Sharif Digital Repository

In the recent years, medical application of robots has been widely developed. Transforming open surgeries to close surgeries has distinguished this novel method to decrease limitations in this type of surgery. In this procedure, two or three small incisions on the skin are used as guides for robotic instruments to enter the cavity, to improve the surgeon’s manipulation and function in surgery. One of challenges in this field is surgeon’s training for laparoscopic surgery. Surgical simulators are used to solve this problem. Lack of instrument for large organs gripping and tissue palpation loss are existing difficulties in available surgical simulators in such a manner that surgeons has no... 

Excellent mechanical properties and high aspect ratio of carbon nanotubes have been the reason for extensive research on nanocomposites reinforced by this nanostructure, and recently metal matrix type of these nanocomposites, due to their advantages, have received great attention. Moreover, nanoporous materials are another type of nanostructured materials which due to their very high porosity have special applications in hydrogen storage, separating molecules, purification and energy absorption. Because of completely neglecting the details of nanoscale structure and not paying attention to the length scale, classical continuum mechanics methods are not precise enough for evaluating different... 

With the development of science and industry increasingly need for seamless and high-strength rings, the attention of many researchers and industrialists paid on the ring rolling process. Then, Studying details of ring rolling process is very important. The most important issues in ring rolling process which are not sufficiently considered are: stress components distribution in ring, real amounts of friction coefficient, pressure distribution over the rollers, required power, required torque and force, and finally the minimum thickness of the ring during the process, all of these parameters have developed as analytical functions. In the present study, the minimum possible thickness of the... 

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... 

Nowadays, robots are become more common in many important applications, such as academic and industrial issues. One of the most important robots are Multi-Arm manipulators which are used in many application such as moving objects, coloring, automatic welding and etc. Working with this kind of robots needs some vital attentions like planning their moving path. It is Because of the large number of obstacles that they face with in the path. Therefore, not only robots are not allowed to collision with themselves, but also they must not touch the obstacles. In the other words, they need Path planning. Generally, the equations of these robots are nonlinear. Therefore, computers and numerical... 

Low back pain is a common medical problem around the world afflicting 80% of the population some time in their life. Low back injury can result from a loss of torso stability. This investigation seeks to apply existing methods to new applications and to develop new methods to assess spinal stability during its dynamical activities. In this study, firstly, optimization method is utilized as an appropriate explanation of role of nervous system in controlling of spine movements. Spine which is a complex structure of vertebrae and cartilage has been modeled by a 3D inverted pendulum with a ball and socket joint at L5/S1 incorporated with 18 muscle fascicles. Planning of point-to-point spine... 

Characterization and simulation of carbon nanotube-reinforced composites at large scale have been a concern of researchers in the past decade. This is due to the computational complication of considering many embedded carbon nanotubes (CNTs). However a simple meshing of organized CNT distribution in the matrix can ease this obstacle. In this study, a finite element approach is employed to investigate the elastodynamic behavior of a wavy CNT-reinforced composite structure. A three dimensional structure with up to 6400 uniformly distributed wavy CNTs is embedded in a polymer matrix. Each wavy nanotube is represented by a set of beam elements. The effect of nanotube waviness and volume fraction... 

Strong van der Waals (vdW) potential fields of carbon nanotubes (CNTs) makes them capable to encapsulate some nanostructures inside their hollow space, which leads to the construction of new hybrid nanostructures under specific conditions. Carbon nano-peapods, carbon nanowires and the hybrid of DNA and CNT are the main categories of hybrid nanostructures of CNT. Characteristics of hybrid nanotubes are unique and different from those of CNT. In nanostructures, the lattice spacing between individual atoms is considerable with respect to the structural dimensions. Also, the range of internal characteristic length is relatively close to external ones. So that utilizing the classical continuum... 

Selection of muscle activation pattern to reach a specific goal by considering the complexities of neuromuscular system and the way it overcomes these complications, are of researchers’ space interest in motor control. One proposed solution for resolving these complexities is the concept of simple module (synergies) that suggests the combination of them leads to more complex activities. In the present work, the existence and arrangement of synergies in the lumbar spine have been studied. For this purpose, a model with 18- muscles at level of L4-L5 under utilized in the static condition. In order to obtain the muscular and stability synergies, a biomechanical model predicting muscle... 

The present study deals with the analysis of Atomic Microscope with crack by making use of Strain Gradient Elasticity theory. Empirical observations represent that in micro dimensions, materials show behaviors, which the classic continuum mechanics theories are not able to explain. Thus, taking advantage of non-classic theories, which are capable of explaining such phenomena or behaviors in analyzing materials in micro dimensions seems necessary and of much significance. In this direction, by applying an Euler-Bernoulli beam assumption and neglecting the shear effects, governing equations and boundary conditions of the problem were obtained via taking advantage of variations in Hamilton... 

