Kinematics of a Focused Wave Group on a Plane Beach: Physical Modeling in the UK Coastal Research Facility

Hunt, Alison; Taylor, Paul H.; Borthwick, Alistair G. L.; Stansby, Peter; Feng, Tong

doi:10.1061/40733(147)61

Cited by 3 publications

(4 citation statements)

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“…In order to fit the coefficients of the perturbation series (3.6), we need both the undisturbed incident wave field η and the total hydrodynamic load F. Given that each harmonic for a wave group is spread over a range of frequencies, we make use of the 'phase-inversion' method of Baldock et al (1996), Hunt et al (2004), Borthwick et al (2006) and Zang et al (2006). The crest and trough focused combinations (C − T)/2 for the odd harmonics and (C + T)/2 for the even harmonics now have the nonlinear harmonics better separated in frequency.…”

Section: Data Processingmentioning

confidence: 99%

“…The use of focused wave groups allows extraction of the higher harmonics in wave-structure interactions by using the 'phase-inversion' method described by Baldock, Swan & Taylor (1996), Hunt et al (2004), Borthwick et al (2006) and Zang et al (2006Zang et al ( , 2009, and more recently generalized by Fitzgerald et al (2014). The 'phase-inversion' method assumes that there is a generalized Stokes-like perturbation expansion in focused wave groups and responses.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2018

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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 nth-harmonic force scales with the nth 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 † Email addresses for correspondence: lifen.chen@uwa.edu.au, chenlifen239@163.com, J.Zang@bath.ac.uk Nonlinear forces on a column 43 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.

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Section: Data Processingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2018

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“…Separation of the linear and nonlinear contributions of free-surface elevation, loads and response from experimental data is possible through the method of harmonic separation. The method was introduced as two-phase separation in Jonathan & Taylor (1997), Walker, Taylor & Eatock Taylor (2004) and Hunt et al (2002), and has been applied in a series of papers in relation to nonlinear responses of a variety of offshore structures (see for instance Zhao et al 2017;Chen et al 2021) and coastal problems (Orszaghova et al 2014;Judge et al 2019;Zheng et al 2020). While originally based on ensemble averaging of large crest and trough events and enabling separation of odd (dominantly linear) and even (dominantly second-order) response contributions, it has later been extended to four-phase separation of wave forcing (Fitzgerald et al 2014) and applied to long time series produced by repeated experiments of phase-shifted input signals.…”

Section: Introductionmentioning

confidence: 99%

Resonant response of a flexible semi-submersible floating structure: experimental analysis and second-order modelling

Lynggård Hansen,

Bredmose,

Vincent

et al. 2024

J. Fluid Mech.

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The dynamics and nonlinear wave forcing of a flexible floating structure are investigated experimentally and numerically. The floater was designed to match sub-harmonic rigid-body natural frequencies of typical floating wind turbine substructures, with the addition of a flexible bending mode. Experiments were carried out for three sea states with phase-shifted input signals to allow harmonic separation of the measured response. We find for the weakest sea states that sub-harmonic rigid-body motion is driven by even-harmonic difference frequency forcing, and by linear forcing for the strongest sea state. The flexible mode was tested in a soft, linearly forced layout, and a stiff layout, forced by second-, third- and fourth-harmonic frequency content, for increasing severity of the sea state. Further insight is gained by analysis of the amplitude scaling of the resonant response. A new simplified approach is proposed and compared with the recent method of Orszaghova et al. (J. Fluid Mech., vol. 929, 2021, A32). We find that resonant surge and pitch motions are dominated by even-harmonic potential-flow forcing and that odd-harmonic response is mainly potential-flow driven in surge and mainly drag driven in pitch. The measured responses are reproduced numerically with second-order forcing and quadratic drag loads, using a recent and computationally efficient calculation method, extended here for the heave, pitch and flexible motions. We are able to reproduce the response statistics and power spectra for the measurements, including the subharmonic pitch and heave modes and the flexible mode. Deeper analysis reveals that inaccuracies in the even-harmonic forcing content can be compensated by the odd-harmonic loads.

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“…This approach was extended to four phases by Fitzgerald et al [5] and has been extended to include even more different phases [6]. This approach has been widely used on studies of focussed wave-groups [7][8][9][10][11][12][13]. -in one study even the 14th harmonic of the fundamental linear input has been cleanly extracted [14].…”

Section: Introductionmentioning

confidence: 99%

Application of Phase Decomposition to the Analysis of Random Time Series From Wave Basin Tests

Adcock

Tang

Bremer

et al. 2019

Volume 9: Rodney Eatock Taylor Honoring Symposium on Marine and Offshore Hydrodynamics; Takeshi Kinoshita Honoring Symposium On

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Many ocean engineering problems involve bound harmonics which are slaved to some underlying assumed close to linear time series. When analyzing signals we often want to remove the bound harmonics so as to "linearise" the data or to extract individual bound harmonic components so that they may be studied. For even moderately broadbanded systems filtering in the frequency domain is not sufficient to separate components as they overlap in frequency. One way to overcome this difficulty is to use input signals with the same linear envelope but with different phases and then use simple addition and subtraction of the resulting signals to extract different harmonics. This approach has been established for the analysis of wave groups. In this paper we examine whether this approach can be used on random time series as well. We analyse random wave time series of wave elevation from the towing tank in Shanghai Jiao Tong University and force measurements on a cylinder taken in the Kelvin tank at the University of Strathclyde. * Also Visiting Prof. University of Oxford. In the open ocean we have no control over the phase of

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Kinematics of a Focused Wave Group on a Plane Beach: Physical Modeling in the UK Coastal Research Facility

Cited by 3 publications

References 0 publications

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

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

Resonant response of a flexible semi-submersible floating structure: experimental analysis and second-order modelling

Application of Phase Decomposition to the Analysis of Random Time Series From Wave Basin Tests

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