3D layered-integrated modelling of mass exchange in semi-enclosed water bodies

Abstract

The flow patterns in semi-enclosed water bodies are generally complicated and have significant effect on the water quality and fluid exchange there. The exchange of of fluid between the semi-enclosed water body and outside is due to two physical mechanisms. The first is the flushing due to tidal effect. The second is the shear induced by the velocity difference between the flow within the water body and outside. To predict the flow and solute transport in these water bodies a three-dimensional layer-integrated numerical model has been developed. To account for the turbulence which consists of the free shear component and the bottom friction component the k-e model is employed. The numerical model has been applied to the cases of tidal flow as well as steady river flow outside a rectangular harbour with or without breakwater. Compared with the available experimental results, the gross mass exchange both due to tidal effect and shear can be estimated satisfactorily by the numerical model. RÉSUMÉLes configurations d'écoulement dans les volumes d'eau semi-fermés sont généralement compliquées et ont un effet significatif sur laqualité de l'eau et les échanges de fluides. L'échange de fluide entre la masse d'eau semi-fermée et l'extérieur est dü a deux mécanismes physiques. Le premier est Ie flot lié a Ia marée. Le second est le cisaillement induit par la difference de vitesse de l'eau entre l'intérieur et l'extérieur. Pour prévoir l'écoulement et le transport d'effluents dans ces masses d'eau, un modèle tri-dimensionnel numérique intégré par couches a été développé. Pour tenir compte de la turbulence qui comprend la composante de cisaillement libre et le frottement au fond, on utilise le modèle k-e. Le modèle numérique a été appliqué aussi bien au cas de la marée qu'a celui d'un écoulement permanent de rivière a l'extérieur d'un port rectangulaire avec ou sans brise-lame. Compare aux résultats expérimentaux disponibles, l'échange de masse brut dü a la marée et a l'écoulement cisaillé, donné par le modèle numérique. peut être considéré comme satisfaisant.

Salinity, Temperature and Turbidity Structure in the Suva Lagoon, Fiji

“…At high tide the area is 6.34×10 7 m 2 and 5.57×10 7 m 2 at low tide with the capacity to hold a mean volume of the lagoon of about 7.77×10 8 m 3 [7] . Generally, the rise and fall of water level due to tides acts as a major flushing mechanism for a lagoon [8] .…”

Correlation of extreme waves and water levels using a third-generation wave model and a 3D flow model

“…In the solution of surface elevation, Eq. (5) is transformed to a Poisson-like equation with h as the only unknown and solved by an iterative method (Li and Gu, 2001). The coupling of the wave model and flow model is through the surface shear stress which is affected both by the wind speed and the wave-induced surface roughness.…”

A layer‐integrated approach for shallow water free‐surface flow computation

“…Shankar et al [9] developed a finite difference model using the same concept to simulate flow patterns for the sudden contraction and expansion flows and show reasonable flow characteristics downstream of an opening. Li and Gu [10] applied the layer-integrated concept to the mass exchange and tidal flushing problem in the harbor. The multi-level or multi-layer approach allows free surface on top layer to vary with time or iteration.…”