Dynamic interaction of parallel moving ships in close proximity

Nowadays,there are many studies conducted in the field of marine hydrodynamics which focus on two vessels traveling and floating in sufficiently close proximity to experience significant interactions.The hydrodynamic behavior of parallel moving ships in waves is an interesting and important topic of late.A numerical investigation has been carried out for the prediction of wave exciting forces and motion responses of parallel moving ships in regular waves.The numerical solution was based on 3D distribution technique and using the linear wave theory to determine the exciting forces and ship＇s motion.The speed effects have been considered in the Green function for more realistic results.The numerical computations of wave exciting forces and motion responses were carried out for a Mariner and Series 60 for the purpose of discovering different Froude numbers and different separation distances in head sea conditions.Based on the numerical computations,it was revealed that the sway,roll and yaw have a significant effect due to hydrodynamic interaction.     

海洋观测平台在波浪中运动响应的数值模拟(英文)

Offshore observation platforms are required to have great ability to resist waves when they are operating at sea. Investigation on the motion characteristics of the platforms in the sea can provide significant reference values during the platform design procedure. In this paper, a series of numerical simulation on the interaction of a triple-hulled offshore observation platform with different incident waves is carried out. All of the simulations are implemented utilizing our own solver naoe-FOAM-SJTU, which is based and developed on the open source tools of OpenFOAM. Duration curves of motion characteristics and loads acting on the platform are obtained, and a comparison between the results of the amplitude in different incident waves is presented. The results show that the solver is competent in the simulation of motion response of platforms in waves.     

Special Issue on Fluid Structure Interaction

<正>All structures at sea are in contact with the water and thus the knowledge of the interaction effects between the fluid and the structure is essential.Depending on the characteristics of the structure,of the fluid and of the relative motion,different mechanisms may be in place and thus different mathematical models may be required for the computation of its interaction.     

Mathematical simulation of steep waves at a focus point

Mathematical models simulating steep waves at a focus point are presented in this paper. Simulations of extreme waves in a model basin were used to determine the loads on floating structures induced by the waves. Based on a new wave theory, numerical test results show that the simulation procedure is effective and the induced motion of water particles in the front of waves is an important factor influencing impact loads on floating bodies.     

液舱晃荡与浮体非线性耦合运动分析(英文)

Nonlinear interactions among incident wave, tank-sloshing and floating body coupling motion are investigated. The fully nonlinear sloshing and body-surface nonlinear free surface hydrodynamics is simulated using a Non-Uniform Rational B-Spline (NURBS) higher-order panel method in time domain based on the potential theory. A robust and stable improved iterative procedure (Yan and Ma, 2007) for floating bodies is used for calculating the time derivative of velocity potential and floating body motion. An energy dissipation condition based on linear theory adopted by Huang (2011) is developed to consider flow viscosity effects of sloshing flow in nonlinear model. A two-dimensional tank model test was performed to identify its validity. The present nonlinear coupling sway motion results are subsequently compared with the corresponding Rognebakke and Faltinsen (2003)’s experimental results, showing fair agreement. Thus, the numerical approach presented in this paper is expected to be very efficient and realistic in evaluating the coupling effects of nonlinear sloshing and body motion.     

30th International Workshop on Water Waves and Floating Bodies

About the Workshop...
The International Workshop on Water Waves and Floating Bodies is an annual meeting of mathematicians and engineers with a particular interest in water waves and their effects on floating and submerged marine structures. The IWWWFB was initiated by Professor D.V. Evans （University of Bristol） and Professor J.N. Newman （MIT） following informal meetings between their research groups in 1984. First intended to promote communications between workers in the UK and the USA, the interest and participation quickly spread to include researchers from many other countries around the world. The workshop places particular emphasis on the participation of younger researchers, on the stimulation of discussions between engineers and scientists, and to the presentation of preliminary basic scientific work before its publication elsewhere. The workshop is an important reference point for organizing and spreading knowledge in this area. In particular, the workshop proceedings are freely accessible through the dedicated internet address www.iwwwfb.org where all contributions from 1986 on can be found.     

