Sharif Digital Repository

In recent decades, due to economic, political and environmental issues, tend to use of the CHP systems (combined heating and power) have increased. CHP systems not only increase energy efficiency, but also decrease fuel consumption and emission levels of systems. The use of CHP technology in the industry has a long history, but the use of these systems in the commercial and residential sector, is considered, recently. As to the residential buildings, both electricity and thermal energy demands fluctuate seasonally and hourly, so it is necessary to take account of the plant’s annual operational strategies for the variations of load demands. In this paper, a nonlinear programming model is... 

The question of the time is one of the obscure and challenging subjects which has been discussed as a mysterious problem in various civilizations. In ancient Greece, the question has been debated among the supporters of existence and eternity. We observe the words of Plato, on the existence of the absolute essence of eternity against the change and transition time instantiated as a conducted river in the Heraclitus view. Other discussions focused on the relationship between the change and displacement, or the the spatial relations to which Aristotle paid attention. With the passing of time from the ancient and medieval eras to the Renaissance period, along with the growth of the science in... 

With the popular choice of using underground structures and tunnel in big cities and with significant damage in recent large earthquake; therefore more attention is given to the behavior of the underground structure in seismic area. The purpose of this thesis is to present the Soil-Tunnel-Structure Interaction analysis performed for different dynamic load condition. Therefore we modeled a 3D intersection part of two different tunnels in homogeneous soil by ABAQUS software. The soil and concrete structure of tunnel is modeled by three dimensional solid finite elements and the boundary of soil is modeled by three dimensional infinite elements with 8 nodes. The results demonstrate the geostatic... 

A brief overview of the proposed research, its aims, engineering relevance and applications Underground space has long been exploited through the history to fulfill different human necessities. Underground facilities built in areas subject to earthquake activity must withstand both seismic and static loads. Some underground structures have experienced significant damage in recent large earthquakes. Tehran is located in seismic zone and investigation and research on the subject has significant role in design and construction of underground spaces for earthquake loads. Underground structures are complex structures which consist of different parts Such as passage way and platform space. Passage... 

Train scheduling is one of the most complicated stages of railway planning. In this stage, the arrival and departure times of trains at stations are determined. In this thesis, we studied train scheduling on a two-way and single track railway in order to minimize the total travel times of trains subject to a set of operational constraints and prayer time related constraints that determines the optimal station for prayer. In this project, we tried to simulate the real constraints exist in IRAN railway network and the objective function considers customer’s and railway management’s satisfaction, simultaneously. First, a mathematical programming is proposed for this problem. After demonstrating... 

The present ph.D. thesis consists of three sections including the static calculation, neutron noise calculation and neutron noise source unfolding in VVER-1000 reactor core. The multi-group, two dimensional neutron diffusion equations and corresponding adjoint equations are solved in the static calculation. The spatial discretization of equations is based on Galerkin Finite Element Method (GFEM) using unstructured triangle elements generated by Gambit software. The static calculation is performed for both linear and quadratic approximations of shape function; baesd on which results are compared. Using power iteration method for the static calculation, the neutron and adjoint fluxes with the... 

Process of casting with evaporative patterns and unbonded sand is a new method that due to different economic, environmental and technological benefits is considered to large and small industrial parts manufacturing in recent years. Different parameters are effective on the surface and metallurgical quality in this process, such as foam density, sand type and size, level and mode of vibration, sand compaction, coating and pouring time and temperature. If coating permeability that is function of type, thickness and concentration of coating is chosen improper, pyrolysis vapor of foam don’t exit completely and in this condition carbon of vapor deposit on the metal surface and produces defect... 

Nurse scheduling problem has received a great amount of attention during recent years. In this problem number of needed nurses from different skill levels is given for each Location-shift during planning horizon, and the goal is to allocate each nurse to shifts, such that the demand of each location-shift is satisfied. Many researches have been done with the aim of minimizing the number of needed nurses to satisfy the demand of locationshifts or maximizing nurses preferences to work in desired shifts. In this research an integer programming model is proposed to minimize the number of needed nurses and maximize nurses preferences simultaneously. The proposed mathematical model is appropriate... 

In this research the risk of oil price for Iran and Opec basket is studied. Several methods in order to estimate Value at Risk (VaR) such as Standard Historical Simulation, Historical Simulation with Autoregressive Forecast, Historical Simulation with moving average forecast, and ARMA are examined. The experiment is performed based on daily oil prices, from January 2005 to December 2009. The data is divided into two smaller time periods. The first, from 2005 to 2008, was used to estimate the model coefficients. The second part of data, i.e., the data gathered in 2009, was used for forecasting purposes. The result of experiment show that Historical Simulation with Autoregressive Forecasts... 

Wireless mesh networks (WMN) appeared as popular communication networks supporting high speed and high throughput applications. They consist of mesh routers and mesh clients and they have unique characteristics like self organizing and self configuring of the mesh nodes that bring a great deal of efficiency, reliability and robustness to networks and decreases networks maintenance cost notably. Also WMNs provide an integration of different types of wireless networks by exploiting the gateway involvement. One of the important group communication technologies that offers high level of bandwidth conservation and efficiency is multicasting. It also decreases the cost of communication compared to... 

In this thesis, two-level optimal control of uncertain and non-uncertain large-scale systems is presented. In the proposed two-level approach, using a decomposition/coordination framework, the large-scale system is first decomposed into several interactive subsystems, at the first-level, where a smaller optimization problem is solved at each subsystem. At the second-level, a substitution type prediction method, as a coordination strategy, is used to predict the interaction between subsystems. The coordinator mainly evaluates the next update for the coordination parameters and continues to exchange information with the first-level, so that the overall optimum solution is obtained. It is shown... 

Regard to high temperature and using dry fuel in engines with CNG (Compressed Natural Gas), wear problems and instability of valve seat insert (VSI) in these types of engines have been increased. Today some of high alloy steel (consist of Cr,Ni,Co,W,Mo, . . .), Ni-base alloy or Co-base alloy are used in manufacturing VSI. It's clear these materials have high price. In powder metallurgy methods high percentage alloy is used for manufacturing VSI. These are the reasons why casting method for VSI manufacturing has been pleasant to be used.
In this project the cast iron has been used for CNG engine VSI, by adding some elements like Mo,V,W, and Nb. The graphite has been used as solid... 

The analysis of gamma-ray spectra of low resolution detectors is difficult and sometimes impossible, as a result of photo peak’s overlapping. The usual methods of radiation spectra analysis based on fitting of peaks to mathematical curves or detecting of peaks with numerical calculation, are valid for high resolution detectors. However these methods are less successful for lower resolution detectors such as the common scintillators. The wide peaks in the spectrum maybe overlap and make it difficult to analysis. To solve this problem, we test here a method, based on the use of the artificial neural network. At first spectra of elements are converted to the patterns which are suitable for the... 

Radiation detection techniques have important applications including prompt gamma neutron activation analysis (PGNAA), radiotherapy dose measurement, medical imaging and homeland security. Pulse height distribution is also a useful parameter in Radionuclide identification. Gamma ray spectroscopy analysis is a common technique in measuring of radiation field to identify the radioactive source.
Probabilistic methods are commonly used for numerical simulation of Pulse height distribution. In Monte Carlo methods, each history is individually tracked and details of interactions are available. Using the Monte Carlo methods for calculation of pulse height distribution leads to more real...