Predicting the capability-polar-plots for dynamic positioning systems for offshore platforms using artificial neural networks

As the capability of polar plots becomes better understood, improved dynamic positioning (DP) systems are possible as the control algorithms greatly depend on the accuracy of the aerodynamic and hydrodynamic models. The measurements and estimation of the environmental disturbances have an important role in the optimal design and selection of a DP system for offshore platforms. The main objective of this work is to present a new method of predicting the Capability-Polar-Plots for offshore platforms using the combination of the artificial neural networks (NNs) and the capability polar plots program (CPPP). The estimated results from a case study for a scientific drilling vessel are presented. A trained artificial NN is designed in this work and is able to predict the maximum wind speed at which the DP thrusters are able to maintain the offshore platform in a station-keeping mode in the field site. This prediction for the maximum wind speed will be a helpful tool for DP operators in managing station-keeping for offshore platforms in an emergency situation where the automation of the DP systems is disabled. It is obvious from the obtained results that the developed technique has potential for the estimation of the capability-polar-plots for offshore platforms. This tool would be suitable for DP operators to predict the maximum wind speed and direction in a very short period of time.     

基于海洋渔业发展的海洋科考船建造和应用

为提高我国海洋科考船的建造和应用水平,促进远洋和极地渔业发展,文章根据国内外海洋科考船的发展历史和现状,分析我国海洋科考船在海洋渔业发展中存在的问题以及海洋科考船的发展趋势,并提出相关建议。研究结果表明:国际海洋科考船发展早、数量多且装备先进;我国海洋科考船发展较快,但仍需提升数量和技术,在建和研发船舶具有世界领先水平;在促进海洋渔业发展方面,我国海洋科考船存在远洋和极地调查能力以及集成功能较弱的问题;基于海洋科考船在提高极地作业能力等方面的发展趋势以及海洋渔业发展需求,我国海洋科考船的建造和应用应加强顶层设计、技术应用和数据共享。     

Adaptive fuzzy controller design for dynamic positioning system of vessels

This paper develops an adaptive fuzzy controller for the dynamic positioning (DP) system of vessels with unknown dynamic model parameters and unknown time-varying environmental disturbances. The controller is designed by combining the adaptive fuzzy system with the vectorial backstepping method. An adaptive fuzzy system is employed to approximate the uncertain term induced by unknown dynamic model parameters and unknown time-varying environmental disturbances. It is theoretically proved that the proposed adaptive fuzzy DP controller can make the vessel be maintained at the desired values of its position and heading with arbitrary accuracy, while guaranteeing the uniform ultimate boundedness of all signals in the closed-loop DP control system of vessels. Simulation studies with comparisons on a supply vessel are carried out, and the results illustrate the effectiveness of the proposed control scheme.     

Feed-forward control for dynamic positioning in random waves based on quadratic impulse function and real-time wave measurement

The real-time estimation of second-order difference-frequency wave forces using real-time random-wave measurement is developed for the FF (feed-forward) control based dynamic positioning of floating offshore vessels and platforms. The efficacy of the developed FF control scheme is validated by using the in-house hull-mooring-riser-thruster fully coupled time-domain computer simulation program through comparisons with the results by the conventional feedback-control-only case. The feedback (FB) control intends to reduce the accumulated position-excursion error, meanwhile the proposed feed-forward control compensates the controllable slowly-varying wave loads by activating thrusters in advance based on the real-time estimation of the second-order difference-frequency wave loadings using the real-time signal of random incident wave. The real-time estimation of the second-order difference-frequency wave loads is done by using the double-convolution integral with pre-calculated QIF (quadratic impulse function). The numerical DP system is successfully implemented with the FF control algorithm in the vessel-thruster fully coupled time-domain simulation program. The developed schemes are applied to a turret-moored FPSO (floating production storage offloading) with six dynamic-positioning (DP) azimuth thrusters in two non-collinear storm conditions. It is clearly demonstrated that the developed FF control scheme performs much better than the conventional feedback-control-only case. The corresponding reductions in horizontal offsets, motions, mooring tensions, and fuel consumptions by using the developed FF control scheme are underscored.     

