bluuebunny/crossref_metadata_2025 huggingface dataset:
Trajectory planning for boundary controlled parabolic PDEs with varying parameters defined on a parallelepiped
Authors: Meurer Thomas , Kugi Andreas
Published: March 2010

The trajectory planning and feedforward tracking control problem is considered for a boundary controlled diffusion‐reaction system with a spatially and time varying reaction parameter defined on a 3‐dimensional parallelepiped. For this, an implicit state and input parametrization in terms of a basic output via a Volterra‐type integral equation with operator kernel is determined, which is solved recursively by means of a series ansatz. The absolute and uniform convergence of the resulting series is verified by restricting the reaction parameter and the basic output to a certain but broad Gevrey class. Hence, assigning an admissible desired trajectory for the basic output directly yields the respective feedforward control, which is required to realize a desired spatio‐temporal transition path. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Controllability of distributed parameter systems: Illustrative examples for an algebraic approach.
Authors: Woittennek Frank , Mounier Hugues
Published: March 2010

Boundary coupled partial differential equations of second order are seen as convolutional systems over a Bézout domain RQ of particular distributions and ultradistributions with compact support. For two simple examples this property of RQ is employed in order two find a flat output, i.e., a variable that allows the parametrization of the system trajectories in an appropriate solution space. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis and assessment of foot posture in children with flat feet
Authors: Pauk J.
Published: March 2010

The paper presents the methods for foot assessment such as: X‐ray, graphic contour testing, ground reaction force, and pressure distribution. Some of this methods can be used just in static. The platforms with sensors are very good tools in assessment foot posture during human walking. The evaluation was carried on 20 typical subjects and 60 children with foot deformities. GRF parameters, compared to clinical radiographic measurement demonstrated generally a good correlation. The analysis of fround reaction force and pressure distribution represent a strong tool to validate clinical tests and can be used for screening, diagnosis and treatment choice in clinical practice. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical simulation of electrical double layers and internal electrodes in microchannels
Authors: Wälter Bettina , Ehrhard Peter
Published: March 2010

We investigate the influence of flow field and electrode reactions onto an electrical double layer (EDL), which is located in the immediate vicinity of the walls of a rectangular microchannel. The precise knowledge of the EDL appears to be important for many technical applications in microchannels of small width, since the electrokinetic effects, as electroosmosis or electrophoresis, in such cases depend on the detailed charge distribution. Furthermore, the influence of internal electrodes onto the flow field is of interest. The mathematical model for the numerical treatment relies on a first‐principle description of the EDL and the electrical forces, caused by the electrical field between internal electrodes. Hence, the so‐called Debye‐Hueckel approximation is avoided. The simulations are time‐dependent and two‐dimensional (plane) in nature and employ a finite‐volume method. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Hybrid Micro–Macro–Model of Finite Plasticity with Discrete CODF–Textures
Authors: Frankenreiter Ilona , Rosato Daniele , Miehe Christian
Published: March 2010

We outline recent developments towards an efficient theoretical and algorithmic modeling of evolving crystal orientation microstructures in finite plasticity of polycrystals. We construct a framework for the description of grain texture induced anisotropy in planar polycrystals based on a hybrid micro‐macro modeling. On the macroscopic side this concerns a purely phenomenological setting of anisotropic finite plasticity based on evolving structural tensors accounting for the deformation‐induced macroscopic anisotropy. On the micro‐mechanical side, the macro‐model is linked with an accompanying microscopic plasticity model that accounts locally for microscopic structural changes in the form of grain re‐orientations. The model‐inherent scale bridging is accomplished by an evolving crystal orientation distribution function (CODF), which governs the evolution of the structural tensors. The evolution of the CODF is updated in a novel format based on the exploitation of two evolution equations in the Lagrangian setting. We discuss an efficient numerical implementation of evolving CODFs discretizing the orientation space. The new approach is compared with a Taylor model. The new model provides an efficient and fast computationally two‐scale approach for the prediction of the complex microstructures evolution in polycrystals. The capability of the proposed method is demonstrated by means of representative numerical examples. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterization of disk brake noise behavior via measurement of friction forces
Authors: Schlagner Stefan , von Wagner Utz
Published: March 2010

