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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.

在过去十年中，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。全面了解内陆架和碎波带之间的沉积物交换，主要是通过底形的迁移发生的，可以显着改善现有的封闭深度的概念，提高我们预测海岸响应的能力。底形迁移是陆架与碎波带之间泥沙输移的主要方式。这些底形的几何形状也决定了内陆架的水动力耗散，其存在和演变是准确预测波浪和海流的关键信息。在过去的二十年中，大量的工作已经进行了碎波带，以了解在短时间尺度上的海上和陆上砂坝迁移的动力学。在碎波带中，床面高程变化较大（1至5 m），而碎波带的跨岸尺度相对较小（10米至至多1至2 km）。在横跨海岸的内陆架上，尺度要大得多，因为在高能波期间，沉积物可以被移动到离岸10公里的地方，但风暴引起的大尺度高程变化通常小于10厘米。量化这两个制度之间的泥沙输运是必不可少的预测长期的海岸线撤退，由于海平面上升。如果在这一转变过程中出现陆上运输，海岸线的撤退速度可能会比当前模型预测的要慢。本研究紧密结合现有的现场观测资料与数值模拟，探讨三个关键的假设演变的底形和过渡到片流。本研究中采用的数值模型SedFoam已经通过社区表面动力学和系统（CSDMS）模型库作为开源模型传播。该项目将大大增强这一开放源代码模型，使其具有涟漪模拟的分辨率能力，新模型（SedLESFoam）也将通过CSDMS作为开放源代码传播。该项目还将促进与格勒诺布尔理工学院（法国）的科学家在实地/实验室数据分析和共同开发SedLESFoam与替代封闭方案方面的密切国际合作。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广泛培训，一名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，一名大学生将被招募来创建一个双球模型的天然沙粒和开发一个动手滑坡实验，参加工程酷Stuffs营的中学生。随着预期的海平面上升率在未来世纪的跨大陆架泥沙输运过程的全面了解将成为重要的，以准确地预测海岸响应。本研究的主要目的是调查主导机制驱动的迁移和演变的底形和过渡到片流。一个新开发的两相模型（SedlLESFoam）将被用来进行模拟指导下的实地观测数据的综合分析。研究结果将检验以下三个假设。首先，床形缩放制度（如轨道与非轨道）之间的过渡是由近床负荷和悬浮负荷运输在一个波周期内的相对量。悬移质与近底质的输移比是描述斜波、水流和波流联合作用下底形演变和迁移的关键参数。第二，在具有轨道尺度波纹的粗粒度环境中，无论波速偏斜度和不对称度如何，床形迁移通常都是向岸的，其可以指向岸上或离岸，这表明向岸定向的波浪强迫的底部边界层流动是强迫涟漪迁移的重要机制，或者需要底部应力的谱分解，由此低频运动具有比高频运动更低的摩擦系数。第三，在充满活力的条件下，接近片流与底形仍然存在，并在片流条件下，没有底形，独特的组合强迫可以驱动瞬间床故障，进一步导致大的传输速率和快速迁移/演变的底形。这些运输过程不能单独参数化的传统的剪切应力为基础的方法。一个紧密结合的研究工作，分析以前收集的现场数据和数值模拟将实施，以了解演变和运输从底形片流。现场数据集包括总计近5个月的旋转成像声纳测量底流和水动力强迫。最近的数据集包括高垂直分辨率的流动和悬浮沉积物领域获得的会聚束脉冲相干多普勒剖面仪。剖面仪数据包含一些第一次现场测量的波边界层流的轨道尺度的涟漪，除了分辨率的涡喷射涡的涟漪。将对这些实地数据进行重新分析，并产生与拟议研究问题相关的事件片段。一个新的连续性解决（或连续性平均）欧拉两相泥沙输运模型没有先验的推移质和悬移质的假设将被验证，其高分辨率的三维和二维流场将被用来解释在现场观察到的事件。研究结果将被用来通知创建新的参数化，可以通过沿海演变模型。

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）

SedFoam-2.0: a 3-D two-phase flow numerical model for sediment transport

DOI：
10.5194/gmd-10-4367-2017
发表时间：
2017-11
期刊：
Geoscientific Model Development
影响因子：
5.1
作者：
J. Chauchat;Zhen Cheng;T. Nagel;C. Bonamy;T. Hsu
通讯作者：
J. Chauchat;Zhen Cheng;T. Nagel;C. Bonamy;T. Hsu

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
期刊：
Coastal Engineering
影响因子：
4.4
作者：
Kim, Yeulwoo;Mieras, Ryan S.;Cheng, Zhen;Anderson, Dylan;Hsu, Tian-Jian;Puleo, Jack A.;Cox, Daniel
通讯作者：
Cox, Daniel

A Numerical Study of Sheet Flow Under Monochromatic Nonbreaking Waves Using a Free Surface Resolving Eulerian Two-Phase Flow Model

使用自由表面解析欧拉两相流模型对单色非破波下面流的数值研究