An Effective Control System of Thrust and Moment Modulation for a Dynamically Positioned Vessel

Dynamic positioning (DP) is an operation method whereby the position of a surface vessel is maintained in close proximity to a required position in the horizontal plane through the controlled application of forces and moments generated by purposely installed thrusters. When estimating thrust, this kind of conventional control system often uses many acceleration sensors, velocity sensors, environment sensors, and filters. Usually, these sensors have measured electrical errors. To reduce the number of sensors used and to decrease the measurement errors, this article presents an effective control system for estimating thrust and moment commands, which is based on energy and impulsemomentum principles. Donha and Brinati's example is followed to verify the feasibility of the present control system, which performs semisubmersible platform positioning using an LQG controller, and the results are feasible and economical. A simulated coring vessel marine positioning in southern Taiwan is presented, which can estimate the counterthrust and moment commands, and the complex environmental forces and moments are described. The results can provide a valuable control system for dynamically positioned vessels.     

An Effective Control System of Thrust and Moment Modulation for a Dynamically Positioned Vessel

Dynamic positioning (DP) is an operation method whereby the position of a surface vessel is maintained in close proximity to a required position in the horizontal plane through the controlled application of forces and moments generated by purposely installed thrusters. When estimating thrust, this kind of conventional control system often uses many acceleration sensors, velocity sensors, environment sensors, and filters. Usually, these sensors have measured electrical errors. To reduce the number of sensors used and to decrease the measurement errors, this article presents an effective control system for estimating thrust and moment commands, which is based on energy and impulsemomentum principles. Donha and Brinati's example is followed to verify the feasibility of the present control system, which performs semisubmersible platform positioning using an LQG controller, and the results are feasible and economical. A simulated coring vessel marine positioning in southern Taiwan is presented, which can estimate the counterthrust and moment commands, and the complex environmental forces and moments are described. The results can provide a valuable control system for dynamically positioned vessels.     

The optimum control of thruster system for dynamically positioned vessels

An offshore vessel with a dynamic positioning system (DP system) needs fast response to produce thrust to counteract the environmental forces acting on it for the purpose of maintaining its position and heading as close as possible to the working position. Therefore, quick and effective modulation of the thrust is the problem to determine the thrust and the rotation angle of the thruster devices of the ship. This paper presents an effective optimum control for a thruster system, using the sequential quadratic method to achieve economical and effective modulation of the thrust and the direction of the thruster. An optimum control study of a 2280 tons DP coring vessel with five rotary azimuth thruster marine positioning is studied in detail, which can quickly and exactly estimate the thrusts and angles of direction of all the thrusters. The results can provide a valuable thruster system for a dynamically positioned vessel.     

The Polar Floats Program

The Polar Floats Program, an adaptation of midlatitude SOFAR float technology to the polar regions, is used to monitor subsurface circulation patterns over large spatial and temporal scales as well as to track mesoscale features in near realtime. The program is comprised of three major components that are now under development: an 80-Hz float transducer, American and French sea-ice-deployable listening stations using ARGOS data telemetry (ARS and SOFARGOS, respectively), and the software needed for real-time tracking. The adaptation of SOFAR technology to the planar regime demands modifications of the existing design from both environmental and acoustical standpoints. The authors describe the development and use of SOFAR technology within a relatively small sector of the north polar region that encompasses several thousand kilometers around Fram Strait (located between Greenland and Spitsbergen)     

船舶机动定位技术及其实现方法

为改善动力定位船舶在高海情下的定位能力,研究了机动定位的控制方式,并设计了一种机动定位模糊控制系统。其特点是模仿人类的航海技巧,通过充分利用环境力,实现船舶的定位与机动。仿真结果表明,在高海情下,机动定位方式可以实现较高精度的定位控制,并且其辅推功率消耗较小。     

A new methodology developed by cetena to assess the seakeeping behaviour of marine vessels

The paper describes an analytical method to determine an operability index for a marine vehicle when its geometric characteristics, the geographical area in which the vessel is supposed to operate, and the limiting criteria for operations are known. The computer program based on strip theory provides reliable results not only for conventional hullforms, but also for catamarans, offshore vehicles, etc. The results are presented in the form of figures for different vessels, namely, crane barge, naval vessels and SWATH type catamarans. The authors are of the opinion that the proposed method would provide the designer with a valid tool to improve the seakeeping qualities of a vessel, while taking into account the limiting conditions imposed due to seaway operations.     

