Sharif Digital Repository

Deployable structures have been used on small satellites since the beginning of such space programmes. Here, the design sequence for a special tensegrity structure, for use as supporting structure for deployable mesh-like antenna will be proposed. The design process is conducted to prevent structural elements from failure, and satisfy the minimum specified natural frequency. In this research, structural modeling is performed based on two external geometric parameters (overall height and diameter), and three internal geometric parameters (elements cross-section properties). The pre-stress in structural element is the last design parameter. Also, materials are pre-assigned. Internal forces of... 

The objective of this project is to design and control a single-stage three-phase unity power factor telecom rectifier. Following a comprehensive literature review on single-stage three-phase AC-DC converters, high-frequency isolated three-switch buck rectifier is selected. In this thesis, the analysis, design, and control of isolated buck converter is based on previously developed methods for classic three-switch buck rectifier. Three-phase isolated buck+boost rectifier is introduced by integrating a boost converter to the isolated three-phase three-switch buck rectifier and modified control structure. The proposed structure is simple and has good performance for heavily unbalanced mains... 

Nowadays, microgyroscopes are among the most important products of MEMS. The production of small, precise and inexpensive gyroscopes has become possible as the result of recent developments in fabrication technology. In this thesis it is intended to introduce a new method for manufacturing more precise microgyroscopes regarding manufacture facilities. Using this new method, sensitivity and resistance of microgyroscopes are increased against noises which are primarily caused by vibration and rotation about undesirable axes. The rotational movement imposed on the gyro is detected through fluid flow within its torus channel. This transformation facilitates the measurement of the initial motion.... 

This research concerns a study of the interaction between tunneling and adjacent structures. Analysis is performed using a full two-dimensional finite element model, which takes into consideration the presence of adjacent structure with regard to distance to tunnel and diameter of tunnel during construction of the tunnel. The soil behavior is assumed to be governed by an elastic perfectly-plastic constitutive relation based on Mohr-Coulomb criterion with a non-associated flow rule. The research is composed of two parts. However, compatibility of each method with beam and solid continuum element models in two dimensional finite element (FE) analysis was investigated. The first part describes... 

In this thesis, we consider design, modeling, and analysis of a single-phase Brushless Doubly-Fed Machine (BDFM). Generally, this type of machine is called the Brushless Doubly-Fed Induction Machine (BDFIM), that is a new class of induction machines. BDFM is a type of AC machines that requires two alternative power sources. One of the stators windings, called Power Winding, is connected to the network grid and the other one, which is called Control Winding, is connected via a converter, which is in the order of one-third of the nominal power of the machine, to the grid. Like the other types of induction machines, BDFM can also work as a generator or motor. The important criteria of this... 

In this thesis, implementing parametric resonance for the purpose of improvement in sensitivity of MEMS gyroscopes is studied. Based on a parametric study on effect of each factor on the sensor’s performance, the desired values for each parameter is determined. Stability of periodic orbits is studied using Floquet Theory. In addition, three expositions are defined and proved in order to make Floquet Theory applicable for stability analysis of origin. Based on this analysis, the relation between stabilities in the system and occurrence of parametric resonance is illustrated. Due to the complexity of dynamics of a parametrically excited MEMS gyroscope, bifurcations are observed in performance... 

thermoacuostic heat pump (THP) is One of the most important thermoacuostic applications which is used for heat lost recovery in industrial applications and civil applications.In this project, we have a quick review on thermoacuostic theory and researches in this field. Also a thermoacuostic heat pump in a lab scale will be designed and analyzed.For achieving this goal, first, mathematical equations of thermoacuostic systems are reviewed; a thermoacuostic heat pump is designed on the base of Tijani method and final model is validated by DeltaEC software. In the next step, after investigating about laboratory equipments which is used in testing process, we generate test matrix and study about... 

Design and modeling of a micromechanism for generating planar, nano-scaled locomotion is the subject of this thesis. First, we introduced the concepts and fundamental definitions used throughout the thesis. Then, based on the classification of the locomotion principles employed in microrobots, the related literature about design and fabrication of different microrobots is investigated. Inertial slip generation and contact force variation, as the preferred group, is utilized for further analysis. Since friction force is the main propelling source in the microrobot’s locomotion principle, different models proposed for this phenomenon are investigated and the Coulomb friction model is selected... 

Cascade impactors are the instruments which are used to assess the particle size distribution and the cut off diameter. Cascade impactors are wildly used for hygiene purposes, environmental, and toxicological studies. However, to find out the accurate size distribution, the cut off diameter of each stage which is different for different types of impactors with different geometry specifications should be determined. In this study first the basis of the cascade impactor operation is described. Next, different types of cascade impactors are introduced, and the Andersen Cascade Impactor (ACI) is chosen to design. The design criteria are explained and the dimension of each stage, entrance cone,... 

This paper investigates the behavior of the Y-shaped bracing system. Because of the special type of eccentricity in this system, the behavior of the frame is strongly dependent on the geometrical changes of the braces. So that even in the elastic region, it shows the geometrically nonlinear behavior. The amount of eccentricity is very effective on the nonlinear behavior of the frame. Also the ratio of cross sections of the bracing members has a very important impact on the expected performance of the frame. The results show that this system tolerates large displacements, and can act like a base isolation system. Firstly, using a two-dimensional accurate modeling related to the geometrical... 