Squealing of disk brakes is a major problem in the field of vehicle design. It is commonly acknowledged, that this squeal is initiated by instability due to friction forces between the pads and the disk, leading to self excited vibrations. This work addresses the mechanical work of these friction forces in order to draw conclusions for the investigation of the noise behavior of disk brakes. Therefore a multi degree of freedom model is used to compare its stability behavior with the frictional work at the pads. The results obtained are applied to experiments in which, on the one hand brake pads with integrated piezoceramic actuators cause a broad band excitation and, on the other hand, dynamic pad velocities/accelerations and friction forces are measured. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulations and Tests of Innovative Friction Laws in Brake Systems
Authors: Bode Kai Henning , Ostermeyer Georg‐Peter
Published: March 2010

Modeling of friction in mechanical systems is classically carried out by an incorporation of suitable algebraic functions. The general layout of these functions depends on the system under consideration [1]. For an analysis of brake systems, whose external parameters generally change rapidly, such steady state descriptions do not suffice. A detailed understanding of these systems and their dynamics requires innovative friction laws, which must be able to also capture transient effects in the contact zone. The tribological interface between brake lining material and brake disc is characterised by a closed‐loop interaction between heat, wear and friction, which causes a continuous growth and destruction of smooth and hard surface structures [2]. This equilibrium of flow can be well reproduced by modern automata methods [3]. It is significantly influenced by external load parameters, such as normal force and sliding velocity, which modulate the life cycle and average size of the contact patches and by that the coefficient of friction over time. Based on this principal mechanism, a new mathematical description of friction has been derived, which uses a set of coupled differential equations. This layout gives insights into the third body dynamics during transient friction events. Therewith, predictions of the surface topography, heat distribution and friction characteristics of different brake lining compositions become possible. The performance of the developed model will be illustrated by a discussion of specific braking events, extracted from industrial testing procedures (AK‐Master test). (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Temporal Regularity of Solutions of Rate‐independent Damage Processes
Authors: Thomas Marita
Published: March 2010

This contribution deals with the temporal regularity of energetic solutions of rate‐independent processes describing the partial, isotropic damage of physically nonlinearly elastic solids. In general, energetic solutions may have jumps. Here we discuss settings that lead to continuity, Hölder‐ or Lipschitz‐continuity in time and we give examples on suitable energy densities. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental investigation of ovine intervertebral disc units in longitudinal loading
Authors: Helfenstein Jörg , Hollenstein Marc , Papes Ondrej , Mazza Edoardo
Published: March 2010

The assessment of the predictive power of material models for soft biological tissues is an important issue when it comes to realistic simulations for medical applications. The determination of the model parameters needs sound experimental data. In our case we want to test the viscoelastic properties of ovine lumbar intervertebral discs (IVD's) in longitudinal loading. The complex geometry as well as the small imposed displacements combined with rather high forces are to be treated. The two vertebrae adjacent to the IVD are mounted using custom made clampings where attention is paid not to prestress the tissue. First tests were done with steel springs in order to check the suitability of the used materials testing machine. No significant compliance of the machine could be detected but a negative hysteresis that might origin from the data acquisition process. Experiments on IVD's gave us an in‐depth insight into the underlying mechanics such that we can now define appropriate protocols for future experiments. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Intraoperative mechanical characterization of human liver
Authors: Hollenstein Marc , Jabareen Mahmood , Breitenstein Stefan , Riener Marc‐Oliver , Clavien Pierre‐Alain , Bajka Michael , Mazza Edoardo
Published: March 2010

The tissue aspiration experiment, the instrumentation for intraoperative measurements and the procedure for quantitative evaluation of the measurement results are presented. This experiment is currently used in a clinical study on the correlation between the mechanical properties of liver tissue and its histopathologic state. To date the liver of 25 patients has been tested. The results indicate a difference of 40% in the initial stiffness between peritumoral normal liver tissue and liver tumor. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental and numerical study of the relaxation behavior of facial soft tissue
Authors: Barbarino Giuseppe. G. , Jabareen Mahmood , Mazza Edoardo
Published: March 2010

Challenges in computational simulation of the mechanical behavior of soft tissues and organs for clinical applications are related to the reliability of the models with respect to the anatomy, the mechanical interactions between different tissues, and the non linear (time dependent) force deformation characteristics of soft biological materials. In this paper a 3D finite element model of the face and neck, which has applications in surgical devices optimization and surgery planning, is presented. Bones, muscles, skin, fat, and superficial muscoloaponeurotic system (SMAS) were reconstructed from magnetic resonance images and their shape, constraints and interactions have been modeled according to anatomical, plastic and reconstructive surgery literature. Non linear time dependent constitutive equations are implemented in the numerical model, based on the Rubin‐Bodner model. For the present calculations a simplified hyperelastic formulation has been used. The corresponding model parameters were selected according to previous work with mechanical measurements ex vivo on facial soft tissue. For determination of model parameters, in particular the ones corresponding to the time dependent behavior, an instrument for measuring the relaxation behavior of the face tissue in vivo was developed. The experimental set‐up is described and results are presented for tests performed on different locations of the face (jaw, mid‐face, parotid regions) and neck. The measured “long term” reaction force of the facial soft tissue is compared to numerical results. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Wave propagation in the soil due to a falling chimney
Authors: Bochert Jana
Published: March 2010

