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This paper examines impact forces resulting from wave-in-deck processes from two separate series of experiments: one with a generic solid deck model, and the other with a combined jacket and deck model, both were conducted with and without an I-beam grillage in-place below the solid deck. A range of inundation levels from 2.1 to 7.1 cm at 1:80 scale is considered. The focus is on global impact forces, which are considered more relevant for integrity assessment of overall bottom-founded structures when survivability is in question and local slamming is not addressed. The objective is to characterise the resultant impact forces as well as to investigate whether there is any interaction between the flows through the jacket and hitting the deck. Focussed wave groups were generated to impinge on the models which were suspended from a carriage over a towing tank. The motion of the support carriage mimics uniform current in-line with the incident waves. Both undisturbed surface elevations as well as impact force time histories were measured. From the first series of tests, a large increase in peak forces as well as high frequency oscillations (force spikes) is observed with the grillage in-place. As soon as the jacket model is in-place for the second series of tests, albeit with a different mounting support arrangement, such a large difference vanishes, which could likely be due to the effect of frequency-dependent transfer functions. We provide experimental evidence of the presence of the jacket in modifying the wave impact on the deck through a significant reduction in the total horizontal impulse. The effects of current on the wave impact forces are also investigated. A simple analytical model based on a momentum argument is used to describe the scaling of horizontal peak force with currents and inundation levels. Finally, the importance of the short duration force spikes as well as vertical impact loads on a real structure at full-scale is discussed based on the same analytical model. [ABSTRACT FROM AUTHOR]

Wave-in-deck loads due to 45 ° oblique transient focus wave groups are investigated using model-scale experiments and computational fluid dynamics simulations with emphasis on comparing with head-on wave impacts for a solid cuboid deck model without and with an I-beam grillage beneath. After validation with experiments, numerical results are extended to consider wave-in-deck loads with 22. 5 ° and 67. 5 ° oblique wave directions. Generally, the head-on wave impacts cause larger longitudinal forces on the deck whereas the oblique cases result in larger downward vertical forces. For the deck with grillage case, Santo et al. (2020) and Wang et al. (2022) show that successive large spikes are observed in the force time series of head-on wave impact due to entrapped air-pocket effects in the grillage. However, here it is found that the large spikes are absent in the force time series for the oblique wave impacts and the patterns of forces are similar to the deck without grillage with rather small or no spikes in the force time series. Interrogation of the numerical flowfield reveals evidence that the asynchronous and less effective air entrapment in the grillage for the oblique cases are responsible for the difference. The maximum positive pressure on the underside of the deck is found to be much larger for the deck with grillage than without due to local slamming of jets formed in the grillage. [ABSTRACT FROM AUTHOR]

Wave impacts on an elevated solid deck due to transient focused wave groups are studied numerically. Previously reported experiments with and without an I-beam grillage beneath the deck by Santo et al. (2020) are reproduced successfully in a three-dimensional numerical wave tank based on a two-phase Navier–Stokes solver. The impact loads on the solid deck are relatively simple. The three-dimensional horizontal force, characterised by a single peak in time, is close to two-dimensional, whereas the vertical force consists of upward force and downward suction force. The downward suction force is related to triangularisation of the wetted area underneath the deck and dominated by the added mass effect, which is a three-dimensional effect and therefore any two-dimensional simulation will overpredict the strongly three-dimensional process and the vertical impact loads. The wave impact loads on the solid deck with a grillage are more complicated, with successive force spikes observed for both the horizontal and vertical loads. The significance of entrapped air pockets in the grillage to global wave impact loads is ascertained through interrogating flow field of numerical experiments. It is found that large upward vertical impulsive forces are caused by high local pressures when entrapped down-wave air-pockets are formed, while large downward suction forces are resulted from both high-frequency up-wave air-pocket effect and the low-frequency added mass effect. Large horizontal impulsive forces are due to the combined effects of the down-wave air-pocket and the upward jetting motion of the wave crests. The entrapped air-pocket effects are found to be more important for vertical than horizontal forces. [ABSTRACT FROM AUTHOR]