bluuebunny/crossref_metadata_2025 huggingface dataset:
Cycle‐based Adaption of a Model‐Predictive Control Strategy for Injection Molding Machines
Authors: Froehlich Christoph , Kemmetmüller Wolfgang , Kugi Andreas
Published: November 2019

Injection molding is one of the most important manufacturing processes in the polymer industry. It is a cyclic process, where the phases of the process are repeated for each produced part. An accurate control of the process variables (e.g. the injection pressure and speed) to their desired values is essential to obtain a constant high product quality. In a recent publication [5], it was shown that the control accuracy can be significantly improved compared to the state of the art by means of a nonlinear model‐predictive control (MPC) strategy. Thereby, an essential point to achieve a high control accuracy is the estimation of the (bascially unknown) volume flow into the mold. In the present work, the benefits of utilizing the measurement information of the previous and the current cycles are examined. An estimator concept is presented which combines the advantages of the high accuracy of an offline estimation with the capability to account for variations of the injection process by an online estimation. The improved control accuracy of the proposed method is shown by simulation studies.
Identification of Radiation Damping Using a Coupled FE/BE Formulation and a Nonlinear Eigenvalue Solver
Authors: Baydoun Suhaib Koji , Marburg Steffen
Published: November 2019

While acoustic radiation damping is a rather small and insignificant aspect of many engineering applications, it is the primary energy‐dissipating mechanism for lightweight structures with large radiating surfaces. Attempts to reduce the vibrational response of those lightweight structures by additional mechanical damping can only be successful if the extent of mechanical damping is comparable or larger than the extent of radiation damping. In this regard, engineers are in need of reliable and flexible methods for the quantification of radiation damping, as well as for the modeling of its effect in an early stage of the design process. In this paper, the modal radiation loss factors are obtained from an eigenvalue analysis of the coupled structural acoustic system. The equations of linear elasticity and acoustics are addressed by finite and boundary element methods respectively. The nonlinear eigenvalue problem is solved by contour integration. The thereby obtained modes represent the structural modes subject to acoustic loading. The modal radiation damping values can be obtained from the complex eigenvalues. The approach is verified based on the example of a honeycomb sandwich panel in air.
An accelerated Boundary‐Domain Integral Method for three‐dimensional fluid flow analysis
Authors: Tibaut Jan , Ravnik Jure
Published: November 2019

The rapid growth of computer power enables performing of more and more complex numerical simulations. However, the need to develop efficient numerical algorithms is always present. In this study, we propose an acceleration of an algorithm to solve the nonlinear system of Navier‐Stokes equations. We present an accelerated Boundary‐Domain Integral method (BDIM). The BDIM is a boundary element method (BEM) based method, thus its computational demands scale as 𝒪(N2), where N is the number of grid nodes. This is due to the fact that the discretization procedure leads to fully populated matrices. However, the computational demands can be reduced to a linear‐logarithmic 𝒪(N log N) complexity, with the implementation of an approximation procedure. In this study, we solve the velocity‐vorticity formulation of the Navier‐Stokes equations and develop an accelerated algorithm for determination of the boundary vorticity in 3D based on ℋ‐matrix and the adaptive cross approximation (ACA) method. We test the algorithm using coupled nanofluid flow and heat transfer. As expected results show that, the acceleration (matrix compression rate) has a negative influence on the solution accuracy.
Kinematics of finite‐dimensional mechanical systems on Galilean manifolds
Authors: Winandy Tom , Eugster Simon R. , Capobianco Giuseppe
Published: November 2019

In a coordinate‐free description of time‐independent finite‐dimensional mechanical systems the configuration manifold plays a central role. In the case of time‐dependent mechanical systems, time needs to be included in the space on which the related physical theory is formulated. In this respect, we show that a so‐called Galilean manifold not only provides a ‘generalized space‐time’ but that it allows the coordinate‐free presentation of a physical theory for time‐dependent finite‐dimensional mechanical systems. The motion of a mechanical system is interpreted as an integral curve of a second‐order vector field on the state space related to the Galilean manifold of the system. Second‐order vector fields, which are the coordinate‐free equivalent of second‐order differential equations, are in one‐to‐one correspondence with the action forms introduced by Loos [4,5]. Because of this bijective relation, the kinetic part of the theory can be formulated by postulating the action form governing the motion of a finite‐dimensional mechanical system.
Rate‐dependent fracture simulation of viscoelastic material by the phase‐field method
Authors: Yin Bo , Kaliske Michael
Published: November 2019

The phase‐field method has been studied for fracture analysis during the last decade. Based on the classical GRIFFITH‐type brittle fracture, good agreements are obtained by comparing to other numerical methods as well as experiments. Furthermore, phase‐field modelling does not depend on any explicit criterion and gets rid of discontinuous displacement tracing. Regarding most elastomers exhibiting both elastic and viscous behaviour simultaneously, it yields a rate‐dependent mechanical response. Investigated by experiments, the fracture process is shown to be rate‐dependent as well. In this work, a viscoelastic rheological model based on REESE & GOVINDJEE [1] is coupled to the phase‐field approach to investigate rate‐dependent fracture evolution within elastomers. The fracture mechanism is based on the volumetric‐isochoric split and the driving force for fracture is defined to be the elastic strain energy potential by both the equilibrium and the non‐equilibrium branches. Representative numerical models are simulated and related findings and potential subsequent perspectives are summarized to close the paper.
Capillary Rise ‐ Jurin's Height vs Spherical Cap
Authors: Gründing Dirk , Fricke Mathis , Bothe Dieter
Published: November 2019

