bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification, Coding, and Reimbursement of Pediatric Malnutrition at an Urban Academic Medical Center
Authors: Bierman Sabrina M. , Peterson Sarah J. , Chen Yimin
Published: March 2018

Background

The American Academy of Nutrition and Dietetics and the American Society of Parenteral and Enteral Nutrition released a pediatric malnutrition consensus statement in 2014 recommending the use of z‐scores as indicators for identification and documentation of malnutrition. A shift in focus is needed on standardizing pediatric malnutrition language at institutions nationwide to make study data comparable. With this standardized language, establishment of institutional baselines for identification, coding, and reimbursement of pediatric malnutrition is crucial to measure process improvements.

Objectives

The objectives of this study were to determine the prevalence of malnutrition among pediatric patients at an urban academic medical center, the frequency of malnutrition codes used, and the reimbursement impact of coding for malnutrition.

Methods

Electronic medical records of pediatric patients admitted from January 2013 to December 2015 were reviewed. Malnutrition was identified based on registered dietitian identification and z‐score. Patients given a malnutrition‐related International Classification of Diseases code upon discharge were identified. A reimbursement calculation was performed: the malnutrition‐related International Classification of Diseases code was removed to determine the difference in reimbursement with vs without the code. Results: Of the 1,532 admissions included in this study, 464 (30%) were identified as malnourished. A total of 152 (33%) malnourished patients were given a malnutrition‐related secondary diagnosis. The calculation revealed that coding for malnutrition resulted in an additional $27,665.70 to the medical center.

Conclusion

Malnutrition coding may have a significant financial impact and processes improvement efforts can be made to improve malnutrition coding.
Venovenous Extracorporeal Membrane Oxygenation in an Adult Patient With Prader‐Willi Syndrome: A Nutrition Case Report
Authors: Pelekhaty Stacy , Menaker Jay
Published: March 2018

Prader‐Willi Syndrome (PWS) is a genetic condition that results in a constellation of symptoms and typically results in hyperphagia and obesity in adulthood. Critically ill adults with PWS present a unique challenge to the nutrition professional, particularly when they require support modalities such as extracorporeal membrane oxygenation (ECMO). The purpose of this case study is to review the nutrition care of a critically ill adult patient with PWS who required venovenous ECMO. The patient was successfully managed with a hypocaloric, high‐protein approach, which did not result in the diagnosis of malnutrition during his hospitalization. The patient was ultimately transitioned off extracorporeal life support and discharged to a rehabilitation facility.
Spectrum mobility management in cognitive two‐tier networks
Authors: Sethom Kaouthar , Pujolle Guy
Published: March 2018

Recently, new type of small Base Station known as “femtocell” has emerged. Femtocells are deployed by customers with minimal or no radio frequency planning in arbitrary locations. Thus, operators must use new approaches rather than the classic network planning and optimization. Self‐organization techniques will allow femtocells to integrate themselves into the network, learn about their environment, and adjust their parameters (power, frequency) accordingly. In this paper, a new spectrum mobility management algorithm is proposed. It allows intelligent use of the spectrum by secondary user (femtocell guest user) accessing spectrum holes unoccupied by primary users (subscriber user) and handing over to new channels or femtocells when primary user appears. Our solution aims to have more adaptive and aware communication system, which can make better use of available natural resources.
Exploring basal sliding with a fluidity‐based, ice‐sheet model using FOSLS
Authors: Allen Jeffery , Manteuffel Tom , Rajaram Harihar
Published: March 2018

