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Concurrent Multi-Scale Approach for Modeling Mechanical Behavior of Crystalline Nano-Structures
, M.Sc. Thesis Sharif University of Technology ; Khoei, Amir Reza (Supervisor)
Abstract
Mindboggling advances in nanotechnology have urged researchers to develop state-of-the-art numerical methods to enable them to simulate and to interpret phenomena at this scale. Unfortunately, Classical models have numerous shortcomings which hinder their applications in new contexts. For instance, classical Continuum Mechanics fails to appropriately depict material behavior at small scales, and, on the other hand, Molecular Dynamics simulations are computationally prohibitive. As a consequence, researchers have devised multi-scale methods during the past decade to overcome these obstacles. In fact, in multi-scale methods information is passed from one mathematical description to the other....
A temperature-related boundary Cauchy-Born method for multi-scale modeling of silicon nano-structures
, Article Physics Letters, Section A: General, Atomic and Solid State Physics ; Vol. 378, issue. 5-6 , 2014 , pp. 551-560 ; ISSN: 03759601 ; Dormohammadi, H ; Aramoon, A ; Sharif University of Technology
2014
Abstract
The surface, edge and corner effects have significant influences in the electrical and optical properties of silicon nano-structures. In this paper, a novel hierarchical temperature-related multi-scale model is presented based on the boundary Cauchy-Born method to investigate not only the surface but also the edge and corner effects in thermal properties of diamond-like structures such as silicon nano-structures at finite temperature. A combined finite element method and molecular dynamics are respectively employed in macro- and micro-scale levels. The temperature-related Cauchy-Born rule is applied using the Helmholtz free energy, as the energy density of equivalent continua relating to the...
Multi-scale modeling of edge effect on band gap offset in polygonal cross-section Silicon nanowires
, Article Computational Materials Science ; Volume 79 , 2013 , Pages 262-275 ; 09270256 (ISSN) ; Dormohammadi, H ; Aramoon, A ; Sharif University of Technology
2013
Abstract
The band gap offset is an effect of coordination numbers (CNs) of atom reduction at the edge of transversal cross-section of Silicon nanowires (SiNWs). In this paper, a hierarchical multi-scale technique is developed to model the edge effect on the band gap shift of SiNWs since the geometric effect is dominant in the energy gap due to the appearance of strain in the self-equilibrium state. The multi-scale model is performed based on the molecular dynamics approach and finite element method for the micro- (atomistic) and macro-scale levels, respectively. The Cauchy-Born (CB) hypothesis is used to relate the atomic positions to the continuum field through the deformation gradient. Finally, the...
A concurrent multi-scale technique in modeling heterogeneous FCC nano-crystalline structures
, Article Mechanics of Materials ; Volume 83 , April , 2015 , Pages 40-65 ; 01676636 (ISSN) ; Jahanbakhshi, F ; Aramoon, A ; Sharif University of Technology
Elsevier
2015
Abstract
In this paper, a multi-scale molecular dynamics-finite element coupling is presented to study the mechanical behavior of heterogeneous nano-crystalline structures. The stiffness and mass matrices of the continuum sub-domain are generated by applying a linear transformation on the matrices obtained via the atomic structure underlying the FE mesh. A Lagrange multiplier method is employed to the transition zone imposing velocity resemblance of the coupling regions. The constraint equations of motion are solved by the multi-time-step decomposition thus giving the opportunity to ascribe different time steps to each individual zone. The molecular dynamics is performed by employing the...
Multi-scale modeling of edge effect on band gap offset in polygonal cross-section silicon nanowires
, Article Computational Materials Science ; Volume 79 , November , 2013 , PP. 262–275 ; DorMohammadi, H ; Aramoon, A ; Sharif University of Technology
2013
Abstract
The band gap offset is an effect of coordination numbers (CNs) of atom reduction at the edge of transversal cross-section of Silicon nanowires (SiNWs). In this paper, a hierarchical multi-scale technique is developed to model the edge effect on the band gap shift of SiNWs since the geometric effect is dominant in the energy gap due to the appearance of strain in the self-equilibrium state. The multi-scale model is performed based on the molecular dynamics approach and finite element method for the micro- (atomistic) and macro-scale levels, respectively. The Cauchy–Born (CB) hypothesis is used to relate the atomic positions to the continuum field through the deformation gradient. Finally, the...
Introducing a Simulation-Based Model to Improve the Design and Layout of Workstations Inside Airport Terminals in Iran
, M.Sc. Thesis Sharif University of Technology ; Alvanchi, Amin (Supervisor)
Abstract
The airport terminal is difficult to plan and design due to the different components and the intricate complexity of its parts. At the airport terminal, we face a queue system which simulation is always a good way to analyze. In addition, computer simulation using modern softwares with the capability to model different types of systems, including the airport terminal, while being less realistic than analytical models, is less costly than operational Exercise.In this study, a supportive approach for better and specific management of Iranian airport terminal buildings with discrete-event simulation is proposed, considering the need for managing the airport terminals building in the country and...
