Waves and Currents in Tide-Dominated Location Off Dahej,Gulf of Khambhat,India

Based on measurements of waves, currents, and tides off Dahej in the Gulf of Khambhat, hydrodynamics are studied. Estimated tidal constituents show that primary lunar semi-diurnal constituent M2 was the strongest constituent, and the amplitude was found to be around 4.5 times stronger than that of the major diurnal constituent K1. Currents were predominantly tide induced with speeds up to 3.3 m/s and were north-northwest during flood tide and south-southeast during ebb tide. Residual cross-shore and along-shore current was found to be varying with the corresponding change in the cross-shore and along-shore wind speed. Influence of tidal current was observed in most of the wave statistical parameters.     

桐花树红树林潮滩近底层悬沙浓度垂向剖面变化特征分析*

观测红树林潮滩在波浪和潮流作用下的近底层垂向剖面悬沙浓度变化过程, 对理解海岸带植被的消能促淤机制和滨海湿地生态修复工程有着重要作用。本文以北部湾七星岛岛尾桐花树红树林潮滩为例, 基于剖面流速仪HR、声学多普勒单点流速仪ADV、浪潮仪T-wave及剖面浊度仪ASM, 获取了研究区域2019年夏季大潮连续3天的水文数据, 同时结合桐花树典型植株实测参数, 分析了潮周期内红树林潮滩近底层垂向剖面悬沙响应波浪、潮流作用及桐花树空间结构的运动过程。结果表明: 1) 桐花树潮滩近底层悬沙浓度和悬沙通量具有涨潮明显大于落潮的潮汐不对称现象, 剖面垂向高悬沙浓度区域在涨潮初期—涨急由距底部0.1~0.37m转变为距底部0.5~0.67m, 落急—落潮末期则由上部转变为下部; 2) 潮周期内悬沙起动和再悬浮阶段发生在以波浪作用主导的涨潮初期和落潮末期, 平流和沉降发生在以潮流作用为主的涨急至落急整个阶段; 3) 涨潮阶段桐花树冠层的茂密枝叶通过减缓流速拦截多于冠层上部40%以上的悬沙, 落潮水体则挟沙自陆向海经过桐花树群落, 使得悬沙浓度下降超过71%。该不对称涨、落潮动力沉积机制有利于悬沙向岸输运, 促进潮滩扩张过程。     

港珠澳大桥青州航道桥桥墩基础冲刷试验研究

桥墩基础冲刷是桥梁毁坏的重要因素,是桥梁基础设计的关键指标之一。目前国内外对于桥墩基础在复杂动力条件下冲刷深度的研究常采用物理模型试验方法,利用正态系列模型方法,在波流水槽中研究了水流、潮流和波流共同作用下青州航道桥索塔基础周围流态变化和局部冲刷特征。研究结果表明,桥墩最大冲刷深度和冲淤范围与水流流速、桥墩轴线与水流夹角和波浪等因素有关;在潮流最大流速和恒定流流速一致情况下,桥墩局部冲刷深度达到平衡后,将会达到与恒定流基本一致的最大冲深;波流共同作用下的最大冲刷深度比恒定流增加10%左右。设计桥墩形状在100年一遇水流和波浪共同作用下桥墩基础局部最大冲刷深度为13.7 m。     

Field observation and analysis of wave-current-sediment movement in Caofeidian Sea area in the Bohai Bay,China

In order to study the mechanism of flow-sediment movement, it is essential to obtain measured data of water hydrodynamic and sediment concentration process with high spatial and temporal resolution in the bottom boundary layer （BBL）. Field observations were carried out in the northwest Caofeidian sea area in the Bohai Bay. Near 2 m isobath （under the lowest tidal level）, a tripod system was installed with AWAC （Acoustic Wave And Current）, ADCP （Acoustic Doppler Current Profilers）, OBS-3A （Optical Backscatter Point Sensor）, ADV （Acoustic Doppler Velocimeters）, etc. The accurate measurement of the bottom boundary layer during a single tidal period was carried out, together with a long-term sediment concentration measurement under different hydrological conditions. All the measured data were used to analyze the characteristics of wave-current-sediment movement and the BBL. Analysis was performed on flow structure, shear stress, roughness, eddy viscosity and other parameters of the BBL. Two major findings were made. Firstly, from the measured data, the three-layer distribution model of the velocity profiles and eddy viscosities in the wave-current BBL are proposed in the observed sea area; secondly, the sediment movement is related closely to wind-waves in the muddy coast area where sediment is clayey silt： 1） The observed suspended sediment concentration under light wind conditions is very low, with the peak value generally smaller than 0.1 kg/m^3 and the average value being 0.03 kg/m^3; 2） The sediment concentration increases continuously under the gales over 6-7 in Beaufort scale, under a sustained wind action. The measured peak sediment concentration at 0.4 m above the seabed is 0.15-0.32 kg/m^3, and the average sediment concentration during wind-wave action is 0.08-0.18 kg/m^3, which is about 3-6 times the value under light wind conditions. The critical wave height signaling remarkable changes of sediment concentration is 0.5 m. The results show that the suspended load sediment concentration is mainly influenced by wave-induced sediment suspension.     

