Flow-induced vibrations of long circular cylinders modeled by coupled nonlinear oscillators |
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Authors: | Fei Ge Xu Long Lei Wang and YouShi Hong |
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Institution: | (1) State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing, 100190, China |
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Abstract: | The dynamics of long slender cylinders undergoing vortex-induced vibrations (VIV) is studied in this work. Long slender cylinders
such as risers or tension legs are widely used in the field of ocean engineering. When the sea current flows past a cylinder,
it will be excited due to vortex shedding. A three-dimensional time domain model is formulated to describe the response of
the cylinder, in which the in-line (IL) and cross-flow (CF) deflections are coupled. The wake dynamics, including in-line
and cross-flow vibrations, is represented using a pair of non-linear oscillators distributed along the cylinder. The wake
oscillators are coupled to the dynamics of the long cylinder with the acceleration coupling term. A non-linear fluid force
model is accounted for to reflect the relative motion of cylinder to current. The model is validated against the published
data from a tank experiment with the free span riser. The comparisons show that some aspects due to VIV of long flexible cylinders
can be reproduced by the proposed model, such as vibrating frequency, dominant mode number, occurrence and transition of the
standing or traveling waves. In the case study, the simulations show that the IL curvature is not smaller than CF curvature,
which indicates that both IL and CF vibrations are important for the structural fatigue damage.
Supported by the National Natural Science Foundation of China (Grant No. 10532070), the Knowledge Innovation Program of Chinese
Academy of Sciences (Grant No. KJCX2-YW-L07), and the LNM Initial Funding for Young Investigators |
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Keywords: | vortex-induced vibration (VIV) vortex-induced wave (VIW) wake oscillator long cylinder fluid-structure interaction |
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