Smoke must be exhausted, as the first action, in probable fire in subways, underground transportation systems and mines in order to survive people exposed to it. To achieving this purpose, the axial fan should be used to move the smoke to the exit lines. These fans should be had same performances in suction and discharge directions (main and reverse directions). This means flow rate should be the same at main and reverse directions. Therefore, fully reversible axial flow fans should be used in emergency ventilations. The fully reversible axial flow fans have same efficiencies in suction and discharge directions. The symmetric profiles should be used in manufacturing of the blades of these... 

Mini-Refinery is a small refinery that would need less time, effort and expenses to build in comparison with current refineries but it would have less capacity of operation. This type of refineries could create the opportunity to refine materials in place and reduce overload pressure on main refineries. In addition, private companies would be able to build them easier, due to their low cost and since the desired capacity of their equipment would be lower than current refineries, more companies would be able to fabricate and sell them. This research has two main chapters to assess the possibility of building a Mini-Refinery, to produce 30000 barrel a day of LPG, Gasoline, Kerosene, Diesel and... 

Turbojet engine combustors play a key role to convert energy with very high rates. To reach this goal, the combustor must satisfy many conflicting requirements. Complexity of the flow field inside the combustormakes the 2D or 3D analysis very difficult. In this thesis, a quasi one-dimensional software is developed applying empirical and analytical 1D relations. Using data for a mini-turbojet engine, the range of some important design parameters is extracted and then a new combustor is designed using both velocity and pressure loss methods. Different disigns are investigated and are compared by employing an extended version of the simulation software. Due to the unacceptable performance... 

Considering the advantages of optical communications and code division multiple access technique, Optical Code Division Multiple Access Networks (OCDMANs) was introduced. Thence, many researchers have suggested methods for creating Quality of Service (QoS) differentiated classes in OCDMANs. In this thesis, we have comprehensive review on the QoS assignment methods and enhance them by offering new techniques. In physical layer, we concentrate on variable chip rate OCDMANs and in MAC sub-layer, a new algorithm named Adaptive Level Control (ALC) is introduced. Then, we focus on the physical design of OCDMANs. Firstly, we solve the problem of one-class OCDMAN and introduce few simple and... 

Pyroshock Test is one of important environment tests in satellite design process.pyroshock or pyrotechnic shock is one of loads that exerted on spacecraft and it's subsystems during launch process. pyroshock can cause failure in some subsystems like sensitive electronic parts, solar cells and so on. For this reason it's necessary to make sure about strength of component under pyroshock which can be done by pyroshock simulator.The purpose of this research is to design a pyroshock simulator that can simulate a pyroshock with given SRS (Shock Response Spectrum) for satellite components.Requirements and constraints for design have been defined such as test item dimensions,weight range and also... 

This thesis discusses design and, simulation procedure of a mono-injector combustion chamber, in order to study and, analyze the ignition and, stable combustion characteristics, for Kerosene and, liquid Oxygen cryogenic propellants. Accordingly, the design and, simulation for the combustion chamber, for Kerosene and, liquid Oxygen propellants is performed. Also, effective parameters on the flame taking place are studied, and finally an algorithm for design and, properties study of cryogenic propellant ignition is presented  

One of the major concerns in the use of light flying objects is propulsion for cruise and take off from land. Creating propulsion force is important in such way that no excessive weight is introduced, especially in case of UAVs. A common trend for propulsion in light flying objects is using propellers. Propellers are commonly driven by an external motive force and due to this force and their geometry, they convert energy from this motive force into the momentum of fluid in which they are immersed as a result a lift force is generated.In the present work, trend of propeller design with optimum performance is introduced with use of vortex theory, optimum energy loss condition or Betz condition... 

Since oil is the essential foundation of Irans economy and our country has access to deep water, the extraction of oil from the deep water is essential to our country. So far, due to the possibility of oil exploration in the shallow water of the Persian Gulf, need to invest in deepwater oil industry has not been one of the priorities. However, it seems that in the near future we will need to invest in deepwater. Among subsea structures which we need to use to extract the oil in deepwater, we can mention wellhead manifolds that are used to expand the oil field, optimisation of pipeline length, gathering and distribution of production and injection of water or gas into the wells. In some cases... 

Exoskeleton is a wearable active device used to augment human power in upper or lower extremities. The integration of robotic devices and conventional physiotherapy is becoming more and more acceptable worldwide. The main scope of this thesis is to design and develop a prototype of a light, low-cost and wearable robotic exoskeleton to rehabilitate the upper extremity in stroke patients at home. For this purpose mechanism of a wearable exoskeleton will be proposed compatible with upper extremity degrees of freedoms with minimum number of actuators which is constructed inexpensively to eliminate the demand of expensive and professional therapists. The conceptual design of such a system should... 

Oil pump is a prominent part which has been described as a vehicle heart. Any malfunction or improper design may lead to engine failure. beside engine, proper design of oil route and lubrication system of vehicle, are main factor in engine design, which provide higher efficiency with lower pressure drop. lubrication system should be able to provide required pressure and flow of oil in vast range of engine rotation speed. also minimum energy waste in higher rpm is a key factor which happens due to reverse flow from output to input of pump in the relief valve. The aim of this thesis focus on design of oil pump and lubrication system of 4 cylinder 16 valve of 1600 cc inline engine. which is...