bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical approximation for dynamic analysis based on NURBS and the Scaled Boundary Finite Element Method
Authors: Méndez Salas Arturo , Chasapi Margarita , Klinkel Sven
Published: December 2018

This contribution deals with a numerical modelling approach for time domain analysis. A parametrization method, established on NURBS as basis functions, is adopted in combination with the principles of the scaled boundary finite element method. This fusion allows a strong domain discretization minimizing the number of degrees of freedom since fewer points are necessary to represent a domain due to the nature of NURBS basis functions and the adopted boundary representation. In this proposal, the differential equation of motion for an idealized linear elastic, homogeneous and isotropic material is solved by applying the weak form along a boundary and scaling direction, and based on an implicit integration scheme. The adopted formulation is carried up to represent an open and a closed boundary. Both cases are under plane strain motion and their performance is studied, compared and validated with help of the conventional FEM. For the close domain, the analytical solution is also used and a damped system.
Reducing structure‐borne noise in thin‐walled structures by local thickness variations
Authors: Miksch Matthias , Aumann Quirin , Müller Gerhard
Published: December 2018

Thickness variations can modulate the propagation of bending waves in thin‐walled structures. A smooth reduction of the thickness results in a decreasing propagation speed and an increasing amplitude of the bending wave. Acoustic black holes (ABH) make use of this modulation to enhance the energy dissipation in the vicinity of this thickness diminution. Using the concept of ABH, no additional mass is needed to reduce structure‐borne noise. Therefore, this concept is suitable for reducing the vibrational energy in lightweight structures, which is vital in aerospace and automotive applications, among others. Locally modifying the thickness of a structure can significantly influence the global energy distribution in the structure. This contribution investigates the influence of different local thickness profiles on the global energy distribution. The results deliver insights for the design of such thickness variations in thin‐walled structures to improve their vibrational behavior. Several numerical models are evaluated to assess the dependency between the geometric design parameters of the thickness variation and the energy distribution in the structure.
A macroscopic model on the dynamic behaviour of open cell foams
Authors: Kirchhof Stephan , Ams Alfons
Published: December 2018

Open cell foams are widely used in engineering which includes an application in areas, where vibration excitations can act on the structures. Therefore dynamical properties as eigenfrequencies and natural modes are of great interest. Here a modelling approach of the dynamic behaviour of open cell foams by macroscopic stochastic models will be discussed. Based on a 3D computed tomography scan of the foam, statistic and spectral analysis has been carried out to determine the parameters of the stochastic model. Additionally a vibration measurement has been done to provide eigenfrequencies, frequency transfer functions and natural modes of the real foam, which can be compared with the simulation results of the macroscopic model.
A multi‐physics approach to investigate the influence of hydrogen on short fatigue crack propagation
Authors: Schippl Volker , Brück Sven , Christ Hans‐Jürgen , Fritzen Claus‐Peter
Published: December 2018

Hydrogen can substantially increase the material degradation under cyclic loading. During short fatigue crack growth, which is often the dominating stage during crack propagation, the crack growth rate is highly influenced by microstructural characteristics such as grain boundaries, the formation of slip bands and the local concentration of hydrogen at the crack tip. To address the problem of prediciting the short crack growth behavior, a multi‐physics approach is presented accounting for these interacting influences.
Towards tensor generalizations of TLS & core problem theory
Authors: Hnětynková Iveta , Plešinger Martin , Žáková Jana
Published: December 2018

Despite the wide attention, there are still several not well understood parts in the theory of total least squares (TLS) formulation of linear algebraic approximation problems. In particular, in the problems with multiple (matrix) right‐hand sides one can ask about the meaning of the nongeneric solution in the context of the original data, the nonexistence of the TLS solution for the so‐called irreducible core problems, etc. In the single (vector) right‐hand side TLS, these problems can be easily explained through the core problem theory or simply do not appear. Here we summarize, how the existing TLS and core problem theory can be generalized to problems with tensor right‐hand sides. Such generalization also gives a natural and wider context for further analysis of the above mentioned questions.
Modelling Thermo‐Viscoplasticity of Case‐Hardening Steels Over Wide Temperature Ranges
Authors: Oppermann Philip , Denzer Ralf , Menzel Andreas
Published: December 2018

The aim of this work is the development of a thermodynamically consistent fully coupled thermo‐viscoplastic material model for metals. The model is based on a split of the free energy into a thermo‐elastic, a thermo‐plastic and a purely thermal part and covers nonlinear cold‐work hardening and thermal softening. Nonlinear temperature dependent effects are accounted for the elastic moduli, the plastic hardening moduli, the thermal expansion, the heat capacity and the heat conductivity. Furthermore, strain rate‐dependency of the current yield stress is realized using a temperature dependent nonlinear Perzyna‐type viscoplastic model based on an associative flow rule. The model and its parameters are fitted against experimental data for case hardening steel 16MnCr5 (1.7131).
Implementation of a Phase Mixture Model for Rate‐Dependent Inelasticity
Authors: Eisenträger Johanna , Naumenko Konstantin , Altenbach Holm
Published: December 2018

Power plant components have to withstand complex thermo‐mechanical loads, i.e. frequent start‐ups and shut‐downs in combination with long holding times at high temperatures induce creep‐fatigue loads. Tempered martensitic steels with high chromium content feature high creep strength and corrosion resistance among other properties such that these alloys are often used for power plant components.

