Numerical simulation of the Adriatic Sea principal tidal constituents

The primary goal of this study was to incorporate data-derived harmonic constants into a complex dynamic model using a form of variational data assimilation, with a view to improve the prediction of 7 dominant tidal constituents in the Adriatic Sea. Firstly, harmonic-constant data for 6 Adriatic stations were fed into a steady-state, 3-D, forward/inverse model to furnish optimal boundary conditions (OBCs). Calculated OBCs were then used to derive individual constituent responses, as well as to synthesise seven-constituent boundary conditions for the time stepping, 3-D model. A separate set of 25 stations provided control harmonic constant data. In validating the model output particular attention has been given to the often-ignored tidal currents. To that end 14 current meter data records were processed into tidal current ellipse parameters and used to examine the comparable model output. Comparison to gauge data has shown that the present solution is better than our own previous one, and shows an improvement over recent solutions by other authors. The model accurately reproduces available data with individual station amplitude differences rarely exceeding 1cm, and with the phase error commonly staying well below 10°. For all tidal constituents individual station differences result in RMSE in the 0.33-0.71-cm range for amplitude, and the 5.6°-19.2° range for phase. Semidiurnal currents appear to be modelled better than the diurnal ones (generally over-predicted). High eccentricity of both data and model-derived ellipses often impaired calculating the proper sense of rotation; inclination of the ellipses proved to be the most robust parameter, successfully predicted for most constituents at all depths

Referencing geostrophic velocities at a northern Adriatic section

We have addressed the merits of two familiar methods to calculate absolute geostrophic currents when applied to a shallow-water section of a marginal sea. The comparison was performed on the basis of monthly collected hydrographic data and relative geostrophic currents (calculated with respect to the 30 m level) at a transect in the northern Adriatic in 1992 and 2000. The computed geostrophic currents were also compared to current-meter data collected continuously in 1992, in the surface and bottom layer of a station on the same section, and filtered with cut-off period of 10 days. When relative currents were converted to absolute the Fomin method (requiring minimal kinetic energy in the water column)pro vided correction closer to filtered Eulerian currents in 21 out of 24 (12 surface plus 12 bottom)comparison pairs. Modification of the sections’s position confirmed that the criterion of mass conservation over the entire section generates absolute correction more susceptible to the position and the extent of the section used in its calculation. Both approximations of absolute geostrophic current worked better when applied to data collected in the warmer part of the year

Vertical structure of bottom Ekman tidal flows: Observations, theory, and modeling from the northern Adriatic

From September 2002 to May 2003, fifteen bottom‐ mounted, acoustic Doppler current profilers measured currents of the northern Adriatic basin. Tidal fluctuations at all seven of the major Adriatic frequencies were synthesized from a response tidal analysis of these measurements. Most observed tidal current ellipses were nearly reversing, but near the bottom, tidal current ellipses all shortened and broadened, semidiurnal currents led upper water column currents, and diurnal tidal current ellipse orientations rotated counterclockwise toward the bottom. Theoretical solutions for a tidally forced, bottom Ekman layer with vertical eddy viscosity of the form A z = β z + k were least squares fit to the observations. Average values were β = 3 · 10− 4 m/s and k = 5 · 10− 4 m2/s. The value of k was important in matching tidal orientation and phase changes, and a nonzero β was important in matching tidal amplitude changes. The Navy Coastal Ocean Model (NCOM) and the Quoddy model were also compared to the observations. The average RMS errors for the bottom Ekman layer were 0.22 cm/s for the best fit theory, 0.35 cm/s for NCOM, and 0.36 cm/s for Quoddy. A z structures from NCOM and Quoddy show that time variation in A z is relatively unimportant for Adriatic tides. The bottom shear stresses from theory were larger in magnitude than those from the bottom drag formulations in NCOM and Quoddy

