海洋柔性立管弯曲加强器参数敏感性分析

针对海洋立管弯曲加强器所受环境载荷与功能载荷的特点,基于有限元法对某海洋柔性立管弯曲加强器结构进行数值分析。通过有限元分析软件建立了弯曲加强器与柔性立管组合等效模型,重点讨论了弯曲加强器的设计参数对其自身防弯性能的影响,根据弯曲加强器的曲率及柔性立管的应力分布,对弯曲加强器结构进行优化设计,得到结论可供设计参考。     

基于神经网络优化算法的海洋动态缓波型立管设计

柔性立管连接海上平台和水下生产系统,缓波型构型可以减轻其受到的顶部张力和疲劳损伤,触地点处系链对于固定水下立管起着重要作用,然而加装系链的缓波型立管系统设计更为复杂。通过缓波型基本理论计算出合理的立管初始状态,之后使用立管分析软件OrcaFlex,在充分考虑环境因素、船体结构、立管材料和线型以及重力块、浮力块、系链等配置参数的情况下,建立缓波型立管系统有限元模型,通过静动态分析验证其满足设定的关于立管构型、张力、弯曲半径,系链张力和FPSO偏移量5个约束条件。结合神经网络优化算法和遗传算法制定出针对文中立管系统的优化算法并通过MATLAB编程将浮力块数量优化至最少,之后基于L-M算法构建神经网络模型,通过迭代训练提升精度,得到最终参数优化结果。通过对比优化前后静动态分析结果可知：优化后浮力块数量大幅减少,立管最大有效张力大幅减小,而悬挂段最低点深度有一定程度的增大,整体构型更趋向于合理的缓波型构型。     

非线性海床土深水缓波型立管动力响应分析

缓波立管的结构形式能够有效改善立管触地区的动力响应,达到保护立管触地区的目的。基于集中质量法和考虑土体弱化的非线性海床土模型,用等效浮力的方法将缓波立管浮力段简化,并在Orca Flex中建立传统钢悬链线立管和缓波立管的集中质量模型进行分析,考虑立管结构形式、浮力段长度和浮力段起始位置的影响,得到立管静态位形、触地点张力和弯矩、立管贯入深度以及触地点海床阻力等结果进行比较。结果表明:浮力段的配置会提高立管静态弯矩分布水平,但合理的缓波立管设计能有效改善立管触地区的动力响应,抑制海底沟槽的发展,达到保护立管触地区的目的。     

基于缓波布置构型的深水立管动力优化机理研究

缓波型立管可以有效降低深水立管的顶端张力,缓解浮式结构运动对立管触地区的耦合作用,从而提高立管触地区的疲劳寿命。通过改进细长杆理论模型以及浮力段等效优化,提出基于多重波形串联布置的深水缓波型立管构型(简称多重缓波型立管),通过对比不同浮式结构垂荡激振以及海流作用下悬链线立管、缓波型立管以及多重缓波型立管的动力响应特征和运动传递路径,探究缓波布置构型对深水立管动力响应的影响规律和对立管触地区运动的解耦机理。结果表明:基于缓波布置构型的深水立管通过构建缓波构型可以大大降低立管触地区的法向运动响应,进而优化该区域的动态曲率及抗疲劳性能;相比于缓波型立管,多重缓波型立管在动态轴力及动态曲率等方面没有显著优势,但在触地区曲率幅值响应上具有一定竞争力。     

内孤立波与深海立管相互作用数值模拟

提出了一种对内孤立波与深海立管相互作用耦合数值模拟方法。流场采用内孤立波数值水槽方法进行模拟,结构响应采用基于薄壳理论的有限元方法进行计算,采用一种将流场和结构响应数据进行实时传输的方法,实现了流体与固体之间的耦合数值模拟。对内孤立波作用下某长径比为1 200的深海立管载荷及其动力响应特性进行了数值模拟与分析。结果表明内孤立波不仅会对深海立管产生突发性剪切载荷作用,而且还会使立管产生大幅度变形响应现象,因此在深海立管设计与应用中,内孤立波的影响是不可忽视的。研究表明,该方法为研究内孤立波作用下深海立管动力特性及其工程预报相关问题提供了一种有效的手段。     

