Flow kinematics of focused wave groups on a plane beach in the U.K. Coastal Research Facility

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

doi:10.1016/j.coastaleng.2006.06.007

Cited by 37 publications

(13 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…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%

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

et al. 2018

View full text Add to dashboard Cite

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.

show abstract

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

View full text Add to dashboard Cite

show abstract

“…The experimental measurements were undertaken as part of an EPSRC-funded investigation undertaken jointly by the Universities of Manchester andOxford in 2001/2002 into the run-up and overtopping of focused wave groups. Details of the experiments are reported by Hunt (2003), Borthwick et al (2006b) and Hunt-Raby et al (2011). As part of the experimental programme, a total of eight normallyincident NewWave focused wave groups were considered, involving four crest-focused and four trough-focused wave groups, covering a range of group amplitudes and focus locations.…”

Section: Ukcrf Experimentsmentioning

confidence: 99%

“…A symmetrybased method for separation of harmonics from the calculated free surface time series is used to identify the second-order error waves (for examples of the application of this method see e.g. Baldock et al (1996), Jonathan and Taylor (1997), Johannessen and Swan (2001), Hunt et al (2004) and Borthwick et al (2006b)). The effectiveness of second-order paddle signals in eliminating the contaminating error waves is also examined.…”

Section: Newwave Propagation On a Flat Bedmentioning

confidence: 99%

Importance of second-order wave generation for focused wave group run-up and overtopping

Orszaghova

Taylor

Borthwick

et al. 2014

Coastal Engineering

Self Cite

View full text Add to dashboard Cite

Focused wave groups offer a means for coastal engineers to determine extreme run-up and overtopping events. Numerical predictions and laboratory measurements are presented for NewWave-type focused wave groups generated by a piston-type paddle generator, and interacting with a plane beach and a seawall in a wave basin. The numerical wave tank is based on the Boussinesq equations for non-breaking waves, and the non-linear shallow water equations for broken waves. Good agreement is achieved between the numerical predictions and laboratory measurements of free surface elevation, run-up distances and overtopping volumes for the test cases driven by linear paddle signals. Errors in run-up distance and overtopping volume are then assessed by repeating the test cases using second-order accurate wave generation signals. Focused wave groups generated using first-order wave-maker theory are found to be substantially contaminated by a preceding long error wave, resulting in erroneously enhanced run-up distances and overtopping volumes. Thus, the use of secondorder wave-maker theory for wave group run-up and overtopping experiments is instead recommended.

show abstract

“…The foregoing discrepancies are largely due to non-linear (second-and higher-order) wave interactions which are modelled by the 2D level I GN equations, but neglected in the analytical solution of the linearised SWEs. The even harmonics of the sloshing motions induced by the initial Gaussian hump can be determined by simulating the free surface time series resulting from releasing the initial hump, and the corresponding free surface time histories driven by an initial trough of equal but opposite shape to that of the hump (following the separation of harmonics method utilised by Borthwick et al (2006), Hunt et al (2004) and Johannessen and Swan (2001), among others). Here, the harmonics are treated as orthogonal functions, and the even harmonics obtained by addition as (ζ c + ζ t /2), where ζ c refers to the free surface elevation time series of the initial Gaussian hump and ζ t the equivalent time series for the initial Gaussian trough.…”

Section: Sloshing In a Tankmentioning

confidence: 99%

One-dimensional and two-dimensional Green–Naghdi equations for sloshing in shallow basins

Jalali

Borthwick

2017

Proceedings of the Institution of Civil Engineers - Engineering

View full text Add to dashboard Cite

This paper presents a verified model of weakly non-linear wave sloshing in shallow basins, based on level I Green-Naghdi (GN) mass and momentum equations derived for mild-sloped beds. The model is verified for sloshing of an initially sinusoidal free surface perturbation in a square tank with a horizontal bed. The model is also used to investigate free surface sloshing of an initial Gaussian hump in closed square basins, over horizontal and nonuniform bed topographies. Analysis of the free surface slosh motions demonstrates that the model gives predictions in satisfactory agreement with the analytical solution of linearised shallow water theory obtained by Lamb. Discrepancies between GN predictions and linear analytical solutions arise from the effect of wave non-linearities arising from the wave amplitude itself and wave-wave interactions.

show abstract

Flow kinematics of focused wave groups on a plane beach in the U.K. Coastal Research Facility

Cited by 37 publications

References 7 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

Importance of second-order wave generation for focused wave group run-up and overtopping

One-dimensional and two-dimensional Green–Naghdi equations for sloshing in shallow basins

Contact Info

Product

Resources

About