Investigation of the interphase effects on the mechanical behavior of carbon nanotube polymer composites by multiscale modeling

, Article Journal of Applied Polymer Science ; Volume 117, Issue 1 , March , 2010 , Pages 361-367 ; 00218995 (ISSN) Montazeri, A ; Naghdabadi, R ; Sharif University of Technology

2010

Abstract

In this article, a multiscale modeling procedure is implemented to study the effect of interphase on the Young's modulus of CNT/polymer composites. For this purpose, a three-phase RVE is introduced which consists of three components, i.e., a carbon nanotube, an interphase layer, and an outer polymer matrix. The nanotube is modeled at the atomistic scale using molecular structural mechanics. Moreover, three-dimensional elements are employed to model the interphase layer and polymer matrix. The nanotube and polymer matrix are assumed to be bonded by van der Waals interactions based on the Lennard-Jones potential at the interface. Using this Molecular Structural Mechanics/Finite Element...

Study the effect of viscoelastic matrix model on the stability of CNT/polymer composites by multiscale modeling

, Article Polymer Composites ; Volume 30, Issue 11 , 2009 , Pages 1545-1551 ; 02728397 (ISSN) Montazeri, A ; Naghdabadi, R ; Sharif University of Technology

2009

Abstract

In this article, a Molecular Structural Mechanics/Finite Element (MSM/FE) multiscale modeling of carbon nanotube/polymer composites with viscoelastic (VE) polymer matrix is introduced. The nanotube is modeled at the atomistic scale using structural molecular mechanics. The matrix deformation is analyzed by nonlinear finite element method considering VE behavior. The nanotube and matrix are assumed to be bonded by van der Waals interactions based on the Lennard-Jones potential at the interface. Using the MSM/FE multiscale model, we investigate the effect of carbon nanotube (CNT) on the improvement of mechanical stability of the nanocomposite. Also, the buckling behavior of these...

Investigating the effect of carbon nanotube defects on the column and shell buckling of carbon nanotube-polymer composites using multiscale modeling

, Article International Journal for Multiscale Computational Engineering ; Volume 7, Issue 5 , 2009 , Pages 431-444 ; 15431649 (ISSN) Montazeri, A ; Naghdabadi, R ; Sharif University of Technology

2009

Abstract

Carbon nanotube (CNT)-reinforced polymer composites have attracted great attention due to their exceptionally high strength. Their high strength can be affected by the presence of defects in the nanotubes used as reinforcements in practical nanocomposites. In this article, a new three-phase molecular structural mechanics/finite element (MSM/FE) multiscale model is used to study the effect of CNT vacancy defects on the stability of single-wall (SW) CNT-polymer composites. The nanotube is modeled at the atomistic scale using MSM, whereas the interphase layer and polymer matrix are analyzed by the FE method. The nanotube and polymer matrix are assumed to be bonded by van der Waals interactions...

Investigation the stability of SWCNT-polymer composites in the presence of CNT geometrical defects using multiscale modeling

, Article 4th International Conference on Multiscale Materials Modeling, MMM 2008, 27 October 2008 through 31 October 2008 ; 2008 , Pages 163-166 ; 9780615247816 (ISBN) Montazeri, A ; Naghdabadi, R ; Sharif University of Technology

Department of Scientific Computing, Florida State University 2008

Abstract

CNT-reinforced polymer composites have attracted attention due to their exceptional high strength. The high strength can be affected by the presence of defects in the nanotubes used as reinforcements in the practical nanocomposites. In this paper, a Molecular Structural Mechanics / Finite Element (MSM/FE) multiscale modeling is used to study the effect of carbon nanotube geometrical defects on the stability of SWCNT-polymer composites. Here, two types of representative volume elements (RVEs) for these nanocomposites are considered with perfect and defected CNT. These RVEs have the same dimensions. The nanotube is modeled at the atomistic scale using molecular structural mechanics whereas the...

