bluuebunny/crossref_metadata_2025_split huggingface dataset:
A remeshing approach for the finite cell method applied to problems with large deformations
Authors: Garhuom Wadhah , Hubrich Simeon , Radtke Lars , Düster Alexander 
Published: December 2021

AbstractThe finite cell method (FCM) is based on an immersed boundary concept with high‐order finite elements. When solving nonlinear problems using the FCM, it is often difficult to reach to the desired load step because of the large distortion of the mesh, particularly when badly broken cells are existing in the mesh. To overcome this problem, a global remeshing strategy is proposed to allow the nonlinear computation to proceed even for very large deformations where the distortion of the cells becomes significant. The core concept is to perform a computation up to a specific deformation state where the distortion of the cells becomes significant. Then, to continue the analysis, a new mesh is introduced. The performance of the proposed method is illustrated using two numerical examples of hyperelasticity.
Influence of passive mechanical properties in healthy and infarcted rat myocardium on the cardiac cycle
Authors: Martonová Denisa , Alkassar Muhannad , Seufert Julia , Holz David , Tuan Duong Minh , Reischl Barbara , Friedrich Oliver , Leyendecker Sigrid 
Published: December 2021

AbstractPassive mechanics plays an important role during the electromechanically coupled cardiac cycle and its behaviour strongly changes after myocardial infarction. In the present work, the cardiac tissue is modelled as a mixture of an active orthotropic intact myocardium and a passive transversely isotropic fibrotic scar structure. We apply the constitutive model on the fully electromechanically coupled simulation of a cardiac cycle using a generic geometry of a rat left ventricle. Finally, the ejection fractions for various parameter sets based on the fitting to experimental data in different animal species as well as for a varying amount of fibrosis are compared. We show that both, the choice of species‐specific passive material parameters and the amount of fibrosis, have a significant influence on the cardiac performance measured by the ejection fraction of the left ventricle.
Design improvement by a simulative investigation of the locomotion of a snake‐like soft robot
Authors: Lamping Frederik , de Payrebrune Kristin M. 
Published: December 2021

AbstractThis work aims to improve the design of a snake‐like soft robot in terms of its velocity of locomotion by a geometric model. Therefore, we determine the locomotion of the snake‐like soft robot as the result of a given excitation curvature and a given friction anisotropy between the robot and the ground.Varying the design parameters of the robot in the model allows to identify important parameters to increase the velocity of locomotion of the snake‐like soft robot. Whereas its body design is sufficient, the transverse friction of its artificial skin is the main parameter to be improved. The transverse friction can be adjusted by turning the scales of the artificial skin. The velocity of locomotion of the robot increases significantly by this simple trick.
Experimental Approach on Lamb Wave Dispersion Diagrams Using 2D Fourier Transformation and Laser Vibrometry
Authors: Barth Tilmann , Lammering Rolf 
Published: December 2021

AbstractLamb wave based Structural Health Monitoring (SHM) is a well‐known approach in today's mechanical engineering [1, 2]. One possible approach to determine the behavior of Lamb waves experimentally lies in the use of a frequency‐based approach using a 2d Fourier transform (2d‐FT) [3–5]. A closer look at this approach reveals that it has been used to represent dispersion relationships in large frequency ranges, but its potential for high accuracy has not been fully exploited. In this work a measurement and evaluation system for the experimental determination of dispersion diagrams is developed. It is able to cover large frequency ranges and it additionally shows a high degree of automation and accuracy. This allows a broadband examination of influences, which have only a small effect on the wave propagation. To verify the accuracy of the developed measurement and data evaluation method, experimental results of an aluminum specimen are compared with those from analytical solutions. A good agreement is achieved.
Reduced Flow Model for Plastics Melt Inside an Extrusion Die
Authors: Key Fabian , Ballarin Francesco , Eusterholz Sebastian , Elgeti Stefanie , Rozza Gianluigi 
Published: December 2021

