Search published articles


Showing 47 results for Analysis

H. Mahdavi-Nasab, Shohreh Kasaei,
Volume 1, Issue 2 (4-2005)
Abstract

Motion estimation and compensation is an essential part of existing video coding systems. The mesh-based motion estimation (MME) produces smoother motion field, better subjective quality (free from blocking artifacts), and higher peak signal-to-noise ratio (PSNR) in many cases, especially at low bitrate video communications, compared to the conventional block matching algorithm (BMA). However, the iterative refinement process of MME is computationally much costly and makes the method impractical in real- (or near real-) time systems. Also, eliminating the iterative refinement step deteriorates the motion estimation result. In this paper, we propose motion adaptive interpolation schemes for noniterative MME, which use BMA to compute the motion vectors (MVs) of mesh nodes. The proposed algorithm aims at compromising the MME and BMA by modifying the interpolation patterns (IPPs) of the MME in an adaptive manner, based on the MVs of mesh nodes. Experimental results show notable rate-distortion improvement over both BMA and conventional non-iterative MME, with acceptable visual quality and system complexity, especially when applied to sequences with medium to high motion activities.
Moniri, Farshad,
Volume 2, Issue 1 (1-2006)
Abstract

Power transformers are key components in electrical power supplies and their failure could cause severe consequences on continuity of service and also generates substantial costs. Identifying problems at an early stage, before catastrophic failure occurs, is a great benefit for reliable operation of power transformers. Frequency Response Analysis (FRA) is a new, well-known and powerful diagnostic test technique for transformers which could find mechanical as well as electrical faults such as detection and positioning of winding short circuit, winding movement, loss of clamping pressure, aging of insulation, etc. Yet there are several practical limitations to affect the accuracy and ease using this test as a regular condition monitoring technique in the field that many of them originated from noise and measuring errors. This paper purposes a transformer automated self diagnosis system can be installed on every power supply as a part of SCADA to extract FRA graphs from transformers and offers high repeatability which is a great benefit for FRA test. This is the first time that KALMAN Filter will be use in order to eliminate narrow-band and wide-band noises from FRA graphs that ends up not only smoothed measurement but also rate of changes that is so valuable in decision making and scheduling for transformers maintenance. So we will have an intelligent system which is able to predict the future of transformer using experience of not only own self but also all the transformers in an integrated network.


M. Abadi, S. Jalili,
Volume 2, Issue 3 (7-2006)
Abstract

Intruders often combine exploits against multiple vulnerabilities in order to break into the system. Each attack scenario is a sequence of exploits launched by an intruder that leads to an undesirable state such as access to a database, service disruption, etc. The collection of possible attack scenarios in a computer network can be represented by a directed graph, called network attack graph (NAG). The aim of minimization analysis of network attack graphs is to find a minimum critical set of exploits that completely disconnect the initial nodes and the goal nodes of the graph. In this paper, we present an ant colony optimization algorithm, called AntNAG, for minimization analysis of large-scale network attack graphs. Each ant constructs a critical set of exploits. A local search heuristic has been used to improve the overall performance of the algorithm. The aim is to find a minimum critical set of exploits that must be prevented to guarantee no attack scenario is possible. We compare the performance of the AntNAG with a greedy algorithm for minimization analysis of several large-scale network attack graphs. The results of the experiments show that the AntNAG can be successfully used for minimization analysis of large-scale network attack graphs.
M. Mahdavi, Sh. Samavi, N. Zaker, M. Modarres-Hashemi,
Volume 4, Issue 3 (10-2008)
Abstract

In this paper we present a new accurate steganalysis method for the LSB

replacement steganography. The suggested method is based on the changes that occur in the

histogram of an image after the embedding of data. Every pair of neighboring bins of a

histogram are either inter-related or unrelated depending on whether embedding of a bit of

data in the image could affect both bins or not. We show that the overall behavior of all

inter-related bins, when compared with that of the unrelated ones, could give an accurate

measure for the amount of the embedded data. Both analytical analysis and simulation

results show the accuracy of the proposed method. The suggested method has been

implemented and tested for over 2000 samples and compared with the RS Steganalysis

method. Mean and variance of error were 0.0025 and 0.0037 for the suggested method

where these quantities were 0.0070 and 0.0182 for the RS Steganalysis. Using 4800

samples, we showed that the performance of the suggested method is comparable with

those of the RS steganalysis for JPEG filtered images. The new approach is applicable for

the detection of both random and sequential LSB embedding.


