Nonlinear vibration modes and instability of a conceptual model of a spar platform

Gavassoni, Elvidio; Gonçalves, Paulo B.; Roehl, Deane

doi:10.1007/s11071-013-1171-6

Cited by 25 publications

(19 citation statements)

References 32 publications

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“…The selection of this type of WEC stems from the numerous reports of parametric pitch/roll for axisymmetric heaving point absorbers [17][18][19][20][29][30][31][32][33][34]39,41,45,46,[48][49][50]. The particular geometry used in this study is a representation of a classic spar platform from the literature [62][63][64][65], comprising a simple vertical cylinder whose natural period of pitch motion is about twice the heave resonant period. The 2:1 ratio of heave to pitch natural frequency makes the floating cylinder prone to parametric excitation in pitch.…”

Section: The Devicementioning

confidence: 99%

“…A numerical model of the cylinder was used by Jingrui et al [63] to study the combination resonance response. Gavasoni et al [64] employed a numerical model for the investigation of nonlinear vibration modes and instability. Giorgi et al [65] demonstrated the potential yaw instability which may arise when including nonlinear kinematics in a nonlinear hydrodynamic model.…”

Section: The Devicementioning

confidence: 99%

“…The hydrodynamic model for the wave structure interaction follows the validated model for the same device from [62][63][64]. The model is able to articulate the occurrence of parametric resonance in the floating cylinder, through the coupled equations for heave x 3 and pitch x 5…”

Section: Numerical Modelmentioning

confidence: 99%

“…The hydrodystatic restoring force and moment terms have time-varying parameters, which enables the existence of parametric resonance in the numerical model. In [63,64], the hydrodystatic restoring force and moment are given by…”

Section: Hydrostatic Restoring Force/momentmentioning

confidence: 99%

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A Real-Time Detection System for the Onset of Parametric Resonance in Wave Energy Converters

Davidson

Kalmár‐Nagy

2020

JMSE

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Parametric resonance is a dynamic instability due to the internal transfer of energy between degrees of freedom. Parametric resonance is known to cause large unstable pitch and/or roll motions in floating bodies, and has been observed in wave energy converters (WECs). The occurrence of parametric resonance can be highly detrimental to the performance of a WEC, since the energy in the primary mode of motion is parasitically transferred into other modes, reducing the available energy for conversion. In addition, the large unstable oscillations produce increased loading on the WEC structure and mooring system, accelerating fatigue and damage to the system. To remedy the negative effects of parametric resonance on WECs, control systems can be designed to mitigate the onset of parametric resonance. A key element of such a control system is a real-time detection system, which can provide an early warning of the likely occurrence of parametric resonance, enabling the control system sufficient time to respond and take action to avert the impending exponential increase in oscillation amplitude. This paper presents the first application of a real-time detection system for the onset of parametric resonance in WECs. The method is based on periodically assessing the stability of a mathematical model for the WEC dynamics, whose parameters are adapted online, via a recursive least squares algorithm, based on online measurements of the WEC motion. The performance of the detection system is demonstrated through a case study, considering a generic cylinder type spar-buoy, a representative of a heaving point absorber WEC, in both monochromatic and polychromatic sea states. The detection system achieved 95% accuracy across nearly 7000 sea states, producing 0.4% false negatives and 4.6% false positives. For the monochromatic waves more than 99% of the detections occurred while the pitch amplitude was less than 1/6 of its maximum amplitude, whereas for the polychromatic waves 63% of the detections occurred while the pitch amplitude was less than 1/6 of its maximum amplitude and 91% while it was less than 1/3 of its maximum amplitude.

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Section: The Devicementioning

confidence: 99%

Section: The Devicementioning

confidence: 99%

Section: Numerical Modelmentioning

confidence: 99%

Section: Hydrostatic Restoring Force/momentmentioning

confidence: 99%

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A Real-Time Detection System for the Onset of Parametric Resonance in Wave Energy Converters

Davidson

Kalmár‐Nagy

2020

JMSE

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“…They provide a solid theoretical and mathematical tool for interpreting a wide class of nonlinear dynamical phenomena. Reduced order models obtained by the use of NNMs are able to capture the contribution of several modes (Gavassoni et al, 2014), thus allowing a smaller number of modes to generate a precise model compared to standard reduction approaches such as those using linear modes.…”

Section: Introductionmentioning

confidence: 99%