bluuebunny/crossref_metadata_2025 huggingface dataset:
Asymptomatic deep vein thrombosis in patients undergoing screening duplex ultrasonography
Authors: Zubrow Marc T. , Urie Jessica , Jurkovitz Claudine , Jiang Xiaozhang , Bowen James R. , DiSabatino Angela , Weintraub William
Published: November 2013

BACKGROUND

Because of concerns for propagating clots into pulmonary emboli by the placement of pneumatic compression boots (PCBs), the standard of care at our institution was to perform a duplex Doppler ultrasound with compression (DUSC) before applying PCBs. We sought to determine the rate of asymptomatic preexisting deep vein thrombosis (DVT) in hospitalized patients who underwent DUSC before PCB.

METHODS

We evaluated consecutive patients who underwent lower extremity DUSC within 48 hours of admission. All patients were assessed for DVT risk factors using the American College of Chest Physicians' criteria (American College of Chest Physicians Conference on Antithrombotic/Thrombolytic Therapy: Evidence‐Based Guidelines, 9th Edition). A t test, Wilcoxon rank sum test, and χ2 or Fisher exact test were used to compare patients characteristics according to DVT status. Logistic regression was used to determine the importance of each risk factor on the risk of DVT.

RESULTS

DUSC was performed during 1136 hospitalizations; 1071 patients were included in the dataset. Of those, 19 patients (1.8%) had asymptomatic DVT and had at least 1 risk factor; 16 (84.2%) had more than 1 risk factor. The only risk factors that were statistically significant were ambulatory dysfunction and thromboembolic disease history.

CONCLUSION

Few patients have asymptomatic DVT upon admission; all of these patients have at least 1 predisposing risk factor. There appears to be no need for DUSC prior to initiation of PCBs. DUSC evaluation for DVT may be of value if there is a history of previous DVT, ambulatory dysfunction, or more than 3 risk factors, as the information may change therapeutic approaches. Journal of Hospital Medicine 2014;9:19–22. © 2013 Society of Hospital Medicine
Functional and evolutionary aspects of axial stability in euarchontans and other mammals
Authors: Granatosky Michael C. , Lemelin Pierre , Chester Stephen G. B. , Pampush James D. , Schmitt Daniel
Published: November 2013

The presence of a stable thoracolumbar region, found in many arboreal mammals, is considered advantageous for bridging and cantilevering between discontinuous branches. However, no study has directly explored the link between osteological features cited as enhancing axial stability and the frequency of cantilevering and bridging behaviors in a terminal branch environment. To fill this gap, we collected metric data on costal and vertebral morphology of primate and nonprimate mammals known to cantilever and bridge frequently and those that do not. We also quantified the frequency and duration of cantilevering and bridging behaviors using experimental setups for species that have been reported to show differences in use of small branches and back anatomy (Caluromys philander, Loris tardigradus, Monodelphis domestica, and Cheirogaleus medius). Phylogenetically corrected principal component analysis reveals that taxa employing frequent bridging and cantilevering (C. philander and lorises) also exhibit reduced intervertebral and intercostal spaces, which can serve to increase thoracolumbar stability, when compared to closely related species (M. domestica and C. medius). We observed C. philander cantilevering and bridging significantly more often than M. domestica, which never cantilevered or crossed any arboreal gaps. Although no difference in the frequency of cantilevering was observed between L. tardigradus and C. medius, the duration of cantilevering bouts was significantly greater in L. tardigradus. These data suggest that osteological features promoting axial rigidity may be part of a morpho‐behavioral complex that increases stability in mammals moving and foraging in a terminal branch environment. J. Morphol. 313–327, 2014. © 2013 Wiley Periodicals, Inc.
Blocked Bacteria Escape by ATRP Grafting of a PMMA Shell on PVA Microparticles
Authors: Knierim Christian , Greenblatt Charles L. , Agarwal Seema , Greiner Andreas
Published: November 2013

This paper reports on the preparation and characterization of living composites consisting of poly(vinylalcohol) (PVA) hydrogel microparticles with living bacteria and a shell of poly(methyl methacrylate) (PMMA). The grafting of the PMMA shell is accomplished in the presence of living bacteria by surface polymerization of PMMA using atom transfer radical polymerization (ATRP). The PMMA shell prevents the uncontrolled bacterial escape from the hydrogel microparticles, which otherwise marks a major problem of these composites. The encapsulation of microparticles with living bacteria by PMMA retards bacteria escape upon contact to water for >20 d. The functionality of the PMMA shell is proven both by the release of fluorescein in buffer and an altered release time of bacteria in buffer solution.
High resolution mass spectrometry based techniques at the crossroads of metabolic pathways
Authors: Junot Christophe , Fenaille François , Colsch Benoit , Bécher François
Published: November 2013

