Abstract
Vortex-induced vibration (VIV) is one of the key issues in marine engineering that occurs when a bluff body is exposed to fluid flow. The effects of VIV can cause significant structural deflection, fatigue damage, and even failure over time.This thesis investigates VIV in marine mooring applications, specifically focusing on the stretch hose component designed by engineers at Woods Hole Oceanographic Institution to maintain "quiet" conditions for subsurface hydrophones. They have conducted empirical tests that suggest that addition of spiral grooves along the length of the stretch hose reduces unwanted noise, but it is not clear that they have selected the optimal design for suppression of VIV and the noise it causes. A comprehensive series of 2D and 3D computational fluid dynamics (CFD) simulations were conducted using ANSYS Fluent. The initial 2D simulations explored the effects of groove rotation on vortex shedding, with three different angles (0°, 15°, 30°) to the incoming flow, one groove depth (1/15 d). The 2D results did not provide consistent intuitive insights due to the geometry. The 3D studies examined two groove depths 1/15 d and 1/10 d and two helical pitches 4d and 6d. The findings show that the effectiveness of helical grooves depends on both Reynolds number and the groove geometry. At moderate range of Reynolds numbers considered, grooves depth of 1/10 d result are more effective, while at higher range of Reynolds numbers considered, shallower grooves with smaller pitch (Gd = 1/15 d, Pt = 4d) are more effective in reducing oscillatory (RMS lift coefficient) and drag forces. By investigating the relationship between VIV and the geometry of the stretch hose, this study gives more insight into VIV prevention techniques, which is critical for ensuring structural integrity in marine environments and accuracy of acoustic measurements.