| Grant number: | 17/06538-3 |
| Support Opportunities: | Scholarships in Brazil - Scientific Initiation |
| Start date: | August 01, 2017 |
| End date: | July 31, 2018 |
| Field of knowledge: | Engineering - Naval and Oceanic Engineering - Hydrodynamics of Ships and Ocean Systems |
| Principal Investigator: | Guilherme Rosa Franzini |
| Grantee: | Giovanna Ribeiro Campedelli |
| Host Institution: | Escola Politécnica (EP). Universidade de São Paulo (USP). São Paulo , SP, Brazil |
Abstract Systems in which one or more parameters of the governing equation of motion depend explicitly one time may be subjected to parametric excitation. Particularly, if the only time-dependent parameter is the stiffness, which varies following a harmonic and monochromatic function, the equation of motion assumes the form of the classical Mathieu's Equation. Depending on the parameters that characterize the parametric excitation (namely, its amplitude and frequency), the trivial solution of the equation of motion may be unstable, giving rise to oscillatory responses. Such a loss of stability is commonly named as parametric instability. In the offshore engineering scenario, the motions of the floating units lead to modulations in the geometric stiffness of slender structures such as, for example, risers and TLP tethers. Hence, these mentioned slender structures may be subjected to oscillations caused by parametric instability phenomenon. This research project aims to numerically investigate the suppression of oscillations caused by parametric instability. Herein, a particular class of suppressors will be studied, namely the non-linear energy sink (NES). A rigid cylinder mounted on an elastic support with one degree of freedom will be considered as the main structure. The stiffness of this main structure is defined by a sinusoidal and monochromatic function. Two types of NES will be investigated, namely the rotating and translational ones. The equations of motion of the system composed by the main structure and the suppressors will be derived using Analytical Mechanics. These equations of motion will be numerically solved. For both types of NES, it will be obtained curves and tables showing the reduction in the oscillation amplitude of the main structure as functions of the type of NES (translational or rotating suppressor) and the parameters that define the suppressor. (AU) | |
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