bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of the Elastic Behaviour of Hybrid‐yarn Reinforced Elastomers using Twisted‐periodic Boundary Conditions
Authors: Storm Johannes , Kaliske Michael
Published: March 2018

Reinforcements of elastomers using hybrid‐yarns allow to take advantage of the bi‐modular stiffness behaviour of those yarns. The initial deformation behaviour is characterised by low stiffness and the potential for finite deformations. Reaching a certain limit of hybrid‐yarn stretch, the mechanical behaviour changes towards larger stiffness and only allows for small further deformations. In comparison to other yarn reinforcements with finite deformations, the achieved material strength is relatively high. The bending behaviour of the involved yarns is approximated using anisotropic hyperelastic material laws. The efficiency of the applied computational homogenisation method is significantly improved by introducing twisted‐periodic boundary conditions. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
External boundary value problems in the quasi static theory of thermoviscoelasticity for Kelvin‐Voigt materials with double porosity
Authors: Svanadze Maia M.
Published: March 2018

In the present paper the linear quasi static theory of thermoviscoelasticity for Kelvin‐Voigt materials with double porosity is considered. The basic external boundary value problems (BVPs) of steady vibrations in this theory are formulated. The uniqueness and existence theorems for regular (classical) solutions of the BVPs are proved by using of the potential method (boundary integral equations method) and the theory of singular integral equations. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
External boundary value problems in the quasi static theory of triple porosity thermoelasticity
Authors: Svanadze Merab
Published: March 2018

In this paper the quasi static linear theory of thermoelasticity for materials with triple porosity is considered. Basic external boundary value problems (BVPs) of steady vibrations are formulated. The uniqueness and existence theorems for regular (classical) solutions of these BVPs are established. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical solution of plane constrained shear problem for single crystals within continuum dislocation theory
Authors: Tran Tuan Minh , Baitsch Matthias , Le Khanh Chau
Published: March 2018

Within the recently proposed Continuum Dislocation Theory (CDT), numerical solutions of simple shear test for single crystals strip using finite elements are performed. Under the assumption of plane constrained deformation of crystal having only one active slip system, the plastic slip, the dislocation density as well as the stress‐strain curve are computed. The results of numerical simulations are compared with those obtained from analytical solutions which show good agreement. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Finite element implementation and simulation of the functional fatigue in shape memory alloys
Authors: Waimann Johanna , Junker Philipp , Hackl Klaus
Published: March 2018

Due to the effects of pseudoelasticity and pseudoplasticity, shape memory alloys (SMAs) are very promising materials for the industrial usage. However, applications of SMA are still challenging due to the functional degradation during cyclic loading. The related effect of functional fatigue which occurs during pseudoelastic loading is modeled by subdividing the diffusionless solid/solid phase transformation into a reversible and an irreversible process which is an experimentally motivated ansatz for the complex material behavior, see e.g. [1]. Thus, we take into account a reversible and an irreversible volume fraction for the austenitic and several martensitic phases. To consider the material's polycrystalline structure and hence, differently oriented grains, we use an orientation distribution function which depends on three Euler angles and affects a high numerical efficiency as presented in [2]. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ideas regarding a physically motivated selection of snapshots for POD calculations – a potential application to z‐pin pullout?
Authors: Weber Wolfgang E. , Fangye Yannick F. , Zastrau Bernd W. , Balzani Daniel
Published: March 2018

In order to keep the computational effort manageable, which arises from the modeling of micro‐heterogeneous materials, methods of model reduction are more and more used in computational mechanics. In this contribution, the proper orthogonal decomposition is analyzed. Applying this method to the pullout of metallic fibers, conclusions are drawn which relate the proper orthogonal modes to the mode shapes related to this physical phenomenon. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computational generation of statistical volume elements of biphasic asphalt concrete and its material behavior
Authors: Wingender Dennis , Schüler Thorsten , Jänicke Ralf
Published: March 2018

Asphalt concrete is a complex mixture appearing as a biphasic material containing mineral aggregates and bitumen and as a triphasic material containing voids in addition [1]. Because of that, the overall material behavior of the asphalt concrete cannot be obtained easily from the known material data of its components and therefore, we apply computational homogenization based on statistical volume elements (SVEs). These SVEs are assumed to be statistically representative to obtain the material properties by finite element simulations and homogenization. We generate these microstructures computationally based on data from XRCT scans. The artificial microstructures show reduced geometrical complexity and therefore, reduced numerical costs compared to direct numerical simulations based on XRCT data. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermomechanics of strain‐induced crystallization in natural rubber under cyclic loading
Authors: Zybell Lutz , Domurath Jan , Schneider Konrad
Published: March 2018

