Documents published in Scipedia

• Modeling small scale processes in Antarctic sea ice

  R. Pathak, T. Ricken, S. Thoms, S. Seyedpour, B. Kutschan

  ECCOMAS 2024.

  
  

  Abstract

  The Antarctic sea ice, which undergoes annual freezing and melting, plays a signif icant role in the global climate cycle. Adverse environmental conditions in the Southern Ocean influence the extent and amount of ice in the Marginal Ice Zones (MIZ), the BioGeo- Chemical (BGC) cycles, and their interconnected relationships. The ’Pancake’ floes are a composition of porous sea ice matrix with interstitial brine, nutrients, and biological com- munities inside the pores. To realistically model these multi-phasic and multi-component coupled processes, the extended Theory of Porous Media (eTPM) is used to develop mod- els capable of simulating the different seasonal variations. All critical variables like salinity, ice volume fraction, and tem perature, among others, are considered and have their equations of state. The phase transition phenomenon is approached through a micro-macro linking scheme. A Phase- field solidification model coupled with salinity is used to model the micro-scale freezing processes and up-scaled to the macro scale eTPM model. This allows for modeling the salt trapped inside the pores. For the biological part, a BGC flux model for sea ice is also set up to simulate the algal species present in the sea ice matrix. Processes like photosynthesis are dependent on temperature and salinity, and are derived through an ODE-PDE coupling with the eTPM model. Academic sim ulations and results are presented as validation for the mathematical model. These high-fidelity models will eventually lead to their incorporation into large-scale global climate models.

  Abstract
  The Antarctic sea ice, which undergoes annual freezing and melting, plays a signif icant role in the global climate cycle. Adverse environmental conditions in the Southern [...]

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• Lightweight AMG preconditioners for CFD simulations on symmetric domains

  À. Alsalti-Baldellou, C. Janna, X. Álvarez-Farré, F. Trias

  ECCOMAS 2024.

  
  

  Abstract
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• Performance analysis of parallel-in-time techniques in modern supercomputers

  J. Plana-Riu, F. Trias, À. Alsalti-Baldellou, G. Colomer, A. Oliva

  ECCOMAS 2024.

  
  

  Abstract

  This paper aims to improve the e ciency of large-scale turbulent simulations by improving the arithmetic intensity of the operations. This is done by applying a parallel-in time ensemble averaging technique so that multiple ow states are run simultaneouslly in the same device. This transforms sparse matrix-vector products into sparse matrix-matrix products, improving the arithmetic intensity. The performance of these operations as well as the speed-ups generated in the operation itself, in the whole iteration and an estimation in the whole simulation is presented, so that for cases in which the averaging interval is signi cantlly longer than the transition interval, remarkable speed-ups in the whole iteration are obtained.

  Abstract
  This paper aims to improve the e ciency of large-scale turbulent simulations by improving the arithmetic intensity of the operations. This is done by applying a parallel-in [...]

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• A Hybrid Hexahedral Solid-shell Element with Self-equilibrated Stresses for the Geometrically Nonlinear Static Analysis of Composite Laminated Structures

  G. Zucco, F. Liguori, A. Madeo

  ECCOMAS 2024.

  
  

  Abstract

  Hybrid nite elements with self-equilibrated assumed stresses have proven to pro vide several advantages for analysing shell structures. They guarantee high performance when using coarse meshes and accurately represent the stress eld. Additionally, they do not require assumptions about the displacement eld within the element domain, and the integration is ef ciently performed only along their contours. This work exploits those advantages to develop a solid-shell nite element for the geometrically nonlinear static analysis of composite laminated structures. In particular, an eight-node nite element, which has 24 displacement variables and 18 stress parameters, is developed. The displacement eld is described only by translations, eliminating the need for complex nite rotation treatments in large displacement problems. A Total Lagrangian formulation is used with the Green-Lagrange strain tensor and the second Piola-Kirchho stress tensor. Thickness locking is cured using an assumed natural strain formu lation for the transversal normal stress, and the assumed stress eld eliminates shear locking. Then, for the analysis of linear-elastic problems, no domain integration is needed, and all the element operators are obtained by line integrals. The resulting formulation is e cient and allows for easy implementation. Computed numerical results show the accuracy and robustness of the presented element when used for both the linear elastic static and geometrically nonlinear elastic static analysis of composite laminated shell structures.

