Marine Energy Technology Symposium

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https://hdl.handle.net/10919/49096

The Marine Energy Technology Symposium, http://www.globalmarinerenewable.com/mets/, is held in conjunction with The Global Marine Renewable Energy Conference (GMREC). All METS papers are peer-reviewed and authors whose papers are accepted to METS will have the opportunity to give a technical presentation at METS. Note that authors must present their paper in-person at METS in order to have their work included in the conference proceedings.

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Layouts for Ocean Wave Energy Farms: Models, Properties, and Heuristic
Snyder, Lawrence V.; Moarefdoost, M. Mohsen (2014-04)
We present models and algorithms for choosing optimal locations of wave energy conversion (WEC) devices within an array, or wave farm. The location problem can have a significant impact on the total power of the farm due to the interactions among the incident ocean waves and the scattered and radiated waves produced by the WECs. Depending on the nature of the interference (constructive or destructive) among these waves, the wave energy entering multiple devices, and thus the power output of the farm, may be significantly larger or smaller than the energy that would be seen if the devices were operating in isolation. Our model chooses WEC locations to maximize the performance of a wave farm as measured by a well known performance measure called the q -factor, which is the ratio of the power from an array of N WECs to the power from N WECs operating independently, under the point absorber approximation . We prove bounds for the q -factor based on the eigenvalues of an important data matrix, and provide an analytical optimal solution for the 2-WEC problem. We propose an iterative heuristic for the general problem and discuss the WEC location problem under uncertainty.
Further Development of SNL‐Swan, a Validated Wave Energy Converter
Porter, Aaron; Ruehl, Kelley; Chartrand, Chris (2014-04)
Commercialization of wave energy will lead to the necessary deployment of Wave Energy Converters (WECs) in arrays, or wave farms. In order for projects in the United States to be approved, regulatory agencies must perform an Environmental Assessment proving little to no environmental impact. However, little is known about the environmental impacts of such wave farms. As a result, the environmental impacts of wave farms are largely determined by numerical wave models capable of modeling large areas (i.e., spectral wave models). However spectral wave models are currently limited in their ability to model WECs. Sandia National Laboratories is developing SNL‐SWAN, a modified version of Simulation WAves Nearshore [1] that includes a validated WEC Module to more realistically model the frequency and sea state dependent wave energy conversion of WECs. This paper will provide an update on its development.
Tidal Distortion as Pertains to Hydrokinetic Turbine Selection and Resource Assessment
Bruder, Brittany; Hass, Kevin (2014-04)
Synthetic M2 and M4 velocity signals with differing relative phase, are quantified by the statistical parameters skewness and asymmetry, to observe the effect of tidal distortion on available and technical energy for hydrokinetic tidal power operations. Signals with high magnitudes of skewness have a bimodal velocity probability distribution. Asymmetric and non-distorted signals with zero skewness have singular peak values. For velocities time series with the same signal energy, such discrepancies does little to change the available kinetic energy. However, upon the application of turbine efficiency curves, technical energy output between signals with varying skewness varies up to 15%. Such discrepancies in energy outputs highlights the importance of phase, tidal distortion, and skewness for technical resource assessments
Determining the Spatial Coherence of Turbulence at MHK Sites
Kilcher, Levi F.; Thomson, Jim; Colby, Jonathan (2014-04)
Although turbulence is thought to be a key variable in the performance and survivability of Marine Hydrokinetic turbines, it has not been fully characterized at sites where they will be deployed. In particular, the conventional metrics of turbulence intensity and turbulent kinetic energy spectra only describe the turbulence at a point. Spatial information is required to estimate the loading across a rotor, for example, and to understand the short-term evolution of turbulence in the vicinity of a device (for potential use in feed-forward control algorithms). Here, we describe a method to collect and analyze data for determining the spatial coherence of turbulence at marine hydrokinetic turbine deployment sites. The approach uses multiple compliant moorings equipped with acoustic Doppler velocimeters and inertial motion units. Analysis of data from previous deployments of a single mooring is used to demonstrate the method, and future deployments are discussed. It is expected that coherence will be highly dependent on scale, with high coherence for large-scale eddies, and low coherence for the smaller, inertial-scale eddies.
