bluuebunny/crossref_metadata_2025 huggingface dataset:
Simple model for turbulent two‐phase combustion with fast chemistry
Authors: Borghi R. , Burluka A. A.
Published: March 2011

The principle of a sample model for atomisation and vaporisation in two‐phase flows is developed and presented. It is based on use of two quantities which are the average liquid mass fraction and the average area of the gas‐liquid interface, both taken per unit mass of two‐phase media. This model can easily be used in combustion modelling when the chemistry is very fast that is when the atomisation, vaporisation and the micro‐scale turbulent mixing are the controlling phenomena. The practical use of this model needs the values of a few constants which are determined from the comparison with the experiments.
Response Surfaces and Robust Design
Authors: Schoofs A. J. G.
Published: March 2011

Response surface methods can be applied for building both global and mid‐range approximation models, to be used in structural optimization as an interface between analysis tools and optimization algorithms. This approach is particularly promising in those areas, where the structural behaviour or analysis process exhibits noise, because conventional optimization strategies often fail in such situations. This capability, together with the flexible approximation interface between analysis and optimization, results in a robust optimum structural design tool. The method is illustrated by means of a car crash safety problem.
Design‐of‐Experiments Methods and their Application to Robust Multicriteria Optimization Problems
Authors: Lautenschlager U. , Eschenauer H. A. , Mistree F.
Published: March 2011

Design‐of‐experiments (DOE) methods are utilized to explore the design space and to build response surface models in order to facilitate the effective solution of multiobjective optimization problems. Response surface models provide an efficient means to rapidly model the trade‐off between conflicting goals. For robust design applications these approximation models are used efficiently and effectively to calculate variances due to noise factors using Taylor series expansions. This combined‐army approach is compared to Taguchi's original crossed‐array approach. The shape optimization of a flywheel with two conflicting design goals is used to illustrate the approach.
Nonlinear Control of Planar Parallel Robots with Redundant Servopneumatic Actuators
Authors: Hahn H. , Klier W. , Leimbach K.‐D.
Published: March 2011

In this paper a nonlinear control algorithm of a planar parallel robot with a redundant actuator configuration will be derived, based on exact linearization techniques. This controller achieves apart from standard degree of freedom decoupling and stabilization of the robot dynamics additional desired overconstraint control of the redundant actuators. This result has been achieved by suitably extending the output vector of the robot and by including an orthogonality relation into the controller design. Computer simulations prove the validity of this control concept.
Robust Control of an Aircraft Model
Authors: Werner H.
Published: March 2011

A new multimodel approach to robust controller design is illustrated by a practical application; for a laboratory aircraft model, a robust controller is designed simultaneously for normal operating conditions and for propeller failure. Based on a linear model for each operating mode, an LMI formulation of the problem and convex programming are used to search for a state feedback controller which achieves the objective. This state feedback design is then realized simultaneously in both operating modes by a controller which is based on fast output sampling. Robust performance is demonstrated by experimental results.
Periodic Solutions of Conservative Non‐Smooth Dynamical Systems
Authors: Kunze M.
Published: March 2011

We consider conservative non‐smooth dynamical systems of the type ẍ+e+a sgn(x) = p(t) with an w‐periodic forcing p, and we first prove the existence of periodic solutions in the non‐resonant case for the corresponding differential inclusion. Moreover, in the resonant case w = 2π, we gave necessary and sufficient conditions on a and the first Fourier coefficient of p for periodic solutions to exist.
Numerical simulation of shock‐turbulence interaction
Authors: Adams N. A.
Published: March 2011

We outline results of numerical and theoretical investigation of shock‐turbulence interaction. Following the strategy of increasing complexity we first consider isotropic turbulence interacting with a normal shock. In the presence of mean‐shear and shock‐obliqueness, turbulence‐structure becomes dependent on additional parameters such as shock‐angle and strain‐rate. Presently, the most complex situation achievable by direct numerical simulation is the interaction of a turbulent boundary layer with a shock along a compression ramp. Based on recent results for a low‐Reynolds number direct simulation it is found that the simplified cases predict correct trends for turbulent structure. The DNS results indicate that explicit compressibility effects such as pressure dilatation and dilatation dissipation are non‐negligible in the interaction region.
Recent Developments in the Statistical Modelling of Turbulent Flows
Authors: Heinz S.
Published: March 2011

Statistical methods are often used to describe transport processes in turbulent reacting flows. However, in many cases of practical relevance one has to consider not only such transports but also their influence on the turbulent reacting flow. Just the simulation of such interactions could not be provided by approaches applied previously. This led, e.g., in respect to the atmospheric chemistry to considerable problems because nonlinear chemical conversion processes, which appear nearly in all cases of practical interest, between emissions and species that are distributed in the ambient flow could only be treated approximately. To overcome these problems, methods are needed that are able to describe not only transport processes but additionally the turbulence. The developments of such techniques requires solutions for three problems: First, suited equations have to be derived that are in consistency with the hydrodynamic equations, second, the capability of such methods has to be demonstrated to reflect the features of complex turbulent flows, and third, it has to be shown that the computational costs of such methods are acceptable. It is described here, in which way these problems could be solved recently, and which advantages arise from the application of such advanced statistical methods.
Dynamic Behavior of Damaged Brittle Solids
Authors: Zhang C. H. , Gross D.
Published: March 2011

