Session: 08-03-01 Fundamental Vortex Induced Vibrations & Cylinder Hydrodynamics

Submission Number: 180548

Spatial Higher-Harmonics During the Vortex-Induced Vibrations of Flexible Cylinders 

This paper presents and discusses some Vortex-Induced Vibration (VIV) results on long flexible cylinders. The main focus of the paper is the rarely addressed issue of higher harmonics in the spatial domain (spatial higher harmonics) rather than the typically discussed higher harmonics in the time domain (temporal higher harmonics). The experimental data comes from the extensive model testing that was conducted by MARINTEK for SHELL in 2011. 

VIV response data and force measurements are known to contain higher harmonics in the temporal domain that can lead to higher fatigue damage rates. In contrast, the higher harmonics in the spatial domain are rarely discussed and they are revealed here by showing spectra in the wavenumber domain. These are shown to be different from the higher harmonics occurring in the temporal domain and usually demonstrated by showing frequency domain spectra. This paper presents a hypothesis on the likely cause of spatial higher harmonics and attributes them to the shape or spatial distribution of the lift force on the flexible cylinder.

The presence of these spatial higher harmonics can have significant implications both when choosing how to instrument a riser and how to conduct the numerical analysis when trying to predict VIV.  Physical measurements of VIV at high mode numbers will require a significantly larger number of sensors to avoid aliasing issues. Similarly, numerical models of risers will also require significantly higher spatial resolution before they can be used with VIV prediction programs.

Presenting Author: Themistocles L. Resvanis AMOG

Presenting Author Biography: -

Authors:

Themistocles L. Resvanis AMOG
J. Kim Vandiver Massachusetts Institute of Technology
Hayden Marcollo AMOG