【作者】 张莉；

【导师】 郭海燕；

【作者基本信息】 中国海洋大学 ， 港口、海岸及近海工程， 2013， 博士

【摘要】 近年来，内波造成海洋工程结构物的破坏屡见报道，对于海洋油气开采中必不可少而又贯通水深的立管而言，内波经过时势必会对其产生重大影响。内波是以怎样的形式作用在细长的海洋立管上，立管在其作用下动力特性如何，当海洋内波与其他海洋环境荷载共同作用时，立管又会呈现怎样的动力响应，这些问题是当前海洋工程学术界和工业界共同面临的挑战。本文试图用实验和数值模拟两种方法探讨内波对圆柱体的作用力，再将此作用力施加在海洋工程中常用的两种立管（顶部施加张力的顶张力立管和自由悬挂的钢悬链线立管）上，用数值方法计算分析其动力特性，最后研究海洋内波与表面波和顶部浮式结构共同作用时海洋立管的动力响应。首先在内波水槽中进行小段竖直圆柱体上内孤立波作用力实验，采用染色摄影技术以及PIV示踪粒子技术获得内孤立波波形和流场时空特征，利用测力系统测量处于不同深度的小段圆柱体作用力，以此为基础，确定内孤立波对长圆柱体作用力沿深度的分布情况。同时探讨内孤立波振幅、圆柱体直径和圆柱体所在深度对作用力大小的影响。其次，采用KdV方程或mKdV方程模拟内孤立波波形、波致水质点速度和加速度，再结合Morison公式建立内孤立波作用力模型，将数值模拟的计算值与实测值进行对比，结果表明：采用KdV或mKdV方程得到的波形、下层流体中内波致流速大小、方向以及流速沿深度的变化情况与实验结果一致。然后，基于达朗伯原理建立顶张力立管的控制方程，采用内孤立波作用力数值模型模拟内孤立波作用力，利用Newmark-β法在时域内对内孤立波作用下顶张力立管的动力反应进行数值求解。基于以上理论编制程序TTR_ISW，并应用该程序对南海实测内孤立波作用下的顶张力立管进行数值模拟。结果表明：顶张力立管在内孤立波强烈的剪切作用下会产生很大的位移和应力，内孤立波波谷传到立管中心线时，立管位移达到最大，两层流体界面附近的顶张力立管区段有可能在此时发生剪切破坏，故对内波多发海域的立管进行设计计算时应该考虑内波作用。研究还表明：顶部张力、内流速度、弹性模量、壁厚等因素对于顶张力立管在内孤立波作用下的响应均有一定程度的影响。另外，基于细长柔性杆理论(the rod theory)考虑大变形建立钢悬链线立管控制方程，采用内孤立波作用力数值模型模拟内孤立波作用力，用Newton-Raphson方法迭代求解钢悬链线立管的静力位形，基于静力平衡位形，在时域内采用Adams-Moulton方法求解钢悬链线立管非线性运动方程，编制相应的计算程序SCR_ISW。应用该程序计算了当内孤立波传播方向与钢悬链线立管所在平面呈不同角度时钢悬链线立管的响应。结果表明：由于钢悬链线立管的三维特性，内孤立波传播方向不同会导致立管的响应不同，当内孤立波作用于钢悬链线立管平面内时立管的响应最大。最后，同时考虑内孤立波、波浪、顶部浮体运动等荷载的共同作用，建立深水顶张力立管和钢悬链线立管在多种荷载作用下的非线性运动方程，用有限元法在时域求解，进而求得立管的联合响应。波浪的模拟采用线性波浪理论，顶部浮体运动采用Sexton推荐的方法，内孤立波作用采用本文建立的作用力模型。计算结果表明：内孤立波对立管的影响远大于表面波的作用，顶部浮体运动的作用也相当显著。当立管遭受这三种荷载联合作用时，立管以表面波和顶部浮体运动的频率振动，而内孤立波的作用类似缓慢但巨大的冲击力。更多还原

