Wave load computation in direct strength analysis of semi-submersible platform structures

A wave load computation approach in direct strength analysis of semi-submersible platform structures was presented in this paper. Considering the differences in shape of pontoon, column and beam, the combination of accumulative chord length cubic parameter spline theory and analytic method was adopted for generating the wet surface mesh of platform. The hydrodynamic coefficients of platform were calculated by the three-dimensional potential flow theory of the linear hydrodynamic problem for platform with low forward speed. The equation of platform motions was established and solved in frequency domain, and the responses of wave-induced loads on the platform can be obtained. With the interpolation method being utilized, the pressure loads on shell elements for finite element analysis (FEA) were converted from those on the hydrodynamic computation mesh, which pave the basis for FEA with commercial software.A computer program based on this method has been developed, and a calculation example of semi-submersible platform was illustrated.Analysis results show that this method is a satisfying approach of wave loads computation for this kind of platform.

Sensitivity Analysis of Air Gap Motion with Respect to Wind Load and Mooring System for Semi-Submersible Platform Design

A design of semi-submersible platform is mainly based on the extreme response analysis due to the forces experienced by the components during lifetime. The external loads can induce the extreme air gap response and potential deck impact to the semi-submersible platform. It is important to predict air gap response of platforms accurately in order to check the strength of local structures which withstand the wave slamming due to negative air gap. The wind load cannot be simulated easily by model test in towing tank whereas it can be simulated accurately in wind tunnel test. Furthermore, full scale simulation of the mooring system in model test is still a tuffwork especially the stiffness of the mooring system. Owing to the above mentioned problem, the model test results are not accurate enough for air gap evaluation. The aim of this paper is to present sensitivity analysis results of air gap motion with respect to the mooring system and wind load for the design of semi-submersible platform. Though the model test results are not suitable for the direct evaluation of air gap, they can be used as a good basis for tuning the radiation damping and viscous drag in numerical simulation. In the presented design example, a numerical model is tuned and validated by ANSYS AQWA based on the model test results with a simple 4 line symmetrical horizontal soft mooring system. According to the tuned numerical model, sensitivity analysis studies of air gap motion with respect to the mooring system and wind load are performed in time domain. Three mooring systems and five simulation cases about the presented platform are simulated based on the results of wind tunnel tests and sea-keeping tests. The sensitivity analysis results are valuable for the floating platform design.

Conceptual Design of a Deep Draft Semi-Submersible Platform with a Moveable Heave-Plate

Based on the principle of turned mass damper(TMD) systems,the conceptual design of semi-submersible platform with a moveable heave-plate(MHS) has been put forward.The heave motion response amplitude operator(RAO) and viscous damping of the MHS platform are calculated by iteration,and the coupling stiffness between the MHS hull and the heave-plate is optimized to decrease the maximum heave motion response of the MHS hull under 10-year survival conditions in the South China Sea.The nu-merical results indicate that the heave motion RAO of the MHS hull can be decreased in the range of predominant wave frequencies,which may provide some reference to the heave motion control of offshore platforms.

Dynamic Performance of a Semi-Submersible Platform Subject to Wind and Waves

By applying experimental and numerical simulations, the motion performance of a semi-submersible platform with mooring positoning system under combined actions of wind and waves is studied. The numerical simulation is conducted by the method of nonlinear time domain coupled analysis, and the mooring forces are calculated by the piecewise extrapolating method. The scale in the model experiment is 1:100, and the mooring system of the model is designed with the method of equivalent water-depth truncation by comparing the numerical and the experimental results, the platform motion and mooring forces subject to wind and waves are investigated. The results indicate that the numerically simulated mooring forces agree well with the experimental results in static equivalent field, but show some difference in dynamic equivalent field; the numerically simulated platform motions coincide well with the experimental results. The maximum motion of the platform under operating conditions is 20.5 m. It means that the horizontal displacement is 2% less than the water depth, which satisfies the operating requirements.

Investigation of the Hydrodynamic Performance of a Novel Semi-Submersible Platform with Multiple Small Columns

This paper presents a novel semi-submersible(SEMI) platform concept, called the multiple small columns(MSC) SEMI that improves upon the hydrodynamic performance of the conventional SEMI. Unlike the conventional SEMI, the proposed MSC SEMI utilizes multiple small circular columns to support the deck and a large pontoon that increases the structural displacement. The novelty of the MSC SEMI is its reduction of the hydrodynamic load on the structure and suppression of its motion response, particularly in the heave direction. The MSC SEMI has the advantages of increasing the added mass, radiation damping, and natural period of the structure. A comprehensive investigation of the hydrodynamic performance of the novel MSC SEMI is conducted in both the time and frequency domains with a special focus on the resulting hydrodynamic load and motion response. Numerical simulation results demonstrate that the MSC SEMI concept can reduce the hydrodynamic load and motion response and improve the hydrodynamic performance of SEMIs as expected.

