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In this research, the phenomenon of vortex-induced vibrations and the effect of control cylinders usage with different configurations on vortex formation, lift and drag coefficients, and fluctuations amplitude at the back of an elastically supported rigid circular cylinder subjected to a uniform fluid flow are studied. Results obtained in the absence of control cylinders are validated with experimental and numerical results of other researchers and a good conformity is reached. After ensuring simulation accuracy and precision, control cylinders of equal diameter with master cylinder are placed as linear and triangular arrangements at the back of master cylinder and the optimal configuration and location of control cylinders are defined. In linear arrangement, at first the effect of a control cylinder usage at 5 different distances from 1.5 to 3.5 times diameter of master cylinder and then two control cylinders with ratios of 1.5, 2 and 2.5 times diameter of master cylinder are studied. At the end, in triangular arrangement, control cylinders are located at intervals of 1, 1.5 and 2 times diameter of master cylinder.

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In recent decades, experimental studies of the vortex-induced vibration (VIV) became one of the interesting fields of science. However, variety of assumptions and methods of experiments have led to different results in various researches. Several parameters such as mass ratio, aspect ratio, degrees of freedom, and boundary conditions affect the VIV response of a simple circular cylinder. The current paper reports and discusses the results of in-water VIV experiments on an elastically mounted rigid cylinder with various types of end conditions. This paper focusses on the effects of the end condition by attaching an endplate to a circular cylinder and the results compared with those from a cylinder with no endplate. The Reynolds number ranges from 5.8×103 to 6.6×104. Experimental setup have also been compared and verified with some classical results of VIV. Results of current study was favorably compatible with previous researchers’ results.
The experimental results show that, the end condition noticeably changes the VIV amplitude especially in the lock-in area. Moreover, non-dimensional amplitudes shift to the higher reduced velocities when the endplate is removed. In the frequency responses, the cylinder with no endplate has lower quantities rather than the cylinder with an attached endplate. Evaluation of lift force coefficients also shows a similar pattern of effects on the non-dimensional amplitude. Consequently, the excitation of the structure in the lock-in region increases, when the endplate from the cylinder’s end is removed.

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Vortex-induced vibration is a critical phenomenon that occurs in offshore structures and causes fatigue and damage to these structures. Previous studies show that these structures show complex and sometimes non-linear behavior. This study uses a rigid cylinder with non-linear support to evaluate the hydrodynamic parameters in these systems. The amount of non-linearity of the support has been changed, and its effect on the hydrodynamic parameters of the system has been investigated. The displacement and velocity of the cylinder were obtained by solving the two-dimensional Reynolds averaged Navier-Stokes and cylinder motion equations. The lift, potential, and vortex coefficients were calculated. Finally, the Strouhal number was determined. The results show that the system's behavior consists of two branches. In branch 1, the motion amplitude of the cylinder is small, but in branch 2, its amplitude is multiplied. By increasing the non-linearity of the support, the range of branch 2 becomes smaller, and the velocity of the cylinder oscillation increases. Raising the support non-linearity reduces the lift force and Strouhal number