A STUDY ON VISCOUS ROLL DAMPING OF A BOX-SHAPED VESSEL IN THE FREQUENCY DOMAIN USING THE DISCRETE VORTEX METHOD

This paper presents a study on viscous roll damping of a floating box-shaped vessel in the frequency domain. The application of the discrete vortex method (DVM) for calculation of the viscous roll damping in regular seas has been validated by model tests. Equivalent roll RAOs associated with a range of regular wave amplitudes are calculated to assess behaviour of the viscous roll damping in relation to incident wave amplitude linearisation. A model test is conducted using the model test facilities of the Marine Hydrodynamics Laboratory at Newcastle University to validate the applicability of the DVM in calculating the roll RAO in regular waves and to study the application of this method to irregular waves. Results of these model tests are presented in this paper.

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Prediction of Roll Damping in the Frequency Domain Using the Discrete Vortex Method

29th International Conference on Ocean, Offshore and Arctic Engineering: Volume 1 ◽

10.1115/omae2010-21000 ◽

2010 ◽

Author(s):

Mohammad Hajiarab ◽

J. Michael R. Graham ◽

Martin Downie

Keyword(s):

Frequency Domain ◽

Model Test ◽

Theoretical Approach ◽

Three Dimensional ◽

Separated Flow ◽

Vortex Method ◽

Roll Damping ◽

Discrete Vortex ◽

Discrete Vortex Method ◽

Good Agreement

This paper describes a theoretical approach to predict roll damping for a three-dimensional barge shaped vessel in the frequency domain by matching a simple discrete vortex method (DVM), describing local separated flow, to an inviscid 3-D seakeeping code. The results are compared with model test experiments to demonstrate validity of the method. A good agreement between the model test RAO and the damped RAO is achieved.

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A Study on Viscous Roll Damping of a Box-Shaped Vessel in the Frequency Domain Using the Discrete Vortex Method

10.3940/rina.wfa.2010.02 ◽

2010 ◽

Author(s):

M Hajiarab ◽

◽

M Downie ◽

M Graham ◽

◽

...

Keyword(s):

Frequency Domain ◽

Vortex Method ◽

Roll Damping ◽

Discrete Vortex ◽

Discrete Vortex Method

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Comparison of RANS Method and Discrete Vortex Method on Simulating the Roll Motion of a Ship With Bilge Keels

Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics ◽

10.1115/omae2018-78474 ◽

2018 ◽

Author(s):

Yichen Jiang ◽

Xiaojie Zhao ◽

Zhihua Zeng ◽

Tiezhi Sun ◽

Jiawen Li ◽

...

Keyword(s):

Numerical Models ◽

Vortex Method ◽

Roll Motion ◽

Fluid Viscosity ◽

Roll Damping ◽

Discrete Vortex ◽

Discrete Vortex Method ◽

Numerical Predictions ◽

Bilge Keel ◽

Rans Method

The prediction of roll motion of a ship section with bilge keels is particularly difficult because the flow separation and vortex shedding under the hull significantly affect the behavior of roll damping. To predict the roll damping and roll motion directly, the numerical models must simulate the fluid viscosity. Recently, Reynolds-averaged Navier–Stokes (RANS) method and Discrete Vortex Method (DVM) have been applied in this area and show promising results. In this paper, we will use both methods to simulate the free roll-decay motion of a ship section with bilge keels. The numerical predictions of the roll time histories will be compared with experimental measurements. Besides, the numerically-predicted vorticity distributions at different time instants near a bilge keel will be shown and compared. Moreover, the computation times for both numerical methods will also be reported. In this work, we will conduct the comparison for a number of cases that are with different bilge-keel heights and bilge-keel installation angles. Thus, the accuracies and the computational efficiencies will be evaluated comprehensively.

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Experimental and Numerical Analysis of a 10 MW Floating Offshore Wind Turbine in Regular Waves

Energies ◽

10.3390/en13102608 ◽

2020 ◽

Vol 13 (10) ◽

pp. 2608

Author(s):

Hyeonjeong Ahn ◽

Hyunkyoung Shin

Keyword(s):

Wind Turbine ◽

Model Test ◽

Model Tests ◽

Offshore Wind ◽

East Sea ◽

Irregular Waves ◽

Offshore Wind Turbine ◽

Regular Waves ◽

Floating Offshore Wind Turbine ◽

Floating Offshore Wind Turbines

Floating offshore wind turbines (FOWTs) experience fluctuations in their platforms, owing to the various wave and wind conditions. These fluctuations not only decrease the output of the wind power generation system, but also increase the fatigue load of the structure and various equipment mounted on it. Therefore, when designing FOWTs, efficient performance with respect to waves and other external conditions must be ensured. In this study, a model test was performed with a 10 MW floating offshore wind turbine. The model test was performed by scaling down a 10 MW FOWT model that was designed with reference to a 5 MW wind turbine and a semisubmersible platform by the National Renewable Energy Laboratory and the DeepCwind project. A scale ratio of 1:90 was used for the model test. The depth of the East Sea was considered as 144 m and, to match the water depth with the geometric similarity of mooring lines, mooring tables were installed. The load cases used in the model test are combined environmental conditions, which are combined uniform wind, regular waves and uniform current. Especially, Model tests with regular waves are especially necessary, because irregular waves are superpositions of regular waves with various periods. Therefore, this study aimed to understand the characteristics of the FOWTs caused by regular waves of various periods. Furthermore, in this model test, the effect of current was investigated using the current data of the East Sea. The results obtained through the model tests were the response amplitude operator (RAO) and the effective RAO for a six degrees-of-freedom motion. The results obtained from the model tests were compared with those obtained using the numerical simulation. The purpose of this paper is to predict the response of the entire system observed in model tests through simulation.

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