Wave radiation by a floating rectangular structure in oblique seas

The linear wave radiation by a long floating rectangular structure in oblique seas of finite depth is investigated by use of the method of separation of variables and the eigenfunction expansion matching method. Analytical expressions for the radiated potentials, wave forces and hydrodynamic coefficients are given. The correctness of these expressions is verified through two specific examples investigated previously by other numerical methods. Using the present analytical solution, the hydrodynamic effects of the angle of incidence, the draft and the width of the structure on the wave forces and hydrodynamic coefficients are discussed in detail which may provide some useful information for the design of rectangular structures in oblique seas.     

Momentum balance in shoaling gravity waves: Comment on ’shoaling surface gravity waves cause a force and a torque on the bottom’ by K. E. Kenyon

In a recent paper, Kenyon (2004) proposed that the wave-induced energy flux is generally not conserved, and that shoaling waves cause a mean force and torque on the bottom. That force was equated to the divergence of the wave momentum flux estimated from the assumption that the wave-induced mass flux is conserved. This assumption and conclusions are contrary to a wide body of observations and theory. Most importantly, waves propagate in water, so that the momentum balance generally involves the mean water flow. Although the expression for the non-hydrostatic bottom force given by Kenyon is not supported by observations, a consistent review of existing theory shows that a smaller mean wave-induced force must be present in cases with bottom friction or wave reflection. That force exactly balances the change in wave momentum flux due to bottom friction and the exchange of wave momentum between incident and reflected wave components. The remainder of the wave momentum flux divergence, due to shoaling or wave breaking, is compensated by the mean flow, with a balance involving hydrostatic pressure forces that arise from a change in mean surface elevation that is very well verified by observations.     

The force of oblique incident wave on the breakwater with a partially perforated wall

1 IntroductionRecently breakwaters with perforated front wallshave been widely used. The use of perforated break-waters mainly has two advantages. Firstly, wave forcesacting on the whole structure can be divided into twoparts on two different walls with a phase difference.To select the distance between the two plates suitably,the total wave force on the whole structure can bemaintained at a low level. Secondly, waves will dissi-pate when they transmit over a porous medium. Thus,the reflection…     

Lateral ice force acting on a vertical cylinder

Ｌａｔｅｒａｌｉｃｅｆｏｒｃｅａｃｔｉｎｇｏｎａｖｅｒｔｉｃａｌｃｙｌｉｎｄｅｒ￥ＳｈｉＱｉｎｇｚｅｎｇａｎｄＣｈｅｎＸｉｎｇ（ＤｅｐａｒｔｍｅｎｔｏｆＯｃｅａｎＥｎｇｉｎｅｅｒｉｎｇａｎｄＮａｖａｌＡｒｃｈｉｔｅｃｔｕｒｅ，ＴｉａｎｊｉｎＵｎｉｖｅ...     

苏北辐射沙洲区间流系分布格局及对大气强迫力的响应

苏北辐射沙洲海域由10余条主沙脊和10余条主水道组成,其沙脊群间水动力的消长决定了沙洲的生成、发展及消亡,形成了滩槽相间、水道交错的独特地貌。黄海旋转潮波与东海前进潮波交汇于沙洲中心弶港,在沙洲外围诸多流系如黄海沿岸流、苏北沿岸水和长江冲淡水等影响下,又受复杂地形和大气强迫对浅水作用的影响,沙洲间余环流结构呈现4种环流结构迥异的特征。本文利用2006-2012年间8次共23站一年四季、涵盖主要沙脊和水道间准同步调查数据,以及沙洲南部4站长达1个月以上连续观测的ADCP资料,结合吕四和洋口港海洋站气象水文数据,分析了沙洲间余流四季输运分布格局,并重点讨论和分析了沙洲南部余流与风应力的响应关系。     

非线性波浪作用下埋置管道上波浪力简化计算

由于浅水区波浪的非线性影响显著,浅埋管道受非线性波浪荷载的影响大,为了保证管道长期运行的稳定性,在管道设计过程中需要充分考虑由非线性波浪引起的波浪力。考虑孔隙水和海床土的压缩性,基于Biot固结理论和一阶近似椭圆余弦波理论,利用分离变量法推导了非线性波浪作用下浅水区埋置管道周围海床的渗流压力,进而给出了埋置管道上的波浪力压力解析解,并与已有的文献结果进行比较。计算结果表明,在椭圆余弦波的作用下,海底管道周围海床内的渗流压力呈正弦分布,且管道所受的波浪力随着管径的增大而增大。     