Strain‐induced crystallization in natural rubber has been widely investigated in the last decades by scattering techniques. Due to dissipative processes and structural changes in the material, deformation processes are accompanied with a significant amount of heat production/consumption. Time‐resolved wide‐angle X‐ray diffraction (WAXD) was used to characterize the structural changes in natural rubber and the local degree of crystallinity during mechanical deformation. By the simultaneous use of an infrared camera, the scattering results could be combined with changes in the temperature of the specimen due to dissipation and crystallization resp. melting of the crystallites. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the numerical modelling of initiation of sediment transport using Smoothed Particle Hydrodynamics
Authors: Falkner Nadine , Steeb Holger
Published: March 2018

Mobilization of solid particles at the interface between a porous and a free flow domain is a relevant subject in many fields of mechanical, civil and environmental engineering. One example is the initiation of sediment transport as it appears in river beds. To approximate this initiation state, various theoretical models exist. Common approaches use two‐domain formulations as in [1] or one‐domain formulations as in [6]. The named approaches were compared with Direct Numerical Simulations (DNS) using Smoothed Particle Hydrodynamics (SPH) in [3]. The results of these simulations showed that the theoretical models often underestimate the occurring velocities at the interface and therefore critical velocities to initialize the motion of single grains can be lower than predicted by theoretical approaches. In our numerical simulations, we study creeping flow in a free flow domain coupled to flow in a porous media applying various porous structures. To investigate velocities and shear stresses at the interface more intensively we then compare our numerical results to data from experiments that were performed on equivalent microstructures. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A thermomechanical analysis of interfaces between the mating parts in ultrasonic wire bonding
Authors: Mostafavi Shimaalsadat , Heider Yousef , Markert Bernd
Published: March 2018

Ultrasonic welding (USW) is an alternative solution for the bonding process especially in automotive industry. Ultrasonic welding of metals is a joining technique as a combination of applying pressure and frictional vibrations within the range of ultrasonic frequencies. In automotive industry, ultrasonic welding is often used for wired connections. As an alternative for crimping technology of multi‐strand aluminum cables in wire bonding, ultrasonic welding is used. This work presents a thermomechanical analysis of the interface between two mating parts in USW. For this reason, the temperature distribution at bonding locations inside a wire bundle due to frictional vibrations and pressure is investigated using the finite element method (FEM). The obvious difference in microsections from different welding samples, which originates from different local temperature rises, was the motivation for this study to further investigate the thermomechanical aspects of the USW by use of finite element simulations. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Untersuchung von Abstiegsanlagen von Horizontalrechen mit Hilfe von Flachwassergleichungen
Authors: Ostermann Lars , Seidel Christian
Published: March 2018

Das Erreichen einer guten ökologischen Durchgängigkeit besitzt in der Wasserkraft eine immer größer werdende Priorität. Wurde zunächst die ökologische Durchgängigkeit im Auf‐ und Abstieg durch die Errichtung von Fischwanderhilfen an den Wasserkraftanlagen maßgeblich verbessert, wird nun in der Wasserkraft eine weitere Optimierung des Abstiegs angestrebt. Hierzu werden den mit der Kraftwerksströmung folgenden Wasserlebewesen, die vor dem Schutzrechen der Wasserkraftanlage stehen, zusätzliche Abstiegsmöglichkeiten geschaffen, um in das Unterwasser zu gelangen. Die Entwicklung besonders geeigneter Abstiegsanlagen, die sowohl eine optimale Kraftwerksanströmung, eine gute Leitströmung in die Abstiegsanlage als auch eine optimale Anströmung der Rechenanlage ermöglichen, stellt dabei eine besondere Herausforderung dar. Die hierbei zu lösende Optimierungsaufgabe wird im Rahmen der Entwicklung einer Forschungswasserkraftanlage für ein Hochleistungswasserr mit Hilfe von flachwassergleichungsbasierten Verfahren durchgeführt und nachfolgend vorgestellt. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Finite‐element‐based simulation of multi‐physics materials
Authors: Schenke Maik , Ehlers Wolfgang
Published: March 2018

From a micro‐structural point of view, many natural or engineered materials can be assigned to the class of multi‐physics materials. Therein, their macroscopic observed behaviour is governed by different micro‐structural physical phenomena. For instance, when electro‐active polymers (EAP) are subjected to an electric field, the resulting chemical and electrical imbalances trigger micro‐structural diffusion processes, which re‐establish the equilibrium state, thereby causing macroscopic deformations. Further examples for these materials are partially or fully saturated porous media (e. g. foams, soils, filters, fibre‐reinforced plastics), chemical‐ or electrical‐active materials (e. g. hydrogels, lithium‐ion batteries, fuel cells) or biological tissues (e. g. bone, cartilage). Addressing the simulation of multi‐physics materials, which often exhibit a complex and heterogeneous micro‐structure, it is convenient to proceed from a macroscopic modelling approach. In this regard, the aforementioned materials can be described exploiting the macroscopic Theory of Porous Media (TPM) as a suitable modelling framework, see, e. g. [1,2].

