Subelement Form-Drag Parameterization in Rough-Bed Flows

Spatial averaging of the Reynolds-averaged Navier–Stokes equations gives the double-averaged Navier–Stokes equations, for which boundary drag appears naturally and explicitly in momentum conservation equations. Increasing use of the double-averaged equations, e.g., for relating flows to three-dimensional bed roughness, for evaluation of profiles of flow stresses and velocities in ecologically significant regions below roughness tops, and for modeling purposes, requires parameterization of boundary drag at subelement scales. Based on seven flows over repeated square-rib roughness and ten flows over repeated fixed simulated sand waves, with measured velocities and bed pressures, expressions for form-drag coefficient CD = f (elevation below roughness top, relative roughness submergence, roughness steepness) are obtained for each of the two-dimensional roughness types. Using these equations, form drag variation with elevation below roughness tops can be calculated using either the double average of the square of local velocity (preferred based on conceptual considerations, trends in coefficient prediction, and also overall drag prediction) or the squared local double-averaged velocity, the roughness area being normal to the flow in each case. Integration of subelement drag given by these expressions is shown to give form-drag coefficient magnitudes and trends for complete individual elements comparable to those obtained by other authors based on measurements or numerical simulations. The ranges of roughness steepness and relative roughness submergence upon which the present equations have been derived need to be noted in consideration of application of the equations. In addition, effective application of the expressions is limited in regions of strongly negative double-averaged velocity. Further work remains to determine drag parameterization for alternative roughness geometries.     

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.     

Effect of Surface Coating Strengthening on Humidity Resistance of Sodium Silicate Bonded Sand Cured by Microwave Heating

The microwave heating sodium silicate bonded sand (SSBS) process is regarded as the most likely molding sand to realize green casting, owing to its low sodium silicate addition, rapid hardening speed, high strength, and excellent collapsibility. However, SSBS can absorb water easily in the air at room temperature. A surface coating strengthening method was used to improve the humidity resistance of SSBS. The properties of SSBS treated by the surface coating strengthening method were compared with that without any treatment. The experimental results indicated that humidity resistance had been improved greatly using the surface coating strengthening method, and comparing to SSBS without any treatment, the compressive strength (σ_6h) of the treated SSBS increased 2.32 times and the moisture absorption rate (w_6h) can be decreased by 45%. The morphology results revealed that there was a surface coating around the treated SSBS. The linear scanning indicated that the nonhygroscopic coat components presented on the boundary of the treated SSBS, and the surface phase analysis manifested that the boundary of the treated SSBS emerged new three phases, including Al₂TiO₅, PbTiO₃, and NaAlO₂, which reduced the free sodium ion content and improved the humidity resistance of SSBS.     

Field and Laboratory Testing of St. Peter Sandstone

The purpose of this project was to evaluate mechanical properties of St. Peter sandstone by in situ testing, and to compare the field data with laboratory results. Direct shear tests were conducted to evaluate the strength-dilatancy behavior, and thin-section microscopy was used to help explain the significant friction angles associated with the material. St. Peter sandstone is nearly cohesionless, but it possesses a friction angle of 57–63° at low confinement. The large angle of internal friction at failure may be due to locking of sand particles or to postdepositional quartz overgrowths. Tests on pulverized densely packed sand and loosely packed sand were conducted in the same manner as the intact specimens and yielded friction angles of about 42 and 34°. Pressuremeter tests were performed in situ and the results were interpreted using an elasto-plastic analysis in terms of total stresses. By appropriate consideration of system stiffness, Young’s modulus was found to be about 0.5 GPa, slightly lower than the laboratory value, although unload-reload cycles were not attempted. Assuming associative behavior, the friction angle was estimated to be at least 56°.     

