Re-creation of site-specific multi-directional waves with non-collinear current

S Draycott,D.R Noble,T Davey,T Bruce,D.M Ingram,L Johanning,H.C.M Smith,A Day,P Kaklis

doi:10.1016/j.oceaneng.2017.10.047

S Draycott, D.R Noble + Show 7 more

Open Access

https://doi.org/10.1016/j.oceaneng.2017.10.047

Copy DOI

Abstract

Site-specific wave data can be used to improve the realism of tank test conditions and resulting outputs. If this data is recorded in the presence of a current, then the combined conditions must be re-created to ensure wave power, wavelength and steepness are correctly represented in a tank. In this paper we explore the impacts of currents on the wave field and demonstrate a simple, effective methodology for re-creating combined wave-current scenarios. Regular waves, a parametric unidirectional spectrum, and a complex site-specific directional sea state were re-created with current velocities representing 0.25, 0.5, and 1.0 m/s full scale. Waves were generated at a number of angles relative to the current, providing observations of both collinear and non-collinear wave-current interactions. Wave amplitudes transformed by the current were measured and corrected linearly, ensuring desired frequency and wavenumber spectra in the presence of current were obtained. This empirical method proved effective after a single iteration. Frequency spectra were within 3% of desired and wave heights normally within 1%. The generation-measurement-correction procedure presented enables effective re-creation of complex wave-current scenarios. This capability will increase the realism of tank testing, and help de-risk devices prior to deployment at sea.

Highlights

Tank testing of physical scale models is an essential element in the development of marine renewable technologies and techniques
A site-specific non-parametric directional spectrum has been obtained from European Marine Energy Centre (EMEC), and re-created at 1:26 scale at the FloWave Ocean Energy Research Facility with current velocities of 0.05, 0.1 and 0.2 m/s
The studies conducted on complex directional wave fields in combination with currents within the FloWave Ocean Energy Research Facility resulted in the following main findings:

Summary

Introduction

Tank testing of physical scale models is an essential element in the development of marine renewable technologies and techniques. Undertaking this testing in laboratories provides a controlled, repeatable, and low-risk environment where technological concepts and operational techniques may be developed (Ingram et al, 2011). A five-stage structured development plan for wave energy systems was outlined by Holmes and Nielsen (2010), which can be related to the widely used Technology Readiness Level (TRL) concept, developed initially by NASA (Mankins, 1995). Using scaled sea conditions based on open sea measurements at wave energy sites when tank testing renewable energy devices, at mid and later stage TRL levels, can improve understanding of device performance prior to deployment at sea. Experiments were carried out in the circular wave basin of the FloWave Ocean Energy Research Facility, enabling both waves and current to be generated in all directions

Objectives

Methods

Results

Discussion

Conclusion