AbstractIn this work, we study the application of Model Order Reduction (MOR) to the flow of plastics melt in an extrusion die. The process is described with a non‐linear model consisting of the Stokes equations in combination with a shear‐thinning material model. The reduction is performed through a Proper Orthogonal Decomposition (POD) approach with subsequent projection. We perform an a‐posteriori error analysis for a quantity of interest, based on the full‐ and reduced‐order solutions. Finally, we explore the computational speedup to prove the aptitude of the reduced model in the context of many‐query scenarios.
Integral‐type non‐local damage simulation of composites using mean‐field homogenization methods
Authors: Lenz Peter , Mahnken Rolf 
Published: December 2021

AbstractThis paper deals with non‐local damage behaviour of composites subjected to eigenstrains. Examples for eigenstrains are thermal, chemical or plastic strains and any combination. Modern materials are often decomposed into several distinct materials, e.g. some reinforcements and a matrix material. A manufacturing process for these modern materials often induces eigenstrains, reversible and non reversible. The induced eigenstrains could lead to an initial damage. It is known that damage leads to mesh dependent simulation results. Therefore, non‐local integral‐type damage for multiphase composites subjected to eigenstrains is considered.
Asymptotically Justified Boundary Conditions for a Viscoelastic Two‐Phase Fiber Model
Authors: Ettmüller Manuel , Arne Walter , Marheineke Nicole , Wegener Raimund 
Published: December 2021

AbstractIn this work we present asymptotically justified boundary/interface conditions for a viscoelastic two‐phase fiber model with flow‐enhanced crystallization. While the model equations are well‐established in the literature, the choice of boundary conditions is still under discussion as they might cause artificial layering at the crystallization onset. We show that our conditions avoid such layering, yielding a regularly perturbed boundary value problem with either continuous or discontiunous interface.
A semi‐analytical approach for the efficient predicition of thermally induced interface crack initiation at bi‐material free edges
Authors: Dölling Sebastian , Bremm Sophia , Kohlstetter Alexander , Felger Julian , Becker Wilfried 
Published: December 2021

AbstractIn the present study, thermally induced interlaminar crack initiation emanating from the free edge of a bi‐material junction is investigated by the example of a uniformly cooled epoxy‐glass bi‐material specimen taken from literature. For this purpose, the coupled stress and energy criterion within the framework of finite fracture mechanics is applied. Interlaminar stresses and energy dissipation due to crack onset are determined efficiently using the semi‐analytical scaled boundary finite element method (SBFEM). Moreover, the effect of the layer thicknesses on crack initiation is studied. For this purpose, dimensional analyses yield simple scaling laws for interlaminar stresses and energy dissipation with respect to the layer thickness such that only few model evaluations are required. The obtained results are compared to a finite element reference solution. For validation purposes, a cohesive zone model is applied additionally. Finally, the obtained predictions are compared to experimental findings from literature.
An extended version of the Intermediate Axis Theorem for a freely rotating rigid body
Authors: Leine Remco , Capobianco Giuseppe 
Published: December 2021

AbstractCurrent numerical schemes for 3D rockfall simulation are not able to correctly represent the stability properties of a freely rotating body. Here, we give a proof using Lyapunov functions of an extended intermediate axis theorem, which not only involves the angular momentum equations but also the orientation of the body. Inspired by the stability proof, we present a novel scheme which respects the stability properties of a freely rotating body and which can be incorporated in numerical schemes for the simulation of rigid bodies with frictional unilateral constraints.
Reanalysis of structures with varying cross‐sectional values based on influence functions
Authors: Carl Oliver , Hartmann Friedel , Zhang Chuanzeng 
Published: December 2021

