{"created":"2021-03-01T06:22:07.461450+00:00","id":5428,"links":{},"metadata":{"_buckets":{"deposit":"fec01a1e-8d5c-4b92-922c-f4632f53589c"},"_deposit":{"id":"5428","owners":[],"pid":{"revision_id":0,"type":"depid","value":"5428"},"status":"published"},"_oai":{"id":"oai:repository.dl.itc.u-tokyo.ac.jp:00005428","sets":["6:278:395","9:233:280"]},"item_7_alternative_title_1":{"attribute_name":"その他のタイトル","attribute_value_mlt":[{"subitem_alternative_title":"浮体式洋上風車のタワーに作用する暴風波浪時の荷重の評価"}]},"item_7_biblio_info_7":{"attribute_name":"書誌情報","attribute_value_mlt":[{"bibliographicIssueDates":{"bibliographicIssueDate":"2012-09-27","bibliographicIssueDateType":"Issued"},"bibliographic_titles":[{}]}]},"item_7_date_granted_25":{"attribute_name":"学位授与年月日","attribute_value_mlt":[{"subitem_dategranted":"2012-09-27"}]},"item_7_degree_grantor_23":{"attribute_name":"学位授与機関","attribute_value_mlt":[{"subitem_degreegrantor":[{"subitem_degreegrantor_name":"University of Tokyo (東京大学)"}]}]},"item_7_degree_name_20":{"attribute_name":"学位名","attribute_value_mlt":[{"subitem_degreename":"博士(工学)"}]},"item_7_description_5":{"attribute_name":"抄録","attribute_value_mlt":[{"subitem_description":"The urgent concern about global warming from the emission of greenhouse gases has provided a strong impetus for engineers and scientists worldwide to research alternative renewable and clean energy. Wind power is one of the fastest growing renewable energy technologies. Onshore wind farms are, however, unsightly and they swallow up valuable land for agriculture and urban development. Already some countries, are considering constructing huge wind farms offshore to take advantage of the generally steadier and stronger winds found in the sea. Moreover, the wind turbines can be larger than those on land because they can be transported to the site by sea. In Japan, the offshore consist of a vast wind resource in deep water where use of conventional bottom-mounted wind turbines is not possible, and floating wind turbines are the most attractive. Thus, it is necessary to consider the effect of floater motion on the tower loading to check the serviceability of the wind turbines which are designed for the bottom-mounted systems. In this study, the theoretical formulae to predict the tower loading of floating offshore wind turbine systems in the extreme wind and wave conditions are proposed. Since the floating offshore wind turbine is affected significantly by floater motion, the conventional fixed-foundation model which is applicable to the onshore wind turbine can not be used theoretically to predict the tower loading of floating offshore wind turbine systems. In this study, SR (Sway-Rocking) model is proposed to consider the floater surge and pitch motions which have large influence on the tower loading of floating wind turbine, so that the tower loading can be estimated by the equivalent static method. In addition, the fluctuating wave load and fluctuating wind load become non-Gaussian processes with multiple peaks corresponding to different frequencies in their spectra, hence, a non-Gaussian peak factor model is proposed in order to predict wave-induced load and wind-induced load on the floating offshore wind turbine tower analytically. Furthermore, in the combination of wave-induced load and wind-induced load, the load reduction factor is proposed since the correlation between their maximum values can be neglected. The essentials of each chapter are as following: Chapter 1 is a review of current situation of offshore wind energy around the world and in Japan. It explains why it is essential to use floating wind turbine systems in Japan. The outline of this dissertation is also presented. In Chapter 2, a literature survey of research and development on floating wind turbines is presented. An overview of the research work that has been undertaken pertaining to floating wind turbine technology thus far is carried out, and based on its conclusions and limitations, objectives of this research are presented. In Chapter 3, two kinds of mooring systems: tension leg mooring and catenary mooring are considered. The methods of describing the behavior of the wind turbines installed with these two kinds of mooring systems are presented. Since surge and pitch are two main wave-induced motions, the equivalent stiffness and damping for these two modes are identified. Thus SR model is proposed, which can be used to calculate the tower loading of floating offshore wind turbine systems. Meanwhile, the problems of using conventional fixed-foundation model have been clarified. In Chapter 4, the tower loading due to surge motion as well as pitch motion is investigated separately by locking the other mode. Then their combination is performed to get the wave-induced load on the floating offshore wind turbine tower. Under irregular wave, the fluctuating wave load on wind turbine tower is a non-Gaussian process with two main peaks in its spectrum corresponding to wave peak frequency and wind turbine tower natural frequency respectively, therefore, a non-Gaussian peak factor model is proposed, so that the maximum