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Results 1-20 of 104.
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Developing the AM G-code based thermomechanical finite element platform for the analysis of thermal deformation and stress in metal additive manufacturing process Mashhood, Muhammad ; Peters, Bernhard ; Zilian, Andreas et al in Journal of Mechanical Science and Technology (2023) The 3D printing process known as SLM involves the melting of the metal powder, which results in a melt-pool. When this melt-pool solidifies, the solidified metal undergoes cooling and reheating in the ... [more ▼] The 3D printing process known as SLM involves the melting of the metal powder, which results in a melt-pool. When this melt-pool solidifies, the solidified metal undergoes cooling and reheating in the presence of air and multiple laser passes for continuous material consolidation. As a result of such thermal cycles, the manufactured part develops permanent thermal deformation and residual stresses. The current work proposes the FEM and AM G-code based numerical strategy to qualitatively analyze the formation of such deformations and stresses at part scale. A multi-physics model was developed by coupling of transient thermal heat equation with non-linear structural solver. To mimic the consolidation of material with laser motion, the finite elements were activated as per the pattern of metal deposition under the influence of AM G-code. A numerical experiment was conducted to virtually manufacture the part with mechanical properties of 15--5PH stainless steel [1]. We found that the thermomechanical FEM model interfaced with the AM G-code translated data helps to evaluate the comparable trends of thermal deformation and residual stress results with already established studies. This demonstrates that with a given set of operational instructions, how the thermal conduction, convection and radiation drive the AM process by thermally loading the deposited material. Furthermore, the AM G-code interfacing facilitated the communication of laser scanning path with numerical FEM solver. We anticipate that such development may enable the manufacturing and simulation engineers to early estimate the possible final deformation of the AM fabricated part. Additionally, the developed strategy may also be the initial step for the physically informed neural networks to optimize the laser scan path for precise manufacturing of the metal parts. [less ▲] Detailed reference viewed: 69 (6 UL)Finite strain poro-hyperelasticity: an asymptotic multi-scale ALE-FSI approach supported by ANNs Dehghani, Hamidreza ; Zilian, Andreas in Computational Mechanics (2023) This contribution introduces and discusses a formulation of poro-hyperelasticity at finite strains. The prediction of the time-dependent response of such media requires consideration of their ... [more ▼] This contribution introduces and discusses a formulation of poro-hyperelasticity at finite strains. The prediction of the time-dependent response of such media requires consideration of their characteristic multi-scale and multi-physics parameters. In the present work this is achieved by formulating a non-dimensionalised fluid–solid interaction problem (FSI) at the pore level using an arbitrary Lagrange–Euler description (ALE). The resulting coupled systems of PDEs on the reference configuration are expanded and analysed using the asymptotic homogenisation technique. This approach yields three partially novel systems of PDEs: the macroscopic/effective problem and two supplementary microscale problems (fluid and solid). The latter two provide the microscopic response fields whose average value is required in real-time/online form to determine the macroscale response (a concurrent multi-scale approach). In order to overcome the computational challenges related to the above multi-scale closure, this work introduces a surrogate approach for replacing the direct numerical simulation with an artificial neural network. This methodology allows for solving finite strain (multi-scale) porohyperelastic problems accurately using direct automated differentiation through the strain energy. Optimal and reliable training data sets are produced from direct numerical simulations of the fully-resolved problem by including a simple real-time output density check for adaptive sampling step refinement. The data-driven approach is complemented by a sensitivity analysis of the RVE response. The significance of the presented approach for finite strain poro-elasticity/poro-hyperelasticity is shown in the numerical benchmark of a multi-scale confined consolidation problem. Finally, to show the robustness of the method, the system response is dimensionalised using characteristic values of soil and brain mechanics scenarios. [less ▲] Detailed reference viewed: 47 (5 UL)Optimal electrode coverage based on a new criterion for piezoelectric energy harvesters Shang, Lan ; ; Zilian, Andreas in Energy Conversion and Management (2023), 284 Piezoelectric energy harvesters (PEHs) are a promising alternative to