Hydroelastic Response Of Very Large Floating Structure Research Articles

Oscillating Wave Surge Converter-Type Attachment for Extracting Wave Energy While Reducing Hydroelastic Responses of Very Large Floating Structures

Abstract This paper presents an oscillating wave surge converter (OWSC)-type attachment, comprising a submerged vertical flap connected to the fore edge of a very large floating structure (VLFS) with hinges and linear power take-off (PTO) systems, for extracting wave energy while reducing hydroelastic responses of VLFS. In terms of reductions in hydroelastic responses of VLFS, the OWSC-type attachment is better than the recently proposed raft wave energy converter (WEC)-type attachment for relatively short waves (T < 7 s) and better than the conventional anti-motion device comprising a submerged vertical flap rigidly connected to the fore edge of VLFS for all wave periods. Importantly, the horizontal wave force acting on the submerged flap for the OWSC-type attachment is smaller than that for the conventional anti-motion device, leading to a more economical mooring system. In terms of wave energy extraction, the OWSC-type attachment is better than the raft WEC-type attachment for intermediate and long waves (T ≥ 7 s). In addition, for maximizing power production, the required flap length for the OWSC-type attachment is much smaller than the required pontoon length for the raft WEC-type attachment (about λ/10 as compared to about λ/3, where λ is the incident wavelength).

Boussinesq-Hydroelasticity coupled model to investigate hydroelastic responses and connector loads of an eight-module VLFS near islands in time domain

When a very large floating structure (VLFS) is deployed not far from the shore line or near the island, the ocean waves and hydroelastic responses of VLFS could be greatly influenced by the complicated topography and inhomogeneous wave. Based on the Boussinesq equation and Cummins’ theory, a three-step time-domain hydroelastic method for VLFS on depth-varying seabed and inhomogeneous waves is established, called Boussinesq-Hydroelasticity coupled method. An eight-module semi-submersible VLFS is studied for numerical assessment using RMFC (rigid module flexible connecto) model; meanwhile, the wave evolution simulation is carried out based on Boussinesq equation. The motions of each module and connector loads are investigated by considering the depth-varying seabed and inhomogeneous wave. Furthermore, the model test is carried out in wave tank for validating the correctness of the numerical results and the Boussinesq-Hydroelasticity coupled method. There is significant shelter effect on the floating bodies arranged behind the island. When the water depth is assumed to be constant by ignoring the influence of seabed topography, the load of connectors will be underestimated.

Hydroelastic responses of a 3-module VLFS in the waves influenced by complicated geographic environment

During the Very Large Floating Structure (VLFS) is deployed not far from the shore line or near the island, the ocean waves and hydroelastic responses of VLFS could be greatly influenced by the complicated geographic environment, particularly for the depth-varying seabed. Firstly, the extreme wave parameters of different recurrence periods at the deployed location are solved by the numerical simulations of wave evolution and propagation in an archipelagic water field using the third-generation wave model. The numerical results are compared with the data from the on-site measurement and model test in a shallow water wave basin. Secondly, one hydroelastic numerical coupled model of the floating structure responding to the waves in shallow water with a specified seabed profile is proposed and validated by comparing with the model test results. Finally, based on the above model, the hydroelastic responses of the VLFS in the waves influenced by complicated geographic environment are obtained. It is concluded that the wave statistics experiences obviously changes when propagating and approaching towards the island; meanwhile, the complicated seabed profile has an apparent influence on the hydroelastic responses of the VLFS.

Reducing hydroelastic responses of pontoon-type VLFS using vertical elastic mooring lines

This paper is concerned with the reduction of hydroelastic responses of pontoon-type very large floating structures (VLFS) via the use of vertical elastic mooring lines connected at the fore and aft edges of VLFS to the seabed. These vertical mooring lines are used in addition to the mooring dolphin-rubber fender system that is used to restrict the horizontal movement of VLFS. The considered rectangular shaped VLFS is modeled as a Mindlin plate floating on an ideal fluid in which the linear potential theory is applicable. The hydroelastic analysis of VLFS with vertical mooring lines modeled as vertical elastic springs is performed in the frequency domain by using the hybrid finite element–boundary element (FE-BE) method. This study examines the effectiveness of vertical elastic mooring lines in reducing hydroelastic responses for various wavelengths, incident wave angles and aspect ratios. The stiffnesses of the mooring lines are optimized for maximum reduction in the hydroelastic response by using the Differential Evolution algorithm. It was found that hydroelastic responses of VLFS could be significantly reduced by using vertical elastic mooring lines with optimal stiffnesses.