The metabolome is the set of small molecular mass compounds found in biological media, and metabolomics, which refers to as the analysis of metabolome in a given biological condition, deals with the large scale detection and quantification of metabolites in biological media. It is a data driven and multidisciplinary approach combining analytical chemistry for data acquisition, and biostatistics, informatics and biochemistry for mining and interpretation of these data. Since the middle of the 2000s, high resolution mass spectrometry is widely used in metabolomics, mainly because the detection and identification of metabolites are improved compared to low resolution instruments. As the field of HRMS is quickly and permanently evolving, the aim of this work is to review its use in different aspects of metabolomics, including data acquisition, metabolite annotation, identification and quantification. At last, we would like to show that, thanks to their versatility, HRMS instruments are the most appropriate to achieve optimal metabolome coverage, at the border of other omics fields such as lipidomics and glycomics. © 2013 Wiley Periodicals, Inc. Mass Spec Rev 33: 471–500, 2014.
Monitoring Pyrrol Polymerization Using On‐Line Conductivity Measurements and Neural Networks
Authors: Brusamarello Claiton Z. , Santos Leila M. , Amaral Monique , Barra Guilherme M. O. , Fortuny Montserrat , Santos Alexandre F. , de Araújo Pedro Henrique Hermes , Sayer Claudia
Published: November 2013

In this work, the chemical oxidative synthesis of polypyrrole was monitored through on‐line conductivimetry. A group of reactions was carried out at two different temperatures (5 °C and 20 °C) with varying concentrations of pyrrole and oxidant agent (FeCl3) to investigate the effect on conversion and conductivity. The relation of electrical conductivity with conversion was not straightforward. To overcome this, a neural network was proposed to predict conversion based on on‐line conductivity measurements. In this way, the neural networks entry variables were: electrical conductivity, reaction temperature, initial oxidant and pyrrole concentrations. As optimization algorithms Levenberg‐Marquardt and Descent Gradient with momentum term were evaluated. Results obtained by the neural networks based on on‐line conductivity measurements showed a good agreement with off‐line conversion data.
Production of Copolymers in a Tubular Reactors Through Nitroxide Mediated Controlled Free‐Radical Polymerization
Authors: Araujo Carolina L. , Pinto José Carlos
Published: November 2013

This work presents experimental results for styrene / methyl methacrylate (MMA) copolymerizations performed in a tubular reactor equipped with lateral feed lines through the nitroxide mediated controlled free‐radical mechanism. Reactions were carried out in solution with a primary feed containing a mixture of styrene, toluene, initiators and TEMPO (2,2,6,6‐tetramethyl‐1‐piperidinoxyl) and a lateral feed containing a mixture of comonomers and TEMPO. The obtained results show that copolymers can be obtained with weight average molecular weights ranging from 30 × 103 to 60 × 103 g/gmol and polydispersities ranging from 1.3 to 1.6, with monomer conversions ranging from 20 to 70 wt%. When the average residence time is manipulated, it can be observed that the average molecular weights increase linearly with time, confirming the “living” character of the reaction system.
Organoaluminum Initiators: Influence of Al Coordination on Polymerization and Product Properties
Authors: Tracht Ursula , Leiberich Ricarda , Paul Hanns‐Ingolf
Published: November 2013

Alkyl aluminum halides are well established initiators for cationic polymerizations. They enable homogeneous polymerization processes in nonchlorinated hydrocarbon processes. Activity and polymer properties can be significantly affected by the choice of the compound used for activating the organoaluminum halide. Three examples of organoaluminum chloride based initiator systems for cationic polymerizations are presented here illustrating different stages of a workflow established for the development and optimization of such initiators and corresponding polymerization processes. Initiator formation via addition of protic compounds to organoaluminum chloride precursors is studied by multiple spectroscopic techniques, in particular IR‐spectroscopy. Differently prepared initiators are tested in lab scale batch polymerizations and continuous mini‐plant polymerizations. The influence of aluminum coordination on polymer properties like molecular weights is analyzed.
Assessment of ischemic penumbra in patients with hyperacute stroke using amide proton transfer (APT) chemical exchange saturation transfer (CEST) MRI
Authors: Tietze Anna , Blicher Jakob , Mikkelsen Irene Klærke , Østergaard Leif , Strother Megan K. , Smith Seth A. , Donahue Manus J.
Published: November 2013

