Experimental and numerical study of the effects of heave plate on the motion of a new deep draft multi-spar platform

The heave motion of a floating structure is critical, as a favorable heave characteristic permits dry tree systems, amongst other benefits. The heave response can be suppressed by installing heave plates. However, the associated hydrodynamic effects, which include viscous damping and added mass, are very complicated. Moreover, there are limited experimental investigations to understand the heave plate effects on actual platform designs. This paper aims to study the abovementioned issue based on a novel deep draft multi-spar (DDMS) platform, for four different configurations (with/without upper and lower heave plates). A set of experiments (free decay, regular and irregular wave tests) are conducted, and compared with time domain and linearized frequency domain analyses. Amongst other things, the investigations and discussions include the added mass and damping coefficients for the platform and heave plates, comparison of experimental and numerical results, and the influence of the heave plates on the surge, heave and pitch motions.     

月池对FDPSO水动力性能的影响分析

采用数值模拟的方法,分析了不同尺寸、位置、吃水的月池对FDPSO船体附加质量和阻尼系数的影响。建立FDPSO三维水动力模型,采用水动力计算软件AQWA,研究了月池在不同尺寸、位置、吃水情况下对FDPSO横荡、垂荡、横摇附加质量和阻尼力的影响。结果表明：月池内流体的“活塞”振荡会增大船体的垂荡运动;FDPSO船体附加质量和阻尼力在频域范围内存在极值,垂向附加质量和阻尼力极值对应的波浪频率位置与月池尺寸、吃水有关,与位置无关。     

深水八角形FDPSO总体性能分析

从技术与经济性角度对比分析现有的FDPSO船型,最终选定八角形FPDSO为目标船型。根据FDPSO功能要求制定技术指标,进行总体设计、总体尺度规划和垂荡板尺寸优化,以及系泊系统设计,完成八角形FDPSO的概念设计,计算分析其运动性能、稳性和系泊系统能力,结果表明八角形FDPSO总体性能满足要求,系泊系统设计合理。     

多点系泊定位FDPSO船体水动力性能数值模拟和模型试验研究(英文)

由于中国南海海域海况十分恶劣,浮式钻井生产储油轮(FDPSO,Floating,Drilling,Production,Storage and Offloading vessel)定位方式的研究是海洋工程界值得关注的课题。文章采用数值模拟和模型试验的方法对多点系泊FDPSO水动力性能开展研究。数值模拟包括FDPSO船体频域水动力性能计算和船体/锚链时域耦合分析。船体频域水动力性能计算得到了水动力系数,波浪力和运动幅值响应算子;时域耦合数值分析得到了中国南海海域一年一遇海况和百年一遇海况下船体六自由度运动时历。模型试验在上海交通大学海洋工程深水池开展,包括静水衰减试验,白噪声试验和不规则波试验。对数值计算结果和模型试验结果进行了比较,验证了数值结果的准确性,并对多点系泊FDPSO在中国南海海域的水动力性能进行了研究。     

Spar平台垂荡板受迫振荡水动力特性研究

首先针对圆形实板以及不同透空率下垂荡板作受迫正弦振荡的水动力特性进行了数值模拟研究,得到垂荡板作正弦振荡的阻力和附加质量系数,进而分析得出透空率对垂荡板阻尼及附加质量的影响规律;其次比较了相同透空率情况下不同小孔数目对垂荡板水动力特性的影响,并比较了不同形状垂荡板的水动力特性;最后还对双板之间的间距进行了优化计算.在此基础上综合考虑垂荡板受迫振荡水动力特性,为深水Spar平台的垂荡板优化设计提供技术指导,使其能够有效地改善Spar平台的垂荡运动性能.     

双层水平板型透空式防波堤消波性能试验研究

用两块相同尺寸的水平板结构作为一种防波堤,上层板位于自由水面处,下层板在其下某一深度处。对此形式防波堤进行了一系列的消浪效果试验研究,利用得到的反射系数和透射系数来反映此结构的消波性能,考查了相对板宽,相对水深和相对板间距及波陡对反射系数和透射系数的影响。     

浮式钻井生产储卸装置运动性能分析

首先介绍了浮式钻井生产储卸装置(FDPSO)设有月池开口的船型特点,为评估月池开口对FDPSO船体运动性能的影响,设计了不同月池尺寸的方案。采用三维势流理论对不同月池尺寸方案水动力性能进行计算,得到FDPSO船体运动传递函数,总结FDPSO船体横摇和垂荡运动响应随月池尺寸变化的规律,并确定合理的目标FDPSO方案。最后对目标FDPSO方案进行运动性能实例分析,评估目标FDPSO方案的耐波性。     

基于N-S方程的航行船舶辐射问题数值模拟

基于N-S(Navier-Stokes)方程,进行了航行船舶辐射问题的数值模拟,包括强制垂荡和强制纵摇的模拟.计算了船舶垂荡和纵摇的附加质量和阻尼.数值模拟中,控制方程--BANS(Reynolds Averaged Navier-Stokes)方程和连续性方程使用有限体积法离散,非线性自由面采用VOF方法处理.文中给出了以不同航速前进的船舶强制垂荡和纵摇的力与力矩,以及船舶垂荡和纵摇的附加质量系数和阻尼系数,并与DUT(Delft University of Technology)的试验数据进行了比较,二者吻合良好.     

