Sharif Digital Repository

The use of carbon nanotubes in Nano-switches is the new technology employed in NEMS. Nano-switches can also perform as a micro-switch where nano-switches have longer life time, consume lower power and have smaller size with respect to micro-switches. As the dimensions get smaller, continuous models lose their accuracy and molecular methods should be utilized. Non local theory, is attempting to change the responses of continuum models assuaging them to the molecular results. In the current project, non local theory is used to rewrite the governing equations of nano tubes motion and the results are compared with the classical results. In this modeling, the axial force and the mid-plane... 

One of the most important parts of oil industry is drilling with rotating drillstrings. In a drillstring because of the contact between bit and formation, contact between drillstring and borehole wall, existence of drilling mud, misalignment in drillstring and stick-slip phenomenon; axial, lateral and torsional vibrations is created. These vibrations may lead to fatigue failures and abrasive wear of tubular, damaging the drill bit and borehole wall. In this thesis the drillsting vibrations is studied using finite element method. To this end, cylindrical superslement with C1 continuity is presented. By using the shape functions of this superelement; kinetic and potential energy of drillstring... 

Vibration is one of the most important factors in design, operation and lifetime of drill strings. There for, investigation of vibrations in drill string, like every other rotary machine, is very important. The main goal of this research is developing a nonlinear model for a drill string system dynamics in an inclined well. Effects of drilling mud flow rate, weight on bit, angular velocity along with viscous damping, on the stability and vibration of a drill string are studied. Dynamic equation of the model is developed considering axial displacement and lateral bending geometric nonlinear coupling. The effect of drilling mud flow is modeled using Paidoussis formulations. Equation of motion... 

Features with sculptured or free-form surfaces appear frequently in computer-aided design of parts common to aerospace, automotive, and die and mold industries. Because of their ability to machine complex features and to achieve good surface finish, ball-end tools are widely used in the finish milling process of sculptured parts. This research has been devoted to the modeling of cutter-workpiece engagement (CWE) boundaries, cutting forces, and stability prediction in ball-end finish milling process of sculptured parts. In the first step, a new analytical model taking into account the effect of surface curvatures was presented for three-axis and five-axis ball-end milling processes. In this... 

Due to importance of micro electromechanical systems (MEMS), inability of the classical continuum theory to predict the mechanical behavior of micro-scale structures accurately, and vast applications of finite element method (FEM) in modeling of the MEMS, in this dissertation, the static and dynamic mechanical behavior of electrostatically actuated micro structures has been investigated using newly developed finite elements based on strain gradient continuum theory. The governing equations and boundary conditions have been developed for longitudinal and torsional behavior of microbars as well as flexural behavior of Euler-Bernoulli and Timoshenko microbeams based on strain gradient... 

Investigation stability of chatter vibration is of great importance in machining processes. Finding frequency response function (FRF) at the tool tip is an effective method to predict stable machining regions. Commonly, the tool tip FRF is obtained using experimental modal analysis but this approach is often time consuming and requires expertise. In addition, changing tool or holder requires modal test which is a disadvantage, consequently modeling methods are of interest for researchers. Moreover, optimum design of machine tool is another benefit of modeling method. Also, in machining with flexible or micro tools in which experimental tests can not be performed, modeling methods would be... 

In this paper, a novel control approach for one-dimensional bilateral teleoperated nanomanipulation system is proposed. While manipulating objects with a nanomanipulator, real time visual feedback is not available. So, force feedback is used to compensate for the lack of visual information. Since nanometer scale forces are dominated by surface forces instead of inertial forces as in macro world, scaling of nanoforces is one of the major issues of teleoperation system. The Hertz elastic contact model is used to model the interactions between the slave robot and the environment. The proposed framework uses the simple proportional derivative control, i.e., the master and slave robots are... 

Atomic force microscope (AFM) has a significant capability of imaging surface topography on an atomic scale. It is also widely used for Nanolithography in MEMS/NEMS (micro/nanoelectromechanical systems). Although the conventional AFMs have a significant capability of nano-scale surface measurements, their probe tips cannot come in close proximity to the sidewalls, no matter how sharp they are. Therefore, no accurate nano-scale measurements at sidewalls and edges can be achieved by these conventional AFMs. In addition, regarding the increasing applications of micro-structures such as micro nozzles, micro gears, micro holes and micro trenches which all of them have sidewalls and edges,... 

In recent decades, the important role of MEMS devices in optical systems has initiated the development of a new class of MEMS called Micro-Opto-Electro-Mechanical Systems (MOEMS), which torsional micromirror is one of these systems. Among variety kinds of micromirrors the dual axis micromirror has hopefully application such as high quality projection display, free-space fiber optical (FSO) communications and endoscopic optical coherence topography. Dual axis micromirror could play a key role in FSO applications such as satellite-to-satellite separated by hundreds of kilometers, as where. In medical applications, micromirror must could be able to rotates θ_x and θ_y.about two axis x and... 

Micro-Structures, especially cylindrical shells, has been widely used in different high tech industries, that this extreme usage emphasis, analyze of the vibration behavior of these structures. For gain an appropriate characteristics for a known purpose we can stiffen cylindrical shells with some rings that lids to improvement in mechanical properties of them. With advent of new materials, such as Functionally Graded Materials (FGM) and unique properties of these materials investigation of vibration behavior and characteristics of micro cylinders which has been made of FGM can be very important and essential. By using FGM materials many mechanical characteristics of these structures can be... 

