11. A coupled domain–boundary type meshless method for phase-field modelling of dendritic solidification with the fluid flowTadej Dobravec, Boštjan Mavrič, Rizwan Zahoor, Božidar Šarler, 2023, izvirni znanstveni članek Povzetek: Purpose - This study aims to simulate the dendritic growth in Stokes flow by iteratively coupling a domain and boundary type meshless method. Design/methodology/approach - A preconditioned phase-field model for dendritic solidification of a pure supercooled melt is solved by the strong-form space-time adaptive approach based on dynamic quadtree domain decomposition. The domain-type space discretisation relies on monomial augmented polyharmonic splines interpolation. The forward Euler scheme is used for time evolution. The boundary-type meshless method solves the Stokes flow around the dendrite based on the collocation of the moving and fixed flow boundaries with the regularised Stokes flow fundamental solution. Both approaches are iteratively coupled at the moving solid–liquid interface. The solution procedure ensures computationally efficient and accurate calculations. The novel approach is numerically implemented for a 2D case. Findings - The solution procedure reflects the advantages of both meshless methods. Domain one is not sensitive to the dendrite orientation and boundary one reduces the dimensionality of the flow field solution. The procedure results agree well with the reference results obtained by the classical numerical methods. Directions for selecting the appropriate free parameters which yield the highest accuracy and computational efficiency are presented. Originality/value - A combination of boundary- and domain-type meshless methods is used to simulate dendritic solidification with the influence of fluid flow efficiently.
Ključne besede: dendritic solidification, Stokes flow, phase-field method, space-time adaptivity, meshless methods, RBF-FD, modified method of regularised sources
Objavljeno v DiRROS: 07.02.2024; Ogledov: 184; Prenosov: 74
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12. Alternative alkali activators based on waste bottle glass and waste cathode-ray tube glassKatja Koenig, Katja Traven, Vilma Ducman, 2021, objavljeni znanstveni prispevek na konferenci Povzetek: Alkali-activated binders are an environmentally friendly alternative to Portland cement, particularly when locally-available raw materials are used. It is well known that alkali activation with a sodium silicate activator generates a hardened binder with higher compressive strength than a binder hardened with sodium hydroxide. As the alkali-silicate activators are produced through energy extensive processes, and their use can significantly increase the carbon footprint of the final products, it is of great significance to develop alternative alkaline activators based on locally-available waste materials. This article assesses the potential to apply waste bottle glass and waste cathode-ray tube (CRT) glass to synthesise alternative alkali activators by the hydrothermal method. Inductively coupled plasma-optical emission spectrometry (ICP-OES) was used to determine silicon and aluminium content in the alternative activators. The influence of dissolution process parameters (time, temperature, particle size) on the concentrations of silicon and aluminium in the alternative activators was investigated. The alternative activators with silicon concentration up to 19 g/L and aluminium concentration up to 0.9 g/L were prepared at T = 120 °C and boiling time 24 h. The alternative alkali activators and, for comparison, also commercial sodium silicate were used in the alkali activation of fly ash powder. The formed pastes were cured at 70 °C for 72 h. Mechanical strength measurements indicated that alkali activation of fly ash with the optimal alternative activator yielded hardened paste with compressive strength of 33 MPa. However, the compressive strength of hardened paste prepared from fly ash and commercial sodium silicate reached 70 MPa. Part of this difference can be ascribed to the lower density of hardened pastes prepared with alternative activators.