conventional electrochemical batteries with the advantage of being self-powered and maintenance-free, but their application is ... [more ▼] Piezoelectric energy harvesters (PEHs) are a promising alternative to conventional electrochemical batteries with the advantage of being self-powered and maintenance-free, but their application is severely restricted by the low electric power output. It has been reported that the power output of PEHs can be enhanced by well-designed electrode coverage. A common design criterion for beam-like PEHs is based on the strain node to avoid electrode charge cancellation. This criterion, however, is not feasible for PEHs subject to complex spatio-temporal excitation patterns, where strain nodes change their position. This work proposes a new design criterion for optimal electrode coverage of beam-like PEHs based on the closed-form solution of the circuit equation that expresses voltage as a function of the beam’s dynamic response, specifically the cross-section rotation. The new criterion maximizes the averaged curvature of the beam segment covered by the electrode using data on the instantaneous rotation field. The improved physical significance and reliability of the presented criterion are discussed. The associated electrode optimization procedure is then exemplified for PEHs driven by fluid flow, which helps to realize a complex excitation pattern. Two numerical studies, both including a variety of combinations of fluid densities and inlet velocities, are performed to demonstrate that an optimal electrode configuration can be obtained with the proposed criterion. Comparison of different electrode configurations in above studies finally leads to useful conclusions on the power output and electrode configuration. [less ▲] Detailed reference viewed: 39 (0 UL)A Reissner-Mindlin plate formulation using symmetric Hu-Zhang elements via polytopal transformations Sky, Adam ; ; Hale, Jack et al E-print/Working paper (2023) In this work we develop new finite element discretisations of the shear-deformable Reissner--Mindlin plate problem based on the Hellinger-Reissner principle of symmetric stresses. Specifically, we use ... [more ▼] In this work we develop new finite element discretisations of the shear-deformable Reissner--Mindlin plate problem based on the Hellinger-Reissner principle of symmetric stresses. Specifically, we use conforming Hu-Zhang elements to discretise the bending moments in the space of symmetric square integrable fields with a square integrable divergence. The latter results in highly accurate approximations of the bending moments M and in the rotation field being in the discontinuous Lebesgue space , such that the Kirchhoff-Love constraint can be satisfied for t tending to zero. In order to preserve optimal convergence rates across all variables for the case t tending to zero, we present an extension of the formulation using Raviart-Thomas elements for the shear stress. We prove existence and uniqueness in the continuous setting and rely on exact complexes for inheritance of well-posedness in the discrete setting. This work introduces an efficient construction of the Hu-Zhang base functions on the reference element via the polytopal template methodology and Legendre polynomials, making it applicable to hp-FEM. The base functions on the reference element are then mapped to the physical element using novel polytopal transformations, which are suitable also for curved geometries. The robustness of the formulations and the construction of the Hu-Zhang element are tested for shear-locking, curved geometries and an L-shaped domain with a singularity in the bending moments. Further, we compare the performance of the novel formulations with the primal-, MITC- and recently introduced TDNNS methods. [less ▲] Detailed reference viewed: 53 (0 UL)Nonlinear local solver Habera, Michal ; Zilian, Andreas Scientific Conference (2022, August) Many engineering applications require solution of a global finite element problem coupled with nonlinear equations of local nature. Local in the sense, that for a known global state the local solution ... [more ▼] Many engineering applications require solution of a global finite element problem coupled with nonlinear equations of local nature. Local in the sense, that for a known global state the local solution could be found on cell-by-cell basis. Examples include plastic deformation problems, static condensation (hybridization) of displacement-stress formulation or just a simple nonlinear constitutive laws to be satisfied at each quadrature point. These types of problems either required special libraries and extensions in order to be solved with FEniCS (and FEniCS-X) tools, or lead to very slow implementations due to hacks and tricks needed to achieve the solution (e.g. monolithic schemes which increase the matrix problem size). In this talk a unified approach tailored for the current state of FEniCS-X interfaces is presented. The approach computes consistent global tangent operator for nonlinear problems. In addition, local equations are formulated