电站下游非恒定流清水冲刷水沙运动特性研究

采用平面二维数学模型,以长江向家坝水电站为例,分析了水电站下游重点滩险河段受日调节非恒定流影响下的河道水流运动规律及在枯水时段受日调节影响的河床冲淤变形规律。对河道水深、流速等分布规律及其对航运条件的影响进行分析,提出水位、流速变率的概念,从而对非恒定流对不同边界条件水流(滩、槽水流)的影响规律进行分析,并对其对航运条件的影响进行探讨。当电站日调节最小下泄流量大于河道航道整治设计流量时,由于洪水波传播过程中的坦化作用,河道最小通航水深将有所增加,对航运有利,但另一方面,由于河道内水位变率、与流速变率增加,将对航行安全带来不利影响。当考虑在日调节水流对河床的冲刷作用时,由于枯水时段,来水含沙量较低,将对滩面产生冲刷,增加主槽过流宽度,同时引起主槽通航水深减小,对航运带来新的不利影响。计算表明,当日调节清水冲刷作用河道冲淤稳定后,河道航行水深将与天然状态接近,而水位、流速变率增加,总体上对河道通航不利。

Flow behavior and microstructure of ZK60 magnesium alloy compressed at high strain rate

Flow behavior and microstructure of a homogenized ZK60 magnesium alloy were investigated during compression in the temperature range of 250-400 ℃ and the strain rate range of 0.1-50 s^-1. The results showed that dynamic recrystallization （DRX） developed mainly at grain boundaries at lower strain rate （0.1-1 s^-1）, while in the case of higher strain rate （10-50 s^-1）, DRX occurred extensively both at twins and grain boundaries at all temperature range, especially at temperature lower than 350 ℃, which resulted in a more homogeneous microstructure than that under other deformation conditions. The DRX extent determines the hot workability of the workpiece, therefore, hot deformation at the strain rate of 10-50 s^-1 and in the temperature range of 250-350 ℃ was desirable for ZK60 alloy. Twin induced DRX during high strain rate compression included three steps. Firstly, twins with high dislocation subdivided the initial grain, then dislocation arrays subdivided the twins into subgrains, and after that DRX took place with a further increase of strain.

Plastic flow behavior of superalloy GH696 during hot deformation

In order to investigate the hot deformation behavior of superalloy GH696, isothermal compression experiments were carried out at deformation temperatures of 880?1120 °C and strain rates of 0.01?10 s?1. And the deformation amount of all the samples was 50%. The strain rate sensitivity exponent (m) and strain hardening exponent (n) under different deformation conditions were calculated, meanwhile the effects of the processing parameters on the values ofm andn were analyzed. The results show that the flow stress increases with the increase of strain rate and the decrease of deformation temperature. The value ofm increases with the increase of deformation temperature and decreases with the increase of strain rate, while the value ofn decreases with the increase of deformation temperature. A novel flow stress model during hot deformation of superalloy GH696 was also established. And the calculated flow stress of the alloy is in good agreement with the experimental one.

Flow behavior and fracture of Al−Mg−Si alloy at cryogenic temperatures

The tensile and fracture behaviors of AA6061 alloy were investigated in order to provide quantitative data about this alloy at cryogenic temperatures.Specimens of AA6061 alloy were solution heat treated before tensile tests at 298,173 and 77 K and tested at strain rates in the range from 0.1 to 0.0001 s^(−1).The results indicate the suppression of the Portevin−Le Chatelier(PLC)effect and dynamic strain aging(DSA)at 77 K.In contrast,at 298 K,a remarkable serrated flow,characteristic of the PLC effect,is observed.Furthermore,the tensile behavior at 77 K,compared with that observed at 173 and 298 K,shows a simultaneous increase in strength,uniform elongation,modulus of toughness,strain-hardening exponent and strain rate sensitivity,which is related to a decrease in the dynamic recovery rate at low temperature.These responses are reflected on the fracture morphology,since the dimple size decreases at 77 K,while the area covered by dimples increases.Comparisons of the Johnson−Cook model show that a good agreement can be obtained for tests at 173 and 77 K,in which DSA is suppressed.

