Sharif Digital Repository

The impact of a method on the turbulence reduction in wind tunnels was evaluated. In this method, by installation of trip strip in the contraction, the unsteady behaviors of flow have controlled, consequently the turbulence intensity and possibility of separations were decreased. Location and diameter of trips were very important in this method. Various sizes of trip strip were installed at different locations in the contraction section of four different wind tunnels to study the most significant aspects of the method. Hot wire anemometry system, 1-D and 2-D probes, were used for turbulence measurement and a new method for direct calibration of a 2-D hot-wire probe was introduced. The new... 

Tool Condition Monitoring (TCM) is a vital demand of advanced manufacturing in order to develop automated unmanned production. Tool condition has an essential influence on machined surface quality and dimension of manufactured parts. Continuing machining operation with a worn or damaged tool will result in damages to workpiece and even the machine tool itself. This problem becomes more important in supplementary machining processes like drilling in which the workpiece is usually at the final stages of production and any damage to workpiece at this stage is irreparable and results in high production losses. In this thesis, sound and vibrations signals are analyzed for drill wear detection.... 

Carbon Nanotube webs exhibit interesting properties when used as thermo-acoustic projectors. This work studies thermo-acoustic phenomena of these sound sources both in near and far field regions. Our three-dimensional simulation and experimental data show pressure waves are highly affected by dimensions of sound sources in near field due to interference effects. Although pressure amplitude increases with increasing frequencies, maximum pressure amplitude reached in lower frequencies may become larger than its maximum amount at higher frequencies because of interference effects. Measurement of different surface area sources shows generation of sound waves in far field is independent of... 

Carbon nanotubes have special thermodynamic properties which makes suitable as a thermo-acoustic sound source. Recently it is shown that by using these nanotubes it is possible to generate strog sound waves in air or water. Experimental analysis of phenomenon can be complicated and expensive. Hence this fact, in this study using molecular dynamic simulation, numerical analysis of sound generation with CNTs in air and water is discussed. For this purpose, the required structue of the system is generated and it has reaced equilibrium. This process has been done for 6 different CNT and for each CNT there are 5 different distances between them. Althogether, 30 different cases has is used for... 

The aim of this project is analysis of fuselage vibration reduction on turboprop aircraft, by using passive methods. In this method by design and installation of tuned vibrant absorber (a system composed of mass and auxiliary spring) which its natural frequency is tuned, taking into account the excitation frequency of the vibrant fuselage body under harmonic force. And the motion of the point which is connected to it, would be ceased. Considering the place limitations and weight in the aircraft design, the designed absorber with respect to space and occupied volume shall be mountable on the aircraft frames and for maximum reduction of skin vibrations and eventually damping of acoustic energy...