Session: 06-13-01 Towed and Undersea Cables and Pipes, Mooring, and Buoy Technology

Paper Number: 79783

79783 - Model Experiments and Numerical Simulations on GPS Buoy With Steep Wave Mooring 

Since several runout accidents of GPS buoy moored with catenary chain were reported, new mooring design for GPS buoy was proposed¹⁾. The runout accidents were due to the breakage of the worn chain in touch down zone. Therefore, the new mooring design is composed with mooring line including sinker and buoyancy modules which form the steep wave configuration. Hereinafter the new mooring design is called “steep wave mooring” since the global form of the mooring line is similar with the steep wave configuration for flexible riser. The main purpose of applying the steep wave mooring is to decouple the vessel motions from the sinker point of the mooring line and eliminating the risk of the chain wear at the sinker point.

1/20 scaled model experiment was conducted to investigate the possibility of the line-to-line collision and entanglement of the mooring lines in moderate environmental condition e.g., 3-5 year return period wave and current conditions. Additionally, 1/60 scaled model experiment was conducted in extreme condition e.g., 100 year return period wave and current. In the 1/60 scaled model experiment the bottom tension of the mooring line and the motions of the GPS buoy were measured. Moreover, the wave observation performance of the wave monitoring buoy was evaluated in 1/20 and 1/60 scaled model experiments. These model experiments were conducted in Deep Sea Basin of National Maritime Research Institute, Japan.

CFD RANS Solver NAGISA²⁾ and lumped-mass mooring solver MoorDyn³⁾ are coupled to predict the buoy motions and the mooring tensions in extreme condition. The simulation results are validated with 1/60 scaled model experiment in the extreme wave condition e.g. condition of 100 year return period.

 

[Reference]

1) Kaita S. et al., 2021, Evaluation of new mooring design for GPS buoy off the coast of Tokushima Kaiyou, Report of the Coastal Development Institute of Technology, No.21 (in Japanese, now printing).

2) Ohashi K. et al., 2019, Development of a structured overset Navier–Stokes solver with a moving grid and full multigrid method, Journal of Marine Science and Technology, Vol. 24, Issue 3, pp.884-901.

3) Hall M. and Goupee A., 2015, Validation of lumped-mass mooring line model with DeepCwind semisubmersible model test data, Ocean Engineering, 104, pp.590-603.

Presenting Author: Motoki Araki National Maritime Research Institute, National Institute of Maritime, Port and Aviation Technology

Authors:

Motoki Araki National Maritime Research Institute, National Institute of Maritime, Port and Aviation Technology
Mitsushi Watanabe National Maritime Research Institute, Japan
Sotarou Masanobu National Maritime Research Institute, Japan
Atsuo Omura Coastal Development Institute of Technology
Shouhei Kaita Coastal Development Institute of Technology
Atsushi Kunita Coastal Development Institute of Technology