Experimental and theoretical study of a cylindrical oscillating water column device with a quadratic power take-off model

The wave power extraction by a cylindrical oscillating water column (OWC) device with a quadratic power take-off (PTO) model was studied experimentally and theoretically. In the experiment, a scaled model OWC was tested in a wave flume, with an orifice being used to simulate a quadratic PTO mechanism. In the theoretical analysis, the quadratic PTO model was linearized based on Lorenz's principle of equivalent work, which allows us to perform a frequency domain analysis using an eigen-function matching method. The effects of higher harmonic components and the spatial non-uniformity of the surface velocity inside the chamber were discussed. A semi-analytical model was proposed to understand the viscous loss affecting the measured capture length. Our treatment of the quadratic PTO model was validated by comparing quasi-linear theoretical capture length and the laboratory measurement. Our results also showed that the effects of spatial non-uniformity and viscous loss could be noticeable for shorter waves.     

CFD investigations of OXYFLUX device,an innovative wave pump technology for artificial downwelling of surface water

No other environmental variable of such ecological importance to estuarine and coastal marine ecosystems around the world has changed so drastically, in such a short period of time, as dissolved oxygen in coastal waters. The prevalent methods for counteracting anoxic sea events are indirect measures which aim to cut-down anthropic loads introduced in river and marine environments. To date, no direct approaches, like artificial devices have been investigated except the WEBAP and OXYFLUX devices. The present paper adopts a numerical approach to the analysis of the pumped surface water as well as the analysis of the dynamic response of the OXYFLUX device. By means of a CFD-RANS code and through the application of overset grid method, the 1/16 OXYFLUX model’s dynamic response and pumping performance are evaluated. The appropriate grid is selected after an extensive sensitivity analysis carried out on 9 different grids. The CFD model is validated by comparing numerical and physical results of heave decay test, heave response, and surface water discharge under the action of regular waves. The extensive comparison with experimental results shows consistently accurate predictions. The main findings of the study show that nonlinear effects remarkable reduce the dynamic behaviour of the OXYFLUX and generate an unexpected second harmonic for pitch response intensifying the overtopping discharge also for small waves caused by the summer's low intensity winds.     

基于OS071X测波雷达的波浪探测分析

文章利用舟山海洋环境监测站2014年第16号台风"凤凰"过境影响期间,对OS071X测波雷达和3m波浪浮标在同一海域内的波浪探测资料进行了对比验证。通过分析,OS071X测波雷达探测反演的有效波高、周期与3m波浪浮标探测结果对比,二者按先后顺序的均方根误差分别为0.27m和0.29m,相关系数分别为0.93和0.90。结果表明,OS071X测波雷达系统的探测精度得到了验证,能够满足实时探测近岸海域波浪的需求。     

Numerical Investigation of Submarine Hydrodynamics and Flow Field in Steady Turn

This paper presents numerical simulations of viscous flow past a submarine model in steady turn by solving the Reynolds-Averaged Navier?Stokes Equations (RANSE) for incompressible, steady flows. The rotating coordinate system was adopted to deal with the rotation problem. The Coriolis force and centrifugal force due to the computation in a body-fixed rotating frame of reference were treated explicitly and added to momentum equations as source terms. Furthermore, velocities of entrances were coded to give the correct magnitude and direction needed. Two turbulence closure models (TCMs), the RNG model with wall functions and curvature correction and the Shear Stress Transport (SST) model without the use of wall functions, but with curvature correction and low-Re correction were introduced, respectively. Take DARPA SUBOFF model as the test case, a series of drift angle varying between 0° and 16° at a Reynolds number of 6.53×106 undergoing rotating arm test simulations were conducted. The computed forces and moment as a function of drift angle during the steady turn are mostly in close agreement with available experimental data. Though the difference between the pressure coefficients around the hull form was observed, they always show the same trend. It was demonstrated that using sufficiently fine grids and advanced turbulence models will lead to accurate prediction of the flow field as well as the forces and moments on the hull.     

Driving forces and their interactions of built-up land expansion based on the geographical detector – a case study of Beijing,China

Scientific interpretation of the driving forces of built-up land expansion is essential to urban planning and policy-making. In general, built-up land expansion results from the interactions of different factors, and thus, understanding the combined impacts of built-up land expansion is beneficial. However, previous studies have primarily been concerned with the separate effect of each driver, rather than the interactions between the drivers. Using the built-up land expansion in Beijing from 2000 to 2010 as a study case, this research aims to fill this gap. A spatial statistical method, named the geographical detector, was used to investigate the effects of physical and socioeconomic factors. The effects of policy factors were also explored using physical and socioeconomic factors as proxies. The results showed that the modifiable areal unit problem existed in the geographical detector, and 4000 m might be the optimal scale for the classification performed in this study. At this scale, the interactions between most factors enhanced each other, which indicated that the interactions had greater effects on the built-up land expansion than any single factor. In addition, two pairs of nonlinear enhancement, the greatest enhancement type, were found between the distance to rivers and two socioeconomic factors: the total investment in fixed assets and GDP. Moreover, it was found that the urban plans, environmental protection policies and major events had a great impact on built-up land expansion. The findings of this study verify that the geographical detector is applicable in analysing the driving forces of built-up land expansion. This study also offers a new perspective in researching the interactions between different drivers.     

