tank wall and then affects the ship motion. Wave forces acting on ship hull and the retardation function are solved by using three-dimensional frequency domain theory and an impulse response function method based on the potential flow theory, and global ship motion is examined coupling with nonlinear tank sloshing which is simulated by viscous flow theory. Based on the open source Computational Fluid Dynamics (CFD) development platform Open Field Operation and Manipulation (OpenFOAM), numerical calculation of ship motion coupled with tank sloshing is achieved and the corresponding numerical simulation and validation are carried out. With this method, the interactions of wave, ship body and tank sloshing are completely taken into consideration. This method has quite high efficiency for it takes advantage of potential flow theory for outer flow field and viscous flow theory for inside tank sloshing respectively. The numerical and experimental results of the ship motion agree well with each other.     

NUMERICAL PREDICTION OF SUBMARINE HYDRODYNAMIC COEFFICIENTS USING CFD SIMULATION

The submarine Hydrodynamic coefficients are predicted by numerical simulations.Steady and unsteady Reynolds Averaged Navier-Stokes(RANS) simulations are carried out to numerically simulate the oblique towing experiment and the Planar Motion Mechanism(PMM) experiment performed on the SUBOFF submarine model.The dynamic mesh method is adopted to simulate the maneuvering motions of pure heaving,pure swaying,pure pitching and pure yawing.The hydrodynamic forces and moments acting on the maneuvering submarine are obtained.Consequently,by analyzing these results,the hydrodynamic coefficients of the submarine maneuvering motions can be determined.The computational results are verified by comparison with experimental data,which show that this method can be used to estimate the hydrodynamic derivatives of a fully appended submarine.     

IDENTIFICATION OF ABKOWITZ MODEL FOR SHIP MANOEUVRING MOTION USING e-SUPPORT VECTOR REGRESSION

By analyzing the data of longitudinal speed,transverse speed and rudder angle etc.in the simulated 10o/10o zigzag test,the hydrodynamic derivatives in the Abkowitz model for ship manoeuvring motion are identified by using ε-Support Vector Regression(ε-SVR) .To damp the extent of parameter drift,a series of random numbers are added into the training samples to reconstruct the training samples.The identification results of the hydrodynamic derivatives are compared with the Planar Motion Mechanism(PMM) test results to verify the identification method.By using the identified Abkowitz model,20o/20o zigzag test is numerically simulated.The simulated results are compared with those obtained by using the Abkowitz model where the hydrodynamic derivatives are obtained from PMM tests.The agreement is satisfactory,which shows that the regressive Abkowitz model has a good generalization performance.     

LIFTING FORCE ACTING ON A GATE WITH HIGH HEAD

The hydrodynamic lifting force acting on a gate with high head is one of the key factors concerning the safety and reliability of gates.The lifting force is closely related to hydrodynamic pressure,and generally,is obtained through the model test.This work presents a method of numerical simulation based on the VOF method for the flow and FEM for the structure of a gate to investigate this kind of the lifting force.The physical model experiments were conducted about the hydrodynamic pressure and the lifting force to verify the numerical results.The comparisons of those two methods show that the maximum relative error is smaller than 11.40 % and the method presented in this paper is feasible and could be used in the designs of hydropower projects.     

A TIME-DOMAIN METHOD TO PREDICT SHIP MOTIONS IN OBLIQUE SEAS AT FORWARD SPEEDS

Time-domain analysis is used to predict wave loading and motion responses for a ship travelling at a constant speed in regular oblique waves.The combined diffraction and radiation perturbations,caused by the steady forward speed of the ship and her motions,are considered as a distribution of normal velocities on the wetted hull surface.The ship-hull boundary condition is exactly fulfilled by expressing the fluid normal velocities as a finite series in terms of the body geometry and the incident wave potential.As far as the authors are aware,no similar work is published todate. The new theory is applied to predict forces and motions at forward speed for a Wigley ship-hull in head waves and a catamaran-ferry in oblique waves.Predictions are compared with published theoretical and experimental results for the Wigley ship-hull,and the comparison is good.For the catamaran,a self-propelled model is built and tested in the large towing tank and seakeeping basin of the China Ship Scientific Research Centre,Wuxi     

