References of "Zilian, Andreas 50003363"
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See detailHigh-performance modeling of concrete ageing
Habera, Michal UL; Zilian, Andreas UL

in Proceedings in Applied Mathematics and Mechanics (in press)

Long-term behaviour of concrete structural elements is very important for evaluation of its health and serviceability range. The phenomena that must be considered are complex and lead to coupled ... [more ▼]

Long-term behaviour of concrete structural elements is very important for evaluation of its health and serviceability range. The phenomena that must be considered are complex and lead to coupled multiphysics formulations. Such formulations are difficult not only from physical perspective, but also from computational perspective. In this contribution attention to computational efficiency and effective implementation is payed. Presented model for concrete ageing is based on microprestress-solidification (MPS) theory of Bazant [1], Kunzel’s model for heat and moisture transport [2] and Mazars model for damage [3]. Ageing linear viscoelastic response, which is immanent to MPS theory and concrete creep, leads to ordinary differetial equation for internal variables solved for every quadrature/nodal point. Numerical structure of the finite element discretisation is examined. Few simplifications on physical model lead to a very efficient linear algebra problem for which standard preconditioned Krylov solvers are reviewed. In parallel, weak and strong scaling tests are performed. All results are produced within open-source finite element framework FEniCS [4]. These models are usually a basis for more involved thermo-hygro-chemo-mechanical (THCM) models with migrating chemical species. It is anticipated, that presented results will help practitioners or other structural engineerers with the choice of suitable and efficient methods for long-term concrete modeling. [less ▲]

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See detailBeam-inside-beam contact: Mechanical simulations of slender medical instruments inside the human body
Magliulo, Marco UL; Lengiewicz, Jakub UL; Zilian, Andreas UL et al

in Computer Methods and Programs in Biomedicine (2020), 196

Background and Objective This contribution presents a rapid computational framework to mechanically simulate the insertion of a slender medical instrument in a tubular structure such as an artery, the ... [more ▼]

Background and Objective This contribution presents a rapid computational framework to mechanically simulate the insertion of a slender medical instrument in a tubular structure such as an artery, the cochlea or another slender instrument. Methods Beams are employed to rapidly simulate the mechanical behaviour of the medical instrument and the tubular structure. However, the framework’s novelty is its capability to handle the mechanical contact between an inner beam (representing the medical instrument) embedded in a hollow outer beam (representing the tubular structure). This “beam-inside-beam” contact framework, which forces two beams to remain embedded, is the first of its kind since existing contact frameworks for beams are “beam-to-beam” approaches, i.e. they repel beams from each other. Furthermore, we propose contact kinematics such that not only instruments and tubes with circular cross-sections can be considered, but also those with elliptical cross-sections. This provides flexibility for the optimization of patient-specific instruments. Results The results demonstrate that the framework’s robustness is substantial, because only a few increments per simulation and a few iterations per increment are required, even though large deformations, large rotations and large curvature changes of both the instrument and tubular structure occur. The stability of the framework remains high even if the modulus of the inner tube is thousand times larger than that of the outer tube. A mesh convergence study furthermore exposes that a relatively small number of elements is required to accurately approach the reference solution. Conclusions The framework’s high simulation speed originates from the exploitation of the rigidity of the beams’ cross-sections to quantify the exclusion between the inner and the hollow outer beam. This rigidity limits the accuracy of the framework at the same time, but this is unavoidable since simulation accuracy and simulation speed are two competing interests. Hence, the framework is particularly attractive if simulation speed is preferred over accuracy. [less ▲]

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See detailIsogeometric analysis of thin Reissner-Mindlin shells: locking phenomena and B-bar method
Hu, Qingyuan; Xia, Yang; Natarajan, Sundararajan et al

in Computational Mechanics (2020), 65(5), 1323-1341

We propose a local type of B-bar formulation, addressing locking in degenerated Reissner–Mindlin shell formulation in the context of isogeometric analysis. Parasitic strain components are projected onto ... [more ▼]

We propose a local type of B-bar formulation, addressing locking in degenerated Reissner–Mindlin shell formulation in the context of isogeometric analysis. Parasitic strain components are projected onto the physical space locally, i.e. at the element level, using a least-squares approach. The formulation allows the flexible utilization of basis functions of different orders as the projection bases. The introduced formulation is much cheaper computationally than the classical $$\bar{B}$$B¯ method. We show the numerical consistency of the scheme through numerical examples, moreover they show that the proposed formulation alleviates locking and yields good accuracy even for slenderness ratios of $$10^5$$105, and has the ability to capture deformations of thin shells using relatively coarse meshes. In addition it can be opined that the proposed method is less sensitive to locking with irregular meshes. [less ▲]

