Mean Flow and Turbulence around a Laboratory Spur Dike

The three-dimensional turbulent flow field around a spur dike in a plane fixed-bed laboratory open channel was studied experimentally using a microacoustic Doppler velocimeter. Mean and turbulence characteristics in all three spatial directions were evaluated at upstream and downstream cross sections near the dike. Results showed that the primary flow separated in both lateral and vertical directions. Two counter-rotating flow circulations, consisting of the lateral and vertical velocity components, originated at the dike section. Downstream of the dike, the circulation in the flow-separation zone is stronger than the one in the contracted primary flow zone. The maximum bed-shear stresses estimated using Reynolds stresses is about three times as large as the mean bed-shear stress of incoming flow.     

Similitude of Large-Scale Turbulence in Experiments on Local Scour at Cylinders

The writers’ experiments on local scour at vertical cylinders placed in a sand bed show that similitude of large-scale turbulence is an important consideration influencing equilibrium depth of local scour. For the range of cylinder diameters used in their experiments, the writers identify a direct trend between equilibrium scour depth (normalized with cylinder diameter) and the intensity and frequency of large-scale turbulence shed from each cylinder; values of normalized scour depth increased when cylinder diameter decreased. The writers offer a scour-depth adjustment factor to account for this trend, which essentially is a scale effect incurred with experiments involving three independent length scales: cylinder diameter, bed-particle diameter, and flow depth. The consequent similitude consideration, or scale effect, has general significance for laboratory studies of local scour associated with hydraulic structures in sediment beds.     

Microcounseling for a counseling-like verbal response set: Differential effects of two micromodels and two methods of counseling supervision.

Compared the use of 2 models employing behavioral supervision and recall interrogation in teaching a counseling-like verbal response set to 16 guidance students. Pre-post1 and pre-post2 criterion performance gains of the experimental Ss and a no-treatment control group (n = 14) were measured on the Counselor Verbal Response Scale. Results from a 2 * 2 factorial design with a single control group reveal that microcounseling Ss gained significantly more in criterion performance than the controls. There was virtually no difference in the effectiveness of the 2 micromodels, and behavioral supervision was somewhat more successful than recall interrogation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modeling of Melt Flow and Surface Standing Waves in a Continuous Casting Mold

Majority of surface and subsurface defects in the continuously cast steel may be attributed to surface standing waves and turbulence. A lot of work has been done on surface defects and on understanding the behavior of the surface waves but there is a dearth of literature connecting the two. Also 3‐D modeling of surface waves with heat transfer and solidification has received little attention. In the present study, a 3‐dimensional mathematical model incorporating turbulent fluid flow, heat transfer, and solidification using a commercial code, FLOW3D, was developed. Using the model, the applicability of Froude criterion for scaling down industrial flow systems was analyzed. Although the small scale models, using this criterion, correctly predict the general fluid flow but the prediction of surface waves is not very accurate. Also, the effect of temperature is difficult to incorporate in water models. The model was used to study the effect of temperature on surface waves and verify the water modeling results. The effects of casting and SEN parameters on the fluid flow and surface waves were studied.     

风口回旋区的数字图像处理方法

风口回旋区对高炉及COREX熔化气化炉冶炼过程起着十分重要的作用,人们对风口回旋区进行了大量的试验与模拟研究.目前通过试验方法得到的风口回旋区仅仅是由若干个测量点确定.物理参数场可以用来准确确定回旋区边界,但是目前为止所有的研究风口回旋区的物理参数场都是由数值模拟确定,并且没有明确的回旋区的定义标准.在本研究中利用CO...     

Critical Bed Shear Stress for Unisize Sediment

The overall, spatially averaged, mean magnitude of local, spatially averaged (over a small area enclosing the particles’ projected area), instantaneous, critical Shields shear-stress parameters required for incipient motion of uniform-sized sand grains, independent of the bed shear-velocity particle Reynolds number, equal to 0.16, is obtained from calibration of a theory for bed load sediment transport, by minimizing the sum of the squares of the deviations between theoretical and experimental bed load rates. Additionally, optimized expressions for a proposed probability density distribution of the bed shear stresses, for its standard deviation, for finite, maximum, and minimum bed shear stresses, and a bed load rate are obtained. In terms of the mean fluid shear stress, a dimensionless, critical, shear-stress parameter equal to 0.0513 is obtained. Investigation of the probability density distribution of the spatially varying, critical shear stresses would allow a more accurate formulation for the case of low transport rates.     

Oblique Flow over Dredged Channels.?I: Flow Description

A 3D investigation of flow across long, straight channels aligned obliquely to the flow direction has been conducted. The applied mathematical model solves the Reynolds-averaged Navier-Stokes equations using a k-ε model for turbulence closure in a curvilinear coordinate system. The uniformity along the channel alignment allows the three momentum equations to be solved in a 2D computational domain. With respect to a steady current entering a channel obliquely, two important flow features arise: (1) The flow will be refracted in the direction of the channel alignment, which may be described by depth-averaged models; and (2) a secondary flow will be introduced due to shear in the velocity profile. This can only be described using a 3D approach. The secondary flow will cause a horizontal deflection of streamlines over the vertical. Only by capturing the 3D flow behavior can the direction and magnitude of the bed shear stress be well modeled. When crossing a channel obliquely, the flow is gradually accelerated in the direction of the channel alignment. Results of the numerical flow model are compared with existing experimental data and good agreement is found.     

