bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation of the stress and strain profiles during intrusion and torque of a premolar
Authors: Dorow Christina , Sander Franz‐Guenter 
Published: June 2004

AbstractSince it is known from literature [1, 2, 3] that root resorption can occur even with small intrusive forces and torque moments, it is very interesting to find out the stresses and strains which are induced in the tooth support unit when a tooth is subjected to external loads and which lead to the resorption process. In this study a three‐dimensional Finite Element model of a lower premolar was generated using Computer Tomography (CT) data. Intrusive forces of 0.5N and torque moments of 3Nmm respectively were applied to the tooth crown. The three principal stresses and strains as well as the hydrostatic pressure and the volumetric strain were calculated within the premolar, the surrounding periodontal ligament (PDL) and alveolus.
A parallel computational approach for free surface flows with structural interactions
Authors: Genkinger Steffen , Wall Wolfgang A. , Ramm Ekkehard 
Published: June 2004

AbstractAn appropriate treatment of instationary free surface flows is of great relevance to many problems in engineering and applied sciences. In this context the presence of structural interactions constitute an additional challenge on the one hand but on the other hand even further broadens the application area. In this study we present a partitioned implicit approach for the efficient and robust treatment of free surface flows within fluid structure interaction simulations.
An Explicit Multi‐Body Contact Algorithm
Authors: Hahn Carsten , Wriggers Peter 
Published: June 2004

AbstractFor the reliable and efficient solution of multi‐body contact problems involving large nonlinear deformations, an explicit time integration scheme is considered. For this kind of algorithms, a semi‐implicit approach for fulfillment of the contact constraints is presented. To apply this method to three‐dimensional problems, the solution of local equilibrium problems is required at the contact surface. An iterative form of the proposed scheme is used to decrease computational effort. Also some remarks are given with respect to contact detection.
Numerical simulation of microstructures based on incremental variational formulations and relaxation methods
Authors: Hoppe Ulrich , Hackl Klaus 
Published: June 2004

AbstractThe use of an incremental variational principle allows the calculation of inelastic material behaviour by means of an elastic potential. Missing quasiconvexity of this potential is a serious deficiency, because the existence of regular solutions cannot be guaranteed and finite–element approximations may become mesh–dependent. These problems can be overcome by the use of relaxed potentials. Results of a rank–one relaxation algorithm for a single–slip plasticity model are presented.
Analysis of inelastic effects in wrinkled membranes
Authors: Hornig J. 
Published: June 2004

AbstractMembranes are very suitable for carrying tensile loads, but they fail partially or completely if compressive in‐plane loads occur. Since membranes do not possess any flexural stiffness they can not carry compressive in‐plane loads. In this case membranes wrinkle. It is essentially to take effects of membrane wrinkling into account. Modern materials applied in membrane structures show not only pure elastic but also viscoplastic or plastic behavior. The question rises, how to treat inelastic effects if wrinkling occurs. The presented method is applicable to elastic‐plastic deformation processes in connection with membrane wrinkling. An approach based on a modified Roddeman theory is used (see [1] and [2]). Due to the existence of unrecoverable deformations, one has to reformulate the wrinkling criterion. As an example, a strain space formulation of plasticity (see Besdo and Tietze [3]) is incorporated into the wrinkling algorithm.
A numerical method for computing the response of composites with periodic microstructure
Authors: Kassbohm Sven , Müller Wolfgang H. 
Published: June 2004

AbstractThe stress‐strain response of a periodic structure due to an applied eigenstrain field is investigated. The periodic structure allows reduction of the problem to a representative volume element (RVE) problem. A review of Fourier series as a particular method of solving the set of differential equations is given, and an example problem is studied. Results of the latter method are compared to results obtained using discrete Fourier transforms in a different way.
Density gradient enhanced topology optimization of continuum structures
Authors: Kotucha Gregor , Hackl Klaus 
Published: June 2004

