一种改进的二次曲线轮廓度误差的评定方法

提出了一种改进的二次曲线轮廓度误差的评定方法。以最小二乘曲线的焦点坐标作为中心划分正方形网格,在其中按一定规则设定标志点,若标志点配对拟合曲线计算所得轮廓度误差过大就将其剔除。然后在误差较小的区域进一步细分网格并配对拟合曲线,再以多次迭代运算的方法最终求得最小条件法下的轮廓度误差值。该方法搜索速度快,计算精度高,适用于任意平面二次曲线的轮廓度误差评定,辅以MATLAB软件实现误差求解的可视化,最后实例证明该算法的可靠性。     

异步电机空载实验曲线的拟合方法研究

在三相异步电动机空载实验中,首先测出各点空载损耗,从中减去定子铜耗,绘制电动机空载实验曲线;再做出其延长线,即可分离出定子铁耗和风摩耗。在电机实验教学中发现做空载曲线延长线的人为因素较大,引起的误差也比较大。本文利用九点式和七点式二次曲线拟合的方法对三相异步电动机空载实验结果进行了计算机处理,结果表明七点式二次曲线拟合方法得到的风摩耗误差最小,较大地提高了定子铁耗和风摩耗的分离精度。     

一种基于图像的覆冰厚度测量方法

为了准确检测出输电线路覆冰厚度以保证系统安全稳定运行,提出一种基于输电线路覆冰图像轮廓拟合的覆冰厚度测量方法。该方法对覆冰图片中感兴趣区域进行高斯滤波、阈值分割等图像预处理;利用提取到的覆冰轮廓进行最小二乘法曲线拟合,应用奇异值分解（SVD）得出最小二乘法的解;通过求取拟合曲线轮廓内的最大长度,得出覆冰的最大像素厚度。根据导线的实际外径和测量出的覆冰前导线像素厚度,得出覆冰的实际厚度。通过模拟试验进行验证,结果表明测量值与实际值误差在2mm以内,测量精度较高。     

浅析评定导轨直线度误差两种方法的运用

两端点连线法和最小条件法是评定导轨直线度误差常用的两种方法。如果误差曲线各点在该误差曲线全长两端点连线的同一侧时,则两种方法的评定结果相等;如果误差曲线各点分布在两端点连线的两侧,则两种方法评定的结果不相等。用两端点连线法求得的误差总是比用最小条件法求得的误差大,极限情况下大一倍。     

在数控编程中快捷计算拟合误差

由曲线方程式所确定的二维非圆曲线、列表曲线是许多机械零件中常见的轮廓线。在数控加工编程过程中,需要对这两类曲线进行拟合分析和拟合误差计算,控制其拟合误差在要求范围之内。这就需要计算点坐标(如基点、节点、中心点等)和两点间增量值,涉及到平面几何作图、代数、三角函数、平面解析几何等数学分析和计算,计算量非常大,计算结果的出错频率和误差也较高。本文探讨了在数控编程拟合二维非圆曲线——椭圆的过程中,利用AutoCAD软件的绘图和查询功能,迅速准确绘制曲线,适时查询拟合过程中的点坐标和两点间增量值,分析其拟合误差,完成大量数学分析和计算工作的方法和步骤。     

平行度误差的关键问题探讨与软件测试

平行度误差评定的关键在于基准拟合,其拟合精度决定误差评定结果之精度。对于平面基准和空间直线基准,数模重新整定,寻求全新算法,并论证其对"最小条件"要求的符合性,且通过了对程序进行的大量算例测试。在高精度基准拟合确定基础上,研发功能完全的平行度误差评定软件,经大量算例测试表明了其评定结果的高精度性。     

虚拟仪器在评定直线度误差实验教学中的应用

针对互换性与技术测量课程中实验教学存在效率低、功能单一的问题,在评定直线度误差实验中引入虚拟仪器技术,通过虚拟仪器设计的测量仪具有采集、存储、分析处理功能,采用LabVIEW作为软件开发平台,对直线度误差中两端点法、最小二乘法和最小区域法3种评定方法给出了相应的评定结果,可显示采样点的偏差值、轮廓曲线及直线度误差,实现了直线度误差可视化测量评定,使学生能直观地理解检测评定原理。     

以最小二乘法直线度评定食品中砷测定的不确定度分析

目的:以最小二乘法直线度评定食品中砷测定过程中存在的不确定度,并找出影响不确定度的因素较大的环节。方法:根据GB/T 5009.11-2003《食品中总砷及无机砷的测定》的方法,应用最小二乘法拟合直线,进行不确定度评估,并计算出合成不确定度。结果:各分量中工作曲线变动性、移液管、样品定容过程及测量重复性引入的不确定度贡献较大,相对扩展不确定度为U=2.5%(k=2)。结论:以最小二乘法直线度评定食品中砷的不确定度,提高了评定的可信度,通过实验各环节的分析,要求操作过程必须细心、准确、规范,尽量减少不确定度。     

