Numerical analysis of shipping water impacting a step structure

Shipping water, the flow washing over and impacting the upper decks of ships and offshore structures, occurs frequently during their service life and often causes structural problems. For engineers to design safe floating structures subjected to shipping water it is essential to gain an in-depth understanding of its depth and flow field, and the resulting impact forces. In this work, Computational Fluid Dynamics (CFD) is applied to understand the physics of shipping water washing over a stepped platform. We find that the most accurate solutions are obtained with the turbulence closure. The hydrodynamic load generated by the shipping water is found to strongly depends on the kinematic energy of the water hitting the step. It is shown that with smaller values of the freeboard a more dynamic flow ensues, with a stronger vortex and larger velocity gradient resulting in deeper shipping water and a larger impact force

Uranium export from a sandy beach subterranean estuary in Australia

Few studies exist on the contribution of subterranean estuaries (STEs) to the oceanic uranium (U) budget. Here, we estimate the dissolved U fluxes out of a quartz sand STE located on the east coast of Australia. Our results indicate that the advective flow of seawater in permeable sands enhances cycling of U in the STE. Dissolved U concentrations ranged from 25 nM in the STE to an effective zero salinity end-member of 3.8 nM in the surface estuary. The dissolved U (salinity corrected) concentrations were positively correlated to Fe (r2 = 0.49 p < 0.001) during a shallow beach time series experiment. These results indicate that reductive dissolution of Fe oxides may be an important process maintaining high concentrations of U in shallow permeable sand STEs. The U export rates from the STE to the surface estuary in this study were estimated to be 1.8 μmol U m−2 day−1 based on shallow saline groundwater exchange pathways and 0.4 μmol U m−2 day−1 based on deep fresh submarine groundwater discharge (SGD). Uranium's behavior in STEs is diverse and site specific. Out of the seven investigations available here and in the literature, three suggested a SGD-derived U source to the coastal ocean, while four suggested a U sink within STEs removing seawater U. Therefore, it remains unclear whether SGD is a source or sink of U to the ocean and additional investigations in contrasting settings are required to resolve the global contribution of SGD to the marine U cycle

Numerical analysis of shipping water impacting a step structure

Shipping water, the flow washing over and impacting the upper decks of ships and offshore structures, occurs frequently during their service life and often causes structural problems. For engineers to design safe floating structures subjected to shipping water it is essential to gain an in-depth understanding of its depth and flow field, and the resulting impact forces. In this work, Computational Fluid Dynamics (CFD) is applied to understand the physics of shipping water washing over a stepped platform. We find that the most accurate solutions are obtained with the k−ε turbulence closure. The hydrodynamic load generated by the shipping water is found to strongly depends on the kinematic energy of the water hitting the step. It is shown that with smaller values of the freeboard a more dynamic flow ensues, with a stronger vortex and larger velocity gradient resulting in deeper shipping water and a larger impact force.QC 20220318</p

Greenhouse Gas Dynamics in a Salt-Wedge Estuary Revealed by High Resolution Cavity Ring-Down Spectroscopy Observations

Estuaries are an important source of greenhouse gases to the atmosphere, but uncertainties remain in the flux rates and production pathways of greenhouse gases in these dynamic systems. This study performs simultaneous high resolution measurements of the three major greenhouse gases (carbon dioxide, methane, and nitrous oxide) as well as carbon stable isotope ratios of carbon dioxide and methane, above and below the pycnocline along a salt wedge estuary (Yarra River estuary, Australia). We identified distinct zones of elevated greenhouse gas concentrations. At the tip of salt wedge, average CO₂ and N₂O concentrations were approximately five and three times higher than in the saline mouth of the estuary. In anaerobic bottom waters, the natural tracer radon (²²²Rn) revealed that porewater exchange was the likely source of the highest methane concentrations (up to 1302 nM). Isotopic analysis of CH₄ showed a dominance of acetoclastic production in fresh surface waters and hydrogenotrophic production occurring in the saline bottom waters. The atmospheric flux of methane (in CO₂ equivalent units) was a major (35–53%) contributor of atmospheric radiative forcing from the estuary, while N₂O contributed <2%. We hypothesize that the release of bottom water gases when stratification episodically breaks down will release large pulses of greenhouse gases to the atmosphere