Slamming load on a very large floating structure with shallow draft

The objective of this paper is to estimate the slamming load acting on a pontoon-type very large floating structure with a shallow draft. Experiments were carried out using elastic models with different rigidities in regular waves. The results revealed that the slamming load was strongly influenced by the rigidity of the model. The conditions under which slamming occurs depended on the extent of the bottom emergence and the velocity of the relative wave height at the bow of the model. These results were related to a simple procedure for estimating slamming load.     

Two degree of freedom flow-induced vibration of cylindrical structures in marine environments: frequency ratio effects

The flow-induced vibration of a cylindrical structure is a very common problem in marine environments such as undersea pipelines, offshore risers, and cables. In this study, the vortex-induced vibration (VIV) of an elastically mounted cylinder at a low Reynolds number is simulated by a transient coupled fluid–structure interaction numerical model. Considering VIV with low damping ratio, the response, hydrodynamic forces, and vortex shedding modes of the cylinder is systematically analyzed and summed up the universal rule under different frequency ratios. On the basis of the analysis, we find that the frequency ratio α is a very important parameter. It decides the locked-in, beat, and phase-switch phenomena of the cylinder, meanwhile, it also influence the vortex mode of the cylinder. The trajectory of the two degrees of freedom (2 DOF) case at different natural frequency ratios is discussed, with most trajectories having a “figure of 8” shape and a few having a “crescent” shape. A fast Fourier transformation technique is used to obtain the frequency characteristics of the vibration of the cylindrical structure. Using the 2 DOF cylinder model in place of the 1 DOF model presents several advantages in simulating the nonlinear characteristics of cylindrical structures, including the capacity to model the crosswise vibration generated by in-line vibration.     

Wave effects on large floating structures with air cushions

An analysis is made of a VLFS which is partially supported by an air cushion. The interface between the air cushion and the water is considered to be a free surface. The elevation of this surface is represented by an appropriate set of Fourier generalized modes, and extended equations of motion are derived for the rigid-body motions and generalized modes. The dynamic effect of the air is represented by appropriate acoustic added-mass coefficients. The hydrodynamic coefficients are evaluated using the B-spline-based panel code HIPAN. Illustrative computations are presented which show significant resonant effects.     

基于MR阻尼器的单自由度系统减振特性分析

在不同频率和振幅的正弦激励下,研究了基于磁流变阻尼器的单自由度弹簧阻尼系统的振动特性,分析了磁流变阻尼器的减振控制效果.主要通过建立磁流变阻尼器的振动实验模型,并在不同激励工况下测试了系统的振动特性.研究结果表明:系统在低频区30Hz内随着激励振幅和频率的提高减振效果越好,且激励频率对减振效果的影响更明显.当激励频率与系统一阶固有频率接近时,系统也具有良好的减振效果.     

破损结构地震反应简化分析法的单自由度破损模型研究

MSP(Multi-step pushover method)法是一种弹塑性推覆方法,可以评估破损状态的建筑结构的地震反应。它以地震反应谱作为输入,根据结构的动力特性分配荷载,逐步推覆,得到破损结构的最大地震反应,简便实用。作者针对MSP法中破损模型的选择和改善问题进行了专门研究和探讨。通过与非线性时程法进行对比,首次提出适用于单自由度体系的破损模型。实例计算表明,本文提出的模型可用,分析误差小,有助于MSP法进一步完善。     

一种新型深水浮式平台及其系泊系统动力响应分析

本文以一种可支持干式采油树的新型深水浮式平台为研究对象,采用频域和时域分析方法,分析不同工况下该平台的运动响应和锚链力特性,并与试验数据相对比以验证数值方法的正确性。在此基础上,重点分析了锚链断裂和伸缩立柱长度对该平台各项性能的影响。研究表明,该新型深水浮式平台具有优越的垂荡运动性能,且伸缩立柱长度对其垂荡运动具有影响。此外,如果发生锚链断裂,将对平台水平运动及锚链力产生较大影响。     

六自由度Stewart平台运动学遗传神经网络正解

近年来,舰载相控阵雷达发展迅速,对其隔振措施和隔振机构的要求也越来越高。Stewart平台为一种通常的空间六自由度并联机器人,在舰载相控阵雷达中具有广泛的应用。为了解析Stewart平台工作空间和设置机构误差步长,必须运动学求解。本文针对当前Stewart平台正解法存在的问题,基于传统的正解法和Stewart平台结构,提出一种遗传神经网络正解算法,通过仿真验证可知,该方法具有较高的收敛性和较快的速度,有进一步推广应用的潜力。     

