ANALYSIS OF DYNAMICAL BUCKLING AND POST BUCKLING FOR BEAMS BY FINITE SEGMENT METHOD

Based on the multi-rigid body discretization model, namely, finite segment model,a chain multi-rigid-body-hinge-spring system model of a beam was presented, then a nonlinear parametrically exacted vibration equation of multi-degrees of freedom system was established using the coordination transformation method, and its resonance fields were derived by the restriction parameter method, that is, the dynamical buckling analysis of the beam. Because the deformation of a beam is not restricted by the discrete model and dynamic equation, the post buckling analysis can be done in above math model. The numerical solutions of a few examples were obtained by direct integrated method, which shows that the mechanical and math model gotten is correct.

FLEXIBLE MULTIBODY SYSTEM DYNAMICS-FINITE SEGMENT METHOD

The principle and method of flexible multibody system dynamics is presented. The dynamic equation have been developed by means of Huston's method based on Kane's equation. In which the flexible members with general cross-section characters were divided into finite segment models under the assumption of small strain. In order to decrease the degrees of freedom of the system and increase the efficiency of numerical calculation. the mode transformation has been introduced. A typical example is presented. and the foregoing method has been perfectly verified.

New normalized nonlocal hybrid level set method for image segmentation

This article introduces a new normalized nonlocal hybrid level set method for image segmentation.Due to intensity overlapping,blurred edges with complex backgrounds,simple intensity and texture information,such kind of image segmentation is still a challenging task.The proposed method uses both the region and boundary information to achieve accurate segmentation results.The region information can help to identify rough region of interest and prevent the boundary leakage problem.It makes use of normalized nonlocal comparisons between pairs of patches in each region,and a heuristic intensity model is proposed to suppress irrelevant strong edges and constrain the segmentation.The boundary information can help to detect the precise location of the target object,it makes use of the geodesic active contour model to obtain the target boundary.The corresponding variational segmentation problem is implemented by a level set formulation.We use an internal energy term for geometric active contours to penalize the deviation of the level set function from a signed distance function.At last,experimental results on synthetic images and real images are shown in the paper with promising results.

AN AUTOMATIC SEGMENTATION METHOD FOR FAST IMAGING IN PET

A new segmentation method has been developed for PET fast imaging. The technique automatically segments the transmission images into different anatomical regions, it efficiently reduced the PET transmission scan time. The result shows that this method gives only 3 min-scan time which is perfect for attenuation correction of the PET images instead of the original 15-30 min-scan time. This approach has been successfully tested both on phantom and clinical data.

Segmentation of Bacteria Image Based on Level Set Method

In biology ferment engineering,accurate statistics of the quantity of bacteria is one of the most important subjects. In this paper,the quantity of bacteria which was observed traditionally manuauy can be detected automatically. Image acquisition and processing system is designed to accomplish image preprocessing,image segmentation and statistics of the quantity of bacteria. Segmentation of bacteria images is successfully realized by means of a region-based level set method and then the quantity of bacteria is computed precisely,which plays an important role in optimizing the growth conditions of bacteria.

Study of the segmentation of active fault by the boundary element method──analysis of the Xianshuihe fault zone

On the basis of the recent geological surveys and the relevant studies of the Xianshuihe fault zone, this paper analyzes the seismogenic mechanism of some faults and characteristic morphology on the fault zone by the boundary element method and discusses the fault segmentation and the related distribution of the earthquake ruptures. The main conclusions are: For the first order segmentation, the Xianshuihe fault zone can be divided into three major segments (the northwestern Luhuo-Qianning segment, the middle linking fracture region and the southeastern Kangding segment). Among them, the differences are not only in geometry and structure, but also in mechanical property and dynamics. Some of the characteristic morphologies on the Xianshuihe fault zone reflect the effects in cumulative deformation due to long-term fault movement, and reveal the fault segmentation in different orders. Such morphologies control, to some extent, the developments and the distributions of the earthquake ruptures on the fault zone.

