浅水域中两船交错运行时的非定常波浪干涉

本文以Green-Naghdi（G-N）方程为基础,采用波动方程／有限元法计算两艘船舶在浅水域交错运动时的非定常波浪干涉特性。把运动船舶对水面的扰动作为移动压强直接包含在Green—Naghdi方程里,以描述运动船体和水面的相互作用。本文以S60 CB=0．6船为算例,给出在两艘船交错运动时,自由面波高,波浪阻力及横向力的变化特征。计算结果发现,当两艘船船首接近时,波浪阻力增加。接着,两艘船船身相向平行航行时,阻力减少。两艘船船尾相遇时,波浪阻力又增加。最后随着两船的远离,波浪阻力趋于正常。两船之间的侧向力呈现相似的变化规律。两船先承受横向排斥力,接着相互吸引,尔后又排斥。最后两船远离,横向力消失。计算结果表明,在两船间距较小和船速较大时,两船间的吸引力相当显著,应该予以充分重视。     

Numerical simulations of wake signatures around high-speed ships

Navier-Stokes equations are solved to obtain the near field flow and to reveal the generation of droplets due to the breaking of the bow wave. With an adaptive refinement of the Octree mesh, the fine scale flow characteristics, the wave breaking and the splashing are well simulated. For high-speed ships, the V-shape ship wave pattern with the angle smaller than the classical Kelvin angle is confirmed by the present numerical results, which can also be applied to the catamaran. Comparisons of the vertical velocity distributions induced by the mono-hull ship and the catamaran are made at different locations in the wake regions.     

THE VOF METHOD FOR STUDY OF WAVE RUN-UP AND BREAKING ON A SLOPING STRUCTURE

The volume of fluid method(VOF method)for numerical simulations describing wave run-up on a sloping structure including the overturning,breaking and.merging phenomena is presented.The flow motions are governed by the classical,two-dimen-sional Navier-Stokes equation for incompressible fluid.Computational results concerning the time evolution of the free surface and pressure distribution along water bed and slope boundary are given,showing how an initial solitary wave undergoes run-up,overturning,breaking and merging on the slope.It is found that most of the wave energy is lost after the wave breaking and merging.     

NUMERICAL STUDY OF SQUARE-STERN SHIP WAVE IN SHALLOW WATER

This paper employed shallow water equations with moving pressure to calculate water waves generated by a square-stern ship in shallow water. The moving ship is considered as moving pressure on free surface. The finite element method with moving grids is used to solve the shallow water equations based on wave equation model [3]. A non-reflection boundary condition [5]is imposed on open boundaries surrounding the ship. 3-D surface elevations, depth-averaged horizontal velocities are presented. The numerical solutions are physically reasonable. It is found that wave resistance coefficients, draftchange and pitch angle vary rapidly in neighborhood of critical flow (Fh=u/ gh= 0. 9 -1. 1). The numerical results also indicate that the wave resistance coefficients, draft change and pitch angle of square-stern ship are larger than those of sharp-stern ship with the same hull structure at the same speed.     

船舶在波浪中大幅度运动的工程算法

本文基于切片理论，计入船体运动时湿表面及其对船体流体动力性能的影响，提出了一种船舶在波浪中大幅度运动的工程估算方法，并通过对一系列６０船型计算，考虑了船舶在迎流中大幅度运动昱的运动特性、与波面的相对运动和船体瞬时受力。这一方法简单实用，对船舶方案设计有积极的意义。     

An iterative Rankine BEM for wave-making analysis of submerged and surface- piercing bodies in finite water depth

A 3-D iterative Rankine Boundary Element Method （BEM） for seakeeping problem in time domain is developed in the framework of linear potential theory. Waves generated by both submerged and surface-piercing bodies moving at a constant forward speed in otherwise calm water, and the resultant steady wave pattern, wave profile and resistance are computed to validate this newly-developed code. A rectangular computational domain moving with the same forward speed as the body is introduced, in which an artificial damping beach is installed at an outer portion of the free surface except the downstream side for satisfying the radiation condition. The velocity potential on the ship hull and the normal velocity on the free surface are obtained directly by solving the boundary integral equation, with the Rankine source used as the kernel function. An iterative time-marching scheme is employed for updating both kinematic and dynamic free surface boundary conditions to stabilize the calculation. Extensive results including the wave patterns, wave profiles and wave resistances for a submerged spheroid and a Wigley hull with forward speed are presented to validate the efficiency of the proposed 3-D time-domain higher-order approach. Finally, the sensitivity of ship-generated waves to the water depth is investigated. Computed results show satisfactory agreement with the corresponding experimental data and other numerical solutions.     

