Session: 09-02-06 Wind Energy: Dynamic Analysis II

Submission Number: 175578

Station Keeping Characteristics of Passive Constant Tension Mooring System for a Hybrid Self-Installation Spar Floating Wind Turbine 

There are growing needs to reduce the project costs and minimize the environmental impacts as floating offshore wind enters commercial development phase. A new solution to drastically reduce the cost of floating platform and mooring system is proposed. It includes the vertical-integration self-installation (VISI) Spar platform and the small footprint passive constant tension (PCT) mooring system. The hybrid VISI Spar has a concrete soft tank and 3 or 4 closely-spaced small diameter hull columns replacing the large diameter single column of the classic Spar. The VISI Spar design also has a “jack-up like” feature which enables shallow water quayside assembly and one-piece sea-towing with the wind turbine for offshore installation. The PCT mooring system is developed based on the mooring theory of LVTF (length-varying tension-fixed) in contrast to the conventional mooring theory of “length-fixed tension-varying”, and a novel gravity-based PCT mechanism enabling the mooring line to maintain a constant tension value while the floater’s offset increases. New PCT mooring systems of small footprint multiple spread anchors (MSA) or single point mooring anchor can be developed to provide low-cost mooring solutions with minimized environmental impacts for station-keeping of floating offshore wind turbines (FOWT) to address the challenges of conventional mooring systems.

In this paper, discussions are first given on the mooring system restoring force characteristics of the novel gravity-based PCT mooring concept as compared to the conventional catenary mooring concept using a simplified model. Preliminary design of a PCT MSA mooring system with anchor radius less than 100 m is performed for station-keeping of the proposed multi-column hybrid Spar platform with a 16 MW wind turbine for 100 m water depth. Time-domain simulations and wave tank model test are conducted to investigate the station-keeping performance of the PCT mooring system under the extreme 50-year return typhoon with over 11 m significant wave and 50 m/s wind for in-line and between-line conditions. The model test was conducted at the coastal and offshore engineering test basin of Hohai University. The model scale is 1:60. A detailed fairlead system is designed and connected to the VISI Spar model for the passive constant tension mooring system. Global motions and mooring line tensions are measured and compared with numerical simulation results.  The findings of this study indicate that the new gravity-based PCT mooring system is capable to provide the required station-keeping forces for the 16 MW hybrid VISI Spar FOWT for the extreme typhoon loads at a much lower installed cost as compared to conventional catenary mooring system.

Presenting Author: Jin Wang Shanghai Jiao Tong University

Presenting Author Biography: Dr. Jin Wang is currently a professor at the School of Ocean and Civil Engineering of Shanghai Jiao Tong University in Shanghai, China. He obtained his Ph.D. and Master degrees in Ocean Engineering from Texas A&M University, USA. He received his bachelor degree in Naval Architecture and Ocean Engineering from Shanghai Jiao Tong University, China.
Dr. Wang has extensive experience in the offshore industry with specialized knowledge in floating platforms and mooring systems for offshore oil and gas, as well as floating offshore wind energy. From 2010 to 2023, he served as board member and vice president of COTEC Offshore Engineering Solutions in Houston, Texas, USA. From 1990 to 2010, he worked at large US and international EPC companies (Technip, Aker, MacDermott, Bechtel) and held senior/lead engineering positions.
Dr. Wang is registered Professional Engineer in Texas, USA and a Fellow of American Society of Civil Engineers. He has published more than 90 technical papers and holds over 40 US and international patents.

Authors:

Jin Wang Shanghai Jiao Tong University
Haoran Li Hohai University
Dongxi Liu Shanghai Maritime University
Xinliang Tian Shanghai Jiao Tong University