新型双船起重拆除平台试验研究

拆除大型海上结构物是一项非常复杂且充满挑战的工程。现提出一种新型海上平台拆除方案,该方案利用三条半潜船来代替具有重型起重装置的单一船舶,通过两艘相同的半潜船将平台上层建筑托起,随后运至第三艘半潜船上完成平台拆除。在风浪流作用下,半潜船和平台的所处方位和运动姿态一直处于动态变化中,这对船舶调节压载的稳定性以及双船运动的同步性提出了要求。为了确保该方案的高效性和安全性,设计了一套完整的模型试验装置,包括船舶模型、平台拆卸辅助设备、六自由度运动采集与分析系统、控制系统、无线通讯系统以及测量系统。开展了相应的水池试验,试验结果验证了双船起重拆除平台方案中双船协同运输这一关键环节的可行性和安全性。     

码头-缆绳-动力定位船舶耦合系统的时频特性分析

为研究系泊状态下动力定位船舶与码头及缆绳间的耦合作用,采取凝集质量法计算系泊缆索有效张力,设置弹簧阻尼单元用以计算码头碰垫间的非线性反力,应用比例-积分-微分控制系统(PID)进行推力控制。在系泊状态下,以动力定位船舶和无动力定位船舶为研究对象,分析了耦合系统中侧推器对消除因一阶波浪载荷而引起的船舶运动影响的作用;针对动力定位船舶,讨论了码头-缆绳及目标位置两个因素对动力定位船舶的定位能力及侧推器性能的影响。结果表明,在选取合理目标位置的情况下,耦合系统中的侧推器性能及动力定位船舶的定位能力均得到了有效提高。     

Polar marine biology science in Portugal and Spain: Recent advances and future perspectives

Polar marine ecosystems have global ecological and economic importance because of their unique biodiversity and their major role in climate processes and commercial fisheries, among others. Portugal and Spain have been highly active in a wide range of disciplines in marine biology of the Antarctic and the Arctic. The main aim of this paper is to provide a synopsis of some of the results and initiatives undertaken by Portuguese and Spanish polar teams within the field of marine sciences, particularly on benthic and pelagic biodiversity (species diversity and abundance, including microbial, molecular, physiological and chemical mechanisms in polar organisms), conservation and ecology of top predators (particularly penguins, albatrosses and seals), and pollutants and evolution of marine organisms associated with major issues such as climate change, ocean acidification and UV radiation effects. Both countries have focused their polar research more in the Antarctic than in the Arctic. Portugal and Spain should encourage research groups to continue increasing their collaborations with other countries and develop multi-disciplinary research projects, as well as to maintain highly active memberships within major organizations, such as the Scientific Committee for Antarctic Research (SCAR), the International Arctic Science Council (IASC) and the Association of Polar Early Career Scientists (APECS), and in international research projects.     

动力定位系统与单波束测深仪在科考船定点作业中的应用

科考船定点作业时会受到海洋风、涌、浪、流等外界环境因素影响，导致工作效率降低，原位测量精度下降，甚至影响作业安全。动力定位系统 （DP） 具有自动定位功能，能够抵抗外界环境因素的影响，可实现科考船高精度定点控位。 单波束测深仪不仅可以测量水深，也可反映水下设备深度信息，可以起到辅助监控水下设备功能。本文在介绍定点作业施工现状与局限性的基础上，分析 DP 系统与单波束测深仪工作原理，以“向阳红 01”船为载体，在定点作业时开启 DP 系统与单波束测深仪，发现该方法可以提高科考船定点作业工作效率、原位测量精度并保障作业安全，可为其他科考船定点作业提供参考。     

A finite element method for dynamic analysis of long slender marine structures under combined parametric and forcing excitations

This paper presents a numerical analysis of lateral responses of a long slender marine structure under combined parametric and forcing excitations. In the development of the 3-D numerical program, a finite element method is implemented in the time domain using the Newmark constant acceleration method. Some example studies are performed for various water depths, environmental conditions and vessel motions. The relative amplitudes of combined excitations to a conventional forcing excitation are examined. The response amplitude of a combined excitation is much greater than that of a forcing excitation in the even number of instability regions of the Mathieu stability chart. The results demonstrate that a combined excitation needs to be considered for the accurate dynamic analysis of long slender marine structures subjected to a surface vessel motion.     

