Prediction of curved oil–water interface in horizontal pipes using modified model with dynamic contact angle

In this study,interface shapes of horizontal oil–water two-phase flow are predicted by using Young-Laplace equation model and minimum energy model.Meanwhile,the interface shapes of horizontal oil–water twophase flow in a 20 mm inner diameter pipe are measured by a novel conductance parallel-wire array probe(CPAP).It is found that,for flow conditions with low water holdup,there is a large deviation between the model-predicted interface shape and the experimentally measured one.Since the variation of pipe wetting characteristics in the process of fluid flow can lead to the changes of the contact angle between the fluid and the pipe wall,the models mentioned above are modified by considering dynamic contact angle.The results indicate that the interface shapes predicted by the modified models present a good consistence with the ones measured by CPAP.

Prediction of loess soil-water characteristic curve by mercury intrusion porosimetry

Mercury intrusion porosimetry(MIP)is a simple and fast way to obtain the pore distribution of soil and can be used to estimate the soil-water characteristic curve(SWCC).In previous studies,soil was assumed to be a perfect wettability material,and the contact angle(CA)of the soil-water interface was taken as zero in the SWCC prediction method.However,the CA has proved to be much greater than zero even for hydrophilic soils according to some soil wettability experiments,and it has a significant effect on predicting the SWCC.In this research,a method for predicting the SWCC by MIP,which takes the CA as a fitting coefficient,is proposed.The pore size distribution curves are measured by MIP,and the SWCCs of two loess soils are measured by pressure plate and filter paper tests.When the CA is taken as70°and 50°for the wetting and drying process,respectively,the SWCCs predicted by the pore size distribution curves agree well with the measured SWCCs.The predicted suction range of the proposed method is 0-105 k Pa.The consistency of the results suggests that utilizing the MIP test to predict the SWCC with a proper CA is effective for loess.

A new slope optimization design based on limit curve method

A new method is proposed for slope optimization design based on the limit curve method, where the slope is in the limit equilibrium state when the limit slope curve determined by the slip-line field theory and the slope intersect at the toe of the slope. Compared with the strength reduction (SR) method, finite element limit analysis method, and the SR method based on Davis algorithm, the new method is suitable for determining the slope stability and limit slope angle (LSA). The optimal slope shape is determined based on a series of slope heights and LSA values, which increases the LSA by 2.45°-11.14° and reduces an invalid overburden amount of rocks by 9.15%, compared with the space mechanics theory. The proposed method gives the objective quantification index of instability criterion, and results in a significant engineering economy.

Experimental study on pressure fluctuation characteristics of slug flow in horizontal curved tubes

In order to study the pressure characteristics of slug flow in horizontal curved tubes,two kinds of curved tubes with central angle 45° and 90° respectively are studied,of which are with 0. 5m circumference and 26 mm inner diameter are used. When the superficial liquid velocity or the superficial gas velocity is constant,the pressure fluctuations and the probability distribution of the average velocity of slug flow are clear for all of the five experimental conditions. The results of experiment show that the pressure characteristics of slug flow in curved tubes have periodic fluctuations. With the rise of central angle,the period of pressure fluctuation is more obvious. The system pressure of the slug flow increases with the increasing of superficial liquid/gas velocity. Meanwhile,the probability distribution of pressure signal shows regularity,such as unimodal,bimodal or multimodal.

Research on Light Response Curve Fitting Model of Four Chamaenerion Plants on the Serzilla Mountains

In order to study the applicability of different light response models to the photoresponse curves of four species of Chamaenerion, four species of Chamaenerion collected from Serzilla were used as test materials. Four common photosynthetic models were used to fit the photosynthetic response curve of the leaves. The results show that: 1) The effect of different photosynthetic response models on photosynthetic response curve of the genus chromasia was different. The fitted value of the correction model of right angled hyperbola was closest to the measured value, the R2 was 0.998, and RE was 0.216. 2) In terms of fitting the photosynthetic parameters, the initial quantum efficiency, light compensation point and dark respiration rate were suitable for fitting with non-right angle hyperbolic model. In terms of fitting the photosynthetic parameters, the initial quantum efficiency, light compensation point and dark respiration rate were suitable for fitting with non-right angle hyperbolic model. 3) The photosynthetic characteristics of C. angustifolium subsp. circumvagum reflect the negative response to high altitude radiation. Under strong radiation, the photosynthetic rate, apparent quantum efficiency, and light saturation point are low. On the other hand, C. conspersum has a positive response to high altitude radiation. C. angustifolium and C. latifolium has a higher light compensation point and higher light saturation point, but it is also positive for high altitude radiation. The response is only a choice of light intensity at different elevations, which also explains the distribution of C. angustifolium and C. latifolium in the salmonella with a single elevation, habitat, and slope.

