bluuebunny/crossref_metadata_2025_split huggingface dataset:
Advancements in multi‐phase unsaturated porous media fracture
Authors: Heider Yousef , Sun WaiChing , Markert Bernd 
Published: January 2021

AbstractThe focus in this research is on introducing an accurate and stable numerical modeling framework and to compare the numerical results with experimental data from the literature for desiccation‐induced fracturing of unsaturated porous materials. The macroscopic modeling approach is based on combined continuum porous media mechanics and a diffusive phase‐field method (PFM). In the case of unsaturated porous media, one has to deal with more than one pore fluid (e.g. water and air). In this, the mechanical behavior can be expressed via using the Bishop's effective stress principle, which considers the total stress, the capillary pressure (air pressure minus water pressure), and saturation degree. The onset of desiccation‐induced fracturing is driven by the capillary pressure, which leads to degradation not only in the effective stresses but also in the capillary pressure itself. In this contribution, we discuss via a numerical example the effect of considering the air pressure variation on the cracking process and numerical stability. Besides, we briefly discuss the potential inclusion of machine‐learning material laws, such as for retention curves and anisotropic permeability, using, e.g., deep recurrent neural networks (RNN) to improve the model accuracy.
Efficient modeling of 3D geometries using octree‐meshes combined with SBFEM and transfinite elements
Authors: Gravenkamp Hauke , Saputra Albert A. , Eisenträger Sascha 
Published: January 2021

AbstractHierarchical octree‐meshes constitute an extremely efficient approach to representing complicated three‐dimensional structures. This is due to their capability to refine meshes locally and adjust the cell size over several orders of magnitude very effectively. As octree‐meshes consist solely of cuboid cells, the mapping of the geometry is trivial. On the other hand, exploiting these advantages in the context of finite‐element‐based modeling strategies is not straightforward due to the presence of hanging nodes. Recently, it has been demonstrated that the scaled boundary finite element method (SBFEM) provides a promising tool for creating discretizations based on such octree‐meshes. In this approach, each cell of the mesh is treated as a three‐dimensional SBFEM subdomain whose boundary is discretized using two‐dimensional finite elements. However, in previous work, an additional triangulation was still required to create conforming meshes on some of the subdomains' faces. In the current contribution, we improve this technique by combining the SBFEM with particular transition elements based on transfinite mappings. The combined approach requires only quadrilateral elements and circumvents any hanging nodes from the beginning. Furthermore, the utilization of transfinite mappings allows for local p‐ and h‐refinement and even combining different classes of shape functions without introducing additional constraints.
Numerical methods in Jost Bürgi's “Coss”
Authors: Ullrich Peter 
Published: January 2021

AbstractFrom 1579 to 1604 Jost Bürgi (1552–1632) worked at the court of the landgraves at Kassel both as constructor of scientific instruments and astronomical desk clocks and as astronomer and mathematician who analyzed the data gained by astronomical observations in order to design the technical devices that he constructed. Generally, little is known about the numerical methods which were used by craftsmen and engineers at that time. Bürgi, however, wrote up a manuscript on “Coss”, i. e., elementary algebra, in which he discusses several numerical methods to approximate zeros of polynomials.
A numerical study of the effect of phase evolution on residual stresses during cooling
Authors: Uebing Sonja , Brands Dominik , Scheunemann Lisa , Schröder Jörg 
Published: January 2021

AbstractThe consideration of residual stresses in forming processes is a promising opportunity to influence the final component's properties in a positive manner. Instead of their minimization, a targeted application of residual stresses can extend life time or durability and enhance manufacturability of metallic components. For this reason, detailed experimental and numerical analyses are an object of current research. Here, the cooling process is simulated in order to analyze the influence of the microscopic phase evolution on the macroscopic stress distribution in a cylinder with eccentric hole made of steel 100Cr6.
Data‐Driven simulation of inelastic materials using structured data sets and tangential transition rules
Authors: Ciftci Kerem , Hackl Klaus 
Published: January 2021

AbstractData‐driven computational mechanics replaces phenomenological constitutive functions by performing numerical simulations based on data sets of representative samples in stress‐strain space. The distance of modeling values, e.g. stresses and strains in Gauss‐points of a finite element calculation, from the data set is minimized with respect to an appropriate metric, subject to equilibrium and compatibility constraints, see [1]. Although this method operates well for non‐linear elastic problems, there are challenges dealing with history‐dependent materials, since one point in stress‐strain space might correspond to different material behaviour. In [2], this issue is treated by including local histories into the data set. However, there is still the necessity to include models for the evolution of internal variables. Thus, a mixed formulation is obtained consisting of a combination of classical and data‐driven modeling.In the presented approach, the data set is augmented with directions in the tangent space of points in stress‐strain space. Moreover, the data set is classified into subsets corresponding to different material behaviour, e.g. elastic and inelastic. Based on the classification, transition rules map the modeling points to the various subsets. The approach and its performance will be demonstrated by applying it to a model of small strain elasto‐plasticity with isotropic hardening.
Computational aspects of the weak micro‐periodicity saddle point problem
Authors: Bharali Ritukesh , Larsson Fredrik , Jänicke Ralf 
Published: January 2021