  Abstract
  Hybrid nite elements with self-equilibrated assumed stresses have proven to pro vide several advantages for analysing shell structures. They guarantee high performance when [...]

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• Hierarchic Large Rotation Shell Model with Warping: Isogeometric Formulation and Modeling of Alternating Stiff/Soft Laminates

  D. Magisano, A. Corrado, L. Leonetti, J. Kiendl, G. Garcea

  ECCOMAS 2024.

  
  

  Abstract

  This paper presents a hierarchic large rotation Kirchho-Love shell model with warping. Two unknowns are introduced for each through-the-thickness function warping, rep resenting its amplitudes in two directions tangent to the shell surface. NURBS are used to approximate reference surface displacement and warping amplitudes in the weak form. The transverse shear strains depend only on the warping parameters linearly and are free from lock ing. A patch-wise reduced integration avoids membrane locking and improves e ciency. Focus is given to composites made up of multiple sti layers coupled with soft interlayers. The alternat ing layup with high sti ness ratios induces a signi cant sectional warping with transverse shear strains concentrated in the soft layers. Two warping models are investigated: WI) all sti layers maintain the same director orthogonal to the deformed surface with independent transverse shear deformations of the soft layers; WZ) a single zigzag function linking these deformations. The numerical tests con rm the great accuracy of the hierarchic shell model in reproducing the solid solution with a small number of discrete parameters, provided that the correct warping model is chosen. WI is reliable for all alternating layups. WZ reduces the unknowns to ve per surface point, regardless of the number of layers, and is accurate for uniform soft layers

  Abstract
  This paper presents a hierarchic large rotation Kirchho-Love shell model with warping. Two unknowns are introduced for each through-the-thickness function warping, rep resenting [...]

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• Recent advances in the postbuckling analysis of composite laminated structures

  F. Liguori, G. Zucco, A. Madeo

  ECCOMAS 2024.

  
  

  Abstract

  The current demand for lightweight structures in a wide range of engineering appli cations leads to using thin-walled composite laminated structures whose behaviour is governed by buckling and postbuckling phenomena. Such a demand is pushing the borders of computational mechanics to enhance methods and algorithms for studying those structures' geometrically non linear responses. This work presents some of the authors' developments in analysing lightweight composite laminated structures. The literature survey introduces a family of nite elements known as MISS elements, where MISS stands for mixed isostatic self-equilibrated stresses. The description of those elements, which are derived from the Hellinger-Reissner functional, is followed by a discussion on their advantages concerning displacement-based elements when studying com posite laminated thin-walled structures. Subsequently, a framework for the postbuckling analysis of composite structures with the MISS-4C element that uses the Koiter multi-modal approach is presented.

  Abstract
  The current demand for lightweight structures in a wide range of engineering appli cations leads to using thin-walled composite laminated structures whose behaviour is governed [...]

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• Post-buckling behaviour and delamination growth in defected variable angle tow composite laminates

  D. Gaetano, F. Greco, L. Leonetti, A. Pranno, G. Zucco

  ECCOMAS 2024.

  
  

  Abstract

  Due to their specific strength and stiffness properties, composite materials are largely used in lightweight structural applications in aerospace, automotive and mechanical engineering. Understanding how these materials fail under service loads is a challenging aspect of designing advanced composite structures. In fact, the failure of composite laminated structures is often governed by complex interactions of multiple interlaminar failure and damage mechanisms. Among them, delamination is one of the damage modes requiring large attention due to the low interlaminar resistance between the different layers comprised in a composite laminate. In addition, this phenomenon may be triggered by defects introduced in the construction phase or by the presence of connections leading to stress concentrations. When coupled with buckling phenomena, delamination inevitably decreases the load-carrying capacity of lightweight composite structures. Variable Angle Tow (VAT) laminates have been proven to improve the buckling and post-buckling response of those structures significantly. However, little is known about the geometrically nonlinear behaviour of VAT composite laminates with delaminations. This work applies the cohesive finite element method to model delamination growth in VAT composite laminates containing initial defects under compressive loading conditions. Numerical simulations investigate the effects of the fibre angle variation on the geometrically nonlinear static response of VAT composite laminates compared to that of their classical straight fibre counterparts.