AbstractThe formulation of topology optimization problems for continuum structures usually requires the introduction of the material density as design variable. In this context the design domain is discretized by finite elements and a constant density distribution within the elements is assumed. To prevent the occurrence of optimal designs characterized by extended regions with intermediate density values, special penalty methods are used. The introduction of those methods results in discontinuities in the global density distribution and often leads to designs containing unfavourable microstructures such as the well‐known checkerboard patterns. To obtain designs free of microstructures, we propose a global density gradient based regularization and discuss the results of numerical studies of several maximum‐stiffnessdesign problems based on the presented approach.
The effect of functional overloading on crestal bone loss around a dental implant
Authors: Lenz Jürgen , Schindler Hans J. , Rong Qiguo , Schweizerhof Karl , Riediger Dieter 
Published: June 2004

AbstractAt the end of the bone remodeling process, frequently funnel‐like collapses of the cortical bone (crestal bone losses) are clinically registered around the neck of dental implants. It is generally suspected that either inflammations or mechanical “overloading” of the bone during the clinical loading phase are responsible for this phenomenon. From the results of this numerical simulation we conclude that overloading might indeed be a major cause for these bone losses.
The Optimal Design of Extrusion Dies by the Finite Element Method
Authors: Lotfi A. 
Published: June 2004

AbstractIn this work, a method for calculation of the optimal shapes of axisymmetrical converging dies by the finite element method is presented. The shape optimization problem considered in this paper is to find the best shape of the die such that the flow rate will be uniform at the die exit.The optimization problem is to minimize an objective function by varying a part of boundary (ie: the shape of die) subject to constraints imposed by the metal forming problem. In this method, the B‐spline functions allow us to determine the shape of the die, using its control points as design variables.
Computational modelling of failure with the discontinuous Galerkin method
Authors: Mergheim Julia , Kuhl Ellen , Steinmann Paul 
Published: June 2004

AbstractThe present contribution is concerned with the computational modelling of failure with the discontinuous Galerkin method, which is attributed to Nitsche's work. In the present work a hybrid method is introduced which consists of the discontinuous Galerkin method and an interface approach. Thereby the DG method is used to model the precritical continuous state, whereby the continuity condition along an internal surface is enforced weakly. The interface approach is applied in the post‐critical state to allow for a jump in the displacements, controlled by a constitutive law. Finally the applicability of the proposed method is illustrated by means of a computational model problem.
Finite element analysis of liquid filled structures under gravity loading
Authors: Rumpel T. , Schweizerhof K. 
Published: June 2004

AbstractThe large deformation analysis of membrane or shell structures loaded and/or supported by liquid can be based on a finite element description for the structure only. Then in statics the effects in the liquid have to be considered by using the equations of state for the liquid, the information about the current volume and the current shape of the structure. The interaction with the structure is then modeled by a pressure resulting from the liquid always acting normal to the current wetted structural part. This description can be easily used to model the filling process without all the difficulties involved with standard discretization procedures. In addition the consistent derivation of the nonlinear formulation and the linearization for a Newton type scheme results in a particular formulation which can be cast into a very efficient solution procedure based on a sequential application of the Sherman‐Morrison formula.
Dynamic dam–reservoir–interaction – treatment of radiation damping by the “Mixed–Variables–Technique”
Authors: Trinks C. , Ruge Peter 
Published: June 2004

AbstractIn this paper, a method for the consistent description of a fluid channel of infinite extent in a fully coupled time–domain dam–reservoir interaction analysis is proposed. The method is based on an analytical solution with respect to the unbounded dimensions of the reservoir. Thus, an accurate representation of radiation damping is achieved.
Effiziente Parameteridentifikation bei Stoffgesetzen für inelastische technische Gummimaterialien
Authors: Besdo D. , Ihlemann J. 
Published: June 2004

AbstractDas Materialverhalten technischer Gummiwerkstoffe bei großen Verformungen ist ausgeprägt nichtlinear und zeigt komplizierte inelastische Effekte. Die Anpassung der Materialparameter entsprechender Stoffgesetze an ein konkretes Material erfolgt in der Regel durch den Vergleich mit Messungen einfacher Belastungszustände. Ein Beispielstoffgesetz zeigt, daß für diese Anpassung durchaus auf Standardalgorithmen mit gut kontrollierbarem Konvergenzverhalten zurückgegriffen werden kann, sofern einerseits das Stoffgesetz hinreichend robust ist, und andererseits geeignete numerische Umsetzungen der Algorithmen bereitgestellt werden.
Identification of Material Parameters for Inelastic Constitutive Models: Design of Experiments
Authors: Harth Tobias 
Published: June 2004