A Coastal Zone Segmentation Variational Model and Its Accelerated ADMM Method

Effective and efficient SAR image segmentation has a significant role in coastal zone interpretation. In this paper, a coastal zone segmentation model is proposed based on Potts model. By introducing edge self-adaption parameter and modifying noisy data term, the proposed variational model provides a good solution for the coastal zone SAR image with common characteristics of inherent speckle noise and complicated geometrical details. However, the proposed model is difficult to solve due to to its nonlinear, non-convex and non-smooth characteristics. Followed by curve evolution theory and operator splitting method, the minimization problem is reformulated as a constrained minimization problem. A fast alternating minimization iterative scheme is designed to implement coastal zone segmentation. Finally, various two-stage and multiphase experimental results illustrate the advantage of the proposed segmentation model, and indicate the high computation efficiency of designed numerical approximation algorithm.

基于四电极多频率扫描的生物阻抗法人体成分测试仪设计

生物阻抗包含丰富的人体病理和生理电信号,可以作为医务人员准确判断病人症状和治疗疾病的主要依据。基于此,提出一种基于Cole-Cole理论的人体多种参数测量系统。构建人体阻抗模型,通过碳纳米材料电极对人体阻抗进行采集分析,得到人体的各种成分参数。通过信号发生电路产生注入人体的低频信号,利用幅度检测电路检测流经人体电流产生的电压,采用分段检测法测得人体不同分段的阻抗信息;信号经放大电路输入RT1052微处理器,对数据和人体成分参数相关性进行分析,得到人体各种成分参数并显示测量结果。通过对系统进行测试分析,得出所设计系统能够准确地对人体蛋白质、脂肪等参数进行测量,误差范围可以控制在5%以内,具有很好的应用前景。

盾构隧道缓和曲线段管片组合轴线拟合计算方法

盾构隧道在缓和曲线部分存在管片拼装问题,因缓和曲线线型复杂,管片拼装点位多变,一直是施工过程中的一个难题。基于错缝拼装要求与楔形管片特点,提出一种在平面范围内,利用循环计算与误差控制的条件判定,综合比选标准环与楔形环组合,完成每环管片拼装施工,最终拟合出既满足规范与控制指标,又可保证线型较为均匀的管片拼装轴线的管片施工设计方法与验证方法。并根据实际工程需要,提出最大允许偏差控制方法和缓圆点附近的管片拼装优化措施,结合珠海市珠机线湾仔北站—湾仔站区间盾构隧道实例,证明了此方法的准确性与适用性,为缓和曲线上控制管片拼装质量提供理论依据。

对称约束的类间方差阈值方法

为了提高现有最大类间方差法(OTSU)的阈值化精度和适应性,提出了一种对称约束的类间方差阈值方法。该方法首先对输入图像使用Prewitt算子构建梯度幅值图像,并根据对称性原则提取对称采样区;然后,基于构建的对称约束类间方差目标函数最大化准则选取阈值,并判断在此阈值下对称采样区是否满足对称条件;当无法满足对称条件时,基于对称采样区对输入图像进行对称修正处理,并应用对称约束的类间方差目标函数对修正后的对称采样区选取阈值;最后,使用最终选取的阈值对输入图像阈值化。在28幅合成图像和70幅真实世界图像集上比较了提出的方法与OTSU法及4种OTSU的改进方法的阈值化性能。实验结果表明,提出方法的误分类率在合成图像和真实世界图像上分别为0.0106和0.016,相较于阈值化精度第2的方法在误分类方面分别降低了91.4%和86.1%。提出的方法虽然在计算效率方面不占有优势,但它对不同模态的测试图像具有更稳健的阈值化适应性和更高的阈值化精度。

基于动态阈值分割法的接触轨图像关键特征点提取方法研究

在地铁系统中,接触轨的状态对于牵引供电系统的安全性至关重要,一旦接触轨几何参数超出正常范围,不仅会导致集电靴无法正常取流,进而影响运营车辆的顺畅运行,而且在极端情况下,还可能引发严重的安全事故。传统的接触轨几何参数测量方法在采集图像时通常面临背景复杂、干扰图像多等问题,以致检测数据量少、检测密度低,从而难以精确提取接触轨的关键特征信息。针对这一问题,文章提出一种新的方法,即结合动态阈值分割法、直线拟合以及投影计算的方式,有效解决接触轨特征点提取的难点,实现几何参数的精确测量。该方法不仅能够准确捕捉到接触轨的细微变化,还能够确保测量结果的可靠性和准确性。为进一步提高测量的便捷性和实用性,研究过程中同步研制出一套接触轨几何参数的便携式测量装置,并在地铁线路上进行现场应用示范,为实际运营中的接触轨状态监测提供有力的技术支持。