The material models, which are usually developed during either academic or industrial research projects, are often implemented into self‐developed programme codes to scrutinise the advancements and but also the limitations of the material models. However, when addressing industrial application scenarios, these codes often lack the necessary functionality, for instance, in terms of modelling features to build complex initial‐boundary‐value problems (IBVP) and user interaction, such as a convenient graphical user interface (GUI). A general coupling allows to overcome these shortcomings. In particular, on the one hand, it provides a straight‐forward transfer of the outcome of research projects, namely, the comprehensive material‐model library of PANDAS into an simulation environment relevant for industrial applications. On the other hand, it gives access, in comparison to the native user‐element subroutines, to a convenient environment for the description user‐defined volume‐coupled multi‐field materials. In this connection, the present contribution exemplarily describes a co‐simulation approach between the commercial finite‐element (FE) package LS‐DYNA and the actual stand‐alone coupled FE‐based solver PANDAS. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Variational Homogenization Approach on Large Strain Micro‐Electro‐Mechanics
Authors: Vallicotti Daniel , Sridhar Ashish , Keip Marc‐André
Published: March 2018

Functional materials have received a lot of attention in recent years. Composite materials of soft polymers with embedded ferroelectric particles are advantageous due to the large deformations possible in such materials. Phenomenological modeling of associated electromechanical coupling phenomena has been extensively covered. However, complex multi‐scale interactions based on a microscopic electric domain evolution and its effect on the overall macroscopic response is of utter importance for the understanding of the underlying physical phenomena. This necessitates the use of multi‐scale approaches such as computational homogenization to reliably predict and in turn enhance the overall material response. We propose a variational framework for micro‐electro‐mechanical response at large deformations embedded into a scale‐bridging scenario by using homogenization techniques in order to define the macroscopic overall response of electro‐active materials. Starting point is a rate‐type saddle‐point variational principle on the microscale yielding the Euler‐Lagrange equations and a Ginzburg‐Landau‐type evolution equation for the polarization order parameter. A challenge is to link the gradient‐type continuum description of the microstructure to a local electro‐mechanical macro‐continuum. This is achieved by exploiting a generalized Hill‐Mandel macro‐homogeneity condition, yielding periodic boundary conditions at the faces of the microstructure. Numerical examples demonstrate the capabilities of the framework and show the effect of particle interactions based on evolving electric domains on the overall macroscopic response. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Diffusion induced void nucleation in SnPb solder joints
Authors: Werner Marek , Weinberg Kerstin
Published: March 2018

Towards a simple and robust model for void‐based fatigue prediction, we investigate the interaction of voids with its surrounding by using a multi‐field method. We couple the concentration fields of tin c1 and lead c2 with an additional field c3, where the latter is assigned with a void field. The interaction potential manifests three stable states. Two are obtained by experimental results of tin‐lead (SnPb) and the void stable state is postulated by construction. The logarithmic form of the thermodynamically consistent configurational entropy is approximated within this study by a fourth order polynom. It has been shown that the interfacial energy coefficient is independent of void's size, but rather depends numerically on the mesh size, which is used in the model presented here. Both governing equations follows a Cahn‐Hilliard‐type equation to mimic the microstructural changes. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transformation strains for bainitic variant evolution in steel
Authors: Ehlenbröker Ulrich , Petersmann Manuel , Antretter Thomas , Mahnken Rolf
Published: March 2018

In our work, we supplement a thermodynamically consistent multi‐scale model for the bainitic phase transformation in a low alloy steel, which takes into account the mechanisms of elasto‐viscoplasticity, phase transformations and heat conduction as well as the poly‐crystalline structure of steel. In order to obtain realistic simulation results, the microscopic conversion procedures for the austenite‐to‐bainite transformation have to be described in an appropriate way. To this end, the transformation strains for the crystallographic variants have been adjusted. For calculation of transformation strains a theory for the formation of dislocated martensite, more precisely a hierarchical packet‐block structure, is used. The calculated transformation strains are used in a simulation of bainite phase transformation in a polycrystalline RVE. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiscale Rubber Friction Analysis on Rough and Flexible Surfaces
Authors: Hartung Felix , Kaliske Michael
Published: March 2018

In this work, a multiscale homogenization approach is introduced to provide friction features between rubber and rough contact partners. Different length scales of the rough surface are considered by using a decomposition of the height difference correlation (HDCF) or the power spectral density function (PSDF) in several sinusoidal waves to accumulate the micro‐ and mesoscopic friction into a macroscopic friction coefficient. By using the finite element method (FEM), the sensitivity of the influencing factors for instance slip velocity and contact pressure may be investigated for rigid and flexible surfaces in the two‐ and the three‐dimensional case. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The influence of a DC electric field on the von Kármán vortex street in the wake of a confined cylinder
Authors: Scholz Mathias , Hardt Steffen , Barz Dominik P. J.
Published: March 2018

