Required test durations for converged short-term wave and impact extreme value statistics — Part 1: Ferry dataset

van Essen, S.M.; Scharnke, Jule; Seyffert, Harleigh C.

doi:10.1016/j.marstruc.2023.103410

Required test durations for converged short-term wave and impact extreme value statistics — Part 1

Title

Required test durations for converged short-term wave and impact extreme value statistics — Part 1: Ferry dataset

Author

van Essen, S.M. (TU Delft Ship Hydromechanics and Structures; Maritime Research Institute Netherlands (MARIN))
Scharnke, Jule (Maritime Research Institute Netherlands (MARIN))
Seyffert, Harleigh C. (TU Delft Ship Hydromechanics and Structures)

Date

2023

Abstract

For the design of maritime structures in waves, the extreme values of responses such as motions and wave impact loads are required. Waves and wave-induced responses are stochastic, so such responses should always be related to a probability. This information is not easy to obtain for strongly non-linear responses such as wave impact forces. Usually class rules or direct assessment via experiments or numerical simulations are applied to obtain extreme values for design. This brings up questions related to the convergence of extreme values: how long do we need to test in order to obtain converged statistics for the target duration? Or, vice versa: given testing data, what is the uncertainty of the associated statistics? Often the test or simulation duration is cut up in ‘seeds’ or ‘realisations’, with an exposure duration of one or three hours based on the typical duration of a steady environmental condition at sea, or the time that a ship sails a single course. The required number of seeds for converged results depends on the type of structure and response, the exposure duration, and the desired probability level. The present study provides guidelines for the convergence of most probable maximum (MPM) wave crest heights and MPM green water wave impact forces on a ferry. Long duration experiments were done to gain insight into the required number of seeds, and the effect of fitting. The present paper presents part 1 of this study; part 2 [1] presents similar results for wave-in-deck loads on a stationary deck box.

Subject

Convergence
Design loads
Experiments
Extreme value statistics
Ferry
Green water
Most probable maximum
Seakeeping
Seed variations
Short-term variability
Wave impact loads
Waves