Sharif Digital Repository

Corneal keratoconus is one of the common eye diseases that usually occurs in the teenage years or the beginning of the third decade of life. In this disease, the cornea thins and loses its original shape and becomes conical. To treat this disease, ophthalmologists use different methods such as using glasses, contact lenses (hard and soft), corneal transplantation, and also corneal cross-linking, each of these methods has limitations, on the other hand, considering that The disease progresses and its severity increases, Ophthalmologists use corneal rings to treat this disease in more advanced stages, implanting a suitable ring in the patient's cornea both increases the strength of the... 

Research in the field of medical science goes back decades and significant progress has been made in understanding the behavior of organs and living tissues. Consequently, scientists need to work towards identifying how to mathematically model the mechanical behavior of these living organisms. If we consider any living entity, we can see that they are a product of atoms, molecules, cells, tissues, and/or organs. Differential geometry and continuum mechanics indicate that during the growth process these organisms are influenced by the phenomena of aging, remodeling and morphogenesis. The majority of research in this area, i.e. the study of these important phenomena in living tissues, has... 

One of the extensively used, yet complex, structures in the industry is pre-twisted Micro/Nano beams. Studying their mechanical behavior helps to have a broader view of them. In this present study, explores and analyzes the behavior of a pre-twisted Micro/Nano beam with a quadrangular/rectangular cross-section using the strain gradient theory and modified couple stress theory. Using the calculus of variations and the Hamiltonian principle the elastodynamics governing partial differential equations of transverse deflection of the pre-twisted Micro/Nano beam with hinged-hinged boundary conditions are derived. Then the mechanical behavior of the pre-twisted Micro/Nano beam in static mode and... 

Todays, advances in manufacturing technologies have led to design and production of micro-scale elements, including the elements employed in micro-electro-mechanical systems (MEMS). Micro-rotating systems like the micro-turbines are that kind of systems at which the high rotational speeds and the complexity of design and analysis have led to a special attention in modeling and investigating of their dynamic-vibrational behavior. In addition, in small scales, using the non-classical continuum mechanics theories such as the couple stress theory and the strain gradient theory is required to obtain the high precise results. On the other hand, attention to the torsional deformation of rotors... 

Nanopositioning systems are devices with the ability of moving objects within nanometer resolution. In the recent years according to the advancements in the nanotechnology fields, there is an urgent and growing need for these systems as precision motion drivers. In the most of the nanopositiong devices some active materials such as piezoelectric elements are widely used as actuators. Piezoelectric materials can generate a mechanical deformation proportional to the applied electrical field. Therefore, theoretically these devices have the ability to set the desired position with the infinite precision.Design, optimization and fabrication of an ultrasonic piezoelectric motor are performed in... 

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... 

From the past, the damask rose has an important place in various pharmaceutical, food, health and cosmetic industries. This product has the largest cultivated area in Iran, which is about 24,000 hectares, equal to 60% of its total cultivation in the world. Considering the conditions required for the cultivation of this plant, including the low water requirement, the expansion of its cultivation has been considered. One of the important obstacles to not expanding cultivation is manual harvesting, which strongly affects the quality and mass of essential oil and rose water. The efforts that have been made so far in the field of designing and producing the rose harvesting machine have not had... 

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... 

Engineering of properties was previously not possible. With the advent of additive manufacturing, it became possible to produce structures with architected microstructures, known as lattice structures. The popularity of these structures, due to their lightweight and tunable properties, has increased the importance of their optimal mechanical analysis. Since direct analysis of these structures is computationally prohibitive due to their high level of detail, homogenization methods have been proposed as an alternative. Since these methods couldn't capture size effects, higher-order homogenization methods were introduced. However, despite their good accuracy, these methods are still rarely used... 

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... 

The analysis of nonlinear forced vibration of micro-rotors (rotating micro-shafts with disks) is carried out under loads of mass eccentricity distribution and in the presence of internal damping. For the analysis, the non-classical continuum theories of couple stress and strain gradient are employed. Vibrational behavior of micro-rotors is extremely sensitive due to the very high rotational speed, which is at the order of several millions per minute speed. The considered nonlinearity is of geometrical type due to the mid-plane stretching. First, the governing equations of motion of micro-rotors are derived by utilizing the Hamilton principle. In the next step, the Galerkin and multiple scale... 