WAVE MAKING COMPUTATION IN TIME DOMAIN FOR MULTI-HULL SHIPS

1. INTRODUCTION For high-speed displacement ships, the wave making at the free surface is an important hydro- dynamic performance. The wave making reduction has attracted more attention for ship designers. The ship wave resistance and ship hull form improvement have been widely investigated. The thin ship theory adopting the Havelock source distribution on the ship centerline plane can be used to analyze the ship wave making profile and the ship wave resistance may be obtained by ship wav…     

WAVE EQUATION MODEL FOR SHIP WAVES IN BOUNDED SHALLOW WATER

1.　 INTRODUCTIONIn the recentyears,waves in coastal shallow water,generated by marine traffic and in-tensified by port expansion,interaction with structures and reflection of land boundaries,has become a crucial factor affecting waterenvironmentsand engineering operation.In com-parison with the wind waves and ocean swells,waves inside harbor exhibitanomalous waveheight in certain areas.The dominantship waves are hardly dissipated in the harbor due tothe interaction with shorelines,and may…     

THE OPTIMIZATION OF THE HULL FORM WITH THE MINIMUM WAVE MAKING RESISTANCE BASED ON RANKINE SOURCE METHOD

The hull form optimization concerns one of the most important applications of wave making resistance theories. In order to obtain a hull form with the minimum wave making resistance, an optimization design method based on the CFD is proposed, which combines the Rankine source method with the nonlinear programming (NLP). The bow-body shape is optimized with the minimum wave making resistance as the objective function. A hull form modification function is introduced to represent an improved hull surface, which can be used to generate a new smooth hull surface by multiplying it by the offset data of the original hull surface. The parameters of the hull form modification function are taken as the design variables. Other constraint conditions can also be considered, for example, in optimizing the lines of the bow, appropriate displacements can be taken as the basic constraints. S60 hull form is selected as the original hull. Three improved hulls are obtained by optimal design. Rankine source method proves to be an effective method in ship form optimization based on analysis of the resistance performance and lines of the improved hull.     

Valid hydrodynamic interaction regions of multiple ships advancing in waves

Based on the 3-D surface panel method combined with the translating-pulsating source Green function, an approximate approach is developed to solve the hydrodynamic interacting problem of multiple ships advancing parallel in waves. Focus is on improving the calculating efficiency. In this approach, each ship is assumed to be in each other＇s far-field, and the near-field term in this Green function is neglected if the source point falls on one ship and the field point on others. Further, a matching relationship between the far-field waves and the interfered regions, which are defined as the overlapping areas between the mean wetted body surface of one ship and the propagating regions of the waves generated by another ship, is introduced to avoid the unnecessary computation of the relative terms of the Green function, if the field point is not in the overlapping areas. The approach is validated through studying the hydrodynamic terms and the free motions of two or three ships in side-by-side arrangement by comparing the obtained results with the model tests and the predictions of the exact method. The average calculating speed for the present approximate method is about 1.65-1.8 times of that for the exact method for solving the hydrodynamic interaction problem of two ships, and 2.56-2.73 times for that of three ships.     

Practical evaluation of the drag of a ship for design and optimization

We consider two major components of the drag of a ship, the“friction drag”and the“wave drag”, that are related to vis-cous friction at the hull surface and wavemaking, and mostly depend on the Reynolds...     

兴波阻力数值预报方法研究及其在集装箱船船型优化中的应用

集装箱船作为一种中高速船，其兴波阻力在总阻力中所占比例较高。从某种意义上讲，船型优化就是寻求最小兴波阻力的船型。本文采用基于势流理论的面元法预报集装箱船的兴波阻力，对两种计算兴波阻力的方法进行了研究比较：第一种是改进的Dawson方法，传统的Dawson方法采用静水面上的叠模流线网格，而改进的Dawson方法是采用静水面上的贴体网格来计算兴波阻力；第二种方法是单模流动法。文中利用这两种方法计算了两条集装箱船，通过和试验值比较，发现这两种方法在设计航速附近的一定范围内都能正确地识别船型变化对兴波阻力的影响，验证了这两种数值预报方法都可以用于船型优化。但是改进的Dawson方法的计算结果更接近实验值，因此改进的Dawson方法更适用于船型优化。     

Numerical simulations of viscous flows around surface ship by level set method

Numerical simulations of viscous flows around surface ships by coupling the 3D incompressible RANS equations with level set method are presented in this paper. The finite difference method is used to discretize the RANS equations with turbulent model SST k − ω. The fully nonlinear boundary condition at the free surface is satisfied at each time step and the evolution of the free surface is achieved by using the level set method. The coupled solver is applied to a benchmark case of viscous flows around an advancing Wigley ship with various Froude numbers. The computational results are in excellent agreement with experimental data. The simulations reveal clearly the generation and evolution of bow and stern waves.

