Session: 09-02-04 WEC Numerical Modeling

Paper Number: 80867

80867 - Modeling Comparison of Flexible-Inflatable and Rigid Small-Scale Heaving Wave Energy Converters 

Inflatable structures have the potential to significantly decrease shipping, installation, and structural material costs when compared with rigid steel structures, but their performance has not been thoroughly investigated for wave energy converters. Here we will answer the question of how well inflatable absorbers at different inflation pressures perform relative to their equivalent rigid absorber counterparts for a small-scale heaving wave energy converter (WEC) with time domain numerical modeling. In this paper we use a generalized modes approach for analyzing a flexible-inflatable WEC absorber at different inflation pressures and compare its performance to an equivalent rigid absorber to see how power production and early-stage economic metrics are affected. The modal mass and stiffness matrices and natural mode shapes of each flexible absorber are found using the ANSYS FEA package, after an initial WEC hull prestress calculation caused by the different inflation pressures. Obtained values are consecutively used as an input into WAMIT, a linear potential flow solver, to find correlating hydrodynamic coefficients for the common six rigid body modes and the additional flexible modes. A time-domain model for the rigid and flexible WEC is then developed in the WEC-SIM framework, which uses the generalized mode hydrodynamics and a tuned spring and damper power take-off (PTO) system to predict power performance for regular wave and irregular wave sea states. The differences in optimal control parameters will also be compared and implications for PTO design discussed. By analyzing these flexible-inflatable WEC absorbers for a range of sea states, device developers and potential marine energy customers will have a better understanding of the feasibility, performance, and potential cost benefits of using inflatable structures for many of the differing applications that make up the growing blue economy.

Presenting Author: Michael Kelly University of California, Berkeley

Authors:

Michael Kelly University of California, Berkeley
Thomas Boerner CalWave Power Technologies
Mohammad-Reza Alam University of California, Berkeley