bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical investigations of polymer‐based fibre‐reinforced structures with fluidically actuated Compressible Constrained Layer Damping
Authors: Holeczek Klaudiusz , Koschichow Roman , Schlieter Tomasz , Ehrig Tom , Kostka Pawel 
Published: December 2018

AbstractLightweight‐focused design often leads to a problematic vibration susceptibility of designed components. To reduce potential environmental and health risks, excessive vibrations have to be mitigated preferably through lightweight‐compatible solutions. The presented studies aim at the establishment of almost weight‐neutral solutions for adaptive tuning of the dynamic behaviour of lightweight components. The proposed unique actuating principle is based on structural cavities generating evanescent deformations when supplied with fluidic medium. These cavities encapsulate compressible, viscoelastic elements which are combined with the surrounding layers and operate according to an extended principle of Constrained Layer Damping. The evanescent morphing is used to deliberately alter the geometrical and material properties of the viscoelastic elements through their compression in order to achieve a damping and stiffness capacity adaptation. The analysed Compressible Constrained Layer Damping (CCLD) object is configured as a three layered beam consisting of the load‐bearing structure as well as constraining layer and compressible viscoelastic layer. The main studies were conducted using a developed finite‐element model. Herein, the geometrical, material and load property range has been parametrised so that generalised conclusions about the CCLD dynamic behaviour could be drawn. The deformation kinematics of the CCLD under combined loads resulting from static tension and flexural vibrations has been analysed. Furthermore, the assessment of the dynamic behaviour adaptation potential for different compressible viscoelastic materials was carried out. The goal of this study was on the one hand to determine a feasible initial configuration of the CCLD for its successful application and on the other hand the assessment of its damping efficiency.
Simulation of thermoforming processes with directed air‐flow
Authors: Wagner Simon , Kayatz Fabian , Münsch Manuel , Majschak Jens‐Peter , Delgado Antonio 
Published: December 2018

AbstractThermoforming is a manufacturing process suitable for mass‐production of simply shaped plastic products. One of the main limitations of the common process is the resulting inhomogeneous wall thickness distribution. The authors show experimentally that it is possible to positively influence the wall thickness distribution by using directed air‐flow. In order to numerically reproduce the process, a simulation model is set up. The simulation results clearly show how the temperature distribution during deformation can be influenced.
Decoupling Structural Acoustic Systems: Investigation of Radiation Damping Mechanisms
Authors: Baydoun Suhaib Koji , Marburg Steffen 
Published: December 2018

AbstractIn the framework of the present project within the DFG priority program 1897 “Calm, Smooth and Smart,” dissipation of kinetic energy of vibrating structures into the acoustic far field is studied. It can be understood as radiation damping and is particularly relevant for weakly damped lightweight structures, music instruments and underwater applications. In this paper, the coupled equations of time‐harmonic elastodynamics and acoustics are addressed respectively by means of finite and boundary element methods and solved monolithically. The loss factor, which quantifies the extent of radiation damping, is determined subsequent to a harmonic analysis by relating radiated sound power to structure‐inherent power. First steps towards more efficient numerical formulations, which enable the consideration of radiation damping in structural simulations, are outlined. They comprise forming the Schur complement and a polynomial approximation of the resulting acoustic impedance matrices.
A direct method for dissipative dynamical systems by using the symplectic Brezis‐Ekeland‐Nayroles principle
Authors: Nguyen An Danh , Markert Bernd 
Published: December 2018

AbstractWe study a direct method for inelastic structures by using the symplectic Brezis‐Ekeland‐Nayroles variational principle, which provides a minimum regulation for whole trajectories. The null minimisation problem of the power balance is established and discretised by the use of the orthogonal collocation method. The proposed approach is illustrated with an example of a thick tube subjected to internal loadings. Numerical results are presented and compared with the analytical solutions.
A Multi‐fidelity Approach Using Physical and Mathematical Surrogates for Crash Optimization
Authors: Komeilizadeh Koushyar , Hefele Rafael , Duddeck Fabian 
Published: December 2018

