Browsing by Author "Paasch, Robert K."

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    Fatigue Life Distribution for a Simple Wave Energy Converter
    Brown, Adam C.; Paasch, Robert K. (2014-04)
    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.
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    Model Predictive and Integral Error Tracking Control of a Vertical Axis Pendulum Wave Energy Converter
    Boren, Blake C.; Batten, Belinda A.; Paasch, Robert K. (2014-04)
    By actively controlling the rotation of its pendulum, a vertical axis pendulum wave energy converter can generate significantly more net electricity from ocean waves than what would otherwise be possible through a passively swinging pendulum. This suggests that such converters can optimize their performance by incorporating active control schemes within their ever– changing ocean wave environment. The challenge of implementing such control, however, necessitates that an active controller be developed. Here, we address such challenges by: (i) deriving the equations of motion for a constrained generic vertical axis pendulum wave energy converter; (ii) modeling an irregular ocean wave environment; (iii) developing a model predictive and integral error tracking controller to enforce a desired control strategy; and (iv) simulating the converter within the modeled wave environment both with and without active control for the purpose of comparing their respective net power generation results. Here, we find that by actively controlling the rotation of the converter's pendulum, both continuous–mean and peak power generation are increased significantly. Simulation results show that active control is capable of increasing continuous–mean net power generation by over 200 percent. These results give strong evidence and support for further vertical axis pendulum wave energy converter development and also for the continued investigation of applying such active controllers to real world scenarios and prototypes.