bluuebunny/crossref_metadata_2025_split huggingface dataset:
Test‐retest repeatability of patterns of brain activation provoked by bladder filling
Authors: Clarkson Becky D. , Tyagi Shachi , Griffiths Derek J. , Resnick Neil M. 
Published: October 2016

ObjectiveTo assess short‐term repeatability of an fMRI protocol widely used to assess brain control of the bladder. fMRI offers the potential to discern incontinence phenotypes as well as the mechanisms mediating therapeutic response. If so, this could enable more targeted efforts to enhance therapy. Such data, however, require excellent test‐retest repeatability.MethodsFifty‐nine older women (age ≥60 years) with urgency incontinence underwent two fMRI scans within 5‐10 min with a concurrent bladder infusion/withdrawal protocol. Activity in three brain regions relevant to bladder control was compared using paired t tests and intra‐class correlation.ResultsThere were no statistically significant differences in brain activity between the two consecutive scans in the regions of interest. Intra‐class correlation was 0.19 in the right insula, 0.32 in the dorsal anterior cingulate cortex/supplementary motor area, and 0.44 in the medial pre‐frontal cortex. Such correlations are considered fair or poor, but are comparable to those from studies of other repeated fMRI tasks.ConclusionsThis is the first evaluation of the repeatability of a bladder fMRI protocol. The technique used provides a framework for comparing different fMRI protocols applied to brain‐bladder research. Despite universal patient response to the stimulus, brain response had limited repeatability within individuals. Improvement of the investigational protocol should magnify brain response and reduce variability. These results suggest that although analysis of fMRI data among groups of subjects yields valuable insight into bladder control, fMRI is not yet appropriate for evaluation of the brain's role in continence on an individual level.
Computational Closed‐Loop Control of Fluid‐structure Interaction (FSCI) for Lightweight Structures
Authors: Mini Andreas , Lerch Christopher , Wüchner Roland , Bletzinger Kai‐Uwe 
Published: October 2016

AbstractThis contribution gives a short introduction into the topic of fluid‐structure‐control interaction (FSCI). This is a multi‐field problem, where three fields are coupled, namely a fluid‐flow, structural dynamics and closed‐loop control of structures. The interactions are identified as surface‐coupling of fluid flow and structural dynamics as well as signal‐coupling of structural dynamics and closed‐loop control.At first a simple model problem is introduced, which allows an efficient investigation of the convergence behavior and stability of such kind of problem. In this context an iterative partitioned approach, using a serial Gauß‐Seidel scheme, is presented. Finally, the insights gained by the model problem are used to set up a multi‐dimensional numerical experiment. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Convolution Quadrature based BEM in acoustics for absorbing boundary conditions
Authors: Pölz Dominik , Sauter Stefan , Schanz Martin 
Published: October 2016

AbstractIn many fields of engineering the acoustic behavior has to be determined, e.g. the sound distribution in a room or the sound radiation into the surrounding. Often, the goal is to obtain a sound pressure field such that disturbing noise is reduced to an acceptable level. In room acoustics, sound absorbing materials are often used to obtain this goal. The mathematical description is done with the wave equation and absorbing boundary conditions. The numerical treatment can be done with Boundary Element methods, where the absorbing boundary results in a Robin boundary condition. This boundary condition connects the Neumann trace with the Dirichlet trace of the time derivative.Here, an indirect formulation, which uses the single layer potential, is used as basic boundary integral equation. The convolution quadrature method is applied for time discretisation, which allows a simple formulation of the Robin boundary condition in the Laplace domain. Convergence studies with a refinement in space and time show the expected rates. A realistic example for indoor acoustics, the computation of the sound pressure level in a staircase of the University of Zurich, show the suitability of this approach in determining the indoor acoustics. The absorbing boundary condition shows the expected behavior. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A new approach to the incorporation of servo constraints in multibody dynamics
Authors: Yang Yinping , Betsch Peter , Altmann Robert 
Published: October 2016

AbstractA new index reduction approach is developed to solve the servo constraint problems [2] in the inverse dynamics simulation of underactuated mechanical systems. The servo constraint problem of underactuated systems is governed by differential algebraic equations (DAEs) with high index. The underlying equations of motion contain both holonomic constraints and servo constraints in which desired outputs (specified in time) are described in terms of state variables. The realization of servo constraints with the use of control forces can range from orthogonal to tangential [3]. Since the (differentiation) index of the DAEs is often higher than three for underactuated systems, in which the number of degrees of freedom is greater than the control outputs/inputs, we propose a new index reduction method [1] which makes possible the stable numerical integration of the DAEs. We apply the proposed method to differentially flat systems, such as cranes [1,4,5], and non‐flat underactuated systems. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cross‐linked actin networks: Micro‐ and macroscopic effects
Authors: Klinge Sandra , Aygün Serhat , Mosler Jörn , Holzapfel Gerhard A. 
Published: October 2016

