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۱Hydrodynamics of three–dimensional density currents
نویسنده(ها):
اطلاعات انتشار: کنفرانس بین‌المللی هیدرولیک سدها و سازه‌های رودخانه‌ای، سال
تعداد صفحات: ۶
Density current is a dense fluid, which is continuously released from a source of rectangular cross section and spreads down a sloping surface inside a lighter, motionless fluid. A CFD code has been developed to describe salt solution density current, which propagates threedimensionally in deep ambient water. The equations of continuity, momentum conservation, and diffusion are solved simultaneously in the fixed Cartesian directions, on a non–staggered grid using finite volume scheme.The velocity–pressure coupling is handled by SIMPLEC model. Comparison of the computed width of the density currents at the different bed slopes and inlet buoyancy fluxes, with the experimental data, shows a good agreement between them. The center–plate velocity profiles are compared with experiment. Results showthe three–dimensional dense layer approaches a normal state shortly after release and the flow behaves as two–dimensional. At low bed slope, lateral propagation increases with concentration and decreases the 3–D length.This solving provides a physical understanding of such complex phenomena.<\div>

۲The Propagation of Turbulent Density Currents on Sloping Beds
نویسنده(ها):
اطلاعات انتشار: Scientia Iranica، هشتم،شماره۲، تابستان ، سال
تعداد صفحات: ۸

۳Hydrodynamics of Two–Dimensional Laminar Turbid Density Currents
نویسنده(ها):
اطلاعات انتشار: Scientia Iranica، دهم،شماره۱، بهار ، سال
تعداد صفحات: ۱۳

۴Numerical Simulation of Free–Surface Waves and Wave Induced Separation
نویسنده(ها):
اطلاعات انتشار: Scientia Iranica، پانزدهم،شماره۳، ۲۰۰۸، سال
تعداد صفحات: ۹
The present study is concerned with the numerical simulation of free–surface waves and wave induced separation in the presence of an intrusion. The results of several simulations are reported. The rst study was performed for a NACA0024 surface piercing hydrofoil over a range of several Froude numbers (0.19, 0.37, 0.55), along with wave breaking at Fr = 1.0 The NACA0024 foil was of particular interest, as it almost has no separation at large depths; thus the e ect of the freesurface wave and the wave induced separation could be studied. Free– surface waves and wave induced separation results were evaluated and compared with both the available experimental data and the previous numerical results. The wave breaking ow was also successfully simulated and results were presented. The second series of simulations were carried out for a circular cylinder in order to investigate the shape e ects on the wave–induced separation. Results suggest that, at high Froude numbers, the free–surface waves are a function of Froude and not the shape of a body. Flow features with regard to separation, free–surface elevations and drag coecients were also studied.

۵Characteristic Variables and Entrainment in 3–D Density Currents
نویسنده(ها):
اطلاعات انتشار: Scientia Iranica، پانزدهم،شماره۵، ۲۰۰۸، سال
تعداد صفحات: ۹
A CFD code has been developed to describe the salt solution density current, which propagates three–dimensionally in deep ambient water. The height and width of the dense layer are two dominated length scales in a 3–D structure of the density current. In experimental e orts, it is common to measure the height and width of this current via its brightness. Although there are analytical relations to calculate the current height in a two–dimensional ow, these relations cannot be used to identify the width and height of a 3–D density current, due to the existence of two unknown parameters. In the present model, the height and width of the dense layer are obtained by using the boundary layer concept. Also, a comparison is made between depth averaged and characteristic variables. Then, the computed velocity and concentration pro les are compared with the experimental data and the results show good agreement between them. In this work, the entrainment coecient was also calculated using depth–averaged parameters and compared with the experimental data. The result has the same trend as the Ellison and Turner experiments. Present results show that the boundary layer concept can be useful in identifying the height and width of a 3–D density current.

۶Investigation of Valve–Closing Law on the Maximum Head Rise of a Hydropower Plant
نویسنده(ها):
اطلاعات انتشار: Scientia Iranica، شانزدهم،شماره۳، ۲۰۰۹، سال
تعداد صفحات: ۷
Piping systems commonly experience the transient–state situation as the result of changes to ow conditions during pump failures, valve closures or turbine load rejection. This paper addresses transients as a consequence of the load rejection of a Francis hydropower plant (Karun 4, Ahwaz, Iran). To control the turbine system and related equipment during load rejection, the valve closing law of wicket gates is of paramount importance. The pressure rise at the end of the pressure shaft, the pressure drop in the draft tube and the speed rise while the electromagnetic braking torque disappears are solely dependent on the closing curve. Thus, an optimum closing law can eliminate the probable risk of damage to the units. This paper develops a computational model to calculate water–hammer system components, such as pressure rise, speed rise, discharge variations and pressure uctuations. Results obtained from the present model are compared and validated with those obtained by a consultant at the Karun project. The e ects of di erent valve–closing laws on the maximum head rise at the end of the pressure shaft and other components are also investigated. Keywords: Method of characteristics; Hydropower plant; Transient ow; Valve–closing law; Karun 4 hydropower plant.

۷Experimental Investigation of Baffle E ect on the Flow in a Rectangular Primary Sedimentation Tank
نویسنده(ها): ،
اطلاعات انتشار: Scientia Iranica، هفدهم،شماره۴، ۲۰۱۰، سال
تعداد صفحات: ۱۲
In primary sedimentation tanks, short–circuiting enlargement of dead zones and high ow mixing problems are caused by circulation regions (dead zones), which can reduce the optimal sedimentation of particles. For proper design of such tanks, the formation of recirculation zones should be avoided. The provision of a bae as a geometrical modi cation of a tank may in uence the ow eld for better sedimentation. Thus, in this study, velocity measurements were performed by a three–dimensional Acoustic Doppler Velocimeter (ADV) to investigate bae e ects on the velocity distribution in a primary rectangular sedimentation tank, quantitatively. E ects of bae positioning were also determined. Mean ow analysis shows how a bae can alter the hydrodynamics of the ow eld. It was quantitatively found that the intermediate bae not only in uences the ow eld in its downstream, but also a ects the ow pattern in its upstream. It was found that the bae setting and its position relative to the inlet and outlet in uences the ow eld and the development of ow. Baed ow may provide better conditions for sedimentation by in uencing velocity pro les. However, further detailed experimental study is necessary to fully capture the bae e ect and obtain further insight into the complex ow eld in a sedimentation tank.