When liquid rises in a capillary, the interface has a shape close to a spherical cap when the Eotvos number is sufficiently small. This assumption is typically used when computing the stationary rise height of the liquid. Considering a continuum mechanical approach it can be shown that the exact shape of a spherical cap is not a solution to the rise problem yet a good approximation. Consequently, the assumption of a spherical cap used in Washburn‐type rise models is justified only for small Eotvos numbers. In this limit, Jurin's height has the largest error.
Thermo‐Mechanical Modeling of Pre‐Consolidated Fiber‐Reinforced Plastics for the Simulation of Thermoforming Processes
Authors: Ziegs Jean-Paul , Weck Daniel , Gude Maik , Kästner Markus
Published: November 2019

Multi‐material design aims at the targeted combination of materials with different characteristics in order to meet technical requirements. Especially the combination of metals and fiber‐reinforced plastics (FRP) has led to innovative lightweight structures with high loading capacity and ductility in recent years. The process chain required to produce such structures is characterized by a variety of process parameters which have a significant influence on the quality of the manufactured workpiece. In order to treat the thermoforming process numerically, we present constitutive models for the metal and composite part to simulate the deformation behavior of these components. In addition, experimental setups are described to identify the required material parameters. Simulations of the manufacturing process will indicate correlations between material as well as process parameters and possible defects of the final structure that may occur during manufacturing.
Oscillations in a system of two coupled self‐regulating spool valves with switching properties
Authors: Schröders Simon , Fidlin Alexander
Published: November 2019

In hydraulic systems, valves can be considered as fundamental components. They serve as control elements to regulate hydraulic power transmission. In order to minimize control effort, self‐regulating spool valves enjoy great popularity. However, their disadvantage is a possible loss of stability, caused by the coupling between hydraulic and mechanical degrees of freedom via pressure feedback areas. So far, the self‐excited oscillations, evoked from the operating point's loss of stability, have mostly been investigated using minimal models of individual valves. In real world applications, for example in automotive transmissions, typically several valves are employed which are coupled by hydraulic pipes. Here, it is expected, that dynamical phenomena occur, which cannot be portrayed by simple models of individual valves. Within this contribution, the oscillatory behaviour of a system employing two coupled self‐regulating valves is discussed. The resulting non‐stationary solutions are characterized by using Floquet theory and computing Lyapunov‐Exponents.
Coupled thermomechanical model for strain‐induced crystallization in polymers
Authors: Aygün Serhat , Klinge Sandra
Published: November 2019

Crystallization in certain polymers, like natural rubber, is characterized by the specific geometrical arrangement of atoms in macromolecules caused by high strains. Starting from crystallization nuclei, polymer chains leave their natural entangled structure, stretch out, fold back and stack. Eventually, they build regions with a regular structure, also called lamellae. The process must be taken into consideration when planning manufacturing processes since it significantly influences mechanical and thermal properties of the final product. The present contribution deals with the thermomechanical model for crystallization of unfilled polymers, which involves displacements and temperature as global degrees of freedom, and the degree of network regularity as an internal variable. The mechanical part of the model uses the dissipation potential with two special features: Firstly, the thermodynamically consistent framework is developed to simulate the reduction of the network regularity during the unloading phase. Secondly, the microstructure evolution under the cyclic tensile load is visualized. The thermal part of the model is based on the solution of the heat equation. The resulting, coupled thermomechanical problem is solved in a monolithic way. Finally, selected numerical examples are compared with experimental data of natural rubber without fillers.
External Vibration Damping of a Robot Manipulator's TCP Using Acceleration Feedback
Authors: Berninger Tobias F. C. , Rixen Daniel J.
Published: November 2019

There are multiple possible applications, which demand high accuracy from industrial robot arms. The usual approach to improve the path accuracy of these robot manipulators is to make the mechanical design as stiff as possible and to employ high fidelity joint controllers, which compensate path inaccuracies with well‐identified models of the manipulator system. These methods are, however, only available to the robot manufactures themselves during their development phase. Companies designing tools for specific high accuracy tasks generally cannot change the design of a given robot manipulator and are bound to its precision. An alternative concept to further increase the path accuracy of a robot manipulator, without making changes to its design itself, might be to employ traditional Active Vibration Damping techniques by adding a supplementary proof‐mass actuator to the robots tool center point with collocated acceleration sensor feedback. This paper explores the feasibility of this idea within a multi body simulation of a simple robot manipulator, which consist of rigid links, flexible joints and is actuated by cascaded joint controllers. The performance of an acceleration feedback controller employed on the robots TCP is evaluated by a test trajectory.
A mixed least‐squares finite element formulation within the framework of the theory of porous media
Authors: Schwarz Alexander , Averweg Solveigh , Bluhm Joachim , Schröder Jörg
Published: November 2019

