scholarly journals Mean Wave Drift Forces on a Barge-Type Floating Wind Turbine Platform with Moonpools

2021 ◽  
Vol 9 (7) ◽  
pp. 709
Author(s):  
Lei Tan ◽  
Tomoki Ikoma ◽  
Yasuhiro Aida ◽  
Koichi Masuda
Keyword(s):  
Wind Turbine ◽  
Wind Turbines ◽  
Vertical Axis ◽  
Wave Drift ◽  
Floating Wind Turbine ◽  
The Mean ◽  
Drift Force ◽  
Reduction Effect ◽  
Wave Drift Forces ◽  
Drift Forces

Barge-type platforms with moonpools are a promising type of foundation for floating offshore wind turbines due to their good seakeeping performance. In this paper, the mean wave drift force on a barge-type vertical-axis floating wind turbine with multiple moonpools was investigated through physical model testing and numerical calculations using WAMIT. The focus was on the characteristics of mean drift load and its optimization potential. The present numerical results indicated that the application of moonpools was useful in reducing horizontal mean drift force at specific frequencies, and the reason was ascribed to the significant radiation effect of the resonant water oscillations in moonpools. The observed reduction effect on mean drift force was shown to be dependent on the viscous damping of moonpool resonance. The experimental results showed that the maximum response of the mean sway drift force was reduced by the gyroscopic effect of rotations of the vertical-axis wind turbine, and this reduction effect became stronger as the rotating speed of the wind turbine increased, but was weakened as wave amplitude increased. The comparisons between experimental data and potential flow predictions indicated that viscous effects should be taken into account to reasonably estimate the mean wave drift forces on barge-type floating wind turbines.

Maximum Likelihood Method as a Means to Estimate the Directional Wave Spectrum and the Mean Wave Drift Force on a Dynamically Positioned Vessel

2002 ◽  
Author(s):  
Olaf J. Waals ◽  
A. B. Aalbers ◽  
J. A. Pinkster
Keyword(s):  
Maximum Likelihood Method ◽  
Wave Spectrum ◽  
Likelihood Method ◽  
Feed Forward ◽  
Wave Drift ◽  
Directional Wave ◽  
The Mean ◽  
Drift Force ◽  
Wave Drift Forces ◽  
Drift Forces

Feed forward in control theory is a method in which real time information about system disturbance is fed into the controller to improve its performance. As such, feed forward of the wave drift forces would improve DP behavior of a ship in terms of fuel consumption as well as position keeping. In the present study the wave drift forces have been divided in a constant part and a low frequent oscillating part. The constant part directly depends on the directional wave energy spectrum. In this paper the directional spectrum and mean drift force will be estimated from six relative wave height measurements on a dynamically positioned vessel. The Extended Maximum Likelihood Method (EMLM) is known to make a reliable estimate of the directional wave spectrum from wave measurements at fixed locations in the wave field. For a wave feed forward application the EMLM had to be implemented on a moving ship. Six relative wave height probes have been installed on board of a shuttle tanker. The EMLM has been applied to these relative motions and the low frequent yawing motion has been taken into account to calculate an earth bound spectral estimate. The estimate for the spectrum is based on a 30min average and is updated every minute in a moving average algorithm. Finally, the mean wave drift force is calculated for the actual heading of the ship.

Mean Wave Drift Force on a Barge-Type Floating Wind Turbine With Moonpools

2021 ◽  
Author(s):  
Lei Tan ◽  
Tomoki Ikoma ◽  
Yasuhiro Aida ◽  
Koichi Masuda
Keyword(s):  
Wind Turbine ◽  
Vertical Axis ◽  
Offshore Wind ◽  
Hydrodynamic Performance ◽  
Vertical Axis Wind Turbine ◽  
Rotating Speed ◽  
Wave Drift ◽  
Floating Offshore Wind Turbines ◽  
Drift Force ◽  
Gyroscopic Effects

Abstract The barge-type foundation with moonpool(s) is a promising type of platform for floating offshore wind turbines, since the moonpool(s) could improve the hydrodynamic performance at particular frequencies and reduce the costs of construction. In this paper, the horizontal mean drift force and yaw drift moment of a barge-type platform with four moonpools are numerically and experimentally investigated. Physical model tests are carried out in a wave tank, where a 2MW vertical-axis wind turbine is modelled in the 1:100 scale. By varying the rotating speed of the turbine and the mass of the blades, the gyroscopic effects due to turbine rotations on the mean drift forces are experimentally examined. The wave diffraction and radiation code WAMIT is used to carry out numerical analysis of wave drift force and moment. The experimental results indicate that the influence of the rotations of a vertical-axis wind turbine on the sway drift force is generally not very significant. The predictions by WAMIT are in reasonable agreement with the measured data. Numerical results demonstrate that the horizontal mean drift force and yaw drift moment at certain frequencies could be reduced by moonpool(s).

