Sharif Digital Repository

In this paper, an innovative seismic lateral force resisting system for tall buildings is introduced. In this system, a novel supplemental part, ribbed bracing system (RBSyst), is attached to Braced Tube System, creating a modified BTS. RBSyst is a supplemental part which is attached to the conventional bracing members to eliminate buckling problem. The behavior of RBSyst under tensile force is similar to that of the conventional braces. However, in compression, it prevents the braces from buckling by length reduction. In order to evaluate the efficiency of this new BTS system by performance- based assessment, two typical 40-story tall buildings with different story modules equipped with... 

Heave and pitch motion of an oscillating airfoil in uniform flow will cause generation of forwarding thrust. Applying a combination of these two motions on flexible foil, one can increase thrust and therefore the efficiency. This is the way that most fishes and other flying animals uses to consume less energy. In this paper, hydrodynamic forces and efficiency of an oscillating airfoil is investigated. A code is developed based on potential flow formulation in combination with Time Stepping Method (TSM) with nonlinear free shear layer dynamic approach to predict the wake behind the lifting bodies. A linear Morino type Kutta condition has been implemented on panels adjacent to trailing edge.... 

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... 

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  

Microfluidic cell culture platforms are ideal candidates for modeling the native tumor microenvironment because they can precisely reconstruct in vivo cellular behavior. Moreover, mathematical modeling of tumor growth can pave the way toward description and prediction of growth pattern as well as improving cancer treatment. In this study, a modified mathematical model based on concentration distribution is applied to tumor growth in both conventional static culture and dynamic microfluidic cell culture systems. Apoptosis and necrosis mechanisms are considered as the main inhibitory factors in the model, while tumor growth rate and nutrient consumption rate are modified in both quiescent and... 

In this study, a novel pseudo-three-dimensional model is developed to find out both fluid and solid temperature distributions in multi-stream plate fin heat exchangers. In this simulation algorithm, heat exchangers can be in either parallel flow or cross flow configuration. The model considerations include: heat leakage of cap plates and side plates, conduction throughout the solid matrix of the heat exchanger, variable physical properties, and inlet mass flow rate maldistribution. Using the computational code, the effects of different factors such as: the number of layers, mass flow variation, inlet mass flow rate maldistribution, and stacking pattern on the thermal performance of the heat... 

In this paper, a comprehensive three-dimensional model of photovoltaic thermal system integrated with phase change material (PVT/PCM) is developed and simulated. The effect of some key parameters using parametric analysis on performance of PVT/PCM system with water as working fluid is investigated. Parameters considered in this study include the properties of PCM (i.e. melting temperature, enthalpy of fusion and thermal conductivity), solar radiation and mass flow rate. The parametric analysis ranges are selected according to the properties of the most of available PCMs on the market, which shows the practical application of the numerical research. Furthermore, a three-dimensional model of... 

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... 

The aim of this paper is to consider the ability of endurance time (ET) method to estimate the seismic response of fixed offshore platforms at various excitation levels. In this way, various sources of nonlinear behaviour and challenging issues in the ET approach are included in the three-dimensional model of a real jacket platform utilising the finite element method. In addition to common-designed, over-designed and under-designed cases of this platform have been investigated to examine the effects of the structural characteristics on the ET response. To consider the accuracy and reliability of this approach, results of the ET method are compared with results of nonlinear time history... 

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... 

The aim of this paper is to consider the ability of endurance time (ET) method to estimate the seismic response of fixed offshore platforms at various excitation levels. In this way, various sources of nonlinear behaviour and challenging issues in the ET approach are included in the three-dimensional model of a real jacket platform utilising the finite element method. In addition to common-designed, over-designed and under-designed cases of this platform have been investigated to examine the effects of the structural characteristics on the ET response. To consider the accuracy and reliability of this approach, results of the ET method are compared with results of nonlinear time history... 

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... 

Background and Objective: Blood flow variation during cardiac cycle is the main mechanism of atherosclerotic development which is dependent on. Methods: The present work mainly tends to investigate stenosis effect in dynamic curvature of coronary artery. This paper presents numerical investigations on wall shear stress profiles in three-dimensional pulsatile flow through curved stenotic coronary arteries for both static and dynamic model. In order to do so, three-dimensional models related to the curved arteries with two degrees of stenosis (30% and 50%). Results: Lower amount of wall shear stress is found near the inner wall of artery distal to the plaque region (stenosis) and in both... 

Horizontal ground heat exchangers (GHEs) have a lower cost in comparison to vertical ones; however, they require more land area. For the sake of reducing the required land area for horizontal GHEs, flat-panel GHEs have been recently introduced. In this piece of research, a 3-D numerical model has been developed to predict the thermal performance of flat-panel GHEs. In this study, at first, the thermal performance of a flat-panel GHE has been compared with that of linear horizontal ones. The results demonstrate that the flat-panel GHE has a better thermal performance of about 27% in comparison to an arrangement of linear GHEs with a value of 0.5 m for pipe spacing. In the second part of this... 

A three-dimensional model has been developed to describe the multiphase release of macromolecular drugs encapsulated in a hydrogel. The heterogeneity of network mesh size was considered by assigning varying diffusion coefficients to the network lattices randomly. Using a stochastic approach, the random nature of diffusion of drug molecules was captured within the network. The simplest form of distribution containing two diffusion coefficients was tested. To generate the drug release profiles for experimental validation under the limitation of computational cost, a simple scaling relationship was employed. Unlike the single-diffusivity model, the dual-diffusivity model showed good agreement... 

In the study, the daily and monthly performance of a photovoltaic thermal system integrated with phase change material is investigated in Shanghai, China. A three-dimensional model of photovoltaic thermal system integrated with phase change material system is developed and numerically simulated. Water is considered as working fluid, and the fluid flow regime is laminar and incompressible. Both quasi-steady and transient models are compared together, and the transient model is selected because of its higher accuracy. Validation analysis is performed on the numerical model to show the reasonable agreement of current research compared to some other research. After obtaining the suitable...