In-line force on a cylinder translating in oscillatory flow

Experiments were conducted with smooth and sand-roughened cylinders moving with constant velocity in a sinusoidally oscillating flow to determine the drag and inertia coefficients and to examine the effect of wake biasing on the modified Morison equation. The various flow parameters such as the relative cylinder velocity. Reynolds number, and the Keulegan-Carpenter number were varied systematically and the in-line force measured simultaneously. The principal results, equally valid for both smooth and rough cylinders, are as follows: the drag coefficient decreases with increasing relative current for a given Reynolds number and Keulegan-Carpenter number; the effect of wake biasing on the drag and inertia coefficients is most pronounced in the drag-inertia dominated regime; and the two-term Morison equation with force coefficients obtained under no-current conditions is not applicable to the prediction of wave and current induced loads on circular cylinders.     

Nonlinear random wave-induced drag force on a vegetation field

This paper provides a practical method by which the drag force on a vegetation field beneath nonlinear random waves can be estimated. This is achieved by using a simple drag formula together with an empirical drag coefficient given by Mendez et al. (Mendez, F.J., Losada, I.J., Losada, M.A., 1999. Hydrodynamics induced by wind waves in a vegetation field. J. Geophys. Res. 104 (C8), 18383–18396). Effects of nonlinear waves are included by using Stokes second order wave theory where the basic harmonic motion is assumed to be a stationary Gaussian narrow–band random process. An example of calculation is also presented.     

Nonlinear heave radiation forces on two-dimensional single and twin hulls

A study of nonlinear heave radiation of two-dimensional single and double hulls has been carried out in the time domain. The problem is analyzed by means of a fully nonlinear mathematical model, referred to as the mixed Eulerian–Lagrangian (MEL) model, which is based on an integral relation formulation coupled with time-integration of the nonlinear free-surface boundary conditions. The integral equation solver is based on a cubic-spline boundary-element scheme in which both potential and velocity continuity conditions can be enforced through the intersection points. The body undergoes periodic forced heave oscillation. By implementing effective wave-absorbing beaches at the two ends of the rectangular numerical tank, long-term steady-state force-histories could be achieved consistently in all computations.Results in terms of radiation forces for rectangular and triangular single- and twin-hull geometries are presented and discussed. Linear hydrodynamic forces in terms of added-mass and damping are validated for the rectangular hull. The Fourier-analyzed results reveal the extent of nonlinear (higher-order) components in the force-signals over different parameters which include the amplitudes of oscillation, hull-spacing for the twin-hulls and water depth.     

Wave uplift force on horizontal panels: a laboratory study

Accurate estimation of wave uplift force is essential to the designs of reliable coastal and marine structures.We presents a series of laboratory work here on the impact of regular waves on horizontal panels,from which an empirical formula to estimate accurately the wave uplift force on panels is established.The laboratory measurements show that the wave uplift force depends mainly on the incident wave height,the wave period,the wave length,the panel width,and the clearance between the subsurface of the panel and the still water level.Among these factors,the impact of the panel width on uplift forces is relatively complicated.Result shows that the relative panel width(i.e.,the ratio of panel width to wave length)plays a more important role in estimating the wave uplift force.Based on our comprehensive laboratory measurements,we further developed an empirical formula to compute wave uplift force on horizontal panels through dimensionless analysis.Compared with other empirical formulas,this formula uses dimensionless variables of clear physical meanings,thus can describe the interaction between waves and the panels in a better way.In addition,the efficiency of the formula to estimate wave uplift force on horizontal panels is verified against existing works.Therefore,the findings in this study shall be useful for understanding the mechanism of wave uplift force on horizontal panels and numerical model validation.     

Hydrodynamics identities and wave-drift force of a porous body

In the present study, hydrodynamic interactions between water waves and porous bodies are investigated. Various hydrodynamic identities, such as the Haskind relation, Bessho-Newman relation etc., are systematically re-examined. Some of these identities, such as the symmetry of added mass and damping and the Haskind-Hanaoka relation, are still valid for porous bodies even without modification to the identities. However, when energy dissipation due to porosity is involved, appropriate supplementation is required to properly consider porous effects. In addition, the calculation of wave drift forces acting on a porous body is formulated either by pressure integration or using momentum conservation as basis. We conclude that porosity dissipation makes a more substantial contribution to wave drift forces than does conventional dissipation created by scattered and radiated waves.     