AbstractIn the context of crash optimization, numerical simulations can be very time consuming, therefore efficient optimization algorithms are indispensable. If the original crash model is considered as the high‐fidelity (most accurate) one, low‐fidelity models trade accuracy for efficiency. A proper combination of high‐ and low‐fidelity models can lead to a more efficient optimization algorithm in total. We developed a new multi‐fidelity, or multi‐model optimization algorithm that is based on nonlinear crash simulations while being accelerated by gradients of the (initial) linear system used as low‐fidelity model.
Fast time‐explicit micro‐heterogeneous wave propagation
Authors: Maier Roland , Peterseim Daniel 
Published: December 2018

AbstractUsing explicit time stepping schemes in the context of wave propagation is very popular due to simplicity and fast computations. However, stability can only be guaranteed if a so‐called CFL condition holds that bounds the time step size with respect to the spatial mesh size. This is a severe restriction in case of micro‐heterogeneous media where spatial finescale features need to be resolved. We show how numerical homogenization in space both reduces the number of degrees of freedom in space and weakens the time step restriction.
A strong discontinuity approach to crystal plasticity theory
Authors: Fohrmeister Volker , Díaz Guillermo , Mosler Jörn 
Published: December 2018

AbstractIn this work, a novel, displacement‐driven approach to crystal plasticity based on embedded strong discontinuities (ESDA) is presented, cf. [1, 2]. In contrast to the classical strain‐driven approach, which connects the Schmid stress to the slip strain at a certain slip system, the novel approach applies a traction‐separation law to connect the Schmid stresses to the slip displacements. Surprisingly, both models show similar mathematical structures, which allows to develop a unifying algorithmic formulation. The elaborated algorithmic formulation is fully implicit and the inequalities characterizing rate‐independent crystal plasticity theory are solved efficiently by means of so‐called Fischer‐Burmeister NCP functions, cf. [3]. The resulting solution scheme is extremely robust – even for an arbitrary number of simultaneously active slip systems.
A CFD‐DEM approach to model the orientation and distribution of non‐spherical fibers in fresh concrete
Authors: Gerland Florian , Schomberg Thomas , Wünsch Olaf 
Published: December 2018

AbstractModern high performance concretes are reinforced by fibers to cast complex parts without reinforcing bars. The orientation and distribution of fibers influence the properties of the final solid and the flow properties of fresh concrete. Therefore it is important to predict the casting process adequately. A promising method for this is CFD‐DEM. The suspending phase is described as a continuum and can be solved using suitable methods such as Finite Volume Method (FVM). The suspended particles are modeled as rigid bodies and simulated using the Discrete Element Method (DEM).This work is based on the CFDEM® engine which uses OpenFOAM® for the suspending phase and LIGGGHTS® for the particles. The modeling of fluid‐particle interaction forces and the momentum coupling between the phases is of outstanding relevance for the applicability of this method. Therefore the influence of particle to mesh size ratio on the accuracy of the coupling as well as the mapping of particle quantities to Eulerian fields is investigated.
Computational homogenization of nematic liquid crystal elastomers based on Landau‐de‐Gennes theory
Authors: Nadgir Omkar , Rambausek Matthias , Keip Marc‐André 
Published: December 2018

AbstractNematic liquid crystal elastomers represent a group of materials, which combine elastic properties of rubber with orientational properties of liquid crystals. The present contribution proposes a variational homogenization principle for nematic liquid crystal elastomers. A symmetric and traceless tensorial quantity represents the nematic order parameter, which is used as a phase field. The model is implemented in a finite element framework and the validation is done with two as well as three dimensional nemato‐mechanical boundary value problems.
Investigations on different Fischer‐Burmeister functions applied to the modelling of ferroelectrics
Authors: Schulte Robin , Bartel Thorsten , Menzel Andreas , Kiefer Björn , Svendsen Bob 
Published: December 2018