This contribution focuses on the simulation of the complex mechanical behavior of the alloy X20CrMoV12‐1 based on a multi‐axial phase mixture model. Within this model, we distinguish two phases: a hard and a soft phase. Both phases are connected via an iso‐strain approach, and nonlinear kinematic hardening as well as microstructural softening effects are taken into account by introducing a backstress and a softening variable as internal variables. The model is implemented into the commercial finite element code ABAQUS with a user material subroutine. For this purpose, the stress update algorithm and the consistent tangent operator are implemented based on the backward EULER method in combination with NEWTON‐RAPHSON iteration. Next, a wide range of benchmarks for uni‐axial as well as multi‐axial stress states is taken into account in order to verify the numerical implementation. Furthermore, a thermo‐mechanical fatigue test based on a typical sequence of start‐ups and shut‐downs of power plants is simulated.
Efficient Quantification of Free and Forced Convection
Authors: Glänzel Janine , Stoll Martin , Unger Roman
Published: December 2018

Thermo‐elastic deformations represent one of the main reasons for positioning errors in machine tools. Investigations of the thermo‐mechanical behaviour of machine tools often rely on accurate simulations involving large‐scale CFD simulations, where the heat transfer coefficient is computed. It has been shown that radial basis functions (RBFs) are a valid tool to reduce the number of CFD simulations by interpolation. We here present an efficient approach for the case of a three‐axis milling machine.
Modelling of nonlinear damage accumulation for the lifetime prediction of adhesively bonded joints
Authors: Kroll Ulrich , Matzenmiller Anton
Published: December 2018

Two enhancements of a continuum damage mechanics model with a creep and fatigue part are presented in order to capture nonlinear damage accumulation of structural adhesive joints subjected to service loading. The enhancements are applied to the fatigue part and have an effect on its lifetime prediction due to variable amplitude loading, while its prediction for constant amplitude loading is not affected. Both approaches are validated by means of the comparison of test data with numerical lifetime predictions for shear loading with variable amplitudes.
Towards a unified Lagrangian multi‐scale model for interacting particles
Authors: Bender Jens , Klar Axel , Kuhnert Jörg
Published: December 2018

The simulation of interacting particle systems by individual tracking in a Lagrangian framework can become virtually impossible in feasible time frames and for large problem sizes. This is why there are many approaches to describe the resulting behavior by continuous equations which are usually much more efficiently solved using an Eulerian grid on a larger scale. Motivated by the development of a Lagrangian generalized finite difference solver using moving point clouds, we work towards a method that can blend between the different scales in a unified framework. To this end, we derive a macroscopic model which still contains microscopic information in the form of an integral term. Different approximations of this term based on the point cloud configuration shall allow for a scaling between the representation of microscopic particles and the solution of a purely macroscopic model by the point cloud. Here we will present an extension of the model to interacting particle systems that involve damping and focus on the macroscopic model performance.
Model reduction of gyroscopic systems in ALE formulation with and without non‐linearities
Authors: Weidauer Tim , Willner Kai
Published: December 2018

Rotating systems are subject to gyroscopic influences which alter their dynamic behaviour. The Arbitrary Lagrangian Eulerian (ALE) formulation is a popular approach for related models, e.g. for the simulation of tire rolling contact. It allows for decoupling the rotational guiding motion from the relative deformation of the rotating structure. At the same time it complicates contact computations as the relative displacement between two material particles is not tracked naturally by the ALE observer. Model reduction techniques for (non‐linear) systems face additional challenges in this context, of which a variety is discussed here for common approaches such as the Second order modal truncation, the Krylov subspace method or the Craig‐Bampton method.
A geometric view on the kinematics of finite‐dimensional mechanical systems
Authors: Winandy Tom , Capobianco Giuseppe , Eugster Simon R.
Published: December 2018

Finite‐dimensional mechanical systems can be described in terms of a set of generalized coordinates and their time‐derivatives. In this case, the Lagrange equations of the second kind provide the equations of motion of these systems. The Volterra–Hamel–Boltzmann equations generalize the Lagrange equations of the second kind in the sense that they allow for more general velocity parametrizations. In this work, we show in the context of scleronomous finite‐dimensional mechanical systems that both sets of equations can be interpreted as being different chart representations of the intrinsic Euler–Lagrange equations on the tangent bundle over the configuration manifold of the mechanical system.
Investigation of Tenocyte Migration Behaviour by Application of the Mechanobiological Concepts
Authors: Dursun Gözde , Ürek‐Yavas Dilmin , Tohidnezhad Mersedeh , Markert Bernd , Stoffel Marcus
Published: December 2018

