Abstract

Response amplitude operator (RAO) curves are commonly employed to assess the dynamic behavior of floating offshore structures in the frequency domain. There are multiple methods used to obtain RAOs for numerical models, scaled physical models, and full-scale tests. While for numerical modeling many studies detail the precise methods used, the literature around experimental RAO curves often do not detail them or leave methodological information incomplete. There exists inadequate experimental evidence in assessing the differences in results obtained by following different RAO generation methods from scaled physical testing. This paper addresses this gap by comparing two most popular RAO generation methods: the energy spectra (ES) and the cross spectral auto spectra (CSAS) method. These are experimentally compared on scaled semisubmersible and spar-buoy platforms in an ocean wave basin. Differences of heave and pitch RAOs generated by different methods are investigated. A method for reasonably collating multiple tests to create a representative RAO is also presented. RAO amplitudes vary significantly and how they decay off beyond certain frequencies is dependent on the method adopted to create them. This variation can be a source of significant uncertainty for floating structures for further analysis, design, control, or repair. Some RAOs (e.g., pitch) are sensitive to scaling and should be considered when converting scaled tests to full-scale equivalent. Detailing methods of RAO generation and comparing approaches of developing them can be important for crucial decisions from scaled physical testing of floating structures at design/development stages.

References

References
1.
Kurian
,
V. J.
,
Idichandy
,
V. G.
, and
Ganapathy
,
C.
,
1993
, “
Hydrodynamic Response of Tension-Leg Platforms—A Model
,”
Exp. Mech.
,
33
(
3
), pp.
212
217
. 10.1007/BF02322576
2.
Henderson
,
A. R.
, and
Patel
,
M. H.
,
2003
, “
On the Modelling of a Floating Offshore Wind Turbine
,”
Wind Energy
,
6
(
1
), pp.
53
86
. 10.1002/we.83
3.
Wayman
,
E. N.
,
Sclavounos
,
P. D.
,
Butterfield
,
S.
,
Jonkman
,
J.
, and
Musial
,
W.
,
2006
, “
Offshore Technology Conference Houston, TX
,”
Coupled Dynamic Modeling of Floating Wind Turbine Systems, No. NREL/CP-500-39481
,
Golden, CO
.
4.
Robertson
,
A. N.
,
Jonkman
,
J. M.
,
Goupee
,
A. J.
,
Coulling
,
A. J.
,
Prowell
,
I.
,
Browning
,
J.
,
Masciola
,
M. D.
, and
Molta
,
P.
,
2013
, “
Summary of Conclusions and Recommendations Drawn From the DeepCwind Scaled Floating Offshore Wind System Test Campaign
,”
International Conference on Ocean, Offshore and Arctic Engineering
,
Nantes, France
,
June 9–14
,
Paper No: OMAE2013-10817
. 10.1115/OMAE2013-10817
5.
Ahmed
,
M. O.
,
Yenduri
,
A.
, and
Kurian
,
V. J.
,
2016
, “
Evaluation of the Dynamic Responses of Truss Spar Platforms for Various Mooring Configurations With Damaged Lines
,”
Ocean Eng.
,
123
, pp.
411
421
. 10.1016/j.oceaneng.2016.07.004
6.
Wright
,
C.
,
O'Sullivan
,
K.
,
Murphy
,
J.
, and
Pakrashi
,
V.
,
2015
, “
Experimental Comparison of Dynamic Responses of a Tension Moored Floating Wind Turbine Platform With and Without Spring Dampers
,”
J. Phys. Conf. Ser.
,
628
(
1
), p.
012056
. 10.1088/1742-6596/628/1/012056
7.
Chandrasekaran
,
S.
,
Madhavi
,
N.
, and
Sampath
,
S.
,
2013
, “
Hydrodynamic Response of Tension Leg Platforms With Perforated Members
,”
Int. J. Ocean Clim. Syst.
,
4
(
3
), pp.
