Although there are a great many researches on vortex-induced vibration of a rigid cylinder either only in 1 DOF or 2 DOF, the problem still exists that the good accuracy by CFD method is often time consuming but solution by many algorithms of semi-empirical method are not accurate enough for the low mass ratio systems. A new time-domain approach is developed for vortex-induced vibrations prediction of single cylinder strip in a 2D plane, including the cross-flow and the inline oscillation. The governing equation was established by classic theoretical derivation, where the intrinsic behavior of self-excitation and self-limitation is involved. The early proposed frequency relationship of vortex-excitation in synchronization is applied with local modifications by experimental measurements, through which the vortex shedding characteristics could be identified as well as the regimes of responding branches. Through comparison with published experimental observations, the solutions have the capability of reproducing important quantities such as the peak amplitudes, the trajectories in crescent-shape and 8-shape, etc. This approach can provide not only accurate but effective solution with the timeconsuming less than 10 seconds in steady current. It is a great enhance compared to the CFD simulations in tens of hours.

In this paper, m is the mass of the circular section in strip. The added mass, mA, is given by mA = CAmd, where md is the displaced fluid mass and CA is the potential added-mass coefficient. Generally, CA = 1.0 for a circular cylinder as the potential component, but not taking the viscosity into account.

In the above group, f is the vortex-excited frequency of oscillation in the cross-flow direction, f0 is the vortex shedding frequency in flow pass stationary cylinder, fNW is the natural frequency in still water. Meanwhile, k is the spring constant and c is the structural damping, A is the amplitude of response, D is the cylinder diameter, Δl is the length of the cylinder strip, ρ is the fluid density, U is the free-stream velocity, and μ is the dynamic viscosity coefficient.

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