【作者】 王珍；

【导师】 蒋昌波；

【作者基本信息】 长沙理工大学 ， 水力学及河流动力学， 2008， 硕士

【摘要】 在海岸地区,引起泥沙运动的最主要动力因素是波浪。从波浪进入浅水开始“触底”的时候起,波浪将会在岸坡发生反射、变形,甚至破碎。海上建筑物如海底管线、小尺度桩柱、大尺度圆柱、防波堤、人工岛等较多修建在海岸地区。当这些建筑物在海洋中存在时,建筑物附近的水流速度分布将被改变,使建筑物周围的底部剪切应力和泥沙输沙率值增大,导致局部冲刷。如果冲刷很严重,将对建筑物基础的稳定性有很大威胁。所以海上波浪作用下泥沙冲刷在海洋工程设计中被愈来愈重视。墩柱是一种较常见的海工建筑物,对于墩柱局部最大冲刷深度的研究结果较多,但对其流场特性研究较少。明基床墩柱是目前研究较少但应用前景广泛的一种海工建筑物,现已用作海上风力发电的基础。由于墩柱和基床的双重影响其局部冲刷形态和流场特性必然与墩柱有所不同。本文通过水槽实验及数值水槽模型模拟波浪从外海传入,到斜坡触底后发生反射、浅水变形、泥沙起动、墩柱及明基床墩柱局部冲淤的完整过程。并试图利用有限的实测资料及数据对波浪作用下沙质海床上大直径圆柱及明基床圆柱局部冲刷问题及流场特性进行研究和探讨。水槽试验中,用浪高仪测量不同位置的波高、波周期,通过分析这些数据,了解波浪在斜坡前的反射、传播过程中的变形和墩柱前的反射、绕射,分析波浪场的改变对局部冲刷的影响。用NDV实时测量建筑物附近的冲刷随时间的变化过程、冲刷发展阶段及平衡冲刷阶段不同位置的三维瞬时流速,用地形仪测量了持续造波15min和60min的三维地形,用数码相机拍摄了60min后的三维地形,了解墩柱及明基床墩柱局部冲刷特性及流场特性,从统计学的角度对其紊动特性进行分析,包括:脉动强度、雷诺应力、紊动动能。基于以上分析探求墩柱及明基床墩柱局部冲刷机理。采用基于Boussinesq方程的波浪数学模型,通过计算单一墩柱和明基床墩柱瞬时流速场、床面平均剪应力、平均涡量场,研究其附近的流场、涡动特性。经试验验证能较好的模拟各位置的波高及墩柱附近流场特性及涡动特性。更多还原

【Abstract】 In the coastal area, the main factor which forces the movement of sediment is the wave. When waves enter into the shallow area, they will reflect, metamorphose, or break up. Constructions at the sea are most built at the coastal lines, such as pipe lines, small scale pile, large scale cylinder, groyne, manpower land, etc. The existing of these constructions will influence the flow nearby, accrete the velocity shear stress, sediment transportation, and result in local scour. If the scour is serious, it will induce the instability of the foundation. So local scour under the wave action is more and more important for coastal engineering design.Large scale cylinder is one of constructions that being usually used. Many researches focus on its local scour, but only a few have studied the flow field. A bedding cylinder is a kind of structure which has broad foreground application but few researches have studied on it. Now it has used as the foundation of the wind power generation at the sea. Bi-influence of the bedding and pole makes local scour and flow field different from the single cylinder.Flume experiment and numerical flume model simulate the whole progress about wave from depth water, enter into shallow water then reflect, metamorphose, sediment movement, local scour around large scale cylinder and bedding cylinder. Accord these limited data this paper tries to analysis the scour character, flow field character and discuss local scour mechanism.On the flume experiment, Wave Height Sensor is used to measure the wave height and period at different locations. NDV is used to measure the scour depth real time and three dimensional instantaneous velocities. Topographic instrument is used to measure the landform at 15 min and 60 min after wave generated. Using numerical camera to take pictures 60 min after wave generated. Base on these data, this paper uses different means to analysis the wave metamorphose and its effect to local scour, scour character, flow field character and scour mechanism.Wave mathematical model based on Boussinesq equation is used to calculate the wave height at different locations and instantaneous flow field, average shear stress and average eddy field around cylinder. Comparing calculated data with the measured data, they have a nice coherence.更多还原