Collaborative Res: Physics of lutoclines and laminarization extracted from turbulence-resolved numerical investigations on sediment transport in wave-current bottom boundary layer

最近的数值研究表明，存在四个不同的制度，波浪引起的细泥沙运输范围从混合运输，形成一个lutocline，并最终在一个完整的流动laminarization范围内的沉积物的可用性和沉降速度。数值模型是基于欧拉-欧拉两相配方简化为细泥沙（小颗粒响应时间），同时解决所有尺度的粘性-泥沙相互作用。该项目将通过数值模拟进一步研究与这些制度相关的四个关键科学问题。首先，一个完整的相位图将被构造为波雷诺数，散装理查森数（沉积物可用性）和无量纲沉降速度与一系列精心设计的模拟的函数的流态。结果将突出潮汐和波浪边界层对沉积物的响应之间的主要差异。其次，随着对层状化开始的更好理解，该模型将被增强以支持非牛顿流变学，以研究流变应力和湍流调制之间的相互作用，以确定流态和流体动力耗散的转变。第三，平均电流将被添加到模拟中。波流相互作用可能会增加泥层的厚度和运输，在最近的野外研究中观察到的Waiapu河（新西兰）的架子。然而，如果水流太强，沉积物可能会被重新夹带并混合均匀，从而阻止重力流的形成。最后，该模型将扩展为粗颗粒的传输。由于波浪雷诺数的降低，粘土和粉砂的共同输运将首先被研究。下一步将是模拟一个完整的多分散系统使用直接正交矩量法的方法。多分散的模拟工作，使人们能够深入了解的过程中所观察到的微观地层在泥占主导地位的environments.Several以前的现场观测大陆架揭示了各种海底状态，由于波流驱动的沉积物运输。这些海底状态的出现有几个重要的影响。例如，一个跃层的形成表明在海床附近捕获了细小沉积物，由此产生的大密度异常可能通过波浪支持的重力流在大陆架上产生大量的近海沉积物搬运。当表面波在泥质海床上传播时，在风暴减弱阶段，由于流体泥层变得层状化，经常观察到高的波浪耗散率。最近对泥质沉积物的微地层学研究表明，在波浪支持的重力流事件期间发生的过程可以与三部分沉积微组构相关联。波浪诱导的流体泥浆输运建模的主要挑战是沉积物和湍流之间的耦合、湍流的过渡性质、流变学和输运的多分散性质。该研究解决了这些挑战，其结果将是有价值的，在进一步解释关键过程中观察到的泥占主导地位的沿海environment.The项目将提高我们的再悬浮和交付的细沉积物跨越大陆边缘，这是沉积物源汇研究的一个关键要素的理解。这项研究还将提高预测海底表层特性的能力，这对水下勘探和波浪预测至关重要。利用现有的波浪水槽，将由本科生开发一个动手实验室实验，以可视化波浪边界层的存在和床附近混合过程的间歇性。这项新设计的实验将用于每年在每个机构的夏季会议期间举行的工程推广活动。在第三年，这个实验将被添加到美国大学流体力学实验室的课程中。特拉华州。

Recent numerical investigations reveal the existence of four distinct regimes of wave-induced fine sediment transport ranging from well-mixed transport, to the formation of a lutocline, and eventually a complete flow laminarization over a range of sediment availabilities and settling velocities. The numerical model is based on an Eulerian-Eulerian two-phase formulation simplified for fine sediment (small particle response time) while resolving all the scales of turbulence-sediment interactions. This project will further investigate four critical science issues related to these regimes via numerical simulations. Firstly, a complete phase map will be constructed of flow regimes as a function of wave Reynolds number, bulk Richardson number (sediment availability) and nondimensional settling velocity with a series of carefully designed simulations. The results will highlight the major differences between the tidal and wave boundary layers in response to sediments. Secondly, with a better understanding of the onset of laminarization, the model will be enhanced to support non-Newtonian rheology in order to study the interplay between rheological stress and turbulence modulation in determining the transition of flow regimes and hydrodynamic dissipation. Thirdly, mean current will be added to the simulations. Wave-current interaction may enhance the mud layer thickness and transport, as observed in a recent field study at the shelf of Waiapu River (New Zealand). However, if the current is too strong, sediments can be re-entrained and become well-mixed and hence the formation of gravity flow is prevented. Finally, the model will be expanded for transport of coarser grains. Concurrent transport of clay and silt due to decreasing wave Reynolds number will be first studied. Next step will be to simulate a complete polydispersed system using a direct quadrature method of moments approach. Polydispersed simulation efforts allow insights into the processes causing the observed microstratigraphy in mud-dominant environments.Several prior field observations on continental shelves reveal a variety of seabed states due to wave-current driven sediment transport. The occurrences of these seabed states have several critical implications. For example, the formation of a lutocline indicates trapping of fine sediments near the bed and the resulting large density anomaly may yield significant offshore sediment transport on the shelf through wave-supported gravity flows. When surface waves propagate over a muddy seabed, high wave dissipation rate is often observed during the waning stage of a storm as the fluid mud layer becomes laminarized. A recent microstratigraphy study of mud deposits suggests a three-part sedimentary microfabric that can be associated by processes occur during wave-supported gravity flow events. The main challenges of modeling wave-induced fluid mud transport are the coupling between sediment and turbulence, the transitional nature of turbulent flow, rheology and the polydispersed nature of transport. This research addresses these challenges and the results will be valuable in further interpreting critical processes observed in the mud-dominant coastal environment.The project will improve our understanding of the resuspension and delivery of fine sediment across the continental margin, which is a critical element of the sediment source to sink study. This study will also improve the ability to predict the surface layer properties of the seabed which is critical to underwater exploration and wave prediction. Using wave tanks already available, a hands-on laboratory experiment to visualize the existence of wave boundary layer and the intermittent nature of the mixing process near the bed will be developed by undergraduate students. This newly-designed experiment will be used in Engineering outreach activities taking place annually during the summer session of each institution. In Year 3, this experiment will be added to the curriculum in the undergraduate fluid mechanics laboratory at U. Delaware.