TY - CONF

T1 - Recent advances in the analysis of extreme metocean events

AU - Ewans, K.

AU - Bhd, S.S.

AU - Jonathan, P.

PY - 2014

Y1 - 2014

N2 - Accurate and reliable estimates of probabilities of rare, extreme metocean events are critical for optimal design of offshore facilities. They ensure facilities are neither over- nor under- designed, allowing target reliability levels to be achieved without undue conservatism. Engineering design requires metocean parameters to be specified with a return-period of 100 years, but often specification to a return period of 10,000 years is required. Modern hindcast data bases, typically used to derive extremal criteria, can be of limited extent, consisting of data for a few decades; hindcasts with periods of more than 50 years remain unusual. In addition, metocean criteria are often stratified by covariate - seasonality or directionality are common examples. Further, specification of joint occurrence of parameters at long return periods is necessary to avoid excessive conservatism, and such criteria may also need to be specified as functions of one or more covariates. Methods used by practitioners to meet these requirements are often somewhat adhoc, based on experience and intuition. In this paper we review recent applications which add statistic rigour and consistency to the estimation of design values. In particular, we present methods for maximising the benefit of limited data sets and deriving consistent extremal criteria with covariate, resulting in criteria that are consistent with respect to multiple covariates, including space, time and directionality. Copyright 2014, Offshore Technology Conference.

AB - Accurate and reliable estimates of probabilities of rare, extreme metocean events are critical for optimal design of offshore facilities. They ensure facilities are neither over- nor under- designed, allowing target reliability levels to be achieved without undue conservatism. Engineering design requires metocean parameters to be specified with a return-period of 100 years, but often specification to a return period of 10,000 years is required. Modern hindcast data bases, typically used to derive extremal criteria, can be of limited extent, consisting of data for a few decades; hindcasts with periods of more than 50 years remain unusual. In addition, metocean criteria are often stratified by covariate - seasonality or directionality are common examples. Further, specification of joint occurrence of parameters at long return periods is necessary to avoid excessive conservatism, and such criteria may also need to be specified as functions of one or more covariates. Methods used by practitioners to meet these requirements are often somewhat adhoc, based on experience and intuition. In this paper we review recent applications which add statistic rigour and consistency to the estimation of design values. In particular, we present methods for maximising the benefit of limited data sets and deriving consistent extremal criteria with covariate, resulting in criteria that are consistent with respect to multiple covariates, including space, time and directionality. Copyright 2014, Offshore Technology Conference.

KW - Design value

KW - Engineering design

KW - Limited data sets

KW - Offshore facilities

KW - Optimal design

KW - Reliable estimates

KW - Return periods

KW - Target reliability

KW - Specifications

U2 - 10.4043/25036-MS

DO - 10.4043/25036-MS

M3 - Conference paper

SP - 3009

EP - 3019

T2 - Offshore Technology Conference-Asia

Y2 - 25 March 2014 through 28 March 2014

ER -