非黏结柔性立管疲劳损伤特性分析

对柔性立管的疲劳损伤特性进行分析,探究抗拉层与抗压层的疲劳特性,并分析弯曲加强器的存在与否对柔性立管疲劳损伤的影响。研究表明:柔性立管最内层抗拉层上的疲劳损伤最大,从内到外,抗拉层的疲劳损伤依次减小;抗压层受到的疲劳损伤远小于抗拉层的疲劳损伤;弯曲加强器的存在可以减小立管的疲劳损伤,并改变抗拉层疲劳危险点的位置。     

深海钢悬链立管触地点动力响应分析

研究深海钢悬链立管(SCR)在海洋环境载荷作用下的动力响应.利用非线性弹簧模拟立管与海床触地点的耦合模型,通过模态分析得到钢悬链立管的动力特性参数;时域动力响应分析获得不同工况下触地点及典型部位的位移、弯矩和应力时程.比较分析表明:浮体垂荡运动对触地点的应力状态影响较大,触地点附近存在钢悬链立管动力响应过程中的位移极值点和弯矩极值点.所提方法为触地点区域模拟分析提供了新思路,给出的分析结论对钢悬链立管设计有一定借鉴意义.     

深水钢悬链立管疲劳寿命评估分析

在时域内分析深水钢悬链立管在平台运动和波流载荷共同作用下的非线性动力响应;采用雨流计数法处理立管节点应力的时间历程,选用DoE.E型S-N曲线分析立管在单一海况和平台运动联合作用下的疲劳损伤;将各方向含概率分布的疲劳损伤进行叠加,得到立管整体的全方向疲劳损伤及疲劳寿命。平台的运动为六自由度的运动预报数据,波流载荷由某海域实际的波浪统计数据采用Morison公式计算所得。计算结果表明钢悬链立管疲劳寿命的极值点分别位于悬挂点附近和触地点附近,对立管疲劳寿命极值点各方向疲劳损伤分布情况进行了分析。所提方法为钢悬链立管疲劳分析提供了新思路,给出的结论对钢悬链立管设计分析有一定借鉴意义。     

基于有限元方法的柔性立管防弯器疲劳寿命分析

防弯器是柔性管系统中的一个关键附件,其与柔性立管相互作用带来的非线性问题使得预测其疲劳寿命十分困难。以南海某油田柔性立管防弯器为例,采用ABAQUS建立了柔性立管与防弯器的“管中管”分析模型,模型中考虑了两者之间的间隙和滑动摩擦,以及材料非线性和接触非线性等因素。在加载方式上利用“位移”载荷取代传统的“力—角度”载荷,更符合工程实际。利用防弯器材料的ε-N疲劳试验曲线,结合防弯器的应力分析结果,得到危险截面的疲劳寿命。考虑材料非线性的管中管模型和疲劳寿命的计算方法,可为今后运动监测数据的利用和防弯器的优化设计提供借鉴。     

非金属柔性立管在海洋潮流下的动力响应特性研究

针对海洋柔性立管在服役期间,整体性能和运动响应受潮流影响较大的问题,本文在海上试验的基础上,采用OrcaFlex对长细比为448的非金属柔性立管模型进行了数值模拟。研究了潮流作用下,流速和流向的改变对于非金属柔性立管受力情况、涡激振动(VIV)响应特性和控制模态的影响。研究结果表明:潮流流向对立管顶张力、曲率和立管整体VIV响应有着显著影响,随着流速增加呈现不同变化规律。柔性立管悬垂段在高流速下更容易激发高阶模态,并呈现出明显的行波特性;立管的悬挂点和触底点为危险区域,随着流向改变易发生疲劳破坏。研究结果对海洋柔性立管总体布置设计具有参考意义。     

Microbial Biomass and Organic Nutrients in the Deep-Sea Sediments of the Central Indian Ocean Basin

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.     

海上大直径钢管桩打桩过程中桩周土强度弱化研究

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。     

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.     

A Review of Some Environmental Issues Affecting Marine Mining

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.     

Increased Particle Fluxes at the INDEX Site Attributable to Simulated Benthic Disturbance

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.     

Determination of In Situ Sediment Shear Strength from Advanced Piston Corer Pullout Forces

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.     

Phylogenetic diversity and phenotypic characterization of cultivable bacterioplankton isolated from polar oceans

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.     

Deep-Sea Sediment Compression Curves: Some Controlling Factors, Spurious Overconsolidation, Predictions, and Geophysical Reproduction

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.