In the present contribution a mixed least‐squares finite element method (LSFEM) based on the Theory of Porous Media (TPM) is presented. In detail, we investigate an incompressible binary model consisting of the phases solid and liquid. The main idea is based on the modeling of saturated porous structures. The resulting finite element is a four‐field formulation in terms of solid displacements, liquid pressure, mixture stresses and a new variable related to the pressure gradient. The conforming discretization of the unknowns in the spaces H(div) and H1 is realized by vector‐valued Raviart‐Thomas and standard Lagrange functions. Finally, a numerical example for liquid saturated porous structures considering an incompressible, linear elastic material behavior at small deformations, demonstrates the applicability of the LSFEM approach to the TPM.
Artificial Neural Network forecasting for monomorphic and polymorphic uncertainty models and comparison with experimental investigations
Authors: Gruhlke Robert , Drieschner Martin , Eigel Martin , Hömberg Dietmar , Petryna Yuri
Published: November 2019

Tools from probability or possibility in terms of fuzzy sets are usable for the description and quantification of uncertainties within numerical simulations. In this work, different monomorphic and polymorphic uncertainty models are applied on linear elastostatic structures with non‐periodic perforations in order to analyze the individual expressiveness. The first principal stress is used as an indicator for structural failure which is evaluated and classified. Artificial Neural Networks are used as surrogate model to compare and assess the uncertainty models with regard to the numerical predictions. Real experiments of perforated plates under uniaxial tension are validated with the help of various uncertainty models.
Thermo‐Mechanical Analysis of a Steam Turbine rotor
Authors: Eisenträger Johanna , Naumenko Konstantin , Kostenko Yevgen , Altenbach Holm
Published: November 2019

In power plants, high temperatures prevail during long holding times. Furthermore, power plants are often started and shut‐down in order to account for gaps or oversupplies in energy production. These loading conditions induce both creep and fatigue loads. Due to their excellent thermo‐mechanical properties, such as high tensile strength and elevated corrosion resistance, heat‐resistant steels are established materials for power plant components. Nevertheless, these steels tend to soften under deformation, which should be accounted for by a constitutive model.

The contribution at hand analyses the thermo‐mechanical behavior of a steam turbine rotor. For this purpose, a unified phase mixture model is introduced. This constitutive model accounts for rate‐dependent inelasticity, hardening, as well as softening by employing an iso‐strain approach with a soft and a hard constituent. While the soft constituent represents areas with a low dislocation density, such as the interior of subgrains, the hard constituent refers to regions with a high dislocation density, i.e. the subgrain boundaries. Furthermore, two internal variables are introduced: a backstress tensor of Armstrong‐Frederick type and a scalar softening variable. The model results in a coupled system of three evolution equations with respect to the inelastic strain, the backstress, and the softening variable.

To allow for the analysis of real power plant components, the model is implemented into the finite element method such that the evolution equations are integrated based on the backward EULER method. The applicability of the model is demonstrated by conducting a thermo‐mechanical analysis of a steam turbine rotor with complex geometry under realistic boundary conditions. In a first step, the instationary temperature field in the rotor is computed in a heat transfer analysis. Thereby, typical steam temperatures in power plants and the corresponding heat transfer coefficients are prescribed. As a next step, the structural analysis is conducted based on the phase mixture model and the obtained temperature field as input. In addition, the time‐dependent rotational frequency and steam pressure are taken into account. Note that the influence of different start‐up procedures such as a cold or a hot start is examined in detail. As a result, the structural analysis provides the stress‐strain hystereses, which constitute the basis for further fatigue and damage assessment.
Characterizing Materials in the Frequency Domain: Validation Experiments
Authors: Katzmann (né Sauer) Josef , Musialak Jana , Steeb Holger
Published: November 2019

High Performance Concrete (HPC) and Ultra High Performance Concrete (UHPC) achieve an effective stiffness or strength which allows constructing highly stressed buildings. Following, we present a mechanical characterization technique for HPC and UHPC, using harmonic excitations from 0.1 Hz up to 1 kHz and displacement amplitudes in the micrometer range. The small‐amplitude excitations are performed by a high‐performance piezo‐electric actuator. To validate the experimental workflow, we characterize the mechanical behaviour of Polymethylmethacrylat (PMMA). In this contribution, we present results gained with two different cylindrical sample sizes. By this comparison we shall ensure that geometrical scaling of samples has no influence on the rheological results of the experiments, apart from a change in Signal‐to‐Noise ratio.
A Priori Error Estimates for an Optimal Control Problem Governed by a Variational Inequality of the Second Kind
Authors: Meyer Christian , Weymuth Monika
Published: November 2019