基于矩阵运算的离心泵性能曲线拟合方法

分析了现行的离心泵性能测试技术和以往的离心泵性能曲线拟合方法,提出了符合现行精确测试技术的离心泵性能曲线最高次数合适的多项式拟合方程。该性能曲线多项式拟合方程严格地经过各测定数据点,多项式系数求解方法采用较为简便的矩阵运算法计算。通过误差分析表明,基于矩阵运算求解的次幂数合适的多项式拟合方程比最小二乘法求解的抛物线拟合方程更精确。     

用谐波分析方法识别零件的圆度误差特征

应用谐波分析法分析判断圆度误差的性质,为提高圆度加工精度提供科学依据.首先通过线性化处理的方法获得被测实际圆在直角坐标系下的最小二乘圆心,并经坐标变换得到实际圆轮廓上测点的极坐标;然后应用傅里叶级数展开法分析实际圆轮廓谐波特征并数字化;最后,在视频仪上对某零件的实际圆轮廓进行数据采集,并根据谐波分析方法对圆度误差的产生原因进行分析判断.结果表明,该方法可行.     

液氮冻结竖直向与水平向温度场特性

分析液氮冻结的现场实施情况,结合工程背景资料建立数值分析模型,通过计算分析并与现场实测成果验证,系统研究液氮冻结过程中竖直方向与水平方向温度场分布特征及其变化规律。结果表明：液氮冻结通过沸腾吸热与对流换热方式达到降温冻结的效果,相较于盐水循环冻结方式,液氮冻结效率高,周期短;但其冻结温度场分布不均匀,在竖直方向上存在较大温差,温度最低区域分布在液氮沸腾区范围,而水平方向上分布较为均匀;温度场中低温区域并不在两排冻结管之间均匀发展,冻结区域向连续墙方向发展的速度比土体方向发展速度快。基于研究成果,提出了液氮冻结加固设计、施工的优化建议,为今后液氮冻结工程提供理论依据与技术参考。     

盐渍土水分下渗能力及水盐动态运移试验

为探究盐渍化土壤水分下渗规律、水分下渗能力及水盐动态运移过程,设计了土壤剖面分层定水头供水及土壤剖面变水头供水下渗实验。测定不同层位土壤水分下渗率、含水率、孔隙水溶液电导率及土壤体电导率等参数,进行入渗条件下水盐动态运移规律分析。试验结果表明:盐渍化土水分下渗规律可由积水入渗Kostiakov模型进行刻画;浅层0~40 cm土壤相对于深层40~60 cm土壤具有较强的拦截和贮存入渗水分能力;盐渍化土壤盐分变动带位于浅层0~40 cm,且20~40 cm深度的土壤盐分波动幅度较大,深层40~60 cm土壤孔隙水溶液盐分向下运移的通量与土壤体盐分对其的补充量达到动态平衡,水分下渗过程中深层土壤孔隙水盐分含量相对平稳。实验结果为盐渍土的防治提供参考。     

Theoretical and experimental studies of heat transfer with moving phase-change interface in freezing and thawing of porous potting soil

Soil in a cold region is subject to frequent freezing and thawing cycles. Soil frozen for a prolonged period may cause adverse freeze damage to the plants due to cell dehydration or root cell rupture. It is important to understand the detailed heat transfer behaviors of the freezing and thawing processes to prevent freeze damage, and to devise proper mitigation measures for effective pot planting in cold regions. A theoretical model was developed to analyze the transient moving phase-change interface heat transfer in the freezing and thawing of porous potting soil. The theoretical derivation is based on the assumption that the soil freezes completely at a single temperature. Microscopic poromechanic effects on heat transfer behavior were ignored. The spatial domain of the problem was simplified to a 1 D spherical coordinate system with variation in the radial direction. Green＇s function was applied to solve for the time-dependent body temperature. Experiments were conducted for validation of the theoretical model Reasonable agreement between the theoretical predictions and experimental measurements was obtained. The theoretical model developed can be easily used to determine the sensitivity of various parameters in the freezing/thawing processes, e.g., thermal properties of soil, ambient temperature, and planting pot size.     