双层直立圆弧型防波堤上绕射波浪力的解析计算

基于微幅波绕射理论,应用特征函数展开法,推导了双层直立圆弧型透空防波堤的波浪绕射解析解,从而将已有的比例边界有限元法拓展为解析算法,并据此对外层与内层防波堤所受波浪载荷进行了解析计算。计算结果表明:应用本文方法对直立透空圆环柱的绕射波浪载荷进行验证计算,所得结果与现有的解析解完全吻合,说明方法可靠。双层堤较单层堤能更有效地减弱波浪作用。波浪的入射角度和特征参数、防波堤张角与半径、防波堤透空系数以及水深等因素的相对变化对双层堤的波浪作用均存在一定影响。     

两层流体中多个圆柱浮体波浪力的解析方法

采用解析方法研究了线性入射波作用下两层流体中多个圆柱形淹没浮体的渡浪力特性.首先基于多极子展开方法,建立了散射势函数的解析表达式,并进一步得到浮体散射渡浪力的计算公式,然后利用边界元方法验证了本文的解析解,最后分析了不同参数的变化对双圆柱形浮体结构波浪力的特有影响.     

海底泥流冲击悬跨管道拖曳力系数分析

海底滑坡是海洋油气工程最危险的地质灾害之一,直接影响海底管线运营安全。滑坡体失稳滑动过程中,由于海水掺和作用逐渐加速转变成快速滑动泥流,冲击海底悬跨管道。基于当前国际通用的计算流体动力学(CFD)方法,采用赫巴模型描述快速滑动泥流,计算分析海底滑坡冲击悬跨管道的受力特性,重点分析悬跨高度对管道法向拖曳力系数的影响。研究发现,管道法向拖曳力系数随悬跨高度的增长而增大,当达到某一悬跨高度时,管道拖曳力系数保持稳定。     

Artificial neural network ability in evaluation of random wave-induced inline force on a vertical cylinder

An approach based on artificial neural network (ANN) is used to develop predictive relations between hydrodynamic inline force on a vertical cylinder and some effective parameters. The data used to calibrate and validate the ANN models are obtained from an experiment. Multilayer feed-forward neural networks that are trained with the back-propagation algorithm are constructed by use of three design parameters (i.e. wave surface height, horizontal and vertical velocities) as network inputs and the ultimate inline force as the only output. A sensitivity analysis is conducted on the ANN models to investigate the generalization ability (robustness) of the developed models, and predictions from the ANN models are compared to those obtained from Morison equation which is usually used to determine inline force as a computational method. With the existing data, it is found that least square method (LSM) gives less error in determining drag and inertia coefficients of Morison equation. With regard to the predicted results agreeing with calculations achieved from Morison equation that used LSM method, neural network has high efficiency considering its convenience, simplicity and promptitude. The outcome of this study can contribute to reducing the errors in predicting hydrodynamic inline force by use of ANN and to improve the reliability of that in comparison with the more practical state of Morison equation. Therefore, this method can be applied to relevant engineering projects with satisfactory results.     

新型开孔工字板组合式防波堤波浪力特性试验研究

开孔工字板组合式防波堤是基于透空板式防波堤的一种新型结构形式,具有自重轻、材料省的特点。为充分了解新型开孔组合式防波堤的受力特性,基于室内水槽物理模型试验,测量新型开孔工字板组合式防波堤上的波压力与结构总力,研究相对波高H/d、相对波长L/B对该新型防波堤结构表面压力的影响,讨论了该新型防波堤所受波浪力荷载与相对波高H/d、相对波长L/B的关系。结果表明,相对波高H/d是决定新型防波堤结构表面波压力和结构总力的主要影响因素。该新型防波堤结构波浪力荷载以垂直方向受力为主,新型防波堤结构所受竖向总力远大于水平总力,最大可达到15倍。新型防波堤水平总力随相对波长L/B先增大后趋于稳定。相对波长L/B=3.617是防波堤结构水平总力变化幅度的分界点。     

The effect of wave-induced radiation stress on storm surge during Typhoon Saomai (2006)

