Evolution of Small Scale Seafloor Topography and Sediment Transport under Energetic Waves: From ripples to sheet flow

能量波下小尺度海底地形和沉积物输送的演变：从波纹到片流

基本信息

批准号：
1635151
负责人：
Tian-Jian (Tom) Hsu
金额：
$ 49.92万
依托单位：
University of Delaware
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2016
资助国家：
美国
起止时间：
2016-09-01 至 2020-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1635151&HistoricalAwards=false
关键词：
Evolution Small Scale Seafloor Topography

项目摘要

Coastal communities throughout the world have experienced exceptionally severe shoreline retreat in the past decade due to accelerated sea-level rise and increased storm intensity. A comprehensive understanding of the exchange of sediments between inner-shelf and surf zone, which primarily occurs through migration of bedforms, can significantly improve the existing depth-of-closure concept and enhance our capability in predicting coastal response. Bedform migration is the major mode of sediment transport between the inner-shelf and the surf zone. The geometry of these bedforms also determines hydrodynamic dissipation in the inner shelf and its existence and evolution are key information for an accurate prediction of waves and currents. In the past two decades an extensive amount of work has been conducted in the surf zone to understand the dynamics of offshore and onshore sand bar migration over short time scales. In surf zone bed elevation changes are large (1 to 5 m), while the across-shore scale of the surf zone is relatively small (10's of meters to at most 1 to 2 km). On the inner shelf across shore scales are much larger as sediment can be mobilized up to 10's of kilometers offshore during energetic waves, yet large scale elevation changes due to storms are usually less than 10 cm. Quantifying the sediment transport between these two regimes is essential to predicting long term shore line retreat due to sea-level rise. If there is onshore transport across this transition, shorelines may retreat slower than predicted by current models. This study tightly integrates existing field observational data with numerical simulations to investigate three key hypotheses on the evolution of bedforms and transition to sheet flows. The numerical model, SedFoam, adopted in this study has already been disseminated as open-source model through the Community Surface Dynamics and Systems (CSDMS) model repository. This project will significantly enhance this open-source model with turbulence-resolving capability for ripple simulation and the new model (SedLESFoam) will also be disseminated as open-source via CSDMS. The project will also facilitate close international collaboration with scientists at the Grenoble Institute of Technology (France) on field/laboratory data analysis and co-development of SedLESFoam with alternative closure schemes. A Ph.D. student will receive broad training in computational fluid dynamics and field data analysis and an early career postdoc researcher will further his training on nearshore modeling. Finally, an undergraduate student will be recruited to create a dual-sphere model for natural sand grain and develop a hand-on landslide experiment for a participating Engineering Cool Stuffs Camp for middle school students.With anticipated increasing rates of sea level rise in the next century a comprehensive understanding of cross-shelf sediment transport processes of the inner shelf will become important to accurately predict coastal response. The primary goal of this study is to investigate the dominant mechanisms driving the migration and evolution of bedfroms and the transition to sheet flows. A newly developed two-phase model (SedlLESFoam) will be used to carry out simulations guided by comprehensive analysis of field observational data. Research outcomes will examine the following three hypotheses. First, transitions between bedform scaling regimes (e.g. orbital vs an-orbital) are determined by the relative amounts of near-bed load and suspended load transport within a wave cycle. The ratio of transport via suspended load to near-bed load is the key parameter for describing the evolution and migration of bedforms under skewed wave, streaming and combined wave and current forcing. Second, bedform migration in coarse grained environments with orbital scale ripples is typically onshore irrespective of wave velocity skewness and asymmetry, which can be directed onshore or off-shore, indicting either onshore directed wave-forced bottom boundary layer streaming is an important mechanism for forcing ripple migration, or a spectral decomposition of bottom stress is required, whereby low frequency motions have a lower friction factor than high frequency motions. Third, in energetic conditions approaching sheet flow with bedforms still present and in sheet flow conditions without bedforms, unique combination of forcing can drive momentary bed failure which further leads to large transport rate and rapid migration/evolution of bedforms. These transport processes cannot be solely parameterized by the conventional shear-stress-based approach. A tightly integrated research effort of analysis of previously collected field data and numerical simulation will be implemented to understand evolution and transport from bedforms to sheet flows. The field data sets encompass a total of nearly 5-month duration of rotary imaging sonar to measure bedfoms, and hydrodynamic forcing. More recent data sets include high vertical resolution flow and suspended sediment fields obtained by convergent beam Pulse Coherent Doppler Profiler. The profiler data contains some of the first in-situ field measurements of wave boundary layer streaming over orbital scale ripples, in addition to resolution of vortex ejection eddies from the ripples. Re-analysis of these field data will be carried out and produce segment of events relevant to the proposed research questions. A novel turbulence-resolving (or turbulence-averaged) Eulerian two-phase sediment transport model without a priori assumption of bedload and suspended load will be validated and its high resolution 3-dimensional and 2-dimensional flow fields will be used to interpret events observed in the field. Findings will then be used to inform the creation of new parameterizations that can be adopted by coastal evolution models.

