Sharif Digital Repository

Here, we investigate the influence of elevated temperatures with negligible ambient oxygen on mechanical properties of various embedded glass fiber reinforced polymer (GFRP) profiles, as well as the application of a predictive Bayesian model for predicting these properties. Both the flexural and compressive properties of FRP profiles were investigated through the tests of I-shaped and box-shaped profiles. To determine the impact of low and high elevated temperature, the profiles were exposed to a wide range of temperatures (i.e., 25–550 °C); effects of the exposure time were also investigated. Experiments showed that specimens exposed to higher elevated temperatures for longer time periods... 

In this research, the mechanical properties of glass and carbon fiber reinforced polymer (FRP) bars with epoxy resin matrices embedded in concrete were investigated under an extensive range of elevated temperatures (i.e., 25–800 °C). Embedded FRP bars with various bar diameters were studied in order to determine bar diameter influence on the results. In addition, analysis of variance (ANOVA) was performed on the experimental results to investigate the contribution of exposure temperature and bar diameter to the tensile behavior of embedded in concrete FRP bars at elevated temperatures. The results show that the tensile strength of embedded FRP bars generally decreases with increasing... 

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... 

In this study, the effects of fiber type (i.e., carbon and glass fibers) and intumescent paint on the tensile performance of fiber reinforced polymer (FRP) sheets at elevated temperatures are investigated. For this purpose, a series of tensile tests were conducted on the glass and carbon fiber reinforced polymer (GFRP and CFRP) sheets, with and without intumescent fire retardant paint, at different elevated temperatures. The studied temperatures ranged from 25 °C to 600 °C. Scanning electron microscopy was also used to examine the effects of elevated temperatures on FRP sheets and the fire protecting mechanism of the intumescent paint. Based on the test results, the tensile strength of the... 

The compressive performance of glass fiber reinforced polymer (GFRP) profiles subjected to elevated temperature was investigated through a large number of (3 0 0) tests. The effects of profile cross-sectional area, slenderness, and temperature on the behavior of the GFRP profiles at temperatures ranging from 25 to 400 °C were determined. It was observed that the compressive strength of the GFRP profiles has been decreased by half as the temperature exceeded 90 °C, i.e., close to the glass transition temperature of the matrix. The temperature and ratio of cross-sectional area to external perimeter were determined as two major parameters affecting section capacity. © 2020 Elsevier Ltd  

This paper investigates the influence of intumescent paint on the performance of FRP bars subjected to low (25–450 °C) and severe (450–800 °C) elevated temperatures. In this research, glass and carbon FRP bars with epoxy resin and coated with nitrogen-based intumescent paint were used. In addition to the temperature effects, a variety of FRP bar diameters were employed to determine its effect on the tensile behavior of FRP bars in the presence of intumescent paint. Further, Bayesian regression methods and ANOVA (ANalysis Of VAriance) were applied on the results to develop a predictive model form and quantify the contribution of the variables in the tensile performance of FRP bars,... 

In a MIMO (Multiple Input Multiple Output) radar system, proper design of transmit signal and receive filter is an advantageous tool to improve the detection performance. Thus, in this paper, we consider the problem of transmit code and receive filter design, in order to maximize the Signal to Noise Ratio (SNR) at the receiver while enforcing a similarity constraint between the transmit space-time code (STC) and a reference STC which has a desirable ambiguity function. We will show that by solving such constrained optimization problem through successive iterations, our proposed method leads to satisfactory results  

Weighting elements to achieve radiation patterns with desired characteristics is a classical work in phased array antennas. These characteristics can be low sidelobe level, narrow beamwidth, high directivity, pattern nulling in special angle and etc. For each of these characteristics, different methods have been introduced. Most of methods have been presented for uniform arrays, however there are lots of methods to obtain a desired pattern for antennas with non-uniform element distances. The problem with these methods is complexity or not very good results. In this paper, fast and easy methods based on Least Square Error that leads to good results are presented. In addition, weighting of... 

Distributed generation connected with AC, DC, or hybrid loads and energy storage systems is known as a microgrid. Campus microgrids are an important load type. A university campus microgrids, usually, contains distributed generation resources, energy storage, and electric vehicles. The main aim of the microgrid is to provide sustainable, economical energy, and a reliable system. The advanced energy management system (AEMS) provides a smooth energy flow to the microgrid. Over the last few years, many studies were carried out to review various aspects such as energy sustainability, demand response strategies, control systems, energy management systems with different types of optimization... 

This paper resolve the salinity-dependent interactions of polar components of crude oil at calcite-brine interface in atomic resolution. Molecular dynamics simulations carried out on the present study showed that ordered water monolayers develop immediate to a calcite substrate in contact with a saline solution. Carboxylic compounds, herein represented by benzoic acid (BA), penetrate into those hydration layers and directly linking to the calcite surface. Through a mechanism termed screening effect, development of hydrogen bonding between –COOH functional groups of BA and carbonate groups is inhibited by formation of a positively-charged Na+ layer over CaCO3 surface. Contrary to the common... 