双自由度舵机执行机构冲击载荷的仿真分析

超高速水下航行体航行过程中工况复杂,在加速段速度跨度大,双自由度舵机执行机构承受了较大的瞬态冲击载荷,有必要对其韧性进行分析校核。本文分别建立旋转机构输出轴、减速箱体和展开机构最后一级齿轮副的多刚体动力学仿真模型,分析各机构在冲击载荷下的应力和变形情况,校核结构韧性的可靠性,同时对旋转机构输出轴进行模态分析。仿真与校核结果为机构优化设计提供参考依据。     

新型桁架箱体浮筏结构重量优化研究

结合桁架结构的优点,将桁架结构应用于传统浮筏形成一种新型桁架箱体浮筏结构,并对其重量进行优化。首先在有限元软件Abaqus中建立了桁架箱体浮筏模型,然后基于模态分析,重力场分析和抗冲击分析,以筏架上、下面板厚度为设计变量,分析了面板厚度变化对结构刚度及强度水平的影响,且在保证足够刚度和强度水平的前提下,浮筏减重可达15.4%。本文的研究可为新型桁架箱体浮筏的结构轻量化设计奠定基础。     

线性连续分层流体中水波与截断圆柱浮体的相互作用

研究了在线性连续分层流体中水波与截断圆柱浮体相互作用的问题.在Boussinesq近似下,基于分离变量法,表明了对给定的频率,当它大于浮力频率时,流场中只有一种模态的平面前进波,当它小于浮力频率时,流场中有无数多个模态的平面前进波.基于特征函数匹配理论,建立了作用在截断圆柱浮体上水动力的计算方法.对作用在截断圆柱浮体上的水平波浪力、垂向波浪力和力矩进行了数值计算分析,表明了在某个频率范围内,流体的线性连续分层效应对这些水动力量的影响是不可忽视的.特别地,在入射波频率小于浮力频率时,高阶模态入射波对截断圆柱浮体水动力的影响也是重要的,在海洋工程的实践中应予以特别关注.     

An anti-motion device for a very large floating structure

We proposed a simple anti-motion device, which is a box-shaped body attached to an edge of VLFS. The performance of this device is investigated theoretically and experimentally in the present work. The theory is based on the eigen-function expansion method and the extension of this method to the oblique sea case is presented. The experiment is carried out in a wave tank with small-scale models. Both experimental results and the theoretical results show that the anti-motion performance of this device is very good at the design period in the case of beam-sea. The theory also demonstrates that this device reduces not only the deformation but also the shearing force and the moment of the platform and it also works well in the oblique sea.     

浮式防波堤结构的研究现状

浮式防波堤作为海洋工程中一类重要的防波堤结构,具有优异的经济性和生态环保性。首先概述了海洋浮式防波堤的发展过程,总结了国内外关于浮式防波堤的最新研究成果,简要介绍了浮式防波堤结构形式的试验研究和数值模拟研究,并根据浮式防波堤下部是否设置阻尼结构划分为箱板式和板阻式两种结构形式,重点探讨了目前研究存在的问题和不足,并从耐久性、设计标准规范与新材料等方面对未来浮式防波堤结构的发展和研究方向做出了展望。     

作用在二维浮体结构上的风荷载研究

针对风对结构物的作用问题,现行规范与计算方法虽能较准确估算风的直接作用力,但可能忽视间接作用力而使估算不足。以二维典型浮体结构为研究对象,采用物理模型试验方法,分析静水条件恒定风和2种不同类型谱的随机风作用下的风荷载。结果表明,API谱随机风所产生的作用力大于Davenport谱随机风的作用力;不同时距的平均风速对浮体结构的荷载影响试验结果差异较大,应引起工程设计人员的充分注意。     

超大型浮体结构碰撞损伤研究

基于LS-Dyna数值仿真软件,以双模块超大型浮体结构为研究对象,开展油轮与双模块超大型浮体结构发生碰撞的数值仿真分析.数值仿真中碰撞场景为邮轮撞击模块中部结构,材料模型采用线性强化弹塑性模型,并计人应变速率引起的材料强化,考虑碰撞发生时的接触及摩擦.通过本文的研究,获得了双模块超大型浮体结构变形及损伤规律,讨论了结构的吸能特性和运动规律等,可为超大型浮体结构的耐撞性设计提供参考.     

