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1.
Offshore floating facilities are fixed by anchoring systems embedded in seabed soils through chains or ropes. The chain inverse catenary profile embedded in soils influences both the anchor failure mechanism and the anchor holding capacity. The chain mobilizes varying soil normal and tangential resistances during motion, hence it is with difficulty to depict the chain profile. The present work proposed a modified method to estimate the chain inverse catenary profile with high accuracy based on the chain equations and the chain yield envelope. A testing arrangement with three load cells and two MEMS (Micro-electromechanical systems) accelerometers included was designed in model tests. By model tests, the loading combinations of the soil tangential and normal resistances on the chain were obtained and the yield envelopes for both chain and rope were determined. In addition, supplemental model tests were performed to validate the modified method proposed in this study, and the testing results indicated that the estimated chain inverse catenary profile was in good agreement with the actual one. Moreover, the testing arrangement is beneficial in investigating the chain-soil-anchor interaction. 相似文献
2.
Mooring systems typically consist of an anchor and a mooring line and chain that connect the anchor to the floating infrastructure. When the anchor connection point (the ‘padeye’) is below the seabed surface, the interaction between the chain and the seabed will affect the amount of load transferred to the anchor and the load angle at the padeye. Reliable methods are needed therefore to assess these aspects in order to determine appropriate anchor design.Available solutions for the interaction between soil and chain generally ignore any reduction in the undrained shear strength of the soil as it is remoulded under the large strains associated with tensioning of the anchor chain. This is an unconservative assumption for anchor design, hence providing motivation for the study presented here. The system behaviour and the interaction of short chain segments with the seabed have been studied using a coupled Eulerian-Lagrangian (CEL) approach. The findings have led to two new design approaches that encapsulate how remoulding of the soil (which affects sliding resistance more than bearing resistance) affects the chain system response. Calculations using these methods captured the modelled chain system response well. Both the global chain analyses and the proposed design approaches suggest that approximately the entire chain load at the seabed surface (the ‘mudline’) is likely to be transferred to the anchor padeye, challenging conventional design practice. 相似文献
3.
Drag anchor is one of the most commonly used anchorage foundation types. The prediction of embedded trajectory in the process of drag anchor installation is of great importance to the safety design of mooring system. In this paper, the ultimate anchor holding capacity in the seabed soil is calculated through the established finite element model, and then the embedded motion trajectory is predicted applying the incremental calculation method. Firstly, the drag anchor initial embedded depth and inclination angle are assumed, which are regarded as the start embedded point. Secondly, in each incremental step, the incremental displacement of drag anchor is added along the parallel direction of anchor plate, so the displacement increment of drag anchor in the horizontal and vertical directions can be calculated. Thirdly, the finite element model of anchor is established considering the seabed soil and anchor interaction, and the ultimate drag anchor holding capacity at new position can be obtained. Fourthly, the angle between inverse catenary mooring line and horizontal plane at the attachment point at this increment step can be calculated through the inverse catenary equation. Finally, the incremental step is ended until the angle of drag anchor and seabed soil is zero as the ultimate embedded state condition, thus, the whole embedded trajectory of drag anchor is obtained. Meanwhile, the influences of initial parameter changes on the embedded trajectory are considered. Based on the proposed method, the prediction of drag anchor trajectory and the holding capacity of mooring position system can be provided. 相似文献
4.
内孤立波中半潜平台动力响应特性 总被引：1，自引：1，他引：0
基于内孤立波mKdV理论,采用时域有限位移运动方程,结合改进的Morison公式,研究了两层流体中内孤立波与带分段式悬链系泊约束半潜平台的相互作用问题。针对东沙群岛南部海域附近某实测内孤立波特征参数,计算分析了在该内孤立波作用下SEDCO-700型半潜平台的内孤立波载荷、运动响应及其系泊张力的变化特性。研究表明,内孤立波不仅会对半潜平台产生突发性冲击载荷作用,使其产生大幅度水平漂移运动,并导致其系泊张力显著增大,因此在半潜平台等深海平台的设计与应用中,内孤立波的影响是不可忽视的。 相似文献
5.
ABSTRACTThe OMNI-Max anchors are newly developed dynamically installed anchors for deep water mooring systems. After installation, the anchor is keyed to a new orientation and position by tensing the attached mooring chain, which is known as the “keying process”. This study conducted 1g model tests to study the trajectories and capacity developments of OMNI-Max anchors in homogeneous and lightly overconsolidated (LOC) clays. A testing arrangement was designed to simulate the anchor keying process with a constant pullout angle at the mudline. A half model anchor which could move against the box glass was used to determine the anchor trajectory in the soil. The effects of padeye offset angle, uplift angle at the mudline, anchor fluke thickness, anchor initial embedment depth, and soil strength on the anchor trajectory and capacity were systematically investigated. Moreover, the critical uplift angle at the padeye and the anchor critical initial embedment depth were discussed. The results indicate that the anchor can dive both in homogeneous and LOC clays under certain conditions. A padeye offset angle of 24–30° is recommended for the OMNI-Max anchor to maintain high capacity and diving trend simultaneously. Besides, the anchor diving trend can be improved with small uplift angles at the mudline and with thick anchor flukes. A critical initial embedment depth of 1.3 times the anchor length is recommended to preclude the anchor from being pulled out. 相似文献
6.
