Mooring Model Experiment and Mooring Line Force Calculation

Mooring model experiment and mooring line tension determination are of significance to the design of mooring systems and berthing structures. This paper mainly involves: (a) description and analysis of a mooring model experiment; (b) derivation of static equilibrium equations for a moored ship subjected to wind, current and waves; (c) solution of mooring equations with the Monte Carlo method; (d) qualitative analysis of effects of pier piles on mooring line forces. Special emphasis is placed on the derivation of static equilibrium equations, solution method and the mooring model experiment.

Prediction of the Mooring Force of a 2-D Floating Oil Storage Tank

A Constrained Interpolation Profile （CIP）-based model is developed to predict the mooring force of a two-dimensional floating oil storage tank under wave conditions, which is validated against to a newly performed experiment. In the experiment, a box-shaped floating oil storage apparatus is used. Computations are performed by an improved CIP-based Cartesian grid model, in which the THINC/SW scheme （THINC： tangent of hyperbola for interface capturing; SW： Slope Weighting）, is used for interface capturing. A multiphase flow solver is adopted to treat the water-air-body interactions. The Immersed Boundary Method （IBM） is implemented to treat the body surface. Main attention is paid to the sum force of mooring line and velocity field around the body. It is found that the sum force of the mooring line increases with increasing wave amplitude. The body suffers from water wave impact and large body motions occur near the free surface. The vortex occurs near the sharp edge, i.e., the sharp bottom comers of the float- ing oil storage tank and the vortex shedding can be captured by the present numerical model. The present model could be further improved by including turbulence model which is currently under development. Comparison between the computational mooring forces and the measured mooring forces is presented with a reasonable agreement. The developed numerical model can predict the mooring line forces very well.

Influence of Regular Wave and Ship Characteristics on Mooring Force Prediction by Data-Driven Model

The study of mooring forces is an important issue in marine engineering and offshore structures.Although being widely applied in mooring system,numerical simulations suffer from difficulties in their multivariate and nonlinear modeling.Data-driven model is employed in this paper to predict the mooring forces in different lines,which is a new attempt to study the mooring forces.The height and period of regular wave,length of berth,ship load,draft and rolling period are considered as potential influencing factors.Input variables are determined using mutual information(MI)and principal component analysis(PCA),and imported to an artificial neural network(NN)model for prediction.With study case of 200 and 300 thousand tons ships experimental data obtained in Dalian University of Technology,MI is found to be more appropriate to provide effective input variables than PCA.Although the three factors regarding ship characteristics are highly correlated,it is recommended to input all of them to the NN model.The accuracy of predicting aft spring line force attains as high as 91.2%.The present paper demonstrates the feasibility of MI-NN model in mapping the mooring forces and their influencing factors.

Analysis for the Deployment of Single-Point Mooring Buoy System Based on Multi-Body Dynamics Method

Deployment of buoy systems is one of the most important procedures for the operation of buoy system. In the present study, a single-point mooring buoy system which contains surface buoy, cable segments with components, anchor and so on is modeled by applying multi-body dynamics method. The motion equations are developed in discrete node description and fully Cartesian coordinates. Then numerical method is used to solve the ordinary differential equations and dynamics simulations are achieved while anchor is casting from board. The trajectories and velocities of different nodes without current and with current in buoy system are obtained. The transient tension force of each part of the cable is analyzed in the process of deployment. Numerical results indicate that the transient payload increases to a peak value when the anchor is touching the seabed and the maximum tension force will vary with different floating configuration. This work is helpful for design and deployment planning of buoy system.

Investigation of Motion of Two Hinged Bodies Moored by Mooring Lines in Waves

In this paper, the motions are studied of a multi-body which is composed of two plates hinged together and moored by eight mooring lines in regular waves. The experimental results are compared with computational results. The linear potential theory and the perturbation method are combined to study this complicated system. The former is used to calculate the wave forces acting on the plates and the motion responses of them, while the latter is used to describe the dynamic character of the eight mooring lines coupled with the two hinged plates. Some response results of each plate are presented and comparisons between calculated results and experimental data are given. All the calculations are confined to regular beam waves.

