Numerical Study of Non-Linear Dynamic Behavior of an Asymmetric Rotor for Wave Energy Converter in Regular Waves

This study conducted a numerical investigation on the non-linear motion problems between a Salter duck-type rotor and large waves using CFD simulations. Regular waves of five different wave heights were generated. First, the linear motion of the rotor from the CFD simulation was verified by comparing it with the existing experimental and frequency domain analysis results. Then, a series of CFD simulations were performed to investigate the non-linear motions of the rotor. In the case of a lower wave height, the CFD simulation results were in good agreement with the experimental and frequency domain analysis results. However, as the wave height increased, the resonance periods were different in each other. In addition, the magnitudes of normalized pitch motions by the wave heights decreased as the wave heights increased. To investigate the aforementioned phenomena, the pitch motion equation was examined using separate CFD simulations. The results showed that changing the restoring moments induced changes in the maximum pitch motions and magnitudes of the normalized pitch motions. In the case of a higher wave height, non-linear phenomena and the changing restoring moments induced non-linear motion.

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Frequency domain analysis for non-linear Volterra systems with a general non-linear output function

International Journal of Control ◽

10.1080/00207170701516389 ◽

2008 ◽

Vol 81 (2) ◽

pp. 235-251 ◽

Cited By ~ 17

Author(s):

X. J. Jing ◽

Z. Q. Lang ◽

S. A. Billings

Keyword(s):

Frequency Domain ◽

Domain Analysis ◽

Frequency Domain Analysis ◽

Output Function ◽

Volterra Systems ◽

Non Linear

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Behaviour of a Suspended Wellbay Module and Flare Tower in Waves During Transit to Shore

Volume 1: Offshore Technology; Offshore Geotechnics ◽

10.1115/omae2019-95001 ◽

2019 ◽

Author(s):

Hoi-Sang Chan ◽

Evren Armaoğlu ◽

Matthew Thomson ◽

Alistair Garner

Keyword(s):

Frequency Domain ◽

Time Domain Analysis ◽

Domain Analysis ◽

Frequency Domain Analysis ◽

Irregular Waves ◽

Scale Model ◽

Response Analysis ◽

Regular Waves ◽

The North ◽

Response Amplitude Operators

Abstract The extended lift operation to deliver the Wellbay module (M5) combined with the Flare Tower (M8) from the Miller Platform in the North Sea to the shore using the Semi-Submersible Crane Vessel S7000 was restricted by the clearances between M5/M8 and the vessel crane booms. A method to calculate the clearances of the M5/M8 normal to the vessel crane booms has been developed and used in a frequency-domain response analysis to define operability limits. Investigations based on a series of scale model tests in regular waves and irregular short-crested waves including motion decay tests in calm water, conducted by the Maritime Research Institute (MARIN) in the Netherlands, were also made to further evaluate the behaviour of the suspended M5/M8 on S7000’s main hooks during transit. The time series of decay motions of the suspended M5/M8 obtained from the decay motion tests and a time domain analysis are compared and used to derive rigging damping. The numerical results of the frequency-domain analysis are validated with the experimental data for response amplitude operators (RAOs) found in regular waves and pink noise waves, significant and 3 hour most probable maximum/minimum (MPM) responses of interest in irregular waves.

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Numerical Study on Sea Keeping Performances of Ship by Exact Linear 3-D Potential Method

Volume 4: Materials Technology; Ocean Engineering ◽

10.1115/omae2007-29170 ◽

2007 ◽

Author(s):

N. M. Golam Zakaria ◽

M. S. Baree

Keyword(s):

Frequency Domain ◽

Wave Height ◽

Time Domain ◽

Domain Analysis ◽

Potential Method ◽

Frequency Domain Analysis ◽

Numerical Calculations ◽

Irregular Waves ◽

Linear Potential ◽

Time Domain Simulation

This paper deals with the numerical calculations of sea-keeping performances of ship in irregular sea condition. Here linear potential theory has been applied for describing the fluid motion and 3-D sink-source technique has been used to determine hydrodynamic forces for surface ship advancing in waves at constant forward speed. Numerical coding based on 3-D potential method has been tested in an extensive manner keeping an eye with the criteria recommended by various ITTC committees [1]. The numerical accuracy of the coding has been examined using some experiment results as well as some other contemporary numerical calculations given by some authors for the case of frequency domain analysis. Taking a typical Panamax Container Vessel and in order to simulate its sea-keeping performances in real sea condition, the frequency domain analysis has been performed. The result is then used for time domain simulation in short crested irregular waves. Unequal frequency spacing has been taken into account to get longer simulation time and also empirical nonlinear roll damping has been taken in the way of time domain simulation. From this time domain simulation, relative wave height has been calculated which could sometimes damage deck equipment as well as posing a risks to personnel in severe sea condition. The effect of speed & wave direction on relative wave height has been considered and finally the numerical results of the maximum and significant values of irregular relative wave heights for these conditions are discussed.

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