The macroscopic dynamic behavior of damaged brittle solids is investigated. Special attention is devoted to the analysis of wave attenuation and dispersion in micro‐cracked solids. Several methods are discussed and numerical examples are presented, to show the dependence of the wave attenuation coefficient and the effective wave velocity in damaged brittle solids on the wave frequency, crack‐size and crack‐density.
Adaptive Finite Element Discretization in Elasticity and Elastoplasticity by Global and Lokal Error Estimators using Local Neumann‐Problems
Authors: Stein E. , Ohnimus S. , Walhorn E.
Published: March 2011

Equivalent to the direct Residual Error Method (REM), the Posterior Equilibrium Method (PEM) is presented for absolute global error estimates, yielding an upper bound with application to elasticity and elastoplasticity. Furthermore, a local residual error estimator is treated, solving local Neumann‐problems.
Mortar Finite Element Methods for Discontinuous Coefficients
Authors: Wohlmuth Barbara
Published: March 2011

In this paper, we consider a mortar finite element method for second order elliptic boundary value problems with discontinuous coefficients. At the interface where the coefficient is discontinuous, different triangulations and/or discretizations are coupled by means of Lagrange multipliers. The numerical algorithm is based on the algebraic saddle point formulation. The coupling of P1 conforming finite elements with P1 conforming and nonconforming Crouzeix‐Raviart elements as studied. Finally, we present the performance of the adaptive refinement process.
Stability of Levitrons
Authors: Dullin Holger R. , Easton Robert W.
Published: March 2011

The Levitron is a magnetic spinning top which can levitate in the constant field of a repelling base magnet. The present work develops an exact theory of the Levitron with six degrees of freedom. The stability of the symmetric relative equilibrium is calculated. The main result is a complete classification of possible Levitrons that allow for an interval of stable spin rates. Stability of the relative equilibrium is lost in Hamiltonian Hopf bifurcations if either the span rate is too large or too small.
Lösungsverhalten der FEM für das ebene Couette‐ und Poiseuille‐Problem eines Oldroyd‐B Fluides
Authors: Reichenbach J. , Aksel N.
Published: March 2011

Es wird ein viskoelastisches Fluid betrachtet, das durch ein Oldroyd‐B‐Modell beschrieben wird. Am Beispiel ebener Schichtenströmungen (Couette‐ und Poiseuille‐Strömung) wird das Verhalten der Galerkin‐FEM untersucht. Der Schlüssel zur Charakterisierung des Lösungsverhaltens des entstehenden nichtlinearen Gleichungssystems ist die Matrix der partiellen Ableitungen (Jacobi‐Matrix). Während für das Couette‐ und Poiseuille‐Problem die bekannten Lösungen reguläre Lösungen des stetigen Dgl. problems sind, besitzen die durch FEM erhaltenen diskreten Systeme für größere Werte der Deborah‐Zahl De stets singuläre Lösungen. Für das Poiseuille‐Problem kann mit wachsender De‐Zahl ein oszillatorisches Verhalten der Fehler der diskreten Näherungen festgestellt werden, dessen genaue Ursache bisher nicht bekannt ist.
A thermodynamic approach to elastic and plastic anisotropy
Authors: Svendsen B.
Published: March 2011

In the framework of a recent thermodynamic formulation of rate‐independent material behaviour as based on a loading rate function, possible effects of the plastic deformation on elastoplastic material behaviour at large deformation are discussed. In particular, attention is focused on the possible effect that such deformation may have on the material symmetry, i.e., anisotropy, of the material behaviour.
Sekundärwirbel in Nachlauf‐ und freien Scherschichten in der Transition
Authors: Brede Martin
Published: March 2011

In freien Scherschichten werden bei der Transition zur Turbulenz in Strömungsrichtung orientierte Sekundärwirbel beobachtet, die deutlich kleiner sind als die Primärwirbel. Die gleichen Strukturen zeigen sich im Zylindernachlauf. Hier treten Sekundärwirbel zusätzlich zu den Kármánwirbeln auf. In beiden Fällen sind die Proportionen der Primär und Sekundärwirbel ähnlich. Experimentelle und numerische Ergebnisse aus Nachlauf‐ und freien Scherschichten werden vorgestellt, um die Übereinstimmungen und Unterschiede der Wirbelstrukturen zu demonstrieren. Zwei Wirbelmodelle werden aus einer experimentellen Untersuchung des Kreiszylindernachlaufs abgeleitet, die die grundlegenden Mechanismen der Transition und die beteiligten Instabilitäten beider Strömungsformen aufzeigen.
Über die Strouhal‐Reynoldszahl‐Gesetzmäßigkeit im Nachlauf eines Kreiszylinders
Authors: Fey U. , Eckelmann H.
Published: March 2011

Aufgrund der Ergebnisse umfangreicher Messungen im Nachlauf von Kreiszylindern wird eine neue Gesetzmäßigkeit für die Wirbelablösefrequenz vorgeschlagen, die erstmals in geschlossener Form die Strouhalzahl Sr als Funktion der Reynoldszahl vom Beginn der Wirbelablösung bei Re = 47 bis zum laminar‐turbulenten Umschlag der Zylindergrenzschicht bei Re > 2 × 105 mit wenigen Koeffizienten als Sr = Sr* + m/ √ beschreibt. In dieser Darstellung zeigen sich mit steigender Reynoldszahl die unterschiedlichen Wirbelbildungsprozesse durch stückweise lineare Zusammenhänge zwischen Sr und dern Kontrollparameter 1/ √ Re Die ‘kritischen’ Reynoldszahlen sind gekennzeichnet durch Schnittpunkte der Geraden. Die vorgeschlagene Gesetzmäßigkeit ist in guter Übereinstimmung mit neueren Messungen anderer Autoren und es zeigt sich, daß für Re > 5000 eine zunehmende Abweichung von der Faustregel 'Sr ≈ 0,21' auftritt.
Enclosing the solution of linear Fredholm integral equations of the second kind
Authors: Gienger A.
Published: March 2011

