BREAKING WAVE FORCES ON VERTICAL CYLINDERS

The breaking wave forces on vertical cylinders in shallow waters were studied by means of experimental methods. The results indicate that the breaking wave pressure is distributed exponentially with respect to water depth. An experimental formula was given using the test data. Compared with test data, the calculated breaking wave forces are in good agreement with the test data.     

内孤立波环境下柱体的受力特性

针对以往孤立波对柱体作用研究多只针对柱体的整体受力开展,少有研究精细获取柱体不同部位受力特性的问题,借助三维大涡模拟(LES)数值波浪水槽,通过提取柱周流场及压强分布,得到柱体所受压差阻力及黏滞力的垂向分布,对柱体在孤立波环境中的受力特性进行了分析,并采用多元线性回归分析,构造综合影响参数分析了柱体受力特性,构建了柱体受力系数经验表达式。结果表明:上下层水体中方柱所受压差阻力约分别为圆柱的1.5倍和3.5倍;作用于柱体上的黏滞力比压差阻力小1或2个数量级,可忽略流体的黏性效应;综合影响参数与相对波幅正相关,与上下水深比负相关。     

SLOW DRIFT DAMPING FORCE ACTING ON A CYLINDER IN WAVES

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A METHOD FOR THIRD ORDER FORCE ON AXISYMMETRIC BODIES

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规则波作用下倾斜桩柱的受力研究

本文通过实验研究,测试了水平桩柱及倾斜桩柱在规则波作用下的波浪力。基于Morison方程和Stokes二阶波理论,分析研究了不同埋深情况下水平桩柱的受力及其水动力系数C_D、C_M随K_C数的变化规律;分析研究了不同倾角情况下,倾斜桩柱的受力及其水动力系数C_D、C_M随K_O数的变化规律,同时还探讨了在同一倾角情况下,桩柱在一端出水和全部埋于水下时,水动力系数C_D、C_M的差别。     

THE IRREGULAR BREAKING WAVE FORCES ON VERTICAL WALL

A method for the calculation of total horizontal wave forces by irregular breaking waves on vertical wall was developed by authors, which was based on physical model test, dimensionless analysis and assessment of real construction. The methods for the determination of pressure distribution of horizontal forces on vertical wall as well as u-plift forces on the bottom of wall are also given. The comparison between calculated results by this method and samples of real construction are very well.     

NONLINEAR DIFFRACTION OF BICHROMATIC WAVES BY A VERTICAL CYLINDER

We present in this paper a semi-analytical solution for second-order wave diffraction by a vertical circular cylinder in bichromatic waves.On the base of the usual assumption of an irrotational flow,the wave-diffraction problems at second-order sum-fre-quency and difference-frequency are considered.The corresponding second-order diffrac-tion potentials are decomposed into three parts,these are associated with the second-order incident wave,the quadratic forcing terms on the free-surface due to the first-order poten-tial,and the linearised'free-wave'component resulting from the boundary condition on the body surface.A particular solution which exactly satisfies the inhomogeneous free-sur-face condition has been derived.Numerical results for the quadratic transfer functions of the second-order force components are given,and are compared with those obtained using numerical solutions(Kim & Yue,1990,Moubayed & Williams 1995).These quadratic functions are useful in calculating the exciting forces on a circula     

WAVE FORCES ON INCLINED CYLINDER IN REGULAR WAVES

Through a series of model tests,the wave forces on horizontal and inclined circularcylinders are measured and analyzed.Based on Morison Equation and Stokes second order wavetheory,the relationship between the hydrodynamic force coefficients with KC number and sub-merged water depth as well for horizontal cylinders are analyzed,also the relationship betweenthe hydrodynamic force coefficients with KC number,inclined angle and the effect of water freesurface as well for the inclined cylinders are investigated.     

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.     

Investigation on forces exerted on a sediment particle in current and wave boundary layer through 3D lattice Boltzmann simulation

The 3-D lattice Boltzmann method is applied to evaluate the forces exerted on a stationary spherical particle in current and wave boundary layer flow in order to analyze the forces contributing to the incipient motion of the sediment particle. Results indicate that for current, the forces reach statistically steady finally at a relative low particle Reynolds number (less than 40). The streamwise drag force is the main driven force while the effect of the spanwise force can be ignored. The reason that results in the phenomenon is also discussed. As for the wave, the cyclical nature of the flow makes the evolution of drag and lift forces become quasi-periodic. The streamwise drag force is still the main driven force, but it changes direction with the flow. Meanwhile, the spanwise vorticity and the pressure around the particle show asymmetric distribution. The influence of spanwise force on the particle can not be neglected.

