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

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

Research output: Chapter in Book/Report/Conference proceeding › Article in proceedings › Research › peer-review

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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 language	English
Title of host publication	Proceedings of the Twenty-eighth (2018) International Ocean and Polar Engineering Conference
Publisher	International Society of Offshore & Polar Engineers
Publication date	2018
Pages	291-298
ISBN (Print)	978-1-880653-87-6
Publication status	Published - 2018
Event	28th International Ocean and Polar Engineering Conference (ISOPE 2018) - Sapporo, Japan Duration: 10 Jun 2018 → 15 Jun 2018

Conference

Conference	28th International Ocean and Polar Engineering Conference (ISOPE 2018)
Country	Japan
City	Sapporo
Period	10/06/2018 → 15/06/2018

Series	Proceedings of the International Offshore and Polar Engineering Conference
ISSN	1098-6189

Keywords

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

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http://legacy.isope.org/publications/proceedings/ISOPE/ISOPE%202018/data/polopoly_fs/1.4192178.1525883490!/fileserver/file/893335/filename/18TPC-0862Kristoffer.pdf#search=%22Preliminary%20Numerical%20Study%22

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 http://legacy.isope.org/publications/proceedings/ISOPE/ISOPE%202018/data/polopoly_fs/1.4192178.1525883490!/fileserver/file/893335/filename/18TPC-0862Kristoffer.pdf#search=%22Preliminary%20Numerical%20Study%22

Kristoffersen, Julie Carøe ; Bredmose, Henrik ; Georgakis, Christos Thomas. / Preliminary Numerical Study on the Influence of a Wind Field on Wave-induced Load on a Circular Cylinder. Proceedings of the Twenty-eighth (2018) International Ocean and Polar Engineering Conference. International Society of Offshore & Polar Engineers, 2018. pp. 291-298 (Proceedings of the International Offshore and Polar Engineering Conference).

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

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{\textquoteright}s sheltering mechanism. Wave field and wave-induced loads are compared for different wind velocities and configurations of a focused wave. Thepresence 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.",

keywords = "Offshore structure, Wave-induced load, Wind effect on wave, Airflow separation",

author = "Kristoffersen, {Julie Car{\o}e} and Henrik Bredmose and Georgakis, {Christos Thomas}",

year = "2018",

language = "English",

isbn = "978-1-880653-87-6",

series = "Proceedings of the International Offshore and Polar Engineering Conference",

publisher = "International Society of Offshore & Polar Engineers",

pages = "291--298",

booktitle = "Proceedings of the Twenty-eighth (2018) International Ocean and Polar Engineering Conference",

note = "28th International Ocean and Polar Engineering Conference (ISOPE 2018) ; Conference date: 10-06-2018 Through 15-06-2018",

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Kristoffersen, JC, Bredmose, H & Georgakis, CT 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. International Society of Offshore & Polar Engineers, Proceedings of the International Offshore and Polar Engineering Conference, pp. 291-298, 28th International Ocean and Polar Engineering Conference (ISOPE 2018), Sapporo, Japan, 10/06/2018. <http://legacy.isope.org/publications/proceedings/ISOPE/ISOPE%202018/data/polopoly_fs/1.4192178.1525883490!/fileserver/file/893335/filename/18TPC-0862Kristoffer.pdf#search=%22Preliminary%20Numerical%20Study%22>

Preliminary Numerical Study on the Influence of a Wind Field on Wave-induced Load on a Circular Cylinder. / Kristoffersen, Julie Carøe; Bredmose, Henrik; Georgakis, Christos Thomas.

Proceedings of the Twenty-eighth (2018) International Ocean and Polar Engineering Conference. International Society of Offshore & Polar Engineers, 2018. p. 291-298 (Proceedings of the International Offshore and Polar Engineering Conference).

Research output: Chapter in Book/Report/Conference proceeding › Article in proceedings › Research › peer-review

TY - GEN

T1 - Preliminary Numerical Study on the Influence of a Wind Field on Wave-induced Load on a Circular Cylinder

AU - Kristoffersen, Julie Carøe

AU - Bredmose, Henrik

AU - Georgakis, Christos Thomas

PY - 2018

Y1 - 2018

N2 - 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. Thepresence 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.

AB - 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. Thepresence 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.

KW - Offshore structure

KW - Wave-induced load

KW - Wind effect on wave

KW - Airflow separation

M3 - Article in proceedings

SN - 978-1-880653-87-6

T3 - Proceedings of the International Offshore and Polar Engineering Conference

SP - 291

EP - 298

BT - Proceedings of the Twenty-eighth (2018) International Ocean and Polar Engineering Conference

PB - International Society of Offshore & Polar Engineers

T2 - 28th International Ocean and Polar Engineering Conference (ISOPE 2018)

Y2 - 10 June 2018 through 15 June 2018

ER -

Kristoffersen JC, Bredmose H, Georgakis CT. 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. International Society of Offshore & Polar Engineers. 2018. p. 291-298. (Proceedings of the International Offshore and Polar Engineering Conference).