A Nonlinear Restoring Effect Study of Mooring System and its Application

Mooring system plays an important role in station keeping of floating offshore structures. Coupled analysis on mooring-buoy interactions has been increasingly studied in recent years. At present, chains and wire ropes are widely used in offshore engineering practice. On the basis of mooring line statics, an explicit formulation of single mooring chain/wire rope stiffness coefficients and mooring stiffness matrix of the mooring system were derived in this article, taking into account the horizontal restoring force, vertical restoring force and their coupling terms. The nonlinearity of mooring stiffness was analyzed, and the influences of various parameters, such as material, displacement, pre-tension and water depth, were investigated. Finally some application cases of the mooring stiffness in hydrodynamic calculation were presented. Data shows that this kind of stiffness can reckon in linear and nonlinear forces of mooring system. Also, the stiffness can be used in hydrodynamic analysis to get the eieenfrequencv of slow drift motions.

Dynamic Response Analysis of a Floating Mooring System

An innovative floating mooring system with two or more independent floating mooring platforms in the middle and one rigid platform on each side is proposed for improving efficiency and safety in shallow water. For this new system, most of collision energy is absorbed through the displacement of floating platforms. In order to illustrate the validity of the system, a series of model tests were conducted at a scale of 1:40. The coupled motion characteristics of the floating mooring platforms were discussed under regular and irregular waves, and the influences of wave direction and other characteristics on dynamic response of the system were analyzed. The results show that the mooring system is safest at 0° of wave incident angle, whereas the most dangerous mooring state occurs at 90° of wave incident angle. Motion responses increase with the increase of wave height, but are not linearly related to changes in wave height.

Experimental Study of Mooring Type Effect on the Hydrodynamic Characteristics of VLFS

Mooring system is a significant part of very large offshore floating structures(VLFS).In this paper,a single module pontoon type VLFS model considering four mooring types is studied through physical model tests to determine the effects of mooring conditions on the hydroelastic response,mooring force,incident coefficient,reflection coefficient and energy dissipation coefficient.Eight mooring cables are symmetrically arranged on both sides of the model.The floating body model satisfies the similarity of stiffness and gravity,while the cable satisfies the similarity of elasticity and gravity.The results show that the effect of mooring type on mooring force is greater than that on hydroelastic response.Increasing the initial tension of the mooring cable will reduce the amplitude of the leeward of the VLFS model.The mooring angle of the mooring cable will affect the maximum mooring force and the initial tension of the mooring line will affect the wave period in which the maximum mooring force occurs.The transmission coefficient and wave energy dissipation coefficient will change regularly with different mooring types.These results may provide a reference to facilitate the mooring design of VLFS.

Influence of Active Control Strategy on the Motion Compensation at the Truncated Point of Mooring Line

The maximum predicting error of the commonly used passive truncated mooring system method may reach 30%due to the difference of dynamic characteristics between the truncated and full-depth mooring line.In this paper,the experimental strategy called three-parameter(displacement,velocity and acceleration)active control method at the truncated point of mooring line is established to implement the synchronous equivalent of motion and force,and the realization of active truncated mooring system for model test is studied theoretically.The influences of threeparameter and one-parameter(displacement)active control strategies on the compensation effects are compared by numerical study.The results show that the established three-parameter active control method can feasibly realize the static and dynamic equivalent of truncated and full-depth mooring system,laying a good foundation for the following physical model test of active truncated mooring system.

Study on Mooring Design and Calculation Method of Ocean Farm Based on Time-Domain Potential Flow Theory

In order to calculate the mooring force of a new semi-submerged Ocean Farm quickly and accurately,based on the unsteady time-domain potential flow theory and combined the catenary model,the control equation of mooring cable is established,and the mooring force of the platform under the wave spectrum is calculated.First of all,based on the actual situation of the ocean environment and platform,the mooring design of the platform is carried out,and the failure analysis and sensitivity analysis of the single anchor chain by the time domain coupling method are adopted:including different water depth,cycle,pretension size,anchor chain layout direction and wind speed,etc.The analysis results confirm the reliability of anchoring method.Based on this,the mooring point location of the platform is determined,the force of each anchor chain in the anchoring process is calculated,and the mooring force and the number of mooring cables are obtained for each cable that satisfies the specification,the results of this paper can provide theoretical calculation methods for mooring setting and mooring force calculation of similar offshore platforms.

