Numerical solution of the flow past a freely oscillating body in waves and currents

The fluid structure interaction due to the flow past a circular cylinder is studied in order to analyze the hydrodynamic loads and the related body motions. The cylinder isrestrained to in-line displacements while cross-flow oscillations are possible through a spring-damper system. After assuming an incompressible laminar flow, the solution of th e fluid dynamic problem is achieved through a fractional step algorithm where a particle method with a deterministic diffusion scheme is used for the dynamics of the vorticity. The fluid velocity i s expressed by an integral representation formula in terms of the vorticity field and of the velocity itself at the boundaries. Therelevant integral equation aresolved via an N log N algorithm and the computed tangential velocity at the solid boundary allows for the generation of vorticity in orderto sartisfy the non-slip conditions. A fast summation techniquefor the rapid evaluation of the velocity is adopted. The investigated range of the Reynolds number (from 95 to 135) shows that, wi thin the lock-in range, the vortex shedding frequency coincides with the natural frequency in still water and that large body displacements occur.