Sharif Digital Repository

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.... 

Embryogenesis, regeneration and cell differentiation in microbiological entities are influenced by mechanical forces. Therefore, development of mechanical properties of these materials is important. Neural network technique is a useful method which can be used to obtain cell deformation by the means of force-geometric deformation data or vice versa. Prior to insertion in the needle injection process, deformation and geometry of cell under external point-load is a key element to understand the interaction between cell and needle. In this paper the goal is the prediction of cell membrane deformation under a certain force, and to visually estimate the force of indentation on the membrane from... 

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... 

In this paper, the continuum damage mechanics model originally proposed by Lemaitre (Journal of Engineering Materials and Technology. 1985; 107: 83-89) is presented through an adaptive finite element method for three-dimensional ductile materials. The macro-crack initiation-propagation criterion is used based on the distribution of damage variable in the continuum damage model. The microcrack closure effect is incorporated to simulate the damage evolution more realistic. The Zienkiewicz-Zhu posteriori error estimator is employed in conjunction with a weighted Superconvergence Patch Recovery (SPR) technique at each patch to improve the accuracy of error estimation and data transfer process.... 

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... 

In poorly developed fractured rocks, the contribution of individual fracture on rock conductivity should be considered. However, due to the lack of data, a deterministic approach cannot be used. The conventional way to model discrete fractures is to use a Poisson process, with prescribed distribution, for fracture size and orientation. Recently, a stochastic approach, based on the idea that the elastic energy due to fractures follows a Boltzmann distribution, has been used to generate realizations of correlated fractures in two dimensions. The elastic energy function has been derived by applying the appropriate physical laws in an elastic medium. The resulting energy function has been used... 

In this study, the main objective is to develop a one dimensional model to predict design and off design performance of an operational axial flow compressor by considering the whole gas turbine assembly. The design and off-design performance of a single stage axial compressor are predicted through 1D and 3D modeling. In one dimensional model the mass, momentum and energy conservation equations and ideal gas equation of state are solved in mean line at three axial stations including rotor inlet, rotor outlet and stator outlet. The total to total efficiency and pressure ratio are forecasted using the compressor geometry, inlet stagnation temperature and stagnation pressure, the mass flow rate... 

We investigate the effect of particle shape on the transportation mechanism in well-drilling using a three-dimensional model that couples computational fluid dynamics (CFD) with the discrete element method (DEM). This numerical method allows us to incorporate the fluid-particle interactions (drag force, contact force, Saffman lift force, Magnus lift force, buoyancy force) using momentum exchange and the non-Newtonian behavior of the fluid. The interactions of particle-particle, particle-wall, and particle-drill pipe are taken into account with the Hertz-Mindlin model. We compare the transport of spheres with non-spherical particles (non-smooth sphere, disc, and cubic) constructed via the... 

The effectiveness of secondary recovery methods in reservoir development studies depends on the knowledge about how fluid-carrying regions (i.e. good-quality rock types) are connected between injection and production wells. To estimate reservoir performance uncertainty, comprehensive simulations on many reservoir model realisations are necessary, which is very CPU consuming and time demanding. Alternatively, we can use much simpler and physically based methods such as percolation approach. Classic percolation assumes connectivity between opposite 2-D faces of a 3-D system; whereas, hydrocarbon production is achieved through active wells that are one-dimensional lines (e.g. vertical,... 

In this work, hybrid of silica nanoparticles (NPs) with sulfonated copolymer has been prepared in order to improve the copolymer properties for Enhanced Oil Recovery (EOR). Some tests are done to find the effectiveness of injecting fluid on Recovery Factor (RF), such as Contact Angle (CA), interfacial tension (IFT), inherent viscosity, and eventually Micro-Model (MM) flooding. In CA test, wettability alteration from Oil-Wet (OW) to Water-Wet (WW) is reached by sedimentation and adsorption of NPs on the rock slice. In addition, IFT reduction is obtained by increasing the NaCl concentration. The viscosity change is investigated for the hybrid and copolymer under simulated high-temperature oil... 

