bluuebunny/crossref_metadata_2025 huggingface dataset:
Stability analysis of nonholonomic extremum seeking systems via Lie brackets approximations
Authors: Grushkovskaya Victoria
Published: January 2021

The paper presents a novel family of dynamic extremum seeking controls for nonholonomic systems with output described by a convex function. It is assumed that the vector fields of the system satisfy the controllability rank condition with first‐ and second‐order Lie brackets. The proposed algorithm consists of two components. The first one is the stabilizing model‐based component constructed based on control strategies for nonholonomic systems. The second one is the extremum seeking model‐free component relying only on the values of the output of the system. The resulting control strategy optimizes the system behavior in the sense of minimizing its output. Namely, the main result of the paper states practical exponential stability of the optimal point, at which the output takes its minimal value.
Transversal vibrations of a toothed belt in linear drives during operation
Authors: Schnürer Dominik , Holl Helmut J.
Published: January 2021

Vibrations of the toothed belt of a linear drive can affect the dynamic positioning accuracy and smoothness which is important for practical applications. An analytical, one‐dimensional model of a belt section is derived, taking into account the preload and flexural rigidity, as well as the non‐linear cable effect and the acceleration forces due to the belt mass. In addition to the case of constant belt length, the temporal change of the length as a result of the axial motion is an essential part of the modeling. The solution of the equation of motion is limited to the dominant transverse deflection of the belt. For the longitudinal extension, the assumption of a quasi‐static solution is taken. A FEM program is implemented to calculate the solution for given operation conditions. The evaluations are made for selected motions according to a path planning with trapezoidal velocity profiles. A modification of individual parameters, based on a practical parameter set, enables the analysis of the respective effects.
Turbulent swirl flow analysis by Kolmogorov's similarity hypotheses
Authors: Čantrak Ðorđe S. , Janković Novica Z. , Nedeljković Miloš S.
Published: January 2021

Turbulent swirl flow generated by the axial fans in pipe is investigated in this paper by using Kolmogorov's similarity hypotheses. It is shown that energy in the inertial subrange is divided among eddies after the “−5/3” law, i.e. Φww ∝ f−5/3, where Φww is spectral density for circumferential velocity and f is the frequency. This is presented for two various axial fans, of which one is carefully designed to generat Rankine vortex, while the second one has solid body circumferential velocity profile.
A semi‐explicit integration scheme for weakly‐coupled poroelasticity with nonlinear permeability
Authors: Altmann Robert , Maier Roland , Unger Benjamin
Published: January 2021

Within the time integration of linear elliptic‐parabolic problems such as poroelasticity, large systems have to be solved in every time step. With a semi‐explicit approach, these systems decouple, leading to a remarkable speed‐up. This paper indicates that this idea can also be applied to nonlinear problems such as poroelasticity with nonlinear permeability. To see this, we consider a related toy problem.
GR decompositions and their relations to Cholesky‐like factorizations
Authors: Benner Peter , Penke Carolin
Published: January 2021

For a given matrix, we are interested in computing GR decompositions A = GR, where G is an isometry with respect to given scalar products. The orthogonal QR decomposition is the representative for the Euclidian scalar product. For a signature matrix, a respective factorization is given as the hyperbolic QR decomposition. Considering a skew‐symmetric matrix leads to the symplectic QR decomposition. The standard approach for computing GR decompositions is based on the successive elimination of subdiagonal matrix entries. For the hyperbolic and symplectic case, this approach does in general not lead to a satisfying numerical accuracy. An alternative approach computes the QR decomposition via a Cholesky factorization, but also has bad stability. It is improved by repeating the procedure a second time. In the same way, the hyperbolic and the symplectic QR decomposition are related to the LDLT and a skew‐symmetric Cholesky‐like factorization. We show that methods exploiting this connection can provide better numerical stability than elimination‐based approaches.
Rot‐free finite elements for gradient‐enhanced formulations at finite strains
Authors: Riesselmann Johannes , Ketteler Jonas , Schedensack Mira , Balzani Daniel
Published: January 2021

This contribution presents a mixed C0 continuous finite element approach for gradient enriched formulations. The approach is based on a split of the Lagrange multiplier into a gradient and a rotational part, through which a decoupled set of variational equations is obtained. Application to numerical examples in the finite strain gradient elasticity framework unveils the reduced computational effort due to the decoupled character of the global system of equations such as the ability to avoid stress localization.
Towards a mathematical model for single molecule structured illumination microscopy
Authors: Hockmann Mathias , Kunis Stefan , Kurre Rainer
Published: January 2021

While structured illumination microscopy (SIM) is a widely used super‐resolution microscopy technique for densely labelled samples, we apply a modified version of the matrix pencil method to single molecule imaging. We prove that under reasonable conditions we can recover up to two times more molecule positions compared to conventional microscopy exactly from noiseless data and include numerical examples illustrating benefits as well as limitations of the algorithm.
Extension of the eigenerosion approach to ductile crack propagation at large strains and its application on hard metal microstructures
Authors: Wingender Dennis , Balzani Daniel
Published: January 2021

