Kelley Ruehl

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

Wave Energy Development Roadmap: Design to commercialization

In order to promote and support development of the wave energy industry, Sandia National Laboratories (SNL) has developed a Wave Energy Development Roadmap. The Wave Energy Development Roadmap outlines the pathway from initial design to commercialization for Wave Energy Converter (WEC) technologies. Commercialization of a wave energy technology is embodied in the deployment of an array of WECs, a WEC Farm. The development process is related to the commonly used metric of Technology Readiness Levels (TRLs). The roadmap incorporates modeling and experimental expectations at corresponding TRLs which provide a guide for the industry to pursue successful design optimizations, prototype deployments, and utility scale commercialization. The roadmap serves the additional purpose of pinpointing research gaps in the development process.

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.

Wave energy: a Pacific perspective

This paper illustrates the status of wave energy development in Pacific rim countries by characterizing the available resource and introducing the regions current and potential future leaders in wave energy converter development. It also describes the existing licensing and permitting process as well as potential environmental concerns. Capabilities of Pacific Ocean testing facilities are described in addition to the regions vision of the future of wave energy.

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

On the development of a semi-submersible offshore floating platform and mooring system for a 13.2 MW wind turbine

We present a study related to the development of a semi-submersible floating offshore platform and moooring system intended to support a very large 13.2 MW wind turbine in a water depth of 200 meters. This three-bladed horizontal-axis wind turbine with 100-m blades (specifically, the SNL100-02 advanced core material design) is the subject of this study. Methodologies applied in the development of models for the tower, platform and mooring system are presented. An optimal size of the platform is sought through an iterative design scheme under various design constraints. The system’s static stability is demonstrated through free-decay simulations in FAST; these are equivalent to free vibration studies on the system for arbitrary initial conditions of the platform. Global dynamic motions including the quasi-static (mean) response due to wind and waves as well as wavefrequency motions are studied. A comparison of the performance for different mooring patterns is undertaken and the behavior of the integrated system to various design load cases is studied.

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.

WEC-Sim Phase 1 Validation Testing: Experimental Setup and Initial Results

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. INTRODUCTION The nascent wave energy industry includes many young researchers and new developers who are eager to make commercialization a reality. One roadblock preventing rapid evolution of a prevailing technology is the industries tendency to avoid freely and openly sharing data. In addition, developers often need to rely on expensive numerical modelling packages and lack the resources for physical model testing data in order to validate their prototypes. WEC-Sim is an open source code, developed by Sandia and NREL, used to model wave energy converter (WEC) performance in operational and extreme waves. WEC-Sim code development is part of the US Department of Energy Wind and Water Power Technologies Office’s initiative to promote and support the emerging wave energy industry. The WEC-Sim code is a time-domain modeling tool developed in MATLAB/Simulink using the multibody dynamics solver SimMechanics [1]. WEC-Sim solves the WEC’s governing equations of motion using the Cummins time-domain impulse response formulation in 6 degrees of freedom (DOF) [2]. The WEC-Sim code has undergone verification through code-to-code comparisons; however validation of the code has been limited to publicly available experimental data sets. While these data sets provide preliminary code validation, the experimental tests were not explicitly designed for code validation, and as a result are limited in their ability to validate the full functionality of the WEC-Sim code. Dedicated physical model tests for WEC-Sim validation are being performed in two phases. This paper will provide an overview of the dedicated WEC-Sim validation experimental wave tank tests performed at the Oregon State University’s (OSU) Directional Wave Basin (DWB) at Hinsdale Wave Research Laboratory (HWRL). Phase 1 of experimental testing was focused on the FOSWEC device characterization, and was completed in winter 2015. Phase 2 will be focused on characterization of the FOSWEC’s dynamics and performance, and is scheduled for spring 2016. This phased approach allowed for initial data to be analyzed, refinements to the numerical and physical model, and evaluation of instrumentation and testing methods. The experiments have been designed explicitly to validate the performance of the WEC-Sim code and its new feature additions. Upon completion, the WEC-Sim validation data set will be made publicly available to the wave energy community, so that it can be used as a numerical benchmarking data set. For the physical model testing, a highly sophisticated and controllable model of a floating wave energy converter, the FOSWEC, has been designed and constructed. FOSWEC instrumentation includes state-of-the-art devices to measure pressure fields, motions in 6 Degrees of Freedom (DOF), multiaxial load cells, torque transducers, position transducers, and encoders. Most of the collected data has redundancy from multiple types of instrumentation. The model also incorporates a fully programmable Power Take-Off (PTO) system which can be used to generate or absorb the hydrokinetic wave energy. Proceedings of the ASME 2016 35th International Conference on Ocean, Offshore and Arctic Engineering OMAE2016 June 19-24, 2016, Busan, South Korea