Marine And Hydrokinetic Research Articles

Design, dynamic modeling and wave basin verification of a Hybrid Wave–Current Energy Converter

Massive and high-density Marine and Hydrokinetic (MHK) energy is contained in the ocean, including waves, tidal streams, and ocean currents. Traditional MHK energy converters harvest energy from only a single MHK energy source, which does not fully exploit the energy potential that co-exists in multiple forms of MHK energy in the ocean. This paper presents the design and dynamics of a Hybrid Wave–Current Energy Converter (HWCEC) that can simultaneously convert both wave and current energy to electricity with a single Power Take-off (PTO) through the engagement and disengagement of the three one-way clutches. The critical design parameters are analyzed through modeling and simulation, including the transmission ratios, the electrical impedance, and the turbine-heave plate distance. Water basin tests in a wave–current tank were conducted, which shows the prototyped HWCEC can improve the electric power output by 38%–71% for regular waves and 79% for irregular waves, while providing a 70% reduction of the Peak to Average Ratio (PAR) of power compared to the baseline Wave Energy Converter (WEC). We further analyze the occurring percentages of the instant power of both WEC and HWCEC in irregular wave tests, shedding new insight on how HWCEC reduces the PAR.

Behavioral responses of fish to a current-based hydrokinetic turbine under mutliple operational conditions.

There is significant international interest in developing current-based marine and hydrokinetic (MHK) technologies to capture the power of tidal energy. However, concerns have been raised regarding the ecological effects of these projects on fish, including the risk of blade collision and behavioral impacts such as the disruption of migratory behavior and food acquisition and displacement from preferred habitats. We conducted mobile hydroacoustic surveys to track fish as they approached a tidal turbine deployed in Cobscook Bay, Maine. There was a significant decline in fish numbers with decreasing distance to the turbine, beginning approximately 140m from the turbine. Similar declines were not observed at control transects or when the turbine was not spinning. The decline in fish numbers appeared to be the result of horizontal displacement, not vertical, movements to avoid the turbine. Noise rather than visual cues or flow field disturbance seemed to be a likely explanation for the reduced number of fish near the turbine. This finding, combined with near-field blade collision studies indicating a low probability of encounter, suggests that a single turbine poses a low collision risk to pelagic fish and that a single turbine is likely to result in minimal behavioral responses by fish. However, the risk may be different with additional devices, which will become more relevant as commercial-scale MHK arrays come under consideration. Therefore, the risks associated with commercial-scale operations will ultimately have to be evaluated to fully understand the ecological impacts of MHK devices.

High-resolution hindcasts for U.S. wave energy resource characterization

The marine and hydrokinetic (MHK) industry is at an early stage of development and has the potential to play a significant role in diversifying the U.S. energy portfolio and reducing the U.S. carbon footprint. Wave energy is the largest among all the U.S. MHK energy resources, which include wave energy, ocean current, tidal-instream, ocean thermal energy conversion, and river-instream. Wave resource characterization is an essential step for regional wave energy assessments, Wave Energy Converter (WEC) project development, site selection and WEC design. The present paper provides an overview of a joint modelling effort by the Pacific Northwest National Laboratory and Sandia National Laboratories on high-resolution wave hindcasts to support the U.S. Department of Energy’s Water Power Technologies Office’s program of wave resource characterization, assessment and classifications in all US coastal regions. Topics covered include the modelling approach, model input requirements, model validation strategies, high performance computing resource requirements, model outputs and data management strategies. Examples of model setup and validation for different regions are provided along with application to development of classification systems, and analysis of regional wave climates. Lessons learned and technical challenges of the long-term, high-resolution regional wave hindcast are discussed.

Environmental Permitting and Compliance Cost Reduction Strategies for the MHK Industry: Lessons Learned from Other Industries

The marine and hydrokinetic (MHK) industry plays a vital role in the U.S. clean energy strategy by providing a renewable, domestic energy source that may offset the need for traditional energy sources. The first MHK deployments in the U.S. have incurred very high permitting costs and long timelines for deploying projects, which increases project risk and discourages investment. A key challenge to advancing an economically competitive U.S. MHK industry is reducing the time and cost required for environmental permitting and compliance with government regulations. Other industries such as offshore oil and gas, offshore wind energy, subsea power and data cables, onshore wind energy, and solar energy facilities have all developed more robust permitting and compliance pathways that provide lessons for the MHK industry in the U.S. and may help inform the global consenting process. Based on in-depth review and research into each of the other industries, we describe the environmental permitting pathways, the main environmental concerns and types of monitoring typically associated with them, and factors that appear to have eased environmental permitting and compliance issues.

Large-eddy simulation of a hydrokinetic turbine mounted on an erodible bed

Marine and hydrokinetic (MHK) energy from free-flowing waves, tides and currents comprises an important source of clean and renewable energy. The development of technologies for harnessing MHK energy and assessing its environmental effects is still at early stage. In this work, we develop a computational model for simulating hydrokinetic turbines with bed-load sediment transport under clear-water scour conditions. Turbulent flow is simulated using large-eddy simulation (LES). The bed surface elevation is simulated by solving the non-equilibrium continuity equation, the so-called Exner-Polya equation. The turbine blades are parameterized as actuator lines. The developed model is applied to simulate the flow past an axial-flow hydrokinetic turbine mounted on an erodible bed in an open channel. A good agreement with measurements is obtained. The effects of turbine operating conditions and sediment particle sizes on the bed-load sediment transport are then examined. Finally the turbine wake characteristics are investigated for a rigid flat bed and the eroded bed under different turbine operating conditions.

