A Practical Algorithm for Selective Harmonic Elimination in Five-Level Converters

Farzad Golshan,Adib Abrishamifar,Mohammad Arasteh 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.6

Multilevel converters are being widely used in medium-voltage high-power applications including motor drive systems, utility power transmission, and distribution systems. Selective harmonic elimination (SHE) is a well-known modulation method to generate high quality output voltage waveforms. This paper presents a new simple practical method for generating a generalized five-level waveform without selected low order harmonics. This method is based on a phase-shifted expression for the SHE problem, which can analytically calculate the exact values of switching angles and the feasible modulation index range for three-level and five-level waveforms. The proposed method automatically determines the number of transitions between levels and generates proper output waveform without solving complex trigonometric equations. Due to the simplicity of the computational burden, the real-time implementation of the proposed algorithm can be performed by a simple processor. Simulation and experiment results verify the correctness and effectiveness of the proposed method.

NSGT-based acoustical wave dispersion characteristics of thermo-magnetically actuated double-nanobeam systems

Farzad Ebrahimi,Ali Dabbagh 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.68 No.6

Herein, the thermo-magneto-elastic wave dispersion answers of functionally graded (FG) double-nanobeam systems (DNBSs) are surveyed implementing a nonlocal strain gradient theory (NSGT). The kinematic relations are derived employing the classical beam theory. Also, scale influences are covered precisely in the framework of NSGT. Moreover, Mori-Tanaka homogenization model is introduced in order to obtain the effective material properties of FG nanobeams. Meanwhile, effects of external forces such as thermal and Lorentz forces are included in this research. Also, based upon the Hamilton’s principle, the Euler-Lagrange equations are developed; afterwards, these equations are incorporated with those of NSGT to reach the nonlocal governing equations of FG-DNBSs. Furthermore, according to an analytical approach, the governing equations are solved to obtain the wave frequencies and phase velocities of FG-DNBSs. At the end, some illustrations are rendered to clarify the influences of a wide range of involved parameters.

Propagation of elastic waves in thermally affected embedded carbon-nanotube-reinforced composite beams via various shear deformation plate theories

Farzad Ebrahimi,Pooya Rostami 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.66 No.4

The current study is dedicated to study the thermal effects of wave propagation in beams, reinforced by carbon nanotubes (CNT). Beams, made up of carbon nanotube reinforced composite (CNTRC) are the future materials in various high tech industries. Herein a Winkler elastic foundation is assumed in order to make the model more realistic. Mostly, CNTs are pervaded in cross section of beam, in various models. So, it is tried to use four of the most profitable reconstructions. The homogenization of elastic and thermal properties such as density, Yong’s module, Poisson’s ratio and shear module of CNTRC beam, had been done by the demotic rule of mixture to homogenize, which gives appropriate traits in such settlements. To make this investigation, a perfect one, various shear deformation theories had been utilized to show the applicability of this theories, in contrast to their theoretical face. The reigning equation had been derived by extended Hamilton principle and the culminant equation solved analytically by scattering relations for propagation of wave in solid bodies. Results had been verified by preceding studies. It is anticipated that current results can be applicable in future studies.

Experimental analysis of thermal gradient in concrete box girder bridges and effects of polyurethane insulation in thermal loads reduction

Farzad Raeesi,Sajad Heydari,Hedayat Veladi 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.83 No.5

Environmental thermal loads such as vertical and lateral temperature gradients are significant factors that must be taken into account when designing the bridge. Different models have been developed and used by countries for simulating thermal gradients in bridge codes. In most of the codes only vertical temperature gradients are considered, such as Iranian Standard Loads for Bridge code (ISLB), which only considers the vertical gradient for bridge design proposes. On the other hand, the vertical gradient profile specified in ISLB, has many lacks due to the diversity of climate in Iran, and only one vertical gradient profile is defined for whole Iran. This paper aims to get the both vertical and lateral gradient loads for the concrete box girder using experimental analysis in the capital of Iran, Tehran. To fulfill this aim, thermocouples are installed in experimental concrete segment and temperatures in different location of the segment are recorded. A three dimensional finite element model of concrete box-girder bridge is constructed to study the effects of thermal loads. Results of investigation proved that the effects of thermal loads are not negligible, and must be considered in design processes. Moreover, a solution for reducing the negative effects of thermal gradients in bridges is proposed. Results of the simulation show that using one layer polyurethane insulation can significantly reduce the thermal gradients and thermal stresses.

Thermal buckling analysis of functionally graded carbon nanotube-reinforced composite sandwich beams

Farzad Ebrahimi,Navid Farazmandnia 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.27 No.2

Thermo-mechanical buckling of sandwich beams with a stiff core and face sheets made of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) within the framework of Timoshenko beam theory is presented. The material properties of FG-CNTRC are supposed to vary continuously in the thickness direction and are estimated through the rule of mixture. Also the properties of these materials should be considered temperature dependent. The governing equations and boundary conditions are derived by using Hamilton's principle and solved using an efficient technique called the Differential Transform Method (DTM) to achieve the critical buckling of the sandwich beam in uniform thermal environment. A detailed parametric study is guided to investigate the effects of carbon nanotube volume fraction, slenderness ratio, core-to-face sheet thickness ratio, and clamped-clamped, simply-simply and clamped-simply end supports on the critical buckling behavior of sandwich beams with FG-CNTRC face sheets. Numerical results for comparison of sandwich beams with uniformly distributed carbon nanotube-reinforced composite (UD-CNTRC) face sheets with those with FG-CNTRC face sheets are also presented.