Flow Improver Polymeric Additives for Crude Oil and Gas Condensate

U radu je dat pregled polimernih aditiva koji služe za sniženje tecišta i poboljšanje reoloških svojstava nafte i plinskog kondenzata. Opisane su temeljne vrste polimera koji se u te svrhe primjenjuju: polimeri na osnovi olefina, posebice etilena, kopolimeri vinil-acetata i alkil-fumarata, esteri akrilne i metakrilne kiseline te polimeri na osnovi anhidrida maleinske kiseline. Prikazan je mehanizam djelovanja aditiva i metode za utvrđivanje njihove djelotvornosti. Dio pregleda obuhvaća rezultate sinteze i primjene vlastitih aditiva za naftu i plinski kondenzat. Posebno je opisan utjecaj kemijske strukture i molekulske mase polimernih aditiva te njihove koncentracije na tecivost i viskoznost. Ispitivanja su provedena na uzorcima nafte s naftnih polja u INI, Števkovica, Obod i Đeletovci i plinsko-kondenzatnih polja Molve, Kalinovac, Stari Gradac i Gola te mađarskog polja Barcs. Rezultati pokazuju da na djelotvornost u primjeni bitno utječu vrste aditiva i nafte, odnosno plinskog kondenzata. Optimalni su rezultati postignuti primjenom aditiva na osnovi kopolimera dugolančanih estera metakrilne kiseline s vinil-karboksilnim kiselinama.This paper describes the problem of paraffin deposition during production, transportation and processing of crude oil and gas condensate. The troublesome paraffin stands for normal hydrocarbons ranging from approximately C18-C38, mixed with small amounts of branched paraffin, monocyclic paraffin, polycyclic paraffin, and aromatics. The amount of paraffin found in crude oils as described in the literature, varies from less than 1 to more than 50 percent. The solubility of paraffin depends on chemical composition, temperature and pressure. Paraffin precipitates at an equilibrium temperature and pressure defined as the cloud point. The paraffin deposits often begin on surfaces cooler than the liquid. The viscosity is increased by the presence of paraffin crystals and if the temperature is reduced sufficiently, the crude oil/gas condensate will become very viscous (pour point). The crude oil/gas condensate viscosity behaves in a Newtonian manner until wax crystals begin to form and, after lowering the temperature, behaves in a non-Newtonian manner. Many options are available to counter the problems caused by paraffin wax deposition. These include various mechanical, thermal and chemical means (for example, steam heating, blending with lighter cutter stocks and treating with chemical additives). A preferred option would be to use wax modifier additives, commonly known as pour point depressants. Crystal modifiers are copolymers from these groups: copolymers of ethylene vinyl acetate, poly alpha-olefins, alkyl fumarate- vinyl acetate copolymers of C18-through C22 methacrylates and copolymers of maleic anhydride esters. The mechanism of paraffin deposition and prevention is described. The additives modify the size and shape of the crystal and inhibit the formation of large wax crystal lattices. With efficient additives, crude oil/gas condensate behaves in a Newtonian manner at low temperature. A section of the paper describes the influence of chemical structure and molecular weight of the flow improver additives for crude oils and gas condensates prepared by the authors of this review article. The additives are based on methacrylic long chain alkyl ester homopolymers or copolymers with vinyl carboxylic acids or vinyl aromatic monomers. The quality of the prepared additives as pour point depressants and rheology improvers was proved by applying them to crude oil from INA fields Števkovica, Obod and Deletovci as well as gas condensate fields Molve, Kalinovac, Stari Gradac, Gola, and Hungarian gas condensate field Barcs. The best results were obtained with the copolymers of methacrylic long-chain alkyl esters with functional monomers

Preparation and Characterization of Electrospun PCL/Silk Fibroin Scaffolds

Natural polymer-based scaffolds are generally considered as favourable matrices for the adhesion and growth of cells in tissue repair. One of the most popular materials in this respect is silk fibroin, known for its wide usage in biomedical applications. This work focuses on the development of electrospun scaffolds based on poly(ε-caprolactone) (PCL) and silk fibroin (SF) evaluated regarding the SF effect on their morphology, surface wetting ability, thermal properties, and HaCaT model cell line biocompatibility. The study revealed that the lowest PCL/SF concentration resulted in highest bead-like morphology formation, relatively thick fibers with the presence of random beads in the case of PCL, while uniform and thinner fibers in the case of increasing PCL/SF content scaffolds. The addition of SF reduced the degree of crystallinity in the PCL due to the less organized crystal structure, and decreased its thermal stability. Both SEM and MTT analyses showed cell presence on all scaffolds three days after cell seeding. Although SF improved PCL hydrophilicity, as shown quantitatively by the MTT assay for improved cytocompatibility properties, more structured electrospun PCL/SF scaffold strategies are required. This work is licensed under a Creative Commons Attribution 4.0 International License

Geostrophic Circulation Patterns in the Northeastern Adriatic Sea and the Effects of Air-Sea Coupling: May-September 2003

CTD data were collected weekly during 20 cruises from May to September 2003 over a 19 station grid in a coastal region of the northeastern Adriatic Sea as part of Project ADRICOSM. Relative geostrophic velocities indicated fine scale circulation patterns in in the area consisting of two pronounced circulation cells, of cyclonic and anti-cyclonic character, and that were present in the area for most of the investigated period.. These motions were induced primarily by spatial variations in the temperature field and may be strengthened during episodes of very strong northeasterly bora wind, when the investigated region is not heated (cooled) uniformly