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Ključne besede: self-lubricating claddings, friction, galling, tribofilm, XPS
Objavljeno v DiRROS: 14.05.2025; Ogledov: 40; Prenosov: 8
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Ključne besede: Early Iron Age, geoarchaeology, micromorphology, microrefuse, archaeometallurgy, smithy, floor construction, floor maintenance, lime plaster, hammerscale
Objavljeno v DiRROS: 13.05.2025; Ogledov: 49; Prenosov: 17
Celotno besedilo (4,12 MB)

Povzetek: This paper studies and assesses different Neumann boundary conditions (BC) implementations in the radial basis function generated finite difference (RBF-FD) method. We analyse four BC implementations by solving a phase-field model for single dendrite growth in supercooled pure melts. In the first BC implementation, the BC are satisfied when constructing interpolation problems in the local support domains near the boundary. In the second one, the BC are satisfied by solving an additional system of linear equations for the field values in the boundary nodes. In the third one, we add a layer of ghost nodes to the boundary nodes; the BC are satisfied by solving an additional system of linear equations for the field values in the ghost nodes. The fourth BC implementation uses the same node distribution as the third one; since we are dealing with the symmetric BC, we set the values in the ghost nodes by direct mirroring. We analyse the influence of the size of a local support domain and the type of node distribution (regular/scattered) on the accuracy. We show that using ghost nodes is recommended to consider Neumann BC in the RBF-FD method accurately when solving phase-field models for dendritic growth.
Ključne besede: dendritic growth, phase-field method, Neumann boundary conditions
Objavljeno v DiRROS: 13.05.2025; Ogledov: 48; Prenosov: 18
Celotno besedilo (1,17 MB)
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Povzetek: Accurate treatment of heat and mass transfer processes inside airlift reactors requires accurate velocity field information. This study presents a novel one-dimensional model forecasting induced liquid flow within an external loop airlift reactor across diverse flow regimes. The approach is grounded on homogeneous flow assumption, augmented by a novel correction term derived through modeling of turbulence-induced pressure losses behind gas structures, employing the separated flow model (Lockhart-Martinelli). The model was assessed by comparing the results with purpose-provided experimental data utilizing air and demineralized water. The gas and liquid superficial velocities ranged from 0.001-0.6 m/s and 0.2–1.1 m/s, respectively. Within ± 10 %, an agreement between the novel model and experimental data was observed for both bubbly, separated, and in- termediate flow regimes. A similarly robust agreement was confirmed through comparisons with five published experimental datasets. The distinctive feature of this model is its ability to accommodate multiple flow regimes in a unified manner. It circumvents the necessity for specific regime modeling by introducing a correction term with a complexity marginally surpassing that of the conventional homogeneous flow approach. Beyond its primary application in airlift reactors, the model provides a unified framework for modeling two-phase flow hydrody- namics in thermal applications, particularly in flow boiling and bubble-induced convective heat transfer systems. The model’s simple yet effective structure also allows for integration into higher-fidelity heat transfer simula- tions, making it valuable for boiling heat transfer studies, enhanced cooling strategies, and industrial multiphase flow applications.
Ključne besede: airlift reactor, homogeneous flow, separated flow, theoretical model, induced flow
Objavljeno v DiRROS: 13.05.2025; Ogledov: 49; Prenosov: 19
Celotno besedilo (4,69 MB)
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Povzetek: The meshfree RBF–FD method is becoming an increasingly popular discretization method for challenging PDE problems due to its flexibility with respect to geometry and its ease of implementation. Using a combination of polyharmonic spline basis functions and polynomial basis functions has proven to be particularly successful with a convergence rate depending on the polynomial degree and good behavior at boundaries due to the contribution of the spline part. A challenge that has been observed is that derivative boundary conditions can give rise to large errors. A known remedy for this problem is to introduce one or more layers of ghost points, which improves the boundary approximations. In a recent paper, Tominec, Larsson, Heryudono (2021), it was shown that using oversampling is another effective way to handle this problem. Oversampling also allows for theoretical analysis of the method, which can then be viewed as a discretization of a continuous least-squares projection. By looking deeper into the error estimates we gain an understanding about how to best implement the method.
Ključne besede: meshless methods, partial differential equations, error estimates
Objavljeno v DiRROS: 09.05.2025; Ogledov: 86; Prenosov: 35
Celotno besedilo (9,81 MB)
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