Sharif Digital Repository

Solar energy-driven generation units can assist in moderating energy-linked environmental issues. For this target, a new solar heliostat-based generation unit is suggested for electricity generation as the crucial product. A heliostat-based solar unit with a closed Brayton cycle and thermal energy storage unit is coupled with a Kalina cycle and an absorption refrigeration unit through a single-effect absorption chiller as an inimitable series of power plants. Exergy, economic, and energy investigations are carried out to scrutinize the efficiency of the introduced unit, and a thorough parametric evaluation is performed. Multi-aspect optimization is implemented to identify the optimum... 

Abstract: Underwater vehicles when yawed to free stream flow, like submarines in a turning maneuver, produce large vortical separated regions. This vortical flow affects acoustic, body drag, control effectiveness and maneuverability. A suitable way to reduce the effects of this separated flow is to use vortex generators. The main goal of this study is to investigate the effect of the vortex generator on the flow field around a standard underwater model employing the vortex generators by using the oil flow visualization method in wind tunnel only in yaw direction (0° ≤ β ≤ 30° angles of attack, due to the experimental cost) and the CFD method in the pitch direction (0° ≤ α ≤ 30° angles of... 

The main focus of this paper is to present thermodynamic and economic analyses and multi-objective optimization of a novel geothermal-solar multigeneration system. The system aims to produce hydrogen, freshwater, electricity, cooling load, and hot water and designed based on geothermal and solar energy. After modeling and thermodynamic and economic analysis, exergy destruction rate, exergy efficiency and, cost rate were calculated for each component of the system. The results showed that the highest amount of exergy destruction was related to parabolic trough collectors (PTCs) and absorption chillers. To select the geothermal fluid of the organic Rankine cycle (ORC), several different fluids... 

System security indices play a crucial role with regard to monitoring system statues. These indices are derived from system measurements which are prone to either intentional or unintentional noises. To alleviate the effect of intentional noises, it is required to protect measurements data from bad data injection. In this regard, this paper intends to propose an approach to determine priority order of protected bus measurements in order to negate the effects of bad data injection on security indices. With this in mind, two security severity indices, the over loading risk index and the under voltage risk index, are considered. Genetic algorithm serves to find the highest deteriorating effect... 

Power system operation is undeniably affected by system security indications providing system operators with insight into power system status. In this regard, any tampered data would compromise power system security. This paper aims at presenting an approach to scrutinize the impact of cyber attacks on the system security indices. With this in mind, two well-known system security indices representing voltage and loading severities are taken into account. The approach uses genetic algorithm to find the most severe conditions for each security index from financial and technical viewpoints. In the former, bad data injection targets to overestimate security indices resulting in unnecessary... 

Scattering of graphene surface plasmons that are obliquely incident on a line discontinuity in graphene surface conductivity is investigated. The analysis is based on a solution of the quasi-static integral equation for surface charge density. It is shown that the reflection coefficient of the graphene plasmons reaches a minimum at a specific angle of incidence that depends on the ratio of conductivities of the two regions surrounding the discontinuity. This effect, which is similar to the well-known Brewster effect, is pronounced for abrupt discontinuities, but becomes weaker as the width of the transition region increases. The results obtained can be used for the design and analysis of... 

Sectionalizing switches (SSs) are often presumed to function fully reliable. However, SSs are exposed to have some malfunctions, whereby undermining their ability to improve service reliability. This study presents a model to integrate SS malfunction probability into SS placement problem. The model aims to minimize the total SSs costs as well as customers interruption cost. The proposed model is formulated in mixed integer programing (MIP), which can be easily solved via several available solvers and gain global optimal solution. The proposed model indicates the extent to which the placement problem is affected by uncertainty associated with SSs functionality, and how not considering SSs... 

Fault indicator (FI) plays a crucial rule in enhancing service reliability in distribution systems. This device brings substantial benefits for fault management procedure by speeding up fault location procedure. This paper intends to develop a new optimization model to optimally deploy FI in distribution systems. The proposed model aims to consider a tradeoff between the total customer interruption cost and FI relevant costs, including capital investment, installation, and maintenance costs. As the main contribution of this paper, the problem is formulated in mixed integer programing, which guarantees global optimum solution achieved in an effective runtime. Moreover, the model takes... 

Automation systems provide substantial improvement in service reliability through speeding up fault management procedure. However, this is at expense of high investments whose justification needs thorough cost/worth analyses. This paper introduces a mathematical model to optimally place automation system devices within distribution networks. The model establishes a trade-off between service reliability improvements and the relevant costs. Among different automation system devices, fault indicators and remote controlled switches are considered here. Also, the impact of manual switches is regarded since their number and location significantly affect the solution of the placement problem. The... 

Sectionalizing switches (SSs) are often presumed to function fully reliable. However, SSs are exposed to have some malfunctions, whereby undermining their ability to improve service reliability. This paper presents a model to integrate SS malfunction probability into SS placement problem. The model aims to minimize the total SSs costs as well as customers interruption cost. The proposed model is formulated in mixed integer programing, which can be easily solved via several available solvers and gain global optimal solution. The proposed model indicates the extent to which the placement problem is affected by uncertainty associated with SSs functionality, and how not considering SSs... 

