bluuebunny/crossref_metadata_2025_split huggingface dataset:
Relaxing mixed integer optimal control problems using a time transformation
Authors: Ringkamp Maik , Ober‐Blöbaum Sina , Leyendecker Sigrid 
Published: October 2015

AbstractMixed integer control systems are used to model dynamical behavior that can change instantly, for example a driving car with different gears. Changing a gear corresponds to an instant change of the differential equation what is achieved in the model by changing the value of the integer control function. The optimal control of a mixed integer control system by a discretize‐then‐optimize approach leads to a mixed integer optimization problem that is not differentiable with respect to the integer variables, such that gradient based optimization methods can not be applied. In this work, differentiability with respect to all optimization variables is achieved by reformulating the mixed integer optimal control problem (MIOCP). A fixed integer control function and a time transformation are introduced. The combination of both allows to change the sequence of active differential equations by partially deactivating the fixed integer control function. In contrast to other works, here different fixed integer control functions are taken into account. Advantages of so called control consistent (CC) fixed integer control functions are discussed and confirmed on a numerical example. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Learning Robot Force/Position Control for Repetitive High Speed Applications with Unknown Non–Linear Contact Stiffness
Authors: Parzer Herbert , Gattringer Hubert , Müller Andreas , Naderer Ronald 
Published: October 2015

AbstractThis paper proposes a learning robot force/position control for high speed force trajectory following. Following high speed force trajectories in different repetitve robotic applications is a challenging field in robot force control. If the end–effector should provide a contact force while following a position trajectory in the non–force controlled direction a parallel force / position control is suitable. However, when it comes to high speed tasks this force control method reaches its limit. The problem can be solved by using an iterative learning control method in combination with the parallel force/position control. In this paper the learning force control method is introduced and experimental results are presented. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Impulse‐based control of simple oscillators within the nonsmooth mechanics approach
Authors: Schindler Thorsten , Mayet Johannes , Seiwald Philipp 
Published: October 2015

AbstractAn impulse‐based control scheme for a simple spring‐mass oscillator subject to set‐valued friction forces is presented. In contrast to PD or PID control laws, the proposed control law prevents non‐zero steady state errors and limit cycles. Motivated by Wouw and Leine [1], it is shown that impulse‐based control laws can lead to satisfactory behavior if the oscillator starts sticking. In order to realize a practical implementation, the equations of motion are extended by a mathematical model of the actuator dynamics. The analysis is undertaken in the framework of nonsmooth mechanical systems. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Relaxed incremental variational approach for damage in arteries
Authors: Balzani Daniel , Schmidt Thomas 
Published: October 2015

AbstractIn this contribution, several extensions of the relaxed incremental variational damage model by BALZANI & ORTIZ [1] are provided, in order to appropriately account for the description of arterial tissues. In particular, the one‐dimensional formulation from [1] is combined with a numerical homogenization scheme. Moreover, hysteresis behavior is included and a new optimization strategy is used to determine the bifurcation parameters when checking for a loss of convexity. The performance of the proposed model is demonstrated in a three‐dimensional finite element simulation of a overstretched simplified atherosclerotic artery. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A porous media approach for plantar tissue during gait
Authors: Boso Daniela P. , Sciumè Giuseppe , Pizzocaro Mattia , Schrefler Bernhard A. 
Published: October 2015

AbstractRecently a new computational model, based on the thermodynamically constrained averaging theory, has been proposed to predict tumor initiation and proliferation and afterwards to study plantar tissue mechanics. The foot tissue is modeled as an elastic porous medium, in large strain regime and completely filled by a fluid phase. By considering the interstitial fluid, it is possible to mimic the viscoelastic behavior of the plantar tissue observed experimentally. Being the global response of the bi‐phase system viscoelastic, it is shown that the duration of stance as well as of each of gait cycle has an influence on tissue stress field. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Comparison of Preconditioners for the Steklov–Poincaré Formulation of the Fluid‐Structure Coupling in Hemodynamics
Authors: Deparis S. , Forti D. , Heinlein A. , Klawonn A. , Quarteroni A. , Rheinbach O. 
Published: October 2015

