bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigating the Effect of Complex Particle Shapes in Partially Liquid‐Filled Particle Dampers using Coupled DEM‐SPH Methods
Authors: Gnanasambandham Chandramouli , Eberhard Peter 
Published: November 2019

AbstractThe process of energy dissipation in particle dampers (PDs) occurs mainly due to relative motion between solid particles within the damper container. The degree of relative motion between solid particles is especially sensitive to vibration amplitude changes. As the vibration amplitude decreases, less relative motion between solid particles is observed, leading to a drastic decrease in the damping performance of PDs. In this work a new approach is investigated, in which the damper contains a combination of both solid and liquid fillings, to overcome the shortcomings of a conventional PD. In order to better understand the underlying energy dissipation mechanisms a simulation model of a partially liquid‐filled particle damper with complex non‐convex shapes is set up. The liquid motion is modeled using the Smoothed Particle Hydrodynamics (SPH) method and the Discrete Element Method (DEM) is used to model the motion of solid particles. A numerical experiment is set up, where a particle damper is attached to a one degree of freedom spring‐mass‐damper system. By analysing the free response behavior of this system, the energy dissipated in various PD configurations is compared. Simulation results show more relative motion, hence more energy dissipation, in the liquid‐filled PD case than in the purely solid filled and purely liquid PD case, especially under low vibration amplitudes. Moreover, numerical studies were performed using a coupled SPH‐DEM approach to study the effect of the particle shape on the energy dissipation in liquid‐filled particle dampers.
Evaluation of source signature during Full Waveform Inversion for seismic reconnaissance in tunneling
Authors: Riedel Christopher , Musayev Khayal , Baitsch Matthias , Hackl Klaus 
Published: November 2019

AbstractBy transmitting seismic waves in the ground the spread, reflected and refracted waves can be recorded at different positions. The arising seismograms contain information of the geology, which can be evaluated with the Full Waveform Inversion (FWI). For the application of FWI for reconnaissance in tunneling extensive information has to be provided to achieve an appropriate model of the geology in front of the tunnel face. Such information are the position and geometry of reflecting boundaries, exact position of sources and receivers, a proper initial model of the distribution of the material parameters. The signal, which is transmitted by the senders, has also an influence on the inversion. Even if the intended source function is known, the effective signal depends on the transfer functions between sender‐soil and soil‐receiver and its identification is challenging. To avoid cumbersome investigations on the source function in advance we applied a simultaneous identification of the source signature during the FWI in the frequency domain. For synthetic models of a 2D tunnel configuration with disturbances, we will show how the calculated source signature of a frequency converges to the real source signature during the iterations of the FWI. The influence of different sender and receiver configurations will be analyzed. Furthermore, the influence of the simultaneous evaluation of the source signature on the results of the FWI will be evaluated. In a post‐processing step of the FWI, the source signature of the whole frequency spectrum will be determined.
A Navier‐Stokes‐Korteweg Model for Dynamic Wetting based on the PeTS Equation of State
Authors: Diewald Felix , Heier Michaela , Lautenschläger Martin , Horsch Martin , Kuhn Charlotte , Langenbach Kai , Hasse Hans , Müller Ralf 
Published: November 2019

AbstractDynamic wetting of component surfaces can be investigated by finite element phase field simulations. Often these models use a double‐well potential or the van der Waals equation to define the local part of the free energy density at a point of the computational domain. In order to give the present model a stronger physical background the molecular dynamics based perturbed Lennard‐Jones truncated and shifted (PeTS) equation of state is used instead. This results in phase field liquid‐vapor interfaces that agree with the physical density gradient between the two phases. In order to investigate dynamic scenarios, the phase field description is coupled to the compressible Navier‐Stokes equations. This coupling requires a constitutive equation that complies with the surface tension of the liquid‐vapor interface resulting from the PeTS equation of state and is comparable to the so‐called Korteweg tensor.
Simulation of vibrational sources and vibroacoustic transfer in wind turbine drivetrains
Authors: Ihlenburg Frank , Zarnekow Marc , Grätsch Thomas 
Published: November 2019

