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The application of ground-penetrating radar (GPR) as a non-destructive technique for the monitoring of ring separation in masonry arch bridges was studied. Numerical modelling techniques were used to simulate tests using GPR—these numerical experiments were backed up and calibrated using laboratory experiments. Due to the heterogeneity of these structures, the signals coming from the interaction between the GPR system and the bridge are often complex, and hence hard to interpret. This defined the need to create a GPR numerical model that will allow the study of the attributes of reflected signals from various targets within the structure of the bridge. The GPR numerical analysis was undertaken using the finite-difference time-domain (FDTD) method. Since “micro regions” in the structure need to be modelled, subgrids were introduced into the standard FDTD method, in order to economize on the required memory and the calculation time. Good correlations were obtained between the numerical experiments and actual GPR experiments. It was shown both numerically and experimentally that significant mortar loss between the masonry arch rings can be detected. However, hairline delaminations between the mortar and the brick masonry cannot be detected using GPR. 相似文献
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在钢结构脉冲涡流缺陷识别中,通常采用信号的峰值幅度、过零时间、主峰面积等特征参数对缺陷进行表征。但上述参数相互关联,存在一定的信息冗余,增加了数据分析量及信息筛选难度,进而影响了缺陷识别的效率。针对上述问题,采用主成分分析法对脉冲涡流信号的6个特征参数进行降维处理,构造了一个主成分特征,减少了信息冗余;将上述主成分特征输入Logistic分类器,实现了对钢结构减薄缺陷的准确识别。结果表明:主成分分析法可以在确保缺陷识别准确率的情况下,有效减少分类器处理的数据量,提高缺陷识别效率。 相似文献
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NDE of masonry structures: use of radar tests for the characterisation of stone masonries 总被引:1,自引:0,他引:1
Ground penetrating radar is being used as a survey tool to study stone and brick masonries. The aim of the research is to produce guidelines for a technical procedure for the acquisition and interpretation of radar traces to detect inclusions, voids and other defects, the effectiveness of repair, the characteristics of leaves in multiple-leaf walls and to find the presence of moisture in a stone masonry wall. This paper shows first results of in situ tests carried out on historic buildings. 相似文献
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文中利用宏观形貌及金相组织观察、化学成分检测、硬度测试等方法对水冷壁管开裂原因及机理进行了研究分析。结果表明,水冷壁管启裂于对接环焊缝与鳍片纵焊缝交叉处,该部位焊接残余应力及弯曲约束力程度较高且基体为不完全相变组织的;加之,环焊缝的基体组织中还存在因焊接工艺不合格或操作不当产生的夹渣和气孔等焊接缺陷。在机组启停或热负荷变化较大时产生的交变应力、焊接残余应力及弯曲约束力的共同作用下,裂纹逐渐于水冷壁管对接环焊缝与鳍片纵焊缝交叉处萌生并不断向内壁延伸,而焊接缺陷的存在又进一步加速了裂纹的扩展,最终导致水冷壁管发生开裂泄漏。
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薄壁铝合金锥形件旋压过程的缺陷分析 总被引:2,自引:0,他引:2
针对铝锥旋压成形中出现的质量缺陷,通过有限元分析模拟其成形过程.分析了产生缺陷的原因,并验证了不同工艺参数条件下旋压制品的成形特点,为制定旋压工艺方案提供参考.同时,在旋压试验中验证、优化模拟结果.结果表明,模拟分析有效地展现了旋压过程中的各种异常变形及其原因,如破裂、翻边、褶皱、失稳等,为制定、优化旋压工艺提供了有益的指导,在旋压加工中有效地避免了上述缺陷,提高了产品质量,简化了工艺试验方案,提高了生产效率. 相似文献
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C. Pislaru J. M. Freeman D. G. Ford 《International Journal of Machine Tools and Manufacture》2003,43(10):385
The paper presents a new use of the Continuous Wavelet Transform for modal parameter identification applied to CNC machine tools. Firstly, the resonant frequencies and damping ratios of the CNC machine tool axis drive are estimated in the frequency domain using the transmissibility relation at resonance. The experimental Bode diagrams are determined using a novel measurement practice for the decoding of signals generated by a position encoder.This paper focuses on a novel application of the Continuous Wavelet Transform to identify the resonance frequencies and corresponding damping ratios of the CNC machine tool axis drive. The proposed method has the ability to detect variations in the amplitude levels of weak components embedded in strong noise and non-stationary processes. The superior ability of the Wavelet Transform to identify accurately modal parameters is demonstrated by comparing the results of the two different methods. 相似文献