The efficient operation of mechanized tunnel drilling machines is strongly determined by the wear resistance of the applied mining tools. Especially in chisels, but also partly in cutting disks, hard metals are used. Their wear mechanism is dominated by surface spalling, i.e. subcritical crack propagation through the material's microstructure mainly consisting of a ductile metal matrix and carbide inclusions. Since this process is mainly governed by the morphology of the microstructure and the mechanical behavior of the individual phases, simulations at the microscale enable the design of improved materials. In this contribution a method for the modeling of this process is presented. The approach is based on the eigenerosion framework introduced in [1] and an algorithmic scheme for large strains is given, which extends the small strain implementation in [2]. For the phases at the microscale the finite strain plasticity formulation [3] is applied. Furthermore, simulations are carried out on the microscale by applying the Finite Cell Method [4] on hard metal microstructures. Here, a specific cell arrangement is constructed which minimizes the required number of cells for a given microstructure morphology. By evaluating the results of these simulations, failure of the material can be investigated on a microscopic level and improvements of the material morphology regarding wear can be realized.
Possibilities and drawbacks using arbitrary precision numbers for structural analysis
Authors: Klarmann Simon , Wackerfuß Jens
Published: January 2021

In various areas of computational mechanics, rounding errors can have a considerable influence on the quality of the simulation results; in some cases, these lead to the termination of the numerical calculation. Rounding errors are caused by limited accuracy in the representation of floating point numbers. Current codes usually use double precision numbers (p = 16 significant digits). Until now, modern multi‐precision libraries with which floating‐point numbers can be processed with arbitrary accuracy are largely unused.

The aim of this article is to show the possibilities and limitations of such libraries in the context of computational mechanics. The accuracy of computations from p = 8 up to p = 128 will be investigated. Examples will be selected which are particularly sensitive to rounding errors. On the basis of a first academic example it is examined which calculation accuracy is necessary to carry out a static analysis on a cantilever beam with a slenderness of up to 1049 with a standard beam FE formulation. In a second example, a load‐bearing structure is analyzed in which the stiffness of its supporting members differs by several powers. Finally, the disadvantages associated with the higher calculation accuracy (CPU time, memory requirements) are discussed.
Determination of the sound insulation property of 2D periodic wall structures by a fluid‐structure interaction model
Authors: Perras Elias , Zhang Chuanzeng
Published: January 2021

The propagation of acoustic and elastic waves in periodical structures, often referred to as phononic crystals (PCs), can be drastically restricted. In the so‐called band‐gaps, which are certain frequency ranges, the wave propagation is prohibited in the PCs. The location and the width of the band‐gaps are determined by the geometrical and the material properties of the PCs. The purpose of this work is to analyze the sound insulation capabilities of wall structures consisting of two‐dimensional (2D) PCs, which are referred to as the PC walls. Since no analytical methods exist to determine the sound insulation capabilities of such geometrically complex periodic structures, a fully coupled fluid‐structure interaction (FSI) model is developed based on the finite element method (FEM). The PC walls are optimized to realize desirable band‐gaps within the audible frequency range. Numerical examples are presented and discussed to demonstrate that the sound insulation capabilities of periodically structured walls are far superior to that of the traditional wall structures in the frequency band‐gaps of the PC walls.
Image‐based stress analysis of porous freeze casts
Authors: Birk Carolin , Lupascu Doru C. , Vadalaà Miriana , Saputra Albert
Published: January 2021

An automatic image‐based mesh generation and modeling approach is applied to static stress analysis of porous materials produced by freeze casting. The scaled boundary finite element method is employed due to its seemles integration with octree meshes. Several aspects related to image processing and numerical efficiency are discussed in order to evaluate the suitability of the SBFEM in the context of modeling foam‐like samples with highly irregular microstructural details.
Bimodal parametric excitation of a micro‐ring gyroscope
Authors: Barakat Ahmed A. , Lima Roberta , Sampaio Rubens , Hagedorn Peter
Published: January 2021

Parametric excitation in vibratory systems is known well over hundred years. Recently it is also being exploited in Micro‐electromechanical Systems (MEMS). One example of these are micro‐ring gyroscopes, which are used in the automotive, the navigation and in the space industries. The sensitivity of such gyroscopes can be impaired by signal noise induced through parasitic capacitance between drive and sense electrodes. Applying parametric excitation and exploiting parametric amplification recently was shown to open new promising paths. On the theoretical side of parametric vibrations, recently it was found that the simultaneous parametric excitations in two coordinates or more with phase difference can lead to very interesting phenomena. The micro‐ring gyroscope is a good example of making use of parametric excitation and amplification to solve some of the problems in the modern MEMS. This work aims at modelling a micro‐ring gyroscope with two simultaneous phase lagged parametric excitations. The equations of motion can be derived using Hamilton's principle, both for an inextensible as well as for the extensible ring, and in the fully symmetric cases the eigenvalue problem can be solved analytically. The completely symmetric problem, leads to two eigenfunctions for any given eigenfrequency, except for the fundamental ones. The axial symmetry is in general destroyed by the way in which the vibrating ring is elastically supported by discrete elastic supports. Instead of truly double eigenfrequencies, the problem then has pairs of two closely spaced eigenfrequencies. In the simplest case, the ring can then be described by two generalized coordinates. Making use of direct excitation of each of the modes, as well as parametric excitation, makes it possible to exploit parametric resonance and parametric amplification. This has been applied before for the micro‐ring gyroscope, however not for the case of parametric excitation in two coordinates and with phase lag between the two parametric excitations. Taking into account this phase lag as an additional parameter, opens several new ways of sensing the angular velocity of the moving base of the micro‐ring gyroscope.
Closed‐form stress solution of open holes in a finite domain
Authors: Nguyen-Hoang Minh , Becker Wilfried
Published: January 2021

