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1.
依据波浪理论,分析了波浪经过网衣后的流体特性和边界条件,研究了网衣的波浪水动力、波浪透射系数与网衣尺度、特征参数、波浪参数等的关系。设计预加张力放射系泊法进行网衣构件水槽波浪试验。试验构件由10种PE网衣和HDPE框架装配而成,试验工况是规则波,周期为0·8—2·0s,波高为50—250mm。结果表明,作用在网衣上的水平波浪力变化规律与波浪基本一致,呈现周期性和不对称性变化;波浪力变化曲线呈现司托克斯二阶波形状,波峰较陡,波谷较平坦,和波面图相似;网衣水平波浪力周期峰值大约与波高的2·6次方、波长的0·8次方成比例,与网衣宽度l线性相关;随着特征参数d/a增大,网衣波浪力呈线性增加变化,透射系数减少,网衣消浪能力主要集中在网衣水表层。同时设计多层网衣组合的柔性浮式防波堤波浪试验,其消浪能力除了与网衣尺寸、特征参数等相关以外,还与网衣间隔距离有一定的关系。水槽试验时波浪最小透射系数下降到71%左右,从经济、实用角度表明,可用网衣来制作能防护渔业设施的柔性浮式防波堤。 相似文献
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方形网箱水平波浪力的迭加计算和实验验证 总被引：4，自引：3，他引：4
采用小直径圆柱体绕流理论和网渔具理论为基础的经验水动力计算法，分别考虑网箱框架是刚性体、网衣和绳索是柔性体的特征，结合正弦波理论对方形网箱及其构件受到的水平波浪力特性进行了分析研究，理论给出了波浪力迭加计算法，并把计算结果与小尺度的网箱水槽实验进行对比验证。结果表明，计算数值与试验数据较接近，平均误差率在15％以内。网箱水平波浪力呈周期性、不对称变化，在波浪周期小于0.72s时，主要以框架的波浪力为主，反之以网衣的为主。在波长为0.8m、周期为0.72s、水深为0.7m、波高为68.3mm情形下，计算结果显示网箱的框架尺寸和形状及其系泊、布局的选择应根据实际海况而定，网箱高度可适当增加，当设置水层下降深度相对于网箱高度比率为20％-40％，时，波浪力峰值下降相对率达68.03％-88.20％，表明可以较大程度地降低其波浪力。 相似文献
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利用基于开源平台Open FOAM自主开发的船舶与海洋工程水动力性能求解器naoe-FOAM-SJTU,数值模拟了近岛礁环境下规则波的演化特性以及带有系泊系统的浮式平台在相应波浪作用下的水动力性能。对于平台的水动力性能的研究发现,仿真结果与试验结果在平台自由衰减运动固有周期及RAO(response amplitude operator)方面吻合良好。对于波浪在近岛礁地形下的演化现象的研究,分析了波浪演化不对称性特性的成因,并分别给出了不同参数下波浪在地形上爬升时演化的具体特性,对于波高变化及波浪演化的频率成分进行量化的探究。研究发现,波浪周期越大,波高变化越明显,演化的非线性现象越明显,且波浪随着传播距离的增大演化出的阶数也在增大。 相似文献
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为了更加切合实际地研究鸭式波浪能转换装置的水动力特性及效率,考虑了鸭式装置可绕定轴转动以及装置的附加质量和附加阻尼,以ANSYS14.0软件为平台建立二维数值波浪水槽,对装置在不同波浪条件作用下的受力情况与运动情况进行了数值模拟与分析。结果表明:(1)在相同波高条件下,随着波浪周期的增大,装置受到的水动力力矩增大,转换效率下降,转换效率最高可达到70%;(2)在相同周期条件下,随着波高的增大,鸭式装置受到的水动力力矩也随之增加,波浪在经过装置后波高会发生衰减;(3)装置转换效率总体可维持在70%左右,但由于波峰到达装置时会有部分波浪从其顶部越过,随着波浪波高增大转换效率缓慢下降。为该装置的实际应用提供理论支持。 相似文献
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随着船舶大型化和港口建设深水化发展,外海不同周期波浪作用下大型系泊船泊稳问题与小型系泊船相比出现了新的特点。为此,利用数值模型方法研究了在不同入射角度和周期的涌浪作用下港内大型系泊船的水动力响应,针对系泊船的泊稳情况探讨了船舶的运动规律和运动特性。研究发现,在涌浪周期较大的情况下,限定波高的泊稳标准不足以用来确定系泊船的正常作业条件,港内泊船的水平运动（纵荡、横荡和艏摇）极易超出运动标准值并影响装卸作业效率,并且船舶的水平运动表现出主要由次重力波主导的低频运动特性,而垂直运动（垂荡、横摇和纵摇）表现出主要由短波主导的波频运动特性。 相似文献
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基于物理模型试验,探究畸形波和不规则波作用下浮体系泊张力差异问题。讨论相对波高、相对周期和畸形波参数α1对系泊张力的影响。结果显示:畸形波参数α1和浮体系泊张力显著相关。在α1=2.0～2.83范围内,畸形波作用下迎浪侧系泊张力最大值可达不规则波作用的1.9倍。在相对波高Hs/d=0.032～0.097范围内,畸形波作用下迎浪侧系泊张力最大值显著大于不规则波的作用结果,但畸形波和不规则波对应的1/3值及平均值几乎一致。就相对周期影响而言,迎浪侧系泊张力最大差别出现在谱峰周期Tp0p范围内。频域方面采用小波分析方法讨论畸形波和不规则波作用下浮体系泊张力时频谱特征,两种波浪作用下系泊张力时频特征有显著差别。 相似文献
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针对35万立方米超大型LNG-FSRU,采用软刚臂单点系泊系统定位方式,运用模型试验与数值计算两种技术手段开展风、浪、流联合作用下水动力研究。软刚臂系泊系统各构件间的连接方式及Yoke重量模拟是数值计算与模型试验的关键,数值计算对构件间的铰接方式与Yoke重量进行模拟,模型试验同样模拟了系泊系统的相似性,并将数值计算结果与模型试验结果进行对比分析。结果表明,软刚臂系泊系统刚度曲线呈非线性,试验结果与数值结果吻合良好,表明对于软刚臂系泊系统的两种模拟是合理的,反映了LNG-FSRU在风、浪、流联合作用下的运动特性,建立的研究方法可用于软刚臂系统的水动力研究。 相似文献