We investigate the influence of a DC electric field on the flow around and in the wake of a confined cylinder by means of numerical simulations. Our results indicate that even very small electrical perturbations have significant impact on the settling time of the lift coefficient. Moreover, the oscillations of the lift coefficient of pure pressure‐driven and pressure‐driven flow with induced electrical field are in anti‐phase. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigating Asymptotic Suction Boundary Layers using a One‐Dimensional Stochastic Turbulence Model
Authors: Fragner Moritz M. , Schmidt Heiko
Published: March 2018

The one‐dimensional turbulence model (ODT) is applied to study turbulent asymptotic suction boundary layers for a Reynolds number of Re = u∞/v0 = 333, where u∞ and v0 are the free stream and suction velocity, respectively. In here we will demonstrate that a large eddy suppression mechanism may reduce the influence of ODT model parameters, such as the viscous cut‐off parameter Z. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spectral Analysis of Large Scale Structures in Fully Developed Turbulent Pipe Flow
Authors: Zanoun El‐Sayed , Öngüner Emir , Shahirpour Amir , Merbold Sebastian , Egbers Christoph
Published: March 2018

The present work focuses on spectral analysis of the streamwise velocity fluctuations obtained, utilizing the Cottbus Large Pipe (CoLaPipe) test facility for R+ ≤ 3500, where R+ is the Reynolds number based on the wall friction velocity, uτ, and the pipe radius, R. Measurements of the streamwise spectra have been conducted using a single hot‐wire probe. Few runs have been also performed using Particle Image Velocimetry (PIV) as a structure visualization evidence and for spatial correlation purposes. The spectral analysis is being carried out to reveal few insights into pipe flow structure, allowing to follow the foot prints of such structures as well as providing estimates of their energy contents. The cumulative energy is examined as a function of the streamwise wavelength, describing the most energetic motions found in spectral data at various wall normal locations. For the current Reynolds number range, the Very Large Scale Motions (VLSM) and the Large Scale Motions (LSM) were evident as localized peaks in pre‐multiplied spectra, having mean wavelengths approximately of 12R, and 3R, respectively. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Slow viscous flow near a superhydrophobic surface with trapped gas bubbles
Authors: Ageev Aleksei , Golubkina Irina , Osiptsov Alexander
Published: March 2018

The Boundary Element Method (BEM) is used to solve the problem of Stokes flow of a viscous fluid over a periodic striped texture of a superhydrophobic surface (SHS), partially filled with frictionless gas bubbles. The shape of the bubble surfaces and the position of the meniscus pinning points relative to the cavity walls are taken into account in the study. Two kinds of flows important for practical applications are considered: a pressure‐driven flow in a thin channel with a bottom superhydrophobic wall and a shear‐driven flow over a periodic texture. We study the flow pattern in the fluid over a single cavity containing a bubble with a curved phase interface shifted into the cavity. A parametric numerical study of the averaged slip length of the SHS is performed as a function of the geometric parameters of the texture. It is shown that the curvature of the phase interface and/or its shift into the cavity both result in the decrease in the average slip length. It is demonstrated that the BEM can be an efficient tool for studying Stokes flows over textured superhydrophobic surfaces with different geometries of microcavities and phase interfaces. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thin liquid droplet on top of a rotating non‐isothermal liquid layer
Authors: Boettcher Konrad , Bothe Mike
Published: March 2018

Wafers are usually coated by using spin‐coating, where centrifugal forces are used to spread a droplet on the rotating wafer. This flow is unstable to the fingering instability, where several segments of the wetting front spread faster than the average, resulting in several fingers. The liquid flows via the existing fingers while the area in between does not get coated. A precise experimental investigation is problematic, as the droplet has to be placed quite exactly in the center of the rotation. Replacing the wafer by a second liquid should lead to a parabolic‐shaped free interface and the droplet should center itself due to gravity. Here, we derive a model for the free interfaces of a thin droplet on top of a rotating liquid by taking gravity, centrifugal forces, friction, (thermo‐)capillary and line forces into account. Additionally, this setup is the simplest example of multiple coating, where several free interfaces and contact lines influence each other. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Elastic wave radiation and scattering in heterogeneous soil using the scaled boundary finite element method
Authors: Birk Carolin , Gravenkamp Hauke , Bazyar Mohammad Hossein
Published: March 2018

A time‐domain approach for the simulation of elastic waves in heterogeneous soil domains is presented. It is based on modelling both near and far field by the scaled boundary finite element method (SBFEM). The SBFEM facilitates the use of a structured mesh in the near field region without the need to circumvent hanging nodes. The quadtree mesh is obtained automatically from image data. Radiation damping in the far field is modelled accurately by means of a displacement unit‐impulse‐response‐based formulation. An example analysis of wave radiation by an alluvial basin illustrates the potential of the proposed methodology. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimization of the piston geometry to generate a desired stress wave shape
Authors: Burgert Jens , Seemann Wolfgang , Hartenbach Felix
Published: March 2018

Impacting rods are used in various devices in practical life but also for scientific experiments. The challenge in modeling is the collision between the impacting rods which leads to a sudden velocity jump at the contact zone. Thus, the non‐smooth problem is difficult to calculate with commercial FE programs.