Open holes are essential design features in many technical structures. For a lightweight optimal design precise stress analysis tools are vital. Focus of this contribution is the stress field determination of an open hole in a rectangular plate of finite width by analytical means, particularly the Airy stress function. This is beneficial in terms of computational effort. To obtain results of high precision, the stress boundary conditions at the straight edges as well as along the hole boundary must be fulfilled. This is reached by supplementing the field modelling the corresponding infinite dimensions problem – the Kirsch solution – with auxiliary functions.
Perspectives in the modeling of biopolymer aerogel networks subject to wetting
Authors: Rege Ameya , Gurikov Pavel , Kalmár József , Milow Barbara
Published: January 2021

Alginate‐based aerogels were shown to be non‐cytotoxic and to feature good cell adhesion, thus drawing their attention towards tissue engineering and regenerative medicine [1]. To this end, their mechanical properties under dry as well as wet conditions were subsequently investigated [2]. Upon wetting, these aerogels showed strong stiffening in their mechanical behavior. In this work, a micromechanically motivated model approach to describe this phenomenon is proposed. The nanofibers in the aerogel network are considered to undergo structural rearrangement upon being subjected to water. Furthermore, the collapse of the micropores (pore diameter below 5 nm) results in the formation of local hydrogel‐like network phase. The constitutive model is based upon the assumption that the total network can be decomposed into a hydrogel‐like network and a restructured aerogel network. The aerogel network is described based on the micromechanical model proposed by Rege et al. [3], while the hydrogel‐like network is modeled based on the phenomenological approach of Gent [4]. This first approach towards modeling shows reliable results against the experimental stress‐strain curves of alginate‐starch aerogels [5].
Constitutive modeling of dynamic recrystallization coupled to viscoplasticity
Authors: Westermann Hendrik , Mahnken Rolf
Published: January 2021

During thermomechanical processing the microstructure is subject to drastic changes. These changes relate to various physical mechanisms such as recrystallization, recovery, grain growth and phase transitions, heavily affecting material properties in engineering components. This enables the targeted adjustment of microstructures and the gradation of macroscopic mechanical properties. During thermomechanical processing the modeling of dynamic recrystallization is of major importance. Thus, we present a thermodynamically consistent framework based on an existing continuum mechanical model. Major improvements, including derived recrystallization volume fractions and clean distinction of true microstresses and nominal microstresses, have been made in comparison to the original model.
Studies on the validity of the reduced bending stiffness method for eccentrically stacked laminates
Authors: Schilling Jakob C. , Mittelstedt Christian
Published: January 2021

The reduced bending stiffness method is used in the framework of computational models for stringer stiffened panels. Here, the stringer foot is often stacked on top of the skin of the panel and leads to a stacked laminate with extensional bending stiffness coupling. The validity of the reduced bending stiffness method for the mentioned laminate type is investigated and assessed, as only unsymmetrical laminates without eccentricity have been considered in existing literature. In exemplary studies, the influence of the coupling effects is shown, which allows drawing conclusions on the error that is introduced in, e. g. closed‐form analytical approximate solutions for the buckling of stringer stiffened panels.
Porosity analysis in SiC/SiC ceramic matrix composites
Authors: Rauscher Sophie-Maria , Kaleel Ibrahim , Raina Arun
Published: January 2021

Ceramic matrix composites made of silicon carbide fibers embedded in silicon carbide matrix (SiC/SiC CMCs) are widely recognized as excellent replacements for denser superalloys such as Nickel based super alloys for high‐temperature applications in aero engines. During the manufacturing process with chemical vapour infiltration, large amount of pores are introduced in the CMC and their presence can have considerable impact on the structural performance of a component. In this work, we analyze the pore size and spatial distribution in SiC/SiC CMCs for different geometrically‐identical specimens. Porosity within specimens are quantified through computed tomography (CT) scans. Different statistical approaches are utilized for describing the amount of pores, their size and spatial distribution within each specimen.
Phase‐field Fracture with Representative Crack Elements for Non‐linear Material Behaviour
Authors: Storm Johannes , Kaliske Michael
Published: January 2021

The mechanical energy potential of phase‐field fracture models is subdivided into a portion which (actively) drives the crack and a passive portion. This decompositions depends further on the crack state (opened, closed) in order to consider the re‐contact of the crack surfaces. The identification of the crack state and the decomposition is mostly approximated based on splits of the deformation or stress tensor. Stobel and Seelig [1], and Steinke and Kaliske [2] have shown unrealistic predictions for the crack kinematic for those models in quasi‐static and dynamic analyses. The approach proposed by these authors allows to predict the crack kinematic consistently. Nevertheless, this model is restricted to linear, isotropic elasticity and small deformations.

