Fatigue Life Distribution for a Simple Wave Energy Converter

Fatigue is known to be a dominant failure mode for systems subjected to wave loading. A time domain simulation of loading on a simple Wave Energy Converter (WEC) was used to develop the distribution of fatigue failures around the assumed 10 year design life of the device. In order to maintain the generality of the paper, the WEC was modeled as a simple, solid, stainless steel rod under wave induced axial tension and compression. This simplified model is seen as a reasonable approximation of a hydraulic ram. The system was subjected to seas that would be typical of the Oregon wave climate. The random waves used for the analysis were generated according to linear wave theory by way of random phase reconstruction of JONSWAP spectra. The model of the Oregon wave climate is also discussed, as it was found that the randomness within the wave climate model greatly affects the variance of the distribution of fatigue life. An equation for stress cycle induced damage was developed according to the Linear Cumulative Damage Theorem (Miner's Rule). Time to failure and several other metrics were recorded for 300 failures in order to develop the probability distribution of fatigue life.