CONCAVE BIOLOGICAL SURFACES FOR STRONG WET ADHESION

Plant leaves, insects and geckos are masters of adhesion or anti-adhesion by smartly designed refined surface structures with micro- and nano- ＇technologies＇. Understanding the basic principles in the design of the unique surface structures is of great importance in the manufacture or synthesis of micro- and nano- devices in MEMS or NEMS. This study is right inspired by this effort, focusing on the mechanics of wet adhesion between fibers having concave tips and a flat substrate via capillary forces. We show that the concave surface can effectively enhance the wet adhesion by reducing the effective contact angle of the fiber, firmly pinning the liquid bridge at its circumferential edge. A critical contact angle is identified below which the adhesion strength can achieve its maximum, being insensitive to the contact angle between the fiber and liquid. The analytical expression for the critical angle is derived. Then a tentative design for the profile of concave surfaces is proposed, considering the effects of chamfering size, deformation and buckling, etc. The effect of liquid volume on the wet adhesion of multiple-fiber system is also discussed.

Influence of depth-thickness ratio of mining on the stability of a bedding slope with its sliding surface in concave deformation

In order to study the influence of depth-thickness ratio on bedding slope stability, whose sliding surface is flexural concave in shape under mining conditions, this paper aims to study the characteristics ofdeformarion and damage of bedding sliding with depth-thickness ratios of 200：1,150：1,120：1,100：1 and 50：1 by adopting numerical simulation analysis software combined with laboratory-made ＂under the influence of mining variable sliding surface slope similar simulation test bed＂, and to propose identification methods for slope stability under the infuence of mining. The results show that mining activities under the slope reduce slope stability. With a decrease in the mining depth ratio, the influence of mining on the slope increases gradually, and the damage to the slope gradually expands, the stability of the slope grad- ually reduces, fracture occurs on the slope toe and the central fissure gradually develops to the surface, and reaches slide threshold when the depth-thickness ratio is 50：1.

Boundary Layer Development on a Concave Surface： Flow Visualization and Hot Wire Velocity Measurements

Gortler vortices are key issues in the design of gas turbine blades. The present study deals with flow visualization over concave surface for gas turbine applications. The aim is to comprehend qualitatively the flow trends, particularly the Gortler vortices formation and development. Gortler vortices have the shape of mushroom-like vortices regularly spaced at 25 mm. These vortices grow and increase in strength more rapidly along the surface in the case of the same grid of turbulence applied to the measuring section. The curvature radius of the studied blade is 0.5 m and the stream turbulence intensity level is 2.6%. The velocity field is measured by hot wire anemometer in the streamwise direction. The velocity profile is found to be highly distorted by the momentum transfer associated with Gortler vortices. The results are compared to Blasius flow and to literature data for a blade with curvature radius equal to 2 m.

Effect of Shape of the Absorber Surface on the Performance of Stepped Type Solar Still

In this work, we have selected three number of stepped type solar stills of the same overall dimensions 620 mm (W) × 808 mm (L) but with different absorber surface areas due to the variation in the shape of the basin surface. The other design parameters like depth of water, thickness of glass cover, insulation thickness, type of condensing cover, absorbing material provided over the basin, and angle of inclination of the still were kept constant to study the effect of shape of the absorber surface over the distillate yield obtained. The shape of the absorber surface provided in the basins of solar stills A, E and F was flat, convex and concave respectively. When the convex and concave type stepped solar stills are used, the average daily water production has been found to be 56.60% and 29.24% higher than that of flat type stepped solar still respectively. Also an economic analysis was made. The payback period of flat type, convex type and concave type stepped solar still is 823 days, 525 days and 637 days respectively. Thus, the convex type solar still gives the returns within the least possible time as compared to other two types of stepped solar stills. The laboratory tests were conducted to test the quality of water after distillation. The tests indicate that the quality of water in terms of pH, electrical conductivity, total hardness, TDS, Alkalinity, Nitrates etc. is well within the desirable limits as prescribed by WHO for Indian specific conditions.

