bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase‐field predictive model for setting of fresh self‐compacting concrete
Authors: Huang Haiqin , Zilian Andreas
Published: December 2018

The initial setting of fresh concrete is mainly caused by the dissolution of cement grains and the precipitation of calcium‐silicate‐hydrates during cement hydration. Progressing hydration drives the transition from a dense suspension to a porous solid phase. Fresh mixture of self‐compacting concrete (SCC) can be considered as a phase‐changing multi‐component material and can be described as a continuum at the macro scale, interacting with a set of transport‐reaction‐diffusion processes which in turn are driven by phenomena at the level of the microstructure. This contribution focuses on a predictive model for the setting of fresh SCC where the liquid‐solid phase transition is captured by a phase‐field variable using the Ginzburg‐Landau type free energy function. Hydration‐related chemical reactions together with heat and mass transfer are volume‐coupled with the mechanical behaviour and determined by the environmental conditions. The weak form of the predictive model is discretised using the finite element method and implemented with the FEniCS computational framework.
An investigation on residual stresses in gas tungsten arc welding
Authors: Ali Baharin Rahim Ali , Nguyen An Danh , Markert Bernd
Published: December 2018

It is known that the gas tungsten arc welding (GTAW) generates high and localised heat gradients in the welded components, leading to the formation of weld bead and residual stresses that affect their fatigue life. In this work, a finite element model of GTAW is presented to estimate the temperature and stress induced by GTAW. The heat and fluid flow (HFF) approach using the enthalpy‐porosity model and the finite element multiphase modelling allows us to simulate the rapid melting and solidification. Moreover, the Marangoni effect, due to a thermally caused surface tension gradient, is also studied. The performance of the proposed finite element model is demonstrated via a simulation of the GTAW process with appropriate boundary conditions on temperature and velocity fields. The model can be extended for further residual stress and distortion analyses.
Analytical investigation of non‐local deformation‐mediated magneto‐electric coupling
Authors: Rambausek Matthias , Keip Marc‐André
Published: December 2018

The research on magneto‐electric materials is concentrated on multi‐ferroics and hard‐matter composites. However, rather recently soft composites also exhibiting pronounced magneto‐electric coupling entered the scene. Such composites are straight‐forward to manufacture and have cheap constituents compared to classical approaches. This contribution is concerned with an analytical estimation of a particular non‐local magneto‐electric coupling effect that exists regardless of the composite nature but relies on the softness of a magneto‐electric material.
Analysis of the nonlinear chaotic behavior of an inverted flexible pendulum system affected by impulses
Authors: Kahar Hartiny , Söffker Dirk
Published: December 2018

In this contribution, the effect of impulses realized by non‐perfect feedback to an inverted flexible pendulum system is studied. Using experimental data from chaotic jumping in an inverted flexible pendulum, several techniques of signal processing and time‐frequency representation are carried out. These methods are used to observe the changes in the nonlinear dynamic properties and time behavior of the system before and during the jumping between equilibrias. The evaluation of the experimentally realized inverted flexible pendulum system for specific control parameters shows that ’chaotic’ jumping behavior between the three equilibrias (with different attraction regions) are depending on the existence of impulses. The results from detailed analysis shows that this is caused by feedback imperfectness. Considering the time‐frequency‐based analysis conducted, it can be stated that the (uncontrolled) impulses causing a temporarily disturbance in the energy distribution between the ’modes’/frequency bands the system vibrates with, which finally leads to a new and more stable distribution in energy, followed by related jumping between the equilibrias.
Optimization based muscle wrapping in biomechanical multibody simulations
Authors: Penner Johann , Leyendecker Sigrid
Published: December 2018

In musculoskeletal simulations muscle lengths and muscle force directions imply the characteristics of muscles acting around joints. Typically, the anatomical structure of the human body forces muscles to wrap around bones and neighboring tissue, thus most muscle paths cannot be represented adequately as straight lines. Therefore, biomechanical simulations require methods to compute musculotendon paths, their lengths, and their rates of length change to determine the muscle forces. This work focuses on a mechanical analogue to find the shortest path on general smooth surfaces, using a discrete variational principle. In this context, the geodesic path is reinterpreted as the constrained, force‐free motion of a particle in n dimensions. The muscle path is then a G1‐continuous combination of geodesics on adjacent obstacle surfaces [1,3,4].
Comparison of experimental data and FEM simulation for a multiferroic nanocomposite
Authors: Lemke Veronica , Webers Samira , Labusch Matthias , Schröder Jörg , Wende Heiko
Published: December 2018

