Sensitivity of vessel responses to environmental contours of extreme sea states

• Published in: Volume 3: Structures, Safety and Reliability
• Main Authors: Armstrong, CJ, Chin, C, Penesis, I, Drobyshevski, Y
• Format: Conference Object
• Language: English
• Published: American Society of Mechanical Engineers 2015
• Subjects: Engineering; Maritime Engineering; Ocean Engineering; Arctic
• Online Access: http://proceedings.asmedigitalcollection.asme.org/ConferenceProceedings.aspx; https://doi.org/10.1115/OMAE2015-41680; http://ecite.utas.edu.au/102150

A comparative study of two methods for the generationof the environmental contours is presented investigating thesensitivity of the predicted extreme vessel responses to thetype of the contour lines. Two approaches for the generationof environmental contours of the significant wave height andpeak period are compared: the Inverse First OrderReliability Method (IFORM) and Constant ProbabilityDensity (CPD) approach. Case studies include several globalresponses of a ship-shaped weather-vaning vessel and asemisubmersible platform. The case studies reveal that thedifferences between the IFORM and CPD contours are morepronounced in the range of long wave periods. Vesselresponses which are less sensitive to long wave periodsexhibit less difference (less than 1.0%) in their maximumvalues between the two types of contours. In contrast,responses which are sensitive to long wave periods showsignificantly larger differences of up to 7.0%. Uncertaintiesalso exist in the predicted extreme responses where theenvironmental contour and the response isoline behavetangentially. Differences between the extreme responsesproduced by the two contours generally decrease with anincrease in return period; however exceptions exist due tothe tangential behaviour. It is advised that these sensitivitiesshould be taken into consideration when the environmentalcontours are used in the design.