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。     

一种非对称无横撑半潜式平台的整体强度评估

本文基于设计波法对某新型半潜式平台的整体强度进行了研究分析。不同于传统半潜式平台结构形式,该新型半潜式平台的浮筒一大一小,对应的两组立柱也是一大一小,因此结构关于中纵剖面是非对称的;此外该半潜式平台没有横撑结构。本文首先确定了作业吃水和自存吃水情况下新型半潜式平台四种典型危险工况对应的设计波参数,然后研究分析了不同危险工况下半潜式平台的整体强度,并对新型半潜式平台与传统半潜式平台在整体强度方面的差异进行了比较。研究结果表明,该新型平台的最大应力最易出现在大立柱内侧与甲板连接拐角区域,而传统有横撑半潜式平台的最大应力多发生在横撑与立柱连接区域。此外,浮筒与甲板之间的大倒角设计有助于提高新型半潜式平台的整体强度。     

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。     

波-流场中孤立桩柱上作用力系数的研究

本文基于波-流场中的线性波理论和模型试验,探讨了在同向波-流场中的孤立桩柱及按莫里逊(Morison)公式计算波-流力时的作用力系数,提出了以波-流场特征系数为参数的相对速度力系数的计算公式,并根据试验中实测的最大波-流力值,用二元线性回归的数理统计方法,求得了拟合最佳的速度力系数和惯性力系数。     

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。     

用Morison公式试算海洋内孤立波对桩柱的作用力和力矩

根据实测流速资料采用Morison公式初步计算了海洋内孤立波对桩柱的作用力和力矩。内孤立波对桩柱的作用力与表面波的作用力是明显不同的。内孤立波的作用力几乎分布在整个深度范围；它在铅直方向不但有量值变化。也有方向改变——第一模态内波的作用力在桩柱的上、下部位作用方向相反。表面波对桩柱的作用力随深度的增大较快的衰减。且深度的改变不会使作用力的方向发生变化。计算结果表明：引起2．1m／s水平流的内孤立波对桩柱产生的总作用力约相当于300m波长、18m波高的表面波的总作用力；由于海洋内孤立波能引起很大的水平流，它对海上石油平台桩柱产生的总作用力以及相对于海面的力矩是不能忽略的。因此，在海上石油平台设计中应充分重视内孤立波的作用。     

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。     

张力腿平台水动力参数计算

张力腿平台作为一种深水平台 ,其半顺应半固定的运动特征 ,成为在复杂的深海海洋环境中进行海洋石油勘探、开采一种重要结构型式。在张力腿平台波浪载荷的计算中根据产生波动流场的因素不同将波浪载荷分为绕射效应和辐射效应。本文对辐射效应深入研究并以附加质量、附加阻尼等水动力参数的形式计算了辐射效应对张力腿平台的载荷影响。在计算水动力参数时将平台简化为浮式直立柱群 ,采用势流理论 ,引进改进平面波法计入柱体间水动力相互作用得到辐射波速度势的半解析解 ,引入大间距假设、通过非平面波修正 ,精确地求解了柱群的辐射波的载荷作用     

内孤立波作用下顶部张紧式立管动力特性

基于内孤立波mKdV理论,采用考虑内流的细长杆动力学方程,结合改进的Morison公式,研究两层流体中内孤立波与顶张立管的相互作用问题。针对东沙群岛南部海域附近某实测内孤立波特征参数,计算分析在该内孤立波作用下某顶张立管的内孤立波载荷与运动响应,以及立管横截面弯矩及其应力的变化特性。研究表明,内孤立波不仅会对顶张立管产生突发性的冲击载荷以及大幅度水平变形,而且还会使其横截面弯矩及其应力显著增大。因此在深海立管的设计与应用中,内孤立波的影响是不可忽视的。     

A Prediction Method of Internal Solitary Wave Loads on the Semi- Submersible Platform

An investigation into the prediction method for internal solitary waves (ISWs) loads on the columns and caissons of the semi-submersible platform found on three kinds of internal solitary wave theories and the modified Morison Equation is described. The characteristics of loads exerted on the semi-submersible platform model caused by the ISWs have been observed experimentally, and the inertial and drag coefficients in Morison Equation are determined by analyzing the forces of experiments. From the results, it is of interest to find that Reynolds number, KC number and layer thickness ratio have a considerable influence on the coefficients. The direction of incoming waves, however, is almost devoid of effects on the coefficients. The drag coefficient of columns varies as an exponential function of Reynolds number, and inertia coefficient of columns is a power function related to KC number. Meanwhile, the drag coefficient of caissons is approximately constant in terms of regression analysis of experimental data. The results from different experimental conditions reveal that the inertia coefficient of caissons appears to be exponential correlated with upper layer depths.