AbstractActin plays a crucial role in the mechanical response of cells. Together with other proteins, it also drives protrusion, motility and cell division. Two important aspects of the mechanical modeling of this kind of protein are considered: its microscopic and macroscopic behavior. At the microscopic level, we start with a model proposed by Holzapfel and Ogden [1] providing a relationship between the stretch of a single polymer chain and the applied tension force. The model is advantageous as it simulates the so‐called ‘exceptional normal stresses’. This effect is typical for biopolymers and contradicts with the Poynting effect typically observed in rubber‐like polymers. The multiscale finite element method (FEM) is applied to simulate the effective mechanical behavior of cell cytoplasm. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling residual stresses in arterial walls based on anisotropic growth
Authors: Zahn Anna , Balzani Daniel 
Published: October 2016

AbstractWith the aim of obtaining a general local formulation for anisotropic growth in soft biological tissues, a model based on the multiplicative decomposition of the growth tensor is formulated. The two parts of the growth tensor are associated with the main anisotropy directions. Together with an anisotropic driving force, the model enables an effective stress reduction by including growth‐induced residual stresses, which is demonstrated in a numerical example of an idealized arterial segment. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical investigations in structures with imperfect material interfaces and cracks
Authors: Judt Paul , Ricoeur Andreas 
Published: October 2016

AbstractNatural fiber reinforced bio‐polymers are in the focus of many research projects to understand and improve the mechanical behavior subjected to different process parameters during production. To provide safe and reliable light weight constructions, special interest is directed towards the damage and fracture behavior of such composite materials. Here, the material's behavior at the imperfect material interface between fiber and matrix plays an essential role and governs inelastic effects at the interfaces on the one hand, and the behavior of growing cracks on the other. The reduction of the elastic potential is related to both energy consuming processes in the system and in general is going along with a reduction of the crack tip loading and a shift of the crack growth direction. In this paper, the crack tip loading analysis in structures with perfect and imperfect material interfaces is presented and applied to different specimens. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On nonlinear damage accumulation and creep‐fatigue interaction of a damage model for the lifetime prediction of adhesively bonded joints
Authors: Kroll Ulrich , Matzenmiller Anton 
Published: October 2016

AbstractDamage accumulation and creep‐fatigue interaction are investigated and depicted for a continuum damage model proposed for the lifetime prediction of bonded steel joints with the structural adhesive BETAMATE 1496V™. The nonlinearity of damage accumulation is caused by the nonlinearity of damage interaction as a result of the identified parameters. In consequence of the nonlinear accumulation, the model allows for the loading sequence effect, which is the influence of the chronological order of the load values on the lifetime. Although the nonlinearity of the damage accumulation is not very pronounced, the model prediction is in good agreement with lifetimes from tests with service loading of the adhesive at hand. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of Hertzian cone cracks using a phase field description for fracture
Authors: Strobl Michael , Morand Lukas , Seelig Thomas 
Published: October 2016

AbstractThe present contribution focuses on fracture caused by indentation loading on the surface of a brittle solid. Its theoretical prediction is a challenging task due to the fact that crack nucleation is not geometrically induced, but is caused by the stress concentration in the contact near‐field. The application of the phase field model requires constitutive assumptions to ensure a tension‐compression asymmetric material response and prevent damage in compressed regions. This is achieved at the cost of giving up the variational concept of brittle fracture. We simulate the indentation of a cylindrical flat‐ended punch on brittle materials like silicate glass. In order to reduce the numerical effort, we exploit axisymmetric conditions for the finite element formulation. After crack initiation stable propagation of a cone crack can be observed in good agreement with experiments. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A fracture angle based three‐dimensional damage model for unidirectional fibre‐reinforced plastics
Authors: Szlosarek Robert 
Published: October 2016