We consider an optimal control problem governed by an elliptic variational inequality of the second kind. The problem is discretized by linear finite elements for the state and a variational discrete approach for the control. We derive nearly optimal a priori error estimates based on L∞‐error estimates for the variational inequality and a quadratic growth condition. Our error analysis yields a convergence rate of order 1 − ϵ for the L2‐norm of the control.
Damage simulation of fiber reinforced composites using mean‐field homogenization methods
Authors: Lenz Peter , Mahnken Rolf
Published: November 2019

Our work presents a two‐scale mean‐field homogenization framework for constitutive multiscale (meso‐macro) modeling of fiber reinforced composites (FRC) including damage. The FRC is decomposed into three distinct linear thermo‐chemo‐elastic material phases. The three phases are unidirectional fibers surrounded by an interface, which is surrounded by a matrix material. Different mean‐field homogenization methods can be used to determine the effective properties. For the damage a distinction is made between four different damage modes namely matrix damage, fiber damage, interface damage and a simultaneous damage of the matrix and the fiber called matrix‐fiber damage. An element deletion algorithm is used to simulate a crack propagation. A representative example demonstrates the different types of damage and a resulting crack propagation in an FRC.
Specimen design for extreme uniaxial tension‐compression tests of rubber materials
Authors: Kanzenbach Lars , Schlomka Clemens , Gelke Sören , Ihlemann Jörn
Published: November 2019

In this contribution a new measurement strategy is presented, which enables in combination with an optimized specimen‐setup the investigation of strains up to a compression level of −70%. The specimen‐setup itself consists of a slender dumbbell structure and a mounting geometry. The main idea of the new measurement strategy is, that for almost incompressible materials the average strain in the symmetry plane can be derived from the tangential strain at the surface. For this, the new measurement strategy is derived, simulated and experimentally tested. Finally, phenomenological characteristics of rubber, like Payne effect, Mullins effect, permanent set, relaxation and creep can be investigated at such extreme compression levels.
A phase field model for thermo‐oxidative aging in cracked polymers
Authors: Voges Jannik , Juhre Daniel
Published: November 2019

When dealing with polymers, the behavior of aging processes is of great interest in many applications in engineering, as the usually very complex mechanisms can result in a drastic reduction of the lifetime of machine parts. In addition, those single mechanisms are coupled, which results in even more complexity. A crack creates new surfaces deeper inside the material and thus enables oxidation processes beyond the original surface. Once being oxidized, the crack resistance might be reduced, which may result in further crack propagation, which, again, enables oxidation even deeper.

In the present work, a new approach for diffusion limited oxidation is introduced. The approach is based on the phase field method, which has become an important and versatile tool to model different phase evolutions in materials. An evolution equation is underlain by a gradient energy term to capture an interface energy and by a second term, which corresponds to the phase change representing the oxidation state. A diffusion equation controls the amount of available oxygen which is able to trigger the phase change. The phase change, in turn, drains a specific amount of oxygen in the coupled system of differential equations. In this work, cracks are able to expedite the oxidation process deeper into the specimen. The model has been implemented into the FE code FEAP and investigated by means of two academic examples.
Emergence of constant tilt angle for vector fields on flexible curves
Authors: Brand Christopher , Dolzmann Georg
Published: November 2019

A model for the evolution of vector fields on flexible curves is investigated. Explicit solutions with radial symmetry demonstrate global existence. Numerical simulations show that configurations with constant tilt angle emerge as stationary states.
Local Fourier analysis of multigrid smoothers for the Stokes problem
Authors: Bolten Matthias , Claus Lisa
Published: November 2019

We present a local Fourier analysis of the Stokes equations for a finite difference discretization on staggered grids. We compare the commonly used Vanka smoother with a non‐overlapping variant of the Vanka smoother. While the latter is computationally cheaper, the convergence depends severely on the order in which the unknowns are updated. In contrast, the convergence of the overlapping method is not affected by the order.
Aspects of the Particle Finite Element Method applied to contact problems
Authors: Schewe Markus , Menzel Andreas
Published: November 2019

The Particle Finite Element Method (PFEM) developed by [1] is designed to allow changes in the outer shape of a body while performing a Finite Element Analysis. This is achieved by repeated remeshing and shape detection of a particle cloud, which represents the body under consideration. The shape detection method creates new surfaces if formerly connected points on the surface move away from each other sufficiently. This method allows to model material separation, e.g. in metal cutting, see [2]. Details on advanced strategies to refine the detected shape are presented. Considering abrasive wear of surfaces, a mechanism‐based approach aims to model such separation of surface particles on a mesoscale. The basis of this approach consists of a contact algorithm that captures the interaction of solid bodies. This contribution presents a contact domain method [3] which is implemented in PFEM. The approach uses the abilities of the shape detection method as a contact search method. Furthermore, strategies for solving large strain boundary value problems using this contact model are discussed. Numerical examples show the abilities of the approach in an exemplary large strain contact problem.
On the calculation of a dry friction coefficient
Authors: Oestringer Lukas J. , Proppe Carsten
Published: November 2019

Normal contact problems of rough surfaces have already been extensively investigated. For Gaussian surfaces, the normal force Fn is often found to be proportional to the real contact area A. Following the approach of Bowden and Tabor [1] for the tangential force Ft = τA, where τ denotes the yield shear stress of the softer surface, the friction coefficient µ = Ft/Fn , as ratio of tangential to normal force, is constant. This result is commonly used to justify Coulomb's friction law.