AbstractThe finite element implementation of the weak micro‐periodicity problem in computational homogenisation requires special preconditioning techniques owing to the saddle point formulation. The saddle point nature arises from enforcing periodicity constraints using Lagrange multipliers. This manuscript addresses the solution techniques and preconditioning options for the aforementioned problem in a monolithic setting. Furthermore, an alternative technique is proposed, based on a linear multi‐point constraints strategy. The latter approach eliminates the Lagrange multiplier Degrees of Freedom (DOFs), thereby preventing the break‐down of conventional incomplete LU (ILU) variants and multi‐grid method based preconditioners.
Numerical Simulation of Viscoelastic Fluid‐Structure Interaction Problems and Drug Therapy in the Eye
Authors: Drobny Alexander , Friedmann Elfriede 
Published: January 2021

AbstractThe vitreous is a fluid‐like viscoelastic transparent medium located in the center of the human eye and is surrounded by hyperelastic structures like the sclera, lens and iris. This naturally gives rise to a fluid‐structure interaction (FSI) problem. While the healthy vitreous is viscoelastic and described by a viscoelastic Burgers‐type equation, the aging vitreous liquefies and is therefore modeled by the Navier‐Stokes equations. We derive a monolithic variational formulation employing the arbitrary Lagrangian Eulerian framework which is solved using the finite element method. To allow large 3D simulations the implementation is parallelized. Furthermore we study the vascular endothelial growth factor (VEGF) therapy in the vitreous which is modeled by four coupled convection‐diffusion‐reaction equations with an additional coupling to the underlying flow.
Parameter study on a phase‐field model for fatigue fracture
Authors: Seiler Martha , Kästner Markus 
Published: January 2021

AbstractRecently, the problem of modelling fatigue fracture has been approached by the phase‐field method. The approach of Seiler et al. [1] focusses on a reduction of computational cost by combing the phase‐field method for fracture with a classic fatigue concept. For this model, we perform a parameter study analysing the influence of the fatigue degradation function and the crack propagation behaviour under cyclic loads with different mean loads. Eventually, we compare the results to a cyclic compact tension test.
On the Computation of Convergence Regions for Sequential Nonlinear Programming Problems
Authors: Mykhailiuk Ivan , Schäfer Kai , Flaßkamp Kathrin , Büskens Christof 
Published: January 2021

AbstractIn this work, we formulate and solve the problem of finding the ball of maximum radius around a local minimum of a nonlinear optimization problem, which is invariant with respect to the gradient descent method. This problem arises in the context of solving sequences of nonlinear optimization problems, in which one usually strives to converge to qualitatively similar solutions. We illustrate our idea with an example of a nonlinear function of two variables.
Simulation of weak‐inertia single‐phase flow in porous materials using Smoothed Particle Hydrodynamics
Authors: Krach David , Steeb Holger 
Published: January 2021

AbstractIntrinsic permeability of a porous material is a crucial material parameter in various application fields like e.g. geosciences, materials science, biological sciences and mechanical engineering. In contrast to the permeability often used in purely linear models, however, it is also a (nonlinear) function of the Reynolds number (Re) with the onset of the influence of inertial forces. In coarse‐grained continuum models the Forchheimer equation describes this incipient influence of viscous momentum exchange but it is based on the adaptation of experimentally obtained data and its range of validity remains a subject for discussion. Performing three‐dimensional Direct Numerical Simulations for single‐phase flow through porous media this work aims to show a smooth transition of effective intrinsic permeability within the interval 0.1 < Re < 1000. We use the fully‐Lagrangian meshless Smoothed Particle Hydrodynamics method (SPH) to solve the weakly compressible Navier‐Stokes equations for pore‐scale resolved flow in the so‐called weak‐inertia regime. Our implementation utilizes HOOMD‐blue thus allows us to perform massively parallel computations which are crucial for these applications.
A phase field approach to study of transformation induced micro–cracking in a martensitic phase transformation
Authors: Borzabadi Farahani Ehsan , Juhre Daniel 
Published: January 2021

