Sharif Digital Repository

One of the main subjects in automotive industries is to enhance the efficiency of internal combustion engines. Wear between cylinder and ring is one of the major parameters reducing the engine performance. So many parameters are affecting the wear losses. Temperature plays a key role on the severity of wear condition in internal combustion engines. In conventional cast iron cylinders, it is not possible to increase the temperature from a defined level, as it causes excessive wear in contact area between cylinder liner and piston ring. One of the major benefits of using ceramic coating is their ability to withstand in higher temperatures, while having adequate hardness to improve wear rate... 

Transfer and scattering matrix methods are widely in use for description of the propagation of waves in multilayered media. When the profile of refractive index is continuous, however, a modified formulation of transfer matrices does exist, which provides a complete analytical solution of the wave phenomena in such structures. Previously reported variations of the so-called Differential Transfer Matrix Method (DTMM) had been limited to Cartesian geometry where layered media form one-dimensional structures and plane waves are used as basis functions. In this work, we extend the formalism to cylindrical geometry with radial symmetry, in which Bessel functions need to be employed as basis... 

Three-dimensional, transient turbulent particulate flow in an FCC riser is modeled using an Eulerian/Granular approach. The turbulence in the gas phase is described by a modified realizable (kg-g) closure model and the kinetic theory of granular flow (KTGF) is employed for the particulate phase. Separate simulations are conducted for a rectangular and a cylindrical riser with similar dimensions. The model predictions are validated against experimental data of Sommerfeld et al (2002) and also compared with the previously reported LES-KTGF simulations of Hansen et al (2003) for the rectangular riser. The (kg-g)-KTGF model does not perform as well as the LES-KTGF model for the riser with a... 

The direction of arrival (DOA) error in dipole 3D arrays is estimated through Monte-Carlo simulations using the standard MUSIC algorithm. Novel 3D geometries are implemented which demonstrate better precision given the same lateral area. The mutual coupling effect is included by changing the search vector in the MUSIC DOA algorithm for the novel 3D geometries. A simple straight forward method is used which does not need complex electromagnetic computations. Simulations show that the proposed method can successfully account for the mutual coupling effects in two dimensional direction finding (both azimuth and elevation angle) with novel 3D array geometries. Reduced DOA estimation error is... 

Novel two-dimensional (2D) and three-dimensional (3D) antenna array geometries for smart antenna application are introduced. Minimum mean square error beamforming algorithm, using these arrays, in presence of signal, noise and interferences is implemented. Beamforming approach is used for every type of array assuming uniform and log-normal distributions for the interference amplitudes. Equal volume cylindrical or prism type arrays with circular, hexagonal, triangular, square and star cross-sections with equal number of elements are considered. Novel geometries consisting of rotated cross-sections are studied as well. In each case, the relative signal-to-interference ratios (SIRs) are... 

Novel two-dimensional (2D) and three-dimensional (3D) antenna array geometries for smart antenna application are introduced. Minimum mean square error beamforming algorithm, using these arrays, in presence of signal, noise and interferences is implemented. Beamforming approach is used for every type of array assuming uniform and log-normal distributions for the interference amplitudes. Equal volume cylindrical or prism type arrays with circular, hexagonal, triangular, square and star cross-sections with equal number of elements are considered. Novel geometries consisting of rotated cross-sections are studied as well. In each case, the relative signal-to-interference ratios (SIRs) are... 

The aim of this work is to investigate flow hydrodynamics in porous media. Random non-overlapping spherical particles in a cylindrical geometry were produced as a porous media. Navier-Stokes equations in three-dimensional porous packed bed have been solved and dimensionless pressure drop has been studied for a fluid flow through the porous media at different Reynolds numbers (based on pore permeability and interstitial fluid velocity). The numerical results are in good agreement with those reported by Macdonald (1979) in the range of Reynolds numbers studied. At higher Reynolds numbers turbulent models such as large eddy simulation (LES) and Reynolds stress model (RSM) also have been...