Research on the unsteady hydrodynamic characteristics of vertical axis tidal turbine

The unsteady hydrodynamic characteristics of vertical axis tidal turbine are investigated by numerical simulation based on viscous CFD method. The starting mechanism of the turbine is revealed through analyzing the interaction of its motion and dynamics during starting process. The operating hydrodynamic characteristics of the turbine in wave-current condition are also explored by combining with the linear wave theory. According to possible magnification of the cyclic loads in the maximum power tracking control of vertical axis turbine, a novel torque control strategy is put forward, which can improve the structural characteristics significantly without effecting energy efficiency.     

波流共同作用下流速垂线分布及其影响因素分析

大量波流相互作用的实验表明,当波浪顺流传播时,平均水面附近的流速减小,而当波浪逆流传播时,平均水面附近的流速增加.为了从理论上解释这种现象,从垂向二维Navier-Stokes方程出发,推导出波浪、潮流共同作用下的水流控制方程;采用微幅波理论简化控制方程,并引入Grant-Madsen波流边界层模型,得到波流共同作用下的紊动切应力及流速垂线分布表达式.通过和实验结果及数值结果的对比,结果预测值和实测值较为吻合,表明公式能反映波高变化及涡粘系数共同对流速垂线分布的影响,且简单实用.利用该公式分析了波浪顺流、逆流流速变化的原因.     

Seabed stress determinations using the inertial dissipation method and the turbulent kinetic energy method

Direct measurements of seabed stress are difficult, especially in field conditions. Several methods for estimating these stresses using current meter data are available. Two of these methods, the Inertial Dissipation Method and the Turbulent Kinetic Energy Method, are described below, and a Matlab program is used to analyse data from a wave-current environment.     

Wave Breaking Phenomena of Irregular Waves Combined with Opposing Current

- Experimental study and theoretical analysis show that the critical value of relative wave height (H/ d)b given by Goda and the critical wave steepness (H/ L)b given by Michell and Miche can be adopted as the spilling breaking indices of regular waves. According to the same principle, a systematic theoretical analysis and experiment of irregular waves have been done by the authors in order to solve the breaking problem of irregular waves. It is indicated that the authors' method for determining wave breaking of regular waves can also be used for irregular waves.     

波、流共同作用下的泥沙起动

对波、流共存时的床面剪切力及摩阻系数等作了探讨,根据泥沙起动试验,建立了泥沙起动Shields曲线,导出了波、流共同作用下层流和紊流时的泥沙起动公式和起动波高、起动水深.     

波流作用下悬浮隧道运动响应纵向截断模型试验研究

利用波流水槽构建悬浮隧道纵向截断模型试验,分析了水流及波浪作用对悬浮隧道运动响应的影响,获得了管体结构的垂向及横向运动响应特性。研究结果表明:水流流速较小时,模型振幅随约化流速Vr增大而增大,而在约化流速为5.8附近,管体振幅达到最大并在这一临界值之后形成较为稳定的振幅值,产生明显的结构共振和涡激振动“锁定”现象。振幅稳定后垂向幅值约为管径的2倍,横向幅值与管径相当。对于波浪单独作用,在波浪较弱时,横向幅值与垂向几乎相等,随着特征KC_n数的增大,响应振幅先增后减。在特征KC_n数小于0.51范围内,垂向振幅大于横向振幅,其余范围则相反。垂向振幅和横向振幅分别在特征KC_n数为0.42和0.55时达到峰值,且两个方向的最大振幅值均与管体的管径相当。相对响应频率随着特征KC_n数的增大而减少,且垂向大于横向。