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在水槽中利用周期（１．０～１．９ｓ）、波高（８．６～１１．７ｃｍ）不同的规则波及波群塑造了沙纹。试验指出；１、沙纹的垂向形态指数及对称性指数符合标准浪成沙纹的相应值；２、沙纹的波长、波高、陡度与波浪水质点近底床水平运动方向的轨迹直径、波浪流的无量纲切应力、沉积物的活动性参数呈函数关系；３、沙纹的对称性与波浪的底部质量输移速率和水质点近底床的水平方向运动速率的比值有关。 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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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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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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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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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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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
18.
Shigehisa Nakamura 《Marine Geodesy》2000,23(1):55-61
Specific properties of the interannual sea level variations and annual tides in the Northwestern Pacific were studied. Several tide stations were monitored. The monthly mean sea level for the year of 1995 was analyzed at each tide station. A seismic event in 1995, some tectonic activity around the subject area, and the Kuroshio (the oceanic western boundary current) may possibly contaminate results which would have occurred from the astronomical annual tide alone. 相似文献
19.
The effect of different fixation and storage protocols on the flow cytometric (FCM) simultaneous analysis of bacterioplankton and phytoplankton in coastal seawater samples (Mediterranean coastal lagoons) was investigated. FCM measurements (cell number, fluorescence and scatter characteristics) were obtained through DAPI staining. Three fixatives [glutaraldehyde (GA), formaldehyde (FA) and paraformaldehyde (PFA)] and two storage (3 months duration) methods (5 °C and −196 °C) were tested. Two dominant populations were detected in studied samples: bacteria and eukaryotic picophytoplankton. Adding fixatives (2% final concentration) appears necessary to obtain FCM exhaustive counts of all the bacteria and phytoplanktonic cells. This was related to the permeation effect of fixatives which allowed a better DAPI staining of the cells. Maximum fluorescence, i.e. optimal staining of the cells was obtained with FA or PFA, and significant lower fluorescences with GA. Fixed samples stored at 5 °C induced rapid cell loss. Only storage in liquid nitrogen of samples fixed with FA or PFA, allows mid-term (≥4 months) preservation of bacteria or picophytoplankton cell numbers, and limited evolution of DAPI-induced fluorescence and scatter characteristics. 相似文献
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