۸Experimental investigation of effects of baffle configurations on the performance of a secondary sedimentation tank
نویسنده(ها): ، ،
اطلاعات انتشار: Scientia Iranica، هجدهم،شماره۴، ۲۰۱۱، سال
تعداد صفحات: ۱۲
Sedimentation tanks are designed for the settling of floated solids in water. These tanks are one of the most important parts of water treatment plants and their performance directly affects the functionality of these plants. One challenging method for increasing the performance of sedimentation tanks is to use baffles. A useful baffle should be installed in a suitable place with a proper height. In this work, an experimental study of particle–laden flow in a rectangular sedimentation tank has been performed and kaolin is used as solid particles. The effects of baffle configurations on the velocity and concentration profiles along the tank were studied. Sedimentation tank performance was directly investigated by measurement of the mean concentration along the tank. In order to determine the best baffle configuration, two positions of single and double–baffle arrangements with various heights were investigated. Results show that the best baffle position and proper baffle height relates to the inlet concentration. In any case, the middle baffle, with suitable height, is efficient and increases sedimentation tank performance.

۹A numerical study of the effects of blood rheology and vessel deformability on the hemodynamics of carotid bifurcation
نویسنده(ها): ، ،
اطلاعات انتشار: Scientia Iranica، نوزدهم،شماره۱، ۲۰۱۲، سال
تعداد صفحات: ۸
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 Carreau–Yasuda) 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. Although the deformability changes hemodynamic factors under the steady state boundary condition, or at the last two phases of the cardiac cycle (when the blood flow in carotid looks like a steady condition), WSS distribution is mostly affected by the blood rheological model. In other words, the influence of shear–thinning behavior at the end–diastolic phase of the cardiac cycle is undeniable unlike the deferability. However, the effects of deformability, like the rheology of blood on WSS could not be neglected at the first two phases of the cardiac cycle when pressure reaches its highest values.

۱۰On the motion of Newtonian and non–Newtonian liquid drops
نویسنده(ها): ، ، ،
اطلاعات انتشار: Scientia Iranica، نوزدهم،شماره۵، ۲۰۱۲، سال
تعداد صفحات: ۱۴
In the present study, the motion of Newtonian and non–Newtonian liquid drops has been investigated experimentally. In order to investigate the effect of bulk fluid on drops, we have used water and air, as two fluids with different properties, and various industrial and biological applications. Image processing is utilized to analyze the images obtained by a high speed camera. The research has been separated into two parts. The first part has been devoted to the experiments in which air is the bulk fluid, and the second is related to the experiment carried out in water. The range of Reynolds number is, approximately, . The major concern of the present study is the size variation of drops and its effect on the drag coefficient. It is proved that the period of size variation of a drop does not vary with properties. Rheological aspects of the problem have also been considered. In air with small density and viscosity, addition of non–Newtonian characteristics to the fluid causes the behavior of the drop to undergo dramatic changes. However, in water, a denser and more viscous bulk fluid, the behavior of Newtonian and non–Newtonian drops (at least for shear thinning fluids) looks the same.

۱۱Na+ permeation through its protein channels, from molecular dynamics to continuum modeling
نویسنده(ها): ، ،
اطلاعات انتشار: Scientia Iranica، بيست و دوم،شماره۲، ۲۰۱۵، سال
تعداد صفحات: ۸
Researchers can reach important information about cell cycles such as migration, growth and muscle contraction, by studying the change of ion concentrations in animal cells. In the current work we have proposed three di erent techniques to study the passive ions motion in protein channels on di erent time scales. Molecular dynamics, Langevin dynamics and continuum models of mass transport are used to investigate ion transport from small to large time scales.

۱۲E effcts of hypertension on Intima–Media Thickness (IMT); application to a human carotid artery
اطلاعات انتشار: Scientia Iranica، بيست و سوم،شماره۴، ۲۰۱۶، سال
تعداد صفحات: ۱۰
A vast number of deaths in the world have been attributed to atherosclerosis. The prominent aim of this study is proposing an accurate and simple model to investigate the process of arterial wall thickening. In order to investigate LDL (Low Density Lipoprotein) accumulation in arterial wall, a four layer model for arterial wall consisting of endothelium, intima, IEL, and media is presented. All layers are treated as homogenous porous media. This model has been solved both numerically and analytically. Obtained accumulated LDL in the intima is used to calculate oxidized LDL flux. Also, the presented model and clinical data are used to prepare the growth model for arterial wall. Furthermore, the e ect of hypertension on ltration velocity and rate of wall thickening has been studied which is in consistent with experimental data. Results show that the average rates of intima thickening of hypertensive patients with 120 mmHg and 160 mmHg transmural pressure are 5.87 m\year and 6.12 m\year, respectively. This rate for healthy subjects with 70 mmHg transmural pressure has been calculated 4.5 m\year. Finally, this model is applied to a carotid artery, and the maximum intimal growth rate for people with 70 mmHg, 120 mmHg and 160 mmHg transmural pressure is calculated 4.68 m\year, 6.28 m\year, and 6.67 m\year, respectively.
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