Numerical Investigation of Flow Motion and Performance of A Horizontal Axis Tidal Turbine Subjected to A Steady Current

Horizontal axis tidal turbines have attracted more and more attentions nowadays, because of their convenience and low expense in construction and high efficiency in extracting tidal energy. The present study numerically investigates the flow motion and performance of a horizontal axis tidal turbine with a supporting vertical cylinder under steady current. In the numerical model, the continuous equation and incompressible Reynolds-averaged Navier-Stokes equations are solved, and the volume of fluid method is employed to track free surface motion. The RNG k-ε model is adopted to calculate turbulence transport while the fractional area/volume obstacle representation method is used to describe turbine characteristics and movement. The effects of installation elevation of tidal turbine and inlet velocity on the water elevation, and current velocity, rotating speed and resultant force on turbine are discussed. Based on the comparison of the numerical results, a better understanding of flow structure around horizontal axis tidal turbine and turbine performance is achieved.

Research on Pitch Control Strategies of Horizontal Axis Tidal Current Turbine

Based on blade element momentum theory and generator characteristic test,a dynamic simulation model of 150 kW horizontal-axis tidal current turbine was established.The matching of the dynamic characteristics between the turbine and generator under various current velocities is studied,and the influence of the pitch angle on the matching is analyzed.For the problem of maximum power output in case of low current speed and limiting power in high current speed,the relation between optimal pitch angle and output power is analyzed.On the basis of dynamic characteristic analysis,the variable pitch control strategy is developed.The performance of the turbine under various tidal conditions is simulated.The research results show that the designed controller enables the turbine to operate efficiently under the condition of low current speed,and achieve the goal of limited power at high current speed.

Design and Test of 1/5th Scale Horizontal Axis Tidal Current Turbine

Tidal current energy is prominent and renewable. Great progress has been made in the exploitation technology of tidal current energy all over the world in recent years, and the large scale device has become the trend of tidal current turbine （TCT） for its economies. Instead of the similarity to the wind turbine, the tidal turbine has the characteristics of high hydrodynamic efficiency, big thrust, reliable sealing system, tight power transmission structure, etc. In this paper, a l/5th scale horizontal axis tidal current turbine has been designed, manufactured and tested before the full scale device design. Firstly, the three-blade horizontal axis rotor was designed based on traditional blade element momentum theory and its hydrodynamic performance was predicted in numerical model. Then the power train system and stand-alone electrical control unit of tidal current turbine, whose performances were accessed through the bench test carried out in workshop, were designed and presented. Finally, offshore tests were carried out and the power performance of the rotor was obtained and compared with the published literatures, and the results showed that the power coefficient was satisfactory, which agrees with the theoretical predictions.

Feedback Control of Plasma Current and Horizontal Position in HT-7

There is a strong magnetic coupling between poloidal field coils of superconducting tokamak HT-7, especially between ohinic heating and vertical field coils. These coils are connected to individual power supply. The control system for the plasma current and horizontal position control has been designed and showed satisfactory results with the feedback control of multivari- able feedforward-decoupling and var-parameter PID controller to simultaneously modulate power supplies. The design and analysls of the control system is presented.

Electric Potential in a Dielectric Sphere Head Produced by a Time-Harmonic Equivalent Current Dipole

A time-harmonic equivalent current dipole model is proposed to simulate EEG source which deals with the problem concerning the capacitance effect. The expressions of potentials in both homogeneous infinite dielectric medium and dielectric sphere on the electroquasistatic condition are presented. The potential in a 3-layer inhomogeneous spherical head is computed by using this model. The influences on potential produced by time-harmonic character and permittivity are discussed. The results show that potentials in dielectric sphere are affected by frequency and permittivity.