AbstractDifferent selected approaches of Fischer‐Burmeister (FB) nonlinear complementarity problem (NCP) functions are investigated towards the local convergence properties and the possible parameter influences. The Fischer‐Burmeister functions are applied to a micromechanically motivated material model for ferroelectric materials. The particular model employed is a laminate‐based modelling approach to simulate the single‐ and polycrystalline tetragonal ferroelectric material behaviour. In this model, the occurring variant fractions are characterised via laminate fractions with additional inequality constraints. To solve the complementarity conditions of these internal variables, the FB approach provides a very efficient scheme compared to common solution schemes as, e.g. active‐set strategies.
Identification of Parameters on an Interpolated Function with Measurement Errors
Authors: Nostitz Niklas , Hendrik Kröger Nils , Ihlemann Jörn 
Published: December 2018

AbstractWhile the identification of material parameters via FEM is an important basis for efficient simulations, the identification itself leads to new problems. In general, each optimization step and error function evaluation is gained with high computational effort. To speed up the identification, an alternative interpolation algorithm is introduced with a gradient free optimization. The combination of this algorithm with a Levenberg‐Marquardt algorithm improves the results with uncertain data.
Constrained Topology Optimization of Dynamic Mechanical Systems
Authors: Held Alexander , Kohlsche Thomas 
Published: December 2018

AbstractWe present a topology optimization procedure for flexible multibody systems, which is subjected to time‐ and space‐dependent constraints. The flexible bodies are parameterized using the solid isotropic material with penalization approach. For the efficient solution of the optimization problem, the pointwise time‐dependent constraints are discretized and aggregated into a single constraint using the Kreisselmeier‐Steinhauser function. The procedure is tested by optimizing the mass of a flexible piston rod, while the deformation within the design domain is constrained.
Thermomechanical mortar contact problems with hierarchical refined NURBS for adhesion and anisotropic friction
Authors: Krüger Melanie , Schulte Jonathan , Dittmann Maik , Hesch Christian 
Published: December 2018

AbstractIn this contribution, we present a novel thermodynamically consistent contact formulation [1]. The thermomechanical framework is written in terms of the first and second law of thermodynamics, providing suitable restrictions on the constitutive law. The contact formulation involves mechanical and thermal contributions across the interface. For the mechanical contribution we apply different contact reactions in normal and tangential direction and decompose the Piola‐traction vector t on the interface. The modeling of contact pressure and adhesion leads to an exponential constitutive model in terms of the normal gap function. Furthermore, the tangential traction is additively decomposed into isotropic and anisotropic parts. For the spatial discretization we employ hierarchical refined NURBS (B‐Splines) and apply a variationally consistent mortar method for the thermomechanical contact interface, see e.g. [2]. In particular, linear Lagrangian shape functions are used for the discrete traction field. The capabilities of this framework are shown within a representative example.
Parameter Identification for Micro Underwater Vehicles
Authors: Duecker Daniel Andre , Kreuzer Edwin , Maerker Gunnar , Solowjow Eugen 
Published: December 2018

AbstractDetailed knowledge of model parameters is key for accurate forward simulations and control design. Identifying these parameters is especially challenging for underwater vehicles as they are subject to hydrodynamics effects which cannot be neglected in the equation of motion. In this work we present a method for hydrodynamic parameter identification of micro underwater vehicles which allow full‐size experiments due to their small size. The low‐cost experimental setup consists mainly on a free fall mass and an angular encoder. In an experimental series the hydrodynamic parameters of the micro underwater vehicle HippoCampus [1] are identified and compared with the analytically derived parameter set.
Time Optimal Path Tracking for Industrial Robots with Low Cost Computational Unit using Model Predictive Control
Authors: Jörgl Matthias , Gattringer Hubert , Müller Andreas 
Published: December 2018