AbstractA Fluid–Structure Interaction (FSI) problem can be reinterpreted as a heterogeneous problem with two subdomains. It is possible to describe the coupled problem at the interface between the fluid and the structure, yielding a nonlinear Steklov–Poincaré problem. The linear system can be linearized by Newton iterations on the interface and the resulting linear problem can be solved by the preconditioned GMRES method. In this work we investigate the behavior of preconditioners of Neumann–Neumann and Dirichlet–Neumann type. We find that, in the context of hemodynamics, the Dirichlet– Neumann, i.e., using Dirichlet boundary conditions on the fluid side and Neumann on the structure side, outperforms the Neumann–Neumann method, except when a weighting is used such that it basically reduces to the Dirichlet–Neumann method. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Extremal loading of soft fibrous tissues: multi‐scale mechanics and constitutive modeling
Authors: Linka Kevin , Khiêm Vu Ngoc , Itskov Mikhail 
Published: October 2015

AbstractIn the current contribution, we present a multi‐scale constitutive model capturing macroscopic inelastic effects (like stress softening and permanent set) in soft tissues under cyclic loading. Soft biological tissues can be described as a biological composite material. The extracellular matrix is hereby reinforced by collagen fibers which themself are an assembly of collagen fibrils embedded in a proteoglycan (PG) rich matrix. Micro‐damage induced by cyclic loading is treated by an interaction scenario between the fibrils and the PGs. At the low strain regime PGs promote sliding between fibrils [1] which leads to the yielding of statistical distributed overlapping segments. The breakage of the PG‐bridges is defined by a decreasing PG‐density. Due to the accumulated damage of the PG connections at high tissue strains, the strains at the fibril level increases. This finally drives the over‐stretching of the fibrils, which is associated with a permanent rupture of the hydrogen bonds inside of the tropocollagen molecules [2]. The so obtained model is in line with recent experimental findings [1, 2] and was additionally validated against experimental data available in literature. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Rupture in soft biological tissues modeled by a phase‐field method
Authors: Raina Arun , Miehe Christian 
Published: October 2015

AbstractWe present an application of the phase‐field method of fracture to the simulation of artery rupture at large strains. To achieve this, the crack driving force function associated with the evolution of the crack phase‐field is modified to account for the inherent anisotropy of the soft biological tissues. The phase‐field methods present a promising and innovative approach to the thermodynamically consistent modeling of fracture. A key advantage lies in the prediction of the complex crack topologies where the cohesive zone approaches to fracture are known to suffer. A regularized crack surface functional is introduced that Γ‐converges to a sharp crack topology for vanishing length scale parameter. The evaluation of the phase‐field follows the minimization of this crack surface functional. The phase‐field variable can be treated as a geometric quantity whose evolution is coupled to the anisotropic bulk response in a modular format in terms of a crack driving state function. A stress‐based anisotropic failure criterion is introduced whose maximum value from the deformation history drives the irreversible crack phase‐field. The formulation is verified by the finite element based simulation of a real arterial cross‐section undergoing rupture in a two‐dimensional setting when subjected to inflation pressure. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Towards the continuum‐mechanical modelling of metastatic tumour growth in the brain
Authors: Schröder Patrick , Wagner Arndt , Ehlers Wolfgang 
Published: October 2015