Chemical exchange saturation transfer (CEST)‐derived, pH‐weighted, amide proton transfer (APT) MRI has shown promise in animal studies for the prediction of infarction risk in ischemic tissue. Here, APT MRI was translated to patients with acute stroke (1–24 h post‐symptom onset), and assessments of APT contrast, perfusion, diffusion, disability and final infarct volume (23–92 days post‐stroke) are reported. Healthy volunteers (n = 5) and patients (n = 10) with acute onset of symptoms (0–4 h, n = 7; uncertain onset <24 h, n = 3) were scanned with diffusion‐ and perfusion‐weighted MRI, fluid‐attenuated inversion recovery (FLAIR) and CEST. Traditional asymmetry and a Lorentzian‐based APT index were calculated in the infarct core, at‐risk tissue (time‐to‐peak, TTP; lengthening) and final infarct volume. On average (mean ± standard deviation), control white matter APT values (asymmetry, 0.019 ± 0.005; Lorentzian, 0.045 ± 0.006) were not significantly different (p > 0.05) from APT values in normal‐appearing white matter (NAWM) of patients (asymmetry, 0.022 ± 0.003; Lorentzian, 0.048 ± 0.003); however, ischemic regions in patients showed reduced (p = 0.03) APT effects compared with NAWM. Representative cases are presented, whereby the APT contrast is compared quantitatively with contrast from other imaging modalities. The findings vary between patients; in some patients, a trend for a reduction in the APT signal in the final infarct region compared with at‐risk tissue was observed, consistent with tissue acidosis. However, in other patients, no relationship was observed in the infarct core and final infarct volume. Larger clinical studies, in combination with focused efforts on sequence development at clinically available field strengths (e.g. 3.0 T), are necessary to fully understand the potential of APT imaging for guiding the hyperacute management of patients. Copyright © 2013 John Wiley & Sons, Ltd.
Multiobjective optimal control of a four‐body kinematic chain
Authors: Ringkamp Maik , Leyendecker Sigrid , Ober‐Blöbaum Sina
Published: November 2013

Optimal control of mechanical systems is an active area of research. However, so far, most contributions are taking only one single objective into account, whereas for many practical problems, one is interested in optimizing several conflicting objectives at the same time. Applying singleobjective optimization to each of them leads to several trajectories each being optimal for one objective, but ignoring all others. In contrast to that, combining all objectives and using multiobjective optimization leads to a variety of trade off solutions taking all objectives into account simultaneously.

We use the direct discretization method DMOCC (Discrete Mechanics and Optimal Control for Constrained systems) to approximate trajectories of the underlying optimal control problems, resulting in restricted optimization problems of high dimension. For the multiobjective part, we apply a reference point technique which successively utilizes an auxiliary distance function to gain the trade off solutions. The presented approach is illustrated by the multiobjective optimal control of a constrained multibody system. A four‐body kinematic chain is controlled in a rest to rest maneuver, for which minimal control effort and minimal required maneuver time are the conflicting objectives. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mechanical Synchronization in Dual‐Rotor Vibroactuator
Authors: Miklós Ákos , Szabó Zsolt
Published: November 2013

In the present work the mechanical behaviour of a dual‐rotor vibrotactor has been investigated with special attention to its stationary motions and their linear stability. After the introduction of the used mechanical model, the formulae for the stationary motions are given, and characteristic stablity charts are presented. The linear stability is investigated for uncontrolled and controlled system as well. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The benefits of training with vibration in stabilizers and postural human muscle strengthening
Authors: Fodor Rault , Vescan Sergiu Dan , Arghir Mariana
Published: November 2013

The mechanical vibrations have been perceived as unhealthy, although in some circunstances these may lead to a human body fortification. The trainings that use the vibrating stimulus have certain advantages to the classical trainings. Stabilizers and postural muscles are less visible, being hidden by large muscle groups and have little growth potential. For this reason most types of training does not focus on training and strengthening them. This article presents the advantages of training muscular groups of the vertebral column performed on vibrating plates. This type of training has the advantage that besides the requiring to all muscles in where the vibratory stimulus reaches, leads to an increase flexibility of joints. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Towards a Standardised Method for Visualisation of Stress Distribution at the Cartilage‐Bone Interface
Authors: Mabuma Joffrey , Markert Bernd , Ehlers Wolfgang
Published: November 2013

The degeneration of articular cartilage is one of the most common causes of pain and disability in middle‐aged and older people. In this context, osteoarthritis is a well‐known clinical syndrome related to cartilage degeneration. The degeneration of normal articular cartilage is not simply the result of aging and mechanical wear. Pathological loads may also increase the risk of degeneration of normal joints, and individuals who have an abnormal joint anatomy or inadequate muscle strength probably have a greater risk of degenerative joint disease.

The goal of this contribution is to investigate the influence of cartilage degeneration on the stress pattern at the cartilage‐bone interface. In this connection, articular cartilage is described as a highly anisotropic and heterogeneous charged biphasic solid‐fluid aggregate in the framework of the Theory of Porous Media (TPM). After calibration of the model under physiological loading conditions, the results of a sensitivity analysis of the model parameters are presented.

