【作者】 严冰；

【导师】 张庆河；

【作者基本信息】 天津大学 ， 港口、海岸及近海工程， 2009， 博士

【摘要】 近年来,随着粉沙质海岸港口建设的发展,粉沙质海岸泥沙问题,特别是航道淤积问题越来越突出。为此,本文针对粉沙质海岸泥沙特点,对泥沙悬浮机理进行研究,建立了波流共同作用下考虑底部高浓度现象的悬沙分布模型,利用该模型改进了三维泥沙数学模型,并对粉沙质海岸航道淤积现象进行了模拟研究。此外,本文还对概化粉沙质海岸悬沙横向分布和航道淤积规律进行了分析。论文的具体研究内容和结论如下:1、基于有限掺混长度理论对水流作用下的悬沙浓度分布进行了研究。模型建立过程中,分析了紊动漩涡与掺混长度之间的关系,推导出同时满足紊流相似假说和掺混长度理论的泥沙掺混长度分布公式。2、对波浪作用下泥沙悬浮机理进行分析,建立了全水深悬沙垂线分布模型。依据Lamb等高浓度含沙水体实验结果,着重对波浪作用下高浓度水体的紊动强度分布、掺混长度进行了分析。在以上工作基础上,采用紊动制约函数直接修正扩散系数的方法,建立了波流共同作用下考虑高浓度现象的悬沙浓度垂线分布模型,与多家实验结果的比较表明了该模型的合理性。3、利用本文建立的波流共同作用下考虑高浓度现象的悬沙浓度垂线分布模型,对Wai和Jiang开发的三维泥沙输运数学模型进行了改进,并通过实验数据验证了该模型能够应用于航道淤积模拟研究。4、以概化粉沙质海岸大风过程航道淤积为例,针对悬移质特别是高浓度含沙水体在航道淤积中的作用进行了模拟和分析。结果表明,强浪是形成底部高浓度含沙水体的根本原因,8级向岸大风作用下,浅滩上含沙量大于20kg/m3的水体厚度可达0.8m-1.25m。泥沙运动轨迹模拟结果表明,航道淤积主要是底部高浓度水体在航道内不平衡输沙所造成,上部泥沙几乎不起作用。另外,推移质输沙也不是主要因素。5、根据破波带内外波能演化规律,对波浪挟沙能力公式进行了改进,考虑了波浪破碎产生的紊动对挟沙能力增大的影响,所建立的公式反映了长周期波挟沙能力大的特性,并通过收集的资料确定了公式中的系数。6、利用文中建立的挟沙能力模型对概化粉沙质海岸上波浪因素对泥沙运动的影响进行了分析。结果表明,对于岸滩平缓的粉沙质海岸,除了紧靠岸边的区域外,波浪底部剪切力是泥沙悬浮的主要因素,而波浪破碎的作用较为有限。7、在高浓度水体悬沙分布模型的基础上建立了粉沙质海岸航道淤积简化计算公式,航道淤积的计算结果表明该公式可以合理反映粉沙质海岸淤积强度。更多还原

【Abstract】 In recent years, with the increase of the port constructions on the silty coast, the problems of the sediment transport, especially the channel siltation become more and more prominent. Therefore, the sediment transport on the silty coast was studied in the present dissertation. On the one hand, the mechanism of sediment suspension under different conditions was analyzed with the fininte mixing length theory and a theoretical model was developed to describle the suspended sediment concentration profile with the high-concentrated near-bottom suspension under combined waves and current. Based on the new theoretical model a three-dimensional sediment mathematical model was improved to simulate the phenomenon of channel siltation on the silty coast. On the other hand, the cross-shore sediment concentration distribution and channel siltation on a generalized silty coast were also investigated.The main results are summarized as follows:1. According to the finite mixing length theory, the characteristics of the suspended sediment in current were investigated. The relation between the turbulent vortex and mixing length was analyzed and a new sediment mixing length equation was derived based on the mixing length theory and Karman’s turbulence hypothesis.2. The mechanism of sediment suspension under waves was discussed. A theoretical model for the sediment concentration distribution under wave was developed. Using the experimental results by Lamb et al, the characteristics of turbulence intensity and mixing length in the water with the high concentrated sediment suspension were analyzed. Based on the conclusions in pure current and pure wave conditions, the vertical distribution model of the suspended sediment for the combined waves and current was devepoled. In this model, the damping of turbulence due to the presence of high sediment concentrations is taken into account. The comparison of the calculated results and measurements shows that the present model is reasonable.3. The three-dimensional mathematical model for the sediment transport by Wai and Jiang was improved through using the present suspended sediment model with hight concentration influence for combined waves and current. The improved mathematical model is verified through comparison between simulated and experimental results of channel siltation.4. The process of channel siltation was simulated by the improved three-dimensional sediment mathematical model to illuminate the effect of suspended sediment on channel siltation. The simulated results show that the strong wave is the source of the high concentrated near-bottom suspensions. The thickness of high concentration suspensions (where concentration >20kg/m3) can be in the range of 0.8m-1.25m due to the shorewards wind of force 8. From the particle trajections of the suspended sediment particle, it is the deposition of high concentration near-bottom suspensions that results in the channel siltation. The bed-load sediment transport also plays a subtle role for channel siltation.5. The sediment carrying capacity formula for waves was improved according to the variation of the wave energy dissipation inside and outside the surf zone. The new formula predicts that the sediment suspension increases with the wave period. Measured data were collected to determine the coefficients.6. The carrying capacity model was used to investigate the effects of wave on the cross-shore sediment suspension on a generalized silty coast. The results show that the main factor for the sediment suspension on silty coast is the bed shear stress of wave instead of the wave breaking except in the surf zone very near the coastline.7. Finally, a simplified formula for channel siltation was developed based on the vertical distribution model of the high concentrated sediment suspension, which was used to calculate the thickness of the channel siltation.更多还原