Cell migration plays a key role in tendon wound healing. The migration characteristics of tenocytes can be motivated by external signals. Our study aims to examine and enhance the migration activities of tenocytes by the appliance of uniaxial mechanical stretch using a custom‐made tensile bioreactor. Uniaxial mechanical stretching is applied to tenocyte‐seeded silicone as well as collagen membranes, which possess different material characteristics. The collagen membranes are considered a promising candidate for tendon tissue engineering due to its biological properties.
Study of the microstructure evolution caused by the strain‐induced crystallization in polymers
Authors: Aygün Serhat , Klinge Sandra
Published: December 2018

The strain‐induced crystallization (SIC) in polymers, such as in natural rubber, is a phenomenon manifesting itself as the natural reinforcement caused by the high deformation. Experimental data obtained from tensile tests show that the crystallization starts at a strain of 200‐400%, whereas, at maximum possible stretches of up to 700%, the volume fraction of the crystallinity reaches its highest degree. The growth and reduction of the crystalline regions cause a hysteresis in the stress‐stretch curve which indicates that the process has a dissipative character. In our work, the described material behavior is simulated by a micromechanical continuum model which involves the degree of network regularity as an internal variable. The focus is on the formulation of the dissipation potential simulating the change of the crystallinity degree during cyclic loading. The current approach furthermore simulates the dependence of the crystal orientation and form on the applied external load, which is achieved by assuming a specific coupling condition between the inelastic deformations and network regularity.
Towards structural optimization of lithium battery anodes
Authors: Werner Marek , Weinberg Kerstin
Published: December 2018

In lithium batteries, multicomponent compositions like LiCoO2 or LiFePO4 are used as cathode material and single substances like graphite are employed as anode material. In the latest battery developments anodes of silicon are introduced. Unfortunately, by now the high volumetric changes of silicon during intercalation — sometimes a factor of four has been reported — lead to pulverization of the anode and restrict long term use. To account for the intercalation induced volumetric swelling and phase segregation in a numerical simulation, the mechanical, thermal, chemical and electrical equations have to be coupled which leads to a complex description based on fourth order partial differential equations. Additionally, the structure of the anode needs to provide minimal compliance but maximal conductivity. In our contribution we provide a concept to combine these competing objectives with a multi‐physics model of battery charging.
Gauss‐Newton‐Secant method for solving nonlinear least squares problems
Authors: Iakymchuk Roman , Yarmola Halyna , Shakhno Stepan
Published: December 2018

We investigate the local convergence of the combined Gauss‐Newton‐Secant method under the classical and generalized Lipschitz conditions for solving nonlinear least squares problems with non‐differentiable operator. Instead of Jacobian, this method uses a sum of the derivative of the differentiable part and the divided difference of the non‐differentiable part of the operator. Numerical experiments are conducted on test problems.
Numerical Shape Optimization to Decrease Failure Probability of Ceramic Structures
Authors: Bolten Matthias , Gottschalk Hanno , Hahn Camilla
Published: December 2018

Ceramic is a material frequently used in industry because of its favorable properties. Common approaches in shape optimization for ceramic structures aim to minimize the tensile stress acting on the component, as it is the main driver for failure. In contrast to this, we follow a more natural approach by minimizing the component's probability of failure under a given tensile load. Since the fundamental work of Weibull [3], the probabilistic description of the strength of ceramics is standard and has been widely applied. Here, for the first time, the resulting failure probabilities are used as objective functions in PDE constrained shape optimization. To minimize the probability of failure, we choose a gradient based method combined with a first discretize then optimize approach. For discretization finite elements are used. Using the Lagrangian formalism, the shape gradient is calculated via the adjoint equation at low computational cost. The implementation is verified by comparing it with a finite difference method applied to a minimal 2d example. Furthermore, we construct shape flows towards an optimal shape in the case of a simple beam.
Gradient‐enhanced ductile damage — a finite deformation framework with application to DP800
Authors: Sprave Leon , Menzel Andreas
Published: December 2018

Gradient‐enhanced ductile damage is implemented in the finite element method by means of an additional field variable, representing non‐local damage which is linked to the local damage variable. At material point level the isotropic damage formulation uses exponential damage functions to circumvent further constraints on the value set of the local damage variable. The ductility of the model is achieved by a coupling of damage to finite strain plasticity. In a multisurface approach the onset of damage and plasticity is each governed by damage and yield criteria respectively. Linear and exponential isotropic hardening is implemented. With the help of the F‐bar method the results of the finite element simulation exhibit mesh independent behaviour. In order to model the behaviour of DP800 with the material model discussed here, elastic and plastic parameters are identified.
Investigating the Reynolds number dependency of the scalar transfer to a wall using a stochastic turbulence model
Authors: Klein Marten , Schmidt Heiko
Published: December 2018

