动力定位船舶伪逆法与混沌粒子群法相融合的推力分配算法研究

动力定位船舶一般都装备冗余推进器,推力分配求解将直接影响最终定位的效果。针对伪逆法在推力分配中存在问题,提出一种把伪逆法和混沌粒子群法(CPSO)相融合的推力分配算法,该组合算法方便处理推力器各种限制条件,计算简单,能兼顾船舶的能耗及操作性,解决奇点问题。最后以某挖泥船为例,仿真结果表明该推力分配算法具备一定的实用指导价值,能有效提高船舶的定位性能。     

快速转向推进器推力优化分配研究

随着船舶推进技术的不断发展,动力定位船舶将更多地使用快速转向推进器以提高其定位性能。快速转向推进器的使用将引入大角度变化率,这会造成优化分配求解域明显的非凸性,给优化问题的求解带来了挑战。针对装备快速转向推进器的动力定位船舶,运用区域外切近似法对其推力分配的非凸性问题进行了凸化,采用增广拉格朗日乘子法对控制力进行了优化分配。仿真结果表明:推荐的凸化处理方法能有效地解决推力分配的非凸问题,分配算法可以充分利用快速转向推进器的机械性能优势,寻找更优的可行解,从而显著地减少动力定位船舶的能耗,提高其定位性能。     

单体喷水推进船舶动力定位控制方法研究

面向一型喷水推进器为动力定位执行机构的单体喷水推进船舶,开展了船舶仿真模型建立、推力分配及进一步动力定位相关控制算法设计与仿真模拟。针对传统的定步长Kalman滤波提出了改进方案,同时考虑到单体喷水推进船舶的特殊性,对推力分配算法进行了优化,并基于荷载前馈的PD控制算法开展了不同工况下的仿真试验。试验结果表明,所提出的喷水推进推力分配算法能够有效控制一型单体喷水推进船舶实现定点、定艏向、移位、转艏等动力定位典型功能,并具备一定抗外部干扰能力。     

半潜式平台动力定位系统推进器失效时域模拟

针对某最新的深水半潜平台,应用PID控制策略和卡尔曼滤波技术相结合的方法对其动力定位能力进行了研究,重点关注在两台推进器于不同时刻分别失效后的平台运动和推进器功率消耗信息。在平台的运动时域分析中,通过采用数值模拟与实验验证相结合的方法来获得平台的水动力数据;而在推力分配过程中,以最小功率消耗为优化目标,并考虑了推进器的机械物理特性及水动力干扰造成的推力损失对推进器的推力进行了分配。结果表明编制的模拟软件具有理想的模拟效果,该平台在指定海况下动力定位能力良好。     

基于人工神经网络的半潜平台动力定位系统推力分配策略研究

针对带有禁止角的半潜平台动力定位系统推力分配算法功率较大的问题,提出了一种基于人工神经网络拟合桨—桨干扰推力损失函数的序列二次规划推力分配算法。该方法考虑了半潜平台桨—桨干扰造成的推力损失,引入推力系数来表达推力损失。利用人工神经网络拟合推力系数,将推力损失加入到推力分配的数学模型中,取消了禁止角。采用序列二次规划求解推力分配数学模型。最后以某半潜式钻井平台为例,选取三种浪向角工况进行推力分配仿真模拟,结果显示该算法在高效分配定位所需推力的同时有效减小了功率消耗,应用前景广泛。     