AbstractIn order to determine the material parameters of a constitutive model, identification experiments of different kinds have to be performed. Usually, the data of those experiments result from tension‐relaxation and tension‐compression tests at different strain rates as well as from creep tests with different hold stresses. However, these experiments are very expensive. Thus, the most important experiments to obtain good parameter estimates should be analyzed. The aim of this research is to find an experimental design which optimizes the balance between the accuracy of the parameter estimates and the experimental costs.
Characterization of the mechanical behavior of nonlinear viscoelastic materials in the range of high strain rates
Authors: Ottenberg Matthias , Weber Herbert 
Published: June 2004

AbstractA method is presented by which the short term behavior of the uniaxial relaxation moduli of nonlinear viscoelastic materials can be determined. For this purpose the wave propagation in prestrained rods which are impacted at one end is studied in the Fourier domain. Measurement of the strain or particle velocity at three positions yields the complex moduli from which the relaxation moduli follow.
Parameter Identification for Granular Materials in Consideration of Micro Rotations
Authors: Scholz Bernd , Ehlers Wolfgang 
Published: June 2004

AbstractGranular materials, as for example sand, show a complex stress‐strain behaviour depending on the stress state and the load history. Furthermore, in experiments the occurrence of a shear band is observed, which results in the localization of the plastic strains. For the consideration of the micro rotations in the shear band, the model is extended by the Cosserat theory, which leads to the regularization of the mathematically ill‐posed localization phenomenon. The aim of the present contribution is the identification of the material parameters of the proposed model. Therfore, a gradient based method is applied. Other methods, e. g. evolution strategies, are inapplicable because of their enormous computational costs.
Displacements and rotations in shear‐deformation of T‐S material
Authors: Sikora Zbigniew , Michalak Rafal , Wyroslak Mariusz 
Published: June 2004

AbstractThe structure of persistent and transient shear bands in granular materials by experimental modeling a quite idealized assembly of two‐dimensional particles, Taylor‐Schneebeli (T‐S) material, is investigated. Flexible stress‐controlled boundaries make possible biaxial compression test (samples 100 cm high and 30‐100 cm wide), i.e. they avoid constraining the motion of particles within the shear bands. The displacement, volumetric strain, void ratio, rotation of the particles, rotation of their neighborhoods can be examined within the shear bands. The importance of particle's rotations inside shear bands can justify the micropolar description of granular materials. For measurement at the microstructure level a conventional digital video technique is used. New digital image processing (DIP) techniques are used for analysis at the microscopic level, giving localization, displacements and rotations of each T‐S rods. Short description of a new plane strain experimental stand and an example of DIP analysis for a selected experimental test are presented. Some comments due to the mathematical model description of granular bodies is also given.
About the propeller influence on aircraft stability derivatives
Authors: Vrdoljak Milan 
Published: June 2004

AbstractPropellers can significantly effect aircraft flying characteristics and stability. Depending on the aircraft configuration this influence of propeller on aircraft stability derivatives can be more emphasized, as for example with single pusher propeller. Methods still used in prediction of propeller stability derivatives are based on blade element theory with the axial component of induced velocity determined from the classical propeller momentum theory. This could lead to uncorrect prediction of induced flow near the propeller and its wake. In presented paper propeller model and prediction of its influence on the aircraft stability derivatives is based on the propeller vortex theory. The numerical model is using discrete vortices to form vortex sheet that is leaving each propeller blade. This model is suitable for implementation in component build–up method used in prediction of propeller driven aircraft stability derivatives and it can be applicable for different aircraft configurations.
Finite element mesh adjusted to singularities applied to 2D flow
Authors: Burda Pavel , Novotný Jaroslav 
Published: June 2004

