Wave Energy Converter Extreme Conditions Modeling Workshop

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Workshop Overview

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.

 
Objectives:
The overall goal of the ECM workshop was to identify research pathways through which national laboratory resources and expertise can be used to improve ECM methods for the benefit of the wave energy industry. The specific objectives of the workshop were to:

  • 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.

 
Key Findings and Recommendations:

  • 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.

 
Workshop Report:
The workshop proceedings, findings, and recommendations were compiled in the final Workshop Report

 
Keynote Presentations:

 
WEC Developer Presentations:

 
Acknowledgements:
The National Renewable Energy Laboratory and Sandia National Laboratories would like to thank all the workshop attendees, who generously took two days out of their busy schedules to share their knowledge and expertise in the area of WEC extreme events modeling.

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).