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arXiv 2023年

作者： Jančič, Mitja Založnik, Miha Kosec, Gregor Institute Jožef Stefan Parallel and Distributed Systems Laboratory Jamova cesta 39 Ljubljana1000 Slovenia Université de Lorraine CNRS IJL NancyF-54000 France Laboratory of Excellence DAMAS Université de Lorraine Metz Nancy France

The growth of dendritic grains during solidification is often modelled using the Grain Envelope Model (GEM), in which the envelope of the dendrite is an interface tracked by the Phase Field Interface Capturing (PFIC) method. In the PFIC method, an phase-field equation is solved on a fixed mesh to track the position of the envelope. While being versatile and robust, PFIC introduces certain numerical artefacts. In this work, we present an alternative approach for the solution of the GEM that employs a Meshless (sharp) Interface Tracking (MIT) formulation, which uses direct, artefact-free interface tracking. In the MIT, the envelope (interface) is defined as a moving domain boundary and the interface-tracking nodes are boundary nodes for the diffusion problem solved in the domain. To increase the accuracy of the method for the diffusion-controlled moving-boundary problem, an h-adaptive spatial discretization is used, thus, the node spacing is refined in the vicinity of the envelope. MIT combines a parametric surface reconstruction, a mesh-free discretization of the parametric surfaces and the space enclosed by them, and a high-order approximation of the partial differential operators and of the solute concentration field using radial basis functions augmented with monomials. The proposed method is demonstrated on a two-dimensional h-adaptive solution of the diffusive growth of dendrite and evaluated by comparing the results to the PFIC approach. It is shown that MIT can reproduce the results calculated with PFIC, that it is convergent and that it can capture more details in the envelope shape than PFIC with a similar spatial discretization. © 2023, CC0.

关键词： Surface reconstruction

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KRCORE: A Microsecond-scale RDMA Control Plane for Elastic Computing

arXiv

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arXiv 2021年

作者： Wei, Xingda Lu, Fangming Chen, Rong Chen, Haibo Institute of Parallel and Distributed Systems SEIEE Shanghai Jiao Tong University China Shanghai AI Laboratory China

We present KRCORE, an RDMA library with a microsecond-scale control plane on commodity RDMA hardware for elastic computing. KRCORE can establish a full-fledged RDMA connection within 10µs (hundreds or thousands of times faster than verbs), while only maintaining a (small) fixed-sized connection metadata at each node, regardless of the cluster scale. The key ideas include virtualizing pre-initialized kernel-space RDMA connections instead of creating one from scratch, and retrofitting advanced RDMA dynamic connected transport with static transport for both low connection overhead and high networking speed. Under load spikes, KRCORE can shorten the worker bootstrap time of an existing disaggregated key-value store (namely RACE Hashing) by 83%. In serverless computing (namely Fn), KRCORE can also reduce the latency for transferring data through RDMA by 99%. © 2021, CC BY.

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A multiscale finite element approach to analyse the effect of shot peening-induced surface roughness on fretting fatigue crack initiation

Results in Engineering

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Results in Engineering 2025年 26卷

作者： Li, Chao Han, Sutao Wang, Can Amanov, Auezhan Wang, Lihua Abdel Wahab, Magd Soete Laboratory Department of Electromechanical Systems and Metal Engineering Faculty of Engineering and Architecture Ghent University Finland Faculty of Engineering and Natural Sciences Tampere University Finland Department of Mechanical Engineering Sun Moon University Korea Republic of School of Aerospace Engineering and Applied Mechanics Tongji University Shanghai200092 China College of Engineering Yuan Ze University Taiwan China Parallel and Distributed Systems Laboratory Jožef Stefan Institute Jamova cesta 39 LjubljanaSI-1000 Slovenia

