bluuebunny/crossref_metadata_2025_split huggingface dataset:
Variational integrator for constrained mechanical systems with pulsed disturbances and optimal feedback control
Authors: Glaas Daniel , Leyendecker Sigrid 
Published: March 2018

AbstractAn approach to minimize the control costs and ensuring a stable deviation control is the Riccati controller and we use it to control constrained dynamical systems (differential algebraic equations of Index 3) with pulsed disturbances. To describe their discrete dynamics, a constrained variational integrator [1] is used. Using a discrete version of the Lagrange‐d'Alembert principle yields a forced constrained discrete Euler‐Lagrange equation in a position‐momentum form that depends on the current and future time steps [2]. The desired optimal trajectory (qopt, popt) and according control input uopt is determined solving the discrete mechanics and optimal control (DMOC) algorithm [3] based on the variational integrator. Then, during time stepping of the perturbed system, the discrete Riccati equation yields the optimal deviation control input uR. Adding uopt and uR to the discrete Euler‐Lagrange equation causes a structure preserving trajectory as both DMOC and Riccati equations are based on the same variational integrator. Furthermore, coordinate transformations are implemented (minimal, redundant and nullspace) enabling the choice of different coordinates in the feedback loop and in the optimal control problem. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Dynamic Programming Approach for Time‐Optimal Path Following of Robots Considering Speed Dependent Torque Constraints
Authors: Oberherber Matthias , Gattringer Hubert , Müller Andreas 
Published: March 2018

AbstractTime‐optimal path following, i.e. moving a robot's end‐effector optimally along a specified geometric path, is a very important and well discussed problem in robotics. Nevertheless, most of the existing approaches concerning this topic neglect the speed dependency of torque constraints. The present paper presents a method for taking such constraints into account within a dynamic programming approach. To this end, the problem is treated in parameter space. This allows for an optimal use of existing resources. Due to the demanding constraints, precise mathematical models of the robots are indispensable. A satisfying match between model and real system can usually be achieved by parameter identification. For this purpose, it is a common way to derive the equations of motion using nominal parameters (masses, position of center of gravity, inertia and friction parameters), rewrite the equations in terms of linearly independent base parameters, and determine them with the help of measurements. Nevertheless, a parametrization of the motor torques has to be introduced in order to be able to consider their constraints within the optimization. In contrast to this, we present a general toolchain, based on the Projection Equation that directly derives the base parameter representation and furthermore the coefficients of the parametrized equations of motion. A verification in terms of a numerical example for a six‐axis industrial robot demonstrate why speed dependent torque constraints are preferable over constant torque constraints for time‐optimal robot trajectories. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Interface‐Reduction for Substructured Mechanical Systems with Constraints Using General Singular Value Decomposition
Authors: Walker Nadine , Eberhard Peter 
Published: March 2018

AbstractModel order reduction is widely used in the simulation of elastic bodies. In substructured settings, model order reduction using moment matching methods has shown to be advantageous. Using these methods, the minimal order of the reduced system depends directly on the number of interactions. This motivates the use of interface reduction methods. In this contribution an approach for interface reduction using a general singular value decomposition (GSVD) is presented. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Variational integrators of mixed order for constrained and unconstrained systems acting on multiple time scales
Authors: Wenger Theresa , Ober‐Blöbaum Sina , Leyendecker Sigrid 
Published: March 2018

AbstractThe considered systems contain dynamics on different time scales caused by different types and stiffnesses in potentials. For the slow motion, a coarse approximation suffices, but to resolve the fast motion, high accuracy is required. To avoid unnecessarily high computational costs, the idea here is to use polynomials of different degrees to approximate the slow and fast dynamics and quadrature formulas of different orders to approximate the different action terms. The approach is extended to holonomically constrained systems, where the Lagrange multiplier theorem is used to introduce constraint forces constraining the motion to the constraint manifold. The computational efficiency of the integrators is shown by means of two examples. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis and Optimization of Inlet and Outlet Boundary Conditions for Flow Simulations in Circle of Willis
Authors: Alimi Aria , Wünsch Olaf 
Published: March 2018

AbstractBlood flow simulation of complex arterial networks in three‐dimensions generally involves assigning multiple inlets and outlets. This work investigates different kinds of boundary condition assigned on inlets and outlets in the Circle of Willis. These boundary conditions will be adopted in a way that a realistic velocity profile and pressure in the main brain arteries are achieved. The result of this work will be used for Fluid–structure interaction simulations. As the force applied on the artery wall depends on the blood pressure, the goal is to achieve a pressure boundary condition based on the in‐vivo flow rates in each artery. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The influence of binder mobility on the viral entry into a cell
Authors: Klinge Sandra , Wiegold Tillmann , Holzapfel Gerhard A. , Gilbert Robert P. 
Published: March 2018

