共查询到20条相似文献,搜索用时 0 毫秒
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A. W. Baggaley 《Journal of Low Temperature Physics》2012,168(1-2):18-30
We present a detailed analysis on the effect of using different algorithms to model the reconnection of vortices in quantum turbulence, using the thin-filament approach. We examine differences between four main algorithms for the case of turbulence driven by a counterflow. In calculating the velocity field we use both the local induction approximation (LIA) and the Biot-Savart integral. We show that results of Biot-Savart simulations are not sensitive to the particular reconnection method used, but LIA results are. 相似文献
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以Fluent数值模拟为基础, 理想二氧化碳气体为工质, 采用5因素5水平的正交分析法, 模拟研究了各结构参数对涡流管制冷性能的影响。结果发现:当冷流比为0.4时, 热端管径为4.32 mm、喷嘴流道数目为2、冷孔板直径2.39 mm、涡流管长103 mm、调节阀出口面积5 mm2的涡流管, 获得最大制冷效应13.53 K。 相似文献
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Claudio Pecorari 《Journal of Nondestructive Evaluation》2013,32(1):104-111
A simple theoretical model which captures the statistical nature of an acoustic emission (AE) signal generated by a stream of solid particles impinging on a flat solid surface is presented. It rests on well-known results dating back to the fundamental work by Hertz, which assumes the impact to be elastic, the particle to be spherical, and the surface on which the particle bounces perfectly flat. The average power of the signal is evaluated in two limits. In the first one, the frequency content of the signal is identical to that of the forces developed during impact. In the second limit, only the low frequency part of the source function contributes to the spectrum of the recorded signal, the transfer function of the measuring system acting as a low-pass filter. In this case, it is shown that the result has an immediate physical interpretation, although its practical relevance is still limited. Additional progress is accomplished by experimentally proving that the statistical average of the particles’ momentum may be replaced with the average flow velocity, a quantity that may be directly measured in real life situations. It is suggested that this simplified version of the theoretical result may provide a useful tool to characterize particle flow in systems of industrial interest. 相似文献
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Acoustic emission was detected during compaction of three different pharmaceutical materials: lactose monohydrate, microcrystalline cellulose and maize starch varying compressive forces between 0 and 60 kN. Acoustic emission signals were recorded on magnetic tape with a microphone and transformed to frequency spectra by using FFT-analysis.
After rough identification of frequency components each spectrum was divided into three bands. By using integrated band powers the acoustic activity on these bands could be compared quantitatively. Many frequency peaks were observed, too, and many of them could be identified. 相似文献
After rough identification of frequency components each spectrum was divided into three bands. By using integrated band powers the acoustic activity on these bands could be compared quantitatively. Many frequency peaks were observed, too, and many of them could be identified. 相似文献
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《Drug development and industrial pharmacy》2013,39(19):2539-2560
AbstractAcoustic emission was detected during compaction of three different pharmaceutical materials: lactose monohydrate, microcrystalline cellulose and maize starch varying compressive forces between 0 and 60 kN. Acoustic emission signals were recorded on magnetic tape with a microphone and transformed to frequency spectra by using FFT-analysis.After rough identification of frequency components each spectrum was divided into three bands. By using integrated band powers the acoustic activity on these bands could be compared quantitatively. Many frequency peaks were observed, too, and many of them could be identified. 相似文献
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Alasdair Crawford Mohamad Ghazi Droubi Nadimul Haque Faisal 《Journal of Nondestructive Evaluation》2018,37(2):33
Acoustic emission (AE) monitoring shows promise as one of the most effective methods for condition monitoring of adhesively-bonded joints. Previous research has demonstrated its ability to detect, locate and classify adhesive joint failure, though in these studies little attention appears to have been paid to the differences in AE wave propagation through the bonded and un-bonded sections of the specimens tested, or to the effects of the wave modes excited or the propagation distances. This paper details an experimental study conducted on large aluminium sheet specimens to identify the effects of the presence of an adhesive layer on AE wave propagation. Three specimens are considered; a single aluminium sheet, two aluminium sheets placed together without adhesive, and an adhesively-bonded specimen. A pencil lead break (PLB) is used as a simulated AE source, and is applied to the three specimens at varying propagation distances and orientations. The acquired signals are processed using wavelet-transforms to explore time-frequency features, and compared with modified group-velocity curves based on the Rayleigh–Lamb equations to allow identification of wave-modes and edge-reflections. The effects of propagation distance and source orientation are investigated while comparison is made between the three specimens. It is concluded that while the wave propagation modes can be approximated as being constant throughout all three specimens, there is a significant change in the received waveforms due to the attenuation of high-frequency components exhibited by the bonded specimen. These findings may be utilised to provide a deeper understanding of acquired AE data, improving the current abilities to identify, locate and characterise damage mechanisms occurring within adhesive joints, ultimately improving safety in the use of adhesive bonding for critical applications. 相似文献
