Documents published in Scipedia

• New predictive models for ballistic limit of spacecraft honeycomb-core sandwich panels subjected to hypervelocity impact

  R. Carriere, A. Cherniaev

  eccomas2022.

  
  

  Abstract

  Parameters of the honeycomb core (such as cell size and foil thickness), as well as the material of the core, influence the ballistic performance of honeycomb-core sandwich panels in cases of hypervelocity impact (HVI) by orbital debris. Two predictive models capable of accounting for this influence have been developed in this study: one utilized a conventional approach based on a dedicated ballistic limit equation, while the other employed an artificial neural network trained to predict the outcomes of HVI on HCSP. BLE fitting and ANN training were conducted using a database composed of 46 numerical experiments, performed with a validated numerical model and ten physical tests derived from the literature. The new ballistic limit equation is based on the Whipple shield BLE, in which the standoff distance between the facesheets was replaced by a function of the honeycomb cell size, foil thickness, and yield strength of the HC material. The corresponding fit factors were determined by minimizing the sum of squared errors between the BLE predictions and the results of HVI tests listed in the database. The BLE was then tested against a new set of simulation data and demonstrated an excellent predictive accuracy, with the discrepancy ranging from 1.13% to 5.58% only. The artificial neural network was developed using MATLAB's Deep Learning Toolbox framework and was trained utilizing the same HCSP HVI database as was employed for the BLE fitting. The ANN demonstrated a very good predictive accuracy, when tested against a set of simulation data not previously used in the training of the network, with the discrepancy ranging from 0.67% to 7.27%. Both of the developed predictive models (the BLE and the ANN) are recommended for use in the design of orbital debris shielding for spacecraft, involving honeycomb-core sandwich panels.

  Abstract
  Parameters of the honeycomb core (such as cell size and foil thickness), as well as the material of the core, influence the ballistic performance of honeycomb-core sandwich [...]

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• Distinct element modelling of the seismic response of historical masonry constructions: insight on the out-of-plane collapse of façades

  P. Meriggi, S. De Santis, R. Fugger, R. Yanez Chura, G. de Felice

  eccomas2022.

  
  

  Abstract

  Façades belonging to historical masonry constructions typically fail by out-of-plane mechanisms. The estimate of their out-of-plane capacity is not a trivial task, due to the different possible collapse modes (overturning, bending, disaggregation, leaf separation, sliding) and to the discontinuous nature of masonry, influencing the non-linear seismic behaviour of walls. Simplified approaches, proposed by building codes, mainly based on the mechanics of the rigid block, may not always be suitable for the purpose. Indeed, they disregard the real morphology of masonry, which instead influences weaker failure mechanisms (such as disaggregation and leaf separation). Furthermore, they neglect the interaction of the façade with the rest of the building and its interlocking with transversal walls. These shortcomings can be overcome resorting to distinct element method (DEM), in which masonry is modelled as an aggregation of discrete units and no-thickness interfaces and the actual morphology of constructions is considered. In this paper, DEM is adopted to investigate the out-of-plane seismic behaviour of façades through non-linear analyses, by focusing on vertical bending and overturning failure mechanisms. The former is studied by comparing results of shake table tests on both single-leaf and double-leaf masonry walls to dynamic simulations in which real accelerograms are applied. The latter is analysed by performing non-linear static analyses on the Romanesque church of St. Maria Maggiore in Tuscania, Italy, by focusing on its façade. Distinct element method provided a realistic description of the behaviour of façades under earthquake loadings, in terms of both seismic capacity, crack pattern and failure mode.

  Abstract
  Façades belonging to historical masonry constructions typically fail by out-of-plane mechanisms. The estimate of their out-of-plane capacity is not a trivial task, [...]

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• Limit analysis of non-periodic masonry by means of Discontinuity Layout Optimization

  M. Schiantella, M. Gilbert, C. Smith, L. He, F. Cluni, V. Gusella

  eccomas2022.

  
  

  Abstract

  Masonry structures forming part of our historical heritage were often constructed using nonperiodic textures. In this case, unlike the situation for masonry with periodic textures, few methods are available to estimate wall strength and, moreover, available methods are often difficult to apply. In this work, Discontinuity Layout Optimization (DLO) is proposed as a method of estimating the failure load and associated mechanism of masonry walls constructed with non-periodic textures. In the first part three different textures are considered (periodic, quasi-periodic and chaotic) with a simplified scheme and a parametric analysis is undertaken, considering the variation of the height of the panel. A further classification for quasi-periodic textures is then provided and a DLO rigid block analysis is carried for square panels to show the influence of such textures. The results highlight the importance of the parameters considered in the analysis, and that DLO is a suitable method to investigate their influence.

