Sharif Digital Repository

In this paper, the whale optimization algorithm is proposed for harmonics elimination in a cascaded multilevel inverter. In selective harmonic elimination pulse width modulation, the selected low-order harmonics are eliminated by solving nonlinear equations, while the fundamental of output waveform is adjusted to a desired value. In this paper, whale optimization algorithm is applied to a 7-level cascaded H-bridge inverter to solve the equations. Also, it was validated by experimental results, since this algorithm has an ability to search in entire solution space, the probability of catching a global best solution is very high. This method has higher accuracy and probability of convergence... 

In this paper, the whale optimization algorithm is proposed for harmonics elimination in a cascaded multilevel inverter. In selective harmonic elimination pulse width modulation, the selected low-order harmonics are eliminated by solving nonlinear equations, while the fundamental of output waveform is adjusted to a desired value. In this paper, whale optimization algorithm is applied to a 7-level cascaded H-bridge inverter to solve the equations. Also, it was validated by experimental results, since this algorithm has an ability to search in entire solution space, the probability of catching a global best solution is very high. This method has higher accuracy and probability of convergence... 

Small Permanent Magnet Synchronous Generators (PMSGs) are widely used in small rooftop wind turbines. In order to inject the electric power generated by the PMSG, into the grid, a back-to-back AC/DC/AC converter is required. In this paper, a low cost with high efficiency converter is proposed for the rectifier stage to obtain the maximum power per ampere of PMSG. This structure based on Discontinuous Conduction Mode Single-Ended Primary Inductor Converter (DCM SEPIC) with a single power electronic switch, proposes a converter which is cost-effective and suitable for the small wind turbine used in residential applications. Furthermore, other advantages of the proposed converter include... 

Small Permanent Magnet Synchronous Generators (PMSGs) are widely used in small rooftop wind turbines. In order to inject the electric power generated by the PMSG, into the grid, a back-to-back AC/DC/AC converter is required. In this paper, a low cost with high efficiency converter is proposed for the rectifier stage to obtain the maximum power per ampere of PMSG. This structure based on Discontinuous Conduction Mode Single-Ended Primary Inductor Converter (DCM SEPIC) with a single power electronic switch, proposes a converter which is cost-effective and suitable for the small wind turbine used in residential applications. Furthermore, other advantages of the proposed converter include... 

V-shaped Interior PM synchronous motors (IPMSMs) are suitable choices for electric vehicle application because of their high power density and efficiency values. This paper aims to find an appropriate winding layout for the Interior PM synchronous motors. For this purpose, five different winding layouts including single-layer and two-layer conventional concentrated, two-layer and four-layer pseudo-concentrated and distributed windings were applied to a baseline three-phase, S-pole, 10kw V-shaped interior PM synchronous motor. The four-layer pseudo-concentrated winding shows better magnetic characteristics among the five winding methods. Therefore, the performance of the baseline V-shaped... 

Direct-drive permanent magnet synchronous generators enjoy numerous advantages including improved reliability, low maintenance, long life, and developed performance characteristics. In recent years, many researchers have worked on these generators to enhance their performance, especially for the wind turbine application. The focus of this paper is on the development of a step-by-step method for the design of a permanent magnet synchronous generator. Then, the winding function method is used to model the generator and calculate its output characteristics analytically. The analytical results of the designed generator are validated using Finite Element Analysis (FEA) and it is demonstrated that... 

Accurate position estimation is an integral part of any motion control system. Besides, instantaneous position of poles plays an important role in electronic drive system of modern PM machines. Resolvers, due to their structure, are the most reliable position sensors in harsh environments. However, resolvers are not as accurate as optical encoders in normal conditions. To increase the accuracy of these sensors, various solutions are used, such as optimization in winding arrangement, rotor and stator contour, slot-pole combinations, and improvements in resolver-to-digital converter. In this paper, fractional slot concentrated winding is used in an axial flux resolver. By the aid of winding... 

Local educational institutions produce in-house English for Specific Purpose (ESP) materials according to the curriculum policies designated and developed by the Ministry of Higher Education In Iran. To this end, this book aims to be used in the Iranian setting at the tertiary level for undergraduate students majoring in Mechanical Engineering. Moreover, the style of English usage in this ESP textbook is American.
Regarding the content of the textbook, it has both thematic organizations in which the topics are relevant and includes sufficient treatment of the target language areas necessary for the students. The principle organizing approach of this textbook is theme-based. In addition,... 

This paper studies unamped oscillations of fractional-order Duffing system. Stability theorems for fractional order systems are used to determine the characteristic polynomial of the system in order to find the parametric ranges for undamped oscillations in this system. We also derive relations for estimating the frequency and the amplitude of the oscillations in this system using a describing function method. Finally numerical simulation results are provided to justify the analysis  

This paper deals with the existence and the characteristics of the limit cycles in the fractional-order Arneodo system. The analysis is done using the describing function method. Our focus is on a special case where two limit cycles exist. The parametric range for the case of interest is derived, and the frequency and the amplitude of the oscillation are predicted. Numerical simulation results are presented to further demonstrate the reliability of the analysis  

This paper studies undamped oscillations of fractional-order Duffing system. Stability theorems for fractional order systems are used to determine the characteristic polynomial of the system in order to find the parametric ranges for undamped oscillations in this system. We also derive relations for estimating the frequency and the amplitude of the oscillations in this system using a describing function method. Finally numerical simulation results are provided to justify the analysis  

As steel plate shear walls are typically used in the building central cores around the elevators and stairs, introduction of an opening as door seems to be inevitable in steel plate shear wall spans. Due to the weakening of the steel plate shear walls’ performance caused by this particular type of opening, the use of stiffeners around the opening is necessary. Nevertheless, introduction of stiffeners around all sides of the opening, which does continue to boundary elements, is very expensive and inefficient. Therefore, the study on the effect of different arrangements of stiffeners on the behavior of steel plate shear walls is significant. In this research, a number of steel plate shear... 