人工砂石粉含量超标对常态混凝土性能的影响试验研究

人工砂石粉含量增大，可以改善碾压混凝土性能，对常态混凝土性能同样具有益化作用。通过正交试验，利用石粉含量不超过２０％的人工砂，可配得Ｃ２０－Ｃ３０、抗渗等级Ｓ８、抗冻等级Ｓ８、抗冻等级Ｄ１５０以上的常态混凝土，并能大为改善混凝土拦和物和易性，减少混凝土胶凝材料用量，降低混凝土生产成本约１５元／ｍ＾３。     

烟草叶片无性繁殖研究

从５～８叶期壮苗截取烟草完整叶片，置（３０±５）℃沙床遮阴保湿培养，６～２４天从主叶脉伤口附近生出许多不定根，移栽后在阳光下能独立存活，并于伤口附近发生新芽，继而发育成完整植株。繁殖系数为１４～４０。     

Mobility and distribution of cadmium, nickel and zinc in contaminated soil profiles from Bangladesh

We investigated the mobility and distribution of cadmium (Cd), nickel (Ni) and zinc (Zn) in four contaminated soil profiles from Bangladesh. The sources of contamination of these profiles were tannery wastes, city sewage and the wastes of pharmaceutical and paper mill factories at different locations in Bangladesh. The samples were collected from the A-, B- and C-horizons of each profile: two sub-samples from the A-horizon at depths of 0–5 cm (A1) and >5 cm (A2), and one sample each from the B- and C-horizons. Soil samples were analysed for total metal content by dissolution in aqua regia followed by sequential extraction of the fractions based on their varying solubility. There were six operationally defined groups of extraction sequences: water soluble (F1), exchangeable (F2), carbonate (F3), oxide (F4), organic (F5) and residual (F6). The total concentration of Cd, Ni and Zn in the A-horizon (0–5 cm) ranged from 0.10 to 0.62, from 31 to 54 and from 85 to 838 mg kg⁻¹, respectively. In the B- and C-horizons, the concentrations of these metals decreased many fold, particularly in the city sewage profile where the decrease for Cd and Zn was approximately fourfold. The distribution of metals among the chemical fractions depended on their total concentrations. In the A1-horizon, Cd had the highest mobility factor [MF = (F1+F2+F3)/(F1+F2+F3+F4+F5+F6) × 100] at 41–43% and Ni had the lowest at 3–13%, while Zn, showed intermediate values at 8–25%. The MF decreased with depth in all soil profiles. Among the fractions, the residual fraction contained the lowest levels of Cd but the highest levels of Ni and Zn. This state affected their relative mobility and distribution in soil profiles. Of the soil profiles, the mobility of all metals was higher in the city sewage soil than in any of the other three soils investigated, suggesting that the former may create a health risk by contaminating agricultural products and ground water as it also contained higher amounts of Cd and Zn.     

井筒内沉积砂柱对流体的渗流阻力分析

本文通过对垂直井筒内固液两相流运动规律和摩阻损失研究，建立井筒物理模型，找出砂柱高度和产量之间的对应关系。经油田现场数据验证表明，预测方法简单，计算结果较准确，为油田高效生产提供了参考。     

Mathematical Modeling of Encapsulated Buffer Performance in Sand Columns

A one-dimensional mathematical model was developed to simulate pH control using an encapsulated phosphate buffer during denitrification in a sand column. The parameters required for the model were obtained from direct physical measurement, from a tracer study to characterize the dispersion coefficient in the column, and from batch experiments designed to obtain an empirical expression describing the variation of the first-order rate constant for the encapsulated buffer core release with pH. First-order kinetic constants describing the rates of denitrification and ethanol biodegradation were obtained by fitting the model to column runs without the encapsulated buffer. With these parameters, the model was subsequently used to predict the performance of column runs containing the encapsulated buffer. Since denitrification was essentially complete in the sand columns, an increase in the effluent pH was observed. This pH increase was counteracted by the controlled release of the acidic core of the encapsulated buffers added in the columns. The model reasonably predicted the release of the encapsulated buffer core and the performance of the encapsulated buffer for controlling pH in the column.     

汾河尖草坪段河道非法采砂治理

文中讲述了汾河尖草坪段河道非法采砂的危害，并提出了治理非法采砂的措施。