In Storm et al. [3], the underlying concept is generalised. The crack kinematics is consistently obtained from a representative, discrete crack model and coupled to the phase‐field model by means of a variational homogenisation formulation. Thus, the crack driving force is a unique result of the framework of Representative Crack Elements. Analytical solutions for the mechanical problem of the representative crack element applied to linear, anisotropic elasticity and linear thermo‐elasticity at small deformations are presented there.

In the current contribution to the method of phase‐field fracture, the framework for Representative Crack Elements is applied to non‐linear bulk materials. The iterative solution scheme for the representative crack element is presented and applied to elasticity with crack surface friction, visco‐elastic and elasto‐plastic materials.
Rate dependent free energy formulations for dynamically excited superelastic SMA wires
Authors: Kaup Andreas , Altay Okyay , Klinkel Sven
Published: January 2021

Superelastic shape memory alloys (SMAs) are metallic two‐phase polycrystal alloys. The transformation between austenite and martensite phases allows superelastic SMAs unique hysteretic energy dissipation capacity, which is particularly interesting for the development of new‐type of intelligent vibration control systems for structures. However, in structural control, most of the vibrations occur in high strain rate regimes, which interfere the release of self‐generated heat and cause atomic lattice destabilization and thus influence the hysteretic dissipation. The present work proposes two different strain rate dependent free energy formulations and aims to improve the accuracy of existing one‐dimensional macroscopic models of SMA wires. The approaches are developed and implemented in different continuum thermomechanical frameworks, without impairing the simplicity and robustness of the solution process. The first approach introduces an additional control variable for the entropy evolution. The second approach uses a phenomenological formulation of the latent heat evolution. The proposed formulations are validated by cyclic tensile tests conducted on SMA wires. The results show that the calculations using the new formulations can represent the superelastic SMA wire response more accurately.
Semi‐analytical assessment of free‐edge stress fields in cylindrically curved cross‐ply laminated shells
Authors: Kappel Andreas , Mittelstedt Christian
Published: January 2021

The present work deals with the semi‐analytical assessment of the three‐dimensional stress fields in cylindrically curved symmetrically and unsymmetrically cross‐ply laminated shells subjected to bending load. The developed approach incorporates a layerwise plane‐strain analysis in the innermost regions of the shell. The closed‐form ‘inner solution’, further on, is upgraded by a displacement‐based approach that enables an adequate depiction of the interlaminar stresses at the free edge. This so‐called ‘free‐edge solution’ employs a discretization scheme of each lamina into a number of numerical plies with respect to the thickness direction. Herein, the displacement field of each layer is specified via a priori unknown displacement‐ and Lagrangian interpolation functions. By applying the principle of minimum elastic potential, the governing equations can be derived in an exact manner and further on can be solved by employing the state space approach. The results of the higher‐order analysis method are verified through comparison with highly detailed finite element simulations and it is found that the semi‐analytical approach works with comparable accuracy, however, only at a fraction of the required computational effort.
A comparative study of an isotropic and anistropic model to describe the micro‐indentation of TWIP steel
Authors: Sridhar Praveen , R.G. Prasad Mahesh , Bilz Raphael , W. Klein Matthias , Vajragupta Napat , M. de Payrebrune Kristin , Smaga Marek
Published: January 2021

In grinding, the crystal grain size of the workpiece material is relatively same range compared to the removal depth. This raises a question if an anisotropic material model, which considers the effect of the crystal grain size and orientations, would better predict the process forces when compared to an isotropic material model. Initially, a simple micro‐indentation process is chosen to compare the two models. In this work, a crystal plasticity model and an isotropic Johnson‐Cooke plasticity model are employed to simulate micro‐identation of a twinning induced plasticity (TWIP) steel. The results of the two models are compared using the force‐displacement curves from the micro‐indentation experiments. In the future, the study will be extended to describe the material removal process during a single grit scratch test.
Multiscale modeling of distributed microcracking in concrete
Authors: Vu Giao , Timothy Jithender J. , Iskhakov Tagir , Meschke Günther
Published: January 2021

Concrete is a quasi‐brittle material with a heterogeneous morphology across multiple scales, which also influences the evolution of damage in case of loading. Damage in concrete structures is initiated by growth of diffuse microcracks that is followed by damage localization eventually leading to structural failure. Thus, diffuse microcracking processes can be considered as failure precursors. Identification and characterization of these precursors can be applied in conjunction with structural health monitoring based on diffuse ultrasonic waves to develop early warning systems against catastrophic failure of concrete structures. To this end, a multiscale model for a simulation‐based description of diffuse damage in concrete is proposed. At the scale of the cement paste, microcrack growth is modeled by a combination of continuum micromechanics and linear elastic fracture mechanics [1]. The micromechanics model is incorporated into a reduced‐order Lippmann‐Schwinger based meso‐model for concrete [2], [3]. The mesoscale model is generated using Random Sequential Adsorption of realistic aggregates based on concave slicing of randomly cut polyhedrons. The influence of the microcrack morphology at the microscale on the diffuse microcracking and overall concrete stiffness degradation is presented.
An implicit high order finite volume scheme with a posteriori limiting for advection networks
Authors: Eimer Matthias , Borsche Raul , Siedow Norbert
Published: January 2021

