A trapezoidal large floating structure discussed in this paper is one of modules of a hexagon accommodation platform which provides life accommodation, ship docking and marine supply in deep ocean. The trapezoidal large floating structure is more than 200 meters in length and only 7 meters in moulded depth, with a high ratio of length to depth. Therefore, it is necessary to consider the 3D hydroelastic response for strength evaluation of the trapezoidal large floating structure. Flat and long structure has significant bending springing response in waves. In this paper, a large 3D hydroelasticity platform (HMOER) is used to calculate 3D hydroelastic response of trapezoidal structure. BEM wave load solver (Hydrostar) is used to calculate wave load and motion, previous 6 flexible modal modes are evaluated for hydroelastic analysis, 3D hydroelastic response involving bending is solved based on modal superposition. Frequency-domain RAOs of VBM and stress are studied by comparing hydroelasticity and rigid-body direct calculation, and then time-domain wave case is designed to pursue spring effect. Some conclusions are obtained to guide structure design.
Large floating structure is very large, generally it is made by connecting many structural modules. Large floating structure is applied for integrative supplying base and platform. It is used for aircraft taking-off and landing, fuel oil supplying, logistical support and sea sightseeing. Usually base-floating structure is very wide and it is seen flat, it is considered there is significant 3D hydroelastic responses. Ohmatsu made a research summary on VLFS (Very large floating structure), he thought that VLFS should focus on design, hydroelasticity, connector, mooring, risks and environmental effect. VLFS has very larger horizontal scale comparing to depth, it is a flat flexible structure so that hydroelasticity should be considered to evaluate structural response in waves.
Hydroelasticity is introduced from the air-elasticity, hydroelasticity is used to study the interaction of structural internal force and hydrodynamics. Hydroelasticity is proposed by Bishop and Price to study linear hydroelastic response of 2D ship structure in 1979. Wu, Price and Biship develop the 2D hydroelasticity to frequency-domain 3D hydroelasticity in 1980s. Yamamoto et al. used the momentum attack theory to carry out the nonlinear water elasticity theory. Wu et al. combined three-dimensional airworthiness theory with structural dynamics and proposed the theory of three-dimensional water elasticity. Ivo Senjanović et al studied wet natural vibrations as well as the transfer function for determining the container ship structural response to wave excitation.