Relationship between rheological behavior and flotation rate in slurry with different chalcopyrite and lizardite concentration

The relationship between viscosity/yield stress and flotation rate in different chalcopyrite and lizardite concentrations was investigated by zeta potential measurements,rheological tests,flotation experiments,and DerjguinLandau-Verwey-Overbeek theoretical calculation.Results indicated that the concentration of minerals would affect the viscosity and yield stress of the slurry.That is,the viscosity/yield stress in the slurry rises accordingly when the concentration of minerals increases.The increase in viscosity/yield stress in slurry is also unfavorable to the enrichment of chalcopyrite but is conducive to the entrainment of lizardite in either single or binary system.Specifically,the flotation rate of chalcopyrite decreases while that of lizardite increases with the rise in viscosity/yield stress.

Hot compressive deformation behavior and constitutive relationship of Al-Zn-Mg-Zr alloy with trace amounts of Sc

Abstract： The hot deformation behaviors of AI-Zn-Mg-Sc-Zr alloy were investigated in a temperature range of 340-500℃ and a strain rate range of 0.001-10 s 1 using uniaxial compression test on Gleeble-1500 thermal simulation machine. The results show that the flow stress increases with increasing strain and tends to be constant after a peak value. The flow stress increases with increasing strain rate and decreases with increasing deformation temperature. The phenomenon of dynamic recovery and dynamic recrystallization can be observed by microstructural evolutions. Based on the hyperbolic Arrhenius-type equation, the true stress-true strain data from the tests were employed to establish the constitutive equation considering the effect of the true strain on material constants （α, β, Q, n and A）, which reveals the dependence of the flow stress on strain, strain rate and deformation temperature. The predicted stress-strain curves are in good agreement with experimental results, which confirms that the developed constitutive equations are suitable to research the hot deformation behaviors of Al-Zn-Mg-Sc-Zr alloy.

Viscosity profile prediction of a heavy crude oil during lifting in two deep artesian wells

It has been known that the productivity of artesian wells is strongly dependent on the rheological properties of crude oils. This work targets two deep artesian wells(>5000 m) that are producing heavy crude oil. The impacts of well conditions including temperature, pressure and shear rate, on the crude oil rheology were comprehensively investigated and correlated using several empirical rheological models. The experimental data indicate that this heavy oil is very sensitive to temperature as result of microstructure change caused by hydrogen bonding. The rheological behavior of the heavy oil is also significantly impacted by the imposed pressure, i.e., the viscosity flow activation energy(Eμ) gently increases with the increasing pressure. The viscosity–shear rate data are well fitted to the power law model at low temperature. However, due to the transition of fluid feature at high temperature(Newtonian fluid), the measured viscosity was found to slightly deviate from the fitting data. Combining the evaluated correlations, the viscosity profile of the heavy crude oil in these two deep artesian wells as a function of well depth was predicted using the oilfield producing data.

Flow stress behavior of high-purity Al-Cu-Mg alloy and microstructure evolution

The flow stress behavior of high-purity Al-Cu-Mg alloy under hot deformation conditions was studied by Gleeble-1500,with the deformation temperature range from 300 to 500 °C and the strain rate range from 0.01 to 10 s-1. From the true stress-true strain curve, the flow stress increases with the increasing of strain and tends to be constant after a peak value, showing dynamic recover, and the peak value of flow stress increases with the decreasing of deformation temperature and the increasing of strain rate.When the strain rate is 10 s-1 and the deformation temperature is higher than 400 °C, the flow stress shows dynamic recrystallization characteristic. TEM micrographs were used to reveal the evolution of microstructures. According to the processing map at true strain of 0.7, the feasible deformation conditions are high strain rate(>0.5 s-1) or 440-500 °C and 0.01-0.02 s-1.

Constitutive analysis of AZ31 magnesium alloy plate

The plastic deformation simulation of AZ31 magnesium alloy at different elevated temperatures （from 473 to 723 K） was performed on Gleeble-1500 thermal mechanical simulator at the strain rates of 0.01, 0.1, 1, 5 and 10 s-t and the maximum deformation degree of 80%. The relationship between the flow stress and deformation temperature as well as strain rate was analyzed. The materials parameters and the apparent activation energy were calculated. The constitutive relationship was established with a Zener-Hollomon （Z） parameter. The results show that the flow stress increases with the increase of strain rate at a constant temperature, but it decreases with the increase of deformation temperature at a constant strain rate. The apparent activation energy is estimated to be 129-153 kJ/mol, which is close to that for self-diffusion of magnesium. The established constitutive relationship can reflect the change of flow stress during hot deformation.