Structural Stress Monitoring and FEM Analysis of the Cutting Operation of the Main Bracket of A Semi-Submersible Platform

For a semi-submersible platform in repair, the eight old main brackets which connect columns with pontoons need to be replaced by new ones. In order to ensure the safety of the cutting operation of the old main bracket and calculate the initial stress condition of new main bracket, the structural stress monitoring of eight key spots is carried out, and then the calibrated finite element model is established according to the field monitoring results. Before cutting the main bracket and all associated structures, eight rectangular rosettes were installed, and a tailored cutting scheme was proposed to release the initial stress, in which the main bracket and associated column and pontoon plates were partly cut. During the cutting procedure, the strains of the monitoring spots were measured, and then the structural stress of the monitored spots were obtained. The stress variation characteristics at different spots during the initial cutting operation were shown and the initial stress condition of the monitored spots was figured out. The loading and support conditions of the semi-submersible platform were calibrated based on the measured initial stress condition, which made the finite element model more credible. The stress condition with the main bracket and associated structures being entirely cut out is analyzed by the Finite Element Method (FEM), which demonstrates the cutting operation to be safe and feasible. In addition, the calibrated finite element model can be used to calculate the initial stress condition of the new main bracket, which will be very helpful for the long-term stress monitoring on the main bracket.

Application of a Newly Built Semi-submersible Vessel for Transportation of a Tension Leg Platform

紧张腿站台(TLP ) 的交通组织因为长距离总是与一个重半运输容器的使用被联系了。这类容器的要求总是是特殊的，并且他们的可获得性是有限的。为华南海深海的工程的未来发展准备，中国近海油工程公司最近造了重电梯运输 vessel-Hai 杨实你 278。这个半能沉入水中的容器有 42 米的 50k DWT，和呼吸的一个排水量能力。理解容器适用性并且在未来为使用准备它深海的工程正在成为逼近的需要。这份报纸考察与 TLP 交通联系的当前的关键问题并且在装载外面和交通期间执行设计 TLP 的详细分析。新建 COOEC 交通容器 HYSY 278 被使用在华南在 Qingdao 从 COOEC 制造院子弄干 TLP 结构的运输到一块油地海。全部进程从制造院子，从容器，在长距离上的 TLP 的干燥运输，并且平台的最后的卸载卸载和平台的漂浮上的 landsite 包括了 TLP 结构的装载外面。水动力学和结构分析被执行评估运输容器和 TLP 结构的行为。特殊注意对与这个新容器的使用联系的批评区域被给予，与任何潜在的限制一起。结果证明 HYSY 278 能有效地被用于与合适的安排和准备得好的操作搬运结构。过程和细节根据学习结果被介绍。特殊注意也从分析基于结果被给未来使用的讨论。

Predictive Control and Implementation of Mooring Automatic Positioning System for Deepwater Semi-Submersible Platform

The automatic positioning control of mooring system for deepwater semi-submersible platform has become a key issue in the research and development field of deep-sea resources. The Dual-Stage Actuator (DSA) proposed in this paper can replace the single actuator to achieve the high speed and high precision positioning by cooperative control. The relative model and control algorithm of motion trajectory (CAMT) are designed and validated, which proves that the method proposed in this paper is effective.

Implementation of Mooring Automatic Positioning System for Deepwater Semi-Submersible Platform Based on Dual-Stage Actuator

The automatic positioning control of mooring system for deepwater semi-submersible platform has become a key issue in the research and development field of deep-sea resources. The Dual- Stage Actuator (DSA) proposed in this paper can replace the single actuator to achieve the high speed and high precision positioning by cooperative control. The relative model and control algorithm of motion trajectory (CAMT) are designed and validated, which proves that the method proposed in this paper is effective.

Hydrodynamic Comparison of a Semi-submersible,TLP,and Spar:Numerical Study in the South China Sea Environment

The South China Sea contains tremendous oil and gas resources in deepwater areas. However, one of the keys for deepwater exploration, the investigation of deepwater floating platforms, is very inadequate. In this paper, the authors studied and compared the hydrodynamics and global motion behaviors of typical deepwater platforms in the South China Sea environment. The hydrodynamic models of three main types of floating platforms, e.g. the Semi-submersible, tension leg platform (TLP), and Truss Spar, which could potentially be utilized in the South China Sea, were established by using the 3-D potential theory. Additionally, some important considerations which significantly influence the hydrodynamics were given. The RAOs in frequency domains as well as global motions in time domains under time-varying wind, random waves, and current in 100-y, 10-y, and 1-y return period environment conditions were predicted, compared, and analyzed. The results indicate that the heave and especially the pitch motion of the TLP are favorable. The heave response of the Truss Spar is perfect and comparable with that of the TLP when the peak period of random waves is low. However, the pitch motion of Truss Spar is extraordinarily larger than that of Semi-submersible and TLP.