Effects of Topography and Current on Horizontal Irrotational Waves in Shallow Water

Based on the Boussinesq assumption, derived are couple equations of free surface elevation and horizontal velocities for horizontal irrotational flow, and analytical expressions of the corresponding pressure and vertical velocity. After the free surface elevation and horizontal velocity at a certain depth are obtained by numerical method, the pressure and vertical velocity distributions can be obtained by simple calculation. The dispersion at different depths is the same at the O (epsilon) approximation. The wave amplitude will decrease with increasing time due to viscosity, but it will increase due to the matching of viscosity and the bed slope, thus, flow is unstable. Numerical or analytical results show that the wave amplitude, velocity and length will increase as the current increases along the wave direction. but the amplitude will increase, and the wave velocity and length will decrease as the water depth decreases.

On the horizontal distribution of algal-bloom in Chaohu Lake and its formation process

Based on the remote sensing images of algae, the present work analyzes the horizontal distribution characteristics of algal blooms in Chaohu Lake, China, which also reveals the frequency of algal blooms under different wind directions. Further, an unstructured-grid, three-dimensional finite-volume coastal ocean model （FVCOM） is applied to investigate the wind-induced currents and the transport pro- cess to explain the reason why algal blooms occur at the detected places. We first deduce the primary distribution of biomass from overlaid satellite images, and explain the formation mechanism by analyzing the pollution sources, and simulating the flow field and transportation process under prevailing wind over Chaohu Lake. And then, we consider the adjustment action of the wind on the corresponding day and develop a two-time scale approach to describe the whole formation process of algae horizontal distribution in Chaohu Lake. That is, on the longer time scale, i.e., during bloom season, prevailing wind determines the primary distribution of biomass by inducing the characteristic flow field; on the shorter time scale, i.e., on the day when bloom occurs, the wind force adjusts the primary distribution of biomass to form the final distribution of algal bloom.

Study on Electrical Potential by Buried Source Electrode within the Horizontally Layered Half-space Model

The paper first studies the analytical expression of electrical potential by a point current source in a uniform half-space medium,and then focuses on the distribution of electrical potential in a horizontally layered half-space model by a point current source within the surface layer or the bottom layer.Finally,the electrical potential by a source electrode in any layer of a layered half-space model is presented.

330 kA铝电解槽异形阴极碳块对水平电流的影响

采用有限元仿真计算,对330 kA铝电解槽传统阴极碳块结构和异形阴极碳块结构的电场进行仿真模拟,主要对铝液中水平电流分布进行分析。研究发现,异形阴极碳块结构相对于传统阴极碳块结构能够在影响压降较小的前提下降低水平电流密度。模拟结果表明,在异形阴极碳块表面凸起中增加隔断并改变凸起角度,对降低铝液中水平电流效果明显,能够降低铝液中最大水平电流密度27.8%,平均水平电流密度34.3%,有效提升了铝电解槽电流效率。

太湖微囊藻漂移—聚集规律——基于风与光共同作用的模拟

针对影响微囊藻在太湖中水平迁移聚集形成水华规律的介观机理尚未揭示的问题,在实测水动力、微囊藻生物量的基础上,建立了考虑风与光共同作用的微囊藻迁移IBM模型。在通过实测数据率定后,对2017年多次发生的水华面积扩大过程进行了模拟。结果表明:风扰动下的微囊藻垂向分布决定了其水平迁移速度,越接近水面,微囊藻的水平迁移速度越快。太湖受到风生流的主导,微囊藻存在“低风下表层慢速迁移、适宜风下表层快速迁移、中下层始终慢速迁移”的3种水平迁移模式。在这3种水平迁移模式下产生了一种长期的“水平迁移累积”,也就是微囊藻向下风向湖湾漂移得快,从湖湾向外迁移得慢,其差值产生了微囊藻在下风向湖湾部聚集的效应。