长波作用下与KC数相关的柔性植被对海岸结构物受力的影响(英文)

Extreme coastal events require careful prediction of wave forces.Recent tsunamis have resulted in extensive damage of coastal structures.Such scenarios are the result of the action of long waves on structures.In this paper,the efficiency of vegetation as a buffer system in attenuating the incident ocean waves was studied through a well controlled experimental program.The study focused on the measurement of forces resulting from cnoidal waves on a model building mounted over a slope in the presence and absence of vegetation.The vegetative parameters,along with the width of the green belt,its position from the reference line,the diameter of the individual stems as well as the spacing between them,and their rigidity are varied so as to obtain a holistic view of the wave-vegetation interaction problem.The effect of vegetation on variations of dimensional forces with a Keulegan-Carpenter number(KC) was discussed in this paper.It has been shown that when vegetal patches are present in front of structure,the forces could be limited to within F*￡1,by a percentile of 92%,90%,55%,and 96%,respectively for gap ratios of 0.0,0.5,1.0,and 1.5.The force is at its maximum for the gap ratio of 1.0 and beyond which the forces start to diminish.     

Mathematical modelling of response amplitude operator for roll motion of a floating body: Analysis in frequency domain with numerical validation

This paper investigates mathematical modelling of response amplitude operator （RAO） or transfer function using the frequency-based analysis for uncoupled roll motion of a floating body under the influence of small amplitude regular waves. The hydrodynamic coefficients are computed using strip theory formulation by integrating over the length of the floating body. Considering sinusoidal wave with frequency （ω ） varying between 0.3 rad/s and 1.2 rad/s acts on beam to the floating body for zero forward speed, analytical expressions of RAO in frequency domain is obtained. Using the normalization procedure and frequency based analysis, group based classifications are obtained and accordingly governing equations are formulated for each case. After applying the fourth order Runge-Kutta method numerical solutions are obtained and relative importance of the hydrodynamic coefficients is analyzed. To illustrate the roll amplitude effects numerical experiments have been carried out for a Panamax container ship under the action of sinusoidal wave with a fixed wave height. The effect of viscous damping on RAO is evaluated and the model is validated using convergence, consistency and stability analysis. This modelling approach could be useful to model floating body dynamics for higher degrees of freedom and to validate the result.     

船首形状对自由液面水下航行体阻力影响的试验研究（英文）

In this paper, towing tank experiments are conducted to study the behavior of flow on a model of the underwater vehicle with various shapes of bows, i.e. tango and standard bows in free surface motion tests. The total resistances for different Froude numbers are considered experimentally. The towing tank is equipped with a trolley that can operate in through 0.05–6 m/s speed with ±0.02 m/s accuracy. Furthermore, the study is done on hydrodynamic coefficients i.e. total, residual and friction resistance coefficients, and the results are compared. Finally, the study on flow of wave fields around bows is done and wave filed around two bows are compared. The Froude number interval is between 0.099 and 0.349. Blockage fraction for the model is fixed to 0.005 3. The results showed that the residual resistance of the standard bow in 0.19 to 0.3 Froude number is more than the tango bow in surface motion which causes more total resistance for the submarine. Finally, details of wave generated by the bow are depicted and the effects of flow pattern on resistance drag are discussed.     

Numerical calculation of coupled damage effects on ship subjected to internal blast loading of warhead北大核心CSCD

［Objective］This paper studies the coupled damage effects of a ship's structure due to the internal blast loading of a warhead. ［Methods］Blast tests with cased charge data are conducted to verify the effectiveness of the coupled SPH-FEM approach, and numerical calculations are then performed on real ship compartment scale model tests to analyze the coupled fragmentation and shockwave damage effects of an explosion in a confined cabin.［Results］The results show that the fragments caused by the detonation of the warhead will first cause local damage to the cabin structure. The shockwave will exacerbate the local damage, and blasted openings will further increase the space for the propagation and diffusion of the shockwave inside the chamber, which will in turn cause damage to the adjacent structures. The simple equivalence of the warhead to a bare charge does not give a true picture of the effect of the warhead on the ship's structure, and fragmentation plays a significant role in the detonation of the warhead.［Conclusions］The results of this study show that employing the coupled SPH-FEM numerical method to calculate the coupling damage effects on a ship's structure can accurately reproduce the warhead damage pattern in tests, thereby providing support for the improved assessment of the damage of naval structures under warhead detonation. © 2022 Chinese Journal of Ship Research. All rights reserved.     