This paper describes a simulation of wave propagation in the soil as a result of an impact. In this specific case, the dynamic load is the velocity of a falling chimney. The impacting parts of the chimney transfer their dynamic forces to the adjacent continuum. This causes vibrations in the surrounding area. In this paper, measurements of velocities in the soil caused by a falling chimney are compared with numerical solutions using a two‐dimensional FEM‐SBFEM model. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Scaled boundary finite element analysis of stress singularities in piezoelectric multi‐material systems
Authors: Mayland Wibke , Becker Wilfried
Published: March 2010

The scaled boundary finite element method (SBFEM) in an extension for piezoelectric materials is used to analyze twoand three‐dimensional stress singularities in piezoelectric multi‐material systems. It is found to be an efficient tool for the analysis of singularity orders of such situations, that turn out to be rather complex. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of High‐Speed Ball Bearings with MSC/ADAMS
Authors: Fritz Felix , Basler Alexander , Seemann Wolfgang
Published: March 2010

High‐speed‐rotors can be supported by angular ball bearings. Therefore, the nonlinear, time‐variant bearing reaction forces are modeled for high revolution rates in this approach. Assuming local deformations, bearing stiffness is modeled with Hertzian contact between balls and races. Centrifugal forces on balls and rings are considered. Under consideration of clearance ratio the contact angle changes due to bearing load, rotational frequency and tilting angle of the inner ring. Since the contact angle determines the direction of reaction force and moment, it is possible to analyze the non‐planar inner ring movement. To be able to attach further machinery parts easily to the bearing model, this approach has been done with the multi‐body simulation software package MSC/ADAMS. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Non‐linearity of multibody dynamic equations with respect to Lagrange multipliers: application to railway dynamics
Authors: Fisette Paul , Lipinski Krzysztof , Samin Jean‐Claude
Published: March 2010

In this paper, the dynamics of multibody systems with closed kinematical chains of bodies is considered. The main focus is set on non‐linearity of the multibody equations with respect to the Lagrange multipliers. When closed chains are considered, loop cutting procedure is a solution to express the constraint equations associated with the loops. Dynamic equations of the multibody tree‐like structure are thus completed with the constraint forces via the Lagrange multipliers. In the considered case of railway vehicles, constraints arise from the contact between the rigid wheels and the rails. Corresponding contact forces applied to the wheels appears via the Lagrange multipliers λ and the tangent creep forces as well. Resulting differential‐algebraic equations can be transformed into an ODE system and then time‐integrated using the coordinate partitioning method [3], when the system is linear with respect to λ. This paper presents an algorithm allowing us to solve this system in case of nonlinearities with respect to λ, which is typical of wheel/rail contact force models. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Holistic Simulation Approach from a Measured Load to Element Stress Using Combined Multi‐body Simulation and Finite Element Modelling
Authors: Harter Matthias , Beitelschmidt Michael
Published: March 2010

The design of vehicle bodies requires the knowledge of the vehicle's structural response to external loads and disturbances. In rigid multi‐body simulation the dynamic behaviour of complex systems is calculated with rigid bodies and neglect of body elasticity. On the other hand, in finite element models large degree of freedom numbers are used to represent the elastic properties of a single body. Both simulation methods can be combined, if the finite element model size is reduced to a degree of freedom number feasible to multi‐body simulation. The application to practical purposes requires the use and interconnection of several different software tools. In this contribution a holistic method is presented, which starts with the measurement or synthesis of loads and excitations, continues with the integration of a reduced finite element model into a multi‐body system, the dynamic response calculation of this combined model, and concludes with the result expansion to the full finite element model for calculating strain and stress values at any point of the finite element mesh. The applied software tools are Simpack, Nastran, and Matlab. An example is given with a railway vehicle simulated on measured track geometry. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Studies on Bone Remodeling Theory Based on Microcracks Using Finite Element Computations
Authors: Kardas Dieter , Nackenhorst Udo
Published: March 2010

