内孤立波下深水半潜式平台系统动力响应研究

我国南海海域海洋环境条件复杂且海水密度垂直层化现象显著,内孤立波活动频繁,因内孤立波而造成海洋开采平台破坏的案例屡见不鲜。依托水动力计算软件AQWA二次开发功能,采用Kdv方程,借助Fortran语言将深水半潜式平台立柱、浮箱、系泊系统3部分的内孤立波作用力叠加到外力项中,联合求解半潜式平台的6自由度动力响应特性。数值模拟结果表明,在内孤立波作用下,半潜式平台的运动及系泊线张力均受到了显著的影响。在不考虑系泊系统受内孤立波作用时,平台在纵荡和横荡方向上产生较大的漂移运动,最大偏移量较无内孤立波情况下增加了8倍;系泊线最大张力提高了17%,增加了系泊线断裂的风险。在考虑系泊系统受内孤立波作用时,平台的纵荡和横荡运动响应在原响应基础上继续提高15%,但是系泊线张力变化不大。内孤立波不同浪向下的平台纵荡和横荡响应相差也很明显;系泊系统合力在不同方向上的大小决定了平台不同方向上运动的大小。     

内孤立波作用下Spar平台的运动响应

建立了内孤立波作用下Spar平台运动响应的时域数值模型,并利用这一模型计算了内孤立波作用下Spar平台的运动响应。其中根据K-dv方程解出内孤立波的波面及水质点速度表达式,应用Morison公式求出内孤立波对Spar平台的水平作用力;由伯努力方程求解压强,通过在平台底面积分求出内孤立波对Spar平台的垂向作用力;在悬链线理论的基础上,分析锚链对平台的作用力,采用四阶Runge-Kutta方法求解运动方程。数值结果表明,当内孤立波不断接近海洋平台时,Spar平台受到的作用力随之增大,海洋平台会产生远大于表面波作用下的水平位移,从而证实了内孤立波是影响海洋平台稳定的重要因素,在海洋平台的设计和评估中内孤立波的作用是不可忽略的。     

内孤立波中半潜平台动力响应特性

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。     

内孤立波作用下Spar平台动力响应特性

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。     

两层流体中内波作用下Spar平台运动响应

研究两层流体中Spar平台在内波作用下的运动响应问题。在线性势流理论框架,提出在内波作用下Spar平台运动响应及分段式悬链线系泊张力特性的计算方法。数值分析两层流体内界面位置、入射内波的波长以及系泊索初始预张力对Spar平台运动响应及其系泊索张力特性的影响规律,结果表明内波对Spar平台纵摇运动响应的影响是小的,但对Spar平台纵荡与垂荡运动响应及其系泊索张力的影响是不可忽视的。因此,在Spar平台的设计中,考虑内波的影响是重要的。     

SPH方法的孤立波与部分淹没结构物相互作用数值计算研究

为研究孤立波作用下结构物周围流场特征,基于无网格SPH方法,建立孤立波与海洋结构物相互作用模型,对不同波幅孤立波作用下部分淹没矩形结构物周围波面、流速、涡量及结构受力特征进行计算分析,探索了相对波高对非淹没结构物周围流场的影响规律。结果表明:流场特征与相对波高密切相关,相对波高较小时,波面、流速、涡量及结构荷载均较为光滑,相对波高在0.2以上时,波峰爬升至结构物顶部并在越过结构物后与水槽内水体碰撞造成流场波动,波面、流速、涡量及结构荷载的波动幅度随着相对波高增大而增大,流场更加复杂,结构物水平和垂向负压也越大,且结构物周围涡分布逐渐向深度方向和下游方向发展。     

相同尺度地形与背景流共振生成内孤立波机制

为研究内孤立波的地形和背景流共振机制,用地形和背景流共振机制计算了3个潜标观测的内孤立波(不同模态、不同波长)的流速和传播速度,并与观测到的内孤立波进行比较。潜标观测的第一模态内孤立波(波长分别为6.4和3.3km)都是下凹型内孤立波,2个内孤立波的传播速度约为1.4m/s、最大振幅约为48m,水平流向结构都是上层西北向、下层东南向,波长3.3km 的内孤立波波峰前后有更明显的下降流和上升流。用共振机制计算出的第一模态和第二模态纬向流速的垂向结构与观测相同,最大纬向流速出现的深度与观测一致,分别相差5和12m。用共振机制计算出的内孤立波传播速度与用 KdV 方程计算的传播速度相当,共振机制计算波速为0.66~1.21m/s,KdV 方程计算波速为0.79~1.40m/s。     

