An experimental decomposition of nonlinear forces on a surface-piercing column: Stokes-type expansions of the force harmonics

Lifen Chen, Jun Zang, Paul Taylor, Liang Sun, Gerald Morgan, James Grice, Jana Orszaghova, Menases Tello Ruiz

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

Wave loading on marine structures is the major external force to be considered in the design of such structures. The accurate prediction of the nonlinear high-order components of the wave loading has been an unresolved challenging problem. In this paper, the nonlinear harmonic components of hydrodynamic forces on a bottom-mounted vertical cylinder are investigated experimentally. A large number of experiments were conducted in the Danish Hydraulic Institute shallow water wave basin on the cylinder, both on a flat bed and a sloping bed, as part of a European collaborative research project. High-quality data sets for focused wave groups have been collected for a wide range of wave conditions. The high-order harmonic force components are separated by applying the 'phase-inversion' method to the measured force time histories for a crest focused wave group and the same wave group inverted. This separation method is found to work well even for locally violent nearly-breaking waves formed from bidirectional wave pairs. It is also found that the th-harmonic force scales with the th power of the envelope of both the linear undisturbed free-surface elevation and the linear force component in both time variation and amplitude. This allows estimation of the higher-order harmonic shapes and time histories from knowledge of the linear component alone. The experiments also show that the harmonic structure of the wave loading on the cylinder is virtually unaltered by the introduction of a sloping bed, depending only on the local wave properties at the cylinder. Furthermore, our new experimental results reveal that for certain wave cases the linear loading is actually less than 40 % of the total wave loading and the high-order harmonics contribute more than 60 % of the loading. The significance of this striking new result is that it reveals the importance of high-order nonlinear wave loading on offshore structures and means that such loading should be considered in their design.
Original languageEnglish
Pages (from-to)42-77
JournalJournal of Fluid Mechanics.
Volume848
DOIs
Publication statusPublished - 2018

Fingerprint

piercing
Piercing
loading waves
Decomposition
harmonics
decomposition
expansion
beds
histories
water waves
research projects
shallow water
hydraulics
Ocean structures
envelopes
Offshore structures
Water waves
hydrodynamics
inversions

Cite this

@article{623ff13da7d94031a9e6e9c4dd837589,
title = "An experimental decomposition of nonlinear forces on a surface-piercing column: Stokes-type expansions of the force harmonics",
abstract = "Wave loading on marine structures is the major external force to be considered in the design of such structures. The accurate prediction of the nonlinear high-order components of the wave loading has been an unresolved challenging problem. In this paper, the nonlinear harmonic components of hydrodynamic forces on a bottom-mounted vertical cylinder are investigated experimentally. A large number of experiments were conducted in the Danish Hydraulic Institute shallow water wave basin on the cylinder, both on a flat bed and a sloping bed, as part of a European collaborative research project. High-quality data sets for focused wave groups have been collected for a wide range of wave conditions. The high-order harmonic force components are separated by applying the 'phase-inversion' method to the measured force time histories for a crest focused wave group and the same wave group inverted. This separation method is found to work well even for locally violent nearly-breaking waves formed from bidirectional wave pairs. It is also found that the th-harmonic force scales with the th power of the envelope of both the linear undisturbed free-surface elevation and the linear force component in both time variation and amplitude. This allows estimation of the higher-order harmonic shapes and time histories from knowledge of the linear component alone. The experiments also show that the harmonic structure of the wave loading on the cylinder is virtually unaltered by the introduction of a sloping bed, depending only on the local wave properties at the cylinder. Furthermore, our new experimental results reveal that for certain wave cases the linear loading is actually less than 40 {\%} of the total wave loading and the high-order harmonics contribute more than 60 {\%} of the loading. The significance of this striking new result is that it reveals the importance of high-order nonlinear wave loading on offshore structures and means that such loading should be considered in their design.",
author = "Lifen Chen and Jun Zang and Paul Taylor and Liang Sun and Gerald Morgan and James Grice and Jana Orszaghova and {Tello Ruiz}, Menases",
year = "2018",
doi = "10.1017/jfm.2018.339",
language = "English",
volume = "848",
pages = "42--77",
journal = "Journal of Fluid Mechanics.",
issn = "0022-1120",
publisher = "Cambridge University Press",

}

An experimental decomposition of nonlinear forces on a surface-piercing column: Stokes-type expansions of the force harmonics. / Chen, Lifen; Zang, Jun ; Taylor, Paul; Sun, Liang; Morgan, Gerald; Grice, James; Orszaghova, Jana; Tello Ruiz, Menases.