This paper studies through numerical simulation a practical compound restrainer to use for the improvement of seismic performance of bridges. A mechanical model has been introduced for the restrainer and a basic optimisation approach has been conducted to evaluate the performance of the restrainer to changes in the properties of its components. A real 2-span simply supported plate girder bridge has been selected for case study. Using a detailed three-dimensional model, several non-linear time history analyses were performed under seismic excitations in order to assess the performance of the bridge retrofitted by conventional restrainers including linear and non-linear viscous dampers on one... 

In this study, a new method for the simulation of the time-dependent behavior of actin cytoskeleton during cell shape change is proposed. For this purpose, a three-dimensional model of endothelial cell consisting of cell membrane, nucleus membrane, and main components of cytoskeleton, namely actin filaments, microtubules, and intermediate filaments is utilized. Actin binding proteins, which play a key role in regulating actin cytoskeleton behavior, are also simulated by using a novel technique. The actin cytoskeleton in this model is more dynamic and adoptable during cell deformation in comparison to previous models. The proposed model is subjected to compressive force between parallel micro... 

Physicians use charts that are prepared by experiments on animals or humans to prescribe drug dosage for patients. This method requires some precious amount of time by the Ministry of Health to approve new drugs to be used in healthcare centers. Three-dimensional modeling of the inner medulla by considering the known physiological features help us to predict the distribution of a drug or any minerals in the kidney. In this study we present modeling of the important species distribution including Na+ and urea in the rat inner medulla that influence the urine concentrating mechanism. We use a C++ code to develop the inner medulla geometry based on physiological data to better capture the... 

This paper presents a three-dimensional phenomenological constitutive model for magnetic shape memory alloys (MSMAs), developed within the framework of irreversible continuum thermodynamics. To this end, a proper set of internal variables is introduced to reflect the microstructural consequences on the material macroscopic behavior. Moreover, a stress-dependent thermodynamic force threshold for variant reorientation is introduced which improves the model accuracy. Preassumed kinetic equations for magnetic domain volume fractions, decoupled equations for magnetization unit vectors and appropriate presentation of the limit function for martensite variant reorientation lead to a simple... 

In the present work, a micro combustor for thermophotovoltaic (TPV) devices is proposed which is included a U-shaped microtube in a box with a secondary fluid in space between U-shaped microtube and box walls. By utilizing the three-dimensional CFD model, combustion characteristics of the premixed lean hydrogen-air mixture in the present micro combustor are studied numerically with detailed chemistry and transport taking into account heat transfer through the wall. The results show that the establishment of secondary flows and better preheating in the curved tubes is caused the flammability limits to be at least four times in comparison with straight tubes. Combustion characteristics are... 

Stress sensitivity is a phenomenon that affects reservoir rock properties, such as permeability and therefore changes the well pressure transient behavior. This paper aims to study these behaviors in stress sensitive reservoirs and evaluate the pressure loss in such reservoirs during the process of hydrocarbon production. A power model is used to correlate the changes in permeability with pore pressure. A novel semi-implicit three-dimensional finite element method has been employed to numerically solve the flow problem. The numerical results have been validated by analytical results obtained in a non-sensitive reservoir. Pressure drawdown test for different scenarios has been studied. The... 

In this article, we propose a three-dimensional model of a low-Reynolds-number swimmer that consists of three small spheres connected to a larger sphere via three perpendicular adjustable rods which enable the micro robot to swim along arbitrary trajectories. Then we focus on dynamic modelling of the swimmer and propose a control method to control the position of the micro swimmer in a low Reynolds number flow. The control aim intended in this article is that the middle sphere to follow a desired trajectory and respective simulation results from control indicates successful accomplishment in application. © 2018 IEEE  

This paper studies through numerical simulation a practical compound restrainer to use for the improvement of seismic performance of bridges. A mechanical model has been introduced for the restrainer and a basic optimisation approach has been conducted to evaluate the performance of the restrainer to changes in the properties of its components. A real 2-span simply supported plate girder bridge has been selected for case study. Using a detailed three-dimensional model, several non-linear time history analyses were performed under seismic excitations in order to assess the performance of the bridge retrofitted by conventional restrainers including linear and non-linear viscous dampers on one...