In recent years, the world has seen a great progress in micro electro-mechanical systems (MEMS). Small size, low weight, high accuracy and low energy consumption have made these devices applicable in a variety of usages. In MEMS devices, mechanical components are used for specific purposes among which one of the most widely used are micro plates. Microplates are used in the structure of many devices such as microswitchs and atomic force microscopes. Therefore, studying of static and dynamic behavior of microplates is important. As the object gets smaller (to the scale of micro and nano meters), the classic theory of mechanics of continuous media cannot predict the behavior due to its... 

Wound healing by engineered scaffolds is a new step in bio-technology and medical studies in recent years. The goal of the current study is to propose a novel structure for a tissue-engineered scaffold to be used in wound healing. Influenced from the multi-layered structure of natural human skin, the fabricated scaffold consists of two layers to maximize similarity with natural skin. This product is comprised of an electrospun layer made of polycaprolactone and polyvinyl alcohol and a hydrogel layer made of chitosan and gelatin. In order to form a porous medium in the hydrogel layer, freeze-gelation was used instead of freeze drying. The evaluation of fabricated scaffolds was performed by... 

Carbon nanoscroll (CNS) is a graphene sheet rolled into a spiral structure. The Equilibrium structure of a CNS depends on the elastic bending energy and van der Waals interactions between layers. In recent decade, research on CNSs received high attention after discovering new techniques to produce high purity CNSs. Modal analysis of the CNS is essential in various applications like sensors and actuators. Therefore, in this research, a shell model for free vibration analysis of the CNS is proposed. After considering CNS as an equivalent shell, the assumed mode technique is used to extract natural frequencies and mode shapes of CNSs in different boundary conditions. The effect of geometric... 

Circular cylindrical shells have been widely used in many engineering structures such as spacecraft, submarines, offshores, and storage tanks. Their high stiffness-to-weight ratio and load-carrying capability make them well suited for use in civil and aerospace structures. The consecutive development of material engineering along with the increasing demands for lightweight, heat-resistant, and high strength structures have led to the usage of advanced materials namely functionally graded (FG) materials in designing such structures. In this thesis, the nonlinear static analysis of thin FG cylindrical shells is carried out using the Donnell’s shell theory with first-order approximation and the... 

In this study, the linear dynamic response of an inclined FGM Timoshenko beam on linear viscoelastic foundation subjected to a traveling mass with constant and variable velocity is investigated. Timoshenko beam theory and von-karman strain-displacement relations are utilized to model the problem. the FGM beam is made of metal and ceramic and it is assumed that material properties of the beam vary continuously in the thickness direction according to the exponential law and the power-law form. The kelvin-voigt damping model is applied to model the internal damping of the FGM beam. The partial differential equations of motion for the bending rotation of cross-section, longitudinal and... 

In this study, an elastic-plastic analysis of fiber reinforced metal matrix composite structures loaded by uniaxial uniform tension in the direction perpendicular to the fiber is carried out by assuming elastic-plastic matrix with kinematic hardening. Representative volume element (RVE) is used for this analysis. The element consists of a combined square field composed of a solid circular cylinder fiber and matrix in plane strain condition. Elastic analysis is carried out using Airy stress function and Michell solution. Unknown coefficients of the Airy stress function are determined by satisfying boundary conditions as well as continuity conditions. The governing equation of plastic zone is... 

Nowadays, cooling towers are widely used in power plants, refineries, petrochemicals and ventilation industries, but the water consumption of these towers is high and because of water crisis in Middle East and Iran, it is necessary to devise in order to reduce the water consumption of these towers. In this study separated hybrid cooling tower are used to investigate the water consumption at power plants. The rigorous Poppe method are used in order to estimate the exact amount of water loss due to evaporation in wet cooling towers. First, the effect of ambient condition, wet cooling tower cells and dry cooling tower size on the performance of hybrid cooling tower are investigated, then the... 

In this study pollution generated by a electronic cigarette in a bus is observed. Resultant smoke from these products consist of different components which may endanger health and one should make sure them amount in general transport vehicles like bus are in permissible limit. These components are initially in liquid shape and evaporate. Tracking liquid particles are done with the aim of Lagrangian approach. For this the geometry is generated at first. Then structured mesh was generated with ICEM CFD which is a powerful mesher. Different conditions of smoking source and bus doors were studies and results were compared.Change of pollutant concentrations is strictly depend on position of... 

The aim of this work is numerical analysis of wave propagation in earth by using spectral element method for single and multi phase with application in oil industry. In this method, numerical solution has high accuracy due to using high order polynomials and appropriate integration points. Also, the mass matrix is diagonal by using this method which results in considerable decrease in computational cost with respect to finite element method.
The wave propagation in the mentioned models is studied by many researchers. The main problem in petroleum industry is large dimension of the model which results in high computational costs. Thus, using the proper numerical approach for these... 

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...