Spatial Distribution Characteristics of Surface Tidal Currents in the Southwest of Taiwan Strait

This study was conducted on the spatial distribution characteristics of surface tidal currents in the southwestern Taiwan Strait based on the quasi-harmonic analysis of current data obtained by two high frequency surface wave radar(HFSWR) systems. The analysis shows that the tidal current pattern in the southwestern Taiwan Strait is primarily semi-diurnal and influenced significantly by shallow water constituents. The spatial distribution of tidal current ellipses of M2 is probably affected by the interaction between two different systems of tide wave, one from the northern mouth of Taiwan Strait and the other from the Bashi Channel. The directions of the major axes of M2 tidal current ellipses coincide roughly with the axis of the Taiwan Strait. The spatial distribution of the magnitudes of the probable maximum current velocity(PMCS) shows gradual increase of the velocity from northeast to southwest, which is in accordance with the spatial distribution of the measured maximum current velocity(MMCS). The directions of the residual currents are in accordance with the direction of the prevailing monsoon wind at the Taiwan Strait and the direction of the Taiwan warm current during summer. The bathymetry also shows a significant effect on the spatial distribution characteristics of tidal currents.

Dynamical Control of Asymmetrically Oblique Tidal Currents to the Sedimentary Characteristics and Development of Linear Sand Ridges in the Liaodong Shoal, East Bohai Sea

The Liaodong Shoal is a group of linear sand ridges located in the east Bohai Sea of China.In this study,54 surface sediment samples have been collected,current measurements at 4 stations have been carried out and bathymetric data were obtained.The current directions are rightward deflected relative to the strikes of the sand ridges.Affected by the narrowing effect of the ridge,the current velocities exhibited an anti-‘C’type vertical profile.The velocities of the lower currents linearly correlate with the water depths.The near-bed current velocities over the troughs are estimated to be higher than those over the ridges,and this feature could be explained by the loss of kinetic energy together with the conversion between kinetic energy and gravitational potential energy.The sedimentary characteristics that are compatible with the tidal dynamics are developed across the ridges and troughs,including grain size compositions,grain size parameters,mineral compositions and Dhm indexes.The existence of the angles between the current directions and the strikes of the sand ridges is the key factor for the growth of the sand ridges.The asymmetric hydrodynamic features between the flood and ebb currents lead to the differences in the topographical and sedimentary characteristics on both sides of a sand ridge.Insufficient material supply led to the degradation of the sand ridges,and the reduction of the tidal current intensity has led to the development of the subordinate sand ridges in the troughs.Sand ridges are migrating.

Numerical calculation of hydrodynamic characteristics of tidal currents for submarine excavation engineering in coastal area

In coastal areas with complicated flow movement, deposition and scour readily occur in submarine excavation projects. In this study, a smallscale model, with a high resolution in the vertical direction, was used to simulate the tidal current around a submarine excavation project. The finite volume method was used to solve Navier-Stokes equations and the Reynolds stress transport equation, and the entire process of the tidal current was simulated with unstructured meshes, generated in the irregular shape area, and structured meshes, generated in other water areas.The meshes near the bottom and free surface were densified with a minimum layer thickness of 0.05 m. The volume of fluid method was used to track the free surface, the volume fraction of cells on the upstream boundary was obtained from the volume fraction of adjacent cells, and that on the downstream boundary was determined by the water level process. The numerical results agree with the observed data, and some conclusions can be drawn: after the foundation trench excavation, the flow velocity decreases quite a bit through the foundation trench, with reverse flow occurring on the lee slope in the foundation trench; the swirling flow impedes inflow, leading to the occurrence of dammed water above the foundation trench; the turbulent motion is stronger during ebbing than in other tidal stages, the range with the maximum value of turbulent viscosity, occurring on the south side of the foundation trench at maximum ebbing, is greater than those in other tidal stages in a tidal cycle, and the maximum value of Reynolds shear stress occurs on the south side of the foundation trench at maximum ebbing in a tidal cycle. The numerical calculation method shows a strong performance in simulation of the hydrodynamic characteristics of tidal currents in the foundation trench, providing a basis for submarine engineering construction in coastal areas.

Experimental Study on Hydrodynamic Characteristics of Vertical-Axis Floating Tidal Current Energy Power Generation Device

To study the characteristics of attenuation, hydrostatic towage and wave response of the vertical-axis floating tidal current energy power generation device （VAFTCEPGD）, a prototype is designed and experiment is carried out in the towing tank. Free decay is conducted to obtain attenuation characteristics of the VAFTCEPGD, and characteristics of mooring forces and motion response, floating condition, especially the lateral displacement of the VAFTCEPGD are obtained from the towing in still water. Tension response of the #1 mooring line and vibration characteristics of the VAFTCEPGD in regular waves as well as in level 4 irregular wave sea state with the current velocity of 0.6 m/s. The results can be reference for theoretical study and engineering applications related to VAFTCEPGD.

