Sharif Digital Repository

The goal of the present study is to simulate the compressible rarefied gas flow by using a high-order finite-difference lattice Boltzmann method. Here, a weighted essentially non-oscillatory lattice Boltzmann method (WENO-LBM) is applied for the solution of the compressible form of the LB equation with the Kataoka-Tsutahara model. The solution procedure is based on the discretization of the convection terms of the LB equation using the fifth-order finite-difference WENO scheme and the temporal term using the third-order explicit total variation diminishing Runge-Kutta scheme for both the continuum and rarefied gas flows. The treatment of implementing the no-slip and slip boundary conditions... 

In this work, a high-order nodal discontinuous Galerkin method (NDGM) is applied and assessed for the simulation of the non-cavitating/cavitating flows. At first, the basic formulation of the NDGM is explained and the properties of the solution method of the NDGM are studied by solving the one-dimensional wave equation. Then, the one-fluid approach with the thermal effects is used to properly model the cavitation phenomenon. Here, the spatial and temporal derivatives in the system of governing equations are discretized using the NDGM and the third-order TVD Runge–Kutta method, respectively. Various numerical fluxes such as the Roe, Rusanov, HLL, HLLC and AUSM+-up and two discontinuity... 

The goal of this study is to investigate the effect of events such as earthquakes on businesses. Earthquakes can have a significant impact on the performance and profitability of businesses. Earthquakes can negatively affect the functionality of community infrastructure systems by damaging their components and this disruption in the functionality of the lifelines of the community can negatively affect the businesses that are dependent on their functionality. In addition, earthquakes will cause casualties and injuries, leading to a decrease in the workforce and the customers’ population. In such a situation, the activity of many businesses is disrupted and even stopped, which in turn has many... 

In this study, the Shokov-BGK model of the Boltzmann equation is reformulated and generalized to consider the real gas effects. At first, the formulation is performed to consider an arbitrary specific heats ratio and the correct Prandtl number for polyatomic gases. Here, the resulting equations of the present formulation are numerically solved by applying the high-order finite-difference weighted essentially non-oscillatory (WENO) scheme. The present solution method is tested by computing the one-dimension Reiman problem with different specific heats ratios for a wide range of the Knudsen numbers. The results are compared with the available gas-kinetic results which show good agreement. It... 

In this study, first nano structure powders of Fe3AL / Al2o3 by different percentages of reinforcement phases (10, 20 and 50 percent of volume) based on mechanical milling procedure was created. To do so, iron, Al and iron oxide (hematite) pure powder based on special weight percentages mixed with each other and milled in 20 to 100 hour periods based on two different weights of ball toward powder: 10 and 20. Morphological variations, particles sizes and powder densities, lattice strain and phase variations in different timing periods of mechanical milling process was studied by Scanning Electron Microscopy(SEM) , analyzing apparatus of particles sizes by laser , gaseous picnometer and X-ray... 

WC-Co hardmetals that are produced through powder metallurgy rout are vastely used as wear resistant parts. In these materials hard particles of wolfram carbide are embodied in a cobalt binder. Because of their high hardness and adequate toughness, hardmetals have found wide range of applications in cutting tool industry. During the last decades a number of researches have been carried out to improve their mechanical and wear properties by different binders and carbide particle sizes. Because of high hardness, Tungsten carbide has a good wear resistant. It has very low thermal expansion coefficient and high wetting ability with molten metals. Unlike high hardness, it has limited toughness.... 

In this study, the numerical simulation of natural and ventilated cavitating flows is performed. The algorithm employs the homogenous, multiphase Navier-Stokes equations with appropriate mass transfer terms.The base line differential equations system is comprised of the mixture volume, mixture momentum and constituent volume fraction equations. A three species differential formulation is considered for constituent volume fraction transport/generation of liquid, condensable vapor and non-condensable gas fields.The system of governing equations is discretized using a cell-centered finite volume Roe’s upwind scheme. Both laminar and turbulent cavitating flows are considered in this study. For... 

In this study, Cu-TiC nanocomposites were produced by high energy ball milling of elemental powders and in situ formation of TiC in the copper base. Cu and 5,10,20 and 40 wt% Ti powder blend were milled for 60 h, then graphite powders were added and milling was continued for 10 h again and Finally Cu-TiC composite powders with 10.68, 20.16, 36.24 and 60.25 vol% of reinforcements (6.18, 12.2, 23.82 and 45.47 wt%) were produced. The effect of time on the solution of titanium in the copper was studied by X-Ray diffraction analysis (XRD). crystallite size and lattice strain of copper were determined 12nm and 1.04% subsequently for Cu-40wt%TiC after 60 h milling. to ensure the formation of... 

In this study, the solution of compressible flows is performed using finite volume lattice Boltzmann method (FVLBM). A model associated with 13 discrete velocity vectors and 2 energy levels is used and the Boltzmann transport equation is solved using a cell-centered finite volume on structured meshes. The values of distribution functions on each cell faceare determined by averaging from their values at the two control points located on the center of two neighboring cells. The fourth-order Runge-Kutta time-stepping scheme is applied to discretize temporal derivative term. The second- and fourth-order numerical dissipation termsareadded to the algorithm to stabilize the solution when solving... 