We propose a new method to enclose the solution X of a linear Fredholm integral equation of the second kind. Given a certain tolerance ϵ we compute an approximation ẍ for X so that || X — ẍ ||∞ < ϵ holds. The method uses a very efficient algorithm to determine ẍ and interval arithmetic to compute an upper bound for ||x ẍ||∞ On some numerical examples we demonstrate the efficiency of our method.
Globale Optimierung nichtdifferenzierbarer Funktionen unter Einsatz von Intervallsteigungen
Authors: Ratz Dietmar
Published: March 2011

Von großer Bedeutung für die Effizienz von Intervallverfahren zur globalen Optimierung sind Techniken zur Elimination von Teilen des Suchbereichs. Hier finden häufig Techniken unter Verwendung von Ableitungen (wie z. B. der Monotonietest) Anwendung. Für nichtdifferenzierbare Probleme kann eine entsprechende Technik unter Verwendung von Intervallsteigungen angegeben werden. Wir beschreiben eine solche Pruning‐ Technik zur Elimination von Teil‐bereichen. Zur Verdeutlichung der Effizienz dieser Technik vergleichen wir zwei Varianten eines Modell‐Algorithmus ausgestattet mit Monotonietest bzw. Pruning‐Schritt anhand von differenzierbaren Beispielen. Abschließend dokumentieren wir dann numerische Resultate für ein nichtdifferenzierbares Optimierungsproblem.
Fluid Structure Interaction in Blood Flow Problems
Authors: Nobile F. , Veneziani A.
Published: March 2011

In this note, we consider some issues relevant for the application of Computational Fluid Dynamics to biomedical vascular investigations. More precisely, models for blood and vessel walls are briefly addressed together with some preliminary results in the numerical study of the fluid‐structure interaction problem arising when investigating blood flow in compliant walls.
On the relevance of “molecular chaos” for granular flows
Authors: Luding Stefan
Published: March 2011

With numerical simulations of dissipative, spherical particles the assumption is tested, that the velocities and the positions of colliding particles are uncorrelated (“molecular chaos”). This assumption is a basic ingredient of all theoretical approaches based on a kinetic theory or a pseudo‐Liouville operator formalism. The numerical model is an event‐driven method for the simulation of rigid spherical particles in two dimensions. In elastic systems, the impact parameter is uniformly distributed or, with other words, the molecular chaos assumption is valid independent of the density. In freely cooling systems, the molecular chaos assumption fails as soon as dissipation becomes strong enough so that convective shear modes are created.
Second‐order and affine estimates for the behavior of viscous polycrystals
Authors: M. Bornert , R. Masson , Castañeda P. Ponte
Published: March 2011

The recently proposed second‐order and affine estimates for the effective behavior of nonlinear heterogeneous materials rely on the same linearization procedure and refer to some “thermoelastic comparison composite”. But both approaches differ in the way the overall nonlinear answer is defined, either through average stress‐strain relations or energy considerations. When combined with the linear self‐consistent model, they provide new tools for the predictions of the behavior of viscoplastic polycrystals (steady state creep). They are compared to each other and to other more classical estimates (incremental and tangent) in the following situations.: a 2D antiplane model problem for which efficient rigorous upper bounds are available, the creep of isotropic aggregates of FCC crystals and HCP crystals with different critical stresses on the basal and prismatic slip systems.
Dynamic Analysis of Rolling Contact Problem by the Space‐Time Element Method
Authors: R. Bogacz , C. Bajer
Published: March 2011

Higher speed of rolling and heavy loads that subject the contact zone in rail‐wheel contact require dynamic analysis with wave effects taken into account. In such a case we can observe polygonization and corrugation of wheels and rails. This phenomenon occurs and increases in nature with the increase of speed and load. Even the steady motion of the roller center along the flat surface without friction results in oscillation of the contact force. Its amplitude increases with the speed while the number of corrugations decreases in the same time. The simulation showed the rotation of the wheel material around the axle. The space‐time element method was applied to refine the time step of integration only for elements being in contact. The spatial refinement allows to determine precisely the contact zone.
Contact in Multibody Systems
Authors: Bremer H. , Ch Glocker
Published: March 2011

Multi Body Systems (MBS) consist of a finite number of interconnected elastic and/or rigid bodies. If its number of d.o.f. varies due to contact it is advantageous to calculate dynamics in terms of subsystems. Partitioning into subsystems is fluent but at least reasonable at points of possible contact. Corresponding equations are then suitably structurized in terms of element matrices yielding a (state dependent) Finite Element structure. When contact(s) take place one ist left either with a (often unsolvable) combinatorical problem or with the question of how to solve the contact case uniquely and in an optimal way. The access to the latter is obtained with Helmholtz 's auxiliary equation leading to Gauss ' principle of least constraints.
Vibration Control by Interface Dissipation in Semi‐Active Joints
Authors: Gaul L. , Nitsche R.
Published: March 2011