Nevertheless, velocity dependent friction coefficients are widely used in many static and dynamic friction laws, although detailed simulative investigations on the physical background of the velocity dependence are missing. For these reasons, a halfspace simulation for rough surfaces subjected to sliding motion is presented here. The simulation includes temperature evolution as well as thermal expansion and their influence on contact forces, real contact area and friction coefficient. It is found that the frictional heat affects all of these variables and in particular leads to a velocity dependent friction coefficient.
Axisymmetric two‐phase flow simulations on space‐time meshes
Authors: Karyofylli Violeta , Kamaldinova Liubov , Simon Marek , Mokrov Oleg , Reisgen Uwe , Behr Marek
Published: November 2019

For reducing the dimensionality and consequently, the complexity of the dynamics related to bubble formation problems, this paper presents an axisymmetric space‐time interface capturing approach [1, 2]. For the description of the moving front, the level‐set method is used, because it is inherently able to account for topological changes of the interface [3], and is combined with a continuum surface force (CSF) model. Different benchmark cases from the literature are used for verifying our numerical approach, and the results are compared with those obtained using the commercial software, ANSYS CFX.
Waveform Iteration with asynchronous communication
Authors: Meisrimel Peter , Birken Philipp
Published: November 2019

Consider the coupling of two multi‐physics systems of time‐dependent ODEs. We propose a new Waveform iteration type method for coupling which uses asynchronous communication to be both parallel in time and fast in convergence. Analytical results show convergence in the continuous setting and numerical results for two coupled head equations show good performance of this method, which is both parallel and converging fast.
Bifurcations and limit cycles due to self‐excitation in nonlinear systems with joint friction: Initialization of isolated solution branches via homotopy methods
Authors: Kappauf Jonas , Hetzler Hartmut
Published: November 2019

The main objective of this contribution is finding isolated stationary solutions, e.g. equilibria or limit cycles, in dynamical systems. Usually, NEWTON‐type methods are applied for solving the resulting algebraic equation system. Here, the most difficult point is finding adequate initial conditions that are providing a solution on the isolated branch. So, there is a need for a more straight forward manner of initialising the continuation of isolated solutions. Within this contribution, homotopy methods are applied. The crucial point is to define a simplified version of the problem F(x; λ), which can be continuously transformed into the original one. As an example, limit cycles of a friction oscillator including COULOMB damping is discussed and two types of homotopy maps are addressed to obtain a starting point for their continuation.
Modeling and simulation of metal bellows in vacuum interrupters
Authors: Boyaci Aydin , Simonidis Christian , Gentsch Dietmar
Published: November 2019

In vacuum interrupters, metal bellows permit the motion of the moving contact with up to long contact strokes while maintaining the ultra‐high vacuum seal. In contrast to most other bellows applications, the opening and closing operation of the vacuum interrupter lead to high‐impulsive motions which additionally excite bellows oscillations. Future requirements of higher switching speeds and operations demand for a simulation‐driven optimization of the metal bellows to increase the mechanical lifetime of the vacuum interrupter.

The damaging effect of the switching operations is investigated on the bellows. A static force is axially applied on the bellows to validate the mechanical model compared with experimental results. Furthermore, a modal analysis is performed to consider the bellows as a flexible body in a multibody simulation. To account for the multiple‐frequency oscillations during the switching operation, a transient simulation is carried out where the excitation of the bellows follows from a travel curve. The global hot spot of mechanical stress is identified for further lifetime evaluations by low‐cycle fatigue methods.
Validation of Finite Element Image Registration‐based Cardiac Strain Estimation from Magnetic Resonance Images
Authors: Berberoğlu Ezgi , Stoeck Christian , Moireau Philippe , Kozerke Sebastian , Genet Martin
Published: November 2019

Accurate assessment of regional and global function of the heart is an important readout for the diagnosis and routine evaluation of cardiac patients. Indeed, recent clinical and experimental studies suggest that compared to global metrics, regional measures of function could allow for more accurate diagnosis and early intervention for many cardiac diseases. Although global strain measures derived from tagged magnetic resonance (MR) imaging have been shown to be reproducible for the majority of image registration techniques, the measurement of regional heterogeneity of strain is less robust. Moreover, radial strain is underestimated with the current techniques even globally. Finite element (FE)‐based techniques offer a mechanistic approach for the regularization of the ill‐posed registration problem. This paper presents the validation of a recently proposed FE‐based image registration method with mechanical regularization named equilibrated warping. For this purpose, synthetic 3D‐tagged MR images are generated from a reference biomechanical model of the left ventricle (LV). The performance of the registration algorithm is consequently tested on the images with different signal‐to‐noise ratios (SNRs), revealing the robustness of the method.
Large‐Scale Quasi‐DNS of Mixed‐Mode Turbulent Combustion
Authors: Zirwes Thorsten , Zhang Feichi , Habisreuther Peter , Bockhorn Henning , Trimis Dimosthenis
Published: November 2019

