Pipe laying simulation with an active reel drive

Dynamic and quasi-static models for analysis of a pipe lay spread are presented in the paper. Depending on the type of a pipe, spooling it on a big drum (reel) may cause plastic deformations. When the pipe is reeled out at sea, again it undergoes plastic deformations. In order to model such a nonlinear behaviour, a model, which includes both elasto-plastic material characteristics and large deformations, is required. Discretisation of the pipe is performed by means of the Rigid Finite Element Method (RFEM), which allows us to study static and dynamic problems, taking into account required properties of the model. Different sea conditions are simulated and analysed. It is shown how operational conditions can limit the ability of laying operation by a dedicated vessel, due to an unstable system response. The second part of the paper presents an upgrade of a passive reel drive by application of an active drive. In the model used for control applications, the pipe is modelled by a neural network. This allows us to perform a real-time calculations. In this fast-response calculation model, nonlinear aspects of the system are taken into account. The improvements in a pipe laying vessel performance are presented by some results of numerical simulations. The conclusions are also formulated.     

Genetic variation of the small yellow croaker (Larimichthys polyactis) inferred from mitochondrial DNA provides novel insight into the fluctuation of resources

The small yellow croaker (Larimichthys polyactis) belongs to the family Sciaenidae, which is an offshore warm fish species and widely distributed in the western Pacific. In this study, the variation of genetic diversity and genetic differentiation among L. polyactis populations was analyzed by mitochondrial DNA control region. A total of 110 polymorphic sites were checked, which defined 134 haplotypes. High level of haplotype diversity (h=0.993±0.002) was detected in the examined range. Population genetic structure analyse (analysis of molecular variance, F_st) showed there were high gene flow among L. polyactis populations. The result showed that there were relatively high genetic diversity and low genetic differentiation among the Yellow Sea and the East China Sea populations, which can be attributed to diverse habitats, wide distribution range and high mutation rate of control region. Using phylogenetic methods, coalescent analyses (neutrality tests, mismatch distribution analysis, Bayesian skyline analyses) and molecular dating interpreted in conjunction with paleoclimatic and physiographic evidence, we inferred that the genetic make-up of extant populations of L. polyactis was shaped by Pleistocene environmental impacts on the historical demography of this species. Besides, relatively constant genetic diversity and larger effective population size were detected in recent L. polyactis population. The result showed that the fishing policy certainly, such as the summer closed fishing, played a role in protecting resources of L. polyactis. This study can offer a wealth of biological novelties which indicates genetic structure of L. polyactis population and provides the foundation for resources protection and policy setting.     

Seismic Response Control of Offshore Platform Structures with Shape Memory Alloy Dampers

In this study, the seismic response control of offshore platform structures with Shape Memory Alloy (SMA) dampers is investigated. A new SMA damper and its restoring force medel are introduced for the calculation of seismic response reduction. Based on an actual platform structure and its mechanical medel, the parameters which may affect the rate of shock absorption are analyzed, such as the number, position and characteristics of the SMA dampers and the condition of the site where the platform is located. The results show that the SMA damper is an effective control device for offshore platforms and satisfactory control can be achieved by proper selection of the parameters.     

基于模糊评价理论的海洋工程采办过程风险分析方法研究

在具体研究了现代项目风险分析和风险管理常用方法基础上,将其中的事故树法、智爆法及风险指数致命度分析法相结合,利用模糊评价理论,建立了海洋工程采办过程风险分析方法。应用该方法对“曹妃甸11-1／2(CFD11-1／2)”项目的采办过程进行风险分析,得到了采办过程中的风险事故树及风险指数排序,并对风险指数较大的风险点提出建议及改进措施,进行风险规避,对工程实践起到了很好的指导作用。     

Small-scale fisheries reform: Expectations,hopes and dreams of “a better life for all”

This article follows the transformation process in the fishing industry with specific reference to the emergence of a limited commercial sector. In the policy domain, this sector was accommodated through a “one size fits all approach” to access rights, requiring it to compete with the large-scale commercial sector for the same resources. The strategies and actions of successful and unsuccessful applicants in four fishing communities in South Africa are examined. The paper identifies the key challenges facing the limited commercial sector as being the lack of skills to complete the application process, start up capital or credit, organisation and financial and business acumen. It highlights the disjuncture between the Marine Living Resources Act's stated aims of sustainability, equity and stability and the realities of implementation at a grassroots level.     