Large space structures often consist of truss elements which are connected by bolted joints. The interface dissipation in these junctions turns out to be the major source of damping. For vibration suppression, the joints are designed such that the normal force in the frictional interface is controlled for improving damping performance. The norma1 contact is varied by active control using a bolt with a piezoelectric washer. A system consisting of two elastic beams connected by a single active joint is considered. The friction phenomena are described by a friction model with velocity dynamics. The effect of displacement‐ and velocity‐induced friction dynamics is considered in the design of the control law. The result is a dynamic controller which prevents frictional energy, stored as potential energy in the bristles, from being returned into the system.
Phonon contribution to friction stress in an atomically flat contact of crystalline solids at low temperature
Authors: Popov V.
Published: March 2011

It has recently been shown both experimentally and theoretically that there is no static friction in a contact of atomically flat crystalline solids provided the periods of their lattices are incommensurate and their interaction does not exceed some critical value. In dielectric materials, the only mechanism of friction in this case is generation of phonons. In the present paper, it is shown that, at low temperatures, the phonon contribution to the friction force can be very small by virtue of the quantum mechanical nature of the elementary excitations in a solid. Incommensurate dielectric crystals could therefore slip at low temperatures practically without friction.
Wave interaction with unilateral and adhesive cracks. Application on impact‐echo
Authors: Stavroulakise G.
Published: March 2011

Breathing, unilateral cracks close under the influence of a compressive loading. Nonsmooth mechanics' tools are used for the study of unilateral, frictional and adhesive cracks. In this framework, a frictionless unilateral crack leads to a variational inequality or to a linear complementarity problem, while frictional or adhesive problems lead to nonconvex variational or hemivariational inequalities. The numerical solution is based here on a convolutional boundary element method. An application on impact‐echo modeling and the influence of unilateral cracks on the classical impact‐echo technique are presented.
Wave propagation in complex structures modelled by medium with internal variables
Authors: Belyaevk A.
Published: March 2011

Governing equations for complex engineering structures are derived by means of the Hamilton variational principle under the assumption that the vibration field has a slowly varying component of an evolutionary type. This function is identified as the displacement of the primary structure, whereas the internal degrees of freedom model substructural vibrations. In the frequency domain of high modal overlap the secondary systems act as dynamic vibration absorbers with respect to primary structure. Wave propagation in the primary structures of complex structure is shown to be modelled by hyperbolic equations with source terms, the latter describing the backward effect of vibrating substructures on the primary structure. In order to take into account uncertain mechanical and spectral properties of real structures propagation of a wave packet in the structure is considered. The evolution of the amplitude of the propagating wave packet is shown to be governed by a boundary value problem of parabolic type. The approach developed presents an alternative to the vibrational conductivity approach and other techniques utilising various sorts of parabolic equations for describing energy propagation in complex structures.
Control of Propagating Waves in Rods by Piezoelectric Actuators and Sensors
Authors: Kurt Schlacher , Andreas Kugi
Published: March 2011

This paper deals with active control of propagating waves in rods. The mechanical models under consideration are characterized by hyperbolic equations with source terms. The latter ones describe the control or disturbance inputs. Piezoelectric layers are used as actuators and sensors to affect the dynamic behavior of the system, The controller design is based on the theory of Lagrangian systems with inputs. One can show that a special pairing of the actuators and sensors simplifies the controller design significantly, but this approach requires a specific design of the actuators and sensors. Smart structures based on piezoelectricity allow to construct spatially distributed devices, which are the prerequisites for the realization of so designed control laws.
On the Influence of the Matrix Compressibility in Two‐Phase Models
Authors: Diennels S.
Published: March 2011

In the theory of porous media the volume fractions are introduced as internal variables. Therefore, additional evolution equations for the volume fractions are required an general. In the present contribution, a binary model consisting of a compressible porous skeleton saturated by a compressible pore fluid is formulated. From this general model, the so‐called hybrid model and the incompressible model are derived. The different behavior of the models is illustrated in two examples.
On Porous Soil Materials Saturated with a Compressible Pore‐fluid Mixture
Authors: Ehlers W. , Blome P.
Published: March 2011

Geomaterials can be understood as consisting of a porous solid skeleton, with the pores saturated by a fluid. The fluid may be water, air or, a water‐air mixture. The mechanical behaviour of the whole soil body, consisting of the soil skeleton and the pore‐fluid, is governed by the properties of its constituents. Since the exact structure of the pore‐space is not known, a homogenization over a representative elementary volume is required in order to obtain a macroscopic approach. The description of the motion of a multiphase‐mixture of immiscible constituents can be performed by the Theory of Porous Media (TPM). Based on the classical mixture theory, the TPM deals with superimposed continua. Additionally, the information of the structure is included via the concept of volume fractions [1–3].

Here, the soil skeleton material is assumed to be incompressible, whereas the pore‐fluid mixture is compressible according to its composition of water and air by variable volume fractions. The pressure‐density‐function of the pore‐fluid is derived within the framework of the TPM. Furthermore, the viscous pore‐fluid allows for a linear momentum exchange (interaction force) between the constituents, which, under special assumptions, leads to the well‐known Darcy law.
Study of structure of porous biomaterials. Application of ultrasonic method
Authors: Kubik J. , Kaczmarek M. , Pakula M.
Published: March 2011

lt is commonly accepted that, in modelling of the mechanical behavior of biological tissues (e.g. cortical and trabecular bones) and porous bone implants “working” in their natural environment, one should take into account the fact that such biomaterials have a multiphase nature and they are composed of solid porous matrix filled with interstitial fluid. Spatial arrangement of matrix structure strongly influences mechanical properties, transport phenomena, and acoustic waves propagating in saturated biomaterials.

