3D Unsteady RANS Modeling of Complex Hydraulic Engineering Flows. I: Numerical Model

A general-purpose numerical method is developed for solving the full three-dimensional (3D), incompressible, unsteady Reynolds-averaged Navier-Stokes (URANS) equations in natural river reaches containing complex hydraulic structures at full-scale Reynolds numbers. The method adopts body-fitted, chimera overset grids in conjunction with a grid-embedding strategy to accurately and efficiently discretize arbitrarily complex, multiconnected flow domains. The URANS and turbulence closure equations are discretized using a second-order accurate finite-volume approach. The discrete equations are integrated in time via a dual-time-stepping, artificial compressibility method in conjunction with an efficient coupled, block-implicit, approximate factorization iterative solver. The computer code is parallelized to take full advantage of multiprocessor computer systems so that unsteady solutions on grids with 106 nodes can be obtained within reasonable computational time. The power of the method is demonstrated by applying it to simulate turbulent flow at R ? 107 in a stretch of the Chattahoochee River containing a portion of the actual bridge foundation located near Cornelia, Georgia. It is shown that the method can capture the onset of coherent vortex shedding in the vicinity of the foundation while accounting for the large-scale topographical features of the surrounding river reach.     

Oscillating Jet Flows in a Thin Slab Mold and their Influence on Meniscus Stability

Sustainability of oscillating liquid steel jets discharging from a submerged, two‐port entry nozzle in thin slab molds has been studied through a water model and mathematically simulated using the Reynolds Stress Model of turbulence combined with the Volume of Fluid model to capture dynamics of the water‐air interface. At casting speeds of 5 and 7 m/min, both jets yield long range time‐dependent Reynolds stresses with high gradients which induce oscillating upper roll flows in the mold providing permanent flow asymmetry. Intermittent vortexes at the water‐air interface are generated by the interaction between the flow arising from the upper roll toward the SEN and a high velocity flow which goes through the gap between the SEN shaft and mold wall oriented toward the narrow wall. These flows gather at expansion of the mold funnel generating intermittent vortexes. Meniscus oscillation decreases in narrower molds even at high casting speeds. At lower casting speed like 5 m/min meniscus oscillation decreases considerably in wide and narrow molds. Turbulence understanding in thin slab molds would help to design submerged entry nozzles for higher steel casting speeds through wide molds with better meniscus stability.     

3D Unsteady RANS Modeling of Complex Hydraulic Engineering Flows. II: Model Validation and Flow Physics

A chimera overset grid flow solver is developed for solving the unsteady Reynolds-averaged Navier-Stokes (RANS) equations in arbitrarily complex, multiconnected domains. The details of the numerical method were presented in Part I of this paper. In this work, the method is validated and applied to investigate the physics of flow past a real-life bridge foundation mounted on a fixed flat bed. It is shown that the numerical model can reproduce large-scale unsteady vortices that contain a significant portion of the total turbulence kinetic energy. These coherent motions cannot be captured in previous steady three-dimensional (3D) models. To validate the importance of the unsteady motions, experiments are conducted in the Georgia Institute of Technology scour flume facility. The measured mean velocity and turbulence kinetic energy profiles are compared with the numerical simulation results and are shown to be in good agreement with the numerical simulations. A series of numerical tests is carried out to examine the sensitivity of the solutions to grid refinement and investigate the effect of inflow and far-field boundary conditions. As further validation of the numerical results, the sensitivity of the turbulence kinetic energy profiles on either side of the complex pier bent to a slight asymmetry of the approach flow observed in the experiments is reproduced by the numerical model. In addition, the computed flat-bed flow characteristics are analyzed in comparison with the scour patterns observed in the laboratory to identify key flow features responsible for the initiation of scour. Regions of maximum shear velocity are shown to correspond to maximum scour depths in the shear zone to either side of the upstream pier, but numerical values of vertical velocity are found to be very important in explaining scour and deposition patterns immediately upstream and downstream of the pier bent.     