On Approximations of the Wave Drift Forces Acting on Semi-Submersible Platforms With Heave Plates

2016 ◽  
Author(s):  
Bernard Molin ◽  
Jean-Baptiste Lacaze
Keyword(s):  
Wave Field ◽  
Scattered Wave ◽  
Diffraction Radiation ◽  
Morison Equation ◽  
Wave Drift ◽  
Horizontal Wave ◽  
Heave Plate ◽  
Drift Force ◽  
Wave Drift Forces ◽  
Drift Forces

The horizontal wave drift force acting on a vertical floating column, without then with a heave plate, is considered. Computations are performed with a diffraction-radiation code and through the Morison and Rainey equations. Focus is on wave frequencies around the heave resonance where the drift force may be significant, even though the scattered wave-field being weak. It is found that the Morison equation overpredicts the drift force while Rainey equations perform rather well.

Numerical Evaluation of Ship Maneuvering Performance in Waves

2018 ◽  
Author(s):  
Min-Guk Seo ◽  
Bo Woo Nam ◽  
Yeon-gyu Kim
Keyword(s):  
Irregular Waves ◽  
Time Signal ◽  
Regular Waves ◽  
Ship Maneuvering ◽  
Wave Drift ◽  
Mmg Model ◽  
Free Running ◽  
Drift Force ◽  
Wave Drift Forces ◽  
Drift Forces

This paper considers a numerical computation of ship maneuvering performance in waves. For this purpose, modular-type maneuvering model (MMG model) is adopted and wave drift forces and moments are included in maneuvering equation of motion. Wave drift forces ware calculated using a seakeeping program based on higher-order Rankine panel method. When calculating the wave drift force acting on a ship, the forward speed, wave heading, wave period and drift angle of the ship are considered as key parameters. It means that ship’s lateral speed is also included to calculate wave drift force. Numerical simulations are carried out in regular waves using S175 containership and computation results are validated by comparing them with results of free-running model test. Using the developed program, numerical simulation in irregular waves are, also, conducted and discussion is made on the sensitivities of time signal of wave elevation on turning performance.

Simulation of Low Frequency Motions in Severe Seastates Accounting for Wave-Current Interaction Effects

2017 ◽  
Author(s):  
Babak Ommani ◽  
Nuno Fonseca ◽  
Carl Trygve Stansberg
Keyword(s):  
Test Data ◽  
Time Domain ◽  
Low Frequency ◽  
Interaction Effects ◽  
Force Coefficients ◽  
Wave Drift ◽  
Current Interaction ◽  
Drift Force ◽  
Wave Drift Forces ◽  
Drift Forces

Today’s industry practice assumes wave drift forces on floating structures can be computed from zero current wave drift force coefficients for the stationary floater, while simplified correction models introduce current effects and slow drift velocity effects. The paper presents an alternative approach which overcomes some of the limitations of today’s procedures. The method, to be applied together with a time domain solution of the low frequency motions, is based on pre-calculation of mean wave drift force coefficients for a range of current velocities. During the low frequency motions simulation, the wave drift forces induced by the irregular waves are computed from the mean drift coefficients corresponding to instantaneous relative velocity resulting from the current and the low frequency velocities. A simple interpolation model, based on a quasi-steady assumption, is applied to obtain the drift forces in time-domain. Since calculation of the wave drift forces on Semi-submersibles in severe sea states with fully consistent methods is out of reach, a semi-empirical model is applied to correct the potential flow wave drift force coefficients. This model takes into account viscous effects, that are important in high seastates, and wave-current interaction effects. The paper compares the wave drift forces and the related low frequency motions computed by the proposed method, with results applying “standard” methods and with model test data. The test data was obtained in the scope of the EXWAVE JIP, with model tests designed to investigate wave drift forces in severe seastates and assess the wave-current interaction effects.