The well known two‐phase model of dynamics of saturated porous materials developed by Biot, [1], and extended by other authors includes three pore structure macro‐parameters (porosity, permeability, and tortuosity). The attenuation and dispersion of wave velocity predicted by the model results mainly from relative motion of phases.

On the other hand, a disease like osteoporosis is identified in both cortical and trabecular bone by an increase of pore space and related changes in the microscopic pore characteristic that does not appear in Biot's model. Such micro‐quantity (characteristic pore or grain size) plays an important role for scattering phenomena at microinhomogeneities in the two‐phase porous materials when the ratio of waves length and average size of pores / grain is not too large.

Taking these facts into account, and using the model which incorporates the relative motion of phases and scattering effects, both the micro‐ and macro‐structure parameters an be determined from wave propagation analysis using the ultrasonic technique and applying wide band spectroscopy.
Numerical description of elastic‐plastic behavior of saturated porous media
Authors: Skolnik J.
Published: March 2011

In this paper, the numerical description of the elasto‐plastic behavior of saturated porous materials, consting of a solid skeleton with liquid filled pores, will be discussed. In particular, frictional materials will be described which show small elastic but mostly plastic deformations.

The elastic‐plastic deformable solid skeleton and the liquid are assumed to be incompressible, where the liquid does not exhibit viscous properties.

The description of the stress state is done within the framework of the geometrically‐linear theory, because small deformations are assumed The elastic strain state shall be expressed by Hooke 's law and the plastic strain state with the help of a single surface yield criterion as well as a non‐associated pow rule.

The numerical description of the initial‐ and boundary‐value problems is done by the finite element method within the framework of the standard Galerkin procedure.
Numerische Simulation von porösen Medien
Authors: Weiss W.
Published: March 2011

Große Bereiche der Ingenieurwissenschaften erfordern die mathematische Beschreibung und die numerische Simulation von Rand‐ und Anfangswertproblemen eines saturierten porösen Körpers. Poröse Medien unterscheiden sich von Einkomponentenkontinua durch ihren heterogenen Aufbau. Im Beitrag werden zunächst die Grundgleichungen für ein ternäres Modell (poröser Festkörper, Flüssigkeit und Gas) aufgestellt. Diese werden anschließend für die numerische Simulation aufbereitet. An zwei Beispielen wird das mechanische Verhalten des dreikomponentigen porösen Mediums unter Belastung dargestellt.
Transition from Quasiperiodicity to Chaos for Three Coaxial Vortex Rings
Authors: Blackmore D. , Knio O.
Published: March 2011

The dynamics of three coaxial vortex rings of strengths Γ1, Γ2 and Γ3in an ideal fluid is investigated. It is proved that if Γj, Γj + Γk and Γ1+ Γ2 + Γ3 are not zero for all j,k = 1,2,3, then KAM and Poincaré Birkhoff theory can be used to prove that if the distances among the rings are sufficiently small compared to the mean radius of the rings, there are many initial configurations of the rings that produce quasiperiodic or periodic motions. Moreover, it is shown that the motion become chaotic as the inter‐ring distances are increased relative to the mean radius.
Comparison of Numerical Schemes Applied to CAA Problems
Authors: Ewert R. , Meinke M. , Schröder W.
Published: March 2011

To compare numerical methods and boundary conditions for computational aeroacoustics (CAA) two‐dimensional aeroacoustic benchmark problems are solved. The numerical methods are the dispersion relation preserving scheme (DRP) of Tam et al. [1] and the compact finite difference scheme proposed by Lele [2]. The acoustic boundary conditions applied are the non‐reflecting boundary condition of Thompson [4,5] and the asymptotic boundary condition of Tam [2]. The benchmark problems used describe the propagation of acoustic, vorticity and entropy waves relative to a mean flow with varied flow direction.
Numerical Simulation of Normal‐ and Oblique‐Shock Vortex Interaction
Authors: Thomer O. , Schröder W. , Meinke M.
Published: March 2011

The dependence of the breakdown topology on the shock‐vortex interaction conditions is numerically investigated. Based on solutions of the Euler equations the unsteady three‐dimensional flow field is studied at several freestream Mach numbers and for normal and oblique shocks. The results of the finite‐volume method using the AUSM approach indicate a strong dependence of the recirculation region downstream of the shock on the shock induced pressure gradient and on the vortex strength.
Period Doubling Bifurcation and Chaos Exhibited by an Isotropic Plate
Authors: Awrejcewicz J. , Krysko V. A.
Published: March 2011

Period doubling bifurcations and chaos exhibited by one layer flexible plate are illustrated and analyzed. Using a difference operators method the problem is reduced to that of solving ordinary differential and algebraic equations.
Lokalisierte Schwingungsformen langer Platten auf der Wasseroberfläche
Authors: Azalinov D.
Published: March 2011