法向承力锚(Vertically Loaded Plate Anchor,VLA)是一种适用于深水的新型系泊基础,它的拖曳安装过程直接决定了其系泊定位的精度和锚体的最终承载能力。综合考虑VLA锚体、锚泊线和上部船体的运动,建立了一种新的准静力整体分析模型。模型包括不断贯入海床的锚体、锚泊线(土中反悬链段和水中悬链段)和安装船体三部分,针对确定的锚泊线长度,安装船运动张紧锚泊线进行安装的过程,计算了此过程中锚体的运动轨迹、锚泊线形态和作用在船体上的锚泊线张力矢量的变化,重点分析了不同抛链长度和海床土体的参数对安装过程控制的影响,发现链长与水深之比达到5时,接近极限贯入深度。 相似文献
7.
由于浅水深条件下悬链线系泊系统的性能对系泊缆长度和几何形状更为敏感,悬链线系泊系统的安装误差对其性能的影响较深水条件下的更为显著。因此首先对适用于半潜漂浮式风机的悬链线系泊系统施工进行研究,分别确定了锚安装位置误差、系泊缆预铺误差和系泊缆与漂浮式基础回接误差的来源,并根据施工条件给出了误差值。之后,以浮体动力学仿真作为手段,对系泊缆系统施工误差对其性能的影响进行基于时域仿真的量化研究。研究表明,锚安装位置误差对系泊系统性能影响不大,但系泊缆预铺和回接的误差对系泊系统性能的影响较大。系泊缆回接的误差可造成系泊缆张力平均值和标准差与设计值偏差近20%,可能对系泊系统疲劳寿命评估产生较大的影响。与系泊缆回接误差相比,系泊缆预铺误差的产生原因更为复杂,由于系泊缆预铺误差往往导致系泊缆长度增长,存在误差的系泊缆张力的各项统计值总体偏小,但可能会造成同组无误差系泊缆的张力过载。 相似文献
8.
拖曳锚由于其承载性能和深水中便于安装被广泛应用于海洋工程系泊系统中,如:适用于悬链式系泊系统的传统拖曳锚和适用于绷紧式系泊系统的法向承力锚。拖曳锚安装过程中涉及诸多运动特性:锚板运动方向、系缆点处拖曳力和拖曳角及运动轨迹。基于大变形有限元分析技术耦合的欧拉-拉格朗日法,并引入缆绳方程,建立起锚-缆绳-海床土耦合作用的有限元分析模型;模拟了拖曳锚在均质和线性强度黏土中的嵌入安装过程,研究了锚板运动方向、系缆点处拖曳力和拖曳角及运动轨迹等运动特性;通过与已有的有限元分析方法及理论方法进行对比,验证了该分析模型的有效性;与已有的有限元分析方法相比,提出的分析模型有效地提高了计算效率。 相似文献
9.
海上浮式风力机受风、浪、流等外部载荷影响,运营期间经常处于偏航工况,给风力机基础运动响应和锚泊载荷带来重要影响.基于经典叶素动量理论及势流理论,建立海上浮式风力机水—气动力耦合分析模型,对在非定常风、不规则波浪联合作用下,风力机偏航时基础运动响应及锚泊载荷等进行分析.研究发现,额定风速工况下,风力机偏航对平台纵荡和纵摇运动影响较大,偏航30°时纵荡和纵摇平均值比偏航0°时分别下降20.68％和37.36％,垂荡运动响应受风力机偏航影响较小;锚泊载荷变化趋势与平台运动及锚链布置有关,平台纵荡对锚泊载荷影响较大,偏航30°时锚链#1有效张力平均值比偏航0°时下降12.98％. 相似文献
10.
参考英国的Kincardine风机采用的新式的Semi-Spar概念,结合spar式基础和半潜式基础的特点,提出了一种新式海上浮式风机平台模型,并基于三维势流理论,利用AQWA软件进行水动力计算,验证新式平台可靠性。分析了在风、浪、流荷载联合作用下,锚链竖向夹角、系缆数量对风机浮式平台运动性能和系泊张力的影响,对系泊系统进行优化,并验证极端工况下的可靠性。结果证明风机平台水平运动和纵摇运动幅值较小,但垂荡幅值略大,而通过减小锚链竖向夹角可以控制平台运动响应幅值,增加系缆数量可以同时减小系泊张力大小。计算结果证明了新型Semi-Spar式海上风机平台可行性,为浮式风机平台及系泊系统的设计提供参考。 相似文献
11.
