Mechanism and experimental research on skin depth in AC magnetic flux leakage testing

随着管道、储罐的推广使用,管道、储罐腐蚀泄漏事故频发。漏磁检测方法是当前最频繁使用的管道无损检测技术。探讨了交流漏磁检测中趋肤深效应的机理。首先,对交流漏磁检测的涡流效应进行实验和分析;然后,根据麦克斯韦方程组推导出模型的三维交流漏磁场分布,分析了不同频率下钢板的磁力线分布情况,从而得出交流漏磁检测中趋肤深度的规律。最后,制造一系列人工缺陷并开展实际漏磁检测实验,以验证三维仿真结果的有效性,对进一步研究该方法的机理提供了理论和实验依据。With the wide use of pipelines and tanks,corrosion leakage accidents happen frequently.The magnetic flux leakage( MFL) testing method is currently the most commonly used nondestructive pipeline inspection technique.In this paper,the mechanism of the skin effect in AC MFL inspection is discussed.Firstly,the eddy current effects in AC MFL detection were tested and analyzed.Then,according to the Maxwell equations,the 3-D MFL field distributions were deduced,and the distributions of the magnetic induction lines under different frequencies in steel plate were analyzed,thus the law of the skin depth in AC MFL inspection was acquired.Finally,a set of artificial defects were made and the actual MFL test experiments were performed to verify the effectiveness of the 3-D simulation results,which provides a theoretical and experiment basis for further studying the mechanism of the method.国家自然科学基金(51177141); 福建省自然科学基金(2010J01310); 中央高校基本科研业务项目(0620ZK1007)资

PWM method of flux linkage trajectory tracking and analysis of its characteristics

提出一种基于磁链轨迹跟踪策略的电动机变频调速方法。该方法不通过空间电压矢量的合成,而直接通过实际磁链矢量来跟踪基准磁链圆轨迹,再由跟踪的结果决定逆变器的开关状态模式,从而实现对脉冲宽度调制(PWM)波的调制输出。对该方法的基本原理进行推导,给出具体的控制策略,并对其产生的PWM波形特性进行系统分析。仿真及物理实验结果表明,该方法幅度调制比可达到1,电压利用率与空间矢量脉宽调制(SVPWM)方法相同,比正弦波脉宽调制(SPWM)提高15.47%;同时验证了其跟踪误差上限的存在性,为进一步分析该方法精确度提供了定量依据。该方法为变频调速的底层实现提供了另一种可行的途径。A frequency control underlying implementation of induction motor was suggested based on flux linkage trajectory tracking.By changing the operate mode of inverter,the actual flux linkage was produced to tracking the reference flux linkage circle,and the corresponding pulse width modulation(PWM) waveform was also generated.The basic theoretical computing equation was deduced,a specific control strategy was suggested,and the characteristics of the PWM waveform generated was analyzed.Simulations and experimental results show that the modulation index is up to 1,and the voltage utilization is same as SVPWM,while 15.47% higher than SPWM.Furthermore,the existence of error upper limit was verified,which provides a quantitative basis for further analysis of the accuracy.国家自然科学基金(51177141); 福建省自然科学基金(2010J01310); 中央高校基本科研业务项目(0620ZK1007

A SVPWM Overmodulation Method Based on Three-Phase Bridge Arm Coordinates

讨论了一种新型的SVPWM过调制方法,并对其过调制性能及谐波成分进行了分析。首先,对经典SVPWM技术进行了分析,探讨了常规过调制策略的实质。其次,引入了新的三相桥臂坐标,在该坐标下将现有的SVPWM的串行合成时间关系推导为并行。最后,给出了线性调制和过调制统一的求解模型,避免了现有过调制算法中控制角和保持角的计算。新方法取消了扇区的概念并简化了计算,可实现从线性调制到六阶梯模式的连续平滑调制。文中介绍了该过调制算法的基本原理,进行了仿真和实验。结果表明,该方法在线性调制和六阶梯模式下调制效果与经典SVPWM方法相当;而过调制区,其输出PWM波形的THd明显小于常规过调制方法。A new overmodulation method based on space vector pulse width modulation(SVPWM) is discussed, and the performance and harmonic components of which are also analyzed.Firstly, the essence of original overmodulation strategy in the classical SVPWM is investigated.Then, a three-phase-bridge-arm coordination is introduced in which the relationship between three up-bridge arm working situations is parallel.Finally, a unified solution of linear modulation and overmodulation is proposed, to avoid the calculation of the reference angle and holding angle in existing strategies.The new method cancels traditional sector division, simplifies the computation, and gives smooth transitions from linear modulation, overmodulation, to six-step operation finally.The overmodulation strategy is theoretically analyzed, simulated and experimented.The results demonstrate that the PWM wave generated by the new method is similar to the classic, and the total harmonic distortion(THD) of the output voltage is markedly reduced.国家自然科学基金(51177141); 福建省自然科学基金(2010J01310); 中央高校基本科研(0620ZK1007)资助项

