High-frequency mooring vibrations caused by vortices shedding occur when ocean currents flow past mooring structures such as surface and subsurface buoys, mooring lines, risers, and other submerged components. As the current moves around these structures, it generates alternating vortices that create pressure fluctuations perpendicular to the flow direction. If the mooring structures are not rigidly mounted, they can be highly sensitive to excitation from vortex shedding, especially when the shedding frequency matches the structure’s natural resonance frequency. This results in resonant vibrations that are primarily transverse to the flow direction. These vortex-induced motions not only cause oscillations but also increase the overall drag force acting on the mooring. The combination of increased drag and continuous movement can significantly affect data collection, causing greater mooring offsets, higher mooring line tensions, and oscillations in tension forces, which in turn contribute to fatigue damage over time.
Excessive mooring vibration can adversely affect the data; vibration introduces spurious velocities and interferes with the proper operation of the tilt sensor. The impact of mooring oscillations must be carefully considered. A general solution to improve on data quality is to design a more stable deployment by considering the components that generate mooring vibrations. The addition of aerodynamic devices may partly prevent and partly reduce the strength of vortex induced vibrations. It may be possible to detect intervals of excessive vibration by closely analyzing velocity and tilt data. Unusual oscillations in the data may indicate periods of strong vortex-induced motion. For more precise vibration measurements, the use of an accelerometer can provide detailed insights into the extent and frequency of mooring oscillations, allowing for more targeted mitigation strategies.
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