The combination of ferromagnetic and ferroelectric materials, so‐called multiferroic composites, increases the opportunities for technical sensors and data storage devices, see [1]. The magnetic and electric constituents have the property to affect each other e.g. an applied electric field modifies the magnetization of the magnetic phase. In nature also single‐phase materials exist with magneto‐electric properties. Though, the interoperation of the magnetization and the polarization is exclusively activated at very low temperature. Therefore, they are not favorable for most of the known technical applications. Considering this, the magneto‐electric (ME) composites can be seen as a good option since their synergy of the magneto‐electric properties is active at room temperature [2] and can be differentiated in two different effects, the direct and the converse ME effect. We will focus on (1‐3) nanocomposite grounded on the experiments made in [3] and [4]. In the experiments, cobalt ferrite nanopillars, embedded in a barium titanate matrix, are characterized. Then, for the numerical FEM‐simulations the material coefficients from [5] and [6] are taken. The change of the strain‐induced in‐plane polarizations of the ferroelectric matrix around one cobalt ferrite nanopillar is calculated. These computed results are compared to the ones of the experimental measurement outcomes.
A data‐driven model order reduction approach for Stokes flow through random porous media
Authors: Grigo Constantin , Koutsourelakis Phaedon‐Stelios
Published: December 2018

Direct numerical simulation of Stokes flow through a random, impermeable rigid body matrix by finite elements requires meshes fine enough to resolve the pore‐size scale and is thus a computationally expensive task. It is well known that on a larger scale, Stokes flow can accurately be approximated by Darcy's law [1] with an effective diffusivity field depending on viscosity and the matrix phase topology. We propose a fully probabilistic Darcy type reduced‐order model which, based on only a few tens of full‐order model runs, is capable to learn a fine‐scale topology to effective diffusion map which is maximally predictive for fine‐scale response. After training, the model provides sharp predictive distributions based on repeated evaluation of the much cheaper Darcy equation only.
Fuzzy uncertainty in forward dynamics simulation using variational integrators
Authors: Eisentraudt Markus , Leyendecker Sigrid
Published: December 2018

In engineering applications, dynamic simulations are usually carried out with precisely defined input parameters. In this contribution, forward dynamics with epistemic parameter‐uncertainty is considered and α‐level discretisation in combination with α‐level optimisation is used to determine the output of the dynamical system – a fuzzy function. A new numerical method for an efficient realisation of α‐level optimisation in this context is developed, which combines forward dynamics steps and local optimisations. A variational integrator, which exhibits special structure preserving properties, is used as the underlying time integration scheme. However, the method can be combined with any time stepping scheme. In detail, an approximative description of the output as a function of the uncertain parameters is developed, which can be used to reduce the complexity of the developed algorithm.
Modeling and Simulation of Hysteresis Effects in Magnetorheological Elastomers
Authors: Kalina Karl A. , Brummund Jörg , Metsch Philipp , Kästner Markus
Published: December 2018

Herein, a finite strain microscale model for magnetorheological elastomers with magnetically hard fillers is presented. Therein, the magnetic hysteresis of the particles are described by a phenomenological, thermodynamically consistent hysteresis model. To connect the microscopic fields to effective macroscopic quantities, a computational homogenization scheme is applied. Using the presented framework, the effective macroscopic magnetic as well as mechanical hystereses are calculated.
Simulation of anisotropic diffusion under large deformations in polymer blends
Authors: Voges Jannik , Juhre Daniel
Published: December 2018

Blending polymers with different properties is a popular method to customize the behavior of a polymer material. For this, in some cases, the materials are mixed in molten form. At high temperatures, this usually yields a single phase, consisting of both the polymers. At lower temperatures, the blend often starts to decompose into two or more phases, which can yield a complex microstructure. One way to control this resulting structure, is to treat the cooling melt mechanically, whereby lamellar patterns are often observed. Performing computer simulations can help to understand the behavior of the mixture and thus help to be able to better control the microstructure of the polymer blends in the manufacturing process. This can improve the performance of the material.

Following a well‐known approach, a phase‐field determines the material distribution in a domain, representing the microstructure of the polymer blend. Here, the Cahn‐Hilliard equation describes the evolution of the mentioned phase‐field, starting with a random initial distribution. The domain is strongly deformed to force a rearrangement of the structure while the blend is decomposing, thus a large deformation framework is considered, cf. [1]. The decomposition process is investigated, using simulations for different deformations and by comparing them to a simulation in the classical undeformed case. Anisotropic diffusion occurs in the deformed domains, which yields regular patterns.
Simulation of angioplasty using isogoemetric laminated composite shell elements
Authors: Roohbakhshan Farshad , Sauer Roger A.
Published: December 2018

The typical treatment for the opening of obstructed arteries or veins is balloon angioplasty. Different computational models, which usually use 3D finite solid elements to model the artery, have been introduced in the literature to analyze the angioplasty procedure. In this work, a laminated composite shell formulation derived from the Kirchhoff–Love shell theory is used to model the artery wall. The corresponding shell is formulated on the mid‐surface of the artery. As only the surface is discretized, the shell formulation is computationally less expensive than the common 3D solid elements, which require volumetric discretization.
Developing a model for the microscopic material behaviour of a tailored formed joining zone of an aluminium‐steel hybrid solid component
Authors: Baldrich Martina , Loehnert Stefan , Wriggers Peter
Published: December 2018

