Effect of sinusoidal corrugated bed on hydraulic jump characteristics

Hydraulic jump characteristics were studied experimentally over six corrugated beds with varying wave steepness, which had corrugation and Froude numbers in the range of 0.286–0.625 and 3.8–8.6, respectively. The effects of wave height and length of corrugation on the basic jump characteristics, including free surface location, velocity, shear stress distribution and energy dissipation, were studied for a range of Froude numbers. The dimensionless hydraulic parameters were found to be a function of the Froude number. The results showed that the tailwater depth and the length of the jump on corrugated beds are smaller than those of the corresponding jump on a smooth bed. The analysis of velocity profiles at different sections in the jump showed that the velocity profiles were similar to those of a simple plane wall jet. The normalized boundary layer thickness δ/b was equal to 0.57 for jumps on a corrugated bed, compared to 0.16 for the simple wall jet. The analysis and comparison of the bed shear force and shear stress coefficient showed that shear stress on a corrugated bed is about 10 times that of a smooth bed. The results of this study are in good agreement with previous results and showed that corrugated beds can be used to dissipate the excess hydraulic jump energy in stilling basins.     

BOUNDARY LAYER EFFECTS ON SOLID PARTICLE MOTION AND EROSIVE WEAR

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STABILITY OF DENSITY STRATIFIED FLOW IN THE BOUNDARY LAYER

1. INTRODUCTION The influence of vertical density variations o the stability of flow past a flat horizontal wall, is in sense related to the case of centrifugal forces actin on a homogeneous fluid flowing along a curved wal When the arrangement is stable, the densit decreases upward, , whereas it becomes unstabl when the variation in density is reversed. In the cas of flow with stable density stratification, turbulen mixing in the vertical direction is impeded becaus heavier particles must…     

Two timescales for longitudinal dispersion in a laminar open-channel flow

At small dimensionless timescales T(= tD/H~2), where t is the time, H is the depth of the channel and D is the molecular diffusion coefficient, the mean transverse concentration along the longitudinal direction is not in a Gaussian distribution and the transverse concentration distribution is nonuniform. However, previous studies found different dimensionless timescales in the early stage, which is not verified experimentally due to the demanding experimental requirements. In this letter, a stochastic method is employed to simulate the early stage of the longitudinal transport when the Peclet number is large. It is shown that the timescale for the transverse distribution to approach uniformity is T= 0.5, which is also the timescale for the dimensionless temporal longitudinal dispersion coefficient to reach its asymptotic value, the timescale for the longitudinal distribution to approach a Gaussian distribution is T= 1.0, which is also the timescale for the dimensionless history mean longitudinal dispersion coefficient to reach its asymptotic value.     

Characteristics of pressure fluctuations beyond spillways with a ledge

Conclusions When calculating the intensity of pressure fluctuation on a revetment for the surface regime beyond a dam with a ledge by the appropriate relations [3] it is necessary to take into account that the dispersion of the turbulent component given by this calculation is commensurate with the dispersion of the wave component of presssure fluctuation, which presently can be determined from the results of hydraulic investigations. The data given in [5] can be used for estimating the intensity of the total value of pressure fluctuation on a revetment for a surface regime beyond a dam with a ledge under conditions of the two-dimensional problem and in the range of relative heights of the ledge d/h_c=3–6.5 and Froude numbers in the vena contracta on the ledge Fr_c=8–50.Translated from Gidrotekhnicheskoe Stroitel'stvo, No. 3, pp. 26–28, March, 1986.     

Discharge Coefficient for Trapezoidal Labyrinth Side Weir in Subcritical Flow

The discharge coefficient of a trapezoidal labyrinth side weir is a function of the Froude number F ₁, the dimensionless effective crest length L/ℓ, the dimensionless weir length L/B, the dimensionless weir height p/h ₁, and the sidewall angle α. A labyrinth weir is an overflow weir, folded in plan view to provide a longer total effective length for a given overall weir width. These weirs have advantages compared to the straight overflow weir and the standard ogee crest. Previous studies on the subject have generally focused on rectangular side weirs located on a straight channel. The present study investigates the hydraulic behavior of a trapezoidal labyrinth side weir. The results show that the discharge coefficient of labyrinth side weirs gives a significantly higher coefficient value compare to that of conventional straight side weirs. Discharge coefficient of the trapezoidal labyrinth side weir is 1.5 to 5.0 times higher than the conventional straight side weir. Consequently, an equation for the coefficient of discharge is introduced. The results predicted by the equation were shown to be very satisfactory using root mean square error (RMSE), mean absolute error (MAE) and correlation coefficient (R) statistics.     

