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Conference programme 

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Poster session

Lead Session Chair:
Stephan Barth, Managing Director, ForWind - Center for Wind Energy Research, Germany
Yuka Kikuchi The University of Tokyo, Japan
Co-authors:
YUKA KIKUCHI (1) F P TAKESHI ISHIHARA (1)
(1) The University of Tokyo, Tokyo, Japan

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Poster
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Presenter's biography

Biographies are supplied directly by presenters at OFFSHORE 2015 and are published here unedited

Yuka KIKUCHI is a Ph.D. candidate at the University of Tokyo, School of Engineering. She has been studying Civil Engineering for six years. Her study topic is about the cost evaluation for offshore wind energy based on engineering knowledge.

Abstract

Assessment of weather window for the construction of offshore wind power plants by using wind and wave simulations

Introduction

In Japan, the two bottom-up offshore wind power plants were built as demonstration projects in order to to investigate the optimal construction techniques under typical environment conditions. It turn out that the severe wind and wave conditions lead to a significant downtime for the construction. Especially, the long-period wave due to the typhoon was a big concern for installation of substructure at Choshi wind farm, one of demonstration sites. Currently the assessment of weather window is required by using wind and wave simulations for the future construction plan of offshore wind farm in Japan.


Approach

This study clarifies the typical environmental requirements for the construction by investigating the experiences at demonstration projects and feasibility study conducted by New Energy and Industrial Technology Development Organization. Then, the wind and wave conditions are simulated by WRF and WW3, and validated with measurement data at the site of the demonstration project, Choshi wind farm. Finally, weather windows for the construction of offshore wind power plants are evaluated by using predicted wave and wind time series data and the investigated environmental requirements. The predicted downtime are validated with the construction record at Choshi wind farm.

Main body of abstract

The assessment of weather window is required when the offshore wind power plants are constructed. Japan has a severe wind and wave condition which leads to extend the construction period. Two bottom-up offshore wind farms have been installed as a demonstration projects in order to investigate the optimal construction technique under severe environmental conditions in Japan.
In this study, the environmental limitations in construction and its required duration time are investigated and summarized by learning demonstration projects and feasibility study in Japan. Then, the wind and wave conditions are simulated by WRF and WW3 at the site of the one demonstration project, Choshi wind farm. The predicted significant wave height underestimates the measurement in the low wave height region. The linear regression method is applied to modify the predictions. The modified predictions of wave height, period and wind speed agree well with measurement data at Choshi wind farm. Finally, weather windows are estimated by using predicted wind and wave time series and the investigated environmental requirements for construction. The predicted weather window agree well with the experience at Choshi wind farm.

Conclusion

Typical construction limit and required duration time are summarized about the significant wave height, significant wave period, and wind speed in relation with work vessels and construction technique.
The predicted significant wave height agree well with the measurement data, but underestimate at the low wave height region of 0.5 ~ 1.0m. Then, the bias is modified with the linear regression model. The modified predicted frequency distribution of wind speed, significant wave height and wave period agree well with measurement data.
The predicted weather window based on modified time series reproduce well the actual downtime in construction of Choshi wind farm.



Learning objectives
The purpose of this study is to investigate the construction requirements under the Japanese severe environmental condition and also to develop the assessment method of the weather window by using wave and wind simulations. The findings in this study will help the site planning and cost reduction of bottom-up offshore wind farm constructions in Japan.