Controller Design for Nonlinear fractional Order Systems in the Presence of Input and Output Constraints

, M.Sc. Thesis Sharif University of Technology Montazeri, Jalil (Author) ; Shahrokhi, Mohammad (Supervisor)

Abstract

The purpose of this thesis is design of an adaptive tracking control for input-quantized strict-feedback fractional order nonlinear systems with unknown dynamics and asymmetric time-varying output constraints. The controller design is achieved by using a hysteretic quantizer to avoid chattering and not needing the quantization parameters. The fuzzy logic method has been used to solve the problem of unknown dynamics. Also, due to the asymmetric time-varying output constraints, the Barrier Lyapunov function has been used. In this thesis, less restrictive assumptions have been considered than the work performed in previous researches.By utilizing the adaptive backstepping approach and based on...

Direct Torque Control of Permanent Magnet Synchronous Machine Using Nonlinear Flux Observer

, M.Sc. Thesis Sharif University of Technology Yaghoubi, Mokhtar (Author) ; Tahami, Farzad (Supervisor)

Abstract

Direct Torque Control (DTC) is one of the vector methods to control Permanent Magnet Synchronous Machines (PMSM). In order to achieve an appropriate control in vector control methods, an accurate estimation of flux is indispensable. Flux estimation should be fulfilled in a wide speed range without considerable dependence on motor parameters. Prevalent flux estimation methods are based on integration of stator voltage which is not feasible in low speed, or performed based on assumption of decoupled equations on d and q axis which is not precise for applications with fast dynamic. Different flux estimation methods are investigated in this thesis with the aim of improving the flux estimation in...

Design and Implementation of a Soft Switched Bidirectional Charger for Vehicle-to-grid (V2G) Applications

, M.Sc. Thesis Sharif University of Technology Akbari, Rasoul (Author) ; Tahami, farzad (Supervisor)

Abstract

Due to the growing oil price and environmental considerations, tendency to use local and environmentally friendly energy sources has increased.Bidirectional transmission can be one of the key features of the smart grid,so the use of car battery connected to the grid as local energy sources makes sense. This can provide network stability, especially during peak load times. Vehicles connected to grid (V2G) is an electric vehicle or a plug-in hybrid electric vehicles can delivered the electricity to the grid. These systems require either two separate power electronic converters can be used for transmission in either directions or a two-way transfer charger. The aim of this project is to design...

Design and Implementation of a Soft-Switched Multiport Bidirectional Converter

, M.Sc. Thesis Sharif University of Technology Mirzahosseini, Ramin (Author) ; Tahami, Farzad (Supervisor)

Abstract

In recent years, multiport bidirectional converters have been a center of attention in renewable energy systems. This research focuses on three-port bidirectional converters. First, series resonant bidirectional converter is precisely analyzed. This analysis includes sinusoidal, exact state space and small signal analysis through phasor concept. This converter can work in higher switching frequencies and higher power ratings in comparison with common DAB bidirectional converter due to its inductor impedance cancellation. To increase power rating a three-phase version is proposed which has reduced output filter capacitance. Then, three-port bidirectional resonant converter is proposed and...

Direct Speed Control of Permenant Magnet Synchronous Machine

, M.Sc. Thesis Sharif University of Technology Dana, Shekoofe (Author) ; Tahami, Farzad (Supervisor)

Abstract

Accurate and fast position controlling is an important issue in today’s industrial needs. Drives used for position control require fast dynamics on speed control. Cascade linear controllers have sluggish response due to bandwidth limitations on speed and current loop. These structures limit the dynamics above all in high power applications where the switching frequency is low. In this thesis, deadbeat direct speed control is proposed, which overcomes limitations by cascade loops resulting in high-speed control dynamics. This approach uses a model of the plant to generate the control signals. According to measured speed and currents, the controller specifies the best voltage vector in order...

