Wave energy converters (WECs), which convert the kinetic energy in ocean waves into electricity, are designed to maximize fluid-structure interactions between the device and the ocean wave environment in order to optimize energy production. As a result, the hydrodynamic loads WECs experience during both normal operation and extreme conditions must be carefully considered during the device design process. Under most operational conditions, the relevant fluid-structure interactions can be modeled using common numerical and experimental methods. Conversely, under extreme conditions, WEC devices experience large amplitude motions, wave overtopping, wave slamming, and other physical phenomena that are difficult to accurately simulate. These extreme conditions often determine the maximum design loads, and accordingly, the prediction of extreme loads is a critical step in the device design process. The WEC industry has adopted extreme conditions design, modeling, and analysis techniques developed for offshore oil & gas and naval architecture applications. While leveraging these existing design and modeling methodologies has greatly benefited the WEC industry in its nascent stages of development, extreme conditions modeling (ECM) methods must be further developed in order to advance technologies towards commercial viability.
To assess the ECM needs of the wave energy industry, Sandia National Laboratories (SNL) and the National Renewable Energy Laboratory (NREL) held an ECM workshop in Albuquerque, New Mexico on May 13–14, 2014. ECM involves several different disciplines, including numerical, experimental, and meteorological and oceanographic (met-ocean) modeling. It also takes into consideration design standards and identification of extreme loading conditions. As described in this report, the workshop was explicitly structured to address each of these topics.
- Review current practices and the state-of-the-art in experimental and numerical modeling methods for predicting device loads, motions, and performance in extreme conditions
- Identify challenges and gaps in the current modeling methods
- Identify research pathways that have the potential to advance ECM methods.
- The wave industry understands that ECM is a critical step in the device design process.
- Numerical and experimental ECM methods developed by the offshore oil & gas and shipping industries, while useful, do not meet the needs of the WEC industry. Accordingly, research is needed to develop WEC-specific ECM methods.
- Open-source experimental data sets are needed to validate WEC device design and analysis methods. The national labs could assist the industry by developing these data sets.
- The WEC industry would benefit from a set of guidelines and best practices that describe how to numerically model WECs in extreme conditions.
- It is difficult to determine what meteorological and oceanographic conditions result in extreme loads on WEC devices. For example, it is not always the largest wave that causes the largest load, making it difficult to determine what wave conditions should be considered when performing survival analysis. The industry would benefit from research that helped develop methods of identifying when extreme events will occur.
- Certification bodies are starting to move towards risk-based certification of WEC devices and WEC developers should adopt a risk-based design approach. Many developers are already beginning to use this approach.
- Uncertainty in how to design WEC devices to survive extreme conditions is slowing the pace of technology development by increasing the investment risk.
- Measurements of Extreme Waves by Jim Thomson (University of Washington / Applied Physics Laboratory)
- Extreme Conditions Modeling Workshop: Numerical Modeling for Lifetime Loads by Armin Troesch (University of Michigan)
- Oil & Gas Experience with Extreme Conditions Modeling by John Halkyard (Halkyard & Associates). This presentation was given by Dominique Roddier (Marine Innovations & Technology)
- Wave Basin Testing by Joop Helder (MARIN)
- National Lab Perspective on WEC Survival Analysis by Ryan Coe (Sandia National Laboratories)
We would also like to thank the WEC developers and Keynote Speakers who allowed us to post their presentation slides on this website.
This workshop was supported by the Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy (EERE), Wind and Water Power Technologies Office (WWPTO).