Fluid-Structure Interaction

Fluid structure interaction examines the effect of a flow field upon a structure and vice-versa and plays an important role in different areas of civil engineering.ethe interaction of steep non-linear water waves with offshore wind turbine foundations is investigated in order to provide information on wave loads and other hydrodynamic effects for design.  The wave field around and loads on an offshore wind turbine foundation are simulated using a numerical model based on fully non-linear Boussinesq equations.  Cartesian cut cell technique is implemented to fit the geometry of the cylindrical structure.

In case of a coastal surge hitting a structure, the wave dynamics can be predicted using the adaptive quadtree grid based Godunov-type shallow water equation solver.  In an idealised test case, the calculation is carried out in a 5 m × 5 m domain, with a horizontal, frictionless bed.  At the centre is placed a circular surface-piercing cylinder of diameter 1 m.  The domain has open inlet and outlet boundaries at its west and east ends.  The north and south lateral boundaries are open.  The shock-like bore propagates from the western (left) inlet to the eastern (right) boundary.  Numerical simulation shows that, once the collision occurs (t = 0), a circular reflected shock wave is instantaneously induced and the flow forms a two-shock system.  The flow is strictly symmetric and the confluence points of the two shocks move along the cylinder surface.  Considering the upper part of the flow, when the angle between the front stagnation point and the shock collision point increases to about 45^o at t = 0.025 s, the collision point separates from the cylinder surface and changes into a triple point.  A diffracted shock appears and a three-shock system is developed together with the incident and reflected shocks, indicating the flow dynamics regime changing from regular reflection to Mach reflection.  Later, the diffracted shock fronts from upper and lower sides of the cylinder curl up and meet at the rear stagnation point behind the cylinder, resulting in vortices and an instantaneous increase of water depth in the wake.  With the complicated wave pattern caused by the shock-shock interaction propagating downstream and together with the vortex motion, a cavity is developed in the wake, which can remain there for a long time.

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