51. A filtering approach for applying the two-fluid model to gas-liquid flows on high resolution gridsBenjamin Krull, Richard Meller, Matej Tekavčič, Fabian Schlegel, 2024, izvirni znanstveni članek Povzetek: The two-fluid model is usually combined with closure forces designed for applications on coarse grids, i.e. bubbles (or particles) are typically assumed to be smaller than a grid cell. Practical applications however include situations where the mesh is comparatively fine, e.g. when meshing the wall boundary layer or in cases with growing bubbles. This may lead to non-convergent behaviour in mesh studies or to void fraction oscillations. To tackle this problem, a filtering approach is proposed, based on an additional diffusion term in the continuity equation. This approach increases the robustness of the results in regions of high spatial resolution, significantly reducing mesh-dependency of the simulation results. The implementation is straightforward, without a need to solve any additional system of equations. It is analysed in four different bubbly flow cases with varying characteristics: 2D/3D, wedge, square, and cuboid computational domains, with resolutions up to 32 cells per bubble diameter, laminar and turbulent flows, and several ways of gas injection. The additional computational effort varies, but is moderate. The proposed approach is applicable in multi-field two-fluid models for which a stable Euler-Euler behaviour on fine meshes is required, for example to prepare the transfer to an interface-resolving volume-of-fluid representation in morphology-adaptive approaches.
Objavljeno v DiRROS: 27.03.2025; Ogledov: 179; Prenosov: 36
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52. Asymmetry propagation in a pipe flow downstream of a 90° sharp elbow bendBlaž Mikuž, Klemen Cerkovnik, Iztok Tiselj, 2024, izvirni znanstveni članek Povzetek: Pipe bends disrupt the flow, resulting in an asymmetric velocity field across the pipe diameter (D). We examined the recovery length required for the flow to return to a symmetric velocity profile downstream of a sharp elbow. The wall-resolved Large Eddy Simulation (LES) approach was applied to reproduce turbulent fluid flow at Reynolds numbers (�� ) of 5600 and 10,000. An additional case in the transitional laminar-turbulent-laminar regime was analyzed at ��=1400 . This analysis explored the behavior of the Dean vortices downstream of the elbow and revealed that, in turbulent cases, these vortices reverse their vorticity direction in the region between 8 D and 10 D. However, they eventually decay in structure as far as 25 D from the elbow. Flow asymmetry was analyzed in a 100 D long pipe section downstream of the elbow using four different criteria: wall shear stress (WSS), streamwise velocity, its fluctuations, and vorticity fields. This study found that in turbulent flows, the distance required for flow recovery is a few tens of D and decreases with increasing ��. However, in the transitional case, the flow separation within the elbow induces instabilities that gradually diminish downstream, and flow asymmetry persists even longer than the 100 D length of our outlet pipe section. WSS proved sensitive for detecting asymmetry near walls, whereas flow profiles better revealed bulk asymmetry. It was also shown that asymmetry indicators derived from velocity fluctuations and vorticity were less sensitive than those obtained from streamwise velocity.
Ključne besede: cevno koleno, flow asymmetry, pipe elbows, secondary flow, flow separation, turbulent flow, recovery length, Large Eddy Simulation
Objavljeno v DiRROS: 27.03.2025; Ogledov: 170; Prenosov: 54
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53. CCL2/C–C chemokine receptor type 2‐mediated interactions among mast cells, basophils, and endothelial cellsMaruša Rihar, Rajia Bahri, Vida Forstnerič, Silvia Bulfone‐Paus, Peter Korošec, 2025, izvirni znanstveni članek Povzetek: Background IL-33 is involved in allergic processes by promoting the release of various mast cell (MC) chemokines, including CCL2. However, it is yet unclear which specific cell type is primarily responsible for producing CCL2 during acute allergic reactions. This study aims to investigate the role of IL-33 in promoting CCL2 production in mast cells and assess the effect of MC-derived CCL2 on basophil migration and endothelial permeability. Methods Human blood-derived MCs (hMCs) were generated from peripheral blood precursors, passively sensitized with IgE, treated with IL-33, and stimulated with anti-IgE. The concentrations of nine cytokines known to influence immune cell chemotaxis (CCL2, CCL5, CCL11, MIP-1α, IL-8, IL-10, IL-13, granulocyte-macrophage colony-stimulating factor (GM-CSF), and vascular endothelial growth factor (VEGF) were assessed in the supernatants of hMCs. Subsequently, we investigated the impact of MC-derived CCL2 on basophil migration in vitro, as well as its effect on endothelial monolayer permeability using human umbilical vein endothelial cells (HUVECs). Results Stimulation with anti-IgE induced a significant release of CCL2, GM-CSF, IL-8 and VEGF from hMCs. Additionally, incubation with IL-33 overnight increased the production of several cytokines. Mast cell-derived CCL2 not only enhanced basophil migration in vitro but also increased endothelial monolayer permeability in HUVECs. The effect was reversed by a C–C chemokine receptor type 2 (CCR2) antagonist, indicating the involvement of CCL2 signaling through the CCR2 receptor. Conclusions IL-33 induces the production of chemotactic cytokines in hMCs. Mast cell-derived CCL2 plays an important role in basophil chemotaxis in vitro and affects endothelial monolayer permeability in the HUVEC model.
