近岸跨海桥群桩基础波流冲刷过程研究

Local scour or deposition at pile groups of coastal bridges caused by intensive variation of shoaling waves is a transient process, which affects structural dynamic performance, and even threatens the safety of bridges. The purpose of this project is to investigate the temporal evolution of pile groups scour or deposition exposed to shoaling or breaking waves using the methods of flow-sediment theoretical analysis, flume experiments and numerical simulations. The interaction mechanism among various parameters and influential factors, including those associating with shoaling wave, pile group and sediment, is illustrated based on the analysis of physical relationships of breaking waves within piles, and their effects on sediment dynamics. Furthermore, the equations of seabed deformation, scour or deposition, correlated with continuation of sediment transportation are established to realize the numerical simulation of temporal scour or deposition process around group of piles. The results of the current project are fundamental and crucial for further study on bridge structure dynamic response and vehicle-bridge of high-speed railway, as well as disaster prevention, coupling with the effects of foundation scour or deposition.

近岸波流剧烈变化可导致跨海大桥群桩基础周围海床面强烈的非恒定冲刷或淤积，影响桥梁结构的动力性能，甚至威胁大桥安全，因此研究群桩波流冲刷或淤积的动态变化规律十分必要。本项目针对跨海大桥常用的群桩基础和近岸波流冲刷特点，采用基于水-沙理论的分析、水沙运动的同步观测试验以及数值模拟方法，研究群桩周围海床冲、淤的时变过程。通过研究近岸带群桩间波流破碎的物理机制、波流结构与泥沙运动的力学关系，揭示近岸波流-群桩-海床泥沙各变量的动态制约机理，建立海底床面冲、淤动态演变方程，从而实现近岸群桩基础波流冲淤实时过程的数值模拟。本项目的研究，为将来研究群桩基础冲、淤对桥梁结构、高速铁路车桥动力响应及灾害防御模拟奠定基础。

围绕海岸带桥梁的群桩基础周围床面冲刷而诱发桥梁结构潜在的不稳定问题，主要开展了海床底坡与群桩影响的底部波流动力演变、群桩-波流作用的泥沙输运及局部床面冲淤和近岸底坡-群桩底床冲淤发展过程研究等关键内容的研究。根据不同的研究主题分别采用了实验室试验和数值模拟方法。获得以下主要结果：（1）近岸浅水特征下，流体运动方程的非线性对波流动力演变有明显影响，波浪向岸爬坡过程中的破碎状态由海岸坡度及相对波高决定；（2）修正了湍流模型中考虑床面粗糙度影响的模拟方程，提出了考虑桩柱局部湍流涡、脉动切应力影响下的泥沙输运和局部冲刷定量计算方法；（3）揭示了桩间布置对马蹄涡流态与床面冲刷分布影响的相关机制，描述了群间冲刷发展的时序与空间状态，发现了群桩周围波流马蹄涡尺度随冲刷时间和冲刷坑尺度增大；（4）冲刷过程的泥沙悬移或推移输运状态和对局部冲刷的贡献可由Rouse数判别，波流作用下桩间床面冲刷的泥沙运动主要表现悬移形式，桩间淤积部位泥沙运动主要表现为推移形式；（5）岸坡上群桩周围的强冲刷主要发生于波流回落时段，该时段波流产生的床面切应力仍为冲刷的显著动力；（6）研究了波流－泥沙－床面变形运动方程在数值计算中的耦合求解，提出了数值模拟波流冲刷过程的近床面离散网格畸变修复技术，实现了在OpenFoam开源平台对群桩波流冲刷动态发展过程的模拟。