In this contribution, an approach to calculate 1D impact problems is presented. The geometries of the impacting rods are approximated with piecewise constant cross sections. On a constant segment, the solution of the wave problem is known by the D'Alembert solution and at each change of cross section the incoming wave is partly reflected and partly transmitted which is considered by transition conditions. This results in a multitude of transmissions and reflections that are all contributing to the final shape of the stress in the rods. Finally, the approach is applied in the field of rock drilling and the stress shape of the impacting rods is presented. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stationary single waves in turbulent open‐channel flow
Authors: Müllner Markus , Schneider Wilhelm
Published: March 2018

Steady two‐dimensional turbulent open‐channel flow is considered. Stationary single‐wave solutions are investigated. The fully‐developed oncoming flow is slightly supercritical. The Reynolds number is very large. The analysis is kept free of turbulence modelling. As stationary solitary waves cannot exist in turbulent flow for a plane bottom with constant roughness [1], two particular perturbations of the conditions at the channel bottom are examined: 1) We revisit the case [1] where the friction coefficient locally differs slightly by a constant from the reference value upstream; 2) An unevenness of very small height in the channel bottom (bump, ramp) is admitted, with the bottom roughness taken constant. An analogy between these cases is presented. In both cases, three stationary solutions for the surface elevation are found: A stable and an unstable solitary wave, respectively, and a single wave of a second kind with smaller amplitude. For the latter, an analysis for weak dissipation yields a uniformly valid solution that is in good agreement with the numerical results for various parameters. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hybrid computational aeroacoustics based on compressible flow data at low Mach numbers
Authors: Schoder Stefan , Toth Florian , Kaltenbacher Manfred
Published: March 2018

In some practical applications (e.g. cavity with a lip), even at low Mach numbers, acoustic feedback mechanisms excite flow structures. The compressible flow simulation cannot distinguish between a pure fluid dynamic part and acoustic phenomena. With this in mind, we propose a workflow based on Helmholtz‐Hodge decomposition, to extract pure source terms of the compressible flow simulation, to model the sound radiation. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Wave Propagation in a beam with random material properties
Authors: Zimmermann Eugen , Eremin Artem , Lammering Rolf
Published: March 2018

Modern composite materials, e.g., carbon fibre reinforced plastics (CFRP), exhibit a complex micro structure due to their fabrication process. The latter, being usually omitted in mechanical models through the homogenization of elastic properties, has a strong influence on the propagation of ultrasonic guided waves [1, 2]. Though it is possible to model the wave phenomena deterministically, taking into account a realistic distribution of fibres and polymer matrix, it is desirable to develop an improved model for the finite element analysis (FEM), which consider the stochastic properties in a more general way. In the current work, an approach for the simulation of waves in a isotropic beam with random material properties is presented. For the numerical computations with the FEM the Young's modulus was discretized by the Karhunen‐Loève Expansion (KLE). Numerical investigations on the excited and propagating guided waves are presented. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structured deformations and applications
Authors: Morandotti Marco
Published: March 2018

The scope of this contribution is to present an overview of the theory of structured deformations of continua and two applications, all of which involve using this rather new formulation of mechanics problems in contexts that are different from one another, thus showing the power and versatility of the theory. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Metropolis‐Hastings Importance Sampling Estimator
Authors: Rudolf Daniel , Sprungk Björn
Published: March 2018

Based on the proposed states of the Metropolis‐Hastings (MH) algorithm we construct a MH Importance Sampling estimator for the approximation of expectations. The new approximation scheme is asymptotically correct and numerical experiments indicate that it can outperform the classical MH Markov chain Monte Carlo estimator. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Objective Functions for the Shape Optimization of Temperature Control Channels in High‐Pressure Die Casting
Authors: Frings Markus , Behr Marek , Elgeti Stefanie
Published: March 2018

In high‐pressure die casting, the quality of the produced cast parts highly depends on the die quality. One die component are temperature control channels. The state‐of‐the art approach for the temperature control channels are boreholes drilled from the sides into the die that are afterwards formed into a closed flow channel by inserting plugs.

Since additive manufacturing methods are available to manufacture the dies, an obvious step is to construct more advanced temperature control channels. The shape of these free‐form channels can be obtained by numerical optimization.