考虑安装误差的弧齿锥齿轮凹凸齿面印痕修正

弧齿锥齿轮作为重型燃气轮机中关键的动力传动部件,其双向传动的运行特点对齿轮凹凸齿面的接触印痕提出了更高的质量要求。为了满足实际需求,通过建立齿面啮合模型,利用考虑安装误差的齿轮接触分析(error tooth contact analysis, ETCA)技术研究了一对弧齿锥齿轮凹面和凸面均为工作面时,接触印痕随安装误差变化的数值规律。同时,以齿面印痕的中点位置、长轴倾角和面积作为印痕参数化处理后的特征值,优化齿轮安装误差调整值,修正印痕的不合理之处,实现凹凸齿面印痕的一致性和重叠性。滚检实验验证了模拟印痕的准确性,该修正规律可以为弧齿锥齿轮副的安装调整提供理论依据。

偏转激光切向修整凹形面金刚石倒角砂轮的研究

为了减小凹形面金刚石砂轮的激光修整误差,建立激光遮蔽效应和激光斜面分散效应误差模型,分析了激光切向修整凹形面金刚石砂轮的误差来源,提出了偏转激光修整凹形面成形砂轮法,并通过理论分析和实验验证,探索了修整参数对凹形面砂轮轮廓精度和圆弧半径的影响。结果表明,在1°~1.5°的偏转角范围内,斜边轮廓修整精度为8μm;在合适的偏转角度下,圆弧半径误差小于10μm;在修整凹弧半径为0.2 mm和0.5 mm、补偿半径分别为0.03 mm和0.06 mm时,凹弧半径误差分别缩小0.02 mm和0.03 mm。偏转激光修整法有效地提高了修整精度,减小了修整误差,为凹形面金刚石修整提供了新思路。

联排凹曲面屋盖的风荷载特性试验研究

为了探究凹曲面屋盖的风荷载特性并为实际工程提供抗风设计参考,对3种联排凹曲面屋盖进行刚性模型风洞测压试验,系统分析联排数及风向角对凹曲面屋盖升力系数、平均风压系数和极值风压系数的影响.结果表明:屋盖整体升力系数随着联排数的增加不断降低,各屋盖的升力系数受风向角影响较大.在不同联排数及风向角下,屋盖整体承受向上的风吸力,屋盖的平均风压系数表现出复杂的波动性;在迎风屋盖边缘处的气流分离现象明显,导致该处存在较大风吸力;越远离迎风侧的屋盖,平均风压系数的波动越小,稳定于-0.1.联排数对极值风压系数的影响不可忽略,尤其是极小值负压系数,边缘屋盖分区极小值负压系数的最小值为-5.1,中间屋盖分区极小值负压系数的最小值为-3.3.基于试验结果,总结给出不同联排凹曲面屋盖分区的平均风压系数和极值风压系数.

乌珠穆沁沙地聚乳酸纤维沙袋沙障地表蚀积特征

沙障的蚀积特征对其发挥防护作用具有重要影响。为探究聚乳酸纤维(polylactic acid fiber,PLA)沙袋沙障对乌珠穆沁沙地沙化治理的效果,设置0.5 m×0.5 m、1.0 m×1.0 m、2.0 m×2.0 m和3.0 m×3.0 m共4种规格的聚乳酸纤维沙袋沙障,采用悬测法测量障格内部凹曲面形态,并分析不同规格沙障内部凹曲面的形态特征、蚀积效应。结果表明,沙障凹曲面中心风蚀深度随沙障规格的增大由5.17 cm增加到21.23 cm,而堆积强度随沙障规格的增大由3.86 g·cm^(-3)降至0.42 g·cm^(-3),障格内由堆积变为风蚀;蚀积系数稳定在1/9~1/8,随沙障规格的增大蚀积系数逐渐减小;障格内风蚀最深点随主风向偏移,障格内与主风向一致的方位风蚀量更大,剖面曲线开口更大;坡顶处凹曲面拟合效果大于坡中和坡底。综上所述,在乌珠穆沁沙地内,风蚀多发生在西北-东南和西-东方向上,且坡顶处形成的凹曲面较稳定,该地区适合布设2.0 m×2.0 m规格PLA沙障,研究结果为PLA沙障在乌珠穆沁沙地防沙工程中的合理应用提供了科学参考。