Estimation of boundary-layer flow of a nanofluid past a stretching sheet: A revised model

The previous model for the boundary layer nanofluid flow past a stretching surface with a specified nanoparticle volume fraction on the surface is revisited.The major limitation of the previous model is the active control of the nanoparticle volume fraction on the surface.In a revised model proposed in this paper,the nanoparticle volume fraction on the surface is passively controlled,which accounts for the effects of both the Brownian motion and the thermophoresis under the boundary condition,whereas the Buongiorno’s model considers both effects in the governing equations.The assumption of zero nanoparticle flux on the surface makes the model physically more realistic.In the revised model,the dimensionless heat transfer rates are found to be higher whereas the dimensionless mass transfer rates are identically zero due to the passive boundary condition.It is also found that the Brownian motion parameter has a negligible effect on the Nusselt number.     

Numerical solution of thermo-solutal mixed convective slip flow from a radiative plate with convective boundary condition

A mathematical model for mixed convective slip flow with heat and mass transfer in the presence of thermal radiation is presented. A convective boundary condition is included and slip is simulated via the hydrodynamic slip parameter. Heat generation and absorption effects are also incorporated. The Rosseland diffusion flux model is employed. The governing partial differential conservation equations are reduced to a system of coupled, ordinary differential equations via Lie group theory method. The resulting coupled equations are solved using shooting method. The influences of the emerging parameters on dimensionless velocity, temperature and concentration distributions are investigated. Increasing radiative-conductive parameter accelerates the boundary layer flow and increases temperature whereas it depresses concentration. An elevation in convection-conduction parameter also accelerates the flow and temperatures whereas it reduces concentrations. Velocity near the wall is considerably boosted with increasing momentum slip parameter although both temperature and concentration boundary layer thicknesses are decreased. The presence of a heat source is found to increase momentum and thermal boundary layer thicknesses but reduces concentration boundary layer thickness. Excellent correlation of the numerical solutions with previous non-slip studies is demonstrated. The current study has applications in bioreactor diffusion flows and high-temperature chemical materials processing systems.     

SIMULATION AND ANALYSIS OF FLOW PATTERN IN CROSS-CORRUGATED PLATE HEAT EXCHANGERS

1. INTRODUCTION Plate heat exchangers have been widely used in different industrial applications owing to their advantages such as high effectiveness, compactness, ease in cleaning, etc[1]. However, since the flow channels formed by corrugations on two op…     

FIVE MODE INTERACTIONS IN A FREE SHEAR LAYER

This study condiders spatially developing free shear layers at moderateReynolds numbers that are formed by the merging of two free streams initially separatedby a splitter plate.To study the nonlinear interactions between the two-and three-dimen-sional fundamental and subharmonic modes in the spatially developing shear layer,the se-lected five modes represent the minimum number that needs to be considered.The objec-tive of this study is to investigate the nonlinear effects arising from the interactions be-tween two-and three-dimensional large-scale coherent structures in a free shear layer.Our attention is focused on the energy exchange mechanisms between the various modes,and the effects of the nonlinear evolution of the phases of the interacting modes.It isshown that depending on the initial modal phase angles the downstream growth of theshear layer and the associated local entrainment can be strongly affected by the presence ofthese nonlinear interactions.This high sensitivity of the shear layer growt     

Monitoring water quality in reservoirs with IRS-1A-LISS-I

An attempt has been made to quantify the relationship between the variation in IRS-IA-LISS-I (Indian Remote Sensing Satellite-1A Linear Imaging Self-Scanning System) radiance data and field measured change in secchi disc depth. Secchi disc depth was measured for 47 predetermined sampling locations on reservoir surface water. At extinction depth (secchi depth), water samples were collected from all the sampling locations. Suspended sediments of eight locations representing various reaches of the reservoir were selected for mineralogical, particle size and optical properties analysis. The LISS-I radiance value in band 1 (0.45–0.52µm) band 2 (0-52–0.59 µm) and band 3 (0.62–0.68 µm) were used in a regression analysis. The absorption infrared band 4 (0.77–0.86 µm) was not included in the analysis. In these, the dependable variable was secchi depth (SD) and the LISS-I-radiance data was the estimator variable. Forty-seven data sets of 20 October 1988 from Tawa reservoir surface water were used to obtain an estimator equation for SD. The verification of the estimator equation was tested by applying it to a data set of 21 measurements of 28 September 1988 for this reservoir. The coefficient of correlation between observed and estimated values for the 28 September 1988 data set wasr=0.92 for SD, indicating that the equation could accurately predict the water clarity (SD) for this reservoir on new occasions from IRS-IA-LISS-I spectral data. It is shown that mineral composition and optical properties of suspended sediments influence the reflected radiance of water quality. It is concluded that IRS-IA-LISS-I data provide a useful means of mapping water quality in reservoir.     

