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采用计算流体动力学(CFD)方法对OC4-DeepCwind半潜式风机基础在30~100 m水深下的水动力特性和非线性波浪荷载进行了研究。基于验证的数值波浪水池,通过结构自由衰减运动及规则波下浮式基础的幅值响应算子(RAO)计算,分析了浮式风机基础的结构动力特性及水动力特性随水深的变化规律,研究了浅水条件下非线性波浪荷载特征。研究结果表明,随着水深的减小,风机基础结构垂荡固有周期略有增大,垂荡和纵摇的阻尼比均呈现逐渐增大的趋势;与黏性流理论计算结果相比,势流结果在浅水波浪工况下对垂荡和纵摇RAO存在显著低估;在浅水波浪作用下,风机基础所受波浪荷载的三倍波频成分占比可超过5%,体现了浅水条件下波浪与结构之间较强的非线性作用。 相似文献
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以三浮筒(Tri-floater)型半潜式风机系统为对象,采用时域方法,考虑垂荡板的黏性阻尼效应,研究系泊缆直径、长度、预张力和布置方式等参数对其在风浪流中动力响应特性的影响规律,提出了一种系泊参数优化方法。在此基础上,根据东海和南海三个不同水深区域百年一遇海洋环境条件,通过调整Tri-floater型浮式基础的吃水和垂荡板等参数,有效地提高了其运动响应周期,减小了其运动响应幅值。同时,根据风机浮式基础运动幅值的设计规范要求,针对三个不同水深区域特点,设计了Tri-floater型浮式基础的系泊系统。计算结果表明,改进后的Tri-floater型半潜式风机系统能满足百年一遇极端环境下的作业要求,适合于东海和南海海洋环境下海上风能资源的开发。 相似文献
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针对一种新型全潜式浮式风机,应用FAST软件建立风电机组-塔筒-浮式平台-系泊系统的时域耦合分析模型,研究其在不同风况下的动力响应。计算结果表明:风速对于该浮式风机的动力响应影响明显,浮式平台的纵荡、纵摇以及风机叶片根部弯矩与风机在不同风速下受到的推力相关,由于新型全潜式浮式风机垂荡方向刚度很大,风速变化对于其垂荡运动影响相对较小;各风况下,系泊缆始终处于张紧状态,新型全潜式浮式风机运动幅值较小,具有良好的运动性能。 相似文献
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垂荡板对半潜式风机基础水动力性能有极大的影响,从而影响基础拖航安装过程的安全。为了研究垂荡板对半潜式基础拖航过程中运动响应的影响,建立了拖缆—WindFloat浮式风机半潜式基础拖航系统模型。首先,基于三维势流理论,采用AQWA开展了拖航系统的频域水动力分析,分析了垂荡板的尺寸及形状对基础水动力性能的影响规律;进一步采用时域方法对拖航系统的运动响应进行分析,探究了垂荡板的尺寸及形状在不同浪向下对基础运动响应的影响规律。结果表明:垂荡板能有效抑制基础的垂荡RAO,但垂荡板形状对基础的水动力性能无明显影响;具有圆形垂荡板的半潜式基础在拖航过程中的运动性能略优于六边形垂荡板,在原设计基础上继续增大垂荡板尺寸对基础运动响应的抑制效果呈现先增大后减小的趋势,说明半潜式风机基础存在一个最优的垂荡板尺寸。 相似文献
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采用多体动力学方法研究了H型浮式垂直轴风力机的动力特性。将风力机叶片和塔柱处理为柔性体,浮式基础处理为刚性体,考虑柔性体的非线性变形,由拉格朗日第二类方程建立了浮式风力机系统的非线性刚—柔耦合多体动力学方程。系统载荷包括浮式基础受的波浪力、风机叶片旋转时受到的气动载荷、塔柱受到的风压载荷、系泊力以及系统阻尼力。编制了模拟系统响应的数值计算程序,该程序可以考虑浮式风力机系统的刚—柔耦合和气动力—水动力耦合效应。以5 MW风力机为例,计算了叶片的固有频率;分析转速对叶片固有频率的影响;计算风、浪联合作用下浮式风力机系统的动力响应。结果表明,随着风机转速的增加,叶片切向固有频率增加、法向固有频率减小;在风、浪联合作用下,浮式基础运动以波浪频率为主,气动载荷贡献较小。 相似文献
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Chandralata Raghukumar G. Sheelu P. A. Loka Bharathi Shanta Nair C. Mohandass 《Marine Georesources & Geotechnology》2001,19(1):1-16
In order to assess the impact of deep-sea mining on the in situ benthic life, we measured the microbial standing stock and concentration of organic nutrients in the deep-sea sediments of the Central Indian Ocean Basin in the Indian pioneer area. Sediments were collected using box core and grab samples during September 1996. The total bacterial numbers ranged from 10 10 -10 11 cells per g -1 dry weight sediment. There was a marginal decrease in the number of bacteria from surface to 30 cm depth, though the subsurface section registered a higher number than did the surface. The highest numbers were encountered at depths of 4-8 cm. The retrievable number of bacteria were two orders less in comparison with the direct total counts of bacteria. An almost homogeneous distribution of bacteria, total organic carbon, living biomass, and lipids throughout the depth of cores indicates active microbial and benthic processes in the deep sea sediments. On the other hand, a uniform distribution of total counts of bacteria, carbohydrates, and total organic carbon in all the cores indicates their stable nature and suggests that they can serve as useful parameters for long-term monitoring of the area after the benthic disturbance. Further studies on temporal variability in this region would not only verify the observed norms of distribution of these variables but would also help to understand restabilization processes after the simulated benthic disturbance. 相似文献
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Derek V. Ellis 《Marine Georesources & Geotechnology》2001,19(1):51-63