Tailored Forming is a complex process joining two materials before forming. Especially the joining zone of the hybrid solid component is a possible weakness. Hence, our goal is to predict and adjust the thermomechanical material behaviour of the joining zone during and after the tailored forming process. The hybrid solid components studied in this work are composed of the aluminium alloy EN AW‐6082 and the steel 20MnCr5. Metallurgical investigations on both materials show a polycrystalline microstructure. In the steel component, the two constituents ferrite and pearlite can be found with nearly the same volume fraction and randomly distributed grains. Furthermore, between the two bulk materials aluminium and steel, a thin layer of brittle intermetallic phases can be observed. In this work, the intermetallic phases are considered to behave purely thermoelastic, whereas the material model for aluminium, ferrite and pearlite represents thermoplastic material behaviour. We present the dislocation density based models for the thermoplastic materials formulated in a continuum mechanics framework. Thereby, different mechanisms of annihilation contributing to the evolution equation for the internal variables will be on focus.
A rate‐dependent damage model for prediction of high‐speed cracks
Authors: Butt Sahir , Meschke Günther
Published: December 2018

Experiments [1] have shown that the energy release rate in high‐speed dynamic fracture processes strongly depends on the the macro crack propagation velocity. This dependence is due to the fact that the rate of the fracture surface creation is proportional to the energy flux into the crack. A crack propagating at high‐speed can create an order of magnitude larger fracture surface in form of micro‐branches than a low‐speed crack. To this end, a crack speed dependent damage model, which is based on the physics of micro‐branching, is presented and incorporated into peridynamic continuum theory. Numerical simulations are carried out on a plexiglas (PMMA) plate to show that the proposed model is capable of reproducing the physical phenomena observed in experiments.
Mixed precision in subspace iteration‐based eigensolvers
Authors: Galgon Martin , Huber Sarah , Lang Bruno
Published: December 2018

We consider the use of mixed precision in three subspace iteration‐based eigensolvers. We show that for several algorithmic steps, computation in single precision will temporarily limit convergence.
Closed‐loop control of turbulent boundary layers using spanwise traveling surface waves
Authors: Albers Marian , Meysonnat Pascal S. , Schröder Wolfgang
Published: December 2018

The drag reduction technique of spanwise traveling surface waves in turbulent boundary layers is investigated in a closed‐loop control setup. The results show a dependence of the local skin friction on the spanwise coordinate and a successful application of the controller to determine the optimal amplitude.
A probabilistic white‐box model for PDE constrained inverse problems
Authors: Koschade Maximilian , Koutsourelakis Phaedon‐Stelios
Published: December 2018

Instead of employing deterministic solvers in a black‐box fashion, we seek to address the inherent challenges of uncertainty quantification by restating the solution of a PDE as a problem of probabilistic inference. In doing so, state variables are treated as random fields, constrained or mutually entangled by underlying physical laws. The resulting fully probabilistic model expresses the PDE operator as prior knowledge and allows the solution of the PDE‐constrained inverse problem simply by introducing the observed data as an additional source of information. We demonstrate the proposed framework for the solution of PDE‐constrained inverse problems in a solid mechanics setting and employ adjoint‐free, second‐order methods to infer the joint posterior over the Hilbert space of displacement, stress and unknown material parameters. The method generalizes to nonlinear problems and higher‐order function spaces, while the Maximum‐A‐Posteriori estimate recovers the results obtained by the mixed Finite Element method derived from the Hellinger‐Reissner variational principle.
Coupling Structure in an Optimal Control Problem with PDEs and ODEs
Authors: Kimmerle Sven‐Joachim
Published: December 2018

We consider a general example for an optimal control problem subject to coupled differential equations (CDEs). As CDEs we define a coupled system of partial differential equations (PDEs) and ordinary differential equations (ODEs). All differential equations here represent a time evolution and are fully coupled. An averaging or evaluation operator, resp., is applied to PDE states entering into an ODE such that the ODE has no spatial dependency. Following a first‐optimize‐then‐discretize method, we derive the adjoint equations by means of the necessary first‐order optimality conditions. We prove that the coupling structure of the CDE problem in the adjoint system is reversed. This feature is observed and exploited in (continuous as well as discretized) optimal control problems in real‐world applications.
Experiments on wave propagation in soft materials
Authors: Aghayan Sam , Reppel Thomas , Bieler Sören , Weinberg Kerstin
Published: December 2018

The wave propagation in a group of soft resin based (3d printed) materials is investigated by using a Split Hopkinson Bar setup. The principal assumptions and the role of pulse shaping, as an approach to achieve constant strain rates and dispersion reduction, is discussed. The measured dynamic elastic modulus is presented and indicates that flexible resins have a dynamic elastic modulus of 20 to 40 MPa.
Pattern formation for a family of models with local/nonlocal interactions
Authors: Daneri Sara , Runa Eris
Published: December 2018

