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1.
《中国海洋大学学报(自然科学版)》2015,(6)
考虑内流作用利用功能原理建立顶张力立管涡激振动响应数值模型,采用尾流振子模型模拟涡激振动升力,利用Hermit插值函数将其离散得到立管振动响应的矩阵方程形式,运用Newmark-β法在时域内迭代求解其动力响应。在山东省海洋工程重点实验室进行了阶段流作用下的大长细比海洋立管涡激振动试验,对比数值模拟和试验结果表明该模型对于考虑内流作用的大长细比海洋立管涡激振动响应预报是有效的,为深水立管涡激振动研究提供一定的借鉴。 相似文献
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基于自主研发的紧致插值曲线CIP (Constrained Interpolation Profile)方法数学模型,对均匀来流条件时不同运动自由度组合下的串列双圆柱涡激振动问题开展二维数值模拟。模型针对雷诺数Re=100,质量比m*=2的串列双圆柱涡激振动问题,选取上、下游圆柱不同运动自由度组合工况进行模拟。重点分析圆柱的升阻力系数、运动位移随折合速度Ur变化的响应。研究表明:当上游圆柱双自由度运动时,随着下游圆柱运动自由度的增加,下游圆柱对上游圆柱涡激振动响应的影响减弱;当下游圆柱双自由度运动时,随着上游圆柱运动自由度的增加,上游圆柱对下游圆柱涡激振动响应的影响变强。研究结果表明圆柱运动自由度组合形式对串列双圆柱涡激振动的影响不可忽略。 相似文献
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圆柱涡激振动研究进展与展望 总被引：1，自引：0，他引：1
圆柱涡激振动广泛存在于机械工程、海洋工程等诸多领域,研究者们取得了许多研究成果,而系统综述圆柱涡激振动的论文距今已近10 a,因此,有必要对近10 a的研究进展进行系统分析。文中系统地总结了近10 a圆柱涡激振动研究成果,阐述了圆柱涡激振动的尾流模态和其对应的响应分支之间的因果关系,分析了影响圆柱涡激振动的关键因素(如质量比、阻尼比和雷诺数)对涡激振动响应的影响,介绍了圆柱涡激振动最大响应振幅的曲线拟合公式及其局限性,最后对圆柱涡激振动的研究方向提出建议。 相似文献
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针对双振子流致振动潮流能转换装置,基于ADINA软件对上游圆柱固定、下游圆柱横向振动的串列双圆柱流致振动,在不同工况下进行了数值模拟,并与文献和试验结果进行了对比分析,验证了该模拟方法的正确性并分析了不同因素(间距L=1.5 D~8.0 D、流速v=0.4~0.75m/s及相应流速v下的雷诺数Re=2.88×10~4~5.76×10~4)对下游圆柱流致振动的影响。结果表明,圆柱间距影响双振子尾流模式和下游振子振动形式;间距L=5 D~7 D范围内下游振子达到最大振幅,比单圆柱涡激振动增大50%。 相似文献
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预测圆柱涡激振动的尾流振子模型中,通常采用线性的耦合模型,例如位移或者速度、加速度耦合来表征结构对尾流的作用。三种线性模型在预测圆柱锁频阶段的动力特性时存在差异,而且适用范围也受质量比的限制。提出了考虑结构与尾流动力非线性耦合的模型,该模型基于加速度耦合并结合速度耦合进行修正,适用范围不受质量比的影响;与实验结果的对比表明该模型可以更合理地给出锁频区域以及结构位移响应和尾流升力。最后,利用新模型讨论了质量比对锁频阶段结构振动幅值、尾流升力及频率比的影响;结果表明,随着质量比的增大,结构锁频区域变窄,结构振幅和尾流升力幅值减小。 相似文献
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《中国海洋大学学报(自然科学版)》2010,(Z1)
基于MATLAB开发海洋立管涡激振动数值模拟系统NSVIV 1.0,系统采用尾流振子模型模拟外流对立管结构的作用,考虑内流对立管结构的影响,对立管的涡激振动动力响应和疲劳寿命进行预测分析。系统界面简洁清晰,使用方便,适用于顶张力立管,为进一步集成功能齐全的海洋立管设计分析软件打下基础。 相似文献
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海洋立管、海底管线和浮式平台系泊缆等柔性圆柱结构的流激振动会造成严重的疲劳损伤。目前,关于单根柔性圆柱流激振动的研究较多。为研究多根柔性圆柱系统的流激振动特性,开展了双柔性圆柱流激振动的模型试验。采用模态分析法将试验测量应变转化为位移。通过分析双柔性圆柱在并列、串列和交错排布方式下的响应位移、控制频率,揭示了双柔性圆柱的流激振动特性。研究结果表明:柔性圆柱并列排布时,两圆柱的相互作用使结构顺流向位移增大;柔性圆柱串列排布时,受遮蔽效应的影响,下游圆柱控制模态较低。由于柔性圆柱的多模态响应特性,"锁频"区后下游圆柱的位移并未显著增大;柔性圆柱交错排布时,下游圆柱发生"Wake-flutter",横流向和顺流向的控制频率接近,顺流向的位移显著增大。 相似文献
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深水浮式平台垂荡运动与水下柔性立管涡激振动的动力耦合 总被引：1，自引：0，他引：1
基于有限元数值模拟,进行了"平台垂荡-顶张力立管涡激振动"整体系统的动响应数值模拟。动响应模型考虑了立管尾迹流场的水动力与结构动力的耦合和垂荡引起的立管结构刚度的时变特性;分析了平台垂荡运动的频率、模态阶数等因素对水下顶张力立管涡激振动的影响。数值结果表明:与不考虑平台运动相比,立管的动响应位移会增大;立管响应幅值随着模态阶数的降低而增大;在响应过程中,尤其对于低阶模态,会出现响应的模态转换现象。鉴于在平台垂荡和涡激振动的共同作用下,立管的动响应会大于涡激振动、参数激励分别单独作用的响应,建议在立管实际工程设计中应该考虑平台运动和涡激振动耦合激励作用下的结构动响应。 相似文献
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悬跨海底电缆作为细长柔性结构,在静力平衡状态下具有一定的垂度,在水流作用下的涡激振动特性与海底管线和海洋立管等结构也有很大的不同,其振动模态受垂跨比影响很大。通过物理模型试验开展了不同垂跨比下悬跨海缆的涡激振动和疲劳损伤特性研究。试验模型按照水弹性相似准则设计,试验中测量了不同流速下海缆模型产生涡激振动时的应变历时数据,采用模态分析法获得了模型涡激振动时的振动模态和振幅。分析了不同流速下海缆模型的振动模态、应变和疲劳损伤的变化和分布特征。试验结果表明：垂跨比显著影响了海缆的涡激振动模态和应变幅值大小。在本试验流速范围内,对一定长度的悬跨海缆模型,当垂跨比较大时,随着流速的增大,模型涡激振动的主响应振动依次出现反对称1阶和对称1阶模态;当垂跨比较小时,模型涡激振动的主响应模态依次出现反对称1阶和对称2阶模态。当涡激振动主响应模态为反对称1阶时,疲劳损伤最大值达到0. 1~0.7。 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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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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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