Hydraulics of Rectangular Dropshafts

A dropshaft is an energy dissipator connecting two channels with a drop in invert elevation. The hydraulics of vertical rectangular shafts was systematically investigated in seven configurations. A particular emphasis was on the effects of shaft pool, outflow direction, and drop height, while geometrically similar shafts (scale 3.1:1) were studied using a Froude similitude. The results demonstrate that rectangular dropshafts with 90° outflow are the most efficient energy dissipators. The shaft pool and drop height have little effect on the rate of energy dissipation. Recirculation time results exhibited marked differences between flow regimes and the longest dimensionless residence times were observed at low flow rates. Although basic flow characteristics were similar between model and prototype, observations of dimensionless bubble penetration depths and recirculation times showed some discrepancy, highlighting limitations of the Froude similitude for studies of air entrainment and residence times in dropshafts.     

Modeling Freckle Segregation with Mesh Adaptation

Modeling the formation of macroscopic segregation channels during directional solidification processes has important applications in the casting industry. Computations that consider thermosolutal convection involve different length scales ranging from the small solute boundary layer at the dendrite tips to the characteristic size of the casting. In general, numerical models of solidification in the presence of a developing mushy zone are computationally inefficient because of nonlinear transport in an anisotropic porous medium. In the current work, mesh adaptation with triangular finite elements is used in conjunction with an efficient fractional-step solver of the momentum equations to predict the occurrence of channel-type segregation defects or freckles. The triangulations are created dynamically using an unstructured grid generator and a refinement criterion that tracks the position of the channel segregates. The efficiency of mesh adaptation is illustrated with simulations showing channel formation and macrosegregation in directional solidification of a Pb–Sn alloy.     

基于相似理论的蒸发冷却器实验模型设计

对高温烟气降温,使其出口温度与设计要求达到良好的一致,一直是实际工程中需要解决的重要问题.宝钢LT系统蒸发冷却器内的流动可以归结为具有蒸发、辐射效应的液滴一空气一蒸汽一灰分的四相流动,文章利用相似理论,导出了原型与模型相似的准则数及边界条件,根据关键准则数相等来确定模型的几何比例、速度比例等,并由此来设计实验模型装置.     

Backwater Prediction due to the Blockage Caused by a Single, Submerged Spur Dike in an Open Channel

A method is proposed for predicting the backwater effect due to a single, submerged spur dike located within an open channel flow. A theoretical analysis based on the momentum principle relates the backwater effect to the drag force exerted by the spur dike on the flow. Experimental data obtained in laboratory flumes having subcritical flow conditions throughout the flow field have been used in developing predictive relationships for the spur dike drag coefficient, which is found to be strongly correlated to the blockage created by the spur dike within the flow cross section. The predictive relationships provide a means of obtaining a first-level estimate of the backwater effect due to a single, submerged spur dike in an open channel flow.     

结构-土-结构体系动力特性的模型实验

为研究邻近结构对土-结构体系动力特性的影响,基于弹性相似律,制作了框架结构在刚性基础（RF）、单一结构土-结构相互作用（SSI）和结构-土-结构相互作用（SSSI）的缩尺模型.采用脉冲激励方法识别出三个模型的频率、模态和阻尼比,并与原型有限元计算结果相比较.实验和数值计算结果表明:相应于SSI体系的模态,SSSI体系的模态成对出现,两阶模态的频率接近而相位相反,且SSI体系相应模态的频率位于这两阶频率之间;由于相邻结构的影响,SSSI体系基础的竖向位移和倾覆转角进一步加强.      

An Analysis of Recirculatory Flow in Gas‐Stirred Ladles

The paper is concerned with the fluid mechanics characterizing the bulk flow region in a gas‐stirred ladle. A theoretical framework, previously derived for the analysis of the gas‐liquid plume region, is extended to include the bulk flow phenomena. In this study, the liquid recirculation and mixing have been quantified in terms of simple dimensionless parameters related to the ladle geometry and gas flow rate. A new correlation for mixing time, consistent with the proper form of the Froude similitude criterion, is presented. The work has implications for the fundamental as well as applied aspects of ladle processing.     

Simple Curvilinear Method for Numerical Methods of Open Channels

Three-dimensional finite-difference or finite-volume models of sinuous open channels (e.g., narrow rivers, estuaries, and reservoirs) generally require boundary-fitted grids and curvilinear flow solution. Cartesian models with square grid cells are simpler to apply, but require a larger number of cells, as the cell size is determined by cross-stream resolution. This paper presents a simplified curvilinear approach suitable for systems where the along-stream length scale is larger than the cross-stream scale. The curvilinear Navier-Stokes equations are manipulated so the left-hand side is identical to the Cartesian momentum equations. The right-hand side then consists of grid-stretching curvature terms. These terms are written as functions of a perturbation parameter, so the first-order curvilinear effects are obtained with the lowest-order perturbation terms. As the Cartesian equations' form is preserved, we can readily adapt a Cartesian model to this perturbation curvilinear approach by adding the small curvilinear terms as explicit momentum sources.     

