Sharif Digital Repository

Ni-Ti shape memory alloys have attracted most of the research in the field of shape memory alloys both because of their complicated and diverse phase transformation characteristics and their optimum properties for various applications which span such a properties as shape memory effect, pseudoelasticity, excellent mechanical properties and biocompatibility. The key properties of these alloys is generated through a thermoelastic martensitic transformation the occurrence of which is extremely sensitive to the metallurgical conditions of the alloy e.g. composition and microstructure. This has led to the development of various procedures implemented in either fabrication, processing or heat... 

The current study is dedicated to free vibration and buckling analysis of thick FGM conical shells conveying hot flows with the consideration of initial geometric imperfections. To this end, the higher order governing equations of motion and the corresponding boundary conditions are derived using Hamiltonian formulations. Due to the solution procedure of Frobenius series expansion, the differential form of equations is obtained by applying by part integration to the integral form of equations of motion. Radial and longitudinal temperature distributions are considered while pressure distribution and geometric imperfection variations are found to be in longitudinal direction, only. The final... 

In the current study, nonlinear vibration and stability of conical shells with both separate and concurrent internal and external flows are studied. External and internal flows are in the supersonic and subsonic regimes, respectively. The Krumhar’s aerodynamic piston theory is utilized to model the external loading on the structure as well as the compressible potential flow model to capture the internal fluid dynamics. The so-called compressible fluid model is obtained via simplification of the Navier-Stockes equations after applying the inviscid and irrotational assumptions. The nonlinear structural equations of motion are derived using the Hamiltonian dynamics approach and utilizing the... 

One of the most important parameters of a smartphone is the ability to operate in a long time with a rechargeable battery. As a result, the design of radio frequency circuits which are used in these cell phones is a consistent challenge for designers. Bluetooth Low-Energy standard (BLE) which is the fourth edition of Bluetooth standard is recently introduced with the aim of transporting low volume data with minimum power consumption. The most important challenge of the design of an RF receiver in the BLE standard is the power consumption. In a typical receiver, the oscillator and the mixer are the most power hungry blocks. Therefore, decreasing the power consumption of these two blocks is... 

Vacuum assisted resin transfer molding (VARTM) is one of the most efficient and low cost process in composite industries. In this process, the preform is covered by a flexible vacuum bag and resin flows into the mold with applying vacuum pressure at the vent. The main objective in VARTM process is preventing voids and dry spots formation in final composite part because these defects may significantly deteriorate the mechanical properties of a structure. Flow front is an important parameter in this process which have a high influence on the void formation. Resin flow control is required to prevent dry spots or micro voids during the VARTM process. In general, the flow control is classified... 

Fire is one the events which threatens the very existence of every building, residential, office, industrial or else. However, this threat is more serious with regard to buildings with steel structures. Steel, despite its many advantages over other structural materials, such as having high strength to weight ratio, ductility, toughness and resilience, has the disadvantage of rapidly losing its strength at elevated temperatures, i.e. in fire. Therefore, it is the responsibility of the designer to make the serious decision of whether to use steel, concrete, timber, or other materials for the structure of the building to be designed. Observations made during full-scale fire tests as well as... 

The objective of this project is to study the behaviour and performance of an innotative floating offshore platform. Such Platform not only can be used for exploring oil from offshore fields, but for creating artificial islands, where land is in short supply. Due to its specific and, at the same time, simple geometry (symmetric), its fabrication does ont involve much complexity. Studies carried out on this platform include the investigation into its structural behaviour under gravitational (including self weight) and bouyancy forces. Studied cases include a number of platforms with different (geometrical) sizes and under 3 various bouyancy conditions (percentage), namely 1) 50% of the height... 

The city of Tehran is dealing with air pollution problems for years. Providing a solution for this problem requires information about different pollutants emission sources. In this subjects, emission factors and emission models are essential tools for decision makers. Among different mobile emission sources in Tehran, motorcycles are of high importance. In this project, for the first time in Iran, exhaust gas pollutants emission of 66 motorcycles with different ages and engine displacement volumes were measured according to Euro-3 standard certification procedure. Measurement results showed that none of the tested motorcycles passed the Euro-3 certification limit on CO emission. Calculations... 

Homogeneous Charge Compression Ignition (HCCI) engines are the new generation of internal combustion engines which have diesel-like thermal efficiency, while they have low nitrogen oxide and soot emission. One of the major problems of HCCI engines is combustion timing control due to its dependence on reactivity of the charge and chemical kinetics. Moreover, limiting operation range between knock and misfiring is the other drawback of using these kind of engines. In the present work, partially homogeneous HCCI combustion in a single cylinder diesel engine is modeled using Computational Fluid Dynamics (CFD) coupled with chemical kinetics. Simulation includes the engine cycle from exhaust valve...