开口式月池水动力特性研究

发布时间：2019-03-29 11:19

【摘要】：月池结构在海洋油气开采工程装备中具有广泛应用。月池作为立管和套管通过的流体区域,其形状和结构形式对于浮体的运动性能具有重要影响。因此,研究月池内流体动力特性对于月池的设计和控制浮体的运动,具有重要的理论和工程意义。本文针对底部全开口的矩形月池展开研究。基于势流理论建立月池流体运动方程,采用新的底部全开口边界条件,研究月池内流体的自振特性及水动力特性;基于拉格朗日理论,建立结构垂荡-横摇及月池流体耦合运动方程,研究月池流体对结构运动稳定性的影响。本文主要工作及结论如下:建立了月池内流体的运动方程及边界条件。假设月池内流体为理想流体,基于势流理论建立了月池内流体的运动方程。根据速度势及其法向导数在月池底部开口处的匹配条件,分别推导了全开口月池流体二维及三维情况时底部边界满足的数学表达式。研究了月池内二维流体自振特性。将月池流体简化为二维流动,采用伽辽金方法展开速度势函数,求解各阶自振频率及对应的模态函数,分析了解的收敛性,研究了月池参数对流体自振频率及振型的影响。结果表明,月池流体具有两类运动形式,即垂向活塞振动及水平方向液面晃荡;垂向运动模态自振频率主要由月池内水深决定,晃荡自振模态频率主要由月池两侧壁间距离决定;当自由液面靠近底面时,自振频率受底面速度影响升高。研究了月池内三维流体的自振特性。利用伽辽金方法将速度势函数展开,将流体的三维自振特性方程转化为二维特征值方程,求解了各阶自振频率及振型,分析了月池几何参数对月池内流体自振特性的影响,与二维结果进行对比,给出了二维模型的适用条件。结果表明,月池长度与宽度比大于3时,月池流体的自振频率基本由宽度方向的阶次决定,可采用二维模型;而长度与宽度相近时,各阶模态的频率与二维计算结果对比相差较大。研究了月池横荡运动时月池内流体的水动力学参数。考虑月池结构横荡简谐运动,利用伽辽金方法求解月池内流体速度势函数的半解析解,计算横荡附加质量、侧壁压力分布及底面的流动速度分布,分析了附加质量随激励频率变化的规律。结果表明,当月池横荡运动频率接近或等于月池流体自振频率时,流体附加质量增加到峰值。在月池流体的自振区间内,流体附加质量为月池自身排水量的数倍。月池底面压力以底面中点为中心对称分布,在自由液面影响范围的侧壁压力明显高于其他位置。建立了月池内流体的等效单摆力学模型,给出了等效单摆参数随月池参数变化的规律。将月池内水深的变化视为月池的垂荡运动,建立不同水深下月池等效模型的参数库。研究表明,二阶单摆等效质量远小于一阶单摆等效质量,在一般的计算中可忽略二阶以上月池晃荡的影响。研究了浮体垂荡-横摇及月池流体的耦合运动特性,分析了月池流体对浮体运动稳定性的影响。根据拉格朗日方程建立了月池-浮体耦合运动方程,考虑月池流体的影响,推导了横摇参数激励的马蒂厄方程,应用佛罗凯理论研究浮体周期解的稳定性,确定横摇运动稳定区间。结果表明,月池流体阻尼明显减小了浮体横摇不稳定区域,对1/2亚谐波振动的不稳定区域作用不明显,增加月池的长度明显减小了浮体横摇稳定区域。研究了Spar平台的分叉与混沌等非线性动力学特性,建立了平台在规则波中的垂荡-纵摇耦合运动方程,计算了平台响应的庞加莱截面等。结果表明,平台运动受波浪频率影响明显,随着波浪频率的变化,平台经历了复杂的非线性运动,包括1/2亚谐运动、周期运动、混沌运动。
[Abstract]:The structure of the moon pool is widely used in the marine oil and gas exploitation engineering equipment. The moon pool, as the fluid area through which the riser and the casing passes, has an important influence on the motion performance of the floating body in its shape and structure. Therefore, it is of great theoretical and engineering significance to design and control the movement of the floating body in the monthly pool. In this paper, a rectangular moon pool with full open bottom is studied. Based on the potential flow theory, the fluid motion equation of the moon pool is established, and a new bottom full-open boundary condition is adopted to study the natural and water dynamic characteristics of the fluid in the moon pool. The effect of the fluid on the stability of the structure was studied. The main work and conclusion of this paper are as follows: the motion equation and the boundary condition of the fluid in the moon pool are established. It is assumed that the fluid in the monthly pool is the ideal fluid, and the motion equation of the fluid in the moon pool is established based on the potential flow theory. According to the matching conditions of the velocity potential and its normal derivative at the bottom opening of the moon pool, the mathematical expression of the bottom boundary of the full-open-moon pool fluid two-dimensional and three-dimensional case is respectively derived. In this paper, the natural vibration characteristics of two-dimensional fluid in the moon pool are studied. The fluid of the moon pool is simplified into two-dimensional flow, the velocity potential function is expanded by the Galerkin method, the natural frequency of each order and the corresponding modal function are solved, the convergence of the analysis is analyzed, and the influence of the parameters of the moon pool on the natural frequency and the vibration mode of the fluid is studied. The results show that the moon pool fluid has two types of motion, that is, the vertical piston vibration and the liquid level in the horizontal direction; the natural frequency of the vertical motion mode is mainly determined by the water depth of the moon pool; the frequency of the sloshing natural mode is mainly determined by the distance between the two sides of the moon pool; and when the free liquid level is close to the bottom surface, The natural frequency is affected by the speed of the bottom surface. The self-vibration characteristics of three-dimensional fluid in the moon pool are studied. By using the Galerkin method, the velocity potential function is expanded, the three-dimensional natural vibration characteristic