symbolically in UFL, and their derivatives are therefore computed automatically. Several low-level examples (incl. plasticity with symbolic yield surface, nonlinear static condensation and materials with implicit constitutive laws) that demonstrate the main concepts are presented. Finally, high-level wrappers for this functionality are presented. These come as a part of package `dolfiny` (https://github.com/michalhabera/dolfiny). [less ▲] Detailed reference viewed: 52 (8 UL)Nonlinear analysis of thin-walled structures based on tangential differential calculus with FEniCSx Zilian, Andreas ; Habera, Michal Scientific Conference (2022, August) We present an approach to implement the Tangential Differential Calculus (TDC) for a variety of thin-walled structures (beams, membranes, shells) in the framework of nonlinear kinematics and/or material ... [more ▼] We present an approach to implement the Tangential Differential Calculus (TDC) for a variety of thin-walled structures (beams, membranes, shells) in the framework of nonlinear kinematics and/or material behaviour. In contrast to classical formulations the TDC describes kinematics, equilibrium and constitutive relation of the thin structure (as two-dimensional manifold) on the basis of a full three-dimensional deformation state. This allows to introduce the undeformed configuration of e.g. a shell directly in terms of a mesh of topological dimension 2 and geometrical dimension 3. Of particular interest is the use of finite elements of higher-order geometrical order to capture the (interpolated) curvature of the manifold with high accuracy. Numerical examples and reference implementations of this work to support nonlinear stress and post-buckling analyses (using a realisation of the classical arc-length method in FEniCSx) will be provided as a part of the package dolfiny (https://github.com/michalhabera/dolfiny). [less ▲] Detailed reference viewed: 59 (3 UL)MATERIAL MODELLING AND FINITE ELEMENT ANALYSIS IN METAL ADDITIVE MANUFACTURING Mashhood, Muhammad ; ; et al Poster (2022, May 31) The additive manufacturing (AM) is competent method for the manufacturing of complex metal parts with wider process flexibility. During manufacturing, the metal part repetitively undergoes heating and ... [more ▼] The additive manufacturing (AM) is competent method for the manufacturing of complex metal parts with wider process flexibility. During manufacturing, the metal part repetitively undergoes heating and cooling under the influence of laser passes and ambient conditions respectively. In turn, the material experiences the thermal strain and residual stress. The aim of the work is to predict them using certain material model. Where the solidified metal part from melt-pool is considered in current analysis. For numerical simulation, Finite Element Method (FEM) is chosen. The heat equation is first solved for thermal profile of AM Process. Afterwards, the structural analysis is performed with such thermal load. The non linear constitutive material model is utilised. For concerned material model, the temperature dependence upon the material properties is also implemented. The resulting Finite Element Analysis (FEA) platform offers the macro-scale thermal solution and the prediction of resulting plastic distortion in material. This prediction however has become more accurate when the variable material property, depending upon the temperature of analysis zone, is introduced. [less ▲] Detailed reference viewed: 38 (2 UL)Data-driven constitutive laws for hyperelasticity in principal space: numerical challenges and remedies Chau, Minh Vu ; Zilian, Andreas Presentation (2022, April 04) This contribution discusses a formalism for data-driven modelling of advanced materials with a special interest in the large deformation response of three-dimensional specimens. The underlying ... [more ▼] This contribution discusses a formalism for data-driven modelling of advanced materials with a special interest in the large deformation response of three-dimensional specimens. The underlying hyperelastic deformation problem is formulated in the principal space using principal stretches and principal stresses. The associated constitutive relation is consequently using principal quantities and captured by the parameter-free representation using a deep neural network. The presentation investigates certain physics-motivated requirements imposed on the architecture of the artificial neural network such as symmetry and objectivity criteria. The training phase of the constitutive ANN operator employs a loss function which ensures the identified consistency conditions. The prediction phase exploits a constitutive blending approach to stabilise the numerical solution procedure in the presence of typically local stretch/stress extrema. The presented approach is implemented using FEniCS and builds on symbolic representation of the ANN operator based on the Unified Form Language (UFL). The neural network is constructed, trained, and tested using PyTorch. Numerical benchmarks demonstrate the ability of the presented