Testing and Accelerated Aging of Conductive Antifouling Paints for Marine Applications
Bunn, Malachi; Yokochi, Alex (2014-04)
Marine hydrokinetic (MHK) device survivability is necessary to understand in order to develop the vast renewable wave and tidal energy resource. Antifouling coatings serve to ensure device longevity by preventing degradation associated with mollusk adhesives and general performance degradation due to hydrodynamic surface changes, clogged pinch points, and added drag. Coatings developed to serve the shipping industry are generally insufficient for MHK service due to finite biocide content, short service life, and operating condition requirements such as continuous movement at elevated speeds. Electrochemical antifouling methods have been shown to be effective in the prevention of fouling organism growth on objects submerged in seawater.[1] Service life has been provided in one study as 8 months with failure due to binder paint film degradation.[2] Appropriate selection of paint binder systems and rigid substrates may extend this time significantly. Degradation of the conductive pigment filler, in this work graphite, may also lead to performance loss and ultimately to system failure. The specific goal of the current work is to model the antifouling process at a charged graphite filled paint electrode and the degradation of system performance due to degradation of the graphite filler. Under accelerated aging conditions no significant degradation has been observed with simulated aging to 20 years of service life.
A Methodology for Wave-to-Wire WEC Simulations
Bailey, Helen; Ortiz, Juan P.; Robertson, Bryson; Buckham, Bradley J.; Nicoll, Ryan S. (2014-04)
This paper looks at the methodology of building a full wave-to-wire WEC (Wave Energy Convertor) simulation and presents examples of its use for a variety of different types of WEC. Wave resource information from the West Coast of Vancouver Island is considered. A detailed wave-body interaction model is generated using ProteusDS software. This model is linked to Simulink, which allows a detailed PTO (Power Take Off) model to be simulated, which will feedback into the motions of the WEC. Three different examples are presented for different WECs. These WECs are Resolute Marine Energy's Surging flap, Seawood Designs' SurfPower and an internal University of Victoria two-body concept.
Ocean Power Technologies Powerbuoy®: System‐Level Design, Development and Validation Methodology
Edwards, Kathleen, A.; Mekhiche, Mike (2014-04)
In this paper the authors will describe a system‐level, multi‐physics based development of PowerBuoy® products at Ocean Power Technologies (OPT). The PowerBuoy is a moored system which extracts useful electrical power from waves. Different PowerBuoy solutions have been developed for different markets (grid connected systems vs. smaller autonomous systems) and/or different customer applications. The PowerBuoy design approach focuses on clarification of operational requirements at the onset of the effort. An iterative closed‐loop process optimizes various aspects of the system. The goal is a solution that addresses all Key Performance Parameters while minimizing life cycle cost. This paper will outline the PowerBuoy design process, which consists of the following steps, illustrated by examples from recent development efforts.
Development and Demonstration of The WEC-Sim Wave Energy Converter Simulation Tool
Lawson, Michael; Yu, Yi-Hsiang; Ruehl, Kelley; Michelen, Carlos (2014-04)
The National Renewable Energy Laboratory (NREL) and Sandia National Laboratories (SNL) have developed WEC-Sim to provide the wave energy converter (WEC) design community with an open-source simulation tool. WEC-Sim models the system dynamics of WEC devices using multi- body dynamics methods and simulates hydrodynamic forces using coefficients predicted from potential flow models. In this paper we describe the methodology used in WEC-Sim and demonstrate the use of the code by simulating three WEC devices. Specifically, we model a two- body point absorber and two oscillating surge devices. For each device we describe how the WEC-Sim model was setup and present simulation results, such as predictions of device motions and power production. For verification and validation purposes, results are compared to corresponding results from other modeling tools and experimental data.
Numerical and Experimental Analysis of the Ocean Sentinel Mooring System to Enable Improved Modeling and Design
von Jouanne, Annette; Baker, Josh; Yim, Solomon C.; Amon, Ean; Moran, Sean; Lettenmaier, Terry (2014-04)
This paper presents the design and analysis of the Ocean Sentinel instrumentation buoy mooring system, including numerical modeling and experimental validation testing during the summer of 2013. The intent of this study is to gather mooring data for the Pacific Marine Energy Center – North Energy Test Site (PMEC-NETS), and increase the understanding of numerical mooring models, which will contribute to improved designs of wave energy converter (WEC) mooring systems. The Ocean Sentinel instrumentation buoy (Ocean Sentinel) was configured in a three-point moor, with load cells on each mooring line, and the system was modeled using OrcaFlex. The model predictions of the mooring line loads are compared with actual experimental loads experienced during the summer 2013 deployment and the results are presented. Based on the results of the field testing, mooring system design improvements are proposed. This paper also includes wave data recorded during the deployment that was used in the numerical model to simulate the deployed conditions, as well as the simulated power output for a WEC array installation located at PMEC-NETS.
