Hydrodynamic Coefficients of Vertical Cylinders of Arbitrary Section

1991 ◽  
Vol 113 (2) ◽  
pp. 109-116 ◽  
Author(s):  
M. Isaacson ◽  
T. Mathai
Keyword(s):  
Vertical Cylinder ◽  
Vertical Direction ◽  
Numerical Approach ◽  
Offshore Structures ◽  
Three Dimensions ◽  
Method Of Integral Equations ◽  
Square Cylinders ◽  
Added Masses ◽  
Arbitrary Section ◽  
Vertical Cylinders

The calculation of added masses and damping coefficients of a large surface-piercing vertical cylinder of arbitrary section extending to the seabed and undergoing harmonic oscillations is described. The linear radiation problem in three dimensions is reduced to a series of two-dimensional problems in the horizontal plane by the use of appropriate eigenfunctions that represent the variation of the velocity potential in the vertical direction. Each of these is solved by a numerical approach based on the method of integral equations. Comparisons are made with an analytic solution available for the case of a circular cylinder. Results are also provided for square cylinders, and the application to typical offshore structures subject to base motions is discussed.

On the Occurrence of Strong Higher Harmonic Wave Forces and Induced Ringing Loads on Vertical Cylinders

2002 ◽  
Author(s):  
John Grue ◽  
Morten Huseby
Keyword(s):  
Harmonic Wave ◽  
Vertical Cylinder ◽  
Offshore Structures ◽  
Load Cycle ◽  
Wave Forces ◽  
Wave Elevation ◽  
Secondary Load ◽  
Steep Waves ◽  
Acceleration Of Gravity ◽  
Vertical Cylinders

Experimental observations of a secondary load cycle in the force acting on a vertical cylinder exposed to long and steep waves are discussed. A complementary discussion of the occurrence of ringing of models of offshore structures is given. The height of the secondary load cycle is typically up to about 0.1–0.15 times the peak to peak force on the cylinder. The load cycle is observed for a nondimensional wavenumber kR in the range 0.1–0.33 and for a Froude number Fr = ωζm/gD exceeding about 0.4. Pronounced ringing occurs for the same parameter range. (k the wavenumber, R the cylinder radius, ω the wave frequency, ζm the maximal wave elevation, g the acceleration of gravity, D = 2R.)

High frequency hydrodynamic coefficients of vertical cylinders

1992 ◽  
Vol 19 (4) ◽  
pp. 606-615
Author(s):  
Michael Isaacson ◽  
Thomas Mathai
Keyword(s):  
High Frequency ◽  
Scattering Problem ◽  
Offshore Structures ◽  
Short Wave ◽  
Alternative Methods ◽  
Local Form ◽  
Ocean Engineering ◽  
Damping Coefficients ◽  
Added Masses ◽  
Vertical Cylinders

Alternative methods of calculating high frequency added masses and damping coefficients of vertical cylinders of arbitrary section are described. Damping coefficients are calculated by a short-wave approximation relating to the local form of waves generated by the oscillating structure. As an alternative, they are also obtained from the exciting forces of the related scattering problem, with these forces obtained by a geometrical optics approximation. Added masses are obtained by discarding the propagating mode and using only the evanescent modes which are free of irregular frequencies. They are also obtained by an application of the Kramers–Kronig relations, which require the infinite frequency added masses and the damping coefficients at all frequencies. Numerical results obtained by the various methods are compared with corresponding analytical results for vertical circular and elliptic cylinders. The practical application of the proposed approach is indicated. Key words: added mass, cylinders, damping, hydrodynamics, ocean engineering, offshore structures, waves.

