Discharge evolution law of debris flow based on a sharp bend physical modeling test

For the basins with debris flow development,its channel terrain exhibits a tortuous shape,which significantly restricts the movement of debris flows and leads to severe erosion effects on the concave bank.Therefore,this study aims to analyze the shear force of debris flows within the bend channel.We established the relationship between the shear force and bend curvature through laboratory experiments.Under the long-term erosion by debris flows,the curvature radius of bends gradually increases,however,when this increasing trend reaches an equilibrium state with the intensity of debris flow discharge,there will be no significant change in curvature radius.In general,the activity pattern and discharges of debris flows would remain relatively stable.Hence,we can infer the magnitude of debris flow discharges from the terrain parameters of the bend channel.

Texture modification and mechanical properties of AZ31 magnesium alloy sheet subjected to equal channel angular bending

Analysis of the recently proposed equal channel angular bending(ECAB)process is provided on thin hotrolled AZ31 magnesium alloy sheets.In particular,effects of deformation temperature and strain path on the texture evolution and mechanical properties are systematically investigated under single pass ECAB at various temperatures and multi-pass ECAB process that involves changes in strain paths.It is found that simultaneous activation of multiple twinning types is successfully introduced during ECAB,which results in obvious tilted component of basal texture.Attributed to the domination of extension twins,weaker basal textures are detected after both single pass ECAB at 150℃and three cross passes ECAB at 200℃.After annealing,the basal texture is further weakened via twin-related recrystallization and the annealed microstructure is featured with mixture of basal and non-basal orientated grains.Additionally,the effect of grain orientation on the mode of plastic deformation and the roles of grain orientation and grain boundary on the local strain accommodation are coherently studied.This study reveals that over 60%increase of uniform elongation with marginal reduction of tensile strength less than 5%can be achieved for single pass ECAB at 150℃and three cross passes ECAB at 200℃,which is the result of larger fraction of grains favored with extension twinning and better local strain accommodation.

FLOATING RATE OF FRAZIL ICE PARTICLES IN FLOWING WATER IN BEND CHANNELS——A THREE-DIMENSIONAL NUMERICAL ANALYSIS

In this article, based on the theory of two-phase flow and laboratory data, a three-dimensionally model is developed to simulate the floating rates of frazil ice particles in water under covered condition. The Lagrangian trajectory method is used in the three dimensional simulation for floating rates of fxazil ice particles along a 180° bend channel. The velocity profiles in longitudinal and transverse directions, the turbulence intensity, and the residual pressure are simulated. Under the condition of gravitational similarity, the simulated floating rates of frazil ice particles in the model bend channel and the prototype bend channels are compared. Results indicate that the profiles for floating rates of ice particles for flows in the model channel are similar to those in the prototype bend channels. The simulated floating rates of ice particles are clearly higher along the convex bank than along the concave bank at each cross section. For the prototype bend channel in a large model scale, the variation of floating rate across each cross section is relatively small.

Impacts of bridge piers on water level during ice jammed period in bend channel——An experimental study

Experiments are carried out in an ＂S-shaped＂ flume in the laboratory under both open flow and ice-jammed conditions to study the impacts of bridge piers in a bend channel on the variation of the water level. The variations of the water level under the ice jammed condition with bridge piers are compared to those without bridge piers in an 180° bend channel. Results indicate that the bridge piers in the S-shaped channel have obvious impacts on the ice accumulation and the water level. The increment of the water level with the presence of the bridge piers is less than that without the bridge piers in the channel. Different arrangements of the bridge piers result in different increments of the water level. When one bridge pier is installed in the straight section of the channel（between 2 bends） and another one at the bend apex（for a convex bank）, the increment of the water level during the equilibrium ice jammed period is between that with a single bridge pier located in the straight section of the bend channel and that with a single bridge pier located at the bend apex. It is also shown that the increment of the water level during the equilibrium ice jammed period increases with the increase of the average thickness of the ice jams.

NUMERICAL SIMULATION OF TWO-DIMENSIONAL DAM-BREAK FLOWS IN CURVED CHANNELS

Two-dimensional transient dam-break flows in a river with bends were theoretically studied. The river was modeled as a curved channel with a constant width and a flat bottom. The water was assumed to be an incompressible and homogeneous fluid. A channel-fitted orthogonal curvilinear coordinate system was established and the corresponding two-dimensional shallow-water equations were derived for this system. The governing equations with well-posed initial and boundary conditions were numerically solved in a rectangular domain by use of the Godunov-type finite-difference scheme, which can capture the hydraulic jump of dam-break flows. The comparison between the obtained numerical results and the experimental data of Miller and Chaudry in a semicircle channel shows the validity of the present numerical scheme. The mathematical model and the numerical method were applied to the dam-break flows in channels with various curvatures. Based on the numerical results, the influence of river curvatures on the dam-break flows was analyzed in details.

TWO-DIMENSIONAL CALCULATION FOR WATER SURFACE LINE OF OPEN BEND CHANNEL

This paper presents a differencial equation for two dimensional distribution of water depth and its condition to determine solution, then obtains the analytic solution of a Cauchy problem. By use of this solution the water depth is able to be determined at any point in total bend, which provides a better understanding of depth distribution in bend in comparison with traditional method of one dimensional calculation. The experimental verification shows that the calculated value by this formula well coincides with measured value.

PROGRESS IN STUDIES ON ICE ACCUMULATION IN RIVER BENDS

River ice is an important hydraulic element in temperate and polar environments and would affect hydrodynamic conditions of rivers through changes both in the boundary conditions and the thermal regime. The river bend has been reported as the common location for the initiation of ice jams because the water flow along a river bend is markedly affected by the channel curvature. In this article, the experimental studies about the ice accumulation in a river bend are reviewed. Based on experiments conducted so far, the criteria for the formation of ice jams in the river bend, the mechanisms of the ice accumulation in the river bend and the thickness profile of the ice accumulation in the river bend are discussed. The two-equation turbulence model is used to simulate the ice accumulation under an ice cover along a river bend. A formula is proposed for describing the deformation of the ice jam bottom. Our results indicate that all simulated thickness of the ice accumulation agrees reasonably well with the measured thickness of the ice accumulation in the laboratory.

A three-dimensional solid-liquid two-phase turbulence model with the effect of vegetation in non-orthogonal curvilinear coordinates

A three-dimensional k-ε-Ap solid-liquid two-phase two-fluid model with the effect of vegetation is solved numerically with a finite-volume method on an adaptive grid to study water-sediment movements and bed evolution in vegetated channels. The additional drag force and additional turbulence generation due to vegetation are added to the relevant control equations for simulating the interaction between vegetation and flow. The flow structure and the bed-topography changes in a 60° partly vegetated channel bend are calculated by the model. The numerical results agree well with the measured ones. Calculated and measured results show that the primary flow velocity reduces much in the vegetation zone and increases in the non-vegetation zone, the secondary flow velocity weakens in the vegetation zone and strengthens in the non-vegetation zone, the sediment movement and bed-topography change also weaken in the vegetation zone and strengthen in the non-vegetation zone, a well-planed vegetation arrangement can improve bank stabilization program, and the k-ε-Ap model can deal with bed-load transport with a more reasonable method than the one-fluid model.