Numerical simulation on magnetic flux leakage evaluation at high speed

High-speed non-destructive inspection (NDI) systems using magnetic flux leakage method (MFL) is in great demand in online metal inspection and defect characterisation, especially in pipeline and rail track inspection. For MFL systems at high speed measurement, in addition to magnetic flux, eddy currents exist in metal specimen because of the relative movement between the probe and specimen. These currents alter the profile of electromagnetic field, which increases difficulty in signal interpretation and defect characterization. In this paper, eddy currents generated by high speed movement and their characterisation in high-speed MFL inspection systems were investigated by using numerical simulations. Besides, the MFL signals from high speed MFL measurement against defect depth were examined.     

交变漏磁检测中螺纹不同缺陷位置的识别方法研究

依据缺陷在螺纹区域的不同位置，将缺陷分为三类，分析了每类缺陷检测信号的特点，提出了识别判据，最后通过对膨胀螺钉上的该三类缺陷的检测，验证了识别模型的正确性。另外，对六角头螺栓结构根部缺陷的检测进行了试验研究，利用测量信号完成了缺陷的检测。     

钢管表面缺陷检测用交变漏磁检测系统

介绍基于A3515霍尔元件的交变漏磁检测系统的设计，包括检测系统的组成和测试方法。钢管裂纹的检测试验表明，该系统能很好地实现钢管表面和近表面裂纹的检测。在对缺陷信号进行分析处理的基础上，提出了基于缺陷环的识别方法。     

钢管漏磁探伤中孔洞缺陷的漏磁场分析

针对钢管孔洞缺陷进行了分析。分别从数学模型和仿真软件建模等方面对孔洞缺陷进行了漏磁场分析，并且将采集的漏磁信号进行处理，得出孔洞半径与漏磁信号之间的关系，为孔洞缺陷信号的识别提供了一定的参考依据。     

一种基于MUSIC算法的涡街信号处理方法

针对涡街流量计易受管道振动和流场扰动引起噪声干扰的问题,提出了一种基于MUSIC算法的涡街信号处理方法.介绍了涡街流量计的测量原理,建立了噪声环境下的涡街信号模型,并阐述了MUSIC算法的基本原理,在此基础上,分别对多种噪声环境下的涡街信号进行仿真研究.仿真结果表明:所提的涡街信号处理方法能有效地抑制噪声,高精度地分辨频率点,对改善涡街流量计的性能有良好的效果.     

运用SPIN对开放授权协议OAuth 2.0的分析与验证

OAuth 2.0协议是一种开放授权协议,主要用于解决用户账号关联与资源共享问题。但是,其弱安全性导致各网络公司海量用户信息泄露,且OAuth 2.0传输数据采用的https通道效率低下,成为黑客攻击对象。提出采用http通道传输OAuth 2.0协议数据,基于Promale语言及Dolev-Yao攻击者模型对OAuth 2.0协议建模,运用SPIN进行模型检测。形式化分析结果表明,采用公钥加密体系对OAuth 2.0协议进行加密不安全。上述建模方法对类似的授权协议形式化分析有重要借鉴意义。     

吉音水利枢纽竖井旋流泄洪洞水力特性试验研究

通过1∶30的水工模型对吉音水利枢纽竖井旋流泄洪洞的水流流态、压力分布、流量系数等水力特性进行了研究,分析了在进水口溢流堰末端增设掺气坎对进水口及竖井内流态及通气孔风速的影响。研究结果表明:在溢流堰末端增设掺气跌坎有利于减小溢流堰面的负压、防止空蚀破坏、简化进口体型设计,且有利于泄洪洞的安全运行。     

The inception cavitating flows over an axisymmetric body with a blunt head-form

The inception cavitating flows around a blunt body are studied based on flow visualizations and velocity field measurements. The main purpose of the present work is to study the incipient cavity evolution and the interplay between the inception cavitation and the local turbulent flows. A high-speed video camera is used to visualize the cavitating flow structures, and the particle image velocimetry(PIV) technique is used to measure the velocity field, the vorticity, and the Reynolds stresses under non-cavitating and inception cavitating flow conditions. It is found that the appearance of visible cavities is preceded by the formation of a cluster of micro-bubbles not attached to the body surface and in a hairpin-shaped vortex structure. During its evolution, the cavity moves downstream with a lower speed. The effect of the incipient cavity is significant on the local vortical structures but slight on the timeaveraged velocity distribution. The mean Reynolds stress distributions in the turbulent shear flow can be substantially altered by the incipient cavities. The presence of the incipient cavities can lead to the production of turbulent fluctuations.     

基于漏磁原理的钢丝绳探伤仪影响因素研究

介绍了钢丝绳探伤仪漏磁检测原理,并使用有限元分析方法分析了传感器零件的材料、钢丝绳的提离距离及断丝根数等对基于漏磁原理的钢丝绳探伤仪检测结果的影响。分析结果表明,提离距离、断丝根数等因素对探伤仪检测结果影响较大,断丝角度、深度等因素影响较小。     

NUMERICAL SIMULATION OF FLOW OVER TWO CIRCULAR CYLINDERS IN TANDEM ARRANGEMENT

In this article,the 2-D unsteady viscous flow around two circular cylinders in a tandem arrangement is numerically simulated in order to study the characteristics of the flow in both laminar and turbulent regimes.The method applied alternatively is based on the finite volume method on a Cartesian-staggered grid.The great source term technique is employed to identify the cylinders placed in the flow field.To apply the boundary conditions,the ghost-cell technique is used.The implemented computational method is firstly validated through simulation of laminar and turbulent flows around a fixed circular cylinder.Finally,the flow around two circular cylinders in a tandem arrangement is simulated and analyzed.The flow visualization parameters,the Strouhal numbers,and drag and lift coefficients are comprehensively presented and compared for different cases in order to reveal the effect of the Reynolds number and gap spacing on the behavior of the flow.The obtained results have shown two completely distinct flow characteristics in laminar and turbulent regimes.