光纤Bragg光栅用于高频应变测试的研究(英文)

提出了一种传感部分采用光纤Bragg光栅(Fiber Bragg grating,FBG)传感器的高频应变测试新方法。设计并构建了基于非平衡马赫-曾德(Mach-Zehnder)干涉仪的高频解调系统。完整的测试系统由FBG传感器、高频应变产生装置和解调系统三部分组成。所产生的应变信号的频率可以通过专门的实验装置来控制,这是一种广泛用于测试材料机械性能的变形分离式霍布金逊压杆(Split Hopkinson PressureBar,SHPB)实验装置,应变持续的时间根据与撞击弹性等径的冲锤长度计算。借助高频振动信号研究了测试系统可测信号的频率范围。给出了振动和冲击实验结果,并进行了讨论。所设计的系统可以实时测试动态应变的幅值,实验结果表明,该系统对频率为8kHz以下的信号具有好的响应。

多通道动态应变观测系统在地震模拟实验中的应用

为了研究实验变形失稳过程中的应变场快速调整阶段和岩石结构破坏过程中的复杂变形场,将高速、高分辨率、多通道的应变观测技术引入构造物理实验,搭建了用以观测瞬态变形场的多通道动态应变观测系统,形成了16Bit分辨率、96通道、3.4kHz采样速度、1με分辨率且连续记录的应变观测系统。通过观测断层失稳过程高速滑动阶段和裂纹扩展过程的力学场时空变化,发现断层粘滑失稳过程的演化具有3个特征阶段:预滑动阶段、高频震荡阶段和低频调整止滑阶段。每个阶段的持续时间、应变速率、频率特性、振幅等都具有自身特点;三维断层扩展模型的实验结果显示,岩桥区断层贯通是一个快速过程,先多点局部扩展,后跳跃式连接。在断层贯通之后,样品整体崩垮之前,存在一个相对稳定的阶段,持续时间为几十ms。多通道动态应变观测系统填补了在地震模拟与岩石力学实验中应变观测频带的空缺,可以获得高密度、高精度的动态应变场,进一步研究瞬态应变场演化与应变波时空过程,为理解从缓慢递进变形到突发失稳释放过程提供了技术支持。

基于小波变换的2013年芦山M_S7.0地震前姑咱台钻孔应变异常时频分析

2013年4月20日芦山M_S7.0地震前,四川省姑咱台四分量YRY-4型钻孔应变仪记录到显著的高频应变畸变信号。为了避免该畸变信号的高频部分在时频演化过程中发生频率混叠现象,同时便于讨论同一研究频段内震前更早记录到的弱应变异常时段与显著应变异常时段的相关性,本文对2012年1月1日至2013年4月20日期间姑咱台的钻孔应变数据进行了时频分析,并使用时域分段的小波变换方法,在局部时频谱中提取了应变异常,分析了各应变异常的频率相关性。结果表明,研究频段内存在两个峰值频率,峰值频率附近频段内弱应变异常时段与显著应变异常时段的相关系数为0.85,统计出的无震时段与其显著应变异常时段之间的相关系数只有-0.007,且已排除远震以及外界环境带来的干扰,因此该峰值频率作为异常频率的可信度较高,由此推测四分量钻孔应变仪所记录到的两种不同程度的应变畸变信号的演化过程可能与芦山M_S7.0地震相关。

大跨混凝土桥梁耦合极值应变的混合粒子预测

针对大跨混凝土桥梁耦合极值应变难以实现精准预测的问题,本文采用加权移动平均法和最小二乘法进行解耦。通过将各分段高低频信号分开,进而采用区间选择方法,得到高/低频应变的极值序列;建立高/低频极值应变的包含2个时变状态变量的动态线性模型,结合贝叶斯粒子滤波理论,基于动态监测并解耦的高/低频极值应变,实现对应极值应变的高精度预测,进而将其相加实现耦合极值应变的混合粒子预测。采用广东省肇庆西江大桥的监测应变数据对本文所提方法进行验证,与普通动态线性模型相比,本文建立的模型对耦合极值应变的预测效果较好。

光纤Bragg光栅在分离式Hopkinson压杆实验中的应用

光纤Bragg光栅用于高频应变的测试是一个重要研究课题．文中介绍了其高频解调原理,探讨了光纤光栅传感器用于分离式霍布金逊压杆(SHPB)实验装置中应变测试的相关问题；推导了弹性杆中传播的应力波σ与传感光纤光栅中光波相位的变化量Δ(?)之间的关系式,进而建立了含有光纤光栅传感变化量的弹性杆应力波计算公式；构建了基于光纤Bragg光栅的动态应变测试系统,对中心波长分别为1550nm和1545nm的裸光纤光栅传感器以及应变片,两种传感器粘贴在被撞击弹性杆(输入杆)表面测试应变的情形进行了比较研究,给出了实验结果．研究表明,光纤Bragg光栅在高频动态应变测量中具有很好的应用潜力和前景,测试方法和结论对于光纤Bragg光栅在高频动态应变的实际测试中具有积极意义．