This paper develops two first‐order system—in this context, first‐order refers to the order of the PDE not to the model—least‐squares, fluidity‐based formulations of a nonlinear Stokes flow model for ice sheets that attempt to overcome the difficulties introduced by unbounded viscosity. One commonly used way to define viscosity, Glen's law, allows viscosity to become unbounded as the strain rates approach zero. Often, numerical approaches overcome these singularities by modifying viscosity to limit its maximum. The formulations in this paper, however, reframe the problem to avoid viscosity altogether by defining the system in terms of the inverse of viscosity, which is known as fluidity. This results in a quantity that approaches zero as viscosity approaches infinity. Additionally, a set of equations that represent the curl of the velocity gradient is added to help approximate the solution in a space closer to H1, which improves algebraic multigrid convergence. Previous research revealed that the first‐order system least‐squares formulation has difficulties in maintaining optimal discretization convergence on more complex domains. This paper discovers that this problem is linked to how the curl equations are scaled and that stronger scalings result in better solver performance but worse discretization convergence. Determining if there is an optimal scaling that balances performance and convergence is still an open question. Additionally, the fluidity‐based formulations are tested with three 2D benchmark problems. Two of these benchmark problems involve basal sliding and one involves a time‐dependent free surface. The fluidity‐based solutions are consistent with the standard Galerkin method using Taylor–hood elements while better resolving viscosity.
Regularization matrices for discrete ill‐posed problems in several space dimensions
Authors: Dykes Laura , Huang Guangxin , Noschese Silvia , Reichel Lothar
Published: March 2018

Many applications in science and engineering require the solution of large linear discrete ill‐posed problems that are obtained by the discretization of a Fredholm integral equation of the first kind in several space dimensions. The matrix that defines these problems is very ill conditioned and generally numerically singular, and the right‐hand side, which represents measured data, is typically contaminated by measurement error. Straightforward solution of these problems is generally not meaningful due to severe error propagation. Tikhonov regularization seeks to alleviate this difficulty by replacing the given linear discrete ill‐posed problem by a penalized least‐squares problem, whose solution is less sensitive to the error in the right‐hand side and to roundoff errors introduced during the computations. This paper discusses the construction of penalty terms that are determined by solving a matrix nearness problem. These penalty terms allow partial transformation to standard form of Tikhonov regularization problems that stem from the discretization of integral equations on a cube in several space dimensions.
A posteriori error estimate for computing tr(f(A)) by using the Lanczos method
Authors: Chen Jie , Saad Yousef
Published: March 2018

An outstanding problem when computing a function of a matrix,f(A), by using a Krylov method is to accurately estimate errors when convergence is slow. Apart from the case of the exponential function that has been extensively studied in the past, there are no well‐established solutions to the problem. Often, the quantity of interest in applications is not the matrixf(A) itself but rather the matrix–vector products or bilinear forms. When the computation related tof(A) is a building block of a larger problem (e.g., approximately computing its trace), a consequence of the lack of reliable error estimates is that the accuracy of the computed result is unknown. In this paper, we consider the problem of computing tr(f(A)) for a symmetric positive‐definite matrixAby using the Lanczos method and make two contributions: (a) an error estimate for the bilinear form associated withf(A) and (b) an error estimate for the trace off(A). We demonstrate the practical usefulness of these estimates for large matrices and, in particular, show that the trace error estimate is indicative of the number of accurate digits. As an application, we compute the log determinant of a covariance matrix in Gaussian process analysis and underline the importance of error tolerance as a stopping criterion as a means of bounding the number of Lanczos steps to achieve a desired accuracy.
Applying functional principal components to structural topology optimization
Authors: Alaimo Gianluca , Auricchio Ferdinando , Bianchini Ilaria , Lanzarone Ettore
Published: March 2018

Structural topology optimization aims to enhance the mechanical performance of a structure while satisfying some functional constraints. Nearly all approaches proposed in the literature are iterative, and the optimal solution is found by repeatedly solving a finite element analysis (FEA). It is thus clear that the bottleneck is the high computational effort, as these approaches require solving the FEA a large number of times. In this work, we address the need for reducing the computational time by proposing a reduced basis method that relies on functional principal component analysis (FPCA). The methodology has been validated considering a simulated annealing approach for compliance minimization in 2 classical variable thickness problems. Results show the capability of FPCA to provide good results while reducing the computational times, ie, the computational time for an FEA is about one order of magnitude lower in the reduced FPCA space.
Comparison of PID and FOPID controllers tuned by PSO and ABC algorithms for unstable and integrating systems with time delay
Authors: Bingul Zafer , Karahan Oguzhan
Published: March 2018

