Experimental Verification of Incomplete Solute Mixing in a Pressurized Pipe Network with Multiple Cross Junctions

Water quality models based on accurate mixing data at cross junctions are important for estimating concentrations of chemical species in municipal water distribution systems. Recent studies indicate that the instantaneous complete (thus “perfect”) mixing assumption potentially can result in an erroneous prediction of water quality. The present study examines the updated “incomplete” solute mixing model at cross junctions in a network having multiple cross junctions. The model performance in predicting solute transport was evaluated through a series of tracer experiments in a pressurized 5×5 network with 9 cross junctions. The perfect mixing model consistently overestimated solute dilution at cross junctions and predicted evenly distributed solute concentration throughout the network. In contrast, the incomplete mixing model demonstrated uneven distribution patterns with a distinct solute plume, and the corresponding results were significantly more accurate than those based on the perfect mixing assumption. Average prediction errors in tracer concentrations were 15 and 66% using the updated and perfect mixing models, respectively, and the difference was statistically significant (P-value <0.001). Therefore, this study concludes that the incomplete mixing model can drastically improve the prediction of solute transport in pressurized pipe systems that have multiple cross junctions.     

泵站水力机械抗气蚀耐磨损工艺研究

在多泥沙（黄河水源）抽水站水力机械使用过程中,除正常的泥砂和机械磨损外,其过流断面以及本体受气蚀的危害,严重影响水力机械运行工况,提高了能源单耗。经过多年的实践,在水力机械过流部件上涂耐磨材料,可以大大提高水力机械使用寿命,降低运行成本。     

Abrasion Characteristics of Ores

Effects of time and size on t₁₀, the abrasion parameter (fineness indicator) using a calibration model for a given ore type is presented. A model for predicting t₁₀ from a small diameter core material for any ore type is also presented. The ores studied are: Ok Tedi 1, Ok Tedi 2, Red Dome, Alcoa, and Broken Hill. Shape factor of the particles that varies with both the particle size and the ore type affects the abrasion characteristics. Abrasion process in a tumbling mill is described by two mechanisms namely (1) chipping, and (2) abrasion, occurring at different rates. The chipping phenomenon depends on the ore and the shape factor. The abrasion phenomenon is independent of t₁₀° (t₁₀° is the ore-specific t₁₀ at 7 × 10^?4 kWh/t tumbling test energy) and the shape factor. Abrasion process occurs at a much slower rate compared to the chipping process. Transition between chipping and abrasion occurs approximately after 2 min of tumbling. The long-term rate is controlled by the abrasion or attrition rather than by the chipping mechanism.     

Modeling the Transient Pumping from Two Aquifers Using MODFLOW

A procedure is proposed for calculating the spatial and temporal variation of drawdown due to pumping a well tapping two aquifers separated by an aquitard, using convolution and MODFLOW. It can take into account the unsteady pumping discharge and cross flow through the intervening aquitard. A discrete pulse kernel method based on superposition/convolution is used to account for the unsteady pumping discharge. The discrete pulse kernels are calculated using MODFLOW. The contributions of the aquifers to the pumped discharge are accounted implicitly and not required to be specified explicitly. Available numerical models (e.g., MODFLOW) require the aquifer contributions that are implicitly controlled, to be specified explicitly. The use of the suggested procedure is illustrated using examples. The contributions of the aquifers are found not in proportion to their transmissivities but vary with time, when the diffusivities of the aquifers are not equal. Applying the new procedure, the numerical models, such as MODFLOW can be used to correctly model the transient pumping from two aquifers with cross flow; thus, it opens up the possibility of numerically accounting for the aquifer heterogeneity while dealing with the flow to a well tapping two aquifers under a transient pumping, which would be otherwise difficult to account for analytically.     

耐磨铸铁研究现状与发展趋势

摘要：从耐磨铸铁的分类、发展历程、现行标准、性能特征、磨损性能影响因素、典型应用等方面论述了国内外耐磨铸铁的研究现状与进展,重点介绍了化学成分、基体组织、热处理工艺和碳化物对耐磨铸铁磨损性能的影响,提出了耐磨铸铁存在韧性低、成本高等问题,以及低成本无镍化,建立理论模型,ZrO2作为形核剂,新型复合碳化物等今后研究方向的建议。     

穿流干燥过程中降速段数学模型

介绍了穿流干燥过程中降速段的工艺特点及其数学模型的选择,给出了此干燥过程的数学模型及相关用途。     

精轧轧辊磨损自适应模型的应用研究

针对攀钢热轧板厂精轧模型在轧制单位中后期出现温度模型及变形模型中轧制参数预报精度下降的现象，提出应用精轧轧辊磨损自适应模型补偿、修正精轧工作辊及支承辊磨损，避免单独依靠厚度调节变量HUVER调节而导致轧制中后期模型预报精度下降。     

Simple Model for Analyzing Transient Pumping from Two Aquifers without Cross Flow

A computationally simple semianalytical model is proposed for calculating the drawdown due to pumping a well tapping two aquifers separated by an aquiclude with no cross flow. The new model can take into account the transient pumping discharge. Equations are proposed for calculating the transient contributions of the aquifers to the pumped discharge and drawdowns in aquifers. The residual drawdowns in the aquifers and the aquifer contributions during recovery period can also be obtained using the proposed model. Based upon a similar principle, another model is also developed that can consider the effect of the well storage. The proposed models can be used to calculate drawdowns neglecting or considering the well storage, in the case of transient pumping from two aquifers having different values of transmissivity and storage coefficient. It is hoped that the new models would be of help to the field engineers and practitioners.     