wave-induced load under irregular wave can be predicted by the equivalent static method. Chapter 5 gives the details of the prediction of wind-induced load. Equivalent static method is adopted to estimate the maximum wind load on floating offshore wind turbine towers. The analytical formulae are proposed to predict the mean wind load, standard deviation and peak factor of fluctuating wind load. The critical parameters in the standard deviation such as mode correction factor, aerodynamic damping ratio and size reduction factor are investigated to identify their dominant influence factors and their characteristics. A consistent non-Gaussian peak factor model which can be reduced to the standard Gaussian form for a Gaussian process is proposed to estimate the maximum wind load by equivalent static method. Finally, considering the wind response correlation between along-wind direction and across-wind direction, a combination formula for wind load on towers is proposed. Chapter 6 presents the combination of wave-induced load and wind-induced load. The reason why the assumption of perfect correlation between them causes overestimation has been clarified. It is shown that the combination without considering any correlation can predict the tower loading accurately. In addition, considering the correlation between wind and wave conditions, the load reduction factor of wave-induced load is proposed, which is found to be almost constant to the mean wind speed at hub height. For tension leg system, the load reduction factor is lower than that given in IEC 61400-3 used for bottom-mounted system, while for catenary system it is a little higher than that of IEC. Chapter 7 summarizes the conclusions of this study. An equivalent SR model which can consider the floater motion is proposed, so that the wave-induced load and wind-induced load on the floating offshore wind turbine tower can be predicted analytically. In addition, the peak factor model considering the non-Gaussian characteristics of fluctuating wave load and fluctuating wind load is proposed in order to predict the maximum wave-induced load and maximum wind-induced load on the floating offshore wind turbine tower analytically. Furthermore, the load reduction factor is proposed in the combination of wave-induced load and wind-induced load by clarifying their characteristics, considering the correlation between wind and wave conditions.","subitem_description_type":"Abstract"}]},"item_7_full_name_3":{"attribute_name":"著者別名","attribute_value_mlt":[{"nameIdentifiers":[{"nameIdentifier":"11335","nameIdentifierScheme":"WEKO"}],"names":[{"name":"許, 楠"}]}]},"item_7_identifier_registration":{"attribute_name":"ID登録","attribute_value_mlt":[{"subitem_identifier_reg_text":"10.15083/00005419","subitem_identifier_reg_type":"JaLC"}]},"item_7_select_21":{"attribute_name":"学位","attribute_value_mlt":[{"subitem_select_item":"doctoral"}]},"item_7_subject_13":{"attribute_name":"日本十進分類法","attribute_value_mlt":[{"subitem_subject":"558","subitem_subject_scheme":"NDC"}]},"item_7_text_22":{"attribute_name":"学位分野","attribute_value_mlt":[{"subitem_text_value":"Engineering (工学)"}]},"item_7_text_24":{"attribute_name":"研究科・専攻","attribute_value_mlt":[{"subitem_text_value":"Department of Civil Engineering, Graduate School of Engineering (工学系研究科社会基盤学専攻)"}]},"item_7_text_4":{"attribute_name":"著者所属","attribute_value_mlt":[{"subitem_text_value":"東京大学大学院工学系研究科社会基盤学専攻"}]},"item_creator":{"attribute_name":"著者","attribute_type":"creator","attribute_value_mlt":[{"creatorNames":[{"creatorName":"Xu, Nan"}],"nameIdentifiers":[{"nameIdentifier":"11334","nameIdentifierScheme":"WEKO"}]}]},"item_files":{"attribute_name":"ファイル情報","attribute_type":"file","attribute_value_mlt":[{"accessrole":"open_date","date":[{"dateType":"Available","dateValue":"2017-06-01"}],"displaytype":"detail","filename":"20120907.pdf","filesize":[{"value":"2.8 MB"}],"format":"application/pdf","licensetype":"license_note","mimetype":"application/pdf","url":{"label":"20120907.pdf","url":"https://repository.dl.itc.u-tokyo.ac.jp/record/5428/files/20120907.pdf"},"version_id":"a5614c7b-74d3-42a2-95ed-cc3d4f751200"}]},"item_language":{"attribute_name":"言語","attribute_value_mlt":[{"subitem_language":"eng"}]},"item_resource_type":{"attribute_name":"資源タイプ","attribute_value_mlt":[{"resourcetype":"thesis","resourceuri":"http://purl.org/coar/resource_type/c_46ec"}]},"item_title":"Prediction of Tower Loading of Floating Offshore Wind Turbine Systems in the Extreme Wind and Wave Conditions","item_titles":{"attribute_name":"タイトル","attribute_value_mlt":[{"subitem_title":"Prediction of Tower Loading of Floating Offshore Wind Turbine Systems in the Extreme Wind and Wave Conditions"}]},"item_type_id":"7","owner":"1","path":["280","395"],"pubdate":{"attribute_name":"公開日","attribute_value":"2013-10-02"},"publish_date":"2013-10-02","publish_status":"0","recid":"5428","relation_version_is_last":true,"title":["Prediction of Tower Loading of Floating Offshore Wind Turbine Systems in the Extreme Wind and Wave Conditions"],"weko_creator_id":"1","weko_shared_id":null},"updated":"2022-12-19T03:47:01.304073+00:00"}