Effects of Four Moon Pools on a Floating System Installed With Twin-VAWTs

2019 ◽  
Author(s):  
Tomoki Ikoma ◽  
Mitsuru Nakamura ◽  
Satsuya Moritsu ◽  
Yasuhiro Aida ◽  
Koichi Masuda ◽  
...  
Keyword(s):  
Vertical Axis ◽  
Linear Potential ◽  
The Moon ◽  
Vertical Axis Wind Turbine ◽  
Floating Structure ◽  
Gyroscopic Moment ◽  
Motion Responses ◽  
Floating System ◽  
Heave Motion ◽  
Linear Potential Theory

Abstract This paper describes characteristics of motion responses and tether tensions of a floating structure with four moon pools, on which one or two vertical axis wind turbine models are installed. Effects of several moon pools founded in a floating structure on motion characteristics have been unclear. In this study, the authors proposed a twin-VAWT installed floating system, which was a pontoon based structure. However four moon pools were set on. The study conducted model experiments in a wave tank using regular waves with 0.6 to 2.0 seconds in wave periods and 0.02 and 0.04 m in wave height. The model had four moon pools and was installed with one or two vertical axis turbine models. From it, gyroscopic moment effects were investigated. Besides, the study performed numerical calculations with the linear potential theory based method which were a Green function method. As a results, responses of the twin-turbine model are not affected by gyroscopic moment. The study discusses motion responses and tether tensions with nonlinear behaviours from mainly the experimental results. Also the effect of moon pools were investigated from the calculations. From comparisons of motion results on calculation models with same displacement but different draft, the results suggested that not only heave motion but also roll motion could be reduced because of the moon pools if the size of the moon pools were optimized.

Response Characteristics of a Floating Structure With Moon Pools Installed With Vertical Axis Wind Turbines

2019 ◽  
Author(s):  
Mitsuru Nakamura ◽  
Tomoki Ikoma ◽  
Hiroaki Eto ◽  
Yasuhiro Aida ◽  
Koichi Masuda
Keyword(s):  
Wind Turbines ◽  
Vertical Axis ◽  
Linear Potential ◽  
Floating Structure ◽  
Response Characteristics ◽  
Gyroscopic Moment ◽  
Vertical Axis Wind Turbines ◽  
Motion Responses ◽  
Floating System ◽  
Linear Potential Theory

Abstract This paper describes characteristics of motion responses and tether tensions of a floating structure with four moon pools, on which one or two vertical axis wind turbines are installed. In this study, the authors proposed a twin-VAWT installed floating system, which was a pontoon based structure. However four moon pools were set on. The study conducted model experiments in a wave tank using regular waves with 0.6 to 2.0 seconds in wave periods and 0.02 and 0.04 m in wave height. The model had four moon pools and was installed with one or two vertical axis turbine models. From it, gyroscopic moment effects were investigated. Besides, the study performed numerical calculations with the linear potential theory based method which were a Green function method. As a results, responses of the twin-turbine model are not affected by gyroscopic moment. The study discusses motion responses and tether tensions with nonlinear behaviours from mainly the experimental results.

Study of Motion Performance of a Floating System With Four Moonpools and a VAWT

2021 ◽  
Author(s):  
Lei Tan ◽  
Satsuya Moritsu ◽  
Tomoki Ikoma ◽  
Yasuhiro Aida ◽  
Koichi Masuda
Keyword(s):  
Potential Theory ◽  
Theoretical Calculations ◽  
Model Tests ◽  
Hydrodynamic Performance ◽  
Linear Potential ◽  
Gyroscopic Effect ◽  
Floating Foundation ◽  
Motion Responses ◽  
Floating System ◽  
Linear Potential Theory