Dynamic recrystallization behavior and kinetics of high strength steel

The dynamic recrystallization behavior of high strength steel during hot deformation was investigated.The hot compression test was conducted in the temperature range of 950-1150 °C under strain rates of 0.1,1 and 5 s-1.It is observed that dynamic recrystallization(DRX) is the main flow softening mechanism and the flow stress increases with decreasing temperature and increasing strain rate.The relationship between material constants(Q,n,α and ln A) and strain is identified by the sixth order polynomial fit.The constitutive model is developed to predict the flow stress of the material incorporating the strain softening effect and verified.Moreover,the critical characteristics of DRX are extracted from the stress-strain curves under different deformation conditions by linear regression.The dynamic recrystallization volume fraction decreases with increasing strain rate at a constant temperature or decreasing deformation temperature under a constant strain rate.The kinetics of DRX increases with increasing deformation temperature or strain rate.

pH Value Effects in Shear Rheology of Concentrated Alumina Suspensions

The influence of pH on the rheological properties of concentrated alumina suspensions was investigated. At various pH values, the alumina exhibited pseudoplastic, near Bingham flow behaviors. The fully-deflocculated suspensions exhibited Newtonian flow behaviors, while the fully-flocculated suspensions demonstrated very high viscosity and shear yield stress.

Development of aluminum rheo-extrusion process using semi-solid slurry at low solid fraction

An aluminum extrusion process is mainly used to fabricate long tubes, beams and rods for various applications. However, this process has a high production cost due to the need for investment of high-pressure machinery. The objective of this work is to develop a new semi-solid extrusion process using semi-solid slurry at low solid fractions. A laboratory extrusion system was used to fabricate aluminum rods with the diameter of 12 ram. The semi-solid metal process used in this study was the gas induced semi-solid （GISS） technique. To study the feasibility of the GISS extrusion process, the effects of extrusion parameters such as plunger speed and solid fi-action on the extrudability, microstructure, and mechanical properties of extruded samples were investigated. The results show that the plunger speed and solid fraction of the semi-solid metal need to be carefully controlled to produce complete extruded parts.

Hot deformation behavior and constitutive relationship of Q420qE steel

Isothermal compression tests at temperatures from 1 273 to l 423 K and strain rates from 0.1 to 10 s-q were carried out to investigate the flow behaviors of Q420qE steel. Stress-strain data collected from the tests were employed to establish the constitutive equation, in which the influence of strain was incorporated by considering the effect of strain on material constants Q, n, a, and lnA. The results show that the flow stress curves are dependent on the strain, strain rate and deformation temperature. They display typical dynamic recrystallization behavior and consist of three stages, i.e., hardening stage, softening stage and steady stage. The flow stress decreases with increasing the deformation temperature and decreasing the strain rate. In addition, the flow stress data predicted by the proposed constitutive model agree well with the corresponding experimental results, and the correlation coefficient and the average absolute relative error between them are 0.990 3 and 3.686%, respectively.

Rheological behavior of hydrolyzed polyacrylamide solution flowing through a molecular weight adjusting device with porous medium

The separate-layer injection in different interlayers and the injection of the same-molecular-weight polymer so- lution in a layer are necessary in the polymer flooding process because of heterogeneous multilayer sandstone reservoirs in EOR projects. To alleviate the matching problems between the layer permeability and the injected polymer molecular weight, a molecular weight adjusting device with porous medium was designed on the basis of mechanical degradation principle. In terms of four variables （polymer concentration, pore diameter, length of shear component and flow rate ）, the theological behavior of hydrolyzed polyacrylamide （HPAM） solu- tion flowing through the device was investigated in detail. The change of these variables is able to control the shear rate of HPAM solutions through ceramic foam, and achieve the desired degree of shear degradation and the final theological parameters-viscosity loss, viscoelasticity and pressure drop. Therefore, a linear relationship between viscosity loss and shearing rate was established so as to obtain the targeted viscosity easily. Field tests in the Daqing Oil Field showed that the polymer molecular weight could drop 20% to 50%. In a word, the results could guide the industrial application of the novel device and the further study of polymer degradation flowing through the porous medium.