AbstractTonal effects in the noise radiation from wind turbines can be traced back to mechanical sources within the drivetrain. A hybrid analytical‐numerical model for the gear transmission error is used to generate the vibrational source for a large‐scale vibroacoustic FE model of a wind turbine drivetrain, and a case study of transfer path analysis is presented.
On the energetics of dynamic cohesive crack formation
Authors: Laschütza Tobias , Seelig Thomas 
Published: November 2019

AbstractDynamic fracture under static loading, as it takes place in the absence of a perfect pre‐crack, is studied from simple 1D and 2D examples. Special emphasis is placed on the cohesive fracture energy which gives rise to a finite duration of the fracture process and – in conjunction with the material's tensile strength – introduces a material specific length scale.In case of the 2D problem (plate with hole under remote tension/compression), a (quasi‐)spontaneous formation of the finite crack increment, as predicted by FFM, can only be identified for compressive loading (stable crack growth). For tensile loading (unstable crack growth), a non‐monotonic dependence of the crack velocity on the hole radius was observed, attributed to a competition between the effects of crack initiation under higher overall stress for smaller holes and a comparatively larger process zone w.r.t. the hole radius.
Numerical Analysis of Fluid‐Film‐Cavitation on Rotordynamic Vibration and Stability Behavior
Authors: Dong Huaxin , Nowald Gerrit , Lu Daixing , Schweizer Bernhard 
Published: November 2019

AbstractThe dynamic vibration and stability behavior of a rotor supported in journal bearings is investigated. In the lubricating film of a hydrodynamic bearing, different cavitation phenomena may occur. Cavitation in hydrodynamic bearings is most commonly caused by surrounding air, which is sucked into the bearing gap and also by outgassing of dissolved gases. Cavitation effects have to be considered in order to precisely analyze the performance of rotor/bearing systems. Numerous approaches have been proposed to treat cavitation using appropriate boundary conditions in the REYNOLDS fluid film equation, which is applied to calculate the hydrodynamic pressure distribution in the bearing gap. These approaches are generally divided into two types: non mass‐conserving and mass‐conserving cavitation models. In this paper, a mass‐conserving cavitation model based on a 2‐phase approach (lubricant/air mixture) is applied. For the 2‐phase model, a relationship has to be defined that describes the dependency between density of the oil/gas‐mixture and the pressure. Different density/pressure models are presented and discussed. Numerical run‐up simulations are performed to study the stability of rotor/bearing systems incorporating different cavitation models. The numerical model for the rotor/bearing system consists of a multibody model for the rotor and a finite element model for the fluid film. Both models are coupled by a co‐simulation approach. The different cavitation models are compared. The influence of the cavitation model and the cavitation parameters on the stability behavior of the rotor/bearing system are analyzed. The cavitation approaches are also compared with respect to accuracy and efficiency.
From cybernetics to mechatronics: Seven decades of interdisciplinary engineering
Authors: Schiehlen Werner 
Published: November 2019

AbstractCybernetics is a transdisciplinary approach for exploring controlled systems. Norbert Wiener defined cybernetics in 1948 as “the scientific study of control and communication in the animal and the machine”. Mechatronics unites the principles of mechanics, electronics and computing to generate simpler, more economical and reliable systems. An industrial robot is a prime example of a mechatronic system, it includes aspects of mechanics, electronics, and computing to do its day‐to‐day jobs. The high reputation of mechatronics as a science was recently underlined by a mark of distinction for Kurt Magnus with a commemorative plaque erected by the foundation Stiftung‐Werner‐von‐Siemens‐Ring and unveiled 2018 at the Technical University of Munich. The Stiftung Werner‐von‐Siemens‐Ring honored the scientific work of Kurt Magnus with respect to “gyroscopes and vibrations as well as co‐founder of mechatronics” including nonlinear oscillations, too.
A Brief Historical Tour of Glacier Ice on Earth and its Role in Climate Dynamics
Authors: Gross Dietmar , Hutter Kolumban 
Published: November 2019

