浮体运动响应的完整二阶时域方法和非线性准陷波现象的研究

发布时间：2018-04-23 11:39

本文选题：二阶频域 + 双色波　；参考：《大连理工大学》2015年博士论文

【摘要】：随着海洋油气资源开发逐渐向深海发展,深海结构物非线性水动力问题成为海洋工程领域的热点问题,对深海平台非线性运动响应问题和多柱式平台准陷波问题的研究成为了海洋工程领域的重要课题。基于以上背景,本文采用间接时域方法对浮体结构物非线性运动响应问题开展了研究,建立了模拟浮体运动响应的完整二阶时域方法；同时,采用模型实验以及数值模拟的方法对多柱式平台的准陷波问题开展了研究,揭示了非线性波浪下多柱式平台的非线性准陷波现象。深海环境条件恶劣,在波浪以及系泊系统等的非线性因素的影响下,结构不再服从简谐运动规律,因此需要采用时域方法对深海结构物的运动响应进行模拟。当采用间接时域方法时,在每个时间步只需求解物体的运动方程,波浪激励力则根据Volterra级数模型求得。因此,间接时域方法较其他全时域方法更加高效并更适合应用于实际工程中。在以往的研究中,基于二阶理论建立的间接时域方法是根据平方传递函数(QTF)对时域内的二阶波浪激励力进行计算的。平方传递函数定义为单位幅值双色波浪下作用于浮体结构上的二阶波浪激励力。对于运动物体而言,平方传递函数是物体一阶运动响应以及入射波浪的函数。由于对平方传递函数的计算是在时域分析的准备阶段中进行的,在其计算过程中物体的运动响应是未知待求的,因此无法直接将平方传递函数应用到时域分析中。基于以上原因,本文依据物体一阶简谐运动幅值以及入射波浪幅值,对浮体结构的平方传递函数进行摄动展开,并由此提出平方传递函数的分解方法。通过对平方传递函数的分解,可以得到三类平方传递函数分量：第一类分量是由双色入射波浪与固定物体相互作用产生的；第二类分量是由物体简谐运动和入射波浪共同作用产生的；第三类分量是由物体不同频率的简谐运动共同作用产生的。对各类平方传递函数分量对应的边值问题开展了研究,应用泰勒级数展开以及摄动展开方法对边界条件进行了推导,采用边界积分方程方法对速度势进行求解。对积分方程中复杂的无穷自由水面积分采用数值离散、级数展开以及渐近展开相结合的方法进行有效准确的计算。在计算得到平方传递函数分量后,应用Volterra级数模型实现了在时域内对运动物体上的二阶波浪激励力的准确计算,进而建立起模拟浮体结构运动响应的完整二阶时域方法。目前的方法较以往的根据平方传递函数建立的间接时域方法在理论上更加严格并且在计算上更加准确。对于线性系泊以及非线性系泊问题,通过将本文运动响应结果与频域结果以及实验结果进行对比,验证了本文方法的准确性和有效性。在验证了本文方法的准确性和有效性后,结合悬链线理论对于实际深海平台的非线性运动响应问题开展了数值模拟研究。对于张力腿平台等多柱式海洋平台,其上部结构由多个立柱结构支撑。由于这些支撑柱体彼此相距较近,相互之间干涉作用较强,在特定的波浪条件下结构内部将发生准陷波现象。伴随着准陷波现象的发生,大量的入射波浪滞留在结构周围,并且仅有少量的散射波浪向远场传播。同时,平台附近局部位置处将出现显著增大的波高,这将对平台的气隙性能带来不利的影响。尽管理论研究和数值模拟研究都表明波浪与多柱式结构相互作用可以引起准陷波现象的发生,然而目前对准陷波现象开展的实验研究工作较少。本文在大连理工大学海岸和近海工程国家重点实验室沿岸水池对四柱结构的波浪绕射问题开展模型实验研究。实验中对柱体附近多个位置处的波面高度进行测量,并将实验结果与数值模拟结果进行对比。通过对比表明即使在波陡较大的情况下二阶绕射理论可以对大尺度结构物周围的波面进行有效模拟。实验中对四柱结构的准陷波现象也开展了研究,实验中会在特定的波浪条件下在局部区域观测到显著增大的波面结果以及近似驻波的波面分布模式。除开展实验研究外,本文应用在势流理论下建立的数学模型对张力腿平台周围非线性波面分布开展数值模拟研究。研究表明,当二阶倍频入射波浪的频率与结构的准陷波频率接近时,这些非线性波浪可以引起二阶准陷波现象的发生。同时,以往在对张力腿平台周围波面分布的研究中,主要关注支撑柱体结构对波面分布的影响,而对下部浮筒结构对波面分布影响开展的研究很少。本文通过对有无浮筒情况下波高结果进行对比,对浮筒结构对波高结果的影响开展了研究,并且着重分析了浮筒结构对一阶和二阶准陷波现象的影响规律。研究表明浮筒结构的存在不会改变准陷波现象发生的频率,然而会对二阶准陷波现象发生时的波面产生显著影响,将进一步抬升局部位置处已显著增大的波面。
[Abstract]:With the development of marine oil and gas resources to the deep sea, the nonlinear hydrodynamic problem of deep-sea structures has become a hot issue in the field of marine engineering. The problem of nonlinear motion response to the deep-sea platform and the study of the multi column platform quasi subsidence have become an important subject in the field of Marine Engineering. The domain method has been studied for the nonlinear motion response of the floating body structure, and a complete two order time domain method is established to simulate the motion of the floating body. At the same time, the model experiment and numerical simulation are used to study the quasi trapping wave problem of the multi column platform, and the nonlinear quasi subsidence of the multi column platform under the non linear wave is revealed. Wave phenomenon, abyssal environment is abominable, under the influence of nonlinear factors such as wave and mooring system, the structure no longer obeys the law of harmonic motion. Therefore, time domain method is used to simulate the motion response of deep-sea structures. When indirect time domain method is used, the motion equation and wave of the object are only needed at each time step. The excitation force is obtained according to the Volterra series model. Therefore, the indirect time domain method is more efficient and more suitable for practical engineering than the other time domain methods. In the previous study, the indirect time domain method based on the two order theory is based on the square transfer function (QTF) to calculate the wave excitation force of the two order in the time domain. The square transfer function is defined as the two order wave excitation force acting on a floating body structure under a double color wave of a unit amplitude. For a moving object, the square transfer function is the function of the first order motion response and the incident wave of a body. The motion response of the object is unknown, so the square transfer function can not be applied directly to the time domain analysis. Based on the above reasons, the perturbation expansion of the square transfer function of the floating body structure is carried out based on the amplitude of the first order harmonic motion of the object and the amplitude of the incident wave, and the decomposition method of the square transfer function is proposed. By the decomposition of the square transfer function, three kinds of square transfer function components can be obtained: the first component is produced by the interaction of two color incident waves with the fixed object; the second component is produced by the