Strength Analysis on Brace Structure for Semi-Submersible in Consideration of Wave Slamming

Slamming on bracings of column stabilized units shall be considered as a possible limiting criterion under transit condition based on the requirements in DNV-OS-C103. However, the wave slamming loads under survival condition were ignored for the strength analysis of the brace structures in many semi-submersible projects. In this paper, a method of strength analysis of brace structure is proposed based on the reconstruction and extrapolation of numerical model. The full-scale mooring system, the wind, wave and current loads can be considered simultaneously. Firstly,the model tests of the semi-submersible platform in wind tunnel and wave tanker have been carried out. Secondly,the numerical models of the platform are reconstructed and extrapolated based on the results of model tests. Then, a nonlinear numerical analysis has been conducted to study the wave slamming load on brace in semi-submersible platform through the reconstructed and extrapolated numerical model. For the randomness of wave load, ten subcases under each condition have been carried out. The value of the 90% Gumble distribution values of the ten subcases are used. Finally, the strength on brace structure has been analyzed considering the wave slamming. The wave slamming loads have been compared between the survival condition and transit condition with the method. The results indicate that wave slamming under survival condition is more critical than that under transit condition.Meanwhile, the wave slamming is significant to the structural strength of the brace. It should be overall considered in the strength analysis of the brace structure.

Numerical and Experimental Study on Hydrodynamic Performance of A Novel Semi-Submersible Concept

The Multiple Column Platform(MCP) semi-submersible is a newly proposed concept, which differs from the conventional semi-submersibles, featuring centre column and middle pontoon. It is paramount to ensure its structural reliability and safe operation at sea, and a rigorous investigation is conducted to examine the hydrodynamic and structural performance for the novel structure concept. In this paper, the numerical and experimental studies on the hydrodynamic performance of MCP are performed. Numerical simulations are conducted in both the frequency and time domains based on 3D potential theory. The numerical models are validated by experimental measurements obtained from extensive sets of model tests under both regular wave and irregular wave conditions. Moreover, a comparative study on MCP and two conventional semi-submersibles are carried out using numerical simulation.Specifically, the hydrodynamic characteristics, including hydrodynamic coefficients, natural periods and motion response amplitude operators(RAOs), mooring line tension are fully examined. The present study proves the feasibility of the novel MCP and demonstrates the potential possibility of optimization in the future study.

基于粘聚单元的层冰-海洋平台碰撞数值模拟

为研究海洋平台的抗冰性能,利用粘聚单元模型,构建层冰与半潜式海洋平台碰撞的有限元模型进行数值模拟,研究碰撞过程的冰力、结构吸能变化。随后进行粘聚单元参数敏感性分析,研究粘聚单元断裂能量释放率与牵引力-位移准则(TSL)曲线形式的变化对冰力的影响。结果显示,采用粘聚单元法模拟计算得到的冰力值与经验公式计算得到的冰力值偏差仅为2.2%,较为吻合,验证了粘聚单元法模拟层冰与海洋结构物碰撞过程的准确性;立柱外板是碰撞过程中平台的主要耗能构件,吸能占比82.67%;冰力值随着断裂能量释放率的增大而增大,但不同形式的TSL曲线对冰力值的影响十分有限。

风-浪-流激励下海上风电半潜平台-脐带缆动力特性分析

随着海上风电的迅速发展,海上风电机组呈现向深远海地区投放趋势。脐带缆作为电力传输的关键组件,在安装与工作时常年受到海流、波浪等载荷作用,为保证脐带缆能在生命周期内安全运行,需对其动力学特性进行详细分析。现有研究多关注脐带缆在波浪载荷作用下的动力学分析,鲜少涉及风、浪、流三相耦合及脐带缆与平台相互作用下脐带缆的动力学特性。为此,对近海地区200 m水深海上风电半潜平台脐带缆动力学特性进行研究,模拟近海海域情况,设计脐带缆结构及参数并建立半潜式海上风电平台、脐带缆模型,通过AQWA软件模拟不同海浪频率。风、浪、流同向作用时的极限海况下,半潜平台及脐带缆的响应情况,得到在随机波浪载荷及风、流载荷的作用下脐带缆的动力学参数。