     

二阶波浪力的切片理论与潜体上的垂向定常力

二阶波浪力的三维理论基本上是对无航速的结构物建立起来的，航速的影响不甚清楚，一些理论问题，例如二阶绕射势辐射条件的提法，直到最近才得以澄清，即使如此，用三维方法完整地求取物体上的二阶波浪力仍十分费时，本文中对有航速的细长物体建立了二阶波浪力的切片理论，旨在提供理论上合理，实用上相对简便的二阶力计算方法，作为完整的二阶波浪力的一个组成部分，文中给出了细长潜体在不同潜深和浪向角时所受的垂向常力及变化趋     

NUMERICAL STUDY OF MULTIDIRECTIONAL FOCUSING WAVE RUN-UP ON A VERTICAL SURFACE-PIERCING CYLINDER

In this article,a numerical model based on improved Boussinesq equations and the Finite Element Method(FEM)with unstructured triangular elements is proposed and verified by experimental results for the focusing wave group interaction with a vertical surface-piercing cylinder.The multidirectional focusing waves with different directional spreading parameters and their interaction with a vertical surface-piercing cylinder are numerically simulated.The directional spreading parameter influences the wave form,that is,a wider directional spreading would induce a narrower wave form in space.The wave run-up on the cylinder increases with the increase of the wave directional spreading parameter,but when the parameter is greater than 30-40,the wave run-up changes only slightly and the influence of the directional spreading can be neglected.A larger diameter cylinder may have a larger wave run-up at the front face.But at the back side,it is other way round.     

NUMERICAL STUDY OF FLOW AROUND AN OSCILLATING DIAMOND PRISM AND CIRCULAR CYLINDER AT LOW KEULEGAN-CARPENTER NUMBER

In order to identify the influence of shape corners on the instantaneous forces in the case of oscillating bodies, the simulated flow field is compared for two kinds of cross sections: diamond prism and circular cylinder. For these two flow configurations, the same Reynolds number and a Keulegan-Carpenter are considered. To compute the dynamic flow field surrounding the body, the Navier-Stokes transport equations in a non-inertial reference frame attached to the body are considered. Hence, a source term is added locally to the momentum equation to take into account the body acceleration. The proposed model is solved using the PHOENICS code. For the oscillating circular cylinder, the simulated results are in good agreement with the experimental data available in the litterature. After validation of this proposed model, flow field for diamond prism is determined. For both bodies, the process of the vortex formation is similar, with the formation of a recirculation zone in the near-wake containing a symmetric pair of vortices of equal strength and opposite rotation. The length of recirculation zone varies approximately linearly with time. However, the in-line force coefficient of the oscillating diamond prism is found to be greatest, since the recirculation zone is longer compared with that of the oscillating circular cylinder.     

THE STATISTIC CHARACTERISTICS OF IRREGULAR BREAKING WAVE FORCES ON VERTICAL WALLS

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Finite element analysis of second order wave radiation by a group of cylinders in the time domain

A finite element based numerical method is employed to analyze the wave radiation by multiple or a group of cylinders in the time domain. The nonlinear free surface and body surface boundary conditions are satisfied based on the perturbation method up to the second order. The first- and second-order velocity potential problems at each time step are solved through a Finite Element Method (FEM). The matrix equation of the FEM is solved through iteration and the initial solution is obtained from the result at the previous time step. The three-dimensional (3-D) mesh required is generated based on a two-dimensional (2-D) hybrid mesh on a horizontal plane and its extension in the vertical direction. The hybrid mesh is generated by combining an unstructured grid away from cylinders and two structured grids near the cylinder and the artificial boundary. The fluid velocity on the free surface and the cylinder surface are calculated by using a differential method. Results for various configurations including the cases of two cylinders and four cylinders and a group of eighteen cylinders are obtained to show the joint influences of cylinders on the first- and second-order waves and forces, including the effects of spacing ratios and wave frequency on the second order waves and the mean force, in particular.     