High-frequency compensation for seismic data based on adaptive generalized S transform

The low-pass fi ltering eff ect of the Earth results in the absorption and attenuation of the high-frequency components of seismic signals by the stratum during propagation.Hence,seismic data have low resolution.Considering the limitations of traditional high-frequency compensation methods,this paper presents a new method based on adaptive generalized S transform.This method is based on the study of frequency spectrum attenuation law of seismic signals,and the Gauss window function of adaptive generalized S transform is used to fi t the attenuation trend of seismic signals to seek the optimal Gauss window function.The amplitude spectrum compensation function constructed using the optimal Gauss window function is used to modify the time-frequency spectrum of the adaptive generalized S transform of seismic signals and reconstruct seismic signals to compensate for high-frequency attenuation.Practical data processing results show that the method can compensate for the high-frequency components that are absorbed and attenuated by the stratum,thereby eff ectively improving the resolution and quality of seismic data.

High Voltage High Frequency Power Transformer for Pulsed Power Applications

This paper presents a new topology for a High Voltage （HV） 50 kV, High Frequency （HF） 20 kHz, multi-cored transformer suitable for use in pulsed power application systems. The main requirements are： high voltage capability, small size and weight. The HV, HF transformer is the main critical block of a high frequency power converter system. The transformer must have high electrical efficiency and in the proposed approach has to be optimized by the number of the cores. The transformer concept has been investigated analytically and through software simulations and experiments. This paper introduces the transformer topology and discusses the design procedure. Experimental measurements to predict core losses are also presented. The losses of epoxy coated nanocrystalline are compared to the losses in a new uncoated core.

Brushless Doubly-Fed Induction Machine as a Variable Frequency Transformer

VFT （variable frequency transformer） has been recently used as art alternative to HVDC （high voltage direct current） to control power flow between asynchronous networks. VFT consumes less reactive power than a back-to-back HVDC system, provides faster initial transient recovery, and has better natural damping capability. VFT is simply a DFIM （doubly-fed induction machine） where the machine torque controls the power flow from stator to rotor and vice versa. The main disadvantage of this VFT is the slip rings and brushes required for the rotor circuit, especially in bulk power transmission. The BDFM （brushless doubly-fed machine） with nested cage rotor machine is proved to be a comparable alternative to conventional DFIM in many applications with the advantage that all windings being in the stator frame with fixed output terminals. In this paper, the BDFM is used as a BVFT （brushless variable frequency transformer）. A prototype machine is designed and simulated to verify the system validity.

High-frequency interference in low strain integrity testing of large-diameter pipe piles

The high-frequency interference exists obviously in low strain integrity testing of large-diameter pipe pile when a transientpoint load is applied. An analytical solution of vertical vibratory response of large-diameter pipe piles in low strain testing isdeduced in this paper. The analytical solution is verified by both numerical simulation and model test results. The time-domainvelocity responses on pile top are analyzed. The calculation results indicate that the time-domain responses at various pointssuffer different high-frequency interferences, thus the peak values and phases of different points are different. The influence ofvibratory modes on high-frequency interference is analyzed. It is found that the high-frequency interference at 90° point main-ly derives from the second flexural mode, but for other points it mainly originates from the first flexural mode. The factors af-fecting the frequency and peak value of interference waves have been investigated in this study. The results indicate that thelarger radius angle between the receiving and 90° points leads to greater peak value of high frequency wave crest. The leasthigh-frequency interference is detected at the angle of 90°. The frequency of interference waves is decreased with the increaseof pile radius, while the peak value is almost constant. The frequency is also related to pile modulus, i.e. the larger pile modu-lus results in greater frequency. The peak value varies with impulse width and soil resistance, i.e., the wider impulse width andlarger soil resistance cause smaller peak value. In conclusion, the frequency of interference waves is dependent on the geomet-rical and mechanics characteristics of the piles such as pile radius and modulus, but independent of the external conditionssuch as impulse width and soil resistance. On the other hand, the peak value of interference waves is mainly dependent on theexternal conditions but independent of the geometrical and mechanics characteristics of the piles. In practice, some externalmeasures should be adopted to weaken high-frequency interference such as using soft hammer, hammer cushion and adoptingsuitable receiving point.