Sectionalizing switches play a crucial role in enhancing service reliability to the end users of distribution networks. However, they might encounter failures, thereby causing interruptions in the networks. The existing switch placement models consider only the pros of switches in improving service reliability, while they fail to deem switches cons in possible failures and thus increasing system interruptions. This letter intends to show the importance of switch failure in the switch placement problem and the extent to which switch failure alters the switches allocation in a network. To do so, we develop a novel model based on mixed integer programming format to integrate the impacts of... 

Sectionalizing switches play a crucial role in enhancing service reliability to the end users of distribution networks. However, they might encounter failures, thereby causing interruptions in the networks. The existing switch placement models consider only the pros of switches in improving service reliability, while they fail to deem switches cons in possible failures and thus increasing system interruptions. This study intends to show the importance of switch failure in the switch placement problem and the extent to which switch failure alters the switches allocation in a network. To do so, we develop a novel model based on mixed integer programming format to integrate the impacts of... 

Automation systems provide substantial improvement in service reliability through speeding up fault management procedure. However, this is at expense of high investments whose justification needs thorough cost/worth analyses. This paper introduces a mathematical model to optimally place automation system devices within distribution networks. The model establishes a trade-off between service reliability improvements and the relevant costs. Among different automation system devices, fault indicators and remote controlled switches are considered here. Also, the impact of manual switches is regarded since their number and location significantly affect the solution of the placement problem. The... 

Sectionalizing switches (SSs) are often presumed to function fully reliable. However, SSs are exposed to have some malfunctions, whereby undermining their ability to improve service reliability. This paper presents a model to integrate SS malfunction probability into SS placement problem. The model aims to minimize the total SSs costs as well as customers interruption cost. The proposed model is formulated in mixed integer programing, which can be easily solved via several available solvers and gain global optimal solution. The proposed model indicates the extent to which the placement problem is affected by uncertainty associated with SSs functionality, and how not considering SSs... 

Sectionalizing switches play a crucial role in enhancing service reliability to the end users of distribution networks. However, they might encounter failures, thereby causing interruptions in the networks. The existing switch placement models consider only the pros of switches in improving service reliability, while they fail to deem switches cons in possible failures and thus increasing system interruptions. This letter intends to show the importance of switch failure in the switch placement problem and the extent to which switch failure alters the switches allocation in a network. To do so, we develop a novel model based on mixed integer programming format to integrate the impacts of... 

A Ground Source Heat Pump (GSHP) is a renewable energy-based HVAC system that extracts or supplies heat from/to the ground via a Ground Heat Exchanger (GHE). One of the most commonly used types of GHE in GSHP systems is the energy pile. In this realm, the GSHP system with a triple helix energy pile has become the focus of attention. To this aim, a comprehensive three-dimensional transient Computational Fluid Dynamics model of the energy pile with triple helix GHE and the surrounding soil is developed. The effect of several parameters, including helix pitch, helix diameter and pipe diameter, on the thermal performance of the system, is investigated. Simulated cases are chosen using the design... 

One way of improving the performance of diesel engines is to produce modifications in the fuel supply systems. In this article, the effects of creating rotationary flow inside the nozzle and changing fuel injection angle on the performance and emission of caterpillar diesel engine have been examined in two separate stages using AVL FIRE software. First, the injector and its spray have been simulated with various geometries. The numerical results of this step indicate that creating rotationary flow inside the nozzle decreases the penetration length, while increases fuel spray cone angle and improves atomization quality. In the subsequent step, the diesel engine has been simulated with its... 

An ultra-broadband absorber of light is proposed by using periodic array of ultra-thin metallic ribbons on top of a lossless quarter-wavelength dielectric spacer placed on a metallic reflector. We propose a fully analytical circuit model for the structure, and then the absorber is duly designed based on the impedance matching concept. As a result, normalized bandwidth of 99.5% is realized by the proposed absorbing structure in mid-infrared regime. Performing a numerical optimization algorithm, we could also reach to normalized bandwidth of 103%  

We propose an unprecedented transmit-array configuration which can mold the incident beam by modulating phase and amplitude wavefronts. The transmit-array is composed of patterned graphene metasurfaces as shunt admittance sheets. Thanks to the exceptional features of graphene such as tunability, thinness, low loss, and high confinement of graphene plasmons, the proposed subwavelength structure passes strict touchstones for nano-photonic and optoelectronic applications. Two flat-optics functionalities, i.e., focusing and splitting, are realized by means of the proposed configuration  

The scattering of graphene surface plasmons normally incident on a line discontinuity in graphene surface conductivity is investigated. The effect of the length of the transition region on the reflection and transmission coefficients is studied. It is shown that the reflection coefficient is reduced by widening the transition region. Based on the results obtained, a transmission line model is derived for the graphene sheet in which the discontinuity is represented by a simple circuit. This model is next used to design graphene-based bandpass and bandstop filters with arbitrary bandwidth in the terahertz regime