Design and Control Scheme of the Mooring System

In this paper,by analyzing the design and control scheme of the mooring system based on theoretical mechanics,force analysis is conducted on the buoy,steel pipe,steel drum,and anchor chain,and a reasonable mathematical model is constructed to solve the problems of the inclination angle of the steel drum and each section of the steel pipe,the shape of the anchor chain,the draft of the buoy,and the swimming area under different wind speeds,thus providing a reliable basis for the design of the system.

基于振动频率法的船舶系缆力试验研究

现有的系缆力测量方法尚无法实现简单、准确、高效地测量单根船舶缆绳的系缆力。参考测量斜拉索索力的计算方法,进行了振动频率法测量船舶系缆力的试验研究。依据实际系泊环境搭建了原型测试平台,并针对可能产生理论误差的影响因素与实际应用要求,进行不同数据采集位置、激励方式、激励位置、浸湿缆绳和不同温度等影响因素的误差试验研究,提出基于环境激励和人工激励的新激励方式。通过分析振动频率法的计算值与原型测试平台的张拉值,得出数据采集位置、激励位置和激励方式对船舶系缆力测量值影响很小,缆绳浸湿下误差率范围增大1.5%左右,低温下(2℃)误差率增加±2%左右,综合误差范围为-5%~4%且误差率可以较好地满足正态分布,通过修正缆绳长度对测量精度进行修正。结果表明该方法具有较强的可行性与应用性,能有效实现简单、准确、高效地测量船舶系缆力。

海洋核动力平台定位系统多体动力学模型试验验证

为验证海洋核动力平台定位系统多体动力学模型的合理性,从而提高该平台长期系泊的可靠性,本文采用多体动力学方法与缩比模型试验方法,对核动力平台定位系统进行建模与验证。基于定位系统多铰连接的拓扑结构,结合多刚体动力学理论,建立了定位系统的多体动力学仿真模型。搭建了定位系统1∶9缩比模型试验平台,并选取2种典型工况进行验证。研究结果表明:定位系统多体动力学模型计算的系泊腿受力与实验结果符合良好,平均误差在2%以内。算例分析发现,系泊腿受力循环次数主要集中在低幅值高均值区域。本文模型试验验证了所提出的定位系统多体动力学模型的可行性与正确性,能够为定位系统系泊能力的评估提供参考和借鉴。

滚装船在拖轮辅助下丁靠斜坡道的船舶系泊试验研究

文章以某码头工程为例,针对1万t滚装船在拖轮辅助下丁靠斜坡道开展船舶系泊物理模型试验,分别对风、浪、流不同组合工况下的缆绳系缆力、船舶运动量等进行了试验研究,给出了作业及系泊条件,可为设计和运营提供参考。结果表明设计方案缆绳布置方式总体较为合理,使用拖轮辅助可以有效地平衡风、浪、流对滚装船的作用力,各组缆绳缆力未超过50%破断力的设计标准;对于系泊系统中各特征量,动力因素的影响次序自大至小依次为:波浪、风和水流,其中波浪周期在影响因素中最为显著;同样的波浪条件下,SW向波浪比WSW向波浪作用更为不利,实际运行管理中应结合波浪数模成果及码头前实际波浪方向调整系泊和作业状态。

风浪流单独及耦合作用下15 MW级浮式基础动力特性研究

了解风浪流等环境荷载效应对浮式基础设计及优化至关重要,为此,以15 MW级漂浮式基础为研究对象,系统性定量分析风浪流环境荷载单独及耦合作用下对浮式基础运动及系泊系统受力的影响。首先,以INOWINDMOOR 12 MW和TaiDa 15 MW浮式基础为原型设计新的15 MW级浮式基础,并在ANSYS-AQWA建立水动力分析模型,风力荷载及海流荷载通过风力系数、流力系数添加;其次,针对风浪流等环境荷载单独及耦合作用下浮式基础运动和系泊受力等特征开展分析。结果表明:浮式基础运动及系泊受力主要受风力和流力的影响,波浪会加剧浮式基础运动及系泊受力的往复性,并加大运动幅度及系泊受力;流荷载对浮式基础运动及系泊受力影响较大,特别是风、浪与流耦合作用时会导致系泊受力明显增加,实际工程设计时,流荷载应给与重点关注。