The effects of wave-induced radiation stress on storm surge were simulated during Typhoon Saomai using a wave-current coupled model based on ROMS (Regional Ocean Modeling System) ocean model and SWAN (Simulating Waves Nearshore) wave model.The results show that radiation stress can cause both set-up and set-down in the storm surge.Wave-induced set-up near the coast can be explained by decreasing significant wave heights as the waves propagate shoreward in an approximately uniform direction;wave-induced set-down far from the coast can be explained by the waves propagating in an approximately uniform direction with increasing significant wave heights.The shoreward radiation stress is the essential reason for the wave-induced set-up along the coast.The occurrence of set-down can be also explained by the divergence of the radiation stress.The maximum wave-induced set-up occurs on the right side of the Typhoon path,whereas the maximum wave induced set-down occurs on the left side.     

Effects of UV-B radiation and different light repair conditions on the early development of the tetraspores of Chondrus ocellatus Holm

The effects of exposure to UV-B radiation,280-315 nm,and dark or dark repair conditions on the early development of Chondrus ocellatus Holm collected from Qingdao coast were studied under the laboratory condition.After being exposed to different doses [0,36,72,108,144 and 180 J/(m 2 · d)] of UV-B radiation,one treatment of tetraspores were put back to normal culture condition (PAR),the other treatment were put into dark condition to repair for 2 h.During the cultivation,the diameter of the tetraspores were recorded every 4 d till the 50th day when vertical branches formed in all treatments.Then at the 50th day,CPDs,phycoerythrin,chlorophyll a and MAAs (Palythine and asterina-330) were measured.The results showed that low doses UV-B radiation could significantly accelerate the growth rate of the tetraspores of C.ocellatus and the growth rate reduced gradually with UV-B radiation keep on increasing.The variation trend of both the phycoerythrin and chlorophyll a concentration reduced significantly ( P < 0.05) once given the UV-B radiation. Under UV-B stress,the CPDs were induced,and the concentrations of CPDs were significant low in dark repair groups.The data of MAAs analyzed by LC/MS in the tetraspores of C. ocellatus suggested that there were two MAAs formed (palythine and asterina-330) after UV-B radiation induced, and low dose of UV-B irradiation could significantly induced the concentration of MAAs.From the growth and development state of the tetraspores,negative effects of UV-B radiation on the dark repair groups were more serious than PAR.     

黏土中桩靴底部吸附力产生机理研究

在海洋工程中,移动钻井平台在作业结束后需要转场时,经常会遇到拔桩困难的问题,桩靴底部的吸附力是上拔力的重要组成部分,明确其产生机理及发展规律对于上拔力计算与缓解上拔困难问题有重要意义。通过室内模型试验研究了黏土中桩靴底部真空度对桩靴吸附力产生机理的影响,试验结果表明,桩靴底部真空度的变化对上拔力的影响显著,而桩靴贯入深度和上拔速率会对真空度产生影响。当真空度达到峰值时,桩靴底部吸附力与上拔力几乎同时达到峰值,因此可以通过减小桩靴底部真空度的措施来减小上拔力。根据试验结果,提出了运用真空吸盘理论来计算桩靴底部吸附力的计算公式。所述吸附力计算方法与试验结果进行对比,其误差较小,对工程实践具有一定的参考意义。     

Numerical simulation of nonlinear wave radiation by a moving vertical cylinder

In this paper the fully nonlinear potential model based on a finite element method is used to investigate the nonlinear wave motion around a moving circular cylinder. The results for the cylinder in transient motion are compared with the experimental data and a much better agreement than the linear theory is found. Further simulation for a circular cylinder in sinusoidal motion is made. It is found that when the ratio of the cylinder diameter D to the wavelength L is relatively small at a fixed motion amplitude the nonlinear components of the runup on the cylinder surface at the second- and third-harmonic frequencies become more important and this is confirmed by the experimental data. Results for the hydrodynamic force are also provided for a cylinder oscillating in a channel. It is noticed that when the frequency of the cylinder motion in a channel is between the first and the second natural frequencies of the symmetric mode, the time history has components not only at the frequency of the cylinder motion but also at the first natural frequency. The latter remains significant over the period that the simulation is made. This has important implications to model testing. If measurement is to be made at such a frequency it may take long time for the motion to become periodic at the frequency of the cylinder motion.