We establish pattern formation for a family of discrete and continuous functionals consisting of a perimeter term and a nonlocal term. In particular, we show that for both the continuous and discrete functionals the global minimizers are exact periodic stripes. One striking feature is that the minimizers are invariant under a smaller group of symmetries than the functional itself. In the literature this phenomenon is often referred to as symmetry breaking. In the continuous setting, to our knowledge this is the first example of a model with local/nonlocal terms in competition such that the functional is invariant under permutation of coordinates and the minimizers display a pattern formation which is one‐dimensional. Such behaviour for a smaller range of exponents in the discrete setting was already shown in [1].
Investigation of process parameter influences in single grain scratch simulations
Authors: Sridhar Praveen , Fares Driss , de Payrebrune Kristin M.
Published: December 2018

Lapping and grinding are manufacturing processes which can be seen as a sequence of many single grain scratches. During grinding, the grains perform an oriented movement, whereas during lapping, the grains lie loosely in the gap between the lapping wheel and the workpiece while moving in a completely disordered manner. The Institute of Applied Structural Mechanics conducts experimental investigations and simulations to better understand the complex process. The goal is to develop a physical force model of the grinding and lapping process, by which process predictions can be made. For this purpose, finite element (FE) scratch simulations with geometrically simplified grains are carried out and the qualitative dependencies, such as the influence of the grain geometry and infeed on the stresses are examined.
Optimal control simulations of two finger grasping
Authors: Phutane Uday , Roller Michael , Leyendecker Sigrid
Published: December 2018

Grasping is a complex human action simulated here as an optimal control problem with a three‐dimensional rigid multibody model composed of two fingers along with the wrist and the forearm. The dynamics is described by a hybrid dynamical system with a given switching sequence (reaching or tree kinematic structure and grasping or closed loop contacts) and unknown switching times. The optimal control problem is solved using the direct transcription method DMOCC (discrete mechanics and optimal control), see [1], leading to a structure preserving approximation. An objective function such as the distance of contact points from the grasped object center of gravity or the sum of normal contact force is minimised subject to the discrete Euler‐Lagrange equations, boundary conditions and path constraints. The object dynamics is also taken into account.
Microstructure modelling using the scaled boundary finite element method
Authors: Birk Carolin , Tian Xinran
Published: December 2018

An automatic approach for the evaluation of effective material properties is presented. It is based on the scaled boundary finite element method (SBFEM). The SBFEM facilitates the use of structured meshes on highly heterogeneous domains. These meshes are obtained automatically from image data. Two examples illustrate the potential of the proposed methodology.
Deformation behaviour of small scale cp‐titanium specimen with large grains
Authors: Bischof Robert , Böhme Luisa , Kuhn Charlotte , Müller Ralf , Kerscher Eberhard
Published: December 2018

To describe the material behaviour of the microstructure of commercially pure (cp‐) titanium with the Finite Element (FE) Method, a crystal plastic material model is used. The anisotropic plastic deformation is considered by specifying the slip systems of the hexagonal‐closed‐packed (hcp) crystal structure. To circumvent the difficulties associated with possible non‐uniqueness of the set of active slip systems, a rate‐dependent formulation is used. Because of the volume preserving plastic deformation, locking effects can arise, which are dealt with by a modified F‐bar deformation gradient. To investigate the material behaviour of cp‐titanium small scale tensile test simulations are performed. Electronic backscatter diffraction (EBSD) investigations of the sample provides the specific grain orientations of the microstructure to perform realistic simulations.
On the Treatment of Plastic Deformation in the Particle Finite Element Method
Authors: Ye Xialong , Müller Ralf
Published: December 2018

The particle finite element method (PFEM) combines the benefits of discrete modeling techniques and approaches based on continuum mechanics. It provides a convenient tool to deal with the problem of large configurational change, such as metal cutting, in which nonlinear plasticity plays a key role [1]. In this article we introduce a phenomenological plasticity model with the help of a multiplicative decomposition of the deformation gradient and an intermediate local configuration into the PFEM framework. Numerical examples of cutting simulations are presented to show the performance of the formulation.
A brief history of logarithmic strain measures in nonlinear elasticity
Authors: Martin Robert J. , Münch Ingo , Eidel Bernhard , Neff Patrizio
Published: December 2018

We demonstrate that the notion of logarithmic strain tensors in nonlinear elasticity theory, which is commonly attributed to Heinrich Hencky, is actually due to the geologist G. F. Becker, who was the first to consider a fully three‐dimensional logarithmic stress response in an 1893 article.
Statistical Methods for Parameter Identification of Temperature Dependent Viscoelastic Models
Authors: Rosero‐Velásquez Hugo , Cottone Giulio , Colinas‐Armijo Natalia
Published: December 2018

A fully fractional stochastic model for linear viscoelastic materials is proposed. Time dependent stress‐strain response for creep tests is described through Adaptive Links theory as a random process of successive micro‐stretching events due to disentanglements between groups of material fibers. The process is modeled by a Continuous Time Random Walk (CTRW) that tends in average to power‐law function, which corresponds to the creep kernel of the usual fractional model for viscoelasticity. Thermal effects are explained through changes in waiting time and jump compliance distribution parameters. Simulated CTRWs are compared with experimental results of specimens of epoxy resin. It was observed that simulated mean function approaches to measurements in long term during the creep phase. Additionally, parameter averages decrease for higher temperatures, representing more frequent jumps of fiber creep strain and faster development of creep process.
Analysis of Anisotropic Interaction Equations for Fingerprint Simulations
Authors: Kreusser Lisa Maria
Published: December 2018

