Documents published in Scipedia

• Quantification of time-averaging uncertainties in turbulence simulations

  D. Xavier, S. Rezaeiravesh, R. Vinuesa, P. Schlatter

  eccomas2022.

  
  

  Abstract

  An automatic method is proposed for the removal of the initialization bias that is intrinsic to the output of any statistically stationary simulation. The general techniques based on optimization approaches such as Beyhaghi et al. [1] following the Marginal Standard Error Rules (MSER) method of White et al. [16] were observed to be highly sensitive to the fluctuations in a time series and resulted in frequent overprediction of the length of the initial truncation. As fluctuations are an innate part of turbulence data, these techniques performed poorly on turbulence quantities, meaning that the local minima was often wrongly interpreted as the minimum variance in the time series and resulted in different transient point predictions for any increments to the sample size. This limitation was overcome by considering the finite difference of the slope of the variance computed in the optimization algorithm. The start of the zero slope region was considered as the initial transient truncation point. This modification to the standard approach eliminated the sensitivity of the scheme, and led to consistent estimates of the transient truncation point, provided that the finite difference time interval was chosen large enough to cover the fluctuations in the time series. Therefore, the step size for the finite difference slope was computed using both visual inspection of the time series and trial and error. We propose the Augmented Dickey­Fuller test as an automatic and reliable method to determine the truncation point, from which the time series is considered stationary and without an initialization bias.

  Abstract
  An automatic method is proposed for the removal of the initialization bias that is intrinsic to the output of any statistically stationary simulation. The general techniques [...]

  • 22
  •  read

• Classification of compromised DOFS data with LSTM neural networks

  V. Usenco, K. Lasn

  eccomas2022.

  
  

  Abstract

  Distributed optical fiber sensors (DOFS) are gaining momentum for in-situ condition monitoring and damage detection purposes. Although DOFS are a versatile sensing method enabling high-resolution strain and temperature mapping, they are also sensitive to mechanical vibrations. Vibrations are typically created by the ambient environment (e.g acoustic background, rotating equipment) which can produce high levels of measurement noise. With physical access to DOFS installations, the principle of acoustic or mechanical vibrations can also be utilized for malicious sensor tampering. The current lack of anomaly-detection systems suggests that practical DOFS applications would benefit from an automated analysis to detect and classify compromised measurements. Noise classification makes it possible to identify its source and potentially remove its effects from the measurement in the future. This would expand the commercial applications of DOFS systems significantly. Neural networks have been used for error detection in cyber-physical applications in numerous studies with high-accuracy results. Specifically, long short-term memory (LSTM) neural network models have become popular in recent years to classify anomalies in sequential e.g time-series data. Our investigation conducted a series of physical experiments using magnitude-controlled mechanical disturbances on bare free-hanging DOFS. Both random low-frequency vibrations at large displacement amplitudes and a constant high-frequency acoustic source at a low amplitude were employed. Experiments revealed that strain patterns are visually different with varying types and levels of disturbances. For the numerical analysis, statistics and machine learningbased approaches were applied for DOFS vibration noise classification, and their accuracy is discussed in detail. Results from the post-processing of compromised DOFS data suggest that it is possible to develop a vibration detection or classification system based on off-the-shelf DOFS interrogation equipment coupled with LSTM numerical tools.

  Abstract
  Distributed optical fiber sensors (DOFS) are gaining momentum for in-situ condition monitoring and damage detection purposes. Although DOFS are a versatile sensing method [...]

  • 7
  •  read

• Multiscale finite element modeling linking shell elements to 3D continuum

  D. Addessi, P. Di Re, C. Gatta, E. Sacco

  eccomas2022.

  
  

  Abstract

  The present paper investigates the response of masonry structural elements with periodic texture adopting an advanced multiscale finite element model, coupling different formulations at the two selected scales of analysis. At the macroscopic structural level, a homogeneous thick shell is considered and its constitutive response is derived by the detailed analysis of the masonry repetitive Unit Cell (UC), analyzed at the microlevel in the framework of the threedimensional (3D) Cauchy continuum. The UC is formed by the assembly of elastic bricks and nonlinear mortar joints, modeled as zero-thickness interfaces. The Transformation Field Analysis procedure is invoked to address the nonlinear homogenization problem of the regular masonry. The performance of the model in reproducing various masonry textures is explored by referring to an experimentally tested pointed vault under different profiles of prescribed differential settlements. The structural behavior of the vault is studied in terms of global load-displacement curves and damaging patterns and the numerical results are compared with those recovered by detailed micromechanical analyses and experimental evidences.

  Abstract
  The present paper investigates the response of masonry structural elements with periodic texture adopting an advanced multiscale finite element model, coupling different formulations [...]

  • 16
  •  read

• Validation of the temperature history during extrusion based additive manufacturing

  R. Hein, F. Winkelmann

  eccomas2022.