AbstractThis paper provides short excerpts of the beginnings of glacier ice research. It is restricted to the period from the beginnings in the 17th century up to the formulation of a flow law in the fifties of the forgoing century. Its role in climate research is not touched; it will be discussed in another publication.
Soil Mechanical Influence on Numerical Foundation Design of Tower Cranes
Authors: Müllner Herbert W. , Meister Herbert R. 
Published: November 2019

AbstractThe static design of foundations for tower cranes is mostly based on calculations of structural safety. Nevertheless further investigations considering the interaction between soil and structure including settlement calculations for evaluating the inclination of the crane are essential for safe and economic foundation solutions. Based on the experience of more than 150 tower crane positions throughout Europe a method has been developed satisfying the normative and crane specifically requirements and meeting the standards of one of the biggest building contractors in Europe.
Filtering and Model Reduction of PDAEs with Stochastic Boundary Data
Authors: Stahl Nadine , Marheineke Nicole 
Published: November 2019

AbstractIn this paper we investigate state reconstruction for gas pipeline networks using model hierarchies derived from model order reduction techniques. The pipeline network is described by partial differential algebraic equations (PDAEs), for which model order reduction was extensively studied in [1]. We use and extend upon the aforementioned results to estimate the system state, when the boundary data is perturbated by an Ornstein‐Uhlenbeck process. We study the performance of state reconstruction based on the derived model hierarchy. Of special interest, hereby, is the relationship between the quality of the state estimation and the underlying reduced order model.
CANFIS‐Based Semi‐active Vibration Control of Stochastically Excited High‐Rise Civil Engineering Structures with Nonlinearities and Uncertainties
Authors: Altay Okyay , Klinkel Sven 
Published: November 2019

AbstractThis study introduces a co‐active neuro‐fuzzy inference system (CANFIS) based vibration control strategy for high‐rise civil engineering structures, such as buildings, wind turbines and towers. The proposed approach uses semi‐active dampers, which are distributed in the structure. Attached to the structural members, semi‐active dampers generate adaptive restoring forces to reduce the structural vibrations by autonomously tuning their parameters. The nonlinear behavior and the uncertainties involved in the mathematical models of both the semi‐active dampers and the structures require sophisticated control strategies. Previous studies have shown that fuzzy logic controllers (FLCs) can overcome these challenges and perform effectively with semi‐active dampers to mitigate the structural vibrations. Nevertheless, FLCs require a predefined parameter tuning of their fuzzy rules and membership functions, which must be performed based on the knowledge of a human expert. Combining FLCs with artificial neural networks (ANNs), hybrid systems are proposed, which can determine the parameters of FLCs by using learning based training and adaptation strategies of ANNs. However, there is only limited research investigating the performance of these adaptive systems in the field of vibration control of civil engineering structures. The present work is concerned with a numerical formulation of such an adaptive system, in particular the CANFIS, and its implementation on a non‐linear seismically excited three‐story steel benchmark building with semi‐active dampers. To determine the premise parameters of the membership functions and the consequent parameters of the fuzzy rules a hybrid training method is performed using the recursive least‐square algorithm and the steepest descent method. Investigations with historic earthquakes show a significant reduction of the roof displacements of the building. For instance, during the Hachinohe earthquake the peak value of the displacement is reduced by 87 %.
An anisotropic brittle damage model with a damage tensor of second order using a micromorphic approach
Authors: Fassin Marek , Eggersmann Robert , Wulfinghoff Stephan , Reese Stefanie 
Published: November 2019