Experimental study on the influence of hydrostatic stress on the Lode angle effect of porous rock

To investigate the deformation mechanisms of rock under hydrostatic stress, destructive experiments were conducted on sandstone under different levels of hydrostatic stress and stress Lode angles. The results reveal that the shape of the strength envelope on the π plane gradually changes from the shape of the Lade criterion to the shape of the Drucker-Prage criterion with an increase in hydrostatic stress.Normally, there exists a deviation between the strain and stress paths for porous rocks on the π plane,and the deviation decreases with an increase in stress Lode angle and hydrostatic stress. A rock failure hypothesis based on the rock porous structure was proposed to investigate the reasons for the abovementioned phenomena. It was found that the shear expansion in the minimum principal stress direction is the dominant factor affecting the Lode angle effect(LAE);the magnitude of the hydrostatic stress induces the variation of the porous structure and influences the shear expansion. Therefore, the hydrostatic stress state affects the LAE. The failure hypothesis proposed in this paper can clarify the hydrostatic stress effect, LAE, and the variation of the rock strength envelope shape.

复合多聚磷酸改性沥青混合料动态力学性能

为研究多聚磷酸(polyphosphoric acid,PPA)+SBS复合改性沥青混合料的动态力学性能,采用单轴压缩动态模量试验,分析温度和频率对动态模量和相位角的影响,并基于改进Havriliak-Negam(i HN)模型构建动态模量和相位角主曲线,同时与SBS改性沥青混合料相对比。结果表明:2种沥青混合料动态模量和相位角随温度和频率的变化呈现相同的趋势,HN模型可准确拟合2种沥青混合料的动态模量和相位角主曲线。相较于SBS改性沥青混合料,PPA+SBS复合改性沥青混合料的相位角在-10、20、50℃时均降低,而动态模量在-10℃时降低,20℃时变化较小,50℃时增加;较宽频域范围内,PPA+SBS复合改性沥青混合料在高温低频下动态模量变大,相位角变小,在低温高频下动态模量变小,相位角变化不大;PPA+SBS复合改性沥青混合料具有更优的动态力学性能。

基于转向架航向角的既有铁路平面线形识别方法研究

轨道平面线形识别是解算轨道不平顺的基础。针对外挂式动态轨道检查仪的实际需要,提出一种基于转向架航向角的铁路平面线形识别方法。首先,通过分段试拟合判定准则自动识别各测点所属线元类型和特征点数量;然后,建立基于转向架航向角的平面线形特征点优化模型;最后,结合云模型改进传统遗传算法的搜索策略提出云遗传算法,实现铁路平面线形精确识别。研究表明,平面线路曲线特征点识别偏差在4 m以内,线形识别准确度均达到97%以上,满足外挂式动态轨道检查仪对轨道不平顺解算的精度要求。

基于压力角的摆线针轮齿廓曲线优化方法

根据摆线针轮传动理论,提出一种基于压力角的齿廓优化方法。将摆线针轮齿廓分为工作段与非工作段,区分影响工作段压力角的因素为修形参数与设计参数,讨论两类参数对压力角的影响,以此两类参数为设计变量,以工作段平均压力角为目标函数,以运动与润滑要求确定边界条件,对RV⁃550E型减速器摆线轮进行优化设计。结果表明,此方法使算例的工作段平均压力角降低了4.14%,使单齿啮合过程的压力角最大值降低了1.35%,优化前后接触齿对最大Mises应力下降了20.77%,发生位置由摆线轮转移至针轮,模型质量减小了9.38%,在确保无根切现象的同时能获得良好的组合修形效果。

一种变速度条件下控制攻击角度和时间的制导律

对攻击角度和时间进行控制,可以使得多枚导弹按照特定的角度和时间对目标进行打击,在军事上有广泛的应用前景.目前已有控制攻击角度和时间的制导律极少考虑速度变化的情况,在实际运用中具有较大的局限性.本文基于贝塞尔曲线加直线的二段式轨迹,首先分析并证明了该轨迹长度和最大曲率的变化规律,在此基础上,通过二分法确定初始轨迹,针对飞行过程中的诱导阻力和其它扰动,设计了Bezier-PI控制算法,通过动态调整轨迹长度来实现攻击时间的高精度控制.该制导算法计算量小,鲁棒性强,适用于弹载计算机实时计算.通过仿真实验,验证了该算法可以高精度的控制攻击时间以及攻击角度.

