Assessment of BSL kω Turbulence Model for Predicting Flow Characteristics in a Solitary Wave Motion

A deep understanding of boundary layer characteristics under wave motion, especially bottom shear stress on the seabed, is critical in sediment transport calculation and modeling. In this present study, boundary layer characteristics under solitary wave motion over the smooth bed are investigated through the Baseline (BSL) kω model. It will also consider the result of a laboratory experiment performed in a closed conduit generation system. The conclusion said that the BSL kω model can replicate well on horizontal and vertical velocity distribution at Reynolds number (Re) = 2.25 x 105. In addition, a turbulent spike which was occurred during decelerating phases of oscillatory motion can be predicted well also by the BSL kω model at Reynolds number (Re) = 6.06 x 105.

Investigation of Ship-Induced Hydrodynamics and Sediment Suspension in a Heavy Shipping Traffic Waterway

In order to investigate the complex hydrodynamics and associated sediment movement resulting from the ship passages in heavy shipping traffic waterways, field measurements were performed in a heavy shipping traffic waterway. Based on the collected waves, flow velocity and water turbidity data, the analyses of the ship-induced hydrodynamics and associated sediment suspension phenomena were conducted. The low-frequency primary wave and high-frequency secondary wave were more pronounced for a barge and yacht in the wave structure, respectively, and contributed more to the flow velocity fluctuations and the bottom shear stress. The ship-induced bottom shear stress can cause significant suspended sediment concentration increase, and there is a correlation between the maximum suspended sediment concentration and maximum ship-induced drawdown height, which can provide a reference for the waterway management.

Effects of hard clam (Mercenaria mercenaria) density and bottom shear stress on cohesive sediment erodibility and implications for benthic-pelagic coupling

The interacting effects of little neck hard clam (Mercenaria mercenaria) density and bottom shear stress on cohesive sediment erodibility were investigated. Short-term stepwise erosion experiments in 30 and 40 cm diameter Gust microcosms over a range of 0.0083 to 0.1932 Pa were performed using sequential 20-minute constant shear stress steps while sampling turbidity regularly. In addition, sediment erodibility was monitored in two one-month long ecosystem experiments with tidal resuspension and 0, 10, and 50 hard clams in 1 m3 shear turbulence resuspension mesocosms (STURM) with an initial stepwise erosion experiment (0.313 to 0.444 Pa). In short-term erosion experiments, a low density of hard clams did not significantly affect sediment erodibility, but a high density of hard clams destabilized muddy sediments through significantly decreased critical shear stresses and higher erosion rates, resulting in higher cumulative suspended mass (CSM). In long-term erosion experiments, the sediment stabilized over time between treatments and decreased to a CSM of approximately 60 g m–2 with different densities of hard clams. This was likely due to development of microphytobenthos, mediated by the filter-feeding clams, bottom shear stress and increased light. Bioturbation by a dense bed of hard clams in interaction with infrequent high bottom shear due to storms may increase CSM in the water column, with subsequent direct and indirect effects on the ecosystem. However, more controlled longer-term erosion studies to determine the interacting effects of long-term exposure to high bottom shear stress, benthos, and microphytobenthos on sediment erodibility and benthic-pelagic coupling are needed.

Research on wind-induced nutrient release in Yangshapao Reservoir, China

Nutrient (total nitrogen (TN) and total phosphorus (TP)) are considered the major indicators to be impacted by wind speed in shallow lakes and reservoirs. As a reservoir situated in Jilin Province, China, Yangshapao Reservoir has been employed for irrigation and urban water use. After 2 years’ observation carried out on water quality and wind speed, it was found that the TN, NH4 and TP are significantly correlated with the bottom shear stress attributed to wind, whereas the dissolved phosphorus (DP) is not. Bottom shear stress is also noticeably associated with dissolved oxygen (DO), thus promoting nutrient release into the water body. In winter, ice can effectively inhibit the wind-induced shear stress, and the TP concentration is evidently lower than in the other seasons. This scenario should be considered in the management of the water quality of the lake and similar lakes.

Numerical investigation on bottom shear stress induced by flushing gate for sewer cleaning

One of the most common strategies for sewer cleaning is to generate flushing flows using flushing gates to store water in the upstream sewer pipe. Therefore it is important to obtain the flow information on the flushing waves and their eroding effects. In this study, the flow characteristics of the flushing wave and the flushing effect were investigated by a transient flow calculation using a commercial computational fluid dynamics (CFD) code. The values of bottom shear stress were obtained and the effect of several factors are discussed. The water depth and the slope were related to the release rate of the storage volume, while the flushing volume determined the flushing distance at long sewer distances. The initial downstream water level was found to dramatically reduce the flushing effect. Equations based on the storage depth were developed to estimate the flushing effect, and suggestions for the installation and operation of flushing gates are provided.