, M.Sc. Thesis Sharif University of Technology ; Alvanchi, Amin (Supervisor)
Abstract
Limited water resources in Iran have made dams an important part of the country’s infrastructure. As a result of the large number of in-progress and expected dam projects in the country, consideration of sustainability factors during planning, construction and operation phases of dam projects can create significant economical, social and environmental impacts in the long term. To come up with an inclusive sustainable development, new sustainability assessment approaches seek for sustainable development at the entire project’s life-cycle; they are looking for sustainable development at all design, construction, operation, maintenance and even demolition phases. In this research we have...
The Insider Threat: Analyzing and Modeling
, M.Sc. Thesis Sharif University of Technology ; Hendesi, Faramarz (Supervisor)
Abstract
Nowadays, most of businesses are becoming computer-based. This trend causes the organizations to become more vulnerable to internal and external threats. Internal threats are done through insiders. Insiders unlike outsiders have capabilities which aid them to easily carry out their illicit activities. Unfortunately, most of research in computer security has focused on the outsider threats, whereas the most damaging is the result of insiders’ illicit activities.This dissertation addresses three primary necessities of the research in the area of insider threat: a consistent definition of insider threat, a classification of types of insider threats, and a classification of vulnerabilities which...
Integrity Analysis in the Time-Delay Systems
, M.Sc. Thesis Sharif University of Technology ; Nobakhti, Amin (Supervisor)
Abstract
Integrity of closed-loop systems with integral action control is characterized by using a series of successively more difficult to obtain conditions: Integral Stabilizable (IS), Integral Controllable (IC), Integral Controllable with Integrity (ICI), and Decentralized Integral Controllability (DIC). The IS condition requires that for a Linear Time-Invariant (LTI) finitedimensional (FD) plant, G(s), one finds a stabilizing decentralized controller with integral action. For G(s) to be IC, in addition to being IS, one should be able to reduce the gain of
all control loops by the same factor from a finite value to (but not including) zero without introducing instabilities. ICI requires that...
all control loops by the same factor from a finite value to (but not including) zero without introducing instabilities. ICI requires that...
Design of a Plantwide Decentrlized Structure Controller for the Tennessee Eastman Challenge Problem
, M.Sc. Thesis Sharif University of Technology ; Nobakhti, Amin (Supervisor)
Abstract
This project focuses on the Tennessee East-man challange problem(TEP) and the impact of setpoint changes and controller tunning on plant performance and profitability. TE has four major units. it is an unstable system due to the reaction within the reactor and a recycle streamcausing snow ball effect. As a result the control of this system is not easy. The study has been conducted along two main directions. First, selecting the optimal values for the setpoints and applying them in the simulation. secondly, try to find better parameter for controller in simulation. Simulation is based on working of Ricker. In TEP like the other multivariable systems, it is ameanable to use a centralized...
A Thesis Submitted in Partial Fulfillment of the Requirement for the Degree of Master of Science in Electrical Engineering
, M.Sc. Thesis Sharif University of Technology ; Nobakhti, Amin (Supervisor)
Abstract
Intraction in multi input multi output (MIMO) system makes control of these systems difficult.There are two ways to control such systems; Centralized and Decentralized control. One way in which a centralized controller is designed is using a precompensator. With application of the pre-compensator, the MIMO sytem is decoupled into several SISO systems and one can control these seperatly. Almost all previews methods for the design of pre-compensator assume that the model of the plant containsno uncertainties.In this thesis a new method is proposed which takes into account model uncertaintes in the design of the pre-compensator.The form of the uncertainties considred an interval-parametric
Convex Methods for the Design of Low Order Dynamic Pre-Compensators
, M.Sc. Thesis Sharif University of Technology ; Nobakhti, Amin (Supervisor)
Abstract
Decentralized control is a typical method for the design of industrial MIMO control systems. However, in most multivariable systems, the existence of large interactions limit the achievable performance of such controllers. In the Nyquist Array design method proposed by Rosenbrock, the system interactions can be reduced using a precompensator, such that a decentralized controller may be used with acceptable performance. A well designed pre-compensator will effectively decouple the system and the multivariable systems may be considered as a set of SISO systems. It is therefore obvious that the key element in the Nyquist Array design method is the design of the pre-compensator. There are two...