基于重叠网格技术数值模拟船舶纯摇首运动

该文采用基于非定常RANS方程的黏性数值模拟方法,对标准船模DTMB5512裸船体在平面运动机构(PMM)控制作用下的纯摇首运动进行了数值模拟。文中数值计算采用基于开源CFD工具包Open FOAM和重叠网格技术开发的多功能水动力学求解器naoe-FOAM-SJTU。根据SIMMAN2014提供的标准算例,对同一运动频率下,在Fn=0.28工况下的3种不同运动幅值的纯摇首运动进行了数值计算,得出了船舶不同工况下的阻力、侧向力和转首力矩的历时曲线。并且根据操纵性数学模型(MMG)推导出相应的水动力导数值,所有计算结果同模型试验数据吻合较好,验证了采用当前处理方法数值求解纯摇首运动的可靠性。     

NUMERICAL SIMULATION OF TRANSIENT FLOW AROUND A SHIP IN UNSTEADY BERTHING MOTION

Ship berthing is a specific maneuver operation. The flow around a berthing ship and the forces acting on the hull are quite different from those for a ship in normal navigation. By solving the unsteady Reynolds-Averaged Navier-Stokes (RANS) equations, the transient flow field around a ship undergoing unsteady lateral motion is simulated and the varying lateral hydrodynamic force acting on the hull is evaluated in this article. The numerical results obtained with different turbulence models are analyzed and compared with experimental results and other numerical results published in literature, and a turbulence model more suitable for simulation of the viscous flow around a ship undergoing unsteady berthing is determined.     

海水经船闸入侵淡水运河的三维数值模拟

为研究船闸运行过程中盐分的输运规律及其对淡水水域的盐度影响,建立了三维k-ε两相混合流数值模型,模型控制方程组采用有限体积法进行离散,流速与压力耦合采用SIMPLEC算法,时间项采用一阶隐式格式,流项采用二阶迎风格式,计算区域采用六面体网格划分。采用某船闸的海水入侵原型试验成果对数值模型进行了验证,闸室内盐度的模拟值与实测值吻合较好。海水入侵淡水水域模拟结果表明:上游航道盐度分布可分为异重流段、过渡段和扩散段,各段盐分输运速度依次减小;各断面的盐度呈周期性变化,在船闸运行一段时间后逐步趋于动态平衡;一个循环内的盐分入侵量在船闸运行初期较大,随着运行时间的增加逐渐减小,并趋于恒定值。研究结果可为船闸的设计与运行调度提供科学依据。     

Numerical estimation of bank-propeller-hull interaction effect on ship manoeuvring using CFD method

This paper presents a numerical investigation of ship manoeuvring under the combined effect of bank and propeller. The incompressible turbulent flow with free surface around the self-propelled hull form is simulated using a commercial CFD software(ANSYS-FLUENT). In order to estimate the influence of the bank-propeller effect on the hydrodynamic forces acting on the ship, volume forces representing the propeller are added to Navier-Stokes equations. The numerical simulations are carried out using the equivalent of experiment conditions. The validation of the CFD model is performed by comparing the numerical results to the available experimental data. For this investigation, the impact of Ship-Bank distance and ship speed on the bank effect are tested with and without propeller. An additional parameter concerning the advance ratio of the propeller is also tested.     

基于CFD的船-舵水动力干扰数值研究

该文采用基于RANS方程求解的CFD方法,对匀速直航的船-舵系统的黏性绕流场进行数值模拟,计算了不同船速和不同舵角下的船-舵水动力干扰系数,计算中忽略了自由面兴波及螺旋桨的影响。文中以KVLCC1船、舵模型为研究对象,首先将数值计算的船舶水动力及船-舵水动力干扰系数结果与模型试验数据进行比较,验证了所采用数值方法的有效性;随后,对船-舵系统、裸船体和敞水舵分别进行计算,通过水动力计算结果的比较以及流场分析,对船-舵水动力相互作用进行了数值研究。     

Prediction of ship-ship interactions in ports by a non-hydrostatic model

Complicated channel geometry and currents may aggravate the interactions between passing ships and berthed ships, which should be evaluated and taken into account in a port design. A method for predicting the ship-ship interactions, based on a non-hydrostatic shallow water flow model, is presented in this paper and is validated by comparing the numerical results with experimental data. The method is subsequently applied to predict the interaction forces acting on a berthed ship due to a passing ship in ports. The influences of the difference of the water depths between the dock and the main channel, the dock geometry, the current and another berthed ship in the dock on the ship-ship interactions are studied. Analysis based on the numerical results is carried out, which is useful for the port design.     

五强溪水电站高水头船闸输水系统动水压力与反向弧门流激振动

本文介绍了五强溪船闸二闸首于1996年12月12日～13日进行的原型观测成果与分析.着重从高水头船闸输水系统不恒定流压力瞬态变化和反向弧门流激振动两方面，分析输水廊道突扩体发生空化空蚀的可能性，以及反向弧门流激振动的危害程度，并对其安全运行作出评估.