This paper deals with optimization and design of an integer order–based and fractional order–based proportional integral derivative (PID) controller tuned by particle swarm optimization (PSO) and artificial bee colony (ABC) algorithms. These algorithms were used to find the best parameters for the best controller performance. A comparative study has been made to highlight the advantage of using ABC‐based controller over a PSO‐based controller. The validity of the controller tuning algorithms was tested in 2 different systems with time delay and a nonminimum phase zero used commonly in process control. The optimal tuning process of the PID and fractional order PID controllers has also been performed with 3 different cost functions. From the perspectives of time‐domain performance criteria, such as settling time, rise time, overshoot, and steady‐state error, the controller tuned by ABC gives better dynamic performances than controllers tuned by the PSO. Moreover, the results obtained from robustness analysis showed that the parameters of controller tuned by ABC are quite robust under internal and external disturbances.
Macromolecular Crowding May Significantly Affect the Performance of an MRI Contrast Agent: A 1H NMR Spectroscopy, Microimaging, and Fast‐Field‐Cycling NMR Relaxometry Study
Authors: Cheng Ren‐Hao , Chen Jie‐Min , Chen Yu‐Wen , Cai Honghao , Cui Xiaohong , Hwang Dennis W. , Chen Zhong , Ding Shangwu
Published: March 2018

Contrast enhancement agents are often employed in magnetic resonance imaging (MRI) for clinical diagnosis and biomedical research. However, the current theory on MRI contrast generation does not consider the ubiquitous presence of macromolecular crowders in biological systems, which poses the risk of inaccurate data interpretation and misdiagnosis. To address this issue, herein the macromolecular crowding effects on MRI contrast agent are investigated with the 1H relaxation rate of water in aqueous solutions of Dotarem with different concentrations of macromolecules. Two representative macromolecular crowder systems are used: polyethylene glycol (with no specific secondary structure) and bovine serum albumin (with compact secondary and tertiary structures). The water 1H relaxation rates in various solutions are measured in a fixed magnetic field and in variable magnetic fields. The results show significant crowding effects for both crowders. The relaxation rate is proportional to the concentration of the MRI contrast agent but shows conspicuous superlinearity with respect to the concentration of the crowder. The size of polyethylene glycol does not affect the relaxivity of water in Dotarem solutions. The above effects are verified with T1‐ and T2‐weighted NMR microimages. These results highlight the importance of the effect of macromolecular crowding on the MRI contrast agent and are valuable for understanding the mechanism of MRI contrast agents and designing new‐generation MRI contrast agents.
Field‐induced plasticity of magneto‐sensitive elastomers in context with soft robotic gripper applications
Authors: Chavez Vega Jhohan , Kaufhold Tobias , Böhm Valter , Becker Tatiana , Zimmermann Klaus , Martens Michael , Schilling Meinhard , Gundermann Thomas , Odenbach Stefan
Published: March 2018

Magnetic hybrid composite materials have the peculiarity to change their mechanical properties when influenced by a magnetic field. This special characteristic can be used to develop smart actuators, sensor systems and control mechanisms. In the paper the use of magneto‐sensitive elastomers (MSE), composed of silicone rubber and silicone oil, with incorporated magnetic particles, in a form‐fit gripper application is considered. The field‐induced plasticity effect of MSE is used, to realise reversible recoverable shape adaptation of the gripper to the objects to be manipulated. The focus lies on the characterisation of the mechanical properties of the MSE for the specific application. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Model Order Reduction for Parametric Non‐linear Mechanical Systems: State of the Art and Future Research
Authors: Meyer Christian H. , Lerch Christopher , Lohmann Boris , Rixen Daniel J.
Published: March 2018

One research objective in the Priority Program 1897 “Calm, Smooth and Smart” of the German Research Foundation (DFG – SPP 1897) is the development of model order reduction techniques for parametric non‐linear mechanical systems to enable efficient design, simulation, analysis, optimization and control of those. As a starting point for our research, this contribution provides an overview of the main challenges and well‐established reduction techniques in this research area, at that stage, neglecting parameter dependencies. This includes simulation‐based as well as simulation‐free reduction bases generation and hyperreduction of the non‐linear force terms. An extension of the Krylov directions in moment matching based on the concept of modal derivatives is also sketched. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Polymorphic Uncertainty Modeling of Heterogeneous Thermo‐Hydro‐Mechanical Coupled Systems under Vague Assumptions on Parameter Correlations
Authors: Schmidt Albrecht , Nguyen‐Tuan Long , Könke Carsten , Lahmer Tom
Published: March 2018