不同结构形式浮式防波堤湿拖过程中的运动响应研究

浮式防波堤是当前海洋工程装备研发的热点,由于浮式防波堤主尺度大,采用半潜船等工程船运输成本高。本文考虑三种不同类型浮式防波堤采用湿拖方式进行运输,采用AQWA软件,利用数值模拟方法,研究不同海况下浮式防波堤各自由度运动响应。研究发现：圆筒型和板架型浮式防波堤适用于不同海况下湿拖;网笼型浮式防波堤湿拖过程中运动响应幅值较大,建议使用半潜船运输。本文通过探究不同浮式防波堤湿拖过程中的运动响应,可为工程实际中浮式防波堤运输提供一定的借鉴和参考。     

舰船锚泊运动与六自由度操纵的数学建模研究

锚泊运动是舰船正常运行时必不可少的运动,当船舶在海上或港口停泊时,都需要借助锚链等进行舰船的定位。由于舰船在海上锚泊时会受到海风、海浪和洋流等作用力,导致锚泊的稳定性、安全性下降,不仅影响舰船的海上定位和作业,还有可能导致严重的事故。因此,研究舰船在多种因素下的锚泊运动具有重要的意义。船舶的锚泊性能与其在海浪中的六自由度运动息息相关,本文利用流体动力学原理建立了舰船锚泊运动的动力学模型,同时建立了非线性波浪力的数学模型,并在此基础上研究了舰船锚泊运动和六自由度操纵运动。本研究主要应用于舰船在恶劣条件下的安全锚泊,并提高舰船的操纵灵活性。     

船舶模拟控制器中的六自由度仿真系统设计

船舶的研发与设计过程非常的浩大而复杂,为了提高船舶的研发效率,同时减少船舶制造过程的下水实验次数,船舶工业领域投入大量精力研制船舶模拟控制平台。通过模拟各种海况,在实验室模拟和仿真船舶在海洋中的姿态和运动,从而降低开发成本和周期。本文对船舶六自由度模拟控制器平台进行系统的运动学分析,并基于运动模型设计船舶模拟控制器的仿真系统,进行船舶横摇角度的仿真分析。     

A consideration of the structural design of a large-scale floating structure

The land area of Japan, especially flat land, is very small compared with its economic size. Large-scale floating structures are one solution to satisfy the demand for space by utilizing the ocean. This paper presents a general view of the dynamic response characteristics of large-scale floating structures, pontoons and semi-submersibles. For example, it is shown that the natural frequencies of eigenmodes are higher than the natural frequency of heaving motion. The response of the outer framework of a structure is shown to be generally larger than the response of the central part. Within the limits of our present understanding of the general dynamic response characteristics of such structures, the design and analysis of semi-submersible, large-scale floating structures is discussed. For a pontoon-type large-scale floating structure, a type whose perimeter structure has been modified to become lighter and more rigid is proposed. With this modification, the dynamic response of the whole structure is imporved.     

Nonlinear dynamics of a submerged floating moored structure by incremental harmonic balance method with FFT

A submerged floating moored structure has a great potential in ocean engineering applications. The nonlinear dynamics of a submerged floating moored structure subjected to vertical excitation with possible slackness in the mooing system are investigated by incremental harmonic balance (IHB) method. Heaviside step function is introduced to describe the nonlinearity in axial stiffness arising from loss of mooring tension. The dimensionless governing equation is derived, and three parameters, frequency ratio η, damping ratio ζ and dimensionless net buoyancy W, are found to be independent. Due to the fact that the restoring force term is function of the unknown displacement and could barely be expressed in an explicit form of time, a fast Fourier transformation (FFT) is implemented in IHB method to simplify the Galerkin average procedure. Both stable and unstable solutions and both period-1 and bifurcated solutions are obtained by IHB method. The stability of the periodic solutions is investigated by Floquet theory. Parameter study is carried out. Results indicate that the system nonlinearity becomes stronger as dimensionless the net buoyancy W and damping ratio ζ decrease. A path to chaotic motions though a series of period doubling bifurcations is found. Multiple solutions are observed, and the domains of attraction are investigated by interpolated cell mapping (ICM) technique.     

VLFS的新型结构设计

作为一种新型的海洋浮式结构,将网架结构的设计理念应用于超大型海洋浮式结构物VLFS的设计.网架结构具有结构强度高、工业化程度高、制造难度低、安装便利和制造工期短等优点.运用ABAQUS有限元软件对新型VLFS浮式结构在海洋环境条件下的应力和应变进行分析,新型VLFS浮式结构的强度、稳定性和耐波性满足工程要求.