In many applications like gas turbines, the combustion process can take place in partially‐premixed environments, where fuel and oxidizer are not fully mixed before combustion. These partially‐premixed or mixed‐mode flames have become a focus of combustion research in the last few years. In this work, a quasi‐DNS of an experimentally measured burner configuration has been conducted. The simulation employs a complex reaction mechanism and detailed molecular diffusion coefficients for each chemical species. Due to the highly resolved numerical grids and the detailed thermo‐physical and chemical properties, the simulation results allow to characterize the flame with the help of flame markers in greater detail than the experiments can provide. The investigated flame exhibits characteristics of a premixed flame near the nozzle. Further downstream both premixed and non‐premixed combustion modes become equally important in terms of the heat release rate. The dataset from the simulation also allows to form joint probability density functions of commonly used control variables to study their correlations depending on the combustion regime.
Distributed sampling for rational approximation of the acoustic scattering of an airfoil
Authors: Bonizzoni Francesca , Pradovera Davide
Published: November 2019

In this paper we compute a reduced order model for a time‐harmonic external acoustic scattering problem with parametric frequency. The employed technique isminimal rational interpolation, an explicit moment‐matching method for Hilbert space‐valued meromorphic maps. We study the approximation and stability properties of this technique for different choices of the sample point set, namely fully distributed in the parameter range, and partially and fully confluent. The proposed technique is also compared with an implicit multi moment‐matching method based on Galerkin projection.
Parallel block–selective algebraic multigrid in foam‐extend
Authors: Uroić Tessa , Jasak Hrvoje
Published: November 2019

We present an extension of a well–known classic algebraic multigrid algorithm, where coarsening is based on selection of equations, for an implicitly coupled pressure–velocity system discretised by the finite volume (FV) method. The resulting coefficient matrix of the linear system is point–ordered, and there are 4 equations for each FV cell: three components of velocity and pressure. A significant challenge is posed in terms of parallelisation of the sequential coarsening process and calculation of coarse level matrix, using the Galerkin projection. In this paper we present the parallelisation strategy and performance of the block–selection AMG.
Symbolic Evaluation of hp‐FEM Element Matrices
Authors: Haubold Tim , Pillwein Veronika , Beuchler Sven
Published: November 2019

In this paper we consider higher order shape functions for finite elements on a triangle. On the reference element Dubiner‐like ansatz functions based on suitable integrated Jacobi polynomials are chosen. It can be proved that the corresponding mass and stiffness matrices are sparse for all polynomial degree p. Due to the orthogonal relations between Jacobi polynomials the exact values of the entries of mass and stiffness matrix can be determined. Using symbolic computation, we can find simple recurrence relations which allow us to compute the remaining nonzero entries in optimal arithmetic complexity.
Controlling Physical Properties on Interfaces Using Parametrised Level Set Methods and Extended Finite Element Method
Authors: Wohlgemuth Felix , Barthold Franz-Joseph
Published: November 2019

The stress field information states a main point of interest, when regarding structural optimisation of bimaterial structures. The introduction of stress criteria along the volume is crucial in the development of new designs. In the case of bimaterials, the stress field along the interface deserves additional attention e.g. to prevent delamination. Tracing the interface through shape optimisation in CAD‐based methods is rather expensive due to the high cost in remeshing techniques. Therefore, level set methods with fixed background meshes are used as in [1].

In this work an approach for controlling strains and stresses on the interface in a framework of shape optimisation is introduced. The geometry description is managed by parametrised level set functions and a sub‐meshing technique is coupled with the extended finite element method. The parametrisation with superellipses allows to reduce the number of design variables to a minimum of six variables per introduced ellipse while holding up a sufficient precision in the geometry description (see [2]). Moreover, it simplifies the shape derivatives as it provides an implicit description for the moving interfaces. The sub‐meshing technique makes it possible to keep existing strategies from homogeneous structures and to transform them on a discontinuous material using enriched shape functions provided by the standard extended finite element method (see [3]). Shape sensitivities are evaluated on the sub‐elements and extrapolated to the interface introducing pseudo nodes. The sensitivity information of the stress field among these pseudo nodes can be used in the framework of stress minimisation as well as for a side condition in a volume minimisation setup.
A unified multiscale modelling approach for concrete fatigue with microscale damage‐mechanism implementations
Authors: Caggiano Antonio , Said Schicchi Diego , Yang Sha , Harenberg Stefan , Malarics-Pfaff Viktoria , Pahn Matthias , Dehn Frank , Koenders Eddie
Published: November 2019

A micro‐scale‐based approach for the numerical analysis of cement‐based materials, subjected to low‐ and high‐cycle fatigue actions, is presented in this paper. The constitutive model is aimed at describing the evolving microstructural changes caused by cyclic loading protocols. The plastic‐damage‐based model is formulated combining the concepts of fracture‐energy theories and damage stiffness degradations, representing the key phenomena occurring in concrete under fatigue.
Evaluating Artificial Neural Networks and Quantum Computing for Mechanics
Authors: Mielke André , Ricken Tim
Published: November 2019