AbstractSince the failure analysis of fibre‐reinforced plastics is not limited to the first‐ply failure, it is mandatory to use adequate damage models to simulate the failure process. The paper describes a damage model for three‐dimensional stress states, which uses the crack orientation of the inter‐fibre fracture (IFF). The fracture angle describes the crack orientation and can be obtained by using Puck's IFF criterion. The fracture angle enables the possibility to take the causal stress situation for the IFF into account. This means that each Young's or shear modulus has its own damage function, which depends on the stress state and the fracture angle. Therefore, the stress‐strain extrapolation method of Schürmann and Weber for two dimensional stress states was advanced and modified for the three‐dimensional stress space. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermally loaded thick‐walled cylindrically curved aluminum/steel‐FGM‐panel
Authors: Haskul Mehmet , Arslan Eray , Mack Werner 
Published: October 2016

AbstractSubject of the investigation is a thick‐walled cylindrically curved shell guided at the ends which is heated at its inner or outer surface. The material is presupposed to be functionally graded obeying a power law. Both the elastic limits according to von Mises and the stress distributions for different grading exponents are discussed. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the acoustics of sonic composites
Authors: Girip Iulian 
Published: October 2016

AbstractThe primary goal of this paper is to propose an alternative method for obtaining the band structures of the 3D sonic composites without/ with point defects. The point defects are vacancies or foreign interstitial atoms which are supported by the interfaces between the hollow spheres and the matrix. The proposed method is used to simulate a sonic plate composed of an array of acoustic scatterers which are piezoceramic hollow spheres embedded in an epoxy matrix. The scatterers are made from functionally graded materials with radial polarization [1, 2]. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Galerkin‐based energy‐momentum time‐stepping schemes for anisotropic hyperelastic materials
Authors: Groß Michael , Ramesh Rajesh , Dietzsch Julian 
Published: October 2016

AbstractThis paper is motivated by dynamic simulations of fiber‐reinforced materials in light‐weight structures, and has two goals. First of all, the introduction of energy‐momentum schemes for nonlinear anisotropic materials, based on GALERKIN approximations in space and time, assumed strain approximations in time and superimposed algorithmic stress fields (compare [1]). Second, to show a variationally consistent design of energy‐momentum schemes using a differential variational principle. We develop a discrete variational principle leading to energy‐momentum schemes as discrete EULER‐LAGRANGE equations. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Isogeometric Reissner‐Mindlin shell analysis ‐ employing different control meshes for displacements and rotations
Authors: Kikis Georgia , Dornisch Wolfgang , Klinkel Sven 
Published: October 2016

AbstractThe main purpose of this paper is the development and implementation of a method for the reduction of the so‐called locking effect in the isogeometric Reissner‐Mindlin shell formulation. In [1] an isogeometric Reissner‐Mindlin shell formulation with an exact interpolation of the director vector based on continuum mechanics was introduced. The numerical examples showed that the accuracy and efficiency increased. However, there are only few effective concepts for the prevention of locking effects for low polynomial degrees. In the work of Beirão da Veiga [2], shear locking is prevented for a Reissner‐Mindlin plate formulation by using suitable solution spaces. Here, the method is extended to the Reissner‐Mindlin shell formulation. Different control meshes are used for displacements and rotations. Furthermore, the basis functions in the direction of the relevant rotation are one degree less than the ones which are chosen for the displacements. That leads to control meshes with different number and location of the control points. The aim is to avoid shear locking due to the coupling of shear strains and curvature since the compatibility requirement for pure bending is then fulfilled. The accuracy and efficiency of this method are investigated for different examples. In addition, the results are compared to the analytical solutions. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Solids in boundary representation ‐ a NURBS based Galerkin formulation
Authors: Klinkel Sven , Chen Lin , Simeon Bernd 
Published: October 2016

AbstractThe present approach deals with a numerical method for the static analysis of solids in boundary representation. A formulation is derived where the geometrical description of the boundary is sufficient to define the elastic boundary value problem for the complete solid. The interior of the domain is described by a radial scaling parameter. Following the idea of the scaled boundary finite element method [1] the scaling of the boundary with respect to a specified scaling center provides a representation for the complete solid. This concept fits perfectly to the boundary representation modeling technique, which is frequently used in CAD to define solids. In CAD the boundary of the solid is described by employing NURBS basis function. In the isogeometric analysis methodology, [2], a trivariate tensor product structure is used to analyze solids. In the present approach, the tensor‐product structure of the solid will be reduced by one dimension to parameterize the physical domain, i. e., the three‐dimensional solid exploits only two‐dimensional NURBS objects, which parameterize the boundary surfaces. Hence, the present approach represents perfectly the isoparametric paradigm, see [3]. However, in [3] the weak form of equilibrium is enforced on the boundary surface. This leads to an ordinary differential equation (ODE) of Euler type, which could be solved by applying a collocation scheme. In the present approach the weak form is employed on the boundary and in scaling direction. The displacement response in the radial scaling direction is approximated by one‐dimensional NURBS. Finally, the Galerkin projection of the weak form yields a linear system of equilibrium equations whose solution gives rise to the displacement response. In conclusion, the presented method is able to analyze solids, which are bounded by an arbitrary number of surfaces. Numerical examples will show the capabilities of the presented method. The accuracy of the method is investigated by comparison to the analytical solution. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of the temperature and wear behaviour of a disc brake
Authors: Lamjahdy Abdelkrim , Ali Jawad , Markert Bernd 
Published: October 2016