In this paper, we describe an implicit high order finite volume scheme for networks of advection equations. Possible oscillations are eliminated using an a posteriori limiting approach. A continuous transition between the different orders is achieved by a convex combination of the numerical fluxes. The scheme shows accurate results even for large CFL numbers.
Fluid‐Structure Interaction of Slender Continua with 3‐Dimensional Flow: An Embedded Finite Element Approach
Authors: Hagmeyer Nora , Mayr Matthias , Popp Alexander
Published: January 2021

The interaction of slender bodies with fluid flow plays an important role in many industrial processes and biomedical applications. The numerical modeling of problems involving such rod‐like structures with classical continuum‐based finite elements poses a challenge because it promptly leads to locking effects as well as very large system sizes. An alternative approach leading to rather well‐posed problems is the use of 1‐dimensional beam theory. Applications of so‐called geometrically exact beam theories have proven to be a computationally efficient way to model the behavior of such slender structures.

This work addresses research questions arising from the application of geometrically‐exact beam theory in the context of fluid‐structure interaction (FSI). In particular, we describe an embedded approach coupling geometrically exact beam finite elements to a background fluid mesh. Furthermore, we elaborate on the conversion between the beam's stress resultants and the 3‐dimensional formulation of the fluid field. A preliminary numerical example will demonstrate the general applicability of the proposed approach for a one‐way coupled problem.
A multiphase model for the cross‐linking of ultra‐high viscous alginate hydrogels
Authors: Diebels S. , Gepp M.M. , Meiser I. , Roland M. , Stracke F. , Zimmermann H.
Published: January 2021

In this study, a model for the cross‐linking of ultra‐high viscous alginate hydrogels is provided. The model consists of four kinetic equations describing the process, including the local accumulation and the depletion of mobile alginate, cross‐linked alginate and cross‐linking cations. For an efficient simulation, finite difference schemes with predictor‐corrector algorithms were implemented.
Representation and stability of internal dynamics
Authors: Lanza Lukas
Published: January 2021

We consider nonlinear multibody systems and present a suitable set of coordinates for the internal dynamics. Furthermore, we derive sufficient conditions on the system parameters of the multibody system such that the internal dynamics are bounded‐input, bounded‐output stable.
Framework for modelling the elastoplastic behaviour of friction welded lightweight structures under tension
Authors: Heppner Eric , Glüge Rainer , Weber Martin , Woschke Elmar
Published: January 2021

Present‐day research in the field of product development are increasingly focused on the efficient use of energy and raw material resources. In the light of this context, the design principle of consistent lightweight construction is gaining more and more importance. One possible approach is the targeted combination of different materials with favourable technological properties in hybrid structures. Against this background, the rotary friction welding (RFW), is particularly advantageous allowing the joining of dissimilar materials, like aluminium and steel in order to create such lightweight structures. The purpose of the paper at hand, is to present a framework for modelling the elastoplastic behaviour of those manufactured structures under the assumption of large deformation and non‐linear material behaviour. Moreover, the presented model was implemented into a finite element analysis program (ABAQUS), in order to simulate a tensile test of a friction welded lightweight structure. Subsequently, the simulation results were critically evaluated using experimental data.
Numerical approach for a continuum theory with higher stress gradients
Authors: Ghasemi Seyed Ali , Muench Ingo , Liedmann Jan , Barthold Franz-Joseph
Published: January 2021

We use an extended balance of linear momentum derived from stress field analysis of higher order terms in power series expansion. Thus, the balance equation accounts for higher gradients of stress in the contiguity of continuum points. Interestingly, it does not coincide with the balance of linear momentum from strain gradient elasticity. As shown in [1], it exhibits an inverse sign for the extended term compared to strain gradient elasticity. We are interested in the mechanical interpretation of this inversed sign since it seems to inverse the stiffening effect of strain gradient elasticity. Therefore, we set up the weak form of our extended balance equation by means of Galerkin's approach. Then, we use the Finite Element Method to approximate the weak form with help of different shape functions. In this context we also use Isogeometric Analysis since it is very promising for a numerical model with higher gradients.
Nonlinear coupled consolidation problem with large strains
Authors: Artamonova Nina , Sheshenin Sergey
Published: January 2021

The consolidation problems involve the study of soil compaction under load with the possibility of liquid outflow [1]. A completely physically and geometrically nonlinear formulation of the consolidation problem is given using the Lagrange approach with adaptation for the solid phase and the Euler approach for the fluid under the assumption of quasistatic deformation of the rock skeleton. Some results of numerical simulation are presented and discussed.
Adaptive Particle Finite Element Method (A‐PFEM) in Metal Cutting Processes
Authors: Ye Xialong , Rodríguez Prieto Juan Manuel , Müller Ralf
Published: January 2021

