Sharif Digital Repository

Meshless methods are a relatively new type of numerical methods that have attracted the attention of many researchers over the past years. So far, a number of meshless methods have been developed and applied to solve problems in various fields of engineering, including solid mechanics and geotechnical problems. The Element-Free Galerkin (EFG) method is adopted in this study for solving the governing partial differential equations of equilibrium and continuity of pore fluid flow for numerical simulation of coupled hydro-mechanical problems. For this purpose, the weak form of the governing equations is derived by applying the weighted residual method and Galerkin technique. The penalty method... 

In this work, the thermomechanical responses during the dissimilar friction stir welding of aluminum alloys have been evaluated employing a three-dimensional model and the finite element software ABAQUS. Furthermore, welding experiments have been conducted under different working conditions and the temperature variations during and after welding as well as the produced residual stresses in various positions of the welded samples were measured using hole-drilling technique. The model results were then examined by experimental data, and a reasonable agreement was observed. It is found that tool rotational speed significantly affects the amount of maximum tensile residual stress while traverse... 

The connectivity of high conductivity pathways in geological formations depend on the spatial distribution of geological heterogeneities that may appear on various length scales. Appropriate modeling of this is crucial within in hydrology and petroleum systems. The approach taken in this study is to use percolation theory to quantify the connectivity, hydraulic conductivity, and breakthrough time behavior between an injector and a producer within such systems. In particular, a three-dimensional overlapping sandbody model is considered which assumes that the geological formation can be split into either conductive flow units (i. e., good sands) or non-conductive units (i. e., poor sands). The... 

Hemodynamic factors, such as Wall Shear Stress (WSS), play a substantial role in arterial diseases. In the larger arteries, such as the carotid artery, interaction between the vessel wall and blood flow affects the distribution of hemodynamic factors. In the present study, both rigid-wall and deformable-wall models are developed in a 3D numerical simulation to assess the effectiveness of arterial rigidity on worsening hemodynamics, especially WSS. Two different rheological models (Newtonian and CarreauYasuda) have been employed to evaluate the influence of blood, non-Newtonian properties, as well. The importance of vessel wall deformability was compared with the rheological model of blood.... 

A new design for a valveless micropumping device has been proposed that integrates two existing pumping technologies, namely, the wall induced traveling wave and the obstacle-type valveless micropump. The liquid in the microchannel is transported by generating a traveling wave on the channel, while the placing of two asymmetric trapezoid obstacles, along the centerline of the channel inlet and outlet, leads to a significant (up to seven times) increase of the net flow rate of the device. The effectiveness of this innovative design has been proved through a verified three-dimensional finite element model. FluidStructure Interaction (FSI) analysis is performed in the framework of an Arbitrary... 

Fluid flow behavior in a porous medium is a function of the geometry and topology of its pore space. The construction of a three dimensional pore space model of a porous medium is therefore an important first step in characterizing the medium and predicting its flow properties. A stochastic technique for reconstruction of the 3D pore structure of unstructured random porous media from a 2D thin section training image is presented. The proposed technique relies on successive 2D multiple point statistics simulations coupled to a multi-scale conditioning data extraction procedure. The Single Normal Equation Simulation Algorithm (SNESIM), originally developed as a tool for reproduction of... 

A new exponential model to depict the moment-rotation (M-θ) relationship of Bolted Endplate Connections (BEC) is proposed. The proposed model represents an approach to the prediction of M-O curves, taking into account the possible failure modes and the deformation characteristics of the connection elements. The presented model has three physical parameters, along with two curve-fitted factors. These physical parameters are generated from dimensional details of the connection, as well as the material properties. By employing simplified connection behavioral models to estimate the connection M-θ behavior, analytical expressions for evaluating major connection parameters, such as initial... 

Peripheral milling is extensively used in manufacturing processes, especially in aerospace industry where end mills are used for milling of wing parts and engine components. Knowledge of the cutting forces is the first necessary stage in analysis of the milling process. In this paper, cutting forces are presented for both two and three dimensional models. Instead of the common linear dependency of cutting forces to the cut chip thickness, two nonlinear models are presented. In the first model, cutting forces are considered as a function of chip thickness with a complete third order polynomial. In the second one, the quadratic and constant terms of the third order polynomial are set to zero.... 

Stay and guide vanes (distributor) are essential parts of a turbine. They are used to control the flow rate and to appropriately transfer the flow momentum to the runner. In this work, flow through the distributor is analyzed. For various Boundary Conditions (BC) and different configurations, threedimensional flows in the distributor of a Francis turbine are evaluated and compared with each other. The numerical simulations were carried out using Fluent software and the results were validated with a GAMM Francis turbine, where the geometry and detailed best efficiency measurements were publically available. In these simulations, the flow was assumed to be steady and the effect of turbulence... 

The purpose of this paper is to model the detailed effects of interactions that take place between components of un-bonded flexible risers, and to study the three-dimensional motion responses of risers when subjected to axial loads, bending moments, and internal and external pressures. A constitutive law for un-bonded flexible risers is proposed and a procedure for the identification of the related input parameters is developed using a multi-scale approach. A generalized finite element structural model based on the Euler-Bernoulli beam theory is developed in which the constitutive law is embedded. The beam theory is enhanced by the addition of suitable pressure terms to the generalized... 