Array Optimization for Tidal Energy Extraction in a Tidal Channel – A Numerical Modeling Analysis
Yang, Zhaoqing; Wang, Taiping; Copping, Andrea (2014-04)
This paper presents an application of a hydrodynamic model to simulate tidal energy extraction in a tidal dominated estuary in the Pacific Northwest coast. A series of numerical experiments were carried out to simulate tidal energy extraction with different turbine array configurations, including location, spacing and array size. Preliminary model results suggest that array optimization for tidal energy extraction in a real-world site is a very complex process that requires consideration of multiple factors. Numerical models can be used effectively to assist turbine siting and array arrangement in a tidal turbine farm for tidal energy extraction.
Analysis of the Impacts of Wave Energy Converter Arrays on the Nearshore Wave Climate
O'Dea, Annika M.; Haller, Merrick C. (2014-04)
This study analyzes the impacts of offshore Wave Energy Converter (WEC) arrays on far-field waves and on nearshore wave-induced hydrodynamic forcing for a variety of array designs and incident wave conditions. The main objective of the study is to provide general conclusions on the nearshore impacts of WEC arrays in order to facilitate the assessment of future field test sites. The study utilizes the spectral wave model SWAN. Two array configurations are simulated, and WEC arrays are located either 5, 10, or 15 km offshore. Input conditions include parametric JONSWAP spectra with a range of offshore wave heights and periods. Trials are conducted with a directional wave field with the dominant direction being shore normal in all cases. Arrays are represented in SWAN through the external modification of the wave spectra at the device locations based on an experimentally-determined Power Transfer Function. Based on an analysis of existing field data, a new threshold for nearshore hydrodynamic impact is also established. The threshold represents an empirical relationship between radiation stress and longshore current magnitude. This threshold value is subsequently used as an indicator of when significant changes in the nearshore forcing are induced by WEC arrays. Results show that the changes in nearshore forcing parameters decrease as the distance between the array and the shore increases. Additionally, a more significant change in nearshore forcing parameters is seen in cases with larger input wave heights and periods and with low directional spread. The incident wave conditions, array configurations, and array locations that lead to nearshore impact are identified and assessed.
Development of an Adaptable Monitoring Package for Marine Renewable Energy Projects Part II: Hydrodynamic Performance
Joslin, James; Rush, Ben; Stewart, Andrew; Polagye, Brian (2014-04)
The Adaptable Monitoring Package (AMP), along with a remotely operated vehicle (ROV) and custom tool skid, is being developed to support near-field (≤10 meters) monitoring of hydrokinetic energy converters. The AMP is intended to support a wide range of environmental monitoring in harsh oceanographic conditions, at a cost in line with other aspects of technology demonstrations. This paper, which is the second in a two part series, covers the hydrodynamic analysis of the AMP and deployment ROV given the strong waves and currents that typify marine renewable energy sites. Hydrodynamic conditions from the Pacific Marine Energy Center's wave test sites (PMEC) and Admiralty Inlet, Puget Sound, Washington are considered as early adoption case studies. A methodology is presented to increase the AMP's capabilities by optimizing its drag profile through a combination of computational fluid dynamic (CFD) modeling and sub-scale experiments. Preliminary results suggest that AMP deployments should be possible in turbulent environments with a mean flow velocity up to 1 m/s.
