Sharif Digital Repository

One of the most essential and costly stages in Concrete Face Rockfill Dams (CFRD) construction is to implement the concrete at the upstream face of the dam without joints. As the face concrete is considered as the most integral part to prevent water penetration in CFRDs, it's quality control is of paramount importance. One of the conventional approaches for quality control of the concrete which is used in CFRD is the compressive strength of laboratory samples. The comparison of laboratory and in situ measurements provides information about the accuracy of the obtained results. This research investigates the correlation of concrete compressive strength determined by using different methods in... 

This study focuses on the spectrochemical estimation of pH and titratable acidity (TA) of apples of Fuji variety at different stages of ripening. A novel approach is proposed for near-infrared (NIR) spectral analysis using hybrid machine learning methods that combine artificial neural networks (ANN) and metaheuristic algorithms. One hundred twenty samples were collected at three ripening stages and spectral data within two bands of NIR were extracted from each sample to predict the acidity properties. Alternatively, the 4 most effective wavelengths were also selected using a hybrid of ANN and the cultural algorithm. The experimental results prove that the models using spectral bands and the... 

After a significant earthquake, the updated status of the structural elements is usually determined based on a qualitative visual inspection. Although visual inspection provides a prompt assessment of the damaged elements, the output of this subjective method is influenced by the experience and decision of a trained inspector, which may vary from case to case. In this study, an innovative machine learning-based procedure is developed to automate damage state identification of non-ductile reinforced concrete moment frames (RCMFs) utilizing visual indices of crack patterns of the concrete surface. An extensive database including 264 surface crack patterns is constructed corresponding to 61... 

In this paper, we study the backaction effect on the force exerted upon Rayleigh particles in guided structures. We show that the backaction becomes stronger as the group velocity of the guided modes is decreased, which is not unexpected since the fall of group velocity increases the interaction time between the particle and the electromagnetic field. Interestingly, the sign of the group velocity affects the pushing and pulling nature of the exerted electromagnetic force. We specifically investigate the case of a single mode optical waveguide both in the propagating and evanescent regimes, and show that the backaction enables us to enhance the ratio of the potential depth to the trapping... 

An exact analysis based on the wave function expansion is carried out to study the scattering of a plane harmonic acoustic wave incident at an arbitrary angle upon an arbitrarily thick helically filament-wound (anisotropic) cylindrical shell submerged in and filled with compressible ideal fluids. Using the laminated approximation method, a modal state equation with variable coefficients is set up in terms of appropriate displacement and stress functions and their cylindrical harmonics to present an analytical solution based on the three-dimensional exact equations of anisotropic elasticity. Taylor's expansion theorem is then employed to obtain the solution to the modal state equation,... 

Determining the shape, area, volume, and direction of flaws using ultrasonic imaging of metallic pieces, is a method estimating the severity of their defects. Different methods are used to process ultrasound images. Among these methods are spectral analyses, statistical, mathematical and intelligent methods. Within each of these, there are some advantages as well as limitations. Prony algorithm, which has been used as a parametric method for extracting exponential components of a signal, has several applications in signal modeling, system identification and classification. In this paper, after simulating pieces of oil pipeline, digital Wavelet transform has been used to reduce the noise of... 

The aim of this study was to evaluate the effects of applying low replacement ratios (0.75% and 1.50% of the binder weight) of nano-SiO2 particles with different specific surface areas (200 and 380 m2/g) on the properties of high-performance concrete (HPC). Mechanical (compressive and splitting tensile strengths), electrical resistivity, non-destructive (ultrasonic pulse velocity), and microstructural (mercury intrusion porosimetry, X-ray diffraction, and scanning electron microscopy) tests were conducted to investigate the macroscopic and microscopic effects of nano-SiO2 particles on HPC characteristics. The results indicated that the performance of nano-SiO2 particles significantly... 

Over the last few decades, polymer concrete (PC) has been finding use in quick repairing of concrete structures. However, there have been only few studies on the mechanical behavior of PC. The aim of this study is to evaluate the mechanical behavior of PC using destructive and non-destructive tests (NDT). The mixtures were prepared with three different polymer ratios (10%, 12%, and 14%) and two different coarse aggregate sizes (4.75–9.5 mm and 9.5–19 mm). The samples were subsequently tested under three different temperatures (−15 °C, +25 °C, and +65 °C). The Taguchi method and analysis of variance (ANOVA) were used to optimize PC mixes based on the compressive, splitting-tensile, and... 