Mechanics of nonlocal advanced magneto-electro-viscoelastic plates

Farzad Ebrahimi,Mohammad Reza Barati,Francesco Tornabene 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.71 No.3

This paper develops a nonlocal strain gradient plate model for damping vibration analysis of smart magneto-electro-viscoelastic nanoplates resting on visco-Pasternak medium. For more accurate analysis of nanoplate, the proposed theory contains two scale parameters related to the nonlocal and strain gradient effects. Viscoelastic effect which is neglected in all previous papers on magneto-electro-viscoelastic nanoplates is considered based on Kelvin–Voigt model. Governing equations of a nonlocal strain gradient smart nanoplate on viscoelastic substrate are derived via Hamilton’s principle. Galerkin’s method is implemented to solve the governing equations. Effects of different factors such as viscoelasticity, nonlocal parameter, length scale parameter, applied voltage and magnetic potential on damping vibration characteristics of a nanoplate are studied.

Development of the FCM-SVR Hybrid Model for Estimating the Suspended Sediment Load

Farzad Hassanpour,Salman Sharifazari,Khaled Ahmadaali,Sara Mohammadi,Zeinab Sheikhalipour 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.6

The accurate estimation of suspended sediment load (SSL) carried by a river is one of the primary issues in river engineering, water resources, and environment projects. Boundary condition and simplification of some important parameters lead to some limitation on the empirical sediment equations which are based on flow and sediment properties. In this study, the potential of a developed Fuzzy C-mean clustering-support vector regression model, as a FCM-SVR hybrid model, was investigated in comparison with sediment rating curve (SRC), artificial neural network (ANN), adaptive neuro-fuzzy inference system (ANFIS), and support vector regression (SVR) models for estimating the daily SSL in Sistan River in Iran. Root mean square error (RMSE), mean absolute error (MAE), determination coefficient (R2), and Nash-Sutcliffe efficiency coefficient (NSE) statistics were utilized to evaluate the accuracy of the models. The result showed that FCM-SVR model estimates SSL (with RMSE, MAE, R2, and NSE equal to 34,415.52 ton/day, 12,256.28 ton/day, 0.922, and 0.918 respectively in testing period) more accurate than other models. The RMSE value, which was 50% lower compared to other models, reveals that this model possesses the lowest error than the other models. Also, the obtained results indicated that the estimated SSLs, using the best FCM-SVR, were in good agreement and linear dependence with observed values. Unlike other models, FCM-SVR model appropriately estimates extreme values of SSL.

Thermo-mechanical vibration analysis of a single-walled carbon nanotube embedded in an elastic medium based on higher-order shear deformation beam theory

Farzad Ebrahimi,Erfan Salari 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.9

In this study, the thermal effect on the free vibration characteristics of embedded Single-walled carbon nanotubes (SWCNTs) based onthe size-dependent Reddy higher order shear deformation beam theory subjected to in-plane thermal loading is investigated by presentinga Navier-type solution and employing a semi-analytical Differential transform method (DTM) for the first time. In addition, the exactnonlocal Reddy beam theory solution presented here should be useful to engineers designing nanoelectromechanical devices. The smallscaleeffect is considered based on nonlocal elasticity theory of Eringen. The nonlocal equations of motion are derived through Hamilton’sprinciple, and they are solved by applying DTM. Numerical results reveal that the proposed modeling and semi-analytical approachcan provide more accurate frequency results of the SWCNTs compared to analytical results and some cases in the literature. The detailedmathematical derivations are presented, and numerical investigations are performed, whereas emphasis is placed on investigating theeffect of several parameters such as small-scale effects, boundary conditions, mode number, thickness ratio, temperature change, andWinkler spring modulus on the natural frequencies of the SWCNTs in detail. The vibration behavior of SWCNTs is significantly influencedby these effects. Results indicate that the inclusion of size effect results in a decrease in nanobeam stiffness and leads to a decreasein natural frequency. Numerical results are presented to serve as benchmarks for future analyses of SWCNTs.

A computer-aided diagnostic system for kidney disease

( Farzad Firouzi Jahantigh ),( Behnam Malmir ),( Behzad Aslani Avilaq ) 대한신장학회 2017 Kidney Research and Clinical Practice Vol.36 No.1

Background: Disease diagnosis is complicated since patients may demonstrate similar symptoms but physician may diagnose different diseases. There are a few number of investigations aimed to create a fuzzy expert system, as a computer aided system for disease diagnosis. Methods: In this research, a cross-sectional descriptive study conducted in a kidney clinic in Tehran, Iran in 2012. Medical diagnosis fuzzy rules applied, and a set of symptoms related to the set of considered diseases defined. The input case to be diagnosed defined by assigning a fuzzy value to each symptom and then three physicians asked about each suspected diseases. Then comments of those three physicians summarized for each disease. The fuzzy inference applied to obtain a decision fuzzy set for each disease, and crisp decision values attained to determine the certainty of existence for each disease. Results: Results indicated that, in the diagnosis of seven cases of kidney disease by examining 21 indicators using fuzzy expert system, kidney stone disease with 63% certainty was the most probable, renal tubular was at the lowest level with 15%, and other kidney diseases were at the other levels. The most remarkable finding of this study was that results of kidney disease diagnosis (e.g., kidney stone) via fuzzy expert system were fully compatible with those of kidney physicians. Conclusion: The proposed fuzzy expert system is a valid, reliable, and flexible instrument to diagnose several typical input cases. The developed system decreases the effort of initial physical checking and manual feeding of input symptoms.

INTELLIGENT FAULT DIAGNOSIS OF GEARBOX UNDER RUNNING-UP CONDITION

Farzad Aminravan,Firooz Bakhtiari-Nejad,Hamidreza Amindavar 한국소음진동공학회 2008 한국소음진동공학회 국제학술대회논문집 Vol.2008 No.7