Viscous Drift Forces on a Semi-Submersible Type Mega-Float Comprised of Circular Cylinders

2004 ◽  
Author(s):  
Shunji Sunahara
Keyword(s):  
Potential Flow ◽  
Flow Theory ◽  
Circular Cylinders ◽  
Mooring System ◽  
Potential Flow Theory ◽  
Wave Drift ◽  
Long Wave ◽  
Drift Force ◽  
Wave Drift Forces ◽  
Drift Forces

An estimation of the wave drift forces acting on a semi-submersible type Mega-float supported by very many columns is very important in order to design its mooring system. It is known that the wave drift forces acting on a train of multiple vertical circular cylinders may be determined using the potential flow theory. However, it has recently been reported that the large wave drift forces acting on a large scale model of a semi-submersible type Mega-float, comprised of many simple circular cylinders, for long wave periods, cannot be explained by the potential flow theory. In addition the forces seem to have a significant influence on the design of its mooring system. At first, it seemed that the measured forces were viscous drift forces. The viscous drift forces are in proportion to the square of the wave particle velocity or the cube of the wave height. Of course, the existence of viscous drift forces has already been established, but it was considered that the forces acting are conditional in that the flow is apt to shed, for example on complex under-water shapes, on radiation problem, in larger height or longer period waves. Also it was thought that the forces acting on simple circular cylinders were negligibly small from the viewpoint of engineering applications. Finally, it was not accurately verified that the forces were viscous drift forces. In this study, model tests were carried out. The wave loads acting on a 16-column platform model and the hydrodynamic forces acting on each column of the model were simultaneously measured. The contribution of the viscous drift force component on the wave drift force acting on a train of vertical circular cylinders was also investigated in detail. It was confirmed that significant viscous drift forces act on circular cylinders for long wave periods. Furthermore an applicable region of viscous and potential components of the wave drift forces acting on vertical circular cylinders was obtained.

Analysis of Wave Drift Forces on a Floating Wave Energy Converter

2008 ◽  
Author(s):  
Nuno Fonseca ◽  
Ricardo Pascoal ◽  
Joa˜o Marinho ◽  
Tiago Morais
Keyword(s):  
Transfer Function ◽  
Wave Energy ◽  
Time History ◽  
Wave Energy Converter ◽  
Mooring System ◽  
Energy Converter ◽  
Wave Drift ◽  
The Mean ◽  
Wave Drift Forces ◽  
Drift Forces

Wave drift forces acting on floating wave energy converters (WEC) are often the most important loading component for the design of the mooring system. On one hand these forces may be, at least, one order of magnitude larger than wind and current forces, and on the other hand the floating structure and mooring system may respond dynamically to the slowly varying wave drift forces. The paper presents an analysis of the wave drift forces on an articulated floating wave energy converter. Particular attention is given to the effects of the wave energy extraction on the time history of the horizontal drift forces. The hydrodynamic calculations are carried out by a frequency domain Green function panel method, resulting on the transfer function of the WEC motions as well as the transfer function of the mean drift forces. The power takeoff system is represented by a simple linear model where the extracted power is related to the relative velocity in the articulation and the damper of the PTO. With the transfer function of the mean drift forces, the variance spectrum of these same forces is calculated for stationary irregular seastates, and finally time histories of the drift forces are produced for typical operational conditions.

scholarly journals Experimental and Numerical Analysis of Wave Drift Force on KVLCC2 Moving in Oblique Waves

2021 ◽  
Vol 9 (2) ◽  
pp. 136
Author(s):  
Min Guk Seo ◽  
Yoon Jin Ha ◽  
Bo Woo Nam ◽  
Yeongyu Kim
Keyword(s):  
Numerical Analysis ◽  
Ocean Engineering ◽  
Validation Data ◽  
Wave Drift ◽  
Motion Responses ◽  
Direct Pressure ◽  
Korea Research Institute ◽  
Drift Force ◽  
Wave Drift Forces ◽  
Drift Forces

In this study, experimental and numerical methods were applied to estimate surge and sway wave drift forces and yaw drift moment acting on KVLCC2, advancing in oblique wave. An experiment was carried out in the ocean engineering basin of the Korea Research Institute of Ships and Ocean Engineering (KRISO). A series of regular wave tests under various heading conditions were conducted to investigate ship motion responses and wave drift forces. A Rankine panel method based on potential flow was adopted in the numerical analysis, and the direct pressure integration method that integrates second-order pressure on the hull surface was applied to compute wave drift force. Through this study, validation data of wave drift force acting on KVLCC2 was established, and the computation capability of the potential-based numerical method was systematically analyzed.

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