Surface tidal currents in the open sea area to the east of the Zhoushan Islands measured with high frequency surface wave radar

Based on the quasi-harmonic analysis of 11 d vector ocean currents obtained from two high frequency sur- face wave radars located at Zhujiajian Island and Shengshan Island, the spatial distribution characteristics of surface tidal currents in the open sea area to the east of the Zhoushan Islands of Zhejiang Province, China are studied. The following conclusions are drawn from the analysis： the tidal current pattern in the open sea area to the east of Zhoushan Islands is primarily regular semidiurnal, which is significantly affected by the shallow water constituents. The directions of the major axes of tidal current ellipses of M2 lie approx- imately in the NW-SE direction. With the increasing of distance away from the coast, the directions of the tidal current ellipses gradually shift toward the E-W direction. The tidal currents are mainly reversing cur- rents. The spatial distribution of probable maximum current velocities decreases gradually from northeast to southwest which is basically in accordance with the spatial distribution of measured maximum current velocities. The residual currents near the coast are larger than those far away from the coast. The directions of the residual currents are basically north by east, and the angle to the due north increases gradually with the increasing distance away from the coast. The topography shows a certain impact on the spatial distri- bution of shallow water constituents, the rotation of tidal currents, the probable maximum currents and the residual currents.

基于电机电流的高压断路器弹簧操作机构的LM-BP故障诊断算法

BP(back propagation)神经网络由于具有线性映射能力强及自适应能力强等优点,常被用于高压断路器弹簧操作机构的故障诊断中,但易陷入局部最小点限制了网络的收敛速度和分类精确度。文中提出了一种基于L-M算法优化BP神经网络的高压断路器操作机构故障诊断方法,分析了神经网络的数学模型及映射关系,运用L-M算法对传统BP网络进行优化,解决了传统BP神经网络梯度下降法存在局部最小化、易产生平坦区等问题,有效地提高了算法的训练速度,同时提高了分类的精确度。诊断结果表明:L-M算法优化后的BP神经网络能有效地实现高压断路器操作机构故障诊断。文中研究内容对高压断路器操作机构故障诊断提供了思路与方法,对提高高压断路器安全可靠性具有重要意义。

潮流作用下环礁断面的流动特征研究

本文首先通过循环水槽试验测量分析了正向和反向潮流影响下概化环礁断面的流动特性,试验结果表明:在正向流和反向流作用时,礁坪上仅存在亚临界流,并可观察到经典的壁面有界流动流速剖面特征;沿礁的平均水位与各个测线上的流速随潮流幅值的增大而增大。本文随后采用雷诺平均的Navier-Stokes方程并结合标准的k-ωSST湍流模型建立数值水槽,进一步研究了多种水动力与礁型因素影响下前后礁外礁缘处的流速变化规律。数值模拟结果表明:后礁外礁缘处的平均流速均大于前礁外礁缘处;平均流速随潮流幅值的增大而增大,随礁坪水深、礁坪宽度、潟湖宽度和礁前斜坡坡度的增大而减小;最后基于数值模拟结果提出了预测各种因素影响下前后礁外礁缘处流速的幂函数型经验公式。

基于FVCOM的普陀山潮流能试验区数值模拟

国内外关于潮流能试验场小范围海域流场特性研究中,缺乏高精度的数学模型模拟真实环境下的水动力特性。本文基于非结构化网格的有限体积海洋数值模型(Finite-Volume Coastal Ocean Model,FVCOM),建立舟山及普陀山-葫芦岛潮流能试验场水域潮汐潮流数值模型,采用大范围区域潮位验证率定模型后得到更精确的小范围开边界条件嵌套小范围区域进行潮流计算。通过4个测站大、小潮的拟合数据和实测潮位、潮流流速、潮流流向数据进行对比,调整装置附近局部区域底摩阻取值,从而概化装置的影响,同时对小范围的潮波传播规律及流场水动力特性进行分析。结果表明:潮流能试验区所处海域潮汐类型为不规则半日潮,潮流以往复流为主;潮流运动传播主要方向为SSE—NNW向,该海域潮流特性空间差异明显;左岸龙南礁内湾区涨潮时呈逆时针传播,落潮时漩涡反向,右侧大龙山咀湾区涨落潮时均无明显涡旋。本研究可以为试验场海域潮流能发电装置阵列布放优化提供理论参考。