Realistic boundary conditions are applied on the cartilage surface of the femoral head obtained from multibody dynamics calculations. Use is made of the Hertzian contact theory for the contact pressure distribution. The applicability of a new rendition technique to visualise simulation results based on a standardised stereographic projection of the von Mises stresses along the curved cartilage‐bone interface is introduced. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Accurate calculation of stress intensity factors for strongly curved cracks applying path‐independent integrals
Authors: Judt Paul , Ricoeur Andreas
Published: November 2013

Path‐independent contour integrals like the Jk‐integral or the Ik‐integral are beneficial to calculate accurate stress intensity factors (SIF). In order to avoid special requirements concerning crack tip meshing and with regard to an efficient calculation of contour integrals including internal boundaries and interfaces, it is beneficial to apply large contours far from the crack tip. In the case of mixed‐mode loading and strongly curved cracks, however, this usually leads to highly inaccurate results. In this paper, several methods are presented considerably improving the calculation of SIF based on Jk‐ and Ik‐integrals. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Numerical Identification of System Properties in a Square Frame
Authors: Zenz Georg , Nachbagauer Karin , Gerstmayr Johannes , Shih Ming‐Hsiang , Yang Yeong‐Bin
Published: November 2013

In this paper the influencing factors of the nonlinear behavior of a highly deformable square frame are aimed to highlight and identify. Therefore, in a first step a square frame consisting of four slender members of equal length has been investigated experimentally. Subsequently to these investigations, a numerical model is set up with a beam finite element model, which is based on the absolute nodal coordinate formulation (ANCF), including geometrical and possible material nonlinearities. The influencing factors as well as the system properties are identified by using a genetic optimization algorithm. The final results show that the highly nonlinear behavior of the square frame can be reproduced accurately in case the nonlinear characteristics of the joints are taken into account carefully. The numerical model combined with the system parameter identification can be utilized for further numerical investigations of non‐standard structures undergoing large deformations. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of geometrically nonlinear LSFEM formulations based on different hyperelastic models
Authors: Steeger Karl , Schwarz Alexander , Schröder Jörg , Starke Gerhard , Müller Benjamin
Published: November 2013

This contribution deals with the solution of geometrically nonlinear elastic problems solved by the least‐squares mixed finite element method (LSFEM). The degrees of freedom (displacements and stresses) will be approximated using suitable spaces, namely W1,p with p > 4 and H(div,Ω). In order to define the stress response of the material, different hyperelastic free energy functions will be presented. The residual forms ℛI of the balance of momentum and the constitutive equation build a system of differential equations of first order. Choosing suitable weighting operators and applying L2‐norms lead to a least‐squares functional ℱ(P,u). The interpolation of the unknowns is accomplished using a standard polynomial interpolation for the displacements and vector‐valued Raviart‐Thomas functions for the approximation of the stresses. The formulations presented will be compared considering a uni‐axial spatial tension test. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determination of the derivative of the tangent stiffness matrix with respect to the load parameter
Authors: Jia Xin , Mang Herbert A.
Published: November 2013

In order to solve the so‐called consistently linearized eigenproblem in the frame of the Finite Element Method (FEM), the derivative of the tangent stiffness matrix $\tilde{\bf{K}}_T$ with respect to the load parameter λ needs to be calculated. In this work, three schemes for calculation of $\dot{\tilde{\bf{K}}}_T$ are presented. The first scheme is based on an analytical expression for the first derivative of e the element tangent stiffness matrix $\tilde{\bf{K}}^e_T$ with respect to λ for the special case of a co‐rotational beam element. The second one is a finite difference approach for computation of $\dot{\tilde{\bf{K}}}_T:=d\tilde{\bf{K}}_T/d\lambda$. The third one is also a finite difference approach. However, it is based on a directional derivative of $\tilde{\bf{K}}_T$. An elastic beam, subjected to a compressive axial force and a small transverse uniform load, is chosen as a numerical example. The effectiveness and the accuracy of the three schemes are compared. The third scheme is found to be not only very practical but also more effective than the two competing schemes. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hot Spots on Brake Disks – Model Reduction and Stability Discussion
Authors: Graf Matthias , Ostermeyer Georg‐Peter
Published: November 2013

Sliding friction results in heat generation. One design aim of brake systems is for the temperature field to rise homogeneously, but experiments have repeatedly shown a characteristic inhomogeneous temperature pattern on the disk, known as Hot Spots. This phenomenon is undesired, as it leads to noise, vibration, and material disruption. The uneven temperature distribution arises from what are known as “Thermoelastic Instabilities”. The solutions for temperature and displacements must be obtained in four dimensions: three spatial dimensions and one time dimension. The industrial design process requires massive parameter studies and a fast solution of the model. To develop such models, strategies which avoid discretization come into the focus. The presented model is based on the application of global Ansatz functions for the fields, which are scaled to fulfil boundary conditions. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Modeling of Cohesive Softening Effects in Thick Adhesive Layers
Authors: Kieser Florian , Klinkel Sven
Published: November 2013