Ključne besede: alkali -activated materials, alternative alkali activators, waste bottle glass, waste cathode -ray tube glass, fly ash, hydrothermal method
Objavljeno v DiRROS: 25.01.2024; Ogledov: 193; Prenosov: 124
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13. Photocatalytic CO2 reduction over mesoporous TiO2 photocatalystsMartin Reli, Peter Nadrah, Miroslava Filip Edelmannová, Rudolf Ricka, Andrijana Sever Škapin, Urška Lavrenčič Štangar, Kamila Kočí, 2024, izvirni znanstveni članek Povzetek: In this study, we investigated different synthesis methods (template-free and template-based) using copolymers of poly(ethylene oxide) and poly(propylene oxide) to enhance the CO2 reduction activity of mesoporous TiO2. Our main goal was to identify key factors affecting photocatalyst efficiency and selectivity. We compared the newly synthesized TiO2 photocatalysts with the commercial photocatalyst P25. Among the materials studied, TiO2-P123 in its pure anatase form demonstrated the highest photoreduction efficiency and CO2 selectivity. In contrast, TiO2-EG, TiO2-F127, and P25, which contained both rutile and anatase phases, exhibited decreased photoactivity due to the formation of a type II heterojunction between the phases and higher oxygen adsorption on rutile's surface. Additionally, we observed that the choice of chemicals for photocatalyst preparation significantly influenced the specific surface area. TiO2-P123, the most active photocatalyst, had the highest specific surface area, providing more reactive sites for improved light absorption efficiency and prolonged electron-hole pair lifetimes, resulting in enhanced photocatalytic activity. We also calculated apparent quantum yields to support our findings.
Ključne besede: CO2 reduction, TiO2, photocatalysis, mesoporous material, Sol-gel method
Objavljeno v DiRROS: 14.11.2023; Ogledov: 379; Prenosov: 40
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15. RILEM TC 247-DTA round robin test : mix design and reproducibility of compressive strength of alkaliactivated concretesJohn L. Provis, Kamel Arbi, Susana Bernal, Dali Bondar, Anja Buchwald, Arnaud Castel, Sundararaman Chithiraputhiran, Martin Cyr, Alireza Dehghan, Katja Dombrowski-Daube, Ashish Dubey, Vilma Ducman, Gregor J. G. Gluth, Sreejith Nanukuttan, Karl Peterson, Francisca Puertas, Arie van Riessen, Manuel Torres-Carrasco, Guang Ye, Yibing Zuo, 2019, izvirni znanstveni članek Povzetek: The aim of RILEM TC 247-DTA Durability Testing of Alkali-Activated Materials is to identify and validate methodologies for testing the durability of alkali-activated concretes. To underpin the durability testing work of this committee, five alkali-activated concrete mixes were developed based on blast furnace slag, fly ash, and flash-calcined metakaolin. The concretes were designed with different intended performance levels, aiming to assess the capability of test methods to discriminate between concretes on this basis. A total of fifteen laboratories worldwide participated in this round robin test programme, where all concretes were produced with the same mix designs, from single-source aluminosilicate precursors and locally available aggregates. This paper reports the mix designs tested, and the compressive strength results obtained, including critical insight into reasons for the observed variability in strength within and between laboratories.
Ključne besede: alkali-activated materials (AAM), mechanical properties, test method, Rilem TC, durability
Objavljeno v DiRROS: 14.09.2023; Ogledov: 256; Prenosov: 148
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16. 3D finite element analysis of a concrete dam behavior under changing hydrostatic load : a case studyPavel Žvanut, 2022, izvirni znanstveni članek Povzetek: In this study, a large arch-gravity Moste Dam was analyzed, where an automated system for the measurements of horizontal displacements of the upper part of the dam was established. Two-dimensional (2D) and three-dimensional (3D) analyses of dam behavior, taking into account the earth pressures and the hydrostatic load, using the finite element method (FEM)-based computer program DIANA, were performed. The influence of lowering the water level of the reservoir by 6.2 m, on the horizontal displacements of the upper part of the dam, at stationary temperature conditions, was investigated. It was found that the results of the performed 2D and 3D FEM analyses fitted in very well with the result of experimentally determined measurement of horizontal displacements (which was 0.48 mm in the upstream direction) that was obtained using a hanging pendulum. An additional comparison of the results of 3D calculations showed that the finite element mesh density had a small effect on the calculated horizontal displacements.
