Sharif Digital Repository

In this study, an analytical method is proposed for design of double-ridged horn (DRH) antenna, which is based on impedance matching of the structure by the method of least squares (MLSs). New basis functions are used for the MLS to obtain optimum impedance functions for the realisation of maximum matching. The resultant reflection coefficients are compared with available methods. The proposed optimum synthesis method is applicable to the arbitrarily tapered DRH antenna with a general cross-section. As two applications, the proposed method is used for the design of linear and non-linear flares of DRH antennas with rectangular and elliptical cross-sections for operation in the frequency band... 

Whole-body vibration (WBV) has been identified as one of the serious risk factors leading to spinal disorders, particularly in professional drivers. Although the influential factors in this area have been investigated epidemiologically, finite element (FE) modeling can efficiently help us better understand the problem. In this study, a modified HYBRID III dummy FE model which was enhanced by detailed viscoelastic discs in the lumbar region was utilized to simulate the effect of WBV on lumbar spine loads. Spinal responses to the vertical sinusoidal vibrations of a generic seat were obtained and spinal injury risk factors were calculated. Effects of variation of excitation frequencies, three... 

The use of acoustic emission (AE) technique for damage diagnostic is typically challenging due to difficulties associated with discrimination of events that occur during different stages of damage that take place in a material or a structure. In this study, an unsupervised kernel fuzzy c-means pattern recognition analysis and the principal component method were utilized to categorize various damage stages in plain and steel fiber reinforced concrete specimens monitored by AE technique. Enhancement of the discrimination and characterization of damage mechanisms were achieved by processing time and frequency domain data. Both domains (time and frequency) were taken into account to propose new... 

In this paper, we propose an accurate visible light indoor localization system for a smartphone using the commercial light-emitting diode (LED) panels which are used primarily for lighting. Each of designed lighting panel contains a space-colorcoded identifier, a matrix with a unique pattern of spatially separated colored LEDs, for labeling different positioning cells while the lighting color is kept white by balancing the number of different sets of colored LEDs. The advantage of this idea is that we do not use the time-frequency domain of visible light communication (VLC) networks resources for positioning signaling. Our positioning technique called geometrical optics positioning algorithm... 

Operational modal analysis techniques classically have been developed based on the assumption that the input to the system is a stationary white noise. While, in many practical cases, the systems are excited by combination of white noise and colored noises (harmonic excitations). Consequently, in conditions where non-white noises are present, the existing OMA methods cannot completely distinguish between the system poles and the induced poles due to colored noises. In order to overcome this weakness of OMA methods, some researches have been conducted in the field. In this paper, a new method is proposed for identifying the modal parameters of the system under the unknown colored noises,... 

Generalized frequency division multiplexing (GFDM) is one of the multicarrier modulation candidates proposed for the 5th generation of wireless networks. Among GFDM linear receivers, GFDM MMSE receiver achieves the best error performance for multipath fading channels at the cost of high numerical complexity. Hence, the combination of GFDM match filter (MF) receiver and double-side successive interference cancellation (DSIC) method is used instead. However, there is a significant gap between the error performance of GFDM MMSE and DSIC/MF receivers for the case of employing modern channel coding. Recently, we have proposed a new multicarrier scheme based on GFDM architecture called generalized... 

Ground-penetrating radar is usually employed to detect such buried objects beneath the ground as pipes, cables, and mines. There exist several methods for monitoring the buried objects, some of which require a relatively long time and heavy computations to create an appropriate image. The signal sent to the environment is reflected due to the characteristic features of the environment, which eventually leads to detection of the buried objects. For detection of the near ground surface targets, there is a very poor distinguishability between the signal reflected from the buried objects and the one from the ground itself. Buried objects in this case are detectable using ultra-wide band signals... 

Partial discharge (PD) measurement is one of the best methods for condition monitoring of transformers. In this paper, we use 5 different types of defects as follows: scratch on winding insulation, bubble in oil, moisture in insulation paper, a very small free metal particle in the transformer tank, and a fixed sharp metal point on the transformer tank, for our PD-related studies. Each type of defect is implemented into 1 of the 5 identical transformer models, which had been developed in the authors' recent work. The continuous wavelet transform is applied to each related measured time-domain PD signals. This process results in an image, for each PD pulse in the time-frequency domain. Using... 

Traditionally, the effects of seismic forces on structures have been mitigated by installing supplemental energy dissipation systems. In this paper, a new approach is explored for the mitigation of earthquake-induced vibrations by obstructing the entrance of seismic energy to the structure through the insertion of some concrete wave barriers within the soil domain. To do so, genetic algorithm (GA) based adaptive optimization methodology is utilized that is capable of finding the efficient layout of the concrete barriers in a manipulated soil zone around the structure. The optimization methodology is coupled with finite element (FE) method for analyzing the complex wave propagation phenomenon... 

In the present study, the development of a neutron noise simulator, DYN-ACNEM, using the Average Current Nodal Expansion Method (ACNEM) in 2-G, 2-D hexagonal geometries is reported. In first stage, the static neutron calculation is performed. The neutron/adjoint flux distribution and corresponding eigen-values are calculated using the algorithm developed based on power iteration method by considering the coarse meshes. The results of the static calculation are validated against the well-known IAEA-2D benchmark problem. In the second stage, the dynamic calculation is performed in the frequency domain in which the dimension of the variable space of the noise equations is lower than the time... 

