Papers by Author: Jie Gu

Abstract: The study used MIKE21 to establish a two-dimensional mathematical model of Changjiang Estuary, doing a numerical simulation about the changes of the velocity along the South and North Passage and the flow spilt ratio of them with different ranges of sea level rise. The results show, with sea level rise, in the North Passage, the rise and fall velocity will increase from beginning to middle, and will reduce at outside, and the flood flow will enhance, the ebb flow will weaken, so it will result in fall deposition here; in the South Passage, the rise and fall velocity will increase at beginning, the rise velocity will reduce and the fall velocity will increase from middle to outside, and the flood flow will weaken, the ebb flow will enhance, so the river will be scoured, it will be conducive to the rivers development here.

Abstract: The change of water split ratio has important impacts on the fluvial process, saltwater intrusion and navigation in estuary area. A 2D hydrodynamics numerical model of the Changjiang Estuary was set up using Delft3D-FLOW. The calculation results are consistent well with the real measured data, which indicates that the model can be used in hydrodynamic analysis. Simulation results show that the ebb water split ratio of the North Branch in the flood season is larger than that in the dry season, while the situation of the South Branch is opposite. Under the condition of different tidal types, the ebb water split ratio for the North Branch is maximum during the spring tide, and minimum during the neap tide, while the one during the middle tide takes the second place.

Abstract: A two-dimensional numerical model was set up to simulate the tidal current of the Yangtze River Estuary with MIKE21 FM. This model has been calibrated and validated with the observed tidal level. We simulated the change of flood and tidal stage in the Yangtze River Estuary after the sea level rising by 20~60cm. The simulate results indicate that: (1)With sea level rising, the extent of rise of the high tide is greater than that of rise of low tide. Under the same sea level rise, the closer to the lower reaches of the Yangtze River Estuary, the more obvious the increase in the low tide level is, the rise of the high tide does not change significantly. (2)For the changes of the tidal range increase, under the same sea level rise, the closer to the upper reaches of the Yangtze Estuary, the greater the tidal range increase is.

Abstract: Sandbar is the main geomorphic unit in estuary, and due to the effects of runoff, tide and fresh-salt water mixing, the sediment movement there differs from others. Taking the Yangtze Estuary as an example, firstly, its sediment transport forms many circles both in longitudinal sections and transverse sections. Secondly, its sediment trapping is controlled by two different mechanisms, tidal current and salt water. The former contains the delay effect of sediment deposition and incipient motion, the asymmetry of flood and ebb, and the separation of flood and ebb, whereas the latter includes the influence of the saltwater wedge density current, the aggregation of the saltwater intrusion fronts, and the trapping of flocculation. Finally, its sediment re-suspension occurs three or four times ,not noly at the moment of flood or ebb maximumbut also at the transferring period from flood to ebb or from ebb to flood.

Abstract: A 2D numerical model about the Changjiang Estuary was set up with MIKE 21 in this study, which was well calibrated and verified with the observed tidal levels, flow velocities and flow directions, the computed results agree well with the measured data. Then the model has been applied to calculate the tidal level in the North Branch during spring and neap tide in flood season. The results show that, from the middle reach to the upper reach of the North Branch, the high tidal level is lower and lower and the low tidal level is upper and upper, so the tidal range is decreased, and tidal range during spring is greater than the one during neap. The tidal peak appearing time in the upper reach of the North Branch lags behind that of the middle reach, which is obviously during neap tide. The tidal level curve of the middle reach of the North Branch is smooth and close to the simple harmonic curve, while that of the upper reach of the North Branch deformities, the tidal level curve of ebb tide change fluctuant, much more obviously at spring tide.

Abstract: A 3D numerical model was performed to simulate the different cases of the water flow across different-shaped square cylinders. Figures of streamlines and turbulent kinetic energy contour lines in different cases were obtained. Through the comparison of streamlines, the areas of strong turbulent kinetic energy and the strongest turbulent kinetic energy nucleus, the results indicated that,(i) two symmetrical vortexes were formed behind the regular quadrilateral square cylinder and the “⊥”-shaped square cylinder ,respectively, and the former were bigger than the latter .While the flow crossed the “±”-shaped square cylinder without forming vortex.(ii) When water flowed around different-shaped square cylinders, from the regular quadrilateral one, the “⊥”-shaped one to the “±”-shaped one, successively, the strong turbulent kinetic energy distribution area, in which turbulence kinetic energy value was above 18,gradually increased; while the strongest turbulence kinetic energy nucleus, whose value of turbulence kinetic energy was the largest among turbulence kinetic energy nucleuses in the strong turbulent kinetic energy distribution area, moved forward gradually and its area was smaller and smaller.

Abstract: A 2D current model about Changjiang River Estuary was set up with Delft3D-FLOW in this research, which was well calibrated and verified with the observed tidal levels and velocities, the computed results of water level and flow velocity magnitude agree well with the measured data. The model has been applied to calculate the flow velocities and the split ebb flow ratio of the North Branch with the diversion angle of 30o and 60o respectively. The computed results show that the smaller the diversion angle of North Branch is, the larger the flow velocities and the split ebb flow ratio will be. Therefore, the diversion angle plays a positive role to the dynamics improvement in the North Branch.

Abstract: Based on the experimental data of sediment particle cloud during the settlement process in the water and combined with the existing sediment settling velocity formulae, a formula for calculation of the settling velocity of sediment particle cloud is proposed. It is verified by using experimentally measured settling velocity data of sediment particle cloud, the results show that the computed values using the formula agree well with the experimental values.

Abstract: At present, the upper reach of the Deepwater Navigation Channel is silted heavily, which brings negative influences on navigation. A two-dimensional numerical model is set up to simulate the hydrodynamics of the Changjiang River Estuary with Delft3D-FLOW in this paper. This model has been validated with the observed tidal level, flow velocity magnitude and direction, and the computed results agree well with the observed data, which also shows the model can well simulate the hydrodynamics of the Changjiang River Estuary caused by the Deepwater Navigation Channel Project. Based on the analysis of computed results, especially the velocity along the South Passage and North Passage, the flood and ebb flow in the Hengsha Passage, and the flow spilt ratio of South Passage and North Passage, it presents that one fundamental reason for the sediment deposition in the upper reach of the Deepwater Navigation Channel is that the velocity along the North Passage is far less than that along South Passage, above all, the velocity in North Passage upstream of the Hengsha Passage is even smaller; another reason is that the flood and ebb flow of Hengsha Passage are large, which weakens the water exchange between the North Passage and South Channel.

Abstract: The flow around two vertical cylindrical piles exposed to a steady current is studied numerically by a three-dimensional hydrodynamic model, which is closured with a k-ε turbulence model. This model is firstly validated by experimental data obtained from a labortory experiment for a steady flow through a circular pile. Then this validated model is used to study flow pattern around two cylindrical piles. Finally, four key physical factors of the size of the horseshoe vortex and lee wake vortex, the maximum current velocity and bottom shear stress are analyzed under the different pile spaces. The main conclusions are: i) the size of the horseshoe vortex increases with the increase of the two pile space, while the size of the lee wake vortex changes slightly; ii) the maximum current velocity and the maximum bottom shear stress decrease with the increase of two pile space, and reach steady after the two pile space larger than six times of cylindrical pile diameter.