Motivated by the simulation of fingerprints we consider a class of interaction models with anisotropic, repulsive‐attractive interaction forces whose orientations depend on an underlying tensor field. This class of models can be regarded as a generalization of a gradient flow of a nonlocal interaction potential which has a local repulsion and a long‐range attraction structure. These anisotropic forces in our class of models cannot be derived from a potential and the underlying tensor field introduces an anisotropy leading to complex patterns which do not occur in isotropic models. This anisotropy is characterized by one parameter in the model. We study the resulting stationary solutions both analytically and numerically by considering the particle model and its continuum counterpart.
Identification of hyper‐ and viscoelastic properties of different flexible FDM printed specimens
Authors: Reppel Thomas , Weinberg Kerstin
Published: December 2018

Additive manufacturing, also known as 3D printing, has become a well‐established method in many different fields of fabrication. It is a preferred method to produce small series or even individual parts of components. The present work aims at the experimental identification of the hyper‐ and viscoelastic properties of two different kinds of highly flexible filaments for fused deposition modeling. A thermoplastic polyurethane TPU and a thermoplastic copolyester elastomer TPC. To this end, several uniaxial tensile tests, as well as relaxation experiments of printed specimens are performed. From the measured data we identify the parameters of different hyperelastic models. For the viscoelastic part we find the parameters of a Prony‐series with N elements of a generalized Maxwell‐model. We also consider a model based on generalized fractional elements [1,3,4].
Influence of the material parameter mapping from computed tomography data on the simulation of a bone‐implant system
Authors: Roland Michael , Tjardes Thorsten , Bouillon Bertil , Diebels Stefan
Published: December 2018

In this study, several mappings for material parameters based on computed tomography image data are tested with respect to their influence on the result of personalized finite element simulations (FEM). Therefore, a standard workflow was implemented including (1) segmentation of routinely acquired clinical tomogram data, (2) definition of several mappings from image–based Hounsfield units to elastic modulus using the apparent density and (3) patient–specific realistic boundary conditions acting during a normal step forward. This setup allows a comparison of simulation results with regard to the used material parameter mapping.
Mean field homogenization schemes for short fiber reinforced thermoplastics based on real microstructural information
Authors: Hessman Patrick Arthur , Welschinger Fabian , Hornberger Kurt
Published: December 2018

The effective elastic properties of a short glass fiber reinforced thermoplastic are estimated using different mean field homogenization schemes. The material's inherently complex microstructure is resolved by means of high resolution x‐ray tomography scans and utilizing a single fiber segmentation algorithm. This raw microstructural data is then directly considered in the models. Finally, the models are discussed and their estimates for the anisotropic effective stiffness tensor are compared to experimentally obtained direction‐dependent Young's moduli.
Bayesian inference for estimating model discrepancy of an electric motor
Authors: John David , Schick Michael , Heuveline Vincent
Published: December 2018

Uncertainty Quantification (UQ) is highly requested in computational modeling and simulation, especially in an industrial context. A main challenge is related to the fact that computational models are rarely able to represent the true physics perfectly and demonstrate a discrepancy compared to measurement data. Further, an accurate knowledge of considered model parameters is usually not available. E.g. fluctuations in manufacturing processes of hardware components introduce uncertainties which must be quantified in an appropriate way. Mathematically, such UQ tasks are posed as inverse problems, requiring efficient methods for their solution. We address this challenge by investigating the influence of model discrepancies onto the calibration of model parameters and further consider a Bayesian inference framework including an attempt to correct for model discrepancy by an additional term. A Markov Chain Monte Carlo (MCMC) method is utilized to approximate the posterior distribution. Synthetic measurement data from an electric motor model and an artificial model error are used to evaluate the framework. The application shows a promising perspective of the framework by good approximation of discrepancy and parameters.
Modeling, identification, and optimization of violin bridges
Authors: Marschke Sandra , Ring Wolfgang , Wohlmuth Barbara
Published: December 2018

We present the derivation and implementation of a mathematical model for the linear elastic structure of a violin bridge. In favour of getting highly accurate simulation results, special effort has been taken to reconstruct the computational geometry from a µ‐CT scan. After laying out our approach for this in detail, we also present first vibroacoustical analysis like solving the eigenvalue problem of elasticity for the orthotropic material law of the wooden bridge and simulation of its dynamical behaviour. We then conclude with explaining our ongoing work of identifiying material paramters by an inverse problem. With this project we are aiming to optimize a violin bridge regarding its material parameters and its shape.
Multi‐factors Optimization Design of Pin‐Fin Structure Using Respond Surface Method
Authors: Wang Xiang , Chen Min , Zhang Shunqi , Tate Derrick
Published: December 2018