Domed roofs have been used in Iran and many other countries to cover large buildings such as mosques, shrines, churches, schools, etc. However their favorable thermal performance made them to be employed in other buildings such as bazaars, or market places, in Iran. The aim of this study was to determine the air pressure distribution over domed roofs, employing a numerical method. In this investigation, a three-dimensional model and a laminar inlet air flow were considered. The k-ε RNG method was employed for the turbulent flow simulation method. Simulation was run under three conditions of windows and a hole on top of the dome being open, or closed. The results were compared with the... 

In this study, the fluid dynamics and convective heat transfer for turbulent flows through a 3-sub channel of a rod bundle, which is representative of those used in VVER-1000, are examined. The rod bundle is constructed from parallel rods in a hexagonal array. The rods are on constant pitch by spacer grids spaced axially along the rod bundle. The geometry details of the bundle and heat flux from the fuel rod are similar to that of the Iranian nuclear reactor under construction. A numerical study using Computational Fluid Dynamics (CFD) was carried out to estimate the flow field, pressure loss and heat transfer coefficients in spacer grids and rod bundles. Turbulence has been modeled using... 

A numerical simulation algorithm based on the finite volume discretisation is presented for analyzing ship motions. The algorithm employs a fractional step method to deal with the coupling between the pressure and velocity fields. The free surface capturing is fulfilled by using a volume of fluid method in which the interface between the liquid (water) and gas (air) phases are computed by solving a scalar transport equation for the volume fraction of the liquid phase. The computed velocity field is employed to evaluate the acting forces and moments on the vessel. Using the strategy of boundary-fitted body-attached mesh and calculating all six degrees-of-freedom of motion in each time step,... 

Urmia Lake, located in a closed basin in north-west Iran, is the largest lake (5000-6000 km2) in the Middle East. It is very saline with total dissolved salts reaching 200 g/l compared with a normal seawater salinity of about 35 g/l. The construction of a causeway, which was initiated in 1979 but then abandoned until the early 2000s, is near completion and will provide road access between the western and eastern provinces. The causeway has an opening 1.25 km long and divides Urmia Lake into a northern and southern basin and restricts water exchange. The flow and salinity regimes are affected by the presence of this new causeway, and there are concerns over the well being of the Artemia... 

The seismic behaviour of a 4-story building is investigated under horizontal excitation of simulated earthquakes. The model has been constructed with a 3D sandwich panel system without any conventional frame system in four storeys on a shaking table. The building has been modelled before construction. Due to the table limit, the scale factor of the model is chosen as 1: 2.35 of a prototype. The shaking table test of the scaled model of the building is carried out under several ground motions to verify the safety of the system. The simulated motions were applied to the model in two-perpendicular directions, simultaneously. The failure mechanism and dynamic behaviour of the model, as a... 

An unstructured grid, finite-volume, and three-dimensional (3D) primitive equation ocean model has been developed to predict oceanic pollutant dispersions in depth and surface of the Caspian Sea for non-chemical reactions of dissolved constituents. The model consists of momentum, continuity, temperature, salinity, and density equations. Physical and mathematical closure has been achieved using Mellor and Yamada turbulent closure sub-models. Since determining a practical definition of salinity that enjoys acceptable accuracy is difficult; therefore, various definitions have been used in this work. A recent definition of salinity stated in the UNESCO Practical Salinity Scale of 1978, PSS78,... 

Dense underflows are continuous currents that move downslope due to their density being heavier than that of the ambient water. In this work, a steady density current with a uniform velocity and concentration from a narrow sluice gate enters into a wide channel of lighter ambient fluid and moves forward downslope. Experiments varying inlet velocity and concentration and hence inlet Richardson numbers were conducted. Numerical simulations were also performed with a low-Reynolds number k-ε model. The results of numerical simulation agree well with the experimental data. © 2009 ASCE  

In this paper, a three-dimensional steady state incompressible turbulent air flow is considered in a large single room. The buoyancy affected turbulent air flow is numerically simulated by solving governing equations. The turbulence modeling includes both κ - ε and zero-equation models and their results are compared to the experimental data. The paper reviews several aspects, such as displacement of radiator system performance, temperature and flow field distribution and comfort conditions. The results show that the best temperature distribution and comfort condition are obtained when the radiator is installed under the window and its height is equal to or greater than that of the window. ©... 

In this paper, the data transfer operators are developed in three-dimensional elasto-plasticity using the Superconvergent Patch Recovery (SPR) method. The transfer operators are defined for mapping of the state and internal variables between different meshes. The internal variables are transferred from Gauss points of old mesh to the nodal points. The variables are then transferred from the nodal points of old mesh to the nodal points of new mesh. Finally, the values are computed at the Gauss points of new mesh using their values at the nodal points. Aspects of the transfer operators are presented in a three-dimensional superconvergent path recovery technique, based on C0, C1 and C2... 

In this paper the development of a quasi-three-dimensional numerical model that can be used for quantifying groundwater inputs and associated contaminant discharged from coastal aquifers into the coastal zone at a regional scale is presented. The present model is called MODSharp. In order to handle problems at a regional scale, the sharp interface approach which is used for conceptualising seawater intrusion, is applied to this model. This model can be used for the simulation of groundwater flow and contaminant transport in layered coastal aquifers at a regional scale. The method of characteristics is used to solve the advection-dispersion equation, which governs contaminant transport in...