Influence of wave-current interactions on fluid force

Influence of wave-current interactions on fluid force on a single cylinder and on two cylinders in tandem is examined. Quantities obtained are spectra of fluid force on elements, total fluid force and its statical moment. Comparisons are made of the cases in which wave-current interactions are considered and ignored. It is shown that interactions affect spectra of element force and statical moment more than do total force spectrum. For two cylinders in tandem, for cylinder spacings, current conditions and frequency range of practical interest, the effect of interactions is slightly reduced.     

WAVE-CURRENT FORCE COEFFICIENTS FOR ISOLATED PILE

Based on the linear wave theory and model experiment results, the wave-current force coefficients for isolated pile are investigated, using Morison's formula to calculate the wave-current force. A formula is'presented for determining the relative coefficients of the drag, in which the feature value of the wave-current field is. proposed and used as an important parameter. According to the maximum wave-current force measured in the experiment, the coefficients of the drag force and inertia force are determined by statistical method of two-variable regression so that both of them are fitted in optimum.     

Wave-current force on horizontal cylinder

For the calculation of wave-current force on horizontal cylinder a modified Morison's equation is used. A redefined Keulegan- Carpenter number KC2 is determined for the horizontal cylinder in wave-current co-existing field. The force coefficients are well related to the redefined KC2 number. As to the comparison with the force on vertical cylinder, the characteristics of force on horizontal cylinder are quite similar to those on vertical cylinder, but the force coefficients for horizontal cylinder are larger than those for vertical cylinder. It is proved by the authors' calculation that the results of monochromatic wave can be used directly for the determination of irregular wave-current force on horizontal cylinder in time domain.     

Truss Spar平台在波流联合作用下运动响应预报方法比较

基于细长体水动力模型比较了Truss Spar平台在波流联合作用下运动响应预报的三种方法。分别采用波流耦合、速度叠加及力叠加计算Truss Spar平台在波流联合作用下的水动力载荷,根据流场水质点运动规律和Truss Spar外部形状特点,分段高效计算水动力载荷。利用Runge-Kutta-Fehlberg方法求解刚体非线性运动方程得Truss Spar在波流场中的运动响应。研究结果表明力叠加法所预报的Truss Spar纵荡和纵摇运动明显大于其他两种方法的相应运动响应预报结果,而波流耦合法与速度叠加法所预报的纵荡与纵摇运动响应幅值相当,三种方法所预报的垂荡运动响应的大小取决于具体波流参数。     

The Lift Forces Acting on a Submarine Composite Pipeline in a Wave-Current Coexisting Field

- A composite pipeline is defined as a main big pipe composed of one or several small pipes. The flow behaviour around a submarine composite pipeline is more complicated than that around a single submarine pipeline. A series model test of composite pipelines in a wave-current coexisting field was conducted by the authors. Both in-line and lift forces were measured, and the resultant forces were also analyzed. The results of lift forces and resultant forces are reported in this paper. It is found that the lift force coefficients for composite pipelines are well related to the KC number. The lift force coefficients for an irregular wave-current coexisting field are smaller than those for a regular wave-current coexisting field. The frequency of lift force is usually twice the wave frequency or higher. The authors test indicates that the resultant forces are about 10 to 20 percent larger than in-line forces (horizontal forces). The effect of water depth is analyzed. Finally, the relationship between lift f     

WAVE-CURRENT FORCE ON VERTICAL PILE

The drag and the interia coefficients Cd,CM of wave-current force on vertical pile are well related to the redefined Keulegan-Carpenter number N' Kc by the test data of the authors. The relation could be also used for irregular wave-current force to calculate in time domain. A simplified method for the calculation of cumulative probabilistic distribution of peak value of irregular wave-current force is also recommended in this paper. These methods were justified by the model test of the authors.     

固壁附近水平圆柱在波浪水流共存场中的流动显示及水动力特征

固壁附近的水平的圆柱体在波浪、波流作用下的受力情况与其周围的流场状态密切相关。为探讨圆柱形成的机理，应当对流场的涡结构有充分的认识，受力过程与记演化过程的同步分析万为重要。本文通过实验研究并对比数值分析的结果，对波浪、波流场中圆柱体受力与流场状态的关系做一初步讨论。     

Modelling the wave-current interactions in an offshore basin using the SWAN model

The theoretical background of the wave-current interactions, including the transformation of the wave spectrum and breaking waves due to currents, are first presented in this work. In the next part of the work, experimental data resulted from studies performed in an offshore wave basin of the Danish Hydraulic Institute concerning the wave-current interactions were presented in parallel with some wave model simulations performed in similar conditions. SWAN, which is presently the state-of-the-art spectral model for the wave transformations, was adopted for performing numerical simulations. In general, a good agreement was encountered between the experimental data and the simulation results.     

