An experimental study of a quasi-impulsive backwards wave force associated with secondary load cycle on a vertical cylinder
Steep wave breaking on vertical cylinder (a typical foundation supporting offshore wind turbines) will induce slam loads. Many questions on the important violent wave loading and the associated secondary load cycle still remain unanswered. We use laboratory experiments with unidirectional waves to i...
| Main Authors: | , , , , , |
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| Format: | Journal article |
| Language: | English |
| Published: |
Cambridge University Press
2024
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| Summary: | Steep wave breaking on vertical cylinder (a typical foundation supporting offshore
wind turbines) will induce slam loads. Many questions on the important violent wave
loading and the associated secondary load cycle still remain unanswered. We use laboratory experiments with unidirectional waves to investigate the fluid loading on vertical
cylinders. We use a novel three-phase decomposition approach which allows us to separate
different types of non-linearity. Our findings reveal the existence of an additional quasiimpulsive loading component that is associated with the secondary load cycle and occurs
in the backwards direction against that of the incoming waves. This quasi-impulsive
force occurs at the end of the secondary load cycle and close to the passage of the
downward zero-crossing point of the undisturbed wave. Wavelet analysis showed that the
impulsive force exhibits superficially similar behaviour to a typical wave-slamming event
but in the reverse direction. To monitor the scattered wave field and extract run-up on
the cylinder, we installed a four-camera synchronized video system and found a strong
temporal correlation between the arrival time of the Type-II scattered wave onto the
cylinder and the occurrence of this quasi-impulsive force. The temporal characteristics of
this quasi-impulsive force can be approximated by the Goda wave impact model, taking
the collision of the Type-II scattered waves at the rear stagnation point as the impact
source. |
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