Turbulence Modeling of Flows over Circular Spillways

To predict the characteristics of flows over circular spillways, a turbulence model based on the Reynolds stress model (RSM) is presented. Circular spillways are used to regulate water levels in reservoirs. The flow over the spillway is rapidly varied with highly curvilinear streamlines. The isotropic eddy-viscosity models such as k-ε models are based on the Boussinesq eddy viscosity approximation that assumes the components of the turbulence Reynolds stress tensor linearly vary with the mean rate of strain tensor. Hence, they cannot very precisely predict the characteristics of flows over the spillway. On the other hand, the non-isotropic turbulence models such as the turbulence Reynolds stress models (RSM) that calculate all the components of the Reynolds stress tensor can accurately predict the characteristics of these flows. The k-ε models and RSM were applied in the present study to obtain the flow parameters such as the pressure and velocity distributions as well as water surface profiles. The previously published experimental results were used to validate the simulation predictions. For flow over a circular spillway, RSM appears to properly validate the characteristics of the flow under various conditions in the field, without recourse to expensive experimental procedures.     

高精度中厚板平面形状预测模型的研究及应用

针对中厚板轧制过程的工艺特点,利用ANSYS/LS-DYNA完全重启动技术建立了三维弹塑性有限元模型。对中厚板轧制过程进行了多工况多道次仿真研究,修正了轧件头、尾平面形状预测模型。根据数值仿真结果和修正模型建立了高精度中厚板平面形状预测模型。依据此模型计算结果设计成形MAS控制方案,经2 800 mm中厚板轧机试验验证...     

大平板湿法卧式电除尘器的设计及性能测定

在工业性试验和生产实践中对大平板湿法卧式电除尘器进行了三项关键性的性能测试：不同煤气流速下电除尘器的伏安特性曲线；不同煤气流速下电除尘器的除尘效率以及影响因素；不同喷水方式对除尘效率的影响。     

平板式筏基柱下冲切计算的调整

文章主要通过分析新旧基础规范在平板式筏基边柱柱下冲切计算方面的变化,进而为筏板基础冲切设计找到了一个新的办法,同时也发现了一些新规律。通过工程实例计算数据的对比,进一步印证文章总结的规律,并为今后的实际应用提供了有益的启示。     

中厚板表面裂纹控制

针对中厚板表面经常出现裂纹缺陷的问题,通过材料显微组织分析、坯料跟踪和对比生产实验,发现中厚板表面裂纹源于板坯裂纹。采取调整钢水成分,优化连铸工艺,提高入炉板坯表面质量等措施,减少了钢板裂纹不合格品,产品合格率提高了4．43％,提高了中厚板质量。     

平立辊协调轧制控制厚板平面形状的试验研究

叙述了平立辊协调轧制控制厚板平面形状的试验过程,通过与常规轧制的比较,说明平辊与立辊的协调作用对中厚板平面形状的控制效果,并对试验结果进行了理论分析。结果表明：平立辊协调轧制对中厚板平面形状的控制非常有效。     

平板垂直接管构件环形焊缝变形的控制

针对焦炉炉顶水封盖底座的平板垂直封闭环形多道焊焊接形式,制定了有效的措施和焊接工艺,圆满完成了构件的制作,成功控制了焊接变形,保证了产品质量。     

Applicability of Sediment Transport Capacity Formulas to Dam-Break Flows over Movable Beds

In this paper, we investigate the extent to which well-known sediment transport capacity formulas can be used in one-dimensional (1D) numerical modeling of dam-break waves over movable beds. The 1D model considered here is a one-layer model based on the shallow-water equations, a bed update (Exner) equation, a space-lag equation for the nonequilibrium sediment transport and an empirical formula calculating the sediment transport capacity of the flow. The model incorporates a variety of sediment transport capacity formulas proposed by Meyer-Peter and Müller, Bagnold, Engelund and Hansen, Ackers and White, Smart and Jaeggi, van Rijn, Rickenmann, Cheng, Abrahams and Camenen, and Larson. We examine the performance of each formula by simulating four idealized laboratory cases on dam-break waves over sandy beds. Comparisons between numerical results and measurements show that for each case better predictions are obtained using a particular formula, but overall, formulas proposed by Meyer-Peter and Müller (with the factor 8 being replaced by 12), Smart and J?ggi, Cheng, Abrahams and Camenen, and Larson rank as the best predictors for the entire range of conditions studied here. Moreover, results show that in the cases where a bed step exists, implementing a mass failure mechanism in the numerical modeling plays an important role in reproducing the bed and water profiles.     