地铁盾构隧道管片安全状态评价

为准确评价地铁盾构隧道管片安全性,基于对地铁盾构隧道管片结构病害的形成机制分析,从管片变形、渗漏水、裂缝、拱顶脱落、材料劣化5个方面建立评价指标体系,划分管片结构安全状态评价等级,构建未确知测度函数,通过基于熵值改进的G2法确定权重,根据置信度识别准则判断风险等级,并将模型应用于某地铁盾构隧道,对其管片结构进行安全状态评价。研究结果表明:采用未确知测度理论能够准确评价隧道管片的安全等级,结果准确,实用性强。

曲线拟合与分段函数组合法在瓦斯抽采量预测中的研究与应用

为减少矿井煤与瓦斯突出、瓦斯爆炸等事故的发生,将井下瓦斯及时抽出是必要的,因此对瓦斯抽采量进行准确地预测愈发重要。在神经网络法、多元线性回归法等预测方法的基础上,根据瓦斯抽采量在时间效应下变化波动大的特性,提出了曲线拟合与分段函数组合法。此方法以瓦斯抽采量衰减为界将瓦斯抽采分为前、后2个阶段,根据实测数据作抽采纯量随时间变化曲线并对变化曲线进行拟合,根据拟合曲线列出预测瓦斯抽采量的计算公式,用于对抽采量进行预测。分别对九里山矿、古汉山矿进行后段抽采量预测与实际的比较,其中九里山矿得到后段预测值的最小相对误差为0.63%,最大相对误差为2.34%,古汉山矿得到后段预测值的最小相对误差为0.09%,最大相对误差为3.23%。表明曲线拟合与分段函数组合法对井下瓦斯抽采量预测是可行的,对井下瓦斯治理具有重要的意义。

改进DeepLabV3+算法提取无作物田垄导航线

机器视觉导航是智慧农业的重要部分,无作物田垄的导航线检测是旱地移栽导航的关键。针对无作物田垄颜色信息相近、纹理差距小,传统图像处理方法适用性差、准确率低,语义分割算法检测速度慢、实时性差的问题,该研究提出一种基于改进DeepLabV3+的田垄分割模型。首先对传统DeepLabV3+网络进行轻量化设计,用MobileNetV2网络代替主干网络Xception,以提高算法的检测速度和实时性;接着引入CBAM(convolutional block attention module,CBAM)注意力机制,使模型能够更好地处理垄面边界信息;然后利用垄面边界信息获得导航特征点,对于断垄情况,导航特征点会出现偏差,因此利用四分位数对导航特征点异常值进行筛选,并采用最小二乘法进行导航线拟合。模型评估结果显示,改进后模型的平均像素精确度和平均交并比分别为96.27%和93.18%,平均检测帧率为84.21帧/s,优于PSPNet、U-Net、HRNet、Segformer以及DeepLabV3+网络。在不同田垄环境下,最大角度误差为1.2°,最大像素误差为9,能够有效从不同场景中获取导航线。研究结果可为农业机器人的无作物田垄导航提供参考。

一种改进Canny算子的图像边缘检测算法

在移动机器人自主作业时,环境中往往存在障碍物,路径规划避障时要进行动态目标检测.Canny边缘检测算法可以与众多动态目标检测算法相结合,提高目标检测的效果.但是传统Canny边缘检测存在着自适应性不强,边缘检测可能不连续,或者检测虚假边缘的现象.本文提出了一种优化Canny边缘检测算法,通过改进的自适应中值滤波来预处理图像,对算法效率及对噪声点的处理做出了优化,紧接着增加梯度计算方向,最后结合改进的大津阈值分割法,提出了三阈值分割法代替原始的阈值分割法使图像边缘信息更加完整准确.仿真结果表明,该算法在边缘检测准确率上对比传统Canny边缘检测,Sobel算子与较新改进算法均有20%左右的提升,该算法优化了传统算法检测的连续性和准确率.