This article reviews information recently available from existing marine and coastal mining for responses to environmental issues affecting marine mining at different depths. It is particularly but not exclusively concerned with those issues affecting seabed biodiversity impact and recovery. Much information has been gathered in the past 10 years from shallow mining operations for construction aggregate, diamonds, and gold, from coastal mines discharging tailings to shallow and deep water, and from experimental deep mining tests. The responses to issues identified are summarized in a series of eight tables intended to facilitate site-specific consideration. Since impacts can spread widely in the surface mixing layer SML, and can affect the biologically productive euphotic zone, the main issues considered arise from the depth of mining relative to the SML of the sea. Where mining is below the SML, the issue is whether it is environmentally better to bring the extraction products to the surface vessel for processing (and waste discharge), or to process the extraction products as much as possible on the seabed. Responses to the issues need to be sitespecific, and dependent on adequate preoperational environmental impact and recovery prediction. For deep tailings disposal from a surface vessel, there are four important environmental unknowns: (1) the possible growth of "marine snow" (bacterial flocs) utilizing the enormous quantities of fine tailings particles (hundreds or thousands of metric tons per day) as nuclei for growth, (2) the possibility that local keystone plankton and nekton species may migrate diurnally down to and beyond the depth of deep discharge and hence be subjected to tailings impact at depth, (3) the burrow-up capability of deep benthos and their ability to survive high rates of tailings deposition, and (4) the pattern and rate of dispersion of a tailings density current through the deep water column from discharge point to seabed. Actions to obtain relevant information in general and site-specifically are suggested. 相似文献
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G. Parthiban 《Marine Georesources & Geotechnology》2000,18(3):223-235
Particle fluxes were measured 7 m above the sea bottom during the predisturbance, disturbance, and postdisturbance periods by using time series sediment traps attached to seven deep-sea moorings deployed in the INDEX experiment site in the Central Indian Basin. The predisturbance particle fluxes varied between 22.3 to 55.1 mg m -2 day -1 . Increased and variable particle fluxes were recorded by the sediment traps during the disturbance period. The increase observed was 0.5 to 4 times more than the background predisturbance fluxes. The increases in particle fluxes (~4 times) recorded by the sediment trap located in the southwestern direction (DMS-1) were the greatest, which could be the result of preferential movement of resuspended particles generated during the deep-sea benthic disturbance along the general current direction prevailing in this area during the experimental period. Also, the traps located closer to the disturbance area recorded greater fluxes than did the traps far away, across the Deep Sea Sediment Resuspension System path. This variability in recorded particle fluxes by the traps around the disturbance area clearly indicates that physical characteristics such as grain size and density of the resuspended particles produced during the disturbance had an important effect on particle movement. The postdisturbance measurements during ~5 days showed a reduction in particle fluxes of ~50%, indicating rapid particle settlement. 相似文献
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Arne Schnack-Friedrichsen Angela M. Davis Jim D. Bennell Dei G. Huws 《Marine Georesources & Geotechnology》2001,19(4):221-243
The interdependence between the seismo-acoustic properties of a marine sediment and its geotechnical/physical parameters has been known for many years, and it has been postulated that this should allow the extraction of geotechnical information from seismic data. Though in the literature many correlations have been published for the surficial layer, there is a lack of information for greater sediment depths. In this article, a desktop study on a synthetic seafloor model illustrates how the application of published near-surface prediction equations to subsurface sediments (up to several tens of meters burial depth) can lead to spurious predictions. To test this further, acoustic and geotechnical properties were measured on a number of sediment core samples, some of which were subjected to loading in acoustically-equipped consolidation cells (oedometers) to simulate greater burial depth conditions. For low effective pressures (representing small burial depths