A Higher Order BEM for Wave-Current Action on Structures ——Direct Computation of Free-Term Coefficient and CPV Integrals

1 .Introduction Research on wave action onforward moving bodies or wave-current action on structures is impor-tant in offshore and coastal engineering.For bodies withsimple geometry,analytic solutions have beendeveloped . Matsuiet al .(1991) and Emmerhoff and Sclavounos (1992) derived analytic solutionsforuniformcylinders infinite andinfinite water depth.Bao and Kinoshita (1993) expendedthe theorytotruncated cylinders .In engineering practice ,structures are complexand numerical methods have…     

基于FLOW-3D的三维数值波流水槽的构建及应用研究

为获得具有自由液面的三维波流水槽,基于FLOW-3D有限差分程序,选用RNG?-?紊流模型,基于线性波速度入口法造波,采用VOF方法对自由液面进行追踪。构建具有自由液面的三维波流联合作用数值水槽,对比压力出流边界与Sammerfeld辐射边界发现,在波流水槽内采用压力出流边界能够保持流体体积守恒,波形稳定;加入的孔隙结构,不仅能保证良好的消波效果,而且流体能够顺利通过,对消除反射波影响效果良好;与实验结果对比发现,垂向时均流速与实验数据拟合较好。波流场中桩柱前形成明显下潜水流及漩涡,是形成局部冲刷主要原因。本文所构建的波流数值模型波形稳定、具有良好的波流特性,能较好反应波浪与水流之间的相互作用,可进一步模拟波流场与结构物之间的相互作用或波流作用下泥沙冲刷等研究。     

西北太平洋浪流相互作用对有效波高的影响研究

西北太平洋强流区会对海浪的特征和分布产生显著的影响,尤其是研究台风过程中海流与海浪的相互作用具有重要的研究意义。本文以ROMS海洋模式和SWAN海浪模式为基础,构建了浪流耦合模式系统,对2013年10月6-17日间的台风“丹娜丝”、“百合”、“韦帕”过程中西北太平洋浪流相互作用中海流对有效波高的影响进行了研究。通过对比模式模拟有效波高与浮标观测资料,发现耦合后的有效波高比非耦合结果更接近观测值,耦合模式中海流的存在对有效波高的分布有明显的影响。研究表明,特别是在有效波高峰值处,海流引起的有效波高增大最大可达1 m。海浪浪向及流向的空间分布以及中国近海浮标处浪向与流向的时间序列表明,流向与浪向反向时,海流的影响造成有效波高增大;二者同向时,有效波高减小。海流对有效波高的调整会沿着海浪传播的方向传播相当一段距离。在西北太平洋的海浪场计算中,引入海流的耦合模式计算结果对改善强流区海浪预报具有重要意义,并且海流的模拟精度对于高精度的海浪预报非常重要。     

Interaction of higher-order water waves with uniform currents

The interaction between current-free higher-order water waves with a wave-free uniform current normal to the wave crests is considered. The combined wave-current motion resulting from the interaction is assumed stable and irrotational. The velocity potential, dispersion relation, the particle kinematics and pressure distribution up to the third order in wave amplitude are developed. The conservation of mean mass, momentum and energy, together with the dispersion relation on the free surface are used to derive a set of four nonlinear equations, through which the relationship between wave-free current, current-free wave and the combined wave-current parameters is established. Numerical results for a range of current values are also presented.     

Formation of Equilibrium Beach Profile of the Abandoned Yellow River Delta Coast in North Jiangsu

The abandoned Yellow River Delta coast is a typical erodible silty and muddy coast in China. The paper analyses the marine dynamic characteristics and the mechanism of beach erosion of this area. Analysis and calculation show that in this sea area wave and tidal current action should be considered. Based on the above analysis, an equilibrium beach profile calculation model is developed, in which the wave-current interaction is considered while sediment supply and sediment re-deposition are neglected. The model consists of four parts: (1) calculation of wave parameters, (2) calculation of velocity due to wave-current interaction at different water depth, (3) calculation of friction velocity and shear stress at different water depths, and (4) calculation of the amount of sediment erosion, erosion intensity and variation of beach profile. Calculated results are in good agreement with observed data. Finally, the evolution tendency is discussed and the equilibrium beach profile of this coast is calculated. B     

波浪对潮流能水轮机性能测试影响的实验研究

随着潮流能开发利用技术日趋成熟,对其测试工作也提出了更高的要求。然而,在潮流能装置性能测试中,波流相互作用的影响往往被忽略,导致测试结果不准确。为了研究波流相互作用对测试的影响方式与程度,采用物理模型试验的方法,对垂直轴潮流能发电装置模型进行了试验研究。通过分析波流作用下装置的扭矩、转速及发电功率,发现波流与发电装置耦合作用明显,相比不存在波浪影响的情况下,叶轮的转动、主轴的扭矩都变得不规则,启动流速变小,同时,扭矩、转速及发电功率的瞬时值显著增大。测试结果表明,波流相互作用对装置性能测试影响显著,平均影响程度约10%,研究结果为今后潮流能发电装置性能测试标准的制定和完善提供了参考和依据。     