  
  

  Abstract

  Additive manufacturing (AM) is considered as a key technology for the efficient production of individualized components. The technique enables the tool-less production of complex geometries and designs that could not be realized cost-effectively with conventional manufacturing methods. The focus of this work is on the Fused Filament Fabrication (FFF), where a thermoplastic filament is extruded trough a nozzle. The material is deposited layer by layer until the final part is build. Thereby, high temperature gradients occur within the part when the hot material is deposited on the lower layers. During the printing process the lower layers are reheated several times so that the material properties are influenced even after the deposition has been made. The thermal history has major effects on crucial material properties such as the degree of crystallization or thermal and mechanical properties. An inadequate degree of crystallization influences both the structural properties such as the stiffness or the degree of bonding and the dimensional accuracy due to subsequent shrinkage effects. Additionally, the temperature gradients cause residual stresses which are partly relaxed to varying part deformations. The remaining stresses can lead to premature failures. To achieve a high and repeatable part quality as well as a low scatter in the final part dimension an in-depth process understanding is required considering the underlying material-process-partinteractions. In order to analyse these complex multiphysical processes, manufacturing process simulations are a suitable method. A main requirement for the numerical analysis of AM processes is the calculation of the thermal history as accurately as possible. The objective of this work is, therefore, to evaluate the prediction accuracy of currently available AM process simulation tools. For this purpose, a gcode-based AM process simulation of a cuboid is performed in order to calculate the transient temperature fields using the Abaqus AM plug-in from Dassault Syst`emes. The cuboid made of PETG is printed with a Prusa i3 MK3.

  Abstract
  Additive manufacturing (AM) is considered as a key technology for the efficient production of individualized components. The technique enables the tool-less production of [...]

  • 2
  •  read

• Voxel-based density registration of trabecular bone: a longitudinal HR-pQCT study of postmenopausal women

  J. Du, M. Huang, S. Li, V. Silberschmidt

  eccomas2022.

  
  

  Abstract

  Bone mineral density (BMD) is one of the important parameters used to characterise bone quality. Clinically, the only recommended method - dual X-ray absorptiometry - can only evaluate a two-dimensional areal BMD. Currently, three-dimensional localised BMD information is absent. HR-pQCT enables the assessments of 3D microstructure down to trabecular bone. Therefore, in this study, a voxel-based density registration (VDR) method is proposed to analyse the longitudinal changes of trabecular-bone density distribution. The VDR techniques were evaluated based on a six-month longitudinal study of five postmenopausal women. The time effect on localised changes of trabecular-bone mineral density was visualized and variations between different anatomical regions were quantified for the first time. Different distributions between anatomical regions were found in bone mineral density of trabecular bone (vBMDtrab), with a change of vBMDtrab at medial region (-0.56%) significantly higher than anterior (-1.58%) (p = 0.032). This study indicates that localised density changes might be used as a prior indicator for the effect of aging or other interventions.

  Abstract
  Bone mineral density (BMD) is one of the important parameters used to characterise bone quality. Clinically, the only recommended method - dual X-ray absorptiometry - can [...]

  • 9
  •  read

• Tangential differential calculus for curved, linear Kirchhoff beams with systematic convergence studies

  M. Kaiser, T. Fries

  eccomas2022.

  
  

  Abstract

  We propose a reformulation of linear Kirchhoff beams in two dimensions based on the tangential differential calculus (TDC). The rotation-free formulation of the Kirchhoff beam is classically based on curvilinear coordinates. However, for general applications in engineering and sciences that take place on curved geometries embedded in a higher-dimensional space, the tangential differential calculus enables a formulation independent of curvilinear coordinates and, hence, is suitable also for implicitly defined geometries. The geometry and differential operators are formulated in global Cartesian coordinates related to the embedding space.

  Abstract
  We propose a reformulation of linear Kirchhoff beams in two dimensions based on the tangential differential calculus (TDC). The rotation-free formulation of the Kirchhoff [...]

  • 12
  •  read

• Photoelasticity of YVO4 through first-principle calculation

  A. mirzai

  eccomas2022.

  
  

  Abstract

  The laser host materials undergo relatively small changes in their intrinsic properties due to various sources during an experiment. These sources are often related to temperature change and vibrations due to crystal mounting, which may cause stress-induced birefringence in laser host materials[1]. Birefringence is a phenomenon that causes optical anisotropy due to external load or residual stress. As a result, the final outcome of the experiments can be affected. One way to reduce probable noises is to predict the change in optical properties with respect to load. In the case of laser host materials, refractive index is one of the most prominent properties that undergoes change. The change in refractive index due to external load in the linear response regime is known as photoelasticity. Therefore, to predict the change pattern of refractive index in a crystal, one needs to know the elastic and photoelastic constants of the material.

