水珠滴落的最小二乘粒子有限元方法模拟

提出了一种最小二乘粒子有限元方法,用其模拟了二维水珠滴落水面并飞溅散开的过程.该法基于拉格朗日描述,在每个时间步上使用扩展的Delaunay划分更新计算网格,并应用α形方法识别自由面形状;用最小二乘有限元方法离散流体运动的Navier-Stokes方程,并推导了一种自适应时间步长方案以提高计算效率和鲁棒性;引入网格拉伸技术修正减小流体质量误差.对水滴飞溅进行仿真,得到了与商用软件Flow-3d比较符合的结果,且具有更清晰锐利的自由面. 关键词： 滴落 网格划分 α形')" href="#">α形 最小二乘有限元     

垂直激励液体表面液滴的存活时间研究

液滴滴落在垂直激励的液体表面,有可能会在表面停留很长时间.本文对该现象进行了实验研究,分析了多种因素对液滴存活时间的影响.结果发现:当驱动频率、驱动振幅、液滴滴落高度处于适当的值时,可以使得液滴存活较长的时间,并且液滴的存活时间会随着液体浓度的改变而改变.     

动态光谱检测中血液散射对等效光程长变化的影响

动态光谱无创动脉血液成分检测方法,从原理上可以去除皮肤等因素带来的个体差异的影响。在使用该方法时,需要考虑血液散射的影响。采用蒙特卡罗模拟仿真方法,对人体指端脉动动脉血液的散射引起的等效光程长变化程度进行了研究,从误差分析的角度对通过动态光谱法测量血液成分浓度的下限进行了评估。     

生物力学中片流的边界元分析

用边界元方法^[1,2]研究了生物力学中肺毛细血管血液的流动,并对肺毛细血管的SFH模型,SFC模型进行了数值模拟,给出血液流动的速度场及血管壁上的面力分布和压力分布.对肺毛细管内皮细胞受的切应力,数值计算表明,正常情况下,在0~4.64×10^-5N/cm²之间,这与Dewey实验结果^[8](0~5×10^-5N/cm²)相一致,肺胞的形态将按使呼吸膜受切应力值最小为原则构形.同时,本文方法还可为数值分析心血管内的血液流动提供一种有效的数值方法,这对生物力学和医学工程是有价值的.     

基于Ward模型的低成本人造龙卷风发生装置及涡旋参量的三维测量

搭建了基于Ward模型的低成本人造龙卷风发生装置.改变进风角度、进风量可改变涡流比,产生不同形态的稳定的可视化涡旋.通过智能车带动热敏风速探头对龙卷风风场参量进行探测,分析不同涡流比下龙卷风不同高度横截面的切向、径向、纵向速度和核心半径等涡旋参量.实验结果表明,龙卷风切向风速随半径先升高后降低,纵向和径向风速随高度的增加而减小.     

血液的荧光光谱特征分析及应用研究

把荧光分析技术应用于血液分析,给出了正常血液与异常血液用不同光波激发测得的荧光光谱曲线,通过比较正常血液与血糖、血脂及胆固醇异常血样的光谱特性,分析其光谱之间的差异。实验结果表明:高血糖全血和高胆固醇、高甘油三脂血清的荧光比正常全血的强,通过荧光强度比较可判断血样是否异常;高血糖全血、高胆固醇血清都表现出特定的荧光峰位,可通过特征荧光峰检测出血清中胆固醇与甘油三脂含量的高低;通过比较Stokes位移的差异,可判断血样是否异常。文章提出的新方法,克服了传统血液检测方法的诸多不足,为血液检测分析提供一种新的途径。与传统的血液检测方法相比,文章提出的方法具有操作简单、分析方便等特点,其研究具有一定的先进性,为疾病诊断提供了有用的实验依据。     

血液激发荧光强度分析及应用

文章采用荧光分析技术, 对血液激发荧光强度进行研究。给出了有关理论分析, 并给出了正常血样与异常血样(高血糖、高胆固醇)对比实验结果。研究发现：血液中血糖的浓度影响血液的激发荧光,其大致趋势是：在相同波长的激发光激发下,随着血糖浓度的提高,血液的激发荧光强度也逐渐增强, 显然,血液中的血糖也是一种荧光物质,其浓度对血液的荧光强度的影响与理论分析相一致,这表明所得的实验结果是合理的,同时还表明了可以通过比较血液的激发荧光强度来区分血液中血糖浓度的高低;研究还发现：胆固醇含量越高,所得的荧光强度也越强。因此,根据血清的荧光强度可以知道血清中胆固醇含量的高低,尤其是当使用波长位于435 nm附近的激发光时,结果非常明显。文章提出的血液激发荧光强度分析技术,为血样快速检测及疾病诊断提供了新的途径。     

用晶格玻尔兹曼方法研究血液在分岔管中的栓塞

血液栓塞形成机理一直是学术界研究的热点.本文将以圆形刚性颗粒在分岔管中的运动模拟血液在微血管中的运动,对血液在分岔管中的栓塞现象作了初步研究.重点研究了当血管发生分岔时,血管中血液流速的变化以及血栓形成的概率.得出结论,压积越大越容易发生栓塞,压差越大越不易发生栓塞.分岔管的入口和分岔处最容易发生栓塞.血液经分岔管后,大管中的压积比小管的高.     

