Integrated Mooring Load Absorber and Monitoring for Wave Energy Converters
Background
Mooring systems account for 18–30% of total structural cost in wave energy converter (WEC) installations, and govern both operational efficiency and extreme-weather survivability.
WECs must be sited in high-energy wave zones to be economically viable, where slack-taut transitions produce snap loads — abrupt tensioning events that are a well-documented source of severe damage in wave energy projects.
Designers are caught between two bad options: a slack catenary profile that minimizes mean loads but invites snap events, or a taut configuration that raises loads and stiffens the coupling to the converter. Conventional materials cannot resolve this trade-off.
Existing mooring sensors depend on batteries, making long-term in-service load monitoring costly and unreliable offshore.
Inspiration
The governing dynamics are the same ones addressed in vehicle suspension design, where stiffness, damping, and inertance are tuned together to control a shock event.
Current marine mitigations — polymer springs, compliant tethers, spring-like inline connectors — modify axial stiffness only. They reduce peak loads, but leave the velocity- and acceleration-dependent terms of the response unused.
An inerter generates resisting force from relative acceleration, directly opposing the sudden velocity change that defines a snap load. It can raise effective mass by two orders of magnitude without adding comparable physical mass to the mooring.
The same electromagnetic element that provides damping also generates electricity, and its voltage is proportional to relative velocity — so damping, energy harvesting, and load sensing can be realized in one device.
Innovation
A regenerative spring–damper–inerter (SDIS) load absorber installed inline with the mooring line, adding a reactive degree of freedom that absorbs shock loads rather than resisting them through material strength alone.
Damping is tuned in closed loop by varying the electrical shunt resistance across the generator, allowing the device to adapt its response to sea state — compliant in normal operation, aggressively damped during extreme events.
Harvested energy powers onboard monitoring, and the generator signal itself serves as a load estimator, enabling self-powered tension monitoring and fatigue tracking without battery replacement.
Modular, interchangeable stiffness and inertance elements let a single platform be configured across mooring profiles and water depths, and the device can be integrated into new mooring chains or retrofitted to existing systems.