Three-Dimensional Numerical Prediction of the Hydrodynamic Loads and Motions of Offshore Structures

2000 ◽  
Vol 122 (4) ◽  
pp. 294-300 ◽  
Author(s):  
Karl W. Schulz ◽  
Yannis Kallinderis
Keyword(s):  
Flow Structure ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Structural Response ◽  
Offshore Structures ◽  
Three Dimensions ◽  
Navier Stokes ◽  
Hydrodynamic Loads ◽  
Drag Coefficients ◽  
Lift And Drag

A generalized numerical method for solution of the incompressible Navier-Stokes equations in three-dimensions has been developed. This solution methodology allows for the accurate prediction of the hydrodynamic loads on offshore structures, which is then combined with a rigid body structural response to address the flow-structure coupling which is often present in offshore applications. Validation results using this method are first presented for fixed structures which compare the drag coefficients of sphere and cylinder geometries to experimental measurements over a range of subcritical Reynolds numbers. Additional fixed structure results are then presented which explore the influence of aspect ratio effects on the lift and drag coefficients of a bare circular cylinder. Finally, the spanwise flow variations between a fixed and freely vibrating cylindrical structure are compared to demonstrate the ability of the flow-structure method to correctly predict correlation length increases for a vibrating structure. [S0892-7219(00)00904-3]

Motion Decay Simulations of a Moored Wave Energy Converter

2020 ◽  
Author(s):  
Changqing Jiang ◽  
Ould el Moctar ◽  
Thomas E. Schellin ◽  
Guilherme Moura Paredes
Keyword(s):  
Wave Energy ◽  
Stokes Equations ◽  
Numerical Approach ◽  
Offshore Structures ◽  
Primary Role ◽  
Viscous Effects ◽  
Restoring Force ◽  
System A ◽  
Cost Reductions ◽  
Catenary System

Abstract Significant cost reductions are required for marine renewable energy to become competitive. Aside from the deployment of arrays, one key area that has been identified as having potential for cost reductions is the mooring system. A challenge, therefore, is to design mooring systems which can satisfy their primary role of station keeping while being affordable and durable. This paper presents the effects of three different mooring configurations on the motion behavior of a buoy type wave energy convertor, considering nonlinear mooring-induced fluid-structure interactions, such as the associated viscous effects. To simulate motion decay, an overset mesh method that coupled a dynamic mooring model with the Navier-Stokes equations flow solver OpenFOAM was adopted. The mooring configurations comprised an all catenary system, a catenary system with buoys, and a catenary system with buoys and clump weights. The favorable agreement between the simulations and experimental measurements validated the coupled numerical approach for simulating different mooring configurations. The mooring systems influenced not only restoring force characteristics, but also total damping of the system, which demonstrated the importance of considering mooring-induced damping when investigating moored offshore structures.

On the Occurrence of Mathieu Instabilities of Vertical Cylinders

2008 ◽  
Author(s):  
Marcelo A. S. Neves ◽  
Sergio H. Sphaier ◽  
Bruno M. Mattoso ◽  
Claudio A. Rodri´guez ◽  
Alberto L. Santos ◽  
...  
Keyword(s):  
Vertical Cylinder ◽  
Design Parameters ◽  
Offshore Platforms ◽  
Spar Platforms ◽  
Motion Responses ◽  
Theoretical Investigations ◽  
Series Of Experiments ◽  
Vertical Cylinders ◽  
Metacentric Height ◽  
Limited Motion

Large offshore platforms with vertical circular cylindrical hull shapes have been designed and employed in recent times. Classical spar platforms and mono-column concepts are just two examples of designs with such simple configuration, supposed to perform limited motion responses in waves. Reports on investigations on the occurrence of parametric resonance of spar platforms have been published recently in which the relevance of Mathieu amplifications have been assessed making use of different mathematical models. However, some uncertainties still remain on the influence of crucial design parameters as, for instance, metacentric height, draft/diameter ratio, associated damping and mooring system. In an attempt to clarify some of these aspects, in this paper the dynamic stability of a vertical cylinder in regular waves is investigated theoretically and experimentally. A coupled non-linear mathematical model is employed to model and simulate the coupled heave, roll and pitch motions. Theoretical aspects related to the development of resonant motions are discussed. In addition to the numerical and theoretical investigations, an extensive series of experiments with a model of a typical mono-column have been recently conducted at LabOceano. The findings of these investigations are compared and summarized.