AbstractDigital building data models are increasingly employed in the design and construction planning of buildings, so that almost the entire planning process is covered with three‐dimensional (3D) models. Starting with available detailed CAD data it is easy to generate 3D models for the design analysis. However, this comes with a price since the complexity of the 3D models requires a high computational effort. Considering the fact that the structural engineer often must investigate numerous design variants and system modifications during the planning stage to reach an optimal solution it makes sense to facilitate the multitude of these recalculations by an easy‐to‐use reanalysis technique.The approximation method we use for reanalysis is referred to as the Sensitivity Analysis with Green's functions (SAGF). The basic principles of the SAGF method can be found in [2,3]. It can be used very advantageously for reanalysis purposes, especially in the presence of complex computational models, and allows for a quick comparison of different design variants. In this paper, the method is used to determine how the system responses (internal forces, displacements) are affected by local changes in the stiffness of frame elements as they are typical for modifications of cross‐sectional values in steel structures such as when haunches are added at nodes.In [1] Abdank already presented an approach to determine the changes in structural response of beams from the subsequent consideration of haunches without performing a complete recalculation. In comparison to this, the presented SAGF method is applied very beneficially in connection with 3D models.Furthermore a 2D implementation of the presented reanalysis technique can be found in the program BE‐FRAMES [4]. It allows for a fast and simple “one‐click”‐reanalysis of various design variants since the designer can traverse the different designs forward and backwards – in a blink of an eye, with simple mouse clicks. An additional benefit is that the program can display influence functions for any displacement and force component so that with this graphical tool the engineer can predict the effects of design changes quite easily.
Learning Mechanical Systems by Hamiltonian Neural Networks
Authors: Dierkes Eva , Flaßkamp Kathrin 
Published: December 2021

AbstractThe great success of machine learning in image processing and related fields also motivated its application to dynamical system identification. In particular, neural networks are trained to learn equations of motion and thus provide an alternative to first‐principle modeling. While these black‐box algorithms are quite flexible regarding the system structure, they often have difficulties in learning basic physics laws which are intrinsic system properties. Recently, Hamiltonian neural networks (HNN) were introduced to explicitly learn the total energy of a system in order to overcome the lack of physical rules. However, Hamiltonian systems often also contain other structures such as symmetries in terms of further invariances. In this contribution, we extend HNN such they respect system invariances in addition to the Hamiltonian. The proposed extension leads to a trade off between energy conservation and conservation of invariance properties, which we investigate exemplarily.
Development of Fibrous SF/PCL Tympanic Membrane Scaffolds via Electrospinning: Modeling and Experimental Verification
Authors: Chen Zhaoyu , Benecke Lukas , Graetz Jonas , Hümbert Martina , Bornitz Matthias , Aibibu Dilbar , Cherif Chokri , Neudert Marcus 
Published: December 2021

AbstractThe ideal tympanic membrane (TM) replacement should meet the requirement of low resistance for dynamic pressures up to about 1 Pa but high resistance for large static pressures up to about 5 kPa. Although electrospun membranes have a great potential to be used as a TM replacement, it is necessary to adjust its microstructure in order to mimic the acousto‐mechanical properties of human TM. Hence, in this work, homogenization modeling and FEM simulation of the middle ear were used to combine the microstructure of electrospun membranes to its macroscale function as TM scaffolds. The simulation results were finally verified with experimental data.
Passage through resonance of two coupled exciters
Authors: Yüzbasioglu Tunc , Fidlin Alexander 
Published: December 2021

AbstractA minimal model of two coupled exciters is considered to investigate passage through resonance of self‐synchronizing systems. An averaging method for partially strongly damped systems [1] is used for asymptotic analysis. Stationary solutions of the system is derived and compared with previous work [2]. The dependency of such solutions on damping and excitation power is shown.
Study on model reduction for position optimization of acoustic black holes
Authors: Meyer Christian H. , Lerch Christopher , Rothe Sebastian , Hoffmann Steffen , Langer Sabine C. , Lohmann Boris , Rixen Daniel J. 
Published: December 2021

