自重湿陷性黄土地基预钻孔浸水处理的可靠度设计方法

为解决传统预浸水法存在的浸水时间长、浸水处理范围难以确定等不足,基于土体中水分运移规律,依据可靠度理论、极限状态设计方法及复合 Poisson 过程原理,提出一种消除黄土湿陷性的处理浸水方法——预钻孔浸水法。给出了利用预钻孔浸水法对自重湿陷性黄土地基进行浸水时,水平向及竖直向浸水影响范围的确定模型;在此基础上结合达西定律给出了浸水孔设计参数如孔深、孔间距及浸水孔个数的确定方法。结合铜川某工程,设计进行了现场预钻孔浸水试验,对该方法的合理性进行了验证,并通过现场钻探、现场勘探、室内湿陷性试验等方法对该方法的处理效果进行了评价。该浸水方法具有浸水时间短、浸水影响范围可根据浸水孔布设进行控制等优点,且浸水处理效果良好,完全符合施工要求。     

Mixing enhancement mechanism of combined H2–Water jets in supersonic crossflows in a combustor with an expanded section

To obtain the mixing enhancement mechanism of H₂–Water combined jets in supersonic crossflows in a combustor with expanded section for rotating detonation ramjet, the flow field shape and spray structure were studied by experimental and numerical methods. The Eulerian–Lagrangian method was used to investigate the diffusion mechanism and H₂–Water interaction law of combined jets with different sequences. At the same time, high-speed photography and the schlieren technique were used to capture the flow field. The effects of jet pressure drop, orifice diameter, orifice spacing, incoming Mach number, and other parameters on the penetration depth of water jets were studied. The results of experiment and simulation show that using H₂–Water combined jets, the penetration depth of the jet spray can be greatly increased and the jet mixing effect can be significantly improved, which will contribute to the engine's ignition and stable combustion. In the case of pre-water/post-H₂, the penetration depth of the hydrogen jet is greater. In the case of pre-H₂/post-water, the hydrogen jet raises the water spray mainly by protecting the integrity of the water column.     

Local scour at offshore windfarm monopile foundations: A review

In this article, current research findings of local scour at offshore windfarm monopile foundations are presented. The scour mechanisms and scour depth prediction formulas under different hydrodynamic conditions are summarized, including the current-only condition, wave-only condition, combined wave-current condition, and complex dynamic condition. Furthermore, this article analyzes the influencing factors on the basis of classical equations for predicting the equilibrium scour depth under specific conditions. The weakness of existing researches and future prospects are also discussed. It is suggested that future research shall focus on physical experiments under unsteady tidal currents or other complex loadings. The computational fluid dynamics-discrete element method and artificial intelligence technique are suggested being adopted to study the scour at offshore windfarm foundations.     

Analysis and proposition of limiting current density measurement protocol

Limiting current density at different temperatures, backpressures, and balance gases can be used to separate molecular diffusion resistance, Knudsen diffusion resistance and local transport resistance of membrane electrode assembly (MEA). However, the measurement of limiting current density has no unified protocol. The diverse choices in the literature, either in the control of current or voltage or in the atmosphere like relative humidity and O₂ concentrations, make it difficult to compare the results and identify the true bottleneck hindering the mass transport. In this work, the current-voltage curves obtained by current scanning/stepping and voltage scanning/stepping methods under dilute O₂ of different concentrations and a wide range of relative humidity were measured and analyzed systematically. It is found that the voltage stepping method is superior to the other three ways of control for the reliable determination of the limiting current density. Aided with simultaneous electrochemical impedance spectroscopy measurement, the limiting current density can be determined with pinpoint accuracy. When the limiting current density is just used to qualitatively evaluate different MEA, the voltage scanning method can be used instead for its high time efficiency. The selection of the atmosphere also plays an important role in suppressing the distortion from excessive water and reducing the spurious contribution from proton conduction resistance. It is found that O₂ concentrations at 0.5 vol% and relative humidity at 90% can give the best estimation of O₂ transport resistance in membrane electrode assembly.     