波流-碎冰耦合作用下平台动力定位辅助系泊模型试验研究

为评估某极区半潜平台的作业安全,开展波流-碎冰耦合作用下冰区半潜平台动力定位辅助系泊的模型试验,对比分析风浪流-碎冰载荷联合作用下平台动力定位系统在有、无加速度反馈工况下的运动及系泊响应,验证加速度反馈策略的有效性。提出切换定位点消冰策略消除半潜式平台立柱前浮冰积聚的现象,对比开启消除浮冰功能前,平台系泊系统张力大幅降低,进一步提高了平台的作业安全。

风浪流载荷联合作用下半潜式风-流综合系统动态响应分析

以DTU 10 MW风力机、OO-Star半潜式平台以及550 kW潮流能发电机组成的半潜式风-流综合系统为研究对象,基于叶素动量理论和动态入流理论建立了风力机/潮流能发电机非定常气动力/水动力计算模型,并通过动态链接库(user_force64.dll)对AQWA二次开发建立了漂浮式风-流综合系统气动-水动-伺服-弹性全耦合仿真模型,研究了风浪流载荷联合作用下,潮流能发电机数量对平台运动、系泊张力和系统总功率的影响。结果表明:安装潮流能发电机数量越多,纵荡平均值越大,纵摇平均值越小,纵摇平均值最高可减小68.17%;3台潮流能发电机与浮式风力机组成的风-流综合系统,其上风向系泊最大张力增大约34.54%;所提模型能够有效提升系统的输出功率,安装3台潮流能发电机时,系统输出功率提升约15.94%。

基于实测数据的半潜式平台贝叶斯模型修正方法研究

随着半潜式平台的长期海上服役,平台的基本设计参数会发生变化,如仍基于原始设计参数对平台进行分析将影响结果的准确性。本文以半潜式平台服役中易发生变化的基本参数(平台排水量、重心高度和三个自由度回转半径)作为修正参数,以平台横摇、纵摇和垂荡自由度的方差和波频功率谱密度构建目标函数,建立可依据实测数据的半潜式平台贝叶斯参数修正方法。以我国某半潜式平台实测数据为例,开展平台的参数修正研究,并基于修正后的参数对平台多年一遇环境荷载下的响应进行对比评估。

基于无模型自适应控制的半潜式平台运动性能研究

南海海域油气资源极其丰富,半潜式平台在该海域工作时常常面临着系泊失效这一重大危险情况。该研究以一艘装配有悬链式系泊系统和DP-3动力定位系统的半潜式平台为研究对象,利用AQWA软件开展系泊失效前后半潜式平台运动性能研究。同时,借助于AQWA软件二次开发功能,将无模型自适应控制作为动力定位系统控制理论,以研究半潜式平台系泊失效后运动性能恢复。数值仿真模拟结果表明,采用无模型自适应控制作为动力定位系统控制理论的半潜式平台能很好地恢复系泊失效后的运动性能,有效地减小系泊失效带来的危害;基于偏格式动态线性化和全格式动态线性化的无模型自适应控制比基于紧格式动态线性化的无模型自适应控制能让半潜式平台更快地恢复运动性能。

考虑翘曲应力的半潜平台扭转极限强度计算方法研究

半潜平台由于结构和受力复杂,目前主要采用非线性有限元整体模型计算其扭转极限承载力,存在建模和计算时间较长、精度较差和不易收敛等问题。一方面进行半潜平台的整体有限元模型的简化研究,提高其计算效率和收敛性;另一方面基于薄壁杆件理论,将该半潜平台截面简化为单壁室截面计算其翘曲应力,提出了基于一跨模型且考虑翘曲应力影响的半潜平台约束扭转极限强度计算的简化增量迭代方法,并编制了相应的计算程序。计算结果表明,所提简化增量迭代方法计算精度较高,能很好地反应翘曲应力对半潜平台约束扭转极限强度的影响,大幅减少了计算约束扭转极限强度的时间,可用于半潜平台的设计。

“深海一号”半潜式生产储油平台长距离湿拖方案论证

针对“深海一号”半潜式生产储油平台拖航方案设计及工程实施面临拖航距离远、拖航路径环境恶劣、拖船资源选择少,以及作业风险高等众多技术难题,通过对比分析平台干拖和湿拖方案,重点分析湿拖过程中的拖航路线、平台吃水、湿拖阻力、拖船配置等关键技术问题,通过水池模型试验验证该方案的可行性,顺利实施了“深海一号”平台的长距离湿拖工作。