AbstractThe growth of metastases in the brain increases the state of stress, create leaky blood vessels and disrupt regular brain cells. Essential steps during the development of metastases are the infiltration of the tissue, the nutrient‐dependent growth and the stimulation of blood‐vessel sprouting. A promising medical treatment can be obtained by the direct infusion of a therapeutic solution into the tissue. Besides experiments, computational models can improve the understanding of brain metastases. In this regard, the liquid‐saturated brain tissue represents a porous material. Therefore, the framework of the Theory of Porous Media (TPM) provides an excellent tool for its description. The continuum‐mechanical theory of a multi‐constituent model and mechanisms of metastases growth are presented in this contribution. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Influence of Growth in Perfusion Dependent Biological Systems – at the Example of the Human Liver
Authors: Werner Daniel , Ricken Tim , Dahmen Uta , Dirsch Olaf , Holzhütter Hermann‐Georg , König Matthias 
Published: October 2015

AbstractBiochemical reactions in the liver are a complex non‐linear and time depending coupled function‐perfusion‐mechanisms. The metabolism of the liver, e.g. nutrient storage, is directly coupled to its blood perfusion. Growth phenomena, such as accumulation of fat, have a strong impact onto micro‐perfusion within the liver. Here, we present the results of a computational model that describes selected coupled functionalities. The metabolic processes take place in the liver cells, the hepatocytes, which are arranged in a delicate system of capillaries, so called sinusoids. Nutrients, oxygen, and other components of the blood are transported through the sinusoids. Due to this highly complex inner structure of the lobules it is impracticable to give a microscopic geometrical description in a continuum mechanical manner. Therefore, a homogenization scheme based on the theory of porous media (TPM) is used; [1]. In case of the presented liver model we consider a porous solid body, that consists of tissue and fat, and a fluid representing blood. In each phase several miscible components are considered. For the microscopic cell level use has been made of an embedded set of ordinary differential equations (ODE) that mimics a simplified metabolism, e.g. glucose utilization and production; [2]. In case of growth of the fat phase we follow a phenomenological approach. Numerical examples for this coupled process are presented and discussed. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical simulation of the fracturing processes in masonry arches
Authors: Carpinteri Alberto , Lacidogna Giuseppe , Accornero Federico , Invernizzi Stefano 
Published: October 2015

AbstractMasonry arch structures, and, more generally, vaulted structures, are traditionally assessed using a well‐established approach, such as linear elasticity or limit analysis, whereby system behaviour at the intermediate stage – which occurs when the material's tensile strength has been exceeded but the collapse mechanism has not yet formed – is disregarded. A more accurate interpretation requires a thorough analysis that can take into account the intermediate cracking stage and uses a constitutive law providing a closer approximation to the actual behaviour of the material. In this paper, an evolutionary fracturing process analysis for the stability assessment of masonry arches is presented. This method makes it possible to capture the damaging process that takes place when the conditions evaluated by means of linear elastic analysis no longer apply and before the conditions assessed through limit analysis set in. Furthermore, the way the thrust line is affected by the opening of cracks and the redistribution of internal stresses can be checked numerically. The results obtained with the described approach are compared with a numerical simulation performed with the finite element code Diana (TNO, The Netherlands) adopting discrete cracking with cohesive laws. Finally, the case study of the arch of the Mosca Bridge over the Dora River in Turin, Italy, is described. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Global approaches for accurate loading analyses and crack path predictions at single and two‐cracks systems
Authors: Judt Paul , Ricoeur Andreas 
Published: October 2015

AbstractBased on the work by Eshelby, the path‐independent Jk‐, M‐, L‐ and interaction‐ or Ik‐integrals were introduced and applied to cracks for the accurate calculation of crack tip loading quantities. Applying the FE‐method to solve boundary value problems with cracks, numerically inaccurate values are observed within the crack tip region affecting the accuracy of local approaches. Simulating crack paths, local approaches face further problems as cracks are running towards interfaces, internal boundaries or other crack faces. Within global approaches, path‐independent integrals are calculated along remote contours far from the crack tip, essentially exploiting numerically reliable data requiring special treatment only for the near‐tip crack faces. To provide path‐independence, additional integrals along interfaces, internal boundaries and crack faces are necessary.In this paper, new global approaches of path‐independent integrals are presented and applied to the calculation of crack paths at two‐cracks systems. A second focus is directed to the accurate loading analysis and crack path prediction considering anisotropic properties and material interfaces. The numerical model provides crack paths which are in good agreement with those obtained from crack growth experiments. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Follower forces as an inverse contact algorithm
Authors: Konyukhov A. , Schweizerhof K. , Izi R. 
Published: October 2015

