Brian Polagye

• University of Washington

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 or high-fidelity numerical models that are too computationally expensive for operational use. To bridge this gap, we propose the use of dynamic mode decompo...

Cross-flow turbine power is a net sum of power generation from rotating blades and power loss from rotating support structures. While the aggregate forces and torques at the turbine level are important for end use, these can inhibit a deeper understanding of fluid-structure interactions. Identification of blade-level forces and torques allows for s...

Cross-flow turbine (known as vertical-axis wind turbines or “VAWTs” in wind) blades encounter a relatively undisturbed inflow for the first half of each rotational cycle (“upstream sweep”) and then pass through their own wake for the latter half (“downstream sweep”). While most research on cross-flow turbine optimization focuses on the power-genera...

Marine energy converters can generate electricity from energetic ocean waves and water currents. Because sound is extensively used by marine animals, the radiated noise from these systems is of regulatory interest. However, the energetic nature of these locations poses challenges for performing accurate passive acoustic measurements, particularly w...

While confinement is understood to increase the power and thrust coefficients of cross-flow turbines, how the optimal rotor geometry changes with the blockage ratio -- defined as the ratio between the array projected area and the channel cross-sectional area -- has not been systematically explored. Here, the interplay between rotor geometry and the...

The performance and near-wake characteristics of a turbine in a confined flow depend on the blockage ratio, defined as the ratio of the turbine projected area to the channel cross-sectional area. While blockage is understood to increase the power coefficient for turbine "fences" spanning a channel, most investigations at the upper range of practica...

Two passive blade pitch control strategies for an axial-flow current turbine were developed and tested experimentally in a recirculating flume. The goal of the control is to regulate mechanical power, while limiting rotor loads, when flow conditions exceed the rated condition. Both strategies use blades fabricated with unidirectional carbon fiber o...

Cross-flow turbine performance and flow fields exhibit cycle-to-cycle variations, though this is often implicitly neglected through time- and phase-averaging. This variability could potentially arise from a variety of mechanisms—inflow fluctuations, the stochastic nature of dynamic stall, and cycle-to-cycle hysteresis—each of which have different i...

Global expansion of marine renewable energy (MRE) technologies is needed to help address the impacts of climate change, to ensure a sustainable transition from carbon-based energy sources, and to meet national energy security needs using locally-generated electricity. However, the MRE sector has yet to realize its full potential due to the limited...

Ocean observation and monitoring relies on data gathered from multiple sources including gliders, cabled observatories, underwater vehicles, and moored buoys. Moored buoys, augmented by resident autonomous underwater vehicles, are potentially well-suited to long-term oceanographic data collection with the resolution and scope of data collection inc...

Because cross-flow turbines rotate perpendicular to their inflow, the blades encounter a continually fluctuating angle of attack and relative velocity that can lead to the unsteady, non-linear phenomenon of dynamic stall. Additionally, because of appreciable deceleration of the flow through the turbine rotor (induction), the relative velocity a bla...

Cross-flow turbines show great promise for extracting power from water currents since their rectangular projected area allows them to achieve high blockage. As a turbine’s blockage ratio—the ratio of the rotor projected area to the channel cross-sectional area—increases, its efficiency and structural loading increase since both kinetic and potentia...

For tidal energy to support access to off-shore electricity, further development is needed to decrease costs and increase reliability of current turbines at relevant scales. Blade pitch control strategies can significantly reduce structural loads in above-rated flow conditions by shedding power through decreased angles of attack. This can be accomp...

Modeling oscillating surge wave energy converter (OSWEC) systems to accurately predict their behavior has been a notoriously difficult challenge for the wave energy field. This is particularly challenging in realistic sea states where nonlinear WEC dynamics are common due to complex fluid-structure interaction, breaking waves, and other phenomena....

Intracycle control for cross-flow turbines employs sinusoidal perturbations in rotational speed to affect turbine power output and loads. This technique is explored for one- and two-bladed turbines with experiments that combine performance measurements with in-rotor flow-field measurements using non-intrusive particle image velocimetry. Performance...

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 pro...

Cross-flow turbine performance and flow fields exhibit cycle-to-cycle variations, though this is often implicitly neglected through time- and phase-averaging. This variability could potentially arise from a variety of mechanisms -- inflow fluctuations, the stochastic nature of dynamic stall, and cycle-to-cycle hysteresis -- each of which have diffe...

