【作者】 张敬；

【导师】 李华军； 梁丙臣；

【作者基本信息】 中国海洋大学 ， 港口、海岸及近海工程， 2010， 博士

【摘要】 波浪、潮流是海岸、河口区的主要动力因素,两者同时存在并且相互作用,相互影响。波浪由外海向海岸传播时,由于地形水深等的变化,发生折射绕射,浅水变形,直到破碎,产生波生近岸流,它也是岸滩演变,物质输移扩散等的重要动力因素。目前,基于水深平均的平面二维波生近岸流模型或波生近岸流相互作用模型已经在工程中得到较为广泛的应用。然而自然界水流在垂向上并不是均匀分布,其垂向变化往往对建筑物的稳定和地形演变造成显著影响。因此,我们不仅仅要了解水位的分布和变化,还需要了解水流的垂向变化,要研究这些问题只有三维模式才能实现。本文是在原有的三维波流耦合数学模型COHERENS-SED基础上将之进行了完善,提高了模型的三维精度,使其能够正确模拟水流结构,特别是垂向结构。首先,将垂向平均辐射应力改进为垂向变化辐射应力,以附加项的形式添加到潮流方程中,研究其对潮位和流速的影响。模拟了均匀坡度的理想地形条件下的波生近岸流场,得到了波生近岸流的垂向环流结构,这与理论分析和试验观测结果相一致,也验证了模型的精确性和可靠性。另一方面,由于波浪运动产生了速度梯度,引起剪切的不稳定性产生湍流,形成非破碎浪致垂向混合,故本文在耦合模式中引入了浪致垂向混合效应,在垂向涡粘系数中加进了波浪引起混合项,改进了垂向混合系数的计算方法。通过建立的一维数值试验来验证波浪的作用和效果,当考虑了浪致垂向混合时,水流的垂向掺混作用明显加强,垂向涡动粘性系数对水平流速的垂向分布起着重要的作用。将改进的三维波流耦合模型应用到黄河三角洲,模拟了河口区的表层和底层波生近岸流的情况,波生近岸流在水深小于5m的浅水区较强,较深处则较弱,可以忽略。垂向变化的波浪辐射应力所产生的波生近岸流在表层比垂向平均的流速大,底层则刚好相反。进一步研究了波生近岸流对泥沙的输运作用,当考虑波生近岸流时,泥沙的扩散范围变大。利用考虑了浪致垂向混合的模型模拟了黄河口的表层、底层流场和淡水扩散,考虑了浪致垂向混合后,表层流速减小,底层流速增大,说明浪致垂向混合使得流速在垂向上分布的更均匀；浪致垂向混合作用增强了表层淡水和底层海水的垂向混合,淡水羽状流被明显的“挤压”在河口附近,减小了向外海扩散的水平距离,可见非破碎浪致垂向混合增强了表层的湍流能量,对河口径流的垂向扩散产生了显著作用。更多还原

【Abstract】 Wave and tide are the two main dynamic factors of coastal and estuary area, they coexist and have interaction with each other. When wave propagates to the shore, it will be refraction, diffraction and shoaling until broken as the result of varied water depth and structure. With wave broking, the wave induced current produced. It can play an important role in sediment transport along shore. At present, the two dimensional wave-current model has applied mostly, but the current was not uniformed in the vertical profile, and the vertical distribution has significant effect on the stability of structure and terrain evolvement. So we not only need to understand the surface changement, but also to find out the vertical variation of current, which can be carried out by the three dimension model.The purpose of this dissertation is to improved the three dimensional wave-current model COHERENS-SED to advance its ability of simulation, especially on the vertical characteristics.Firstly, vertical varied radiation stress is introduced into the model by adding to the fluid government equations. Then setting up numerical simulations with ideal terrain which are uniformed slope to study the vertical circulation in and out the wave broken zone. The results are agreement with the theory and measurement.At the other hand, due to waves act on the water surface, it makes the velocity gradient which will lead to the turbulence to enhance the vertical mixing induced by waves. So wave induced vertical mixing also be introduced into the coupled model through eddy viscosity coefficient. Carrying out some one-dimention numerical simulations in vertical direction, we find out the turbulence mixing of water flow was intensified by wave motion, the vertical eddy viscosity coefficient has a significant effect on the distribution of velocity in the vertical profile.Finally, applying the improved coupled model to Huanghe Delta, to study the wave induced current of surface layer and bottom layer. We obtained some conclusions:wave induced current was stronger in shallow water with depth little to 5m, it can be ignored in deep water zone. Surface current velocity caused by vertical varied radiation stress was larger than vertical averaged velocity, and bottom velocity was smaller than vertical averaged velocity. More over, the sediment transport under wave induced current was studied, and sediment will transport further with the effect of wave induced current. Then the condition of fresh water flowing into sea with wave induced vertical mixing was discussed, and making conclusions as follows:the surface velocity became smaller and the bottom velocity increased when wave vertical mixing was included, which shows the effect of wave on vertical distribution of momentum and energy.更多还原