  Abstract
  The laser host materials undergo relatively small changes in their intrinsic properties due to various sources during an experiment. These sources are often related to temperature [...]

  • 0
  •  read

• Effect of graphite-particle morphology on thermomechanical performance of compacted graphite iron: Numerical modelling

  M. Cao, E. Palkanoglou, K. Baxevanakis, V. Silberschmidt

  eccomas2022.

  
  

  Abstract

  Compacted graphite iron (CGI) is used in numerous applications, e.g., in the automotive industry, in tools and pipes, thanks to its excellent thermomechanical properties. Despite its extensive industrial use, its fracture at the microscale was not thoroughly investigated. Interfacial debonding is the main mechanism of fracture of CGI at the microscale and is based on the deformational incompatibility between graphite and the surrounding matrix. To study this decohesion, a two-dimensional micromechanical model of elliptical inclusions embedded in a metallic matrix is generated. An elastoplastic response is assumed for both constituents, and cohesive finite elements are applied to the graphite-matrix interface to simulate decohesion. A parametric analysis of interfacial features such as thickness and stiffness is performed to identify the effect of these parameters on debonding. The obtained results provide insights into the thermomechanical behaviour of CGI at the microscale and enable more effective modelling of this engineering alloy.

  Abstract
  Compacted graphite iron (CGI) is used in numerous applications, e.g., in the automotive industry, in tools and pipes, thanks to its excellent thermomechanical properties. [...]

  • 34
  •  read

• An efficient strategy of parcel modeling for polydispersed multiphase turbulent flows

  L. Bahramian, J. Muela, C. Oliet, C. Pérez-Segarra, F. Trias

  eccomas2022.

  
  

  Abstract

  A three-dimensional particle-laden two-phase turbulent flow by employing the Eulerian-Lagrangian method using multiphase Particle-In-Cell model is implemented to analyze the effects of parcel modeling. In order to achieve an optimal trade-off between accuracy and computational cost, a hybrid approach is proposed. This approach is a combination of two typical models: the volume fixed model, in which each parcel has the same volume, and the number fixed model, in which each parcel has the same number of particles. This approach is studied for the particle-laden turbulent flow benchmark case of Boreé et al. [1], with a mass loading of 22%, by using large eddy simulation through a two-way coupling between continuous and polydispersed phases.

  Abstract
  A three-dimensional particle-laden two-phase turbulent flow by employing the Eulerian-Lagrangian method using multiphase Particle-In-Cell model is implemented to analyze the [...]

  • 4
  •  read

• A numerical analysis of CO2 storage by adsorption using ZIF-8

  G. Fonseca da Silva, L. Rodrigues Capello Silva, M. Oliveira Pelic, B. Galelli Chieregatti, J. de Sá Brasil Lima

  eccomas2022.

  
  

  Abstract

  In 21st century, the reduction of CO2 concentration in the atmosphere is one of the most challenges of the humanity, specifically in the engineering. To start a possibility solution proposal, this work consisted in an analysis of carbon dioxide storage, using adsorption by ZIF8, a material that belongs to a class called Zeolitic Imidazolate Frameworks, which have high porosity, high thermal resistance and chemical stability. The main contribution of this work is to verify which parameters are relevant in the CO2 storage capacity by adsorption. To archive this goal, the study was made through computational simulations using the open source FreeFem++ software, inputting a specified quantity of pure CO2, entering in an 1,82 liter tank filled by the adsorbent until its internal pressure reached 1,0 MPa. First, the isothermal curve was validated with the literature, and after adjusting the parameters of adsorption model, called Dubinin Astakov (D-A). The simulations were performed, varying CO2 inlet flow, the tank’s aspect ratio with the values of 1; 1,9; 3; 5 and 7, and the external wall’s heat transfer coefficient with values of 5, 700 and 1000 W/m²K. Each simulation generated at each step the tank’s average and maximum temperatures, internal pressure, and the carbon dioxide adsorption density. All the simulations started with a standard temperature of 300 K and pressure of 100 kPa. Temperature and adsorption density distributions were generated to analyze in which part of the tank the adsorption is higher. The results showed that the regions where the temperatures are higher, the adsorption is lower, and in the end of the simulation, the simulations with the lower average temperatures had the higher adsorption density. The highest values of adsorption density were obtained with higher surface areas under the influence of forced convection, rather than natural convection, and with lower CO2 inlet flow. The highest adsorption density reached was 15,67 %, in a simulation with 50% of the tank’s volume per minute as CO2 inlet flow rate, aspect ratio of 7,0; and 700 W/m²K heat transfer coefficient. The average temperature obtained in the end of this simulation was 326,20 K and it took 3644 seconds for the tank to achieve the internal pressure of 1,0 MPa.

  Abstract
  In 21st century, the reduction of CO2 concentration in the atmosphere is one of the most challenges of the humanity, specifically in the engineering. To start a possibility [...]

  • 6
  •  read