AbstractThe current contribution deals with the simulation of the viral entry into a cell. There are two dominant mechanisms typical of this process: the endocytosis and the fusion with the cellular membrane. However, we only focus on the first scenario. To this end, we consider a virus as a substrate with a constant concentration of receptors on the surface. Opposite to this, the concentration of receptors of the host cell varies and these receptors are free to move over the membrane. When the contact with the cell surface has been achieved, the receptors start to diffuse to the contact (adhesion) zone. The membrane in this zone inflects and forms an envelope around the surface of the virus. This is the way the newly formed vesicle imports its cargo into the cell. In order to simulate the process described, we assume that the differential equation typical of the heat transport is suitable to simulate the diffusion of receptors. We also formulate two boundary conditions: First, we consider the balance of fluxes on the front of the adhesion zone. Here, it is supposed that the velocity is proportional to the gradient of the chemical potential. The second subsidiary condition is the energy balance equation depending on four different contributions: the energy of binding receptors, the free energy of the membrane, the energy due to the curvature of the membrane and the kinetic energy due to the motion of the front. The differential equation itself along with two boundary conditions forms a well‐posed problem which can be solved by applying a direct method, for example the finite difference method. The contribution also includes numerical examples showing the distribution of receptors over the membrane as well as the motion of the front of the adhesion surface. The influence of the mobility of receptors has been studied in particular. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Multi‐scale and Multi‐phase Model for the Description of Toxicity caused by Paracetamol in Biological Tissue using the Example of the Human Liver
Authors: Lambers Lena , Waschinsky Navina , Werner Daniel , Ricken Tim 
Published: March 2018

AbstractThe human liver is the most important organ according to metabolism processes in the human body and responsible for the detoxification of medications and toxins. During detoxification processes the harmful components are transported via the blood perfusion and metabolised in the liver cells. Toxic amounts of drugs can harm the liver and affect the important liver functions. The critical dose of medications varies due to different individual preconditions of the human body. Additionally the detoxification can be affected by several liver diseases for example a non‐alcoholic fatty liver disease (NAFLD). To analyse the depletion of medicines and the interaction between the detoxification and NAFLD, we use a multi‐scale and multi‐phase model to calculate the hepatotoxicity in the human liver using the example of the pain killer paracetamol. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On a Tri‐Scale and Multiphase Model for the Description of Perfusion coupled to Fat Growth Effects in Liver Tissue
Authors: Waschinsky Navina , Werner Daniel , Ricken Tim , Dahmen Uta , Dirsch Olaf 
Published: March 2018

AbstractIn the European Union, fatty degeneration of the liver is a major problem in human health care. Approximately 20% to 30% of individuals in Western countries have a non‐alcoholic fatty liver disease (NAFLD). The high number of people concerned can be explained by the high sensitivity of the liver due to negative environmental influences as addiction to high fat diets or alcohol consumption. High fat diets are the leading cause for NAFLD (steatosis), which is characterized by an accumulation of lipid droplets in the liver tissue. The growing fat has a high impact on the perfusion of the blood through the liver. The anatomy of the organ is characterized by a complex vascular system which changes on the different scales from a vascular branching tree to micro vessels, called sinusoids, in liver lobules. To capture the interplay between fat deposition arising in the microstructure and the perfusion on the organ scale it is important to couple the processes on each scale. For this we present a computational model for the human liver which is composed of three coupled sub models for the organ, lobule and cell scale. Due to the complexity of the organ we apply a multi‐component/tri‐phasic/tri‐scale approach, which is founded on the publication of Ricken et al. [2], coupling all relevant aspects to visualize the coupling between the fat metabolism and the hepatic perfusion. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Asymptotic analysis of notch induced crack nucleation
Authors: Felger Julian , Becker Wilfried 
Published: March 2018

AbstractIn the present study, a semi‐analytical asymptotic approach is used in order to analyse the change of total potential energy due to the initiation of a crack at a sharp re‐entrant corner. The semi‐analytical solution nature allows for reducing the numerical effort compared to a purely numerical treatment and provides a deeper physical insight into the fracture mechanics problem. Finally, the obtained asymptotic solutions are compared to numerical reference solutions. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A model for coupled inelastic deformation and anisotropic damage behaviour of concrete
Authors: Monnamitheen Abdul Gafoor A. H. , Dinkler Dieter 
Published: March 2018

