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

Peter Stansby,Efrain Carpintero Moreno

doi:10.3390/w12102818

Abstract

There has been considerable modelling and wave basin validation of the multi-mode, multi-float, moored wave energy converter M4. The 6 float (2 power take off) (PTO) configuration is considered here with mooring from a buoy with light inextensible cables. Large mean mooring forces and very large peak or snap forces were measured in large waves while the rotational response about the hinges (for power take off in operational conditions) was predominantly linear. Modelling has been extended with elastic mooring cables connected directly to the base of the bow float and to the buoy. The experimental mean force is input to the linear diffraction/radiation model. The device response is effectively unchanged. The peak mooring force and tensions remain large with direct connection to the base of the bow float but are only slightly greater than the mean forces with elastic cables to the buoy, and an elastic hawser provides a further slight reduction. For the largest waves measured, the force was about 10% of the dry weight of the platform. The idealized efficient modelling may inform more detailed design while efficient methods for determining highly nonlinear mean forces remain to be established.

Highlights

Many concepts for offshore wave energy conversion have been considered and devices are generally classed as point absorbers, terminators or attenuators, e.g., see reviews [1,2]
Mean mooring force has been demonstrated elastic cables to a buoy snap forcesThe in extreme waves such balances the mean hydrodynamic force whichgreater is independent of mooring for the force same that the peak force magnitude is only slightly than the mean forces.configuration
An elastic cable from buoy to float provides a further slight reduction snap balances mean hydrodynamic force which is independent of mooring configuration for theinsame forces which is beneficial

Summary

Introduction

Many concepts for offshore wave energy conversion have been considered and devices are generally classed as point absorbers, terminators or attenuators, e.g., see reviews [1,2]. There has been considerable modelling and wave tank validation of M4 [3,4,5,6], demonstrating relatively high capture widths, up to about one wavelength corresponding to the energy period in irregular waves or three stern float diameters, for the 6 float version. This is shown in a video frame from laboratory testing, the scale being approximately 1:50. This version has one bow float, three mid floats and two stern floats, called 1-3-2; the stern floats are connected by beams to hinges above the outer mid floats for power take off (PTO), provided by mechanical damping from an actuator

Results

Discussion

Conclusion