This project has received funding from the European Union’s Horizon 2020
research and innovation programme
Under certain conditions time varying parameters of dynamical systems cause parametric resonance which leads to an exponential increase in oscillation amplitude. Parametric res- onance has been widely observed in floating bodies. Depending on application objectives parametric resonance can be both desired and undesired. In both avoiding parametric resonance or triggering it, a robust control of the system is necessary. This thesis considers the application of Tuned-Mass-Dampers (TMDs) and Nonlinear Energy Sinks (NESs) to passively suppress parametric pitch and roll motions from heaving floating bodies, with the objectives of vertical stability in ships, marine based sensors and spar platforms, and maximizing power output from heaving motion in wave energy converters. We present a numerical investigation considering a case study of a simplified two degrees of freedom system, comprising a heaving and pitching cylinder representing the floating bodies. The performance of the NES and TMD, in mitigating the parametric pitch motion of the cylinder is analyzed. Read
Floating sensor buoy devices (FSBDs) are used mainly to gather data from underwater and water surface to respond to naval as well as maritime industry requests. Due to their complex access on the sea, the FSBDs are self powered. Among the renewable energy options, wave energy converters (WECs) have many advantages. One particular method to extract the consistently dense, sea wave energy, is a via heaving buoy, equipped with an internal, inertial power take-off (PTO), thereby acting as a point absorber. A noted unresolved problem for this type of WEC, is large amplitude pitch/roll motion. This has a two-fold negative effect on the FSBD system: (1) Reduction of electrical energy from the WEC system (2) Deteriorated wireless sensor network capability, due to misalignment of vertical antenna. Parametric resonance can be the cause of very large amplitude, unstable, pitch/roll motions in floating bodies. However, this nonlinear phenomenon, has not previously been implemented in the literature for this type of WEC-FSBD. The objective of this study is therefore to include the effect of parametric resonance, when ensuring the vertical stability of a WEC-FSBD device. Read
The wave energy conversion is a clean and inexhaustible energy source. However, under the current power performance level, the technology has to undergo some changes in order to be competitive. The conventional model of wave energy converter (WEC) is designed to resonate with the frequency of incoming waves. At resonance, the velocity of the system is in phase with the dynamic pressure and force of the wave, so that the amplitude of oscillations linearly increases, generating a massive amount of energy. As an alternative, the model can be oscillated by the periodic parameter with frequency twice its natural frequency. This practice stimulates an exponential increase in the amplitude of oscillations and explained by the phenomenon called parametric resonance. Parametric resonance could increase the amount of generated energy, and hence improve the performance of WEC. In this work, the phenomenon of parametric resonance is utilized on the single degree of freedom model mimicking a simpli ed WEC device. The model incorporates a mass modulation as a periodic parameter and exploits its eect on power performance. The parameters describing the model, such as damping and mass modulation coe cients have to be de ned and optimized. Also, the long-term solution as stability diagram and Floquet theory is suggested to simplify the complexity of the non-linear model. Read
This project has received funding from the European Union’s Horizon 2020
research and innovation programme