Most optimizations on pin fin heat sink only involve the relationship between single factor variable and performance. This study aims to find out the optimized solution for coupled effects of parameters based on RSM (Response Surface Methodology). Height and diameter of cylindrical pin‐fin are adopted as designed parameters, according to numerical simulation the interaction of different parameters are investigated and an optimized scheme is achieved.
Mesoscale Simulation of Shape Memory Alloy Film Damping
Authors: Ahmadi Shahabeddin , Jacob Kiran , Wendler Frank , Kohl Manfred
Published: December 2018

This paper presents a macroscale and mesoscale dynamic analysis of the forced vibration of a free‐standing bridge of superelastic shape memory alloy TiNiCuCo for novel miniature scale damping devices with ultra‐low fatigue properties. The effects of pre‐straining and excitation load are investigated in order to define an optimum operation point for a SMA bridge damper device. The analysis is performed under non‐isothermal conditions by taking into account the heat transfer and the rate‐dependence of release and absorption of latent heat.
Numerical Study of Long Separation Bubble on Slotted Thick Airfoil
Authors: Ramzi Mdouki
Published: December 2018

This work is aimed to examine the potential of two types of slots to control the long laminar separation bubble LoSB developed on the suction side of the thick symmetric NACA0021 airfoil. Two dimensional simulations are carried out under steady state and incompressible regime with the correlation‐based intermittency turbulent model in order to predict the boundary layer transition aspect. Two slots are included separately in the airfoil and are proposed as a passive tool to manipulate the LoSB under the effect of pressure gradient between both high and low pressurized zones. The results without control are confronted with experimental data and give a good validation. Concerning the controlled configurations, the transversal slot fails to manipulate the LoSB, while the longitudinal slot reveals its positive potential to control the LoSB and therefore enhancing the lift coefficient of the airfoil and the length of the SB, however, the drag coefficient was increased.
A finite‐element framework for the modelling and simulation of phase transforming magnetic solids using energy relaxation concepts
Authors: Bartel Thorsten , Kiefer Bjoern , Buckmann Karsten , Menzel Andreas
Published: December 2018

In this contribution we present a variational framework suitable for the finite element implementation of energy relaxation‐based dissipative magnetostriction and magnetic shape memory alloy models. Inspired by the non‐local nature of the magnetostatic energy stored in the self‐field associated with magnetised solids, three global fields are considered: the displacement field, the scalar magnetic potential, and additional state variable fields that parameterise the microstructure. This global variational three‐field problem is enhanced by the consideration of Karush‐Kuhn‐Tucker parameters—stemming from restrictions w.r.t. the microstructural variable evolution—at each node of the finite element mesh. This approach allows the simulation of magnetomechanically fully‐coupled, microstructure evolution‐driven responses in arbitrarily shaped domains.
Computational study of the interaction between degradation of biodegradable magnesium implants and bone remodelling
Authors: Ma Songyun , Markert Bernd
Published: December 2018

Biodegradable magnesium implants are increasingly applied to promising orthopaedic fixation devices due to obvious advantages over conventional permanent implants. However, potential risks of environment assisted corrosion failures during their service in human body have not been systematically studied [1], which leads to a limitation of the extensive applications of the magnesium implants. In addition, the influence of the degradation process of magnesium implants on the bone remodelling after surgery is also a critical factor. Therefore, a modelling approach is required to understand their interactions with the physiological environment and improve the design of biodegradable magnesium implants with respect to the healing efficiency of fractured bones. In the present work, three‐dimensional computer simulations are conducted for a fractured femur fixed by the bone plate and screws to investigate the service behaviour of magnesium implants and their interaction with the bone healing process. A mechano‐regulatory model based on the biphasic stimuli is used to simulate tissue differentiation and bone remodelling of the fractured femur. A corrosion damage model is used to describe the complex degradation process of mechanical integrity of magnesium implants under physiological loadings. The simulation results are consistent with the experimental observation. The present modelling approach provides an efficient tool in the design and the performance evaluation of biodegradable magnesium implants.
Simulation of PCM‐saturated porous solid matrix for thermal energy storage using the phase‐field method
Authors: Sweidan Abdel Hassan , Heider Yousef , Markert Bernd
Published: December 2018

Latent heat storage systems using phase change materials (PCMs) are considered an attractive technique for storing the available thermal energy due to their high energy storage capacity, compactness and ability to store heat at an almost constant temperature. However, the PCMs suffer from their low thermal conductivity that affects the heat transfer rates and leads to slow charging and discharging processes. Therefore, many approaches have been adopted for improving the low thermal conductivity of PCMs. In the underlying research work, a latent heat storage medium using a PCM‐saturated highly conductive porous metal foam is being studied. High porosity cellular metal foams are proved to be promising materials for enhancing the heat transfer performance of the PCMs due to their high surface area to volume ratio, ultra light weight and relatively high thermal conductivity. A macroscopic description of the PCM‐saturated porous material with intrinsically coupled and incompressible solid and fluid constituents is presented, based on the Theory of Porous Media (TPM). The heat transfer process between the metal foam and the PCM is described using the local thermal non‐equilibrium model, where the phase‐field method (PFM) is employed to account for the phase change process. The PFM relies on specification of the free energy density function and employs a phase‐field variable that defines the state of the material (solid or liquid). Finally, numerical examples using the finite element method are presented to show the ability of the phase‐field‐porous media approach in simulating the phase change problems on the macro scale.
Flatness‐based control of a rigid body carried by multiple heavy ropes
Authors: Irscheid Abdurrahman , Gerbet Daniel , Rudolph Joachim
Published: December 2018

