瑞利波超前探技术在瓦斯突出预测中的应用

介绍了瑞利波探测法在阳泉煤矿进行瓦斯突出预测预报中的应用,通过对现场采集数据的处理、总结分析,以及开采验证,认为瑞利波超前探测技术可以有效发现瓦斯聚集区,对煤矿安全生产具有指导作用.     

Heat and mass transfer analysis of combined convection in a horizontal rectangle

In this study, the heat and mass transfer of combined free and forced convection in the horizontal rectangle is explored. The governing equations together with the boundary conditions are solved numerically by using the finite volume method. The innovative idea in this study is to appropriately modify the Semi-Implicit Method for Pressure-Linked Equations algorithm and thereby, the numerical solutions of the flow variables such as the temperature and the concentration in addition to the components of velocity and the pressure are computed. The Richardson numbers (Ri) for distinct gases and liquids are calculated for different Rayleigh numbers at low (Re = 50) and high (Re = 5000) Reynolds numbers. The dimensionless parameters, such as the Reynolds number (Re), the Prandtl number (Pr), and the Schmidt number (Sc) are appropriately chosen to calculate the Richardson numbers. Consequently, combined free and forced convection effects are analyzed. Furthermore, the heat and mass transfer aspect for distinct gases and liquids is critically examined using empirical correlations. The accuracy and the validation of these results are ensured owing to the solutions obtained from correlations being advised in this study and those are existing in the literature.     

Clustering of Yb in silica-based glasses synthesized by SPCVD

Light absorption and scattering are studied in silica-based slab lightguides with different contents of aluminum, ytterbium and phosphorous in the silica core. The slab lightguides used in the experiments were fabricated from the structures of doped silica deposited on the inner surface of a substrate silica tube via surface-plasma chemical vapor deposition (SPCVD). The synthesized glasses contained 0.004–0.4 at. % of Yb, as well as various contents of Al and P ranging from 0 to 1 at. %. Loss spectra of the slab lightguides are measured in the 300–1050 nm wavelength band, with the influence of the profusion of deposited glass on the loss spectra investigated by means of substrate tube external processing at a temperature of ∼1600 °C in the flame of a hydrogen-oxygen burner. We found that a combination of the temperature of the inner surface of the substrate tube during the deposition process and the subsequent profusion of the deposited structure essentially influence the distribution uniformity of ytterbium ions in the glass volume. If aluminum and phosphorous are present in the glass, such profusion can influence the formation of ytterbium clusters in opposite ways.     

Laser ultrasonic characterisation of branched surface-breaking defects

Surface-breaking defects often have a geometry which is more complicated than the ‘normal slot’ used in many calibration tests, and this geometry will affect the reflection and transmission of ultrasonic surface waves incident on the defect. We present here measurements on defects with varied branched geometries, designed to simulate stress corrosion cracking (SCC) type defects, characterising the geometry using laser-based ultrasonic generation and detection of Rayleigh waves. We show the behaviour of the near-field enhancement and the far-field reflection as a function of branch position and length, and signal analysis which can be used to gain further information for characterising the defect geometry. The experimental results and finite element method (FEM) models presented in this paper highlight the potential of this technique to test components prone to developing SCC, in order to identify and characterise surface-breaking defects.     

A Bayesian approach for sparse flaw detection from noisy signals for ultrasonic NDT

Ultrasonic pulse-echo methods for flaw detection have been widely employed as an effective strategy for nondestructive evaluation, and flaw detection plays an important role due to its ability to detect localized damage in structures. In practice, flaw damage typically occurs in a few areas in the material, resulting in only a few echoes that exist in a received signal, which motivates us to detect flaws using sparse representation methods. In this study, the noisy signal is modelled by a linear combination of modulated Gaussian pulses, which form an over-complete dictionary. The over-complete dictionary is designed such that the sparseness of the representation is expected. A robust sparse Bayesian learning framework is employed with the goal of enforcing model sparseness and reducing the source of ill-conditioning in the inversion problem for flaw detection. Useful information, including the range of frequency and bandwidth parameters of the flaw echoes, is also estimated. Based on this information, we propose a post-processing scheme for structure noise elimination and flaw detection. The capability of the proposed method is quantitatively evaluated by simulation studies and is further validated by the experimental data.     