We numerically investigate the Reynolds number dependency of the transport of a passive scalar in incompressible, fully‐developed turbulent channel flows. The stochastic one‐dimensional turbulence (ODT) model is used to make such numerical simulation feasible up to the friction Reynolds number Reτ = uτ δ/ν ≈ 5200 (channel half‐height δ, friction velocity uτ, kinematic viscosity ν) in the Schmidt number range 1 ≤ Sc = ν/Γ = 400 (mass diffusion coefficient Γ). The ODT simulations exhibit a turbulent boundary layer for which we show that the simulated mass transfer coefficient K+ follows the functional dependency suggested by Schwertfirm and Manhart, Int. J. Heat Fluid Flow 28, 1204–1214 (2007). The agreement is good for Sc ≤ 25 but a different scaling is obtained for Sc ≥ 49 investigated.
Couette flow with geometrically induced unsteady effects
Authors: Scholle Markus , Marner Florian
Published: December 2018

Film flow over surfaces containing topography is a key feature of a number of coating technologies. To date, detailed theoretical investigations of the same, underpinned by the long‐wave approximation, have been used to study the nature of the associated free‐surface disturbance formed; the internal flow structure being more‐or‐less of secondary importance. In the work reported here, a recently developed approach is used to explore the internal flow, embodying unsteady effects, for a related model problem in which the free‐surface is replaced by a moving upper boundary with its own topographical profile.
Feature‐based Classification of Protein Networks using Confocal Microscopy Imaging and Machine Learning
Authors: Asgharzadeh Pouyan , Özdemir Bugra , Reski Ralf , Birkhold Annette I. , Röhrle Oliver
Published: December 2018

Fluorescence imaging has become a powerful tool to investigate complex subcellular structures such as cytoskeletal filaments. Advanced microscopes generate 3D imaging data at high resolution, yet tools for quantification of the complex geometrical patterns are largely missing. Here we present a computational framework to classify protein network structures. We developed a machine‐learning method that combines state‐of‐the‐art morphological quantification with protein network classification through morphologically distinct structural features enabling live imaging–based screening. We demonstrate applicability in a confocal laser scanning microscopy (CLSM) study differentiating protein networks of the FtsZ (filamentous temperature sensitive Z) family inside plant organelles (Physcomitrella patens).
PDE‐constrained optimization models for scientific processes
Authors: Pearson John W.
Published: December 2018

We survey a number of practical applications of PDE‐constrained optimization problems across science and engineering.
On the analysis of microstructural residual stresses in hot bulk forming parts under specific cooling
Authors: Brands Dominik , Chugreev Alexander , Kock Christoph , Niekamp Rainer , Scheunemann Lisa , Uebing Sonja , Behrens Bernd‐Arno , Schröder Jörg
Published: December 2018

A precise representation of the residual stresses, their development in numerical simulations as well as their interpretation in experimental results requires a profound knowledge of the thermal, mechanical as well as metallurgical properties of the considered material. This publication presents initial approaches for the calculation of residual stresses. For this purpose, the thermo‐mechanical behaviour of two steel alloys 42CrMo4 and 100Cr6 with regard to the martensitic phase transformation is investigated. Using a quenching and forming dilatometer by TA Instruments Inc., the martensite start temperatures are investigated depending on different deformation states of the materials. In addition, an artifitial microstructure is investigated regarding the inducing of residual stresses, representing the volumetric change after temperature related microscopic phase transformations.
Mathematical models of bio‐inspired rotatable sensors with elasticities for object scanning
Authors: Merker Lukas , Will Christoph , Steigenberger Joachim , Behn Carsten
Published: December 2018

Rats and mice use some special tactile hairs in their snout region for a non‐visual exploration of their environment. These hairs, known as mystacial macro‐vibrissae, are each embedded in their own elastic support, called follicle‐sinus complex. This consists of several mechanoreceptors converting tactile information into neural impulses for the central nervous system (CNS). Using their vibrissae, rats and mice are capable of detecting distances to objects, object contours and surface textures. Due to this outstanding ability vibrissae frequently serve as a paradigm for technical tactile sensors. In this paper, we present a model for object shape scanning and contour reconstruction. Here, we especially focus on the important property “elasticity” of the follicle‐sinus complex, which has rarely been taken into account for object scanning in literature. We set up models for three different elastic supports. Based on solutions of the arising boundary‐ and initial‐value problems, we simulate the scanning process, investigate the related support reactions during a single rotational quasi‐static sweep of a straight vibrissa along a strictly convex object contour and reconstruct its shape. In doing this, we investigate the influence of the different elasticities of the model on the scanning and reconstruction procedure.
Hydro mechanical coupling using a hybrid dimensional approach and interface element formulations
Authors: Schmidt Patrick , Steeb Holger
Published: December 2018