The investigation of the microcrack theory supports the research work of understanding the microstructural behaviour of physiological loaded bones. Microcracks in cortical bone are assumed to have a stimulatory effect on osteocytes – the sensor cells for the bone remodeling process. In this contribution an approch to simulate microcrack initiation and propagation inside a 3D anisotropic and inhomogenious FEA model of cortical bone tissue will be shown. The numerical formulations are based on computational continuum damage mechanics. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An efficient quantitative ultrasonic elastography based on variational mesh refinement
Authors: Arnold Alexander , Bruhns Otto T. , Mosler Jörn
Published: March 2010

Palpation is often utilised in medicine to detect pathological changes in soft tissue such as those associated with breast cancer or prostate tumor. Ultrasound elastography can be used to measure the stiffness in regions deeper than those reachable by palpation. Conceptually, ultrasound echo signals are measured before and after a defined compression. A displacement field can be calculated with these signals and subsequently, the stiffness distribution can be determined using quantitative elastography. In this regard, the difference between measured und estimated displacement fields is minimised (inverse problem). The region of interest is discretised using the finite element method. In order to reduce the resulting numerical costs and to improve the accuracy of the method, a variational mesh refinement combined with a clustering technique known from digital image compression is elaborated and presented. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electromechanics of Cardiac Tissue: A Unified Approach to the Fully Coupled Excitation‐Contraction Problem
Authors: Göktepe Serdar , Kuhl Ellen
Published: March 2010

This contribution is concerned with a new, unified finite element approach to the fully coupled problem of cardiac electromechanics. In contrast to the existing numerical approaches suggested in the literature; to the best of our knowledge, for the first time, we propose a fully implicit, purely finite‐element‐based approach to the coupled problem. The system of coupled algebraic equations obtained by simultaneous linearization of non‐linear weighted residual terms is solved monolithically. The put forward modular algorithmic framework leads to an unconditionally stable and geometrically flexible structure that can readily be extended towards complex ionic models of cardiac electrophysiology. The performance of the proposed approach is illustrated by the coupled electromechanical analysis of a biventricular generic heart model. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An anisotropic viscoelastic model for collagenous soft tissues at large strains – Computational aspects
Authors: Ehret Alexander E. , Itskov Mikhail , Weinhold Georg W.
Published: March 2010

This paper focusses on computational aspects related to a recently proposed anisotropic viscoelastic model for soft biological tissues at large strains [1]. A key aspect of this model is the generalisation of micromechanically motivated one‐dimensional constitutive equations to three dimensions by numerical integration over the unit sphere. A strong effect of this procedure on the accuracy and in particular on the material symmetry of the model is observed. Finally a finite element example of an artery subject to normotensive blood pressure is presented. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Dynamic Analysis of the Flow Process Through the Aortic Valve Leaflet Model
Authors: Konderla Piotr , Krzysztof Patralski
Published: March 2010

The object under study is an aortic valve, located in the aortic annulus. The aortic valve leaflet has been assumed to be a three‐dimensional object. The computations were performed using the Ansys CFX system. The result of our analysis takes the form of a model describing the interaction between two domains. The opening of the aortic valve model was obtained by iteration process. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determination of Feasible Muscle Forces in Human Walking Using Static Optimization and Hill's Muscle Dynamics Constraints
Authors: Ou Ye , Kecskeméthy Andrés
Published: March 2010

Static optimization is a widely used technique for solving the redundant problem of muscle‐force determination for given inverse dynamics. There are different cost functions, such as minimal metabolic energy, minimal forces, minimal fatigue, which lead to different results. One problem in this setting is that the resulting time histories of the ensuing equilibrium forces may not be feasible with respect to the muscle dynamics, i.e., the resulting force gradients at the muscle cannot be reproduced by the dynamics of the corresponding muscle. In this paper, a combined method is presented which takes into account the limitations induced by the muscle dynamics by applying static optimization techniques at each time step and prescribing minimal and maximal constraints for the forces by extrapolating the force values from previous steps using feasible muscle activation values. Thus, both the advantages of fast static optimization and the guarantee of feasible time histories of the muscle forces can be achieved. Moreover, joint forces turn out to be 20–40% higher in swing phase than those predicted with classical static optimization. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Real‐time FEM for the Virtual Surgery of Soft Tissues
Authors: Willberg Christian , Gabbert Ulrich , Berger Harald
Published: March 2010