Tidal currents, particularly in narrow channels, can be challenging to characterize due to high current speeds (>1 m s ⁻¹ ), strong spatial gradients, and relatively short synoptic windows. To assess tidal currents in Agate Pass, Washington, we cross evaluated data products from an array of acoustically tracked underwater floats and from acoustic D...

Buoyancy-controlled underwater floats have produced a wealth of in situ observational data from the open ocean. When deployed in large numbers, or “distributed arrays,” floats offer a unique capacity to concurrently map 3D fields of critical environmental variables, such as currents, temperatures, and dissolved oxygen. This sensing paradigm is equa...

When we hear about offshore energy in the news media and other popular information sources, images of oil platforms and, more recently, wind farms flash across our screens. However, there is a new, rarely known sector of offshore energy under development that is focused on harnessing the renewable power contained in ocean waves and currents and con...

Cross-flow turbine performance is sensitive to multiple dimensionless parameters, including the Reynolds number, blockage ratio, and Froude number, based on both turbine submergence depth and overall channel depth. Here, we experimentally isolate the effects of each parameter. Turbine performance and free surface deformation were characterized in a...

Heave plates are one approach to generating the reaction force necessary to harvest energy from ocean waves. In a Morison equation description of the hydrodynamic force, the components of drag and added mass depend primarily on the heave plate oscillation. These terms may be parameterized in three ways: (1) as a single coefficient invariant across...

Acoustic emissions from current energy converters remain an environmental concern for regulators because of their potential effects on marine life and uncertainties about their effects stemming from a lack of sufficient observational data. Several recent opportunities to characterize tidal turbine sound emissions have begun to fill knowledge gaps a...

Cross-flow, or vertical-axis, turbines are a promising technology for capturing kinetic energy in wind or flowing water and their inherently unsteady fluid mechanics present unique opportunities for control optimization of individual rotors or arrays. To explore the potential for beneficial interactions between turbines in an array, as well as to c...

In this study, we explore the role of heave plate topology on fluid reaction forces using three, representative shapes: a hexagonal flat plate, a hexagonal conic with an open top, and the same with a closed top that encloses a fluid mass. We force each test article sinusoidally in a quiescent tank and decompose the reaction force using forms of the...

Historically, energy constraints have limited the spatial range, endurance and capabilities of ocean observation systems. Recently developed wave energy conversion technologies have the potential to help overcome these limitations by providing co-located and persistent power generation for ocean observations, enabling new opportunities for ocean re...

Governments are increasingly turning toward public–private partnerships to bring industry support to improving public assets or services. Here, we describe a unique public–private collaboration where a government entity has developed mechanisms to support public and private sector advancement and commercialization of monitoring technologies for mar...

Cross-flow turbines convert kinetic power in wind or water currents to mechanical power. Unlike axial-flow turbines, the influence of geometric parameters on turbine performance is not well-understood, in part because there are neither generalized analytical formulations nor inexpensive, accurate numerical models that describe their fluid dynamics....

This study presents an efficient system that smooths fluctuations in electrical power from a cross-flow (i.e., “vertical-axis”) turbine. The proposed solution is a two-stage approach consisting of a low-pass filter and a bi-directional buck-boost converter. The design and stability characteristics of the system are presented, followed by time-domai...

Cross-flow, or vertical-axis, turbines are a promising technology for capturing kinetic energy in wind or flowing water and their inherently unsteady fluid mechanics present unique opportunities for control optimization of individual rotors or arrays. To explore the potential for beneficial interactions between turbines in an array, coherent struct...

Straight-bladed crossflow turbines are computationally explored for harvesting energy in wind and water currents. One challenge for crossflow turbines is the transient occurrence of high apparent angles of attack on the blades that reduces efficiency due to flow separation. This paper explores kinematic manipulation of the apparent angle of attack...

The majority of utility-scale horizontal-axis current turbines use either speed or pitch control to maintain a constant power output once the currents exceed a certain threshold: the turbine-specific “rated speed”. In this study, we experimentally characterized power performance and turbine loading over a range of blade pitch settings and tip-speed...

In oscillatory flow, drag and inertial forces experienced by flat plates and cylinders depend on the Keulegan–Carpenter number. Here we demonstrate that this extends to an asymmetric hexagonal conic heave plate suitable for a point absorber wave energy converter. The forces on three geometric scales of this plate were measured throughout forced osc...

Cross-flow turbines, also known as vertical-axis turbines, convert the kinetic energy in moving fluid to mechanical energy using blades that rotate about an axis perpendicular to the incoming flow. In this work, the performance of a two-turbine array in a recirculating water channel was experimentally optimized across 64 unique array configurations...

