3 results found
Ma L, Swan C, 2020, The effective prediction of wave-in-deck loads, Journal of Fluids and Structures, Vol: 95, ISSN: 0889-9746
The present paper concerns the extreme wave loads acting on an offshore structure; specifically the wave-in-deck loading component that arises when the height of an incident wave crest exceeds the elevation of the topside structure. In this case wave inundation occurs, the resulting loads on the topside structure represent a significant part of the total wave load. A new model for the effective prediction of this important loading component is presented. This is based upon the conservation of momentum, is formulated in a Lagrangian frame of reference, can incorporate any incident wave form, and takes due account of the porosity (or openness) of the topside structure. Comparisons between the model predictions and wide-ranging laboratory observations are shown to be in good agreement; the latter based upon deterministic focused wave events that are known to be representative of the largest waves arising in realistic sea-states. In addition, comparisons are also made with independent cfd calculations. Taken together, the proposed model is shown to accommodate changes in the spectral shape, the spectral peak period, the incident crest elevation (and hence the level of inundation), the directional spread of the incident waves, and the porosity of the topside structure. Importantly, this agreement applies to both non-breaking and breaking waves, involves no empirical calibration, and can be achieved with limited computational resources. As such, the model is ideally suited to design/re-assessment calculations in which the reliability of any offshore structure must be based upon a rigorous assessment of the long-term distribution of the total wave loads, including any wave-in-deck loading component.
Ma L, Swan C, 2020, An experimental study of wave-in-deck loading and its dependence on the properties of the incident waves, Journal of Fluids and Structures, Vol: 92, Pages: 1-21, ISSN: 0889-9746
Recent advances in the description of extreme ocean waves have led to the definition of more severe design conditions. These changes include increases in the sea-state severity for a given return period, the nonlinear amplification of crest elevations beyond second-order and, perhaps most importantly, the occurrence of wave breaking in both intermediate and deeper waters. These developments raise important questions as to whether present design practice, commonly based upon simplified regular wave theories, provides a realistic estimate of the maximum design loads on fixed offshore structures. This is especially relevant if the applied wave load involves the loss of an effective air-gap and, the occurrence of wave-in-deck (wid) loading; the latter believed to be the most common cause of failure in severe seas.To address these issues, an extensive laboratory study of wid loading has been undertaken. This paper presents the first part of the findings from this study; the aim being to provide an improved physical understanding of wid loading in a wide range of incident wave conditions. The study shows that the applied loads are critically dependent upon both the wave shape and the water particle kinematics arising at the highest elevations within the wave crest; both properties being strongly influenced by the occurrence of wave breaking, particularly wave over-turning. Indeed, the occurrence of wave breaking leads to markedly different load time-histories with important consequences for both the maximum applied load and the onset of a dynamic excitation. The results presented herein provide important guidance as to the effective modelling of these critical loading events.
Swan C, Latheef M, Ma L, et al., 2016, The loading and reliability of fixed steel structures in extreme seas: recent advances and required improvements., The Third Offshore Structure Reliability Conference, OSRC
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