Evaluation of sensitization in stainless steel 304 and 304L using nonlinear Rayleigh waves

Austenitic stainless steels have a wide range of applications in the energy industry, but the corrosion resistance of these stainless steels can be reduced by sensitization, particularly in the heat affected zones in welds. Sensitization is the formation of chromium carbide precipitates along the grain boundaries, causing the formation of a zone of chromium depletion around the grain boundary. Since chromium is the primary alloying element that makes stainless steel corrosion resistant, this chromium depleted zone is susceptible to intergranular stress corrosion cracking (IGSCC). Sensitization occurs when a stainless steel is exposed to a high temperature for an extended time period, such as during welding. The objective of this research is to determine the sensitivity of nonlinear ultrasound to the presence of sensitization by using nonlinear Rayleigh waves to quantitatively track the sensitization of 304 and 304L stainless steels as a function of holding time at 675 °C. The effect of the carbon content of the alloys (304 versus 304L) to the sensitization process and the measured nonlinearity parameter, β are investigated. Annealing of these specimens isolates the effect of just sensitization, removing the presence of cold work which can also affect the material nonlinearity. Complementary electrochemical potentiodynamic reactivation (EPR) measurements and microscopy are used to confirm the absence or presence of sensitization. The results show that the acoustic nonlinearity parameter is sensitive to the presence of chromium carbide precipitates in sensitized austenitic stainless steels.     

一种新型的在瑞利信道下盲检测器设计

针对采用卡尔曼滤波或线性预测方案进行信号检测时,需要已知信道模型参数或预先估计信道参数这一局限性问题,提出一种新型的瑞利信道下的盲检测器。盲检测器通过设计粒子学习算法,能够在未知的信道衰落模型参数和噪声模型参数条件下检测信号。为了提升检测器的性能,采用信号延迟判决技术。仿真结果表明,盲检测器性能优异,已接近在已知信道模型参数下检测器的性能。该盲检测器易于并行设计实现,具有很高的实用价值。     

Wind characteristics and energy potential assessment in Akure,South West Nigeria: econometrics and policy implications

This paper analysed 11 years of daily mean wind-speed data, measured at Akure, Ondo State, Nigeria, using Weibull and Rayleigh distribution functions. While both distributions showed good agreements in extreme-value estimation patterns, investigation of their wind-speed characteristics modelling criteria, using goodness-of-fit statistics, revealed that the wind data followed the Weibull more than Rayleigh. Monthly wind-speed of Akure city ranged from 1.41 to 4.24 m/s by the Weibull fittings and from 1.40 to 4.16 m/s by the Rayleigh fittings. Overall results, of 2.71 m/s (Weibull) or 2.70 m/s (Rayleigh) mean wind-speed and 18.51 W/m² (Weibull) or 22.26 W/m² (Rayleigh) mean power density, indicated Akure a low wind-speed site, requiring low wind-speed turbine for generating wind energy. Econometric analyses of power output simulations using such turbine system resulted in affordable wind energy cost. These bear policy implications for sustainable wind energy usage in this and similar regions of the world.     

应用瑞雷波法检测某堤防修复效果

瑞雷波法是一种新兴的地球物理勘探方法,可广泛应用于质量检测及工程勘察中。介绍瑞雷波法勘探原理,结合汉口八厂联防(九一七油库—朱家河大桥)防洪大堤裂缝修复效果检测实例,简述瑞雷波法勘探的野外工作方法、资料处理及达到的地质效果。     

瑞利波勘探技术的发展与应用

对国内外瑞利波勘探技术的发展现状进行了总结。介绍了瑞利波勘探在工程地质领域的应用及瞬态法探测煤矿井下地质构造所取得的研究及应用成果。对今后瑞利波勘探技术的研究和发展方向提出了自己的观点，首次提出了多分量瑞利波勘探的思想。