The virtual surgery of soft tissues, such as the virtual laparoscopy, requires realistic 3D models of all the inner organs belonging to the virtual scenario, which in connection with fast numerical algorithms have to assure the real‐time performance of the simulation. The simulation has to take into account the interaction of the surgical instruments with the organs, the contact behavior between the organs including self contact as well as cutting, stitching, bleeding, coagulation etc. Recently, different approaches have been published to achieve a real time performance with sufficient accuracy. In the paper a finite element approach is presented, which includes the geometrical and physical nonlinear dynamic behavior of the organs during the surgery as well as the required contact conditions between the organs and the organs with surgical instruments. Some simplifications of the standard procedure (contact search, updating rate, etc.) to increase the computational speed as well as the beneficial behavior of an implicit time integration scheme resulting in larger time steps are discussed. In the paper some examples are presented to demonstrate the performance and the accuracy of the approach. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Design of the exoskeleton as a rehabilitation system
Authors: Tuliński J. , Jasińska‐Choromańska D.
Published: March 2010

The presented paper concerns development of a parallel kinematic structure of a palm fingers exoskeleton as a prospective solution for common design difficulties encountered in typical serial‐kinematics exoskeletons for the fingers rehabilitation. The performed state of the art review showed that in spite of over 40 years of development of exoskeletons, considered to be particularly useful as programmable medical devices, there is not achieved the acceptable level of safety and usability. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Free vibration of sandwich plates with impact‐induced damage
Authors: Burlayenko Vyacheslav N. , Sadowski Tomasz
Published: March 2010

Free vibrations of impact‐damaged sandwich plates with honeycomb and foam cores are studied. It is assumed that damages caused by impact events are to exist before the vibration start and to be constant during oscillations. The influence of the impact damage modes involving the core crushing (planar damage), face sheets fracture (indentation) and the core to face sheets interface degradation (debonding) on the natural frequencies and associated mode shapes of the sandwich plates was investigated using commercially available finite element code ABAQUS. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Implementation of a cohesive zone model for crack closure analysis of rotors
Authors: Liong Rugerri Toni , Proppe Carsten
Published: March 2010

The presence of a crack in a rotor introduces a local flexibility which affects its dynamic response. Moreover, the crack may open and close during the vibration period. The crack status is a function of time and also depends on the rotational speed and the vibration amplitude of the rotor. This nonlinear case is still a challenging research topic especially in the field of closing crack in the rotating shaft. A cohesive zone model is developed in order to analyze the stiffness of a crack in a rotating shaft. The proposed expression will be compared to three different crack models, namely, a breathing crack model, a switching crack model and an open crack model. Moreover, a cohesive law to predict and to analyse the stress at the crack tip is presented. The numerical model is implemented using a finite element formulation. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of experimental and numerical results on metallic plates subjected to explosions
Authors: Pyrzowski Łukasz , Kłosowski Paweł , Woznica Krzysztof , Pennetier Olivier
Published: March 2010

A comparative study of dynamic response including damage and rupture processes of thin metallic plates subjected to shock‐wave impulses – explosions is presented. The results of the finite element numerical analysis are related to experiments. Due to high strain rate during explosions the elasto‐viscoplastic Chaboche's constitutive law including damage effects has been applied. For the assumed model proper material parameters identification has been done. In the dynamic, geometrically non‐linear analysis the MSC.Marc system has been used. A good correlation between numerical and experimental results has been observed. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of domain structures in cracked ferroelectric materials
Authors: Xu Bai‐Xiang , Müller Ralf , Schrade David , Gross Dietmar
Published: March 2010

The domain structure around a crack tip plays a significant role in the fracture behavior of ferroelectrics. A continuum phase field model is used to investigate the microstructure at the crack front. The concept of the Eshelby momentum tensor and configurational forces is then generalized to account for the contributions of the polarization term. Implementation of the generalized configurational force in the Finite Element code enables us to numerically obtain the driving force at the crack tip, which corresponds to the crack‐tip energy release rate. Calculations show that additional positive electric fields tend to prohibit crack growth, whereas additional negative electric fields tend to promote crack growth. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Formulation and Application of the Initially Rigid Cohesive Finite Element Method
Authors: Geißler Gordon , Kaliske Michael
Published: March 2010

The presented procedure for cohesive crack propagation is based on an adaptive finite element (FE) implementation, which enables the introduction of cohesive surfaces in dependence on the current crack state. In contrast to already existing formulations, the focus of the present model lies on failure processes that can be described at quasi‐static conditions within an implicit framework. Furthermore, an extension for mesh independent crack propagation in terms of an additional mesh adaptive formulation is presented. By the evaluation of the failure criterion considering the preferred crack direction, a new crack tip coordinate is computed and the discretization is accordingly adjusted. The remaining mesh is modified for the new boundary representation. The application of the proposed method is shown by the numerical investigation of a concrete fracture specimen from an experimental research project. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A variational coupled damage‐plasticity model via gradient enhancement of the free energy function
Authors: Dimitrijevic Bojan J. , Hackl Klaus
Published: March 2010