This work is concerned with the material modeling of the inelastic behavior of bonding and debonding effects in adhesive layers. High‐strength adhesives are applied in building industries utilizing thick adhesive layers due to huge building elements and construction tolerances. Therefore a continuum approach is presented to describe the nonlinear material behavior. In the failure criterion two stress invariants are used, which involves the hydrostatic pressure as well as the deviator stress state. A non‐associated flowrule, which determines the evolution of the inelastic variables, is required to ensure the thermodynamical consistency of the model. Hardening and softening are included as well as the rate‐dependency of the adhesive. Furthermore the viscoplastic approach is used for regularization of the mesh dependency in case of material softening. The nonlinear material model is implemented in a finite element program. The material tangent modulus is incorporated to obtain quadratic convergence for the global equilibrium iteration. The identification of material parameters is discussed on the simulation of typical experiments for adhesive materials. As a drawback of the presented phenomenological material model, the large number of parameters involved in the constitutive description is discussed. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermodynamically consistent modeling of yield surface distortion
Authors: Shi Baodong , Mosler Jörn
Published: November 2013

From a macroscopic point of view, the deformation of most metals results in an evolution of the symmetry groups characterizing the isotropy of the considered materials. With respect to plastic deformation for instance, the shape of the macroscopic yield surface evolves during deformation. In the present paper, a novel constitutive framework capturing this evolution is proposed. This framework is based on the fundamentals of thermodynamics. Furthermore, it also shows a variational structure such that all state variables follow jointly from minimizing an incrementally defined energy functional. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Application and evaluation of hyper‐ and hypoelastic‐based plasticity models in the FE simulation of metal forming processes
Authors: Brepols Tim , Vladimirov Ivaylo N. , Reese Stefanie
Published: November 2013

Metal forming processes are usually accompanied by large plastic strains and rotations of the material elements which emphasizes the need for reliable finite strain elastoplasticity models in corresponding FE simulations. In this work, two specific finite strain hyper‐ and hypoelastic‐based plasticity models with combined nonlinear isotropic and kinematic hardening are presented and compared in numerical FE simulations. Although both models led to remarkably different results in a shear‐dominated single element deformation test, the structural simulation of a standard deep drawing process delivered nearly congruent results which suggests that both models are equally well‐suited for modeling metals in common forming processes. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Configurational Forces in Crystal Plasticity
Authors: Lohkamp Richard , Müller Ralf , Aurich Jan , Schneider Frank
Published: November 2013

The surface morphology of micro machined surfaces depends on the heterogeneous microstructure. A crystal plasticity model is used to describe the plastic deformation in cp‐titanium with its hcp crystal structure. Therefore the basal and prismatic slip systems are taken into account. Furthermore, self and latent hardening are considered. The rate dependency is motivated by a visco plastic evolution law. The cutting process of cp‐titanium is modeled within the concept of configurational forces for a standard dissipative media. This framework is implemented into the finite element method. An example illustrates the effects of the microstructure on plastic deformation and configurational forces. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of the Homogenization on the Transient Behaviour of Size Distributed Polycrystals
Authors: Rieger Florian , Böhlke Thomas
Published: November 2013

The deformation in polycrystals is often heterogenous, e.g. due to grain size dependent hardening. In a semi‐analytical representative volume element (RVE), a log‐normal distributed grain size is assumed together with a grain size dependent local plastic behavior. The numerical results are well approximated by a simple analytical expression. The effect of the homogenization comparison stiffness on the transient behaviour is explained using a simplified localization equation. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Application of a viscoplastic material model on a combined quasi‐static‐electromagnetic forming process
Authors: Kiliclar Yalin , Demir O. Koray , Vladimirov Ivaylo N. , Kwiatkowski Lukas , Reese Stefanie , Tekkaya A. Erman
Published: November 2013

The prediction and simulation of material behavior by finite element methods has become indispensable. Furthermore, various phenomena in forming processes lead to highly differing results. In this work, we have investigated the process chain on a cross‐shaped cup in cooperation between the Institute of Applied Mechanics (IFAM) of the RWTH Aachen and the Institute of Forming Technology and Lightweight Construction (IUL) of the TU Dortmund.

A viscoplastic material model based on the multiplicative decomposition of the deformation gradient in the context of hyperelasticity has been used [1,2]. The finite strain constitutive model combines nonlinear kinematic and isotropic hardening and is derived in a thermodynamically consistent setting. This anisotropic viscoplastic model is based on the multiplicative decomposition of the deformation gradient in the context of hyperelasticity. The kinematic hardening component represents a continuum extension of the classical rheological model of Armstrong‐Frederick kinematic hardening. The constitutive equations of the material model are integrated in an explicit manner and implemented as a user material subroutine in the commercial finite element package LS‐DYNA with the electromagnetical module. The aim of the work is to show the increasing formability of the sheet by combining quasi‐static deep drawing processes with high speed electromagnetic forming. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of the influence of Spectral Elements for elastic wave propagation on the CFL‐Condition
Authors: Asmus Andreas , Lammering Rolf
Published: November 2013

For the simulation of the interaction of elastic waves in CFRP plates with inhomogeneities and defects the spectral finite element method (SEM) is under investigation. The SEM uses high‐order shape functions which are composed of Lagrange polynomials with nodes at the Gauss‐Lobatto quadrature (GLq) points. In this way we obtain a diagonal mass matrix which makes an explicit time scheme more efficient. The goal of this work is to investigate the effect of SEM on the CFL‐Condition. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A coupled chemo mechanical model for polymer degradation and erosion processes
Authors: Seydewitz Robert , Böl Markus
Published: November 2013