Objavljeno v DiRROS: 27.03.2025; Ogledov: 157; Prenosov: 87
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54. Extending intergranular normal-stress distributions using symmetries of linear-elastic polycrystalline materialsSamir El Shawish, 2024, izvirni znanstveni članek Povzetek: Intergranular normal stresses (INS) are critical in the initiation and evolution of grain boundary damage in polycrystalline materials. To model the effects of such microstructural damage on a macroscopic scale, knowledge of INS is usually required statistically at each representative volume element subjected to various loading conditions. However, calculating INS distributions for different stress states can be cumbersome and time-consuming. This study proposes a new method to extend the existing INS distributions to arbitrary loading conditions using the symmetries of a polycrystalline material composed of randomly oriented linearelastic grains with arbitrary lattice symmetry. The method relies on a fact that INS distributions can be accurately reproduced from the first (typically) ten statistical moments, which depend trivially on just three stress invariants and a few material invariants due to assumed isotropy and material linearity of the polycrystalline model. While these material invariants are complex averages, they can be extracted numerically from a few existing INS distributions and tabulated for later use. Practically, only three such INS distributions at properly selected loadings are required to provide all relevant material invariants for the first 11 statistical moments, which can then be used to reconstruct the INS distribution for arbitrary loading conditions. The proposed approach is demonstrated to be accurate and feasible for an arbitrarily selected linear-elastic material under various loading conditions.
Ključne besede: linear-elastic material, INS distributions, polycrystalline materials
Objavljeno v DiRROS: 27.03.2025; Ogledov: 145; Prenosov: 73
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56. T+cc via the plane wave approach and including diquark-antidiquark operatorsIvan Vujmilović, Sara Collins, Luka Leskovec, Emmanuel Ortiz Pacheco, M. Padmanath, Saša Prelovšek, 2024, objavljeni znanstveni prispevek na konferenci Ključne besede: tetraquark, lattice QCD studies, quark mass
Objavljeno v DiRROS: 27.03.2025; Ogledov: 119; Prenosov: 78
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57. A short-term investigation of diel vertical migrations of the calycophoran Siphonophora in the open south Adriatic Sea (July 2003)Davor Lučić, Adam Benović, Mirna Batistić, Mira Morović, Ivona Onofri, Juan Carlos Molinero, Tjaša Kogovšek, Barbara Gangai, Marijana Miloslavić, 2011, izvirni znanstveni članek Povzetek: Morning, midday, evening and night repetitive sampling was used to demonstrate calycophoran diel vertical migration (DVM) at a fixed station in the oligotrophic southern Adriatic Sea at 8 depth intervals. Of 20 calycophoran species collected, most of them inhabited layers of specific temperature and light intensity, and migrated during the night. The deep species Kephyes ovata is primarily non-migratory. Typical nocturnal movements to the surface were recorded for Lensia conoidea and sphaeronectes koellikeri. Lensia subtilis and eudoxoides spiralis migrated toward the surface in the evening but sank deeper at night. Lensia meteori and Lensia fowleri reached upper layers at midday. The DVM of sphaeronectes irregularis was irregular and independent of diel light patterns. Though low in numbers, some calycophorans were found above the thermocline at night. For mesopelagic species, however, higher summer surface temperatures proved an effective barrier to migration above 100 m. Thus, certain species could be represented as key species of planktonic cnidarian assemblages found within a certain depth range. Though not homogenous, and while some undertake nocturnal migrations in both directions, all are interrelated by preferences of bathymetric distribution and specific DVM behavior.