Heutzutage werden verschiedene Objekte auf der Wasseroberfläche konstruiert, unter anderem sogenannte Schwimmflugplätze, wo man das Verhalten langer dünner Platten auf seichtem Wasser als erste Annäherung studieren kann. Zu Phänomenen, die bei Verwendung solcher Strukturen entstehen, gehört auch das Phänomen der Wellenlokalisierung im Gebiet der Struktur. Unser Ziel ist nicht nur die Bedingungen zu finden, bei denen dieses Phänomen der Wellenlokalisierung am Gebiet der Platte und ihre Resonanz möglich sind, sondern auch zu zeigen, daß ähnliche Effekte für praktisch alle Körper mit einem Einschluß kennzeichnend sind. Es ist offensichtlich, daß die Platte auf der Wasseroberfläche auch als ein Einschluß betrachtet werden kann.
Energy transfer from low to high frequency modes due to repeated impacts
Authors: Belyaev A. K.
Published: March 2011

Numerical simulation of energy exchange between the vibration modes in an elastic bar colliding with rigid walls is performed. After a large number of impacts the vibration energy is observed to be equally distributed over the degrees of freedom. Since the energy equipartition is typical for the thermal motion, the present study is useful for understanding the mechanism of transfer of mechanical energy into thermal one. The concept of the impact oscillator is generalised to mechanical systems with distributed parameters.
Reliability and Sensitivity Analysis of Trusses
Authors: Sieniawska R. , Wysocka A. , Zukowski S.
Published: March 2011

An approach for integrating the random nature of load with elastic‐plastic strains of the structure and calculating the reliability and sensitivity of trusses is presented. The paper contains some theoretical basis and practical proposition for solving the problem. Some numerical results are shown.
Modified Boundary Integral Equations for Asymmetric Composite Laminates with Singular Corner Points
Authors: Zakharov D. D. , Becker W.
Published: March 2011

The boundary value problem for laminates under coupled bending and stretching is studied using boundary integral equations, whose kernels are modified so far, that singular terms with Kirchhoff's force become integrable.
Variational Approach to Contact, Friction and Wear Problems
Authors: Zmitrowicz A.
Published: March 2011

Modern methods of analysis of contact problems are based on the variational approach which together with the finite element method expand possibilities of analysis in many cases. In this contribution, generalizations of classical variational formulations are given in the case of contact of rubbing and wearing solids. Using the finite element method, discretized forms of the Variational functional are presented.
Detection of Defects in a Plate Using Rayleigh‐Lamb Waves
Authors: Conry M. J. , Crane L. J. , Gilchrist M. D.
Published: March 2011

Nondestructive testing of materials is essential wherever they are used in safety critical applications. Conventional ultrasonic techniques, such as C‐scanning, generally use waves propagating normal to the plane surface. While accurate, such methods are slow for structures with large plane areas. The use of longitudinal waves offers the possibility of quicker testing of such structures.

This paper considers the reflection of low frequency Rayleigh‐Lamb waves by a two dimensional, centrally embedded vertical defect in aluminium plate. A numerical method is used, based on results from dimensionless analytical work. It is shown that such longitudinal ultrasonic waves can successfully detect structural defects.
Numerical Simulation of Interface Debonding during Fibre Pull‐Out Tests
Authors: Döbert C. , Mahnken R. , Stein E.
Published: March 2011

The Pull‐Out experiment is used for determination of the bond strength between fiber and matrix an fiber reinforced composites. An interface crack growth between both constituents and a contact friction behaviour on the cracked area can be observed in the experiment. In our contribution this mechanical behaviour of the interface is simulated in the framework of Interface Damage Mechanics. The displacement discontinuities during the progressive decohesion are related to constitutive equations extended by a damage model. The contact/friction behaviour after complete separation is described by a friction model analogous to the classical theory of plasticity.
Bruchmechanische Analyse piezoelektrischer CT‐Proben
Authors: Gruebner O. , Kamlah M.
Published: March 2011

In diesem Beitrag werden Finite‐Elemente‐Analysen für elektromechanisch belastete piezoelektrische CT‐Proben vorgestellt. Insbesondere wird dabei auf verschiedene Möglichkeiten eingegangen, die elektrischen Randbedingungen von Rissen in Piezokeramiken zu modellieren, wobei der Einfluß der Permeabilität des Rißmediums auf die Ermittlung der bruchmechanischen Kenngrößen diskutiert wird.
Compressive Behaviour of Metal‐Matrix Composites: Accuracy of Homogenisation
Authors: Guz I. A.
Published: March 2011

Asymptotic accuracy of the continuum theory of plastic fracture under compassion for the metal matrix composites with periodic structure is proved. The particular mode of stability loss, which corresponds to the continuum approximation is determined within the model of piecewise‐homogeneous medium. The investigation is carried out for three‐dimensional non‐axisymmetrical problems.
Optimal Design of Vibration Absorbers
Authors: Glora M. , Bestle D.
Published: March 2011

The tendency of reducing energy consumption leads to extensive use of lightweight structures in vehicle dynamics. As a consequence bodies of cars and trains become sensitive to structural vibrations. For damping of such vibrations, the use of passive absorbers is a common approach. Passive systems, however, have to be tuned for a given resonance frequency of the structure and are sensitive to changes of this frequency due to variations in loads or excitation. Mechatronics enables the use of actively controlled absorption systems that don't lack this disadvantage.
Elasto‐plastic Analysis of Fracture Specimens using the Boundary Element Method
Authors: Potrc Iztok , Sadl Rudolf
Published: March 2011