Examining the Impacts of Tidal Energy Capture from an Ecosystem Services Perspective

AbstractAs governments from the local to national level have recognized the need to integrate renewable sources into their energy portfolios, there has been a recent push to harness diverse sources of ocean energy, including those generated by tides and waves. Despite the potential benefits, development of these marine and hydrokinetic (MHK) resources has raised concerns in terms of their potential socioeconomic and environmental impacts. An ecosystem services perspective offers a useful means of monitoring how MHKs will affect both people and nature by enabling the identification of the benefits provided by functioning ecosystems to people, including biodiversity, tourism and recreation, and food provision. To illustrate the value of this approach in evaluating the potential impacts of an MHK project, we present the case study of the Muskeget Channel Tidal Energy Project (United States) and identify the types of data and analytical tools that could be used to develop an ecosystem service assessment of MHK development in this study region. To complement this case study, we also reviewed the published literature on tidal energy and other MHK project types, which highlighted how little is known about the ecological effects of MHK development in coastal and marine ecosystems. Integrating ecosystem service knowledge into projects like Muskeget Channel can contribute to more scientifically informed MHK siting processes and more effective, ecosystem-based management of the diverse human activities undertaken in coastal and marine environments.

Design and Implementation of a Marine Animal Alert System to Support Marine Renewable Energy

AbstractPower extracted from fast-moving tidal currents has been identified as a potential commercial-scale source of renewable energy. Marine and hydrokinetic (MHK) device developers and utilities are pursuing deployment of prototype tidal turbines to assess technology viability, site feasibility, and environmental interactions. Deployment of prototype turbines requires environmental review and permits from a range of regulatory authorities. Ensuring the safety of marine animals, particularly those under protection of the Endangered Species Act of 1973 and the Marine Mammal Protection Act of 1972, has emerged as a key regulatory challenge for initial MHK deployments. The greatest perceived risk to marine animals is from strike by the rotating blades of tidal turbines. Development of the marine animal alert system (MAAS) was undertaken to support monitoring and mitigation requirements for tidal turbine deployments. The prototype system development focused on the Southern Resident killer whale (SRKW), an endangered population that frequents Puget Sound, Washington, and is seasonally present in the part of the sound where deployment of prototype tidal turbines is being considered. Passive acoustics were selected as the primary means to detect the SRKWs because of the vocal nature of these animals. The MAAS passive acoustic system consists of a two-stage process involving the use of an energy detector and a spectrogram-based classifier to distinguish between SKRW calls and background noise. A prototype consisting of two 2D symmetrical star arrays separated by 20 m center to center was built and evaluated successfully in the waters of Sequim Bay, Washington, using whale-call playback.

Modeling tidal stream energy extraction and its effects on transport processes in a tidal channel and bay system using a three-dimensional coastal ocean model

This paper presents a numerical modeling study for simulating in-stream tidal energy extraction and assessing its effects on the hydrodynamics and transport processes in a tidal channel and bay system connecting to coastal ocean. A marine and hydrokinetic (MHK) module was implemented in a three-dimensional (3-D) coastal ocean model using the momentum sink approach. The MHK model was validated with the analytical solutions for tidal channels under one-dimensional (1-D) conditions. Model simulations were further carried out to compare the momentum sink approach with the quadratic bottom friction approach. The effects of 3-D simulations on the vertical velocity profile, maximum extractable energy, and volume flux reduction across the channel were investigated through a series of numerical experiments. 3-D model results indicate that the volume flux reduction at the maximum extractable power predicted by the 1-D analytical model or two-dimensional (2-D) depth-averaged numerical model may be overestimated. Maximum extractable energy strongly depends on the turbine hub height in the water column, which reaches a maximum when turbine hub height is located at mid-water depth. Far-field effects of tidal turbines on the flushing time of the tidal bay were also investigated. Model results demonstrate that tidal energy extraction has a greater effect on the flushing time than volume flux reduction, which could negatively affect the biogeochemical processes in estuarine and coastal waters that support primary productivity and higher forms of marine life. ► Model validation of tidal energy extraction against an analytical solution. ► 3-D effects on velocity, power extraction and volume flux. ► Volume flux reduction predicted by 1-D and 2-D models may be overestimated. ► Effects of tidal energy extraction on flushing time.

Marine‐hydrokinetic energy and the environment: Observations, modeling, and basic processes

Research at the Interface of Marine Hydrokinetic Energy and the Environment: A Workshop; Minneapolis, Minnesota, 5–7 October 2011 Marine and hydrokinetic (MHK) energy harvesting technologies convert the kinetic energy of waves and water currents into power to generate electricity. Although these technologies are in early stages of development compared to other renewable technologies, such as solar and wind energy, they offer electricity consumers situated near coastlines or inland rivers an alternative energy technology that can help meet renewable portfolio standards. However, the potential environmental impacts of MHK energy are far from well understood, both in general principles and in site‐specific cases. As pressure for new MHK energy licenses builds, accelerated research in providing the scientific understanding of harnessing the natural power of water for renewable energy at a competitive cost and without harming the environment becomes a priority.