双隐含层BP神经网络模型在老哈河水质预测中的应用

为了快速准确预测老哈河水质,采用老哈河2011-2015年水质监测数据,运用拉格朗日插值法补充缺失值,分别对化学需氧量、生化需氧量、高锰酸盐指数和总磷浓度建立Levenberg-Marquardt优化的双隐含层BP神经网络模型,利用2011-2014的数据建立训练网络,以2015年的数据进行验证与测试。结果表明:五日生化需氧量预测模型,第一隐含层节点数为4,第二隐含层节点数为12时,决定系数0.751 6(P=0.000 3),平均相对误差25.73%;化学需氧量预测模型,第一隐含层节点数为12,第二隐含层节点数为10时,决定系数0.887 5(P0.000 1),平均相对误差27.69%;高锰酸盐预测模型,第一隐含层节点数为6,第二隐含层节点数为3时,决定系数0.854 7(P0.000 1),平均相对误差28.90%;总磷预测模型,第一隐含层节点数为12,第二隐含层节点数为12时,决定系数0.889 2(P0.000 1),平均相对误差17.94%。应用拉格朗日插值法对缺失数据进行补充后建立的双隐含层BP神经网络模型相对误差均小于28.90%,模型的预测效果较好,其中总磷浓度预测效果最好。通过拉格朗日插值,可以建立老哈河赤峰段甸子点位污染指标的双隐含层人工神经网络模型进行水质预测。     

基于格子玻尔兹曼方法的近壁区空化泡生长溃灭过程模拟

基于格子玻尔兹曼热流耦合模型,兼顾温度场与流场的相互影响,对近壁区空化泡的生长和溃灭过程开展了系统研究,分析了泡壁无量纲距离和初始输入温度对空化泡演化过程和溃灭强度的影响,并对比了被动标量模型与热流耦合模型的差异。结果表明:空化泡受壁面限制,生长过程中无法保持圆形,其最大半径与泡壁无量纲距离之间存在幂函数关系,当泡壁无量纲距离大于1.6时,则为线性关系;空化泡最大半径与输入能量为线性关系,与初始输入无量纲温度之间存在幂函数关系;热流耦合模型考虑了高温对表面张力的影响,与被动标量模型模拟结果相比,其溃灭阶段获得的射流体积更大,微射流更集中,但溃灭强度更小。     

Armour Layer Analysis of Local Scour around Bridge Abutments Under Ice Cover

A set of experiments was conducted for the local scour around bridge abutments under ice cover in non‐uniform sediments. By taking into account of the grain size of the armour layer and ice cover roughness, the dimensionless maximum scour depth is analysed. With an increase in grain size of the armour layer, the dimensionless maximum scour depth decreases. With the increase in ice cover roughness, the dimensionless maximum scour depth increases correspondingly. By using dimensional analysis, a regression relationship supports this conclusion. The conclusions drawn from this study provide crucial evidence for the protection of bridge foundations in winter time. Copyright © 2014 John Wiley & Sons, Ltd.     

梯级水库输水线路伪鱼腥藻属时空分布特征及影响因子分析

根据中国南方某城市A、B、C 3座重要的地表供水和原水调蓄梯级水库输水线路上2013年5月—2014年6月水环境理化指标和伪鱼腥藻属监测数据,从生物和环境的角度来探究梯级水库输水线路伪鱼腥藻属时空分布特征,应用相关分析法对伪鱼腥藻属细胞密度与其环境影响因子进行相关性分析。结果表明:1伪鱼腥藻属细胞密度有明显的季节变化趋势,且季节性变化与水温显著相关(P0.05)。2伪鱼腥藻属细胞密度在垂直方向上分布出现3种类型:a层b层c层,b层a层c层,c层a层或b层。3伪鱼腥藻属细胞密度沿梯级水库输水线路直线增加。4伪鱼腥藻属细胞密度与水温和TP质量浓度呈显著正相关(P0.05),与TN和TP的浓度比呈显著负相关(P0.01)。     