extending to around 10 meters subsurface), the general applicability of established relationships was confirmed: the prediction of porosity, bulk density, and mean grain size from acoustic velocity and impedance appears generally possible for the investigated sedimentary environments. As effective pressure increases through, the observed relationships deviate more and more from the established ones for the near-surface area. For the samples tested in this study, in some instances increasing pressure even resulted in decreasing velocities. There are several possible explanations for this abnormal behavior, including the presence of gas, overconsolidation, or bimodal grain size distribution. The results indicate that an appropriate depth correction must be introduced into the published prediction equations in order to obtain reliable estimates of physical sediment properties for greater subsurface depths. 相似文献
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海上大直径钢管桩打桩过程中,桩周土体受到强烈扰动而发生强度弱化,掌握桩周土体强度弱化规律对于准确预测打桩过程、保证工程安全具有重要意义。为研究土体强度弱化规律,开展了环剪试验模拟打桩对桩周土体的扰动,测试土体强度随剪切速率的变化规律,建立了描述土体强度弱化规律的拟合公式,引入到打桩分析软件中。研究结果表明:土体的强度折减程度不仅与土体本身的性质有关还受到土体的埋深和剪切速率的影响,埋深越深土体强度折减程度越低,剪切速率越高土体强度折减越高,在打桩分析中可采用这里推荐的线性折减方法来模拟不同深度处土体强度的折减规律。 相似文献
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Geoacoustic Inversion via Genetic Algorithm and Its Application to Manganese Sediment Identification
An acoustic inversion method using a wide-band signal and two near field receivers is proposed and applied to multiple layered seabed models including a manganese sediment. The inversion problem can be formulated into a probabilistic model comprised of signals, a forward model, and additive noise. The forward model simulates wide-band signals, such as chirp signals, and is chosen to be the source-waveletconvolution plane wave modeling method. The wavelet matching technique, using weighted least-squares fitting, estimates the sediment sound-speed and thickness on which determination of the possible numerical ranges for a priori uniform distribution is based. The genetic algorithm is applied to a global optimization problem to find a maximum a posteriori solution for determined a priori search space. Here the object function is defined by an L 2 norm of the difference between measured and modeled signals. Not only the marginal pdf but also its statistics are calculated by numerical evaluation of integrals using the samples selected during importance sampling process of the genetic algorithm. 相似文献
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The advanced piston corer (APC) has been used by the Ocean Drilling Program since 1985 for recovering soft sediments from the ocean floor. The pullout force measured on extracting the core barrel from the sediment is shown to correlate with the average shear strength of the sediment core measured in the ship's laboratory. A simple rule of thumb is derived relating the shear strength of the sediment to the pullout force. Multiple APC holes at individual sites allow the consistency of the pullout measurements to be assessed. The effects of different operational procedures during APC coring are also explored. Although generally applicable, the correlation between pullout force and laboratory measurements of shear strength breaks down for some APC holes, possibly because of the disturbance of some sediment types during the APC coring process. A better understanding of the physical process of APC coring, and its effect on the properties of the sediment both inside and immediately outside the core barrel, would indicate what confidence can be put on the measurement of pullout force as a way of evaluating the in situ shear strength of deep sea sediments. 相似文献
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《海洋学报(英文版)》2014,(11):161-F0003
<正>Acta Oceanologica Sinica(AOS)is a comprehensive academic journal edited by the Editorial Committee of Acta Oceanologica Sinica and is designed to provide a forum for important research papers of the marine scientific community which reflect the information on a worldwide basis.The journal publishes scholarly papers on marine science and technology,including physics,chemistry,biology, 相似文献