In A.E. Copping and L.G. Hemery (Eds.), OES-Environmental 2020 State of the Science Report: Environmental Effects of Marine Renewable Energy Development Around the World.

Multibeam sonars can be used to detect and classify marine fauna under conditions when optical sensors are ineffective. In this work, we compare the detection and classification capabilities of two multibeam sonars with different operating frequencies, the Tritech Gemini 720is (720 kHz) and the Teledyne BlueView M900-2250 (2250 kHz). The two sonars...

Straight-bladed cross-flow turbines are computationally explored for harvesting energy in wind and water currents. One challenge for cross-flow turbines is the transient occurrence of high apparent angles of attack on the blades that reduces efficiency due to flow separation. This paper explores kinematic manipulation of the apparent angle of attac...

Autonomous platforms already make observations over a wide range of temporal and spatial scales, measuring salinity, temperature, nitrate, pressure, oxygen, biomass, and many other parameters. However, the observations are not comprehensive. Future autonomous systems need to be more affordable, more modular, more capable and easier to operate. Crea...

Cross-flow turbines convert kinetic power in wind or water currents to mechanical power. Unlike axial-flow turbines, the influence of geometric parameters on turbine performance is not well-understood, in part because there are neither generalized analytical formulations nor inexpensive, accurate numerical models that describe their fluid dynamics....

While flow confinement, or blockage, is known to affect current turbine performance and wake evolution, there have been limited experimental investigations of the wake evolution of cross-flow turbines under variable confinement. In this study, velocity data were collected in the near wake of a laboratory-scale (0.51 m diameter) cross-flow turbine u...

Integrated instrumentation packages are an attractive option for environmental and ecological monitoring at marine energy sites, as they can support a range of sensors in a form factor compact enough for the operational constraints posed by energetic waves and currents. Here we present details of the architecture and performance for one such system...

Cross-flow turbines, also known as vertical-axis turbines, convert the kinetic energy in moving fluid to mechanical energy using blades that rotate about an axis perpendicular to the incoming flow. In this work, the performance of a two-turbine array in a recirculating water channel was experimentally optimized across sixty-four unique array config...

Multibeam sonars are widely used for environmental monitoring of fauna at marine renewable energy sites. However, they can rapidly accrue vast volumes of data, which poses a challenge for data processing. Here, using data from a deployment in a tidal channel with peak currents of 1-2 m/s, we demonstrate the data-reduction benefits of real-time auto...

In laboratory experiments involving wind or water turbines, it is often desirable to correct measured performance for the effects of model blockage. However, there has been limited experimental validation of the analytical blockage corrections presented in the literature. Therefore, the objective of this study is to evaluate corrections against exp...

Modal analysis techniques are used to identify patterns and develop reduced-order models in a variety of fluid applications. However, experimentally acquired flow fields may be corrupted with incorrect and missing entries, which may degrade modal decomposition. Here we use robust principal component analysis (RPCA) to improve the quality of flow-fi...

While biofouling is known to degrade the performance of marine energy conversion systems, prior experimental work has not explored this topic for cross-flow turbines. Here, we present experiments that investigate the impact of biofouling on turbine power output and structural loads. Using additive manufacturing, a three-dimensional scan of a barnac...

High-resolution, four-dimensional mapping of currents in tidally-dominated, coastal settings can be conducted with a range of instrumentation. Here, we assess four approaches to data collection: an X-band radar, a stationary (bottom-mounted) acoustic Doppler current profiler (ADCP), a mobile (vessel-based) ADCP, and a swarm of Lagrangian floats. Us...

In October, 2018 the BOLT Lifesaver, a BOLT-class wave energy converter developed by Fred. Olsen Ltd., was deployed at the US Navy’s Wave Energy Test Site in Kane’ohe, Hawaii. The Lifesaver is an autonomous system, with no cable to shore. For a full year prior to the deployment, researchers and industry partners at the University of Washington, Uni...

When experimentally evaluating the performance of a wind or water current turbine, one must impose a regulating torque on the turbine rotor by electrical or mechanical means. Some options limit this controlling torque to a purely resistive quantity, while servomotors and stepper motors allow torque to be applied in the direction of turbine rotation...

Active acoustic sensors are widely used in oceanographic and environmental studies. Although many have nominal operating frequencies above the range of marine mammal hearing, they can produce out-of-band sound that may be audible to marine mammals. Acoustic emissions from four active acoustic transducers were characterized and compared to marine ma...

