Experimental investigation on tunnel sonic boom

Upon the entrance of a high-speed train into a relatively long train tunnel, compression waves are generated in front of the train. These compression waves subsequently coalesce into a weak shock wave so that a unpleasant sonic boom is emitted from the tunnel exit. In order to investigate the generation of the weak shock wave in train tunnels and the emission of the resulting sonic boom from the train tunnel exit and to search for methods for the reduction of these sonic booms, a 1300 scaled train tunnel simulator was constructed and simulation experiments were carried out using this facility.In the train tunnel simulator, an 18 mm dia. and 200 mm long plastic piston moves along a 40 mm dia. and 25 m long test section with speed ranging from 60 to 100 m/s. The tunnel simulator was tilted 8° to the floor so that the attenuation of the piston speed was not more than 10 % of its entrance speed. Pressure measurements along the tunnel simulator and holographic interferometric optical flow visualization of weak shock waves in the tunnel simulator clearly showed that compression waves, with propagation, coalesced into a weak shock wave. Although, for reduction of the sonic boom in prototype train tunnels, the installation of a hood at the entrance of the tunnels was known to be useful for their suppression, this effect was confirmed in the present experiment and found to be effective particularly for low piston speeds. The installation of a partially perforated wall at the exit of the tunnel simulator was found to smear pressure gradients at the shock. This effect is significant for higher piston speeds. Throughout the series of train tunnel simulator experiments, the combination of both the entrance hood and the perforated wall significantly reduces shock overpressures for piston speeds ofu _p ranging from 60 to 100 m/s. These experimental findings were then applied to a real train tunnel and good agreement was obtained between the tunnel simulator result and the real tunnel measurements.     

Thermographic signal reconstruction for vibrothermography

Vibrothermography, also known as thermosonics or sonic infrared, is a method of nondestructive evaluation that finds cracks or delaminations from the heat given off in response to vibration. In vibrothermography, finding cracks requires identifying and localizing pulsed surface and subsurface heat sources from a time sequence of infrared images. Traditionally this identification involves manually stepping through and studying the images. Careful observation of the heating and subsequent cooling is needed to distinguish cracks from false indications. In this paper, we present an algorithm that reduces the entire time sequence to a single static plot. The plot uses only a few coefficients per pixel to reconstruct the original sequence; this is possible because the reduction is based on a physical model. As an added bonus, the algorithm reduces noise and improves sensitivity. A single false-color image summarizes all the information from the entire sequence, simplifying the task of identifying cracks.     

Sonic spray ionization interface for liquid chromatography-mass spectrometry

A sonic spray ionization (SSI) interface for liquid chromatography-mass spectrometry (LC-MS) analysis was optimized for analysis of 2-[(1R)-3-[bis(1-methylethyl)amino]-1-phenylpropyl]-4-methyl-phenol (tolterodine), used as a model drug substance, and the influence of different parameter settings was evaluated using factorial design. A comparison between SSI and electrospray ionization (ESI) was made for tolterodine, tolterodine metabolites, and a set of steroids.SSI was found to give slightly poorer repeatability and broader peaks for tolterodine compared to ESI. However, there was no significant difference in chromatographic peak shape, and the repeatability using SSI was similar to that obtained using ESI if a ratio (area of tolterodine/area of metabolite) was used. In this study, the sensitivity was higher using SSI. For the analysis of pregnanolone, less water loss was obtained using SSI, probably due to less energy being transferred to the analyte upon ionization.     

Shape-optimal design of graded index sonic crystal formations using natural cubic splines

Noise reduction through upward refraction can be achieved by artificial means, using a graded index sonic crystal. In addition to upward refraction, it will be shown that these periodically spaced cylinder formations can simultaneously benefit from band-gap phenomena. The aim of this paper is to present a method to optimise the broadband noise reducing performance of graded index sonic crystals, in a frequency range from well below to well above the lowest band-gap frequency. A design technique based on the creation of complex cylinder formations has been explored, in which the effective propagation speed is spatially varied using natural cubic splines. Sets of complex barrier shapes are compactly described by re-locating a number of control points in a two-dimensional cartesian plane and connecting the control points by (curved) line segments. In addition to the cluster shape, a complex graded index sonic crystal structure was formed by varying the lattice constant and the cylinder radius, where the cylinder radius was varied as a function of height. All these parameters were optimised with a multi-objective genetic algorithm, for structures based on horizontally oriented acoustically hard cylinders, located above a perfectly reflecting ground plane. A four-lane outdoor situation, with a traffic scenario consisting of 95% light and 5% heavy duty vehicles driving at 70 km/h has been studied in a two-dimensional domain. For such a configuration we obtained a spatially averaged mean reduction of 4.2–5.3 dBA, with structures covering an effective cross-sectional area of 1 m². It was found that the insertion loss among the studied traffic lanes was reasonably constant. In addition, it was found that the low-frequency performance of the studied structures is enhanced by incrementing the barrier-height while increasing the number of scatterers as a function of height.     