Heterogeneous material properties can be found in new hybrid materials as well as in existing engineering constructions, e.g. dams. The material properties can be modeled by correlated random fields, taking into account their possible interdependencies. The vaguely known random field parameters like correlation coefficient and correlation length are described by fuzzy sets. Applying those fields in a reliability analysis result in failure probability fuzzy sets that can be interpreted by the engineer. This proposed methodology is applied to a simple illustrative one‐dimensional model to show the principle procedure. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Monolithic Solution Scheme for a Phase Field Model of Ductile Fracture
Authors: Noll Timo , Kuhn Charlotte , Müller Ralf
Published: March 2018

A phase field model for elastic‐plastic fracture is presented, which is based on an energy functional composed of an elastic energy contribution, a plastic dissipation potential and a fracture energy. The coupling of the mechanical fields with the fracture field is modeled by a degradation function. Due to the proposed coupling it is possible to solve the global system of differential equations in a monolithic iterative solution scheme. Numerical simulations are presented, where the choice of the degradation function is investigated and a staggered is compared to monolithic iteration scheme. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phase‐Field Models for the Failure of Anisotropic Continua
Authors: Dal Hüsnü , Gültekin Osman , Aksu Denli Funda , Holzapfel Gerhard A.
Published: March 2018

This study presents a phase‐field approach for an anisotropic continuum to model fracture of biological tissues and fiber‐reinforced composites. We start with the continuous formulation of the variational principle for the multi‐field problem manifested through the deformation map and the crack phase‐field at finite strains which leads to the Euler–Lagrange equations of the coupled problem. In particular, the coupled balance equations derived render the evolution of the anisotropic crack phase‐field and the balance of linear momentum. In addition, we propose a novel energy‐based anisotropic failure criterion which regulates the evolution of the crack phase‐field. The coupled problem is solved using a one‐pass operator‐splitting algorithm composed of a mechanical predictor step and a crack evolution step. Representative numerical examples are devised for crack initiation and propagation in carbon‐fiber‐reinforced polymerg composites. Model parameters are obtained by fitting the set of novel experimental data to the predicted model response; the finite element results qualitatively capture the effect of anisotropy in stiffness and strength. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Variational interface zone model for modeling of fluid induced fracture propagation
Authors: Khisamitov Ildar , Meschke Günther
Published: March 2018

A novel variational framework for an interface zone model is developed and extended to poroelasticity. As was previously promoted in [1,2], the total energy of the system is composed by the bulk potential and fracture surface energy. In contrast to the phase‐field method, the fracture surface is approximated directly along the edges of the finite elements in terms of interface zero‐thickness finite elements. By introducing a new degree of freedom c (damage field) on the interface level, the solution is found by the minimization of the total potential energy with respect to the displacements and the damage field. An elastic interface constitutive law allowing for a normal and tangential displacement opening is adopted in the pre‐fracture regime. Assuming, that a crack propagates according to the Griffith's criterion of brittle fracture, fracture initiates and propagates in normal opening mode. Biot's theory is applied both to the bulk and interface elements for the simulation of fluid driven fracture in fully saturated materials. The pressure field within the interfaces is averaged between the pressure at the bulk element faces. Pressure continuity is enforced by means of a penalty functional. The flow within the fracture is modeled by the cubic law taking the displacement and damage variables into account. A number of numerical benchmark tests, which include comparisons with experimental results and analytical solutions, are performed to demonstrate the performance of the model. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling of the gelation process of biopolymers using the phase‐field method
Authors: Zhou Bei , Heider Yousef , Markert Bernd
Published: March 2018

Biopolymer gels have many applications in tissue engineering. In recent years, biopolymer gels are widely used as scaffold material in the 3D bioprinting technique for tissues and organs. To optimise the printing process, it is important to study and understand the temperature‐ and time‐dependent gelation kinetics of biopolymer gels.

