Abstract
In design storm sea states, wave-in-deck forces need to be analysed for fixed and floating offshore platforms. Due to the complex physics of wave impact phenomena, numerical analyses should be complemented by model test data. With a large statistical variability, such experiments usually involve running many 3-h storm realisations. Efforts are being done to establish efficient procedures and still obtain improved statistical accuracy, by means of an initial simplified screening based on parameters derived from the incident wave record only. Here, we investigate the vertical rise velocity of the incident wave elevation at a fixed point in space, which indirectly measures both the local slope and the near-surface orbital velocity. A derived simple deck slamming model is also suggested, to support the check of the physical basis of the approach. Correlation against data from a GBS wave-in-deck model test is used for checking this model. The results show that, although there is a significant random scatter in the measured impact forces, especially in the local slamming forces but also in the global forces, there is a correlation to the rise velocity. Comparisons to the simple load model also show promising results when seen on background of the complex physics and random scatter of the impact problem.
Highlights
Wave-in-deck loads on fixed and floating platform decks in stormy weather has become an increasingly important issue for the offshore industry during the last decades
We address the relevance of the rise velocity in wave impact problems as seen from a theoretical point of view
We propose a simplified two-dimensional (2D) formulation of the peak value of the wave-induced, local horizontal slamming pressure from a long-crested head sea wave impact on a finite vertical wall, based on Equation (1) and on: (i) an assumed relationship and similarity between the vertical rise velocity ∂η/∂t and the free-surface orbital velocity u; and (ii) the fact that the orbital velocity u can, at least in a linear regular wave, be written as the product of the phase velocity and the local steepness ∂η/∂x = kA: u = Cp·(kA)
Summary
Wave-in-deck loads on fixed and floating platform decks in stormy weather has become an increasingly important issue for the offshore industry during the last decades. At least for steep design sea states such as those indicated in Figure 1 it is important to have proper knowledge of such loads, and to include it in structural design. The need for this is further emphasised by actual events such as the COSL Innovator accident December 2015 in the North Sea [1]. Updated and new industry guidelines have been established, such as DNV GL’s new guidelines OTG-13 [2] and OTG-14 [3] for mobile units Both the air-gap and load problems have been addressed at least since the 1990s [4,5,6], initially mostly for fixed platforms. It has for quite some time been well reflected in general industry recommendations, exemplified by DNVGL’s RP-C205 which was recently updated [7] while it was originally issued in 2007
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