Force and torque exerted by internal solitary waves in background parabolic current on cylindrical tendon leg by numerical simulation

Abstract

An internal gravity wave (IGW) model is employed to simulate the generation of internal solitary waves (ISWs) over a sill by tidal flows, and it is shown that the simulated ISW-induced current field agrees basically with that observed. Then we use this model to study the force and torque exerted by ISWs in background parabolic current on small-diameter cylindrical tendon leg of the oil platform. Eight numerical experiments are designed and the results are compared. It is found that, no matter whether a background parabolic current is considered or not, the maximum force lies at the depth of turning point (where the horizontal current in upper layer begins to turn to zero and flow against that in lower layer), a negative extremum torque appears at the depth of turning point, and the maximum torque appears at the bottom of tendon leg. With background parabolic currents, the depth of turning point becomes shallower, and the magnitude of force decreases with depth from the depth of turning point either upward or downward. In case the affecting depths of background parabolic currents are the same, both the maximum force and its appearing depth decrease with increasing current curvature. If the maximum current velocities are the same, the maximum force decreases whilst the depths of the maximum force and turning point increase with increasing current curvature. If the background current curvatures are the same, both the maximum force and its appearing depth decrease with increasing affecting depth of parabolic current.