Integrity and Reliability Testing of a HDPE Taut Mooring System Belt

Abstract

The integrity of the mooring system is critical for the safe station-keeping of any floating structure. For motion dependent wave energy converters, the additional requirement is to provide sufficient compliance to allow the power take-off working principle to function. This paper presents the physical testing carried out as part of the MARINET2 test programme. The mooring system design for the Calwave wave energy converter is tested in order to validate the actual physical performance of the mooring system. The tests are carried out at the Dynamic Marine Component Test facility (DMaC), capable to replicate the forces (up to 30 tonnes) and motions (up to 1m / 30°) with submersed test specimens of up to 6 meters length. The tests explore the Minimum Breaking Strength (MBS) as a primary measure of integrity, but will also perform repeated cyclic loading, simulating low-cycle fatigue behaviour of the mooring system. The tests also assess the mooring response and integrity under simulated Accidental Limit State (ALS) conditions, where the device’s power take-off will be locked and the mooring loads are expected to increase considerably. A key finding of the tests is the importance of the termination pattern and quality, which has a direct influence on the mooring MBS. The static and dynamic stiffness for the tested HDPE belts is also determined. The paper will be of interest to technology developers, mooring designers and stakeholders concerned with the integrity, durability and validation of offshore mooring systems.