Optimal Cross-Sectional Spacing in Preissmann Scheme 1D Hydrodynamic Models

Choosing a suitable set of cross sections for the representation of the natural geometry of a river is important for the efficiency of one-dimensional (1D) hydraulic models, but only few guidelines are available for the selection of the most suitable distance between cross sections, depending on the hydraulic problem at hand. This issue is investigated by examining models of a ～ 55?km reach of the River Po, Italy, and a ～ 16?km reach of the River Severn, United Kingdom, for both of which high quality laser scanning altimetry are available. The high-resolution digital terrain models of the two river reaches enabled the construction of a series of hypothetical topographical ground surveys with different spacing between cross sections, which could be used as input to a standard 1D model (UNET). Both historical and synthetic flood events for the two river reaches were simulated, and the results were then analyzed to quantify the accuracy associated with each resolution and to assess how survey resolution impacts the performance of standard 1D models. The study results agree with the available suggestions in the literature and provide useful guidelines for 1D hydrodynamic modeling.     

Design for Shear in Curved Composite Multiple Steel Box Girder Bridges

Modern highway bridges are often subject to tight geometric restrictions and, in many cases, must be built in curved alignment. These bridges may have a cross section in the form of a multiple steel box girder composite with a concrete deck slab. This type of cross section is one of the most suitable for resisting the torsional, distortional, and warping effects induced by the bridge’s curvature. Current design practice in North America does not specifically deal with shear distribution in horizontally curved composite multiple steel box girder bridges. In this paper an extensive parametric study, using an experimentally calibrated finite-element model, is presented, in which simply supported straight and curved prototype bridges are analyzed to determine their shear distribution characteristics under dead load and under AASHTO live loadings. The parameters considered in this study are span length, number of steel boxes, number of traffic lanes, bridge aspect ratio, degree of curvature, and number and stiffness of cross bracings and of top-chord systems. Results from tests on five box girder bridge models verify the finite-element model. Based on the results from the parametric study simple empirical formulas for maximum shears (reactions) are developed that are suitable for the design office. A comparison is made with AASHTO and CHBDC formulas for straight bridges. An illustrative example of the design is presented.     

Response Prediction of RC Beams Externally Bonded with Steel-Reinforced Polymers

This paper deals with an innovative technique for strengthening reinforced concrete (RC) structures using steel-reinforced polymer (SRP) materials. The results of an experimental campaign using RC beams strengthened in flexure with carbon fiber-reinforced polymer or SRP laminates are summarized, and the experimental outcomes are compared to the predictions provided by analytical models and code formulations in terms of flexural strength, curvature of the cross section, deflections, and crack widths. Under ultimate conditions, the ACI 440.2R-02 approach provided conservative flexural strength, and a modified expression for the bond coefficient km was proposed. Under serviceability conditions, good agreement was obtained between experimental results and a theoretical model developed by the writers. Comparisons of code models in terms of both crack width and deflections highlighted the need for a calibration of code formulas to account for effects due to externally bonded reinforcement.     

Abrasion and toughness property maps for WC/Co hardmetals

Abstract

WC/Co hardmetals are generally designed for applications where resistance to wear, particularly abrasion or erosion, needs to be high but without the low toughness often found in very hard materials. Consequently, mapping the relation between wear characteristics and toughness is fundamental to the process of grade selection in commercial hardmetals. In current research at NPL wear resistance has been assessed using the ASTM B611 abrasion test method and toughness through Palmqvist fracture toughness. Both these tests are now well understood, especially the uncertainties associated with the measurements. Both of the two main types of property map are considered: those concerned with properties associated with end use, e.g. abrasion and toughness; and those concerned with relating microstructural parameters to the property of interest i.e. abrasion and its dependence on WC grain size. Comments are made on the effects of WC grain size distribution and mean grain size.     

Full Torsional Behavior of RC Beams Wrapped with FRP: Analytical Model

Torsion failure is an undesirable brittle form of failure. Although previous experimental studies have shown that using fiber-reinforced polymer (FRP) sheets for torsion strengthening of reinforced concrete (RC) beams is an effective solution in many situations, very few analytical models are available for predicting the section capacity. None of these models predicted the full behavior of RC beams wrapped with FRP, account for the fact that the FRP is not bonded to all beam faces, or predicted the ultimate FRP strain using equations developed based on testing FRP strengthened beams in torsion. In this paper, an analytical model was developed for the case of the RC beams strengthened in torsion. The model is based on the basics of the modified compression field theory, the hollow tube analogy, and the compatibility at the corner of the cross section. Several modifications were implemented to be able to take into account the effect of various parameters including various strengthening schemes where the FRP is not bonded to all beam faces, FRP contribution, and different failure modes. The model showed good agreement with the experimental results. The model predicted the strength more accurately than a previous model, which will be discussed later. The model predicted the FRP strain and the failure mode.     

