Sharif Digital Repository

Millions of people due to factors such as osteoporosis, aging, sports incidents, and accidents face complications from bone fracture injuries every year. Nitinol shape memory alloy and Gyroid metamaterial have attracted researchers to use them as suitable replacements to fill empty areas of broken bones. In this research, numerical modeling and additive manufacturing were used to take advantage of the special properties of both nitinol and gyroid structures. In the modeling section, finite element modeling of the superelastic effect and the one-way shape memory effect of sheet and solid gyroids in cubic and cylindrical geometries with different porosities were done. As a result of the... 

Subdural hemorrhage (SDH) is one of the most common traumatic brain injuries. The mortality rate of SDH is over 30 percent. In addition, patients require to visit hospital for treatment and further healthcare. According to the costs of treatment and frequency of injuries, prevention of SDH is essential. 3D-Finite element modeling of human head is an appropriate tool for evaluation of injury risk and setting up a prevention tolerance criteria. The aim of this study is to create a 3D finite element model of human head with special consideration of vessels. Vessels are modeled by truss elements at current finite element models of human head; however, geometry of vessels is regarded as simple... 

Nowadays, in many of industrial processes, it’s necessary to measure acceleration of a moving object. Among the different type of accelerometers, the piezoelectric type are most useful and the most widely used. These sensors come in various configurations.
In the past, analytical and semi-empirical models have been used to design piezoelectric accelerometers. In these methods, based on some assumptions, the accelerometer nonlinear model is replaced with a linear model and the equivalent circuit model has been used to model accelerometer behavior. In these methods, the behavior of accelerometer become different from the expected one.
Recently, with the invention of efficient computing... 

Systems composed of electrical and mechanical elements in micrometer scale are called microelectromechanical systems which are commonly fabricated on silicon substrates. These systems are in connection with environment by the means of sensors and actuators. Thermal microactuators as one of the most applicable actuators produce force and displacement on the basis of thermal expansion.Recently, by the advent of some polymers compatible with microfabrication methods such as SU8 and due to their remarkable thermal properties,polymeric thermal microactuators are attracting more attention in a way that polymeric type of almost every predesigned thermal microactuators are fabricated and much... 

In this dissertation, the location and severity of the damage are obtained using a new robust Power Spectral Density (PSD) sensitivity-based model updating method. PSD of structural response is highly sensitive metric to parameter change and provides vast information about the structure. The proposed damage detection method uses the sensitivities of measured responses in frequency domain, for FE model updating in an efficient way, by developing a quasi-linear sensitivity equation of structural response. The system of equations are solved using Least Square method. Only stiffness parameters were updated through model updating and change in mass parameters were neglected. In this study, proper... 

Spine biomechanical models suffers from either simplification in passive disc components modeling (modeling via torsional spring or beam elements) in musculoskeletal (MS) models or shortcomings in detailed muscles modeling (via a simple force and torque vector) in detailed finite element (FE) models. Considering these, that is aimed in this study to develop a hybrid MS-FE model which the calculated muscle forces by a MS model (developed based on geometrical and mechanical properties of FE model) for a desired static posture, being applied to a detailed FE model. Considering the change of discs stiffness in FE model under the applied muscles and gravity forces, the equivalent stiffness in MS... 

Structural Health Monitoring (SHM) is a multidisciplinary emerging research field. SHM assesses the health state of the structure through processing and interpreting of signals and can predict remain life of the structure. Damage detection with Piezoelectric Wafer Active Sensors (PWAS) is one of the effective and emerging methods of SHM. One of the most critical parts of aerial structures is lap joints in which SHM could be very effective. In this research, damage detection of lap joints using lamb wave propagation has been studied. A 3D model of an aluminum lap joint presented. The PWAS are modeled separately and bonded to the host structure and coupled electromechanically with the... 

Offshore jacket platforms are one of the most motivating structures for damage detection due to their importance and productivity. In this study, the goal is to investigate the application of finite element model updating as a robust method for damage detection in this kind of structure. This method is based on minimizing a cost function which shows the difference between some features of the model and damaged real structure. Therefore, this method can be used for damage detection by comparison between updated model, which is updated by measured data from damaged structure, and the initial model which precisely shows the previous or undamaged status of the structure. The vibration features... 

The Brushless Doubly-Fed Machine (BDFM) is a machine which incorporates the robustness of the squirrel cage induction machine and the speed and power factor control of a synchronous machine. All of these advantages are obtainable from a relatively low rating power electronic converter (e.g. 30 % of the machine’s rating). The stator of a BDFM is furnished with two balanced three phase windings of conventional design (power and control winding). These windings differ in pole number and are often excited at different frequencies. Hence, there is no direct magnetic coupling between them. The power winding is connected to a constant-voltage, constant-frequency source and the control winding is... 

With the emergence of a variety of surgical glues in the market and utilizing them in recent years, nowadays, based on the post-surgery studies, it has become transparent that there are additional factors, such as the long-term effect of surgical glues on tissue, to consider beyond the sealants ability to act as a mechanical barrier or a means to buttress friable tissue so that it can hold sutures. Mechanical properties of the surgical glues have especially a significant role in the applications that the tissue undergoes cyclic loading (such as arteries’ tissues). A mismatch between the mechanical properties of the tissue and the sealant can result in the remodeling of the artery that may... 

