Towards an understanding of the marine fouling effects on VIV of circular cylinders: a probe into the chaotic features

The current paper addresses the possibility of chaotic dynamics in the VIV response of cylinders covered by marine biofouling. The fouling was simulated by machining uniformly distributed pyramidal protrusions on the surface of the test cylinder. The Reynolds number varied from 5.8× 10^3 to 6.6× 10^4 . The zero-one tests, Hilbert Transforms and Poincaré maps were used to analyse the VIV test results. The chaos analysis showed that in the early initial branch and in the ending part of the synchronisation, the VIV signals for both the smooth and the artificially biofouled cylinders happened to be chaotic. The signals in between showed non-chaotic dynamics. The chaotic extent grew wider with the artificially biofouled cylinder than those with the smooth cylinder and in the lift force signals as compared to the displacement signals. Our estimates for the chaotic regions in the low mass-damping smooth cylinder interestingly agreed well with (i) zones for the “quasi-periodic” regime and (ii) the region marked as “no observed shedding pattern” in the literature. They singled out these regions because of their irregular dynamics but failed to appreciate these as chaotic. Here, we argue that these regions are in fact quite susceptible to chaos.