推进器失效对深海采矿船动力定位性能的影响分析

深海中蕴藏着丰富的矿产资源,深海采矿船是深海采矿的重要装备,通过动力定位系统控制采矿船的海上位置,动力定位系统由若干推进器组成。采矿船在海上受到风浪流作用,推进器一旦失效极易发生采矿船运动失控等安全事故,本文研究推进器不同失效方式下动力定位性能,分析推进器不同失效方式动力定位功能的损失。根据势流理论计算波浪载荷,数值模拟深海采矿船不同位置的单个推进器失效和多个推进器失效方式下的时域运动响应,对比各种失效方式对深海采矿船纵荡、横荡、艏摇三个自由度运动的影响,分析各种失效方式对剩余推进器推力的影响。研究结果表明：采矿船空载90°浪向,推进器不同失效模式对于纵荡运动影响远小于对横荡和艏摇运动影响,船艉单推进器失效对于纵荡和艏摇动力定位的影响大于两个推进器失效影响;对于采矿船多自由度运动动力定位两个推进器失效大于单推进器失效影响;一侧两个推进器或两侧推进器同时失效,对动力定位的影响相同,对于横荡运动的影响最大。本文揭示了深海采矿船推进器失效对于采矿船运动的影响程度和机理,对于深海采矿船的安全作业具有指导意义。     

动力定位采矿船高海情下的运动响应分析

本文对具有动力定位深海采矿船高海情下的运动响应及运动特性开展研究。针对具有6个推进器构成的动力定位系统,考虑高海情及空载和满载两种典型工况,基于推力最小和运动最小条件,应用卡尔曼滤波器结合线性二次型最优控制理论的控制算法优化推力,进行动力定位系统的参数整定,实时优化调整推力的方向和大小,计算采矿船高海情下的运动和推力的时间历程响应和分析运动特性。经计算,得到了深海采矿船空载和满载工况在高海情下实施海上定位的浪向及需要的推力大小,确定了采矿船动力定位系统在高海情下的适应性,评估了高海情下深海采矿船的定位能力。     

船舶在平整冰区行进过程的离散元分析

船舶在冰区航行中,冰荷载是船舶结构设计和安全航行的重要影响因素。采用具有黏结破碎特征的离散单元法对船舶在平整冰区的航行过程进行了数值分析。在船舶破冰过程的离散元模拟中,平整冰由球形颗粒黏结而成,同时考虑了海水浮力和拖曳力对海冰单元的作用,颗粒间的黏结作用可在海冰与船体的相互作用过程中发生破碎;船体由三角形单元构造,分析了在海水浮力、推进器推力及海冰共同作用下船体的六自由度运动特性。通过船体与海冰相互作用的离散元分析,确定了船舶在破冰过程中海冰作用在船体上的冰荷载,探讨了船舶推进器推力和海冰厚度对冰荷载的影响,并与Lindqvist船体冰阻力经验公式进行了对比。     

动力定位系统的推力系统设计

在总结前人研究成果以及动力定位系统实例的基础上,提出推力系统设计方案,将之应用于动力定位系统的模型试验,并通过初步的动力定位模型试验验证了所设计的推力系统的有效性。     

全耦合S型铺管动力定位时域分析

为研究S型铺管船铺管工况下的动力定位系统性能,进行了船体-托管架-管道的耦合作用下的动力定位模拟。采用广义弹性面接触法模拟托管架上托辊,莫里森杆构建托管架模型,集中质量法计算管道受力,并应用PID和Kalman滤波相结合的控制系统和序列二次规划法进行分配的推力系统,进行了全耦合S型铺管动力定位时域分析;研究了船体波频运动对于管道-托管架耦合作用力和动力定位系统的影响;比较分析了铺管工况和非铺管工况下的定位精度影响;同时应用API规范对管道应力进行校核,验证了该耦合模拟的正确性。结果表明,垂荡和艏摇对于管道-托管架-船体之间的耦合作用力对动力定位系统影响很大,在动力定位系统设计时,需要着重考虑。减小纵摇和迎浪铺管是使铺管作业和动力定位系统安全有效的重要方法。     

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.     

Assessing the Validity of Seismo-Acoustic Predictor Equations for Obtaining Seabed and Sub-Surface Sediment Physical Properties

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.     

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.     

Interannual Sea Level Variations and Annual Tides in the Northwestern Pacific

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.     

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.     

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.     

Flow Cytometric Analysis of Coastal Lagoon Bacterioplankton and Picophytoplankton: Fixation and Storage Effects

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.