Extreme wave elevations beneath offshore platforms, second order trapping, and the near flat form of the quadratic transfer functions

J. R.  Grice; Paul H Taylor; Rodney Eatock Taylor; Jun Zang; D A G Walker

doi:10.1016/j.compfluid.2015.06.025

Extreme wave elevations beneath offshore platforms, second order trapping, and the near flat form of the quadratic transfer functions

J. R. Grice, Paul H Taylor, Rodney Eatock Taylor, Jun Zang, D A G Walker

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Abstract

Extreme free surface elevations due to wave-structure interactions are investigated to second order using
Quadratic Transfer Functions (QTFs). The near-trapping phenomenon for small arrays of closely spaced
columns is studied for offshore applications, and the excitation of modes by linear and second order interactions
is compared. A simple method for approximating near-trapped mode shapes is shown to give
good results for both linear and second order excitation. Low frequency near-trapped mode shapes are
shown to be very similar whether excited linearly or to second order. Approximating surface elevation
sum QTF matrices as being flat perpendicular to the leading diagonal is investigated as a method for
greatly reducing lengthy QTF calculations. The effect of this approximation on second order surface elevation
calculations is assessed and shown to be reasonably small with realistic geometries for
semi-submersible and tension-leg platforms.

Original language	English
Pages (from-to)	13-25
Number of pages	13
Journal	Computers and Fluids
Volume	119
Early online date	3 Jul 2015
DOIs	https://doi.org/10.1016/j.compfluid.2015.06.025
Publication status	Published - Jul 2015

Keywords

Second order
QTF approximation
Wave-structure interactions
Near-trapping

Access to Document

10.1016/j.compfluid.2015.06.025

C&F_Grice_flatQTF_2015
Creative Commons Attribution Non-Commercial No Derivatives licence
Accepted author manuscript, 14.2 MBLicence: CC BY-NC-ND

Cite this

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title = "Extreme wave elevations beneath offshore platforms, second order trapping, and the near flat form of the quadratic transfer functions",

abstract = "Extreme free surface elevations due to wave-structure interactions are investigated to second order usingQuadratic Transfer Functions (QTFs). The near-trapping phenomenon for small arrays of closely spacedcolumns is studied for offshore applications, and the excitation of modes by linear and second order interactionsis compared. A simple method for approximating near-trapped mode shapes is shown to givegood results for both linear and second order excitation. Low frequency near-trapped mode shapes areshown to be very similar whether excited linearly or to second order. Approximating surface elevationsum QTF matrices as being flat perpendicular to the leading diagonal is investigated as a method forgreatly reducing lengthy QTF calculations. The effect of this approximation on second order surface elevationcalculations is assessed and shown to be reasonably small with realistic geometries forsemi-submersible and tension-leg platforms.",

keywords = "Second order, QTF approximation, Wave-structure interactions, Near-trapping",

author = "Grice, {J. R.} and Taylor, {Paul H} and {Eatock Taylor}, Rodney and Jun Zang and Walker, {D A G}",

year = "2015",

month = jul,

doi = "10.1016/j.compfluid.2015.06.025",

language = "English",

volume = "119",

pages = "13--25",

journal = "Computers and Fluids",

issn = "0045-7930",

publisher = "Elsevier",

}

TY - JOUR

T1 - Extreme wave elevations beneath offshore platforms, second order trapping, and the near flat form of the quadratic transfer functions

AU - Grice, J. R.

AU - Taylor, Paul H

AU - Eatock Taylor, Rodney

AU - Zang, Jun

AU - Walker, D A G

PY - 2015/7

Y1 - 2015/7

N2 - Extreme free surface elevations due to wave-structure interactions are investigated to second order usingQuadratic Transfer Functions (QTFs). The near-trapping phenomenon for small arrays of closely spacedcolumns is studied for offshore applications, and the excitation of modes by linear and second order interactionsis compared. A simple method for approximating near-trapped mode shapes is shown to givegood results for both linear and second order excitation. Low frequency near-trapped mode shapes areshown to be very similar whether excited linearly or to second order. Approximating surface elevationsum QTF matrices as being flat perpendicular to the leading diagonal is investigated as a method forgreatly reducing lengthy QTF calculations. The effect of this approximation on second order surface elevationcalculations is assessed and shown to be reasonably small with realistic geometries forsemi-submersible and tension-leg platforms.

AB - Extreme free surface elevations due to wave-structure interactions are investigated to second order usingQuadratic Transfer Functions (QTFs). The near-trapping phenomenon for small arrays of closely spacedcolumns is studied for offshore applications, and the excitation of modes by linear and second order interactionsis compared. A simple method for approximating near-trapped mode shapes is shown to givegood results for both linear and second order excitation. Low frequency near-trapped mode shapes areshown to be very similar whether excited linearly or to second order. Approximating surface elevationsum QTF matrices as being flat perpendicular to the leading diagonal is investigated as a method forgreatly reducing lengthy QTF calculations. The effect of this approximation on second order surface elevationcalculations is assessed and shown to be reasonably small with realistic geometries forsemi-submersible and tension-leg platforms.

KW - Second order

KW - QTF approximation

KW - Wave-structure interactions

KW - Near-trapping

UR - http://dx.doi.org/10.1016/j.compfluid.2015.06.025

UR - http://www.sciencedirect.com/science/article/pii/S004579301500208X

U2 - 10.1016/j.compfluid.2015.06.025

DO - 10.1016/j.compfluid.2015.06.025

M3 - Article

SN - 0045-7930

VL - 119

SP - 13

EP - 25

JO - Computers and Fluids

JF - Computers and Fluids

ER -

Extreme wave elevations beneath offshore platforms, second order trapping, and the near flat form of the quadratic transfer functions

Abstract

Keywords

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Jun Zang

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Extreme wave elevations beneath offshore platforms, second order trapping, and the near flat form of the quadratic transfer functions

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Jun Zang

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