AbstractIn this study, a coupled phase field (PF) method for the simulation of crack propagation and martensitic phase transformations is developed. In order to investigate the crack field and martensitic microstructure evolution the concept of the thermodynamic driving force, interfacial energy, the elastic energy, and the kinetic of phase field equations are introduced (time dependent Ginzburg Landau equation) [1]. The weak form and an algorithm for the solution of corresponding equations are implemented in the finite element program (FEAP). Since the phase transformation can form during the application of high amount of stresses, the influence of microcrack propagation on the formation of the martensitic phase has been studied. The crack tip produces high amount of concentrated stresses, which lead to a change in the distribution of the martensitic phases and it can also deviate the crack direction [2].
A machine learning enhanced structural response prediction strategy due to seismic excitation
Authors: Thaler Denny , Bamer Franz , Markert Bernd 
Published: January 2021

AbstractIn this contribution, we present a fast prediction approach to estimate response statistics of the crude Monte Carlo simulation using artificial neural networks. Hereby, the neural network is trained within an initial response subset, based on which a forecast can be evaluated in an early state of the Monte Carlo simulation.
The influence of compatibility equations of non‐linear elasticity on convergence for spectral method solutions
Authors: Flajs Rado 
Published: January 2021

AbstractIn structural mechanics the stresses are of a primary interest. Due to the required regularity of the approximation it is often inconvenient to obtain the stresses from the displacement methods. Mixed and hybrid methods are thus proposed to avoid this obstacle. The compatibility conditions should be fulfilled in order to obtain a unique solution.In this paper the compatibility equations of non‐linear elasticity are considered. Despite its very long history, this issue has not been satisfactorily resolved for non‐simply‐connected bodies until recently [1]. Its well known however, that the compatibility conditions are linearly dependent.The aim of the present contribution is to include the spectral methods [2] in order to improve the finite element solution procedure for the reversible elastodynamics problem [3], formulated for a large strain deformation with the deformation gradient tensor as one of the basic unknowns. In the case of the small strains the components of the deformation gradient tensor are of different magnitude. The main contribution is the derivation of the solution strategy in order to take this information into account. Applying this strategy to the implicit time integration method the exponent decrease of the condition numbers of the iteration matrices was achieved. Consequently the accuracy of the calculations should increase and the convergence for spectral method solutions should considerably improve. The theoretical findings are confirmed by a selected numerical example from structural mechanics.
On Spray Modeling with Quadrature‐Based Moment Methods
Authors: Pütz Michele , Pollack Martin , Hasse Christian , Oevermann Michael 
Published: January 2021

AbstractSpray modeling requires a proper representation of the dispersed phase and involves models for a variety of physical phenomena. On the population scale, a properly formulated population balance equation provides a complete statistical description of the particle system. However, in most cases the high dimensionality entails prohibitive computational costs. Quadrature‐based moment methods (QBMM) limit the description of particle populations to a set of only a few moments and thus considerably reduce computational complexity. In order to apply QBMM to sprays, models for many involved physical processes must be formulated consistently in the QBMM‐context. We study secondary droplet breakup with QBMM using a simple well‐established spray breakup model and simplified setups.
Model order reduction with dynamically transformed modes for the wave equation
Authors: Black Felix , Schulze Philipp , Unger Benjamin 
Published: January 2021

AbstractIn this contribution, we apply a recently introduced nonlinear model reduction framework based on dynamically transformed modes to the linear wave equation with periodic boundary conditions. We demonstrate that under reasonable assumptions, the reduced‐order model can be evaluated efficiently. Consequently, we obtain that the state variables of the reduced‐order model are constant or linear functions with respect to time.
On A Hybrid Concept for Approximating Self‐Excited Periodic Oscillations of Large‐Scaled Dynamical Systems
Authors: Kappauf Jonas , Hetzler Hartmut 
Published: January 2021

AbstractConcerning the approximation of self‐excited periodic oscillations in large‐scaled mechanical systems involving strong nonlinearities, this contribution suggests a concept for an efficient treatment. The presented Hybrid FD‐HB method takes the advantages of both schemes Harmonic Balance and Finite Difference to enhance the ratio of computational cost and accuracy for mechanical systems with many degrees of freedom. Within this contribution the residual equations, required when applying a NEWTON‐RAPHSON‐scheme, are derived and the method is applied to a stiff nonlinear mechanical system.
Computational Stability Analysis of Diffusion‐Deformation Processes at Finite Strains
Authors: Sriram Siddharth , Polukhov Elten , Keip Marc-André 
Published: January 2021