Characteristics of underground fluid storage and properties related to heat transport and underground matter are of high interest in the community of porous and fractures media. Especially once hydro‐mechanical phenomena in fluid filled fractures are of interest, such as inverse waterlevel fluctuations during well stimulations (Noordbergum effect), the numerical coupling of the fluid and the porous domain is challenging. Existing strategies such as direct numerical simulations or coarse‐grained approaches (Biot's theory) either fail due to technical issues (number of Degrees of Freedom (DoF)) or are not capable of intuitively taking permeability changes based on the deformation state into account. This work proposes a fully coupled scheme using hybrid‐dimensional element formulations and zero‐thickness interface elements that naturally describes flow in deformable fractures surrounded by porous media.
Fast generation of initial estimates for indirect optimal control
Authors: Callies Rainer
Published: December 2018

For the numerical solution of optimal control problems for large systems of ordinary differential equations (ODE) the indirect approach can be applied: Using optimal control theory based on the Maximum Principle the problem is transformed into a boundary value problem which is then solved numerically. In addition to the equations of motion, a set of differential equations for the adjoint variables is derived from the Hamiltonian. A main challenge for indirect methods was up to now the generation of initial estimates for the adjoint variables. A new approach is presented based on the estimated or experimentally observed controls of a suboptimal solution. They are formally integrated backwards; together with the algebraic constraints on optimal solutions (optimality condition and constant Hamiltonian) an inverse problem is formulated and solved to obtain reliable estimates for the adjoint variables on a predefined grid. By homotopy techniques the so obtained optimal solution of a modified problem is transferred into the solution of the original problem. As an example the optimal flight trajectory of an aerobatic aircraft in an Red Bull Air Race is calculated.
Layout of a Driver‐in‐the‐Loop Simulator for Validation of Human Body Models
Authors: Kempter Fabian , Fehr Jörg
Published: December 2018

In the field of crash simulation, advanced human body models (HBMs) with muscle representation become more and more important because of their ability to emulate the behavior of real human occupants more accurately than dummy models. To get experimental validation data for these models concerning muscle activation and time‐variant stiffness properties, a low‐cost Driver‐in‐the‐Loop (DiL) simulator based on a Porsche exhibition driving simulator is implemented. Driver kinematics and muscle activation are tracked by computer stereo vision and surface electromyography (SEMG). For improved driver immersion, kinematic feedback is provided by a six DoF motion platform, a force‐feedback wheel and a bassshaker at the back of the driving seat. The DiL‐simulation is based on a Simulink model, generated by the software package PreScan, with included mathematical models of vehicles, sensors, drivers, etc. The vehicle states, available in the generated Simulink model, are used to activate the motion platform via UDP protocol. Because of the physical limitations of the platform movement, the so‐called Motion Cueing Algorithms (MCA) are necessary to emulate real driving sensation by providing motion cues which minimize the required translational platform movements.
On extremum seeking controllers based on the Lie bracket approximation in domains with obstacles
Authors: Grushkovskaya Victoria , Zuyev Alexander , Ebenbauer Christian
Published: December 2018

In this paper, we consider the problem of extremum seeking in the presence of obstacles. The analytical expression of the cost function as well as locations and shapes of the obstacles are assumed to be partially or completely unknown. We describe a broad family of control algorithms for a unicycle type system, which provides a solution of the above problem based on Lie bracket approximation ideas. The obtained controllers generalize some known results and allow to construct new control strategies. Furthermore, it is shown that gradient‐free control algorithms can be used for excluding the attraction of trajectories to undesirable equilibriuma in obstacle avoidance problems.
On construction of general solutions of equations of elastostatic problems for the elastic bodies with voids
Authors: Gulua Bakur , Janjgava Roman
Published: December 2018

The linear theory of thermo‐elastic materials with voids was for the first time considered in the work Iesan. A two‐dimensional system of equations of plane deformation is written in the complex form and its general solution is represented by means of two analytic functions of a complex variable and one solution of Helmholtz equation. The constructed general solution enables one to solve analytically a sufficiently wide class of plane boundary value problems of the elastic equilibrium with voids.
A semi‐analytical approach for prediction of volume flow rate in nip‐fed reverse roll coating process
Authors: Jang Zia , Litfin Oliver , Delgado Antonio
Published: December 2018

Reverse roll coating, one of the most widely adopted coating techniques, is considered as a self‐metered process. Its volume flow rate in the coating bead is analytically unpredictable due to the presence of the dynamic contact point. In an attempt to approximate the volume flow rate in the coating bead, the position of the dynamic contact point was numerically approximated by computational fluid dynamics (CFD) and then introduced to Navier‐Stokes equations. As a result, this semi‐analytical approach represented a non‐linear correlation of the volume flow rate with speed ratio and capillary number.
A Computational Two‐Scale Model for the Simulation of Dual‐Phase Steels under Cyclic Loading
Authors: Gandhi Ashutosh , Balzani Daniel , Brands Dominik , Scheunemann Lisa , Schröder Jörg
Published: December 2018