低能Kr+离子束诱导蓝宝石晶体实验研究

使用微波回旋共振离子源制备蓝宝石(A向)自组织纳米结构,研究不同入射角度下Kr+离子束刻蚀蓝宝石表面形成的自组织纳米结构及其形成过程.采用等离子体与离子束刻蚀设备在不同入射角度下对蓝宝石样品表面进行刻蚀并通过Taylor Surf CCI2000非接触式表面测量仪和原子力显微镜分别对刻蚀后的蓝宝石样品的刻蚀速率及表面形貌进行分析.研究表明:当离子束能量为400eV,加速电压为200V,离子束流密度为310μA/cm2时,小角度入射下,蓝宝石样品表面出现纵向尺度较小的有序点状纳米结构;随着入射角度的增加,样品表面形成条纹状纳米结构,30°时形成短程有序且纵横比为0.87的条纹状结构;入射角度继续增加,纵向高度减小直至纳米结构消失;当角度达到60°附近,蓝宝石表面又出现条纹状结构,70°时形成了短程有序且纵横比为1.07的条纹状结构.自组织纳米结构的形成先以"岛状"形式出现,随后岛上生长出条纹状纳米结构,随着刻蚀时间的增加,岛状条纹结构纵向尺度增大且有序性增强,纳米结构的横向周期不变.     

激光照射血细胞的衰变规律和损伤机制研究

采用FLS900型稳态荧光光谱仪对红色激光持续照射的正常离体血液和酒精中毒离体血液进行了荧光检测,得到了血液物质成分变化及荧光光谱特征随时间衰变的规律.研究结果表明：随着血液离体时间的延长,当407 nm的紫光激励时,在605 nm处的荧光峰峰位保持不变只是强度缓慢减弱,但两者均在离体后的14 h和10 h出现了谱形突变,并在474 nm处产生了一个强荧光峰.比较分析发现激光对正常离体血液的衰变有明显的延缓作用,对酒精作用破坏的红细胞也有部分修复功能,但当激光持续照射一定时间后却导致了细胞的形态改变进而加速了细胞的溶血进程,产生了大量的内源性荧光物质还原烟碱腺嘌呤二核苷酸.本文的研究结果能为血细胞活性衰变规律以及功能结构研究提供有意义的参考.     

Using digital anaglyphy to improve the relief effect of SEM micrographs of bloodstains

Anaglyphy is a stereoscopic technique based on the superimposition of two images of the same view, taken from slightly different angles as well as in two different colours. This superimposition produces a depth effect when viewed through glasses having one red and one green, blue or cyan lens acting as a colour filter. The nearly flat surface of a chip of grey chert was thin-smeared with peripheral human blood. Two months later, the specimen was fixed to a microscope stub as horizontal as possible, coated with gold, and examined via secondary electrons by a scanning electron microscope (SEM). After obtaining SEM micrographs, anaglyphs were digitally generated. The best results were obtained using pairs of SEM micrographs acquired at 10° differing angle and at SEM-stage tilts that were symmetric from the horizontal plane. The relief effect was more accentuated at low magnification. The most ergonomic colour combination for viewing bloodstain anaglyphs was red–cyan. Digital anaglyphy provides a simple and feasible method to improve the relief effect of SEM micrographs of bloodstains. Moreover, as a first consequence of this improvement, the results obtained in this research reveal that the outermost erythrocyte layer of a thin bloodstain – coinciding, in general, with the smear surface – can be much more uneven than that previously suggested by customary SEM micrographs.     

A monostatic illumination function with surface reflections from one-dimensional rough surfaces

When solving scattering or emissivity problems for rough surfaces, the shadowing effect is often taken into account. Furthermore, for rough surfaces with large root mean square slope, surface reflections of the incidence or emission ray should not be neglected, especially at large observation angles. In this paper, a model of the monostatic statistical illumination function for one-dimensional rough surfaces with single surface reflection is developed, which is based on the Smith illumination function. A Monte Carlo ray-tracing algorithm is used to evaluate the accuracy of the present model. It is shown that, when neglecting the correlation between heights and slopes of the surface, the present model agrees quite well with the Monte Carlo result. Moreover, the result is improved if the correlation between heights and slopes is taken into account. For practical purposes, an empirical factor is introduced to improve the performance of the uncorrelated first-order illumination function to avoid computing the correlated one, which takes a long computation time. Besides, the first-order illumination function is significant at large observation angles, which could be promising to overcome problems in models of surface infrared emissivity where underestimation occurs compared with experimental measurements.     

