核磁共振找水仪发射机电源技术研究

阐述核磁共振找水仪工作原理,并得出探测地下水深度主要受发射机发射脉冲矩影响的结论。根据找水仪发射机原理,分析出电容供电的过程中电压快速衰减的问题,导致发射机发射的有效时间短,激发的电流脉冲矩小;进而使地下水不能够充分的极化,接收弛豫信号小,还限制了仪器的探测的深度。针对找水仪发射机电源设计,论文提出在电容放电过程中同时采用恒压源对电容进行补偿,延缓电容的衰减过程。延长发射的脉冲时间,增大激发的电流脉冲矩,提高了发射机的极化地下水的效率,并有助于提升装置的探测深度。     

地面核磁共振(NMR)找水仪发射机的研制

地面核磁共振找水方法是目前世界上唯一直接找水的地球物理方法。本文介绍一种基于谐振原理的大功率，高精度地面核磁共振发射机。该发射机采用DDS产生当地拉莫尔频率，通过大功率开关电路产生功率方波，由发射线圈和谐振电容产生谐振，实现大功率发射。本设计具有输出功率大，频率精度高，重量轻等优点，已成功用于地面核磁共振找水仪样机中。     

扫频式磁共振探测电感测量仪的研制

针对核磁共振找水仪在实际应用过程中存在着电感测量不精确导致的难以获得最佳谐振信号的问题,基于串联谐振最佳谐振点电流最大的原理,设计了扫频式电感测量仪器。信号发生器产生的扫频方波信号经过驱动板和IGBT及配谐电容加到电感线圈上,用霍尔电流传感器采集出最大电流以及最大电流时刻信号源产生的信号频率,以此精确地计算出电感值,利用此方法设计一种扫频式电感测量仪以匹配找水仪,从而获得最佳谐振核磁共振找水信号。     

含集总源均匀传输线暂态响应的时域求解

为解决含集总源均匀传输线的暂态响应问题,将传输线的电路模型和时域有限差分法（FDTD）应用到分析传输线暂态过程的求解中。开展了电路理论、计算数学、程序设计等方面的分析,建立了一种简单、快速、有效的时域数值解法。利用有限时域差分理论对偏微分方程组进行了离散,提出了一种全新的差分计算格式。并根据电压、电流在始端、终端上的约束关系,运用传输线集中参数的等效模型确定了边界条件,通过仿真计算得到了响应波形。此外,对传输线在不同边界条件、传输线耦合等情况下的暂态过程进行Matlab编程计算得到了仿真波形,并借助EMTP-ATP软件对此仿真结果进行了验证。研究结果表明,该研究为均匀传输线暂态响应提供了一种简单可行的方法。     

闪烁体衰减常数值的脉冲波形测量方法

根据闪烁体发光衰减规律和衰减时间常数的定义,建立了闪烁探测器电流输出波形后沿特征量与闪烁体发光衰减时间常数的简洁关系,提出用测量脉冲波形后沿获得闪烁体发光衰减常数的三种简易方法,给出了相应的简单估算公式;在脉冲辐射源场中,测量了新型CeF3闪烁体对快脉冲γ辐射源的时间响应波形,用测量的波形脉冲后沿得到了CeF3衰减常数值;这种方法测量的结果与国外同行其它测量方法得到的结果基本一致.     

低频正弦波形发生器仿真与设计

利用核磁共振方法勘查地下水就是利用一个铺在地面上的线圈发射并接受NMR信号，线圈中需通入某一谐振频率(拉莫尔频率即氢质子在地磁场中的旋进频率)的正弦波作为激发源。欲获得合适的正弦波，分析了谐振电路的频率特性，对低频正弦波形发生器进行仿真，得到相应的仿真结果，从而设计了实际发射电路，并通过室内实验获得与仿真电路一致的结果，解决了将直流电源能量转化为交流能量发射的实际需要。该正弦波形发生器优点在于发射波形没有衰减，且发射电流持续时间可调节。     

基于回线型结构的大电流精确测量装置

本文设计了一种适用于测量航空电磁发射机发射电流的大电流采样电阻装置,在测量航空电磁发射机发射电流时,为了减小PWM控制策略及外部环境造成的干扰影响,需要一种零电抗的采样分流电阻。对奥地利国家计量院BEV和加拿大NRC联合研制的套筒型大电流分流器进行了改进研究。用有限元分析法计算了回线型结构电阻的电感与结构的关系,并且实际制作了该结构的4种样品,进行了实际测量;证明了有限元方法得出结论的正确性,并最终确定了一种采样电阻的尺寸。测试结果表明,与过去采用的直板型采样电阻结构相比,失真度提高了一个数量级。同时此测量结构还适用于其他快速变化大电流的测量场合。     

配电网合环冲击电流的暂态过程分析与仿真

在进行配电网合环操作分析时,以往只考虑合环后稳态电流是否越限,而忽略了合环冲击电流的暂态过程。针对这一不足,在理论分析的基础上,结合配电网特点建立了数学模型,推导出了合环冲击电流的计算方法,并探讨了影响合环冲击电流的主要因素。最后利用PSCAD/EMTDC软件对实际算例进行了暂态仿真计算。计算和仿真波形结果验证了该方法的正确性和有效性,对实际电网的调度运行具有一定的指导意义。     

