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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Analysis and Proof‐of‐Concept Experiment of Liquid‐Piston Compression for Ocean Compressed Air Energy Storage (OCAES) System
Park, Joong-kyoo; Ro, Paul I.; He, Xiao; Mazzoleni, Andre P. (2014-04)
An analysis and a proof‐of‐concept experiment of liquid‐piston compression were conducted for a table‐top Ocean Compressed Air Energy Storage (OCAES) prototype. A singlecylinder‐ type piston surrounded by water was modeled and analyzed based on convection heat transfer with fully developed internal flow, the assumption adopted by earlier liquid piston study in literature. Transient numerical results of this model were calculated for a polytropic compression with different polytropic index values for 2.5‐second stroke. Also, an experimental model of the liquid piston was built with two different materials, polycarbonate and aluminum alloy, for a compression chamber. Temperature data were measured at six different stroke times to examine any difference in heat transfer rates affected by stroke frequency. The temperature within each cycle was measured during compression from 1 bar to 2.2 bars. It was found that longer stroke time induces smaller temperature rise in the air. The local temperature rise was observed to be 80 °C at 2.5‐second stroke and 7 °C at 40‐second stroke. While the simulations predict a temperature rise of 48.6 °C for a compression stroke time of 2.5 seconds, the temperature rise calculated for adiabatic compression was found to be 98.8 °C. This implies that the heat transfer characteristics of a liquid piston compression process are effective in reducing the air temperature. The experimental results with longer stroke times proved a nearisothermal nature of the liquid piston compression system. Overall, the experimental study outlined in this paper not only confirms the near‐isothermal nature of the liquid piston system but also enables further study of the expansion cycle using the liquid‐piston concept. More importantly, the current study paves a way for future work on a larger scale OCAES system demonstration based on liquid‐piston concept.
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.
Annex IV - Investigating Environmental Effects of Wave and Tidal Devices Through International Cooperation
Copping, Andrea; Hanna, Luke; Battey, Hoyt (2014-04)
The pace of development for marine energy projects worldwide continues to be hindered by uncertainty surrounding potential environmental effects of wave and tidal devices and the balance of system. In response to this continued uncertainty, member nations of the Ocean Energy Systems (OES) developed a collaborative project – Annex IV – to increase collection and sharing of knowledge, research collaborations around high priority environmental interactions, and relevancy of the information to permitting (consenting) processes. The culmination of Annex IV Phase 1 is a searchable database of current literature and reports on environmental effects of marine energy development, and an analysis of three key interactions of devices and the marine environment.
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.
CACTUS Open Source Code for Hydrokinetic Turbine Design and Analysis: Model Performance Evaluation and Public Dissemination as Open Source Design Tool
Michelen, Carlos; Murray, Jonathan C.; Neary, Vincent S.; Barone, Mathew (2014-04)
Sandia National Laboratories recently released an open source code for design and analysis of axial‐flow and cross‐flow marine and hydrokinetic (MHK) turbines, CACTUS (Code for Axial and Cross‐flow TUrbine Simulation), and has initiated an outreach effort to promote its use among MHK researchers and developers. Our aim in this paper is to summarize the recent developments in CACTUS, and present model performance evaluation results that demonstrate CACTUS's potential use as a design and optimization tool for marine hydrokinetic turbines. We present several model validation tests to evaluate the model's ability to predict MHK turbine performance. The results show both the potential use of CACTUS as a design tool and its current limitations. At least two more model validation tests are planned for 2014 as part of this effort: scaled model tests of DOE's Reference Model 1(RM1) and Reference Model 2 (RM2) turbines in 2014 at the University of Minnesota's St. Anthony Falls Laboratory (SAFL).
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.
Design and Initial Component Tests of an integrated Avian and Bat Collision Detection System for Offshore Wind Turbines
Flowers, Jeremy; Albertani, Roberto; Harrison, Trevor; Polagye, Brian; Suryan, Robert M. (2014-04)
We describe the development and initial testing of a multi‐sensor instrumentation package capable of detecting avian and bat interactions with offshore wind turbines. The system design emphasizes the ability to detect collisions with the blades, tower, and nacelle of a turbine and to provide taxonomic classification of the animal involved in the collision. This system will allow the environmental impacts of offshore wind turbines to be remotely monitored and help ensure that the benefits of renewable power generation are not outweighed by mortality of protected species. Conceptual design of the complete system, initial testing of vibration sensors, and proof of concept for sensor integration and event detection are presented.
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.
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.
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.
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.
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.
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.
Evaluation of Hycom as a Tool for Ocean Current Energy Assessment
VanSwieten, James H.; Meyer, Imke; Alsenas, Gabriel M. (2014-04)
This paper provides a global ocean circulation model based world-wide assessment of two flow characteristics and presents a direct comparison between model based predictions and in situ measurements in two regions. Four years (2009-2012) of HYbrid Coordinate Ocean Model (HYCOM)-generated data were used to estimate the average kinetic energy flux and flow direction variability in eight regions with time-averaged power density of at least 500 W/m². A direct comparison was then made between model calculated flow statistics those calculated from Acoustic Doppler Current Profiler data in both South Africa and the Southeast United States. Included analysis and discussion is intended to provide model predictions of the ocean current resource and assess the accuracy that can be expected when this model is used for making these predictions. This paper focuses on model predicted kinetic energy flux, flow speeds, and current direction variability, as these are important to the development and installation of OCT devices.