Defensive responding on the MMPI-2 in family custody and access evaluations.

The objective of this study was to examine defensive underreporting on the Minnesota Multiphasic Personality Inventory-2 (MMPI-2) with a sample of parents involved in custody dispute litigation. With a composite score derived from 2 nontraditional validity indicators—the Wiggins Social Desirability scale (WSD) and the Superlative scale (S), which had previously been identified as the best predictors of fake-good responding, 74% of litigants were identified as underreporting compared with 52% identified using traditional Lie (L) and Correction (K) scale criterion. Litigants identified as underreporters whether using either the WSD-S criterion or the L-K criterion, had clinical scale profiles that were similar to those identified as nonunderreporters. The outcome of this study suggests that the WSD and S scales are perhaps more useful in the identification of defensive underreporting than the L and K scales. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Applicability of Quasisteady and Axisymmetric Turbulence Models in Water Hammer

Two of the existing turbulence water hammer models, namely the two-layer and the five-layer eddy viscosity models, are implemented and analyzed and the accuracy of their quasi-steady and axisymmetric assumptions evaluated. In addition, a dimensionless parameter P (ratio of the time scale of radial diffusion of shear to the time scale of wave propagation) for assessing the accuracy of quasi-steady turbulence modeling in water hammer problems is developed and applied. It is found that the results of both models are in reasonable agreement, confirming that the turbulence modeling of water hammer flows is insensitive to the magnitude and distribution of the eddy viscosity within the pipe core. Comparison of model results with available data shows that the quasi-steady assumption becomes more accurate as the dimensionless parameter P increases. Furthermore, the analysis shows that the quasi-steady assumption is highly accurate as long as the simulation time is below the diffusion time scale and that this assumption causes an almost linear increase in the difference between model results and data with time. The accuracy of the flow axisymmetry assumption is evaluated by applying both models to a water hammer problem where flow asymmetry has been observed experimentally. It is found that the difference between models and data grows exponentially and reaches 100% after six wave periods.     

Transport and Entrapment of Particles in Steel Continuous Casting

A particle-capture model based on local force balances has been developed, implemented into computational models of turbulent fluid flow and particle transport, and applied to simulate the entrapment of slag inclusions and bubbles during the continuous casting of steel slabs. Turbulent flow of molten steel is computed in the nozzle and mold using transient computational fluid flow models, both with and without the effects of argon gas injection. Next, the transport and capture of many particles are simulated using a Lagrangian approach. Particles touching the dendritic interface may be pushed away, dragged away by the transverse flow, or captured into the solidifying shell according to the results of a local balance of ten different forces. This criterion was validated by reproducing experimental results in two different systems. The implications of this criterion are discussed quantitatively. Finally, the fluid flow/particle transport model results and capture criterion are applied together to predict the entrapment distributions of different sized particles in a typical slab caster. More large particles are safely removed than small ones, but the entrapment rate into the solidifying shell as defects is still very high.     

Predicting the critical conditions and stress-strain curves for dynamic recrystallization in SPHC steel

 The hot compression tests were carried out on a SPHC steel at the temperature range of 900～1150℃ and strain rate range of 0.1～10s-1, which the maximum true strain is 0.8. The activation energy of tested steel was calculated, which was 299.4 KJ /mol. The critical stresses and strains for initiation of dynamic recrystallization were determined based on changes in the work hardening rate ( ) as functions of the flow stress ( ) or strain ( ), respectively. The dependence of the peak strain ( ), the peak stress ( ), and the steady state stress ( ) were determined based on the Zener-Hollomen parameter. The mathematical models of the flow stress evolution were established in the hardening and dynamic recovery region and dynamic recrystallization region, respectively. The average error between experimental and predicted curves was around 3.26%.     

Three-Dimensional Numerical Model for Flow and Bed Deformation around River Hydraulic Structures

This paper describes a numerical model developed to simulate flow and bed deformation around river hydraulic structures. The model solved the fully three-dimensional, Reynolds-averaged Navier–Stokes equation expressed in a moving boundary-fitted coordinate system to calculate the flow field with water and bed surfaces varying in time. A nonlinear k-ε turbulence model was employed in order to predict flow near the structure where three-dimensional flow is dominant. The temporal change in bed topography was calculated by coupling a stochastic model for sediment pickup and deposition using a momentum equation of sediment particles in order to account for the effect of nonequilibrium sediment transport. In validating the numerical model, a spur dike and a bridge pier, which are considered to be typical river-engineering structures, were selected. By comparing the numerical results with observed laboratory experimental data, the model was found to reproduce flow and scour geometry around these structures with sufficient accuracy.