     

An experimental investigation of hydrodynamic coefficients for a vertical truncated rectangular cylinder due to regular and random waves

The research into hydrodynamic loading on ocean structures has concentrated mostly on circular cross-section members and relatively limited work has been carried out on wave loading on other cross-sections such as rectangular sections. These find applications in many offshore structures as columns and pontoons in semi-submersibles and tension-leg platforms. The present investigation demonstrates the behaviour of rectangular cylinders subject to wave loading and also supplies the hydrodynamic coefficients for the design of these sections.This paper presents the results of wave forces acting on a surface piercing truncated rectangular cylinder set vertically in a towing tank. The experiments are carried out in a water depth of 2.2 m with regular and random waves for low Keulegan–Carpenter number up to 6. The rectangular cylinder is of 2 m length, 0.2 m breadth and 0.4 m width with a submergence depth of 1.45 m from still water level. Based on Morison equation, the relationship between inertia and drag coefficients are evaluated and are presented as a function of KC number for various values of frequency parameter β, for two aspect ratios of cylinders, equals to 1/2 and 2/1. Drag and inertia coefficients obtained through regular wave tests are used for the random wave analysis to compute the in-line force spectrum.The results of the experiments show the drag and inertia coefficients are strongly affected by the variation in the aspect ratios of the cylinder. The drag coefficients decreases and inertia coefficients increases with increase in Keulegan–Carpenter number up to the range of KC number tested. The random wave results show a good correlation between measured and computed force spectrums. The transverse forces in both regular and random waves are found to be small compared to in-line forces.     

Probability distribution of random wave forces in weakly nonlinear random waves

Based on the second-order random wave theory, the joint statistical distribution of the horizontal velocity and acceleration is derived using the characteristic function expansion method. From the joint distribution and the Morison equation, the theoretical distributions of drag forces, inertia forces and total random wave forces are determined. The distribution of inertia forces is Gaussian as that derived using the linear wave model, whereas the distributions of drag forces and total random forces deviate slightly from those derived utilizing the linear wave model. It is found that the distribution of wave forces depends solely on the frequency spectrum of sea waves associated with the first order approximation and the second order wave–wave interaction.     

关于小直径垂直桩柱结构的波浪力研究

本文归纳了应用Morison方程中涉及的研究成果。分别从阻力系数和惯性力系数。规则波与不规则波，二阶力和线性化，桩群受力等方面进行了论述。对目前该领域的研究给出了系统的介绍。     

In-line force on a cylinder translating in oscillatory flow

Experiments were conducted with smooth and sand-roughened cylinders moving with constant velocity in a sinusoidally oscillating flow to determine the drag and inertia coefficients and to examine the effect of wake biasing on the modified Morison equation. The various flow parameters such as the relative cylinder velocity. Reynolds number, and the Keulegan-Carpenter number were varied systematically and the in-line force measured simultaneously. The principal results, equally valid for both smooth and rough cylinders, are as follows: the drag coefficient decreases with increasing relative current for a given Reynolds number and Keulegan-Carpenter number; the effect of wake biasing on the drag and inertia coefficients is most pronounced in the drag-inertia dominated regime; and the two-term Morison equation with force coefficients obtained under no-current conditions is not applicable to the prediction of wave and current induced loads on circular cylinders.     

Wave forces acting on a submerged horizontal circular cylinder in oblique waves and on a vertical cylinder in deep waves

This paper presents a method of estimating wave forces acting on a submerged horizontal circular cylinder fixed in oblique waves.The experiments show that drag and inertia coefficients in beam sea are available for calculating the wave forces in oblique waves.Wave forces exerted on a vertical circular cylinder in deep waves are also investigated.The experimental results show that wave forces acting on the vertical cylinder coincide approximately with hydrodynamic forces acting on a submerged circular cylinder in an oscillating fluid.     

流向Morison 型波浪力的高阶矩分析

通过理论研究定量地说明流向Morison波浪力,即拖曳力和惯性力的高阶统计矩随采样次数增加的规律.主要应用二阶Stokes波理论,推导了流向Morison波浪力的前四阶累积量.计算了作用于实际海底管线上的流向Morison波浪力的偏斜度和峰度.结果表明,随着采样次数的增加,拖曳力和惯性力的偏斜度和峰度驱于收敛.文中给出的方法为后续理论工作奠定了基础.     

Experimental study of hydrodynamic forces and wave forces exerted on a truss structure

The drag and added mass coefficients of a truss leg of an ocean platform are obtained by using the forced-oscillation technique in a still water. Higher order forces and lift forces are also measured.The drag and inertia coefficients of the truss leg model are obtained by measuring the wave forces acting on it in regular deep waves. The moment lever of the wave force is compared with theoretical results.