A Coupled VOF-Eulerian Multiphase CFD Model to Simulate Breaking Wave Impacts on Offshore Structures

2016 ◽  
Author(s):  
Pietro D. Tomaselli ◽  
Erik Damgaard Christensen
Keyword(s):  
Wave Breaking ◽  
Bubble Column ◽  
Vertical Cylinder ◽  
Air Entrainment ◽  
Offshore Structures ◽  
Laboratory Scale ◽  
Breaking Wave ◽  
Cfd Model ◽  
Bubble Plume ◽  
Wave Induced

Breaking wave-induced loads on offshore structures can be extremely severe. The air entrainment mechanism during the breaking process plays a not well-known role in the exerted forces. This paper present a CFD solver, developed in the Open-FOAM environment, capable of simulating the wave breaking-induced air entrainment. Firstly the model was validated against a bubble column flow. Then it was employed to compute the inline force exerted by a spilling breaking wave on a vertical cylinder in a 3D domain at a laboratory scale. Results showed that the entrained bubbles affected the magnitude of the force partially. Further analyses on the interaction of the bubble plume with the flow around the cylinder are needed.

scholarly journals Comprhensive Approach to the Analysis of the 3D Kinematics Deformation with appliction to the Kenai Peninsula

2011 ◽  
Vol 1 (1) ◽  
pp. 59-73 ◽  
Author(s):  
M. Hossainali ◽  
M. Becker ◽  
E. Groten
Keyword(s):  
Surface Deformation ◽  
Regularization Parameter ◽  
Vertical Direction ◽  
Three Dimensions ◽  
Deformation Tensor ◽  
Deformation Analysis ◽  
Kenai Peninsula ◽  
3D Kinematics ◽  
South Central ◽  
Lagrangian Formulations

Comprhensive Approach to the Analysis of the 3D Kinematics Deformation with appliction to the Kenai PeninsulaThe problem of analyzing surface deformation of the Earth's crust in three-dimensions is discussed. The isoparametric and Lagrangian formulations of deformation are extended from 2D to 3D. Analytical and numerical investigation of problem conditioning proves that analyzing the 3D kinematics of deformation can be an ill-posed problem. The required mathematical elements for solving this problem, including sensitivity analysis of the deformation tensor and regularization, are proposed. Regularized deformation tensors were computed using the method of truncated singular value decomposition (TSVD). The optimal regularization parameter was attained by minimizing regularization errors. Regularization errors were assessed using the corresponding 2D results of deformation analysis. The proposed methods were applied to the GPS network in the Kenai Peninsula, south-central Alaska, in order to compute the 3D pattern of postseismic crustal deformation in this area. Computed deformation in the vertical direction is compared to the existing pattern of vertical deformation obtained from the combination of precise leveling, gravity and GPS measurements from other studies on this area.

A Study of a Heaving Vertical Cylinder in a Towing Tank

1989 ◽  
Vol 33 (02) ◽  
pp. 107-114 ◽  
Author(s):  
S. M. Çalisal ◽  
T. Sabuncu
Keyword(s):  
Numerical Study ◽  
Wave Length ◽  
Vertical Cylinder ◽  
Addition Theorem ◽  
Linear Potential ◽  
Hydrodynamic Coefficients ◽  
Infinite Domain ◽  
Towing Tank ◽  
Vertical Cylinders ◽  
Water Tanks

The effects of tank walls on experimentally measured hydrodynamic coefficients are of concern to researchers. In this numerical study of heaving vertical cylinders in a towing tank, the nonresonant, linear potential flow around a heaving cylinder in a towing tank has been formulated. The method used is based on a matching technique and on Graf's addition theorem. The calculations suggest that "blockage" or "wall effect" is more pronounced in shallow water tanks. A resonant frequency ω, corresponds to the frequency of a wave with a wave length equal to the width of the tank. For frequencies higher than ωr hydrodynamic coefficients are very close to infinite domain values for large values of the ratio of the tank beam to the cylinder radius. For frequencies less than ωr blockage correction to the hydrodynamic coefficients is necessary.

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