A36高强度船用热轧球扁钢产品开发

采用低碳、添加Al＋Ti＋Nb＋V合金组合细化晶粒元素的设计成分,优化转炉（LD）或电炉（EC）加LF（VD）精炼工艺,优化Φ400 mm和Φ650 mm生产线轧制工艺,成功开发了A36高强度球扁钢,产品性能达到了船级社认证考核指标。     

高温平板水雾冷却换热系数的数值分析

 利用有限元耦合场数值模拟计算方法进行了高温平板纯水喷雾冷却的模拟。研究了射流出口高度、平板表面温度及喷嘴流量对换热系数的影响。模拟结果表明：在其它参数不变的情况下,随着喷射距离（200mm～500mm）的减小,换热系数总体呈增加趋势;随着平板表面温度在（1050K～1200K间）的增加,换热系数总体呈减小趋势;随着射流流量或压力的增加,换热系数呈增加趋势。     

中厚板轧制轧件头尾翘曲研究进展

轧件头尾翘曲问题成为中厚板轧制生产中的关键问题之一,直接影响板材的成材率和产品质量。本文综述了近年来国内外关于中厚板轧制轧件头尾翘曲的最新研究进展,分析了轧件上下表面的温度差、轧制压下率、轧制导入角、异径异速轧制和变形区几何形状等对板材翘曲的影响,并介绍了中厚板轧制轧件头部翘曲的控制模型研究现状。     

厚板及高强钢板的板型控制

本文介绍了厚板及高强钢板常见的板型缺陷,分析了其形成原因,提出了相应的控制措施。     

Experimental Study of Fine Sand Particle Settling in Turbulent Open Channel Flows over Rough Porous Beds

Results are presented from laboratory studies investigating the behavior of fine sand particles within turbulent open channel flow conditions flowing over rough, porous beds. A particle tracking technique was employed to record and analyze sand particle motion within the flow, while mean and fluctuating flow velocities were measured by an acoustic Doppler velocimeter probe. Measured particle settling rates show a strong influence from flow turbulence, being generally enhanced in the near-bed and intermediate flow regions and retarded in the outer flow region, compared to their fall velocity in still water conditions. Experiments also reveal the relative degree of settling enhancement to increase with decreasing particle size. Correlation between particle and small-scale fluid motions is demonstrated through a quadrant analysis technique, with higher-order events for the two phases found to be dominated by ejections and sweeps associated with the bursting process. Particle interactions with large-scale turbulent flow structures, revealed through flow visualization with a moving frame of reference, are found to result in particle accumulation in peripheral trajectories on the downflow side of local eddy structures. Analytical and theoretical considerations suggest that both these turbulence scales provide preferential transportation mechanisms that will account for the enhanced sand particle settling rates observed.     

基于ANSYS平台的中厚板控冷过程的温度场有限元模拟及分析

利用ANSYS大型有限元分析软件对中厚板轧后控冷过程温度场进行了有限元模拟 ,得到了钢板在水冷条件下的温度时间历程曲线及瞬态温度场分布 ,为制定合理的控冷工艺提供了有力的指导     

Depth-Averaged Model of Open-Channel Flows over an Arbitrary 3D Surface and Its Applications to Analysis of Water Surface Profile

A new set of depth-averaged equations is introduced to study the flow over an arbitrary three-dimensional (3D) surface. These equations are derived based on a generalized curvilinear coordinate system attached to the 3D bed surface, therefore it allows us to include the effect of centrifugal force due to the bottom curvature. These general equations make it possible to analyze flows over complex terrain without the limitation of mild slope assumption used in conventional depth-averaged models. This new model is then applied to calculate the water surface profiles of (1) flow over a cylindrical surface; (2) flow over a circular surface; and (3) flow with an air-core vortex at a vertical intake. A simple hydraulic experiment is conducted in the laboratory to observe the water surface profile of flow over a circular surface. The results obtained from the model are in good agreement with experimental measurements and calculation by an empirical formula. Consequently, it demonstrates the applicability of the model in cases of flow over a highly curved bottom.     

30mm以上规格低合金钢板矫直工艺浅析与应用

针对韶钢3 450 mm中厚板生产线30 mm以上规格低合金钢板矫直弯曲率偏高问题,对现有的矫直设备能力及工艺参数进行了分析,并对矫直力和矫直扭矩进行了校核,确定了对30 mm以上规格低合金钢板实施大压下量矫直技术,并优化了矫直工艺,通过现场实施,矫直弯曲率大幅度降低.