Particle image velocimetry (PIV) is an experimental technique used to measure fluid flow fields. However, PIV fields often have spurious and missing velocity vectors that degrade subsequent analyses. Standard post-processing involves the identification and replacement of outliers based on local information. We present a method to identify and fill...

For economic reasons, above a certain water speed, it is desirable for current turbines to maintain a constant power output. This requires a control strategy to shed power. Here, such a strategy is evaluated through simulation and laboratory experiment for a helically bladed turbine with four blades and a straight-bladed turbine with two blades. Th...

Cross-flow turbines have a number of potential advantages for hydrokinetic energy applications. Two novel control schemes for improving cross-flow turbine energy conversion are introduced and demonstrated through scale experiments. The first aims to alter the local flow conditions on the blades through varying blade kinematics as a function of rota...

Cross-flow or vertical-axis turbines are flow energy conversion devices in which lift forces cause blades to rotate around an axis perpendicular to the flow. In marine currents, rivers, and some wind energy applications, cross-flow turbines are a promising alternative to more conventional axial-flow turbines. The performance implications of the cho...

There are multiple applications where tracking and classification of targets detected in multibeam sonar data is required, ranging from environmental studies to marine security. Target tracking from a fixed frame of reference is well-established, but if the sonar is mounted to a surface-following platform or vessel, the tracking task is complicated...

Passive acoustic localizing arrays are utilized in shallow water for applications ranging from environmental monitoring to marine security. Although large-aperture hydrophone arrays can provide accurate estimates of source position, they can be costly to deploy and maintain. Small-aperture arrays can be used to estimate the incident azimuth and ele...

A general method for predicting and evaluating the performance of three candidate cross-flow turbine power-maximizing controllers is presented using low-order dynamic simulation, scaled laboratory experiments, and full-scale field testing. For each testing mode and candidate controller, performance metrics quantifying energy capture (ability of a c...

Quantifying and mitigating environmental risks presented by marine energy conversion systems requires a variety of sensors (active acoustic, passive acoustic, and optical). The operation of these sensors must satisfy three directives to be effective: (1) do not alter the environment through operation of sensors; (2) capture rare events; and (3) do...

In this paper we present the effect that different operating regions of a cross flow turbine have on the Levelised Cost of Electricity (LCOE) of the turbine power system. An optimal LCOE for a cross flow turbine is typically assumed to occur when the turbine is operating at its maximum hydrodynamic efficiency. However, by adjusting the turbine's sp...

Observations and predictions regarding oceanic intrusions at the entrance to Puget Sound, WA (USA), are presented. Four years of seabed observations at Admiralty Inlet show episodic periods high salinity, coincident with landward residual currents near the seabed. The observed residual currents are consistent with an estuarine exchange flow during...

The acoustic characteristics of marine energy converters are of interest to those attempting to quantify their environmental effects at larger scale. Such efforts are complicated by the time variation in marine energy converter sound caused by changes in the environmental forcing and converter operation, the difficulty of identifying marine energy...

When conducting tidal energy resource characterization and assessment, it is important to capture the strong variations of tidal currents in time and space. Field measurements can quantify many of these variations, which have both deterministic and stochastic components. The deterministic components occur on timescales of hours to years. As such, t...

Wave energy converters produce sound as a consequence of their operation, but the specifics are not well-understood. Here, we present observations of two point-absorbing wave energy converters deployed at the US Navy’s Wave Energy Test Site in Kaneohe, HI. Measurements are obtained by free-drifting instrumentation packages which acoustical isolate...

A method for constructing a non-dimensional performance curve for a cross-flow hydrokinetic turbine in sheared flow is developed for a natural river site. The river flow characteristics are quasi-steady, with negligible vertical shear, persistent lateral shear, and synoptic changes dominated by long time scales (days to weeks). Performance curves d...

As progress toward the commercial deployment of wave energy converters accelerates, it is important to ensure that these renewable energy systems do not have unintended, adverse environmental consequences. While the sound from wave energy converters is unlikely to cause acoustic injury to marine animals, it may affect their behavior. Here, we prese...

No PDF available ABSTRACT The detection and classification of targets in shallow water environments (e.g., depth < 20 m) is of increasing interest, both in security applications and more general environmental studies. Here, we report the ability of a cabled integrated instrumentation system to detect and classify targets in a shallow (15 m deep), n...

Wind energy production in the U.S. is projected to increase to 35% of our nation’s energy by 2050. This substantial increase in the U.S. is only a portion of the global wind industry growth, as many countries strive to reduce greenhouse gas emissions. A major environmental concern and potential market barrier for expansion of wind energy is bird an...

