41. Formulation of the method of fundamental solutions for two-phase Stokes flowZlatko Rek, Božidar Šarler, 2024, original scientific article Abstract: The method of fundamental solutions with a subdomain technique is used for the solution of the free boundary problem associated with a two-phase Stokes flow in a 2D geometry. The solution procedure is based on the collocation of the boundary conditions with the Stokeslets. It is formulated for the flow of unmixing fluids in contact, where the velocity, pressure field, and position of the free boundary between the fluids must be determined. The standard formulation of the method of fundamental solutions is, for the first time, upgraded for the case with mixed velocity and pressure boundary conditions and verified on a T-splitter single-phase flow with unsymmetric pressure boundary conditions. The standard control volume method is used for the reference solution. The accurate evaluation of the velocity derivatives, which are required to calculate the balance of forces at the free boundary between the fluids, is achieved in a closed form in contrast to previous numerical attempts. An algorithm for iteratively calculating the position of the free boundary that involves displacement, smoothing and repositioning of the nodes is elaborated. The procedure is verified for a concurrent flow of two fluids in a channel. The velocity and velocity derivatives show fast convergence to the analytical solution. The developed boundary meshless method is easy to code, accurate and computationally efficient since only collocation at the fixed and free boundaries is needed.
Keywords: Stokes equations, two-phase flow, free boundary problems, method of fundamental solutions, subdomain technique
Published in DiRROS: 28.02.2024; Views: 117; Downloads: 66
 Full text (3,40 MB)
This document has many files! More... |
42. An improved local radial basis function method for solving small-strain elasto-plasticityGašper Vuga, Boštjan Mavrič, Božidar Šarler, 2024, original scientific article Abstract: Strong-form meshless methods received much attention in recent years and are being extensively researched and applied to a wide range of problems in science and engineering. However, the solution of elasto-plastic problems has proven to be elusive because of often non-smooth constitutive relations between stress and strain. The novelty in tackling them is the introduction of virtual finite difference stencils to formulate a hybrid radial basis function generated finite difference (RBF-FD) method, which is used to solve small-strain von Mises elasto-plasticity for the first time by this original approach. The paper further contrasts the new method to two alternative legacy RBF-FD approaches, which fail when applied to this class of problems. The three approaches differ in the discretization of the divergence operator found in the balance equation that acts on the non-smooth stress field. Additionally, an innovative stabilization technique is employed to stabilize boundary conditions and is shown to be essential for any of the approaches to converge successfully. Approaches are assessed on elastic and elasto-plastic benchmarks where admissible ranges of newly introduced free parameters are studied regarding stability, accuracy, and convergence rate.
Keywords: Von Mises elasto-plasticity, radial basis function, finite differences, polyharmonic splines, two dimensions, hybrid discretization
Published in DiRROS: 28.02.2024; Views: 120; Downloads: 61
Full text (5,24 MB)
This document has many files! More... |
43. Characterization of hFOB 1.19 cell line for studying Zn-based degradable metallic biomaterialsEva Jablonská, Lucie Mrázková, Jiří Kubásek, Dalibor Vojtěch, Irena Paulin, Tomáš Ruml, Jan Lipov, 2024, original scientific article Abstract: In vitro testing is the first important step in the development of new biomaterials. The human fetal osteoblast cell line hFOB 1.19 is a very promising cell model; however, there are vast discrepancies in cultivation protocols, especially in the cultivation temperature and the presence of the selection reagent, geneticin (G418). We intended to use hFOB 1.19 for the testing of Zn-based degradable metallic materials. However, the sensitivity of hFOB 1.19 to zinc ions has not yet been studied. Therefore, we compared the toxicity of zinc towards hFOB 1.19 under different conditions and compared it with that of the L929 mouse fibroblast cell line. We also tested the cytotoxicity of three types of Zn-based biomaterials in two types of media. The presence of G418 used as a selection reagent decreased the sensitivity of hFOB 1.19 to Zn2+. hFOB 1.19 cell line was more sensitive to Zn2+ at elevated (restrictive) temperatures. hFOB 1.19 cell line was less sensitive to Zn2+ than L929 cell line (both as ZnCl2 and extracts of alloys). Therefore, the appropriate cultivation conditions of hFOB 1.19 during biomaterial testing should be chosen with caution.
Keywords: zinc degradable materials, in vitro cytotoxicity testing, hFOB 1.19 osteoblasts
Published in DiRROS: 28.02.2024; Views: 142; Downloads: 58
Full text (1,81 MB)
This document has many files! More... |
44. Mechanisms of premature fracture in modular neck stems made of CoCrMo/Ti6Al4V and Ti6Al4V/Ti6Al4V alloyDrago Dolinar, Miro Gorenšek, Klemen Avsec, Barbara Šetina, Matej Hočevar, Matjaž Godec, Borut Žužek, Mojca Debeljak, Monika Jenko, John T. Grant, Boštjan Kocjančič, 2023, original scientific article Abstract: In this paper, we present the mechanisms of premature fracture of modular neck stems in two case studies: (I) when the neck and stem are both made of the same Ti6Al4V alloy, and (II) when the neck and stem are made from two different alloys, CoCrMo and Ti6Al4V alloy. Our study integrates two orthopedic patients who have undergone primary uncemented THA for usual indications in two orthopedic centers (Community Health Centre and University Medical Centre). Both centers are part of the national public health care system. Both surgeries were performed by two skilled orthopedic surgeons with more than 10 years of experience in THA. The survivorship of the modular neck of cast CoCrMo alloy was 24 months. The survivorship of the modular neck from Ti6Al4V alloy was 84 months. Multivariate analyses were performed to assess the differences in the fretting, corrosion, and fatigue of the two prematurely failed modular neck stems: stereo light microscopy (SLM), scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS), and electron backscatter diffraction (EBSD). Patient demographic information, including sex, age, body mass index, survivorship of implants, and reason for the revision, was collected from medical records. We found that fretting and fatigue occurred on both neck-stem retrievals due to additional galvanic corrosion, but the CoCrMo/Ti6Al4V alloy system suffered more corrosion due to additional galvanic corrosion and fractured earlier than the Ti6Al4V/Ti6Al4V metal alloy system. Both metallic alloy systems used in this application are known to be highly corrosion-resistant, but the bio-tribo-corrosion processes need to be understood in detail and characterized so that appropriate improvements in design and materials can be made.
