TY - JOUR

T1 - Evaluating environmental joint extremes for the offshore industry using the conditional extremes model

AU - Ewans, K.

AU - Jonathan, P.

PY - 2014

Y1 - 2014

N2 - Understanding extreme ocean environments and their interaction with fixed and floating structures is critical for the design of offshore and coastal facilities. The joint effect of various ocean variables on extreme responses of offshore structures is fundamental in determining the design loads. For example, it is known that mean values of wave periods tend to increase with increasing storm intensity, and a floating system responds in a complex way to both variables.Specification of joint extremes in design criteria has often been somewhat ad hoc, being based on fairly arbitrary combinations of extremes of variables estimated independently. Such approaches are even outlined in design guidelines. Mathematically more consistent estimates of the joint occurrence of extreme environmental variables fall into two camps in the offshore industry - response-based and response-independent. Both are outlined here, with emphasis on response-independent methods, particularly those based on the conditional extremes model recently introduced by (Heffernan and Tawn, 2004), which has a solid theoretical motivation. We illustrate an application of the conditional extremes model to joint estimation of extreme storm peak significant wave height and peak period at a northern North Sea location, incorporating storm direction as a model covariate. We also discuss joint estimation of extreme current profiles with depth off the North West Shelf of Australia. Methods such as the conditional extremes model provide valuable additions to the metocean engineer's toolkit. © 2013 Elsevier B.V.

AB - Understanding extreme ocean environments and their interaction with fixed and floating structures is critical for the design of offshore and coastal facilities. The joint effect of various ocean variables on extreme responses of offshore structures is fundamental in determining the design loads. For example, it is known that mean values of wave periods tend to increase with increasing storm intensity, and a floating system responds in a complex way to both variables.Specification of joint extremes in design criteria has often been somewhat ad hoc, being based on fairly arbitrary combinations of extremes of variables estimated independently. Such approaches are even outlined in design guidelines. Mathematically more consistent estimates of the joint occurrence of extreme environmental variables fall into two camps in the offshore industry - response-based and response-independent. Both are outlined here, with emphasis on response-independent methods, particularly those based on the conditional extremes model recently introduced by (Heffernan and Tawn, 2004), which has a solid theoretical motivation. We illustrate an application of the conditional extremes model to joint estimation of extreme storm peak significant wave height and peak period at a northern North Sea location, incorporating storm direction as a model covariate. We also discuss joint estimation of extreme current profiles with depth off the North West Shelf of Australia. Methods such as the conditional extremes model provide valuable additions to the metocean engineer's toolkit. © 2013 Elsevier B.V.

KW - Conditional extremes

KW - Covariates

KW - Floating structures

KW - Joint extremes

KW - Offshore design

KW - Environmental variables

KW - North west shelf of australia

KW - Ocean environment

KW - Significant wave height

KW - Design

KW - Estimation

KW - Offshore structures

KW - Storms

KW - continental shelf

KW - design

KW - floating offshore structure

KW - numerical model

KW - offshore application

KW - storm

KW - wave field

KW - Australia

U2 - 10.1016/j.jmarsys.2013.03.007

DO - 10.1016/j.jmarsys.2013.03.007

M3 - Journal article

VL - 130

SP - 124

EP - 130

JO - Journal of Marine Systems

JF - Journal of Marine Systems

SN - 0924-7963

ER -