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The acoustic emission technique is a non-destructive testing method used for inspection and surveillance of structures and pressurized components. In particular, the purpose of the measurement on the 5 MW research reactor SAPHIR was to investigate and evaluate the abnormally high noise levels during operation of the heat exchangers of the cooling system. The results showed that 5 heat exchangers out of the total of 9 (assembled in 3 groups) were responsible for the higher noise level. This is probably due to some abnormal vibration of the tube bundles therein, caused by the through-flow of the pool water. Indeed, attempts of localizing the source showed that there must be several, distributed sources. 相似文献
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Daniel Nies Birgit Rehmer Birgit Skrotzki Robert Vaßen 《Advanced Engineering Materials》2012,14(9):790-794
Thermal barrier coatings allow increasing the operating temperature and efficiency of land‐, sea‐, or air‐based turbines. As failure of the coating may result in serious damage of the turbine, reliable estimation of its lifetime is essential. To assess the lifetime, cyclic tests are conceived to combine thermal loading by heating the surface of the coating with laser irradiation and nondestructive methods for damage determination. Using laser irradiation allows a high reproducibility of the thermal load. The temperature of the sample surface during thermal loading is determined by an infrared‐camera which also enables the possibility to detect damage in the coating via thermography. Additionally, four acoustic sensors, attached to the experimental setup, are used to detect damage in the sample and determine the source of acoustic events. Results of acoustic emission correlate well with thermographic images that visualize the formation and evolution of damage through delaminations in the samples. 相似文献
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We simultaneously monitored humidity and AE from active corrosion under insulation (CUI). For humidity monitoring, we developed
an optical fiber sensor based on the moisture dependency of absorption of laser light by connecting coating of polyvinyl alcohol
and CoCl2 coating and pullulan coating in series on the fiber as a cladding layer. The sensor could be used to measure humidity of
65–95% RH at 80°C. The temperature dependence of the sensor was as small as 2.5% RH/10°C. We monitored active CUI by the acoustic
emission technique and humidity sensing under wetting and drying cycles. Most AE signals were produced during the drying process
in each wetting and drying cycle, and the AE rate increased with the time of wetness (period of humidification). 相似文献
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耐火材料声发射信号可分为单一突发型和叠加突发型两种,通过分析其波形特征,将上升时间、持续时间、幅度、能量、计数和质心频率作为区分这两种信号的特征参数,利用K均值聚类方法,实现耐火材料不同损伤类型的声发射信号分类。利用该方法对MgO-C耐火材料受压损伤信号进行分析,研究结果表明:单一突发型信号主要频率成分单一集中,信号主要呈现50~60kHz和150~160kHz两种频率段,叠加突发型信号主要频率成分为上两种频率成分的叠加;将信号分为3类,第1类和第2类信号反映了具有计数少、持续时间短和能量小特点的单一突发型信号,第2类信号的损伤强度大于第1类,第3类信号反映了具有计数多、持续时间长和能量大特点的叠加突发型信号。 相似文献
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Acoustic Emission (AE) of the materials that are subject to stress and strain states is a methodology for non-destructive
investigation, originally applied to industrial steel structures. Here it is proposed by the authors for identifying the damage
in masonry buildings.
This experimental method was used to monitor the masonry structure of an historical building, “Casa Capello”, located in the
centre of the Rivoli Municipality (near Turin, Italy). This house, built on pre-existing 14th century foundations, was thoroughly
restructured at the end of the 18th century and has recently undergone restoration and enlargement works.
Non-destructive AE tests were carried out on a few masonry portions of the building in order to evaluate and define the development
of the cracking phenomena which had been observed in a number of structural parts after the collapse of a breast wall on the
down hill side of the building. With the measurement system adopted, entailing no loading or invasive procedures, it proved
possible to predict the arrest of crack growth and the concomitant onset of a new stability condition. 相似文献
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采集铁基合金涂层在不同接触疲劳损伤阶段的声发射信号,并采用dB10基本小波对其进行5层小波分解和重构,分析了疲劳损伤声发射信号的波形和频率特征。结果表明:裂纹萌生阶段的原始声发射信号以连续型为主,裂纹的稳定扩展阶段以混合型为主,裂纹的失稳扩展阶段以突发型为主;通过小波变换实现了将疲劳损伤声发射信号与干扰波分离,获得了高信噪比的疲劳损伤特征信息;在不同的疲劳损伤阶段,声发射信号的频率分布各不相同。随着疲劳损伤的加剧,各层的波形幅值呈增大的趋势,并且疲劳损伤频率分布范围也更加的广泛。 相似文献
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Automatic Classification of Acoustic Emission Patterns 总被引:2,自引:0,他引:2
Abstract: The problem of automatic classification of acoustic emission signals using techniques derived from pattern recognition is addressed in this paper. The data were taken from laboratory experimental work on a box girder of a bridge in which the acoustic emission (AE) generation mechanism and location were monitored. Two statistical methods and a neural network procedure have been used to classify the data into groups representing different AE generation mechanisms. The classifiers are constructed using the traditional AE features – four parameters from each burst. Principal component analysis is used to reduce the dimension of the AE data feature vectors to two dimensions, resulting in simple visualisations of the data. 相似文献
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