张力腿平台内孤立波作用特性数值模拟

依据三类内孤立波理论KdV、eK dV和MCC的适用性条件,采用Navier-Stokes方程为流场控制方程,以内孤立波诱导上下层深度平均水平速度作为入口边界条件,建立了两层流体中内孤立波对张力腿平台强非线性作用的数值模拟方法。结果表明,数值模拟所得内孤立波波形及其振幅与相应理论和实验结果一致,并且在内孤立波作用下张力腿平台水平力、垂向力及力矩数值模拟结果与实验结果吻合。研究同时表明,张力腿平台内孤立波载荷由波浪压差力、粘性压差力和摩擦力构成,其中摩擦力很小,可以忽略;水平力的主要成分为波浪压差力和粘性压差力,粘性压差力与波浪压差力相比较小却不可忽略,流体粘性的影响较小;垂向力中粘性压差力很小,流体粘性影响可以忽略。     

基于遥感的南海北部中尺度涡对内孤立波传播的影响

海洋内孤立波和中尺度涡是南海北部常见的中尺度动力过程。本文利用2010-2015年的Terra/Aqua-MODIS、ENVISAT ASAR和多源卫星高度计资料开展了南海海洋内孤立波和中尺度涡遥感探测研究,分析了中尺度涡对内孤立波传播方向的影响。结果表明,中尺度涡和内孤立波主要在南海东北部海域共存,当二者共存时,气旋（冷涡）促使内孤立波偏离原来的传播方向,向西偏南方向传播;反气旋（暖涡）促使内孤立波向西偏北方向传播,气旋与反气旋改变的内孤立波传播方向刚好相反。内孤立波和中尺度涡共存时间主要集中在3-9月,其中,3月受气旋和反气旋的共同作用,内孤立波传播方向几乎无变化;4月和5月,主要受气旋影响,内孤立波偏离原来传播方向向南传播;6-9月,主要受反气旋影响,内孤立波偏离原来的传播方向向北传播。本文利用遥感手段探索了海洋中尺度涡对内孤立波传播方向的影响,结果与现场观测结果一致。     

风浪流中涡激共振对Spar型浮式风机运动响应的影响

以Spar型浮式风机为研究对象,研究涡激力对于浮式风机系统运动的影响。对多体动力学软件FAST进行二次开发,加入涡激力的计算接口,实现了在平台涡激、波激、空气动力载荷及系泊联合作用下的Spar浮式风机系统的运动响应的计算。计算了在风、浪、流联合作用下,频率锁定现象发生时,Spar基础的运动响应,分析了风浪下Spar风机运动响应的涡激运动特性,并研究了不同的入流角度的影响。结果表明:考虑涡激力后,Spar基础的横荡运动明显增大;风浪流同向时,风浪的存在会抑制流载荷引起的横荡在涡泄频率的运动;在流与风浪垂直时,会激发Spar基础的更大的纵荡运动响应。     

Experimental Study on Ocean Internal Wave Force on Vertical Cylinders in Different Depths

A series of experimental studies about the force of internal solitary wave and internal periodic wave on vertical cylinders have been carried out in a two-dimensional layered internal wave flume. The internal solitary waves are produced by means of gravitational collapse at the layer thickness ratio of 0.2, and the internal periodic waves are produced with rocker-flap wave maker at the layer thickness ratio of 0.93. The wave parameters are obtained through dyeing photography. The vertical cylinders of the same size are arranged in different depths. The horizontal force on each cylinder is measured and the vertical distribution rules are researched. The internal wave heights are changed to study the impact of wave heights on the force. The results show that the horizontal force of concave type internal solitary wave on vertical cylinder in the upper-layer fluid has the same direction as the wave propagating, while it has an opposite direction in the lower-layer. The horizontal force is not evenly distributed in the lower fluid. And the force at different depths increases along with wave height. Internal solitary wave can produce an impact load on the entire pile. The horizontal force of internal periodic waves on the vertical cylinders is periodically changed at the frequency of waves. The direction of the force is opposite in the upper and lower layers, and the value is close. In the upper layer except the depth close to the interface, the force is evenly distributed; but it tends to decrease with the deeper depth in the lower layer. A periodic shear load can be produced on the entire pile by internal periodic waves, and it may cause fatigue damage to structures.     

