Sharif Digital Repository

Torque variations caused by intermittent combustion and inertia effects of reciprocating components, exert significant torsional excitation on crankshaft of internal combustion engines. These excitation induces considerable torsional vibration on crankshafts. Therefore, modeling and analysis of crankshaft torsional vibration and absorber systems, especially in automobiles engine that crankshaft tolerate high amplitude excitations coupled with heavy inertia effects has high importance. In this study, ability of centrifugal pendulum vibration absorber and dual mass flywheel which used in rotating machinery for vibration reduction, will be examined. At first, cranktrain will be torsionaly... 

In the aftermath of mass-casualty events, main resources may be overwhelmed by the sudden jump in demand. To ration these resources with considering the patients priority for help, mean triage. For prioritizing the patient for help, the limitation of resources should be considered. These resources can be different. This thesis at the first step investigates how the priority assignment can be done in a clearing system and what the potential benefits would be when there are same resources in the system. At the next step, the difference between resources is considered. So in this thesis, the problem of priority assignment of patients in an emergency system is modeled and analyzed at first with... 

Because of importance of knowing angular velocity in a lot of engineering problems, Rate gyroscopes is widely used in different engineering fields. Among all kinds of gyroscopes, proof mems MEMS gyroscopes are mostly used because of their low cost and light weight. Improvement of the accuracy of the MEMS gyroscopes and their based inertial navigation systems is intended in this thesis considering some undesirable conditions on the gyro and trying to solve the gyro’s equations in that conditions. Existing linear or angular acceleration on the structure that the gyro is installed on is one of these undesirable conditions; Quadrature error in the gyroscope is the other one. In this thesis, the... 

During all operations in oil and gas reservoirs, it is possible to cause formation damage. These damages can greatly reduce the rate of production. One of the major damages that can seriously affect the performance of a reservoir is the damage caused by drilling fluid. The main purpose of this thesis is to study the main mechanisms of formation damage caused by water-based drilling fluid using a glass micromodel for the first time. An accurate understanding of the mechanisms of formation damage can provide a good understanding of the selection of the type and concentration of materials used, as well as appropriate methods to control and eliminate damages. for controlling the drilling fluid... 

Motion strategies result from the management of priorities by the central nervous system in response to complex interactions with the peripheral nervous system, the musculoskeletal system, and the surrounding environment. The use of physics-based predictive neuro-mechanical simulations can play an important role in discovering and studying these complexities. With the development of detailed musculoskeletal models and neural models that include the control principles of the higher layers of the nervous system, it is possible to synthesize natural human movements, such as rising from a squat, without the need for experimental data and in novel conditions and environments. This can contribute... 

In this article, research has been carried out on the control technique of autonomous mobile robots to navigate in unknown environments, avoiding static and moving obstacles using eight ultrasonic sensors for obstacle recognition.
In this article we used simple three wheeled robots. Each robot has a passive caster wheel and two active fixed wheels which can act independently. In addition robots have holonomic constraints like maximum acceleration, maximum speed and maximum angular velocity, so robot’s speed and orientation change independently and these changes are small in each time step. Each robot has eight ultrasonic sensors, each of them cover 22.5 degree of space from robot‘s... 

In this thesis, a new location-pricing model considering inventory costs has been developed. We should locate a certain number of distribution centers over the market area as a network and also determine the price and inventory of product in each distribution center for reach the maximum profit. A mathematical model was developed to maximize the earned profit. A hybrid algorithm is developed as a solution method including a tabu search algorithm for determining distribution centers location and an exact solution for determining pricing and inventory in each distribution center. Algorithm performance is compared against GAMS optimization solver and exact method.

 

Permanent magnets play an essential role in the structure of the electric motor, but due to limited resources, many efforts have been made to meet the need for them. One of the most important types of non-permanent electric motors is reluctance motors. Despite their antiquity in design, torque ripples have led to the limited use of reluctance motors, but advances in science have made it possible to control these ripples.As a result of the major advantages such as low manufacturing costs, high efficiency, and uncomplicated structure, these motors have been the subject of many researches. One way to eliminate the problem of torque ripples is to increase the number of teeth, but in the common... 

Most elderly and physically disabled people suffer from lack of functionality and dexterity in their elbow or wrist. These disabilities are due to the damages mostly caused by sport surgery, spinal surgery, or stroke. Therefore, design of an assistive exoskeleton robot for upper limb movements seems necessary. The purpose of this study is to design, fabricate and deliver a control algorithm for an assistive wearable robot. The robot has three degrees of freedom in order to help the flexion/extension of elbow and wrist. Dynamic and kinematic model of elbow, forearm, and wrist is developed to determine the amounts of torques which are required in the joint actuators mounted on the robot.... 

