Oscillations of a cylindrical body submerged in a fluid with ice cover

The linear plane problem of oscillations of an elliptic cylinder in an ideal incompressible fluid of finite depth in the presence of an ice cover of finite length is solved. The ice cover is modeled by an elastic plate of constant thickness. The hydrodynamic loads acting on the body are determined as functions of the oscillation frequency and the positions of the cylinder and plate.     

Wavy mode of the streaked flow around an oscillating cylinder in a stratified fluid at rest

The structures of the flow induced by a vertical circular cylinder performing transverse oscillations in a linearly stratified fluid at rest are investigated. The density gradient inhibits the onset of the three-dimensional instability. The instability appears as regularly spaced streaked flows along the cylinder axis. Each streaked flow follows a wavy path in the horizontal plane in a certain range of amplitude and frequency of the oscillations.     

Hydrodynamic forces acting on a cylinder set in motion abruptly

An attempt has been made to measure directly the forces (drag and lift) that act on a cylinder under the conditions of a fairly complicated unsteady motion in which the velocity is acquired almost instantaneously from the state of rest.     

Horizontal submerged jet in a stratified fluid

The problem of jet flow excited in a viscous density-stratified fluid by a point source of momentum acting horizontally is considered. Simplified asymptotic equations are obtained in the boundary layer approximation. It is shown that the vertical velocity component is small and the motion in the jet has a layered structure. The longitudinal velocity distributions in the jet are measured experimentally. It is shown that these distributions are affine and can be satisfactorily approximated by Schlichting's well-known boundary layer solution for a round submerged jet in a fluid uniform with respect to density.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No.6, pp. 10–16, November–December, 1993.We are grateful to I. A. Filippov for assisting with the experiments.     

The in-line forces acting on an elastically mounted cylinder oscillating in still water

The drag and the inertia coefficients of the in-line force were determined experimentally based on the Morison equation. The interrelationship of the in-line force coefficients with the frequency ratio, the amplitude ratio, and the y-direction response were carefully examined. The experimental results show that the frequency ratio is more important in determining the drag coefficient than either the Reynolds number or the reduced velocity, and that the drag coefficient is highly coupled to the y-direction response. Paper was presented at 1985 SEM Spring Conference on Experimental Mechanics held in Las Vegas on June 9–14, 1985.     

Waves generated on an ice cover by a source pulsating in fluid

A point source of variable intensity located at rest in a plane infinitely deep fluid layer under an ice cover is considered. The general expression for perturbations of the fluid-ice interface is obtained. In the case of the long operation in the pulsating regime the wave established on the ice cover is found.     

A nonlinear model of vortex-induced forces on an oscillating cylinder in a fluid flow

A nonlinear model relating the imposed motion of a circular cylinder, submerged in a fluid flow, to the transverse force coefficient is presented. The nonlinear fluid system, featuring vortex shedding patterns, limit cycle oscillations and synchronisation, is studied both for swept sine and multisine excitation. A nonparametric nonlinear distortion analysis (FAST) is used to distinguish odd from even nonlinear behaviour. The information which is obtained from the nonlinear analysis is explicitly used in constructing a nonlinear model of the polynomial nonlinear state-space (PNLSS) type. The latter results in a reduction of the number of parameters and an increased accuracy compared to the generic modelling approach where typically no such information of the nonlinearity is used. The obtained model is able to accurately simulate time series of the transverse force coefficient over a wide range of the frequency–amplitude plane of imposed cylinder motion.     

Wave generation by an oscillating submerged cylinder in the presence of a floating semi-infinite elastic plate

The results of solving the linear problem of steady-state oscillations of a horizontal cylinder submerged in fluid on whose upper boundary a semi-infinite elastic plate with free edge floats are given. The remaining part of the fluid surface is free. The contour-distributed mass source method is used. The corresponding Green’s function is constructed using eigenfunction expansions. The hydrodynamic load and the amplitudes of vertical displacements of the free surface and elastic plate are calculated. Equivalence relations which demonstrate both symmetry of the apparent mass and damping factors and connection of the damping factors with the wave amplitudes in the far field are derived.     

The frequency components of fluid-lift forces acting on a cylinder oscillating in still water

A circular cylinder oscillating with sinusoidal motion in still water is a simple experimental model of circular structural members exposed to continuous wave motion. The measured fluid forces are analyzed using a unique Fourier technique from which fluid-force components can be understood and predicted for structural analysis.     

Mixed convection from a cylinder oscillating vertically in a quiescent fluid

 The problem of heat convection from a vertically oscillating cylinder in a quiescent fluid is investigated. The governing equations of motion and energy are solved numerically in a non-inertial frame of references to determine the flow field and heat transfer characteristics under different conditions. The main dominating parameters are Keulegan–Carpenter number, KC, frequency parameter, β, Grashof number, Gr and Prandtl number, Pr. The ranges considered for these parameters are KC ≤ 10, β≤40 and Gr ≤ 10⁵ while Prandtl number is kept constant. The study revealed that the effect of amplitude and frequency of oscillation on heat transfer is strongly influenced by the Grashof number range. In the forced convection regime (Gr = 0), the increase of KC creates extensive vortex motion at all cylinder positions that leads to a significant increase in heat transfer. A similar trend, but with a lesser extent, is also observed for the increase of β. However, at high Grashof numbers, the effect of oscillation on heat convection is only significant at large values of KC. Received on 5 June 2000 / Published online: 29 November 2001     