Shot peening (SP) is a widely used surface treatment technique that enhances the mechanical performance of materials, notably improving fatigue resistance by inducing compressive residual stresses (RS) and modifying surface characteristics. While the overall benefits of SP on fatigue life are well-documented, the specific role of SP-induced surface roughness in fretting fatigue behaviour remains unclear. This study develops a multiscale framework based on finite element method (FEM) to isolate and quantify the influence of surface roughness resulting from SP on fretting fatigue. At the microscale, detailed FEM simulations are conducted to assess how surface topography affects local contact stresses, thereby extracting critical features brought by roughness. These features are then integrated into a macroscale model to construct a SP-treated model that accounts for the effects of surface roughness. Numerical results reveal that while surface roughness has a minimal effect on crack initiation location and orientation, it significantly affects crack initiation lifetime by redistributing contact stresses more favourably. Furthermore, incorporating experimentally measured roughness profiles into the numerical models enhances the accuracy of fatigue life predictions. These findings underscore the importance of considering surface roughness in numerical simulations to achieve reliable predictions of fretting fatigue behaviour in SP-treated materials. © 2025 The Authors

关键词： Residual stresses

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Meshless method stencil evaluation with machine learning

arXiv

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arXiv 2022年

作者： Rot, Miha Rashkovska, Aleksandra Jozef Stefan International Postgraduate School Jamova cesta 39 Ljubljana1000 Slovenia "Jožef Stefan" Institute Parallel and Distributed Systems Laboratory Jamova cesta 39 Ljubljana1000 Slovenia

Meshless methods are an active and modern branch of numerical analysis with many intriguing benefits. One of the main open research questions related to local meshless methods is how to select the best possible stencil - a collection of neighbouring nodes - to base the calculation on. In this paper, we describe the procedure for generating a labelled stencil dataset and use a variation of pointNet - a deep learning network based on point clouds - to create a classifier for the quality of the stencil. We exploit features of pointNet to implement a model that can be used to classify differently sized stencils and compare it against models dedicated to a single stencil size. The model is particularly good at detecting the best and the worst stencils with a respectable area under the curve (AUC) metric of around 0.90. There is much potential for further improvement and direct application in the meshless domain. © 2022, CC BY.

关键词： Classification (of information)

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On h-refined meshless solution to Navier-Stokes problem in porous media: comparing meshless Lattice Boltzman Method with ACM RBF-FD approach

arXiv

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arXiv 2024年

作者： Strzelczyk, Dawid Rot, Miha Kosec, Gregor Matyka, Maciej Institute of Theoretical Physics Faculty of Physics and Astronomy University of Wroclaw pl. M. Borna 9 Wroclaw50-204 Poland Parallel and Distributed Systems Laboratory Jožef Stefan Institute Jamova cesta 39 Ljubljana1000 Slovenia Jožef Stefan International Postgraduate School Jamova cesta 39 Ljubljana1000 Slovenia

In this paper, two mesh-free CFD solvers for pore-scale fluid flow through porous media are considered, namely the Lattice Boltzmann Method with the two relaxation time collision term and the direct Navier-Stokes solver under the artificial compressibility limit. The porous media is built with a regular arrangement of spherical grains with variable radii, which allows control of the porosity. Both solvers use the same h-refined meshless spatial discretization to adequately capture the underlying geometry and the same Radial Basis Function (RBF) method to approximate the involved fields and partial differential operators. First, the results are compared with the data from the literature in terms of drag coefficient and permeability at different porosities achieving excellent agreement with the reported results. Next, the simulations are extended beyond the porosity range reported in the literature using proposed h-refined CFD solvers. The results are supported by convergence and timing analyses and discussions on meshless parameters such as stencil size and refinement settings. © 2024, CC BY.

