Characteristic loads for design of offshore structures are defined in terms of their annual exceedance probability, q. In the Norwegian Petroleum Regulations, q = 10−2 is required for the ultimate limit state (ULS), while q = 10−4 is required for the accidental limit state (ALS). In principle, a full long-term analysis (LTA) is required in order to obtain consistent estimates. This is straightforward for linear response problems, while it is a challenge for nonlinear problems, in particular if they additionally are of an on–off nature. The latter will typically be the case for loads due to breaking wave impacts. In this paper, the challenges related to estimation of characteristic slamming loads are discussed. Measured slamming loads from a model test are presented, and the observed large variability is discussed. The stochastic nature of slamming loads is studied using a simplified linear relation between the sea states and the Gumbel distribution parameter surfaces. The characteristic slamming loads with q-annual probability of exceedance are estimated from an LTA using the short-term distribution of the slamming loads and the long-term distribution of the sea states. The effect of integrating over a smaller area of the scatter diagram of the sea states is studied. The uncertainties in response from slamming loads are compared to a more common response process, and the relation between variability and the number of realizations in each sea state is looked into.

References

References
1.
PSA
,
2015
, “
The Facilities Regulations
,”
P. S. A.
Norway
, ed.,
Petroleum Safety Authority
Norway
.
2.
Norsok
,
2007
, “
N-003 Actions and Actions Effects
,” Standards Norway.
3.
Baarholm
,
G. S.
, and
Haver
,
K. S.
,
2009
, “
Application of Environmental Contour Lines—A Summary of a Number of Case Studies
,”
International Conference on Floating Structures for Deepwater Operations University of Strathclyde Glasgow
, Scotland, UK.
4.
Suyuthi
,
A.
, and
Haver
,
S. K.
,
2009
, “
Extreme Loads Due to Wave Breaking Against Platform Column
,”
International Offshore and Polar Engineering Conference
, Osaka, Japan, July 21–26, pp.
472
479
.
5.
Roos
,
J.
,
Swan
,
C.
, and
Haver
,
S.
,
2010
, “
Wave Impacts on the Column of a Gravity Based Structure
,”
ASME
Paper No. OMAE2010-20648.
6.
Clauss
,
G. N. F.
,
Haver
,
S. K.
, and
Strach
,
M.
,
2010
, “
Breaking Wave Impacts on Platform Columns-Stochastic Analysis and DNV Recommended Practice
,”
ASME
Paper No. OMAE2010-20293.
7.
Oberlies
,
R.
,
Khalifa
,
J.
,
Huang
,
J.
,
Hetland
,
S.
,
Younan
,
A.
,
Overstake
,
M.
, and
Slocum
,
S.
,
2014
, “
Determination of Wave Impact Loads for the Hebron Gravity Based Structure (GBS)
,”
ASME
Paper No. OMAE2014-23503.
8.
Haver
,
S.
,
2007
, “
A Discussion of Long Term Response Versus Mean Maximum Response of the Selected Design Sea State
,”
ASME
Paper No. OMAE2007-29552.
9.
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
.
10.
Winterstein
,
S. R.
,
Ude
,
T. C.
,
Cornell
,
C. A.
,
Bjerager
,
P.
, and
Haver
,
S.
,
1993
, “
Environmental Parameters for Extreme Response: Inverse FORM With Omission Factors
,”
International Conference on Structural Safety and Reliability
(
ICOSSAR
),
Innsbruck
,
Austria
, Aug. 9–13.
11.
Haver
,
S.
, and
Kleiven
,
G.
,
2004
, “
Environmental Contour Lines for Design Purposes—Why and When?
,”
ASME
Paper No. OMAE2004-51157.
12.
Bury
,
K. V.
,
1975
, “
Statistical Models in Applied Science
,”
A Wiley Publication in Applied Statistics
,
Wiley
,
New York
, pp.
371
375
.
13.
DNV
,
2014
, “
C205—Environmental Conditions and Environmental Loads
,” Det Norske Veritas AS, Hovik, Norway,
Recommended Practice DNV-RP-C205
.
14.
Forristall
,
G. Z.
,
2000
, “
Wave Crest Distributions: Observations and Second-Order Theory
,”
J. Phys. Oceanogr.
,
30
(
8
), pp.
1931
1943
.
You do not currently have access to this content.