畸形波作用下半潜浮式风机系泊失效停机响应分析

半潜浮式风机逐渐在深海风电开发中受到关注,建立风机、平台与系泊结构耦合数值计算模型,通过FAST与AQWA链接进行风机塔基荷载及平台运动响应相互耦合传递,基于随机波与极限波组合模型生成畸形波时程序列,进行半潜浮式风机系泊失效全过程时域模拟计算分析,得出系泊锚链张力、风机、塔筒和平台运动时程响应,探究系泊失效、风机停机和叶片变桨速率对浮式风机平台系泊结构动力响应的影响。结果表明：畸形波作用下浮式平台和系泊结构动力响应显著,系泊失效导致塔基剪力增加,平台纵荡和纵摇运动响应显著增大;风机停机会引起系泊锚链张力显著减小,转子推力、塔基剪力和叶尖挥舞位移响应逐渐衰减,平台纵荡、纵摇和横摇运动响应显著减小;随着叶片变桨速率增加,风机转子推力和塔基剪力波动幅值增大。     

内孤立波对小直径直立桩柱作用力的实验研究

内孤立波具有较大的振幅与较强的垂向剪切,能对海洋工程设施产生极大的破坏作用。本文设计实验研究了内孤立波与直立小直径桩柱的相互作用,采用粒子图像速度测量法(PIV)测量内孤立波的流速场,并采用自行设计的测力天平测量桩柱受力,测量分析了内孤立波对小直径直立桩柱产生作用力的实验值,与Morison公式计算的理论值比较。实验结果表明,第一模态内孤立波的流速方向以及作用力在桩柱的上下部分方向相反,产生很强的速度切变和扭力,对小直径直立桩柱造成破坏。通过与Morison公式计算的理论值比较,发现实验值与理论值的大小以及分布规律基本相同。     

Effects of mesoscale eddies on the internal solitary wave propagation

The mesoscale eddy and internal wave both are phenomena commonly observed in oceans. It is aimed to investigate how the presence of a mesoscale eddy in the ocean affects wave form deformation of the internal solitary wave propagation. An ocean eddy is produced by a quasi-geostrophic model in f-plane, and the one-dimensional nonlinear variable-coefficient extended Korteweg-de Vries (eKdV) equation is used to simulate an internal solitary wave passing through the mesoscale eddy field. The results suggest that the mode structures of the linear internal wave are modified due to the presence of the mesoscale eddy field. A cyclonic eddy and an anticyclonic eddy have different influences on the background environment of the internal solitary wave propagation. The existence of a mesoscale eddy field has almost no prominent impact on the propagation of a smallamplitude internal solitary wave only based on the first mode vertical structure, but the mesoscale eddy background field exerts a considerable influence on the solitary wave propagation if considering high-mode vertical structures. Furthermore, whether an internal solitary wave first passes through anticyclonic eddy or cyclonic eddy, the deformation of wave profiles is different. Many observations of solitary internal waves in the real oceans suggest the formation of the waves. Apart from topography effect, it is shown that the mesoscale eddy background field is also a considerable factor which influences the internal solitary wave propagation and deformation.     

波浪作用下锚链系泊浮式防波堤动力响应的数值模型研究

浮式防波堤充分利用波能在水深方向的分布特性,在满足工程消浪要求的同时对海域水沙交换影响较小,且能够快速布置,在某些实际工程有一定应用前景。为了深入了解波浪作用下浮式防波堤的动力响应,基于OpenFOAM标准求解器olaFlow,在刚体运动求解计算中植入锚链求解模块MOODY(mooring cable dynamics),实现了基于重叠网格方法的浮体运动与锚链受力耦合求解,建立了锚链系泊浮式防波堤动力响应的二维数值模型。利用该数值模型对锚链系泊单方箱浮式防波堤在波浪作用下的透射系数、运动响应、锚链张力进行了模拟,并和相关试验结果进行了比较。结果表明,模型能够准确模拟二维波浪和浮式防波堤的相互作用,并用于三维模型的改进。     

Wind and wave induced behaviour of offshore guyed tower platforms

Offshore guyed tower platforms belong to the group of compliant offshore platforms which are most suited for deep water exploration. The basic feature of compliant offshore platforms is that they are designed to move with the waves, in at least some degrees-of-freedom. As far as excitation of wave frequencies is concerned, the system opposes wave forces by inertial effects. The offshore guyed tower derives its stability against lateral movement from its mooring system.In this study, the response of offshore guyed towers to random forces generated by wind and wave is investigated. The exposed portion of the tower is subjected to the action of turbulent wind, while the submerged portion is acted upon by random wave forces. The analysis includes the nonlinearities due to the Morison equation of drag force, the variable submergence effect due to waves, the instantaneous position of the tower and force excursion relation of the mooring lines. A parametric study is conducted to investigate the behaviour of the tower under waves, and the combined effect of wind and wave forces.     

