Deformation measurement of a monopile subject to vortex- induced vibration using digital image correlation

• Published in: Ocean engineering Vol. 221; p. 108548
• Main Authors: Tödter, Simon, el Sheshtawy, Hassan, Neugebauer, Jens, el Moctar, Ould, Schellin, Thomas E.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.02.2021
• Subjects: Digital image correlation; Experimental study; Fluid structure interaction; Optical measurement; Vortex induced vibration; Optical measurement; Fluid structure interaction; Vortex induced vibration; Experimental study; Digital image correlation
• ISSN: 0029-8018; 1873-5258
• DOI: 10.1016/j.oceaneng.2020.108548

Monopile towers used for offshore wind turbines are sensitive to Vortex-Induced Vibration (VIV). Here, their structural response to VIV was experimentally investigated with models of a partially and a fully immerged offshore monopile. The partially and fully immersed model cylinders had aspect ratios of 18.75 and 28.13, respectively. They were subject to reduced velocities of up to 9.78 and 5.45, respectively, corresponding to Reynolds numbers of up to 77120 and 63680, respectively. Normalised transverse motion amplitudes of up to 1.19 were measured. “Strouhal-like” numbers down to 0.13 were obtained, and they decreased with increasing flow velocity and corresponding motion amplitude. The 3D Digital Image Correlation (DIC) processing method was used to measure response without influencing model properties and the flow field. To assess the suitability of DIC for VIV investigations, results obtained from the conventional technique using triaxial accelerometers were compared. The influence of different processing methods, pattern designs and their assemblies, the repeatability of the model tests, and the influence of ventilation were investigated also. Additionally, forces and torques were measured directly. Results from these three measurement techniques were compared and discussed. •Experimental investigation of vortex induced vibration (VIV) in water flow.•Suitability study of digital image correlation to investigate VIV.•Comparative measurements with accelerometers, load cell, and digital image correlation.•Optical measurement of displacements without disturbing flow/structural properties.•Results verify the suitability of the optical measurement technique.