Applied Mechanics and Materials Vols. 212-213

Abstract: Internal waves have a significant impact on the hydrodynamic and stratification characteristics in the density stratified lakes and oceans. In order to reveal the features of internal waves, a three-dimensional numerical wave tank in regular terrain based on the computational fluid dynamics (CFD) model was established to simulate the processes of non-linear internal solitary waves propagation and evolution. The concept of a fraction volume of fluid (VOF) was employed to track the interface of the two-layer fluid. Comparisons were made between CFD model and weakly non-linear KdV theory, it was shown that the wave amplitude predictions by the CFD model agreed well with the KdV equation. On the other hand, the convergence flow and divergence flow at the water surface were captured successfully by the simulated spatial and temporal distributions of velocity. Some peculiar hydrodynamic characteristics, e. g. turbulence kinetic energy and its dissipation rate in the numerical wave tank were also identified and examined. Consequently, this paper provides a reliable method for understanding the phenomenon of internal waves in stratified water bodies.

Abstract: Make Use of three-dimensional flow field turbulence numerical simulation of unsteady flow k~εturbulence model and tracking the free surface VOF method of long-distance inverted siphon. By numerical calculation of flow characteristics and pressure distribution, carried out with the model test contrast, the results were coordinate and meet the requirements of design. But vortex formed in the filling process, it is recommended to optimize the inverted siphon inlet section. The method of combining calculation and test on the long-distance inverted siphon provide the reference for the design and operation.

Abstract: Abstract: U-shaped section channel is widely used in water conservancy projects. But the critical depth computation equation for U-shaped section channel is a transcendental equation and no analytic solution. a formulae for calculation critical depth of U-shaped channels were derived by selecting proper variables and fitting curves. The existing graphic and trial methods were replaced. The engineering case shows that the proposed formulae are simple and accurate. The maximum relative error of the critical depth is less than 0.683%, It will be greatly convenient for the designers.

Abstract: 【Objective】The calculation of turbulent boundary layer development in hydraulic jump region is put forwarded.【Method】According to the analysis of predecessors’ researches about plane adhesive wall jet flow of rectangular channel, Based on the momentum integral equation of turbulent boundary layer and the velocity distribution formula of adhesive wall jet flow, turbulent boundary layer development of hydraulic jump region in rectangular channel is researched.【Result】Formulas of the development of boundary layer in hydraulic jump region and drag coefficient are obtained, the accuracy of equations are verified by the example. 【Conclusion】The calculation has enlightened effect on the hydraulic characteristics of hydraulic jump.

Abstract: When density current flowing through width abrupt changed channel, produced local energy loss will have some impact on density current transport. Especially for Xiaolangdi reservoir which has such a complex terrain，this effect even greater. This paper on the basis of turbid density current in width abrupt changed channel studies，through theoretical analysis，obtained the formula about upstream and downstream hydraulic factors and local energy loss. The formula was verified by Xiaoliangdi antetype observation data and channel experiment data, the inaccuracy of results were analyzed, through verification , got the satisfactory results.

Abstract: Surface tension associated with temperature is usually considered non-negligible to affect discharge capacity of sharp-crested weir when head is low. In the study, a two-dimensional numerical model verified by experiments was applied to simulate the effect of water temperature on discharge capacity of clinging flow for a rectangular sharp-crested weir at low head levels. The results showed that with a same flow rate, differences in the elevation of free surface were minimal between different temperature levels despite a slightly higher elevation of free surface at lower water temperature. The head-discharge relationships were very similar for different temperature levels. This study concluded that the effect of water temperature on head-discharge relationships and the discharge capacity of clinging flow for a rectangular sharp-crested weir was negligible at low heads.

Abstract: Turbulence shear stress is an important dynamic characteristic of flow in tidal channel. In the paper, the new vertical distribution of the tidal turbulence shear stress, which can reflect the development of the stress profile over the tidal period, is proposed. The comparison between computed result and the data from field and experiment measurements indicates that the proposed vertical distribution which agrees well with the measurements can well depict the upward concave distribution in phase of accelerating process and upward convex in phase of decelerating process. Through analyzing the amplitude and phase variation along the depth on different conditions, it is found that it is the nondimensional parameter , namely the ratio of tidal period, turbulence intensity and water depth that determines the form of turbulence shear stress distribution during tidal period.

Abstract: Random walk modeling has been extensively used for oil dispersion studies. However, there is some misusing about the expression. The aim of this study is to clarify the essence of the method. Expressions used in published papers are reviewed firstly, and different methods are discussed. The results show that the random method can successfully predict the dye patch dimensions and the dilution of the dye with time in contrast with the other method. Also, some critical factor in applying the random walk method is emphasized in the paper. Two types of formula used to simulate the turbulent diffusion are discussed. Results have shown a need for care in determining the concentrations from the random walk model.

Abstract: The diffusion motion is one of the important items in the shallow water equations, and it is a crucial factor for the stability to simulate the shallow water flow in the numerical model. In this paper, a 2D model for the simulation of shallow water flow by convection and diffusion over variable bottom is presented, which is based on the FVM (finite volume method) over triangular unstructured grids. The format of Reo’s approximate Riemann is adopted to solve the flux terms. And the bed slope source term is treated by split in the form of the flux eigenvector. For the diffusion terms, the divergence theorem is employed to obtain the derivatives of a scalar variable on each triangular cell. Then, the flow around a pillar is simulated, which flow pattern is similar with the actual flow. Thus it is proved that the model could be applied to simulate the complicated current structure in the water area around hydraulic construction.

Abstract: In order to study the characteristics of flow field in the process of wave impact, two-dimensional regular wave numerical models were established based on the software FLUENT. RANS equations were adopted. The standard equations were used to close the Reynolds equations. VOF method was used to reconstruct the free surface. After three typical cases of wave slamming on open-piled structures were reproduced, the models were verified by experimental data and the flow field surrounding the structure was displayed visually. Then the processes of wave impact under various wave height, period and over height were simulated. The influences of the three parameters on the distribution of vertical velocities were analyzed, which shows that the distribution rule of the vertical velocities is similar to the wave impact pressures.