The experimental and theoretical investigations on the behaviour of pontoon-type floating breakwaters are presented. A two-dimensional finite element model is adopted to study the behaviour of pontoon-type floating breakwaters in beam waves. The stiffness coefficients of the slack mooring lines are idealized as the linear stiffness coefficients, which can be derived from the basic catenary equations of the cable. The theoretical model is supported by an experimental programme conducted in a wave flume. The motion responses and mooring forces are measured for three different mooring configurations, and the results are reported and discussed in detail in this paper. The wave attenuation characteristics are presented for the configurations studied. 相似文献
12.
With the application of innovative anchor concepts and advanced technologies in deepwater moorings, anchor behaviors in the seabed are becoming more complicated and pose a great challenge to the analytical methods. In the present work, a large deformation finite element (FE) analysis employing the coupled Eulerian–Lagrangian technique is performed to simulate the installation/mooring line, and then is applied to analyzing comprehensive anchor behaviors in the seabed. By connecting cylindrical units with each other using connector elements, the installation/mooring line is constructed. With the constructed installation/mooring line, FE simulations are carried out to investigate comprehensive anchor behaviors in the seabed, including long-distance penetration of drag anchors, keying of suction embedded plate anchors and non-catastrophic behavior of gravity-installed anchors. Through comparative studies, the accuracy of the proposed method is well examined. A parametric study is also undertaken to quantify the effects of the frictional coefficient, initial embedment depth, and soil weight on the profile of the embedded anchor line and the shackle load. The present work demonstrates that the proposed FE model, which incorporates the installation/mooring line and the anchor, is effective in analyzing the comprehensive anchor behaviors in the seabed. 相似文献
13.
系泊系统是半潜式支持平台抵抗恶劣海洋环境作用、限制平台偏移、实现海上定位的重要设备，辐射状多点系泊是常用的布置方式。针对该平台系泊系统开展了设计方法和分析流程研究，阐述了系泊系统配置设计，包括系泊缆的数量、抛出长度、单根系泊缆的刚度、直径、破断负荷、定位锚的型式、最大抓力等；系泊系统的布置设计，包括系泊缆之间的水平夹角、系泊绞车、导缆器、定位锚的位置等；同时归纳风载荷、流载荷以及波浪慢漂载荷的常用估算方法；总结适用于该类平台系泊系统设计的规范要求。将上述方法和流程应用于某型半潜式支持平台系泊系统的开发和设计，采用系泊定位分析程序MIMOSA对该系统的定位能力进行分析，研究了系泊缆形状、夹角等参数随张力的变化特征，同时系泊缆按照船级社的规范要求进行衡准，反复调整和优化系泊系统的配置和布置方式，直至系泊系统满足要求，最终设计出较合适的系泊系统。相关方法、流程和结论为实际工程项目提供重要的设计思路。 相似文献
14.
从提高锚泊系统收放时效性入手,提出了一种半潜式钻井平台复合式锚泊系统组分配比优化设计方法,旨在尽可能降低复合式锚泊系统的钢链配比长度,提高收放效率。结合锚泊系统设计参数,制定优化设计准则,建立优化分析流程,采用ANSYS-AQWA建立锚泊定位半潜式平台水动力分析模型,获得平台运动参数和锚链动力参数,对平台漂移量、锚链最小安全系数、走锚临界张力、锚链最小卧底长度和起锚力进行无量纲指标分析,并综合考虑张力倾角与预张力对优化结果的影响,获得复合式锚泊系统钢链与钢缆的最优配比关系,确定最优钢链长度为395 m,较原钢链长度缩短225 m,钢链收放时间降低36%,进一步提高锚泊系统收放时效性,并降低平台可变荷载。 相似文献
15.
以三类内孤立波理论(Kd V、e Kd V和MCC)的适用性条件为依据,采用Morison和傅汝德-克雷洛夫公式分别计算Spar平台内孤立波水平力和垂向力,结合时域有限位移运动方程,建立了有限深两层流体中内孤立波与带分段式系泊索Spar平台相互作用的理论模型。以东沙群岛某海域实测内孤立波为对象,数值分析了在内孤立波作用下某经典式Spar平台的内孤立波动态载荷、运动响应及其系泊张力的变化特性。研究表明,内孤立波不仅会对Spar平台产生突发性冲击载荷,使其产生大幅度水平漂移运动,而且还会使其系泊张力显著增大。因此,在Spar平台等深海平台的设计应用中,内孤立波的影响不可忽视。 相似文献
16.