P. M. Farahabadi, H. Miar-Naimi, A. Ebrahimzadeh,
Volume 5, Issue 1 (3-2009)
Abstract

New equations are proposed for frequency and amplitude of a ring oscillator. The method is general enough to be used for all types of delay stages. Using exact largesignal circuit analysis, closed form equations for estimating the frequency and amplitude of a high frequency ring oscillator are derived as an example. The method takes into account the effect of various parasitic capacitors to have better accuracy. Based on the loop gain of the ring, the transistors may only be in saturation or experience cutoff and triode regions. The analysis considers all of the above mentioned scenarios respectively and gives distinct equations. The validity of the resulted equations is verified through simulations using TSMC 0.18 µm CMOS process. Simulation results show the better accuracy of the proposed method compared with others.
J. Beiza, S. H. Hosseinian, B. Vahidi,
Volume 5, Issue 3 (9-2009)
Abstract

This paper presents a novel approach for fault type estimation in power systems. The Fault type estimation is the first step to estimate instantaneous voltage, voltage sag magnitude and duration in a three-phase system at fault duration. The approach is based on time-domain state estimation where redundant measurements are available. The current based model allows a linear mapping between the measured variable and the states to be estimated. This paper shows a possible for fault instance detection, fault location identification and fault type estimation utilizing residual analysis and topology error processing. The idea is that the fault status does not change measurement matrix dimensions but changes some elements of the measurement matrix. The paper addresses how to rebuilt measurement matrix for each type of faults. The proposed algorithm is shown that the method has high effectiveness and high performance for forecasting fault type and for estimating instantaneous bus voltage. The performance of the novel approach is tested on IEEE 14-bus test system and the results are shown.
C. Lucas, F. Tootoonchian, Z. Nasiri-Gheidari,
Volume 6, Issue 3 (9-2010)
Abstract

In this paper a brushless permanent magnet motor is designed considering minimum thrust ripple and maximum thrust density (the ratio of the thrust to permanent magnet volumes). Particle Swarm Optimization (PSO) is used as optimization method. Finite element analysis (FEA) is carried out base on the optimized and conventional geometric dimensions of the motor. The results of the FEA deal to the significant improvement of the all objective functions.
C. Lucas , Z. Nasiri-Gheidari , F. Tootoonchian,
Volume 6, Issue 4 (12-2010)
Abstract

In this paper particle swarm optimization (PSO) is used for a design optimization of a linear permanent magnet synchronous motor (LPMSM) considering ultra low thrust force ripples, low magnet consumption, improved efficiency and thrust. The influence of PM material is discussed, too and the modular poles are proposed to achieve the best characteristic. PM dimensions and material, air gap and motor width are chosen as design variables. Finally 2-D finite element analyses validate the optimization results.
M. R. Homaeinezhad, A. Ghaffari, H. Najjaran Toosi, M. Tahmasebi, M. M. Daevaeiha,
Volume 7, Issue 1 (3-2011)
Abstract

