11. An improved local radial basis function method for solving small-strain elasto-plasticityGašper Vuga, Boštjan Mavrič, Božidar Šarler, 2024, izvirni znanstveni članek Povzetek: 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.
Ključne besede: Von Mises elasto-plasticity, radial basis function, finite differences, polyharmonic splines, two dimensions, hybrid discretization
Objavljeno v DiRROS: 28.02.2024; Ogledov: 180; Prenosov: 108
 Celotno besedilo (5,24 MB)
Gradivo ima več datotek! Več... |
12. 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, izvirni znanstveni članek Povzetek: 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.
Ključne besede: micro jet, electric field, experimental study, flow focusing, Taylor cone, gas dynamic virtual nozzles
Objavljeno v DiRROS: 07.02.2024; Ogledov: 312; Prenosov: 114
Celotno besedilo (1,94 MB)
Gradivo ima več datotek! Več... |
13. 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: 225; Prenosov: 79
Celotno besedilo (1,07 MB)
Gradivo ima več datotek! Več... |