罗源湾潮致余流特征及其对物质分布的影响

基于MIKE 3开展了罗源湾的三维数值模拟,以流场和断面垂向流速阐释了罗源湾的潮流分布特征,计算了罗源湾的潮致余流场,采用拉格朗日粒子追踪法模拟了具有粒子特性的物质在湾内的运移并分析了粒子的运动规律,结合潮流和潮致余流特征讨论了罗源湾不同区域的物理自净能力。研究结果表明,罗源湾西北部、东北岸内凹处和内湾口处形成了余环流结构,湾内不同区域的物质分布与潮致余流结构有明显相关性,粒子在罗源湾西北部海域运移缓慢,而湾口及可门水道附近具有较好的自净能力。本研究为进一步探讨罗源湾污染物质分布机制提供了科学依据,为罗源湾的污染控制和环境保护提供了技术支撑,研究方法也为其他海湾的相关研究提供借鉴参考。

山东半岛南部海域周日潮流观测数据准调和分析与应用

潮流对海上交通安全、生态保护等具有重要影响,掌握潮流特征对潮流预报、航行安全和科学研究具有重要意义。周日潮流观测数据因数据时长较短,潮流特征分析往往不够精准可靠。本文采用引入差比关系的准调和分析法就1次周日潮流观测数据展开分析,并就潮流表示方法进行了简要介绍。以山东半岛南部海域验流数据为例进行实验,结果表明:该方法可以为观测海区提供较为可靠的潮流特征值,为航行安全和海洋发展提供基础数据保障,同时本文研究方法也将为周日潮流观测数据分析提供参考。

THE HYDRODYNAMIC CHARACTERISTICS OF FREE VARIABLE-PITCH VERTICAL AXIS TIDAL TURBIN

The hydrodynamic characteristics of free variable-pitch vertical axis tidal turbine are investigated by combining experimental and numerical simulations. The variations of hydrodynamics are obtained based on testing the kinematics and the dynamics of the turbine under different flow and structural conditions. Through analyzing the movement of the turbine and the characteristics of the flow field by numerical simulations, it is shown how the turbine＇s performance is improved.

Experimental Investigation of a Hydraulic Turbine for Hydrokinetic Power Generation in Irrigation/Rainfall Channels

The development of microchannels with open flow for use in irrigation and rainy areas is challenged by electricity generation via hydrokinetic devices in shallow and low velocity flows.Conventional hydrokinetic turbines are known to be highly dependent on current speed and water depth.Another drawback of conventional turbines is their low efficiency.These shortcomings lead to the need to accelerate the flow in the channel system to enhance the extracted power.The method of deploying a novel turbine configuration in irrigation channels can help overcome the low performance of conventional hydrokinetic turbines.Therefore,this study experimentally presents a bidirectional diffuser-augmented channel that includes dual cross flow/Banki turbines.Results show that the maximum efficiency of the overall system with two turbines is nearly 55.7%.The efficiency is low relative to that of hydraulic turbines.Nevertheless,the result can be considered satisfactory given the low head of the present system.The use of this system will contribute to a highly efficient utilization of flows in rivers and channels for electrical energy generation in rural areas.

永磁悬浮支撑的刚性圆柱振子流致振动幅频特性分析

将永磁悬浮支撑与流致振动潮流能转换装置相结合,探索永磁悬浮支撑结构作为弹簧在流致振动潮流能发电领域的应用可行性。为了对比永磁弹簧与金属弹簧所提供恢复力对刚性圆柱振子流致振动的影响,通过ANSYS Maxwell软件计算得到永磁弹簧的磁力,拟合出永磁弹簧的弹性恢复力曲线方程,将弹性恢复力曲线方程代入Star-CCM+计算出刚性圆柱振子在不同流速下的幅频特性,然后将计算结果与金属弹簧系统进行比较。结果显示永磁弹簧支撑振子流致振动幅频特性与金属弹簧的相似,在上端分支能达到最大振幅比,频率随着流速增加总体呈增加趋势。但在计算流速区间内,永磁弹簧支撑振子的振幅比与频率都比金属弹簧支撑振子大,振动性能更优。

琼州海峡西南部秋季海流特征分析

为深入了解琼州海峡西南部海域的潮流特征,采用准调和分析方法对2022年秋季琼州海峡西南部实测海流资料进行分析,得到潮流性质、潮流特征和余流特征,并计算潮流最大可能流速。结果表明:琼州海峡西南部潮流以规则全日潮流为主,近岸则为不规则全日潮流,潮流运动形式为往复流;涨潮流以西向流为主,落潮流以东向流为主;潮流最大可能流速为0.85~2.58 m/s,方向为W-E、SW-NE;余流流速在0.01~0.23 m/s之间,余流流向以西向为主。本研究丰富了调查海区水文资料,为该海域开发利用和通航安全等提供基础数据。

