Grain/turbulence-scale numerical simulation of heterogeneous sediment transport and their parameterization in coastal models
Abstract
In the coastal environments, sediment properties are almost always heterogeneous. The long term goal of the proposed work is to develop an open-source, multiphase model for turbulence/grain-scale and wave-scale sediment transport processes to order to understand heterogeneous sediment transport processes in the coastal environments. For the proposed two year project, our objectives are (1) to continue investigating vertical grading effects and grain shape on sediment transport in wave bottom boundary layer for energetic wave condition and improving sediment transport parameterizations in coastal morphodynamic models and (2) to understand how the bimodal distribution of cohesive sediment transport, namely, the fluffy flocs and denser aggregates, can dictate vertical distribution of turbulence and suspended sediment transport in tidal boundary layer in order to develop an effective flocculation parameterization in coastal modeling systems. As part of the ONR iFMSIP initiative, we developed a CFD-DEM numerical model to study vertical grading effects in wave-driven sediment transport. Since the foreshore grain distribution is the most heterogeneous segment of a sandy beach, our study can be considered as first step toward understanding heterogeneous coastal sediment transport. Major findings, including model development and the armoring/exposure effects on onshore sand transport and equilibrium concentration are discussed. We need to further expand the effort for wider grain size range, grain shape and wave-current interaction so that newly improved parameterizations can be complete for coastal morphodynamic models. Moreover, through discussion with Dr. Paul Hill (Dalhousie University) and his colleagues, we are aware of an interesting dataset on new insight of fine sediment dynamics during their South Korean field work. An unexpected negative correlation between surface turbidity and tidal flow intensity was observed due to a de-coupling between surface turbidity and high concentration fluid mud near the bed. They hypothesized that the observed vertical variability of fine sediments can be explained by the co-existence of fluffy flocs and denser aggregates. This is yet another example demonstrating the importance of sediment heterogeneity in natural systems. To better assess underwater environmental parameters through remote sensing in high turbidity regions, understanding the dynamics of the heterogeneity of fine sediment is necessary.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 04, 2018
- Source ID
- N000141812785
Entities
People
- Tian-jian Hsu
Organizations
- Office of Naval Research
- United States Navy
- University of Delaware