【作者】 陈杰；

【导师】 蒋昌波；

【作者基本信息】 长沙理工大学 ， 港口、海岸及近海工程， 2011， 博士

【摘要】 海啸在近岸地区会引起剧烈的泥沙运动和岸滩演变。本文基于波浪水槽实验对海啸波作用下岸滩剖面和床沙组成变化开展研究。实验采用1/10和1/20的组合坡度,斜坡分别采用两种和三种粒径泥沙堆砌而成,并采用三种不同的水深,选取N波来模拟海啸波,同时进行了规则波和不规则波作用下的对比实验。实验对波浪的破碎、上爬、回落和水跃过程,每个波作用后的地形变化以及初始和最终的泥沙粒径组成进行了测量和记录。实验结果表明N波作用下岸滩发生了明显的冲刷和淤积,呈沙坝剖面,回落的水流使得前滩和滩肩发生冲刷,泥沙在离岸区域水跃发生处淤积,研究结果与其他学者的实验结果一致。当水深足够大时,N波几乎不会引起地形变化,这一实验结论与现场观测得到的结果一致,表明海啸中淤积的泥沙主要来源于近岸地区,而非深海。实验研究考虑床沙级配变化和岸滩坡度的影响,对海啸波作用下岸滩剖面变化和床沙组成变化规律进行深入分析。通过泥沙采样分析发现,淤积沙坝泥沙粒径呈粗化趋势,研究结果与海啸现场观测结果一致,实验首次揭示了海啸作用下非均匀输沙、粗化等独特现象。同时发现N波作用后得到的岸滩剖面的形状与部分规则波和非规则波作用后的实验结果相同,均为离岸淤积沙坝剖面,但是泥沙粒径变化结果却相反,而这些结果并不矛盾,均遵循(?)eliko(?)lu(2006)提出的泥沙运动的基本原则,细颗粒泥沙会在强烈的紊动作用下从床面中被筛选出来,并被搬运到低紊动地区,此过程造成了剧烈紊动区泥沙的粗化。在实验研究的基础上,本文基于Boussinesq方程耦合泥沙运动和地形演变模型,同时考虑了床沙组成变化计算,建立了海啸作用下岸滩和床沙级配变化平面二维数学模型。模型考虑波浪破碎和底部摩擦的作用,采用Wei (1999)原函数造波的方法,动边界处理采用线性外插法,地形演变方程采用WENO格式进行离散求解。通过一系列的验证和实验数据的比较,证明本文建立的数学模型能很好的模拟海啸波的传播、破碎、上爬和回落过程,能较好的模拟岸滩的冲淤变化过程,同时能较好的模拟床沙的组成变化过程,并对Engelund (1972)、Ackers (1973)和Van Rijn (1984)全沙输沙率经验公式进行对比研究。最后利用建立的数学模型分析了海啸波作用下岸滩和床沙级配变化特点,进一步获得了海啸波作用下岸滩剖面变化和床沙组成变化规律。更多还原

【Abstract】 Tsunami waves may move a significant amount of coastal sediment and cause significant changes of beach profiles in the affected coastal regions.The 2D laboratory experiments were performed to investigate beach profile changes and sorting of sand grains under the tsunami waves on the fine beach. The incident wave was N-wave. The initial 1/10-1/20 combined beach slope mainly composed of two or three sediment grain sizes was exposed to the N-waves in three different water depths. The incident wave also used regular waves and irregular waves for comparative study. The wave breaking, uprush, back-wash, hydraulic jump, bed profiles, initial and final distributions of sediment grain size were measured.The experimental results show that the wave motion and sediment transport were not really affected by the bed profile changes that occurred after running waves on the bed profile. The strong down rush resulted in erosion on the foreshore and deposition seaward of wave run down. The results agreed qualitatively with other experimental results. These was no changes of beach profiles under N-wave action when the water depth enough. This result agreed qualitatively with coastal retreat field observed after tsunamis. Those were all suggested that the majority of the deposit sources were from the beach rather than the deep ocean floor.The influence of sorting of sand grains and beach slope were considered in this experimental study. The characteristics of beach profile changes and sorting of sand grains under the tsunami waves were obtained. The sands sampling was performed in ten different feature locations after 6 waves. It was shown that the mean grain size increased in the deposition region. The results agreed qualitatively with the post-tsunami field observations. The nonuniform sediment transport and coarsening of the bed were laboratorial investigated for the first time.Also our experimental final profile was similar to some regular wave experimental results which were classified into bar type. However, the N-wave experimental grain sorting was opposite to regular wave results. Two results were in accord with basic rules that finer grains are winnowed from the bed in the most energetic areas by a turbulent process and are carried away to less energetic areas, resulting in a coarsening of the bed in the more energetic areas ((?)eliko(?)lu, 2006).Based on experimental investigations, the comprehensive two dimension plane numerical model was developed with the capability of modeling tsunami wave, including the effects of sediment transport, morphological changes and changes of sediment grain size distribution. The hydrodynamic model adopts on highly nonlinear and weekly dispersive Boussinesq equations and couples the sediment transport and morphological evolution models. The Weighted Essentially Non-Oscillatory Schemes (WENO) was implemented for spatial discretization of morphological bed level equations. The wave breaking model, bottom friction, source function method (Wei, 1999) and moving boundary algorithm were all implemented in the numerical model.The combined model was validated using available laboratory experiments. The coupling numerical model could well resolve the solitary wave propagate, break, runup and rundown on the beach, also could simulate scouring process and sorting of sand grains. The Engelund (1972), Ackers (1973) and Van Rijn (1984) total load empirical formulas were also investigated.The changes of beach profile and sorting of sand grains by tsunami-like waves were investigated by this numerical model. The characteristics of beach profile changes and sorting of sand grains by tsunami-like waves were further obtained.更多还原