AbstractThe present paper describes a simplified model for isotropic damage developed on continuum damage theory. The model characterizes the distinct behaviour of concrete in tension and compression using a unified equivalent strain, which governs the growth of damage. In reality, concrete exhibits distributed micro‐cracking pattern under multi‐directional loads. Therefore, the model is extended to incorporate damage induced anisotropy inherently for a reliable representation of damage, and captures the direction of possible damage evolution. Moreover, the model takes the inelastic behaviour of material into account based on the extended version of Lubliner failure criterion. The model is validated with experimental data. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiscale simulation of fracture of coated silica nanoparticles reinforced composites
Authors: Ma Songyun , Scheider Ingo , Bargmann Swantje , Markert Bernd 
Published: March 2018

AbstractNanocomposites exhibit excellent fracture toughness due to adding nanoparticles into the polymer matrix. The present work aims at developing a multiscale modelling approach to investigate fracture behaviour of nanocomposites with core‐shell nanostructures. In this context, a nonlocal damage model based on the micropolar theory is proposed to describe the damage behaviour of graded shell layers of nanoparticles. The simulation results show the capability of the present model to study the effect of shell morphology and shell material on the fracture toughness of nanocomposites within this multiscale simulation framework. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fatigue Damage and Degradation Model for Carbon Fibre Reinforced Polymer Materials
Authors: Abdul Hamid Zalikha Murni , Hohe Jörg , Gall Monika , Fliegener Sascha , Gumbsch Peter 
Published: March 2018

AbstractA major issue concerning Carbon Fibre Reinforced Polymer (CFRP) materials under cyclic loading is that the materials often undergo material degradation starting from the initial stage of the loading. For a laminate that consists of different fibre orientation plies, this becomes crucial as it causes redistribution of stresses and strains during the lifetime of the component. Understanding the importance of a reliable fatigue damage and degradation model in the development of reliability assessment of CFRP materials, the present studies contribute to this by considering the effect on a single‐ply material level, exclusively under fatigue loading. The model is restricted to be applied to stiff and brittle materials with characteristic properties similar to those of carbon‐epoxy composites. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An efficient Monte Carlo simulation strategy based on model order reduction and artificial neural networks
Authors: Bamer Franz , Koeppe Arnd , Markert Bernd 
Published: March 2018

AbstractIn this paper, we present a new approach that enables the Monte Carlo simulation of complex nonlinear systems with considerably less computational effort compared to the classical Monte Carlo simulation. Hereby, we propose a combination of the proper orthogonal decomposition and neural networks. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multi‐stage parameter identification of structural models from experimental data of varying assembly levels
Authors: Greiner Benjamin , Wagner Jörg F. 
Published: March 2018

AbstractClassical applications of the Finite Element Method (FEM) in the aerospace industry use structural models to predict dynamical properties during all design and integration phases. During development, test results are used for the identification and updates of model parameters. In recent years, the availability of structures with electromechanical components, such as actively controlled subsystems or systems with structural health monitoring, has extended the amount of available data suitable for parameter identification in operational conditions even beyond the development phase.The contribution presents an approach of using measurement data from different stages of structural assemblies for the identification and update of model parameters. Estimating parameters for subassembly models is preferred, because it is often more intuitive than a global approach in a complex model. Estimation uncertainties propagating to higher assembly levels have to be considered when assessing the model accuracy of a composed model. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
FE‐Simulation based analysis of residual stresses and strain localizations in ECAP processing
Authors: Horn Tobias , Silbermann Christian , Ihlemann Jörn 
Published: March 2018

AbstractEqual Channel Angular Pressing (ECAP) is a method to introduce severe plastic deformation into a metal billet without changing it's profile. In special cases the strain localizes and so‐called shear and matrix bands are induced. These localizations are simulated and analyzed with respect to the residual stresses by using the finite element method. We found that in contrast to the components of the stress tensor, only a small difference in the von‐Mises stress between shear and matrix bands occurs. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An algorithmic stress formula for energy conserving time integration in a mixed framework for polyconvex large strain elasticity
Authors: Janz Alexander , Peter Betsch , Hesch Christian 
Published: March 2018

AbstractThe present work deals with a mixed variational formulation of elastodynamics along with an Energy‐Momentum consistent (EMC) discretization in space and time. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On Evaluation of Multithreaded FEM Code for Composite Shell Computations
Authors: Jarzebski Pawel , Wisniewski Krzysztof , Wagner Werner 
Published: March 2018

AbstractThe paper concerns parallelization of an FE code for machines with shared memory in order to speedup computations of large composite shell models. The loop over elements was parallelized in the research code FEAP [5] using OpenMP, see [2] for details. The multithreaded solver was also applied. In the previous paper [3], the performance for 12 cores have been shown. In this work we show its performance for up to 32 cores. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison between substructure and FE2 modeling of beam‐like structures
Authors: Klarmann Simon , Gruttmann Friedrich 
Published: March 2018

