Sharif Digital Repository

Flows generated by density differences are called gravity or density currents which are generic features of many environmental flows. These currents are classified as the conservative and non-conservative flows whether the buoyancy flux is conserved or changed respectively. In this paper, a low Reynolds k-ε turbulence model is used to simulate three dimensional density and turbidity currents. Also, a series of experiments were conducted in a straight channel to study the characteristics of the non-conservative density current. In experiments, Kaolin was used as the suspended material. Comparisons are made between conservative and non-conservative's height, concentration and velocity profiles... 

The use of classical Bossiness approximation is a straightforward strategy to take into account the buoyancy effect in incompressible solvers. This strategy is highly effective if the density variation is low. However, ignoring the importance of density variation in high thermo buoyant flows can cause considerable deviation in predicting the correct fluid flow behavior and heat transfer phenomenon. Indeed, there are many technological and environmental problems where the Bossiness approximation is not valid. In this study, an incompressible algorithm is suitably extended in order to solve compressible flow problems with natural-convection heat transfer. In this regard, the density field is... 

The main objective of the current work is to utilize Lattice Boltzmann Method (LBM) for simulating buoyancy-driven flow considering the hybrid thermal lattice Boltzmann equation (HTLBE). After deriving the required formulations, they are validated against a wide range of Rayleigh numbers in buoyancy-driven square cavity problem. The performance of the method is investigated on parallel machines using Message Passing Interface (MPI) library and implementing domain decomposition technique to solve problems with large order of computations. The achieved results show that the code is highly efficient to solve large scale problems with excellent speedup. Copyright © 2004 by ASME  

This paper presents the effects of a non-uniform magnetic field on the hydrodynamic and thermal behavior of ferrofluid flow in a wavy channel by 3D numerical simulation. The wavy surfaces at the top and bottom of the channel are heated by constant heat fluxes. Moreover, the sidewalls are adiabatic. In the wavy section, in the perpendicular direction of the main flow, the magnetic field that linearly varies along the direction of the main flow is applied. The mathematical model that is consistent with the principles of ferrohydrodynamics and magnetohydrodynamics is used for the problem formulation. The results indicate that the wavy wall enhances the heat transfer rate on the bottom of the... 

The use of the classical Boussinesq approximation is a straightforward strategy for taking into account the buoyancy effect in incompressible solvers. This strategy is highly effective if density variation is low. However, ignoring the importance of density variation in highly thermobuoyant flow fields can cause considerable deviation from the correct prediction of fluid flow behavior and the accurate estimation of heat transfer rate. In this study, an incompressible algorithm is suitably extended to solve high-density-variation fields caused by strong natural-convection influence. The key point in this research is the way that an ordinary incompressible algorithm is extended to... 

Generally, the flow in settling tanks is stratified, but the effect of buoyancy force on the flow field depends on the inlet concentration of particles and flow bulk velocity. A common approach for increasing settling tanks performance is to use baffles which can reduce effects of the unfavorable phenomena such as short circuiting between inlet and outlet and density currents in primary and secondary settling tanks, respectively. The suitable position of the baffles is related to the importance of buoyancy force. As a result, effects of inlet Reynolds and Froude numbers on the strength of buoyancy force are studied for a secondary settling tank and the results show that neither Reynolds nor... 

Density Current is formed when a fluid with heavier density than the surrounding fluid flows down an inclined bed. These types of flows are common in nature and can be produced by; salinity, temperature inhomogeneities, or suspended particles of silt and clay. Driven by the density difference between inflow and clear water in reservoirs, density current plunges clear water and moves towards a dam, while density current flows on a sloping bed. The vertical spreading due to water entrainment has an important role in determining the propagation rate in the longitudinal direction. In this work, two-dimensional steady-state salt solutions' density currents were investigated by means of... 

