This paper predicts the wake-induced vibration of tandem cylinders with pivoted rotational or translational motion using the fluid–structure interaction technique. Large eddy simulation using a dynamic Smagorinsky subgrid-scale model is applied for the turbulent flow. Structural computation is applied to obtain the displacement of the downstream cylinder in the cross-flow direction. Conditions such as damping ratio, natural frequency, and mass ratio of pivoted rotational motion are the same as those of translational motion. The computational conditions are Re=3790, 8470 and 15 160, corresponding to U*=5.0, 11.2 and 20.0, respectively. The unsteady characteristics of lift, drag, and cross-flow motion of tandem cylinders are investigated. Distributions of pressure, λ2 criterion, vorticity, and streakline are also investigated. Finally, the energy harvesting capability of the pendulum system is compared with the translation system.
Modeling a nonlinear ocean wave is one of the primary concerns in ocean engineering and naval architecture to perform an accurate numerical study of wave-structure interactions. The high-order spectral (HOS) method, which can simulate nonlinear waves accurately and efficiently, was investigated to see its capability for nonlinear wave generation. An open-source (distributed under the terms of GPLv3) project named "HOS-ocean" was used in the present study. A parametric study on the "HOS-ocean" was performed with three-hour simulations of long-crested ocean waves. The considered sea conditions ranged from sea state 3 to sea state 7. One hundred simulations with fixed computational parameters but different random seeds were conducted to obtain representative results. The influences of HOS computational parameters were investigated using spectral analysis and the distribution of wave crests. The probability distributions of the wave crest were compared with the Rayleigh (first-order), Forristall (second-order), and Huang (empirical formula) distributions. The results verified that the HOS method could simulate the nonlinearity of ocean waves. A set of HOS computational parameters was suggested for the long-crested irregular wave simulation in sea states 3 to 7.
In this paper, the numerical analysis method for the cross-flow vortex-induced vibration (CF VIV) analysis based on the proposed procedure for CF VIV analysis of slender structures is developed. In order to consider the changes in the incoming flow according to the static configuration of the slender structures due to the current, the proposed procedure has three stages. A slender structure is modeled as the lumped-mass line, and the dynamic relaxation method known as the numerical technique for a slender structure with large geometric nonlinearity is applied in the static analysis. The comparison studies with a commercial program are carried out to validate the developed code. The vortex-induced force on slender structures is considered with the synchronization model. To verify the developed CF VIV analysis procedure and numerical method for a slender structure, VIV analysis of the tensioned flexible risers under a uniform and shear current is performed. The simulated results of CF RMS displacement show good agreement with the results of the model test It is found that a tensioned riser vibrates with one dominant frequency in resonance with the nth mode, even though multi-frequencies components of the vortex shedding along the riser due to the shear current occurs.
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