AbstractFollower forces on a surface are defined as the forces which are keeping their constant directions with regard to the surface. A typical example is pressure, which is acting always in the direction of the normal. The linearization is necessary in order to solve a problem using an implicit scheme in the case of large deformations. Consider, for example, pressure p acting on a surface s, defined by the vector r(ξ1, ξ2). In this case, a weak form is written as:

Formally, as shown in [1], [2] the following linearization can be formulated as

which is recovering an apparent unsymmetrical structure with regard to Δu and δu and, therefore, corresponding unsymmetrical tangent matrix. Though, the system is initially conservative an initially looking unsymmetrical structure is derived due to the linearization of the normal in the Cartesian coordinate system. A special complicated transformation for integrals with closed boundaries was necessary to show the symmetry in this case, see in [3], [4]. Nevertheless, as mentioned by Simo in [5], linearization in a covariant form is always leading to the symmetric structure for conservative systems.Application of the covariant derivation has become a standard tool within the geometrically exact theory of contact interaction, see in [6], [7]. The corresponding symmetry of tangent matrices for all conservative cases is then automatically fulfilled, moreover, they are obtained for all contact pairs such as surface‐to‐surface, curve‐to‐curve, curve‐to‐surface in a close covariant form. Using these transformations, one can treat contact tractions not as unknown variables to be computed, but as given external forces which are keeping their direction in the local coordinate system. This case we can call an inverse contact algorithm. The main results of the geometrically exact theory for contact interactions for surface‐to‐surface contact pairs are outlined first in order to obtain all relationships for the inverse contact algorithm. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigations on clamping effects with Die‐Less‐Hydroforming‐Structures
Authors: Metzger Andreas , Ruff Daniel C. , Ummenhofer Thomas 
Published: October 2015

AbstractWhen using a special forming technology called “Die‐Less Hydroforming” to create objects, due to the lack of a conventional forming tool (like a die or a punch) and depending on a particular cutting of the blank geometry, it is possible to generate some special clamping effects when inflating the seal‐welded blanks. In our contribution, we present results of a study of these clamping effects in extracts, which have been investigated by means of practical inflating tests as well as numerical forming simulations using LS‐DYNA with “Die‐Less‐Hydroforming”‐samples having a special geometry that looks like a “Pac‐Man”. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stress concentration control in the problem of plane elasticity theory
Authors: Odishelidze Nana , Criado Aldeanueva Francisco , Criado Francisco 
Published: October 2015

AbstractIn engineering practice, one of the important problems is the problem of finding full‐strength contours which permits to control stress concentration at the hole boundary. The article addresses the mixed problem of plane elasticity theory for doubly‐connected domain with partially unknown boundary conditions. In the presented work the stress state of the given body and full‐strength contours were defined. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On one contact problem of plane elasticity theory with partially unknown boundary
Authors: Tsintsadze Magda , Odishelidze Nana 
Published: October 2015

AbstractApplications of elastic plates weakened with full‐strength holes are of great interest in several mechanical constructions (building practice, in mechanical engineering, shipbuilding, aircraft construction, etc). It's proven that in case of infinite domains the minimum of tangential normal stresses (tangential normal moments) maximal values will be obtained on such contours, where these values maintain constant(the full strength holes). The solvability of these problems allow to control stress optimal distribution at the hole boundary via appropriate hole shape selection. The paper addresses a problem of plane elasticity theory for a doubly connected domain S on the plane z = x + iy, which external boundary is an isosceles trapezoid boundary; the internal boundary is required full‐strength hole including the origin of coordinates. In the provided work the unknown full‐strength contour and stressed state of the body were determined. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Kink banding in laminated composite structures
Authors: Völlmecke Christina , Zidek Robert A. E. 
Published: October 2015

