A quasi three-dimensional numerical model is developed to studyvortex-induced vibration (VIV) of two tandem flexible circularcylinders. In this model, the whole cylinder is divided into manysections along its length. The hydrodynamics of each section arerepresented by the solution of the two-dimensional Navier-Stokesequations. The dynamic response of the flexible cylinder ispredicted by the solution of the three-dimensional equations ofmotion of a tensioned vertical cylinder. Simulations of twoidentical cylinders are carried out with a same mass ratio of 2.453and a large aspect ratio of 3691. The centre-to-centre distancebetween two tandem cylinders is 5D. A low Reynolds number of200 is used in the simulations, and the reduced velocity based onthe fundamental natural frequency is 32.1. The numerical resultsshow that the sixth mode vibration is excited on the upstreamcylinder and its dynamic response is very similar to that of theisolated cylinder. However, due to the effect of wake interference,the response of the downstream cylinder is quite different fromthat of the upstream cylinder. It is mainly controlled by the thirdorder mode although multi-mode vibration is involved. Thehighly irregular vortex shedding pattern of the downstreamcylinder is distinct to the regular 2S vortex shedding mode of theupstream cylinder.
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