Flatness‐based trajectory planning for the distributed‐parameter system consisting of a rigid body carried by multiple heavy ropes is discussed. The suspension points (controlled ends) of the ropes are assumed to be freely movable. The other ends of the ropes are parametrized by a flat output of the nonlinear boundary system at the load that describes the motion of the rigid body. This parametrization is then used to express the solution of the linearized partial differential equations for the heavy ropes under small angle approximations around a vertical equilibrium configuration by the means of operational calculus. It is shown that the system trajectories of the ropes depend on distributed delays and advances of the flat output trajectory at the load‐side boundary system. Evaluating the derived parametrization of the heavy ropes at the controllable ends yields the desired open‐loop controller by using a planned trajectory for the flat output. This control can be used to realize a desired transition of the load position and orientation in finite time. The introduced method is illustrated for the example of a linear infinite‐dimensional model of two heavy ropes carrying a rigid rod.
A Filter‐Based Motion Cueing Algorithm for a Redundant Driving Simulator
Authors: Ellensohn Felix , Breyer Manuel , Schwienbacher Markus , Venrooij Joost , Rixen Daniel
Published: December 2018

A Motion Cueing Algorithm (MCA) determines the simulator's input subject to the driving dynamics demands. Main limitations form the technical restrictions of the simulator's actuators on position, velocity and acceleration level. This paper shows a filter‐based MCA for a redundant motion system exhibiting nine degrees of freedom (DoF). The redundant DoF are distributed by a frequency divider. A parameter optimization scheme is shown to estimate the unknown parameters of the MCA subject to the tilt restrictions and the exploitation of the actuators.
Numerical investigations of diffusion coefficients in the context of multi‐component gas transport within the Theory of Porous Media
Authors: Thom Andrea , Ricken Tim , Koßler Marvin , Gehrke Tobias , Denecke Martin , Widmann Renatus , Schulte Marcel , Schmidt Thorsten C.
Published: December 2018

In order to simulate methane oxidation within landfill covers in changing environmental conditions, a computational approach via the extended Theory of Porous Media (eTPM) was created. Its purpose is to gain an overall view on the ongoing processes such as concentration progression of methane, oxygen, carbon dioxide and nitrogen. For that, advective and diffusive transport mechanisms as well as energy production from the exothermic oxidation reaction are considered. Regarding the diffusive gas transport different approaches to model the diffusion coefficient are made use of.
Damage evolution in fiber reinforced polymer‐metal joints – modeling and simulation
Authors: Hirsch Franz , Kästner Markus
Published: December 2018

In this contribution, the interface behavior of an aluminum component connected to an FRP is considered on the microscale. Different local features, e.g. the surface roughness, fibers near the interface and local failure of the polymer material and their effects on the overall interface characteristics are investigated. Computational homogenization schemes enable the derivation of effective traction‐separation laws for representative interface elements. The polymer material can exhibit large deformations up to failure, which is modeled with a gradient‐enhanced finite strain elastic‐plastic damage model.
A nonlinear FE‐HMM formulation along with a novel algorithmic structure for finite deformation elasticity
Authors: Eidel Bernhard , Fischer Andreas , Gote Ajinkya
Published: December 2018

This contribution presents a nonlinear formulation of the Finite Element Heterogeneous Multiscale Method (FE‐HMM) for the homogenization of microheterogeneous solids. Moreover, a novel algorithmic structure is proposed for FE‐HMM, FE2 and alike, which enables for hyperelastic constitutive laws a considerable speed‐up compared to the existing standard.
A coupled thermo‐poro‐mechanical model of the breast applied to breast cancer detection
Authors: Niedermeyer Angela , Ma Songyun , Markert Bernd
Published: December 2018

Recently, diagnostic methods based on infrared thermographic imaging of the skin have shown promising results regarding skin cancer detection. The application to breast cancer has not yet led to satisfying results. The challenge lies in determining the location and intensity of the embedded cancerous heat source from measured infrared radiation of the breast surface. For this purpose, a coupled poro‐thermo‐mechanical constitutive model of the breast is proposed here, which describes the energy transport in this soft tissue. In this work, numerical simulations of a breast model containing a tumor are conducted to study the correlation between skin temperature and tumour characteristics. The results demonstrate that the proposed modelling approach can be employed to determine optimal measurement conditions such as surrounding temperature and to evaluate the potentialities of transient measurements.
Improving school education in science, technology, engineering, and mathematics: practical methods and an international cooperation
Authors: Gunesch Roland , Robin Nicolas
Published: December 2018

