Sustainable Marine Structures

Mooring Fatigue Lifetime of Point-Absorber Wave Energy Converters in Monsoon Climates: Gulf of Thailand and Andaman Sea

Kornpaphop Ruttanawijit

Department of Energy Technology, Faculty of Engineering and Industry Technology, Rambhai Barni Rajabhat University, Chanthaburi 22000, Thailand

Yodchai Tiaple

Department of Maritime Engineering, Faculty of International Maritime Studies, Kasetsart University, Sriracha Campus, Chonburi 20230, Thailand

Noppong Sritrakul

Department of Mechanical Engineering, Faculty of Engineering and Industrial Technology, Silpakorn University, Sanam Chandra Palace Campus, Nakhon Pathom 73000, Thailand

DOI: https://doi.org/10.36956/sms.v8i3.3356

Received: 27 May 2026 | Revised: 8 June 2026| Accepted: 26 June 2026 | Published Online: 21 July 2026

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Abstract

Mooring failure is a leading structural barrier to wave energy converter (WEC) commercialisation, and fatigue—rather than ultimate strength—governs mooring service life. Yet all published WEC mooring fatigue studies use North Sea or North Atlantic wave climates; no region-specific estimate exists for the monsoon-dominated waters of Southeast Asia. This study presents the first mooring fatigue lifetime assessment for the RM3 reference point absorber under the contrasting wave climates of the Gulf of Thailand and the Andaman Sea. A Dirlik frequency-domain framework—validated for bimodal RM3 mooring loads against time-domain rainflow counting by Martinez-Puente et al.—is applied with site-specific Hₛ–Tₚ occurrence weighting derived from 24 years (2000–2023) of ERA5 hourly reanalysis, cross-validated against regional WAM/SWAN hindcasts. Damage is accumulated using Palmgren–Miner's rule across five sensitivity cases: base, slack, taut, biofouling, and a combined worst case. Base-case design fatigue lifetimes (DFF = 3) are 30 years at the Gulf of Thailand and 19 years at the Andaman Sea—the latter falling below the conventional 25-year target despite its roughly threefold-greater wave resource. Seasonal damage is near-uniform between the two monsoons at the Gulf but strongly southwest monsoon-dominated (67%) at the Andaman Sea. Biofouling reduces lifetime by 23–29%, and the combined worst case drives the Andaman lifetime to 8.9 years, below the 10-year inspection threshold. The results inform inspection scheduling, mooring configuration, and design-fatigue-factor selection, demonstrating that site-specific monsoon weighting is essential for credible WEC mooring fatigue assessment in Southeast Asian waters.

Keywords: Wave Energy Converter; Mooring Fatigue; Dirlik Method; Monsoon Wave Climate; Gulf of Thailand; Andaman Sea

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