AbstractThe work presents a gradient‐extended ansisotropic damage model for brittle materials utilizing a second order damage tensor. In order to take into account tension compression asymmetry (TCA), the strain tensor is split into a tension and a compression related part by means of a spectral decomposition. The formulation is based on a global incremental potential allowing for large time/load steps. The gradient extension is accomplished using the micromorphic approach. Although using a damage tensor of second order, only one scalar additional degree of freedom (micromorphic variable) is introduced. First, the effects of TCA are illustrated with a simple uniaxial loading case at integration point level. Afterwards, the effect of the additionally introduced artificial viscosity, used in order to circumvent snapback situations, is shown for a structural example (without TCA). Finally, a structural example considering TCA is presented for which spurious failure in compression can be avoided.
Water‐induced failure mechanics for concrete
Authors: Aldakheel Fadi , Tomann Christoph , Lohaus Ludger , Wriggers Peter 
Published: November 2019

AbstractThis work outlines a micro‐mechanical framework for modeling water‐induced damage mechanism of concrete. Concrete has a highly heterogeneous micro‐structure and its composite behavior is very complex. Due to that various effects must be considered for analyzing failure response at micro scale, e.g. modeling the solid skeleton, fluid bulk phases and their interaction. For obtaining a deeper understanding of the influence of water on the concrete at the micro‐level, a micro‐computed‐tomography (micro‐CT) scan has been conducted at IfB to illustrate the micro‐structure geometry and concrete content. These data are required to build the constitutive model and the design of the numerical simulations, in line with [1]. Then a micro‐mechanical model is developed for the coupled problem of fluid‐saturated heterogeneous porous media at fracture. The modeling of microscopic cracks in porous heterogeneous media can be achieved in a convenient way by a continuum phase‐field approach, which is based on the regularization of sharp crack discontinuities [2,3]. This avoids the use of complex discretization methods for crack discontinuities, and can account for complex crack patterns. The numerical examples proposed in this contribution stem out from the DFG Priority Program SPP 2020 “Cyclic Damage Processes in High‐Performance Concretes in the Experimental Virtual Lab”.
A new domain‐based implicit‐explicit time stepping scheme based on the class of exponential integrators called sEPIRK
Authors: Straub Veronika , Ortleb Sigrun , Birken Philipp , Meister Andreas 
Published: November 2019

AbstractReliable simulations of flows in real applications involve the task of discretizing both space and time in an accurate and efficient way. To cope with the large semidiscrete systems resulting from a space discretization on appropriate grids, which often include comparatively few very small cells near solid walls for boundary layer resolution, an implicit‐explicit time stepping scheme can be the most efficient variant. We present such a type of scheme utilizing recent exponential integrators called sEPIRK and show its computational advantages opposed to IMEX‐Runge‐Kutta schemes.
On predictive modelling of yield stress increase in fresh cement paste
Authors: Huang Haiqin , Zilian Andreas 
Published: November 2019

AbstractFreshly mixed concrete is composed of cement paste as fluid‐like component and aggregates as solid particulate component. Development of yield stress in fresh mortar is significant for reliable and high‐quality concrete operation as too low or too high yield stress causes process‐ability challenges like the multi‐layer problem, aggregate flocculation or blockage. Traditional experimental tests on the evolution of yield stress are costly since a wide spectrum of different material and environmental conditions needs to be studied. Progressing hydration, thermal effects and mechanical loading/unloading may influence spatial distribution of the apparent yield stress. However, this local information is very difficult to obtain using traditional laboratory tests and virtual fresh concrete testing is therefore promising.In the context of a single‐component flow approach to homogenized modelling of the cement paste composition at the macro‐scale, the microstructural evolution affecting the development and distribution of apparent yield stress is taken into account by a thermo‐chemo‐mechanical phase‐field model bridging the micro‐macro length scales by using a Ginzburg‐Landau‐type free energy function. The phase‐field, that describes the smooth spatial transition between fluid‐like and solid‐like behaviour of cement paste in the setting phase, is governed by bond‐building chemical processes (hydration) and reversely‐acting mechanical effects (bond breakup). The resulting set of coupled nonlinear advection‐reaction‐diffusion equations are formulated in the Eulerian framework and discretized in space using the weighted residuals method and finite differences in time. Implementation of the predictive model is demonstrated using the FEniCS framework, together with numerical examples supporting model validation.
Mechanical properties assessments of as‐cast light alloys predicted by a new size‐sensitive variant of Differential Effective Medium theory
Authors: Parashkevova Ludmila , Drenchev Ludmil 
Published: November 2019