超声喷雾电离源的研制与表征

研制了超声喷雾电离源(SSI)。采用核糖核酸A、溶菌酶等样品和商品化的线性离子阱质谱仪对该电离源进行了表征。实验发现,对于生物大分子,超声喷雾电离质谱(SSI-MS)能够获得与电喷雾质谱(ESI-MS)类似的多电荷离子。但与同等条件下ESI-MS所获得的谱图相比,SSI主要获得低价态的多电荷离子。在此基础上,系统考察了SSI-MS各主要操作参数对不同价态蛋白质多电荷离子信号强度的影响,并提出了SSI离子化的可能机理。结果表明,在喷雾气压3.4~3.6 MPa、喷雾口到质谱入口的距离4~6 mm、离子传输管温度250~300℃、样液流速50~100μL/min、2%~5%甲酸酸性且不含甲醇的条件下,各价态蛋白质离子信号强度及信号分布均达到最优;而离子传输管温度越高,喷雾压力越大或溶剂中甲醇等挥发性成分越高,则越有利于低价态离子的形成。     

聚苯硫醚纤维的抗张强度与工艺和结构的关系

以熔融纺丝法制备出不同结晶度的各向同性聚苯硫醚纤维作为样品,根据密度和声速测定值确定出PPS晶相和无定形相的本征横向声模量E0⊥,c(4.40 GPa)和E0⊥,am(1.99 GPa).利用密度梯度法测定出的结晶度Xc和X-衍射法测定的晶区取向因子fc,按照Samules模型计算出不同牵伸和定型工艺下制备的PPS纤维样品的非晶区取向因子(fam),在此基础上分析PPS纤维抗张强度与牵伸定型工艺参数、结构之间的关系.结果表明,PPS纤维的最佳牵伸温度及紧张热定型温度分别在90℃和190℃附近;提高PPS纤维的牵伸温度及紧张热定型温度可以增加纤维的结晶度,在一定范围内对纤维抗张强度的增加有促进作用;但较高的牵伸温度及紧张热定型温度不利于纤维非晶区取向的提高,造成PPS纤维抗张强度降低.牵伸倍数的增加可以有效提高PPS纤维的非晶区取向程度,抗张强度也随着增加.     

锚杆锚固质量无损检测的研究

本文介绍了一种无损检测锚杆锚固质量的新技术。通过模型试验,分析了声频应力波在锚固体系中的反射相位特征和能量衰减变化规律,探讨了测定锚固力的无损拉拔试验,并将结果成功应用于潘一矿巷道锚杆锚固工程的施工质量检测。     

Measurements of Young’s and shear moduli of rail steel at elevated temperatures

The design and modelling of the buckling effect of Continuous Welded Rail (CWR) requires accurate material constants, especially at elevated temperatures. However, such material constants have rarely been found in literature. In this article, the Young’s moduli and shear moduli of rail steel at elevated temperatures are determined by a new sonic resonance method developed in our group. A network analyser is used to excite a sample hanged inside a furnace through a simple tweeter type speaker. The vibration signal is picked up by a Polytec OFV-5000 Laser Vibrometer and then transferred back to the network analyser. Resonance frequencies in both the flexural and torsional modes are measured, and the Young’s moduli and shear moduli are determined through the measured resonant frequencies. To validate the measured elastic constants, the measurements have been repeated by using the classic sonic resonance method. The comparisons of obtained moduli from the two methods show an excellent consistency of the results. In addition, the material elastic constants measured are validated by an ultrasound test based on a pulse-echo method and compared with previous published results at room temperature. The measured material data provides an invaluable reference for the design of CWR to avoid detrimental buckling failure.     

充液圆槽中单极声波仪器响应数值模拟与分析

为了实现声波测井仪器工作状态的快速检测,工程人员通常将仪器水平放置在载液圆槽中进行发射和接收测试,然而对于这种非轴对称结构中的声波导传播规律尚缺乏数值模拟和理论分析,因此迄今仍难以形成有效的测试规范和标准。本文利用三维有限差分算法模拟了载液圆槽中的单极测井仪器声波响应,对比了不同的圆槽物理、几何参数以及液体性质条件下单极子声场首波的幅度和相慢度大小。分析结果表明,单极仪器激发的首波慢度仅由圆槽的物理特征所决定,与圆槽几何参数、声源频率及液体特性无关;而首波幅度大小则与圆槽几何尺寸、圆槽和液体弹性波速等诸因素具有明确的对应关系。本研究结果可为用于仪器测试或速度刻度的圆槽模型井优化设计提供理论依据。     

Simulation of wireline sonic logging measurements acquired with Borehole–Eccentered tools using a high-order adaptive finite-element method

The paper introduces a high-order, adaptive finite-element method for simulation of sonic measurements acquired with borehole-eccentered logging instruments. The resulting frequency-domain based algorithm combines a Fourier series expansion in one spatial dimension with a two-dimensional high-order adaptive finite-element method (FEM), and incorporates a perfectly matched layer (PML) for truncation of the computational domain. The simulation method was verified for various model problems, including a comparison to a semi-analytical solution developed specifically for this purpose. Numerical results indicate that for a wireline sonic tool operating in a fast formation, the main propagation modes are insensitive to the distance from the center of the tool to the center of the borehole (eccentricity distance). However, new flexural modes arise with an increase in eccentricity distance. In soft formations, we identify a new dipole tool mode which arises as a result of tool eccentricity.