Abstract In this paper the hydrodynamic performance of a barge-type floating foundation installed with four moonpools and a VAWT was investigated through model tests and theoretical calculations. The characteristics of wave-induced motion responses and tether tensions and the effects of turbine rotations were examined. Physical model tests were conducted in a wave tank using regular waves with the wave period ranging from 0.6 to 1.6 seconds and 0.01 or 0.02 meters in amplitude. A 2-MW-class VAWT was modelled with a scale ratio of 1/100 in the experiments. By varying the mass and the rotational speed of the turbine, gyroscopic moment effects were studied. In addition, numerical calculations based on the linear potential theory and Green function method were carried out to estimate motion responses and tether tensions. The present results indicate that the gyroscopic effect due to turbine rotations can be profound. It was found that the first-order motions of the floating system were substantially reduced by the gyroscopic effect, while the second-order motions and tether tensions may be significantly increased. Moreover, the viscous damping of water motions in moonpools was found not negligible. As a result, theoretical models based on linear potential theory should be used with care in hydrodynamic analysis with regard to the floating systems with VAWT rotations. In addition, the present in-house program code was validated against WAMIT through comparing hydrodynamic predictions of a floating foundation with four moonpools, with reasonable agreement.

Characteristics of OWC Type WEC Dampers Installed on a Very Large Floating Structure

2020 ◽  
Author(s):  
Tomoki Ikoma ◽  
Shoichiro Furuya ◽  
Yasuhiro Aida ◽  
Koichi Masuda ◽  
Hiroaki Eto
Keyword(s):  
Wave Energy ◽  
Sea Water ◽  
Prediction Method ◽  
Hydrodynamic Performance ◽  
Floating Body ◽  
Hydrodynamic Characteristics ◽  
Linear Potential ◽  
Floating Structure ◽  
Combined System ◽  
Floating System

Abstract Oscillating water column (OWC) type wave energy converters (WECs) have been researched and developed. OWC WECs are relatively friendly to maintain them in operation because all of mechanical units are set above a sea water surface. In addition, a feature of an OWC device is similar to an air dumper system. Thus, it should be possible not only to harvest wave energy but also to reduce motion of a floating system at the same time. As well as WEC system should be used with other ocean renewable energies as a combined system. This paper describes hydrodynamic characteristics of OWC devices and wave fields around them of multi-OWC devices equipped large floating structures. For this research, the linear potential theory based in-house programme code was applied to calculate hydrodynamic performance of OWC regions and elastic motion behaviours of the structures. Besides, calculation results were compared with some experimental results of characteristics of OWC devices on reference papers published. Then we proved validity of the calculation method. We have quantitatively summarized how much the reduction effect can be seen according to the aircushion placement and the number of aircushions on the floating body. the paper investigated arrangement of OWC devices on the floating structure with several variations. Using the prediction method, effects of arrangement of OWC devices on the performances are investigated.

Numerical Modeling and Experimental Comparison of the Response of Elastically Connected Barges

2018 ◽  
Author(s):  
Daniele Dessi ◽  
Edoardo Faiella
Keyword(s):  
Numerical Model ◽  
Model Development ◽  
Numerical Code ◽  
Experimental Comparison ◽  
Mooring Line ◽  
Linear Potential ◽  
Offshore Platforms ◽  
Floating System ◽  
The Time Domain ◽  
Linear Potential Theory

This paper presents a numerical model for the investigation of some hydroelastic issues related to floating systems used for the transportation and installation of components of offshore platforms, e.g., topsides. The system consists of two symmetric barges, linked together by the carried structure to form a catamaran-like layout. The flexibility of the transported structure may allow for proper excitation of the float-over system under oblique wave conditions at certain wave lengths, both during transportation and installation phases. The developed numerical code, based on multi-body dynamics and linear potential theory regarding the calculation of hydrodynamic loads, allows for a robust and fast description of the flexible floating system dynamics, including also the effect of mooring-line dynamics in the time-domain. Comparison with experimental data from a previous experimental campaign [1] shows that, notwithstanding the simplifying assumptions in the numerical model development, the amplitude of the relative pitch rotation between the barges due to the system flexibility can be properly described with the present approach.