Ključne besede: sea, medusae, biological research, abundance, bathimetric distribution, siphonophora, calycophoran siphonophores, composition, Adriatic Sea
Objavljeno v DiRROS: 26.03.2025; Ogledov: 96; Prenosov: 68
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58. Alien species in the Mediterranean Sea by 2012. A contribution to the application of European Union's Marine strategy framework directive (MSFD) : Part 2. Introduction trends and pathwaysArgyro Zenetos, Lovrenc Lipej, 2012, pregledni znanstveni članek Povzetek: More than 60 marine non-indigenous species (NIS) have been removed from previous lists and 84 species have been added, bringing the total to 986 alien species in the Mediterranean [775 in the eastern Mediterranean (EMED), 249 in the central Mediterranean (CMED), 190 in the Adriatic Sea (ADRIA) and 308 in the western Mediterranean (WMED)]. There were 48 new entries since 2011 which can be interpreted as approximately one new entry every two weeks. The number of alien species continues to increase, by 2-3 species per year for macrophytes, molluscs and polychaetes, 3-4 species per year for crustaceans, and 6 species per year for fish. The dominant group among alien species is molluscs (with 215 species), followed by crustaceans (159) and polychaetes (132). Macrophytes are the leading group of NIS in the ADRIA and the WMED, reaching 26-30% of all aliens, whereas in the EMED they barely constitute 10% of the introductions. In the EMED, molluscs are the most species-rich group, followed by crustaceans, fish and polychaetes. More than half (54%) of the marine alien species in the Mediterranean were probably introduced by corridors (mainly Suez). Shipping is blamed directly for the introduction of only 12 species, whereas it is assumed to be the most likely pathway of introduction (via ballasts or fouling) of another 300 species. For approximately 100 species shipping is a probable pathway along with the Suez Canal and/or aquaculture. Approximately 20 species have been introduced with certainty via aquaculture, while >50 species (mostly macroalgae), occurring in the vicinity of oyster farms, are assumed to be introduced accidentally as contaminants of imported species. A total of 18 species are assumed to have been introduced by the aquarium trade. Lessepsian species decline westwards, while the reverse pattern is evident for ship-mediated species and for those introduced with aquaculture. There is an increasing trend in new introductions via the Suez Canal and via shipping.
Objavljeno v DiRROS: 26.03.2025; Ogledov: 213; Prenosov: 88
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59. Uporaba numeričnih modelov ob razlitjih nafte na morjuDušan Žagar, Vanja Ramšak, Matjaž Ličer, Boris Petelin, Vlado Malačič, 2012, pregledni znanstveni članek Povzetek: Razlitje nafte v morju ima številne škodljive posledice na okolje in gospodarstvo. Potrebno je takojšnje ukrepanje pristojnih služb, ki si ob razlitju lahko pomagajo tudi z matematičnimi modeli, s katerimi je mogoče simulirati procese širjenja in razgradnje nafte. V prispevku je predstavljen pregled procesov in modelov širjenja naftnih madežev v morskem okolju. Opisan je model NAFTA3d in prikazana je njegova uporaba. Predstavljeni so vhodni podatki in rezultati modela na dveh možnih razlitjih v Tržaškem zalivu, pri čemer so upoštevane dejanske (nestacionarne) vremenske in hidrodinamične razmere. Prikazane so simulacije po taktičnem in prognostičnem načinu. Z vgrajenimi procesi in možnostjo povezav z različnimi modeli cirkulacije je lahko model NAFTA3d koristno dodatno orodje za ustrezne službe, ki skrbijo za omejitev širjenja in omilitev posledic ob morebitnih razlitjih nafte na morju.
Ključne besede: morje, numerično modeliranje, naravne nesreče, cirkulacijski modeli, izlitja nafte, onesnaževanje, NAFTA3d, Jadransko morje
Objavljeno v DiRROS: 26.03.2025; Ogledov: 88; Prenosov: 63
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60. Numerični modeli za določanje stanja morja v Jadranskem morjuMatjaž Ličer, Dušan Žagar, Maja Jeromel, Martin Vodopivec, 2012, pregledni znanstveni članek Povzetek: V prispevku predstavljamo glavne razloge za numerično modeliranje morja v Jadranskem morju in na kratko opisujemo modele, ki se trenutno uporabljajo v ta namen. Predstavljeni so cirkulacijski model POM za severno Jadransko morje, valovni model SWAN in model razlitja ogljikovodikov v morskem okolju NAFTA3d. Prikazani so tudi nekateri rezultati vseh navedenih modelov in trenutni načrti njihove implementacije.
Ključne besede: morje, numerično modeliranje, naravne nesreče, cirkulacijski modeli, izlitja nafte, onesnaževanje, POM, Jadransko morje
Objavljeno v DiRROS: 26.03.2025; Ogledov: 73; Prenosov: 58
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