水动力学研究与进展:英文版最新文献

Standing waves occur frequently at the inlet due to the change of the flow direction from an approach channel to the drop-shaft. The performance of the standing wave, characterized by the relative height, the location and the extent, is theoretically and experimentally investigated in the present paper. It is shown that the height of the standing wave decreases with the increases of the approach flow Froude number and the sub-channel number in the inlet, but increases with the increase of the curvature of the dropshaft. The errors of the expressions for the relative height, the location and the extent of the standing wave, are 9.7%, 7.8% and 13.1%, respectively, as compared with the experimental data.

In most of partially averaged Navier-Stokes (PANS) methods, the Reynolds stress is solved by a linear hypothesis isotropic model. They could not capture all kinds of vortexes in tubomachineries. In this paper, a PANS model is modified from the RNG k − ɛ turbulence model and is used to investigate the influence of the nonlinear shear stress on the simulation of the high pressure gradient flows and the large curvature flows. Comparisons are made between the result obtained by using the PANS model modified from the RNG k − ɛ model and that obtained by using the nonlinear PANS methods. The flow past a curved rectangular duct is calculated by using the PANS methods. The obtained nonlinear shear stress agrees well with the experimental results, especially in the high pressure gradient region. The calculation results show that the nonlinear PANS methods are more reliable than the linear PANS methods for the high pressure gradient flows, the large curvature flows, and they can be used to capture complex vortexes in a turbomachinary.

Cavity shedding of cavitating flows around an axisymmetric body belongs to the unsteady cavitating flows in the condition of steady incoming current. The periodic characteristics of unsteady cavitating flows around an axisymmetric body at small angles of attack are investigated experimentally and numerically. The evolution and shedding process of the three-dimensional sheet cavitation are computed numerically by the Reynolds averaged Navier-Stokes equations and the RNG k − ɛ model. The modification approach for eddy viscosity coefficient in the transition area of the two-phase flow is adopted to reproduce the shedding process of cavitating flows. The computed frequency of the cavity shedding coincides with the experimental data for the cases of unsteady cavitating flows around axisymmetric bodies with four headforms. Given the cavitation number, the shedding process of the cavitating flow depends heavily on the headform of the axisymmetric body. If the angle of attack of the axisymmetric body is greater than a critical value, the violent shedding of the sheet cavitation seems to be depressed.

Owing to its ability of modelling large deformations and the ease of dealing with moving boundary conditions, the material point method is gaining popularity in geotechnical engineering applications. In this paper, this promising Lagrangian method is applied to hydrodynamic problems to further explore its potential. The collapse of water columns with different initial aspect ratios is simulated by the material point method. In order to test the accuracy and stability of the material point method, simulations are first validated using experimental data and results of mature numerical models. Then, the model is used to ascertain the critical aspect ratio for the widely-used shallow water equations to give satisfactory approximation. From the comparisons between the simulations based on the material point method and the shallow water equations, the critical aspect ratio for the suitable use of the shallow water equations is found to be 1.

This paper investigates the potential extreme tsunami hazards of the worst case scenario of the magnitude M_w = 9.30 in South China Sea (SCS) as the Manila Trench is becoming one of the most hazardous tsunami source regions. Using nonlinear shallow water equations model, the time series of surface elevation, arrival time, spatial distributions of maximum wave amplitude and velocity distribution are presented. The characteristics of wave and currents are analyzed. The numerical results indicate that most of the energy of tsunami wave distributes in central and north part of SCS. The offshore regions around SCS will be influenced significantly by the tsunami currents generated by an earthquake in the Manila subduction zone. The maximum wave amplitude near Guangdong Province, Hainan Island, and Taiwan Island exceeds 4 m and velocities at the majority of measured locations near coast exceeds 2 m/s. Nested grid with high resolution is used to study the impacts of the tsunami on Hainan Island, Taiwan Island, and Lingding Bay. The regions with high hazard risk due to strong currents are identified. Finally, a fast tsunami warning method in SCS is developed and discussed, which can provide tsunami warning information in 5 min.

The present paper proposes a multiphase flow approach for capturing the time-resolved collapse course of bubble clusters in various geometrical configurations. The simulation method is first verified by computing the dynamic behavior of an isolated vapor bubble placed in a uniform ambient pressure. The comparison between the numerical result and the theoretical solution indicates that the method can accurately capture the bubble shape, the characteristic time and the extremely high pressure induced by the collapse. Then the simulation method is applied to investigate the behavior of two kinds of bubble clusters in hexagonal and cubic geometrical configurations. The predicted collapsing sequence and the shape characteristics of the bubbles are generally in agreement with the experimental results. The bubbles transform and break from the outer layer toward the inner layers. In each layer, the bubbles on the corner first change into a pea shape and cave before collapsing, then the bubbles on the sides begin to shrink. It is also found that, in comparison with the case of an isolated single bubble, the central bubble in the cluster always contracts more slowly at the early stage and collapses more violently at the final stage.

Most of the present knowledge on submarine landslides relies upon back-analysis of post-failure deposits identified using geophysical techniques. In this paper, the runout of slides on rigid bases is explored using the material point method (MPM) with focus on the geotechnical aspects of the morphologies. In MPM, the sliding material and bases are discretised into a number of Lagrangian particles, and a background Eulerian mesh is employed to update the state of the particles. The morphologies of the slide can be reproduced by tracking the Lagrangian particles in the dynamic processes. A real case history of a submarine slide is back-analyzed with the MPM and also a depth-averaged method. Runout of the slides from steep slopes to moderate bases are reproduced. Then different combinations of soil and basal parameters are assumed to trigger runout mechanisms of elongation, block sliding and spreading. The runout distances predicted by the MPM match well with those from large deformation finite element analysis for the elongation and block sliding patterns. Horst and grabens are shaped in a spreading pattern. However, the current MPM simulations for materials with high sensitivities are relatively mesh sensitive.

This paper presents the numerical modelling of one and two-dimensional poroelastic solid flows, using the material point method with double point formulation. The double point formulation offers the convenience of allowing for transitions in the flow conditions of the liquid, between free surface flow and groundwater flow. The numerical model is validated by comparing the solid flow velocity with the analytical solution. The influence of the Young's modulus on the solid flow velocity is discussed for both one and two-dimensional analysis cases. The effect of the shape of the two-dimensional solid is investigated. It is shown that the solid stiffness has an effect on the poroelastic flow velocity, due to swelling and bending for the one and two-dimensional cases, respectively. The shape is found to be an important factor on the flow velocity of the poroelastic solid.

In this paper, the effect of the dike line adjustment on the Qiantang Tidal Bore (QTB) is studied by physcial experiments. A lab-scale physical model of the Qiantang Estuary is built and the tidal bore is generated. With this model, the formation and pro-pagation processes of the tidal bore are simulated with or without the dike line adjustment. It is shown that the adjusted dike line changes the direction of the reflected tidal bore. The height of the tidal bore increases in the upstream region where the dike line is contracted. In the tested bent and forking regimes, the bore height at the upstream station is increased by 0.10 m and 0.04 m, respectively. Furthermore, the crossing bore still exists near the Daquekou station and the location slightly moves by about 3 km to the downstream region.