安装高度对水平轴潮流能水轮机尾流特性的影响

为探究水轮机的安装高度对水轮机尾流场的影响,本文以水平轴潮流能水轮机为研究对象,采用计算流体力学(Computational Fluid Dynamics,CFD)方法对水轮机尾流特性进行分析.分别设置水轮机的中心距离海底高度为1.5D、2.0D、2.5D(D为水轮机直径),对水轮机尾流场的轴向、径向上的速度亏损以及涡量结构图进行分析.研究结果表明:安装高度为1.5D时,约在下游轴向位置X/D=15(X为轴向距离)处,梢涡与海底碰撞导致涡结构发生破损,这也使得该工况在下游X/D=15后的速度亏损明显大于安装高度2.0D和2.5D,而安装高度为2.0D和2.5D工况的速度变化基本一致.同时从3种工况不同轴向位置速度亏损图可以看出,从下游X/D=10开始,最大亏损速度均出现在中心轴线的位置.因此在考虑到对下游流场的影响和安装的成本时,建议安装高度为2.0D.

黄骅港水文要素季节性特征分析

为深入了解黄骅港海域不同季节的潮流特征和水文条件,根据该海域2020~2021年的海洋水文资料,基于潮流准调和分析及统计分析的方法,对潮流和温盐沙等水文特征进行分析。结果表明:本观测海域潮流属规则半日潮类型,潮流涨潮历时大于落潮历时;含沙量由近岸向外海呈逐渐减小的分布特征;盐度各个站位在春夏季相差皆不大,位于大口河河口处的测站盐度春夏季高、秋季低的特征明显,在其他站位季节变幅较小;各测站均表现为夏季最高,冬季水温最低的变化规律。依据具有代表性的典型潮观测数据能较好地表现出其季节性水文特征和变化规律,为下一步的模型试验和环境影响评价提供基础依据。

灌河口海域潮流特征分析

运用灌河口海域大潮期6个测站潮流资料,根据准调和分析理论编程计算,结果显示:观测海域的潮流特征表现为规则半日潮,M2半日分潮是主要的潮波,潮差较大;浅水分潮比值远大于0.04,表明本海域的潮波在浅水区变形颇为显著;潮流运动主要表现为旋转流的形式,运动方向为NW—SE;余流的流速在垂向上有表层>中层>底层的特征,而不同水层的余流方向有较大的差异。

池壁效应对水平轴潮流涡轮水动力性能影响分析

为了分析池壁效应对水平轴潮流涡轮水动力性能的影响,本文采用数值仿真与模型试验的方式测试直径300 mm潮流涡轮的水动力性能,并对数值仿真方法进行验证;采用Bahaj修正方法与数值仿真方法对不同流域、流速下涡轮的能量转换效率以及阻力系数进行对比,进一步分析池壁效应对涡轮桨盘处以及尾流区域流场的影响。研究结果表明:池壁效应对水平轴潮流涡轮的水动力性能影响明显,其对能量转换效率影响伴随尖速比的增加逐渐增大;池壁效应对潮流涡轮桨盘处的轴向流速以及流场分布影响较小,但对潮流涡轮尾流区轴向速度恢复影响明显。研究结果可为水平轴潮流涡轮水动力性能的数值仿真研究与试验提供相关数据以及参考。

涌潮水力学特性试验研究

通过在涌潮水槽中测试分析不同潮前水深、涌潮高度条件下的涌潮传播速度、涌潮水流速度等要素,得到潮头充分破碎涌潮的相对潮高大于0.5、佛劳德数大于1.1。验证了基于动量方程得到的涌潮传播速度计算公式的可靠性。建立了涌潮流速与潮前水深、涌潮高度及涌潮传播速度的经验关系。

兴化湾潮汐潮流特性及工程影响分析

福建省兴化湾内大量围填、疏浚工程建设直接影响湾内水动力环境。依据2009年2月水文观测资料,对实测资料进行分析,并利用潮汐调和分析、潮流准调和分析、潮流数值模拟等方法得到了兴化湾海区的潮汐、潮流特性以及湾内工程前后的潮位、潮流场和余流场特征。分析研究表明,兴化湾潮汐属于正规半日潮,浅水效应较弱;潮流为不正规半日潮流,浅海分潮作用较强;湾内潮波逐渐有驻波特征,形成湾内潮波的两股潮流流向稳定,呈往复流,其中兴化水道潮流涨潮占优,南日水道潮流落潮占优;工程实施后,基于调和常数的2013年7月潮位预报与实测潮位吻合较好,同时潮汐潮流性质不变,在港池、航道水域流速有所增加;兴化、南日两水道涨、落潮通量均减小,全湾纳潮量有所减少;湾内余流场整体不变,口门处涡漩有所加强。