Numerical Model Development and Validation for the WECCOMP Control Competition Preprint

This paper details the development and validation of a numerical model of the Wavestar device developed in WEC-Sim. This numerical model was developed in support of the wave energy converter (WEC) Control Competition (WECCCOMP), a competition with the objective of maximizing WEC power production through innovative control strategies. WECCCOMP has two stages: numerical implementation of control strategies, and experimental implementation. The work presented in this paper is for support of the stage one numerical implementation, where contestants are provided a WEC-Sim model of the Wavestar device to develop their control algorithms. This paper details the development of the numerical model in WEC-Sim and of its validation through comparison to experimental data. INTRODUCTION In order for ocean wave energy to be a viable solution for our energy future, the levelized cost of electricity (LCOE) must be cost-competitive with other energy generation sources. LCOE is defined as the ratio of total cost to the total electrical energy produced over a wave energy converter’s (WEC’s) lifetime, often reported in units of $/kWh. Accordingly, there are two mechanisms to reduce LCOE: reduce the costs over the lifetime of the device, or increase its overall electrical energy production. While these two LCOE reduction mechanisms can be done independently, the most advantageous approach taken by many device developers and researchers is to simultaneously reduce cost and increase performance. ∗Address all correspondence to this author. Competition is often used to promote innovation and reduce technical and market barriers. In the wave energy field, one such competition is the U.S. Department of Energy (DOE) Water Power Technologies Office-sponsored Wave Energy Prize [1]. The Wave Energy Prize was an 18-month design-build-test competition designed to increase the diversity of organizations involved in WEC technology development, with the aim to double the energy captured from ocean waves [2]. Upon completion of the Wave Energy Prize, four teams surpassed the goal of doubling energy captured, and the winner (AquaHarmonics) demonstrated a five-fold technology improvement. Similarly, a hydrodynamic modeling competition for numerical modeling and simulation of a rigid body subject to incident waves was presented by GarciaRosa at OMAE 2015 [3]. This code competition was run by the Center for Ocean Energy Research at Maynooth University, the basis of which was detailed in an OMAE 2014 publication by Costello on numerical model comparison to experimental data for a submerged horizontal cylinder [4, 5]. Related to competitions are international code comparison efforts, such as the International Energy Agency (IEA) Ocean Energy Systems (OES) Task 10 effort on modeling WECs, and the IEA OES Offshore Code Comparison Collaboration (OC3) through Offshore Code Comparison Collaboration, Continued with Correlation (OC5) efforts on modeling floating offshore wind turbines [6, 7]. The work presented in this paper is in support of the international WEC Control Competition (WECCCOMP), a competition with the objective of maximizing WEC power production through innovative control strategies. The first stage of WECCCOMP is implementation of WEC control in a numerical simulation at model scale using the WEC-Sim code. Contestants will This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel. gov/publications 1 then be down selected, and the second stage involves implementation of WEC control in an experimental wave tank. This paper details development and validation of the WECCCOMP numerical model of a WEC at scale model in WEC-Sim. The WEC selected for WECCCOMP is a scale model of the Wavestar WEC, a device that is currently operating in Denmark [8]. Prior to WECCCOMP, the Wavestar device was tested in the wave tank at Aalborg University; data from which has been used to validate the numerical model of the Wavestar decive developed in WEC-Sim. For more information on the details of WECCCOMP, refer to the EWTEC 2017 publication by Ringwood et al. on the announcement of the competition and the WECCCOMP website [9, 10].