We present a coupled damage‐plasticity model, whose regularization is achieved through gradient enhancement of the free energy function by introducing new variables. They serve to transport the values of the inelastic variables across the element boundaries, and their gradients play regularisation role in the model. Variational formulation results in a pure minimisation problem, leading to model non‐local in nature and preserving C0 interpolation order of the variables. Numerical examples illustrating the performance of the proposed model are presented. It is shown that the pathological mesh dependence is efficiently removed, together with the difficulties of numerical calculations in the softening range. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Variational–Based Formulation of Regularized Brittle Fracture
Authors: Hofacker Martina , Welschinger Fabian , Miehe Christian
Published: March 2010

The paper performs a comparative study of variational‐based brittle fracture with its gradient‐type regularization, and outlines aspects of the numerical implementations of both approaches. The latter smoothes out sharp displacement discontinuities of cracks. On the side of discrete crack modeling, we propose a variational framework of configurational‐force‐driven crack propagation. The latter provides the basis for the computation of material nodal forces and drives the crack propagation in our proposed finite element framework with adaptive nodal doubling. Such a formulation is of limited applicability for the modeling of crack inititation in homogeneous bodies without defects and in situations with complex crack branching. This can be overcome by a regularized crack modeling. Here, an elliptic approximation of the crack surface term yields a regularized two field functional, where an additional scalar field approximates the set of discontinuities. We provide a simple interpretation of such a transition from the sharp crack to the regularized setting. It results in a smooth continuum‐damage‐type theory with a specific gradient‐damage and hardening terms, depending on a length scale that represents the width of a zone that surrounds the crack. Such a variational framework is implemented by a coupled two‐field finite element framework in a staightforward manner. We compare representative numerical results obtained by both methods for selected crack patterns and highlight the pro and contra of both meshes. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Simulation Model for Shield Tunnelling and its Interactions with Partially Saturated Soil
Authors: Nagel Felix , Stascheit Janosch , Meschke Günther
Published: March 2010

The design of shield supported tunnel construction in urban areas requires the reliable determination of the expected time‐variant ground response and the prognosis of possible critical conditions endangering the soil stability. In partially saturated soil the response of the surrounding underground depends strongly on the interactions between the construction process and the surrounding underground and its constituents. The paper gives an overview on a Finite Element model for the simulation of shield supported tunnel advance in partially saturated soil that is capable of accounting for these interactions. Special emphasis is laid on the description of the surrounding underground, modelled as a three phase continuum within the Theory of Porous Media (TPM). Applicability of the simulation model is discussed by results obtained from the simulation of compressed air application for the heading face support. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Identification of a Flexible Cantilever Beam Equipped in Piezoelements for Vibration Control System
Authors: Koszewnik Andrzej
Published: March 2010

The identification of an active vibration damping system with the use of piezoelements glued to the structure is presented in the paper. Lab stand was completed with smart beam, power amplifier and charge amplifier. First, the open‐loop system was identified in the frequency domain in using experimental setup The piezo‐stripes to have worked in the mode of actuators and sensors, respectively. For the frequency range from 1 Hz to 400 Hz we obtained Bode plots with help of the Dynamic Signal Analyzer. Frequency characteristics are a base for further calculations. Second, the mathematical model was obtained by finite elements methods and was adjusted to the experimental results by least square sum approach. Third, observable canonical‐form in state space model was derived by using of the LMFD method (Left Matrix Fraction Description). Finally, a minimal realization of the transfer function was reached by Balance method. The transfer function describes the first three resonances and first three anti‐resonances in considered frequency range. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Time‐dependent reliability assessment of structures using uncertain fractional rheological models
Authors: Freitag Steffen , Kaliske Michael , Graf Wolfgang
Published: March 2010

In this paper, a concept for time‐dependent reliability assessment of civil engineering structures is presented. This concept bases on the uncertainty model fuzzy randomness. The time‐dependent behaviour of materials with fading memory is captured by means of rheological models using uncertain fractional time derivatives. The presented method can be applied to the reliability assessment of engineering constructions. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mechanical model of a mistuned 2DOF‐structure coupled by viscous damping
Authors: Laborenz Jacob , Siewert Christian , Panning Lars , Wallaschek Jörg , Gerber Christoph
Published: March 2010