不规则波作用下明基床上开孔沉箱垂直力分析

通过水槽物理模型试验,对不规则波作用下明基床上开孔沉箱所受到的波浪力进行了较为系统的试验研究,分析讨论了开孔沉箱总水平力峰(谷)值时刻对应的总垂直力与基床相对高度、开孔率、波陡、相对水深、消浪室相对宽度等影响因素之间的关系,并与暗基床的研究成果做了对比讨论,给出了明基床上开孔沉箱总垂直力比值(总水平力极值时刻对应的总垂直力/总垂直力极值)与各影响因素之间的计算关系式,研究结果可为工程应用提供参考。     

波流耦合作用下渤海及北黄海风暴潮增水及海浪过程的数值模拟

本文基于三维波流耦合FVCOM-SWAVE数值模式,采用Jelesnianski参数化风场与再分析数据集ECMWF风场数据叠加而成的合成风场作为外力驱动力,模拟了1818号"温比亚"台风引起北黄海及渤海海域风暴潮增减水及波浪的生长与消减过程,进而分析该海域在"温比亚"台风作用下波浪对流速垂向分布的影响。研究结果表明:合成风场得到的风速最大值及出现时刻与实测数据符合较好,合成风场较为合理,能够为模拟波流耦合机制下海域水动力变化提供准确的风场条件;几个测站的风暴潮增水模拟结果与实测数据较为吻合,FVCOM-SWAVE耦合系统合理地再现了"温比亚"台风在黄渤海引发的风暴潮增水以及台风浪过程。此外,计算结果显示"温比亚"期间黄渤海海域最大有效波高分布于台风中心外围,且位于台风前进方向上,波浪最大有效波高值与台风强度有关;在台风过境期间,波流相互作用对近岸海域流速的垂向分布具有一定影响,考虑波流相互作用可有效提高台风风暴潮数值模拟精度。研究结果对台风灾害预报、防灾减灾及港口建筑选址具有一定的参考意义。     

Transient effects in wave-current boundary layer flow

Previous studies of combined wave and current bottom boundary layer flow have concentrated on the final converged state of the flow following the addition of waves to a current. While this final state is of primary interest to modellers and engineers, it pre-supposes that such a state is actually attained in reality, and this may not always be the case. In addition, it overlooks the interesting and complicated transient effects which occur as a wave-current flow evolves from one state to another. The present study concentrates attention on the transient effects predicted by a “one-equation” turbulence closure model. Results of case studies are presented in which waves are superimposed co-linearly on a current (“forward problem”), and are then removed from the converged wave-current flow (“backward problem”). Two formulations of the “forward” and “backward” problems are discussed. In the first the steady component of the pressure gradient driving the mean flow is held constant throughout, and in the second the steady component of the mass flux is held constant. In each case the detailed evolution of the profiles of mean velocity, turbulent energy, mixing length, eddy viscosity and shear stress are discussed. More generally, the question of the convergence timescale of a combined wave-current flow is considered, and a convergence criterion is proposed.     

Numerical study of wave and longshore current interaction

Wave and longshore current interaction was examined based on the numerical models.In these models,water waves in the presence of longshore currents were modeled by parabolic mild slope equation,and wave breaking induced longshore currents were modeled by shallow water equation.Water wave provided the radiation stress gradients to drive current.Wave and longshore current interactions were considered by cycling the wave and longshore current models to a steady state.The experiments for regular and irregular breaking wave induced longshore currents by Hamilton and Ebersole（2001） and Reniers and Battjes（1997） were simulated.The numerical results indicate that the present models are effective for simulating the interaction of wave and breaking wave induced longshore currents,and the numerically simulated longshore current at wave breaking point considering wave and longshore current interaction show some disagreement with those neglecting the wave-current interaction,and the breaking wave induced longshore current effect on wave transformation is not obvious.     

Numerical investigation of the effect of current on wave focusing

In the present study,a numerical wave tank is developed to simulate the nonlinear wave-current interactions based on High Order Spectral(HOS) method.The influences of current on wave focusing are investigated by use of numerical model.The current is assumed to be constant in space.Focused waves with different amplitudes and frequency spectra are simulated with and without current.The focused wave characteristics,such as surface elevation,the maximum crest and frequency spectrum,with different current are compared.The results show that the opposing current increases the maximum crest and the energy transform during wave focusing process,and vice versa for the following current.     

Interaction of waves with non-colinear currents

The present paper reports on a study of the interaction of a current-free monochromatic surface wave field with a wave-free uniform current field in a three-dimensional flow frame. The wave and the current fields are not necessarily collinear with each other. The formulation of the wave-current field is done under the assumption of irrotational and inviscid flow. We have developed the three dimensional expressions describing the characteristics of the combined flow in terms of mass, momentum and energy transport conservation. These equations are found efficient to describe the sought-for combined wave-current field. The parameters describing the wave-current field after the interaction are the surface disturbance amplitude and length, mean water depth, mean current-like parameter and direction of the combined flow, which would be calculated from a set of equations that satisfy conservation of mean mass, momentum and energy flux and a dispersion relation on the free surface before and after the interaction. The results are shown in terms of relative changes in wave heights and lengths, current-like parameters and final directions obtained for the combined wave-current field with respect to current-free wave and wave-free current pre-interaction parameters.