Carlos Michelen

Preliminary Verification and Validation of WEC-Sim, an Open-Source Wave Energy Converter Design Tool

To promote and support the wave energy industry, a wave energy converter (WEC) design tool, WEC-Sim, is being developed by Sandia National Laboratories and the National Renewable Energy Laboratory. In this paper, the WEC-Sim code is used to model a point absorber WEC designed by the U.S. Department of Energy’s reference model project. Preliminary verification was performed by comparing results of the WEC-Sim simulation through a code-to-code comparison, utilizing the commercial codes ANSYS-AQWA, WaveDyn, and OrcaFlex. A preliminary validation of the code was also performed by comparing WEC-Sim simulation results to experimental wave tank tests.Copyright

IMPLEMENTING NONLINEAR BUOYANCY AND EXCITATION FORCES IN THE WEC-SIM WAVE ENERGY CONVERTER MODELING TOOL

Wave energy converters (WECs) are commonly designed and analyzed using numerical models that combine multibody dynamics with hydrodynamic models based on the Cummins equation and linearized hydrodynamic coefficients. These modeling methods are attractive design tools because they are computationally inexpensive and do not require the use of highperformance computing resources necessitated by high-fidelity methods, such as Navier-Stokes computational fluid dynamics. Modeling hydrodynamics using linear coefficients assumes that the device undergoes small motions and that the wetted surface area of the devices is approximately constant. WEC devices, however, are typically designed to undergo large motions to maximize power extraction, calling into question the validity of assuming that linear hydrodynamic models accurately capture the relevant fluid-structure interactions. In this paper, we study how calculating buoyancy and Froude-Krylov forces from the instantaneous position of a WEC device changes WEC simulation results compared to simulations that use linear hydrodynamic coefficients. First, we describe the WEC-Sim tool used to perform simulations and how the ability to model instantaneous forces was incorporated into WEC-Sim. We then use a simplified one-body WEC device to validate the model and to demonstrate how accounting for these instantaneously calculated forces affects the accuracy of simulation results, such as device motions, hydrodynamic forces, and power generation. Other aspects of WEC-Sim code development and verification are presented in a companion paper [1] that is also being presented at OMAE2014.

DEVELOPMENT OF PTO-SIM: A POWER PERFORMANCE MODULE FOR THE OPEN-SOURCE WAVE ENERGY CONVERTER CODE WEC-SIM

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.Copyright

COER Hydrodynamic Modeling Competition: Modeling the Dynamic Response of a Floating Body Using the WEC-Sim and FAST Simulation Tools

The Center for Ocean Energy Research (COER) at the University of Maynooth in Ireland organized a hydrodynamic modeling competition in conjunction with OMAE2015. Researchers were challenged to predict the dynamic response of a floating rigid-body device that was experimentally tested in a series of wave-tank tests. Specifically, COER set up a blind competition, where the device specifications and test conditions were released, but the experimental results were kept private until all competition participants submitted their numerical simulation results.The National Renewable Energy Laboratory and Sandia National Laboratories entered the competition and modeled the experimental device using both the WEC-Sim and FAST numerical modeling tools. This paper describes the numerical methods used to model the device and presents the numerical modeling results. The numerical results are also compared to the experimental results provided by COER at the completion of the competition.© 2015 ASME

WEC-Sim Phase 1 Validation Testing: Numerical Modeling of Experiments

The Wave Energy Converter Simulator (WEC-Sim) is an open-source code jointly developed by Sandia National Laboratories and the National Renewable Energy Laboratory. It is used to model wave energy converters subjected to operational and extreme waves. In order for the WEC-Sim code to be beneficial to the wave energy community, code verification and physical model validation is necessary. This paper describes numerical modeling of the wave tank testing for the 1:33-scale experimental testing of the floating oscillating surge wave energy converter. The comparison between WEC-Sim and the Phase 1 experimental data set serves as code validation. This paper is a follow-up to the WEC-Sim paper on experimental testing, and describes the WEC-Sim numerical simulations for the floating oscillating surge wave energy converter.