Sharif Digital Repository

In this work, the spectral difference lattice Boltzmann method (SDLBM) is extended and applied for accurately computing two-dimensional viscous compressible flows on structured meshes. Here, the compressible form of the discrete Boltzmann-BGK equation with the Watari model is considered and the numerical solution of the resulting LB equation is obtained by using the spectral difference method. The main benefit of the use of the LB method in simulating compressible flows is that a same formulation can be applied to compute the inviscid and viscous portions of the flowfield. Note that the LB formulation for simulating the viscous flows is the same as that used for the inviscid ones, however,... 

In compression resin transfer molding (CRTM), resin injection and mold closing occur during the mold filling stage. In this paper, numerical simulation of threedimensional flow in compression resin transfer molding (CRTM) is presented. Numerical method is based on the control volume/finite element method (CVFEM) and the numerical algorithm to update the flow front at each time step is based on quasi-steady state approach. Numerical scheme presented in this article can be used to predict the flow progression, pressure distribution, mold clamping force in full threedimensional mold. Numerical example provided in the paper demonstrates the effectiveness of the developed numerical simulation in... 

In this paper some advantage of online monitoring in power transformer and the sensors that can be used for partial discharge detection are described. Several detected PD in one power transformer and one distribution transformer are depicted. Matlabs wavelet package is employed to de-noise the recorded signals. As it appear from the captured and the denoised signals, PD signals in an aged power transformer are often enough large that can be easily detected through the noisy measured signals. By examination of the frequency spectrum of several PD signal in this paper it is obvious that this signal contain two major frequency band, one under 1 MHz and the other one between 7 to 9 MHz. © 2008... 

To locate accurately the occurrence of a partial discharge in a power transformer winding, a wide frequency band model of the winding is required. In this paper a wide frequency band Multi Conductor Transmission Line model (MTL) is employed to simulate the propagation of PD signal in transformer windings. The MTL model is briefly reviewed and the related equations of the model are reformulated to easily simulate occurrence of a PD signal along the winding. Software is developed in Matlab to calculate the windings resonance frequencies and the magnitudes of over-voltages occurring between different disks along the winding. Then propagation of PD signal in a power transformer (900MVA, 525kV),... 

We carry out molecular dynamics simulations of nanoindentation to investigate the effect of cementite size and temperature on the deformation behavior of nanocomposite pearlite composed of alternating ferrite and cementite layers. We find that, instead of the coherent transmission, dislocation propagates by forming a widespread plastic deformation in cementite layer. We also show that increasing temperature enhances the distribution of plastic strain in the ferrite layer, which reduces the stress acting on the cementite layer. Hence, thickening cementite layer or increasing temperature reduces the likelihood of dislocation propagation through the cementite layer. Our finding sheds a light on... 

Molecular dynamics simulations combined with quantitative atomic displacement analyses were performed to study the deformation behaviors of polycrystalline cementite (Fe3C). At low temperature and large grain size, dislocation glide acts as the preferred deformation mechanism. Due to the limited number of slip systems at low temperature, polycrystalline cementite breaks by forming voids at grain boundaries upon tensile loading. When the temperature rises or the grain size reduces, grain boundary sliding becomes the primary mechanism and plastic deformation is accommodated effectively  

There have been significant developments in the design and application of algorithms for both one-dimensional signal processing and multidimensional signal processing, namely image and video processing, with the recent focus changing from a step-by-step procedure of designing the algorithm first and following up with in-depth analysis and performance improvement to instead applying heuristic-based methods to solve signal-processing problems. In this book the contributing authors demonstrate both general-purpose algorithms and those aimed at solving specialized application problems, with a special emphasis on heuristic iterative optimization methods employing modern evolutionary and swarm... 

A low gel content poly (styrene-ran-butadiene)/poly (methyl methacrylate) (SBR/PMMA) core/shell particles dispersed in a good solvent for the shell was wet spun into a coagulation bath at room temperature. The SEM micrographs of as spun fibers showed various surface topographies and fiber diameters, ranging from 4.2 up to 20 μm depend upon the draw ratio. The osmium tetroxide stained cross-section of fibers observed by transmission electron microscope (TEM), indicated a heterogeneous morphology consisting of dark cores and fairly light shells, which is a result of self-stratification to an overall core/shell morphology in fiber cross-section. The inner core consisted of higher concentration...