To find the optimal shape of the channels, appropriate objective functions are required. This contribution is focused on such objective functions. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimization of topology and shape by combining phase field modeling and discrete stochastic algorithms
Authors: Keller Alexander , Münch Ingo , Wagner Werner
Published: March 2018

We propose a concept for the comprehensive optimization of load bearing structures. The main idea is to decompose the optimization task. First, we use a phase field model to evolve the topology as basic design. The parameters of this process are the filling level of the design domain and the tendency to nucleate more or less holes. Second, we use an interface to set up a subsequent structural model, where cross‐sections and positions of nodes are simultaneous optimization parameters of a metaheuristic optimization method. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Exploration of Internal Response Sensitivities of Materially Nonlinear Structures
Authors: Liedmann Jan , Barthold Franz‐Joseph
Published: March 2018

In this paper the idea of design exploration in the context of structural design sensitivity analysis considering elastoplastic material behaviour is outlined. Sensitivity information involves the influence of history dependent material behaviour and is obtained analytically by means of a variational approach. Applying singular value decomposition (SVD) to response sensitivities provides deep insight into sensitivity information and can be used to identify design changes with major influence on structural response. With this additional information, it is possible to refine an optimisation problem and reduce its complexity. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Open‐source tool‐chain for optimal input design for dynamical systems
Authors: Mayr Simon , Grabmair Gernot
Published: March 2018

In this paper we present a free tool for semi‐automated matching of virtual and real prototypes in a wide range of industrial applications. Within the introduction we would like to explain the motivation behind the development of our tool. After a short description of the basic principles of input design for dynamical systems, we are focusing on the individual steps of the tool‐chain, implemented in our software. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Geometrically nonlinear crystal plasticity implemented into a discontinuous Galerkin element formulation
Authors: Alipour Atefeh , Wulfinghoff Stephan , Bayat Hamid Reza , Reese Stefanie
Published: March 2018

Single crystal viscoplasticity, with a regularization technique for the power law, is presented and implemented into a discontinuous Galerkin (DG) framework. Although single crystal plasticity has been extensively studied, its examination with the regularization method in combination with a DG formulation leads to a numerically efficient and robust model. The performance of the DG framework in crystal viscoplasticity is shown by an example. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Adjoint based topology optimization of conjugate heat transfer systems
Authors: Goeke Stephan , Wünsch Olaf
Published: March 2018

This paper presents a topology optimization method for coupled thermal problems. Heat transfer linked with the forced convection flow inside cooling channels is investigated using a conjugate model. This model includes both the full Navier‐Stokes equations for the fluid medium and the energy equations for both fluid and solid. In this present work, the adjoint method is extended to such conjugate heat transfer (CHT) systems to optimize their performance by the use of gradient based methods. This performance is usually a compromise between an increase in heat flux or temperature distribution at a surface and maintaining a low pressure loss within the system. To exemplify the method a uniform temperature distribution is chosen and evaluated numerically. For implementation the open source CFD Software OpenFOAM is used. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Motion planning problem with obstacle avoidance for step‐2 bracket‐generating systems
Authors: Grushkovskaya Victoria , Zuyev Alexander
Published: March 2018

This paper considers the obstacle avoidance problem for control‐linear systems satisfying the Hörmander condition with the first‐order Lie brackets. To solve the problem under consideration, we use a family of oscillating periodic control functions with state‐dependent coefficients. The proposed approach is shown to be applicable for different shapes of obstacles and various potential functions generating collision‐free paths. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling and evaluation of cyber‐physical systems in civil engineering
Authors: Legatiuk Dmitrii , Dragos Kosmas , Smarsly Kay
Published: March 2018

A cyber‐physical system (CPS) is a coupled system integrating computing, networking, and physical processes. Through actuation, cyber‐physical systems control the physical processes, usually with feedback loops, where the physical processes affect computing and networking processes, and vice versa. In civil engineering, the most common fields of CPS applications are structural health monitoring (SHM) and structural control. A typical CPS task is the assessment of a structure based on (i) collected measurement data and (ii) a corresponding model. However, for an accurate and precise assessment of a structure, the CPS itself must be modeled and evaluated. In this paper, a conceptual modeling and evaluation approach is proposed, in which each part of a CPS is evaluated individually. In this study, the conceptual approach is presented for modeling and evaluation of CPS in civil engineering. The evaluation is based on an abstract approach allowing a discussion of a principle (i.e. general) model structure of a CPS, identifying critical issues to be studied in more detail in future research. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Real‐time model adaptation
Authors: Chen Stephanie , Büskens Christof
Published: March 2018

Solving an engineering problem starts with the description of the problem in mathematical formulas and the identification of parameters. The generated model is then used to simulate the behavior of the underlying system. However, most systems are not static. They change over time. Thus, the model needs to be adapted to these activities otherwise the predictions are wrong.