181
196
. 10.1260/1759-3131.4.3.181
8.
Murray
,
J.
,
Yang
,
C. K.
,
Yang
,
W.
,
Krishnaswamy
,
P.
, and
Zou
,
J.
,
2009
, “
An Extended Tension leg Platform Design for Post-Katrina Gulf of Mexico
,”
Proceedings of the 19th International Offshore and Polar Engineering Conference
,
Osaka, Japan
,
June 21–26
,
International Society of Offshore and Polar Engineers
, pp.
120
127
.
9.
Cermelli
,
C.
,
Roddier
,
D.
, and
Aubault
,
A.
,
2009
, “
WindFloat: A Floating Foundation for Offshore Wind Turbines—Part II: Hydrodynamics Analysis
,”
ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering
,
Honolulu, HI
,
May 31–June 5
,
Paper No: OMAE2009-79231
. 10.1115/OMAE2009-79231
10.
Olinger
,
D.
,
DeStefano
,
E.
,
Murphy
,
E.
,
Naqvi
,
K.
, and
Tryggvason
,
G.
,
2012
, “
Scale-Model Experiments on Floating Wind Turbine Platforms
,”
50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition
,
Nashville, TN
,
Jan. 9–12
, p.
375
.
11.
Garcia-Rosa
,
P. B.
, and
Ringwood
,
J. V.
,
2015
, “
On the Sensitivity of Optimal Wave Energy Device Geometry to the Energy Maximizing Control System
,”
IEEE Trans. Sustain. Energy
,
7
(
1
), pp.
419
426
. 10.1109/TSTE.2015.2423551
12.
Bhattacharyya
,
R.
,
1978
,
Dynamics of Marine Vehicles
,
John Wiley & Sons Inc.
,
New York
.
13.
Faltinsen
,
O.
,
1993
,
Sea Loads on Ships and Offshore Structures
, Vol.
1
,
Cambridge University Press
,
Cambridge, UK
.
14.
Suleiman
,
B. M.
,
Fahey
,
S. F.
,
Nayfeh
,
A. H.
, and
Hajj
,
M. R.
,
2001
, “
Estimation of Response Amplitude Operators for Ships via the Circular-Hyperbolic Decomposition
,”
J. Ship Res.
,
45
(
2
), pp.
103
110
. 10.2514/6.2000-1344
15.
Ramachandran
,
G. K. V.
,
Robertson
,
A.
,
Jonkman
,
J. M.
, and
Masciola
,
M. D.
,
2013
,”
Proceedings of the 23rd International Offshore and Polar Engineering
,
Anchorage, AK
,
June 30–July 5
,
National Renewable Energy Laboratory (NREL)
, pp.
369
376
.
16.
Weldeslassie
,
M.
,
2014
, “
Investigation of Which Sea State Yield the Dominating Contribution to Fatigue Accumulation in Offshore Structures
,”
Master’s thesis
,
University of Stavanger
,
Norway
.
17.
Harris
,
F. J.
,
1978
, “
On the Use of Windows for Harmonic Analysis With the Discrete Fourier Transform
,”
Proc. IEEE
,
66
(
1
), pp.
51
83
. 10.1109/PROC.1978.10837
18.
Chakrabarti
,
S. K.
,
1994
,
Offshore Structure Modeling
, Vol.
9
,
World Scientific
,
Singapore
.
19.
Hayes
,
M. H.
,
2009
,
Statistical Digital Signal Processing and Modeling
,
John Wiley & Sons
,
New York
.
20.
O’Donnell
,
D.
,
Murphy
,
J.
, and
Pakrashi
,
V.
,
2018
, “
Dynamic Response Distribution Fits of a Floating Spar Platform in an Ocean Wave Basin for Structural Changes
,”
First International Conference on Health Monitoring of Civil and Maritime Structure
,
Croydon, London
,
Feb. 5–6
, pp.
1
7
.
