Sharif Digital Repository

The phenomena of surface, interface, and size effects are the determinative factors in the prediction of the mechanical behavior of multiphase nanowires. The interatomic bond lengths and charge density distribution associated with the surface and interface layers of the relaxed configuration of such nanostructures, in the absence of any external loadings, differ from those of the bulk remarkably. Second strain gradient theory due to its competency in capturing the above mentioned effects will be employed to examine the relaxation of carbon-coated silicon nanowire, carbon nanoshell, and silicon nanowire. Using this theory their effective Young's modulus will also be estimated. To this end,... 

We extend a hybrid finite-volume-element (FVE) method to treat the laminar reacting flow in cylindrical coordinates considering the collocation of all chosen primitive variables. To approximate the advection fluxes at the cell faces, we use the upwind-biased physical influence scheme PIS and derive a few new extended expressions applicable in the cylindrical frame. These expressions are derived for both the Navier-Stokes and reactive flow governing equations, of which the latter expressions are considered novel in the finite-volume formulation. To validate our derived expressions, the current results are compared with the experimental data and other available numerical solutions. The results... 

The main purpose of this work is investigation of coolability of a boiling debris bed. The main governing equations are derived using volume averaging technique. From this technique some specific interfacial areas between phases are appeared and proper relations for modeling these areas are proposed. Using these specific areas, a modification for the Tung/Dhir model in the annular flow regime is proposed. The proposed modification is validated and the agreements with experimental data are good. Finally, governing equations and relations are implemented in the THERMOUS program to model two-phase flow in the debris bed in the axisymmetric cylindrical coordinate. Two typical configurations... 

The stress distribution on open-ended Carbon Nanotubes (CNTs) embedded in a composite material is considered in this work and an analytical solution for the stress distribution has been obtained. The effects of CNT's thickness and CNT's length on the distribution of stress have been investigated. To find the governing relations, continuity equations of the axisymmetric problem in cylindrical coordinate (r,o,z) are used. Under some assumptions, the governing equations are solved and by using constitutive equations and applying the boundary conditions, an equation which relates the stress applied to the representative volume element with the stress distribution on the CNT, has been found. The... 

Metal-oxide gas sensors are widely used for detection of detrimental H2S gas. Among them, SnO2-CuO system has been proved to be an excellent candidate. The previous theoretical 2D thin bilayer model was able to explain some aspects of H2S sensing performance of this promising system. However, experimental researches have indicated that response values for this system are very diverse and various SnO2-CuO multicomponent heterostructures such as rods, wires and particles have much higher response than their thin bilayer counterparts. Understanding the reason behind this differences would help fabrication of optimized sensor element. However, the previous model cannot address this issue mainly... 

In this work, the conservation forms of the reacting ow governing equations are treated mainly using a cell-centered finite-volume approach with a collocated storage of all trans- port variables. However, the finite volume formulations are suitably incorporated with the finite element expressions. As an innovation, a physical influence upwinding scheme is suitably extended to the cylindrical coordinate system to approximate the convective terms of the governing conservation laws at the cell faces. This treatment firstly respects the physics of flow and secondly provides the necessary coupling of velocity and pressure fields in this frame. The numerical solution of laminar, buoyant difiusion... 

The present investigation is devoted to the fully developed slip flow mixed convection in vertical microducts of two different cross sections, namely, polygon, with circle as a limiting case, and rectangle. The two axially constant heat flux boundary conditions of H1 and H2 are considered in the analysis. The velocity and temperature discontinuities at the boundary are incorporated into the solutions using the first-order slip boundary conditions. The method considered is mainly analytical in which the governing equations in cylindrical coordinates along with the symmetry conditions and finiteness of the flow parameter at the origin are exactly satisfied. The first-order slip boundary... 

In this paper, strain gradient thermo-elasticity formulation for axisymmetric Functionally Graded (FG) thick-walled cylinders is presented. For this purpose, the elastic strain energy density function is considered to be a function of gradient of strain tensor in addition to the strain tensor. The material properties are assumed to vary according to a power law in radial direction. Using the constitutive equations and equation of equilibrium in the cylindrical coordinates, a fourth order non-homogenous governing equation for thermo-elastic analysis of thick-walled FG cylinders subjected to thermal and mechanical loadings is obtained and solved numerically. Results show that the intrinsic... 

This is a theoretical study that extends a classical method of treating the convection heat transfer in complex geometries to gaseous slip flow forced convection in microchannels with H1 thermal boundary condition. Through this line, the momentum and energy equations in cylindrical coordinates are made dimensionless. Afterward, solutions are presented that exactly satisfy the dimensionless differential equations along with the symmetry condition and finiteness of the flow parameter at the origin. The first-order slip boundary conditions are then applied to the solution utilizing the least squares matching method. Though the method is general enough to be applied to almost any arbitrary cross... 