气动载荷对半潜式海上风机运动响应的影响分析

以DeepCwind海上风机为研究对象,利用有限元软件ANSYS AQWA进行风机频域水动力数值仿真分析,得到水动力参数以及幅频响应曲线,将得到的水动力参数导入到FAST软件中,对风机气动-水动-锚泊系统的时域耦合运动分析。在此基础上,讨论了气动载荷对于半潜式风机运动响应的影响。结果表明,气动载荷对于半潜式风机运动响应的影响较大且不可忽略,横摇,横荡以及首摇运动随着气动载荷的增大而增大,垂荡运动随着气动载荷的增大而减小,风作用在叶片上所产生的气动阻尼削弱了垂荡运动,增强了横荡、横摇和首摇运动。     

Trapped Modes in a Three-Layer Fluid

In this work, trapped mode frequencies are computed for a submerged horizontal circular cylinder with the hydrodynamic set-up involving an infinite depth three-layer incompressible fluid with layer-wise different densities. The impermeable cylinder is fully immersed in either the bottom layer or the upper layer. The effect of surface tension at the surface of separation is neglected. In this set-up, there exist three wave numbers: the lowest one on the free surface and the other two on the internal interfaces. For each wave number, there exist two modes for which trapped waves exist. The existence of these trapped modes is shown by numerical evidence. We investigate the variation of these trapped modes subject to change in the depth of the middle layer as well as the submergence depth. We show numerically that two-layer and single-layer results cannot be recovered in the double and single limiting cases of the density ratios tending to unity. The existence of trapped modes shows that in general, a radiation condition for the waves at infinity is insufficient for the uniqueness of the solution of the scattering problem.     

三层流体中的捕获模态分析（英文）

In this work, trapped mode frequencies are computed for a submerged horizontal circular cylinder with the hydrodynamic set-up involving an infinite depth three-layer incompressible fluid with layer-wise different densities. The impermeable cylinder is fully immersed in either the bottom layer or the upper layer. The effect of surface tension at the surface of separation is neglected. In this set-up, there exist three wave numbers: the lowest one on the free surface and the other two on the internal interfaces. For each wave number, there exist two modes for which trapped waves exist. The existence of these trapped modes is shown by numerical evidence. We investigate the variation of these trapped modes subject to change in the depth of the middle layer as well as the submergence depth. We show numerically that two-layer and single-layer results cannot be recovered in the double and single limiting cases of the density ratios tending to unity. The existence of trapped modes shows that in general, a radiation condition for the waves at infinity is insufficient for the uniqueness of the solution of the scattering problem.     

带有月池的非对称结构物水波辐射和激励力（英文）

A highly efficient "hybrid integral-equation method" for computing hydrodynamic added-mass, wave-damping, and wave-exciting force of general body geometries with a vertical axis of symmetry is presented. The hybrid method utilizes a numerical inner domain and a semi-infinite analytical outer domain separated by a vertical cylindrical matching boundary.Eigenfunction representation of velocity potential is used in the outer domain; the three-dimensional potential in the inner domain is solved using a "two-dimensional" boundary element method with ring sources and ring dipoles to exploit the body symmetry for efficiency. With proper solution matching at the common boundary, both radiation and diffraction potentials can be solved efficiently while satisfying the far-field radiation condition exactly. This method is applied to compute the hydrodynamic properties of two different body geometries: a vertical-walled moonpool with a bottom plate that restricts the opening and a spar-like structure with a diverging bottom opening inspired by designs of floating Oscillating Water Columns. The effects of the size of the bottom opening on the hydrodynamic properties of the body are investigated for both geometries. The heave motion of the floater as well as the motion of the internal free surface under incident wave excitation are computed and studied for the spar-like structure.     

母船垂荡运动下拖缆响应研究

基于弯矩平衡方程和有限元离散单元法建立拖缆离散动力学模型,通过对拖缆离散方程组线性化处理,将非线性动力学方程转化为关于求解角度的线性问题。设定缆绳初始形态,通过时间迭代对方程求解得到拖曳系统稳定运动形态。母船在海面会发生升沉运动,由于母船垂荡运动对水下拖缆的耦合影响,拖曳系统稳定形态受到破坏,拖缆受力发生改变,系统可能处于危险状态。考虑母船垂荡运动的耦合效应,通过MATLAB对拖曳系统进行仿真计算,得到拖缆的运动参数和受力响应情况,对拖曳系统在实际作业中提供参考。     

Comparative assessment of liquid sloshing in dry and wet storage tank of floating offshore platform