防弹头盔用三维机织预制体的曲面成型性研究

三维机织预制体(Three Dimensional Woven Preforms,3DWP)因其较好的成型性和显著的层间承载能力,有望实现头盔曲面一体化成型,减少裁片与原材料浪费。因防弹头盔多曲面、高曲率的结构特点,研究3DWP在曲面成型时的变形机制对于指导头盔的一体化成型至关重要。一种衬经层层角连锁3DWP在高曲率、大变形时的曲面成型性被系统地研究,从面内与层间维度、宏细观尺度全面地阐述了3DWP的变形机理和褶皱缺陷的形成机制。实验结果表明:3DWP在成型过程中同纬度下沿45°方向的面内剪切变形最明显,凹面的最大面内剪切角为38°,大于凸面的35°;3DWP经纱列和纬纱列的最大层间剪切角分别为34.83°和27.76°;成型后3DWP已达到其面内剪切锁紧角62°,细观上诱发了纱线的屈曲,宏观上形成了脊形的褶皱;在褶皱区域,面内剪切角最大值仅为4.8°,层间剪切角最大值为18°。对实际应用中防弹头盔增强织物结构选择以及成型工艺具有指导意义。

改进丰富卷积特征算法的液滴边缘检测模型

液滴图像边缘的高精度提取是测量水接触角较为关键的一环,针对常规边缘提取方法噪声鲁棒性差、边缘提取不完整、精度低的问题,本文提出了一种改进丰富卷积特征(RCF)的液滴边缘检测模型。首先,在深度特征提取阶段引入特征融合模块,使用多个特征让模型更加鲁棒,减少过拟合的风险;其次,设计多感受野模块代替RCF后边的contact层,通过多个感受野来提取更多的语义信息,使边缘细节更加丰富;然后,在模型每一层之前引入高效通道注意力机制,增强模型对图像中重要特征的关注程度;最后,设计并引入MaxBlurPool下采样技术,减少计算量和参数量,提高平移不变性。在自制液滴数据集上的实验结果表明,本文模型的固定轮廓阈值(ODS)提高到0.816、单图像最佳阈值(OIS)提高到0.829、检测准确率高达90.17%,相较原模型提高了1.85个百分点,能够准确检测液滴边缘特征。

材料表面润湿性对超微量胶液分配及封装效果的影响

为了在微纳元件的封装中实现pL级超微量胶液的分配,根据不同材料表面具有不同表面润湿性的性质,提出了一种微纳量级的点胶方法。首先,使用自主搭建的超微量点胶系统进行pL级胶液分配实验,该系统点样的平均体积误差≤±1.1%,转移液滴的最小体积约为19.6 pL;然后,通过改变表面润湿性的单因素实验分析接触角对胶液转移量的影响,实验结果表明,接触角可以直观反映材料表面的润湿程度,即接触角越小,表面润湿性越好,转移液滴体积越大;最后,根据接触角与转移液滴体积的实验数据进行非线性曲线拟合,推导出了转移液滴体积预测公式,利用该公式预测的转移液滴体积与实测体积之间的平均差异率为2.32%。

钢结构半刚性连接节点研究现状

半刚性连接具刚度、延性和载荷能力,抗震性能优越,施工难度低,是实用且经济的连接方式。但半刚性连接受力复杂,力学特性分析难度大,且国内规范中缺乏针对性的分类标准和设计方法。综合国内外文献规范,简述了梁柱节点的分类及特点,详细介绍了钢结构半刚性节点连接类型、研究方法和研究成果,通过分析当前研究进展,指出未来所需研究的问题与方向,为钢结构半刚性节点研究、设计与实际运用提供思路与参考。