     

滑坡涌浪影响下船舶安全锚泊范围试验研究

由于水库蓄水水位的变化,库区时常发生山体滑坡,滑坡涌浪作用于锚泊船舶时可能会使船舶的锚链拉断,造成较大灾害。为研究滑坡涌浪传播特性和降低涌浪对船舶造成的损害,通过岩体滑坡涌浪概化模型试验,并基于多元线性回归分析方法,得到了首浪高度、涌浪高度衰减系数和最大锚链拉力的经验公式,进而推导出静水中船舶安全锚泊限制范围的计算公式。上述公式的确定,可为制定滑坡地点附近锚泊船舶的安全避险措施和预测滑坡涌浪产生的破坏范围提供依据。      

TIME-DOMAIN ANALYSIS OF WAVE FORCES ON SHIPS WITH FORWARD SPEED

Analyses of wave forces on Wigley and Series 60 ships at forward speedare presented in time domain which is based on a free surface transient Green functionwith linearized condition. The main effort focus on the investigation of the numerical sta-bility of time stepping calculation and the waterline intergal contribution to the excitingforces. Numerical study shows that the stable results can be obtained when a wall-sided as-sumption is used at the stern only and the effect of waterline can be neglected. Compar-isons have been made between the present time domain calculations and other works. Nu-merical results for the added resistance on a C_B=0.8 ship in short waves are presentedbased on the assumption that the steady disturbance of ship hull can be neglected.     

壁湍流猝发和自由表面波破碎条件

应用G.K.Batchlor交界面流动的边界条件和小扰动稳定性理论,给出了壁湍流猝发、边界层边界的夹带和自由表面波的破碎条件和解释。发现这些现象可作为类比的相似流动来研究。当在边界层假设中保留p/n的边界层厚度的高阶小量(即p/n≠0),就可得到湍流的猝发现象。     

Iterative Rankine HOBEM analysis of hull-form effects in forward-speed diffraction problem

A time-domain numerical algorithm based on the higher-order boundary element method and the iterative time-marching scheme is proposed for seakeeping analysis. The ship waves generated by a hull advancing at a constant forward speed in incident waves and the resultant diffraction forces acting on the hull are computed to investigate the hull-form effects on the hydrodynamic forces. A rectangular computational domain travelling at ship's speed is considered. An artificial damping beach for satisfying the radiation condition is installed at the outer portion of the free surface except the downstream side. An iterative time-marching scheme is employed for updating both kinematic and dynamic free-surface boundary conditions for numerical accuracy and stability. The boundary integral equation is solved by distributing higher-order boundary elements over the wetted body surface and the free surface. The hull-form effects on the naval hydrodynamics are investigated by comparing three different Wigley models. Finally, the corresponding unsteady wave patterns and the wave profiles around the hulls are illustrated and discussed.     

LARGE EDDY SIMULATION FOR PLUNGING BREAKER WAVE

1 .　INTRODUCTIONInthenear shoreregion ,aswavespropagateintoshallowwater ,theprocessofshoalingleadstotheincreaseofwaveheight ,however ,thisprocesscannotcontinue ,andatacertain positionthewavebreaks .Inpractice ,breakingwavesarepow erfulagentsforgeneratingturbulence ,whichplaysanimportantroleinmostofthefluiddynamicalprocessesthroughoutthesurfzone ,suchaswavetransformation ,generationofnear shorecurrent ,diffusionofmaterials ,andsedimenttransporta tion .Manynumericalstudieshavebeenconductedt…     

水面舰船加装减阻节能球鼻艏研究

该文基于波形叠加的消波原理,对一艘仿阿雷.伯克级大型驱逐舰加装减阻节能球鼻艏进行研究,研究表明大型驱逐舰加装减阻节能球鼻艏可获得较好的减阻效果。文中首先给出了基于细分曲面表达船型,采用船体曲面法向量分量表示源强的船舶兴波阻力及波形计算的数值方法,通过与实验结果的比较,分析了该方法的合理性和有效性;在此基础上通过逆向设计法优化计算和分析得到了一仿阿雷.伯克级大型驱逐舰船型加装减阻节能球鼻艏消波减阻定性规律和定量效果,在特定的中高航速下通过减阻节能球鼻艏优化设计可以使兴波阻力最多减少33.7%。     

船舶进出闸室对系缆力的影响

船舶进、出闸室时,船行波在闸室内引起较大水面波动,造成闸室内系缆船舶的系缆力增大,影响闸室内的船舶停泊安全;大型船舶进、出闸室时,产生的船形波作用更强,对系缆船舶的系缆力影响更大。通过1∶36.3三峡船闸的物理模型和相同比尺5 000 t级典型大型船舶模型,采用系列物理模型试验,对船舶进出船闸时闸室内系缆船舶的系缆力进行了研究。研究结果表明,闸室内有系缆船舶时,船舶进、出闸的航行速度对系缆船舶的系缆力影响很大,进、出闸速度越快,其系缆力也越大。三峡船闸中,当水深5.5 m,闸室内有系缆船舶,大型船舶偏航进、出闸室时,为保证船舶停泊安全,航行船舶的进、出闸速度宜小于0.5 m/s。