AbstractBeam elements are a powerful tool to model large structures which possess beam‐like behavior. In order to perform those calculations, the most essential part are effective material properties. Different approaches are possible to obtain these, like in [1]. An extension to take inhomogeneities in length direction of the beam into account, can be done with the FE2 scheme, see e.g. [2]. This approach has the drawback of a length dependency of the shear stiffness, resulting from the double fulfillment of the equilibrium condition.A more flexible way to overcome these problems is substructure modeling. Beam elements are perfectly suited for this approach because of their 1D geometrical characteristic. The most essential part is to reduce the cross‐section to a point with beam‐like kinematics. Like in the FE2 approach, the application of suitable boundary conditions is necessary.This work aims at the comparison between substructure and FE2 modeling of beam‐like structures. It is worth mentioning that the steps of a calculation within the substructure approach are the same as in FE2 . Both cases will be compared with suitable numerical examples. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nonlocal balance of angular momentum from stress field analysis
Authors: Münch Ingo 
Published: March 2018

AbstractNonlocal theories drop the principle of local action such that the stress field in the contiguity of a continuum point is represented by a nonlinear tensor‐function. Therefore, its power series expansion has higher order terms and the balance of linear momentum becomes nonlocal, see [1, 2]. Here, we focus on the balance of angular momentum by considering up to quadratic terms in the approximation of the stress field. This yields nonlinear tractions on the surface of spatial unit cells, where an algebraic formula for the couple stress tensor can be found. However, couple stress is an auxiliary quantity, which is usually motivated as work conjugated to curvature. With help of some algebra in ℝ3 × ℝ3 × ℝ3 it is found, that the curl of the stress field rules the nonlocal balance of angular momentum. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Topology Optimization for Injection Molding of Short Fiber‐Reinforced Plastics
Authors: Ospald Felix , Herzog Roland 
Published: March 2018

AbstractWe investigate an approximate approach for compliance‐based topology optimization of short fiber‐reinforced plastic (SFRP) parts. The approximation consists in the replacement of the costly filling and fiber orientation simulation by the solution of an eikonal equation, which determines the principal fiber orientation. The optimization problem is then solved using the classical SIMP method in combination with a transversely isotropic material law and a projected gradient method. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling of shell structures using the scaled boundary finite element method
Authors: Wallner Milan , Birk Carolin , Gravenkamp Hauke 
Published: March 2018

AbstractIn view of recent trends towards lightweight structural designs, the numerical modelling of shell structures is a subject of high interest. Here, major challenges are associated with locking effects. This contribution presents a first approach to the numerical analysis of shell structures using the scaled boundary finite element method (SBFEM). First studies such as a simplified plane strain arch formulation to approximate an axisymmetric cylindrical shell are presented. This approximation already shows a high correlation with the membrane theory of shells. Furthermore, first results obtained for 3D shell formulations illustrate the potential of the proposed approach based on the SBFEM. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of Ultrasound on Friction Induced Vibrations during Tightening of Bolted Joints
Authors: Baramsky Nicolaj , Seibel Arthur , Schlattmann Josef 
Published: March 2018

AbstractThe assembly of bolted joints is often based on the assumption that the joint has been assembled as the design guidelines prescribe. However, during the tightening process, errors can occur, some of which can be affiliated with friction‐induced vibrations. In order to improve the automated tightening process and reduce the influence of friction‐induced vibrations, an additional high frequency torque is applied to the bearing of the bolted joint. This leads to a significant increase in tightening efficiency, lower tightening torque, and lower pretension force increments during the tightening process. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural stability of nonlinear valve train systems in automotive engines
Authors: Busch Martin 
Published: March 2018

AbstractValve trains are applied in automotive combustion engines to accomplish the alternation of load, see Ref. [1]. Since the system undergoes high‐frequent oscillations, it shows a nonlinear behavior with several instabilities. In the current work, the structural stability is investigated. A stable operation of the valve train is crucial for the efficiency of the engine. Further, the stability behavior is important from a simulation point of view since instabilities are challenging for numerical solvers. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determination of Material Parameters from Imperfect Cyclic Plasticity Test Data
Authors: Arslan Eray , Mack Werner , Zigo Milan , Kepplinger Gerhard 
Published: March 2018

AbstractDue to small deficiencies in standard test devices and/or procedures, uniaxial cyclic plasticity test data – even of the same specimen – often show noticeable uncertainties. Hence, depending on the way of calculation, the parameter values for a material model based on these data may exhibit perceptible variability. In the present contribution this issue is addressed, and some remedies are suggested. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)