In this paper, motion response of a moored floating structure interacting with a large amplitude and steep incident wave field is studied using a coupled time domain solution scheme. Solution of the hydrodynamic boundary value problem is achieved using a three-dimensional numerical wave tank (3D NWT) approach based upon a form of Mixed-Eulerian–Lagrangian (MEL) scheme. In the developed method, nonlinearity arising due to incident wave as well as nonlinear hydrostatics is completely captured while the hydrodynamic interactions of radiation and diffraction are determined at every time step based on certain simplifying approximations. Mooring lines are modelled as linear as well as nonlinear springs. The horizontal tension for each individual mooring line is obtained from the nonlinear load-excursion plot of the lines computed using catenary theory, from which the linear and nonlinear line stiffness are determined. Motions of three realistic floating structures with different mooring systems are analyzed considering various combinations of linear and approximate nonlinear hydrodynamic load computations and linear/nonlinear mooring line stiffness. Results are discussed to bring out the influence and need for consideration of nonlinearities in the hydrodynamics and hydrostatics as well as the nonlinear modelling of the line stiffness. 相似文献
17.
The penetration behavior and trajectory of the drag anchor in seabed soils are not only determined by properties of the anchor and soil, but also controlled by the installation line especially the segment embedded in the soil. Correctly understanding and describing reverse catenary properties of the embedded line are crucial for improving the drag embedment performance, precisely predicting the anchor trajectory, and solving the positioning problem in offshore applications. The investigation on reverse catenary problems demonstrates that, the reverse catenary shape of the embedded line has to be solved almost through numerical incremental methods. In the present study, based on the mechanical model for the embedded line, the relationship between the tension and geometry of the embedded line, and the interactional equation between the anchor and embedded line are derived. By introducing the concept of the initial embedment depth of the installation line, the reverse catenary equation and the expression for calculating the length of the embedded line are obtained for soils with a linear strength, and the position of the embedment point can be reasonably solved through the derived reverse catenary equation. The reverse catenary equation is then introduced into the kinematic model for drag anchors, which combines the drag anchor, the installation line and the movement of the anchor handling vessel being an interactional system. More information related to the drag embedment problem can be definitely gained through the present work, including not only the anchor behaviors such as the trajectory, penetration direction and ultimate embedment depth, but also the properties of the installation line for both the embedded and horizontal segments. By comparing with drum centrifuge tests and model flume experiments, the efficiency of the theoretical method for predicting the anchor trajectory is well verified. 相似文献
18.
对称式布置锚链系统的线性化处理 总被引：6，自引：2，他引：6
用悬链线方程求解了不同锚链状态的锚链力 ,并用多项式回归了锚链力与锚固点位移的关系 ,由此求得锚链恢复力刚度系数。分析了对称式布置锚链系统的非线性程度 ,阐述对称式布置锚链系统所提供的恢复力作线性化处理的可行性及方法 ,并给出了对称布置锚链系统的线性刚度矩阵。为各类受对称式布置锚链系统约束的浮动结构物的动力分析提供了理论依据 相似文献
19.
Effect of Failure Mode of Taut Mooring System on the Dynamic Response of A Semi-Submersible Platform
Mooring system failure can lead to largely different dynamic response of floating structures when compared to the response under the condition of intact mooring system. For a semi-submersible platform with taut mooring system under extreme environmental conditions, the typical mooring system failure includes anchor line breaking failure due to the broken anchor line, and the anchor dragging failure caused by the anchor failure in the seabed soil due to the shortage of the anchor bearing capacity. However, study on the mooring failure caused by anchor failure is rare. The current work investigates the effect of three failure modes of taut mooring system on dynamic response of a semi-submersible platform, including one line breaking failure, two lines breaking failure, and one line breaking with one line attached anchor dragging failure. The nonlinear polynomial mooring line model in AQWA was used with integrating the load and displacement curve from the anchor pulling study to characterize the anchor dragging behavior for mooring system failure caused by the anchor failure. The offsets of the platform and the tension of mooring lines were analyzed for mooring system failure with 100-year return period. It is found that the mooring failure of one line breaking with one line attached anchor dragging is a case between the other two mooring failures. The traditional mooring analysis considering only the damaged condition with one line breaking is not safe enough. And the simple way of mooring analysis of two lines breaking is too conservative for the costly offshore engineering.
相似文献20.
Analyzed are the merits and demerits of catenary mooring system and taut mooring system, which are commonly used nowadays. As falling somewhere between these two systems, a new mooring system integrating catenary with taut mooring is proposed. In order to expound and prove the advantages of this new system, the motion performance of a semi-submersible platform is simulated by employing full time domain coupled analysis method. A comparison of the result of new mooring system with that of taut mooring system shows that the movement of the platform using the new type mooring system is smaller than that using the taut mooring system, which ensures a better working condition. Furthermore, the new mooring system is also compatible with the characteristics of catenary mooring system, which eliminates the requirement of anti-uplift capacity of the anchors. 相似文献