Dual‐Phase (DP) steels exhibit excellent macroscopic properties such as high strength, ductility and energy absorption. However, the increase of strength also results in a large springback behavior which should be considered for an optimal production process design. Thus, accurate modeling of springback during forming applications is important. The macroscopic behavior of DP steels is closely tied to the phenomena taking place on the microstructural level. The presence of kinematic hardening and graded properties in ferrite together with complex interactions of the different phases at the microscale have a large influence on the macroscopic springback response. Therefore, a micro‐macro scale bridging approach is proposed wherein statistically similar representative volume elements (SSRVEs) are considered to capture the DP‐steel microstructure, c.f. [1], [2], [5]. This ensures effective modeling of the microstructure while significantly reducing the complexity of the microstructural morphology and thus reducing the computing time. A mixed hardening model, see [8], along with the initial volumetric strain approach, see [3], enables incorporating the kinematic hardening as well as graded properties in the microstructure. Multiscale calculations of cyclic tests show the performance of the model by measuring the Bauschinger factor and the attained stress levels during deformation.
Simulation of cardiac electromechanics of a rat left ventricle
Authors: Duong Minh Tuan , Holz David , Alkassar Muhannad , Dittrich Sven , Leyendecker Sigrid
Published: December 2018

This work presents the modelling and simulation of the cardiac electromechanics of a rat left ventricle (LV) under normal and pathological conditions. The 3D LV model is constructed from MRI images of a rat heart. The electrical wave propagates through the whole heart to trigger the mechanical contraction. Our coupled electromechanical problem is formulated based on the mono‐domain and the active stress approach. An implicit finite element‐based method is employed to monolithically solve the problem for the LV. The numerical results show significant differences in the electromechanical behaviour of the healthy and infarcted model.
On efficient computation of 3‐d simulation within TPM2‐Framework
Authors: Bartel Florian , Ricken Tim , Schröder Jörg , Bluhm Joachim
Published: December 2018

With this contribution we would like to communicate the state of the art of TPM2 application to realistic engineering problems. First of all, a conceptional overview of TPM2 is shortly given, secondly we illustrate the benefit of Computer Tomography (CT) technology to capture geometry and create finite element meshes. Further, the application of the domain decomposition (DD) method for parallel execution will be shown on an example of a fluid saturated porous unit cube and finally we give advise for additional acceleration of computational runtime via model order reduction (MOR) for the TPM2‐Framework.
Multi‐field modeling of thermomechanical coupled fracture problems
Authors: Schulte Jonathan , Krüger Melanie , Dittmann Maik , Hesch Christian
Published: December 2018

In this contribution we focus on a novel variationally consistent formulation for thermomechanical coupled fracture problems. To be specific, we aim on a phase‐field approach to fracture such that the resulting system consists of three fields, the deformation map, the thermal field as well as the crack phase‐field. In the sense of Griffith energy criterion for brittle fracture, a crack initiates or continues upon the attainment of a critical crack energy density. This critical energy exhibits strong temperature dependence, which is approximated by a linear interpolation within our framework. The material behaviour is governed by a modified Helmholtz free energy function in terms of the elastic part of the deformation gradient and the temperature. Postulating that fracture requires a local state of tension, we apply an anisotropic decomposition of the principle stretches of the deformation gradient and reduce the tensile contributions by a suitable degradation function, see [1] for more details. Accordingly, we are able to derive local constitutive relations for the first Piola‐Kirchhoff stress tensor, the entropy density and the phase‐field driving force in variationally consistent manner, see [2]. A further constitutive relation is the Duhamel's law of heat conduction. In case of fracture, the conduction degenerates locally such that we achieve a pure convection problem and the heat transfer depends on the crack opening width. Here, we formulate the conductivity tensor in terms of the phase‐field parameter. Eventually, various numerical examples will show the accuracy and capability of the proposed multi‐field approach to fracture.
Numerical modeling of solid particles motion in suspensions using Smoothed Particle Hydrodynamics
Authors: Kijanski Nadine , Steeb Holger
Published: December 2018

Suspensions and their applications can be found in many fields of mechanical, civil and environmental engineering. To consider the flow behavior as well as fluid‐solid interactions in dilute suspensions, we present 3D Direct Numerical Simulations (DNS) of a single‐phase fluid with discrete solid particles. We therefore developed a numerical implementation based on the general‐purpose particle simulation toolkit HOOMD‐blue [1, 3] extended for the usage of Smoothed Particle Hydrodynamics (SPH) [2, 5]. Since both the fluid and the solid part can be discretized by particles, SPH as a Lagrangian particle method presents a good choice to model this particular non‐linear problem. To describe solid contact and interaction forces, we consider two solid contact models. The first model is a simplified Hertz‐Mindlin contact model [4] as used in classical DEM simulations. The second model is a lubrication force model as presented by [6]. To review the results of the approach, we discuss an example with two non‐spherical solid grains in a single‐phase fluid under shear flow.
Structural Optimisation Using Parametrised Level Set Methods and Extended Finite Element Method
Authors: Wohlgemuth Felix , Barthold Franz‐Joseph
Published: December 2018

