A new approach to estimate environmental contours in the original physical space by direct Monte Carlo simulations rather than applying the Rosenblatt transformation has recently been proposed. In this paper, the new and the traditional approach to estimating the contours are presented and the assumptions on which they are based are discussed. The different results given by these two methods are then compared in a number of case studies. Simultaneous probability density functions are fitted to the joint distribution of significant wave height and wave period for selected ocean locations and environmental contours are estimated for both methods. Thus, the practical consequences of the choice of approach are assessed. Particular attention is given to mixed sea systems. In these situations, the two approaches to environmental contours may be very different while for other wave conditions the contours are similar.

References

References
1.
Haver
,
S.
,
1987
, “
On the Joint Distribution of Heights and Periods of Sea Waves
,”
Ocean Eng.
,
14
(
5
), pp.
359
376
.
2.
Winterstein
,
S.
,
Ude
,
T.
,
Cornell
,
C.
,
Bjerager
,
P.
, and
Haver
,
S.
,
1993
, “
Environmental Parameters for Extreme Response: Inverse FORM With Omission Factors
,”
6th International Conference on Structural Safety and Reliability
.
3.
Huseby
,
A. B.
,
Vanem
,
E.
, and
Natvig
,
B.
,
2013
, “
A New Approach to Environmental Contours for Ocean Engineering Applications Based on Direct Monte Carlo Simulations
,”
Ocean Eng.
,
60
, pp.
124
135
.
4.
Huseby
,
A. B.
,
Vanem
,
E.
, and
Natvig
,
B.
,
2013
, “
A New Method for Environmental Contours in Marine Structural Design
,”
ASME
Paper No. OMAE2013-10053.
5.
Rosenblatt
,
M.
,
1952
, “
Remarks on a Multivariate Transformation
,”
Ann. Math. Stat.
,
23
(
3
), pp.
470
472
.
6.
Haver
,
S.
, and
Winterstein
,
S.
,
2009
, “
Environmental Contour Lines: A Method for Estimating Long Term Extremes by a Short Term Analysis
,”
Trans. Soc. Nav. Archit. Mar. Eng.
,
116
, pp.
116
127
.
7.
Vanem
,
E.
, and
Bitner-Gregersen
,
E.
,
2012
, “
Stochastic Modelling of Long-Term Trends in the Wave Climate and Its Potential Impact on Ship Structural Loads
,”
Appl. Ocean Res.
,
37
, pp.
235
248
.
8.
Baarholm
,
G. S.
,
Haver
,
S.
, and
Økland
,
O. D.
,
2010
, “
Combining Contours of Significant Wave Height and Peak Period With Platform Response Distributions for Predicting Design Response
,”
Mar. Struct.
,
23
(
2
), pp.
147
163
.
9.
Leira
,
B. J.
,
2008
, “
A Comparison of Stochastic Process Models for Definition of Design Contours
,”
Struct. Saf.
,
30
(
6
), pp.
493
505
.
10.
Sagrilo
,
L.
,
Næss
,
A.
, and
Doria
,
A.
,
2011
, “
On the Long-Term Response of Marine Structures
,”
Appl. Ocean Res.
,
33
(
3
), pp.
208
214
.
11.
Moan
,
T.
,
Gao
,
Z.
, and
Ayala-Uraga
,
E.
,
2005
, “
Uncertainty of Wave-Induced Response of Marine Structures Due to Long-Term Variation of Extratropical Wave Conditions
,”
Mar. Struct.
,
18
(
4
), pp.
359
382
.
12.
Jonathan
,
P.
,
Ewans
,
K.
, and
Flynn
,
J.
,
2011
, “
On the Estimation of Ocean Engineering Design Contours
,”
ASME
Paper No. OMAE2011-49886, pp. 695–705.
13.
Huseby
,
A. B.
,
Vanem
,
E.
, and
Natvig
,
B.
,
2015
, “
Alternative Environmental Contours for Structural Reliability Analysis
,”
Struct. Saf.
,
54
, pp.
32
45
.
14.
Bitner-Gregersen
,
E.
,
2012
, “
Joint Long Term Models of Met-Ocean Parameters
,”
Marine Technology and Engineering: CENTEC Anniversary Book
,
C.
Guedes Soares
,
Y.
Garbatov
,
N.
Fonseca
, and
A.
Teixeira
, eds., Vol.
1
.,
CRC Press
,
London
, pp.
19
34
.
15.
Bitner-Gregersen
,
E.
, and
Haver
,
S.
,
1989
, “
Joint Long Term Description of Environmental Parameters for Structural Response Calculation
,”
2nd International Workshop on Wave Hindcasting and Forecasting
.
16.
Bitner-Gregersen
,
E.
, and
Haver
,
S.
,
1991
, “
Joint Environmental Model for Reliability Calculations
,”
First International Offshore and Polar Engineering Conference (ISOPE), The International Society of Offshore and Polar Engineering (ISOPE)
.
17.
Bitner-Gregersen
,
E.
,
2005
, “
Joint Probabilistic Description for Combined Seas
,”
ASME
Paper No. OMAE2005-67382, pp. 169–180.
18.
Bitner-Gregersen
,
E.
,
2010
, “
Uncertainties of Joint Long-Term Probabilistic Modeling of Wind Sea and Swell
,”
ASME
Paper No. OMAE2010-20682, pp. 493–504.
19.
Huseby
,
A. B.
,
Vanem
,
E.
, and
Natvig
,
B.
,
2014
, “
A New Monte Carlo Method for Environmental Contour Estimation
,”
European Safety and Reliability Conference (ESREL)
, pp.
2091
2098
.
20.
Ewans
,
K.
,
Bitner-Gregersen
,
E.
, and
Guedes Soares
,
C.
,
2006
, “
Estimation of Wind-Sea and Swell Components in a Bimodal Sea State
,”
ASME J. Offshore Mech. Arct. Eng.
,
128
(
4
), pp.
265
270
.
You do not currently have access to this content.