【Abstract】 There are more and more reports about the destruction of offshore structuresinduced by internal waves in recent years. As one of the indispensable facilities in themarine oil and gas exploration, marine riser goes through the whole depth of oceanthus internal wave may have great effect on the riser. Ocean engineering faces greatchallenges including the mechanical behavior of the slender marine riser sufferinginternal wave, the response and failure mode of the riser under internal wave and theresponse of the riser under combined excitation of internal wave, surface wave andthe motion of the floating structure. In this thesis, the force vertical distributionpattern of the circular cylinder under internal solitary wave is investigated bothexperimentally and numerically. The internal solitary wave forces are imposed on thetwo types of riser commonly used in the offshore engineering (top tensioned riser andsteel catenary riser), and dynamic charecteristics for these two risers are analyzednumerically. Moreover, the dynamic responses of risers under combined excitation ofinternal wave, surface wave and vessel motion are simulated respectively.Firstly, the force of a piece of short circular cylinder under internal solitarywave is investigated in an internal wave flume. The dyeing photography technologyand PIV tracer particle technology are adopted to obtain the wave shape and thetemporal and spatial characteristics of internal wave field. A special force measuringsystem is adopted to obtain the force of a short piece of cylinder in different depth,and on this basis the force distribution along the depth of the long cylinder underinternal solitary wave is analyzed. In addition, the influences of internal solitary waveamplitude, the depth of cylinder located and the diameter of cylinder on the force arediscussed.Secondly，the KdV theory or mKdV theory is adopted to obtain the wave profile,the fluid velocity and acceleration induced by internal solitary wave. Then, combined with Morison formula, the internal solitary wave force model for a cylinder isestablished. The simulated results are compared with the measured results. It showsthat the simulation results of wave profile, the velocity direction, the value of velocityin lower layer, and the variation pattern of velocity along the depth coincide with theexperimental data.Afterwards, based on D’Alembert principle, the governing equation of the toptensioned riser (TTR) is established. The force of internal solitary wave exerted on theriser is numerically simulated and dynamic responses of the TTR undergoing internalsolitary wave are analyzed in time domain by using Newmark-β method. Acomputation programm for solving the differential equations in time domain iscompiled (TTR_ISW) and numerical results are obtained. The results show thatinternal solitary wave may induce quite large displacements and stresses in TTR. Asthe internal solitary wave crest passes by the centre of the riser, the maximumdisplacement and stress along the riser occur. The riser section located in the vicinityof the interface of two layer fluid may be destroyed by the strong shear current, andthe load of internal solitary wave should be concerned in riser analysis. The influencesof the internal wave amplitude, internal flow, top tension, elastic modulus and wallthickness on the riser extreme response are discussed.Further, based on the slender rod theory, the governing equation of steel catenaryriser (SCR) is obtained, and the internal solitary wave force model is used to calculatethe hydrodynamic force induced by internal solitary wave. The static problem issolved iteratively by the Newton-Raphson method, while the dynamic responses aregained by using Adams-Moulton method in time domain. Based on the theorymentioned above, a computer program (SCR_ISW) for static and dynamic analyses ofSCR is developed. The cases for different angles between the propagation direction ofinternal solitary wave and the SCR’s plane are calculated by use the programm. Theresults show that, when the angle equals0degree, the max dynamic effective tensioninduced by internal solitary wave occurs.In addition, the combined excitation of internal solitary wave, surface wave andvessel motion is considered for calculating the dynamic response of marine riser. The governing equations for TTR and SCR under combined excitation are establishedrespectively, and the equations are solved by using finite element method (FEM) intime domain. Airy wave theory is chosen to simulate the fluid velocity andacceleration of surface wave, vessel motion is involved by using the method proposedby Sexton, and internal solitary wave is caculated by using the force modelestablished in this thesis. The caculated results show that the action of internal solitarywave on the riser is like a slow powerful impact, and is much larger than that ofsurface wave. When the riser is under combined excitation, it vibrates at frequenciesof both surface wave and vessel motion, while the amplitude of vibration is dominatedby internal solitary wave.更多还原