基于改进Canny边缘检测的堆叠货箱分割定位方法

为了提高集装箱卸货的自动化水平,针对集装箱内堆叠货箱难分割定位的问题,提出了一种基于改进Canny边缘检测的堆叠货箱分割定位方法。通过阈值分割和形态学处理进行图像预处理,去除背景干扰,提取堆叠货箱区域图像,基于改进Canny算法对堆叠货箱进行边缘检测,根据堆叠货箱边缘特征进行筛选并基于最小二乘法进行直线拟合,解决边缘线条不连续和虚假边缘问题,对边缘进行区域化处理,以此将堆叠货箱分割成独立的货箱区域,提取每个独立货箱的最小外接矩形,得到货箱中心点的位置信息。实验结果表明,该方法对堆叠货箱有很好的分割效果,定位精度小于5 mm,满足定位精度要求。

基于pix2pixHD的类平面图空间分割清晰度提升及评价方法研究

用图像转译算法生成建筑平面图的研究存在训练难、取样难、控制难、评价难等问题。为了探索更有效的训练及评价方法,文章基于先前研究,探索经典算法pix2pixHD在建筑“类平面图”生成上的应用方法。在样本实验中,发现算法的学习偏好,通过对pix2pixHD算法与“夹芯线”样本的结合运用,提升生成模型的学习效果,使生成图的空间分割线更加清晰;在算法实验中,通过改进评价生成图与真实图像素相似度的计算方法,提升评价的精确度,并提出用于量化评价空间分割清晰度的“矢量比值”算法。通过两种评价方法的优势互补,量化模型的学习效果和生成图质量,以获得生成效果好且有一定创新能力的生成模型。研究结果可初步验证基于图像转译算法,从条件图到矢量结果图路线的可行性,可为训练高质量的建筑平面图生成模型提供理论与实践基础。

基于改进U-Net的冬季休眠期矮化苹果树修剪枝条分割方法

针对冬季休眠期矮化苹果树果园修剪中人工修剪及半自动化修剪作业效率低的问题,在U-Net网络模型基础上,通过VGG16与U-Net结合构建改进的U-Net网络模型,采用VGG16作为上采样特征提取网络,运用注意力机制SEnet增强图像特征提取能力,提升分割精度,进而与下采样提取的图像特征进行融合,实现端到端图像分割效果。结果表明,测试集上SE2网络模型(改进U-Net网络模型)的MIo U、MPA均大于原始U-Net网络模型;在SE2网络模型中,当r=8时测试集的MIo U、测试集的MPA、训练集的F_(score)、测试集的F_(score)均最大,分别为89.59%、94.17%、0.942806、0.944506;在试验台上对SE2网络模型(r=8)进行性能验证,表明SE2网络模型(r=8)分割性能较好。

基于不同河道汇流方法的新安江模型研究

为了提高五强溪流域水文模型的洪水预报精度,在新安江水文模型河道汇流模块中加入局地惯性波法,局地惯性波法不考虑迁移惯性项,适用于库区洪水演算。研究考虑了五强溪流域的水库型河道特征,在河道汇流方面建立了分段马斯京根法和局地惯性波组合的汇流方案。选取2020年~2022年五强溪流域洪水过程,与传统新安江模型对比,进行结果讨论分析。结果表明,分段马斯京根法仍是最简便、准确和稳定的汇流演算方法,但在水库型河道中构建分段马斯京根法和局地惯性波法的汇流方案,具有一定的创新性,取得了较高的模拟精度,为实时洪水预报提供了新的研究方案和路线。

基于分割法的抛物面固面天线热变形抑制

为满足未来高分辨率微波遥感航天器对于大口径高形面精度的空间可展开天线的需求,提出了一种能有效降低偏馈固面天线在轨因热变形造成形面误差的新方法,即分割法。采用5 m口径的偏馈固面抛物面天线,分析了天线热变形对其电性能尤其是主波束效率的影响。对连续固面天线六点支撑下不同支撑位置对其热变形的影响进行了研究。在温差为200℃的均匀温度场下,分析了不同形状单胞的形面误差,随后确认采用正六边形作为分割单胞并对其形面误差与尺寸的关系进行了研究。研究了分割单胞的尺寸及排布方式对天线的形面误差及电性能的影响,并验证了分割单胞之间的缝隙对天线电性能的影响,最终确定分割方案。结果显示,分割后天线形面误差从500μm降低至5μm,主波束效率下降值从6.72%下降至1.77%。