CSRMT正交水平发射源电磁场分布规律研究

可控源射频大地电磁法(controlled source radio-magnetotellurics, CSRMT)测量通常使用发送频率1~1 000 kHz的人工场源,正交水平电偶源和正交水平磁偶源是人工源电磁法众多发射源中实现张量电阻率测量的优质场源。为此,本文基于水平电偶极子源和水平磁偶极子源电磁场解析公式,计算了均匀半空间模型正交水平电偶极子源和正交水平磁偶极子源的电磁场。结果表明,发射频率大于100 kHz时,应考虑位移电流;而张量视电阻率和阻抗相位在远区可以忽略位移电流的影响;固定模型电阻率、改变收发距时,模型计算表明高频电磁场远区测量范围更大;固定收发距、改变模型电阻率时,模型计算表明电磁场远区范围受电阻率影响较大,高阻模型需要更高的频率才会出现远区观测条件。磁偶源相较于电偶源,在张量视电阻率和相位上与实际值的偏差更小,更适于地质分析。

水平分层大地对低架天线电流分布影响分析

论文研究在水平分层大地条件下,不同接地方式对甚低频水平低架天线在有耗半空间中的电流分布特性。建立了水平低架天线的数学结构模型,理论推导了甚低频水平低架天线的电流分布公式,采用数值分析软件解析了大地介质层厚度、电导率对天线电流分布的影响。结果表明,在改变大地上下介质分层厚度时,对于中间馈电的天线,采用两端接地的方式比两端架空方式的天线性能好约0.485%。同样,改变大地上下介质层电导率时,采用天线接地的方式比架空的方式的性能好约0.385%。

可调频旋转磁场仪的装置设计与磁场测量

在教学演示仪器中利用三相交流电产生旋转磁场的传统方法存在仪器损耗大、安全隐患多、成本昂贵等问题。本论文设计了一种可调频旋转磁场的产生装置,在四个辐射状横放的带铁芯螺线管中通入低压直流电,通过PLC板编程对电流进行换向,同时改变换向时间可使置入装置中心的小磁针的偏转周期发生变化,从而达到可调频的效果。螺线管中通入单相恒定直流电时,小磁针不发生偏转;通入双相矩形脉冲电流时,小磁针以45°角步进旋转。磁场方向的转速取决于电流的换向频率。该装置不仅规避了传统方法的不足,且同时兼具定性演示和定量测量双重功能,可作为一款性能优异的实验教学仪器。

我国页岩气钻完井关键技术现状及发展趋势

页岩气作为一种重要的非常规天然气资源,其开采对能源行业和全球供需格局有着深远影响,深入研究钻完井技术体系是加快页岩气规模效益开发的关键。在概述全球及国内页岩气勘探开发现状的基础上,指出了我国在钻完井技术方面存在的挑战和提升空间;系统分析了我国在页岩气钻完井领域的关键技术进展,包括地质工程一体化导向钻井、丛式水平井钻井、井身结构优化、提速工具和优快钻井、精细控压钻井和高效固井技术等,以及这些技术在实际应用中取得的成效;讨论了在“碳达峰”“碳中和”背景下,加快页岩气钻完井关键技术攻关的重要性,提出了深化地质工程一体化研究、持续发展“一趟钻”钻井技术、加快推广丛式水平井钻井技术、持续优化低成本高性能钻井液体系和发展安全高效的优快钻井技术等发展建议,以期对我国页岩气钻完井关键技术水平的提高起到推动作用,提高我国在全球页岩气领域的竞争力。

水流与海浪对HATST功率性能的CFD模拟

为确保涡轮机的长期可靠性,在设计潮流涡轮机时应考虑海浪条件。使用直径为0.9 m的三叶片水平轴潮流涡轮机(Horizontal Axis Tidal Stream Turbine,HATST)作为基准模型,采用计算流体动力学(Computational Fluid Dynamics,CFD)开源软件OpenFOAM预测HATST在海浪和水流条件下的性能。对其进行网格依赖性测试以选择最佳网格数,捕捉流动特征。将生成的波浪轮廓与三阶Stokes波浪理论结果进行比较,发现模拟结果与理论结果一致。研究不同波频和波幅对HATST功率性能的影响,结果表明,波幅对功率性能的影响较为明显,波频的影响相对较小。

