Addressing barriers to development, deployment, and evaluation of marine hydrokinetic devices.
Sandia’s Water Power Technology program seeks to reduce the cost and time required to deploy marine hydrokinetic (MHK) devices. We utilize numerical modeling and experiments to develop solutions to the concerns and needs of both developers and regulators. Our work includes:
Developing tools for identifying and mitigating environmental risks
Providing data to accelerate permitting
Creating professional development opportunities for developers and researchers
Engaging in ocean planning to incorporate MHK technologies in the nation’s marine spatial plans
Predicting Environmental Effects
Regulators and developers have little information about the potential effects of MHK devices on aquatic environments. To address this problem, Sandia gathers hard-to-obtain data using predictive modeling, laboratory experiments, and field monitoring. We also conduct research to improve environmental monitoring tools and mitigation options. Our research enables developers to design devices and array configurations with optimal power production and minimal environmental impact.
Strike Impacts to Sensitive Species
Sandia works with researchers from Pacific Northwest National Laboratory (PNNL) to determine the possible consequences of a marine mammal colliding with a tidal turbine. Sandia uses its high-power computational platforms to simulate impacts while PNNL performs biological assessments.
In 2014, this research removed barriers to the installation of the SNOPUD ducted turbine in Puget Sound. Regulators were concerned about a shrouded turbine installation harming the already endangered species. Using Sandia’s unique structural dynamics code, PRESTO, we simulated multiple scenarios in which a shrouded turbine struck a Southern Resident killer whale. PNNL used our simulations and data about the whale’s physical characteristics to assess the biological impacts of the strike. The results showed, even in the worst-case scenario with a full range of blade impact speeds, significant harmful damage to the whale’s tissue was unlikely. With this information, regulators were able to grant permits for the turbines installation.
Sandia and PNNL are now performing similar computational and biological assessments to determine the effects of a unducted turbine strike on a harbor seal.
Modeling Array Effects
While studies of small numbers of MHK devices show that they are unlikely to cause perceptible affects to physical aquatic environments, the potential effects of large arrays are still unknown. Sandia develops and refines numerical modeling methods to predict the effects of differing numbers and configurations of wave and current energy converters on water and sediment movement, water quality, and possible aquatic habitats. Data from these simulations allow developers to maximize power generation while minimizing negative environmental impacts.
Sandia uses modeling to investigate the potential impact of CEC arrays on environments.
Models and data show reduced wave energy on the lee side of a wave energy converter (WEC). Unfortunately, existing models are unable to predict the environmental effects of wave energy removal caused by multiple WECs. Therefore, Sandia is refining the open-source spectral wave model, SWAN, to accurately represent the influence of WEC operation on wave propagation. The new code, SNL-SWAN, includes a “WEC Module” that provides siting guidance for developers and enables regulators to make timely, accurate permitting decisions.
Using SNL-SWAN to Predict Nearshore Effects in Monterey Bay, California
Using SNL-SWAN, Sandia researchers wave height reduction caused by several different WEC sizes and designs. While, there was a significant change in wave height near the devices, almost no changes were evident near the shoreline.
Sandia investigated the possible positive and negative environmental impacts of a WEC array using SNL-SWAN. Large arrays of WECs must be installed in order to produce enough power for a commercial grid. Before developers can install such arrays, industry and regulators must determine whether there is potential for WEC arrays to alter nearshore wave propagation and circulation, thereby altering the environment. To answer this question, Sandia used SNL-SWAN, a modified version of the wave modeling software SWAN, to compare the wave conditions in Monterey Bay, California with and without an array of 50 WECs. Our models included output from 18 nearshore locations and two different device designs. SNL-SWAN calculates relative capture width, the ratio of incident wave power to the wave power captured by specific WEC devices. This value can be used to calculate the wave energy transmission coefficient which is used to evaluate a device’s effects on wave propagation and nearshore hydrodynamics. Our models showed the most significant changes on the lee side of the array along angles of incident wave direction and minimal changes on the western side of the array due to wave shadowing by land. In addition, we identified one of the WEC devices produced less change in wave height than the other design.
Regulators’ and stakeholders’ concern about current energy conversion (CEC) devices disrupting natural flow is a major barrier in the permitting process. Unfortunately, little information about the environmental effects of CEC devices exists. Sandia is developing, refining, and validating hydrodynamic modeling tools to simulate CEC influences on aquatic environments. Using these open-source tools, developers will be able to balance CEC power performance with environmental effects.
Sandia used SNL-EFDC to model the potential environmental impacts of a CEC array in Cobscook Bay.
In 2007, the Ocean Renewable Power Company expressed interest in installing an array of five TidGen® tidal turbines in Cobscook Bay, Maine. While one device was already in the bay, stakeholders were concerned that multiple devices would potentially alter the physical environment. Using SNL-EFDC, Sandia researchers developed hydrodynamic models which determined the array would not cause significant environmental alterations, leading to accelerated deployment. We modeled the movement of sediment, rates of tides, and flushing characteristics for areas adjacent to and far from the existing device. By comparing these simulations with baseline environmental data, we determined the alteration to sediment movement, tides, and flushing was negligible. The Ocean Renewable Power Company used the information from our models to file a draft pilot license application in 2009.
Acoustic Generation and Propagation Modeling
Regulations prevent developers from deploying devices that generate enough noise to constitute disturbance to marine species. Because of the complex nature of acoustics modeling and the lack of measured data, meeting these requirements is an issue for developers. Sandia has partnered with the Applied Research laboratory at Penn State University to develop and validate open-source tools for modeling MHK noise generation and propagation. This free tool will make it easier for developers and regulators to determine the amount of noise created by a device and the potential effects of the noise on the environment.
Installation of the 1:8.7 scale rotor in the 1.22 m Garfield Thomas Water Tunnel at Penn State University.
Sandia is investigating the use of CHAMP (Combined Hydro-Acoustic Modeling Program), a stochastic structural-analyses developed by Penn State University, to predict the radiated sound from an underwater turbine. To validate predictions, we developed a novel sub-scaled turbine which we tested in the Applied Research Laboratories’ 1.22m diameter water tunnel.
Common methods for predicting the propagation of sound underwater are too limited to accurately predict the dissemination of noise from MHK devices. Sandia is developing Paracousti, a tool which will more accurately map sound propagation for individual turbines and turbine arrays. A 3-D, finite-difference solution to the governing velocity-pressure equations allows our tool to model spatially varying sound speeds, bathymetry, and bed composition, resulting in more accurate predictions.
Sandia conducts acoustics tests in the water tunnel at the Applied Research Laboratory at Penn State.
Predicted sound pressure levels from reference CEC turbine