Computation of Added Mass and Damping Coefficients of a Horizontal Circular Cylinder in OpenFOAM

2016 ◽  
Author(s):  
Hao Chen ◽  
Erik Damgaard Christensen
Keyword(s):  
Free Surface ◽  
Analytical Solution ◽  
Numerical Computation ◽  
Added Mass ◽  
Forced Oscillations ◽  
Surface Zone ◽  
Computational Domain ◽  
Frequency Range ◽  
Two Phase ◽  
Damping Coefficients

This paper presents numerical computation of added mass and damping coefficients of a slender horizontal cylinder in the free surface zone, which typically serves as a fish cage floater. A fully viscous two phase flow solver in OpenFOAM was employed in the numerical computation. The purpose was to validate the capability of this solver and dynamic mesh functionality. A two dimensional numerical wave tank was set up, and two wave relaxation zones were used to reduce the size of the computational domain. Harmonic forced oscillations of the cylinder were performed at different frequencies and amplitudes. The mesh at free surface zone was refined based on the radiated wave heights at different oscillation frequencies in order to properly resolve the radiated waves. The result shows that in most frequency ranges, the numerical computation agreed well with the experimental data and analytical solution. However at low frequency range for added mass coefficient in heave motion, deviations were observed, and it was due to the effect of finite water depth. In addition for sway motion at high frequency range, the damping coefficient was underestimated comparing with analytical solution. This was believed to be as a result of high steepness of the radiated waves.

An Analysis of Heave Added Mass and Damping of a Surface-Effect Ship

1981 ◽  
Vol 25 (01) ◽  
pp. 44-61
Author(s):  
C. H. Kim ◽  
S. Tsakonas
Keyword(s):  
Free Surface ◽  
High Speed ◽  
Surface Effect ◽  
Practical Method ◽  
Added Mass ◽  
Damping Coefficients ◽  
Calm Water ◽  
Surface Effect Ship ◽  
Long Time ◽  
Computational Procedures

The analysis presents a practical method for evaluating the added-mass and damping coefficients of a heaving surface-effect ship in uniform translation. The theoretical added-mass and damping coefficients and the heave response show fair agreement with the corresponding experimental values. Comparisons of the coupled aero-hydrodynamic and uncoupled analytical results with the experimental data prove that the uncoupled theory, dominant for a long time, that neglects the free-surface effects is an oversimplified procedure. The analysis also provides means of estimating the wave elevation of the free surface, the escape area at the stern and the volume which are induced by a heaving surface-effect ship in uniform translation in otherwise calm water. Computational procedures have been programmed in the FORTRAN IV language and adapted to the PDP-10 high-speed digital computer.

On the harmonic oscillations of a rigid body on a free surface

1965 ◽  
Vol 21 (3) ◽  
pp. 427-451 ◽  
Author(s):  
W. D. Kim
Keyword(s):  
Integral Equation ◽  
Free Surface ◽  
Rigid Body ◽  
Potential Problem ◽  
Harmonic Oscillation ◽  
Added Mass ◽  
The Body ◽  
Rigorous Solution ◽  
Damping Coefficients

The present paper deals with the practical and rigorous solution of the potential problem associated with the harmonic oscillation of a rigid body on a free surface. The body is assumed to have the form of either an elliptical cylinder or an ellipsoid. The use of Green's function reduces the determination of the potential to the solution of an integral equation. The integral equation is solved numerically and the dependency of the hydrodynamic quantities such as added mass, added moment of inertia and damping coefficients of the rigid body on the frequency of the oscillation is established.

The Heave Damping Coefficients of Bulbous Cylinders, Partially Immersed in Deep Water

1967 ◽  
Vol 11 (03) ◽  
pp. 151-153
Author(s):  
W. Frank
Keyword(s):  
Deep Water ◽  
Added Mass ◽  
Damping Coefficient ◽  
Frequency Range ◽  
Damping Coefficients

The heave added mass and damping coefficients of several partially immersed bulbous and nonbulbous cylinders are computed. For each of the bulbous forms there is a frequency at which the damping coefficient vanishes, whereas the nonbulbous cylinders exhibit nonzero damping over the frequency range considered.