Ključne besede: concrete dam, finite element method, material properties, structure behavior, measuring instruments, monitoring, ime series analysis, horizontal displacements, hydrostatic pressure
Objavljeno v DiRROS: 21.06.2023; Ogledov: 363; Prenosov: 205
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17. Attic dust: an archive of historical air contamination of the urban environment and potential hazard to health?Martin Gaberšek, Michael J. Watts, Mateja Gosar, 2022, izvirni znanstveni članek Povzetek: A comprehensive study of attic dust in an urban area is presented. Its entire life cycle, from determining historical emission sources to recognising the processes that take place in attic dust and its potential to impact human health is discussed. Its chemical composition and morphological characteristics of individual solid particles reflect past anthropogenic activities. High levels of Be-Cd-Cu-Sb-Sn-Pb-Te-Zn and occurrence of Cu-Zn shavings are typical for an industrial zone characterised by a foundry and a battery factory. High levels of Co-Fe-Mo-Ni-W-Ba-Cr-Mg-Mn-Nb-Ti and occurrence of various solid Fe-oxides, particularly spherical particles, were identified in another industrial zone, which was dominated by the automotive and metal-processing industries. Emissions from coal combustion affected the distribution of S-Se-Hg-Tl-As-Ag-U. The predominant mineral in attic dust is gypsum, which was presumably formed in situ by the reaction of carbonate dust particles and atmospheric SO2 gas. The high oral bioaccessibility of As-Cd-Cu-Pb-Zn in the gastric phase and high bioaccessibility of As-Cu-Cd-Ni in the gastrointestinal phase were identified. Determined characteristics of attic dust and identified possibilities of prolonged human exposure to it indicate that attic dust should be treated as an excellent proxy for historical air contamination as well as a potentially hazardous material for human health.
Ključne besede: multi-element composition, scanning electron microscopy, oral bioaccessibility, unified BARGE method, urban geochemistry
Objavljeno v DiRROS: 23.06.2022; Ogledov: 595; Prenosov: 225
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19. Effect of temperature on MgO activity in the CaO-SiO[sub]2-MgO-Al[sub]2O[sub]3 system measured by molten tinYongchun Guo, Fengman Shen, Haiyan Zheng, Shuo Wang, Xin Jiang, Qiangjian Gao, 2022, izvirni znanstveni članek Ključne besede: blast furnace, slag system, activity of MgO, reference-slag, method, enthalpy, solution
Objavljeno v DiRROS: 22.06.2022; Ogledov: 481; Prenosov: 135
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20. Geophysical investigations in the Radovna River Spring area (Julian Alps, NW Slovenia)Anja Torkar, Marjana Zajc, Jure Atanackov, Andrej Gosar, Mihael Brenčič, 2021, izvirni znanstveni članek Povzetek: The Radovna River Valley is located in the north-western part of Slovenia in the Julian Alps, where there is an extensive intergranular aquifer whose depth to pre-Quaternary bedrock is unknown. Therefore, to obtain information about the depth of the valley and the geometry of the aquif er two geophysical methods were used in our study; ground penetrating radar (GPR) and seismic reflection method. The low-frequency GPR method has shown to be useful for determining the depth of the groundwater and the predominant groundwater recharge. Also, the high-resolution seismic method provided an insight about the morphology of the pre-Quaternary basement with the deepest point at 141 meters below surface. Measurements of hydrogeological parameters such as groundwater level and river discharge measurements were carried out in the study area. Both data analyses showed that groundwater level and river discharge are highly fluctuatingand rapidly changing, indicating a well-permeable aquifer, implying that such an aquifer is extremely sensitive and vulnerable to extreme climate events. Both the geophysical methods and the hydrogeological information have provided important information about the morphology of the valley and the alluvial aquifer, as well as increasing the knowledge about the Radovna springs system, which will contribute very important information for future hydrogeological studies.
Ključne besede: Ground penetrating radar, Seismic reflection method, Radovna spring, hydrogeology, aquifer geometry, glacial valley, groundwater table
Objavljeno v DiRROS: 09.03.2022; Ogledov: 736; Prenosov: 322
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