关键词： Porous materials

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Refined radial basis function-generated finite difference analysis of non-Newtonian natural convection

arXiv

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arXiv 2022年

作者： Rot, Miha Kosec, Gregor Jozef Stefan International Postgraduate School Jamova cesta 39 Ljubljana1000 Slovenia Jožef Stefan Institute Parallel and Distributed Systems Laboratory Jamova cesta 39 Ljubljana1000 Slovenia

In this paper we present a refined Radial Basis Function-generated Finite Difference (RBF-FD) solution for a non-Newtonian fluid in a closed differentially heated cavity. The non-Newtonian behaviour is modelled with the Ostwald-de Waele power law and the buoyancy with the Boussinesq approximation. The problem domain is discretised with scattered nodes without any requirement for a topological relation between them. This allows a trivial generalisation of the solution procedure to complex irregular three dimensional (3D) domains, which is also demonstrated by solving the problem in a two dimensional (2D) and 3D geometry mimicking a porous filter. The results in 2D are compared with two reference solutions that use the Finite volume method in a conjunction with two different stabilisation techniques, where we achieved good agreement with the reference data. The refinement is implemented on top of a dedicated meshless node positioning algorithm using piecewise linear node density function that ensures sufficient node density in the centre of the domain while maximising the node density in a boundary layer where the most intense dynamic is expected. The results show that with a refined approach, more than 5 times fewer nodes are required to obtain the results with the same accuracy compared to the regular discretisation. The paper also discusses the convergence with refined discretisation for different scenarios for up to 2·105 nodes, the impact of method parametres, the behaviour of the flow in the boundary layer, the behaviour of the viscosity and the geometric flexibility of the proposed solution procedure. © 2022, CC BY.

关键词： Navier Stokes equations

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Strong form mesh-free hp-adaptive solution of linear elasticity problem

arXiv

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arXiv 2022年

作者： Jančič, Mitja Kosec, Gregor Parallel and Distributed Systems Laboratory Institute Jožef Stefan Jamova Cesta 39 Ljubljana1000 Slovenia Jožef Stefan International Postgraduate School Jamova Cesta 39 Ljubljana1000 Slovenia

We present an algorithm for hp-adaptive collocation-based mesh-free numerical analysis of partial differential equations. Our solution procedure follows a well-established iterative solve–estimate–mark–refine paradigm. The solve phase relies on the Radial Basis Function-generated Finite Differences (RBF-FD) using point clouds generated by advancing front node positioning algorithm that supports variable node density. In the estimate phase, we introduce an Implicit-Explicit (IMEX) error indicator, which assumes that the error relates to the difference between the implicitly obtained solution (from the solve phase) and a local explicit re-evaluation of the PDE at hand using a higher order approximation. Based on the IMEX error indicator, the modified Texas Three Step marking strategy is used to mark the computational nodes for h-, p- or hp-(de-)refinement. Finally, in the refine phase, nodes are repositioned and the order of the method is locally redefined using the variable order of the augmenting monomials according to the instructions from the mark phase. The performance of the introduced hp-adaptive method is first investigated on a two-dimensional Peak problem and further applied to two- and three-dimensional contact problems. We show that the proposed IMEX error indicator adequately captures the global behaviour of the error in all cases considered and that the proposed hp-adaptive solution procedure significantly outperforms the non-adaptive approach. The proposed hp-adaptive method stands for another important step towards a fully autonomous numerical method capable of solving complex problems in realistic geometries without the need for user intervention. Copyright © 2022, The Authors. All rights reserved.

关键词： Errors

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A hybrid RBF-FD and WLS mesh-free strong-form approximation method

arXiv

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arXiv 2022年

作者： Jančič, Mitja Kosec, Gregor "Jožef Stefan" Institute Parallel Distributed Systems Laboratory Jamova cesta 39 Ljubljana1000 Slovenia "Jožef Stefan" International Postgraduate School Jamova cesta 39 Ljubljana1000 Slovenia

Since the advent of mesh-free methods as a tool for the numerical analysis of systems of Partial Differential Equations (PDEs), many variants of differential operator approximation have been proposed. In this work, we propose a local mesh-free strong-form method that combines the stability of Radial Basis Function-Generated Finite Differences (RBF-FD) with the computational effectiveness of Diffuse Approximation Method (DAM), forming a so-called hybrid method. To demonstrate the advantages of a hybrid method, we evaluate its computational complexity and accuracy of the obtained numerical solution by solving a two-dimensional Poisson problem with an exponentially strong source in the computational domain. Finally, we employ the hybrid method to solve a three-dimensional Boussinesq’s problem on an isotropic half-space and show that the implementation overhead can be justified. Copyright © 2022, The Authors. All rights reserved.