In: Journal of Fluid Mechanics., Vol. 848, 2018, p. 42-77.

Research output: Contribution to journalArticle

TY - JOUR

T1 - An experimental decomposition of nonlinear forces on a surface-piercing column: Stokes-type expansions of the force harmonics

AU - Chen, Lifen

AU - Zang, Jun

AU - Taylor, Paul

AU - Sun, Liang

AU - Morgan, Gerald

AU - Grice, James

AU - Orszaghova, Jana

AU - Tello Ruiz, Menases

PY - 2018

Y1 - 2018

N2 - Wave loading on marine structures is the major external force to be considered in the design of such structures. The accurate prediction of the nonlinear high-order components of the wave loading has been an unresolved challenging problem. In this paper, the nonlinear harmonic components of hydrodynamic forces on a bottom-mounted vertical cylinder are investigated experimentally. A large number of experiments were conducted in the Danish Hydraulic Institute shallow water wave basin on the cylinder, both on a flat bed and a sloping bed, as part of a European collaborative research project. High-quality data sets for focused wave groups have been collected for a wide range of wave conditions. The high-order harmonic force components are separated by applying the 'phase-inversion' method to the measured force time histories for a crest focused wave group and the same wave group inverted. This separation method is found to work well even for locally violent nearly-breaking waves formed from bidirectional wave pairs. It is also found that the th-harmonic force scales with the th power of the envelope of both the linear undisturbed free-surface elevation and the linear force component in both time variation and amplitude. This allows estimation of the higher-order harmonic shapes and time histories from knowledge of the linear component alone. The experiments also show that the harmonic structure of the wave loading on the cylinder is virtually unaltered by the introduction of a sloping bed, depending only on the local wave properties at the cylinder. Furthermore, our new experimental results reveal that for certain wave cases the linear loading is actually less than 40 % of the total wave loading and the high-order harmonics contribute more than 60 % of the loading. The significance of this striking new result is that it reveals the importance of high-order nonlinear wave loading on offshore structures and means that such loading should be considered in their design.

AB - Wave loading on marine structures is the major external force to be considered in the design of such structures. The accurate prediction of the nonlinear high-order components of the wave loading has been an unresolved challenging problem. In this paper, the nonlinear harmonic components of hydrodynamic forces on a bottom-mounted vertical cylinder are investigated experimentally. A large number of experiments were conducted in the Danish Hydraulic Institute shallow water wave basin on the cylinder, both on a flat bed and a sloping bed, as part of a European collaborative research project. High-quality data sets for focused wave groups have been collected for a wide range of wave conditions. The high-order harmonic force components are separated by applying the 'phase-inversion' method to the measured force time histories for a crest focused wave group and the same wave group inverted. This separation method is found to work well even for locally violent nearly-breaking waves formed from bidirectional wave pairs. It is also found that the th-harmonic force scales with the th power of the envelope of both the linear undisturbed free-surface elevation and the linear force component in both time variation and amplitude. This allows estimation of the higher-order harmonic shapes and time histories from knowledge of the linear component alone. The experiments also show that the harmonic structure of the wave loading on the cylinder is virtually unaltered by the introduction of a sloping bed, depending only on the local wave properties at the cylinder. Furthermore, our new experimental results reveal that for certain wave cases the linear loading is actually less than 40 % of the total wave loading and the high-order harmonics contribute more than 60 % of the loading. The significance of this striking new result is that it reveals the importance of high-order nonlinear wave loading on offshore structures and means that such loading should be considered in their design.

U2 - 10.1017/jfm.2018.339

DO - 10.1017/jfm.2018.339

M3 - Article

VL - 848

SP - 42

EP - 77

JO - Journal of Fluid Mechanics.

JF - Journal of Fluid Mechanics.

SN - 0022-1120

ER -