A data driven modeling method has been developed. The resulting models are adaptable in real time, which will also been shown. The approach is tested on a real application of a gas engine, which has been changed significantly by a renovation. Therefore, the old model cannot be used anymore and model updates are generated with different forgetting rates. They are compared to each other and to a new model. Using this comparison a recommendation is given which method is to be favored. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On Goal Oriented Time Adaptivity using Local Error Estimates
Authors: Meisrimel Peter , Birken Philipp
Published: March 2018

We consider adaptive time discretization methods for ordinary differential equations where one aims to control the error in a quantity of interest of the form

, with j : ℝd → ℝ. In this setting we propose a new timestep controller based on local error estimates of the quantity of interest. The new method converges when the tolerance goes to zero.

We experimentally compare the new scheme with the classic norm‐based time‐adaptivity based on local error estimates as well as the dual‐weighted residual (DWR) method. The results show significantly lower efficiency for the DWR method. The local error based schemes are similarly efficient, with the new scheme showing significant improvement in some cases. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multirate finite step methods with varying step sizes
Authors: Naumann Andreas , Wensch Jörg
Published: March 2018

Many partial differential equations consist of slow and fast scales. Often, the right hand side of semidiscretized PDEs can be split additively in corresponding fast and slow parts. Many methods utilise the additive splitting of these equations, like generalized additive Runge‐Kutta (GARK) methods or multirate infinitesimal step methods. The latter one treat the slow part with macro step sizes, whereas the fast part is integrated a ODE solver. The corresponding order conditions assume the exact solution of the auxiliary ODE, i.e. assume an infinite number of small steps. We extend the MIS approach by fixing the number of steps, which leads to the multirate finite steps (MFS) method. The order conditions are derived, such that the order is independent in the number of small steps in each stage. Finally, we confirm the theoretical results by numerical experiments. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Remarks on the numerical range with respect to a family of projections
Authors: Dada Waed , Kerner Joachim
Published: March 2018

In this note we report on the recently introduced concept of the numerical range of a bounded linear operator on a Hilbert space with respect to a family of projections. The importance of this new concept lies in the fact that it unifies and generalizes well‐established versions of the numerical range such as the classical numerical range introduced by Toeplitz and Hausdorff, the quadratic numerical range as well as the block numerical range. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Well‐posedness of Bayesian inverse problems in quasi‐Banach spaces with stable priors
Authors: Sullivan T. J.
Published: March 2018

The Bayesian perspective on inverse problems has attracted much mathematical attention in recent years. Particular attention has been paid to Bayesian inverse problems (BIPs) in which the parameter to be inferred lies in an infinite‐dimensional space, a typical example being a scalar or tensor field coupled to some observed data via an ODE or PDE. This article gives an introduction to the framework of well‐posed BIPs in infinite‐dimensional parameter spaces, as advocated by Stuart (Acta Numer. 19:451–559, 2010) and others. This framework has the advantage of ensuring uniformly well‐posed inference problems independently of the finite‐dimensional discretisation used for numerical solution. Recently, this framework has been extended to the case of a heavy‐tailed prior measure in the family of stable distributions, such as an infinite‐dimensional Cauchy distribution, for which polynomial moments are infinite or undefined. It is shown that analogues of the Karhunen–Loève expansion for square‐integrable random variables can be used to sample such measures on quasi‐Banach spaces. Furthermore, under weaker regularity assumptions than those used to date, the Bayesian posterior measure is shown to depend Lipschitz continuously in the Hellinger and total variation metrics upon perturbations of the misfit function and observed data. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Genetic analyses of undifferentiated small round cell sarcoma identifies a novel sarcoma subtype with a recurrent CRTC1‐SS18 gene fusion
Authors: Alholle Abdullah , Karanian Marie , Brini Anna T , Morris Mark R , Kannappan Vinodh , Niada Stefania , Niblett Angela , Ranchère‐Vince Dominique , Pissaloux Daniel , Delfour Christophe , Maran‐Gonzalez Aurelie , Antonescu Cristina R , Sumathi Vaiyapuri , Tirode Franck , Latif Farida
Published: March 2018

In recent years, undifferentiated small round cell sarcomas (USRCSs) have been divided into a variety of new, rare, sarcoma subtypes, including the group of Ewing‐like sarcomas, which have the morphological appearance of Ewing sarcomas, but carry CIC–DUX4, BCOR–CCNB3 and other gene fusions different from the classic EWSR1–ETS gene fusion. Using high‐throughput RNA‐sequencing (RNA‐seq) analyses, we identified a novel recurrent gene fusion, CRTC1–SS18, in two cases of USRCS that lacked any known translocation. RNA‐seq results were confirmed by reverse transcription polymerase chain reaction, long‐range polymerase chain reaction, and fluorescence in situ hybridization. In vitro, we showed that the cells expressing the gene fusion were morphologically distinct and had enhanced oncogenic potential as compared with control cells. Expression profile comparisons with tumours of other sarcoma subtypes demonstrated that both cases clustered close to EWSR1–CREB1‐positive tumours. Moreover, these analyses indicated enhanced NTRK1 expression in CRTC1–SS18‐positive tumours. We conclude that the novel gene fusion identified in this study adds a new subtype to the USRCSs with unique gene signatures, and may be of therapeutic relevance. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Fertility perspectives and priorities among male adolescents and young adults in cancer survivorship
Authors: Nahata Leena , Caltabellotta Nicole M. , Yeager Nicholas D. , Lehmann Vicky , Whiteside Stacy L. , O'Brien Sarah H. , Quinn Gwendolyn P. , Gerhardt Cynthia A.
Published: March 2018