The absorption of wave energy by a three-dimensional submerged duct

1981 ◽  
Vol 104 ◽  
pp. 189-215 ◽  
Author(s):  
J. R. Thomas
Keyword(s):  
Three Dimensional ◽  
Added Mass ◽  
Axisymmetric Body ◽  
The Body ◽  
Forced Oscillations ◽  
Radiation Problem ◽  
Absorption Length ◽  
Damping Coefficients ◽  
Sea Bed ◽  
Linear Spring

It has been shown (Evans 1976) that the power absorbed by a general, axisymmetric body depends solely upon the added-mass and damping coefficients. These coefficients are fundamental properties of the body, representing the component of the force on the body proportional to the acceleration and velocity of the body respectively in the radiation problem, where the body is forced to oscillate in the absence of incoming waves.In the present paper these coefficients are determined by solution of the radiation problem, for a mouth-upward cylindrical duct situated on the sea bed and fitted with a piston undergoing forced oscillations. The added-mass and damping coefficients are then used to study the power absorption properties of the duct when the power take-off is modelled by a linear-spring–dashpot system attached to the piston. Curves of the added mass, damping coefficients and absorption length (a measure of the power absorbed) as functions of wavenumber are presented, for different duct diameters and different depths of submergence.

Experimental Assessment of Hydrodynamic Coefficients of Disks Oscillating Near a Free Surface

2009 ◽  
Author(s):  
Hemlata Wadhwa ◽  
Krish P. Thiagarajan
Keyword(s):  
Free Surface ◽  
Circular Disk ◽  
Added Mass ◽  
Rate Of Change ◽  
Forced Oscillations ◽  
Base Case ◽  
Published Data ◽  
Hydrodynamic Coefficients ◽  
Widespread Application ◽  
Field Development

The use of different types of subsea equipment is continuously increasing in offshore field development. Installation operations such as lifting and lowering of these equipments require knowledge of the hydrodynamic coefficients of the object. An accurate prediction of these coefficients on typical subsea structures is a challenging task. The main coefficients in this context relate to added mass, damping and slamming effects. Formulations have been presented by various authors in literature for evaluating these coefficients for simple shapes. Some of them have found widespread application in the industry. The authors have considered a solid circular disk as a base case for initiating study on subsea module hydrodynamics. Experiments were conducted on an oscillating solid disk of diameter 200 mm and thickness 2 mm near the free surface. Forced oscillations were conducted at amplitudes varying from 3mm–36mm and frequencies 0.9–1.5 Hz respectively. The forces on the disk were measured using a submersible high-sensitivity load cell. The motions of the disk were restricted to axial (heave) direction, and were measured with a displacement transducer. The measured forces and displacement were analyzed using a Fast Fourier Transform algorithm to separate the added mass and damping effects. From the rate of change of added mass with depth of submergence, slamming forces were identified. The measured coefficients were compared with similar published data by Vu et al [1] and Tao & Dray [2]. The paper presents various formulations for added mass, damping and slamming obtained from literature and currently in use in the industry. These formulations are compared with measured values of the coefficients and suggestions are made on the importance of these formulations for flat subsea structures.

An Analytical Solution for Free Flexural Vibration of a Thin Cylindrical Shell Submerged in Acoustic Half-Space Bounded by a Free Surface

2018 ◽  
Vol 18 (03) ◽  
pp. 1850042
Author(s):  
Peng Wang ◽  
Tian-Yun Li ◽  
Xiang Zhu ◽  
Wen-Jie Guo ◽  
Rui Nie
Keyword(s):  
Cylindrical Shell ◽  
Free Surface ◽  
Analytical Solution ◽  
Half Space ◽  
Surface Effect ◽  
Flexural Vibration ◽  
Added Mass ◽  
Immersion Depth ◽  
Thin Cylindrical Shell ◽  
Test Environment