Machining is very common in industry, e.g. automotive industry and aerospace industry, which is a nonlinear dynamic problem including large deformations, large strain, large strain rates and high temperatures, that implies some difficulties for numerical methods such as Finite element method. One way to simulate such kind of problems is the Particle Finite Element Method (PFEM) which combines the advantages of continuum mechanics and discrete modeling techniques. In this work we introduce an improved PFEM called the Adaptive Particle Finite Element Method (A‐PFEM). The A‐PFEM introduces particles and removes wrong elements along the numerical simulation to improve accuracy, precision, decrease computing time and resolve the phenomena that take place in machining in multiple scales. At the end of this paper, some examples are present to show the performance of the A‐PFEM.
On the boundary element method for Stokes flow in domains with discontinuous boundaries
Authors: Rajski Michal P. , Harmel Maximilian , Sauer Roger A.
Published: January 2021

The classical boundary element method (BEM) has difficulties capturing the solution accurately in the presence of boundary discontinuities. It exhibits higher error values in the proximity of corners than on the rest of the boundary. In an attempt to remedy this problem a two‐dimensional constant uniform flow across a square domain with an outflow condition on one side is considered and analyzed in depth. This leads to the conclusion that the free term from classical approaches needs to be reformulated for the degrees of freedoms lying at the corner points. This modification improves the accuracy of the BEM up to machine precision, which opens interesting directions for further research.
Unimodular transformations for DAE initial trajectory problems
Authors: Trenn Stephan , Unger Benjamin
Published: January 2021

We consider linear time‐invariant differential‐algebraic equations (DAEs). For high‐index DAEs, it is often the first step to perform an index reduction, which can be realized with a unimodular matrix. In this contribution, we illustrate the effect of unimodular transformations on initial trajectory problems associated with DAEs.
Trajectory Planning for Closed Kinematic Chains Applied to Cooperative Motions in Health Care
Authors: Knoll Carsten , Jia Xuehua , Heedt Robert
Published: January 2021

Physical interaction of humans can be a challenging. For some practically relevant situations a reasonable model is given by a closed kinematic chain of a planar rigid body mechanism. From a control perspective a cooperative motion, e. g. assisted standing‐up, can be seen as an optimal control problem (OCP) with input and state restrictions. Due to the algebraic constraints and the comparably high number of joints involved, proper formulation of such a problem is not trivial. In this contribution we compare two different modeling approaches: discretization of the full dynamical problem and iterative solution of consecutive stationary problems. The latter turns out to be significantly faster while still providing – in some sense – optimal solutions.
Material modeling of ferritic steel on microscopic length scale under cyclic loading
Authors: Ahmed Shahbaz , Loehnert Stefan , Wriggers Peter
Published: January 2021

A material model for the polycrystalline microstructure of formable steels is developed to determine the residual stress state resulting from incompatible plastic deformation of individual grains under non‐monotonic loading. The glide of mobile dislocations on a specific slip system mainly governs the shear rates. During the movement, dislocations experience several types of resistance. The existing immobile dislocation structures on non‐parallel slip planes reduce the slip activities. This is reflected in a nonlinear isotropic hardening criterion. Furthermore, piled up dislocations on parallel slip planes also create hindrance to mobile dislocations. This effect creates residual stresses within the material which are taken into account by an additional kinematic hardening law. Residual stresses play a crucial role as well, especially during cyclic loading. Both, nonlinear isotropic and kinematic hardening criteria can define the plastic character of ferritic steel under non‐monotonic loadings.
Two‐Point Velocity Correlations in Fully Developed Turbulent Pipe Flow at Shear Reynolds Number of Reτ ≈ 4000
Authors: Zanoun El-Sayed , Egbers Christoph , Dewidar Yasser
Published: January 2021

The aim of this study is to report about the large‐scale pipe flow structures using the two‐point velocity correlations at a radial location of y/R = 0.5 and 41 azimuthal positions for shear Reynolds number Reτ ≈ 4000. The streamwise velocity component was measured, utilizing two single‐wire probes, simultaneously, based on various azimuthal probe separations. One dimensional pre‐multiplied energy spectra, and two‐point joint statistics were adopted. Both the low and the high wavenumber motions were highlighted using the pre‐multiplied cross‐spectral density. The cross‐power spectral analysis for all the 41 measurement points indicates strong correlation between the hot‐wire signals with small azimuthal separation, on contrary, the peak of the spectrum is getting damped as the azimuthal distance increases. For present shear Reynolds number, the large and the very large scale motions showed wavelengths of ≈ 3R and 14R, respectively, at half of the pipe radius.
Static response of a slightly precurved layered beam with interlayer slip
Authors: Ladurner Dominik , Adam Christoph , Furtmüller Thomas
Published: January 2021

This contribution addresses moderately large deflections of a slightly precurved simply supported beam composed of three layers symmetrically disposed about the central axis. The elastic beam layers are flexibly bonded and thus exposed to interlayer slip. Since the displacements of the supports are fully restrained, the static response is geometrically nonlinear. The results of an application example demonstrates the grave effect of interlayer slip on the nonlinear deflection of slightly precurved layered beams.
How the mathematical understanding of the theory of dynamical systems can be improved with computer‐assisted experimentation
Authors: Gunesch Roland
Published: January 2021

This article presents several examples of how the theory of dynamical systems can be studied by exploration (in particular, by using computer simulations), shows typical cases where the inclusion of computer tools is useful for learning and understanding these dynamical systems, and also points out typical difficulties and limitations of this approach.

