Marine Hydrokinetics Technology: Technology Development

Sandia National Laboratories leads work to examine the cost-effectiveness and reliability of technology for the Department of Energy’s (DOE’s) Marine and Hydrokinetic (MHK) program, which include wave, current/tide, and thermal-energy conversion. The research will focus on developing and advancing the science and tools needed to bring new water-power technologies to market and evaluating methods designed to improve the performance of existing hydropower facilities. MHK research will also evaluate the use of Sandia’s lake facility, used for large-scale wave testing. In partnership with Oak Ridge National Laboratory (ORNL), Pacific Northwest National Laboratory (PNNL), and the National Renewable Energy Laboratory (NREL), activities will evaluate new device designs and conduct basic research in materials, coatings, adhesives, hydrodynamics, and manufacturing to assist industry in bringing efficient technologies to market.

Wave Energy System Design and Modeling

The amount of energy captured and converted by a wave-energy device is a primary consideration in the design of wave-energy generators. The energy output over the life of the device must be sufficient to pay for design, fabrication, installation, operation, and maintenance. It is desirable to be able to operate wave devices at, or very near, resonance in order to maximize the motions and the resulting energy capture. The linear potential flow solutions often used to analyze the motion of floating bodies such as oil and gas platforms assume that the wave surface slope is small, the body is in steady state motion, and that the body motions are small. These solutions also assume that the flow is inviscid, nonturbulent, and has no boundary layer. Because these assumptions result in a linear system of equations, they can be fairly easily solved in the frequency domain, which is typically the case for the analysis of oil and gas platforms.

For the purpose of developing design and analysis tools applicable to industry and university needs, the team will examine both normal and extreme operating conditions. For example, the devices must be designed to survive both long-term average conditions and infrequent, but extreme storms. The following tasks are directed at modeling the external wave conditions for use in existing simulation tools, as well as developing and validating new computer design, analysis, and simulation tools to predict machine performance, loads stability, extreme loads, and fatigue loads.

The objective of this research is to review these classical solutions and verify the situations and conditions under which linear solutions can be used to analyze energy-producing bodies with large relative motion and when nonlinear time domain solutions are needed. Both large-scale and small-scale models will be employed at appropriate resolutions to capture the fluid physics in near field regions for device specific applications and study the performance of the devices/device array and far field for hydrology implication on device arrays.

Ocean, River, and Current/Tidal Energy System Design and Modeling

Sandia and its partners will study large scale hydrology effects and smaller scale affects near or on a device or array of devices. Hydrology efforts include modeling of the hydrodynamics and sediment or particulate effects on the devices or array of devices. Design tools and analysis work includes code modification and the development of fluid dynamics and structural computation analysis techniques. These tools may also have the opportunity to be used and validated in the testing, evaluation and reliability tasks.

The inflow characteristics will also need to be modeled for ocean, tidal and river current situations. While the dominant characteristics of a water current inflow model will be embodied in the turbulence and spatial variability of current itself, the combination of inflow turbulence models with wave kinematics models may be needed when rotors are installed near the free surface in open ocean currents. The importance of these effects on the structural loading will be reviewed and added to the codes. In the longer term, additional enhancements will be incorporated depending on program priorities, and these enhancements could include technologies such as flow augmentation devices (cowlings, shrouds, etc.).

Sandia’s objective is to develop or refine models and tools for advancing the design and predictability of current devices or systems. Areas of focus will initially be on hydrodynamic interactions with turbine systems and then to couple this with structural models.  The team will develop a design methodology for rotor blades and design of water turbines including hydrofoils that optimize performance, and minimize the effects of cavitation, as well as minimizing corrosion and the related environmental impacts of many coatings. The team will also develop enhanced water turbine performance models for rotor design and energy capture estimation, including cavitation; seabed boundary and free surface effect; and initiate the development of array prediction models for multiturbine arrays.

Finally, the team will develop ocean/river inflow models suitable for computing turbulence-induced loads with sufficient accuracy to calculate fatigue, dynamic, and ultimate loads for water turbine design and direct use with various dynamics codes. A shared Sandia-NREL activity will integrate near-field and far-field models.

Advanced Materials and Manufacturing

Advanced materials and manufacturing activities will review the current state-of-the-art for marine applications and help develop new methods, processes, composites, and coatings for use in MHK environments. This work is divided into two subtasks: 1) Manufacturing and 2) Materials and Coatings. the team will explore both existing and new techniques with regard to materials and their manufacturing processes.

Sandia’s objective is to identify and/or develop materials and manufacturing processes that advance the performance and the reliability of both wave and current/tidal power devices. Areas of focus will be on coatings, composites, and molding processes.

System Reliability and Survivability

Similar to other early stage renewable technologies, the MHK industry features a wide variety of device types. It is likely that the industry will eventually settle on a small number of configurations due to efficiency, reliability, cost, or other metrics. To accelerate this process, Sandia and NREL will perform a series of device performance and model evaluations to point out the specific advantages and disadvantages of each.

the team will modify existing performance codes capable of predicting wave device and turbine machine performance in a steady, unbounded free-surface to account for the presence of channel floor and surface boundaries, and to incorporate simple geometries. The analysis codes already available include the NREL WT_Perf code for horizontal-axis wind turbines, and the Sandia VDART3/CACTUS performance code for vertical-axis wind turbines. Performance calculations using newly developed codes along with modified design codes will differentiate proposed technologies and identify promising concepts. We will document the results of these calculations in a report that will provide the water power industry with performance characterization, supported by engineering analysis, of MHK device classes.

Instrumentation, Testing and Evaluation

Engineering design of MHK machines requires a thorough understanding of the mean and turbulent inflow conditions that are prevalent at installation sites. In addition, sites and technology application vary widely necessitating and examination at several sites. Therefore, the first four subtasks are related to investigations involving four different sites.

In collaboration with the National Marine Renewable Energy Centers (NMRECs), ORNL, PNNL, and other partners, the team will review existing standards to develop protocols for laboratory and open ocean wave, current and tidal testing that will be used to guide field experiments. This task will also cover instrumentation and testing that spans both the wave, current and tidal technology areas. The work will cover the development of custom prototype instrumentation and data acquisition packages that will be functionally verified and deployed at up to three field tests in collaboration with key partners. The field data will be used to develop and validate inflow models, MHK machine design codes and support environmental impact assessments. Laboratory-scale testing will be done to investigate materials and coatings, hydrofoil performance, and small-scale array effects.

Test and evaluation is initially important for model development and validation, for prototype testing, and deployment of commercial devices. This area of focus is invaluable for predicting and understanding performance and reliability of MHK systems. To improve the test-validation and model-development process, the team will
• Develop protocols for laboratory and open ocean wave, current, and tidal testing that will be utilized to guide field experiments.
• Characterize mean and turbulent flow conditions in the field at several sites with an attempt to accomplish this before and after prototype device deployment in order to inform turbulent models and machine design codes.
• Conduct laboratory testing to support materials R&D and small-scale array research.
• Perform a wave test facility assessment to determine the utility of U.S.-based facilities. Included in the assessment will be a study on the potential use of a DOE owned lake facility at Sandia’s New Mexico site for wave testing.
• Develop prototype instrumentation and data-acquisition packages that will be functionally verified and deployed at up to three field tests in cooperation with key partners.