Reproducing an opposing sea in an experimental wave basin based on a hindcast spectrum
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ORIGINAL ARTICLE
Reproducing an opposing sea in an experimental wave basin based on a hindcast spectrum Hidetaka Houtani1,2 · Daichi Ota2 · Harukuni Taguchi2 · Michio Ueno2 Received: 6 June 2019 / Accepted: 21 August 2020 © The Japan Society of Naval Architects and Ocean Engineers (JASNAOE) 2020
Abstract An opposing sea was generated in an experimental wave basin. Here, an opposing sea is defined as a sea in which the wave spectrum has two peaks that are separated almost 180° in direction. Such an opposing sea can be observed, for example, when wind waves coexist in the opposite direction with swells. The opposing sea generation is based on an actual sea spectrum hindcast by a third-generation wave model. The experiment was carried out in an actual sea model basin (ASMB) at National Maritime Research Institute. The ASMB is fully surrounded by 382 flap-type wave makers with incident wave absorbing capacity. The estimation of the directional spectrum by the maximum likelihood method (MLM) revealed that the opposing sea was successfully generated in the basin, although an analysis of the corresponding numerical wave field indicated that the MLM inherently estimated the spectrum with wider directional spreading. The reproduction of the opposing sea in this study indicates that any deep-sea wave field with arbitrary directional spectrum can be reproduced in such a wave basin with absorbing wave makers on the periphery. Keywords Wave generation · Opposing sea · Marine accident · Fully directional wave basin
1 Introduction Ocean waves are one of the direct or indirect causes of marine accidents. During an analysis of a marine accident, a directional spectrum representing the sea state at that time and place is important information. The sea state at the point of a marine accident cannot necessarily be expressed well by a standard spectrum, although various types of standard wave spectra have been proposed [1]. For example, it is difficult to apply a standard spectrum for a sea state, such as a crossing sea in which wind waves and swell coexist as they have different spectral peaks in wave frequency and direction [1]. However, it is reported that a large number of marine accidents occur in such crossing sea states [2, 3]. Moreover, marine accidents in opposing seas, in which the two peak directions of wind waves and swell are almost 180° different, have been also reported [4, 5]. * Hidetaka Houtani [email protected]‑tokyo.ac.jp 1
The University of Tokyo, 7‑3‑1 Hongo, Bunkyo, Tokyo, Japan
National Maritime Research Institute, 6‑38‑1 Shinkawa, Mitaka, Tokyo, Japan
2
Experimentally reproducing a marine accident in a wave basin is one approach to investigate the cause of a marine accident related to waves (e.g., [6]). In such experimental approaches, it is important to reproduce the wave field during the time of the marine accident realistically in a wave basin. The wave field of a marine accident would be reproduced more realistically in a wave basin by generating waves based on a hindcast spectrum rather than a
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