Time filter

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Mashreghi A.R.,University of Yazd | Saberifar S.,Iran Alloy Steel Company IASCO | Hejazi S.J.,Civil Aviation Technology College
Journal of Failure Analysis and Prevention | Year: 2013

In this study, the fracture of a locomotive engine oil pump shaft is investigated. According to the reports, all oil pump shafts of this type fail in short periods of time due to the fracture at a location on the shaft which is in contact with a pinion. Stress analysis showed that the shaft bears torsion and cyclic bending stresses in the fracture site. The fracture surface observations revealed that the cracks are generated from the surface, and fatigue fracture occurs due to the cyclic bending stresses. According to the laboratorial analysis, the shaft is a surface-hardened low alloy steel. The lack of suitable pre-heat treatment and surface hardening and the roughness created by the slippage between the shaft and the pinion are concluded to be responsible for the failure of the oil pump shaft. © 2013 ASM International.

Neyestanak A.A.L.,Islamic Azad University at Tehran | Nazari S.A.,Sharif University of Technology | Sadeghbeigi N.,Iran University of Science and Technology | Karimzadeh A.,Civil Aviation Technology College
International Journal of Electrochemical Science | Year: 2014

Electrical behavior of hybrid conductive composites made of phenolic resin, graphite woven, glass woven and graphite nano powder has been studied for the first time in the present research to apply as collecting plates in electro static precipitators. To this purpose, two types of four-layer composites smeared with phenolic resin by different amounts of graphite nano powder then produced at 120°C and 200 bars with proper curing cycle. Finally, electrical resistivity of all the plates undergoing impact loading after different rapping cycles was measured by means of a repetitive rapping tester system particularly manufactured for this task. This study performs changes in mechanical behavior of the samples and their effects on electrical resistivity which can be so effective to choose the proper composite as the collecting plate in electro static precipitators. © 2014 The Authors.

Yadegari A.M.,Iran Telecommunication Research Center | Moini R.,Amirkabir University of Technology | Sadeghi S.H.H.,Amirkabir University of Technology | Mazlumi F.,Civil Aviation Technology College
NDT and E International | Year: 2010

The paper proposes a modeling technique for output signal prediction of a rectangular waveguide probe with finite flange when scanning a surface long crack in a metal at a finite lift-off. The modeling technique approximates the crack-probe interaction with a two-dimensional problem. In this problem, a parallel-plate waveguide with finite flange scans a long crack in a perfect conductor. The method of moments is employed to solve the governing electric field integral equation. The solution provides the reflection coefficient in the parallel-plate waveguide from which the probe output signal is obtained. The main feature of the model is solving the three-dimensional problem in a two-dimensional frame work, thus reducing the degree of complexity and computation time. To validate the accuracy of the model, several simulation results are presented at an operating frequency in the X-band and are compared with their experimental counterparts. To demonstrate the efficiency of the model, we compare our results with those obtained using the well-known HP-HFSS finite element code. It is shown that the proposed model requires less than half of the time taken to solve the same problem running on the same computer. © 2009 Elsevier Ltd. All rights reserved.

Mazlumi F.,Civil Aviation Technology College | Gharanfeli N.,Amirkabir University of Technology | Sadeghi S.H.H.,Amirkabir University of Technology | Moini R.,Amirkabir University of Technology
NDT and E International | Year: 2013

This paper describes the development of a novel microwave probe system for detection and sizing of surface cracks in metals. The probe, which is based on the substrate integrated waveguide (SIW) technology, consists of five parts, namely, a microwave oscillator, an envelope detector, a microstrip line, a transition section, and an open-ended SIW. To evaluate the performance of the probe, theoretical and experimental results are presented for the scans of two metallic specimens containing long surface cracks. It is shown that the SIW probe is capable of detecting and sizing surface cracks of a few millimeters deep while being relatively compact and light as compared to the conventional open-ended rectangular waveguide probes. © 2012 Elsevier Ltd.

Rashtian M.,Civil Aviation Technology College | Hemmatyar A.M.A.,Sharif University of Technology | Hashemipour O.,Shahid Beheshti University
International Journal of Electronics | Year: 2012

Thermal noise is one of the most important challenges in analogue integrated circuits design. This problem is more crucial in switched-capacitor (SC) filters due to the aliasing effect of wide-band thermal noise. In this article, a new simple method is proposed for estimating the power spectrum density of output thermal noise in SC filters, which have acceptable accuracy and short running time. In the proposed method, first using HSPICE simulator, accurate value of accumulated sampled noise on sampler capacitors in each clock state is achieved. Next, using difference equations of the SC filter, frequency response of the SC filter is shaped by time domain analysis. Based on the proposed method, a SC low-pass filter and a second-order SC band-pass filter are analysed. The results are validated by comparing to the previously measured data. © 2012 Copyright Taylor and Francis Group, LLC.