THE RADIATION PROBLEM OF MULTIPLE STRUCTURES WITH SMALL GAPS IN BETWEEN

1. INTRODUCTION Recently, with the exploitation and utilization of ocean resources, various pontoon-type floating structures are widely applied. For example, Very Large Floating Structure (VLFS) is used as floating airport, multiple floating structures ar…     

Analytical approach to entropy generation and heat transfer in CNT-nanofluid dynamics through a ciliated porous medium

The transportation of biological and industrial nanofluids by natural propulsion like cilia movement and self-generated contraction-relaxation of flexible walls has significant applications in numerous emerging technologies. Inspired by multi-disciplinary progress and innovation in this direction, a thermo-fluid mechanical model is proposed to study the entropy generation and convective heat transfer of nanofluids fabricated by the dispersion of single-wall carbon nanotubes(SWCNT) nanoparticles in water as the base fluid. The regime studied comprises heat transfer and steady, viscous, incompressible flow, induced by metachronal wave propulsion due to beating cilia, through a cylindrical tube containing a sparse(i.e., high permeability) homogenous porous medium. The flow is of the creeping type and is restricted under the low Reynolds number and long wavelength approximations. Slip effects at the wall are incorporated and the generalized Darcy drag-force model is utilized to mimic porous media effects. Cilia boundary conditions for velocity components are employed to determine analytical solutions to the resulting non-dimensionalized boundary value problem. The influence of pertinent physical parameters on temperature, axial velocity, pressure rise and pressure gradient, entropy generation function, Bejan number and stream-line distributions are computed numerically. A comparative study between SWCNT-nanofluids and pure water is also computed. The computations demonstrate that axial flow is accelerated with increasing slip parameter and Darcy number and is greater for SWCNT-nanofluids than for pure water. Furthermore the size of the bolus for SWCNT-nanofluids is larger than that of the pure water. The study is applicable in designing and fabricating nanoscale and microfluidics devices, artificial cilia and biomimetic micro-pumps.     

300m级特高土石坝施工期心墙沉降监控模型研究

心墙沉降是两河口高土石坝的控制性安全监测项目,结合室内试验、监测、施工进度等资料,研究了心墙砾石土的沉降特性,建立了施工期沉降监控模型。研究表明:沉降变形的发展呈明显的阶段性,即沉降环埋设初期的快速沉降期、填筑进度平缓进行的匀速沉降期以及填筑高峰期的加速沉降期;以填筑因子与时效因子为组合的监控模型具有良好的解析力与拟合度,计算实例4个测点判定系数R 2在0.938~0.972;施工期沉降产生的主导因素是填土层上覆的外压荷载,就已填筑高程1/2~2/3区段而言,施工期沉降变形所占的填筑分量与时效分量分别约占95%与5%;监控模型具有良好的外延性,在近1个月外延区间中预测误差不超过9.04 mm,通过不断延长建模时序以修正模型参数,可提高预测精度进而指导施工。     

The spectral characteristics of dissolved organic matter from sediments in Lake Baiyangdian,North China

Dissolved organic matter (DOM) extracted from sediment samples in Lake Baiyangdian was investigated using UV -Vis absorption and fluorescence spectroscopy. Two parameters, the ratios of absorbance and dissolved organic carbon at 254° nm (SUVA₂₅₄) and the integral area from 240° nm to 400° nm (A_{240 -400}), were used to assess the molecular weight and aromaticity of DOM. The surface sediments showed a relatively low aromaticity of DOM due to the impact of environmental pollution. Synchronous fluorescence spectra showed an extremely high fraction of the protein-like region (PLR). Parallel factor analysis (PARAFAC) of excitation -emission matrix spectra revealed four fluorescent components occurring in sediment DOM: two humic-like (C1 and C2) components and two protein-like (C3 and C4) components. The PARAFAC-PCA displayed three PCA factors (factors 1, 2 and 3) which accounted for 48.250%, 25.927% and 25.391%, respectively, of the variance in fluorescent component. The humic-like components 1 and 2 concurrently showed positive factor 1 loadings. Factor 2 was mainly explained by the tryptophan-like component C3. A non-humic component 4, having a low factor loading in the other two factors, showed an extremely high factor 3 loading. The EEM -PARAFAC-PCA showed varying contributions of terrestrial versus autochthonous DOM sources in lake sediments.