闸墙长廊道侧支孔船闸阀门运行方式优化试验研究

船闸阀门开启时间对闸室通航效率、输水廊道压力和闸室停泊条件等产生影响,针对阀门运行方式优化问题,采用物理模型试验对船闸进水口水位、阀门段输水廊道压力特性、闸室和下引航道内船舶系缆力等水力特性进行分析,结果表明:闸室和下引航道内前横、后横和纵向3个方向的船舶系缆力均随阀门开启时间增大而减小,且纵向船舶系缆力大于横向船舶系缆力。随着阀门开启时间增加,充水时阀门段输水廊道压力先减小后增大,泄水时则逐渐增大。综合考虑当阀门开启时间为6 min时船闸整体运行效果较好,该成果可为实际船闸运行提供技术支撑。

高水头船闸大型船舶导航墙停泊条件研究

高水头船闸导航墙水流条件复杂,大型船舶在导航墙待闸存在船舶靠泊和系缆设施安全等问题。以葛洲坝二号船闸导航墙停泊条件研究为例,通过模型试验、系缆力测试等技术方法,分析不同工作水头下船闸充泄水、船闸人字门启闭过程中上、下游导航墙不同停泊位置的船舶停泊条件及其变化规律,提出船舶系缆力超过设计值的对策措施。研究表明:上游导航墙停泊条件良好,船舶系缆力较低;下游导航墙受船闸泄水影响大,且与船闸工作水头密切相关,停泊条件较差,采取优化船闸阀门运行及泄水工艺、避开船闸泄水影响范围、增加船舶系缆数量等措施,可起到降低单个系船柱船舶系缆力的作用,下游导航墙系缆设施及船舶停泊条件预期满足要求。

基于深度神经网络的船舶系泊受灾预报研究

为避免船舶系泊于码头时遭受恶劣海况而发生的缆绳断裂等问题,通过深度神经网络建立了系泊受灾预测模型,来快速获得系泊船舶所有系泊缆绳的受力。模型输入特征数量为11个,涵盖风、浪、流、涌、船舶吃水及船舶系泊方式等基本参数,输出特征为系泊系统中所有缆绳的受力。对模型的测试结果表明,相比于径向基神经网络,模型具有较高的预测精度,每组测试工况下的平均相对误差不超过10%。可将该模型用于在恶劣海况来临前对系泊系统的安全评估和风险分析,有助于相关人员及时采取应对措施,从而保证系泊系统的稳定性与可靠性。

单点系泊油轮运动响应分析及运动控制

基于数值模拟,对单点系泊系统动力响应进行研究,探究单点系泊系统在波流不同向和特殊作业工况下油轮的运动规律和系泊力的影响因素,并给出船体控制的方法。研究结果表明,波流夹角、波浪和流速会对船体运动和系泊力大小产生显著影响;在船尾处0°方向和船侧135°方向施加拉力,会降低船体运动幅值及系泊缆绳拉力。最后给出了该系泊系统的极限作业海况条件。

波浪与系缆方式对系泊船舶响应的影响研究

系泊船舶响应的影响因素很多,且十分复杂。针对影响系泊船舶响应的主要因素(波浪和系缆方式)开展研究,通过船舶系泊物理模型试验,研究波浪条件及系缆方式对系泊船舶响应的影响规律,其中波浪条件包括不同的波向及波浪周期,系缆方式包括不同缆绳配置(有无缆尾索)和不同系缆布置方案。研究结果表明,45°斜向浪作用下系泊船舶的运动量和系缆力均明显小于横浪作用下的结果;试验波浪周期范围(T=3.5~6.0 s)内,系泊船舶的运动量和系缆力均随着波浪周期的增大而变大;从船舶系泊安全角度看,设置缆尾索是有利的;码头前后沿共同系缆布置可明显提高船舶系泊(非装卸作业时)的抗风浪流能力。