Discrete Element Modeling of Blade–Strike Frequency and Survival of Fish Passing Through Hydrokinetic Turbines
Richmond, Marshall C.; Romero-Gomez, Pedro (2014-04)
Evaluating the consequences to fish from blade-strike on marine hydrokinetic (MHK) turbine blades is important for incorporating environmental objectives into the integral optimization of machine performance. For instance, experience with conventional hydroelectric turbines has shown that innovative shaping of the blade and other machine components can improve hydraulic performance while reducing negative impacts to fish and other aquatic life. In this work, we used unsteady computational fluid dynamics (CFD) simulations of turbine flow and discrete element modeling (DEM) of particle motion to estimate the frequency and severity of collisions between a horizontal axis MHK tidal energy device and drifting aquatic organisms or debris. Two metrics are determined with the method: the strike frequency and the survival rate estimate. To illustrate the procedure step-by-step, an example case of a simple runner model was run and compared against a probabilistic model widely used for strike frequency evaluation. The results for the example case showed a strong correlation between the two approaches. In the application case of the actual MHK turbine flow, turbulent flow was modeled using detached eddy simulation (DES) in conjunction with a full moving rotor. The CFD-simulated power and thrust were satisfactorily comparable to experimental results conducted in a water tunnel on a reduced-scale (1:8.7) version of the turbine design. A cloud of DEM particles was injected into the domain to simulate fish or debris entrained into the turbine flow. Because various studies have pointed out the importance of fish volitional behavior, an assumed avoidance rate of 90% was applied to the particle sample. The strike frequency was the ratio of the count of colliding particles to the crossing sample size. The fish length and approaching velocity were test conditions in the simulations of the MHK turbine. Comparisons showed that DEM-based frequencies tend to be greater than previous results from Lagrangian particles and probabilistic models, mostly because the DEM scheme accounts for both the geometric aspects of the passage event —which only the probabilistic method does— as well as the fluid-particle interactions —which only the Lagrangian particle method does. With the full particle sample (0% avoidance), the DEM-based survival rates were generally high (above 90% in all studied cases), and comparable to previously reported laboratory results for small fish but not for mid-size fish mainly because of the considerable differences in rotor design between the CFD and laboratory models. With an assumed avoidance rate of 90%, the survival rates increased to nearly 99% across all scenarios. These results point to the need for further research and development of field monitoring methods for operating turbines to better understand the potential interaction between fish and MHK devices. The modeling framework can be used for applications that aim at evaluating the biological performance of MHK turbine units during the design phase and to provide information to regulatory agencies needed for the environmental permitting process.
Development of an Adaptable Monitoring Package for Marine Renewable Energy Projects Part I: Conceptual Design and Operation
Rush, Ben; Joslin, James; Stewart, Andrew; Polagye, Brian (2014-04)
The Adaptable Monitoring Package (AMP), along with a remotely operated vehicle (ROV) and custom tool skid, is being developed to support near-field (≤10 meters) monitoring of hydrokinetic energy converters. The AMP is intended to support a wide range of environmental monitoring in harsh oceanographic conditions, at a cost in line with other aspects of technology demonstrations. This paper, which is the second in a two part series, covers the hydrodynamic analysis of the AMP and deployment ROV given the strong waves and currents that typify marine renewable energy sites. Hydrodynamic conditions from the Pacific Marine Energy Center's wave test sites (PMEC) and Admiralty Inlet, Puget Sound, Washington are considered as early adoption case studies. A methodology is presented to increase the AMP's capabilities by optimizing its drag profile through a combination of computational fluid dynamic (CFD) modeling and sub-scale experiments. Preliminary results suggest that AMP deployments should be possible in turbulent environments with a mean flow velocity up to 1 m/s.
Dynamic Modelling of Compliant-Moored Submerged Systems with Applications to Marine Energy Converters
Nichol, Tyler; DuBuque, Geoff; Fabien, Brian (2014-04)
This paper presents a full‐range‐of‐motion numerical model of the dynamic characteristics of compliant‐moored submerged systems in unsteady fluid flow using a first‐principles approach. The program, implemented using the MATLAB software package, is in development with the primary intention of being applicable to in‐stream hydrokinetic turbines, though many wave energy converter and offshore wind turbine platform systems will also be capable of being modeled. A Lagrangian frame of reference is adopted to generate the equations of motion of a given system. The external forces presently considered in the model are those of gravity, buoyancy, and fluid drag, with plans to include more sophisticated fluid effects as the project advances. The development of the kinematic system and the body drag model are discussed. Additionally, two validation tests are presented. The results of the validation tests provide confidence that the methods employed have the potential to realistically simulate the dynamic behavior of compliant-moored systems once more detailed effects of fluid loading are accounted for.
Control of a Helical Cross‐Flow Current Turbine
Cavagnaro, Robert; Fabien, Brian; Polagye, Brian (2014-04)
Adaptive control strategies utilizing preview information of upstream velocity are promising approaches for enhancing performance and reducing loads on hydrokinetic turbines. A control scheme relating a turbine's characteristic performance curve and rotation rate to an optimal torque setpoint is implemented experimentally and in simulation for a laboratory‐scale helical cross‐flow turbine. Energy extraction performance for schemes employing adaptive/preview techniques is compared to performance under constant speed and non‐adaptive control. Results in simulation indicate significant improvement over constant speed operation and modest improvement over non‐adaptive strategies. Experimental results for adaptive strategies are comparable to non‐adaptive strategies, due to uncertainty in instantaneous performance curves.
