Hydroelasticity effects on water-structure impacts

T Mai,D M Greaves,A Raby,C Mai

doi:10.1007/s00348-020-03024-3

T Mai, D M Greaves + Show 2 more

Open Access

https://doi.org/10.1007/s00348-020-03024-3

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Abstract

Local and global loadings, which may cause the local damage and/or global failure and collapse of offshore structures and ships, are experimentally investigated in this study. The research question is how the elasticity of the structural section affects loading during severe environmental conditions. Two different experiments were undertaken in this study to try to answer this question: (i) vertical slamming impacts of a square flat plate, which represents a plate section of the bottom or bow of a ship structure, onto water surface with zero degree deadrise angle; (ii) wave impacts on a truncated vertical wall in water, where the wall represents a plate section of a hull. The plate and wall are constructed such that they can be either rigid or elastic by virtue of a specially designed spring system. The experiments were carried out in the University of Plymouth’s COAST Laboratory. For the cases considered here, elasticity of the impact plate and/or wall has an effect on the slamming and wave impact loads. Here the slamming impact loads (both pressure and force) were considerably reduced for the elastic plate compared to the rigid one, though only at high impact velocities. The total impact force on the elastic wall was found to reduce for the high aeration, flip-through and slightly breaking wave impacts. However, the impact pressure decreased on the elastic wall only under flip-through wave impact. Due to the elasticity of the plates, the impulse of the first positive phase of pressure and force decreases significantly for the vertical slamming impact tests. This significant effect of hydroelasticity is also found for the total force impulse on the vertical wall under wave impacts.Graphic abstractHydroelasticity effects on water-structure impacts: a impact pressures on dropped plates; b impact forces on dropped plates; c, d, e, f wave impact pressures on the vertical walls; g wave impact forces on the vertical walls; h wave force impulses on the vertical walls: elastic wall 1 vs. rigid wall (filled markers); elastic wall 2 vs. rigid wall (empty markers)

Highlights

Hydroelasticity in marine applications is discussed in the early works of Chuang (1970), Bishop and Price (1979), Faltinsen (1997, 2000) and Faltinsen et al (2004)
There is a critical influence of the impact velocity and the relative angle between the hull and water surface on the impact loads: the impact load increases with increasing impact velocity and decreasing deadrise angle (Wagner 1932; Zhu 1995)
Kinematic and inertia effects have been identified as two types of hydroelasticity effects during an impact event (Stenius et al 2013); kinematic effects are associated with the structure response, i.e. the structural deformation changes the geometry, velocity and acceleration conditions at the fluid–structure boundary; and on the other hand inertia effects are associated with the rise time of loading of the structure

Summary

Introduction

Hydroelasticity in marine applications is discussed in the early works of Chuang (1970), Bishop and Price (1979), Faltinsen (1997, 2000) and Faltinsen et al (2004). Craft speed, and severity of environmental loadings, the localized hydroelasticity effects have become more of an issue for achieving optimized structures. A classic example being the hull-water impacts of high-speed craft which can produce large transient hydrodynamic impact loads on the hull/bottom structure (von Karman 1929). A flexible structure will be deformed under hydrodynamic loading and this deformation of the structure will affect the local flow-field between the structure and water, and thereby the spatial and temporal pressure distributions on the structure. Kimmoun et al (2009) have investigated hydroelasticity experimentally by considering wave impacts on a flexible vertical wall. Their study investigated pressure distribution on the flexible wall, and deflection of the wall under various types of impact.

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