  Abstract
  Masonry structures forming part of our historical heritage were often constructed using nonperiodic textures. In this case, unlike the situation for masonry with periodic [...]

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• Nonlinear macroelement based on Bouc-Wen formulation with degradation for the equivalent frame modelling of masonry walls

  D. Liberatore, D. Addessi, A. Paoloni

  eccomas2022.

  
  

  Abstract

  The equivalent frame model takes into account the shear and bending mechanisms that take place in piers and spandrels through plastic hinges. It represents a good compromise between accuracy and computational burden in the analysis of complex masonry walls. For the purposes of dynamic analysis, in addition to the hysteretic behaviour of the plastic hinges, it is also necessary to introduce their degradation of strength and stiffness. This study presents a macroelement model for piers and spandrels in which the bending mechanism is described by two hinges at the ends of the macroelement, and the shear mechanism by a shear link. They are characterized by a hysteretic behaviour with progressive plasticity, described by the Bouc-Wen model, and by degradation of strength and stiffness. Degradation is described through a damage parameter, which governs both strength and stiffness decay, and a flexibility increase parameter, which only governs stiffness reduction. In this way it is possible to independently control both strength and stiffness degradation. The model is applied to simulate experimental tests on panels, highlighting a good agreement with the experimental results.

  Abstract
  The equivalent frame model takes into account the shear and bending mechanisms that take place in piers and spandrels through plastic hinges. It represents a good compromise [...]

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• Mesh adaptation of ablating hypersonic vehicles

  J. Breil, C. Roche, M. Olazabal

  eccomas2022.

  
  

  Abstract

  The ablation of a vehicle during atmospheric reentry leads to a degradation of its surface state. Ablated wall interacts with the boundary layer that develops around the object. The deformation can be seen as a ripple or a roughness pattern with different characteristic amplitudes and wavelengths. The effect on the flow is taken into account either by means of modelizations or by direct simulation by applying the deformation to the mesh. Mesh regularization techniques can be used in order to take into account wall deformations during a simulation. In this work we apply our regularization directly to a mesh which has been already deformed. The meshes will be adapted for use in a parallel CFD Navier-Stokes code. A refinement of the mesh close to the wall is required to correctly capture the boundary layer, but also to accuratly represent the geometry of the wall deformation. For the numerical methods used, a constraint of orthogonality is added to the mesh impining on the wall.

  Abstract
  The ablation of a vehicle during atmospheric reentry leads to a degradation of its surface state. Ablated wall interacts with the boundary layer that develops around the object. [...]

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• Rocking Analysis for the bell tower of Sant’anna in Cervino

  A. Gesualdo, M. Guadagnuolo

  eccomas2022.

  
  

  Abstract

  In seismic prone areas ecclesiastical masonry complexes have shown a very high vulnerability, as detected after the last Italian earthquakes, such as those occurred in L'Aquila (2009), Emilia-Romagna (2012), Central Italy (2016), and Ischia (2017). These are particular types of aggregate buildings subjected often to partial collapses, due to the presence of highly vulnerable elements, like the bell towers. Preliminary analyses should including straightforward and quick methods are necessary. In this paper the bell tower vulnerability is analyzed taking into account the rocking behaviour of the tower only and considering the contribute of the entire ecclesiastical complex as a rigid body sliding with a fixed friction coefficient with respect to the foundations. It is shown that suitable values of maximum oscillations and horizontal displacements are obtained. The case study is the ecclesiastical complex of S. Anna in Cervino (Caserta, Italy).

  Abstract
  In seismic prone areas ecclesiastical masonry complexes have shown a very high vulnerability, as detected after the last Italian earthquakes, such as those occurred in [...]

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• Data-led Mechanical and Thermal Analysis of Layered Structures Based on Parametric Finite Element Analysis and Neural Network

  J. Ren

  eccomas2022.

