Computational Fluid Dynamics Analysis of Non-Cohesive Sediment Transport in Open Channel Flow

Predicting sediment transport has numerous implications in Civil Engineering and related fields. When there is excess sediment deposit in waterways, ships that move people and goods cannot navigate them. Loss of sediment that surrounds hydraulic support structures (e.g., bridge piers) may cause structural hazards. In the present dissertation research, computational fluid dynamics (CFD) was applied to improve the prediction capability of sediment transport in turbulent environments, with a focus on open channel flows. The CFD tool used is FANS3D (Finite Analytic Navier-Stokes code for 3D flow), which solves the Reynolds-Averaged form of Navier-Stokes equations in general curvilinear coordinate systems. The code was coupled with sediment transport models to solve the hydrodynamics and the resulting transport phenomena. For flows in domains with complex geometries, the overset grid technique was adopted, wherein multiple blocks with different shapes and structures form the mesh. The wall function approach was implemented to account for roughness effects of the physical domain’s boundary surfaces. After validation with experimental results, the coupled model was utilized in four practical applications: transport of suspended sediment in a channel bend, scour around abutment, backfilling of scour hole under a unidirectional flow, and scour around an offshore wind turbine support structure

Nitrogen doping of carbon nanoelectrodes for enhanced control of DNA translocation dynamics

Controlling the dynamics of DNA translocation is a central issue in the emerging nanopore-based DNA sequencing. To address the potential of heteroatom doping of carbon nanostructures to achieve this goal, herein we carry out atomistic molecular dynamics simulations for single-stranded DNAs translocating between two pristine or doped carbon nanotube (CNT) electrodes. Specifically, we consider the substitutional nitrogen doping of capped CNT (capCNT) electrodes and perform two types of molecular dynamics simulations for the entrapped and translocating single-stranded DNAs. We find that the substitutional nitrogen doping of capCNTs stabilizes the edge-on nucleobase configurations rather than the original face-on ones and slows down the DNA translocation speed by establishing hydrogen bonds between the N dopant atoms and nucleobases. Due to the enhanced interactions between DNAs and N-doped capCNTs, the duration time of nucleobases within the nanogap was extended by up to ~ 290 % and the fluctuation of the nucleobases was reduced by up to ~ 70 %. Given the possibility to be combined with extrinsic light or gate voltage modulation methods, the current work demonstrates that the substitutional nitrogen doping is a promising direction for the control of DNA translocation dynamics through a nanopore or nanogap based of carbon nanomaterials.Comment: 11 pages, 4 figure