The test suite effectiveness concerns the ability of test suites to reveal faults. Mutation testing is a de facto standard to assess the test suite effectiveness. However, mutation testing is a time-consuming process. Over the years, researchers have proposed two kinds of approaches. The first category is related to code coverage criteria and assess the total test suite effectiveness. The second is known as Predictive Mutation Testing (PMT). The suggested approach is probabilistic, being in different levels of abstraction (macro and micro). First, in the macro level, there is a code coverage criterion that not only does outperform existing code coverage but also does not have a statistically... 

Oil composition plays an undeniable role on the low salinity water flooding (LSWF) efficiency. This property directly affects the kinetics of wettability alteration through electrostatic interactions and interfacial tension (IFT). For instance, mixing in stagnant zones through a thin water film is considered as one of the most important diffusion controlled phenomenon which is goverened by Non-Fickian solute transport model. The major two potentials controlling the solute transport in thin film are salinity gradient and electrostatic potentials, which can be affected by oil composition and surface charges. This study aims to investigate the effect of oil composition on low salinity... 

Considering the water tensions, especially in the Middle East, water resources for the implementation of water-based EOR methods are shown to be critically limited. Water sources such as industrial wastewater hold great potential to be used for this purpose due to their significant available volume and the need for their disposal because of environmental regulations. In this research, the potential of injecting industrial wastewater, as low-salinity water, in an Iranian carbonated oil reservoir has been thoroughly investigated by conducting core-scale experiments. In this regard, we also developed a guideline for designing various types of experiments to use this "unconventional" injection... 

It is the main idea of present thesis to provide a micromechanical method as a general treatment for several fundamental problems of the piezoelectric inhomogeneities. For initial demonstration of pertinent methodology, a single piezoelectric inhomogeneity of ellipsoidal geometry, under non-uniform far-field loading is considered. Accordingly, it is taken equivalent to elastic and dielectric inclusion problems connected by proper eigenstrain-electric field. This approach is named the electro-mechanical equivalent inclusion method (EMEIM) and requires that the electroelastic fields of the inhomogeneity to be equal to fields of the equivalent inclusions. Afterwards, the complex problem of... 

Morphing concepts can potentially improve the performance and fuel consumption of modern aircrafts. Smart materials can reduce the weight and complexity, and also are of the best choices to improve efficiency and reliability for realizing morphing wings. Developing of a simple model and optimization of smart piezocomposite actuators position of a thin wing with variable camber is considered. The goal is to gain desired properties in incompressible subsonic regime. Lifting surfaces of a composite wing are simplified using shell model. Keeping the problem simple, a piezocomposite patch is used to change the shell curvature. Basic modes are extracted from FEM software and behavior of bimorph... 

The heart is a vital part of the body whose primary function is to pump blood throughout the body. The world's leading cause of deaths is due to heart problems. Today, most countries invest heavily in solving these problems and preventing the resulting deaths. One solution for patients with advanced heart disease is to use ventricular assist devices. This device is Used in parallel to the patient's heart, completely or partially replaces the normal functioning of the heart and provides much of the blood needed by the body. The purpose of this study is to design, manufacture and parametrically optimize a ventricular assist pump and its driver system. Since blood is clotted in contact with... 

Aerodynamics loads and aeroheating during reentry, are one of the challenging issues in designing One of the main challenges in the design and application of reusable spacecrafts is the aerodynamic and thermal loads acting on their structures during reentry into the atmosphere. For this reason, all the concepts/prototypes presented in the 20th century were either not fully reusable, or were partially canceled, or did not have economic justification. In this report, the aerodynamic loads on the first stage of a launch vehicle during the launch and return phases have been investigated. Due to the fact that the main part of the first stage of the vehicle includes fuel and oxidizer tanks, the... 

Improving efficiency of heat exchangers has always been an important concern for the industry. Pulsating Heat Pipes (PHPs) are novel and efficient technology in the field of heat transfer. PHPs are widely used in solar water heaters, solar desalination systems, etc. In this research, thermal performance of Open Loop Pulsating Heat Pipes (OLPHPs) using three different ferrofluids (ferrofluid without surfactant and nanoparticles’ coating, ferrofluid with coating of nanoparticles, and ferrofluid with surfactant) is experimentally investigated. In addition, effects of charging ratio (20, 40, 60, and 80%), heating power (20, 30, 40, 50, 60, 70, 80, 100, 120, 140, 160, 180, 200, 240, 280, 320,... 

The collision of moderately large asteroids and comets also referred to as Near-Earth Objects (NEO's) with earth would have catastrophic consequences. Such events have occurred in the past and may occur again in the future. However, for the first time in known history, humanity may have the technology required to counter this threat. Methods studied for mitigation of this hazard are based on deflecting asteroid's trajectory and are normally divided into two basic categories: high energy impulsive methods, and long-duration low-thrust methods. Two parts of mission to be optimized are the trajectory of spacecraft to reach the target and the deflection strategy which could be analyzed by the...