Sharif Digital Repository

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

The effects of combined task demands on the way muscles are recruited to balance external loads during posture and movement is of great importance in quantitative analysis of upper arm function. Pain and disability of shoulder joint is becoming more important as population spends more often interacting with computers in seated position and carrying repetitive tasks using upper extremities. Shoulder joint that is more dependent on the muscles for its normal function than other joints such as hip due to its small articular surface and large range motion has been used here to study its coordination during isometric exertions. Since, the numbers of tasks that could be performed are enormous. In... 

In this thesis, the formulation of beams and plates in the micro- and nano scales is presented based on the second strain gradient theory (SSGT) introduced by Mindlin. The SSGT is a non-classical continuum theory that includes the second-order gradients of strain tensor in its formulation and this leads to more accurate modeling for mechanical behavior of materials than the strain gradient theory. On the other hand, due to the ever-increasing use of micro- and nano-electromechanical systems, analysis of the mechanical behavior of their deformable components for design and construction is of particular importance. For this purpose, analysis of Timoshenko beams and Euler-bernoulli beams made... 

In modelling of large deformations in deformable solids, rate type constitutive equations are of great importance. In order to fulfill the material objectivity conditions it is necessary to choose an objective rate of stress tensor. On the other hand, using corotational rates, because of their special properties (which are resulted of the fact that varaition of parameters are computed from an observer connected to a rotated triad), in rate type non-linear elastic constitutive equations (called hypo-elastic equations) are notable. In this thesis, the necessary conditions for a linear rate type isotropic tensor-valued function of a tensor argument and its rate to be integrable are driven. In... 

Nowadays, the usage of beam-shaped structures has widely spread in micro- and nano-electromechanical systems; consequently, scholars are extremely interested in precise modeling of static and dynamic behaviors of them. As the beams utilized in MEMS and NEMS structures have thicknesses in the order of microns and sub-microns, the experimentally validated small scale effects would be considerable in their behavior. In fact, experiments manifest that the size-dependent behavior is an intrinsic feature of materials when they are used in small-scale structures. In the classical continuum mechanics, there exists no material length scale parameter. Thus, the classical theory is unable to capture... 

A single-degree-of-freedom model is considered for flexible exercise bars based on the lumped-element approach. By considering the side segment of a flexible exercise bar as a cantilever beam with an equivalent mass at the free end, its free-vibration response and forced one under excitation of the grip of the flexible bar is written parametrically. Some experiments are performed on a specific flexible bar to obtain numerical values for the parameters in the model to have it quantitatively known. In the next step, simulation of the model results in the response of the flexible bar under a considered excitation. The response is imported into a multi-segment musculoskeletal software, AnyBody,... 

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... 

Spinal Column is one of the most important parts of musculoskeletal system. Injuries in this region are so rampant and causing vast expense. Risk factors related to spine injuries included personal related ones such as, age, sex, muscles’ strength and career related ones such as body positions at work place and loads. Since in vivo measurements have many restrictions, developing biomechanical models that simulate the response of a person to given loads and conditions has important role in preventing injuries and improving working conditions. Inputs to current models of the spine are considered to have mean value, therefore muscles’ forces and other outputs of these models have single value... 

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... 

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... 

owning to the side effects and disadvantages of conventional methods of cancers treatments such as chemotherapy, currently, scientists are attempting to find new methods to replace them. Furthermore, many human diseases like SCID and Hemophilia are due to genetic disorders and scientists are also seeking to find permanent treatments instead of available temporary ones for them. in recent years, regarding the obtained achievement, Gene Therapy is being considered as a promising method for both cancers and genetic disorders treatment. But due to low efficiency of this method at this stage, there is an endevour among researchers for a more profound comprehension of the basics of gene therapy to...