AbstractThis paper deals with time optimal path tracking along prescribed geometric paths for robotic systems, like computerized numerical control (CNC) machines. These machines are typically controlled by a low cost microcontroller computational unit (MCU). Such MCUs are commonly used in industrial applications but are limited in view of computational performance. In many cases, these robotic systems have not only a MCU on which e.g. a motion controller is implemented, but also an associated desktop computer that serves as input device and transmits raw data to the MCU. Therefore, the calculation of the time‐optimal path following can be divided into two steps, where the paths are in our case defined as B‐Splines. On the desktop computer, an approximation of the solution is recursively calculated using a log‐barrier method, which solves a convex reformulated path tracking problem with velocity and torque constraints. This log‐barrier solution serves then as a reference generator for a model predictive controller (MPC), which is implemented as a trajectory tracking controller on the MCU. Due to the special formulation of the MPC, the continuity of the solution can be chosen arbitrarily. Thus the method is suitable for control of elastic systems, where C4 continuity is required to avoid vibrations. Assuming that the MPC works well as tracking controller, it is possible to consider only input constraints for the MPC and thus to minimize the computational effort. At last, a validation by means of simulation results is shown, in which the ACADO Toolkit is used for the MPC implementation.
Simulation‐based investigation of the influence of the micro‐structure and disorder on damage evolution in concrete
Authors: Gudžulić Vladislav , Khisamitov Ildar , Timothy Jithender J. , Meschke Günther 
Published: December 2018

AbstractConcrete is a material with a random disordered microstructure across multiple scales. The effective macroscopic material behavior of concrete is strongly dependent on the material properties and the interactions of the individual constituents at the micro‐scale. Failure of concrete as a quasi‐brittle material is generally characterized by fracture processes occurring within the fracture process zone (FPZ) that governs strain softening behavior, followed by localization of damage eventually leading to structural failure. The aim of this study is to investigate the influence of micro‐structure and initial disorder on damage evolution in a strongly heterogeneous material such as concrete. The principal mechanism of failure is assumed to be governed by a cascade of localized micro‐cracking and re‐distribution of stresses [1]. This mechanism is modeled within the scope of this work using a voxel‐sized finite element approximation of the disordered micro‐structure with a non‐uniform distribution of strengths for each material phase. Further, the behavior of the crack and the fracture process zone is linked to a simple stochastic model for analyzing disorder ‐ the fiber bundle model.
Numerical analysis of thin‐walled structures based on the scaled boundary finite element method
Authors: Wallner Milan , Birk Carolin , Gravenkamp Hauke 
Published: December 2018

AbstractThe efficient load‐carrying behaviour of thin‐walled shells is one of the reasons for the continuing popularity of these structural elements across several fields of engineering. Locking effects limit the applicability of traditional finite element analysis (FEA) and require significant user experience in this context. Thus, shell formulations that do not show the emergence of locking effects are still a research subject. Since modelling of plates using the scaled boundary finite element method (SBFEM) showed no occurrence of locking effects the SBFEM seems to be a promising technique to avoid locking when modelling shell structures. This contribution presents the numerical analysis of thin‐walled shells using the SBFEM. Several benchmark problems for shell elements have been investigated and the results for the Scordelis‐Lo roof are presented in detail.
Structural optimisation on multiple scales based on numerical homogenisation techniques
Authors: Kijanski Wojciech , Barthold Franz‐Joseph 
Published: December 2018

AbstractStructural analysis procedures and predictions of the physical behavior of complex structures with heterogeneous materials are usually based on the well‐known and established numerical homogenisation techniques with effective stress and material parameters, i.e. FE2 methods with effective

and

. The general goal is to enhance these methods with elements from variational sensitivity analysis and to formulate optimisation problems with objective functions, constraints and design parameters on multiple scales. The focus of this contribution is the sensitivity analysis of effective stresses or the corresponding Langrange multiplier 𝛌 respectively, which is incorporated in solution strategies based on the Lagrange formalism, as presented in [3] or [4]. The obtained sensitivity information can be used to setup optimisation problems for individual microscale representations and to control effective parameters within the overall optimisation procedure on single scales.
Single crystal plasticity – A mesoscale based approach for modeling the mechanics of additively manufactured Inconel 718
Authors: Kergaßner Andreas , Mergheim Julia , Steinmann Paul 
Published: December 2018