一种时域电磁法剩余油探测装置的参数研究

提出了一种非接触式剩余油探测装置的参数设计方法.通过两种观测装置在均匀介质中时域电磁响应特性的对比,确定了最佳观测装置结构.分析了发射信号脉冲宽度和关断时间对响应信号的影响.研究了发射线圈电性与实际发射波形关断时间的关系,提出了发射线圈参数的选择原则.讨论了斜阶跃波激励下接收线圈的过渡过程,并给出了匹配电阻和接收线圈分布电容的估算方法.根据分析结果最终设计了装置参数并进行了室内实验.结果表明,不论从响应信号幅度还是延迟时间,均可对不同电导率的介质进行有效识别,为今后时间域电磁法剩余油探测的井下实验奠定了基础.     

基于误差可靠性分布的航空管道动力学响应实验与分析

通过管道稳态正弦基础激励动态响应实验,得到管道特定位置在不同激励频率下动力学响应实验数据;通过考虑了加速度传感器引起附加质量的航空管道模态特性及响应计算,并分别与管道实验数据进行对比分析;将计算值和实验值之间的误差作为分布变量,进行可靠性分布拟合和优良性检验;基于变量分布特性,结合发动机工作频率范围和数值计算结果,得到某型复杂航空管道在不同可靠度下的等效应力和位移响应值,并对其进行安全评估。结果表明:管道约束状态对模态测试和动态响应结果影响较大,数值计算结果和实验测试结果之间的误差服从正态分布,该分布可用于评估复杂管道的动力学特性。     

车内声品质评价系统的研究

研究现有声品质评价方法,开发一套集声音数据可视化管理、声品质主要评价参数计算、声品质主观评价打分及评价结果自动处理为一体的声品质评价系统,并应用该系统进行稳态车内噪声评价实验,证明了系统的正确性和工程应用价值.     

钢板硬斑的增量涡流扫查成像方法与仪器

硬斑测试是高端钢板产品质量评价的关键内容。本文基于增量涡流检测原理,研制了国产化的钢板硬斑磁检测仪器,并对仪器功能和性能进行了实验测试。首先,研制了增量涡流检测传感器,开发了基于交流电桥测试和相位旋转解调方法的增量涡流检测电路,集成了专用仪器;其次,利用仪器在Cr12MoV钢板和X70管线钢中开展了多组检测试验,结果表明：传感器的横向分辨率可达10 mm,增量涡流信号解调波形峰峰值U_p随表面硬度增加近似线性下降。在高出基准34.8%的硬斑区域内,U_p值下降约75%。利用U_p这一敏感参数对X70管线钢进行扫查成像,可准确识别出宽约10 mm的硬斑。上述研究结果为高端钢板硬斑的在线无损检测提供了方法和仪器支撑。     

High-performance time-resolved fluorescence by direct waveform recording

We describe a high-performance time-resolved fluorescence (HPTRF) spectrometer that dramatically increases the rate at which precise and accurate subnanosecond-resolved fluorescence emission waveforms can be acquired in response to pulsed excitation. The key features of this instrument are an intense (1?μJ/pulse), high-repetition rate (10 kHz), and short (1 ns full width at half maximum) laser excitation source and a transient digitizer (0.125 ns per time point) that records a complete and accurate fluorescence decay curve for every laser pulse. For a typical fluorescent sample containing a few nanomoles of dye, a waveform with a signal/noise of about 100 can be acquired in response to a single laser pulse every 0.1 ms, at least 10(5) times faster than the conventional method of time-correlated single photon counting, with equal accuracy and precision in lifetime determination for lifetimes as short as 100 ps. Using standard single-lifetime samples, the detected signals are extremely reproducible, with waveform precision and linearity to within 1% error for single-pulse experiments. Waveforms acquired in 0.1 s (1000 pulses) with the HPTRF instrument were of sufficient precision to analyze two samples having different lifetimes, resolving minor components with high accuracy with respect to both lifetime and mole fraction. The instrument makes possible a new class of high-throughput time-resolved fluorescence experiments that should be especially powerful for biological applications, including transient kinetics, multidimensional fluorescence, and microplate formats.     

基于声-固耦合模型的车内噪声响度参数的预测与分析研究

针对传统A计权声压级评价指标对噪声低频成分衰减较大,常常出现车内声压级达标,声品质不合格的问题。引入心理声学参数的响度参量,利用虚拟仿真技术分析评价车内声学特性。建立驾驶室声-固耦合有限元模型,结合试验激励数据,进行基于模态的声学响应计算。在Matlab平台上,建立车内声品质客观心理声学参数响度的计算模型,对比预测驾驶室内场点的声压级和响度分布,结合声压级和响度结构板块贡献量分析,研究声压级和响度参量评价驾驶室结构特性的差别并识别驾驶室主要噪声源。以此为基础指导优化驾驶室结构阻尼铺设位置,综合提高车内声学品质。     

虚拟式数控机床在线测量仪系统及其实现

将虚拟仪器技术引入数控机床在线测量仪,通过三维测头与工件的接触或碰撞,机床数控系统向虚拟仪器系统返回测量结果.结合测头与工件的具体几何位置关系进行补偿和形位误差计算处理,得到加工工件的质量评价参数及可视化展现.介绍了虚拟式数控机床在线测量的功能及其功能实现,重点分析了测量软件的实现以及减小测量误差的方法和措施.     