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See detailNon-localised contact between beams with circular and elliptical cross-sections
Magliulo, Marco UL; Lengiewicz, Jakub UL; Zilian, Andreas UL et al

in Computational Mechanics (2020), 65

The key novelty of this contribution is a dedicated technique to e fficiently determine the distance (gap) function between parallel or almost parallel beams with circular and elliptical cross-sections ... [more ▼]

The key novelty of this contribution is a dedicated technique to e fficiently determine the distance (gap) function between parallel or almost parallel beams with circular and elliptical cross-sections. The technique consists of parametrizing the surfaces of the two beams in contact, fixing a point on the centroid line of one of the beams and searching for a constrained minimum distance between the surfaces (two variants are investigated). The resulting unilateral (frictionless) contact condition is then enforced with the Penalty method, which introduces compliance to the, otherwise rigid, beams' cross-sections. Two contact integration schemes are considered: the conventional slave-master approach (which is biased as the contact virtual work is only integrated over the slave surface) and the so-called two-half-pass approach (which is unbiased as the contact virtual work is integrated over the two contacting surfaces). Details of the finite element formulation which is suitably implemented using Automatic Di fferentiation techniques are presented. A set of numerical experiments shows the overall performance of the framework and allows a quantitative comparison of the investigated variants. [less ▲]

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See detailContact between shear-deformable beams with elliptical cross-sections
Magliulo, Marco UL; Zilian, Andreas UL; Beex, Lars UL

in Acta Mechanica (2020), 231

Slender constituents are present in many structures and materials. In associated mechanical models, each slender constituent is often described with a beam. Contact between beams is essential to ... [more ▼]

Slender constituents are present in many structures and materials. In associated mechanical models, each slender constituent is often described with a beam. Contact between beams is essential to incorporate in mechanical models, but associated contact frameworks are only demonstrated to work for beams with circular cross-sections. Only two studies have shown the ability to treat contact between beams with elliptical cross-sections, but those frameworks are limited to point-wise contact, which narrows their applicability. This contribution presents initial results of a framework for shear-deformable beams with elliptical cross-sections if contact occurs along a line or at an area (instead of at a point). This is achieved by integrating a penalty potential over one of the beams’ surfaces. Simo-Reissner Geometrically Exact Beam (GEB) elements are employed to discretise each beam. As the surface of an assembly of such beam elements is discontinuous, a smoothed surface is introduced to formulate the contact kinematics. This enables the treatment of contact for large sliding displacements and substantial deformations. [less ▲]

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See detailData Centric Engineering and Data-Driven Modelling - Computational Engineering Lab Report 2019
Bordas, Stéphane UL; Peters, Bernhard UL; Viti, Francesco UL et al

Report (2019)

https://www.cambridge.org/core/journals/data-centric-engineering

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See detailToward fluid-structure-piezoelectric simulations applied to flow-induced energy harvesters
Hoareau, Christophe UL; Shang, Lan UL; Zilian, Andreas UL

Poster (2019, November 15)

The subject deals with the simulation of flow-induced energy harvesters. We focus in particular on the modelling of autonomous piezo-ceramic power generators to convert ambient fluid-flow energy into ... [more ▼]

The subject deals with the simulation of flow-induced energy harvesters. We focus in particular on the modelling of autonomous piezo-ceramic power generators to convert ambient fluid-flow energy into electrical energy. The vibrations of an immersed electromechanical structure with large amplitude have to be taken into account in that case. One challenge consists in modelling and predicting the nonlinear coupled dynamic behaviour for the improved design of such devices. The set of governing equations is expressed in integral form, using the method of weighted residuals, and discretized with finite elements using the open source package FEniCS. Preliminary results of separated problems using FEniCS will be detailed and discussed (e.g. Navier-Stokes with or without moving meshes, nonlinear elasticity, aeroelasticity and electromechanical coupling). The objective is to validate each problem independently before coupling all the phenomena in a monolithic framework. Those simulations involve nonlinearities at many levels of modeling. The perspective of using reduced order models to limit the computational cost (in time and memory) will be discussed in an outlook to this work. [less ▲]

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See detailPoroelastic material characterisation by means of Artificial Neural Network
Dehghani, Hamidreza UL; Zilian, Andreas UL

Presentation (2019, November 13)