Spatio-Temporal Resolution of Different Flow Measurement Techniques for Marine Renewable Energy Applications
Lyon, Vincent; Wosnik, Martin (2014-04)
Marine hydrokinetic (MHK) energy conversion devices are subject to a wide range of turbulent scales, either due to upstream bathymetry, obstacles and waves, or from wakes of upstream devices in array configurations. The commonly used, robust Acoustic Doppler Current Profilers (ADCP) are well suited for long term flow measurements in the marine environment, but are limited to low sampling rates due to their operational principle. The resulting temporal and spatial resolution is insufficient to measure all turbulence scales of interest to the device, e.g., "blade-scale turbulence." The present study systematically characterizes the spatial and temporal resolution of ADCP and Acoustic Doppler Velocimetry (ADV). Simulations were used to quantitatively investigate the flow scales that each of the instruments can resolve in low and high turbulence intensity flows. For comparison, measurements were conducted at the UNH Tidal Energy Test Site in Great Bay Estuary at General Sullivan Bridge. The purpose of the study is to supply data for mathematical modeling to improve predictions from ADCP measurements, which can help lead to higher-fidelity energy resource assessment and more accurate device evaluation, including wake measurements.
Development of a Driving Electric Dynamometer Rotor Emulator for MHK In‐Stream Turbines
Laing, William, E., Jr.; VanSwieten, James H. (2014-04)
As marine and hydrokinetic (MHK) technologies which convert the flow of fluid into useful electrical power are developed, it is desirable to simulate drivetrain performance and refine control strategies in a laboratory prior to field installation. This paper presents and evaluates a technique developed to operate the prime mover of a dynamometer so that it drives a machine under test like an MHK turbine's rotor. The approach utilizes environmental and rotor numerical models to calculate hydrodynamic torque. Relationships between shaft torque, shaft speed, and variable frequency drive native torque reference were used to modify torque reference settings to achieve actual emulated torque values. The accuracy at which physical shaft torque matches theoretical hydrodynamic torque was then evaluated for three basic operating states: locked rotor, spin up/down, and variable flow operation. Percent‐error of averaged measured and theoretical shaft torque during simulation of these states was 9.7%, 5.5%, and 5.2%, respectively, demonstrating the success of applying the proposed technique.
Experimental and Numerical Analysis of a Scale-Model Horizontal Axis Hydrokinetic Turbine
Javaherchi, Teymour; Seydel, Joseph; Stelzenmuller, Nick; Aliseda, Alberto (2014-04)
This paper presents an experimental/numerical study of a scale-model Horizontal Axis Hydrokinetic Turbine (HAHT). The model turbine is based on the DOE Reference Model 1 (DOE RM1), with a modified geometry to reproduce performance at the flume scale Reynolds numbers. These modifications were necessary to overcome the strong Reynolds number effect on the NACA–6 airfoil family used on the design, and therefore on the device performance in experimental analysis. The performance and wake structure of a single turbine was analyzed with measurements conducted on a 45:1 scale physical model of the modified design of the DOE RM1 rotor. The details of the rotor flow field and wake evolution are analyzed from numerical solution of the RANS equations solved around a computational model of the scale-model turbine. A comparison between the experimental and numerical results is presented. These comparisons highlight the strengths as well as limitations of the experimental and numerical analysis for these types of HAHT characterizations. On a more general sense, these comparisons provide useful guidelines for developing a set of experimental flume scale data and to use it to validate numerical tools, and as pilot projects start to go in the water in the US, to perform a similar type of analysis and design validation of full scale devices.
A Framework for Optimizing the Placement of Current Energy Converters
Roberts, Jesse; Nelson, Kurt; Jones, Craig; James, Scott C. (2014-04)
This study investigates the potential environmental impacts and performance of a small array of tidal energy converters (TECs) in Cobscook Bay, ME; TECs are a subset of current energy converters (CECs) that are specifically deployed in tidal channels. A previously constructed coarse-grid, regional-scale hydrodynamic model of Cobscook Bay was coupled to a refined domain centered on a proposed TEC deployment location. All models were developed with Sandia National Laboratories-Environmental Fluid Dynamics Code (SNL-EFDC). An optimization framework was then constructed that used results from the refined model to determine optimal device placement locations that maximize array performance and minimize potential environmental effects. Within the framework, environmental constraints can be included to limit CEC-induced changes in flow, sediment transport, or other physical phenomena that might affect the health of aquatic species (i.e., altering fish-swimming behavior and sediment-transport trends that could affect benthic habitat or the stability of the CEC infrastructure). Simulation results were compared between model runs with optimized array configurations, and the originally proposed deployment locations. The optimized array had roughly a 17% increase in power generation. The framework developed also provides regulators and developers with a tool to assess environmental impacts and device-performance parameters for the deployment of CEC devices.

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