Abstract:
The unsteady flow past a circular cylinder which starts translating and rotary oscillating impulsively from rest in a viscous fluid is investigated at Reynolds numbers $Re=200$ and 1000, rectilinear speed ratios $\alpha =0.5$, 2.0 and 4.0, and for forced oscillating frequencies $f_{s}$ between 0.1 and 2.0. Numerical solutions of the Navier-Stokes equations are obtained by a finite volume method based on unstructured colocated meshes. The discretized schemes of the convective fluxes, diffusive fluxes and unsteady term are all of second-order accuracy. The SIMPLE algorithm is adopted to deal with the pressure-velocity coupling. The varieties of force coefficients with the control parameter are obtained after the discussion. The amplitudes of lift coefficients at natural shedding frequency and forced oscillating frequency respectively are determined by the amplitude spectra analysis, which show clearly the competitive relationship between the two frequencies. Based on this relationship, the region of the classification of flow structure modes is given at last.

Abstract:
A train of surface waves is normally incident on a half immersed circular cylinder in a fluid of finite depth. Assuming the linearized theory of fluid under gravity an integral equation for the scattered velocity potential on the half immersed surface of the cylinder is obtained. It has not been found possible to solve this in closed form even for infinite depth of fluid. Our purpose is to obtain the asymptotic effect of finite depth “h ” on the transmission and reflection coefficients when the depth is large. It is shown that the corrections to be added to the infinite depth results of these coefficients can be expressed as algebraic series in powers of a/h starting with (a/h)2 where “a ” is the radius of the circular cylinder. It is also shown that the coefficients of (a/h)2 in these corrections do not vanish identically.

Abstract:
We consider a nonlinear 4th-order degenerate parabolic partial differential equation that arises in modelling the dynamics of an incompressible thin liquid film on the outer surface of a rotating horizontal cylinder in the presence of gravity. The parameters involved determine a rich variety of qualitatively different flows. We obtain sufficient conditions for finite speed of support propagation and for waiting time phenomena by application of a new extension of Stampacchia's lemma for a system of functional equations.

Abstract:
The near wake of a circular cylinder in linearly stratified flows of finite depth was experimentally investigated by means of flow visualization and measurements of vortex shedding frequencies, at Reynolds numbers 3.5×10^{3}-1.2×10^{4} and stratification parameters k_{d} 0-2.0. The non-dimensional parameter k_{d} is defined ask_{d}=Nd/U, where N is the Brunt-Vaisala frequency, d, the diameter of the cylinder, and U, the approaching flow velocity. The study demonstrates that as k_{d} increases from zero, the vortex shedding from a circular cylinder progressively strengthens, while the Strouhal number gradually becomes lower than that for homogeneous flow. This phenomenon can be explained by the effect of the increasingly stable stratification which enhances the two-dimensionality of the near-wake flow of the circular cylinder; the enhanced two-dimensionality of the flow strengthens the roll-up of the separated shear layer. Above a certain value of k_{d}, however, vortex formation and shedding are strongly suppressed and the Strouhal number rises sharply. This observation is attributable to the development of stationary lee waves downstream of the circular cylinder because the lee waves strongly suppress vertical fluid motions.

Abstract:
Cylindrical structures are commonly used in offshore engineering, for example, a tension-leg platform (TLP). Prediction of hydrodynamic loadings on those cylindrical structures is one of important issues in design of those marine structures. This study aims to provide a numerical model to simulate fluid-structure interaction around the cylindrical structures and to estimate those loadings using the direct-forcing immersed boundary method. Oscillatory flows are considered to simulate the flow caused by progressive waves in shallow water. Virtual forces due to the existence of those cylindrical structures are distributed in the fluid domain in the established immersed boundary model. As a results, influence of the marine structure on the fluid flow is included in the model. Furthermore, hydrodynamic loadings exerted on the marine structure are determined by the integral of virtual forces according to Newton’s third law. A square array of four cylinders is considered as the marine structure in this study. Time histories of inline and lift coefficients are provided in the numerical study. The proposed approach can be useful for scientists and engineers who would like to understand the interaction of the oscillatory flow with the cylinder array or to estimate hydrodynamic loading on the array of cylinders.