Infertility is a common and distressing late effect of cancer treatment among male survivors. Investigators examined desire for parenthood, prioritization of fertility compared to other life goals, and reports of fertility‐related discussions among a cohort of male adolescent and young adult survivors. Eighty percent desired a biological child, yet only 31% ranked having a child among their “top 3” life goals. Only 40% reported fertility‐related discussions with their health care providers in survivorship. Given the importance of biological children among this cohort, future guidelines should encourage a more proactive approach to providing fertility counseling and offering testing, to mitigate distress and prevent unplanned pregnancies.
Multiscale enhancement behavior of nano‐silica modified CF/PEEK composites prepared by wet powder impregnation
Authors: Chen Junlin , Zhang Tao , Wang Kai , Zhao Yan
Published: March 2018

The mechanical performance of modified multiscale carbon fiber (CF) reinforced poly(ether‐ether‐ketone) (PEEK) composites is improved through wet powder impregnation. The complex PEEK suspension is prepared by mixing nano‐silica and PEEK powders in water homogeneously. The CFs are pulled through the complex PEEK suspension, and the modified multiscale PEEK prepregs and composites are prepared by a series of drying and consolidation process. The increasing energy storage, decreasing tan δmax and the area under the tan δ curve in the dynamic mechanical tests indicate strong interface interactions of modified multiscale CF/PEEK composites. The interlaminar shear strength increases by 15.6% from 72.2 to 83.5 MPa for 2.5 wt% nano‐silica addition, showing significant improvement in resisting the delamination damage. Besides, the same addition makes the flexural strength and modulus increase by 13.9 and 8.6%, respectively. The modified multiscale CF/PEEK composites exhibit higher flexural strength and modulus at elevated temperature than the pristine composites. Furthermore, the enhancement mechanisms for the modified multiscale CF/PEEK composites are proposed and illustrated, which contributes to future research on multiscale enhancement for conventional composites. POLYM. COMPOS., 40:1187–1197, 2019. © 2018 Society of Plastics Engineers
Diagnostic accuracy and clinical outcomes associated with prenatal diagnosis of fetal absent cavum septi pellucidi
Authors: Pilliod Rachel A. , Pettersson David R. , Gibson Thomas , Gievers Ladawna , Kim Amanda , Sohaey Roya , Oh Karen Y. , Shaffer Brian L.
Published: March 2018

Background

Absence of the cavum septi pellucidi (CSP) on prenatal imaging is historically associated with additional anomalies; however, recent cases of isolated absent CSP have also been identified. This study seeks to assess the accuracy of prenatal imaging in evaluating isolated absent CSP and to describe the spectrum of clinical outcomes.

Methods

This is a retrospective observational study of all prenatally diagnosed absent CSP cases between 2011 and 2016 at our institution. Cases with additional structural parenchymal abnormalities were excluded. Clinical outcomes were abstracted from available records.

Results

We identified 15 cases of prenatally diagnosed isolated absent CSP. All patients were initially diagnosed on ultrasound (US) and 11/15 patients had fetal magnetic resonance imaging (MRI) confirming the diagnosis. Prenatal US and MRI were concordant in all cases. Of the continuing pregnancies, 2 neonatal deaths occurred related to extreme prematurity. Two cases of septo‐optic dysplasia were identified in our cohort.

Discussion

In this study, fetal MRI and US had a high degree of accuracy with concordant postnatal imaging. Our study is similar to other case series suggesting that a range of clinical outcomes is possible with isolated absent CSP, but long‐term patient follow up is necessary.
How can gender affect psychopathology in Lebanese school‐age children?
Authors: Khamis Vivian
Published: March 2018

This study investigated the extent to which gender differences in coping, school and family environments could account for variation in psychopathology among school‐age children. Participants were 665 middle school students. Results showed no gender differences for PTSD. Females scored higher on emotional problems and prosocial behavior whereas males scored higher on conduct problems. ADHD was higher among children with LD, whereas emotional and conduct problems were higher in females with LD. Emotional and conduct problems increased more by age in females. Gender differences were found in various patterns of predictor–outcome relations. While emotion‐focused coping was associated with emotional and peer problems in both genders, it was associated with conduct problems in females only. Problem‐focused coping was positively associated with prosocial behaviors in females whereas it was negatively associated with peer problems in males. In addition, family environment was negatively associated with emotional problems and PTSD symptomatology in females, whereas school environment was negatively associated with emotional problems in males. Clinical and research implications were discussed.