Effect of Short-Crestedness on Extreme Wave Impact: A Summary of Findings From the Joint Industry Project “ShorTCresT”

Abstract

Long-crested waves are typically used in the design of offshore structures. However, the corresponding statistics, kinematics and loading are significantly different in short-crested waves and up to date, there is no state-of-the-art methodology to apply short-crested models instead. The objective of the “ShortCresT” Joint Industry Project was to take into account short-crestedness in the design of offshore structures against extreme waves based on a good description of their spectral characteristics, statistics, kinematics, breaking and loading and to deliver (empirical) design recommendations and methods. This paper gives an overview of the findings of ShorTCresT regarding wave crest and height distributions, a comparison of basin and field data, the role of wave breaking, the most realistic directional model, hindcast models as well as the related platform loading.

Finding Dangerous Waves—Review of Methods to Obtain Wave Impact Design Loads for Marine Structures

“…Real wave crest height distributions balance these two effects. Spectral bandwidth does not play a significant role [109]. Individual freak or rogue waves (higher than predicted by this theory) may also play a role in certain wave environments.…”

“…The second-order wave crest distribution of Forristall [126] is often used as alternative to the linear Rayleigh distribution, but e.g., Refs. [109,125,127] show that even higher-order effects are observed in basins and at sea. Wave steepness increases the importance of higher-order effects and thus the wave crest heights, until wave breaking starts dissipating energy (see Fig.…”

“…9 illustrates that spatial effects may play a large role in the occurrence and details of the impact. This can probably not be fully neglected in extreme value prediction [109].…”

“…Again, these can be linear or non-linear. Hennig et al [109] recommend the use of second-order wave kinematics in design studies, possibly with an additional non-linear correction for the highest wave crests. Kinematics of waves above the free surface level can be obtained using methods such as Wheeler stretching or the second-order formulations of [102].…”

On the distribution of maximum crest and wave height at intermediate water depths

“…Within the project rigorous efforts have been made in order to minimize these uncertainties, and to account for the effects of remaining uncertainty. Other research (CresT, ShorTCresT and Loads JIPs, see Buchner et al 2011, Hennig et al 2015 has concluded that wave basin testing is absolutely necessary to quantify tails of extreme waves. The current work attempts to combine numerical and basin modelling of extreme waves wisely to achieve this efficiently.…”