Poroelastic problems require multiscale and multiphysics techniques that are expensive and time-consuming, which result in either several simplifications or costly experimental tests. The latter motivates ... [more ▼]

Poroelastic problems require multiscale and multiphysics techniques that are expensive and time-consuming, which result in either several simplifications or costly experimental tests. The latter motivates us to develop a more efficient approach to address more complex problems with an acceptable computational cost. In this manuscript, first, the necessary equations derived from Asymptotic homogenisation for poroelastic media are mentioned. Then, the variational formulation of the cell problems is carried out and solved by the open-source FE package FEniCS. This is followed by presenting the advantages and downsides of macroscale properties identification via asymptotic homogenisation and the application of Artificial Neural Network (ANN) to solve the issues stated as its downsides by means of bypassing the process of solving the cell problems. Finally, we study a practical example, namely, spatial dependent porosity (in macroscale) to demonstrate the feasibility of using the provided framework to include more details. Further applications, including growth and remodelling, are subjects of future articles. [less ▲]

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See detailOn predictive modelling of yield stress increase in fresh cement paste
Huang, Haiqin UL; Zilian, Andreas UL

in Proceedings in Applied Mathematics and Mechanics (2019), 19(1),

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See detailSimultaneous finite element analysis of circuit-integrated piezoelectric energy harvesting from fluid-structure interaction
Ravi, Srivathsan; Zilian, Andreas UL

in Mechanical Systems & Signal Processing (2019), 114

Flow-driven piezoelectric energy harvesting is a strongly coupled multiphysics phenomenon that involves complex three-way interaction between the fluid flow, the electromechanical effect of the ... [more ▼]

Flow-driven piezoelectric energy harvesting is a strongly coupled multiphysics phenomenon that involves complex three-way interaction between the fluid flow, the electromechanical effect of the piezoelectric material mounted on a deformable substrate structure and the controlling electrical circuit. High fidelity computational solution approaches are essential for the analysis of flow-driven energy harvesters in order to capture the main physical aspects of the coupled problem and to accurately predict the power output of a harvester. While there are some phenomenological and numerical models for flow-driven harvesters reported in the literature, a fully three-dimensional strongly coupled model has not yet been developed, especially in the context of flow-driven energy harvesting. The weighted residuals method is applied to establish a mixed integral equation describing the incompressible Newtonian flow, elastic substrate structure, piezoelectric patch, equipotential electrode and attached electric circuit that form the multiphysics fluid-structure interaction problem. A monolithic numerical solution method is derived that provides consistent and simultaneous solution to all physical fields as well as to fluid mesh deformation. The approximate solution is based on a mixed space-time finite element discretization with static condensation of the auxiliary fields. The discontinuous Galerkin method is utilized for integrating the monolithic model in time. The proposed solution scheme is illustrated in the example of a lid driven cavity with a flexible piezoelectric bottom wall, demonstrating quantification of the amount of electrical energy extractable from fluid flow by means of a piezoelectric harvester device. The results indicate that in order to make reliable predictions on the power output under varying operational states, the realization of strong multiphysics coupling is required for the mathematical model as well as the numerical solution scheme to capture the characteristics of flow-driven energy harvesters. [less ▲]

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See detailModel order reduction applied to ALE‐fluid dynamics
Baroli, Davide UL; Zilian, Andreas UL

in Proceedings in Applied Mathematics and Mechanics (2019)

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See detailNon-localized Contact Between Beams with Non-Circular Cross Sections
Magliulo, Marco UL; Zilian, Andreas UL; Beex, Lars UL

in Proceedings in Applied Mathematics and Mechanics (2019)

In this contribution, we introduce a contact formulation between beams finite elements with (hyper)elliptical cross sections. The contact scheme allows to model scenarios in which the contact area is ... [more ▼]

In this contribution, we introduce a contact formulation between beams finite elements with (hyper)elliptical cross sections. The contact scheme allows to model scenarios in which the contact area is finite or the contact area occurs along a line. Although some contact schemes are yet able to do this, they require one of the beams to have a circular cross section. Here however, we focus on non-circular cross-sections. Consequently, new projections are required, in which the beam surfaces are used explicitly to formulate contact kinematics. [less ▲]

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See detailPhase-field predictive model for setting of fresh self-compacting concrete
Huang, Haiqin UL; Zilian, Andreas UL

in Proceedings in Applied Mathematics and Mechanics (2018), 18(1),

The initial setting of fresh concrete is mainly caused by the dissolution of cement grains and the precipitation of calcium-silicate-hydrates during cement hydration. Progressing hydration drives the ... [more ▼]

