共查询到20条相似文献,搜索用时 15 毫秒
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Saumitra Jain S. Suriya Prakash K. V. L. Subramaniam 《Journal of Nondestructive Evaluation》2016,35(4):59
An active sensing approach is employed to analyze the damage behavior of concrete cylinders under compression using smart aggregates. The smart aggregate sensor used in this study is developed by embedding a soldered water-proof piezo-ceramic patch inside stiff cement mortar. These smart aggregates are embedded at the desired locations in the concrete cylinders. A pair of smart aggregates is used with one acting as an actuator and other as a sensor. Wavelet packet analysis is used to analyze the recorded signals. Variation of cracking pattern observed at different levels of loading modifies the signal characteristics. Experimental investigations are carried out by testing eight concrete cylinders with and without steel fibers. The experimental result shows that the proposed method of using smart aggregates and evaluating damage index based on wavelet analysis is effective in monitoring the health of the concrete cylinders. Compression tests on steel fiber reinforced concrete cylinders indicate that the addition of fibers improves the ductility and post peak behavior under compression. Damage index variation shows that the steel fibers resist the crack propagation and results in improved performance. 相似文献
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国内的低速柴油机制造厂 ,船舶设计部门、造船厂和船东好象已经有一种共识 :艉机舱推进轴系使用低速五缸柴油机作主机时 ,都要用扭振减振器。但是 ,只要在设计时合理选用柴油机转速 ,并采用高强度低合金钢来制造中间轴 ,这类轴系大部分是不需要扭振减振器的。 相似文献
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Kiełczyński P Szalewski M 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2007,54(6):1199-1206
The electro-elastic behavior of a viscoelastically loaded layered cylindrical resonator (sensor) comprising two coupled hollow cylinders is presented. The inner cylinder is a piezoelectric ceramic tube. The outer cylinder is a non-piezoelectric (passive) metallic cylinder. An analytical formula for the electrical admittance of a compound layered cylindrical resonator loaded with a viscoelastic liquid is established. Admittance (conductance) diagrams were obtained using a continuum electromechanical model. The established analytical formulas enable the determination of the influence of the liquid viscosity, material, and geometrical parameters of a compound cylindrical resonator on the response characteristics of the compound sensor. In the paper, the sensor implications resulting from the performed analysis are described. Moreover, the algorithm of the method developed by the authors to evaluate the rheological parameters of a viscoelastic liquid is presented. Good agreement between the theoretical results and experimental data is shown. The analysis presented in this paper can be utilized for the design and construction of cylindrical piezoelectric viscosity sensors, annular accelerometers, filters, transducers, and multilayer resonators. 相似文献
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以压力传感器与数显仪表的测量原理为基础,简述了发动机点火装置中的气压压力及气流压力校准装置及校准方法,给出了测量不确定度的评定. 相似文献
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Palma AJ López-González J Asensio LJ Fernández-Ramos MD Capitán-Vallvey LF 《Analytical chemistry》2007,79(8):3173-3179
This report addresses the task of calibrating an optical sensor for oxygen determination. Detailed analyses of the functional dependences from our measurement system results have been carried out with the additional aim of temperature compensation. As a result, an empirical calibration function has been successfully derived for the luminescent quenching-based oxygen sensor included in a self-designed portable instrument. This function also compensates for the temperature influence on the quenching luminescence process in the range from 0 to 45 degrees C. Moreover, the calibration procedure is extremely simple because only a single standard is needed. In fact, the oxygen measurement system can be calibrated with exposure to an open air atmosphere, and therefore, neither laboratory standards nor trained personnel are required. The method has been applied to a set of 11 units of the mentioned sensor (up to 24% oxygen concentration) giving an overall deviation between our calibrated system results and the laboratory standards of 0.3% oxygen concentration (calculated with 95% confidence level). The proposed calibration function has shown itself to be applicable for different sensing film thicknesses and luminophore concentrations using the same fittings parameter. Additionally, this function has been successfully applied to other oxygen dyes. Good agreement has also been found when the performance of the instrument was compared to a commercially available portable instrument based on an electrochemical sensor. We believe that this work could be an interesting finding for spreading the use of optical sensors for atmospheric oxygen determination in commercial measurement equipment for different purposes in confined working atmospheres, such as mines, undergrounds, warehouses, vehicles, and ships. 相似文献
