In this paper, linear and frequency-domain hydroelastic analysis is performed for investigating the behavior of a free floating, annular and flexible plate. A "dry" mode superposition approach is utilized, where the flexible mode shapes are determined through the derivation of analytical expressions. The diffraction/radiation problem is solved using a higher-order boundary element method. Focus is given on the effect of the flexural rigidity and of the internal to external radius ratio on the physical quantities describing the behavior of the plate. Resonance effects of the fundamental modes of water motion in the interior circular region of the annular plate are also discussed.
The broad interest in utilizing efficiently the ocean space for the realization of various infrastructures satisfying emerging social needs has boosted the development of the technology for Very Large Floating Structures (VLFSs) (Wang et al., 2008). A fundamental feature of a VLFS is its structural flexibility, resulting from the existence of large horizontal dimensions compared to its vertical one. Thus, the elastic response of a VLFS is more dominant compared to its rigid body motions and the assessment of the performance of a VLFS requires inclusion of hydroelasticity in the corresponding numerical analysis.
Up to now, hydroelastic analysis of VLFS of various shapes has been implemented by many researchers through the development of several numerical methods, which can be categorized (Loukogeorgaki et al., 2014) into direct (e.g. Kashiwagi, 1998b; Namba and Ohkusu, 1999; Khabakhpasheva and Korobkin, 2002; Ohkusu and Namba, 2004; Andrianov and Hermans, 2006a; 2006b; Eatock Taylor, 2007; Kim et al., 2007) and mode superposition methods. In the latter methods, the generalized (flexible) modes concept is introduced for describing the structural deformations in addition to the six rigid-body modes, which in turn requires the calculation of flexible mode shapes. In most cases, the effect of the surrounding fluid on the aforementioned calculation is not taken into account; therefore, the hydroelastic analysis is implemented utilizing "dry" mode shapes, which are determined through either analytical expressions (modal functions) (e.g. Newman, 1994; Wu et al., 1995; Kashiwagi, 1998a; Eatock Taylor and Ohkusu, 2000) or numerical models based on the Finite Element Method (FEM) (e.g. Taghipour et al., 2006). Alternatively, by including the added mass and the hydrostatic-gravitational stiffness in a solution of the eigenvalue problem, the use of "wet" mode shapes in the hydroelastic analysis can be realized (Hamamoto and Fujita, 2002; Loukogeorgaki et al., 2012).