In this study, a new long-duration holter electrocardiogram (ECG) major events detection-delineation algorithm is described which operates based on the false-alarm error bounded segmentation of a decision statistic with simple mathematical origin. To meet this end, first three-lead holter data is pre-processed by implementation of an appropriate bandpass finite-duration impulse response (FIR) filter and also by calculation of the Euclidean norm between corresponding samples of three leads. Then, a trous discrete wavelet transform (DWT) is applied to the resulted norm and an unscented synthetic measure is calculated between some obtained dyadic scales to magnify the effects of low-power waves such as P or T-waves during occurrence of arrhythmia(s). Afterwards, a uniform length window is slid sample to sample on the synthetic scale and in each slid, six features namely as summation of the nonlinearly amplified Hilbert transform, summation of absolute first order differentiation, summation of absolute second order differentiation, curve length, area and variance of the excerpted segment are calculated. Then all feature trends are normalized and superimposed to yield the newly defined multiple-order derivative wavelet based measure (MDWM) for the detection and delineation of ECG events. In the next step, a α-level Neyman-Pearson classifier (which is a false-alarm probability-FAP controlled tester) is implemented to detect and delineate QRS complexes. To show advantages of the presented method, it is applied to MIT-BIH Arrhythmia Database, QT Database, and T-Wave Alternans Database and as a result, the average values of sensitivity and positive predictivity Se = 99.96% and P+ = 99.96% are obtained for the detection of QRS complexes, with the average maximum delineation error of 5.7 msec, 3.8 msec and 6.1 msec for P-wave, QRS complex and T-wave, respectively showing marginal improvement of detection-delineation performance. In the next step, the proposed method is applied to DAY hospital high resolution holter data (more than 1,500,000 beats including Bundle Branch Blocks-BBB, Premature Ventricular Complex-PVC and Premature Atrial Complex-PAC) and average values of Se=99.98% and P+=99.97% are obtained for QRS detection. In summary, marginal performance improvement of ECG events detection-delineation process in a widespread values of signal to noise ratio (SNR), reliable robustness against strong noise, artifacts and probable severe arrhythmia(s) of high resolution holter data and the processing speed 163,000 samples/sec can be mentioned as important merits and capabilities of the proposed algorithm.
M. Aghamohammadi, S. S. Hashemi, M. S. Ghazizadeh,
Volume 7, Issue 1 (3-2011)
Abstract

This paper presents a new approach for estimating and improving voltage stability margin from phase and magnitude profile of bus voltages using sensitivity analysis of Voltage Stability Assessment Neural Network (VSANN). Bus voltage profile contains useful information about system stability margin including the effect of load-generation, line outage and reactive power compensation so, it is adopted as input pattern for VSANN. In fact, VSANN establishes a functionality for VSM with respect to voltage profile. Sensitivity analysis of VSM with respect to voltage profile and reactive power compensation extracted from information stored in the weighting factor of VSANN, is the most dominant feature of the proposed approach. Sensitivity of VSM helps one to select most effective buses for reactive power compensation aimed enhancing VSM. The proposed approach has been applied on IEEE 39-bus test system which demonstrated applicability of the proposed approach.
F. Mohseni-Kolagar, H. Miar-Naimi,
Volume 7, Issue 3 (9-2011)
Abstract

Due to the nonlinear nature of the Bang-Bang phase-locked loops (BBPLLs), its transient analysis is very difficult. In this paper, new equations are proposed for expression of transient behavior of the second order BBPLLs to phase step input. This approach gives new insights into the transient behavior of BBPLLs. Approximating transient response to reasonable specific waveform the loop transient time characteristics such as locking time, peak time, rise time and over shoot are derived with acceptable accuracy. The validity of the resulted equations is verified through simulations using MATLAB SIMULINK. Simulation results show the high accuracy of the proposed method to model BBPLLs behavior.
H. Yaghobi, K. Ansari, H. Rajabi Mashhadi,
Volume 7, Issue 4 (12-2011)
Abstract