AbstractWe apply the finite element method to solve the Navier Stokes equations for the incompressible fluid flow either in axisymmetric tube with abrupt changes of diameter or in a channel with backward and forward steps. We first discuss the asymptotic behaviour of the solution in the vicinity of nonconvex internal angles where the velocity components as well as pressure posses singularities. Compared with usual adaptive strategy based on a posteriori error estimates, in this paper we suggest and apply an alternative approach for the mesh refinement near the corners. It makes use of the asymptotic behaviour near the corners. We present numerical results and comment on the pros and cons with respect tu usual adaptive refinement strategy.
Accurate three‐dimensional simulation of lid‐driven cavity flow
Authors: Albensoeder Stefan , Kuhlmann Hendrik C. 
Published: June 2004

AbstractThe numerical simulation of the one‐sided lid‐driven cavity is a classical benchmark problem. However, no reliable results are available for three‐dimensional flows slightly above their onset. In this study, we develop an accurate numerical code based on collocation methods for solid and periodic boundary conditions in span direction. The corner singularities of the problem are reduced by incorporation of analytical solutions. A convergence study is performed and, as an example, the bifurcation from the primary instability is calculated in a cavity with a square cross‐section.
Instabilities and bifurcations in lid‐driven cavity flows
Authors: Kuhlmann Hendrik C. , Albensoeder Stefan 
Published: June 2004

AbstractThe three‐dimensional flow of an incompressible Newtonian fluid in a rectangular slab is calculated numerically using a pseudo‐spectral method. The fluid motion is driven by two facing sidewalls which can move in parallel or anti‐parallel directions. Examples for bifurcations from two‐dimensional to three‐dimensional flows are given for spanwise periodic systems. For a comparison with previous experimental results rigid end walls are also considered. Differences between periodic and rigid end conditions are highlighted.
SUPG stabilization of meshfree methods for convection‐dominated problems
Authors: Fries Thomas‐Peter , Matthies Hermann G. 
Published: June 2004

AbstractStreamline‐Upwind/Petrov‐Galerkin (SUPG) stabilization of meshfree methods with stabilization parameters calculated from standard formulas, which have their roots in mesh‐based methods, often leads to unsatisfactory results. A new procedure for obtaining adequate SUPG stabilization parameters for meshfree methods is presented. It is shown that the Kronecker‐δ property is very advantageous for a successful stabilization because this leads to local stabilization criteria. If the meshfree shape functions lack this property, a stabilization based on local properties – i.e. on nodes in the neighbourhood – cannot be sufficient for highly convection‐dominated problems.
Natural Convection in Wide Spherical Shells
Authors: Futterer B. , Brucks A. , Hollerbach R. , Egbers C. 
Published: June 2004

AbstractWe have studied the problem of natural convection in wide spherical shells both experimentally and numerically, and find that there are critical Rayleigh numbers at which the convection changes in fundamental ways. For sufficiently low Ra the convection is steady, but above a certain value it becomes time‐dependent, with plumes dripping off the south pole in distinct pulses. For higher values still these convective pulses become irregular in time. The experimental results show though that even at these very high Rayleigh numbers the convection remains purely axisymmetric. A two‐dimensional numerical code is therefore used to study these flows in more detail, and reveals the same transition from steady to periodic to chaotic behavior. Finally, the dependence of the critical Rayleigh number and the period on the Prandtl number are explored.
Wärmeübergang am angeströmten und gleichzeitig bewegten Kreiszylinder mit und ohne Krümmungseffekt
Authors: Gampert B. , Beyene T. 
Published: June 2004

AbstractIn dieser Arbeit werden Wärmeübergänge am angeströmten und gleichzeitig bewegten Kreiszylinder mit und ohne Krümmungseffekt aus den Grenzschichtgleichungen mit Hilfe von analytischen und numerischen Lösungen bestimmt. Es werden Fälle bei denen die Wandgeschwindigkeit größer oder kleiner als die Anströmgeschwindigkeit ist untersucht. Es wird eine laminare inkompressible Strömung konstanter Stoffwerte angenommen.
The Mechanics of Drug Dissolution
Authors: McMahon N. M. , Crane M. , Ruskin H. J. , Crane L. 
Published: June 2004