Fluctuating fluid forces acting on a circular cylinder and interference with a plane wall

The flow around a circular cylinder placed close to a horizontal plane wall was investigated experimentally. Fluctuations of lift and drag of the cylinder and wall interference effects were studied in terms of the gap height between the cylinder and wall and the thickness of the turbulent wall boundary layer. The fluctuating fluid forces acting on the cylinder sharply increased, and the regular vortex shedding, i.e. Kárman vortex streets, started to form beyond a critical gap height. The formation of Kárman vortex streets was abruptly interrupted when the bottom of the cylinder came in contact with the outer layer of the boundary layer developed on the wall. This critical gap height correlated well with the thickness of the boundary layer.     

Oscillations of a cylinder piercing a linearly stratified fluid layer

The plane problem of the small steady-state oscillations of a horizontal cylinder arbitrarily located in a three-layer fluid whose upper and lower layers are homogeneous and whose middle layer is linearly stratified is considered in the linear formulation using the Boussinesq approximation. The fluid is assumed to be ideal and incompressible. The method of mass sources distributed along the body contour is used in the internal wave generation regime and an integral equation for the fluid pressure is derived in the non-wave regime. The hydrodynamic load acting on the body is calculated as a function of the oscillation frequency of the cylinder and its location. The results are compared with experimental data.     

Vibrations of a circular cylinder submerged in a fluid with a non-homogeneous upper boundary

Results of solving a linear problem on steady vibrations of a horizontal cylinder submerged in a fluid, whose upper boundary is partially closed by a solid lid, whereas the rest of the surface is free, are presented. Multipole and eigenfunction expansion methods are used. Reciprocity relations are derived. Added-mass and damping coefficients and the wave amplitudes on the free surface of the fluid are calculated.     

Electronic compensation of a force transducer for measuring fluid forces acting on an accelerating cylinder

In measuring the fluid forces acting on an accelerating cylinder, it is important to remove the force required to accelerate the cylinder mass from the total force sensed by the force transducer. A low-cost data-acquisition system which electronically subtracts the cylinder inertia force from the total force is described along with appropriate-filter circuits. An experimental procedure for obtaining the correct subtraction condition is outlined. The results indicate that less than two percent of the inertia force remain in the fluid-force signal and all significant spurious high-frequency noise has been eliminated by the filter circuits. These concepts and circuits can be applied to many different measurement environments.     

Quantitative interpretation of vortices from a cylinder oscillating in quiescent fluid

 The instantaneous, quantitative patterns of vortices arising from sinusoidal oscillation of a cylinder in quiescent fluid are experimentally characterized for the first time using high-image-density particle image velocimetry. The near-wake does not indicate a separated layer of distributed vorticity leading to a single, large-scale vortex. Rather, for sufficiently high Reynolds number, a sequence of small-scale vorticity concentrations is formed. Agglomeration of only a fraction of the adjacent concentrations forms a larger-scale vortex. Simultaneously, vorticity concentrations of opposite sense are formed along the base (rear) of the cylinder. Streamline patterns typically indicate, however, only the larger-scale vortex; it has a circulation smaller than the total circulation of all vorticity concentrations that are not revealed by the streamlines. These observations are interpreted in the context of the effective resolution of the flow images. Received: 27 October 1995 / Accepted: 27 August 1996     

Hydrodynamic characteristics of a wing in a stratified fluid near the bottom

The problem of the motion of a thin wing in a stratified fluid near the bottom is considered. A solution is found using the logarithmic dynamic potential. The dependence of the hydrodynamic force and moment on the input parameters, namely, the Strouhal and Froude numbers and the distance to the bottom, is studied. An important feature of the amplitudes of nonstationary loads on the wing is their nonmonotonic character in the case where the frequency of vibrations is lower than the Brunt-Väisälä frequency, which is explained by the interaction between the wing's vibrations and the internal waves reflected from the bottom.     

On the flow field induced by an oscillating disk submerged in a semi-infinite viscous fluid with a surfactant surface film

On the basis of the unsteady Stokes' equation the problem of the flow field induced by an oscillating disk fully immersed in a semi-infinite viscous fluid with a surfactant surface layer is solved. The effect of the insoluble surfactant on the hydrodynamics of the oscillating disk is found for varying values of the ratio of the coefficient of the surface shear viscosity to the coefficient of viscosity of the substrate fluid, and depth of the disk below the surface. A new theoretical analysis for obtaining the surface shear viscosity is suggested.     

Secondary flow in the neighborhood of a cylinder oscillating in a viscoelastic fluid

Measurements were made of the steady secondary flow which is caused by a cylinder executing small-amplitude oscillations perpendicular to the cylinder generators. Test fluids were a water-glycerine mixture and two non-Newtonian fluids: aqueous solutions of Separan AP-30 and PolyHall 295 polyacrylamide polymers. The fluids were contained in a cylinder whose center coincides with the rest position of the oscillating cylinder. Experimental results are consistent with a theoretical analysis for a three-constant Oldroyd fluid model in its simplified convected-Maxwell form. Both experiment and theory show that at an oscillation frequency of 40 Hz the secondary flow of the dilute polymer solutions is, essentially, in a sense opposite from that of a Newtonian fluid.