In general crack problem, the geometry and loading encountered are too complex for the determination of the fracture parameters analytically. To this end, numerical methods have been developed as possible solution. The boundary element method, used in this paper is one of the powerful numerical methods. An elasto‐plastic analysis of fracture specimens is performed. The welded specimen fracture behaviour and its deviation regarding the parent material is investigated. The obtained results are compared whit the experimental results and the results given by FEM.
A threedimensional boundary element analysis of elasto‐plastic cracked prolems
Authors: Iztok Potrc , Janez Kramberger
Published: March 2011

Based on the theoretical background, the formulation for the three‐dimensional elasto‐plastic analysis has been enhanced and implemented in the computer program. The algorithm utilities the initial stamen approach to satisfy the material non‐linearity. The discrimination inculpates the continues and the discontinuous boundary elements. Also included are the domain cells with the linear and quadratic approximation. The non‐linear boundary element results are presented to demonstrate the accuracy and usefulness of the method.
Fracture Parameter for Thermoplasticity Relative to Material Scaling
Authors: Sansen P. , Dufrenoy P. , Weichert D.
Published: March 2011

This study deals with a fundamental approach on energetic formulation of a rupture criterion of a solid under thermoplastic solicitation. This approach consists of a calculation of an energy from which will appear a macroscopic crack for a given cycle of solicitation. On the basis of the Noether's theorem, this study is undertaken in the case of the dilatation symmetry, by taking into account plasticity and thermochemical loading (M modified integral). This integral emanates from a discrete lagrangian describing the thermoinelastic system from classical field theory. It represents a conservation law analogues to the Budiansky and Rice interpretation.
Ductile Fracture of honeycombs
Authors: Schmidt I. , Fleck N. A.
Published: March 2011

Crack growth initiation and subsequent resistance in a hexagonal honeycomb made out of ductile base material is investigated in a numerical study. The elasto‐plastic base material is characterized by its yield strain, failure strain and the ratio of ultimate strength to yield strength, assuming a bilinear stress‐strain relationship. Of the base materials' fracture properties, only the specific fracture energy is prescribed. K‐Resistance curves are calculated under the assumption of small scale yielding.
A new approach for a 3D deep drawing using an Asymptotic Numerical method
Authors: Abichou H. , Zahrouni H. , Potier‐Ferry M.
Published: March 2011

This paper presents an Asymptotic Numerical Method (A.N.M.) to simulate a 30 bemispherical deep‐drawing of a circular sheet. An elastoplastic model based on the plasticity deformation theory is adopted The problem discretisation is performed by a shell finale element well adapted for problems involving large displacements and large rotations. A comparison with results obtained by the help of the industrial code Abaqus evaluates the performance and the interest of the method.
Valve gear refinement
Authors: Avsec J. , Marcic M.
Published: March 2011

After the 3000‐hour engine test the manifestations of an intensive wear appeared on the exhaust side of valve gear. The paper describes a new type of valve gear cam ‐MULTICAM which consists of seven curves and allows an optimum cam design. In order to calculate the cinematic and dynamic values and to asses the minimum oil film thickness in the valve gear, the mathematical model was used. By means of the new cam design the Hertz pressures were reduced at the point of contact between the cam and the cam follower and the lubrication properties at the top of the cam were improved.
Adaptive Discretisation of Shell Problems
Authors: Axel Hecht , Carsten Carstensen , Darius Zarrabi
Published: March 2011

A seven parameter Reißner‐Mindlin shell kinematic is employed for a elastoplastic material with hardening. The resulting nonlinear minimization problem is discretised within a finite element method on the mid surface of the shell. A posteriori error estimates are discussed and related adaptive algorithms are presented. Numerical examples illustrate the theoretical results.
Adaptive Methods for Euler and Navier‐Stokes Equations
Authors: KlikovÁ Alice
Published: March 2011

The numerical calculations show that the local fineness of the mesh has an important influence on the numerical results. In our contribution, two types of error indicators for Euler and Navier‐Stokes equations are presented. These indicators are used for adaptive refinement of the mesh and thus for improving the precision of the approximate solution and minimazing the computational time.
Aspects of Adaptive Remeshing Techniques in Finite Elasticity
Authors: Koch A. , Miehe C.
Published: March 2011

One of the major difficulties in applying the finite element method to boundary value problems of finite elasticity is the design of a suitable mesh in order to maximize the accuracy of the solution and to minimize the numerical cost. The basic problem in this context is the error estimation of the nonlinear problem. Our aim is to present possible a posteriori error estimators for finite elasticity which operate in the linear tangential space of the nonlinear problem.
Automatic derivation of sensitivity terms for mixed Galerkin‐collocation problems
Authors: Korelc J.
Published: March 2011

The paper presents the use of the SMS system (Symbolic Mechanics System) for the automatic derivation and coding of sensitivity terms in finite element analysis. General symbolic derivation of analytical sensitivity terms for general mixed Galerkin‐collocation problems is difficult due to the complex (implicit) interactions between different levels of computation. The approach implemented in SMS avoids this problem by combining several techniques: symbolic capabilities of Mathematica, automatic differentiation technique, simultaneous optimisation of expressions and stochastic evaluation of the formulae.
Re‐analyses of Tests on Snow Specimens by Means of Elasto‐Visco‐Plasticity Models
Authors: Liu W. N. , Meschke G. , Mang H. A.
Published: March 2011

