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NREL Researchers Apply New Extreme Condition Wave Response Methodology

April 13, 2016

Extreme wave-induced loads are often the key cost driver for wave energy converter (WEC) designs. Therefore, in an effort to better understand the effects that extreme wave conditions can have on wave energy applications, researchers at NREL have applied a technique called the most likely extreme response (MLER) method to evaluate the maximum displacement and loads of a point absorber WEC experiencing anticipated 100-year waves.

The MLER waves were generated for two device configurations—with heave-only and heave/pitch degrees of freedom—under five extreme sea states.

From the sea states that were considered, researchers were able to identify different operational regimes with associated nonlinear dynamics and modeling challenges:

  • Steep, short-period waves are sensitive to the wave-surface capturing methodology as they are prone to breaking
  • Taller waves can cause the device to leave the water and re-enter at an oblique angle (see figure 1).

These extreme responses are not well predicted by common engineering analyses, and results are expected to help guide and improve industry design practices as well as accelerate device development. Moreover, the MLER analysis technique facilitates the application of high-fidelity computational fluid dynamics and potentially reduces the need for costly long-term simulations or tank tests.

NREL researcher Yi-Hsiang Yu will present this research at the American Society of Mechanical Engineers 35th International Conference on Ocean, Offshore and Arctic Engineering.

—Wayne Hicks