Estimation of on-site directional wave spectra using measured hull stresses on 14,000 TEU large container ships
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ORIGINAL ARTICLE
Estimation of on‑site directional wave spectra using measured hull stresses on 14,000 TEU large container ships Xi Chen1 · Tetsuo Okada1 · Yasumi Kawamura1 · Taiga Mitsuyuki1 Received: 11 April 2019 / Accepted: 30 July 2019 © The Author(s) 2019
Abstract Container ships are becoming larger and larger in recent years, requiring more evident assurance of the structural safety. To achieve this, it is essential to grasp actual stress history experienced by the ship structures to facilitate efficient design and maintenance, and to use them for optimal operation of the ship. To perform accurate estimation of these stress histories, it is important to precisely estimate the sea state which the ship is actually encountering. In this study, the authors studied a new method to estimate directional wave spectra using measured ship responses and discussed the following three cases. The first one is the combination of two components, vertical bending stress and horizontal bending stress. The second one is the combination of three components, vertical bending stress, horizontal bending stress and double bottom bending stress. The last one is the combination of three components of ship motion (pitch, roll and heave). The estimated sea states are compared with the ocean wave hindcast database and radar data, and then, accuracy and selection of appropriate combination of the responses are discussed. Keywords Container ship · Monitoring · Measurement · Wave spectrum · Vertical bending stress · Horizontal bending stress · Double bottom bending stress
1 Introduction Container ships are becoming larger and larger in recent years, requiring more evident assurance of the structural safety. To achieve this, it is essential to grasp actual stress history experienced by the ship structures to facilitate efficient design and maintenance, and to use them for optimal operation of the ship. To perform accurate estimation of these stress histories, it is important to precisely estimate the sea state which the ship is actually encountering. Okada [1] proposed a concept to evaluate the directional wave spectrum from the measurement results of the motion * Xi Chen chin‑xi‑[email protected] Tetsuo Okada okada‑[email protected] Yasumi Kawamura kawamura‑yasumi‑[email protected] Taiga Mitsuyuki mitsuyuki‑taiga‑[email protected] 1
Faculty of Engineering, Yokohama National University, Kanagawa 240‑8501, Japan
and stress of the hull, and to use it to estimate the stress history at any parts of the ship hull in combination with the associated stress response functions. This kind of concept is considered to be realized by giving shape to the digital twin as illustrated in Fig. 1. The digital data consist of the Basic Ship Model (upper middle in Fig. 1) as well as the Basic Ship Characteristics (lower middle in Fig. 1) which include response functions throughout all the parts of the hull structures. On the other hand, onboard the actual ship, real-time monitoring is conducted with regard to various information including ship motion and stresses at spec
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