Nickel aluminides are intermetalics with complex structures that have high metlting points. However, brittlement at room temperature and low high_temperature strength (above 700 ̊C) can be mentioned as their short comings. Nowadays, many efforts have been proceeded to produce theirs composites, so that one can benefit from ceramics and intermettalics properties simultaneously. In this project, the main was aim to produce NiAl matrix nanocomposite reinforced with Alumina Al2O3. The composite is processed using milling and mechanical alloying. This is a good way to produce intermetallics and their composites with high melting points without any need to supply high temperature during... 

In applications such as high duty sliding contacts and other electrical components requiring good electrical- and thermal-conductivity, proper mechanical wear resistance in combination with arc erosion resistance are required.The Cu/TiB2 nano-composite seems to be a good candidate for such cases. At present work TiB2 nano-particles has been selected as reinforcement, due to its valuable properties, i.e., high melting point (2850 - 2900 °C), low linear CTE (8.10 µmm-1 °C-1), thermal conductivity (60.0 - 120 W/m-K) as well as low specific electrical resistivity (10 - 30 μΩ.cm) and high hardness (25-35 GPa HV). Additionally, there are limited articles which have focused on evaluation of... 

In this study, the ultrafine-nanometric yttria stabilized zirconia (YSZ) particles were used for reinforcing of copper metal powder. To producing of bulk nanocomposite specimens, the copper powder and the proper volume percent of reinforcement powders (i.e. 2, 3 and 5) were mixed using Turbula mixer for one hour. Before the mixing of two metallic powders and ceramic nanoparticles, for separation of agglomerated zirconium oxide nanoparticles that witch leads to producing of nanocomposite specimens with satisfactorily distributed secondary phase, the ultrasonic devise with enough quantity of ethanol as neutral liquid have been used for 15 minutes. The powders mixture have been placed under... 

In the present work, the deformation and collapse of a single cavitating bubble near solid boundaries is simulated by solving the preconditioned, homogenous, multiphaseNavier-Stokes equations. Up to now, all studies in the literature performed by the volume of fluid (VOF)approach to capture the bubble surface have been based on the pressure-based category in which the flow variables are calculated through solving the Poisson equation. Here, the density-based category is applied and the solution methodology is based on the artificial compressibility approach. The compressible form of the Navier-Stokes equations is applied inside the bubble and the liquid phase is assumed to be incompressible.... 

Project cost overrun is one of the most frequently occurring issues in the construction industry. Past research studies have investigated the project cost overrun problem from various perspectives. However, to date, only a few studies have focused on the identification of the root causes of projects cost overruns. A close review of these studies reveals that the studies often provide limited insight into the root causes of project cost overrun. These studies fail to consider the impact of project delivery system as a defining project characteristic that may influence construction cost overruns. In addition, past studies have relied on surveys that are not necessarily precise and highly... 

In this study, to synthesize molybdenum disilicide nano powder, mixed powder of Mo and Si were ball milled for 15, 30, 45 and 55 hours. By the results of the analyses, milled powders for time intervals of 55 hours were heat treated to release the stresses. This process was carried out in an argon vacuum tube furnace at 1000˚C for 1 hour. XRD analysis was carried for sample. Finally, MoSi2 powder with 86.62 nm crystallite size was used as reinforcement. Cu-MoSi2 composite powder with 2, 3, 5wt% were produced. Cu-MoSi2 with 2wt% reinforcement was milled for 60 hours. Powder composite was compacted by Spark Plasma Sintering . Microstructure of composite was investigated by scanning electron... 

In the present study, the computation of the viscous compressible flow over two-dimensional geometries is performed by using the immersed boundary method and applying a second-order finite volume scheme. For the solution of the governing equations, a uniform Cartesian grid that is not coincident with the body surface is used and the boundary conditions on the wall are satisfied by the ghost-cell immersed boundary method. The spatial discretization of the fluid equations is carried out using the second-order central difference finite volume scheme and the time integration is performed by applying the fourth-order Runge-Kutta method. To stabilize the solution algorithm and reduce unwanted... 

In earthquake-prone communities, the post-earthquake functionality of hospitals is crucial. Hospitals can dramatically reduce earthquake casualties if they can remain functional and retain service continuity. A variety of earthquake-induced problems such as damage to hospital components, unavailability of medical staff, disruption in medicine supply, and failure of supporting infrastructure systems can negatively affect the functionality of a hospital. Hospital administrators and facility managers require appropriate tools to assess the effect of these problems on hospital functionality. This research presents a probabilistic framework to assess the functionality of hospitals following... 

FIDIC as a proposed model for a contract and including patterns of regular international contract projects. In Iran, many giant construction projects such as petroleum projects, power plants, roads and water networks was signed based on FIDIC contract pattern and These projects have been faced with many challenges .The main challenges for this contract are not ready. Improper translation of the original, traditional look owners to contractors, FIDIC modern approach depends on the project parties (owner - Consulting - contractors), Iran's judicial laws, lack of private land ownership and the absence of allocated budget that indicates the appropriate use of this model contracts in Iran. To... 

Production of copper-zirconium amorphous alloys by mechanical alloying and the process of changing crystal structure to amorphous, was examined. The amount of progress of amorphization has been checked by x-ray analysis after different hours of milling. By increasing the percentage of zirconium in this type of alloy, the process of amorphization has been improved. But There is a limiting factor which is due to the tendency of zirconium to produce oxide and nitride phase. Also, the effect of excessive elements on crystal structure changing has been checked. Hence, adding elements like nickel or aluminum has a different effect on the process of amorphization. adding aluminum to the system...