  Abstract
  Due to their specific strength and stiffness properties, composite materials are largely used in lightweight structural applications in aerospace, automotive and mechanical [...]

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• Numerical and analytical evaluation of resin flow during PCB pressing cycles

  C. Schipfer, J. Zuendel, Q. Tao, T. Krivec, P. Fuchs, M. Gramueller

  ECCOMAS 2024.

  
  

  Abstract

  This paper presents a comprehensive sequence of analytical methods for evaluating printed circuit board (PCB) pressing processes, augmented by numerical finite element (FE) simulations. The study considers the properties of the prepreg material, the structure of the PCB copper layer, and various pressing process parameters, all of which can be adjusted according to specific requirements. Our results are validated through experiments and compared with the established Squeeze Flow Model. The pro posed methodology identifies potential weaknesses in the design of the copper layer, material selection, and pressing parameters prior to production. Additionally, the implementation of this methodology in an interactive user interface allows for rapid and efficient results, facilitating timely decision-making and process optimization

  Abstract
  This paper presents a comprehensive sequence of analytical methods for evaluating printed circuit board (PCB) pressing processes, augmented by numerical finite element (FE) [...]

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• Computational analysis of non-proportional biaxial shear reverse experiments superimposed by different cyclic loads

  Z. Wei, S. Gerke, M. Brünig

  ECCOMAS 2024.

  
  

  Abstract

  This paper deals with anisotropic ductile damage and fracture behavior under low positive stress triaxialities. Novel tension–shear biaxial low–cycle experiments with different numbers of loading cycles (up to twenty) have been performed using a cruciform biaxially loaded specimen. During the experiment, a tensile preload is first imposed on the horizontal axis until it reaches 3kN; then, it is kept constant while different shear cyclic loading sequences are superimposed on the vertical axis until failure. All cyclic loadings are driven to a large strain range to investigate ductile damage, and the same amplitude is maintained for each repeated reverse loading cycle within a single loading pattern. In addition, numerical simulations are performed with an anisotropic stress-state-dependent plastic-damage continuum model, also considering the Bauschinger effect. The experimental and numerical analysis of the evolution of the first principal total strain and damage strains highlights the influence of the cyclic loading history on the material behavior. Moreover, fracture surfaces are examined by scanning electron microscopy to analyze the different mechanical performances at the micro-level

  Abstract
  This paper deals with anisotropic ductile damage and fracture behavior under low positive stress triaxialities. Novel tension–shear biaxial low–cycle experiments with [...]

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• Adaptive Refinement Techniques using Multiresolution Wave Propagation Simulations Guided by Inherent Convergence Indicators

  D. Dimitriou, A. Samara, D. Saravanos

  ECCOMAS 2024.

  
  

  Abstract

  The multiresolution finite wavelet domain method has been meticulously studied in wave propagation simulations. The multiresolution procedure always starts with the coarse solution, and then finer solutions can be superimposed on the coarse solution, until convergence is achieved. Based on remarkable observations on the multiple resolution components of the method, a residual-based convergence indicator that reveals convergence at the coarse solution is developed. This convergence metric is rapidly applicable and straightforward and can also divulge the spatial and temporal ranges/domains that the already obtained solution needs to be enhanced. In that way, an automatic adaptive refinement technique is proposed for the local enrichment of the solution, only in the specific grid points and time-steps that it is needed. A numerical case study regarding wave propagation in an inhomogeneous rod manifests the effectiveness and accuracy of the proposed automatic refinement methodology, as also the performance of the suggested convergence indicator.

  Abstract
  The multiresolution finite wavelet domain method has been meticulously studied in wave propagation simulations. The multiresolution procedure always starts with the coarse [...]

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