Dynamic consequence analysis of marine electric power plant in dynamic positioning

Diesel-electric power and propulsion systems with electric thrusters are the industry standard for vessels with dynamic positioning (DP) systems. Diesel engines are paired with generators in generator sets and are used to produce electric power used by thrusters and main propellers during stationkeeping and transit, and other consumers such as hotel load, drilling drives, cranes, and heave compensators. Consequence analysis is used to verify the safety of a DP operation. It is used to check whether there is sufficient running power and thruster capacity available to retain sufficient thrust to maintain vessel position after a worst single failure. Recently, extensions of class rules enable standby generators to be considered in this analysis. This provides a more efficient configuration as relatively fewer generator sets may be running. However, DP performance is degraded during the transition from the fault occurrence until the plant is completely recovered. It is important to determine if this degradation leads to a loss of position during the transition. This study presents a simulation-based dynamic consequence analysis method that can be used to dynamically simulate fault scenarios such that the dynamics of the transient recovery can be analyzed. This analysis can be used for decision-support to configure marine electric power plants in DP. Results from the simulation study show that the currently used static consequence analysis method may provide non-conservative results under certain configurations.     

Performance of a northwestern Mediterranean bottom trawl fleet: How the integration of landings and VMS data can contribute to the implementation of ecosystem-based fisheries management

The European Union has established a framework to achieve or maintain good environmental status in the marine environment by 2020. The Marine Strategy Framework Directive requires the application of the ecosystem approach to the management of human activities, covering all sectors having an impact on the marine environment. However, fisheries in the Mediterranean are far from a systematic implementation of an ecosystem-based fisheries management (EBFM). Aiming to address this issue, this study explores the potential of the relationship between daily yield by vessel (landings and income by species) and vessel position (known via vessel monitoring system) as a tool for fleet management. This approach is possible due to the current dynamics of Mediterranean fleets, with vessels returning daily to the harbour where landings are registered as weight and income by vessel. Moreover, vessels of >15 m total length have been compulsory monitored by VMS since 2005. A bottom trawl fleet that operates in the northwestern Mediterranean was chosen to develop this approach. Different groups of trawlers were identified, which could be linked to the strategies displayed by the fishermen that were mainly driven by the target species dynamics. Accurate knowledge of the fishing targets driving the fleet dynamics and of the fishing strategies at the vessel level (i.e. fishing ground habitat where the fishing pressure is exerted and corresponding landings) are shown to be a feasible tool for fleet management.     

20th anniversary of the Institute of Marine Sciences and marine science in Tanzania — what next step

On July 1st 1999, the Institute of Marine Sciences (IMS), University of Dar Es Salaam celebrated its 20th anniversary. IMS was established as a lead institute for conducting advanced marine research and training in Tanzania. Its 20th anniversary accords us an opportunity to reflect on the advances of marine science in Tanzania. Being a coastal nation and by recognizing the importance and potentials of the ocean and coastal area, Tanzania, since its independence has been doing efforts to set-up sound marine policies and institutional framework and build the nation's capability, including human, in marine affairs. A careful study of Tanzania's marine science policies, institutional framework, and human capability indicates that the situation has improved satisfactorily, especially in human capacity. However, the country's capability in conducting basic and advanced marine science research remains poor due to the lack of a research vessel. The major problem has been the high construction and running costs of a research vessel. I am proposing two approaches from other countries, i.e., Japan, Germany, USA, and UK that can be adopted in Tanzania. Firstly, the research vessel can be acquired as a national resource, i.e., bought and owned by the government. Secondly, relevant and capable beneficiaries, departments, and organizations e.g., the navy, can buy the vessel and make it available to the marine science community. Acquiring a multipurpose marine research vessel is an important next step that Tanzania needs to make in marine science. I am also proposing formulation of a national policy to guide marine science research and development, and the establishment/selection of a lead agency with full authority to manage and supervise all marine and coastal area development/economic activities.     

Dynamic Positioning System Design for A Marine Vessel with Unknown Dynamics Subject to External Disturbances Including Wave Effect

China Ocean Engineering - In this paper, a new control system is proposed for dynamic positioning (DP) of marine vessels with unknown dynamics and subject to external disturbances. The control...