双曲面球型减隔震支座震后自复位性能研究

为研究桥梁双曲面球型减隔震支座的震后自复位性能并评价现有表征方法,采用公式推导、试验和有限元计算方法,综合对比分析支座的静态残余位移和震后残余位移。基于支座结构推导静态残余位移理论公式,并以竖向设计承载力5000 kN支座为例,进行支座自复位性能的拟静力试验验证;进行双曲面球型减隔震支座模拟地震振动台试验,分析静态残余位移和震后残余位移的差别;以32 m跨典型铁路混凝土简支箱梁为背景,建立MIDAS Civil有限元模型,通过非线性时程分析方法,分析单次和连续2次地震波输入工况下支座的震后残余位移和自复位能力。结果表明:支座静态残余位移为支座等效曲率半径与支座等效摩擦系数的乘积,支座自复位性能的静态残余位移与理论值较为符合,二者偏差为4.92%;振动台试验和非线性时程分析下的支座震后残余位移平均值均为2 mm左右,均低于静态残余位移的5%;双曲面球型减隔震支座支承下的桥梁减隔震体系可以避免产生累积性的震后残余位移,具有强复位能力,而目前用静态残余位移来评价双曲面球型减隔震支座的震后自复位性能较为不妥。

关于试验容器及试验油量对家用便携式凹面电磁灶输入功率影响的探讨

检测人员在依据现行国家标准GB 4706.29-2008《家用和类似用途电器的安全便携式电磁灶的特殊要求》第10章输入功率和电流对家用便携式凹面电磁灶进行输入功率试验时,对同一凹面电磁灶使用不同尺寸的试验容器及不同容量的油量进行输入功率试验,检测结果存在一定差异,从而影响符合性判定。经过对电磁灶的相关标准研究发现,对带有非平面灶面的电磁灶,试验容器采用企业提供的配锅,但试验油量正在考虑中。本文通过研究不同尺寸的试验容器及不同容量的油量对同一家用便携式凹面电磁灶输入功率试验结果的影响,旨在找到输入功率与试验容器及试验油量的关联性,为家用便携式凹面电磁灶输入功率试验中标准试验油量的确定提供参考。

Experimental study of single-row chevron-jet impingement heat transfer on concave surfaces with different curvatures

To address the curvature effect on single-row chevron-nozzle jet impingement heat transfer on concave surface,a series of experiments are conducted in the present investigation.Four concave surfaces including one semi-cylindrical concave surface and three parabolic concave surfaces with different width-to-depth ratios are tested under three typical Reynolds numbers(Re=5000,10000 and 15000)and several dimensionless nozzle-to-surface distances ranging from 1 to 8.The results show that the concave curvature has a clear impact on chevron-nozzle jet impingement heat transfer,tightly dependent on jet Reynolds number and impinging distance.In general,the semicylindrical concave surface produces the highest longitudinally-averaged Nusselt number at the leading line of concave surface.Under a low jet Reynolds number,the parabolic concave surface with a highly curved curvature produces higher longitudinally-averaged Nusselt number at the leading line and more uniform longitudinally-averaged Nusselt number distribution along the curvilinear direction.However,the longitudinally-averaged Nusselt number at the leading line of concave surface is the lowest for the highly curved surface under a high jet Reynolds number and large impinging distance.In comparison with the round-nozzle,chevron nozzle plays a more significant role on improving jet impingement heat transfer at small impinging distances.

Experimental study of curvature effects on jet impingement heat transfer on concave surfaces

Experimental study of the local and average heat transfer characteristics of a single round jet impinging on the concave surfaces was conducted in this work to gain in-depth knowledge of the curvature effects.The experiments were conducted by employing a piccolo tube with one single jet hole over a wide range of parameters：jet Reynolds number from 27000 to 130000,relative nozzle to surface distance from 3.3 to 30,and relative surface curvature from 0.005 to 0.030.Experimental results indicate that the surface curvature has opposite effects on heat transfer characteristics.On one hand,an increase of relative nozzle to surface distance（increasing jet diameter in fact）enhances the average heat transfer around the surface for the same curved surface.On the other hand,the average Nusselt number decreases as relative nozzle to surface distance increases for a fixed jet diameter.Finally,experimental data-based correlations of the average Nusselt number over the curved surface were obtained with consideration of surface curvature effect.This work contributes to a better understanding of the curvature effects on heat transfer of a round jet impingement on concave surfaces,which is of high importance to the design of the aircraft anti-icing system.

