Publications

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This paper details the development and validation of a numerical model of the Wavestar wave energy converter (WEC) developed in WEC-Sim. This numerical model was developed in support of the WEC Control Competition (WECCCOMP), a competition with the objective of maximizing WEC performance over costs 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 numerical implementation, where contestants are provided a WEC-Sim model of the 1:20 scale 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.

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The WEC-Sim project is currently on track, having met both the SNL and NREL FY14 Milestones, as shown in Table 1 and Table 2. This is also reflected in the Gantt chart uploaded to the WEC-Sim SharePoint site in the FY14 Q4 Deliverables folder. The work completed in FY14 includes code verification through code-to-code comparison (FY14 Q1 and Q2), preliminary code validation through comparison to experimental data (FY14 Q2 and Q3), presentation and publication of the WEC-Sim project at OMAE 2014 [1], [2], [3] and GMREC/METS 2014 [4] (FY14 Q3), WEC-Sim code development and public open-source release (FY14 Q3), and development of a preliminary WEC-Sim validation test plan (FY14 Q4). This report presents the preliminary Validation Testing Plan developed in FY14 Q4. The validation test effort started in FY14 Q4 and will go on through FY15. Thus far the team has developed a device selection method, selected a device, and placed a contract with the testing facility, established several collaborations including industry contacts, and have working ideas on the testing details such as scaling, device design, and test conditions.

In the wave energy industry, there is a need for open source numerical codes and publicly available experimental data, both of which are being addressed through the development of WEC-Sim by Sandia National Laboratories and the National Renewable Energy Laboratory (NREL). WEC-Sim is an open source code used to model wave energy converters (WECs) when subject to incident waves. In order for the WEC-Sim code to be useful, code verification and physical model validation is necessary. This paper describes the wave tank testing for the 1:33 scale experiments of a Floating Oscillating Surge Wave Energy Converter (FOSWEC). The WEC-Sim experimental data set will help to advance the wave energy converter industry by providing a free, high-quality data set for researchers and developers. This paper describes the WEC-Sim open source wave energy converter simulation tool, experimental validation plan, and presents preliminary experimental results from the FOSWEC Phase 1 testing.

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WEC-Sim (Wave Energy Converter-SIMulator) is an open-source wave energy converter (WEC) code capable of simulating WECs of arbitrary device geometry subject to operational waves. The code is developed in MATLAB/Simulink using the multi-body dynamics solver SimMechanics, and relies on Boundary Element Method (BEM) codes to obtain hydrodynamic coefficients such as added mass, radiation damping, and wave excitation. WEC-Sim Version 1.0, released in Summer 2014, models WECs as a combination of rigid bodies, joints, linear power take-offs (PTOs), and mooring systems. This paper outlines the development of PTO-Sim (Power Take Off-SIMulator), the WEC-Sim module responsible for accurately modeling a WEC's conversion of mechanical power to electrical power through its PTO system. PTO-Sim consists of a Simulink library of PTO component blocks that can be linked together to model different PTO systems. Two different applications of PTO-Sim will be given in this paper: a hydraulic power take-off system model, and a direct drive power take-off system model.