深海系泊浮体物面非线性时域耦合动力分析

文章基于三维时域势流理论和弹性细长杆理论,研究并提出了深海系泊浮体物面非线性时域耦合动力分析方法。该方法采用时域物面非线性理论方法在瞬态位置直接时域模拟系泊浮体所需水动力,结合有限元方法计算系泊缆索的动力响应,利用异步耦合方法实现浮体和系泊缆索的时域耦合动力求解。既满足系泊浮体时域水动力耦合,又满足系泊浮体和系泊缆索动力耦合。通过对二阶非线性不规则波作用下深海系泊半潜式平台的时域耦合响应特性进行研究,将不同海况下物面非线性时域耦合静力响应和动力响应与间接时域耦合动力响应的三种方法计算结果进行比较。研究结果表明,系泊缆索动力响应明显,平台瞬态空间位置对垂荡低频运动影响较大,有必要在平台瞬时湿表面采用动力响应方法进行深海系泊浮体时域耦合响应分析。     

考虑浮体弹性变形的锚泊系统分析方法

传统的锚泊系统分析方法一般是假设结构物为刚性不可变形的,这种假设对于常规海洋结构物的锚泊系统分析,其精度是可以接受的,然而对于弹性体(比如超大型浮体)来说,这种浮体刚性的假设显然是不合理的.本文基于摄动理论,分别给出了锚泊浮体(同时包括弹性体和刚性体)和锚泊系统的一阶运动方程.分别用三维水弹性理论和Goodman-Iance法求解浮体的动力响应和锚泊线的运动,并给出了两者之间的协调关系.通过数值算例分析表明,对于超大型浮体,其弹性特性对锚泊系统特性的影响是不可忽略的.     

Fluid-structure-material coupling analysis for a floating laminated structure consisting of high-stiffness panels and a soft core

This paper presents a fluid-structure-material coupling analysis for the interaction between water waves and a very large floating laminated structure (VLFLS), which is consisted of two enhanced ultrahigh-performance concrete (UHPC) panels and a middle lightweight foamed rubber core. The representative volume element (RVE) method is used to design the mechanical properties of enhanced UHPC and foamed rubber, and the parameterized formulas are presented to reveal the dependency between macroscale mechanical properties and mesoscale hierarchical characteristics. By idealizing the rubber core as a uniformly distributed spring layer, an eighth-order differential equation of motion of the laminated structure is derived. In the context of linear potential flow theory, a hydroelastic analytical model is developed for the floating laminated structure with finite length under wave action. In the process of solving velocity potentials, a complicated dispersion equation for the wave motion below the laminated structure is derived, and this equation contains two pairs of conjugate complex roots with positive real parts. The various hydrodynamic quantities, including reflection coefficient, transmission coefficient, deflection, shear force, and bending moment, are calculated. The hydroelastic model is confirmed by considering the convergence of calculation results and the energy conservation of wave propagation. The coupled effects of wave action, material characteristics, structural parameters, and edge conditions on the hydroelastic and mechanical response of the floating laminated structure are clarified to provide important information regarding the optimal design of such structures.     