Convective heat transfer on flat and concave surfaces subjected to an impinging jet form lobed nozzle

A tri-dimensional lobed nozzle is concerned in the jet impingement on a flat target and a concave target in the current study. The jet impingement heat transfer experiments are conducted under two jet Reynolds numbers(Re=10000 and 20000) and four nozzle-to-surface distances(H/d=2, 4, 6 and 8). Simultaneously, to characterize the flow dynamics of lobed jet impingement onto different target surfaces, some computations are conducted under a specific jet Reynolds number. The results show that the lobed jet is capable of achieving an increase of stagnation Nusselt number about 25% in relative to the round jet at small nozzle-tosurface distances. However, at large nozzle-to-surface distances, the lobed jet otherwise weakens the convective heat transfer in the vicinity of jet stagnation, especially under high jet Reynolds number. When compared to the flat target, approximately a20%–30% reduction of stagnation Nusselt number is produced on a concave target, which is attributed to the combined effect of destabilization and confinement due to the concave curvature.

NUMERICAL SOLUTIONS OF REYNOLDS AVERAGED NAVIER-STOKES EQUATIONS FOR 3-D TURBULENT FLOW OVER CONCAVE SURFACES OF DISCHARGING STRUCTURES

This paper is conserned with a numerical method for the solution of complete Reynolds averaged Navier Stokes equations for three dimensional flows over the concave surfaces of discharging structures. A non orthogonal body fitted coordinate system was used to deal with the complex physical geometry, and finite volume method (FVM) was employed to solve the convective transport equations for mean velocities and turbulence parameters (k, ε). It is indicated through the numerical example that the calculated results are in good agreement with the experimental ones, and it is also proved that this numerical method used to predict the characteristics of turbulent flow over the concave surfaces of discharging structures is feasible.

基于响应曲面分析的纬编3D凹孔针织物保暖性能研究

为探究组织结构设计参数对纬编3D凹孔针织物保暖性能的影响,拓展3D凹孔针织物在保暖服装中的应用。首先运用控制变量与正交试验法,采用DRYAERN^(■)纱线与氨纶纱线,改变组织循环内吊针路数、连续成圈针数及平针路数3个设计参数,织造成15种3D凹孔针织物,测试其厚度与克罗值;其次基于响应曲面法分析3个参数对织物保暖性能的影响并建立关于克罗值的数学回归模型。结果表明:3个参数中对织物保暖性能影响最为显著的是吊针路数,其次是平针路数,最小的是连续成圈针数;连续成圈针数与平针路数的交互作用对织物保暖性能有显著影响,相关回归模型的拟合精度较高;研究为开发保暖性能优良的3D凹孔针织物提供了高效的工艺参数方案。

基于等残留高度的数控加工刀具轨迹规划方法

刀具轨迹规划是复杂工件曲面制造与加工中的核心环节,对于工件成品质量有着极其重要的影响。为获得加工性能良好、较为光顺的刀触点轨迹,设计一种基于等残留高度的数控加工刀具轨迹规划方法。考虑曲面的曲率变化,首先,以减小相邻两个轨迹线间的依赖性为目的,利用等残留高度法规划刀具的移动轨迹。为使刀触轨迹线能够达到自由曲面边界,设计基于密切圆追踪的边界处理方法,实施简单的延伸处理。通过设定的距离判定条件与角度判定条件实施奇异折线点的判定,实现刀具轨迹的奇异波动处理,使所生成的轨迹过渡平缓、光滑连续,真正具备较好的加工性能。测试结果表明,设计方法的残留高度值主要分布在0.2~0.25这一区间内,占比达到53.28%,而0.25~0.3的占比较低,说明该方法能够充分地利用残留允差,有着较高的加工效率。