formalism to describe non-trivial load-deformation trajectories of 3D test specimens. [less ▲] Detailed reference viewed: 113 (7 UL)THE EVOLUTION OF THERMAL DISTORTION AND STRESSES AT MACRO SCALE FOR METAL ADDITIVELY MANUFACTURED PART Mashhood, Muhammad ; Zilian, Andreas ; Peters, Bernhard et al Scientific Conference (2022, February 05) [1] R.K. Ganeriwala, M. Strantza, W.E. King, B. Clausen, T.Q. Phan, L.E. Levine, D.W. Brown, N.E. Hodge, Evaluation of a thermomechanical modelfor prediction of residual stress during laser powder bed ... [more ▼] [1] R.K. Ganeriwala, M. Strantza, W.E. King, B. Clausen, T.Q. Phan, L.E. Levine, D.W. Brown, N.E. Hodge, Evaluation of a thermomechanical modelfor prediction of residual stress during laser powder bed fusion of Ti-6Al- 4V, Additive Manufacturing(2019), Vol. 27., 489–502. [2] M. S. Alnaes, J. Blechta, J. Hake, A. Johansson, B. Kehlet, A. Logg, C. Richardson, J. Ring, M. E. Rognes and G. N. Wells, The FEniCS Project Version 1.5, Archive of Numerical Software(2015), Vol. 3., 100:9–23. [less ▲] Detailed reference viewed: 30 (1 UL)AI-supported Modelling of Brain tissue as Soft Multiscale Multiphysics (Poroelastic) medium Dehghani, Hamidreza ; Zilian, Andreas Presentation (2022, January) Detailed reference viewed: 15 (2 UL)Stochastic porous media, towards a digital meniscus Obeidat, Anas ; Zilian, Andreas in Bulletin of the American Physical Society (2022) Detailed reference viewed: 23 (0 UL)Modeling and simulation of thin-walled piezoelectric energy harvesters immersed in flow using monolithic fluid–structure interaction Shang, Lan ; ; Zilian, Andreas in Finite Elements in Analysis and Design (2022), 206 Detailed reference viewed: 26 (1 UL)Thermo-mechanical modelling for metal additive manufacturing Mashhood, Muhammad ; ; et al Scientific Conference (2021, October 27) [1] Alnaes, M. S. Blechta, J. Hake, J. Johansson, A. Kehlet, B. Logg, A. Richardson, C. Ring, J.Rognes, M. E. and Wells, G. N. The FEniCS Project Version 1.5. Archive of Numerical Software(2015), Vol. 3 ... [more ▼] [1] Alnaes, M. S. Blechta, J. Hake, J. Johansson, A. Kehlet, B. Logg, A. Richardson, C. Ring, J.Rognes, M. E. and Wells, G. N. The FEniCS Project Version 1.5. Archive of Numerical Software(2015), Vol. 3., 100:9–23. [2] Carraturo, M. and Kollmannsberger, S. and Reali, A. and Auricchio, F. and Rank, E. An immersed boundary approach for residual stress evaluation in SLM processes. [less ▲] Detailed reference viewed: 33 (1 UL)Simulation of gas-dynamic, pressure surges and adiabatic compression phenomena in geometrically complex respirator oxygen valves Obeidat, Anas ; ; Bordas, Stéphane et al in Thermal Science and Engineering Progress (2021), 24 Gas-dynamic pressure surges and adiabatic compression phenomena are generally hard to predict numerically. In this contribution, we study the effect of the pressure reserve capacity on the compressible ... [more ▼] Gas-dynamic pressure surges and adiabatic compression phenomena are generally hard to predict numerically. In this contribution, we study the effect of the pressure reserve capacity on the compressible gas-dynamics pressure surge and adiabatic compression in a fitted respirator oxygen valve geometry. A three-dimensional remeshed smoothed particle hydrodynamics method for the simulation of isotropic turbulence is used, the method is coupled with Brinkman penalisation technique for flow simulation inside the complex valve geometry. Simulations are carried out for three different pressure reserve quantities, to replicate the opening of the valve, two time-based pressure inlet boundary condition functions were simulated along with an impulsively started scenario. A geometrical sensitivity analysis is provided, where the simulation is performed on a modified valve design which exhibits a damping effect on the gas dynamics and flow characteristics, which has a favourable effect on the valve functionality and safety. It is found that the capacity of the pressure reserve has a considerable effect on the simulated flow fields (velocity, temperature), as the temperature could rise 6.0X the reference temperature, and up to 2.7X the reference velocity. The numerical results are compared with a previous study carried out by Rotarex S.A., demonstrating that the remeshed particle-mesh method coupled with Brinkman penalisation provides a good quality simulation and the results are in agreement with the reference solution. [less ▲] Detailed reference viewed: 100 (11 UL)AI-aided, incremental numerical approach for fi nite strain poroelasticity: On the brain tissue deformation Dehghani, Hamidreza ; Zilian, Andreas Scientific Conference (2021, May 21) Detailed reference viewed: 56 (3 UL)Multiphysics Modelling of Flow-Driven Piezoelectric Energy Harvesters Shang, Lan ; Hoareau, Christophe ; Zilian, Andreas Poster (2021, May 21) Detailed reference viewed: 99 (8 UL)Semantic and Relational Spaces in Science of Science: Deep Learning Models for Article Vectorisation Kozlowski, Diego ; Dusdal, Jennifer ; Pang, Jun et al in Scientometrics (2021) Over the last century, we observe