Establishment of a color tolerance for yarn-dyed fabrics from different color-depth yarns

Yarn-dyed fabric is often woven from warp and weft yarns in the same color depth to ensure a uniform color appearance. The difference in color depth between warp and weft tends to result in the uneven color of the yarn-dyed fabric. This article aims to establish a color tolerance for yarn-dyed fabric that can be woven with a qualified color appearance but from the warp and weft yarns in different color depths. A total of 27 yarn-dyed fabric samples in three color series (red, yellow, and blue) were evaluated by using the yarn-dyed fabric from warp and weft yarns in the same color depth of 2% (on weight of fabric, owf) as the standard. Visual assessment and instrumental measurement of color were carried out to establish the color tolerance ellipse that was defined as CMC (Color Measurement Committee) color differences (2:1) of no more than 1.00. It was found that the color strengths (K/S) and color differences (ΔE_CMC(2:1)) of these fabric samples for each color series had linear relationships with the color depths of warp and weft yarns. The color tolerance ellipses indicated that, even though the warp and weft yarns had an apparent color difference, they could be woven in fabrics with relatively uniform color appearance and meet the requirements for yarn-dyed fabric. This work provided valuable insight into the production of qualified yarn-dyed fabrics from unqualified dyed yarns.     

Color determinants of surface stratification

Although color plays a crucial role in the demarcation of surfaces in the visual field, its role in depth perception is not well understood. Certain special effects of color on depth perception that arise from optical factors such as chromatic aberration (chromostereopsis) have been studied, but less is known about the role of perceptual factors of color in determining depth relations. The present study explores the role that the different attributes of color such as hue, chroma, and lightness play in the stratification of surfaces in depth. In two experiments, subjects manipulated specific dimensions of colors (hue, chroma, lightness, and whiteness) while making judgments of coplanarity of either two or more abutting surfaces. The results demonstrate that for surfaces to appear coplanar, their lightness has to be proportional to the natural (intrinsic) lightness of the hues. No meaningful effects of chroma, whiteness, or blackness were found in depth stratification. The results suggest a primary role of the natural lightness of hues in depth perception.     

Microcrack healing in zirconia ceramics under a DC electric field/current

Flash event caused by a DC electric field/current was applied to the crack healing in 8 mol % Y₂O₃ stabilized cubic ZrO₂ polycrystals (8Y-CSZ). The flash event, which occurred by applying the DC power higher than a critical value of 100 mW/mm³, successfully healed the microcrack within several minutes without any healing agents at a furnace temperature of 800 °C. As compared to the healing treatment under static annealing, the healing phenomena were accelerated about 2 times under the flash treatment even at the same temperatures, suggesting that the enhanced healing phenomena cannot be explained only by the temperature effect. Since the rate of grain growth was accelerated under the flash treatment, the flash healing would be accelerated through the current-enhanced diffusional processes. This study shows for the first time that the flash event has a potential to apply to the crack healing process in the ceramic materials and composites.     

FeOOH–CoS composite catalyst with high catalytic performances for oxygen evolution reaction at high current density

Water electrolysis is an efficient approach for high-purity hydrogen production. However, the anodic sluggish oxygen evolution reaction (OER) always needs high overpotential and thus brings about superfluous electricity cost of water electrolysis. Therefore, exploiting highly efficient OER electrocatalysts with small overpotential especially at high current density will undoubtedly boost the development of industrial water electrolysis. Herein, we used a simple hydrothermal method to prepare a novel FeOOH–CoS nanocomposite on nickel foam (NF). The as-prepared FeOOH–CoS/NF catalyst displays an excellent OER performance with extremely low overpotentials of 306 and 329 mV at 500 and 1000 mA cm⁻² in 1.0 M KOH, respectively. In addition, the FeOOH–CoS/NF catalyst can maintain excellent catalytic stability for more than 50 h, and the OER catalytic activity shows almost no attenuation no matter after 1000 repeated CV cycles or 50 h of stability test. The high catalytic activity and stability have exceeded most non-noble metal electrocatalysts reported in literature, which makes the FeOOH–CoS/NF composite catalyst have promising applications in the industrial water electrolysis.     

Influence of anode current density on carbon parasitic reactions during electrolysis

In the electro-deoxidation process, carbon parasitic reaction (CO₃^2- + 4e^-=C + 3O^2-) usually occurs when using carbon materials as the anode, which leads to increase of the carbon content in the final metal and decrease of the current efficiency of the process. The aim of this work is to reduce the negative effect of carbon parasitic reaction on the electrolysis process by adjusting anode current density. The results indicate that lower graphite anode area can achieve higher current density, which is helpful to increase the nucleation site of CO₂ bubbles. Most of CO₂ would be released from the anode instead of dissolution in the molten CaCl₂ and reacting with O^2- to form CO₃^2-, thus decreasing the carbon parasitic reaction of the process. Furthermore, the results of the compared experiments show that when the anode area decreases from 172.78 to 4.99 cm², CO₂ concentration in the released gases increases significantly, the carbon mass content in the final metal product decreased from 1.09% to 0.13%, and the current efficiency increased from 6.65% to 36.50%. This study determined a suitable anode current density range for reducing carbon parasitic reaction and provides a valuable reference for the selection of the anode in the electrolysis process.