Experimental Validation and Comparison of Numerical Models for the Mooring System of a Floating Wave Energy Converter

Abstract

The mooring system of floating wave energy converters (WECs) has a crucial impact on power generation efficiency, cost of delivered energy, proper operation, reliability and survivability. An effective design, addressing such competing objectives, requires appropriate mathematical models to predict mooring loads and dynamic response. However, conversely to traditional offshore engineering applications, experience in modelling mooring systems for WECs is limited, due to their unique requirement of maximising the motion while minimising loads and costs. Even though modelling approaches and software are available for this application, guidelines and critical comparison are still scarce. This paper proposes a discussion and validation of three mooring-line models: one quasi-static approach (developed in-house) and two dynamic lumped-mass approaches (the open source MoorDyn and the commercial OrcaFlex). The case study is a 1:32-scale prototype of a floating oscillating water column WEC tested in a wave tank, with three mooring lines, each one comprising of a riser and a clump weight. Validation, performed by imposing fairlead displacements and comparing resulting tensions, shows good agreement. The small scale may induce numerical instabilities and uncertainties in the parameter estimation. Finally, likely due to internal resonance of this particular mooring system, high-frequency content in the mooring tension is found, albeit absent in the kinematics of the floater.

Real-Time Wave Excitation Forces Estimation: An Application on the ISWEC Device

“…The main advantage consists in reducing the computational burden of the simulation at the expense of model accuracy. More accurate mooring models are presented in [44] considering two dynamic lumped-mass approaches (the open source MoorDyn [45] and the commercial OrcaFlex 11.0e [46]) where mooring actions are resolved coupling both the hydrodynamics and gyroscope model of the WEC in the MoorDyn and Orcaflex enviorments. When the system model is not reducible to a series of analytical equations or, even more, is based only on observed data the implementation KF model is not trivial.…”

Study of Snap Loads for Idealized Mooring Configurations with a Buoy, Inextensible and Elastic Cable Combinations for the Multi-Float M4 Wave Energy Converter

“…While withstanding peak loads is essential, inhibiting and damping platform motion by mooring is an added benefit. However, wave energy conversion requires platform motion and damping is detrimental [10][11][12][13]. There is a widespread consensus in the wave energy community that mooring system design and modelling is a major challenge that needs to be overcome [12].…”

Numerical investigation on the effect of the vessel rolling angle and period on the energy harvest

“…Ruriko et al, 15 Engstrm et al, 16 and Amarkarthik and Sivakumar 17 developed the point absorption wave energy converter. What's more, Horno et al 18 and Paduano et al 19 proposed a unit utilizing the current energy. A detailed study of the closed loop behavior of a gravity-based first-generation TEC (tidal energy converters) is provided, the effectiveness of the proposed control system and its excellent performance are demonstrated through numerical simulations and experimental studies.…”