A Prediction Method of Hydroelastic Motion of Aircushion Type Floating Structures Considering With Draft Effect Into Hydrodynamic Forces

2008 ◽  
Author(s):  
Tomoki Ikoma ◽  
Masato Kobayashi ◽  
Koichi Masuda ◽  
Chang-Kyu Rheem ◽  
Hisaaki Maeda
Keyword(s):  
Potential Theory ◽  
Water Waves ◽  
Large Scale ◽  
Prediction Method ◽  
Linear Potential ◽  
Wave Loads ◽  
Floating Structure ◽  
Model Experiments ◽  
Very Large Floating Structure ◽  
Linear Potential Theory

An aircushion type floating structure can prevent to enlarge the wave drifting force restraining the hydroelastic response of it in water waves. The floating structure should be large scale to incident waves in order to make the best use of such advantages, i.e. it is a very large floating structure. The linear potential theory is useful to easily handle the wave force etc. on the aircushion type floating structure theoretically because it is predicted that its theory can give good results of behaviors of water elevation within aircushions and pressure and of wave loads on the structure qualitatively. The authors have confirmed from our past model experiments that non-linear effect does not always increase but for some exceptions. A prediction method of hydroelastic responses for the aircushion type very large floating structure by using the three-dimensional linear potential theory is shown in this paper. The validity of the method is proven and the application of the method is investigated by comparing the theoretical results with the results of the past model experiments.

scholarly journals Nonlinear Lifting Line Theory Applied to Vertical Axis Wind Turbines: Development of a Practical Design Tool

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
David Marten ◽  
Georgios Pechlivanoglou ◽  
Christian Navid Nayeri ◽  
Christian Oliver Paschereit
Keyword(s):  
Wind Turbine ◽  
Large Scale ◽  
Unsteady Aerodynamics ◽  
Vertical Axis ◽  
Design Tool ◽  
Offshore Wind ◽  
Vertical Axis Wind Turbine ◽  
Floating Structure ◽  
Horizontal Axis Wind Turbine ◽  
Lifting Line

Recently, a new interest in vertical axis wind turbine (VAWT) technology is fueled by research on floating support structures for large-scale offshore wind energy application. For the application on floating structures at multimegawatt size, the VAWT concept may offer distinct advantages over the conventional horizontal axis wind turbine (HAWT) design. As an example, VAWT turbines are better suited for upscaling, and at multimegawatt size, the problem of periodic fatigue cycles reduces significantly due to a very low rotational speed. Additionally, the possibility to store the transmission and electricity generation system at the bottom, compared to the tower top as in a HAWT, can lead to a considerable reduction of material logistics costs. However, as most VAWT research stalled in the mid 1990s, no sophisticated and established tools to investigate this concept further exist today. Due to the complex interaction between unsteady aerodynamics and movement of the floating structure, fully coupled simulation tools modeling both aero and structural dynamics are needed. A nonlinear lifting line free vortex wake (LLFVW) code was recently integrated into the open source wind turbine simulation suite qblade. This paper describes some of the necessary adaptions of the algorithm, which differentiates it from the usual application in HAWT simulations. A focus is set on achieving a high robustness and computational efficiency. A short validation study compares LLFVW results with those of a two-dimensional (2D) unsteady Reynolds-averaged Navier–Stokes (URANS) simulation.

Calculating the aerodynamics of vertical axis wind turbines

2012 ◽  
Vol 34 (3) ◽  
pp. 169-184 ◽  
Author(s):  
Hoang Thi Bich Ngoc
Keyword(s):  
Wind Turbine ◽  
Incidence Angle ◽  
Vertical Axis ◽  
Rotor Blades ◽  
Vertical Axis Wind Turbine ◽  
Horizontal Axis Wind Turbine ◽  
Velocity Triangle ◽  
Relationship Of ◽  
The Relationship

Vertical axis wind turbine technology has been applied last years, very long after horizontal axis wind turbine technology. Aerodynamic problems of vertical axis wind machines are discussible. An important problem is the determination of the incidence law in the interaction between wind and rotor blades. The focus of the work is to establish equations of the incidence depending on the blade azimuth, and to solve them. From these results, aerodynamic torques and power can be calculated. The incidence angle is a parameter of velocity triangle, and both the factors depend not only on the blade azimuth but also on the ratio of rotational speed and horizontal speed. The built computational program allows theoretically selecting the relationship of geometric parameters of wind turbine in accordance with requirements on power, wind speed and installation conditions.

Design and Analysis of Vertical Axis Wind Turbine

2017 ◽  
Author(s):  
Prof. R.K. Bhoyar ◽  
Prof. S.J. Bhadang ◽  
Prof. N.Z. Adakane ◽  
Prof. N.D. Pachkawade
Keyword(s):  
Wind Turbine ◽  
Vertical Axis ◽  
Vertical Axis Wind Turbine
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