The application of computer simulations to the study of the theory of dynamical systems is a particularly interesting case of seamless learning.
Bestrophin‐derived peptide, WP17, elicits cell wall disruption‐mediated bactericidal activity against Micrococcus luteus and anti‐neoplastic effect against murine melanoma cells
Authors: Ravichandran Gayathri , Raju Stefi V. , Sarkar Purabi , N. T. Saraswathi , Al Olayan Ebtesam M. , Aloufi Abeer S. , Elokaby Mohamed A. , Arshad Aziz , Mala Kanchana , Arockiaraj Jesu
Published: January 2021

The cDNa sequence of Bestrophin‐1 (BEST‐1) was identified from a previously constructed transcriptome data set of freshwater prawn Macrobrachium rosenbergii (Mr). Basal and temporal gene expression analysis of MrBEST‐1 showed its antimicrobial immune effectiveness during viral and bacterial infections. The protein sequence encoded by cDNA of MrBEST‐1 was examined and a short antimicrobial molecule, named WP17 was identified using a bioinformatics tool. Further, the antibacterial ability of the identified WP17 peptide was evaluated against a number of bacterial strains, in which the peptide showed potential bactericidal activity against Micrococcus luteus (MTCC 6164), Staphylococcus aureus (ATCC 9144), Escherichia coli (ATCC 9637), Klebsiella pneumonia (CI 7376) and Bacillus subtilis (ATCC 6051). Based on the results, further assays focused on M. luteus MTCC 6164. The mode of action of MrWP17 on M. luteus MTCC 6164 was analyzed using FACS and FESEM. Toxicity analysis suggested that WP17 impaired the viability of cells in murine melanoma cells (B16F10); however, no cytotoxicity was observed against kidney embryonic cells (HEK293), even at higher concentrations. Similarly, the gene expression analysis of WP17 peptide treated murine cells elicited an extrinsic apoptotic pathway. In the present study, we have demonstrated the involvement of MrBEST‐1 in immune mechanisms through its short peptide molecule that has potential antimicrobial activity.
What’s really in a deal? Evidence from textual analysis of M&A conference calls
Authors: Hu Wenyao , Shohfi Thomas , Wang Runzu
Published: January 2021

Using a sample of 814 transcripts from 2011 to 2018, we examine information within merger and acquisition conference calls. Textual analysis reveals significant differences between the content of M&A call transcripts and both contemporaneous corporate press releases and prior earnings conference calls. We find participation of target executive types in M&A calls occurs more frequently in diversifying acquisitions and is related to payment choice consistent with promoting managerial sector‐specific skills and incentive alignment, respectively. Retention of participating target executives is associated with a negative market reaction. We also identify a negative relation between textual sentiment and market reaction consistent with a response to higher levels of information asymmetry. Greater quantitative information, however, is positively related to the market reaction of M&A calls. We develop targeted M&A motive dictionaries to identify financial and strategic content within call transcripts. Consistent with prior literature on merger motivation, deals with more finance (strategy)‐oriented words have a higher (lower) market reaction. Overall, our results show that deal‐related textual analysis explains a highly significant and economically important component of gains/losses to acquirers.
Nutzen und Risiken psychiatrischen Handelns und das Selbstbestimmungsrecht des Patienten
Authors: Helmchen Hanfried
Published: January 2021

Die Geschichte der Psychiatrie zeigt, dass ein Selbstbestimmungsrecht des psychisch Kranken im 19. Jahrhundert weitgehend unbekannt war, erst spät in der 2. Hälfte des 20. Jahrhunderts mit dem rechtlichen Konzept der Einwilligung nach Aufklärung, dem „informed consent“, in der Medizin bekannt wurde und seit Beginn des 21. Jahrhunderts in der medizinischen Praxis zunehmend wahrgenommen und respektiert wird; diese Wahrnehmungsänderung trägt zu einem Wandel von einer paternalistischen zu einer partizipativen ärztlichen Einstellung bei. Im Kontext einer emanzipatorischen Entwicklung der Gesellschaft nimmt mit den wachsenden Möglichkeiten wirksamer Therapien, die selten ohne Risiken sind, die Notwendigkeit zu, den Patienten über den intendierten Nutzen und potenzielle Risiken der empfohlenen Intervention zu informieren und ihm damit die Voraussetzung zu schaffen, sein Selbstbestimmungsrecht wahrzunehmen. Zudem wachsen mit dem Übergang von einer sehr erfolgreichen Akutmedizin mit allerdings oft nur kurzem Arzt-Patienten-Kontakt zur Langzeitmedizin chronischer Erkrankungen die Möglichkeiten, den Patienten, insbesondere den psychisch Kranken, seine individuellen Eigenheiten, seine Einschränkungen und Fähigkeiten besser wahrzunehmen, ihn als Individuum, als Menschen in seiner jeweiligen Eigenart zu erleben und sein Selbstbestimmungsrecht zu respektieren, indem wir ihm dabei helfen, Nutzen und Risiken einer empfohlenen Intervention zu verstehen und selbstbestimmt abzuwägen.
Versorgungswirklichkeit der urologischen Endoprothetik in Deutschland von 2006 bis 2016
Authors: Baunacke Martin , Groeben Christer , Borkowetz Angelika , Uhlig Annemarie , Leitsmann Marianne , Volkmer Björn , Thomas Christian , Huber Johannes
Published: January 2021

