Sharif Digital Repository

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... 

In this work, a mathematical model was developed to simulate the urinary concentration mechanism. A 3-D geometry was derived based on the detail physiological pictures of rat kidney. The approximate region of each tubule was obtained from the volume distribution of structures based on Walter Pfaller's monograph and Layton's region-based model. Mass and momentum balances were applied to solve for the change in solutes concentration and osmolality. The osmolality of short and long descending nephrons at the end of the outer medulla was obtained to be 530 mOsmol/kgH2O and 802 mOsmol/kgH2O, respectively, which were in acceptable agreement with experimental data. The fluid osmolality of the short... 

Machining of ceramics often involves many challenges due to their high hardness, brittleness, and low-thermal conductivity. Laser Assisted Machining (LAM) is a promising technology for improving the machinability of hard-to-cut materials. In this work, the effect of laser heating in the LAM process on Slip Cast Fused Silica (SCFS) ceramics is investigated by conducting a numerical thermal analysis of laser effects on material behavior. A transient three-dimensional heat transfer analysis for Laser Assisted Turning (LAT) of SCFS is performed using finite-element method. Temperature distributions in SCFS cylindrical specimens are obtained. Moreover, the influence of laser parameters, such as... 

Machining of ceramics often involves many challenges due to their high hardness, brittleness, and low-thermal conductivity. Laser Assisted Machining (LAM) is a promising technology for improving the machinability of hard-to-cut materials. In this work, the effect of laser heating in the LAM process on Slip Cast Fused Silica (SCFS) ceramics is investigated by conducting a numerical thermal analysis of laser effects on material behavior. A transient three-dimensional heat transfer analysis for Laser Assisted Turning (LAT) of SCFS is performed using finite-element method. Temperature distributions in SCFS cylindrical specimens are obtained. Moreover, the influence of laser parameters, such as... 

Mechanized tunneling method using Tunnel Boring Machine (TBM) is being extensively employed in urban areas, especially when excavation takes place underneath the groundwater table. In this study, three-dimensional coupled Finite Element Analyses (FEA) have been performed to investigate the interaction mechanism between mechanized twin tunnels construction of Shiraz metro (line 2) and groundwater. Firstly, two soil constitutive models (Mohr-Coulomb and Modified Cam-Clay model) of Shiraz lean clay are validated against drained triaxial compression test data. Varying the permeability of the grout layer within the specified range, the base numerical model is then calibrated by the field data of... 

In this paper, a fully coupled three-dimensional dynamic analysis is carried out to investigate the dynamic behavior of pile foundations in liquefied ground. A critical state bounding surface plasticity model is used to model soil skeleton, while a fully coupled (u- P) formulation is employed to analyze soil displacements and pore water pressures. Furthermore, in this study, variation of permeability coefficient during liquefaction is taken into account; the permeability coefficient is related to excess pore water pressure ratio. Results of a centrifuge test on pile foundations are used to demonstrate the capability of the model for reliable analysis of piles under dynamic loading. Then, the... 

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... 

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... 

Background: Accurate tracking of the heart surface motion is a major requirement for robot assisted beating heart surgery. Method: The feasibility of a stereo infrared tracking system for measuring the free beating heart motion was investigated by experiments on a heart motion simulator, as well as model surgery on a dog. Results: Simulator experiments revealed a high tracking accuracy (81 μm root mean square error) when the capturing times were synchronized and the tracker pointed at the target from a 100 cm distance. The animal experiment revealed the applicability of the infrared tracker with passive markers in practical heart surgery conditions. Conclusion: With the current technology,... 

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... 

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...