In this paper the vibration amplitude reduction of a mechanical system is investigated when applying a damper between different DOF of that structure. Thereby, an elementary mechanical model consisting of two mass‐spring elements with slightly differing eigenfrequencies and which are connected via a viscous dashpot damper is regarded. To investigate the systems behavior, an analysis of the transfer function and its poles and zeros in the L APLACE domain is performed when varying the damping constant. This reveals that the achievable amplitude reduction depends on the mistuning of the system and that even ideal viscous damping leads to a coupling which results in a shift of eigenfrequencies. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Shaking table experimental study on the effectiveness of polymer bearings for seismic isolation of structures
Authors: Banaś A. , Jankowski R.
Published: March 2010

Seismic isolation has been recognised to be a very effective way of protecting structures from damage during earthquakes. It allows us to extend the natural period of the structure and therefore avoid resonance with the ground motion. Moreover, by increasing damping in the isolation devices, more energy can be dissipated and thus the structural response can be further reduced. The aim of this paper is to show the results of the study focused on verification of the applicability of the innovative method of seismic isolation by installing bearings made of a polymer mass, which is an especially designed flexible elastoplastic two‐component grout based on polyurethane resin. In the study, a model structure was tested experimentally on a shaking table under earthquake excitation. First, the structure was fixed directly to the table and its response was recorded. Then, the response of the structure with polymer bearings installed at its base was observed and both responses were compared. The results of the study show that equipping the structure with the polymer bearings can considerably reduce the structural response under earthquake excitation. The innovative method considered in the study has been verified to be an effective seismic isolation technique. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Imperfection Sensitivity or Insensitivity of Zero‐stiffness Postbuckling … that is the Question
Authors: Jia Xin , Hoefinger Gerhard , Mang Herbert A.
Published: March 2010

Zero‐stiffness postbuckling of a structure is characterized by a secondary load‐displacement path along which the load remains constant. In sensitivity analysis of the (initial) postbuckling path it is usually considered as a borderline case between imperfection sensitivity and imperfection insensitivity. However, it is unclear whether zero‐stiffness postbuckling as such is imperfection sensitive or insensitive. In this paper, Koiter's initial postbuckling analysis is used as a tool for sensitivity analysis. Distinction between two kinds of imperfections is made on the basis of the behavior of the equilibrium path of the imperfect structure. New definitions of imperfection insensitivity of the postbuckling behavior are provided according to the classification of imperfections. A structure with two degrees of freedom with a zero‐stiffness postbuckling path is studied, considering four different imperfections. The results from this example show that zero‐stiffness postbuckling is a case of transition from imperfection sensitivity to imperfection insensitivity for imperfections of the first kind and that it is imperfection insensitive for imperfections of the second kind. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of classical Winter's bracing requirements of compressed truss chord with stability analysis of 3D truss‐model
Authors: Iwicki P.
Published: March 2010

Most code requirements concerning bracing are based on principles developed by Winter. The present research is devoted to study a lateral buckling of truss with linear elastic side supports. The classical Winter's model of truss chord in the case of out of the truss plane buckling is compared with nonlinear analysis of 3D truss model. Full bracing condition, that permits the truss chord to support load level corresponding to an unbraced length equal to the distance between braces is calculated. Then an approximate buckling load with less than full bracing is developed and the model is modified to account for unequal normal force distribution in compressed chord. The coefficient of buckling length related to side support distance in function of bracing stiffness is also calculated. The results are compared to design code requirements. It is shown that buckling length of truss chord with side supports considered as elastic elements is larger than assumed in design codes. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Is hilltop buckling imperfection sensitive or insensitive?
Authors: Hoefinger Gerhard , Jia Xin , Mang Herbert A.
Published: March 2010

Hilltop buckling is the coincidence of a snap‐through point with a bifurcation point on the primary equilibrium path. An originally imperfection sensitive structure cannot be modified such that it shows both hilltop buckling and imperfection insensitivity. This is a rule for designing structures for imperfection insensitivity and guarantees validity of Koiter's postbuckling analysis, which would fail for imperfection insensitive hilltop buckling. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical analysis of laminated shells under in‐plane axial compression
Authors: Sabik A. , Kreja I.
Published: March 2010

The authors of the paper present numerical stability analysis of axially compressed laminated shells. The analysis is carried out by using the commercial code NX‐Nastran and authors' own program. In both cases the Equivalent Single Layer approach is adopted, in which the laminated shell is treated as an orthotropic single layer panel with the resultant stiffness calculated for the multilayered cross‐section. Since the distribution of displacement in the thickness direction is assumed to be linear (First Order Shear Deformation), the shell kinematics is consistent with the Reissner‐Mindlin type theory. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling problems of steeply inclined cableway subjected to moving load
Authors: Knawa Marta , Bryja Danuta
Published: March 2010

