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Zhang J.,Shanghai JiaoTong University | Zhang J.,Key Laboratory of Estuarine and Coastal Engineering | Wang X.,Nanyang Technological University | Liang D.,Shanghai JiaoTong University | Liu H.,Shanghai JiaoTong University
Engineering Applications of Computational Fluid Mechanics

Detached-eddy simulation (DES) is proposed for simulating shallow water flow in the present paper. Compared to the traditional numerical model used in river flow simulation that is based on hydrostatic assumption, the non-hydrostatic pressure terms are introduced into the momentum equations to improve the accuracy of simulating flow over a distinct, uneven bottom. The numerical scheme is a finite volume method based on an unstructured grid in the horizontal plane, and the σ coordinate in the vertical direction to fix the free surface and the uneven bottom. The in-house codes are paralleled by OpenMP. While most of the domain (including the near bottom zone and the upstream and downstream boundary zones) is designed as a Reynolds-Averaged Navier Stokes (RANS) zone, only a local computational zone is simulated by large-eddy simulation (LES), which is implemented by means of properly designing the grid scales. A case study of flow over a series of five dunes was used to validate the model, focusing on the influence of the inflow condition on the small-scale vortical structures. As an improved method to inspire much more sufficient velocity fluctuation, a zonal detached-eddy simulation (ZDES) technique was introduced into the present model. The same case study was also carried out in a RANS model for comparison with the hybrid RANS and DES or ZDES results. The proposed model is shown to be equally effective in the prediction of small-scale vortical structures in shallow water flow with free surface, and to have potential for simulating large-scale flows, such as natural river flows. © 2015 The Author(s). Published by Taylor & Francis. Source

Han L.,Shanghai JiaoTong University | Zhang J.-X.,Shanghai JiaoTong University | Zhang J.-X.,Key Laboratory of Estuarine and Coastal Engineering | Wei Q.-F.,Design and Research Institute | And 2 more authors.
Shuidonglixue Yanjiu yu Jinzhan/Chinese Journal of Hydrodynamics Ser. A

This paper investigates the spatial distribution characteristics of the backwater effect, and proposes a new way to determine the corresponding backwater coefficient based on series hydraulics tests in an open channel. The high-precision ultrasonic water depth measurement system is used to obtain the water surface elevation of the interest areas near the cylinder pier. Based on the measured data, the backwater amplitude is systematically analyzed, and a new relationship characterizing the backwater effect and various flow conditions is verified. Quantitative analyses further clarify the influence scope of the backwater effect and the water depth variation characteristics, leading to a new empirical formula for calculating backwater degree. These results can be regarded as numerical simulation standards for generalizing bridge piers in the large-scale research of hydrodynamics in the future. Source

Ma G.,Key Laboratory of Estuarine and Coastal Engineering | Ma G.,Old Dominion University | Shi F.,University of Delaware | Liu S.,Tongji University | Qi D.,Key Laboratory of Estuarine and Coastal Engineering
Applied Ocean Research

The paper presents measurements of sediment deposition in the navigation channel of Changjiang Estuary during the construction of the world largest jetty-spur system. A significant change of sediment deposition pattern is found after the second stage of the project, which extended the previous 25 km long jetties built in the first stage to about 50 km. The measurements show that the main deposition region migrated from the lower reach to upper reach of the navigation channel, with the strongest deposition occurred at the upper middle reach. The physical mechanisms inducing the migration of the sediment deposition region are studied numerically using the finite-volume coastal ocean model (FVCOM). Model results reveal that the tidal currents as well as the sediment processes in the northern passage are greatly changed by the structures. With the extension of the structures, suspended sediment concentration decreases at the upper reach and increases at the lower reach, resulting in a seaward migration of turbidity maximum in the northern passage. The changes of suspended sediment concentration distributions are mainly caused by the adjustments of tidal currents at ebb. The analysis based on the local momentum balance identifies two mechanisms causing these adjustments. © 2013 . Source

Zhang J.-X.,Shanghai JiaoTong University | Zhang J.-X.,Key Laboratory of Estuarine and Coastal Engineering | Sukhodolov Alexander N.,Leibniz Institute of Freshwater Ecology and Inland Fisheries | Liu H.,Shanghai JiaoTong University | Liu H.,Key Laboratory of Estuarine and Coastal Engineering
Journal of Hydrodynamics

The hydrodynamics of geophysical flows in oceanic shelves, estuaries, and rivers are often studied by solving shallow water equations under either hydrostatic or non-hydrostatic assumptions. Although the hydrostatic models are quite accurate and cost-efficient for many practical applications, there are situations when the fully hydrodynamic models are preferred despite a larger cost for computations. The present numerical model is implemented by the finite volume method (FVM) based on unstructured grids. The model can be efficiently switched between hydrostatic and non-hydrostatic modules. The case study shows that for waves propagating along the bar a criterion with respect to the shallowness alone, the ratio between the depth and the wave length, is insufficient to warrant the performance of shallow flow equations with a hydrostatic approach and the nonlinearity in wave dynamics can be better accounted with a hydrodynamic approach. Besides the prediction of the flows over complex bathymetries, for instance, over asymmetrical dunes, by a hydrodynamic approach is shown to be superior in accuracy to the hydrostatic simulation. Source

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