AbstractThe presented analytical approach is aimed to evaluate the mechanical properties of multiphase alloys regarded as “in situ” multiphase composites. The materials of interest are composites with high volume fraction of phases embedded into the micropolar matrix. According to the two‐steps homogenization procedure adopted, the multiphase Representative Volume Element (RVE) is equivalent to a RVE containing several pseudo grains. Each pseudo‐grain is a two‐phase composite with predominant non‐matrix phase. The new size‐ sensitive variant of Differential Effective Medium (DEM) homogenization scheme for a two‐phase composite is described in close form for sphere‐like inclusions. The particular case when the inclusions and the matrix have one and the same bulk modulus is applied to model the elastic behaviour of cast Mg alloys with discontinuous precipitations. The analytical solutions obtained for a composite with zero bulk modulus of inclusions are appropriate for modelling of high porosity materials with closed cells.
Multi‐Fidelity Optimization using Reduced Order Models
Authors: Tolle Kevin , Marheineke Nicole 
Published: November 2019

AbstractOptimal control problems constrained to nonlinear partial differential equations appear in many applications. Because the discretization of these problems leads to large‐scale systems, a direct approach is not always viable. We consider the aggressive space‐mapping approach using surrogate models derived with the help of model order reduction techniques in order to efficiently solve such problems, while maintaining an acceptable accuracy. Numerical results based on a medical application (laser‐induced thermotherapy) are used to evaluate the effectiveness of the proposed approach.
Efficient reliability analysis coupling importance sampling using adaptive subset simulation and PGD model reduction
Authors: Robens-Radermacher Annika , Unger Jörg F. 
Published: November 2019

AbstractOne of the most important goals in civil engineering is to guaranty the safety of constructions. National standards prescribe a required failure probability in the order of 10−6 (e.g. DIN EN 199:2010‐12). The estimation of these failure probabilities is the key point of structural reliability analysis. Generally, it is not possible to compute the failure probability analytically. Therefore, simulation‐based methods as well as methods based on surrogate modeling or response surface methods have been developed. Nevertheless, these methods still require a few thousand evaluations of the structure, usually with finite element (FE) simulations, making reliability analysis computationally expensive for relevant applications.The aim of this contribution is to increase the efficiency of structural reliability analysis by using the advantages of model reduction techniques. Model reduction is a popular concept to decrease the computational effort of complex numerical simulations while maintaining a reasonable accuracy. Coupling a reduced model with an efficient variance reducing sampling algorithm significantly reduces the computational cost of the reliability analysis without a relevant loss of accuracy.
The explicit jump discretization with Lippmann‐Schwinger solvers for thermal computational homogenization problems
Authors: Dorn Christian , Schneider Matti 
Published: November 2019

AbstractWe present a Lippmann‐Schwinger equation for the explicit jump discretization of thermal computational homogenization. Our solution scheme is based on the fast Fourier transform and thus fast and memory‐efficient. We reformulate the explicit jump discretization using harmonically averaged thermal conductivities and obtain a symmetric positive definite system. Thus, a Lippmann‐Schwinger formulation is possible. In contrast to Fourier and finite difference based discretization methods the explicit jump discretization does not exhibit ringing and checkerboarding artifacts.
Investigation of elastic grinding pins
Authors: Lamping Frederik , de Payrebrune Kristin 
Published: November 2019

AbstractIn order to develop a grinding tool for shape adaptive grinding, elastic grinding pins are used as an example to investigate the behaviour of those tools. In the following, we describe the results for test tubes machined with elastic grinding pins. Therefore, the surface profile of the test tubes is analysed for different parameter sets. The varied parameters are the size of the grinding particles and the stiffness of the base material.The interdependencies between the parameters are as expected: larger particles and stiffer material lead to a rougher surface. This is the case for both acrylic glass and steel tubes. However, irregularities in the uniformity of the specimens surface indicate that the manufacturing process has still to be improved at different points.