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UENO, T. Numerical investigations on passive supression of vortex-induced vibrations using non-linear vibration absorber: a wake-oscillator approach. 2019. Dissertation (Master of Sciences) Escola Politécnica, University of São Paulo, São Paulo, 2019. Vortex-induced vibrations (VIV) represent a fluid-structure interaction problem commonly found in several engineering areas. In the offshore engineering scenario, VIV plays an important role in risers dynamics. The suppression of this resonant phenomenon has required several efforts due to its impact on the reduction of the lifespan due to structural fatigue. Among other suppression solutions, it can be highlighted the use of non-linear vibration absorbers (NVAs). This research aims at numerically investigating the effectiveness of a particular class of NVAs as a passive suppressor of rigid cylinders mounted on elastic supports with one or two degrees of freedom subjected to VIV. The wake dynamics is studied through phenomenological models. The equations of motion are obtained and numerically integrated focusing on the identification of the influence of the NVA parameters on the response of the cylinder. Oscillation amplitude curves as functions of the reduced velocity are the main contribution of this work. Complementarily, response time series allow discussing the dynamics of the coupled system throughout the lock-in range of reduced velocities. In order to quantify the efficiency of the NVA, a suppression criterion based on the oscillation amplitude of the cylinder is evaluated as a function of reduced velocities and in the form of color maps defined in a space of control parameters for specific reduced speeds. The parametric study herein described shows that the mass of the suppressor has more influence on the VIV suppression than the other parameters for both 1-dof VIV (only cross-wise oscillations are allowed) and 2-dof VIV (concomitant in-line and cross-wise oscillations). In general, the suppression has proved to be greater in the 1-dof VIV condition. In 2-dof VIV, the rotative NVA may cause amplification of the in-line response.

Supressão passiva de vibrações induzidas pela emissão de vórtices utilizando absorvedores não lineares de vibração: uma abordagem via modelos fenomenológicos.