Modeling of Temperature–Frequency Correlation Using Combined Principal Component Analysis and Support Vector Regression Technique

A good understanding of environmental effects on structural modal properties is essential for reliable performance of vibration-based damage diagnosis methods. In this paper, a method of combining principal component analysis (PCA) and support vector regression (SVR) technique is proposed for modeling temperature-caused variability of modal frequencies for structures instrumented with long-term monitoring systems. PCA is first applied to extract principal components from the measured temperatures for dimensionality reduction. The predominant feature vectors in conjunction with the measured modal frequencies are then fed into a support vector algorithm to formulate regression models that may take into account thermal inertia effect. The research is focused on proper selection of the hyperparameters to obtain SVR models with good generalization performance. A grid search method with cross validation and a heuristic method are utilized for determining the optimal values of SVR hyperparameters. The proposed method is compared with the method directly using measurement data to train SVR models and the multivariate linear regression (MLR) method through the use of long-term measurement data from a cable-stayed bridge. It is shown that PCA-compressed features make the training and validation of SVR models more efficient in both model accuracy and computational costs, and the formulated SVR model performs much better than the MLR model in generalization performance. When continuously measured data is available, the SVR model formulated taking into account thermal inertia effect can achieve more accurate prediction than that without considering thermal inertia effect.     

Wear resistance of quenched and tempered AISI 4137H steel

Abrasive wear resistance of quenched and tempered AISI 4137H steel was studied using the dry sand/rubber wheel test. The variables studied included hardness, tempering temperature, and cleanliness of the steel. The effect of sulfide inclusions on the relative wear performance of the steel was examined. Debris from the wear tests was analyzed using SEM and sieve analysis. The effects of steel cleanliness and sulfide inclusion shape on abrasion resistance are explained in terms of the relative ease for chip formation and its subsequent detachability during the abrasion process.     

GCr15轴承钢棒材连轧过程的二维和三维模拟

借助商业有限元软件MSC.Marc建立了GCr15轴承钢150 mm×150 mm坯至φ32 mm棒材的12道次连轧过程的二维和三维模型,并对比了二维和三维模型对轧制过程轧件截面形状、温度的模拟结果。结果表明,与三维模型相比,二维模型模拟得到的轧件截面宽展偏大,但计算效率较高,得出的温度曲线接近三维模型的模拟结果;给定工艺参数的三维模拟较二维模拟准确;模型模拟得到的出口轧制速度和温度与实测值吻合。     

Theoretical antideuteron-nucleus absorptive cross sections

Antideuteron-nucleus absorptive cross sections for intermediate to high energies are calculated using an ion-ion optical model. Good agreement with experiment (within 15 percent) is obtained in this same model for mean p-nucleus cross sections at laboratory energies up to 15 GeV. We describe a technique for estimating antinucleus-nucleus cross sections from N mean N data and suggest that further cosmic ray studies to search for antideuterons and other antinuclei be undertaken.     

The effect of air abrasion on shear bond strength to dentin with dental adhesives

This study compared the effects of different dentin surface treatments on the shear bond strengths of three adhesive systems. The adhesive systems included a resin-modified glass ionomer, Fuji II LC, and two dentin bonding systems, One Step and Scotchbond Multi-Purpose Plus. The surface treatments compared for each adhesive system were as follows: 1) the controls, which were conditioned, 2) air abrasion at 120 psi without conditioning, 3) air abrasion at 160 psi without conditioning, 4) air abrasion at 120 psi with conditioning, and 5) air abrasion at 160 psi with conditioning. The KCP 1000 Whisperjet was used for all air-abrasive specimens. Controls for each adhesive material (Fuji II LC, One Step, Scotchbond Multi-Purpose Plus) were bonded using manufacturers' recommendations. Results showed that air abrasion significantly lowered bond strength of the resin-modified glass ionomer, conditioned or nonconditioned (P < 0.01). Air abrasion alone significantly lowered bond strengths of the dentin bonding agent systems (P < 0.01). However, air abrasion plus conditioning of the dentin surface resulted in bond strengths that were similar to the conditioned-only specimens (P < 0.01).     

热带钢连轧机工作辊冷却水优化设计

 轧辊热凸度是影响热带钢连轧机负载辊缝的重要因素,高效率的工作辊冷却水系统是生产高质量热轧板带的重要保证。为了设计工作辊的冷却水量及分布,建立了工作辊横断面温度场计算模型、轴对称平面温度场计算模型和热凸度计算模型。在此基础上,采用优化设计方法对1450热带钢连轧机工作辊冷却水量及其沿轧辊周向和轴向的分布进行优化设计。     

六辊UCM轧机中间辊倒角优化

 本文采用影响函数法对UCM六辊轧机的辊系弹性变形进行了分析与计算,研究了不同的中间辊倒角对辊间接触压力的影响,为减少辊间接触压力峰值,优化出了适合不同带宽的中间辊倒角形状参数,从而减缓了轧辊的磨损,避免了轧辊剥落现象。