Developing a Sustainable Model for Bridge Maintenance in Big Organisations
, M.Sc. Thesis Sharif University of Technology ; Alvanchi, Amin (Supervisor)
Abstract
For increasing longevity of a structure, it is not enough to notice only to designing aspects. In operation phase of a construction, we can increase the level of service and longevity. Asset-based Organizations, in addition to design their new assets, should maintain them. Infrastructures, such as road, bridge, dam, and water network, are important because of social and economic aspects. So they need special attention. There are efficient models for infrastructure maintenance that consider infrastructure element information, such as condition rate, weight, dimensions, deterioration rate, and cost of maintenance as inputs and give planning for maintenance in future. This planning, involves a...
Conditions for Integrity of Multivariable Systems with Input Saturation
, M.Sc. Thesis Sharif University of Technology ; Nobakhti, Amin (Supervisor)
Abstract
Multivariable control systems as used in the industry usually contain integral action in order to improve tracking of the output with respect to step reference changes. These systems are usually subject to input saturation due to actuator or sensor nonlinearities. The aim of this work is find the conditions for the integrity concept of such multivariable system, e.g. IS, IC, ICI and DIC. First we develop the conditions on the controller gains necessary stabilize the systems and then show that these conditions can changes when one examines integrity conditions
Decentralized Integral Controller Design to Possess Integrity
, M.Sc. Thesis Sharif University of Technology ; Nobakhti, Amin (Supervisor)
Abstract
Design of fault tolerant controllers with a reliable and robust control structure that can accommodate sensor and actuator failure is a challenging problem. In the process control literature, the term “integrity” is used to characterize these properties for decentralized control systems. It refers to the ability to retain system stability when one or some of the control loops get in or out of service or when loop gains are detuned.Conditions pertaining to the integrity of the closed-loop system are described by a series of successively more difficult to attain criteria whose evaluation is only based on the process steady state gains. These are Integral stabilizibility (IS), Integral...
Disturbance Diagnosis In Plant-wide Processes
,
M.Sc. Thesis
Sharif University of Technology
;
Nobakhti, Amin
(Supervisor)
Abstract
In continous chemical process, disturbances usually propagate along the process. This project describes a data-driven method for identifying the direction of propagation of disturbances using historical process data. The concept is the application of Transfer Entropy, a method based on the conditional probability density functions that measures directionality of variation. For demonstration purposes the transfer entropy method is used to isolate the root-cause of the disturbance in the Tennassee Eastman benchmark process
Disturbance Reduction Servo Motor Controller Design and Implementation
, M.Sc. Thesis Sharif University of Technology ; Nobakhti, Amin (Supervisor)
Abstract
The servomechanisms have wide industrial application such as robotics, Computer Numerical Control (CNC) machines, automated manufacturing and solar tracking. Several methods have already been proposed for servo motor control that the most important of them are Proportional Integral Derivative (PID), H2/H--, intelligent based controllers, and model predictive control. Problem specifications and user requirements, will determine the appropriate approach in each case. The aim of this thesis is construction of a real-life camera stabilizer to be used in the motion picture industry. Effects of base movement on the performance should be decreased by choosing appropriate sensors and control...
Optimization of Sparse Control Structures in Multivariable Systems
, Ph.D. Dissertation Sharif University of Technology ; Nobakhti, Amin (Supervisor)
Abstract
In this thesis, the optimal control structure selection and design of sparse multi-variable control systems is addressed. A fundamental challenge which frequently emerges in engineering, social, and economic sciences, is the optimal selection of a subset of elements, in order to maximally fulfil a design objective. In practice, it is required to solve this underlying selection problem in conjunction with a non-linear or non-convex optimization which is designed to ensure desired performance. The requirement to solve these two problems simultaneously is what makes it inherently difficult; one which has thus far eluded efforts to develop a systematic means of determining its solution. In spite...
A Neural Network Based Model for Cost Estimation of Industrial Building at the Project's Definition phase
, M.Sc. Thesis Sharif University of Technology ; Alvanchi, Amin (Supervisor)
Abstract
Annually there are many small-scale industry projects implemented in Iran, most of which are financed by local financial institutes. The financing agreements between project owners and financial institutes are usually formed and finalized during the initiation phase and are based on feasibility studies done at the early stages; before project design and construction begin. However, in many cases actual costs of projects exceed the costs estimated in feasibility studies which have been approved by financial institutes. Limited financial resources in the country, from one side, and the lengthy process of increasing the project financing limit, from another side, cause delays in the project...
Sustainability Assessment of Embankment Construction
, M.Sc. Thesis Sharif University of Technology ; Alvanchi, Amin (Supervisor)
Abstract
Damming projects always have been important while construction, operation and even demolition due to their major effects on society, environment and economy. Although researchers have focused on one or a few phases of construction projects to develop sustainable infrastructures, the research community has to consider long term effects of developments too. There are a variety of such effects that ignoring them will cause construction of not convenient infrastructures i.e. air pollution and over-consumption of energy resources while construction, operation and demolition. Therefore, it is suggested to consider life cycle assessments to include all bad effects in all phases of a project. Dams...