AbstractAerosols are defined in the simplest form as a mixture of solid or liquid particles suspended in a gas [1]. Brake dust is an aerosol, generated as a result of erosion between brake disc and brake pad. The aerosols can cause visual disorder, heart and lung diseases, short term acute symptoms like asthma, bronchitis and long term chronic irritation and inflammation of the respiratory track, which can lead to cancer. Therefore, it is important to know which factors are affecting the erosion rate of brakes. The main objective of this work is to measure the erosion rate of brake discs and brake pads, depending on temperature changes and deformation by performing experiments and simulations at varying velocities and load conditions. The general purpose, commercially available finite element solver Abaqus is used for performing the thermomechanically coupled simulations. Archad's Wear Law is used for the wear calculation. Experiments are conducted by using a pin on disc test bench. Temperature changes are measured by using thermocouples and erosion rates by measuring the total volume loss. At the end, relationships between erosion rates and temperature changes for different brake disc velocities and load conditions are investigated and experimental and simulation results are compared and discussed. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A three‐dimensional discrete element model for heterogeneous solids under mechanical loading
Authors: Ockelmann Felix , Dinkler Dieter 
Published: October 2016

AbstractThe Discrete Element Method (DEM) is used to model solids under quasi‐static and dynamic loading. In order to model elastic bodies, a microscopic model must be able to represent the macroscopic properties of the material. An energy‐based approach to determine the model parameters is presented for an unit cell assemblage of 13 particles in the hexagonal close packing of spheres. The stored strain energy in the unit cell is added up and the specific strain energy expression is derived with respect to the macroscopic strains. The resulting stress‐strain relations can be compared to the constitutive equations of the elastic continuum. To avoid cubic anisotropy for Poisson's ratios above zero, an advanced octahedrongap‐filled hexagonal close packing of spheres is presented and validated.This approach for regular lattices can be transferred to heterogeneous materials with the goal of describing porous media such as cement stone. Therefore it is possible to use the presented regular lattices with statistically distributed properties or to investigate irregular distributions of particles. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Vibrations of a beam‐string complex system under a moving force
Authors: Rusin Jarosław 
Published: October 2016

AbstractIn this paper, the dynamic response of an Euler‐Bernoulli beam and string system traversed by a constant moving force is considered. The force is moving with a constant velocity on the top beam. The complex system is finite, simply supported, parallel one upon the other and continuously coupled by a linear Winkler elastic element. The classical solution of the response of a beam‐string system subjected to a force moving with a constant velocity has a form of an infinite series. The main goal of this paper is to show that in the considered case the aperiodic part of the solution can be presented in a closed, analytical form instead of an infinite series. The presented method of finding the solution in a closed, analytical form is based on the observation that the solution of the system of partial differential equations in the form of an infinite series is also a solution of an appropriate system of ordinary differential equations. The dynamic influence lines of complex systems may be used for the analysis the complex models of moving load. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Particle Finite Element Simulations of Cutting Processes in Manufacturing
Authors: Sabel Matthias , Sator Christian , Müller Ralf 
Published: October 2016

AbstractThe cutting of metals is an important process in manufacturing and challenges established methods in the field of computational mechanics. The particle finite element method (PFEM) combines the benefits of particle based methods and the standard finite element method (FEM) to account for large deformations and separation of material. In cutting simulations the workpiece is realised as a set of particles, whose boundary is detected by the α‐shape method. After the boundary detection, the particles are meshed with finite elements. Since metals show a plastic behavior under large deformations, a suitable material model needs to be considered. Numerical examples show the effect of the choice of the parameter α on the cutting force. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)