顺应式海洋平台慢漂运动物理模型试验研究

为研究顺应式海洋平台慢漂运动的影响因素,以截断圆柱和漂浮方箱为例进行了不规则波作用下的慢漂运动模型试验。测量了不同系泊刚度条件下的漂浮方箱以及相同系泊刚度条件下的截断圆柱和漂浮方箱在静水中自由衰减运动和在不规则波中的运动响应,并将运动响应分解成一阶波频运动响应和二阶低频运动响应,分析了系泊刚度和浮体形状对浮体运动的影响。通过物理模型试验发现了系泊刚度及浮体形状对顺应式系泊浮体一阶运动标准差和二阶低频运动平均漂移值和标准差的关系。结果表明由于顺应式浮体的固有周期远离波浪谱峰周期时,系泊刚度以及浮体形状对慢漂运动的一阶运动响应影响不大;二阶低频运动相对偏离平衡位置的平均值和标准差均随系泊刚度增大而减小,浮体形状同样对慢漂运动的二阶低频纵荡运动响应影响较大。试验结果为实际海洋工程的外形选择和系泊刚度选择提供数据支持。     

Numerical simulation of solitary wave scattering by a circular cylinder array

The interaction of a solitary wave with an array of surface-piercing vertical circular cylinders is investigated numerically. The wave motion is modeled by a set of generalized Boussinesq equations. The governing equations are discretized using a finite element method. The numerical model is validated against the experimental data of solitary wave reflection from a vertical wall and solitary wave scattering by a vertical circular cylinder respectively. The predicted wave surface elevation and the wave forces on the cylinder agree well with the experimental data. The numerical model is then employed to study solitary wave scattering by arrays of two circular cylinders and four circular cylinders respectively. The effect of wave direction on the wave forces and the wave runup on the cylinders is quantified.     

实验室造波条件对内孤立波发展影响的直接数值模拟

内孤立波具有振幅尺度大、能量集中的特点,其引起流场和密度场的迅速变化可能对海洋工程结构物以及水下潜体造成严重威胁。因此研究不同造波条件下生成的内孤立波运动的流场特征具有重要的学术意义和实际应用价值。采用直接数值模拟方法和给定的初始密度场密度跃迁函数,对重力塌陷激发内孤立波的运动过程进行研究,探讨了不同造波条件下,激发产生的内孤立波波型、涡度、振幅和水平速度等流场特征。结果表明:(1)直接模拟数值方法能够模拟内孤立波传播过程中的密度界面波型反转现象;(2)从定性和定量的角度,证实了不稳定内孤立波传播过程中存在能量的向后传递;(3)对于相同的台阶深度(水闸两侧初始密度界面的高度差),初始涡流保持相同,但是随着上下层水深比的减小,其强度下降显著;(4)台阶深度对初始涡流的垂直结构的影响要大于上下层水深比,且台阶深度对内孤立波的振幅、水平速度的影响显著。     

Effect of wave nonlinearity on fatigue damage and extreme responses of a semi-submersible floating wind turbine

Floating wind turbine has been the highlight in offshore wind industry lately. There has been great effort on developing highly sophisticated numerical model to better understand its hydrodynamic behaviour. A engineering-practical method to study the nonlinear wave effects on floating wind turbine has been recently developed. Based on the method established, the focus of this paper is to quantify the wave nonlinearity effect due to nonlinear wave kinematics by comparing the structural responses of floating wind turbine when exposed to irregular linear Airy wave and fully nonlinear wave. Critical responses and fatigue damage are studied in operational conditions and short-term extreme values are predicted in extreme conditions respectively. In the operational condition, wind effects are dominating the mean value and standard deviation of most responses except floater heave motion. The fatigue damage at the tower base is dominated by wind effects. The fatigue damage for the mooring line is more influenced by wind effects for conditions with small wave and wave effects for conditions with large wave. The wave nonlinearity effect becomes significant for surge and mooring line tension for large waves while floater heave, pitch motion, tower base bending moment and pontoon axial force are less sensitive to the nonlinear wave effect. In the extreme condition, linear wave theory underestimates wave elevation, floater surge motion and mooring line tension compared with fully nonlinear wave theory while quite close results are predicted for other responses.