The main problem of steel-reinforced concrete structures is corrosion of steel reinforcements which leads to premature failure of the concrete structures. This problem costs a lot annually to rehabilitate and repair these structures. In order to improve the longterm performance of reinforced concrete structures and for preventing this corrosion problem, Fiber Reinforced Polymer (FRP) bars can be substituted of conventional steel bars for reinforcing concrete structures. This study is a numerical study to evaluate structural behavior of the simply supported concrete beams reinforced with FRP bars in comparison with steel-reinforced concrete beams. The commercial Finite Element Modeling... 

The Brushless Doubly-Fed Machine (BDFM) is a machine which incorporates the robustness of the squirrel cage induction machine and the speed and power factor control of a synchronous machine. All of these advantages are obtainable from a relatively low rating power electronic converter (e.g. 30% of the machine’s rating). The stator of a BDFM is furnished with two balanced three phase windings of conventional design (power and control winding). These windings differ in pole number and are often excited at different frequencies. Hence, there is no direct magnetic coupling between them. The power winding is connected to a constant-voltage, constant-frequency source and the control winding is... 

Background: Degeneration of intervertebral joints due to kinetical alterations after fusion surgery is a prevalent back disorder. While in-vivo studies are limited to medical imaging techniques, in-vitro and in-silico (passive FE modeling) investigations lack the crucial role of muscle forces. Available musculoskeletal modeling studies, not only suffer oversimplification of intervertebral joints, but have some shortcomings in incorporation of the contributing factors (that may alter postoperative kinetics). On the other hand, one of the main shortcomings in the available musculoskeletal models is their inability to account for dynamic effects and modeling transient events. Purpose: 1-... 

Vibrating ring gyroscopes (VRG) as MEMS devices are employed to micro scale systems for determination of the rotation rate and rotation speed of them. It is experimentally approved that micro scale structures behaves differently in comparison to macro scale systems, Therefore higher order continuum theories are required for modeling and analysis of these systems. In addition to that there is no comprehensive investigation on the dynamic performance of ring gyroscopes in the literature, In view of this in the present research the static and dynamic analysis of vibrating ring gyroscopes based on the strain gradient theory and the proposed finite element model of the gyroscope is performed. The... 

There is a large, at times contradictory body of investigations relating low back pain and spinal curvature in sagittal plane. The previous studies have not been subject-specified, and they have not considered the active tissues in the models. The mechanical load has a significant impact on the prevalence of low back pain and the geometry of lumbar spine in the sagittal plane is one of the most important characteristics in determining the load sharing of the spine. Thus, it is essential to know how the geometry load affects the load sharing of the lumbar spine. As a matter of fact, the purpose of this project is to know how the geometry of the lumbar spine affects the load sharing. Thus,... 

One of the most important manufacturing methods using technologies AM, is the SLS method. This method because it would significantly reduce the construction time is the ability to build a variety of materials, is pervasive. The SLS devices input is part CAD file which is then part layered, a layer of powder is poured on the bed. Each layer is defined contour on the part and then scanned by laser inner layer is hatched by laser. Scanning algorithms and hatching in the SLS is an important part of building that has an impact on properties part and a lot of research has been done about it. synthetic scan algorithms presented in this study. The purpose of this algorithm is that part warpage and... 

Gearbox is one of the important components of power transmission chain in the car which the engagement of the gears inside it causes noise. The following thesis, is in line with the project that was defined as "NVH reduction of the Tiba X200 gearbox" and to increase the correlation between university and industry, the aim of which was to improve all the noise sources in the mentioned vehicle. The purpose of this project is to reduce the noise of the gearbox shell by using reinforcing blades called ribs. For this purpose, first the desired changes were made in Solidworks software on the 3D model of the gearbox shell, and then the finite element model of the gearbox shell was prepared in... 

Existing design methods for steel frames has been improved over the last three decades in order to incorporate the behavior of semi-rigid steel connections in furtherance of frame design and since the analysis and design of structures is often done based on the assumption of completely rigid or pinned behavior,therefore, the actual behavior of connections and their modeling can help to understand the actual behavior of structures.Knowledge of the initial rotational stiffness of the connection is important for elastic analysis of structures. Investigations show that structures with semi-rigid connections have many features which are the causes to prefer these kinds of connections to the... 

In this study, the behavior of box column subjected to constant axial load with cyclic lateral force have been investigated by Finite Element method. The resulf of FE anslysis are in a good agreement with experimental result in predicting of behavior and performance of box column. In order to investigation of behavior uses of some performance indices such as axial shortening, over strength, plastic hinge length, out of plane deformation and rotation capacity. The effect of significant parameter such as axial force to yield strength ratio, flange whidth to thickness ratio of flange, web whith to thickness ratio of web, global slenderness ratio and loading protocol on performance indices have... 

The interaction of perpendicularly tunneling beneath existing metro station is investigated. In this paper E4R7 station, in line 7 of Tehran Metro (Tehran Urban and Suburban Railway co., TUSRC); Iran has been studied. This existing station has some special specifications such as a new pre-supporting system that is called Concrete Arch Pre-supporting System (CAPS). Construction of CAPS is mainly based on an Old Iranian small water tunnels excavation method, Quanat, which is faster and more economical than other common methods. CAPS is a rib like structure consisting of concrete piles and arch beams constructed around underground space before its construction. This method has been utilized in...