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UBC Theses and Dissertations

Dynamic response of a floating structure with a flexible air chamber Shiratani, Hiroshi


Although floating structures have been widely used for many purposes, their dynamic response in waves limits the extent of their usefulness. Thus, approaches to reducing their response in waves would extend the range of prospective applications of such structures. In this context, a new type of floating structure is proposed in the present study, intended to achieve a notable reduction of the dynamic response to waves. The proposed structure is equipped with a flexible air chamber bounded by a rubber membrane attached on the bottom of a rectangular body, and a piston between the body and the air chamber. The objective of the present study is to assess whether the proposed structure is practically effective for the reduction of the dynamic response. First, a preliminary examination was conducted to understand the basic characteristics of the proposed structure. In this examination, two methods to predict the hydrostatic states of the proposed structure were introduced. An experimental investigation of the dynamic response of the proposed structure was carried out in the wave flume of the Hydraulics Laboratory of the Department of Civil Engineering, the University of British Columbia. In the free condition, the motions of the experimental model under waves were recorded with a video camera. Then, the dynamic responses were obtained from the records. The performance of the proposed structure was evaluated through a comparison with that of the equivalent rectangular structure. In addition, for heave mode, a closed set of solutions of simplified governing equations was introduced, and the predicted heave responses were compared with the measured responses. The video images of the experimental model under waves were examined to understand qualitatively the dynamic behavior. Furthermore, the dynamic response characteristics in the heave mode were examined analytically. A primary conclusion of this study is that the proposed structure with a suitably proportioned air chamber could have the ability of reducing the dynamic response, and a properly designed piston could enhance the structure's performance if its roll motion is restrained externally.

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