In nowadays polymer materials are used in a multitude of different applications. A promising class of smart materials are biodegradable polymers. The present work proposes a micromechanical motivated description of degradation. Since degradation leads finally to an eroding material both cases of erosion, namely bulk and surface erosion, are considered. Degradation is modelled in a strong coupled chemo mechanical framework for an arbitrary spatial motion problem. Deformations arising due to surface erosion are described as material motion. Finally, the modelling concept is embedded in a finite element method. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coupled chemomechanics and phase field modeling of failure in electrode materials of Li‐ion batteries
Authors: Dal Hüsnü , Miehe Christian
Published: November 2013

We propose a canonical finite strain theory for diffusion‐mechanics coupling for the intercalation induced stress generation in Li‐ion electrode particles. The intrinsic coupling arises from both mechanical pressure gradient‐induced diffusion of Li‐ion particles and diffusion induced swelling/shrinkage leading to mechanical stresses. In addition, we extend the finite strain theory for diffusion‐mechanics coupling to chemomechanical fracture of electrode particles by introducing a nonlocal crack phase field which replaces a sharp crack topology with a smooth diffuse interpolation between the intact and broken states of the material. We employ a semi‐implicit Galerkin‐type finite element method for the solution of resulting set of differential equations. In addition to the mechanical, chemical and crack phase field, we introduce the pressure as an independent field variable in order to reduce the smoothness requirements on the interpolation functions. We illustrate characteristic features of the proposed model by means of representative initial‐boundary value problems. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Modeling of Fluid‐Structure Interaction of Blood in a Vein by Simulating Conservation of Mass and Linear Momentum with the Finite Element Method in FEniCS
Authors: Lofink Paul , Müller Wolfgang H.
Published: November 2013

In medicine a fundamental understanding for blood flow in human arteries is significantly important. In socalled hemodynamics engineers all over the world simulate blood flows in healthy and diseased vessels. Scientific findings in this area help to improve cardiovascular assisting devices and to plan surgical operations. The difficulty with such simulations is the interaction of the blood flow with the elastic vessel wall, which deforms due to changing flow conditions. We will present a two‐dimensional model for blood flowing through an arterial vessel and investigate the balance of mass and the balance of linear momentum. We will adjust these balance equations appropriately and define time dependent boundary conditions. The necessary partial differential equations for the fluid‐structure interaction will be solved by using the finite element method in FEniCS [1]. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Influence of Incompressibility on the Microstructure of Dielectric Elastomers
Authors: Klassen Markus , Xu Bai‐Xiang , Müller Ralf
Published: November 2013

Dielectric elastomers (DE's) are considered in recent times for the development of so called smart actuators. This relatively soft material is deformed under the influence of an external electric field. It is an ideal candidate for application in which complex surface deformations are desired.

To increase the deformation range the insertion of material inclusions seems to be a good alternative. In the current work a mixed three field formulation in proposed to handle the quasi incompressibility of DE's for numerical simulations. A numerical analysis is performed in which the mixed formulation is compared with a standard displacement formulation. The results show the importance of the consideration of the nearly incompressible behaviour for the case of heterogeneous DE's. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Generalized boundary conditions and effective properties in cracked piezoelectric solids
Authors: Gellmann Roman , Ricoeur Andreas , Merkel Eugen , Wang Zhibin
Published: November 2013

In this paper we present two subjects of our actual research in the field. The first deals with the boundary conditions at the crack faces. The well known model by Hao and Shen gives opportunity to take the finite dielectric permeability of the crack into account, without having to solve the two‐ or three‐dimensional coupled boundary value problem of solid material and crack medium. This approach, however, is based on the assumption of the electric field being perpendicular to the crack faces. We investigate this problem for arbitrary poling and field directions based on a combined analytical‐numerical approach. The second focus of the paper is on the effective properties of piezoelectrics with cracks. Here, homogenization procedures are applied and extended towards coupled field problems including e.g. Maxwell stresses at internal boundaries and interfaces. Effective elastic, dielectric and piezoelectric constants exhibit interesting effects. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Solution of Inverse Task of Mechatronic Systems by Means the Classical and Unclassical Methods of Modelling and Analysis
Authors: Buchacz Andrzej
Published: November 2013