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Oedometer tests have been carried out on 70 undisturbed surficial clays (at approximately 250 mm below the mudline), mostly collected by free-fall corers from sites widely scattered throughout the deep-sea North Atlantic. Acoustic measurements were also made, initially on contiguous samples and ultimately on the same sample using a geophysically instrumented oedometer which also collected electrical resistivity data. Apart from those quiescent areas below the carbonate compensation depth, such as north of the West Indies where very fine clays exist, most of the samples are silty clays whose geotechnical-geophysical properties are dependent on the type of clay minerals present (and their ability to take in moisture), the sand-size fraction, and the quantity of carbonate present. Thus the pure clays have high compressibilities which decrease on the addition of coarse particles, while the converse is true for the acoustic parameters, these increasing with the sand fraction. Using the notion of the intrinsic compression line for all samples, and comparison to it of the measured compression curves, it is clear that, contrary to some previously held ideas, most deep-sea clays are normally consolidated; the addition of carbonate has the effect of creating an open, stronger sediment skeleton. Interestingly, where information is available, the variation with depth of a sample's acoustic velocity follows the void ratio pressure relationship of the compression curve. This allows the construction of an in-situ sediment compression curve using the in-situ geophysical observations. 相似文献
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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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Phylogenetic diversity and phenotypic characterization of cultivable bacterioplankton isolated from polar oceans 总被引：1，自引：0，他引：1
A set of 27 marine planktonic bacteria isolated from the polar regions was characterized by 16S rDNA sequencing and physiological and biochemical testing. More than half of these bacteria were positive for caseinase, gelatinase and 13-glucosidase, and could utilize glucose, maltose or malic acid as carbon source for cell growth. Twelve isolates expressed nitrate reduction activities. Except for one antarctic isolate BSwlO175 belonging to Actinobacteria phylum, these isolates were classified as γ-Proteobacteria, suggesting that γ-Proteobacteria dominated in cultivable marine bacterioplankton at both poles. Genus Pseudoalteromonas was the predominant group in the Chukchi Sea and the Bering Sea, and genus ShewaneUa dominated in cultivable bacterioplankton in the Prydz Bay. With sequence similarities above 97%, genus Psychrobacter was found at both poles. These 27 isolates were psychrotolerant, and significant 16S rDNA sequence similarities were found not only between arctic and antarctic marine bacteria （ 〉 99% ）, but also between polar marine bacteria and bacteria from other aquatic environments （ ≥ 98.8% ）, including temperate ocean, deep sea, pond and lake, suggesting that in the polar oceans less temperature-sensitive bacteria may be cosmopolitan and have a bipolar, even global, distribution at the species level. 相似文献