ABSTRACT

In this study, the problem of linear wave propagation over a fixed and floating poroelastic medium is studied theoretically. The floating poroelastic medium is assumed to be homogeneous, isotropic and elastic, and allows slightly heaving motion. Lan-Lee's poro-elastomer theory is extended to derive a new analytical solution for describing the problem. Using general solutions for each region and the matching boundary conditions, a set of simultaneous equations is thus developed and solved numerically. Wave reflection, transmission and energy dissipation induced by different key parameters of a poroelastic medium are studied.

INTRODUCTION

Humans have imitated the floating natural vegetation to build floating islands centuries ago. The ancient Peruvian population built the Islands of Uros in Lake Titicaca to escape violent attacks from more aggressive tribes of the Collas and the Inca. In order to protect the land demand for economic development of densely populated coastal cities and areas, the relevant research on wave defense and interaction between floating breakwaters, offshore floating platforms (Lee and Lee, 1993; Oliver et al., 1994; Khabakhpasheva and Korobkin, 2002; Nakamura et al., 2003; Diamantoulaki et al., 2008; Zhao et al., 2012; Ruol et al., 2013; Yeh et al., 2013; Burcharth et al., 2015; Tsai et al., 2016; Dolatshah et al., 2018; Emami and Gharabaghi, 2018; Yu et al., 2018) and VLFS (Very Large Floating Structures) (Takagi, 1996; Utsunomiya and Watanabe, 2006; Wang and Tay, 2011; Lamas-Pardo et al., 2015; Shirkol et al., 2016; Sun et al., 2018) in coastal and offshore areas have been carried out in recent decades. In addition, ecological floating islands have been widely recognized as an effective tool for habitat restoration in many European countries and the United States (Winston et al., 2013), and have been commercially used in water environments in many countries. The composition of the ecological floating island basically inherits the natural vegetation floating island with permeability and softness (deformability). Most of the research on artificial ecological floating islands focuses on issues such as ecological environment, water quality improvement, and landscape maintenance (Nakamura et al., 1996; Francis, 2009; Winston et al., 2013). Research on the reduction of wave energy to protect waterfront functions is less intensive and generally appears in case studies (Gaffney and Munoz, 2010; Zhu and Zou, 2016). Due to the flexibility of soft material, the deformation induced by water waves disturbs flow field in the vicinity of the structure when compared with impermeable reflective concrete counterparts (Lan, 2018). For the wave attenuation effect caused by the permeable structures, different structural material properties have different wave damping characteristics, such as the flow configurations of Darcy, Darcy-Forchheimer and vegetation drag resistance, etc. Therefore, in academic and practical studies, ecological floating islands need to consider both the flexibility and permeability of the floating medium composition, such as the poroelastic type.

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