Data-driven modeling of an oscillating surge wave energy converter using dynamic mode decomposition

Modeling wave energy converters (WECs) to accurately predict their hydrodynamic behavior has been a challenge for the wave energy field. Often, this results in either low-fidelity, linear models that break down in energetic seas, or high-fidelity numerical models that are too computationally expensive for operational use. To bridge this gap, we propose the use of dynamic mode decomposition (DMD) as a purely data-driven technique that generates an accurate and computationally efficient model of an oscillating surge WEC (OSWEC). Our goal is to model and predict the behavior of the OSWEC in monochromatic and polychromatic seas without knowledge of the governing equations or incident wave field. We generate the data for the algorithm using a semi-analytical model and the open-source code WEC-Sim, then evaluate how well DMD can describe past dynamics and predict future state behavior. We consider realistic challenges including noisy sensor measurements, nonlinear WEC dynamics, and irregular wave forcing. In each of these cases, we generate accurate models for past and future OSWEC behavior using DMD, even with limited sensor measurements. These findings provide insight into the use of DMD on systems with limited time-resolved data and present a framework for applying similar analysis to lab- or field-scale experiments

Acoustic Characterization of a Hydrokinetic Turbine

Abstract— This study describes the sound produced by a hydrokinetic turbine operating in a riverine environment near Iguigig, AK (USA). Drifting spar buoys equipped with hydrophones and GPS loggers were used to characterize temporal and spatial variability in turbine sound over a range of turbine operating conditions. Because of the quasi-stationary nature of river flows, multiple replicates could be obtained under steady-state operation. The sound from this turbine consists primarily of tones (ascribed to the generator) and broadband emissions (ascribed to blade vibration). The frequency of the tones varies in proportion to the turbine rotation rate. At the closest point of approach, for an optimally operating turbine, one-third octave levels are elevated by up to 40 dB relative to braked conditions. Broadband spatial patterns suggest relatively limited sound directivity. This study highlights the benefits of using Lagrangian drifters to characterize turbine sound (e.g., flow noise mitigation, spatially-resolved acoustic fields) and challenges (e.g., positional accuracy, self-noise contamination). Further analysis is required to interpret spatial variability in the context of acoustic propagation in riverine environments

Acoustic characterization of sensors used for marine environmental monitoring

Acknowledgements The authors wish to acknowledge Benjamin Brand for his assistance with the Acoustic Test Facility set-up, Jessica Noe for her assistance designing sonar mounts, James Joslin for his assistance with cables for sonar operation, and Mark Wood for his assistance with icListen hydrophones. This study would not have been possible without their contributions. Funding This work was funded by the US Department of Energy [grant number DE-EE0007827]. Emma Cotter is supported by a National Science Foundation Graduate Research Fellowship [grant number DGE-1762114].Peer reviewedPostprin

A parametric evaluation of the interplay between geometry and scale on cross-flow turbine performance

Cross-flow turbines harness kinetic energy in wind or moving water. Due to their unsteady fluid dynamics, it can be difficult to predict the interplay between aspects of rotor geometry and turbine performance. This study considers the effects of three geometric parameters: the number of blades, the preset pitch angle, and the chord-to-radius ratio. The relevant fluid dynamics of cross-flow turbines are reviewed, as are prior experimental studies that have investigated these parameters in a more limited manner. Here, 223 unique experiments are conducted across an order of magnitude of diameter-based Reynolds numbers ($\approx 8\!\times\!10^4 - 8\!\times\!10^5$) in which the performance implications of these three geometric parameters are evaluated. In agreement with prior work, maximum performance is generally observed to increase with Reynolds number and decrease with blade count. The broader experimental space identifies new parametric interdependencies; for example, the optimal preset pitch angle is increasingly negative as the chord-to-radius ratio increases. Because these experiments vary both the chord-to-radius ratio and blade count, the performance of different rotor geometries with the same solidity (the ratio of total blade chord to rotor circumference) can also be evaluated. Results demonstrate that while solidity can be a poor predictor of maximum performance, across all scales and tested geometries it is an excellent predictor of the tip-speed ratio corresponding to maximum performance. Overall, these results present a uniquely holistic view of relevant geometric considerations for cross-flow turbine rotor design and provide a rich dataset for validation of numerical simulations and reduced-order models.Comment: SUBMITTED to Renewable and Sustainable Energy Review

Study of the Acoustic Effects of Hydrokinetic Tidal Turbines in Admiralty Inlet, Puget Sound