Design and Implementation of High Efficient Charger for Plug-in Hybrid Vehicles with Power Factor Correction Feature

, M.Sc. Thesis Sharif University of Technology Yazdani, Farzad (Author) ; Tahami, Farzad (Supervisor)

Abstract

In this project the novel zero-voltage-switching topology for power factor correction bridgeless boost rectifier is proposed. By employing an improved ZVS pulse-width-modulation (PWM) switch cell, ZVS of all the main switches is achieved without additional current or voltage stress of main switches. Also for the auxiliary switch the zero-current-switching is provided. In all modes of opretion of this converter, the power path is provided by maximum two semiconductor so the conduction loss of converter is low as in conventional converter. With this features the efficiency of proposed converter is very high

Hybrid Modeling and Control of DC-DC Series Resonant Converters for Applications of Wide Range Power

, Ph.D. Dissertation Sharif University of Technology Afshang, Hamid (Author) ; Tahami, Farzad (Supervisor)

Abstract

The subject of control and stabilization of dc-dc series resonant converter (SRC) is still a challenge in power electronics. The conventional controller design and stability analysis for this converter are based on the model which is derived using the sinusoidal approximation and averaging followed by linearization about an operating point. This model is not applicable to a SRC that operates below resonance especially in discontinuous conduction mode (DCM) because the sinusoidal approximation is no longer acceptable. However, a SRC may be purposely designed to operate in DCM. Therefore, it is essential to investigate the stability analysis and controller design using a more sophisticated...

Control of Quasi-Resonant Converters Using Model Predictive Control

, M.Sc. Thesis Sharif University of Technology Ebad, Mehdi (Author) ; Tahami, Farzad (Supervisor)

Abstract

DC-DC switching convertors are power electronic circuits that have various applications nowadays. Quasi-resonant convertors are a kind of these convertors that are of great interest due to their simple structure and soft switching. The goal of controlling these convertors is to achieve constant output voltage while varying the input voltage and the load by choosing a proper switching frequency. Classic controllers show drawbacks in the case of high input voltage and load tolerance, and this nonlinear behavior of the systems results in some practical challenges. In this thesis, nonlinear predictive controller for quasi-resonant Buck convertors is designed. Having designed the linear...

Control of Quasi-Resonant Converters Using Multiple Model Fusion

, M.Sc. Thesis Sharif University of Technology Nejadpak, Aarsh (Author) ; Tahami, Farzad (Supervisor)

Abstract

Nowadays, power electronics converters with pulse width modulation (PWM) are widely used in different power circuits. Operation of semi-conductive switches during on and off conditions causes switching dissipation and consequently decreases the efficiency of the PWMs. Recently, by increasing the required power for power electronics applications, quasi-resonant converters attract attentions. Quasi-resonant converters, by adding resonant circuits to the PWM converters causes the soft switching operation (switching with zero current or voltage) and decreases the energy loss. In conventional control methods of these converters, the nonlinear average circuit model is linearized around the...

Design of Electrical Drive for Steer-by-Wire Systems

, M.Sc. Thesis Sharif University of Technology Afshang, Hamid (Author) ; Tahami, Farzad (Supervisor)

Abstract

Hydraulic steering technology has been used in vehicles for decades. Recently, a trend has been seen towards the use of electronic steer-by-wire systems that provide greater design flexibility by customizing the connection between the steering wheel and the steering mechanism. Steer-by-Wire systems (SbW) offer the potential to enhance steering functionality by enabling features such as automatic lane keeping, park assist, variable steer ratio, and advanced vehicle dynamics control. The lack of a steering intermediate shaft significantly enhances vehicle architectural flexibility. The task of a SbW system is two-fold: turning the steered wheels by tracking the hand wheel (HW) rotation and...

Wireless Power Transfer System Design using Selected Harmonic for Electric Vehicle Charging

, Ph.D. Dissertation Sharif University of Technology Moradi, Adel (Author) ; Tahami, Farzad (Supervisor)

Abstract

Long lasting portable power is an ultimate desire for electronic devices. The limited capacity of the batteries in addition to the heavy weight and extra costs are the main challenges of the batteries for energy storage in large electrical devices like electric vehicles. Wireless Power Transmission (WPT) technology can address these issues by providing online electric power for these portable devices. Furthermore, this technology can supply electric devices especially portable ones by eliminating cables and connectors with more reliability.The current research is focused on optimum design of the wireless power transfer system for electric vehicle charging applications. The optimization of...

