A quasi-cloaking phenomenon to reduce the wave drift force on an array of adjacent floating bodies. (February 2018)

• Record Type: Journal Article
• Authors: Zhang, Zhigang; He, Guanghua; Kashiwagi, Masashi; Wang, Zhengke
• Is Part Of: Applied ocean research. Volume 71(2018)
• Page Start: 1
• Page End: 10
• Publication Date: 2018-02
• Subjects: Cloaking -- Wave drift force -- Scattered-wave energy -- HOBEM -- Wave interaction theory -- Geometric parameters; Ocean engineering -- Periodicals; 620.416205
• DOI: 10.1016/j.apor.2017.11.011
• Languages: English
• ISSNs: 0141-1187

Abstract

Highlights: A quasi-cloaking phenomenon is first found and reported in the present study with proper arrangement of outer floating bodies. The wave drift force acting on the main floating body is obviously reduced at the multiple arrangements of floating bodies due to the quasi-cloaking phenomenon. The influences of geometrical parameters of the outer surrounding cylinders on the wave drift force are systematically investigated and discussed. Abstract: The mooring of offshore floating structures, such as offshore platforms, in large waves against drift forces and rotational moments is a challenging problem in offshore engineering. To accurately investigate such problems, called positioning problems, the time-averaged steady forces of the second order known as the wave drift forces must be taken into account. Fortunately, a cloaking phenomenon occurs under certain conditions and dramatically reduces the wave drift force acting on such a floating body, as previously reported by several researchers. In the diffraction problem of water waves, cloaking refers to the condition where there is no scattering in the form of radial outgoing waves. The reduction of wave drift force on a truncated cylinder with the occurrence of cloaking phenomenon has been numerically and experimentally confirmed. In this paper, the arrangement of several small circular cylinders at regular intervals in a circle concentric with a fixed floating body is considered as an effective means of reducing the wave drift force. Using a combination of a higher-order boundary element method (HOBEM) and wave interaction theory, the influences of the geometric parameters of the outer surrounding cylinders on the wave drift force and the total scattered-wave energy are systematically investigated and discussed. A quasi-cloaking phenomenon is first found and reported in the present study, which is beneficial and flexible for application in practical engineering. More than one quasi-cloaking trigger (where a trigger is an occurrence condition) can be found simply by varying the distance between the inner and outer floating bodies.