An important tool for assessing a radar's performance is the ambiguity function. On the other hand, many different schemes have been designed for the transmit waveforms of a MIMO radar. For each one, a criterion has been chosen to improve the performace, e.g. achieving better missed detection. In this paper, considering the ambiguity function as the benchmark, we propose a waveform design scheme, which optimizes the ambiguity function of the MIMO radar system  

Flow hydrodynamics of laminar falling film of aqueous Li Br solution (Li Br - H2O) on a horizontal elliptical tube has been investigated in this research. The film velocity distribution and film thickness, namely, the flow characteristics are determined by solving analytically simultaneous simplified Navier - Stokes equations and continuity equation in polar and Cartesian coordinates. The analysis is based on steady state laminar flow of falling liquid film of Li Br - H2O on a horizontal elliptical tube in polar model and Cartesian model (CM), for cases in which traction on the film surface is considered negligible. Models are compared with each other in three cases of aspect ratios (Ar),... 

Velocity distributions in (r,θ) directions are evaluated by solving simultaneous simplified Navier-Stokes equations (NSE) and continuity equation (CE) in polar coordinate. The analysis is based on steady state laminar flow of thin falling liquid film on a horizontal circular tube, for cases in which traction on the film surface is considered negligible. It is a common geometry for part of engineering problems such as evaporator, condenser, absorber, generator of absorption chillers and other similar units in mechanical and chemical engineering. Knowledge of the velocity profiles is usually needed for: 1 - solving governing energy and species equations 2- estimating the average and film... 

Velocity distributions in (r,θ) directions are evaluated by solving simultaneous simplified Navier-Stokes equations (NSE) and continuity equation (CE) in polar coordinate. The analysis is based on steady state laminar flow of thin falling liquid film on a horizontal circular tube, for cases in which traction on the film surface is considered negligible. It is a common geometry for part of engineering problems such as evaporator, condenser, absorber, generator of absorption chillers and other similar units in mechanical and chemical engineering. Knowledge of the velocity profiles is usually needed for: 1- solving governing energy and species equations 2- estimating the average and film... 

This work concerns the experimental investigation of surfactant alternating CO 2 injection in carbonate rocks. The core samples provided from a low-temperature fractured light oil reservoir, located in southwest Iran. The experiments were designed to observe the effect of CO 2-foam injection on gas mobility and oil recovery at different surfactant concentrations. The core samples were initially saturated with synthetic/field brine, 5,000 ppm, and then flooded with live oil to reach connate water saturation at reservoir condition, 115F and 1,700 psia. The commercial surfactant used was sodium lauryl sulfate as an anionic surfactant. The results of this work, along with field-scale simulation... 

Knowledge of Air-water two phase flows is significant to different engineering systems such as chemical reactors and power plant and petrochemical and petroleum industry. One of the most industrial cases of two phase flow is two phase flow in vertical large pipes. In this paper in order to find two phase flow behavior along vertical large diameter pipes we simulate air inlets with different number of holes and different hole diameters in the same flow rate of air. In addition, flow characteristics such as cross-sectional void fraction and velocity and pressure were considered. To achieve this aim, main equations of flow have been developed for investigation of flow behavior in air-water two... 

The present work investigates the thermal performance of a five turn Open Loop Pulsating Heat Pipe (OLPHP). The effects of working fluid namely water and ferrofluid, heat input, ferrofluid concentration, charging ratio, and orientation will be considered. Experimental results show that using ferrofluids can enhance the thermal performance in comparison with the case of distilled water. In addition, applying a magnetic field on the OLPHP charged with ferrofluid reduces its thermal resistance. Variation of the ferrofluid concentration results in different thermal performance of the OLPHP. Best charging ratio for the distilled water and ferrofluid without magnetic field is 60 % in most of the... 

Accurate estimation of the capacity curve of offshore jacket structures to achieve performance levels and ductility is of great importance. Proper modeling of compressive members to correctly investigate global and local buckling is crucial in estimation of the capacity curve. Buckling modes and deformations due to local buckling can be considered, if the compressive braces are modeled by shell or solid elements. The purpose of this paper is to achieve the correct compressive behavior of braces with solid type elements and investigate the effects of five different parameters such as D/t, L/D, mesh size, mesh size ratio, and imperfections. ABAQUS FE software is used for this purpose. The... 

Accurate estimation of the capacity curve of offshore jacket structures to achieve performance levels and ductility is of great importance. Proper modeling of compressive members to correctly investigate global and local buckling is crucial in estimation of the capacity curve. Buckling modes and deformations due to local buckling can be considered, if the compressive braces are modeled by shell or solid elements. The purpose of this paper is to achieve the correct compressive behavior of braces with solid type elements and investigate the effects of five different parameters such as D/t, L/D, mesh size, mesh size ratio, and imperfections. ABAQUS FE software is used for this purpose. The...