基于相对速度矢量控制的机动目标角度约束拦截制导律

为提高导弹在攻击角度约束下对机动目标的拦截效能,提出了一种基于相对速度矢量控制的制导策略。通过运动矢量合成建立了虚拟的相对运动坐标系,将常速拦截机动目标问题转化为变速攻击静止目标问题,并基于二阶贝塞尔曲线设计了满足相对航迹角约束的相对运动轨迹,使用轨迹跟踪算法生成制导指令以控制相对速度矢量。仿真结果验证了所提制导律的有效性和优越性。

计及质心侧偏角动态自适应的无人驾驶汽车横坡弯道跟踪控制

针对无人驾驶汽车在横坡弯道处因发生偏离期望轨迹甚至严重侧滑而失去稳定性的问题,提出质心侧偏角动态自适应控制策略。为应对汽车垂直载荷发生变化而导致轮胎侧偏刚度改变的情况,通过多组数据拟合得到载荷匹配图,进而设计基于模型预测算法的横向轨迹跟踪控制器,根据汽车入弯速度选择预测时域并结合道路弯度选择瞬态、稳态质心侧偏角,通过在线优化生成最佳前轮转角。最后搭建CarSim/Simulink联合在线仿真系统和实车系统进行验证,结果表明:所提控制策略能够保证汽车在横坡倾角为7%左右及弯道路面下不会出现严重的侧滑,从而提高了无人驾驶汽车在横坡弯道跟踪任务中的跟踪精度,使汽车具有良好的横向稳定性。

应用于光纤的高压隔离开关状态识别技术

为了解决传统高压隔离开关状态检测方法中无法直接获取分合闸状态的问题,设计了一种应用于光纤的高压隔离开关角度测量传感器,通过最小二乘法,对传感器的输入输出特性曲线进行拟合,采用曲线拟合法进行非线性补偿,以降低传感器的非线性误差。并建立了基于二元回归分析的温度补偿模型对传感器进行温度补偿。实验结果表明:采用曲线拟合法进行非线性补偿后,传感器的非线性误差从15.7%降至5.7%。进行温度补偿后的零位温度系数降低了近3倍,灵敏度温度系数降低了9倍以上,相对误差降低了4.52个百分点,且传感器的平均绝对误差为0.49%,满足设计需求。

高速公路线形设计研究

高速公路线形设计是高速公路建设中的关键环节,其设计质量直接关系到道路的安全性、舒适性和经济性。论文阐述了高速公路线形设计的基本理论,包括高速公路线形设计基本概念、基本原则及影响因素,讨论了高速公路线形设计要点,包括平面线形、纵断面和平纵面设计。

盘扣式模板支架节点安全性能试验及数值模拟研究

盘扣式模板支架是一种由国家大力推崇的新型模板支架。盘扣节点的转动刚度对于盘扣式钢管脚手架的稳定承载力起着重要作用。但现有研究均未考虑盘扣节点顺/逆时针转动刚度差异对模板支架承载力的影响。为验证数值模拟所得盘扣节点力矩-转角曲线的准确性,通过对盘扣式支撑脚手架水平杆与立杆连接处节点进行试验研究,考虑顺、逆时针加载两种方案,依据试验结果得出两种方案下的支撑脚手架半刚性节点的M-θ曲线,基于有限元方法对盘扣节点的转动刚度性能进行了数值研究。结果表明:逆时针转动的承载能力和转动刚度均大于顺时针转动的情况,考虑顺/逆时针转动刚度差异的完整力矩-转角曲线更适用于盘扣式钢管脚手架稳定承载力计算;试验验证了有限元法在模拟盘扣节点加载过程中的适用性,证明了有限元方法在研究盘扣节点力学性能方面的适用性和有效性。

伏龙大桥工程路线与阻水率设计总结

伏龙大桥受地理位置限制,有许多控制设计的关键因素需从方案阶段就开始充分考虑。为使防洪评价报告能顺利通过相关审批,在桥梁路线优化设计时,就要充分考虑关键因素阻水率的影响,规划路线经过局部优化,以避免大斜交。从方案设计到施工图阶段,阻水率这一指标在路线优化和总体方案确定的过程中,起到了决定性作用。防洪评价过程中的阻水率对设计路线和方案近乎有“一票否决权”。故从方案阶段开始关注阻水率,避免了方案返工。优化阻水率可从跨径、桥墩尺寸、与水流夹角等方面进行。