Development of A Depth-Integrated Longshore Current Model with Unstructured Grids

A depth-integrated model for simulating wave-induced longshore current was developed with unstructured grids. Effects of surface roller and horizontal mixing under combined waves and currents were incorporated in the numerical model. Recommended values of model coefficients were also proposed based on sensitivity analysis. Field observations and three series of laboratory measurements including two cases conducted on the plane beach and one implemented on the ideal inlet were employed to examine the predictive capability of this model. For the field case and laboratory cases conducted on the plane beach, numerical results were compared favorably with the measured data. For the case with an ideal inlet, simulated circulation pattern is supposed to be reasonable although some deviations between numerical results and measured data still can be detected.

Shear in Pacific’s Wide Warm Surface Currents

Within the two poleward wide warm surface currents that cross mid-latitudes on the eastern sides of the North and South Pacific Oceans, a single prediction is made that they have a horizontal velocity shear such that their mean speeds monotonically increase from east to west. This prediction is inspired mainly by a re-examination of the east/west asymmetric observations previously documented: the longitudinal maximum in sea surface temperature in the eastern parts of both oceans at mid-latitudes is located significantly west of the region of maximum mixed layer depths, which occur in the middle of these currents. Also the application of recent dynamical considerations discussed below stimulated the prediction, which include the application of Bernoulli’s law to streamlines in the flows as well as the geostrophic balance in the cross-stream direction. These caused the rethinking of an earlier explanation, which upon reflection now seems less suitable than the present one.

水平轴潮流能水轮机实验方法发展现状

潮流能可预测性强、能量密度大,具有广阔的开发前景。水平轴潮流能水轮机是发电效率最高的潮流能装置,世界各国对水平轴潮流能水轮机进行了大量实验研究。本文阐述了国内外水平轴潮流能水轮机的实验方法,包括实验设施、实验模型、实验平台和测量方法;并从均匀流和复杂环境两个方面对水平轴水轮机的模型实验现状进行总结和评价;分析目前水平轴潮流水轮机模型实验中存在的不足,并对未来的水轮机模型实验提出了一些建议,这对潮流能的开发具有重要意义。

卧式新建导管架张紧式外加电流阴极保护系统安装方案研究

目的填补卧式新建导管架平台施工技术的空白,同时解决张紧式ICCP系统在卧式新建导管架平台的工程应用问题。方法以张紧式ICCP系统在某卧式新建导管架的首次工程应用为背景,对张紧式ICCP复合缆-电极系统在该导管架上的陆上安装、导管架运输、海上安装等环节开展方案研究,设计出适用于卧式新建导管架张紧式ICCP系统的安装方案。结果为了保证卧式建造导管架张紧式ICCP系统的可靠安装,设计采用滑索牵引方法,并对复合缆-电极系统海上安装期的自存工况进行校核,可保障张紧式ICCP复合缆-电极系统的安全和顺利安装。结论该套张紧式ICCP安装方案不仅实现了张紧式ICCP在卧式新建导管架的首次工程应用,也为后续新建导管架张紧式ICCP系统的设计与安装提供了参考。

Experimental study of hydrodynamic performance of full-scale horizontal axis tidal current turbine

In this paper, experiments of both the model turbine （1 kW） and the full scale （10 kW） turbine are carried out in a towing tank and a basin, respectively, and the test of the full scale turbine on the sea is conducted. By comparison between the model turbine （D = 0.7 m） and the full scale turbine （D = 2.0 m）, it is shown that the maximum power coefficient increases with the increase of the diameter of the turbine. The test results on the sea are used to study the hydrodynamic performances of the horizontal axis turbine, and provide a basis for the design. Experimental results can validate the accuracy of the numerical simulation results.