Ultrasonic waves have been extensively used in many industrial applications including clean devices, pipes and vessels. A clear extension of this usage is the removal of wellbore contaminants by exposing it to high-power ultrasonic waves. In this paper, a mathematical model for ultrasonic propagation through the porous medium around the wellbore is presented. The equations of wave propagation are written in a cylindrical coordinate according to Biot theory and the induced stress in the rock are calculated at each point using finite difference approach Comparison of imposed local stresses with adhesion forces between scales and rock, the properties of ultrasonic transducer, such as frequency... 

Investigation of response of reinforced concrete (RC) structures due to axisymmetric macrocell corrosion of rebars is of concern after propagation of microcracks within the concrete medium. The geometry, boundary and interfaces conditions of the present problem are identical to those stated in part I. As seen in the companion paper, the exact solution to the boundary value problem corresponding to the uncracked steel-rust-concrete composite was possible. After appearance of the microcracks the concrete behavior becomes nonlinear anisotropic with post-cracking softening, and the associated problem is analytically intractable. Therefore, it is proposed to employ a novel meshless method, namely... 

In this work, we derive a few new advective flux approximation expressions, apply them in a hybrid finite-volume-element (FVE) formulation, and solve the turbulent reacting flow governing equations in the cylindrical frame. To derive these advective-kinetic-based expressions, we benefit from the advantages of a physical influence scheme (PIS) basically, extend it to the cylindrical frame suitably, and approximate the required advective flux terms at the cell faces more accurately. The present numerical scheme not only respects the physics of flow correctly but also resolves the pressure–velocity coupling problem automatically. We also suggest a bi-implicit algorithm to solve the set of... 

In this paper, strain gradient thermo-elasticity formulation for Functionally Graded (FG) thick-walled cylinders is presented. Elastic strain energy density function is considered to be a function of gradient of strain tensor in addition to the strain tensor. The material properties are assumed to vary according to power law in radial direction. Using the constitutive equations and equation of equilibrium in the cylindrical coordinates, fourth order non-homogenous governing equation for thermo-elastic analysis of thick-walled FG cylinders subjected to thermal and mechanical loadings is obtained and solved numerically. Results show that the intrinsic length parameter affects the stress... 

In this work, an efficient bi-implicit strategy is suitably developed within the context of a hybrid finite volume element method to solve axisymmetric turbulent reactive flow in a model gas turbine combustor. Based on the essence of a control-volume-based finite-element method, the formulation benefits from the geometrical flexibility of the finite element methods while the discrete algebraic governing equations are derived through applying the conservation laws to discrete cells distributed in the solution domain. To enhance the efficiency of method, we extend the physical influence upwinding scheme to cylindrical coordinates. This extension helps to improve the advection flux... 

A numerical model is developed to simulate the borehole heat exchanger both in the short and long time. In this regard, the computational domain is divided into the inside and outside borehole regions. A two-dimensional finite volume method is implemented in a cylindrical coordinate system for modeling of the outside borehole. Also, a thermal resistance-capacity model is presented for the borehole cross section. This model is extended to take into account the fluid transport through the U-tube and the temperature variation of the borehole components with depth. The governing equations of the two regions are solved iteratively in each time step. The proposed model is verified with the... 

The unsteady flow of blood through stenosed artery, driven by an oscillatory pressure gradient, is studied. An appropriate shape of the time-dependent stenoses which are overlapped in the realm of the formation of arterial narrowing is constructed mathematically. A msathematical model is developed by treating blood as a non-Newtonian fluid characterized by the Oldroyd-B and Cross models. A numerical scheme has been used to solve the unsteady nonlinear Navier-stokes equations in cylindrical coordinate system governing flow, assuming axial symmetry under laminar flow condition so that the problem effectively becomes two-dimensional. Finite difference technique was used to investigate the... 

Generally, in most areas, groundwater level is deep and heat sources (e.g., energy piles)are embedded in unsaturated soil media. Therefore, in order to accurately analyze the soil response close to heat sources, both heat and moisture transport in unsaturated soil domain should be considered. Thermal loading changes the moisture content in the porous media. In this study, the energy conservation and mass fluid continuity equations derived from hydrothermal analysis of a partially saturated soil medium are considered in cylindrical coordinate system. To make the analytical solution possible, partial differential equations (PDEs)are turned into ordinary differential equations (ODEs), through...