Problems of structural modeling of multi‐span bicable ropeway systems due to significant inclination of a track are discussed in this paper with reference to the vibration analysis. The analytical continuous model of a cableway is formulated in a form which enables to describe in‐plane vibrations of steeply inclined carrying cable subjected to traveling passenger carriers modeled by moving pendulums. The nonlinear interaction between carrying cable and moving carriers is taken into account in the moving load definition. Effects of a steep track slope are discussed on the basis of equations of motion of the system. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Methods of Analysis of Discrete ‐ Continuous Systems Vibrations and Their Application to Railway Transport Problems
Authors: Kumaniecka A.
Published: March 2010

In the paper some aspects of the interaction between the current collector and the overhead equipment have been presented. A model of the system that consists of a discrete subsystem modelling the pantograph and a continuous subsystem modelling the contact wire has been introduced. The dynamic interaction between the discrete oscillator of two degrees of freedom and a continuous string has been studied. At the contact point of the pantograph and the wire a varying component of force appears. It is the source of waves that propagate along the contact wire. There are also two standing sources of wave generation, i.e. varying forces at the points of catenary supports. General results have been illustrated by numerical examples in which the effect of wave propagation is confirmed. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the influence of contact mechanics on friction induced flutter instability
Authors: Hetzler Hartmut
Published: March 2010

Within this contribution, the general form of perturbation equations for systems of moving elastic bodies is derived and examined with respect to symmetry and definiteness properties. The contact is enforced by a penalty formulation, which is motivated by a constitutive contact model relying on statistical data of the surface. Evaluating Hamilton's Principle and carrying out a linearization about a stationary transport motion, the general perturbation equations are derived. The resulting differential operators are stated and discussed. The findings are exemplified for a rotating cicular Timoshenko beam with frictional contacts. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the modelling of vehicle‐road interaction
Authors: Vogt Heike , Seemann Wolfgang
Published: March 2010

During the last years axle loads and demand for transport have been increasing steadily. Although a lot of experimental data exists on the corrugation of roads by heavy vehicles, basic investigations concerning vehicle‐road interaction are still necessary to improve the understanding of the process. Therefore, a simple model is built which will allow for some analytical reflections. The road exhibits viscoelastic and plastic characteristics whereas the vehicle is approximated as a simple quarter car model. Results of long term simulations are presented. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bifurcation analysis of a stochastic non‐smooth friction model
Authors: Gaus Nicole , Proppe Carsten
Published: March 2010

Non‐smooth friction systems such as systems with dry friction show several bifurcation phenomena. The discontinuity of these so called slip‐stick vibrations makes these systems interesting and there has been a lot of research in this field, see for example Hinrichs [1]. Due to the non‐smooth friction force even the deterministic system shows a rich bifurcation behavior. Measurements indicate that the friction coefficient which plays a large role in the system behavior is not deterministic but can be described as a friction characteristic with added white noise. Therefore, the stochastic characteristic is introduced into the non‐smooth system and the change of the bifurcation behavior is studied. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determination of natural modes of linear mass‐spring vibration systems by Laguerre polynomials
Authors: C. Müller Peter
Published: March 2010

Chain structured vibration systems with N degrees of freedom with massesmjand stiffnesseskjhave been discussed in detail [1]. Some of them can be solved explicitly, others only numerically. Here, an inverse problem is considered: Howmj,kj,j= 1, …, N, should be chosen such that the related eigenvalue/eigenvector‐problem can be solved by Laguerre polynomials? (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling of lateral oscillations in the interface of brake systems
Authors: Dombek Dominika , Ostermeyer Georg‐Peter
Published: March 2010

The research of the dynamics in the boundary layer of brake pads can afford revealing technical expertise concerning different phenomena occurring in brake systems (e.g. squealing, judder, Hot Spots). For manufacturers of brake systems, the phenomenon “squealing” is of particular interest due to the desired driving comfort. The mentioned phenomena have been researched by numerous scientists. Different models have been developed and approved by experimental results. The authors agree upon the fact that the main excitation mechanism of the mentioned effects in brake systems is caused by the variation of the lateral (in‐plane) friction force and friction torque respectively [1]. A model describing the dynamical interaction of friction and wear in the contact zone of brake systems has been introduced in [2]. Based on this theory, the brake pad's boundary layer consists of characteristic hard and smooth structures on the mesoscopic length scale. A new concept of the initiation of the squealing mechanism is based on the synchronisation mechanism of these so‐called patches emerging from the dynamical interaction of the friction partners. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)