CFD-DEM simulation of three-dimensional aeolian sand movement

A three-dimensional CFD-DEM model is proposed to investigate the aeolian sand movement.The results show that the mean particle horizontal velocity can be expressed by a power function of heights.The probability distribution of the impact and lift-off velocities of particles can be described by a log-normal function,and that of the impact and lift-off angles can be expressed by an exponential function.The probability distribution of particle horizontal velocity at different heights can be described as a lognormal function,while the probability distribution of longitudinal and vertical velocity can be described as a normal function.The comparison with previous two-dimensional calculations shows that the variations of mean particle horizontal velocity along the heights in two-dimensional and three-dimensional models are similar.However,the mean particle density of the two-dimensional model is larger than that in reality,which will result in the overestimation of sand transportation rate in the two-dimensional calculation.The study also shows that the predicted probability distributions of particle velocities are in good agreement with the experimental results.     

近景测量系统全景彩色图像光谱法色度校正

在三维多模式扫描近景测量系统中,使用彩色线阵CCD(电荷藕合器件)可得到景物的一维线状彩色信息,将连续获得的不同角度上的一维彩色图像拼接起来即可形成全景彩色图像。直接在电脑彩色CRT(cathode ray tube, 阴极射线管)显示器上输出该图像,将发生色度失真,需要进行色度校正。通过光谱法色度校正,使得在电脑彩色CRT显示器上输出的图像和原始景物尽可能地保持色度不失真。     

Topometry for locally changing materials

Three-dimensional topometry is supplemented with ellipsometric measurements on the same pixel raster for calculation of the phase of the reflected waves and correction of the height fields. Lateral resolution is <1mum . The ellipsometric angles are determined by phase shifting and contrast evaluation. Three-dimensional fields of the ellipsometric angles, the real and the imaginary parts of the refractive index, and the corrected topography of the heights are presented.     

Using coloured structured light in 3-D surface measurement

The widest used algorithms for 3-D surface measurement using structured fringe patterns are phase stepping and Fourier fringe analysis. The techniques currently employed use mostly monochrome fringe patterns as a tool for phase information measurement and further surface reconstruction. However, the information contained in colour images is much more than that of monochrome, in this case, a new colour technique can be employed to analyse a measured scene with colour fringe patterns.This paper presents a new method for improving the measurement of 3-D shapes by using colour information of the measured scene as an additional parameter. The new method is based on primary colours (red, green and blue) to increase the number of the illuminated fringe patterns, which will remove or significantly reduce the common drawbacks of existing methods. The proposed technique produces a number of coloured structured lighting patterns, which are projected from different angles onto the scene. These patterns are analysed using masking algorithms, a specially adapted multi-colour version of the standard Fourier fringe analysis method and calibration routines. In this way a number of the standard difficulties are overcome.     

Stability limit of a granular monolayer

A granular monolayer is composed by spherical grains on a horizontal plate. The plate is then tilted until the monolayer breaks down. This critical angle has been measured for different widths and heights of the rectangular monolayer. The highest critical angles are found when one of these two characteristic lengths is less than about 30 bead diameters. When the polydispersity is less than one percent, the monolayer may be stable till angles close to 90^°. Arches induce large critical angles. On the other hand, for a large and high monolayer, the critical angle saturates towards a lower value. This angle is related to the static friction of a grain on the plate. A model based on the block dynamics is proposed to describe the behavior of the avalanche angle as a function of the size of the monolayer and the polydispersity of the beads.-1     

Effective probability density function of rough surface slopes when strong shadowing is present

It is shown that at low grazing angles, the slope probability density function (PDF) of the nonshadowed part of a rough surface can differ significantly from the slope PDF of the overall surface, if surface heights and slopes are functionally dependent. If the surface steepness has a tendency to increase with height, the effective slopes of the illuminated part of the surface can be significantly steeper than the average slope of the surface as a whole. This fact can play a crucial role in any theoretical interpretation of experimental results concerning radar scattering by the sea surface at low grazing angles.     

高速列车地面效应数值模拟研究

采用定常RANS方法对高速列车的地面效应进行分析,研究地面效应影响下高速列车气动力的变化规律.研究地面效应对不同侧偏角下高速列车气动力的影响,发现地面效应对073176;侧偏角下的气动力影响最大,并随着侧偏角的增大地面效应的影响逐渐变小;研究当列车与地面相对高度发生变化时高速列车气动力的变化规律,数值模拟结果揭示了高速列车气动升力存在的升力翻转效应,并对不同高度下列车底面的压力脉冲变化规律进行分析.     

Effective probability density function of rough surface slopes when strong shadowing is present

Abstract

It is shown that at low grazing angles, the slope probability density function (PDF) of the nonshadowed part of a rough surface can differ significantly from the slope PDF of the overall surface, if surface heights and slopes are functionally dependent. If the surface steepness has a tendency to increase with height, the effective slopes of the illuminated part of the surface can be significantly steeper than the average slope of the surface as a whole. This fact can play a crucial role in any theoretical interpretation of experimental results concerning radar scattering by the sea surface at low grazing angles.