Rashtian M.,Civil Aviation Technology College | Hashemipour O.,Shahid Beheshti University | Navi K.,Shahid Beheshti University | Jalali A.,Shahid Beheshti University
Journal of Circuits, Systems and Computers | Year: 2011

In this paper, a new switched opamp is presented in order to improve the operation of auto-zeroed switched capacitor circuit. This approach results in a considerable reduction in power consumption and a moderate speed improvement. Based on the above improvement, a second-order band-pass filter with a center frequency of 833 kHz and quality factor of 8 is realized and compared with previous works. The proposed switched opamp is also utilized in the structure of a novel z to -z2 block for the design of pseudo two-path band-pass filters. A second-order pseudo two-path band-pass filter with the same specification of the previous work is designed, simulated, and compared. © 2011 World Scientific Publishing Company.

Rashtian M.,Civil Aviation Technology College | Hashemipour O.,Shahid Beheshti University | Navi K.,Shahid Beheshti University | Jalali A.,Shahid Beheshti University
International Journal of Engineering, Transactions B: Applications | Year: 2010

In this paper, a modified auto zeroed integrator is used to design and simulate a low-voltage high-Q switched capacitor pseudo 2-path filter. The filter is a sixth-order Chebyshev band-pass filter operating at sampling frequency of 1MHz and center frequency of 250 kHz with a quality factor of 50. The proposed filter has both low-voltage and high speed properties of the auto zeroed integrators and accurate center frequency of N-path band-pass filters. The operating voltage is 1.5v with no use of voltage bootstrapper circuit. Simulation is done using HSPICE and 0.25μm CMOS technology.

Ghabeli L.,Civil Aviation Technology College | Derpich M.S.,Federico Santa María Technical University
IEEE International Symposium on Information Theory - Proceedings | Year: 2014

In this paper, we study a 3-node asymmetric full-duplex AWGN two-way relay channel with relay private messages where two nodes can communicate with each other only through a third node called the relay, while the relay can itself exchange private messages with two other nodes. Cut-set upper bound and single sided genie upper bound are presented for this channel. To obtain an achievable rate, we use a superposition of nested lattice codes and random Gaussian codes for encoding at the senders, and successive interference cancelation for decoding at the receivers. It is shown that capacities are achieved within constant gaps 2/3 and 2.5/3 bits/sec/Hz per user of single sided genie for restricted and non-restricted models, respectively. © 2014 IEEE.

Effatnejad R.,Islamic Azad University at Karaj | Choopani K.,Islamic Azad University at Karaj | Effatnejad M.,Civil Aviation Technology College
2016 International Conference on Industrial Informatics and Computer Systems, CIICS 2016 | Year: 2016

The presence of the non-linear charges is the most important issue in examining the microgrids. These charges cause the harmonic network, reduce the quality of the power, and cause the difficulty in controlling the frequency, because there is a part of power in other frequencies with no control. This paper investigates the designing the parallel active filter in order to improve the power quality and frequency control. Since the savers should be inevitably used in this kind of networks, therefore, the double-sided inverters of DC to AC are needed. Thus, this paper aims to propose a design for inverter control algorithm so that there is a connection between saver and network for power exchange, the harmonic currents are removed, and an effective frequency control is achieved. Therefore, the complementary theory-based control algorithm of the momentary power (GTIP1) [12] will be explored and the goals are followed based on this algorithm. © 2016 IEEE.

Effatnejad R.,Islamic Azad University at Karaj | Zare A.,Islamic Azad University at Karaj | Choopani K.,Islamic Azad University at Karaj | Effatnejad M.,Civil Aviation Technology College
2016 International Conference on Industrial Informatics and Computer Systems, CIICS 2016 | Year: 2016

Damping low frequency oscillations of power systems is one of the most important determinants of system stability. Due to the increasing growth of wind farms with high penetration levels in power systems as well as their participation and control, it seems important to increase the damping system oscillations. In this paper, doubly fed induction generators (DFIGs) were used for damping the power oscillations. For this purpose, a fuzzy controller as a power oscillation damper (FPOD) was applied to DFIG control loop as backup control and also input and output scales of fuzzy controller were optimized by particle swarm optimization (PSO) algorithm. The main reason was use this hybrid approach is to enhance disturbance rejection and reduction, through fuzzy systems. In order to clarify the DFIG capability in mitigating the inter-area oscillations, non-linear simulations were carried out by MATLAB/Simulink. Simulation study in a four-machine two-area power system show that the DFIG with a FPOD controller was superior to the conventional POD in terms of stabilizing effect as well as robustness against various power generating and loading conditions, unpredictable network structure, and random wind patterns. © 2016 IEEE.

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