To gain more insight into the mechanical behavior of snow for the purpose of numerical simulations of the traction mechanism of a rubber tread moving on a snow‐cowered road, three pertinent material models are investigated numerically by means of re‐analyses of tests on snow specimens. Based on a comprehensive comparison of the obtained results, one of these three models is found to be superior to the other two. The technical background of this work is the design of winter tires.
Zur inititalen Identifizierung von Verzweigungspunkten auf nichtlinearen Last‐Verschiebungspfaden
Authors: Mang H. A. , Helnwein P.
Published: March 2011

Mit Hilfe der konsistenten Linearisierung der klassischen Beulbedingung ist es vielfach möglich, Stabilitätsgrenzen auf nichtlinearen Last‐ Verschiebungspfaden ab initio mat für technische Zwecke ausreichender Genauigkeit abzuschätzen. Da sich für Verzweigungspunkte andere Schätzfunktionen als für Durchschlagspunkte als in einem bestimmten Sinn optimal erwiesen haben, ist es notwendig, die jeweils aktuelle Art der Stabilitätsgrenze ab initio zu identifizieren. In diesem Zusammenhang wird die Existenz zusätzlicher Orthogonalitätsrelationen zwischen sogenannten Verzweigungsmoden und den übrigen Eigenvektoren des zugrunde liegenden linearen Eigenproblems nachgewiesen.
Zur Analyse dynamischer Mehrdeutigkeitslösungen von nichtlinearen parametererregten Systemen
Authors: Hortel M. , Škuderová A.
Published: March 2011

ZUT Untersuchung von dynamischen Eigenschaften mechanischer Systeme mit kinematischen Bindungen, z.B. bei elastisch gelagerten Zahnradübersetzungsgetrieben, wird ein Approximationsverfahren skizziert, das auf der Transformation der Differentialrandwertaufgabe in ein Integrodifferentialgleichungssystem beruht.
Einspielanalyse von Verbundwerkstoffen
Authors: Schwabe F. , Hachemi A. , Weichert D.
Published: March 2011

Das Einspielverhalten eines regelmäßig strukturierten heterogenen Verbundwerkstoffes wird untersucht. Dazu wird das Verhalten einer repräsentativen Einheitszelle des Werkstoffes betrachtet. Mat Hilfe der Homogenisierungstechnik wird der Übergang von Mikro‐ zu Makrostruktur hergestellt, so daß für den gesamten Werkstoff eine Aussage zum Einspielverhalten getroffen werden kann.
Generalisation of Boussinesq's Equation over Triangularly shaped Bases
Authors: Skrinar M.
Published: March 2011

The equation for the computation of stresses directly in an arbitrary point of the half‐space loaded with a linear load distributed over a rectangular base according to Boussinesq s equations that has been presented recently is applicable if the bases can be described with rectangular areas only. For nonrectangular bases the integration over an arbitrary quadrilateral with a uniform load was performed, but the procedure required enormous computational efforts and yielded only approximate results. The paper presents a new integration over a triangular area which allows the analysis of practically any polygonal base shape with a linear load, thus eliminating all limitations of shape and load.
Viscous Creep of Steel Structures in Fire
Authors: Srpčič S.
Published: March 2011

When analysing the mechanical behaviour of steel structures at high environmental temperatures as expected in real fire, the viscous creep deformations may play a significant role. The paper presents the nonlinear analysis of steel planar beams and frames, subjected to time dependent temperature and mechanical loadings. In the FEM‐based numerical procedure, the viscous part of the total strain increment is described by the Williams‐Leir modification of Harmathy's equation of nonlinear viscous creep of steel. The numerical example shows the influence of the creep intensity on the mechanical response of a steel beam structure in hypothetical fire. Due to the creep softening, considerable increase of deflections can be expected at statically determinate structures and significant stress redistributions at statically indeterminate ones.
The general mechanics equation of the system with nonholonomic constraints
Authors: Osinski Z.
Published: March 2011

The paper presents the method for preparing the general mechanics equation and obtaining the equation of motion for the system with nonholonomic equations. The concept of generalised forces together with related quasicoordinates, quasivelocities and quasiaccelerations is applied. Presented form of the general equation is a uniform representation replacing equivalently known mechanics principles, This form of the equations is a good basis for the computer aided design incorporating symbolic calculus required for description of mechanical systems with nonholonomic constraints.
Eine verbesserte Beschreibung der Wirkungen nichtklassischer Dämpfung
Authors: Raue A. , Heuer R.
Published: March 2011

In der vorliegenden Arbeit wird die Schwingungsantwort yon Bernoulli‐Euler‐Balken mit externen viskosen Dämpfern unter‐sucht. Nach Anwendung der modalen Projektion unter Verwendung der Eigenformen des ungedämpften Balkens bleiben die beschreibenden Differentialgleichungen dämpfungsgekoppelt. Die Lösung wird iterativ mit den Koppeltermen als zusätzliche Anregung nach Abspaltung quasistatischer Anteile von der Gesamtlösung gefunden und der Lösung des Systems ohne Koppelterme gegenübergestellt. Speziell wird der beidseitig gelenkig gelagerte Balken unter zeitlich harmonischer Gleichlast und unsymmetrischer Dämpferanordnung untersucht.
Pseudo‐Shakedown viskoplastischer Flächentragwerke
Authors: Stoffel M. , Schmidt R. , Weichert D.
Published: March 2011

Werden Flächentragwerke wiederholt Impulsbelastungen ausgesetzt, kann sich ein Grenzverhalten in ihren inelastischen Verformungen einstellen. In dieser Arbeit wird die Ursache dafür näher untersucht.