PARAMETERS OPTIMIZATION OF CONTINUOUS WAVELET TRANSFORM AND ITS APPLICATION IN ACOUSTIC EMISSION SIGNAL ANALYSIS OF ROLLING BEARING

Morlet wavelet is suitable to extract the impulse components of mechanical fault signals. And thus its continuous wavelet transform (CWT) has been successfully used in the field of fault diagnosis. The principle of scale selection in CWT is discussed. Based on genetic algorithm,an opti-mization strategy for the waveform parameters of the mother wavelet is proposed with wavelet en-tropy as the optimization target. Based on the optimized waveform parameters,the wavelet scalogram is used to analyze the simulated acoustic emission (AE) signal and real AE signal of rolling bearing. The results indicate that the proposed method is useful and efficient to improve the quality of CWT.     

A rail vibration test and analysis method for the electromagnetic launching process

During the electromagnetic launching (EML) process, rail vibrations occur due to the electromagnetic force generated by an acute current. These vibrations result in a reduced launch velocity and decreased launch efficiency. To measure the vibration amplitude of a rail accurately and to analyze the internal relationships between current strength, rail material and vibrations, a small transient vibration in a strong electromagnetic field was studied in this paper. Related experiments were also performed on the test system. Fiber-optic displacement sensors were used to collect vibration data at key locations along the rail. Using virtual instrument technology, a software platform was designed that displayed the vibration waveform and analyzed the time, frequency domain and other parameters. We collected data on the vibration response and the modal parameters of the rail and determined the natural frequencies of the electromagnetic launch system by performing a modal analysis of its vibrations and dynamic responses that combined experimental and theoretical methods. Methods of optimizing the structure’s vibration and dynamic response and of assessing the damage to it could be studied further on the basis of the results described in this paper.     

光纤激光焊接的碳排放建模与多响应评价

全球暖化的背景下,环境影响与制造质量的协同探究成为了研究热点之一。激光焊接广泛应用于汽车、航空航天、轨道交通等制造业,但其碳排放高、能量利用率低。因此,亟需对激光焊接工艺的碳排放特性进行研究,并协同焊接质量展开综合评价。通过搭建激光焊接的碳排放监测平台,分析激光焊接平台各系统(激光发生器、冷水机、机器人、保护气体系统)的碳排放特性,构建激光对接焊的碳排放模型,计算了各系统不同阶段的碳排放占比。采用最优拉丁超立方采样法,开展激光对接焊实验,将拉伸强度和焊缝完整性作为焊接性能的评价指标,分析了激光工艺参数(激光功率、焊接速度、离焦量)对碳排放和焊接性能的影响。实验结果表明,焊接速度对碳排放影响最大,而激光功率对拉伸强度和焊缝完整性的影响最大。对于三个响应指标,激光功率呈正向作用,而焊接速度呈负向作用。根据提出的多响应综合评价方法,对25组激光对接焊的实验结果进行了评分与优劣排序。提出的方法可为激光低碳制造的工程评价提供一定的参考。     

压力容器上声发射源的新型定位方法

压力容器裂纹扩展时产生的弹性波在传播时声压遵从指数衰减规律,本文提出一种利用声衰减对声发射源进行源定位的新方法。用AE21C型声发射仪对自制的小型高分子合成纤维材料容器以铅笔芯折断产生信号为模拟源进行了实验测量,证明这种新的源定位方法可行,并具有无须测量传播介质衰减特性、无须测量声速等优点。     

Micro-arc Oxidation Inverter Power Supply Based on the Limited Bipolar Soft-switch Control Method

In order to overcome many limitations of the conventional power supplies, such as ponderosity, big wastage, and simplex output characteristic, a dual-inverter power supply is designed to meet the different requirements of micro-arc oxidation. The main circuit structure and principle of the dual-inverter power supply for micro-arc oxidation is described, the control system and the control adjustment method are also introduced. The dual-inverter technology is adopted in micro-arc oxidation power supply. The limited bipolar control mode is applied in the power inverter circuit for adjusting the voltage, and various voltage waveform can be obtained by controlling the chopper circuit. Meanwhile, the control accuracy and response speed are improved greatly because of the higher inverter frequency. The power supply can output direct current(DC) waveform, DC pulse waveform, symmetry alternating current(AC) waveform, asymmetry AC waveform, and so on. Besides, the parameters such as pulse width, range, frequency, duty cycle can be adjusted. The experimental result shows that the power supply has many advantages, such as stable output, wonderful waveform consistency and obvious advantage in technique, and it can meet the requirements of micro-arc oxidation process fully.