Keywords: total hip arthroplasty, modular neck, Ti6Al4V alloy, CoCrMo alloy, corrosion
Published in DiRROS: 07.02.2024; Views: 229; Downloads: 126
Full text (5,12 MB)
This document has many files! More... |
45. Grain size distribution of DP 600 steel using single-pass asymmetrical wedge testUrška Klančnik, Peter Fajfar, Jan Foder, Heinz Palkowski, Jaka Burja, Grega Klančnik, 2023, original scientific article Keywords: wedge test, hot-rolling, grain size distribution, dual-phase steel
Published in DiRROS: 07.02.2024; Views: 176; Downloads: 73
Full text (4,64 MB)
This document has many files! More... |
46. Thermal fatigue degradation progress in SiMo ductile cast iron under oxidation conditionsMilan Terčelj, Jaka Burja, Goran Kugler, Primož Mrvar, 2023, original scientific article Keywords: metallurgical engineering, exhaust manifolds, cast irons, casting, microscopic characterization and microanalysis, thermal fatigue, material defect, microstructural control
Published in DiRROS: 07.02.2024; Views: 197; Downloads: 147
Full text (36,47 MB)
This document has many files! More... |
47. An experimental study of liquid micro-jets produced with a gas dynamic virtual nozzle under the influence of an electric fieldBor Zupan, Gisel Esperanza Peña-Murillo, Rizwan Zahoor, Jurij Gregorc, Božidar Šarler, Juraj Knoška, Alfonso M. Gañán-Calvo, Henry N. Chapman, Saša Bajt, 2023, original scientific article Abstract: The results of an experimental study of micro-jets produced with a gas dynamic virtual nozzle (GDVN) under the influence of an electric field are provided and discussed for the first time. The experimental study is performed with a 50% volume mixture of water and ethanol, and nitrogen focusing gas. The liquid sample and gas Reynolds numbers range from 0.09–5.4 and 0–190, respectively. The external electrode was positioned 400–500 μm downstream of the nozzle tip and an effect of electric potential between the electrode and the sample liquid from 0–7 kV was investigated. The jetting parametric space is examined as a function of operating gas and liquid flow rates, outlet chamber pressure, and an external electric field. The experimentally observed jet diameter, length and velocity ranged from 1–25 μm, 50–500 μm and 0.5–10 m/s, respectively. The jetting shape snapshots were processed automatically using purposely developed computer vision software. The velocity of the jet was calculated from the measured jet diameter and the sample flow rate. It is found that micro-jets accelerate in the direction of the applied electric field in the downstream direction at a constant acceleration as opposed to the standard GDVNs. New jetting modes were observed, where either the focusing gas or the electric forces dominate, encouraging further theoretical and numerical studies towards optimized system design. The study shows the potential to unlock a new generation of low background sample delivery for serial diffraction measurements of weakly scattering objects.
Keywords: micro jet, electric field, experimental study, flow focusing, Taylor cone, gas dynamic virtual nozzles
Published in DiRROS: 07.02.2024; Views: 212; Downloads: 95
Full text (1,94 MB)
This document has many files! More... |
48. Metal artefacts and remains of armour from Kozlov Rob castle : metallurgical analyses as a tool for identification and interpretation of fragmentary archaeological findsJakob Kraner, Tomaž Lazar, Miha Mlinar, Jaka Burja, 2023, original scientific article Keywords: archaeology, castle, Kozlov Rob, Slovenia, armour, helmet, metallography
Published in DiRROS: 07.02.2024; Views: 155; Downloads: 78
Full text (3,92 MB)
This document has many files! More... |
49. Study on dissolution of Ba-containing inoculant in ductile cast iron melt and nucleation of graphiteMarica Tonkovič-Prijanovič, Primož Mrvar, Jaka Burja, Črtomir Donik, Mitja Petrič, 2023, original scientific article Keywords: inoculant, inoculant dissolving, reaction zone, phase composition, graphite nucleation, ductile cast iron, barium inoculant
Published in DiRROS: 07.02.2024; Views: 139; Downloads: 66
Full text (17,37 MB)
This document has many files! More... |
50. Small cellular particles from European spruce needle homogenateMarko Jeran, Anna Romolo, Vesna Spasovski, Matej Hočevar, Urban Novak, Roman Štukelj, Vid Šuštar, Matic Kisovec, Apolonija Bedina Zavec, Ksenija Kogej, Aleš Iglič, Polonca Trebše, Veronika Kralj-Iglič, 2023, original scientific article Keywords: Picea abies, spruce needles, extracellular particles, extracellular vesicles, small cellular particles, interferometric light microscopy, exosomes, cell-to-cell communication, drug delivery
Published in DiRROS: 07.02.2024; Views: 157; Downloads: 105
Full text (2,49 MB)
This document has many files! More... |
