ON THE IMPORTANCE OF CONSIDERING MULTIPLE SEASTATE REALIZATIONS WHEN ESTIMATING DESIGN LOADS IN MULTI-DIRECTIONAL SHALLOW-WATER WAVES

Andrew Cornett,Scott Baker

doi:10.9753/icce.v36v.management.46

Abstract

The objectives of this work are to close some of the knowledge gaps facing designers tasked with designing new offshore structures or upgrading older structures located in shallow waters and exposed to energetic multi-directional waves generated by passing hurricanes or cyclones. This will be accomplished by first investigating and characterizing the natural variability of the maximum wave heights and crest elevations found in multiple 2-hour long realizations of several short-crested shallow-water near-breaking seastates. Following this, the variability and repeatability of peak pressures and peak loads exerted on a 1/35 scale model of a gravity-based offshore structure are explored. The analysis focuses on establishing extreme value distributions for each realization, quantifying their variability, and exploring how the variability is diminished when results from multiple seastate realizations and repeated tests are combined. The importance of considering multiple realizations of a design wave condition when estimating peak values for use in design is investigated and highlighted.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/16bCsMd0OMc

Highlights

Practitioners tasked with designing new offshore structures or upgrading older structures located in shallow waters and exposed to energetic multi-directional waves generated by passing hurricanes or cyclones must first estimate the maximum wave heights and crest elevations at the site, and estimate the corresponding extreme pressures and loads exerted on the structure
The variability in the distributions of peak pressures and peak local and global loads exerted on a gravity-based offshore structure will be explored
Pressure and load data were measured in a set of 1/35 scale physical model experiments (Fig. 2) conducted to determine extreme wave pressures and loads on the substructure and super-structure of a gravity-based structure located in ~15 m water depth (Baker et al, 2019)

Summary

INTRODUCTION

Practitioners tasked with designing new offshore structures or upgrading older structures located in shallow waters and exposed to energetic multi-directional waves generated by passing hurricanes or cyclones must first estimate the maximum wave heights and crest elevations at the site, and estimate the corresponding extreme pressures and loads exerted on the structure. Due to the complexity and nonlinearity of the processes involved, and a current deficit of knowledge concerning both near-breaking multi-directional shallow-water wave conditions and the effect of such waves on structures, these design tasks are quite challenging (Taylor et al, 2020) In such situations designers often resort to scale model tests and/or computational fluid dynamics simulations to investigate both the wave conditions and the wave-structure interactions and develop pressure and load estimates for use in design (Cornett et al, 2013). Because neither of these approaches is exact, the resulting pressure and load estimates must be associated with a considerable degree of uncertainty which introduces considerable risk to the design process (Huang et al, 2017)

OBJECTIVES

RESULTS AND DISCUSSION