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波浪对透空式三维结构物的冲击作用研究
Wave Impact on the Three-dimensional Open Structure
【作者】 丁兆强；
【作者基本信息】 大连理工大学 ， 港口、海岸及近海工程， 2009， 博士
【摘要】 随着二十一世纪海洋开发规模的不断扩大,愈来愈多的海上石油平台、岛式码头和开敞式码头等透空式结构物在外海深水地区兴建起来。然而,由于结构物底部设计高程不足和海底沉降等原因,在遭遇恶劣海况的情况下,会造成结构物上部结构的净空不足,当大波浪通过结构物底部时,波浪会与其接触并且产生极大的冲击作用,从而影响到结构物上部结构的稳定和安全。因此,波浪冲击荷载的预报在海岸和近海工程设计中越来越受到重视,已成为近年来被广泛关注并亟待解决的重要课题,开展有关波浪冲击作用的研究,有着重要的科学价值和实际意义。本文应用物理模型试验和数值模型计算相结合的手段,对透空式三维结构物所受到的波浪冲击作用进行了系统地研究。首先,通过物理模型试验开展了不同参数的波浪对不同位置方形结构物的冲击作用研究,分别对规则波和随机波冲击作用的试验数据进行了统计分析,比较了正向波和斜向波作用于结构物底面的冲击压力分布特征,讨论了入射波相对波高、结构物相对板宽和相对净空与结构物底面所受到的波浪冲击力之间的关系,给出了波向角β对结构物底面冲击力的影响;并对随机波浪冲击作用的试验数据进行了谱分析,给出了不同波向角条件下结构物底面冲击压力谱零阶矩的分布特征,讨论了不同相对波高、结构物相对板宽和相对净空对冲击力谱零阶矩的影响规律,总结出了冲击力谱零阶矩的经验公式,并且给出了冲击力与冲击力谱零阶矩之间关系的经验表达式。其次,建立了基于VOF方法的求解波浪冲击作用的三维数值模型,采用VOF方法跟踪流体自由表面,以连续方程和N-S方程为基本控制方程;基于线性波浪理论,设置了规则波数值造波边界、海绵层阻尼消波边界和Sommerfeld辐射条件,海绵层内的衰减系数选取为根号形式;提出了反映波浪冲击特性的三维冲击边界条件。应用方形结构物的物模试验结果验证了所建立的数值模型;进一步研究了底面积相同但长宽比不同的矩形结构物底面的冲击压力分布特征和冲击力变化特性,为研究三维波浪冲击问题提供了新的计算手段。
【Abstract】 With the development of the ocean exploitation on Tweenty-one centrury, more and more open structures, such as offshore oil platforms, detached wharfs and open style wharfs etc. are built up in deep water. However, because of under-design altitude of the panel, the settlement of the seabed etc., while encountering the abominable sea-conditions, the wave-impact force caused by the wave slamming when the water contacts the subface of the structure threaten the stability and safety of the superstructures. Thus, the forecast of wave slamming loads in the design of coastal and offshore engineering is more and more valued and has become an important subject. It is significant to research the characteristics in the process of the wave impact deeply.This paper presents the experimental investigation of the slamming on the three-dimensional open structure in the splash zone, and also the contrastive analysis by the numerical simulation results.First of all, the experimental investigation of the slamming on the three-dimensional open structure in the splash zone is developed. The statistical distribution characteristics of the perpendicular wave impact pressures are compared with that of the oblique wave on the underside of the open structure. The relation between wave impact forces and the parameters such as the relative wave height, the relative structure width and the relative clearance of the structure is also discussed. The effect of the wave direction ft on the wave impact forces on the underside of the structure is determined. The spectral analysis of unidirectional irregular wave slamming is presented. The distribution characteristics of the zeroth order moment of the perpendicular and oblique wave impact pressure spectrum along the subface of the structure are given. And the effect of different incident wave parameters such as the relative wave height, the relative structure width and the relative clearance on the nondimensional zeroth order moment of the impact force spectrum are discussed. The experiential expressions of the dimensionless zeroth order moment of the impact force spectrum for different wave incident angles are summarized. And also the empirical expression of the impact forces and zeroth order moment of the impact force spectrum are given.Then, the three-dimensional numerical wave basin based upon the VOF method is established. VOF is used for tracing the free surface, the governing equations are continuity equation and N-S equations, based on the linear wave theory, wave-maker is set, and the numerical sponge layer and SRC achieve the damping elimination to the incident wave, the radical sign style of the attenuation quotient is chosen. In connection with the wave slamming problem, the three-dimensional wave impact boundary conditions are introduced. The numerical computation results of wave impact on the three-dimensional foursquare open structure in the splash zone for different parametric cases are verified by the experimental results. Meanwhile, the characteristics of the wave impact pressures and wave impact forces on the underside of the rectangular structure with different length-breadth ratio are given. New calculation method is provided for the study of three-dimensional wave slamming problem.