Experimental study on the anti-jacking-up performance of a screw pile for photovoltaic stents in a seasonal frozen region

The soils in seasonal frozen regions freeze and thaw frequently, causing severe frost heave and thaw settlement problems, which bring challenges to piles of photovoltaic stents. In this paper, laboratory tests are conducted with different types of screw piles under freezing conditions, with also using smooth piles for contrast. The aim is to simulate the freezing process of screw piles according to practical working conditions based on the similarity principle. Internal thermal resistance is ignored. The change laws of temperature, displacement, as well as the influence factors of types of screw piles are analyzed. The results indicate that: with a freezing depth of 30 cm, which is half of the pile length, large-double-bladed screw piles perform the best in antijacking-up, while all-bladed screw piles perform the worst, independent of the types of soil samples tested. The fitting relationship between jacking-up displacement and freezing depth is also proposed for each type of pile. Results obtained can provide an important reference to site construction in seasonal frozen regions.     

俄罗斯萨哈(雅库特)共和国中部热喀斯特湖成因及发育规律

在全球不断变暖的大环境下, 中国冻土区受气候影响而产生的各类结构性变化已经对人类生活产生相应的负面影响, 而位于俄罗斯西伯利亚地区的萨哈(雅库特)共和国面临同样的问题, 热喀斯特湖的发育对研究区内的领土开发、农耕地开垦、畜牧业等均已产生破坏性影响.借鉴俄罗斯对冻土的丰富研究, 为我国相关研究提供思路.通过梳理相关资料,...     

计算机模拟H钢冷却过程中温度场的变化规律

应用有限元软件SUPERFORM2002对经热轧后的H型钢在冷却过程中温度的变化进行了计算机模拟，得到了H型钢在冷却过程中温度场的变化规律。分析了相变对温度场计算的影响，并把计算值与实测值进行了对比，其结果表明：计算值与实验值吻合得较好。     

Numerical Simulation of Heat Transfer Characteristics of Horizontal Ground Heat Exchanger in Frozen Soil Layer

At present ,during the design of ground source heatpump (GSHP) systems ,technical attention is always fo-cused on vertical borehole heat exchangers and surroundingsoil[1 ,2],butthe effects of their shallowhorizontal connect-ing pipes ,or horizontal ground…     

岳阳地区柑橘冻害调查及其应对措施

2008年我国南部地区长时间的低温雨雪天气使岳阳地区柑橘产区遭受了严重冻害.针对在受冻害产区进行的大面积调查,并分析岳阳地区柑橘受冻的主要原因,笔者认为相应的冻后补救及防冻措施应以合理修剪、合理施肥、适当浇水、加强管理为主.岳阳地区果树的发展方向则应以发展落叶果树为主,柑橘生产以温州蜜柑的早熟、特早熟为主,适当发展一些有特色的其它水果.     

近平板状食品速冻过程冻结时间的数值计算与实验验证

以冻库中近似大平板状的盘装柠檬片和香蕉片为实验对象,采用数值计算法模拟其冻结过程并建立描述平板状食品冻结过程传热特性的偏微分方程,通过数值计算获得柠檬片和香蕉片冻结时间的数值解,并与在-80℃、-120℃介质温度下实测的样品中心温度值比较验证.结果表明：对比原料中心温度在-20℃、-10℃、0℃、10℃、15℃五个温度点实测值与计算值,香蕉片在-80℃和-120℃冻结温度下的预测值与实测值误差绝对值的平均值分别为11.42%、11.81%,柠檬片在-80℃冻结温度下的预测值与实测值误差绝对值的平均值为6.49%,说明数值法计算结果与实测值有较好的吻合度,数值计算法在预测冻结时间方面有一定的精度和适用范围.     

Exothermic process of cast-in-place pile foundation and its thermal agitation of the frozen ground under a long dry bridge on the Qinghai-Tibet Railway

A number of dry bridges have been built to substitute for the roadbed on the Qinghai-Tibet Railway, China. The aim of this study was to investigate the exothermic process of cast-in-place （CIP） pile foundation of a dry bridge and its harm to the stability of nearby frozen ground. We present 3D heat conduction functions of a concrete pile and of frozen ground with related boundaries. Our analysis is based on the theory of heat conduction and the exponent law describing the adiabatic temperature rise caused by hydration heat. Results under continuous and initial conditions were combined to establish a finite element model of a CIP pile-frozen ground system for a dry bridge under actual field conditions in cold regions. Numerical results indicated that the process could effectively simulate the exothermic process of CIP pile foundation. Thermal disturbance to frozen ground under a long dry bridge caused by the casting temperature and hydration heat of CIP piles was substantial and long-lasting. The simulated thermal analysis results agreed with field measurements and some significant rules relating to the problem were deduced and conclusions reached.