Preliminary Numerical Study on the Influence of a Wind Field on Wave-induced Load on a Circular Cylinder

Julie Carøe Kristoffersen, Henrik Bredmose, Christos Thomas Georgakis

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Abstract

The design load for offshore structures can be established from experimental and numerical investigations. When these are conducted, only the indirect effect of wind is taken into account. I.e. the wave spectrum is defined from fetch and wind speed. Nevertheless, the wind can have a direct effect on steep waves if airflow separation and vortexes develop above the waves. This could potentially cause increased waveinduced loads or change the breaking probability for waves and thereby the load statistics. This paper presents preliminary results from numerical simulations on how a local wind field affects wave kinematics and wave-induced loads on a cylinder. The waves are generated as spatio-temporal focused wave train. The wave field, including surface elevation and kinematics, is computed with the fully nonlinear potential solver program, OceanWave3D. The wave-induced load on the cylinder is computed from the output of the kinematics and the FNV force model. The wind forcing term is modelled by means of Jeffrey’s sheltering mechanism. Wave field and wave-induced loads are compared for different wind velocities and configurations of a focused wave. The
presence of wind above a steep non-breaking wave increases the surface elevation until breaking is initiated for high wind velocity. The maximal wave-induced load for an initial non-breaking wave is obtained for the highest wind velocities due to the sudden initiation of breaking. The capability of the wind to increase surface elevation and load for wind above initially breaking waves is more questionable. The numerical model simply exchanges the energy transfer between breaking dissipation and wind energy differently depending on wind velocity and wave field; nevertheless, no significant increase in surface elevation or load is discovered in this case. The highest wind velocity can, on the contrary, lead to a second breaking wave, which increases the line force. Finally, the numerical simulations are validated successfully against experimental investigations without wind.
Original languageEnglish
Title of host publicationProceedings of the Twenty-eighth (2018) International Ocean and Polar Engineering Conference
PublisherInternational Society of Offshore & Polar Engineers
Publication date2018
Pages291-298
ISBN (Print)978-1-880653-87-6
Publication statusPublished - 2018
Event28th International Ocean and Polar Engineering Conference (ISOPE 2018) - Sapporo, Japan
Duration: 10 Jun 201815 Jun 2018

Conference

Conference28th International Ocean and Polar Engineering Conference (ISOPE 2018)
CountryJapan
CitySapporo
Period10/06/201815/06/2018
SeriesProceedings of the International Offshore and Polar Engineering Conference
ISSN1098-6189

Keywords

  • Offshore structure
  • Wave-induced load
  • Wind effect on wave
  • Airflow separation

Cite this

Kristoffersen, J. C., Bredmose, H., & Georgakis, C. T. (2018). Preliminary Numerical Study on the Influence of a Wind Field on Wave-induced Load on a Circular Cylinder. In Proceedings of the Twenty-eighth (2018) International Ocean and Polar Engineering Conference (pp. 291-298). International Society of Offshore & Polar Engineers. Proceedings of the International Offshore and Polar Engineering Conference