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.
Experimental Study of Tribological Performance of Bearing-Seal Assembly of Hydrokinetic Devices in Sedimented Water
Ali, Muhammad; Ravens, Thomas M.; Petersen, Todd H.; Bromaghin, Angus F.; Jenson, Sean R. (2014-04)
In this study, wear of polymer and ceramic coated bearings for use in hydrokinetic devices were investigated in sedimented water under the loading conditions similar to those expected in the field using a customized flume. This work is a continuation of the study performed in [1, 2] in which three polymer bearings, namely Vesconite, CIP, Feroform T814, and one ceramic coated bearing, namely Poly Crystalline Diamond Coated (PCD) along with two mechanical seals were tested in clean water for 60 hours. The results showed that PCD bearings experienced least amount of wear followed by Feroform T814, CIP, and Vesconite. The load side surfaces of polymer bearings exhibited a circular wear pattern whereas PCD bearings did not show any distinctively identifiable wear pattern. Following the same testing methodology, 60 hours long tests were conducted in fresh sedimented water on the same types of (new) bearings and seals. The data showed that bearings had similar (or less) total wear in sedimented water as compared to clean water, however, the drive shaft experienced a significant surface wear. In addition, the loading side of polymer bearing surfaces developed a circular wear pattern with significantly higher wear on the edge surfaces.
Externally Bonded FBG Strain Sensors Structural Health Monitoring of Marine Hydrokinetic Structures
Schuster, Michael; Fritz, Nathan; McEntee, Jarlath; Graver, Tom; Rumsey, Mark; Hernandez-Sanchez, Bernadette; Miller, David M.; Johnson, Erik (2014-04)
To reduce operations and maintenance costs, mitigate failures, and improve capacity factor, structural health‐monitoring systems can provide key information to improve management of marine hydrokinetic devices. While present systems include instrumentation to measure power output, few adequately monitor mechanical load and structural response, which are equally important for determining device performance and integrity. Fiber optic fiber Bragg grating (FBG) sensors could prove to be a reliable and unobtrusive measurement tool for marine power; however, externally adhered FBGs have not been extensively studied on submerged, dynamic structures. Thus investigations on thebBond integrity between sensor and structure of a kinetic system, FBG strain sensors were tested in dry and environmentally soaked conditions under both static and fatigue loads. Composite coupons were strained in a fatigue testing system and monitored. Dry results demonstrated very high correlation and response from the FBG sensors, up to coupon failure. The environmentally soaked samples and sensors were subject to many failure modes and verified the developer's recommendation to not externally adhere the FBG strain sensors without additional mechanical and environmental protections.
Fatigue Life Distribution for a Simple Wave Energy Converter
Brown, Adam C.; Paasch, Robert K. (2014-04)
Fatigue is known to be a dominant failure mode for systems subjected to wave loading. A time domain simulation of loading on a simple Wave Energy Converter (WEC) was used to develop the distribution of fatigue failures around the assumed 10 year design life of the device. In order to maintain the generality of the paper, the WEC was modeled as a simple, solid, stainless steel rod under wave induced axial tension and compression. This simplified model is seen as a reasonable approximation of a hydraulic ram. The system was subjected to seas that would be typical of the Oregon wave climate. The random waves used for the analysis were generated according to linear wave theory by way of random phase reconstruction of JONSWAP spectra. The model of the Oregon wave climate is also discussed, as it was found that the randomness within the wave climate model greatly affects the variance of the distribution of fatigue life. An equation for stress cycle induced damage was developed according to the Linear Cumulative Damage Theorem (Miner's Rule). Time to failure and several other metrics were recorded for 300 failures in order to develop the probability distribution of fatigue life.
Field Measurement Test Plan to Determine Effects of Hydrokinetic Turbine Deployment on Canal Test Site in Yakima, WA, USA
Gunawan, Budi; Neary, Vincent S.; Roberts, Jesse; Dallman, Ann; Grovue, Shane; Mortensen, Josh; Heiner, Bryan (2014-04)
The primary goal of the Department of Energy’s Water Power Program is to efficiently develop and utilize the country’s marine hydrokinetic (MHK) and conventional hydropower (CH) resources. The program has recently identified the need to better understand the potential for hydrokinetic energy development within existing canal systems that may already have integrated CH plants. Hydrokinetic (HK) turbine operation can alter water surface elevations and modify the flow in a canal. Significant water level alterations and hydrodynamic energy losses are generally undesirable not only for CH plan operations, but also for irrigation and flood management operations. The goal of this study is to better understand the effect of operating individual and arrays of devices on local water operations through field measurements and numerical modeling. A methodology to study the effect of hydrokinetic turbine deployment in a test site in Roza Canal, Yakima, WA, is presented. The methodology comprises detailed water level and velocity measurements to characterize energy gradeline and inflow and wakeflow fields. Results from a preliminary testing are also discussed.

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