Hintergrund

Die Behandlung von Harninkontinenz und erektiler Dysfunktion verbessert die Lebensqualität vieler Patienten. Insbesondere die Endoprothetik mit Sphinkter- und Penisprothesen erzielt hierbei sehr gute Ergebnisse, wenn konservative Therapieoptionen ausgeschöpft sind. Ziel dieser Studie ist eine Darstellung der Entwicklung und aktuellen Versorgungslage der Sphinkter- und Penisprothesenimplantation in Deutschland.

Material und Methoden

Wir führten eine Analyse der Diagnosis-Related-Groups-Abrechnungsdaten in Deutschland im Zeitraum von 2006 bis 2016 durch. Die Versorgungslage im Jahr 2016 beschrieben wir auf Basis der Qualitätsberichtsdaten der deutschen Krankenhäuser.

Ergebnisse

Von 2006 bis 2012 stieg die Zahl der implantierten Sphinkterprothesen in Deutschland von 739 auf 1112 (p < 0,001) und die Zahl der implantierenden Kliniken von 129 auf 206 (p < 0,001). Von 2012 bis 2016 fielen die Fallzahlen auf 980 und die Zahl der Kliniken auf 198. Im Jahr 2016 implantierten 168 (88 %) urologische Kliniken 1–9 Sphinkterprothesen und 23 (12 %) Kliniken ≥ 10 Sphinkterprothesen. Die 10 Top-Kliniken (≥20 Sphinkter) implantierten 34 % (283/839) aller Sphinkter. Von 2006 bis 2013 stieg die Zahl der implantierten Penisprothesen kontinuierlich von 263 auf 503 (p < 0,001) sowie die Zahl der implantierenden Kliniken von 71 auf 107 (p < 0,001). Von 2013 bis 2016 stagnierte die Fallzahl (p = 0,9) und die Zahl der implantierenden Kliniken (p = 0,5). Der Anteil implantierter Penisprothesen im Rahmen von Geschlechtsumwandlungen stieg von 17 % im Jahr 2006 auf 25 % im Jahr 2016 (p = 0,03). Im Jahr 2016 implantierten 83 (85 %) urologische Kliniken 1–6 Penisprothesen und 14 (15 %) Kliniken ≥ 7 Prothesen. Die 7 Top-Kliniken (≥20 Prothesen/Jahr) implantierten 232/448 (52 %) der Prothesen.

Diskussion

Der Versorgungsstand der urologischen Endoprothetik in Deutschland zeigt eine deutliche Zentrenbildung, aber auch eine große Zahl von Kliniken mit geringer Fallzahl. Seit 2012/2013 zeigt sich eine Stagnation der Fallzahlen von Penis- und Sphinkterprothesenimplantationen, die in Zusammenschau mit den Prostatektomiefallzahlen eine Unterversorgung vermuten lässt.
The Role of Portable Incisional Negative Pressure Wound Therapy (piNPWT) in Reducing Local Complications of Post-bariatric Brachioplasty: A Case-Control Study
Authors: Facchin Federico , Pagani Andrea , Marchica Paolo , Pandis Laura , Scarpa Carlotta , Brambullo Tito , Bassetto Franco , Vindigni Vincenzo
Published: January 2021

Background

Due to the great impact of bariatric surgery on the overweight epidemic, the number of post-bariatric body-contouring procedures is constantly increasing worldwide. The portable incisional negative pressure wound therapy (piNPWT) is a promising medical device for accelerating wounds closure and controlling post-operative complication, which have been shown promising results in post-bariatric population. We aimed to evaluate the role of piNPWT in optimizing wound healing and controlling post-operative complications after a post-bariatric brachioplasty.

Patients and Methods

26 post-bariatric female patients who underwent a brachioplasty followed by either a piNPWT (14 cases) or a standard wound treatment (12 controls) were analyzed. The number of post-operative dressing changes, the rate of local post-operative complications (re-operation, hematoma and serosa development, dehiscence and necrosis), the time to dry as well as the scar quality and hospitalization length were evaluated.

Results

None of the patients prematurely stopped treatment with piNPWT due to intolerance. The piNPWT patient group showed a significant lower healing time as well as a significant reduction of the number of post-operative dressing changes and hospital stay. Despite the scarring process was excellent from the functional point of view in the long term, we noticed a higher rate of hyperchromic scarring at 90 days after surgery.

Conclusion

The piNPWT is a cost-effective and user-friendly medical tool that increase and promote wound healing. We suggest the use of this device in post-bariatric patients who undergo a brachioplasty, especially if there is the need to minimize the number of post-operative dressing changes.

Level of Evidence IV

This journal requires that authors assign a level of evidence to each article. For a full description of these evidence-based Medicine ratings, please refer to Table of Contents or the online Instructions to Authors www.springer.com/00266.