Due to the features like small dimensions, low manufacturing cost and low power consumption, micro-electromechanical systems (MEMS) are widely utilized in engineering applications. Many experimental investigations have indicated that the mechanical behavior of constructive microelements of these systems isn’t predictable by classical continuum theory. Therefore, to analyze the behavior of microelements, the non-classical continuum theories which can capture size effects should be utilized. On the other hand, various experimental observations have confirmed that thermoelastic damping (TED) is a dominant source of energy dissipation in microelements, in contrast to the non-small parts and... 

In the present study, by considering the damage effects, the governing equations for elastoplastic behavior of a rotating disk are derived. Then several numerical solutions are presented for specific examples. First, by means of elastic strain energy functions along with the damage appearing in the literature and irreversible Thermodynamics laws, an analytical solution is generated for a rotating disk undergoing elastic deformations. For this purpose, the components of strain tensor are obtained in terms of the damage variable and the stress tensor components. Then, by employing the damage evolution relations mixed with the damage surface relation, damage variable is derived as a function of... 

Cardiovascular diseases are one of the leading causes of death in the world. Identifying the mechanical behavior of arteries and their growth and remodeling under applied loadings can help to better understand the progression of the disease and provide more effective clinical interventions. Therefore, many researchers in recent decades have turned their attention to modeling the process of stress-mediated growth and remodeling in soft tissues. Among the most important models proposed to study this process are the constrained mixture model proposed by Humphrey et al. and the volumetric growth model proposed by Hoger et al.. The constrained mixture model is based on the continuous turnover of... 

Keratoconus is a progressive disease in which the cornea becomes thin and due to the presence of internal pressure in the eye and its application to the cornea, the cornea becomes bulging and conical. In recent years, due to the relatively large number of patients with keratoconus and also the ability of this disease to progress over time, the need to study and research on the treatment of this disease is noticeable. Early and non-surgical methods for the treatment of keratocous are use glass and contact lenses, but since the disease is progressive and usually appears more severely over time, ophthalmologists use the method of corneal ring implant for treatment.In this study, 9 types of... 

Incapability of the classical continuum mechanics theory to justify the experimental observations of the mechanical response of the small-scale structures and parts motivated the researchers to pursue the introduction and utilization of the non-classical continuum theories for analysis and design of such structures and parts. In this paper, utilizing the modified couple stress theory and the strain gradient theory as well-known and powerful non-classical continuum theories, the mechanical response, including the displacement and stress fields, for micro-rotating disks with angular acceleration is investigated. The governing differential equations of motion and the corresponding boundary... 

This thesis is a research corresponding to Super-Hydrophobic condensation substrates with Nanometer texture. In this study, the foresaid surfaces are fabricated by two methods that are Nano-composite paint and Electrophoretic coating. As a summary for the first method (the Super-Hydrophobic Nano-composite paint), the hybrid coating contains two mineral and organic phases; The organic phase is a two-part clear-coat polyurethane and plays the role as a polymer matrix in Nano-composite structure. Silica Nano-particles are the mineral phase and the two phases of Nano-composite have made connection with silane compounds. Also, surface-modification in Nano-particles for giving hydrophobicity... 

Additive manufacturing enables fabricating lattice structures with tailored mechanical responses based on lattice materials. Full exploitation of such a possibility requires reliable and efficient mechanical analysis tools to be explored by topology optimization algorithms for designing the interior architecture of the structures to meet the desired mechanical behavior. However, detailed mechanical analysis of lattice-based structures using the conventional finite element approach is prohibitively expensive due to lattices’ complex and fine features that demand adopting very fine space discretization. As an alternative, equivalent models based on the homogenization principle have widely been... 

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 concept of generalized strains is a well-established subject in the classical continuum mechanics. The characteristics and various applications of the generalized strains have been the point of interest of many researchers in the classical continuum mechanics. The aim of this thesis is the introduction of generalized strains in the micropolar theory, as a non-classical continuum theory. A set of generalized strains is suggested for the deformation of macro-elements. Moreover, a set of generalized strains is proposed for the micro-structures. Since the rate of strains possesses a significant importance in the constitutive equations of nonlinear analysis of solids, expressions for the rate...