滚花机构中凹辊曲面图案的3D建模及多轴加工

该文主要对滚花机构中凹辊曲面结构进行了3D建模设计与创新,同时研究并优化了凹辊滚花图案的多轴加工工艺,主要包括刀轨设计、刀具选用、切削参数设置,最终形成了集3D设计到多轴加工的高质量加工策略。实验数据分析结果表明,此加工策略可有效提高滚花机构中凹凸辊曲面加工质量,提高加工效率,具有广阔的市场应用前景。

仿生凹坑间距对高速磁悬浮列车气动减阻影响研究

对车尾后缘布置仿生凹坑的高速磁悬浮列车进行数值模拟,研究仿生凹坑间距对磁悬浮列车气动性能的影响。研究结果表明,当气流流过尾车流线型前端仿生凹坑时,会在凹坑内部产生高速涡旋,使得车尾附近产生高速回流,增大尾车表面的正压区域面积,且凹坑间距越小,高速回流区范围越大,正压区域也越大。同时仿生凹坑对尾流涡旋有收紧、沉降作用,还会使得尾涡强度降低。当仿生凹坑间距过于密集,凹坑间距小于2.4×10^(-2)H(H为列车高度),整车阻力会增加;当凹坑间距增大至2.4×10^(-2)H~6.0×10^(-2)H,整车减阻率随凹坑间距增大而持续增大至2.66%;当凹坑间距进一步增大至7.2×10^(-2)H,整车减阻率下降为1.6%。

旋带掩模电解织构化圆柱表面及其润湿性分析

在圆柱面工件上高效、低成本地创制功能化极端润湿性表面仍面临重大技术挑战。对此提出旋带掩模电解织构技术。该技术直接选用市售带状柔性电绝缘多孔高分子编织布为活动掩模,以中性盐Na NO3溶液为电解液,基于旋带电解印制方式对金属圆柱表面进行织构化处理。介绍其工作原理,分析圆柱表面微织构形貌与几何廓形的演化过程,试验探究极间电压、旋带速度、加工次数等对表面织构特征的影响,评测氟化后的不同微结构特征的织构化表面的润湿性。结果表明:圆柱表面织构特征显著受加工次数的影响,随加工次数的增加,圆柱表面经历“反复复制”掩模印制阵列凹凸微结构、阵列凹凸微结构叠错-细化、微纳米分级结构分级化等表面微织构化演化过程;用时仅需249 s制备的外径49 cm、长50 cm的SUS304圆柱面(氟化后)微-纳米分级结构表面对水/甘油/十六烷的接触角分别为160.4°、158.5°、153.6°、滚动角分别为2.1°、5.6°、8.6°;呈现优异的超双疏极端润湿性且机械耐久性好。旋带掩模电解织构技术在圆柱面工件制取机械耐久性极端润湿性功能表面方面呈现高效、低成本、便于实施等优势。

几何特征引导的物体点云模型多层级分割

扫描物体点云的大量出现使得点云表面形状分析成为计算机图形学领域的研究热点。结构提取、形状编辑以及人-物交互等许多任务都需要尽可能精细的点云部件分割。由于浅层几何特征不易提取、形状缺失和噪声干扰等问题,扫描点云模型的部件分割(尤其细小部件实例检测)相对困难。因此,提出一种几何特征引导的物体点云模型多层级部件实例分割方法,根据点云表面局部弯曲程度提取凹、凸和边界特征,首先沿全局最显著凹线分割模型大致结构,再筛选几何特征差异明显的片段根据局部较浅特征进行细分,最后针对部分片段进行凹-凸协同分割,得到多层级分割结果。沿着由深到浅的几何特征,进行由粗到细的三次分割,能够更好地兼顾尺度不一的部件,实现了更细粒度的部件实例分割。实验结果表明,该方法在真实物体扫描点云和CAD物体模型采样点云上达到了较理想的分割效果,为真实物体点云部件分割提供了更精细且有效的方法。