Hydrokinetic turbines will be a source of noise in the marine environment - both during operation and during installation/removal. High intensity sound can cause injury or behavioral changes in marine mammals and may also affect fish and invertebrates. These noise effects are, however, highly dependent on the individual marine animals; the intensity, frequency, and duration of the sound; and context in which the sound is received. In other words, production of sound is a necessary, but not sufficient, condition for an environmental impact. At a workshop on the environmental effects of tidal energy development, experts identified sound produced by turbines as an area of potentially significant impact, but also high uncertainty. The overall objectives of this project are to improve our understanding of the potential acoustic effects of tidal turbines by: (1) Characterizing sources of existing underwater noise; (2) Assessing the effectiveness of monitoring technologies to characterize underwater noise and marine mammal responsiveness to noise; (3) Evaluating the sound profile of an operating tidal turbine; and (4) Studying the effect of turbine sound on surrogate species in a laboratory environment. This study focuses on a specific case study for tidal energy development in Admiralty Inlet, Puget Sound, Washington (USA), but the methodologies and results are applicable to other turbine technologies and geographic locations. The project succeeded in achieving the above objectives and, in doing so, substantially contributed to the body of knowledge around the acoustic effects of tidal energy development in several ways: (1) Through collection of data from Admiralty Inlet, established the sources of sound generated by strong currents (mobilizations of sediment and gravel) and determined that low-frequency sound recorded during periods of strong currents is non-propagating pseudo-sound. This helped to advance the debate within the marine and hydrokinetics acoustic community as to whether strong currents produce propagating sound. (2) Analyzed data collected from a tidal turbine operating at the European Marine Energy Center to develop a profile of turbine sound and developed a framework to evaluate the acoustic effects of deploying similar devices in other locations. This framework has been applied to Public Utility District No. 1 of Snohomish Country's demonstration project in Admiralty Inlet to inform postinstallation acoustic and marine mammal monitoring plans. (3) Demonstrated passive acoustic techniques to characterize the ambient noise environment at tidal energy sites (fixed, long-term observations recommended) and characterize the sound from anthropogenic sources (drifting, short-term observations recommended). (4) Demonstrated the utility and limitations of instrumentation, including bottom mounted instrumentation packages, infrared cameras, and vessel monitoring systems. In doing so, also demonstrated how this type of comprehensive information is needed to interpret observations from each instrument (e.g., hydrophone data can be combined with vessel tracking data to evaluate the contribution of vessel sound to ambient noise). (5) Conducted a study that suggests harbor porpoise in Admiralty Inlet may be habituated to high levels of ambient noise due to omnipresent vessel traffic. The inability to detect behavioral changes associated with a high intensity source of opportunity (passenger ferry) has informed the approach for post-installation marine mammal monitoring. (6) Conducted laboratory exposure experiments of juvenile Chinook salmon and showed that exposure to a worse than worst case acoustic dose of turbine sound does not result in changes to hearing thresholds or biologically significant tissue damage. Collectively, this means that Chinook salmon may be at a relatively low risk of injury from sound produced by tidal turbines located in or near their migration path. In achieving these accomplishments, the project has significantly advanced the District's goals of developing a demonstration-scale tidal energy project in Admiralty Inlet. Pilot demonstrations of this type are an essential step in the development of commercial-scale tidal energy in the United States. This is a renewable resource capable of producing electricity in a highly predictable manner

The Gallery 2012

This is a digital copy of the print book produced by the Gallery 2012 team. Contents: Preface p. 3, Core p. 5, Graphic Design p. 23, Illustration p. 55, Painting p. 73, Photography p. 87, Printmaking p. 105, Metals & Jewelry p. 129, Sculpture & Ceramics p.147. Files for individual sections may be viewed on the detailed metadata page by clicking on the book title.https://rdw.rowan.edu/the_gallery/1004/thumbnail.jp

The Gallery 2011

This is a digital copy of the print content produced by the Gallery 2011 team. The Gallery 2011 consists of a box containing a leaflet, four books, and a USB drive. The leaflet lists the works contained on the USB drive in the areas of Time Based Media and Web Design, and provides credits for the Gallery design production team. Content from the USB drive is not included. The four books contain the artistic works of students in the following genres: Core Studio/Painting, Graphic Design/Illustration, Photography/Printmaking, and Jewelry & Metals/Three Dimensional. Files for individual sections may be viewed on the detailed metadata page by clicking on the book title.https://rdw.rowan.edu/the_gallery/1005/thumbnail.jp