In humans, the heart is roughly the size of a large fist and weighs between about 280 to 340 grams in men and 230 to 280 grams in women. Your body has about 5.6 liters of blood. The human heart is an organ that pumps blood throughout the body via the circulatory system, supplying oxygen and nutrients to the tissues and removing carbon dioxide and other wastes. Any damage to the heart, will affect on the other organs. They are four valves within the heart, in which aortic valve is the most important and crucial part of the heart. Calcium sediment on aortic valve leaflets causes reduction in the flexibility of the leaflets, one of the most common heart diseases. In this study, the flexibility... 

This study aims to provide a multiscale model of traumatic brain injury including the three levels of macro, meso, and microscale information. In order to do this, a macroscale voxel-baed model of human head was constructed. The model was designed and generated to include mesoscale tissue information as well as a voxel-based approach to include voxel-based microscale data and to be coupled in a multiscale framework. Next, three different microscale models were constructed. The variations of fractional anisotropy within one standard deviation in the regions (including 60% to 70% of voxels) can change the stiffness of the tissue by up to the considerable amount of 40%. The microscale models... 

Heart is a muscular organ, which pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste to the lungs. Heart is sort of like a pump, or two pumps in one. The right side of heart receives blood from the body and pumps it to the lungs. The left side of the heart does the exact opposite: It receives blood from the lungs and pumps it out to the body. However, in end-stage heart failure, the heart can no longer pump enough blood to meet the body’s needs, in which case implantable left ventricular assist devices provide support for patients at risk of death from end-stage heart failure.Centrimag... 

Keratoconus is a progressive corneal illness that appears due to reduced thickness of cornea in some area. Normal cornea has semi sphere shape with uniform thickness from center of cornea to the limbus. However, keratoconic cornea’s shape becomes conic. One of the treatments in moderate state of keratoconus is implantation of IntraStromal Corneal Ring Segments( ICRS). Ring Segments are made of PMMA and inserted in 0/7- 0/8 of depth of cornea.In this study, before surgery data from 3 patient’s cornea images were prepared in order to 3D modeling of cornea, for importing to FEM software( ABAQUS). Material properties of cornea is considered hyperelastic second-order Ogden Model; elastic... 

During the past decade, micromachining technology has become available to fabricate micron-sized mechanical parts. The miniaturization of almost all types of devices and systems is arguably a greater opportunity for commercial profit and beneficial technological advances (e.g., micromechanical, microfluidic, microthermal, micromagnetic, microoptical and microchemical). However, instead of the traditional evolutionary engineering effort to reduce size and power while simultaneously increasing the performance of such a diverse set of systems, the field of microelectromechanical systems (MEMS) represents an effort to radically transform the scale, performance and cost of these systems by... 

Fabrication of various microelectromechanical sensors and actuators with low levels of energy consumption on one hand and the recent advances of microelectronic circuits technology leading to vast reduction in size and power consumption of CMOS circuitry on the other hand, have proposed the idea of developing MEMS-based environmental energy harvesting devices to provide their required power. These energy harvesters are an appropriate alternative for former heavy batteries of limited lifetime and can be utilized as a sustainable energy source for small intelligent systems. In the present research, the behavior of MEMS piezoelectric vibrational energy harvesters in nonlinear regime considering... 

Due to pollution and destructive effects on the environment, while consuming a large amount of fossil fuels that can be converted into high value-added products, gasoline cars are gradually replaced by electric cars. Modern electric vehicles are generally designed and manufactured on the platform of gasoline vehicles. In the present study, it is tried to design three models of electric vehicles based on the SAINA vehicle. Initially, for the first model, an electric motor instead of the SAINA gasoline engine is employed to provide the power required for the vehicle. Then, for the second model, two electric motors are used namely one in the rear axle and one in the front. The third model uses... 

Kidney stone disease is one of the diseases that a large number of people experience each year.A Common method for the treatment of kidney stone is the use of acoustic waves, which have attracted the attention of doctors in recent decades. Because of the different structure of kidney stones, the waves transmitted to break these stones are usually performed at different frequencies. Most kidney stones are calcium that can be broken down by using acoustic wave frequencies in the range of 40-20 KHz. Most available lithotripters for the treatment of percutaneous nephrolithotomy (PCNL) are two types: Pneumatic and piezoelectric lithotripters. The lithotripter in this thesis is a piezoelectric... 

When the human body is subjected to high accelerations, cardiac function and blood supply to the body can be changed. Due to the complex geometrical and mechanical properties of heart, finite element method is useful way for analysis of response of this structure under different load types. Modeling heart using finite element method requires mechanical and geometrical properties of heart. Soft tissues modeling, such as heart muscle using finite element method is one of the most challenging issues in field of biomechanics. In this thesis, the mechanical properties of heart are obtained by performing experimental compression tests on samples of fresh bovine heart. Using obtained experimental... 

Nowadays functionally graded materials (FGM's) are widely used in different engineering applications such as aerospace, solid mechanics And biomechanics among others. FGM's are inhomogeneous composites made of two different materials, usually a metal and a ceramic with continuous variation of properties. Recently these materials according to their special characteristics are used in micro and nano electro mechanical systems. As size decreases in mechanical systems due to interatomic forces, energy balance law won't be valid locally and therefore classical equations of elasticity may not be used anymore. To overcome this problem,nonlocal theories of elasticity were initiated in works of...