Control of Three-phase UPS with Nonlinear Load Using Disturbance Observer Considering Transformer Concerns

, M.Sc. Thesis Sharif University of Technology Shahriari, Zohair (Author) ; Tahami, Farzad (Supervisor)

Abstract

Nowadays, non-linear loads comprise an important part of electrical grids. One of the most essential sources of nonlinear loads is switching power supplies, which mainly include power electronic rectifiers. When power outage occurs, Uninterruptible Power Supplies (UPS) must be able to supply these loads. The nonlinearity of the load has a significant effect on the Total Harmonic Distortion (THD) of the output voltage, which may not be easily reduced, especially in three-phase inverters. Furthermore, the presence of isolating transformers in these power supplies limits the control of harmonics and intensifies the nonlinear effects of the system.In this Master Thesis, a disturbance observer is...

Design of Soft-Switching Inverter Using Wide Bandgap Transistors for Electric Vehicle

, M.Sc. Thesis Sharif University of Technology Elyasi, Bijan (Author) ; Tahami, Farzad (Supervisor)

Abstract

The electric vehicle inverter, as one of the most important components of the vehicle, needs to have a high efficiency and also be able to work at high temperatures. Due to passing a large part of the battery power through this part and being one of the components that has the biggest power in an electric vehicle , traction inverter Efficiency has a big impact on the total efficiency of the whole vehicle . By increasing the battery voltage of electric vehicles, in order to achieve a higher charging power, the electric vehicle inverter must be able to withstand a voltage of about 800 volts input .On the other hand, in electric car inverters, the goal is to reach a power density of 100kw / L....

Modeling and Control of LLC Resonant Converter Based on Theories of Hybrid Systems

, M.Sc. Thesis Sharif University of Technology Barzkar, Ashkan (Author) ; Tahami, Farzad (Supervisor)

Abstract

In comparison to pulse width modulation (PWM) converters, the ability of soft switch-ing enables resonant converters to operate at high frequencies, as the result of which these converters enjoy high efficiency, high power density, and low electromagnetic interference (EMI). Among resonant tank topologies, the LLC resonant tank is a very desirable structure, as the LLC resonant converter can operate in boost mode and properly regulate the output voltage under light loads and despite large variations in the input voltage and/or the load. However, there are major modeling issues with resonant converters, since conventional modeling approaches cannot properly model fast dynamics of these...

Design and Implementation of a High-Efficient High-Power-Density Telecom Battery Charger using Planar Matrix Transformers

, M.Sc. Thesis Sharif University of Technology Nazerian, Emad (Author) ; Tahami, Farzad (Supervisor)

Abstract

In creating a telecom battery charger there are three challenging factors which are high power density, high efficiency and modularity. A telecome battery charger consist of a rectifier with power factor correction capability and a DC-DC converter. The power stage of DC-DC converter with high output current and low output voltage has a vital role in the battery charger. The isolation transformer and magnetic component of LLC resonant tank are two huge and heavy parts of the DC-DC converter. With the emergence of GaN and SiC switches pushing frequency to to megahertz is possible which resulted in decreasing the volume of passive divices. But with increasing the frequency, designing of the...

Design and Implementation of the Rectifier Stage for 80 Plus Titanium Efficiency Telecom Power Supplies

, M.Sc. Thesis Sharif University of Technology Rahmanian, Mostafa (Author) ; Tahami, Farzad (Supervisor)

Abstract

With the ever-increasing expansion of the fifth generation telecommunication networks, achieving high efficiency for the power sources used in these networks becomes important due to their average power and wide use. For this reason, different and strict standards have been defined for efficiency. 80 plus is a certification program that aims to promote the efficient use of energy in power supplies including computers, servers and telecommunications applications. The highest level of this standard is called 80 plus titanium. This standard defines the minimum acceptable efficiency in different loads, which for example is equal to 96% in 50% load. The power supplies consist of two layers of...