A reliable and accurate diagnosis of inter-turn short circuit faults is a challenging problem in the area of fault diagnosis of electrical machines. The purpose of this challenge is to be more efficient in fault detection and to provide a reliable method with low-cost sensors and simple numerical algorithms which not only detect the occurrence of the fault, but also locate its position in the winding. Hence, this paper presents a novel method for diagnosis of different kinds of inter-turn winding faults in a salient-pole synchronous generator using the change in the magnetic flux linkage. It describes the influence of inter-turn winding faults on the magnetic flux linkage distribution of the generator. The main feature of the proposed method is its capability to identify the faulty coils under two types of inter-turn winding faults. Also, simple algorithm, low cost sensor and sensitivity are the other feature in the proposed technique. In this method, generator air gap flux linkage is measured via search coils sensor installed under the stator wedges. Theoretical approach based on Finite Element Method (FEM) together with experimental results derived from a 4-pole, 380U, 1500 rpm, 50 Hz, 50 KVA, 3-phase salient-pole synchronous generator confirm the validity of the proposed method.
S. Haji Nasiri, M. K. Moravvej-Farshi, R. Faez,
Volume 8, Issue 1 (3-2012)
Abstract

Time domain analysis of multilayer graphene nanoribbon (MLGNR) interconnects, based on ‎transmission line modeling (TLM) using a six-order linear parametric expression, has been ‎presented for the first time. We have studied the effects of interconnect geometry along with ‎its contact resistance on its step response and Nyquist stability. It is shown that by increasing ‎interconnects dimensions their propagation delays are increased and accordingly the system ‎becomes relatively more stable. In addition, we have compared time responses and Nyquist ‎stabilities of MLGNR and SWCNT bundle interconnects, with the same external dimensions. ‎The results show that under the same conditions, the propagation delays for MLGNR ‎interconnects are smaller than those of SWCNT bundle interconnects are. Hence, SWCNT ‎bundle interconnects are relatively more stable than their MLGNR rivals.‎
S. R. Mousavi-Aghdam, M. R. Feyzi, Y. Ebrahimi,
Volume 8, Issue 1 (3-2012)
Abstract

This paper presents a new design to reduce torque ripple in Switched Reluctance Motors (SRM). Although SRM possesses many advantages in terms of motor structure, it suffers from large torque ripple that causes problems such as vibration and acoustic noise. The paper describes new rotor and stator pole shapes with a non-uniform air gap profile to reduce torque ripple while retaining its average value. An optimization using fuzzy strategy is successfully performed after sensitivity analysis. The two dimensional (2-D) finite element method (FEM) results, have demonstrated validity of the proposed new design.
M. Masoumi,
Volume 8, Issue 1 (3-2012)
Abstract

Differential Power Analysis (DPA) implies measuring the supply current of a cipher-circuit in an attempt to uncover part of a cipher key. Cryptographic security gets compromised if the current waveforms obtained correlate with those from a hypothetical power model of the circuit. As FPGAs are becoming integral parts of embedded systems and increasingly popular for cryptographic applications and rapid prototyping, it is imperative to consider security on FPGAs as a whole. During last years, there has been a large amount of work done dealing with the algorithmic and architectural aspects of cryptographic schemes implemented on FPGAs, however, there are only a few articles that assess their vulnerability to such attacks which, in practice, pose far a greater danger than algorithmic attacks. This paper first demonstrates the vulnerability of the Advanced Encryption Standard Algorithm (AES) implemented on a FPGA and then presents a novel approach for implementation of the AES algorithm which provides a significantly improved strength against differential power analysis with a minimal additional hardware overhead. The efficiency of the proposed technique was verified by practical results obtained from real implementation on a Xilinx Spartan-II FPGA.
F. Tootoonchian, K. Abbaszadeh, M. Ardebili,
Volume 8, Issue 3 (9-2012)
Abstract

Resolvers are widely used in electric driven systems especially in high precision servomechanisms. Both encapsulated and pancake resolvers suffer from a major drawback: static eccentricity (SE). This drawback causes a significant increase in resolver output position error (RPE) which could not be corrected electronically. To reduce RPE, this paper proposes a novel structure with axial flux. Proposed topology, design guidelines, optimization procedure and several key features to improve the sensitivity of axial flux resolver (AFR) against SE are studied. Furthermore, to minimize RPE an optimized design is attained. The machines are investigated in detail by using d-q model and 3D time stepping finite-element analysis. The results of theses two methods are compared and both prototype machines (proposed and optimized) are built. In order to evaluate proposed topologies, an experimental test setup is devised. Finally, the experimental results of the prototype machines verified the analysis results.
R. Ghazi, N. Pariz, R. Zeinali,
Volume 9, Issue 2 (6-2013)
Abstract

