【作者】 王睿；

【导师】 牛小静；

【作者基本信息】 清华大学 ， 水利工程， 2015， 硕士

【摘要】 近海岸滩演变研究在海岸保护和海岸工程建设中受关注的问题。波浪是岸滩剖面演变的重要动力因子,其在近岸浅水区的强烈非线性对泥沙输移及岸滩演变具有非常显著的影响。高效准确地模拟近岸水波的特征要素和非线性特征,进而建立更为准确的岸滩剖面演变模型,也是近年来海岸泥沙研究的热点问题之一。本研究基于相平均的波浪模型,利用波高、水深、周期等波浪特征参数重构波周期内的时间过程,进而将重构得到的流速过程用于非恒定泥沙运动计算,最终形成岸滩演变模型。构建的岸滩演变模型保持了基于相平均波浪模型计算的高效性,同时也较好地重现了波浪周期内非恒定流动过程对泥沙运动的影响,充分考虑了近岸波浪非线性对岸滩演变的作用,具有与相位分解模型同样的模拟能力。模型分为三个模块:近岸波高计算模块、近底面流速过程重构模块、泥沙运动和底床演变模块。近岸波高的计算基于波能守恒方程,并针对传统模型中关于强非线性波模拟存在的问题提出了修正。传统波能守恒方程在波浪具有强非线性时得到的波高存在较大的误差。特别是在模拟分析规则波时,研究发现传统波能守恒波浪模型对波高的估计明显偏小。本文提出了对波浪模型进行非线性修正的办法,有效地提高了规则波的模拟精度。近底面波浪流速过程重构借鉴前人研究成果,根据所得波高水深等条件给出近底面流速过程,该方法很好的重现近岸波浪非线性引起的近底流速不对称和歪斜。泥沙运动和岸滩演变模块,选用了一个能很好反映波浪非线性影响的输沙率计算方法,并考虑了底坡对底床变形的影响。本研究构建的模型首先应用于规则波作用下的岸滩演变模拟,分别对模型各个模块进行了验证。通过与实验数据的对比,分析了波高计算中三种不同的非线性修正方法,结果表明三种模型均能够提高波高的模拟精度;对比了三种不同的规则波破波模型,证明计算所采用的破碎模型具有较广泛的适用性。通过与VOF方法得到的高精度数值计算结果对比,检验了近底面流速重构方法的有效性。进一步将模型应用于大型波浪水槽中岸滩演变实验的模拟,验证了模型的可靠性。本研究通过修改模型中的破碎子模型,将其进一步推广至不规则波的情况。利用修改后的模型模拟了不规则波在斜坡地形上的传播过程及不规则波作用下斜坡演变过程。模拟结果与实验数据吻合良好。将模型与目前在近海岸滩演变中应用较广泛的Xbeach模型进行对比,可以看到短波作用下的岸滩演变过程,本文提出的模型能够更好地反映水下沙坝的形成。更多还原

【Abstract】 The evolution of nearshore topography is a major concern in coastal protection and coastal engineering. Wave is one of the most important dynamic factors in causing such evolution. The strong nonlinearity of waves in shallow water significantly affects the sediment transport and, consequently, also the topography evolution. Development of a numerical model for nearshore wave motion including the nonlinear effects so that the topography evolution can be more accurately predicted has been a hot issue in the study of coastal sediment transport.This study is based on the phase-averaged wave model. The periodic wave processes are reconstructed based on their relations with the wave parameters such as wave height water depth, wave period, etc. The reconstructed process of wave velocity can be used in unsteady sediment transport calculation, and then a topography evolution model can be developed. The model developed in this study keeps the efficiency of the phase-averaged model, and also describes the effect of the temporal variation of the velocity on sediment transport, which is the same with the phase-resolved wave model.There are three modules in the model: nearshore wave module, wave processes reconstruct module, sediment transport and seabed evolution module. The nearshore wave height is calculated based on wave energy balance equation, and a modification to including the effect of wave nonlinearity is introduced. Using the traditional wave energy balance equation, a significant underestimation on wave height is found when the wave nonlinearity is strong, especially in case of regular waves. This is because the relationship between wave energy and wave height is based linear theory in the traditional wave energy balance equation. Therefore, the modification is proposed in the wave model for regular waves, which is proved can greatly improve the accuracy of regular wave. The reconstruction of periodic wave processes is based on previous study on the analytical approximation of wave form. The periodic wave process is then linked with the wave parameters given in the wave model, such as wave height, water depth and wave period. Using this procedure, the asymmetry and skewness of nearshore waves can be well described. And compared with phase-resolved wave model, this method has obvious advantage on computational efficiency. In the module of sediment transport and seabed evolution, a sediment transport formula which can describe the effect of the wave nonlinearity is adopted and the effect of the bed slope is concerned.Firstly, the model is verified and applied in simulation of the topography evolution under regular wave s. In the wave module, three nonlinearity modification methods are juxtaposed and the result suggests that all of the three methods can improve the computational accuracy of regular wave height simulation. Discussion on wave break models is also made and the result suggests that the breaking model adopted is widely applicable. The wave processes reconstruction module is proved to be reliable by comparing with the result of the NS-VOF method. The whole model is then applied in reproducing of the topography evolution experiment in a large scale wave flume. The model is used to predict the evolution of various slope beaches under the regular wave with various wave height and period. The results show a good agreement with experiment data.The model is further applied in the irregular wave condition. The wave breaking formula using in the wave model is changed to fit the random behavior of irregular waves. The model is applied to simulate irregular wave propagation on the uniform and various slope, and topography evolution under irregular waves is also simulated. The simulation results present good agreement with experiment data. Compared with XBeach model, which is widely used in simulating nearshore morphology evolution, the model performs better in simulation of the bar formation under short waves.更多还原