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Hu X.-Y.,Changsha University of Science and Technology | Hu X.-Y.,Hunan Province Key Laboratory of Water | Zhang Q.-S.,Changsha University of Science and Technology | Ma L.-J.,Changsha University of Science and Technology
Shuikexue Jinzhan/Advances in Water Science | Year: 2011

The length of transition section is an important parameter of continuous meandering rivers, which has a profound influence on the flow regime in the second bend. Based on the experimental results from the physical models, an air-water two-phase flow model is derived for flow simulation in the continuous bends. Both re-normalisation group(RNG) k-epsilon model and volume of fluid method(VOF) are used in the model derivation. Through inspecting various flow regimes due to different lengths of transition sections, it is found that the effect of flow in the front bend on the second bend can be weakened when the length of transition section increases. However, the flow in the second bend will be stabilized when the length exceeds a threshold value. The front bend has a neglectable influence on the flow in the second bend thereafter. Thus, a critical length of transition section can be defined, which can be used as the base value for the design of transition section in practical application. Source


Chen J.,Changsha University of Science and Technology | Chen J.,Hunan Province Key Laboratory of Water | Jiang C.,Changsha University of Science and Technology | Jiang C.,Hunan Province Key Laboratory of Water | And 2 more authors.
Natural Hazards | Year: 2016

Devastating tsunami waves can mobilize substantial amount of coastal sediment. Scouring is the primary damage caused by tsunamis. Offshore submerged or emerged breakwaters are coastal structures that are commonly employed to provide protection to valuable coastal beaches from energetic ocean waves. However, the protection capabilities of tsunami scour by submerged or emerged breakwater are less understood compared to tsunami runup and tsunami inundation. A set of laboratory experiments are reported in this study on protection of tsunami-induced scour by submerged or emerged breakwaters on a sandy beach. FLOW-3D is used in this paper to calculate flow field of tsunami wave propagation over the breakwater in order to help us to understand the sediment transport and tsunami scour process. Our experiments show that the submerged breakwater could not effectively reduce the tsunami scouring and only could affect the height and position of deposition sand bar. The emerged breakwater could significantly effectively reduce the tsunami scouring on the sandy beach; meanwhile, local scouring caused by plunging jet occurs mainly on the both sides of the structure. It is also found that for typical tsunamis, the scour depth at shoreward is unlikely to reach its equilibrium stage. Local scouring damage is one of the main factors leading to the destruction of coastal structures during a tsunami event. The most important governing parameters on local scouring around breakwater were defined. The final empirical relations that define the magnitude and position of local scouring around the breakwater were presented. The information reported in this study is useful for local authorities to assess potential tsunami damage of structure and to have a better plan for tsunami preventing and reducing. © 2015, Springer Science+Business Media Dordrecht. Source


Chen J.,Changsha University of Science and Technology | Chen J.,Hunan Province Key Laboratory of Water | Jiang C.,Changsha University of Science and Technology | Jiang C.,Hunan Province Key Laboratory of Water | And 2 more authors.
Acta Oceanologica Sinica | Year: 2010

In this study, characteristics of flow field and wave propagation near submerged breakwater on a sloping bed are investigated with numerical model. The governing equations of the vertical twodimensional model are Reynolds Averaged Navier Stokes equations. The Reynolds stress terms are closed by a nonlinear k - ε turbulence transportation model. The free surface is traced through the PILC-VOF method. The proposed numerical model is verified with experimental results. The numerical result shows that the wave profile may become more asymmetrical when wave propagates over breakwater. When wave crest propagates over breakwater, the anticlockwise vortex may generate. On the contrary, when wave hollow propagates over breakwater, the clockwise vortex may generate. Meanwhile, the influenced zone of vortex created by wave crest is larger than that created by wave hollow. All the maximum values of the turbulent kinetic energy, turbulent dissipation and eddy viscosity occur on the top of breakwater. Both the turbulent dissipation and eddy viscosity increase as the turbulent kinetic energy increases. Wave energy may rapidly decrease near the breakwater because turbulent dissipation increases and energy in lower harmonics is transferred into higher harmonics. © 2010 The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg. Source


Chen J.,Changsha University of Science and Technology | Chen J.,Hunan Province Key Laboratory of Water | Jiang C.-B.,Changsha University of Science and Technology | Jiang C.-B.,Hunan Province Key Laboratory of Water | And 2 more authors.
Shuikexue Jinzhan/Advances in Water Science | Year: 2011

The study of hydrodynamics in the surf and swash zone is essential to understanding the nearshore sediment transport and coast beach evolution. A numerical model is developed to analyze the flow mechanism in surf and swash zone under the influence of submerged breakwater. The two-dimensional Reynolds Averaged Navier-Stokes equations, together with a nonlinear k-ε turbulence model, and a finite difference method are employed in the model development. For a better simulation of wave breaking, a piecewise linear interface construction volume of fluid technique is utilized, which has good accuracy in describing air/water surfaces. The numerical model is validated with the experimental data and used to analyze the influence of submerged breakwater. The numerical results indicate that the location of breaking point and hydrodynamic characteristics in surf and swash zone are changed by the submerged break-water. The wave height (H), wave length (L), depth of submergence (R) and crest width (B) play an important role in influencing hydrodynamic processes in these two zones. Under the same incident wave, the maximum turbulent kinetic energy and turbulence dissipation rates in two zones decrease as B/R increases. The dimensionless numbers of Re, Fr and St are deduced form RANS equations and used to describe hydrodynamics in surf and swash zones. The wave breaking could take place near the shore as RL/BH increases, meanwhile Re and Fr increases, and at the same time St decreases. Source


Jiang C.-B.,Changsha University of Science and Technology | Jiang C.-B.,Hunan Province Key Laboratory of Water | Deng B.,Changsha University of Science and Technology | Deng B.,Hunan Province Key Laboratory of Water | And 4 more authors.
Chuan Bo Li Xue/Journal of Ship Mechanics | Year: 2012

With the necessity of simulating the large-scale complex interface flow, this paper presents a three-dimensional gas-liquid two-phase flow numerical model, in which the three-dimensional unsteady Navier-Stokes equations is discretized by the finite volume method and the free flow surface can be caputured by a high-resolution scheme of VOF method (STACS) and the programs are parallelized. This model is used to simulate the typical fluid flow with free-surface, such as ZALESKA problem, 3D deformation and dambreak flow on a wet bottom. The results show that the presented model is able to effectively simulate complex inter-face flow with high resolution. The model can be applied in further investigation of the interaction between wave and ship as well as the role of ship wave on the waterway structures or the bank. Source

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