In this paper the modelling by means of the different category graphs and analysis of vibrating subsystem of mechatronic systems by means of the exact and approximate methods have been presented. That approach was to nominate the relevance or irrelevance between the characteristics obtained by means of the exact method (only for the mechanical subsystem) and the approximate method. Such formulation concerns mostly the relevance of the natural frequencies‐poles of the characteristics both mechanical subsystems and mechatronic systems. Approximate solutions requiring all the conditions for vibrating mechanical and/or mechatronic systems have been finding and it may be introduction to synthesis of these systems, modeled by different category graphs. Research limitation is following, that torsional vibrating continuous mechanical subsystem and mechatronic systems are linear type. Presentation the introduction to synthesis of considered class of mechatronic bar‐systems with a constant changeable cross‐section is practical implications of this work. Originality of such formulation is focused on the use of the different category graphs for modelling and synthesising by different methods represented by graphs of vibrating bars to the synthesis of considered discrete‐continuous mechatronic systems. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrical elements as implementation of active reduction of vibrations
Authors: Białas Katarzyna
Published: November 2013

The major aim of this study is to show how to carry out the process of structural and parametrical synthesis that is understood as a design method of the system with active suppression of vibrations. Active components are implemented as electric components. The other objective is to analyze how the active subsystem interacts with the overall investigated structure. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Non‐isothermal gas flow in microchannel with equal wall temperatures
Authors: Milićev Snežana S. , Stevanović Nevena D.
Published: November 2013

A non‐isothermal two‐dimensional compressible subsonic slip gas flows is analyzed in this paper. It is pressure‐driven steady flow in microchannels with variable cross section (convergent, divergent, and constant height channel). Since the flows correspond to microspaces, the rarefaction effect is taken in account. The obtained gas temperature profiles are non‐uniform. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On Symmetric Boundary Conditions in the Context of Viscoelastic Fluid Flows
Authors: Al‐Baldawi Ammar , Alves Manuel A. , Wünsch Olaf
Published: November 2013

In order to reduce the numerical cost of three dimensional flow problems with geometrical symmetry, the use of symmetric boundary conditions is standard. For Newtonian fluid flow problems this approximation is usually appropriate, particularly when the Reynolds number is small. In the case of viscoelastic fluid flow simulations with stabilization techniques, such as the so‐called DEVSS and/or Log‐Conformation tensor methods, at high Deborah number flows this implementation is not straightforward, as in the Newtonian case. It is well known that viscoelastic models (e.g. Maxwellian models), show (purely) elastic flow instabilities when the Deborah number is increased above a critical value, even under creeping flow conditions. In this work we present numerical simulations with different stabilization techniques and different differential viscoelastic models at high Deborah number flows. As a test‐case, we compare the flow in a full two‐dimensional cross‐slot geometry to show the asymmetrical behavior of the viscoelastic fluid flow. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of higher interpolation orders in mixed LSFEM for the incompressible Navier‐Stokes equations
Authors: Serdas Serdar , Schwarz Alexander , Schröder Jörg , Turek Stefan , Ouazzi Abderrahim , Nickaeen Masoud
Published: November 2013

The focus of this contribution is the examination of the influence of different interpolation orders (especially for the pressure field) by solving the stationary incompressible Navier‐Stokes equations with least‐squares finite elements. We consider two different div‐grad first‐order systems which result in a three‐field formulation with stresses, velocitites and pressure, see e.g. SCHWARZ & SCHRÖDER [1] and BOCHEV & GUNZBURGER [2]. Additionally, a numerical example is presented to show the performance of the considered formulations. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Near‐separating, self‐similar turbulent boundary layer
Authors: Vigdorovich Igor
Published: November 2013

The self‐similar flow in a turbulent boundary layer, which is in a state close to separation as a result of the effect of adverse pressure gradient, is investigated. Such a boundary layer has a triple‐deck asymptotic structure. Between outer and near‐wall regions above the logarithmic sublayer, i. e. the constant‐stress layer, an intermediate region — the gradient sublayer — is formed, where the shear stress varies linearly due to adverse longitudinal pressure gradient. In the external part of the gradient sublayer, the velocity profile obeys the square‐root law. The velocity profile obtained from the solution for the outer region satisfies a slip condition on the wall. The slip value decreases as the similarity parameter $\Omega = \sqrt{- \delta^* U'/U}$ increases and vanishes at the value of Ω = 0.0911, which corresponds to separation, here δ* is the displacement thickness, and U and U′ are the free‐stream velocity and its derivative with respect to the longitudinal coordinate. In this case, the exponent m in the law specifying the free‐stream self‐similar velocity distribution increases, with separation occurring not at the minimal value of m = −1/3, which corresponds to the strongest adverse pressure gradient, but at the value m = 0.228. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Frequency Domain Waveform Inversion in a Tunnel Environment
Authors: Musayev Khayal , Hackl Klaus , Baitsch Matthias
Published: November 2013