Land cover classification is one of the most important applications of POLSAR images. In this paper, a hybrid biogeography-based optimization support vector machine (HBBOSVM) has been introduced to classify POLSAR images of RADARSAT 2 in band C acquired from San Francisco, USA. The main purpose of this classification is to minimize the number of features and maximize classification accuracy. The proposed method consists of three main steps: preprocessing, feature selection and classification. As preprocessing, radiometric calibration, speckle reduction and feature extraction have been performed. In the proposed HBBO, the combination of onlooker bee of artificial bee colony (ABC) and... 

Accurate estimation of the in-plane shear modulus of solids reinforced by nano-/micro-size elliptical multi-coated fibers is the focus of this paper. It is well-known that at the scales comparable to the nanoscopic length scales of the material, traditional theory of elasticity ceases to hold and, moreover, due to lack of consideration of such length scales has an innate weakness of sensing the size effect. Therefore, it is proposed to formulate and calculate the effective shear modulus of the nano-/micro-composite within micropolar theory which introduces two material characteristic lengths into the field equations. For this purpose, Mori-Tanaka theory is extended to treat nested... 

Nanoscopic elastic behavior of the field quantities in the vicinities of nanosize defects and nano-inhomogeneities cannot be properly described within the size independent classical theory. As a remedy to this type of dilemmas and enhancement of the accuracy of the solution, polar or gradient continuum theories may be utilized. The current work is concerned with composites consisting of micropolar matrix and micropolar ellipsoidal particles with periodic distribution throughout the three dimensional space. In particular, the analytical determinations of the effective micropolar elastic moduli tensor, effective micropolar couple stress moduli tensor, and effective micropolar characteristic... 

Nanoscopic elastic behavior of the field quantities in the vicinities of nanosize defects and nano-inhomogeneities cannot be properly described within the size independent classical theory. As a remedy to this type of dilemmas and enhancement of the accuracy of the solution, polar or gradient continuum theories may be utilized. The current work is concerned with composites consisting of micropolar matrix and micropolar ellipsoidal particles with periodic distribution throughout the three dimensional space. In particular, the analytical determinations of the effective micropolar elastic moduli tensor, effective micropolar couple stress moduli tensor, and effective micropolar characteristic... 

This paper presents the effect of robotics assisted language learning (RALL) on the vocabulary learning and retention of Iranian English as foreign language (EFL) junior high school students in Tehran, Iran. After taking a vocabulary pre-test, 46 beginner level female students at the age of 12, studying in their first year of junior-high participated in two groups of RALL (30 students) and non-RALL (16 students) in this study. The textbook used was the English book (Prospect-1) devised by the Iranian Ministry of Education for 7th graders, and the vocabulary taught and tested (pre-test and post-test) were taken from this book. Moreover, the treatment given by a teacher accompanied by a... 

This study aims at examining the effect of Robot Assisted language learning (RALL) on the anxiety level and attitude in the English language learning classroom. Forty-six female students who were beginners at the age of 12 participated in this study and were randomly assigned into two groups of RALL (30 students) and non-RALL (16 students). The treatment was given by a teacher accompanied by a humanoid robot assistant for the RALL group. Two questionnaires of anxiety [15] and attitude [19] were utilized to measure the students' anxiety and attitude. The results of descriptive and t-tests indicated that there was lower anxiety and positive attitude towards English learning in the RALL group... 

This study aimed to examine the effect of robot assisted language learning (RALL) on the anxiety level and attitude in English vocabulary acquisition amongst Iranian EFL junior high school students. Forty-six female students, who were beginners at the age of 12, participated in this study and were randomly assigned into two groups of RALL (30 students) and non-RALL (16 students). The textbook, the materials, as well as the teacher were the same in the two groups. However in the RALL group, the treatment was given by a teacher accompanied by a humanoid robot assistant. Two questionnaires of anxiety and attitude were utilized to measure the students’ anxiety and attitude (Horwitz et al. 1986;... 

This paper presents the design characteristics of a new robot Assistant for Social Aims (RASA), being an upper-torso humanoid robot platform currently under final stages of development. This project addresses the need for developing affordable humanoid platforms designed to be utilized in new areas of social robotics research, primarily teaching Persian Sign Language (PSL) to children with hearing disabilities. RASA is characterized by three features which are hard to find at the same time in today’s humanoid robots: its dexterous hand-arm systems enabling it to perform sign language, low development cost, and easy maintenance. In this paper, design procedures and considerations are briefly...