In the framework of level‐set‐based optimisation, several approaches to solve bi‐material and topological problems have been developed. In this study a combined concept of different approaches is introduced, joining together a parametrised geometry description with superellipses or b‐splines and a modified approach for the extended finite element method within an optimisation setup of topological and shape iterations introduced by Allaire [1]. The parametrisation with geometric figures or splines allows us to reduce the number of design variables to a minimum whereas we hold up a sufficient precision in the geometry description. Moreover it simplifies the shape derivatives as we gain an implicit description for the moving interfaces. In order to solve the boundary value problem of structural mechanics, we introduce a modified extended finite element approach which uses a sub‐meshing technique that enables us to keep existing strategies from homogeneous structures and transform them onto a discontinuous material using enriched shape functions provided by the standard extended finite element method. Shape sensitivities are evaluated on the sub‐elements and extrapolated to the element nodes. The topological derivative as developed by Novotny [4] is evaluated and prescribes the initiation of new discontinuities as inclusions or holes.
Simultaneous Registration of Image Sequences – a novel singular value based images similarity measure
Authors: Brehmer Kai , Wacker Benjamin , Modersitzki Jan
Published: December 2018

The comparison of images is an important task in image processing. For a comparison of two images, a variety of measures has been suggested. However, applications such as dynamic imaging or serial sectioning provide a series of many images to be compared. When these images are to be registered, the standard approach is to sequentially align the j‐th image with respect to its neighbours and sweep with respect to j. One of the disadvantages is that information is distributed only locally. We introduce an alternative so‐called SqN approach. SqN is based on the Schatten‐q‐norm of the image sequence gradients, i.e. rank information of image gradients of the whole image sequence. With this approach, information is transported globally. Our experiments show that SqN gives at least comparable registration results to standard distance measures but its computation is about six times faster.
Investigating the effect of Nano‐silica on the depth of water penetration in concrete used in seawater: Case study of Caspian Sea
Authors: Arasteh Khoshbin Omolbanin , Ricken Tim
Published: December 2018

One of the requirements of concrete structures is functional continuity whatever for it is required to be resistance in a particular period. Water during cementing process leads to hydration causing concrete hardness, whereas after hardening of concrete in most cases damages it's structure and properties. Dams, waveguides, docks and oil platforms in the seawater are subject to gradual erosion, which is very slow but measurable. Seawater due to the properties of sulfate, acid and alkali is a significant threat to concrete durability. Reducing the water absorption into the concrete body is the primary step to address the concrete erosion. Changing the concrete characteristics is an approach to increase concrete density and decrease its porosity leading to erosion reduction. Adding fine‐grained such as Nano derivatives can fill the void space within the concrete and reducing seawater absorption. In this research, we study the effect of Nano‐silica with 1% and 5% replacement ratios instead of cement on compressive strength and water penetration depth for concrete in environments of the Caspian Sea.
Evaluation of the Reduced Order Models for Thermoelastodynamic Response of Geometrically Nonlinear Finite Element Models
Authors: Karamooz Mahdiabadi Morteza , De Crescenzo Francesco , Meyer Christian H. , Rixen Daniel J.
Published: December 2018

This work deals with model order reduction of geometric nonlinear FE models under thermal loads. The nonlinear reduced order model (NLROM) is developed in a non‐intrusive approach. Namely, the NLROM can be constructed in any FE package which has the ability to solve nonlinear static problems, without requiring to deal with the governing equations of the full‐order model in closed form. The identification of the nonlinear stiffness tensors as well as thermal induced terms can be performed using either force based or displacement based estimation techniques. The Implicit Condensation (IC) method properly develops the NLROM for transverse displacement and has been also extended to approximate the in‐plane motion, which is called Implicit Condensation and Expansion (ICE). Here, ICE is extended for the thermoelastodynamic problem to accurately approximate the in‐plane motion in the presence of temperature fields.
Model‐based geometry reconstruction of quantum dots from TEM
Authors: Maltsi Anieza , Koprucki Thomas , Niermann Tore , Streckenbach Timo , Tabelow Karsten , Polzehl Jörg
Published: December 2018

The reconstruction of geometric properties of semiconductor quantum dots (QDs) from imaging of bulk‐like samples (thickness 100‐300 nm) by transmission electron microscopy (TEM) is a difficult problem. A direct reconstruction by solving the tomography problem is not feasible due to the limited image resolution (0.5‐1 nm), the highly nonlinear behavior of the dynamic electron scattering, nonlocal effects due to strain and strong stochastic influences due to uncertainties in the experiment. We present a mathematical model for the numerical simulation of TEM images. This includes elasticity theory to obtain the strain profile coupled with the Darwin‐Howie‐Whelan equations, describing the propagation of the electron wave through the sample. Furthermore, we introduce a novel concept for 3D model‐based geometry reconstruction of QDs from TEM images. The approach includes a geometric model for the QD configuration in real space, a database of simulated TEM images and a statistical procedure for the estimation of the geometric properties and the classification of QD types.
Analysis of pullout behavior of single steel fibers embedded in concrete using phase‐field modeling
Authors: Pise Mangesh , Brands Dominik , Gebuhr Gregor , Schröder Jörg , Anders Steffen
Published: December 2018

