Bret Bosma

Large-scale ocean wave energy plant modeling

In order for wave energy conversion to be a commercially viable technology, wave energy researchers, developers, investors and utilities need an estimate of a wave energy converters (WEC) power output at a potential installation site. The wind industry has developed generic turbine models that capture the general dynamics of large-scale proprietary wind turbine designs in order to estimate a turbines power output for a given wind climate. Similar generic models need to be developed for WECs. Current WEC deigns vary significantly in design and technology. The focus of this paper is on developing a generic model structure for one of the prominent WEC designs, the two body point absorber. The model structure is developed by using time domain equations of motion (EOM) to define systems and subsystems as well as their corresponding inputs and outputs. The generic model structure is then extended by developing a hydraulic power take-off (PTO) system model.

Wave energy converter modeling in the frequency domain: A design guide

Wave energy converter research continues to advance and new developers are continuing to emerge, leading to the need for a general modeling methodology. This work attempts to outline the design methodology necessary to perform frequency domain analysis on a generic wave energy converter. A two-body point absorber representing a generic popular design was chosen and a general procedure is presented showing the process to obtain first pass preliminary performance results. The result is a design guide that new developers can adapt to their particular design and wave conditions, which will provide the first steps toward a cost of energy estimate. This will serve the industry by providing a sound methodology to accelerate the new development of wave energy converters.

Modeling of a two-body wave energy converter driven by spectral JONSWAP waves

Wave Energy Converter (WEC) design strives to produce as much power as possible across differing wave conditions. It is especially true of autonomous WECs (used, for example, to power an ocean buoy sensing system) because they are smaller and they need to maximize the amount of power produced under minimal wave energy conditions. This is because the electrical power required is considered a constant load. Autonomous WECs (AWECs) also tend to operate near shore where the wave spectral content spans a larger frequency range. This paper describes the type of spectral waves to be used during the design and simulation stage, then presents results from the WEC hydrodynamic finite element analysis (FEA) that uses integrated optimal control with both monochromatic and spectral waves. A comparison is made of these results against a SPICE simulation using a two-body equivalent circuit. Using these results, plus integrating the effects of losses in the power take-off (PTO), conclusions are reached regarding the preferred control method. It was found that damping control may be the preferable control scheme for this application.

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

Wave lab testing of a two-body autonomous wave energy converter

Wave Energy Converter (WEC) design strives to produce as much power as possible across differing wave conditions. It is especially true for an autonomous WEC (AWEC) used, for example, to power an ocean buoy sensing system, because they are smaller and they need to maximize the amount of power produced under low-energy wave energy conditions. An AWEC is a wave energy device that is not tied to a land-based electric utility. This paper describes the testing results and conclusions from actual wave lab testing of a WEC intended for autonomous applications. The results are compared to previous WEC hydrodynamic finite element analysis (FEA) that used integrated optimal control with both monochromatic and spectral waves. Conclusions are drawn with respect to the power absorption capability of the AWEC when the wave source is a monochromatic wave versus richer frequency spectral waves.

A programmable mooring controller for tank testing of scaled wave energy converters

Ocean wave energy can be a promising contributor to the renewable generation portfolio for coastal communities. Developing economically feasible wave energy converters requires thorough testing of the scaled version of these devices in test tanks. One of the challenges of scaled testing is to accurately represent and model all physical characteristics of the full scale converter. This paper presents the design, construction, and performance of a small-scale active mooring system that can be programmed to accurately emulate common mooring configurations for wave energy converters. This allows for a flexible, accurate, and cost effective system to test mooring designs and their effects on overall performance and behavior of the wave energy converters in small-scale testing. With this system mooring characteristics can be changed on the fly without the need for any hardware changes. This allows quick validation of various mooring designs without increased cost in equipment and tank time.