AbstractNoise radiation of plate structures is a common problem with the design of machines in mechanical engineering. Noise can be reduced by designing passive damping measures. One of these measures can be the application of an ‘acoustic black hole’ (ABH). It is a targeted adaptation of the thickness of plate‐like structures to direct the acoustically critical bending waves to a certain region – the ABH. There, an applied damping material can dissipate the vibration energy very efficiently. A major challenge in design of this measure is to find an optimal position of the ABH with respect to low vibrations. Optimization can be a tedious task, especially for complex industrial geometries where the dicretized equations of motion can have millions DoF.This contribution shows on the example of a study on a rectangular plate how model reduction can help to reduce the computational costs for this position optimization. Three different reduction methods are shown: First, a condensation of internal state variables from the viscoelastic evolution equations via Schur complement. Second, modal truncation applied to the condensed equations from the first method and third, moment matching applied to the full order model. Computed mean squared‐admittance levels are compared to show the accuracy of the methods. Speed‐up and accuracy results show that Schur complement and moment matching are promising approaches while a naive modal truncation can lead to wrong results.
Unique identification of stiffness parameters for nonlinear, anisotropic textile fabrics based on full‐field measurements on a single experiment
Authors: Makhool Lubna , Balzani Daniel 
Published: December 2021

AbstractThis work discusses a hybrid experimental‐numerical framework by which the stiffness parameters for nonlinear anisotropic textile fabrics can be uniquely identified. In the experimental part, a non‐standard setup has been designed to activate the deformation modes in a free energy function describing the mechanical material behavior. As a result, one inhomogeneous deformation field is captured by means of measuring full‐field kinematics, which includes sufficient information regarding the nonlinear response for varying deformation modes and intensities. In the numerical part, the measured full‐field data are inserted into a suitable discretized model of the specimen. Reformulating the free energy function to be linear in material parameters is considered in order to enable the definition of a quadratic objective function in terms of differences of discrete internal and external forces and hence to assure the uniqueness of the parameter identification. Finally, the sensitivity of the method to noisy data is studied.
Influence of Residual Stresses and Fiber Orientation on Smooth Muscle Contraction in Arterial Walls
Authors: Uhlmann Klemens , Balzani Daniel 
Published: December 2021

AbstractIn this contribution, we present a combined material model which couples three aspects of the arterial wall: a smooth muscle model embracing a stretch‐dependent calcium function, residual stresses induced by growth, and fiber reorientation. The model enables the investigation of the respective influence of all three aspects on each other. For this purpose, simulation results of arterial rings under varying intravascular pressure are analyzed.
On the forward simulation and cost functions for the ultrasonic material characterization of polymers
Authors: Itner Dominik , Gravenkamp Hauke , Dreiling Dmitrij , Feldmann Nadine , Henning Bernd , Birk Carolin 
Published: December 2021

AbstractIn this contribution, we describe the identification of the elastic properties of polymers in use‐specific setups, in particular the high‐frequency behavior (compared to quasi‐static or low‐frequency behavior that is usually characterized). Such a parameter search can be expressed as an inverse problem by comparing experimental measurements with adequate simulated data. We employ an axisymmetric scaled boundary finite element formulation to model the propagation of ultrasonic guided waves through cylindrical polymeric samples as the so‐called forward model of an optimization procedure. The simulated dynamic response is compared to a reference signal, and gradient descent‐based optimization is used to find the best possible material parameter fit. We present a cost function based on the wavelet convolution that results in a locally convex cost surface well suited for gradient descent optimization.
Stochastic modeling of transient neutral and stably‐stratified Ekman boundary layers
Authors: Klein Marten , Maier Roland Erich , Schmidt Heiko 
Published: December 2021