In this contribution, a constitutive framework of elasto‐plastic phase‐field model for fracture is applied to simulation of pullout test of single steel fiber embedded in concretes and compare it to the experimental results. For the description of the mechanical behavior the Drucker‐Prager plasticity model is used. The aim is to examine the pullout behavior of a single steel fiber and its influence on the overall material behavior. Therefore, the mechanical behavior of concrete is studied in experimental single fiber pullout test. The predictive capability of the above mentioned model is analyzed in detail by simulating a single fiber pullout test and compared against the experimental data.
Hyperelastic material modeling of graphene based on density functional calculations
Authors: Shirazian Farzad , Ghaffari Reza , Hu Ming , Sauer Roger A.
Published: December 2018

A new parameter set for the graphene material model of [1] is obtained. The material model is anisotropic hyperelastic and calibrated by a trial data set generated by density functional theory (DFT). The DFT experiments are one pure dilatation test and two uniaxial stretch tests along the armchair and zigzag directions. The strain energy is computed from ab‐initio simulations and used to calibrate the parameters of the hyperelastic model. The strain energy and stresses from the new parameter set are calculated and verified with the results of [1].
Adjoint shape optimization for fluid‐structure interaction
Authors: Heners Jan Ph. , Radtke Lars , Düster Alexander , Hinze Michael
Published: December 2018

A partitioned approach for the solution of the adjoint associated to the coupled system of time‐dependent fluid‐structure interaction is presented. Allowing for an efficient computation of both sensitivity and gradient distributions relying on the adjoint method, an optimization strategy based on the steepest descent algorithm is applied. The performance of the developed shape optimization process improving flow conditions and related cost functionals is demonstrated by application to ducted flow situations and common fluid dynamic design tasks considering the interaction between fluid loads and structural deformations. Both physical capability and feasibility are discussed in terms of theoretical and numerical aspects in order to evaluate the efficiency of the realized optimal control process.
Experimental and numerical characterisation of fibre‐metal‐elastomer laminates by using DMA regarding its damping behaviour
Authors: Sessner Vincent , Liebig Wilfried V. , Kärger Luise , Weidenmann Kay A.
Published: December 2018

Hybrid carbon fibre‐elastomer‐metal laminates consist of alternating layers of carbon fibre reinforced plastics, elastomer layers and aluminium sheets. These laminates offer great potential for a lightweight structural material with adjustable damping properties. The material damping is strongly influenced by the viscoelastic properties of the elastomer layers which damp by the principle of constrained layer damping when the laminate is vibrated. In this study the material damping was experimentally characterised by three point bending dynamic mechanical analysis (DMA). In this regard, HyCEML specimens were tested on different frequencies and temperatures. The loss factor, storage‐ and loss modulus were measured to characterise the damping over the temperature and the frequency range. Time‐temperature superposition was applied to determine the damping characteristics at higher and lower frequencies. The experimental results were compared to numerical studies on the basis of a characterisation of the single constituents. A test setup with a cantilever beam under free vibration was chosen for the comparison of experimental and numerical results. Detailed multi‐layer finite element models were generated offering high flexibility in terms of type and number of finite elements especially in the direction of laminate thickness. For this purpose, existing material models were used to investigate the influence of each component on the system's damping behaviour. The damping in the free vibration experiments was determined with the logarithmic decrement at the free end. Also the numerically and experimentally determined first eigenfrequencies were compared. It could be shown that the laminate damping is strongly dependent on the glass transitions of both the carbon‐fibre reinforced plastics and the elastomers. The numerically determined first eigenfrequency matched the experimental with a deviation of 10 %, the logarithmic decrement of the experimental results was more than 50 % higher. The damping behaviour of the HyCEM laminate, however, is underestimated by the numerical investigation, since nonlinear viscoelastic effects are not yet considered.
Geometry‐Inspired Control of the Brockett‐Integrator in Cylindrical Coordinates
Authors: Knoll Carsten , Xue Yifan , Röbenack Klaus
Published: December 2018

The so‐called Brockett‐Integrator is a famous control system. On the one hand it has a very simple structure (second order polynomial, three state components, two affine inputs, no drift) and fulfills the Lie‐Algebra‐Rank‐Condition for (strong) local accessibility. Nevertheless, it has the challenging control property, that it does not admit a continuously differentiable control law, which stabilizes the origin.

In this contribution we consider the system in cylindrical coordinates. If the first time derivatives of the radius and the orientation are chosen as the new inputs, the transformed system dynamics is even simpler (in terms of expression length) than in usual Cartesian form. Moreover, the system can be decomposed into two subsystems and a differentially flat output can be easily read off. Based on this partially decoupled system dynamics we formulate a simple three‐staged control law which drives the system into the origin by aiming for a minimal arc length in the (original) state space.