过去十年，由于海平面加速上升和风暴强度增加，世界各地的沿海社区经历了异常严重的海岸线后退。全面了解内陆架和海浪带之间的沉积物交换（主要通过床型迁移发生）可以显着改进现有的闭合深度概念，并提高我们预测海岸响应的能力。底形运移是沉积物在内陆架和海浪带之间迁移的主要方式。这些床形的几何形状也决定了内陆架的水动力耗散，其存在和演化是准确预测波浪和水流的关键信息。在过去的二十年中，人们在冲浪区进行了大量的工作，以了解短时间尺度上海上和陆上沙洲迁移的动态。冲浪区的河床高程变化较大（1至5 m），而冲浪区的跨岸规模相对较小（数十米至最多1至2公里）。在内陆架上，跨海岸的尺度要大得多，因为在高能波浪期间沉积物可以被移动到近海 10 公里处，但风暴引起的大规模海拔变化通常小于 10 厘米。量化这两种状态之间的沉积物输送对于预测由于海平面上升而导致的长期海岸线后退至关重要。如果在这一转变过程中存在陆上运输，海岸线的退缩速度可能会比当前模型预测的要慢。这项研究将现有的现场观测数据与数值模拟紧密结合起来，研究关于地床形态演化和席状流转变的三个关键假设。本研究中采用的数值模型 SedFoam 已通过社区表面动力学和系统 (CSDMS) 模型存储库作为开源模型进行传播。该项目将显着增强这个开源模型，具有用于纹波模拟的湍流解析能力，并且新模型 (SedLESFoam) 也将通过 CSDMS 作为开源进行传播。该项目还将促进与格勒诺布尔理工学院（法国）科学家在现场/实验室数据分析方面的密切国际合作，以及共同开发 SedLESFoam 和替代封闭方案。博士学位学生将接受计算流体动力学和现场数据分析方面的广泛培训，早期职业博士后研究员将进一步接受近岸建模方面的培训。最后，将招募一名本科生来创建天然沙粒的双球模型，并为参与的中学生工程酷玩营开发动手滑坡实验。预计未来海平面上升速度将加快本世纪，全面了解内陆架跨陆架沉积物输送过程对于准确预测沿海响应将变得非常重要。本研究的主要目标是研究驱动床层迁移和演化以及向席状流转变的主导机制。新开发的两相模型（SedlLESFoam）将用于在现场观测数据综合分析的指导下进行模拟。研究结果将检验以下三个假设。首先，床形尺度状态之间的转变（例如轨道与非轨道）是由波浪周期内近床载荷和悬浮载荷传输的相对量决定的。悬浮荷载与近床荷载的输送比是描述斜波、流流和波流联合强迫下地床形态演化和迁移的关键参数。其次，具有轨道尺度波纹的粗粒环境中的床形迁移通常发生在陆上，无论波速偏斜和不对称性如何，其可以定向在陆上或离岸，表明陆上定向波浪强迫底部边界层流是强迫的重要机制。需要进行波纹迁移或底部应力的谱分解，由此低频运动比高频运动具有更低的摩擦系数。第三，在接近仍存在床型的片状流的能量条件下和在没有床型的片状流条件下，独特的强迫组合可以驱动瞬时床破坏，这进一步导致大的传输速率和床型的快速迁移/演化。这些传输过程不能仅通过传统的基于剪切应力的方法进行参数化。将实施对先前收集的现场数据的分析和数值模拟的紧密结合的研究工作，以了解从床形到片流的演变和传输。现场数据集包含总共近 5 个月的旋转成像声纳持续时间，用于测量地床形态和水动力。最近的数据集包括通过会聚光束脉冲相干多普勒轮廓仪获得的高垂直分辨率流和悬浮沉积物场。除了来自波纹的涡流喷射涡流的分辨率之外，剖面仪数据还包含一些对轨道尺度波纹上流动的波边界层的首次现场测量。将对这些现场数据进行重新分析，并产生与提议的研究问题相关的事件片段。将验证一种新颖的湍流解析（或湍流平均）欧拉两相沉积物输运模型，无需先验假设床荷和悬浮荷载，其高分辨率 3 维和 2 维流场将用于解释观测到的事件在外地。然后，研究结果将用于为沿海演化模型采用的新参数化的创建提供信息。

项目成果

期刊论文数量（6）

专著数量（0）

科研奖励数量（0）

会议论文数量（0）

专利数量（0）

An Eulerian two-phase model for steady sheet flow using large-eddy simulation methodology

使用大涡模拟方法的稳定片流的欧拉两相模型

DOI：
10.1016/j.advwatres.2017.11.016
发表时间：
2024-09-13
期刊：
Advances in Water Resources
影响因子：
4.7
作者：
Zhen Cheng;Zhen Cheng;T. Hsu;J. Chauchat
通讯作者：
J. Chauchat

A numerical study of sheet flow driven by velocity and acceleration skewed near-breaking waves on a sandbar using SedWaveFoam

使用 SedWaveFoam 对沙洲上由速度和加速度倾斜的近破碎波驱动的面流进行数值研究

DOI：
10.1016/j.coastaleng.2019.103526
发表时间：
2019-10
期刊：
Coastal Engineering
影响因子：
4.4
作者：
Kim, Yeulwoo;Mieras, Ryan S.;Cheng, Zhen;Anderson, Dylan;Hsu, Tian;Puleo, Jack A.;Cox, Daniel
通讯作者：
Cox, Daniel

Interaction of Superimposed Megaripples and Dunes in a Tidally Energetic Environment

潮汐能环境中叠加的巨型波纹和沙丘的相互作用