This article showcases an international cooperation between academic institutions with the goal of improving STEM education (science, technology, engineering and mathematics) in middle schools and high schools.
Ensemble reachability of parametric harmonic oscillators via mixed open‐loop and feedback control
Authors: Schönlein Michael
Published: December 2018

This paper considers the problem of ensemble reachability of parametric controlled harmonic oscillators. It is shown that the usage of mixed open‐loop and feedback controller a larger parameter space can be dealt with in contrast to purely open‐loop control inputs.
Towards the generation of dry patient‐specific human aortic valve models from medical imaging data
Authors: Morales Ortuno Sergio , Röehrle Oliver
Published: December 2018

Considering the geometry of the human aortic valve as one of the key factors influencing directly on its function, deformation and performance, we focus on the generation of 3‐D Finite Element Models (FEMs) of these valves under healthy and diseased conditions from patient‐specific geometries extracted from medical imaging data.
Partitioned simulation of the fluid‐structure interaction of flexible marine propellers in unsteady flow conditions
Authors: Lampe Tobias , Radtke Lars , Abdel‐Maksoud Moustafa , Düster Alexander
Published: December 2018

Regarding new propeller materials and designs, vibrations and large deformations are becoming increasingly relevant. Therefore, simulation methods need to be developed which take into account the interaction of fluid and structure while retaining a computational effort suitable for the design stage. In the approach presented here, the fluid mechanical subproblem is solved by means of the software panMARE, which is based on the potential theory. The structural‐mechanical subproblem is engaged using different structural solvers as well as modelling approaches. Information exchange between the subproblems is managed by the software comana.
Interactive Web Apps for Visualizations in Mathematics and Engineering
Authors: Taddei Francesca , Rüth Benjamin , Karpfinger Christian , Müller Gerhard
Published: December 2018

Depicting numbers in a graphical way has always been crucial to understand and explain the physical phenomena behind. Interactive graphical applications bring the understanding to a higher level, where the users get actively engaged. Moreover, interactive visualization of data, equations etc.… help to motivate students and strengthen the sharing of knowledge. At the Technical University of Munich, the Chair of Structural Mechanics and the Research Group Algebra developed interactive applications in the fields of mechanics and higher mathematics. Students can access the applications online at any time, without installation or special requirements, and, thus, can actively explore the content with a very low entry barrier. For example, they can experiment with a spring‐mass‐damper system and let it enter the resonance by changing the frequency of the excitation; or they can search for local maxima and minima of a function with side conditions with the Lagrange multipliers in an interactive and graphical way. The interactive process enhances the understanding, even if the user does not interact with a strategy but just uses his intuition. These applications can be also used to explain complex concepts to the general public. The source code is publicly available on
https://github.com/ChairOfStructuralMechanicsTUM/Mechanics_Apps
.
Lower gamma globulin level before conditioning is a risk factor for cytomegalovirus antigenemia after pediatric allogeneic stem cell transplantation
Authors: Kobayashi Ryoji , Hori Daiki , Matsushima Satoru , Sano Hirozumi , Suzuki Daisuke , Kobayashi Kunihiko
Published: December 2018

Background

Despite the development of early detection methods and new antiviral drugs, cytomegalovirus (CMV) infection remains a persistent and sometimes severe complication of stem cell transplantation (SCT). CMV antigenemia has become widely used for early detection of CMV infection after SCT.

Procedure

We retrospectively analyzed risk factors for CMV antigenemia in pediatric patients following allogeneic SCT. We analyzed 74 pediatric patients who received allogeneic SCT at Sapporo Hokuyu Hospital between April 2007 and March 2018 and were alive over three months after SCT.

Results

Of the 74 patients, 22 (29.7%) were CMV antigenemia positive. On univariate analyses, many patients with CMV antigenemia tested positive for CMV antibody before SCT (P < 0.001), and had lower gamma globulin levels before conditioning (P = 0.014). Multivariate analysis additionally confirmed that pre‐SCT CMV antibody positivity (P < 0.001) and preconditioning gamma globulin levels under 655 mg/dL (P = 0.004) were independent risk factors for post‐SCT CMV antigenemia.

Conclusions

These results indicate the importance of assessing gamma globulin levels in pediatric patients prior to SCT.
Adolescent and young adult cancer care: Financial hardship and continued uncertainty
Authors: Parsons Susan K. , Kumar Anita J.
Published: December 2018

Since 2005, there has been a steady increase in the number of new cancer diagnoses among adolescents and young adults (AYA) in the United States (US), likely due to improved awareness and detection within this age group, as well as the possible contribution of insurance expansion under the Patient Protection and Affordable Care Act. AYAs with cancer remain highly vulnerable financially, a situation that will only worsen with proposed rollbacks in access to and affordability of healthcare. In this review, we will discuss existing aspects of financial hardship and highlight areas of uncertainty, based on the current US political climate.