The popularization of Machine Learning (ML) and the advent of Noisy Intermediate‐Scale Quantum (NISQ) devices for Quantum Computing (QC) sparked new inspiration for the search for techniques reducing computation time in mechanics. We evaluate artificial neural networks (ANNs) as candidates for creating computationally fast surrogate models for otherwise time‐consuming simulations, using a multiscale and multiphase model describing processes in the human liver. We also give a short overview of interesting quantum‐enhanced algorithms capable of reducing computational cost in parts of complex simulations.
Modelling silica bilayers based on experimental data
Authors: Stratmann Jan , Ebrahem Firaz , Bamer Franz , Markert Bernd
Published: November 2019

In order to investigate the behavior of 2D silica glass subjected to mechanical loading, we develop an algorithm for the realization of 2D newtork glasses consisting of corner‐sharing SiO3 triangles that build rings of different shapes and sizes. Our algorithm extends the network ring by ring in circular manner around the existing configuration. A random engine generates the size of each new ring driven by experimentally evaluated ring statistics that depend on the current number of neighboring rings taken from real 2D silica layers. The method produces continuous random network models with ring size distribution observed in real 2D silica layers and provides the basis for the mechanical investigation of network glasses.
Small strain crystal plasticity based on the primal‐dual interior point method
Authors: Scheunemann Lisa , Nigro Paulo S.B. , Schröder Jörg , Pimenta Paulo M.
Published: November 2019

The paper presents a novel approach for rate‐independent single crystal plasticity based on the Infeasible Primal‐Dual Interior Point Method in a small strain framework. Therein, the principle of maximum dissipation together with the yield functions on the slip systems in the crystal are considered as the constrained optimization problem. The constraint conditions adapted using slack variables and a Lagrangian is formulated using barrier functions. The equations are linearized and solved using Newton's method. Numerical examples are presented for slip on the individual slip systems in a single crystal under global rotation.
Numerical analysis of the thermally induced damage in remote laser cut carbon fibre reinforced polymers
Authors: Schmidt Benjamin , Rose Michael , Zimmermann Martina , Kästner Markus
Published: November 2019

Remote laser cutting in carbon fibre reinforce polymers is a promising machining technology which can reduce the main drawback in laser cutting, the heat affected zone. This contribution presents a two‐step modelling approach for the simulation of remote laser cut carbon fibre reinforce polymers, consisting of a damage model for the initially intact material and a model for the thermally damaged material.

The static damage behaviour was modelled with the Pinho material model [1], which stands out due to its physically based failure criteria. Initial thermal damages caused by the heat input were modelled with the damage parameters of the Pinho model. The dimensions of the heat affected zone are taken from polished micro sections of the material around the cutting edge.

As a numerical example, comparative tensile tests of milled and laser cut open hole specimens were simulated. The advantage of these specimens is the notch effect around the holes in the heat affected zone, which amplifies the differences between the two cutting technologies.
Effect of nitrogen plasma treatment on the crystallinity and self‐bonding of polyetheretherketone (PEEK) for biomedical applications
Authors: Fedel Mariangela , Micheli Victor , Thaler Martin , Awaja Firas
Published: November 2019

Polyetheretherketone (PEEK) is a thermoplastic material with outstanding properties and high potential for biomedical applications, including hermetic encapsulation of active implantable devices. Different biomedical grade PEEK films with initial degree of crystallinity ranging from 8% to 32% (with or without mineral filling) were inspected. PEEK surfaces were treated with nitrogen RF plasma and the effects on materials crystallinity and self‐bonding were evaluated. In particular, the relationship between auto‐adhesive properties and crystalline content of PEEK before and after plasma treatment was examined.

PEEK samples showed different bonding strength depending on their degree of crystallinity, with higher self‐bonding performance of mineral‐filled semi‐crystalline films. XRD did not show any modification of the PEEK microstructure as a result of plasma treatment, excluding a significant influence of crystallinity on the self‐bonding mechanisms. Nevertheless, plasma surface treatment successfully improved the self‐bonding strength of all the PEEK films tested, with larger increase in the case of semi‐crystalline unfilled materials. This could be interpreted to the increase in chain mobility that led to interfacial interpenetration of the amorphous phase.
Incidence and predictors of treatment‐related conjugated hyperbilirubinemia during early treatment phases for children with acute lymphoblastic leukemia
Authors: Hashmi Saman K. , Navai Shoba A. , Chambers Tiffany M. , Scheurer Michael E. , Hicks M. John , Rau Rachel E. , Gramatges Maria M.
Published: November 2019