A complete study of the hydrodynamic force on a moving single bubble sonoluminescence in N-methylformamide is presented in this work. All forces exerted, trajectory, interior temperature and gas pressure are discussed. The maximum values of the calculated components of the hydrodynamic force for three different radii at the same driving pressure were compared, while the optimum bubble radius was determined. The maximum value of the buoyancy force appears at the start of bubble collapse, earlier than the other forces whose maximum values appear at the moment of bubble collapse. We verified that for radii larger than the optimum radius, the temperature peak value decreases  

This paper theoretically and experimentally investigates the exchange flow due to temperature differences between open water and a canopy of aquatic plants. A numerical model is used to study the interfacial shape, frontal velocity and total volumetric exchange, and their dependence on a dimensionless vegetation drag parameter. The numerical predictions are consistent with the laboratory measurements. There is a short initial period in which the force balance is between buoyancy and inertia, followed by drag-dominated flow for which there is a balance between buoyancy and drag forces. After the initial stage, the gravity current propagating into the canopy takes a triangular shape whereas... 

Natural convection in cavity has become one of the classical heat transfer problems with a large volume of research performed both experimentally and numerically. There are several permutations of the cavity problem related to its shape, its boundary conditions, the properties of circulating fluid, etc. Among them, the most interesting one is that of a rectangular cavity, which is maintained at hot and cold temperatures on its opposing side walls while its horizontal walls are thermally insulated. Contrary to the past works, we study the cavity with small to high temperature differences. This produces a wide range of compressibility effects in the cavity, which need to be treated carefully... 

In this paper the dynamic response of the leg of a tension leg platform (tether) subjected to the load simulated as ocean wave at the top of the leg is presented. The structural model is very simple but several complicated factors such as foundation effect, buoyancy and simulated ocean wave load are considered. Two continuous models are proposed to present the structural system and the mentioned effects. The problem is solved by means of non-harmonic Fourier expansion in terms of eigenfunctions obtained from a non-regular Sturm-Liouville system  

Despite great advancement in the lattice Boltzmann method and its application in fluid flow problems, there are still major restrictions in treating either the solution domains with complex boundaries or buoyant flow problems. The past experience shows that the heat equation is a source for instabilities which jeopardizes the stable solution of the lattice Boltzmann method in solving fluid flow problems with heat transfer. The instabilities Increase with increasing buoyant force strength. In this work, we suggest a new approach to overcome the restrictions through implementing the advantages of finite volume method in LBM. In this regard, the lattice Boltzznann equation is incorporated with... 

While for shallow waters the use of old offshore jackets still seems efficient and justifiable, for deep and ultra-deep waters such platforms cannot be used. During the past few decades the old generation of fixed offshore platforms was succeeded by the new floating platforms and new designs such as FPSOs. A new family of floating offshore platforms has been developed. These should be able to respond to size, weight and space for operating equipment, i.e. they can be constructed to have a wide range of load-bearing capacities. Use is made of the old concept of Life Saving Tubes, which in their simplest form can be a toroidal shaped tyre inner tube. The Torus-shaped idea can be further... 

An updated Lagrangian finite element formulation of a three-dimensional annular section beam element is presented for large displacement and large rotation dynamic analyses of flexible riser structures. In this formulation a new linearization method is used to avoid inaccuracies normally associated with other linearization schemes. The effects of buoyancy force as well as steady state current loading are considered in the finite element solution for riser structures response. The formulation has been implemented in a nonlinear finite element code and the results are compared with those obtained from other schemes reported in the literature  

Negative magnetophoresis is a novel and attractive method for continuous microparticle sorting inside a magnetic medium. In this method, diamagnetic particles are sorted based on their sizes using magnetic buoyancy force and without any labeling process. Although this method provides some attractive features, such as low-cost fabrication and ease of operation, there are some obstacles that adversely affect its performance, especially for biological applications. Most types of magnetic media, such as ferrofluids, are not biocompatible, and the time-consuming process of sample preparation can be threatening to the viability of the cells within the sample. Furthermore, in this method, both the... 

In this paper, a three-dimensional steady state incompressible turbulent air flow is considered in a large single room. The buoyancy affected turbulent air flow is numerically simulated by solving governing equations. The turbulence modeling includes both κ - ε and zero-equation models and their results are compared to the experimental data. The paper reviews several aspects, such as displacement of radiator system performance, temperature and flow field distribution and comfort conditions. The results show that the best temperature distribution and comfort condition are obtained when the radiator is installed under the window and its height is equal to or greater than that of the window. ©...