An analytical solution is proposed for the free flexural vibration of a finite cylindrical shell submerged in half-space bounded by a free surface in the low frequency range. The motion of the shell is described by the Flügge shell theory and the fluid surrounding the shell is assumed to be an acoustic media. The free surface effect is considered by satisfying the pressure release boundary condition. The accuracy of the present method is verified through comparison with the finite element solution. To throw light on the influence mechanism of free surface on the coupled modal frequencies, a modal added mass is introduced and calculated. Numerical results show that when the shell is close to the free surface, the presence of free surface will make a negative contribution to the modal added mass and finally result in the corresponding increase of the coupled modal frequencies. But the free surface effect will decrease when the immersion depth of the cylindrical shell increases. Finally, the free surface effect can be neglected if the immersion depth is higher than four times the shell radius. This conclusion is helpful to select proper test environment for an experiment on the dynamic characteristics of submerged cylindrical shells.

Numerical Investigation of the Flow Features Around Heave Plates Oscillating Close to a Free Surface or Seabed

2014 ◽  
Author(s):  
Carlos A. Garrido-Mendoza ◽  
K. P. Thiagarajan ◽  
Antonio Souto-Iglesias ◽  
Benjamin Bouscasse ◽  
Andrea Colagrossi
Keyword(s):  
Free Surface ◽  
Vortex Shedding ◽  
Flow Characteristics ◽  
Added Mass ◽  
Offshore Structures ◽  
Vortical Structures ◽  
Damping Coefficients ◽  
Solid Disk ◽  
Flow Features ◽  
Heave Plate

Performance of heave plates used in offshore structures is strongly influenced by their added mass and damping, which are affected by proximity to a boundary. A previous paper by the authors presented numerical simulations of the flow around a circular solid disk oscillating at varying elevations from seabed [1]. The force calculated was used to evaluate the added mass and damping coefficients for the disk. The simulations suggest that as the structure moves closer to the seabed the added mass and damping coefficients (Ca and Cb) increases continuously. In order to understand the physics behind the added mass and damping trends, when a heave plate is moving near a seabed or closer to the free surface, the flow characteristics around the heave plate are examined numerically in this paper. Flow around oscillating disks is dominated by generation and development of phase-dependent vortical structures, characterized by the KC number and the distance from the seabed or free surface to the heave plate. Numerical calculations presented in this paper have comprised the qualitative analysis of the vortex shedding and the investigation of the links between such vortex shedding and, on one hand the damping coefficient, and on the other hand, pairing mechanisms such as the shedding angle.

scholarly journals Hydrodynamic Forces Exerting on an Oscillating Cylinder under Translational Motion in Water Covered by Compressed Ice

Water ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 822
Author(s):  
Yury Stepanyants ◽  
Izolda Sturova
Keyword(s):  
Lift Force ◽  
Wave Motion ◽  
Translational Motion ◽  
Added Mass ◽  
Hydrodynamic Forces ◽  
Wave Resistance ◽  
Translational Velocity ◽  
Damping Coefficients ◽  
Incompressible Ideal Fluid ◽  
Theoretical Results

This paper presents the calculation of the hydrodynamic forces exerted on an oscillating circular cylinder when it moves perpendicular to its axis in infinitely deep water covered by compressed ice. The cylinder can oscillate both horizontally and vertically in the course of its translational motion. In the linear approximation, a solution is found for the steady wave motion generated by the cylinder within the hydrodynamic set of equations for the incompressible ideal fluid. It is shown that, depending on the rate of ice compression, both normal and anomalous dispersion can occur in the system. In the latter case, the group velocity can be opposite to the phase velocity in a certain range of wavenumbers. The dependences of the hydrodynamic loads exerted on the cylinder (the added mass, damping coefficients, wave resistance and lift force) on the translational velocity and frequency of oscillation were studied. It was shown that there is a possibility of the appearance of negative values for the damping coefficients at the relatively big cylinder velocity; then, the wave resistance decreases with the increase in cylinder velocity. The theoretical results were underpinned by the numerical calculations for the real parameters of ice and cylinder motion.

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