The initial setting of fresh concrete is mainly caused by the dissolution of cement grains and the precipitation of calcium-silicate-hydrates during cement hydration. Progressing hydration drives the transition from a dense suspension to a porous solid phase. Fresh mixture of self-compacting concrete (SCC) can be considered as a phase-changing multi-component material and can be described as a continuum at the macro scale, interacting with a set of transport-reaction-diffusion processes which in turn are driven by phenomena at the level of the microstructure. This contribution focuses on a predictive model for the setting of fresh SCC where the liquid-solid phase transition is captured by a phase-field variable using the Ginzburg-Landau type free energy function. Hydration-related chemical reactions together with heat and mass transfer are volume coupled with the mechanical behaviour and determined by the environmental conditions. The weak form of the predictive model is discretised using the finite element method and implemented with the FEniCS computational framework. [less ▲]

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See detailModelling and analysis of flow-driven energy harvesting devices and associated reduced order models
Zilian, Andreas UL; Baroli, Davide UL

Scientific Conference (2018, June)

A specific class of energy harvester devices for renewable energy resources allows conversion of ambient fluid flow energy to electrical energy via flow-induced vibrations of a piezo-ceramic composite ... [more ▼]

A specific class of energy harvester devices for renewable energy resources allows conversion of ambient fluid flow energy to electrical energy via flow-induced vibrations of a piezo-ceramic composite structure positioned in the flow field. This energy converter technology simultaneously involves the interaction of a composite structure and a surrounding fluid, the electric charge accumulated in the piezo-ceramic material and a controlling electrical circuit. In order to predict the efficiency and operational properties of such future devices and to increase their robustness and performance, a mathematical and numerical model of the complex physical system is required to allow systematic computational investigation of the involved phenomena and coupling characteristics. The presentation will discuss a monolithic modelling approach that allows simultaneous analysis of the harvester, which involves surface-coupled fluid-structure interaction, volume-coupled electro-mechanics and a controlling energy harvesting circuit. Based on a finite element discretisation of the weighted residual form of the governing equations, time- and frequency-domain analysis enables investigation of different types of structures (plate, shells) subject to exterior/interior flow with varying parameters, and attached electrical circuits with respect to the electrical power output generated. Consequently, options for parametric reduced-order modelling of flow-driven energy harvesters will be discussed. [less ▲]

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See detailXDMF and ParaView: checkpointing format
Habera, Michal UL; Zilian, Andreas UL; Hale, Jack UL et al

Scientific Conference (2018, March 21)

Checkpointing, i.e. saving and reading results of finite element computation is crucial, especially for long-time running simulations where execution is interrupted and user would like to restart the ... [more ▼]

Checkpointing, i.e. saving and reading results of finite element computation is crucial, especially for long-time running simulations where execution is interrupted and user would like to restart the process from last saved time step. On the other hand, visualization of results in thid-party software such as ParaView is inevitable. In the previous DOLFIN versions (2017.1.0 and older) these two functionalities were strictly separated. Results could have been saved via HDF5File interface for later computations and/or stored in a format understood by ParaView - VTK’s .pvd (File interface) or XDMF (XDMFFile interface). This led to data redundancy and error-prone workflow. The problem essentially originated from incompatibilities between both libraries, DOLFIN and ParaView (VTK). DOLFIN’s internal representation of finite element function is based on vector of values of degrees of freedom (dofs) and their ordering within cells (dofmap). VTK’s representation of a function is given by it’s values at some points in cell, while ordering and geometric position of these points is fixed and standardised within VTK specification. For nodal (iso- and super-parametric) Lagrange finite elements (Pk , dPk ) both representations coincide up to an ordering. This allows to extend XDMF specification and introduce intermediate way of storing finite element function - intrinsic to both, ParaView and DOLFIN. The necessary work was done as a part of Google Summer of Code 2017 project Develop XDMF for- mat for visualisation and checkpointing, see https://github.com/michalhabera/gsoc-summary. New checkpointing functionality is exposed via write checkpoint() and read checkpoint() methods. [less ▲]

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See detailMultiscale Modeling of Discrete Mesomodels for Dry-Woven Fabrics
Magliulo, Marco UL; Beex, Lars UL; Zilian, Andreas UL

Scientific Conference (2018, March)

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See detailPhase-field predictive model for setting of fresh self-compacting concrete
Huang, Haiqin UL; Zilian, Andreas UL

Scientific Conference (2018, March)

Detailed reference viewed: 115 (11 UL)