Surfactant components of marine organic matter as agents for biogeochemical fractionation and pollutant transport via marine aerosols

The role of surfactant organic matter in marine aerosol production has been studied under conditions in which there is a large coverage of whitecaps on the sea surface. To improve the knowledge of matter exchange and pollutant recycling from the sea surface into the atmosphere, a spray drop adsorption model (SDAM) was developed and the validity of the proposed model verified by the following experimental results: (1) an increase of surfactant matter on the sea surface during rough sea conditions (‘surface wave concentration'); (2) an (hyperbolic-like) increase of the enrichment ratio (ER) of surfactant fluorescent organic matter (SFOM), made up predominantly by humic substances (HS), as the particle size decrease; (3) a similar behaviour for elements with pollutant properties, and which are known to interact with HS and other surfactant materials, considered pollution tracers. An additional laboratory experiment, based on the adsorption model conditions, gives enrichment ratio greater than unity for K and Ca. The first results on marine aerosols trapped in marine clouds (at 1000 m above sea level and at 100 km from the coast) seem to further support the proposed model and its ability to predict the transition from saline to almost entirely organic particles for the smaller fractions of marine aerosols. The possible contribution of these particles to the recycling and to the long range transport of pollutants via marine aerosols has been considered.     

In situ velocity profiles in gassy sediments: Kiel Bay

Acoustic behavior of gas-bearing sediments is significantly different from that of gas-free sediments. In situ velocity profiles and acoustic signal characteristics in gas-bearing sediments of the upper several meters of the sea floor in Kiel Bay are presented in this study. Observed velocities in gas-bearing sediments are both higher and lower than those of the gas-free sediments. Small amounts of gas appear to cause signal reverberation without much attenuation. whereas large amounts of gas cause substantial attenuation.     

An iterative method for boundary element solution of large offshore structures using the GMRES solver

The GMRES approach is used to solve complex matrix solution arising from boundary element analysis of large offshore structures. This makes it possible to solve problems with large numbers of panels on a workstation with a much smaller memory than typical high performance computers. The speed of the solver is compatible with direct solvers when the enough RAM is available. Otherwise, an iteration procedure can be used. By using an out-of-core treatment, typical RAM requirement is reduced to a size approximately linearly proportional to the panel number n instead of being proportional to n². The code is first verified with direct solver for cases with small number of panels. The applicability to large offshore structure of the model is demonstrated for a TLP case.     

Prediction of hydrodynamic forces on submarine pipelines using an improved Wake II Model

The hydrodynamic force model for prediction of forces on submarine pipelines as described includes flow history effect (wake effects) and time dependence in the force coefficients. The wake velocity correction is derived by using a closed-form solution to the linearized Navier–Stokes equations for oscillatory flow. This is achieved by assuming that the eddy viscosity in the wake is only time dependent and of a harmonic sinusoidal form. The forces predicted by the new Wake (Wake II) Model have been compared to Exxon Production Research Company Wake Model in terms of time histories (force shape) and magnitudes of peak forces. Overall, the model predictions by the Wake II Model are satisfactory and represent a substantial improvement over the predictions of the conventional models. The conventional force models representing adaptations of Morison's equation with ambient velocity and constant coefficients give predictions that are in poor agreement with the measurements especially for the lift force component. The Wake II Force Model can be used for submarine pipeline on-bottom stability design calculations for regular waves with various pipe diameters.     

Static bay beach concept for scientists and engineers: A review

Headland-bay beach (HBB) is one of the most prominent physiographic features on the oceanic margin of many countries in the world. Under the influence of a predominant swell, its curved periphery in natural environment may reach static equilibrium and remains stable without sediment supply from updrift and/or a riverain source within its own embayment. Coastal scientists and engineers have attempted to develop mathematical expressions to quantify this ideal bay shape since the 1940s. As the scenario with depleting sediment supply has become a common reality on many parts of the world coastline in more recent time, some coastal engineers have advocated a rational approach to mimicking the static bay shape found in nature in order to mitigate beach erosion as well as for coastal management. Nowadays, many useful applications have emerged since the publication of the parabolic bay shape equation (PBSE) developed for static equilibrium planform (SEP) in late 1980s. The advance in modern computer technologies and international collaboration has further facilitated the exchange of knowledge and applications of this static bay beach concept (SBBC).     

Comparison of long-, medium- and short-term variations of beach profiles with and without submerged geological control

Victoria Beach (Cadiz, Spain) comprises a rocky flat outcrop in its northern zone and a sand-rich southern zone. These natural features allowed for a 5-year monitoring period and subsequent analysis of two different profiles (one in each zone) based on differences in bottom contours. Topo-bathymetric data were analysed using empirical orthogonal functions (EOFs) to determine changes over the short-, medium- and long-term. Several morphologic phenomena were identified (generalised erosion, seasonal or summer–winter tilting of the profile around different hinge points, berm development and its posterior destruction, etc.) in terms of their importance in explaining the variability of the collected data for both profiles. It is worth mentioning that both profiles undergo parallel regression in the medium-term. Thus, the 1st eigenfunction enabled us to identify the true regression of the beach shoreline, independent of seasonal or summer–winter slope changes. Reconstruction of profiles using EOF components demonstrated that though accretion periods in the medium-term were similar for both types of profiles, the accretion speed was much faster in the sand-rich profile than in the reef-protected profile (1.01 m³/day versus 0.33 m³/day). Moreover, the seasonal erosion rate and the subsequent shoreline retreat for the sand-rich profile were much larger than for the reef-protected profile (121 m³/year versus 29 m³/year). Analysis in the short-term (changes induced by a single day's storm) showed an instantaneous tilting of the profile, with the mobilised sand volume being much greater for the sand-rich than for the reef-protected profile (68 m³/m versus 12 m³/m).     

Study of A Geo-Acoustic Model of Gas-Bearing Sediment and Its Application in Sediment with Low Acoustic Velocity

A new geo-acoustic model for gas-bearing sediment is proposed based on the work of Dvorkin and Prasad, and Biot theory. Only five geophysical parameters: sediment mineral composition, free gas saturation, tortuosity (also known as the structure factor), permeability, and porosity, are considered in the model. A benefit of this model is that we need only five parameters instead of ten parameters in the Biot’s formulas for acoustic velocity and attenuation calculation. Here the model is demonstrated with the in-situ experimental data collected from the Hangzhou Bay, China. The results of this study suggest that free gas content in sediment is the most critical condition resulting in a low acoustic velocity (compressional wave). The respective contributions of the other four parameters in the model are also discussed.