AbstractAn analytical model for kink band deformations occurring in laminated composites is proposed based on geometric and potential energy principles. Whilst nonlinear material behaviour and imperfections are included the model considers a symmetric, multi‐directional laminate lay‐up where the kink band is assumed to occur in the central 0° laminae. First results compared to data in the literature are presented offering encouragement. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Rotordynamics of Two‐Pole Turbo Generators with Refined Modelling of the Unbalanced Magnetic Pull
Authors: Boy Felix , Hetzler Hartmut 
Published: October 2015

AbstractWithin this contribution the rotordynamic behaviour of two‐pole turbo generators is discussed. In the investigation a basic model originally proposed by Kellenberger [1], introducing a refined description of the unbalanced magnetic pull (UMP), is reviewed and extended. The analysis comprises the investigation of lateral stability behaviour and stationary torque characteristic for a magnetic eccentricity. There are two main results of the contribution: firstly it is shown, that the non‐radial component of the UMP has the same structure as the restoring forces due to a non‐circular shaft, but opposite sign. Secondly it can be seen from the extended model, that an eccentric point of application of the UMP may change the systems stationary torque characteristic significantly. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the chaotic behavior of the non‐ideal vibrating systems
Authors: Chiroiu Veturia , Dumitriu Dan 
Published: October 2015

AbstractThe paper discusses the chaotic behavior of a vibrating structure coupled to an energy source. The structural response of this system may act like energy sink under certain conditions so that a part of the energy supplied by the source is spend to vibrate the structure rather than increasing the drive speed, according to the Sommerfeld effect [1]. The energy source is influenced by the response of the system and consequently, the system exhibits jumps at critical values of the energy source. The system mimics a disappearance of the energy in the resonance regions which can affect the stability of the system, sending it to chaos [2‐4]. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
1 : 3‐Resonance in a Hopf–Hopf bifurcation
Authors: Steindl Alois 
Published: October 2015

AbstractWe investigate the bifurcating solutions at a Hopf–Hopf interaction point with an internal 1 : 3 resonance. It turns out, that the transitions from single to mixed modes can be described by Duffing or Mathieu szenarios. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On vibrations in non‐linear, forced, friction‐excited systems
Authors: Tiedemann Merten , Stender Merten , Hoffmann Norbert 
Published: October 2015

AbstractTo accelerate the development of non‐linear, friction‐excited systems, i.e. automotive friction brakes, novel test procedures are being developed. These include the study of the system's forced vibrations. However, there is a lack of knowledge concerning feasible test procedures, the assessment of the gathered data, and the possible vibration phenomena. In this context, the contribution at hand discusses vibrations in non‐linear, forced, friction‐excited systems. In the pre‐flutter regime proposed criteria for identification of parameter regions in which limit cycle oscillations can occur are challenged. In the post‐flutter regime frequency spectra for different excitation conditions are studied. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling the moisture and temperature dependent material behavior of adhesive bonds
Authors: Goldschmidt Florian , Diebels Stefan 
Published: October 2015

AbstractAlthough bonding has been known for a long time, the mechanical behavior of adhesive bonded joints comes more and more into the focus of scientific attention. During usage, adhesives are exposed to environmental influences like temperature, moisture and radiation. Due to the fact that adhesives usually consist of polymers, these influences change their mechanical behavior.In the presented work, a viscoelastic cross‐linked polyurethane that behaves incompressible is investigated. A three‐dimensional mechanical model is presented, which takes into consideration influences of changes in temperature as well as in the moisture concentration inside the adhesive layer and its thickness on the mechanical behavior. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)