AbstractA numerical method for approximating the mass flux from a dissolving cylindrical drug compact, a tablet, is presented. The tablet consists of alternating layers of drug and inert material. The dissolution takes place in a non‐reactive medium using a standard stirring device and is considered to be two dimensional and steady. A finite difference scheme is used to generate an approximation to the concentration boundary layer. By integrating across the velocity* concentration profile at the trailing edge, the mass flux is estimated. This value differs by 0.9% from the recent estimate of Crane et al. who used a Pohlhausen approximation to the concentration boundary layer. The finite difference concentration profile at the trailing edge also agrees very well with the equivalent Lévêque exact solution. We conclude that the finite difference model is behaving as expected.
Homogenisierungsmethoden zur Berechnung der Sauerstoffdiffusion und ‐reaktion in Faserverbundstrukturen
Authors: Nasdala Lutz 
Published: June 2004

AbstractDie diskrete Modellierung von Faserverbundstrukturen führt zu einem sehr großen numerischen Aufwand, so dass die Materialeigenschaften von Fasern und Matrix in der Regel gemittelt werden müssen. Bei der Berechnung von Sauerstoffdiffusions‐ und ‐reaktionsvorgängen ergibt sich die Schwierigkeit, dass aufgrund der Oxidation die Massenbilanz nicht erfüllt werden kann. Die Güte des gemittelten Materialparametersatzes hängt neben den Ausgangsmaterialien auch wesentlich davon ab, ob die Diffusion in oder quer zur Faserrichtung betrachtet wird.
Numerical Solution of Transonic Turbulent and Two‐phase flow in Turbine cascades
Authors: Dobeš Jiří , Fořt Jaroslav , Halama Jan 
Published: June 2004

AbstractPresented model of transonic flow with condensation is based on Navier‐Stokes equations for mixture, algebraic turbulence model and Hill's approximation for the description of liquid phase [2]. Two finite volume methods are introduced. Numerical results for single‐phase 2D flow of air in turbine cascade SE1050, two‐phase 2D flow in Laval nozzle and two‐phase 2D flow in turbine cascade SE1050 are presented.
Numerical Simulation of Particles in Steel Strand Casting Flow
Authors: Javurek Mirko , Kaufmann Bernhard 
Published: June 2004

AbstractThe liquid steel flow and the particle transport of non‐metallic inclusions in the liquid domain inside the strand of a continuous steel casting system are numerically investigated. The whole liquid domain inside the solidified shell is simulated, and the loss of liquid steel due to solidification is considered. Assuming a constant drift velocity, a kind of Euler‐Euler multiphase model is implemented to calculate the particle behavior inside the liquid steel respectively the particle removal at the boundaries. Both steady and unsteady simulations of the particle behavior are performed. The influence of particle size (0 to 1 mm), casting speed and slab format is considered for the particle concentration distribution along and across the strand.
Numerical Modeling of Fluid‐Structure Interaction with Free Surface Flows
Authors: Kölke Andreas , Walhorn Elmar , Hübner Björn , Dinkler Dieter 
Published: June 2004

AbstractFor the numerical analysis of interactions of immiscible two‐fluid flows and lightweight elastic structures a discretization method based on stabilized space‐time finite elements is applied. The level set method provides a description of the material distribution and interface location of the two‐phase fluid. The choice of an enriched basis allows the capturing of discontinuous gradients of fluid variables, introduced by changing material properties at the interface.
Propagation of Acoustical Waves in an Axisymmetrical Duct With Swirling Mean Flow
Authors: Boltalova N. , Schemel C. , Thiele F. , Michel U. 
Published: June 2004

AbstractA 3D axisymmetric Computational Aero Acoustic (CAA) procedure is extended to predict the propagation and radiation of the unsteady disturbances from a duct with swirling mean flow into the far field. Based on axisymmetric mean flow and acoustical boundary conditions, the 3D task is decomposed into a series of 2D problems using Fourier series expansions in the azimuthal direction. The numerical procedure is validated by the analytical solution within a solid body rotational, subsonic mean flow in a straight circular duct and the numerical results show a very good agreement.