【作者】 李雪临；

【导师】 任冰； 王永学；

【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】 在海岸和近海工程中,波浪的冲击作用对位于浪溅区的透空式建筑物的安全有很大影响。在波浪冲击过程中,当波峰刚接触到建筑物底面时会产生历时很短但强度极大的冲击压力,这种极强的冲击荷载会引起建筑物上部结构的失稳或造成结构连接处的疲劳破坏。随着二十一世纪我国海洋开发规模的扩大,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。因此,开展波浪冲击过程的流场变化特性研究,有着重要的科学价值和实际意义。本文从物理模型试验和数值模拟两方面出发,对位于浪溅区的透空式结构物的波浪冲击特性进行了研究。物理模型试验方面,利用先进的瞬态全场测量技术—粒子图像测速(PIV)技术,研究了波浪对位于浪溅区的透空式建筑物上部结构冲击过程中的瞬时流场变化特性。通过对采集到的CCD图像的互相关分析,直观地显示了波浪冲击作用发生时结构物底面不同瞬时的流场状态,得到了瞬间的全场流体水质点的速度矢量,并且应用概率分析法研究了瞬时冲击压力峰值与波浪水质点瞬时运动速度之间的关系。数值模拟方面,首先建立了基于流体体积法(VOF)的随机波无反射数值波浪水槽。在水槽造波端,基于线性造波机理论设置了随机波的主动吸收式造波边界,即造波板的运动在生成目标波浪的同时,还产生一个抵消造波板二次反射波的附加运动。在数值波浪水槽的末端,设置了海绵层阻尼消波边界,实现了随机波的阻尼消波。通过水槽右端为直墙边界时的全反射情形和水槽内含有潜堤的部分反射情形的数值计算结果,验证了主动吸收式造波机的性能和沿水槽长度方向不同位置处入射波的稳定性。其次,利用本文所建立的数值模型对波浪冲击过程的压力变化特性、流场变化特性以及二者之间的关系进行了统计分析。研究了结构物底面波浪冲击压力及水质点垂向运动速度的分布规律,讨论了相对入射波高、结构相对宽度和相对净空等因素对结构物底面最大冲击压力及水质点最大垂向运动速度的影响规律,并给出了随机波冲击压力峰值与水质点垂向运动速度统计值之间的关系。最后,通过引入嵌套网格细分方法实现了建筑物附近的近域流场和外域流场的同步耦合求解。提出了网格重叠带上的速度、压力和波面的匹配边界条件,应用该模型对冲击过程中结构物附近的流场进行了精细模拟,并应用物理模型试验结果验证了采用嵌套网格算法的耦合数值模型的计算流场精度,且对耦合数值模型和全流场均匀细分网格算法的计算流场精度和计算效率进行了比较分析。更多还原

【Abstract】 In coastal and offshore engineering,the wave impact in the splash zone has great influence on the safety of the open structures.In the process of wave slamming,the impact pressure with short duration and high peaks occurs when the water contacts the subface of the structure,which causes the destabilization of superstructure and the fatigue failure of joints. Along with the expansion of the ocean exploitation in the 21th century,the forecast of wave slamming loads in the design of coastal and offshore engineering is increasely valued and has become an important subject.It is significant to deeply research the characteristics in the process of the wave impact.This paper presents the experimental investigation and numerical simulation of the slamming on the horizontal plate suspended over the water surface in the splash zone.In the model experiment,the advanced instantaneous measuring technique,Particle Image Velocimetry(PIV),is applied to acquire the instantaneous velocity field of wave slamming. From the cross-correlation analysis results of the images captured by the CCD camera,the flow fields of the wave impacting on the structure are displayed visually,and the instantaneous whole-field fluid velocity vectors are obtained.The relation between the instantaneous pressure peaks and the according velocities of water particles is studied by probability analysis.In the numerical simulation,firstly,a numerical irregular wave flume with active absorption of re-reflected waves is simulated using VOF method.An active absorbing wave-maker based on linear wave theory is set on the left boundary of the wave flume.The absorbing waves are generated to eliminate the waves coming back to the generating boundary due to reflection from the outflow boundary and the structures.As for the end of the numerical flume,the numerical sponge layer achieves the damping elimination to the irregular wave.On the conditions of total reflection and partial reflection,the numerical results using the non-reflecting numerical wave flume are compared with that of the ordinary numerical wave flume to verify the performance of the non-reflecting numerical wave flume and the stability of the incident waves along the numerical wave flume.Secondly,the characteristics of pressure and flow field in the irregular wave impacting is investigated by use of the unreflected numerical model.The distributions of characteristic pressures and corresponding vertical velocities of fluid are presented.The influence of relative wave height,relative structure width and relative clearance on wave impact pressure and vertical velocity of fluid is discussed.The relation between irregular peak impact pressures and corresponding peak vertical velocities of fluid is analyzed.Finally,the synchro coupling between the neighbouring flow field of the structure and the external area is achieved by introducing the nested grid refinement(NGR) technique based on VOF method.The boundary conditions of velocity,pressure and wave surface in a 2D SOLA-VOF code is described.Detailed numerical simulation of flow field in the process of wave impact on the marine structures is implemented.The precision of the computed flow fields with nested grid and uniform grid are compared with the experimental flow fields.The computational efficiency of nested grid and uniform grid is discussed.更多还原