In this study, a thermodynamic model is proposed to describe the gelation kinetics of thermoreversible gels, which are driven by the coil‐to‐helix transition. In this model, the gelation process is assumed to proceed in two steps. The process starts from the reference state, in which the solution consists of solvent molecules and polymer chains with n segments in random coil configuration. Polymer chains firstly change from the random coil state to the partially helical state, followed by the aggregation of helical parts of polymer chains. This formation and the followed aggregation of helices lead to the eventual polymer network. With the help of the phase‐field method, numerical simulations of a spatial and time varied gelation process of droplets in 3D bioprinting are performed using the finite element method (FEM). (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Drag reduction of spanwise transversal traveling surface waves with stepwise amplitude increase
Authors: Meysonnat Pascal S. , Albers Marian , Schröder Wolfgang
Published: March 2018

The effect of sudden amplitude changes of a spanwise traveling surface wave on turbulent boundary layers is investigated numerically using high resolution large‐eddy simulation (LES). The results show drag reduction of up to 9 percent and an adaptation of the turbulent flow to the changed input parameter within 100 convective times. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Building blocks for a leading edge high‐order flow solver
Authors: Huismann Immo , Stiller Jörg , Fröhlich Jochen
Published: March 2018

An important trend in Computational Fluid Dynamics is towards high‐order methods, as they offer a substantially lower discretization error for the same number of degrees of freedom (DOF). Examples are the Spectral‐Element Methods (SEM) and Discontinuous Galerkin (DG) methods. Unfortunately, with most implementations the work load of such solvers increases drastically with the number of DOF, for example, when increasing the polynomial degree of the approximation. This issue gets particular pressing for elliptic solvers which are a vital building block in the time‐stepping of the incompressible Navier‐Stokes equations, resulting from pressure projection methods or implicit treatment of viscous terms. So far, this drastic increase of resources has hampered the use of SEM for higher polynomial degrees, such as 16 or more.

The present contribution is located at this particular “Frontier of CFD” and proposes an SEM with linear scaling in the number of degrees of freedom. It is achieved independent of the polynomial degree, independent of the aspect ratio of elements, and involves constant iteration count when increasing the number of elements. The method is based on combining static condensation with block‐Jacobi preconditioning and iterative substructuring. The latter two lead to a constant iteration count, while the former warrants linear operator complexity.

In the presentation, the scheme is described in detail and applied to the construction of a Helmholtz solver. This solver is extremely fast and able to solve the Helmholtz equation with 1010 unknowns on 240 cores in acceptable time. It thus enables competitive high‐order SEM simulations even on small clusters and in this way expands the frontier of CFD towards highly accurate results requiring comparatively modest resources. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Variational integrator for constrained mechanical systems with pulsed disturbances and optimal feedback control
Authors: Glaas Daniel , Leyendecker Sigrid
Published: March 2018

An 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

Time‐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

Model 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

The 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

Blood 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

The 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

The 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

In 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

In 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

The 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

Nanocomposites 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

A 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

In 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

Classical 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

Equal 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

The 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

The 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

Beam 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

Nonlocal 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

We 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

In 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

The 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

Valve 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

Due 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)
Modelling the thermoplastic material behaviour of a tailored formed joining zone on a microscopic length scale with focus on the steel component
Authors: Baldrich Martina , Zeller Sebastian , Loehnert Stefan , Wriggers Peter
Published: March 2018

Since Tailored Forming is a complex process and the joining zone of the hybrid solid component is a possible weakness, our goal is to simulate the thermomechanical material behaviour of the joining zone during the Tailored Forming process. Investigations on the steel component of the joining zone show a polycrystalline microstructure with the two constituents pearlite and ferrite. In this work, the pearlitic phase is considered to be purely thermoelastic whereas the material model for the ferritic phase represents thermoplastic material behaviour. Besides reasons for the choice of the mentioned material models, we present the thermoplastic material model developed by Zeller et al. [1]. Based on the experimental observation that the persistent deformation is a result of slip of dislocations, state variables are defined to formulate a necessary shear stress to move dislocations as well as temperature and deformation dependent evolution equations for the introduced state variables. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)