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... 

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... 

This study investigates the mechanical properties of lightweight polymer concrete (LWPC) containing four different polymer ratios (10%, 12%, 14%, and 16%) tested at three different temperatures (−15 °C, +5 °C, and +25 °C) using destructive and non-destructive tests. In addition, a series of expressions are suggested to predict the splitting-tensile, flexural and impact strength of LWPC based on the main parameters and compressive strength. The analysis of variance (ANOVA) method was also used to determine relative contributions of the experimental parameters. The results of the destructive tests show that increasing the polymer ratio caused an increase in the compressive, splitting-tensile,... 

An efficient Non-Destructive Evaluation algorithm has been developed in order to extract the required information for pattern recognition of defects in the conductive samples. Using high-Tc gradiometer RF-SQUIDs in unshielded environments and incorporating an automated two dimensional non-magnetic scanning robot, samples with different intentional defects have been tested. We have used a developed noise cancellation approach for the improvement of the effectiveness of the used inverse-problem technique. In this approach we have used a well examined Finite Element Method (FEM) to apply a noise reduction filtering on the obtained raw magnetic image data before incorporating the signal... 

In this paper, a pulsed THz imaging system in normal geometry is presented experimentally and the effect of placing a pinhole in front of a covered sample on image quality has been investigated too. Also, the improvement of image quality by using ray transfer matrix is described theoretically. Finally, by using contour system the results are evaluated and the accuracy of THz imaging system is tested. © 2016 IEEE  

A three-phase dual active bridge (DAB) converter is designed and constructed as the DC/DC stage of a 50 kW fast charger station. Recently introduced 300A SiC power modules and drivers are utilized in the converter to obtain a high efficiency. Each module has two interconnected switches with anti-parallel diodes resembling a converter leg. It is observed that the driver halts the module operation as a result of protective actions such as over-current, gate under-voltage, or gate overvoltage. In such case the module operates as a leg with two diodes until an external hardware signal resets the driver. The aim of this paper is to provide analysis, simulation and experiments for a three-phase... 

Damage detection and structural health monitoring using the electromechanical impedance method has been accepted as an effective technique between various approaches of nondestructive evaluation. Many efforts have been made on experimental methods for obtaining the impedance of structures. However, expensive experimental methods encourage researchers to develop theoretical models. In this paper, a new theoretical model is developed for damage detection of L-shaped beams, which are basic components in frame structures, with an embedded piezoelectric wafer active sensor. For this purpose, a chirp signal of voltage is used to activate a piezoelectric patch for inducing local strains that lead... 

Ultrasonic Testing (UT) is one of the most common types of nondestructive methods that is being used in various industries, especially in the automotive industry. In this paper, qualitative and quantitative control of resistance spot welds on three-sheet joints was studied. Initially, mathematical model of ultrasonic waves was extracted for triple sheet joints. Then, acoustic simulation of ultrasonic testing on spot welds was performed using Finite Element Method (FEM). Afterwards, A Multilayer Perceptron (MLP) neural network was used to classify spot welds based on their diameter. There was a mean error of 20.9 % between peak amplitudes of numerical and theoretical models which the most... 

Journal-bearings play a significant role in industrial applications and the necessity of condition monitoring with nondestructive tests is increasing. This paper deals a proper fault detection technique based on power spectral density (PSD) of vibration signals in combination with K-Nearest Neighbor and Support Vector Machine (SVM). The frequency domain vibration signals of an internal combustion engine with three journal-bearing conditions were gained, corresponding to, (i) normal, (ii) corrosion and (iii) excessive wear. The features of the PSD values of vibration signals were extracted using statistical and vibration parameters. The extracted features were used as inputs to the KNN and... 

Crack detection by Piezoelectric Wafer Active Sensors (PWAS) is one of the emerging methods of Non-destructive Evaluation (NDE). These sensors can assess the health state of the structure in far filed through the analyzing the high frequency Lamb wave propagation. As PWAS is the essential part of this method, simulation and modeling of these sensors and their interaction with the host structure, strongly affect the accuracy of results. In this study, unlike the previous works, in which some certain areas of the host structure were considered as a sensor and actuator, the direct simulation of electro-mechanical interaction of the PWAS and the host structure is modeled among modeling the PWAS...