In order to explore the characteristics of the single-layer liquid sloshing in offshore dry oil storage tank and the two-layer liquid sloshing in offshore wet oil storage tank, two series of experiments were carried out: one was free surface sloshing in a closed rectangular tank partially filled with colored water, and the other was interfacial sloshing in the identical tank but completely filled with white oil and colored water. The tank was mounted on a shake table and was subjected to harmonic horizontal excitation with different excitation amplitudes and a wide range of excitation frequencies, including the first seven natural modes of single-layer or two-layer liquid system. The present study find that the frequency responses of interfacial sloshing wave are analogous to those of the free surface sloshing wave, but smaller in amplitudes. The experiments also produce results that are unique to the two-layer liquid sloshing. For example, when the external excitation frequency is equal to or close to the odd mode natural frequency of two-layer liquid system, a complicated three-dimensional (3D) gravity-capillary wave might be generated at the oil-water interface. Finally, the comparisons of free surface and interfacial sloshing in the viscous damping ratio, higher sloshing modes, impact pressure amplitude and mass center displacement were conducted, which revealed the superiority of wet storage technology in structural safety and dynamic stability.     

多浮体铰接薄板结构运动响应研究

应用Newman的广义运动模态分解方法和拉格朗日乘子法,基于波浪辐射和绕射理论建立了铰接多浮体结构水动力响应的运动方程,应用预修正快速傅里叶变换(p FFT)的边界元方法对由15块板组成的铰接多浮体结构的运动响应进行了研究。数值结果表明该p FFT方法计算精度和计算速度均很高,可用于任意形状和约束状态的多体结构的水动力分析。板间距的改变对铰接点处垂荡和横摇影响较大。     

驳船升沉运动和波浪联合作用对沉管管段运动特性的影响

文章探讨驳船吊挂沉放法进行沉管管段的沉放作业过程中,驳船升沉运动和波浪联合作用对沉管管段运动特性的影响。采用边界元方法求解作用在沉管管段的波浪力,驳船升沉运动考虑为简谐运动,应用四阶Runge-Kutta方法求解沉管管段的运动方程。通过数值算例分析,探讨了驳船做不同振幅与不同相位的升沉运动和波浪联合作用下沉管管段的运动特性。     

大吨位沉船打捞多体系统耦合水动力特性研究

双驳船抬吊法是大吨位沉船打捞中主要采用方法之一。两艘驳船、难船构成的系统具有尺度大、间距小等特点,波浪环境形成复杂水动力耦合效应,基于势流理论,增加人工阻尼修正其粘性影响,利用AQWA软件开展单驳船、两驳船约束其一、两驳船耦合三种状态多体系统水动力数值预报研究,重点分析不同状态下驳船运动响应及波浪载荷,探讨了驳船约束模式、浪向角及周期对驳船水动力影响规律,探明了浪向角与周期对驳船耦合水动力及运动响应不利干扰,对指导沉船打捞多体系统的空间布局与作业海况具有重要意义。     

波浪运动补偿平台广义升沉位移的实时预报

具有波浪运动补偿功能的稳定平台可有效减少船舶在风浪中的摇摆和升沉运动对某些海上作业和设备的影响.为了有效地进行波浪运动补偿,需要对该平台的广义升沉位移(横摇、纵摇以及升沉的耦合作用结果)进行极短时预报.本文采用时间序列分析理论中的自回归(AR)模型作为预报模型,对波浪运动补偿平台的广义升沉位移进行极短时预报.在以往的研究中,通常采用递推最小二乘法AR模型进行在线参数估计.但是采用递推最小二乘法进行参数估计容易引起参数爆发,从而影响AR模型的稳定性.针对该问题,本文采用阻尼递推最小二乘法对AR模型进行在线参数估计,并结合实验获得的平台控制点的广义升沉位移数据进行实时建模预报.仿真结果表明,采用阻尼递推最小二乘法进行参数估计能抑制参数爆发,并能提高AR模型实时预报精度.     

一种新型水下平台的水平面运动控制

新型水下平台用于从水面布放设备至海底,或从海底回收至水面指定位置,其主要运动形式为垂向无动力下潜或上浮。为了克服垂向运动过程中来自水平方向洋流的扰动,需要对平台的水平位置和首向进行控制。针对平台水动力系数等模型参数难以计算,水平洋流未知、且水平推进系统布置特殊的特点,设计了不依赖于模型参数且具有全局稳定性的水平面运动控制系统,并应用Lagrange方法对推力分配进行了优化从而减小运动控制的总功耗。最后通过仿真对控制算法进行了验证。     

冲击载荷下加筋板非线性瞬态分析

本文用半解析的方法分析了横向冲击载荷下加筋板的非线性瞬态响应。考虑膜力的存在，忽略筋截面上的剪切应力，引入板的应力函数，采用离散加筋板模型，运用能量原理建立加筋板的动响应控制方程。假设挠度为双级数形式，运用迦辽金法，将加筋板的动响应方程转化为一个多自由度的动力系统，采用数值方法来求解。本文最后给出了几个模型的计算结果。