equation of the fluid is converted into a two-dimensional characteristic value equation, the natural vibration frequency and the vibration mode of each step are solved, the influence of the moon pool geometry parameter on the natural vibration characteristics of the fluid in the moon pool is analyzed, and compared with the two-dimensional result, The applicable conditions of the two-dimensional model are given. The results show that, when the ratio of the length and width of the moon pool is greater than 3, the natural vibration frequency of the moon pool fluid is determined by the order of the width direction, and the two-dimensional model can be adopted; and when the length is close to the width, the frequency of each step mode is much larger than that of the two-dimensional calculation result. The hydrodynamic parameters of the fluid in the moonpool were studied. In this paper, the semi-analytical solution of the potential function of the fluid velocity in the moon pool is calculated by means of the Galerkin method, and the law of the variation of the additional mass with the excitation frequency is calculated by using the Galerkin method to solve the semi-analytical solution of the potential function of the fluid velocity in the moon pool. The results show that the additional mass of the fluid is increased to the peak when the frequency of the transverse motion of the moon pool is close to or equal to the natural frequency of the fluid in the moonpool. In the self-vibration interval of the moon pool fluid, the additional mass of the fluid is several times the self-displacement of the moon pool itself. The bottom surface pressure of the moon pool is distributed symmetrically with the middle point of the bottom surface, and the pressure of the side wall in the influence range of the free liquid level is obviously higher than the other positions. The equivalent single pendulum mechanical model of the fluid in the monthly pool is established, and the law of the equivalent single pendulum parameter with the change of the parameter of the moon pool is given. The variation of water depth in the moonpool is considered as the heave motion of the moon pool, and the parameter library of the equivalent model of the moonpool under different water depth is established. The results show that the equivalent mass of the second-order single pendulum is far less than the equivalent mass of the first order pendulum, and the influence of the second-order above-mentioned moonpool sloshing can be neglected in the general calculation. The coupling motion characteristics of the floating-body heave-roll and the moon pool fluid are studied, and the effect of the moon pool fluid on the movement stability of the floating body is analyzed. On the basis of the Lagrange's equation, the coupling motion equation of the moon pool and the floating body is established, the influence of the moon pool fluid is taken into account, the Mathieu equation excited by the roll parameter is derived, and the stability of the periodic solution of the floating body is studied by using the wave-wave theory, and the stability interval of the rolling motion is determined. The results show that the fluid damping of the moon pool obviously reduces the unstable region of the floating body, and the effect of the unstable region of the 1/2 subharmonic vibration is not obvious, and the length of the moon pool is obviously reduced, and the stable region of the floating body is obviously reduced. In this paper, the nonlinear dynamic characteristics of the Sar platform are studied. The heave-pitch-coupled motion equation of the platform in regular wave is established, and the Pincare section of the platform response is calculated. The results show that the motion of the platform is affected by the wave frequency, and with the change of the wave frequency, the platform experiences complex nonlinear motion, including 1/2 subharmonic motion, periodic motion and mixed motion.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：U674.381

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