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Modeling and simulations of the OceanGrazer’s floater blanket under irregular wave:a Port-Hamiltonian approach

Boer, Roelof Jan (2018) Modeling and simulations of the OceanGrazer’s floater blanket under irregular wave:a Port-Hamiltonian approach. Research Project, Industrial Engineering and Management.


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The Ocean Grazer device is a novel wave energy converter developed at University of Groningen. It is a novel hybrid renewable energy device which can harvest wind and wave energy to provide short-to-medium term energy output that can be stored on-site and allows it to decouple the variability of renewable energy sources from the supply to the grid. As part of the design process, the development of an accurate mathematical model, describing the physical interaction of the wave and the floater blanket of the Ocean Grazer, and subsequently their interaction with the power take-off systems becomes an essential element in this complex and costly design process. Such a model will enable the Ocean Grazer's group to optimize the mechanical design, to develop the control algorithms for maximizing the energy capture, and more importantly, to predict the overall behavior of the device prior to its deployment in the ocean. In this research thesis, we extend the previous work on the modeling of the wave-floater blanket interaction. The first contribution of the thesis is the development of a port-Hamiltonian model that describes the wave-floater blanket simulation. The generic dynamical model is applied to the case of a floater blanket with ten floaters, under irregular waves, and is validated with the existing computer model using WEC-sim. The second contribution of the thesis is the performance analysis of the Ocean Grazer's floater blanket (with ten-floaters) connected to linear PTO systems. As part of our first contribution, we investigate the modeling of a realistic irregular wave based on the well-studied Bretschneider wave spectrum. In particular, we present the design of such an irregular wave generator by employing a white-noise generator coupled with a specially designed band-pass filter. Using this realistic irregular wave time series, we validate the dynamic behavior of the ten-floater case that is modeled using our port-Hamiltonian model. The simulation is compared with that using the popular WEC-sim computer model that is widely used for simulating various wave energy converters. For the regular wave, a maximum error of 0.0125 meters on a relative body displacement of 1 meter, which corresponds to an error percentage of 1.25% For the irregular wave, the error percentage is about 1.88% During the investigation of the performance of the floater-blanket, several experiments where conducted. Analysis learns that under irregular wave input, concerning the contribution of energy, the radiation system is dominant over the mechanical system. The model behaves opposite under regular wave input, where the mechanical system is dominant. During the experiments the captured energy shows a sharp decline at higher order dampening coefficients and is different under regular and irregular wave inputs. The results of experiments using Ocean Grazer's scaled lab setup, due to the assumptions, aren't regarded as sufficiently accurate, but suggest a different power-capture than assumed in previous work, further research is recommended.

Item Type: Thesis (Research Project)
Supervisor name: Jayawardhana, B. and Vakis, A.
Degree programme: Industrial Engineering and Management
Thesis type: Research Project
Language: English
Date Deposited: 30 Aug 2018
Last Modified: 02 Nov 2018 13:50

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