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本文分析了液压系统闭环辨识特点,提出了闭环辨识的实验条件,并在微机控制的液压系统闭环辨识实验装置上进行了验证。 相似文献
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针对阀控液压对称执行机构频率响应数据模型辨识问题,提出了一种功率谱估计闭环间接辨识方法,并分析了传感器分辨率、信号数据长度、窗函数、数据分段对辨识精度的影响。该方法首先使用改进的扫频信号对阀控液压对称执行机构进行扫频测试,然后对数据进行功率谱估计闭环间接辨识得到液压执行机构开环频率特性,最后对各种因素对辨识精度的影响进行了仿真分析。仿真结果表明:使用功率谱估计进行参数辨识时,传感器分辨率和精度越高、激励数据越长,使用hamming窗函数、2分段数据进行辨识信号前处理可得到更高的参数辨识精度。 相似文献
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An inverse analysis using a finite element model for identification of rheological parameters 总被引:1,自引:0,他引:1
In order to reduce the discrepency between experimental and numerical development, a parameter automatic identification procedure from rheological test is formulated as an inverse problem. The direct model which permits to simulate the large strain behaviour during the rheological test is a Finite Element Code. The inverse problem is formulated as finding a set of rheological parameters starting from a known constitutive equation. The goal is to compute the parameter vector which minimizes an objective function representing, in the least square sense, the difference between experimental and numerical data. The high nonlinearity of the problem to be solved, requires the use of an accurate evaluation of the sensitivity matrix by analytical differentiation of governing equations with respect to the parameters. Thus the optimisation algorithm is strongly coupled with the finite element simulation. This method, namely a Computer Aided Rheology (CAR) methodology is possible in principle for all tests able to be simulated. This paper concerns the thermoviscoplastic deformation during torsion and tension tests. 相似文献
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A. Petek 《CIRP Annals》2009,58(1):283-286
Before starting, the production forming processes require real experiments in order to accurately define forming limits. For this reason and because incremental sheet metal forming technology requires a relatively long production time, an autonomous on-line system for fracture identification has been developed. The system is a versatile tool for the identification of the location and time of the occurrence of the fracture, without human influences or oversight. The system is based on an investigation of the forming forces, responsive to very small variations, appearing during the forming process, and works effectively with different material types, material thicknesses and product shapes. 相似文献
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对模具电极用夹具利用ANSYS软件对其进行模态分析,得到系统的固有频率和振型,为模具电极用夹具的设计及动力学分析提供参考依据。利用ANSYS分析模块对模具电极用夹具结构进行优化分析,最优结果是:夹具的最大节点位移为3.32×10-3mm,最大节点应力为7.61MPa,总体积为2.14×105mm3,与优化之前的结果相比较,体积减少了33.1%。 相似文献
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箱式发电机定子铁芯套机座后其模态会发生变化,为防止发电机机座与定子在运行中发生共振等现象,在设计时就要对发电机模态进行详细仿真分析。本文利用有限元分析法和试验检测方式对某型号发电机定子套机座的模态进行对比分析,为进一步研究该类型风力发电机定子刚度提供依据。 相似文献
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控制理论的发展与制造过程识别策略研究 总被引:4,自引:0,他引:4
基于控制理论及其发展趋势,阐述了经典控制理论、现代控制理论和智能控制理论在制定制造过程识别策略中的应用,并在分析与研究各种策略的特点与存在问题的基础上,指出了发展方向。 相似文献
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针对冷轧钢卷卷取后带钢表面出现挫、划伤缺陷的问题,对缺陷宏观与微观形貌进行了分析,研究了冷轧钢卷卷取后带钢表面的挫、划伤缺陷的形成机理,即带钢在卷取过程中沿卷筒周向的静态卷取张力不能与动态的摩擦力相平衡而造成带钢层与层之间的打滑碰撞,导致带钢表面出现挫伤和划伤缺陷。为此,从卷取张力、速度波动的抑制,张力制度的优化,设备的维护,运输装备的改造等方面提出了相应措施,并将其应用到某2 030 mm五机架冷连轧机组,挫、划伤缺陷的发生率从1.2%下降到0.1%,保证了产品质量,取得了较大的经济效益。 相似文献
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针对客户反馈的SAE6150工具钢表面花斑形貌问题,对其宏观形貌和成分进行了检测分析,发现产生花斑形貌的直接原因是由于原料盘条表面存在不平整的微凹坑,平面和凹坑面在光的反射作用下呈现明暗不同的视觉色差,从而形成肉眼可见的花斑形貌。微凹坑产生的原因是盘条在轧制过程中表面残留氧化铁皮轧制压入而造成的;另外,盘条拉拔前的鳞皂化处理致使大量皂化液进入凹坑凝固后形成塞积物,盘条拉拔后凹坑难以去除而形成黑白相间的花斑形貌。为此,提出了相应改进措施,从根本上解决了热轧盘条表面缺陷问题。 相似文献