AbstractIn this contribution the mesoscopic material behavior of columnar grained Inconel 718 is modeled with a gradient enhanced crystal plasticity formulation and simulated by means of Finite Elements. A Voronoi tessellation based method is used to model the grain structure. On the mesoscale, the thermo‐mechanical behavior is modeled using a thermal gradient‐crystal‐plasticity model, allowing for relative misorientations on the grain boundaries. Computational homogenization and macroscopic experimental data are used to inversely identify elastic and plastic mesoscopic mechanical parameters. With the homogenized RVE at hand the parameters of a general anisotropic yield criterion for the macro scale are identified.
Internal Thickness Extrapolation
Authors: Töller Felix , Löhnert Stefan , Wriggers Peter 
Published: December 2018

AbstractModeling of thin joining zones is one application of Cohesive Zone Elements (CZE). Traction Separation Laws (TSLs) used as constitutive models in most CZEs that can be found in literature cannot fully capture all damage causing deformation modes induced by forming of hybrid components. An approach to overcome this deficiency by using bulk material models within a Cohesive Zone Element is presented.
An Anisotropic Phase‐Field Approach to Fracture in Coupled Electro‐Mechanics
Authors: Sridhar Ashish , Keip Marc‐André 
Published: December 2018

AbstractStructural reliability analysis of piezoelectric ceramics needs the modeling of failure under coupled electro‐mechanical actions. Based on experimental results available in the literature, we suggest a non‐associative dissipative framework where the fracture phase field is driven by the mechanical part of the coupled electro‐mechanical driving force. Proposed degradation functions account for different electrical crack boundary conditions. The modeling capability of the framework is demonstrated by means of representative numerical examples.
A Method to Quantify Material Parameter Uncertainties Resulting from Microstructure Variation based on Artificial Microstructures
Authors: Miska Niklas , Balzani Daniel 
Published: December 2018

AbstractThe macroscopic behavior of many materials is dependent from their microstructure morphology. As the morphology is often random, the macroscopic response of the material is uncertain. In this paper we propose a method to capture the statistics of the variability of the morphology of the real material, transfer this variability to artificial microstructures and perform virtual tests to quantify the uncertainty of the resulting macroscopic response.
Intrinsically locking‐free formulations for isogeometric beam, plate and shell analysis
Authors: Oesterle Bastian , Bieber Simon , Sachse Renate , Ramm Ekkehard , Bischoff Manfred 
Published: December 2018

AbstractIn this contribution a class of formulations for beams, plates and shells is presented, which intrinsically avoids locking, independent of the utilized discretization scheme. The key idea is the reparametrization of the kinematic equations to avoid locking on theory level – prior to discretization. Thus, the resulting formulations are locking‐free for any equal‐order interpolation. As demonstrator, we present both mixed and primal concepts for Timoshenko beams in both weak and strong form, as well as their theoretical relationships. Besides a weak form Galerkin‐type solution using B‐Splines, we show the generality of the presented concepts by employing isogeometric collocation based on the corresponding Euler‐Lagrange equations of the boundary value problem. The quality of both stress resultants and displacements is investigated. Although the underlying concept addresses beams, plates and shells, the present contribution illustrates the methodology for the Timoshenko beam.
Limitation of an adjustable two degree‐of‐freedom damper system for directional damping
Authors: Tan Aditya Suryadi , Dahlmann Martin , Sattel Thomas 
Published: December 2018

AbstractFor a better and more flexible damping, a smart damper is required. Such damper should be able to adjust the damping magnitude and damping direction independently. In this work, two degree‐of‐freedom (DOF) damping with two fixed orthogonal damping directions is investigated. The damping magnitude can be adjusted independently for each damping direction. This kind of adjustment can be realized through the implementation of field responsive fluid, such as electro‐ or magnetorheological fluid. In order to describe the behavior of the damping system, investigations were conducted for several combinations of damping magnitude and velocity directions. It is shown that fully independent damping adjustment is only possible to be realized along the fixed orthogonal damping directions. Therefore, it is not possible to control the direction of the damping independently with only two damping elements. It can be concluded, that the possibility to influence the damping direction is found to be still challenging.