双浮体自由垂向振荡响应特性

双圆柱体系统在波能装置和防波构件中得到应用，该系统是一个多自由度受迫阻尼振荡系统，阻力和激励力都来自于波浪力。本文采用线性波理论和特征函数展开皮配法，在平面入射波条件下，求解了双圆柱体垂荡运动辐射速度势和圆柱体固定不动时的绕射速度势，推导了附加质量、阻尼系数、波浪激励力表达式，列出了浮体垂荡运动微分方程。最后讨论了下浮体尺度及位置对系统响应特性的影响。数值计算表明无论下浮体尺度及位置如何变化，它只影响到浮体垂荡响应在低频端的值，下浮体的振幅值总是小于入射波的振幅值，而且它在一个较窄的频率范围内从较大的值很快变化接近于零。下浮体半径与上浮体半径之比的变化不仅影响到两个浮体的响应幅值，而且也影响到曲线的变化趋势；两浮体距离的变化对曲线的变化趋势影响不大，但对曲线的幅值有影响；下浮体厚度的变化只少许改变了响应曲线的幅值。     

波浪和水流对大直径圆柱的共同作用力

本文将波流共同对圆柱作用的速度势分成合模势（无自由表面的绕流速度势）、流兴波势和非定常波势三部分。忽略小量的流兴波势，考虑合模势对非定常波势的影响，用直接边界元法求出非定常波势，从而求出波流共同对圆柱的作用力，提出了沿流线的自由表面条件和波流共同作用下散射波的幅射条件。文中给出了波流对大直径圆柱作用力曲线，可供工程设计使用，适用条件是相对水深ｄ／Ｌ＞０．１５，相对流速Ｕ／ｃ＜０．２。     

孤立波作用下破碎区单圆柱附近流动特性数值研究

为了合理分析孤立波作用下破碎区单圆柱附近的水流结构以及圆柱受力特性,该文利用OpenFOAM开源程序求解基于Navier-Stokes方程的三维数值模型,该模型采用S-A IDDES湍流模型,使用修正的VOF方法捕捉自由液面。研究发现,该数值模型能合理捕捉到孤立波与圆柱相互作用过程中复杂的液面形态变化;圆柱附近自由液面沿柱面呈三维分布,上爬过程的柱前雍高显著大于回落过程的柱后雍高;回落过程中柱前形成的尾涡在强度和范围上大于上爬过程中柱后形成的尾涡;圆柱表面的动水压强随水深的增长呈近似线性增长,最大值位于上爬过程中最大雍高时刻的迎浪点位置;圆柱所受的波浪力与柱面附近自由液面雍高历时相符,且上爬过程圆柱受到的波浪力明显大于回落过程。     

沉入式大圆筒结构入土深度计算方法研究

沉入式大圆筒结构是一种适用于软土地基的新型港口与海岸水工建筑物。本文在由水平力和力矩平衡条件建立的入土深度计算方法的基础上，进一步考虑竖向力平衡条件，建立了沉入式大圆筒结构满足稳定性要求的新的入土深度计算方法。针对一工程实例的设计条件，研究了土性指标取值、波浪力大小和竖向力平衡条件对沉入式大圆筒结构稳定性(入土深度)的影响。结果表明，土性指标和波浪力对大圆筒结构的稳定性均有显著影响，且土性指标的影响大于波浪力的影响；当竖向力较大时，竖向力平衡条件对大圆筒结构的稳定性也有较大影响。建议在实际工程设计中，应准确选取土性指标，并采用考虑竖向力平衡条件的稳定性计算方法。     

A 3-D numerical study of solitary wave interaction with vertical cylinders using a parallelised particle-in-cell solver

This paper aims to provide a better understanding of the interaction between solitary waves and vertical circular cylinders. This is achieved via process based numerical modelling using the parallel particle-in-cell based incompressible flow solver PICIN. The numerical model solves the Navier-Stokes equations for free-surface flows and incorporates a Cartesian cut cell method for fluid-structure interaction. Solitary waves are generated using a piston-type wave paddle. The PICIN model is first validated using a test case that involves solitary wave scattering by a single vertical cylinder. Comparisons between the present results and experimental data show good agreement for the free surface elevations around the cylinder and the horizontal wave force on the cylinder. The model is then employed to investigate solitary wave interaction with a group of eleven vertical cylinders. The wave run-up and wave forces on the cylinders are discussed.