  
  

  Abstract

  The mechanical and thermal behaviours of layered structures is of great importance for many advanced material systems and loading conditions. The responses of layered structures are controlled by the constitutive properties of each layer as well as the thicknesses. A comprehensive data-based approach is essential for both material analysis and design in direct or inverse problems. In this work parametric numerical modelling and Artificial Neural Network (ANN) are jointly used to develop data for layered structures. Mechanical and thermal finite element (FE) models are used to produce data for different material property and thickness domains. The use of ANN program is established and evaluated for different loading conditions. Using indentation as a typical case for mechanical loading and localized heating as typical example for thermal loading, ANN program was used to predict the behaviour of layered structures with different properties and layer thicknesses. Use of the data system in establishing dominating factors, synergetic effect on mechanical-thermal performance in advanced materials design is discussed.

  Abstract
  The mechanical and thermal behaviours of layered structures is of great importance for many advanced material systems and loading conditions. The responses of layered structures [...]

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• Explorative In-situ Analysis of Turbulent Flow Data Based on a Data-Driven Approach

  C. Gscheidle, J. Garcke

  eccomas2022.

  
  

  Abstract

  The Proper Orthogonal Decomposition (POD) has been used for several years in the post-processing of highly-resolved Computational Fluid Dynamics (CFD) simulations. While the POD can provide valuable insights into the spatial-temporal behaviour of single transient flows, it can be challenging to evaluate and compare results when applied to multiple simulations. Therefore, we propose a workflow based on data-driven techniques, namely dimensionality reduction and clustering to extract knowledge from large simulation bundles from transient CFD simulations. We apply this workflow to investigate the flow around two cylinders that contain complex modal structures in the wake region. A special emphasis lies on the formulation of in-situ algorithms to compute the data-driven representations during run-time of the simulation. This can reduce the amount of data inand output and enables a simulation monitoring to reduce computational efforts. Finally, a classifier is trained to predict characteristic physical behaviour in the flow only based on the input parameters.

  Abstract
  The Proper Orthogonal Decomposition (POD) has been used for several years in the post-processing of highly-resolved Computational Fluid Dynamics (CFD) simulations. While the [...]

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• Fluid-Structure Interaction Analyses of Amniotic Fluid with a Comprehensive Fetus Model Exposed to External Loading

  G. Kurgansky, J. Arias, E. Frankini, S. Echeverri, R. Chan-Akeley, M. Toma

  eccomas2022.

  
  

  Abstract

  A history of trauma during gestation is a risk factor for poor pregnancy outcomes. A multidisciplinary approach is vital to protect the mother's and the fetus' safety. Even though pregnancy-related trauma is uncommon, it is one of the leading causes of morbidity and mortality in pregnant women and fetuses. Hence, it is axiomatic to study the mechanism of the traumatic injuries to the fetus. The development of next-generation protective devices depends on our understanding of these mechanisms. Computational fluid-structure interaction simulations are used to study the effect of external loading on the fetus submerged in the amniotic fluid inside the uterus. A multitude of resulting variables is utilized to understand the cushioning function of the amniotic fluid on the fetus.

  Abstract
  A history of trauma during gestation is a risk factor for poor pregnancy outcomes. A multidisciplinary approach is vital to protect the mother's and the fetus' safety. [...]

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• Single-edge notched tension testing for assessing hydrogen embrittlement: a numerical study of test parameter influences

  R. Depraetere, M. Cauwels, W. De Waele, T. Depover, K. Verbeken, S. Hertelé

  eccomas2022.

  
  

  Abstract

  To evaluate the feasibility of the safe use of existing gas grids for the transport and storage of hydrogen gas, the phenomenon of hydrogen assisted degradation of steel used in the pipeline grid has to be examined. A finite element based framework developed for describing this phenomenon at the continuum scale is used to assist in the design and analysis of experimental characterisation of the tearing resistance. The framework is based on the complete Gurson model for ductile damage and takes into account damage acceleration due to the local hydrogen concentration, and the diffusion of hydrogen. Simulations representing single edge notched tension (SENT) fracture toughness tests of an API 5L X70 grade steel are performed and results are discussed in terms of crack growth resistance curves. Side grooves are included in the geometry of the SENT model to promote uniform crack growth. Different boundary conditions are employed, simulating ex-situ and in-situ hydrogen charging of specimens. Moreover, the effect of the applied deformation rate on the dynamics of hydrogen diffusion and the resulting toughness values is investigated. Accordingly, guidance regarding experimental SENT testing for the hydrogen assisted tearing resistance degradation is provided, in terms of test conditions (in-situ/ex-situ) and deformation rate.

  Abstract
  To evaluate the feasibility of the safe use of existing gas grids for the transport and storage of hydrogen gas, the phenomenon of hydrogen assisted degradation of steel used [...]

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