浮托安装进船过程中护舷碰撞力实测研究

浮托安装法广泛应用于大型组块海上安装。导管架平台上部组块浮托安装进船过程中,风、浪、流引起的浮托驳船横向运动造成浮托驳船与导管架桩腿的碰撞,碰撞力可能会对导管架结构造成损伤。陆丰7-2上部组块浮托安装中,为了监测碰撞力大小,设计了碰撞力海上监测系统。通过在导管架外侧四个桩腿上安装光纤光栅应变传感器对碰撞过程中导管架桩腿进行应力监测,进而计算碰撞力。对碰撞过程,载荷作用位置、方向进行简化,并对载荷大小及垂向作用位置对计算的影响进行了研究。结构分析模型简化后,测点von-Mises应力与碰撞力大小成正比,对导管架整体结构建模计算并取局部结构计算比例系数,结合应力实测数据计算出进船过程中驳船对导管架桩腿碰撞力。     

木本植被覆盖岸坡上波浪爬升过程的数值模拟研究

近岸木本植物构成的生态缓冲带作为新型的海岸软防护结构,兼具功能性和生态友好性,在沿海工程建设中愈发受到关注,如何深入开展其防护效果的机理研究是目前亟待解决的问题。本文采用数值模拟方法,在N-S方程中分别考虑树枝和树干的拖曳力影响,提出了木本植被作用下波浪沿斜坡爬升的表面波衰减的连续介质等效模型,并采用MAC法来跟踪自由曲面上的水颗粒轨迹。本文以波浪沿1/30的斜坡爬升为算例,对比讨论了有无植被作用下波浪的传播过程,并将算例结果与以往试验结果规律进行对照,验证了数值模型的有效性。最后,分别讨论了植物枝干的高度、密度、树枝倾斜角度等植被特性和波浪因素对植被消浪效果的影响,得到植被消浪的基本规律。文中的计算结果也可为实际的护岸工程和生态景观设计提供参考。     

日照港30万吨油码头船舶泊稳物理模型试验研究

日照港拟在岚北港区建设30万吨级原油码头,通过实验测定了船舶在风、浪、流作用下对码头结构的作用力、船舶运动量最大值、最大缆绳拉力、船舶对护舷撞击能量和撞击力,为工程结构设计和操船规程的制定提供可靠依据。     

中国高技能劳动力与一般劳动力的空间分布格局及其影响因素

基于2000和2010年全国人口普查分县数据和地级行政单元数据,采用不均衡指数和空间自相关分析等方法,刻画中国高技能劳动力和一般劳动力的空间分布格局及其变化,并采用空间滞后模型,识别高技能劳动力与一般劳动力空间分布的决定因素及其变化。结果表明：① 两类劳动力总体的空间特征均为东南密集,西北稀疏;② 2000—2010年,高技能劳动力在空间分布上呈集中化的趋势,而一般劳动力呈分散化的趋势;③ 十年间高技能劳动力集聚区虹吸作用加强,其分布越发集中于沿海特大城市群,而一般劳动力集聚区回波作用加强,其分布越发均衡;④ 空间回归分析结果表明,职工平均工资、是否直辖市或省会、每万人在校高校学生、是否沿海城市、常住人口数和空间溢出效应在十年中一直都是决定高技能劳动力和一般劳动力空间分布的主要因素,而失业率、中学生师比、二氧化硫排放量和绿地率在2010年也成为影响两类劳动力空间分布的主要因素。对比两类劳动力的模型结果可得,高技能劳动力的空间分布受行政因素、高校因素和地区生活舒适度的影响更大,而一般劳动力的空间分布受劳动力市场因素的影响更大。     

基于STIRPAT模型的内蒙古沙漠化地区环境压力分析

实现经济与生态环境的协调发展,已经成为当前治理沙漠化的巨大挑战。如何定量分析人类活动和自然条件对环境的影响,是当前环境经济学界研究的热点问题。以内蒙古自治区71个沙漠化县为研究对象,以1986-2010年为研究区间做面板空间计量实证分析。选取了人口、富裕度、技术水平、风速和降水作为环境基础指标构建STIRPAT模型,从环境压力内在驱动角度定量分析不同的自然因素和人为因素对沙漠化地区环境的综合影响。结果表明:在观测数据范围内,富裕度、技术水平、风速和降水是内蒙古自治区环境压力的主要驱动因素;富裕度每增加1%,环境压力显著增加0.096%;技术水平每变化1%,将引起环境压力相应发生0.084%的变化;风速和降水每变动1%分别使得沙漠地区环境压力显著地增加0.640%和减少0.216%。