波浪中两浮体水动力干扰模型试验研究综述

波浪中两浮体的水动力干扰问题主要来自于海上补给作业实践。目前,国内外已有多家水池机构可开展两浮体的零航速模型试验,而有航速状态下两船模型试验的数据十分稀少且珍贵。为此,文章重点介绍了国内外相关机构开展的两浮体间流体共振模型试验、零航速和有航速下的两浮体模型试验概况,并分析了波浪中有航速两船水池模型试验的主要技术难点。     

Nonlinear hydrodynamic responses of submerged moving payload in vicinity of a crane barge in waves

The wave interaction with a submerged cylindrical payload subjected to constrained motions in presence of a nearby floating crane barge is investigated in the three-dimensional numerical wave tank using a fully nonlinear potential flow model in the time domain. Numerical simulations are carried out to investigate the hydrodynamic features of this submerged payload under pendulum motion in water waves as well as while it moves towards the sea bed at a constant vertical velocity. It is known that the presence of multiple side by side floating bodies in waves can create significant drift motion. In the present study the similar drift motion is observed for the side by side floating barge and submerged payload and it appears that the submerged payload under constrained motions may face a very large mean drift motion of nearly seven times that of the incident wave amplitude in the beam sea upstream condition. Emphasis is also given towards investigating and understanding the influences of natural frequency of the payload and shielding effect due to the presence of the floating barge. It is found that natural frequency coupled with shielding effect generates remarkable low frequency components in payload responses both in the head sea and the beam sea situations. The effect of different cable lengths, wave maker frequencies and downward moving velocities on payload responses under several geometric setups are studied and compared, and interesting features such as increased low frequency movement of the payload near the natural frequency region and existence of considerable low frequency motions even at a greater depth (while the payload is quite below the free surface) are observed.     

波浪作用下单体网格式浮架受力的数值模拟

模型试验表明重力式网箱在波浪作用下，单纯浮架的受力贡献比例较大。本文运用波浪理论，通过建立浮架、锚绳及浮子的运动方程，采用五阶龙格-库塔进行数值求解，得到了单体网格式锚碇单纯浮架的数值计算模式。将计算模型简化为四点锚碇，并将计算结果与实验结果进行了比较，二者符合程度较好。在此基础上，比较了单体网格式锚碇与四点锚碇单纯浮架的受力，结果表明网格式锚碇方式浮架受力较小。     

基于高阶边界元法和波浪交互理论的三维相邻多浮体问题研究

在解决三维相邻多浮体的水动力问题时,正确处理各浮体之间的相互作用是分析计算的关键所在。文章分别运用高阶边界元法和波浪交互理论对一个由箱型浮体组成的三维多浮体问题进行求解,通过对比分析浮体所受波浪力和水下表面压力分布结果,验证两种方法计算结果的精确度,研究该模型的水动力特点;并通过改变各浮体之间的距离,寻求波浪交互理论在求解三维多浮体问题中的适用性,对该方法在浮体间距不满足限制条件时的计算结果进行解释。     

A study on the estimation of the seaquake response of a floating structure considering the characteristics of seismic wave propagation in the ground and the water

 Seaquakes, which are characterized by the propagation of vertical earthquake motion at the sea bottom as a compression (longitudinal) wave, are reported to cause damage to ships, and their effect on floating structures is a matter of great concern. To comprehend the basic properties of seaquakes, we first discuss a method to calculate the displacement of the seabed when it is subjected to hydrodynamic pressure. To investigate the interrelationship between the vibration of a floating structure and the deformation of the seabed, a new boundary integral equation is derived which assumes that the seabed is a semiinfinite homogeneous elastic solid in order to analyze the seaquake-induced hydrodynamic pressure acting on the floating structure. By considering the propagation of the seismic wave in the ground and in the water, the incident wave potential in seaquake problems is also deduced and its characteristics are discussed. Finally, the response of a very large floating structure in a seaquake is investigated using a fluid force analysis method, and considering the interrelationship between the vibration of the floating structure and the deformation of the seabed. Received: August 19, 2002 / Accepted: November 11, 2002 Address correspondence to: H. Takamura (hiroaki_takamura@nishimatsu.co.jp) Updated from the Japanese original, which won the 2002 SNAJ prize (J Soc Nav Archit Jpn 2001;189:87–92,93–100 and 190:381–386)