Cross-flow turbines, also known as vertical-axis turbines, are attractive for power generation from wind and water currents.Some cross-flow turbine designs optimize unsteady fluid forces and maximize power output by controlling blade kinematics within one rotation. One established method is to dynamically pitch the blades. Here we introduce a mecha...

Cross-flow turbines, also known as vertical-axis turbines, have numerous features that make them attractive for wind and marine renewable energy. To maximize power output, the turbine blade kinematics may be controlled during the course of the blade revolution, thus optimizing the unsteady fluid dynamic forces. Dynamically pitching the blades, simi...

A cross-flow hydrokinetic turbine with a projected area (product of blade span and rotor diameter) of 0.7 m2 is evaluated in open-water tow trials at three inflow speeds ranging from 1.0 m/s to 2.1 m/s. Measurements of the inflow velocity, the rotor mechanical power, and electrical power output of a complete power take-off (PTO) system are utilized...

International Network Offshore Renewable Energy, North American Symposium 2015

Biofouling mitigation measures for optical ports can extend the duration of oceanographic deployments, but there have been few quantitative studies of field performance. Results are presented from a 4-month field test of a stereo-optical camera system intended for long-term environmental monitoring of tidal turbines. A combination of passive (coppe...

Velocity spectra are essential in characterizing turbulent flows. The Acoustic Doppler Velocimeter (ADV) provides three-dimensional time series data at a single point in space which are used for calculating velocity spectra. However, ADV data are susceptible to contamination from various sources, including instrument noise, which is the intrinsic l...

The development, implementation, and testing of a stereo-optical imaging system suitable for environmental monitoring of a tidal turbine is described. This monitoring system is intended to provide real-time stereographic imagery in the near-field (<10 m) of tidal turbines proposed for deployment in Admiralty Inlet, Puget Sound, Washington. Postdepl...

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 envi...

Flow-noise resulting from oceanic turbulence and interactions with pressure-sensitive transducers can interfere with ambient noise measurements. This noise source is particularly important in low-frequency measurements (f < 100 Hz) and in highly turbulent environments such as tidal channels. This work presents measurements made in the Chacao Channe...

As the marine energy industry explores the potential for generating significant power from waves and tidal currents, there is a need to ensure that energy converters do not cause harm to the marine environment, including marine animals that may interact with these new technologies in their native habitats. The challenge of deploying, operating, and...

Acoustic Doppler sensors used for flow measurements at energetic tidal sites present an inherent “Doppler noise” in the measured signal, varying with hardware configuration and flow conditions. At scales comparable to the sensors’ sampling frequencies, the corresponding perturbations notably contaminate the signal, and cannot be corrected in the ti...

In addition to utility-scale power generation (e.g., rated capacities greater than 106 W), there are also possibilities for tidal current generation at the micro-scale (e.g., rated capacities less than 102 W) that could provide power to autonomous oceanographic instrumentation. This paper presents performance characteristics of a high-solidity, hel...

Station keeping, a vessel-based spatial surveying method for resolving details of the hydrokinetic resource, is presented in the context of the general methodology and also for the specific case of a survey conducted in northern Admiralty Inlet, Puget Sound, WA, in June 2011. The acoustic Doppler current profiler (ADCP) measurements collected durin...

Tidal energy resource characteristics are presented from a multi-year field study in northern Admiralty Inlet, Puget Sound, WA (USA). Measurements were conducted as part of a broader effort to characterize the physical and biological environment at this location ahead of a proposed tidal energy project. The resource is conceptually partitioned into...

Tidally driven currents and bed stresses can result in noise generated by moving sediments. At a site in Admiralty Inlet, Puget Sound, Washington State (USA), peak bed stresses exceed 20 Pa. Significant increases in noise levels are attributed to mobilized sediments at frequencies from 4-30 kHz with more modest increases noted from 1-4 kHz. Sedimen...

Oceanic intrusions of dense, hypoxic water regularly occur at the entrance to Puget Sound, WA (USA), and may be significant to regional dissolved oxygen levels. Seabed observations at Admiralty Inlet from 2009 to 2013 show a strong correlation of low dissolved oxygen concentrations with high salinity, coincident with residual currents directed inwa...

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) and long-range monitoring of hydrokinetic energy converters. The goal for the AMP is to develop a system capable of supporting a wide range of environmental monitoring in harsh oceanographic...