The aim of the waveform inversion is to find an optimal model for the distribution of the elastic stiffness such that its response is consistent with the seismic data. In this study, a high‐order finite element method is being used to solve the forward problem in the frequency domain and a gradient‐based approach is followed to invert the model where an adjoint method eases the computational struggle by reducing the number of the required forward simulations significantly. Perfectly Matched Layers (PML) are implemented in order to absorb waves on the fictitious boundaries of the considered geometry. The model is inverted only over a limited number of frequencies. This reduces the number of the required forward simulations and the nonlinearity of the inverse problem. Every model is unique and has to be investigated before being inverted; appropriate boundary conditions, placement of the source and receiver locations, and an initial model close to the real model are crucial points to be considered separately and carefully. Applications to the reconnaissance problem in a tunnel environment are shown. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Vortex Generation in a Liquid Metal Duct Flow near a Magnetic Dipole
Authors: Tympel Saskia , Boeck Thomas , Krasnov Dmitry , Schumacher Jörg
Published: November 2013

The generation of vortical structures by a strong magnetic dipole field in a liquid metal duct flow is studied by means of three‐dimensional direct numerical simulations. The dipole is considered as the paradigm for a magnetic obstacle which will deviate the streamlines due to Lorentz forces which act on the fluid elements. Our model uses the quasi‐static approximation applicable in the limit of small magnetic Reynolds numbers. The analysis covers the stationary flow regime at smaller flow Reynolds numbers Re as well as the fully time‐dependent regimes at higher values with a turbulent flow in the wake of the magnetic obstacle. We present a systematic study of these two basic flow regimes on Re and the Hartmann number Ha, a measure of the strength of the magnetic dipole field. Furthermore, three orientations of the dipole are compared, the streamwise, spanwise and wall‐normal ones. The most efficient generation of turbulence at a fixed distance above the duct occurs for the spanwise orientation in which we can observe the formation of Hartmann layers at the top plate. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Lattice Boltzmann Constraints for Standard Optimization Problems
Authors: Linke T. , Büskens C. , Meier S.
Published: November 2013

This paper presents a simultaneous analysis and design (SAND) approach for the control of incompressible, stationary fluid problems ruled by the lattice Boltzmann equation. Therefore the discretized lattice Boltzmann fix point problem is used as constraint for the optimization problem. This allows for the use of standard non‐linear programming techniques.

To validate the proposed method a topology optimization problem is solved with the NLP solver WORHP at moderate Reynolds numbers (Re< 1000) for a 2‐dimensional flow domain. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Homogenization and Geometric Linearization for Multi‐Well Energies
Authors: Jesenko Martin , Schmidt Bernd
Published: November 2013

The concept of linear elasticity is to assume that the stored energy has one‐well structure and to consider small displacements. The energy function is then expanded around the equilibrium state and higher‐order terms are neglected. It was proved in [3] that this concept really gives results that provide a good approximation for the actual problem. On the other hand, for materials with fine periodic structure we accomplish a simplification of the problem in an analogous manner by homogenizing the energy. It was recently shown by Müller and Neukamm in [8] that both processes, homogenization and linearization, are interchangeable for such elastic energies. If we consider an energy with multiple wells then, under some reasonable conditions, it is also possible to (geometrically) linearize the problem. The second author proved that quasiconvexification of the limit function yields the desired result. We present that in this case both processes still commute. This is not a priori clear since the proof by Müller and Neukamm significantly rests upon the one‐well structure and properties of quadratic forms. They also provide an example when the statement does not hold. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Hencky strain energy ‖log U‖2 measures the geodesic distance of the deformation gradient to SO(n) in the canonical left‐invariant Riemannian metric on GL(n)
Authors: Neff Patrizio , Eidel Bernhard , Osterbrink Frank , Martin Robert
Published: November 2013

The well‐known isotropic Hencky strain energy appears naturally as a distance measure of the deformation gradient to the set of rigid rotations in a canonical left‐invariant Riemannian metric on the general linear group GL(n). Objectivity requires the Riemannian metric to be left‐GL(n) invariant, isotropy requires the Riemannian metric to be right‐O(n) invariant. The latter two conditions are satisfied for a three‐parameter family of Riemannian metrics on the tangent space of GL(n). Surprisingly, the final result is basically independent of the chosen parameters.

In deriving the result, geodesics on GL(n) have to be parametrized and a novel minimization problem, involving the matrix logarithm for non‐symmetric arguments, has to be solved. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Some Fixed Point Results for a Sequence of Mappings on G‐Metric Space
Authors: Gajić Ljiljana , Lozanov Crvenković Zagorka
Published: November 2013

In the setting of generalized metric spaces, so called G‐metric spaced introduced by Z. Mustafa and B. Sims in 2006, some fixed point results for mappings with contractive iterate at a point and common fixed point results for infinite family of self mappings will be presented. The results are generalizations of well known results in the metric space. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Smoothing inexact Newton methods for NCP with various nonmonotone techniques
Authors: Rapajić Sanja , Pap Zoltan
Published: November 2013

Various iterative methods for solving nonlinear complementarity problems (NCP) are developed in recent years. In this paper we propose Jacobian smoothing inexact Newton methods for NCP with different nonmonotone strategies. The methods are based on semismooth equation reformulation of NCP by Fischer‐Burmeister function. Nonmonotone line‐search techniques are used for globalization procedure. Numerical performance of algorithms are compared. (© 2013 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)