AbstractNeutral and stably‐stratified Ekman boundary layers (EBLs) are numerically investigated with a stochastic one‐dimensional turbulence (ODT) model. EBLs achieve the bulk‐surface coupling in Earth's atmosphere. They are numerically challenging due to transient and non‐universal turbulence properties even at small scales. ODT addresses this problem by distinguishing turbulent‐advective from molecular‐diffusive transport processes for a vertical column along which all relevant scales of the flow are resolved. We demonstrate the model's capabilities for economical, accurate, and stratification regime independent simulation of EBLs for the wind‐turning angle. ODT reproduces and extrapolates reference direct numerical simulation results consistent with observations. We conclude that ODT may be useful for modeling of atmospheric surface layers.
Nonlinear vibrations of rotating rings and shells under the usage of the finite element method
Authors: Schmidt Rico , Ams Alfons 
Published: December 2021

AbstractUntil now several studies of rotating structures like rings or shells have been done. To model such problems in a right way, geometrical nonlinearity has to be considered. Different methods can be used, to solve the corresponding eigenvalue problem. In this article the focus will be placed on the finite element method.In contrast to flat elements curved ones can cause some numerical inconveniences. They include a tremendous loss of convergence on the one hand, on the other hand the appearance of zero energy modes. In addition, centrifugal and Coriolis effects have to be taken into account. For certain examples the results of different FE‐models are shown and compared with global approaches as well as measurement data.
Phase field modeling and simulation of the evolution of twelve crystallographic martensite variants in austenitic parent grains – three‐dimensional simulations
Authors: Graf Marius , Kuntz Matthias , Autenrieth Hermann , Diewald Felix , Müller Ralf 
Published: December 2021

AbstractDue to its outstanding strength martensitic microstructures are of great importance in steels. Accordingly, this work deals with a simulation model capable of simulating the evolution of the martensitic microstructure. The focus is on the consideration of twelve crystallographic martensite variants corresponding to the Nishiyama‐Wassermann orientation relationship. For this, the phase field method, which regularizes sharp interfaces as smooth transition zone on basis of order parameters is used. The order parameters are used to interpolate between the initial parent phase austenite and the final product phase martensite. The evolution of a martensitic microstructure initiated by a supercooling under isothermal conditions is considered. In order to define the displacive characteristics of the martensite variants, the well‐known phenomenological theory of martensite crystallography is deployed. Three‐dimensional simulations using the finite element method in the small strain context show the applicability of the model to polycrystalline structures.
Variational Settings and Domain Decomposition Based Solution Schemes for a Coupled Deformation‐Diffusion Problem
Authors: Kiefer Björn , Prüger Stefan , Rheinbach Oliver , Röver Friederike , Roth Stephan 
Published: December 2021

AbstractOur general goal is to study chemo‐mechanical problems at various length scales by means of a fully‐integrated approach in terms of a co‐design of variational formulations and tailored parallel solvers. Based on prior experience in electro‐magneto‐mechanics [1], we know that the advantages and disadvantages of different variational settings for such coupled problems is always multifaceted. Theoretical characteristics, physical interpretability and numerical aspects may even play competing roles in this regard. In this work, we particularly consider the swelling of hydrogels as a first model problem featuring finite deformation coupled to the diffusive solute transport. The 3D finite‐element simulation of a free‐swelling cube under solute flux control is studied as a representative numerical example. As a first step towards seamless integration, we discuss the implementation of the hyperelastic subproblem into the open source finite element library deal.II which directly interfaces with the Fast and Robust Overlapping Schwarz (FROSch) preconditioner. Using this environment, an additional numerical study is performed with respect to the scaling behavior of the finite deformation Neo‐Hookean model in parallel computations.
Differentially definable functions: a survey
Authors: Jiménez-Pastor Antonio , Pillwein Veronika 
Published: December 2021

AbstractMost widely used special functions, such as orthogonal polynomials, Bessel functions, Airy functions, etc., are defined as solutions to differential equations with polynomial coefficients. This class of functions is referred to as D‐finite functions. There are many symbolic algorithms (and implementations thereof) to operate with these objects exactly. Recently, we have extended this notion to a more general class that also allows for good symbolic handling: differentially definable functions. In this paper, we give an overview on what is currently known about this new class.