纪念五四宪法颁布暨全国人民代表大会成立五十周年理论研讨会纪要

今年 9月是五四宪法颁布、全国人民代表大会成立五十周年。五四宪法是新中国的第一部宪法 ,为我国的社会主义民主法制奠定了基础 ,具有划时代的意义。坚持和完善人民代表大会制度 ,是新的历史条件下推进政治体制改革和社会主义政治文明建设的重要内容。基于“以学术表达纪念、以纪念促进学术”的目的 ,中国社会科学院法学研究所于 2 0 0 4年 9月 5日举办了“纪念五四宪法颁布暨全国人民代表大会成立五十周年理论研讨会”。来自全国各地的 70余位代表莅临会议 ,研讨了诸多热点和前沿问题

Approach to design tension of filament winding for thick composite pipes using a neural network

提出了一种纤维缠绕厚壁复合材料管的张力优化设计方法。介绍了纤维缠绕控制系统的工作原理,并讨论了缠绕厚壁复合材料管成型质量的影响因素。针对厚壁复合材料管纤维缠绕过程,利用弹性叠加原理建立了计算缠绕张力导致复合材料管残余内应力变化的模型和方法。分别比较了利用现有恒张力、恒力矩和锥度张力三种常规模式缠绕厚壁复合材料管的内应力分布特性。设计了一种独特的神经网络结构,并通过误差反向传播实现了对纤维缠绕张力的优化设计。以实验验证说明神经网络收敛优化过程的主要机制,结果表明,通过该神经网络优化的纤维缠绕张力能满足特殊内应力(如等应力)分布设计的需要。A novel design approach was presented to optimizing the winding tension for thick composite pipes in this paper.The theories of filament winding machine control system were introduced,and the factors that influence the forming quality of thick composite pipes were discussed.An approach of calculating the residual inner stress and deformation in tension winding for thick fiber composite pipes according to superposition principle of the elastic theory was advanced.The inner stress distributions in the thick pipes wound with constant tension,constant torque and taper tension patterns separately were compared.A peculiar neural network structure was presented for optimizing the winding tension with error back propagation.Experiments were conducted to identify dominant mechanisms during neural network convergence process.The results show that the winding tension optimized by this network can meet the design requirement with special inner stress distributions such as isostress.国家自然科学基金(51177141

兰州重离子加速器的新低温泵

本文介绍了兰州重离子加速器新型大口径无液氮低温泵——HIRFL800。它是由一台改良的小型单级机械制冷机和一台标准的二级制冷机组成的。泵对氮和氢的抽速分别为24000和26000 L/s。自1989年以来,用八台HIRFL低温泵,在100 m~3大真空室上,获得了5×10~(-6)Pa的真空度

兰州重离子加速器前束线真空系统改造

介绍了兰州重离子加速器 (HIRFL)前束线真空系统的基本结构 ,给出了HIRFL前束线真空系统改造前的流导、气体负荷及压力分布情况。提出了具体的改造方案。使真空系统达到了设计要求 :泵口压力小于 5× 10 -6Pa ,两泵中心平面压力小于 1× 10 -5Pa。结果表明HIRFL前束线真空系统的改造方案是可行

扇聚焦回旋加速器(SFC)真空室改造

介绍了兰州重离子加速器的注入器SFC真空室的基本情况,为满足新建的放射性束流线RIBLL和冷却储存环CSR对HIRFL加速重离子的需要,对SFC真空室进行了改造。新真空室采用二次真空技术,在加速器中心平面真空度达到了8×10-6Pa

3-D FEM Simulation of Lift-off Effects on Magnetic Flux Leakage Testing

随着管道、储罐的推广使用,管道、储罐腐蚀泄漏事故频发.漏磁检测方法是当前最频繁使用的管道无损检测技术.该文应用三维有限元分析方法探讨了漏磁检测方法中提离值对检测结果的影响.首先,根据麦克斯韦方程组推导出缺陷处的三维漏磁场分布;再通过AnSyS软件建立振动条件下的漏磁检测三维有限元仿真建模,分析了不同提离值下缺陷漏磁信号的分布.然后,制造一系列人工缺陷并开展实际漏磁检测实验,以验证三维仿真结果的有效性.最后,通过最小化振动和电磁噪声误差,得到不同尺寸缺陷对应的最佳提离取值.该研究可为检测人员优化探测器结构、提高漏磁检测精度提供有效参考依据.With the increase of pipelines and steel tanks,corrosion leakage accidents happen frequently.The magnetic flux leakage( MFL) method is currently the most commonly used pipeline inspection technique.In this paper,three-dimension( 3-D) finite element analysis has been used to examine the effect of lift-off on MFL signals.Firstly,according to Maxwell equations,the 3-D MFL field distributions of defects were deduced.Then,the 3-D finite element simulation model of MFL under the vibration conditions was established in ANSYS and the MFL signals of defects at different lift-off were analyzed.To confirm the 3-D simulation results,a set of artificial defects was made and the MFL experiments were performed.Finally,the best lift-off at different sizes of defects was achieved by minimizing the errors caused by vibration and electromagnetic noise.This research can be used to optimize the detector structure to increase MFL detection measurement accuracy.国家自然科学基金(51177141); 福建省自然科学基金(2010J01310); 中央高校基本科研业务项目(0620ZK1007