Conjugated hyperbilirubinemia (CHB) and liver transaminase elevation are known complications of acute lymphoblastic leukemia (ALL) therapy, but host risk factors are poorly understood. Among 373 children diagnosed with ALL between 2011 and 2016, clinically significant CHB and transaminase elevation were observed in 15 (4.0%) and 12 (3.2%) children, respectively, during induction and consolidation. Body mass index ≥95th percentile (odds ratio 9.20, 95% confidence interval 2.56–32.96) was the only host factor independently associated with CHB, and no host factors were associated with transaminase elevation. Obese patients warrant closer monitoring of hepatic function to facilitate early intervention prior to the development of severe, adverse hepatic events.
Cognitive mediators of adaptive functioning outcomes in survivors of pediatric brain tumors treated with proton radiotherapy
Authors: Roth Alexandra K. , Ris M. Douglas , Orobio Jessica , Xue Judy , Mahajan Anita , Paulino Arnold C. , Grosshans David , Okcu M. Fatih , Chintagumpala Murali , Kahalley Lisa S.
Published: November 2019

Background

Cranial radiotherapy (RT) is associated with risk for cognitive and adaptive dysfunction. Proton RT (PRT) is a technique hypothesized to spare cognition by reducing exposure to nontarget brain tissue. However, little is known regarding functional outcomes in survivors of pediatric brain tumor (BT) treated with PRT. The present study examined the relationship between cognitive and adaptive outcomes in pediatric BT survivors post‐PRT.

Methods

Survivors treated with either focal (n = 33) or craniospinal irradiation (CSI; n = 37) PRT completed neurocognitive evaluations approximately 5 years post‐treatment. Results of intelligence testing and ratings of adaptive functioning are reported. Mediation models examined the relationship among radiation field, cognition, and adaptive functioning.

Results

The PRT CSI group demonstrated worse cognitive outcomes than the PRT Focal group across each cognitive index (Cohen's d = 0.56–0.70). Parent ratings of adaptive functioning were also worse in the PRT CSI group than the PRT Focal group (Global Adaptive Composite, d = 0.53; conceptual skills, d = 0.67). Cognitive performance fully mediated the relationship between radiation field and adaptive outcomes, while controlling for group differences in tumor histology and RT dose.

Conclusions

Focal PRT survivors demonstrated generally positive outcomes with weaknesses in processing speed and aspects of adaptive functioning. CSI exposure was associated with more consistently poor cognitive and adaptive outcomes. The increased risk for adaptive dysfunction in the PRT CSI group appeared due to the effects of CSI on cognition. Efforts to reduce the volume of tissue exposure to RT remain important.
Predictors of survival in patients with high‐risk neuroblastoma who failed tandem high‐dose chemotherapy and autologous stem cell transplantation
Authors: Yi Eun Sang , Son Meong Hi , Hyun Ju Kyung , Cho Hee Won , Ju Hee Young , Lee Ji Won , Yoo Keon Hee , Sung Ki Woong , Koo Hong Hoe
Published: November 2019

Objective

This study aims to explore prognostic factors for high‐risk neuroblastoma patients with response failure to tandem high‐dose chemotherapy and autologous stem cell transplantation (HDCT/auto‐SCT).

Methods

Survival outcomes were compared according to characteristics at initial diagnosis, at relapse/progression, and after relapse/progression in patients who experienced relapse/progression after tandem HDCT/auto‐SCT from 2006 to 2018.

Results

Forty‐nine patients experienced relapse/progression after tandem HDCT/auto‐SCT during the study period: 43 received salvage treatment and 30 underwent allogeneic SCT (allo‐SCT) after reinduction treatment. Although all six patients who did not undergo salvage treatment died, 13 of the 43 patients who did remain alive. The 3‐year probabilities of event‐free survival (EFS) and overall survival (OS) from initial relapse/progression among the 49 patients were 14.4% ± 5.2% and 21.2% ± 6.4%, respectively. A higher neuron‐specific enolase (NSE) level (>24 ng/mL) at relapse/progression was an independent prognostic factor for worse OS. Nine of 30 patients who underwent allo‐SCT remain alive, and the 3‐year probabilities of EFS and OS from allo‐SCT were 16.5% ± 7.2% and 21.6% ± 8.3%, respectively. A higher NSE level and no incorporation of high‐dose 131I‐metaiodobenzylguanidine (HD‐MIBG) treatment into allo‐SCT were independent prognostic factors for worse EFS and OS after allo‐SCT.

Conclusion

The results suggest that a higher serum NSE level at relapse/progression is a predictor of worse prognosis in patients with response failure to tandem HDCT/auto‐SCT, and that incorporation of HD‐MIBG treatment into allo‐SCT may improve outcomes.
Omic approaches to pediatric bone sarcomas
Authors: Tirtei Elisa , Cereda Matteo , De Luna Elvira , Quarello Paola , Asaftei Sebastian Dorin , Fagioli Franca
Published: November 2019

Over the last decade, next‐generation sequencing technologies have improved our ability to assess biological aspects, at genomic and transcriptomic levels, on a large scale— and have been increasingly used for the management of adult cancers. However, their efficacy and feasibility within pediatrics is still under investigation. “Omic” approaches represent an opportunity to understand the oncogenic mechanisms driving the onset and progression of bone sarcoma and improve the clinical management of young patients with bone sarcomas. This review focuses on the current genomic and transcriptomic characteristics of managing pediatric patients, affected by Ewing sarcoma and osteosarcoma.