a steady and exponentially growth of scientific publications globally. The overwhelming amount of available literature makes a holistic analysis of the research within a ... [more ▼] Over the last century, we observe a steady and exponentially growth of scientific publications globally. The overwhelming amount of available literature makes a holistic analysis of the research within a field and between fields based on manual inspection impossible. Automatic techniques to support the process of literature review are required to find the epistemic and social patterns that are embedded in scientific publications. In computer sciences, new tools have been developed to deal with large volumes of data. In particular, deep learning techniques open the possibility of automated end-to-end models to project observations to a new, low-dimensional space where the most relevant information of each observation is highlighted. Using deep learning to build new representations of scientific publications is a growing but still emerging field of research. The aim of this paper is to discuss the potential and limits of deep learning for gathering insights about scientific research articles. We focus on document-level embeddings based on the semantic and relational aspects of articles, using Natural Language Processing (NLP) and Graph Neural Networks (GNNs). We explore the different outcomes generated by those techniques. Our results show that using NLP we can encode a semantic space of articles, while with GNN we are able to build a relational space where the social practices of a research community are also encoded. [less ▲] Detailed reference viewed: 119 (23 UL)ANN-aided incremental multiscale-remodelling-based finite strain poroelasticity Dehghani, Hamidreza ; Zilian, Andreas in Computational Mechanics (2021) Mechanical modelling of poroelastic media under finite strain is usually carried out via phenomenological models neglecting complex micro-macro scales interdependency. One reason is that the mathematical ... [more ▼] Mechanical modelling of poroelastic media under finite strain is usually carried out via phenomenological models neglecting complex micro-macro scales interdependency. One reason is that the mathematical two-scale analysis is only straightforward assuming infinitesimal strain theory. Exploiting the potential of ANNs for fast and reliable upscaling and localisation procedures, we propose an incremental numerical approach that considers rearrangement of the cell properties based on its current deformation, which leads to the remodelling of the macroscopic model after each time increment. This computational framework is valid for finite strain and large deformation problems while it ensures infinitesimal strain increments within time steps. The full effects of the interdependency between the properties and response of macro and micro scales are considered for the first time providing a more accurate predictive analysis of fluid-saturated porous media which is studied via a numerical consolidation example. Furthermore, the (nonlinear) deviation from Darcy’s law is captured in fluid filtration numerical analyses. Finally, the brain tissue mechanical response under the uniaxial cyclic test is simulated and studied. [less ▲] Detailed reference viewed: 80 (7 UL)Data science meets computational mechanics Dehghani, Hamidreza ; Zilian, Andreas Report (2021) Detailed reference viewed: 89 (4 UL)Frictional interactions for non-localised beam-to-beam and beam-inside-beam contact ; Lengiewicz, Jakub ; Zilian, Andreas et al in International Journal for Numerical Methods in Engineering (2021), 122(7), 1706-1731 This contribution presents the extensions of beam-to-beam and beam-inside-beam contact schemes of the same authors towards frictional interactions. Since the schemes are based on the beams’ true surfaces ... [more ▼] This contribution presents the extensions of beam-to-beam and beam-inside-beam contact schemes of the same authors towards frictional interactions. Since the schemes are based on the beams’ true surfaces (instead of surfaces implicitly deduced from the beams’ centroid lines), the presented enhancements are not only able to account for frictional sliding in the beams’ axial directions, but also in the circumferential directions. Both the frictional beam-to-beam approach as well as the frictional beam-inside-beam approach are applicable to shear-deformable and shear-undeformable beams, as well as to beams with both circular and elliptical cross-sections (although the cross-sections must be rigid). A penalty formulation is used to treat unilateral and frictional contact constraints. FE implementation details are discussed, where automatic differentiation techniques are used to derive the implementations. Simulations involving large sliding displacements and large deformations are presented for both beam-to-beam and beam-inside-beam schemes. All simulation results are compared to those of the frictionless schemes. [less ▲] Detailed reference viewed: 394 (7 UL) |
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