AbstractIn the present work, we investigate the onset of structural instabilities occuring in soft hydrophilic elastomers undergoing geometrically constrained swelling, which is characterized by large elastic deformations coupled with transient fluid diffusion. We model this phenomenon using a minimization‐based variational formulation having the deformation map and the fluid flux as the independent variables [1,3]. The space‐time‐discrete form of the variational problem is implemented using a conforming Raviart–Thomas‐type finite element formulation, which yields a symmetric and positive definite global tangent matrix for a stable deformation state. The onset of instability is captured as the point where the tangent matrix loses its positive definiteness [4,5]. To validate the proposed theoretical framework, we consider the surface wrinkling phenomenon observed in constrained hydrogel bilayers subjected to fluid diffusion. Variations in the critical buckling load and the corresponding mode number with respect to the geometry and material parameters of the bilayer are studied. These studies could, for instance, serve as potential design guidelines for applications of such materials in microsensors or in the fabrication of soft microgears for actuators, where the buckling modes are exploited to produce a desired mechanical output [8].
Efficient Simulation of Random Fields by Trigonometric Polynomial and Low‐rank Tensor
Authors: Liu Dishi , Vondřejc Jaroslav , Matthies Hermann 
Published: January 2021

AbstractWe propose a fast and economic representation of stationary random fields in trigonometric polynomial, utilizing the prowess of fast Fourier transform (FFT) and low‐rank tensor approximation. With the method we are able to generate large random fields with discretization size up to 220 which are otherwise well beyond the capacity of PCs. We also illustrate the approach to the specified property of random field by increasing rank in the tensor approximation.
Material optimization for controlling interfacial damage in composite structures
Authors: Singh Sukhminder , Stingl Michael 
Published: January 2021

AbstractAdvances in the computational modeling of fracture in solid structures have opened up possibilities for structural design optimization. The rate‐independent structural problem considering damage in its original form is ill‐posed due to the non‐unique nature of the solution, that poses difficulty in using gradient‐based algorithms for material optimization. To overcome this issue, this work introduces a viscosity parameter in the governing state equations and, thus renders the structural problem well‐posed. Material interfaces are modeled using an exponential, initially‐elastic cohesive law and linear elasticity is assumed throughout the structural domain. The time‐dependent fracture problem is solved via incremental variational approach with finite element discretization of the displacement field. Finally, the effectiveness of the method is illustrated by a material optimization example using a smooth gradient‐based solver with first‐order material sensitivities.
Inheritance mode and metabolic mechanism of the sulfoximine insecticide sulfoxaflor resistance in Oxycarenus hyalinipennis (Costa)
Authors: Wazir Shabana , Shad Sarfraz A 
Published: January 2021

AbstractBACKGROUNDDusky cotton bug (DCB), Oxycarenus hyalinipennis (Costa) (Hemiptera: Lygaeidae), is a key insect pest of cotton. It causes huge losses to cotton and many other economically important crops. Sulfoxaflor is a newly introduced systemic insecticide that is effective against many sap‐feeding insect pests such as aphids, whiteflies and true bugs. The present study was designed to characterize the inheritance of sulfoxaflor resistance in DCB. Moreover, the role of synergists in reducing sulfoxaflor resistance in DCB was also assessed.RESULTSA field population of DCB has developed 1132.0‐fold resistance to sulfoxaflor after 11 selected generations in the laboratory. Nonsignificant difference of reciprocal crosses was observed depending on the LC50 (median lethal concentration) values (95% confidence intervals overlapped), suggesting an autosomal mode of sulfoxaflor resistance inheritance. The degree of dominance of 0.7 for F1 (Sulfo‐Sel Pop ♀ × Lab‐Pop♂) and 0.6 for F1'(Sulfo‐Sel Pop ♂ × Lab‐Pop♀), respectively, suggested that sulfoxaflor resistance was incompletely dominant. According to the monogenic model, the number of genes involved to induce sulfoxaflor resistance revealed that sulfoxaflor resistance was polygenic in nature. The realized heritability (h2) value for sulfoxaflor resistance was 0.2. The synergists experiment indicated that esterases were involved in the sulfoxaflor resistance mechanism in DCB.CONCLUSIONSThe current results indicate that there is autosomal, incompletely dominant and polygenic inheritance of sulfoxaflor resistance in DCB. Our results would be helpful in delaying sulfoxaflor resistance against DCB in the field. © 2021 Society of Chemical Industry
Immigrants and legal status: Do personal contacts matter?
Authors: Cremaschi Simone , Devillanova Carlo 
Published: January 2021

AbstractUsing unique Italian survey data on both documented and undocumented immigrants, we empirically quantify the correlation between different types of personal contacts and immigrants' documentation probability, while also uncovering the contacts' indirect associations via immigrant labour market outcomes (employment status and job characteristics). Our results indicate that contacts with both natives and family members have a positive and quantitatively large effect on immigrant documentation probability, conditional on a large set of covariates. Contacts with members of the same ethnic group, by contrast, increase documentation probability only moderately, an effect explainable by these co‐ethnics' association with employment probability. Moreover, our findings support the hypothesis that native contacts can connect immigrants with jobs that favour documentation.