In this paper, the effect of Static VAr Compensator (SVC) parameters on the nonlinear interaction of steam power plant turbine-generator set is studied using the Modal Series (MS) method. A second order representation of a power system equipped with SVC is developed and then by MS method the nonlinear interaction of torsional modes is assessed under various conditions and the most influencing factors are determined. The results show that the stress conditions and some SVC control parameters will adversely affect the dynamic performance of a power system by increasing the nonlinear interaction of torsional modes. In this situation, the MS method can precisely provide a reliable prediction of the torsional oscillations amplitudes and the frequency content of the output system response. As the angle and speed of turbine-generator segments are used as input signals in several controllers, the frequency content of these signals are quite important in designing such controllers. This analysis is performed on a 4-areas WSCC system, which is equipped with a SVC. The obtained results can provide some important guidelines for coordinate operation and design of FACTS controllers to reduce the risk of shaft failure arising from torsional interaction in long term.
H. Fallah Khoshkar, A. Doroudi, M. Mohebbi,
Volume 10, Issue 4 (12-2014)
Abstract

This paper studies the effects of symmetrical voltage sags on the operational characteristics of a Permanent Magnet Synchronous Motor (PMSM) by Finite Element Method (FEM). Voltage sags may cause high torque pulsations which can damage the shaft or equipment connected to the motor. By recognizing the critical voltage sags, sags that produce hazardous torque variations could be prevented. Simulations results will be provided and the critical voltage sags are recognized. A simple theoretical analysis will also be presented to obtain a qualitative understanding of the phenomena occurring in PMSM during symmetrical voltage sags
M. Hosseini Abardeh, R. Ghazi,
Volume 11, Issue 1 (3-2015)
Abstract

The matrix converter instability can cause a substantial distortion in the input currents and voltages which leads to the malfunction of the converter. This paper deals with the effects of input filter type, grid inductance, voltage fed to the modulation algorithm and the synchronous rotating digital filter time constant on the stability and performance of the matrix converter. The studies are carried out using eigenvalues of the linearized system and simulations. Two most common schemes for the input filter (LC and RLC) are analyzed. It is shown that by a proper choice of voltage input to the modulation algorithm, structure of the input filter and its parameters, the need for the digital filter for ensuring the stability can be resolved. Moreover, a detailed model of the system considering the switching effects is simulated and the results are used to validate the analytical outcomes. The agreement between simulation and analytical results implies that the system performance is not deteriorated by neglecting the nonlinear switching behavior of the converter. Hence, the eigenvalue analysis of the linearized system can be a proper indicator of the system stability.
M. Rasoulpoor, M. Mirzaie, S. M. Mirimani,
Volume 12, Issue 1 (3-2016)
Abstract

This paper investigates the effect of metallic sheaths on losses and temperature of medium voltage power cables. Two grounding methods of sheaths, including both ends bonding and single point bonding that causes different situations on cable ampacity, are considered. Electrical losses of cables that are main sources of heat are calculated in both conductor and metallic sheath of the cables. Sheathed and unsheathed medium voltage single conductor cables in flat and trefoil formations with different distances are considered, while calculated losses are compared in different constructions. Calculations of resistive losses are performed based on finite element method (FEM) and IEC standard formulations. The results of two methods are compared and analyzed. Moreover, the effects of eddy currents and circulating currents of sheath on total resistive losses are evaluated. Finally, thermal analysis based on FEM is executed to achieve maximum temperature of cable in different constructions. Simulation results show the importance of metallic sheaths and grounding system effects in power cable ampacity analysis.



Page 1 from 3    
First
Previous
1
 

Creative Commons License
© 2022 by the authors. Licensee IUST, Tehran, Iran. This is an open access journal distributed under the terms and conditions of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) license.