1,721,438 research outputs found
A mesh-based Graph Neural Network approach for surrogate modeling of Lagrangian free surface fluid flows
No full textThe study of free surface fluid flows is of significant interest across various research fields, including civil, aerospace, and biomedical engineering. Among the numerical methods used to address free surface problems, the Particle Finite Element Method (PFEM) stands out as a robust and efficient approach. PFEM solves the governing equations using the standard finite element method while addressing mesh distortion through a fast and efficient remeshing procedure. In recent years, deep learning (DL) algorithms have demonstrated remarkable successes in learning from examples, and their application to datasets generated from numerical simulations could result in surrogate models able to reduce the computational cost of classical numerical methods. In the context of free surface fluid simulations, particularly noteworthy are attempts to employ Graph Neural Networks (GNNs) given their ability to process unstructured data that cannot be represented as structured grids, which are typical of these applications. In this work, we introduce NeuralPFEM (NPFEM), a GNN-based approach for surrogate modeling of free surface fluid simulations. NPFEM learns the system's temporal evolution in an autoregressive manner, preserving the same structure of a standard numerical solver. It inherits its hybrid nature from PFEM, combining features of particle-based and mesh-based methods. This hybrid approach distinguishes NPFEM from existing methods, such as the Graph Neural Simulator (GNS), which are purely particle-based. As a result, to construct the graph during training, NPFEM exploits the mesh connectivity already available in the dataset, while GNS must reconstruct graph connectivity at every training step based on particle distributions. During prediction, NPFEM employs PFEM mesh generation algorithm and particle redistribution tools to build the graph connectivity, ensuring a more uniform particle distribution within the domain and producing a mesh-based output solution. This approach preserves mesh quality and mitigates undesirable effects like particle clustering. We evaluate the results both qualitatively and quantitatively, comparing them with those obtained from PFEM. Moreover, we compute physical quantities out of the learned solution. In particular, the output mesh structure, combined with the joint prediction of the velocity and the pressure fields, facilitates the calculation of forces and stresses, a first step in the direction of applying this kind of tool to Fluid–Structure Interaction (FSI) problems
Pipeline flotation in liquefied sand: A simplified transient model
Full text linkSubmarine buried pipelines are often laid in trenches backfilled with loose sandy soil, which is intrinsically prone to liquefaction. When liquefaction is triggered, the soil tends to behave as a viscous fluid with vanishing shear strength and very limited ability to restrain structural displacement, for instance during the occurrence of pipeline flotation. Recently, a 2D CFD-based approach for the analysis of pipe flotation in liquefied sand has been proposed by Pisano et al. (2020), in which soil reconsolidation effects are phenomenologically captured by considering rheological parameters that evolve in space and time as pore water pressures dissipate. Despite a remarkable agreement with experimental data from the literature, the complexity and computational costs of such approach may still hinder its applicability to pipeline engineering practice. To overcome this limitation, a simplified model is proposed herein, in which all the forces governing the motion of the pipe are expressed via simple analytical relationships. After thorough validation against 2D CFD results and relevant experimental data, it is concluded that the new simplified model largely retains the predictive capability of Pisano et al.’s framework in combination with negligible computational costs.Geo-engineerin
Challenging the Limits of Fluid FEM Modelling in 3D Concrete Printing
No full text3D Concrete Printing (3DCP) is emerging among additive manufacturing technologies for the construction industry. With 3DCP complex structural components can be built without formwork in a layer-wise fashion, enhancing accuracy, optimizing material use and reducing construction times and waste. However, to fully exploit and control 3DCP it is necessary to develop adequate numerical predictive tools: solid FEM models have been used to predict buildability, while fluid or particle methods are preferred to assess pumpability and extrudability. Currently, a unified numerical framework to simulate the overall 3DCP process is missing. This work intends to take a first step in that direction. A single-phase fluid model of 3DCP based on the Particle Finite Element Method (PFEM) is illustrated. Fresh concrete is modelled with the Bingham law and the static yield stress is increased in time in the layers to reproduce material structuration. In the PFEM framework, a wide range of different phenomena typical of 3DCP can be simulated. In the specific, two 3D printing applications are shown: the virtual printing of a cylindrical object and the prediction of structural failure due to elastic buckling in a rectilinear wall
A hybrid Lagrangian-Eulerian particle finite element method for free-surface and fluid-structure interaction problems
Full text linkThe dynamics of fluid flows with free surfaces and interacting with highly deformable structures is a complex problem, attracting considerable attention. The Particle Finite Element Method (PFEM) is one of the various numerical methods recently proposed in the literature to simulate this type of problems. It is a mesh-based Lagrangian approach, particularly suited for problems with fast changes in the domain topology, since the fluid boundaries and the Fluid-Structure Interaction (FSI) interface are naturally tracked by the position of the mesh nodes. However, when nonhomogeneous boundary conditions are imposed on velocities or when there are regions where the topology varies moderately, for example, in confined portions of the fluid domain characterized by fixed boundaries, an Eulerian formulation turns out to be more convenient. To exploit the advantages of both formulations, an adaptive hybrid Lagrangian-Eulerian approach is presented in this work. According to the proposed method, nodes on the fluid free-surface and on the FSI interface are treated as Lagrangian, while the remaining nodes can be either Eulerian or Lagrangian. Furthermore, to increase the efficiency of the method, an algorithm to automatically detect runtime the transition zone between the two kinematic descriptions is devised. To validate the proposed approach, several numerical examples are developed and their results are compared to those available in the literature
Variationally consistent self-stabilized Virtual Elements for 2D locking-free elastoplasticity
No full textA variationally consistent numerical approach based on the Virtual Element Method (VEM) is presented for the analysis of 2D elastoplasticity problems. The mixed Hu-Washizu functional of elasticity is extended to incorporate the energy contributions specific to the finite-step elastoplastic problem. It is demonstrated how the governing equations of the discretized elastoplastic problem - including the loading-unloading conditions - emerge naturally as the stationarity conditions of the VEM-discretized functional. Spurious hourglass modes are prevented by formulating a self-stabilized version of Virtual Elements (VEs) that exploits the possibility offered by the mixed approach to define strain and displacement approximations of the same order. The insensitivity of VEs to element distortion and the possibility to use polygonal elements with any shape and number of edges is tested with the analysis of several benchmarks from the literature. It is shown how accurate solutions can be obtained also in the case of non-convex quadrilateral or pentagonal elements. Additionally, the role of internal moment degrees of freedom in preventing elastoplastic locking at the plastic failure limit is elucidated
3d fluid–structure interaction simulation with an Arbitrary–Lagrangian–Eulerian approach with applications to flying objects
Full text linkAir-structure interaction is a key aspect to account for during the design of Micro Air Vehicles. In this context, modelisation and numerical simulations represent a powerful tool to analyse aerodynamic performances. This work proposes an advanced fluid-structure interaction numerical technique for the simulation of dragonfly wings, considered one of the most interesting model due to their complex flapping kinematic. The fluid subproblem, described by incompressible Navier-Stokes equations, is solved in a Finite Element Arbitrary-Lagrangian-Eulerian framework, while the solid subproblem is addressed using structural Finite Element, such as membranes and beams. Moreover, a novel remeshing algorithm based on connectivity manipulation and refinement procedure has been implemented to reduce element distortion in fluid mesh, thus increasing the accuracy of the fluid solution. Firstly, the deformation of a single hindwing has been studied. Secondly, the dragonfly model is enriched by incorporating the forewing and a simplified thorax geometry. Preliminary results highlight the complex dynamic of the fluid around the body as well as the efficiency of the proposed mesh generation algorithm
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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