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The results of experimental studies on estimating the lift force and lift coefficient of a rotating cylinder of constant cross section are presented. The data on the effect of the flow rake angle on the aerodynamic characteristics of rotating cylinders within a range of angles from 0° to 90° are analyzed. It has been established that a decrease in the lift coefficient is observed at flow rake angles above 30°, so the wind engine element shows a positive result within a range of rake angles from–30 ° ≤ α ≤ 30°. The data of these experimental studies can be used for the development of wind engines with blades designed as rotating cylinders with a smooth surface. 相似文献
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An optical air mass flux sensor based on a compact, room-temperature diode laser in a fiber-coupled delivery system has been tested on a full-scale gas turbine engine. The sensor is based on simultaneous measurements of O(2) density and Doppler-shifted velocity along a line of sight across the inlet duct. Extensive tests spanning engine power levels from idle to full afterburner demonstrate accuracy and precision of the order of 1-2% of full scale in density, velocity, and mass flux. The precision-limited velocity at atmospheric pressure was as low as 40 cm/s. Multiple data-reduction procedures are quantitatively compared to suggest optimal strategies for flight sensor packages. 相似文献
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G. D. Mitchell A. A. Bell 《Journal of research of the National Institute of Standards and Technology》1991,96(5):541-546
Coulometry has been established as an important and reliable method for the determination of acidic compounds. The analytical method and simple apparatus described here arc applied to the precise and accurate determination of sulfur dioxide in nitrogen, specifically in compressed gas cylinders at nominal concentrations of 50 and 100 µmol/mol (ppm). This method is constant current coulometry where the magnitude of the current is set by the balance between the electrochemical generation of OH−, the flow of SO2, and the chemical reaction of the solution. The method is direct, rapid, and can be refined further to provide analysis at the nanomol/mol level. 相似文献
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In this paper a general weight function was derived to evaluate the thermal stress intensity factors of a circumferential crack in cylinders. The weight function derived is valid for a wide range of thin- to thick-walled cylinders and relative crack depth. Closed-form stress intensity factor based on the weight function method was derived as a function of the Biot number and relative depth and various inner-to-outer radius ratios of cylinders. The accuracy of the analysis has been examined using the finite element method results and were compared to existing solutions for uniform loading in the literature for special geometries, indicating an excellent agreement. 相似文献
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Dr.-Ing. Ioannis E. Margaronis 《Forschung im Ingenieurwesen》1992,58(1-2):13-25
The torsional vibrations calculation of Diesel engines is usually performed for different speeds of revolutions but for uniform
operation and behaviour of each cylinder. This condition is true only for new of very well maintained engines but generally
the different cylinders operate with considerable deviations from its design conditions. This situation may influence strongly
the torsional vibrations of the system, since the spectrum of the exciting forces is different. In some cases this non uniform
operation of the different cylinders may induce severe torsional stresses leading to serious vibrations or even to damage.
This contribution presents same theoretical and experimental results obtained on this subject taking into account usual engines
conditions showing wrong injection timing, not proper operation of the turbocharging device, incorrect valve timing, excessive
wear of piston rings and/or piston liners etc. All these faults result in an exciting force spectrum that is different in
frequency and/or phase from the corresponding of uniform normal operation of each cylinder. This deviating spectrum can be
predicted and practical measured by the thermodynamic behaviour and the indicators diagrams of the engine and the corresponding
stresses can be calculated accordingly. The torsional stresses on the intermediated shaft can measured using strain gauges
method and the bridge voltage output converting to numerical file stored on a miniature computer which running with the shaft.
The method reported here has been verified for two identical ship engines MIRRLEES JVSS12 having different faults. The corresponding
results after both engines has been tuned properly are reported too to show the influence of the improper maintenance.