关键词： Finite difference method

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Natural Convection of Non-Newtonian Fluids in a Differentially Heated Closed Cavity

Natural Convection of Non-Newtonian Fluids in a Differential...

引用

Proceedings of the International Convention MIPRO

作者： Miha Rot Gregor Kosec “Jožef Stefan” Institute Parallel and Distributed Systems Laboratory Ljubljana Slovenia Jožef Stefan” International Postgraduate School Ljubljana Slovenia

Fluids in computational hydrodynamics are often considered Newtonian, meaning a constant viscosity, but that is just a crude approximation for many real-world examples. Accounting for Non-Newtonian behaviour can provide a significant improvement in simulation accuracy. We present a meshless solution for the natural convection of a power-law non-Newtonian fluid driven by differentially heated cavity walls. The Navier-Stokes and heat transport equations are coupled using the Boussinesq approximation and numerically solved with the generalized finite differences, explicit Euler stepping and Chorin's projection method.

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Fretting wear mechanism of GH4169 dovetail joint specimens treated with hybrid laser shock peening

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Tribology International 2025年 209卷

作者： Fang, Xiuyang Wang, Zheng Wahab, Magd Abdel Gong, Jianen Liu, Xiong Liu, Xing Cai, Zhenbing School of Mechanical Engineering Southwest Jiaotong University Chengdu610031 China Tribology Research Institute Key Lab of Advanced Technologies of Materials Southwest Jiaotong University Chengdu610031 China Soete Laboratory Department of Electrical Energy Metals Mechanical Constructions and Systems Faculty of Engineering and Architecture Ghent University Gent9000 Belgium College of Engineering Yuan Ze University Taiwan China Parallel and Distributed Systems Laboratory Jožef Stefan Institute Jamova cesta 39 LjubljanaSI-1000 Slovenia DongFang Electric Machinery Co. LTD Deyang618000 China State Key Laboratory of Advanced Electromagnetic Technology Huazhong University of Science and Technology Hubei Wuhan430074 China

Aero engine blade structure is prone to severe fretting wear under centrifugal forces and vibration loads, resulting in greatly reduced engine service life, which is a typical fretting damage problem. In this paper, without Absorbing layer Nanosecond Laser Shock Peening (wAN-LSP) and without Absorbing layer Nanosecond superimposed Femtosecond hybrid Laser Shock Peening (NF-LSP) are utilized to strengthen the surface of GH4169 dovetail joint specimens, which is a common material for engine blades, to explore its strengthening mechanism and fretting wear evolution law. The findings indicate that the surface roughness of the wAN-LSP specimen rises from 0.28 μm to 1.16 μm. The thermal effects of wAN-LSP lead to the formation of a molten layer roughly 10.97 μm thick on the surface, accompanied by numerous pits, ablation holes, and micro-cracks. In contrast, NF-LSP treatment effectively eliminates the surface oxidation defects made by the thermal effects of wAN-LSP, leading to a slight decrease in surface roughness. Both wAN-LSP and NF-LSP treatments enhance the surface hardness of the specimens, creating a plastic deformation layer roughly 400 μm deep, but the near surface hardness of NF-LSP treated specimen is further improved compared to that of the wAN-LSP specimen. The wear mechanism observed in the GH4169 dovetail joint specimens following wAN-LSP and NF-LSP treatment are identified as abrasive wear and oxidation wear. Initially, as the number of cycles raises, the wear volume of GH4169 specimen treated with wAN-LSP is higher than that of untreated specimen, but subsequently, it becomes lesser than that of the untreated specimen. This phenomenon results from the interplay between the molten layer and hardened layer. In the initial stage of wear, despite the surface strengthening of the wAN-LSP specimen, the presence of molten layer significantly diminishes the fretting wear resistance of the material. As wear progresses, the molten layer is removed, revealing the be

关键词： Abrasion

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