joint action of the simple harmonic motion of the object and the incident wave; the third component is the common harmonic motion of the different frequencies of the object. The boundary value problem corresponding to all kinds of square transfer function components is studied. The boundary conditions are derived by Taylor series expansion and perturbation expansion method. The velocity potential is solved by the method of boundary integral equation. Numerical dispersion and series expansion are adopted for the complex free surface integral in the integral equation. An effective and accurate calculation is made with the method of combining the open and asymptotic expansion. After calculating the square transfer function components, the Volterra series model is applied to calculate the two order wave excitation force on the moving object in the time domain, and then a complete two order time domain method is established to simulate the dynamic response of the floating body structure. The method is more rigorous and more accurate in theory than the previous indirect method based on square transfer function. For linear mooring and nonlinear mooring, the accuracy and effectiveness of this method are verified by comparing the results of the motion response with the results of frequency domain and experimental results. After verifying the accuracy and effectiveness of this method, a numerical simulation is carried out on the nonlinear motion response of a practical deep-sea platform with catenary theory. For a multi column offshore platform, such as tension leg platform, the superstructure is supported by a number of column structures. There will be a quasi trapping wave in the structure within a specific wave condition. With the occurrence of the quasi wave phenomenon, a large number of incident waves are left around the structure, and only a small amount of scattered waves propagate to the far field. At the same time, a significant increase of wave height will be found at the local position near the platform, which will affect the air gap of the platform. Although theoretical and numerical simulation studies have shown that the interaction of wave and multi column structure can cause the occurrence of the quasi collapse phenomenon, there are few experimental researches on the phenomenon of the phenomenon of the trapping wave at present. In this paper, the coastal pool of the National Key Laboratory of coastal and offshore engineering of Dalian University of Technology is four A model experiment is carried out for the wave diffraction of a column structure. In the experiment, the height of the wave surface at several locations near the column is measured, and the experimental results are compared with the numerical simulation results. The comparison shows that the two order diffraction theory can be effective on the wave surface around the large scale structure even in the case of large wave steepness. In the experiment, the quasi trapping wave of four column structures is also studied. In the experiment, the significant increasing wave surface results and the approximate wave surface distribution patterns are observed in the local region under the specific wave conditions. In addition to the experimental study, this paper applies the mathematical model established under the potential flow theory to the tension leg platform. The numerical simulation of the nonlinear wave surface distribution is carried out. It is shown that these nonlinear waves can cause the occurrence of the two order quasi trapping waves when the frequency of the two order frequency doubling waves is close to the quasi notch frequency of the structure. At the same time, in the previous study on the distribution of wave surface around the tension leg platform, the main concern of the supporting column structure is the wave. The influence of surface distribution on the impact of the lower buoy structure on the wave surface distribution is seldom studied. In this paper, the influence of the buoy structure on the wave height is studied and the influence of the buoy structure on the first and two order quasi trapping waves is analyzed. The existence of the tube structure will not change the frequency of the quasi trapping wave, but it will have a significant influence on the surface of the two order quasi - notch phenomenon, which will further raise the wave surface which has been significantly increased at the local position.

【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：P75;TV139.2

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