The help of professorD.A. Kouremenos in the present work is greatly appreciated. 相似文献
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亚硝酸盐是水中最常见的污染物之一,其检测长期以来一直是国内外研究的热点问题。制备了聚苯胺载银修饰玻碳电极(Ag/PANI/GCE)并将其应用于水中亚硝酸根的电化学检测。初步研究了亚硝酸根在电极表面的电化学行为的影响因素,并分析了所制备电极材料检测亚硝酸根的灵敏度、稳定性以及抗干扰性能。结果显示,所制备的Ag/PANI/GCE电极材料的电化学稳定性好,可以对水中的亚硝酸根浓度进行有效的检测,同时具有稳定性好、灵敏度较高、抗干扰性能强等优势,具有较高的研究价值和较好的应用前景。 相似文献
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Ebru Birlik Özkütük Sibel Emir Diltemiz Elif Özalp Tevfik Gedikbey Arzu Ersöz 《Materials Chemistry and Physics》2013
In this study, a novel quartz crystal microbalance (QCM) based on the modification of paraoxon imprinted polymer (TCM-Cd(II)-paraoxon) film onto a quartz crystal sensor has been developed for the determination of paraoxon. The sensor is based on a molecular imprinted polymer (MIP) which can be synthesized using paraoxon as a template molecule, Thiourea Modified Chitosan-Cd(II) (TCM-Cd(II)) as the metal-chelate monomer, ephychlorohydrin as a crosslinking agent. The MIP particles have been characterized by FTIR measurements and QCM sensor has characterized using AFM and ellipsometer. The performance of the paraoxon imprinted sensor has indicated that a selective and sensitive paraoxon imprinted sensor could be fabricated. The sensor is able to discriminate paraoxon in solution owing to the specific binding of the imprinted sites. The obtained paraoxon imprinted sensor has 0.02–1 μM linear range and low detection limit (0.02 μM). The selectivity studies have shown that the selectivity of prepared paraoxon imprinted sensor has found as being very high in the presence of parathion which is similar in structure with paraoxon. The paraoxon imprinted sensor has been repeatedly used for more than 7 months in many continuous experiments. 相似文献
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用光纤燃烧传感器测量汽油机的燃烧时间参数 总被引:4,自引:2,他引:2
介绍了一个光纤燃烧传感器+(OMA4光多通道分析仪组成的测量系统,用以测量汽油机燃烧火争光谱。光谱分析结果再次证实了燃烧火焰中CH(431.5nm),C2(516.nm),H2O3(589nm)等自由基的特征光谱同C粒子的热宫续光谱叠加在一起,构成了火焰光谱。根据光谱曲线中H2O光强峰值变化可以确定汽油机燃烧过程中重要的时间参数。着火延迟期和燃烧持续期。由于汽油机燃烧循环环变动大,与单色仪+BOX 相似文献
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Matko V. Donlagic D. Koprivnikar J. 《IEEE transactions on instrumentation and measurement》1994,43(3):436-441
In the paper, the use of a differential oscillator sensor structure in a capacitance sensor is presented. Investigations focused on the design and operation analysis of the oscillator differential structure in which the oscillation frequencies of the two oscillators are very close, and on the application analysis of capacitive-dependent crystals. In addition, the excitation of the entire sensor with stochastic test signals has been analyzed by the correlation deconvolution method which is also called the direct digital method (DDM). The compensation of temperature and voltage influences, as well as disturbing noise signals, are included. The area of operation and the uncertainty of the sensor with and without the test signal are given as well. When designing the capacitance sensor, the problems regarding the source of stable oscillation, compensation of temperature, the influence of supply voltage, noise, and A/D and D/A conversion occur in the operation range under 1pF. The pulse width module, which forms pulse-width modulated high-frequency current pulses, is the proposed solution. With these pulses, the capacitor in the integration element is charged or discharged. In this way, we benefit from the fact that the capacitor's voltage increases linearly if it is charging by a constant current. As the charging is affected only by the current pulses which require an adequate current, the disturbing noise signals do not affect the capacitor charging. The correlation determination of the measuring value is primarily important for the determination of end values. Several experiments have been carried out to investigate the method's possible applications. The method is linear in the range of work and ensures the uncertainty in the range below 0.01%. The experimental results of 0-1 ml volume measurements are shown. The volume measurement uncertainty (0-1 ml) Is less than 0.05% (T=15 to 25°C) 相似文献