The use of acoustic emission (AE) technique for damage diagnostic is typically challenging due to difficulties associated with discrimination of events that occur during different stages of damage that take place in a material or a structure. In this study, an unsupervised kernel fuzzy c-means pattern recognition analysis and the principal component method were utilized to categorize various damage stages in plain and steel fiber reinforced concrete specimens monitored by AE technique. Enhancement of the discrimination and characterization of damage mechanisms were achieved by processing time and frequency domain data. Both domains (time and frequency) were taken into account to propose new... 

Operational modal analysis based on power spectral density transmissibility functions (PSDT) is a powerful tool to identify the modal parameters with low sensitivity to excitations. The rotor systems may have the asymmetric damping or stiffness matrices which can lead to increase the difficulties of the identification procedure. In this paper, a new method is proposed to identify the modal parameters of the asymmetric rotary systems by the operational modal analysis based on the power spectral density transmissibility functions. For pole extraction from the PSDT function, a proper parametric identification method such as the Poly-reference Least Squares Complex Frequency-domain method... 

In recent years, different studies have proposed new methods for DNN-based feature extraction and joint acoustic model training and feature learning from raw waveform for large vocabulary speech recognition. However, conventional pre-processed methods such as MFCC and PLP are still preferred in the state-of-the-art speech recognition systems as they are perceived to be more robust. Besides, the raw waveform methods - most of which are based on the time-domain signal - do not significantly outperform the conventional methods. In this paper, we propose a frequency-domain feature-learning layer which can allow acoustic model training directly from the waveform. The main distinctions from... 

In this paper, asymptotic swarm stability of fractional-order swarm systems in the presence of uniform time-delays is studied. By using a frequency domain approach, the necessary and sufficient condition on the values of time-delay is derived to guarantee the asymptotic swarm stability under a directed/undirected interaction graph. Numerical examples are given to confirm the obtained analytical results. © 2015 Informa UK Limited, trading as Taylor & Francis Group  

Z-source family has been widespread in photovoltaic (PV) applications. In trasformerless grid-connected PV systems, the common mode voltage (CMV) time variations, cause the leakage current flow. This current flows through the stray capacitance of the PV panels. For a Z-Source Inverter (ZSI), the CMV would have higher high-frequency harmonics, due to the shoot through states within the switching cycles. In this paper, the CMV of a ZSI is analyzed and a simple method is proposed for the harmonic reduction of the CMV in the ZSI. The CMV reduction method is based on changing the switching states. The CMV in reduced method is compared to the CMV in the traditional ZSI in frequency domain by using... 

Abnormal operating conditions for the timing belt can lead to cracks, fatigue, sudden rupture and damage to engines. In this study, an intelligent system was developed to detect and classify high-load operating conditions and high-temperature operating conditions for timing belts. To achieve this, vibration signals in normal operating conditions, high-load operating conditions and high-temperature operating conditions were collected. Time-domain signals were transformed to the frequency domain and the time-frequency domain using the fast Fourier transform method and the wavelet transform method respectively. In the data-mining stage, 25 statistical features were extracted from different... 

This study is conducted aiming to identify the dynamics of a tapered beam, embedded by piezoelectric layer. Narrowing the tip of the beam equipped with piezoelectric patches leads to optimize the output power after excitation by the frequency sweep input. An accelerometer is installed on the beam base, which measures the acceleration that is applied to the system. Piezoelectric sensors also measure the generated voltage. The experimental test data is handled through CIFER software, using Fourier transform and Bode plot in the frequency domain, to obtain appropriate transfer functions. MATLAB is used for nonlinear simulation and validation of discrete transfer functions by a set of data that... 

This paper investigates the applicability of frequency-domain system identification technique to achieve the equivalent linear dynamics of an autonomous underwater vehicle for control design purposes. Frequency response analysis is performed on the nonlinear and coupled dynamics of the vehicle, utilizing the CIFER® software to extract a reduced-order model in the form of equivalent transfer functions. Advanced features such as chirp-z transform, composite window optimization, and conditioning are employed to achieve high quality and accurate frequency responses. A particular frequency-sweep input is implemented to the nonlinear simulation model to achieve pole-zero transfer functions for yaw... 

This paper deals with the development of a qualified thermal-hydraulic nodalization for modeling Station Black-Out (SBO) accident in PSB-VVER Integral Test Facility (ITF). This study has been performed in the framework of a research project, aiming to develop an appropriate accident management support tool for Bushehr nuclear power plant. In this regard, a nodalization has been developed for thermal-hydraulic modeling of the PSB-VVER ITF by MELCOR integrated code. The nodalization is qualitatively and quantitatively qualified at both steady-state and transient levels. The accuracy of the MELCOR predictions is quantified in the transient level using the Fast Fourier Transform Base Method... 

In this paper, asymptotic swarm stability of fractional-order swarm systems in the presence of uniform time-delays is studied. By using a frequency domain approach, the necessary and sufficient condition on the values of time-delay is derived to guarantee the asymptotic swarm stability under a directed/undirected interaction graph. Numerical examples are given to confirm the obtained analytical results