Abstract:
A direct forcing method for the simulation of particulate flows based on immersed boundary-lattice Boltzmann method is used to study the flow of power-law fluid through an infinite array of circular cylinders with cylinder separations of 20a (a is the cylinder radius) with laminar shedding behind cylinders. Time averaged drag coefficient, maximum of lift coefficient and Strouhal number are given out with the power-law index in the range of 0.4 ≤ n ≤ 1.8 and Re in the range of 50 ≤ Re ≤ 140.

Abstract:
In this paper we have investigated a circular band formation of fluid-rigid particle mixtures in a fully filled cylinder horizontally rotating about its cylinder axis by direct numerical simulation. These phenomena are modeled by the Navier-Stokes equations coupled to the Euler-Newton equations describing the rigid solid motion of the non-neutrally particles. The formation of circular bands studied in this paper is not resulted by mutual interaction between the particles and the periodic inertial waves in the cylinder axis direction (as suggested in Phys. Rev. E, 72, 021407 (2005)), but due to the interaction of particles. When a circular band is forming, the part of the band formed by the particles moving downward becomes more compact due to the particle interaction strengthened by the downward acceleration from the gravity. The part of a band formed by the particles moving upward is always loosening up due to the slow down of the particle motion by the counter effect of the gravity. To form a compact circular band (not a loosely one), enough particles are needed to interact among themselves continuously through the entire circular band at a rotating rate so that the upward diffusion of particles can be balanced by the compactness process when these particles moving downward.

Abstract:
The radiated electromagnetic (EM) fields from a rotating current-carrying circular cylinder were numerically simulated in two dimensions using the method of characteristics (MOC), and the numerical results were presented in this paper. To overcome the difficulty of the grid cell distortion caused by the rotating cylinder, the passing center swing back grids (PCSBG) technique is employed in collaboration of MOC in a modified O-type grid system. In order to have clear demonstration of radiated EM fields, the circular cylinder is set to be evenly divided in radial direction into an even number of slices that are made of perfect electric conductor (PEC) and non electric non magnetic material, alternatively. The surface current is assumed to have a Gaussian profile and to flow uniformly along the axial direction on the PEC surface. The radiated electric and magnetic fields around the cylinder were recorded as functions of time and reported along with the corresponding spectra which were obtained through proper Fourier transformation. Several field distributions over the whole computational space are also given.

Study of atmospheric ice accretion on a
non-rotating vertical circular cylindrical object was carried out at dry and
wet ice conditions. Both numerical and experimental techniques were used during
this study. 3D numerical study was carried out using computational fluid
dynamics based approach, whereas experimental study was carried out at Cryospheric
Environmental Simulator ‘CES’ in Shinjo, Japan. A good agreement was found
between experimental and numerical results. The dimensions of the cylindrical
object used to measure the atmospheric ice load on structures along this study,
were selected as per the ISO12494 standard. Results provide useful information
about ice growth and intensity along circular cylindrical objects at different
atmospheric temperatures. This research work also provides a useful base for
further investigation of atmospheric ice accretion on structures particularly
circular power network cables, & tower masts installed in the cold regions.

Abstract:
In this work, effects of Prandtl number on the heat transfer characteristics of an unconfined rotating circular cylinder are investigated for varying rotation rate (α = 0 - 5) in the Reynolds number range 1 - 35 and Prandtl numbers range 0.7 - 100 in the steady flow regime. The numerical calculations are carried out by using a finite volume method based commercial CFD solver FLUENT. The isotherm patterns are presented for varying values of Prandtl number and rotation rate in the steady regime. The variation of the local and the average Nusselt numbers with Reynolds number, Prandtl number and rotation rate are presented for the above range of conditions. The average Nusselt number is found to decrease with increasing value of the rotation rate for the fixed value of the Reynolds and Prandtl numbers. With increasing value of the Prandtl number, the average Nusselt number increases for the fixed value of the rotation rate and the Reynolds number; however, the larger values of the Prandtl numbers show a large reduction in the value of the average Nusselt number with increasing rotation rate.