Model tests of a stiffness-similar jack-up, Part 2: In-place and hull-in-water conditions

Abstract

This paper, Part 2 of a series, presents a comprehensive study involving ocean basin model tests of a novel stiffness-similar jack-up structure. The objective is to generate a high-quality dataset for the development of structural digital twins. The focus is on the model test design and selected results for in-place and hull-in-water conditions. The generic jack-up model was instrumented with strategically placed sensors on the hull, legs, leg-to-hull connections, and spudcan modules. The novel use of polycarbonate for the jack-up legs ensures stiffness similarity, enabling the use of strain gauges to derive axial member forces. Boundary forces were meaningfully measured, because of the representative modelling of the foundation and leg-to-hull connection fixity. The test cases encompassed long-crested waves, including conditions with and without current. In addition, oblique waves were modelled by rotating the entire jack-up model. Both extreme and operating scenarios were considered. In operating scenarios, the dynamic responses of the jack-up structure were found primarily governed by structural resonance, while wave frequency responses became comparable in extreme scenarios. For extreme scenarios, dynamic wind loads, consistently Froude-scaled to the model scale, were applied using a servomotor in the presence of random waves. Comparisons between results with and without the applied dynamic wind loads revealed noticeable differences in damping characteristics. The hull-in-water condition exhibited significantly larger motion and structural responses, emphasising its criticality in jack-up operations. The findings underscore the importance of considering the hull-in-water condition in the analysis and operation of jack-up structures.