21.
Jaksic
,
V.
,
O'Shea
,
R.
,
Cahill
,
P.
,
Murphy
,
J.
,
Mandic
,
D. P.
, and
Pakrashi
,
V.
,
2015
, “
Dynamic Response Signatures of a Scaled Model Platform for Floating Wind Turbines in an Ocean Wave Basin
,”
Philos. Trans. R. Soc., A
,
373
(
2035
), p.
20140078
. 10.1098/rsta.2014.0078
22.
Pakrashi
,
V.
,
O'Shea
,
R.
,
Jaksic
,
V.
, and
Murphy
,
J.
,
2015
, “
The Hurst Exponent as an Indicator of the Behaviour of a Model Monopile in an Ocean Wave Testing Basin
,”
J. Phys.: Conf. Ser.
,
628
(
1
), p.
012057
. 10.1088/1742-6596/628/1/012057
23.
O’Donnell
,
D.
,
Murphy
,
J.
,
Desmond
,
C.
,
Jaksic
,
V.
, and
Pakrashi
,
V.
,
2017
, “
Tuned Liquid Column Damper Based Reduction of Dynamic Responses of Scaled Offshore Platforms in Different Ocean Wave Basins
,”
J. Phys.: Conf. Ser.
,
842
(
1
), p.
012043
. 10.1088/1742-6596/842/1/012043
24.
O'Donnell
,
D.
,
Srbinovsky
,
B.
,
Murphy
,
J.
,
Popovici
,
E.
, and
Pakrashi
,
V.
,
2015
, “
Sensor Measurement Strategies for Monitoring Offshore Wind and Wave Energy Devices
,”
J. Phys.: Conf. Ser.
,
628
(
1
), p.
012117
. 10.1088/1742-6596/628/1/012117
25.
Roddier
,
D.
,
Cermelli
,
C.
,
Aubault
,
A.
, and
Weinstein
,
A.
,
2010
, “
WindFloat: A Floating Foundation for Offshore Wind Turbines
,”
J. Renewable Sustainable Energy
,
2
(
3
), p.
033104
. 10.1063/1.3435339
26.
Chakrabarti
,
S.
,
1998
, “
Physical Model Testing of Floating Offshore Structures
,”
Dynamic Positioning Conference
,
Oct. 13–14
, Vol.
1
, pp.
1
33
.
27.
Vakilabadi
,
K. A.
,
Khedmati
,
M. R.
, and
Seif
,
M. S.
,
2014
, “
Experimental Study on Heave and Pitch Motion Characteristics of a Wave-Piercing Trimaran
,”
Trans. FAMENA
,
38
(
3
), pp.
13
26
.
28.
Malekpour
,
S.
,
Gubner
,
J. A.
, and
Sethares
,
W. A.
,
2018
, “
Measures of Generalized Magnitude-Squared Coherence: Differences and Similarities
,”
J. Franklin Inst.
,
355
(
5
), pp.
2932
2950
. 10.1016/j.jfranklin.2018.01.014
29.
Guevara
,
M. A.
, and
Corsi-Cabrera
,
M.
,
1996
, “
EEG Coherence or EEG Correlation?
,”
Int. J. Psychophysiol.
,
23
(
3
), pp.
145
153
. 10.1016/S0167-8760(96)00038-4
30.
Miles
,
J. H.
,
2011
, “
Estimation of Signal Coherence Threshold and Concealed Spectral Lines Applied to Detection of Turbofan Engine Combustion Noise
,”
J. Acoust. Soc. Am.
,
129
(
5
), pp.
3068
3081
. 10.1121/1.3546097
31.
O’Donnell
,
D.
,
Murphy
,
J.
, and
Pakrashi
,
V.
,
2020
, “
Damage Monitoring of a Catenary Moored Spar Platform for Renewable Energy Devices
,”
Energies
,
13
(
14
), p.
3631
. 10.3390/en13143631
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