调谐质量阻尼器对海洋平台的减振效果分析

目前调谐质量阻尼器(TMD)的研究和设计多数是依据结构的第一阶模态进行的,忽略了TMD对结构其它模态的影响。为了明确TMD是否会对结构的高阶模态造成不利的影响以及影响的程度,论文采用模态分析法将海洋平台-TMD系统进行模态分解,推导出系统各阶模态的状态空间方程。并以一海洋平台为算例,讨论TMD针对结构的某一摸态进行设计时对各阶模态响应的减振效果,仿真的结果表明TMD对设计的模态有较好的减振效果,但对平台的其它模态响应的减振幅度有限,甚至产生不利影响,使某些模态的振动响应增幅较大。     

不同营养条件下铜绿微囊藻(Microcystis aeruginosa)和小球藻(Chlorella vulgaris)的生长竞争行为

蓝藻的暴发通常是藻类之间竞争的结果,了解环境中蓝藻与其它藻类的竞争特点和生存策略对揭示藻华暴发的机制及治理具有重要意义。本文以营养竞争为例,以铜绿微囊藻(Microcystis aeruginosa)和小球藻(Chlorella vulgaris)为受试对象,通过测定细胞密度、胞内C、N、P、S四种主要元素含量以及培养基中总氮(TN)、总磷(TP)的消耗,研究不同营养等级(超富营养、富营养、中营养、贫营养)以及单独N、P限制下两种藻在单独培养和共生培养条件下的生长特征和竞争行为。结果表明:(1)在超富营养、富营养、中营养、贫营养条件时,单独培养下的两种藻生物量与营养丰富程度呈正相关;(2)共培养条件下,在高营养水平时铜绿微囊藻在竞争中占优势,低营养水平时小球藻具有竞争优势;(3)胞内C、N、P、S的测定发现,随着营养水平的下降,两种藻胞内N、P的百分含量逐渐减少,而C、S并未呈现显著变化;(4)N限制时,铜绿微囊藻的半饱和常数Ks及最大比增长率μmax均大于小球藻;P限制条件下铜绿微囊藻的半饱和常数Ks小于小球藻,而最大比增长率μmax大于小球藻。综合分析,同一营养条件下,铜绿微囊藻竞争优势的先决因子是N,小球藻是P。因此,从营养竞争与生物适应力角度考虑,降低水体中富余的N或适当提高P的浓度可让小球藻获得竞争优势,对限制单一物种的形成具有平衡作用,可作为防治藻华的潜在方法。     

Adaptive Predictive Inverse Control of Offshore Jacket Platform Based on Rough Neural Network

The offshore jacket platform is a complex and time-varying nonlinear system,which can be excited of harmful vibration by external loads.It is difficult to obtain an ideal control performance for passive control methods or traditional active control methods based on accurate mathematic model.In this paper,an adaptive inverse control method is proposed on the basis of novel rough neural networks (RNN) to control the harmful vibration of the offshore jacket platform,and the offshore jacket platform model is established by dynamic stiffness matrix (DSM) method.Benefited from the nonlinear processing ability of the neural networks and data interpretation ability of the rough set theory,RNN is utilized to identify the predictive inverse model of the offshore jacket platform system.Then the identified model is used as the adaptive predictive inverse controller to control the harmful vibration caused by wave and wind loads,and to deal with the delay problem caused by signal transmission in the control process.The numerical results show that the constructed novel RNN has advantages such as clear structure,fast training speed and strong error-tolerance ability,and the proposed method based on RNN can effectively control the harmfid vibration of the offshore jacket platform.     

南海北部海域油气勘探保障建设选址适宜性研究

为分析南海北部海域油气勘探保障建设选址的适宜性,在广泛研究备选区特征资料的基础上,基于层次分析法(Analytic Hierarchy Process, AHP)原理,以自然环境因素、开发环境因素、基础设施与投资情况以及其他因素作为一级评判准则,建立了包括12项二级评判准则的递进层次结构模型,并以永兴岛、赵述岛和晋卿岛作为3个假定备选区,来验证分析评价模型的有效性和可靠性。AHP评判结果显示,3个备选区的整体优劣指数依次为0.587 1, 0.212 1, 0.200 8;AHP模型的一致性比例CR值为0.020 3。通过分析和筛选影响远海油气勘探保障建设的选址因子,构建基于AHP原理的选址评价模型,可用于分析评价南海北部岛礁油气勘探保障建设选址的适宜性。