bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical simulation of suction cavitation in hydrodynamic journal bearings
Authors: Schmidt Marcus , Reinke Peter , Beckmann Tom 
Published: November 2019

AbstractThe prediction of cavitation in journal bearings is one of the current challenges in the field of computational fluid dynamics. Hydrodynamic journal bearings are used in a wide range of technical and industrial applications because they provide low friction and minimal wear. A failure of the bearing system during operation can be caused by suction cavitation. Cavitation describes the phase change from liquid to vapour of a fluid caused by a decrease in pressure below the fluid's vapour pressure at an approximately constant temperature. The implosion of vapour cavities adjacent to the surface of the bearing liner stresses the liner material which in turn can lead to material erosion. The particular case of suction cavitation can be observed, if the bearing is operated under high loads resulting in high eccentricity between shaft and bushing combined with a significant increase in gap width. Suchlike operating conditions are not uncommon for internal combustion engines with a power of 0.1 to 1.0 MW per cylinder. As a result of the transient shaft displacement a suction effect builds up within in the lubricating film accompanied with a strong pressure gradient. Due to the fluid dynamics of the lubricant film flow at the given pressure gradient, the liquid can only equalize the void caused by the shaft displacement until the fluid pressure reaches the vapor pressure and then vapor is generated. The vapor forms a three‐dimensional layer across the lubricating film. Whereas, current flow calculations for hydrodynamic journal bearings are carried out by means of 2D methods which are limited to analyze the three‐dimensional and transient flow in those areas of the journal bearing where cavitation occurs. This work presents the application of a transient, 3D numerical simulation of the two‐phase fluid flow in a journal bearing under conditions of cavitation. The numerical simulations were performed using the code OpenFOAM, which is based on the finite volume method and uses time‐dependent three‐dimensional, incompressible Navier‐Stokes equations. The study on hand discusses the influence of minimal film thickness and displacement velocity vs. the structure of the vapour distribution. The numerical results include images of complex three‐dimensional flow structures and vapor distributions inside the lubricating film.
Determination of material parameters for a multiphasic modeling of hydrogels
Authors: Mau Beatrice , Erfkamp Jan , Guenther Margarita , Wallmersperger Thomas 
Published: November 2019

AbstractStimuli‐responsive hydrogels are electroactive polymers classified as smart materials, consisting of a solid, fluid and ionic phase. As a result of external stimuli, for example through a variation of the chemical conditions in the surrounding solvent, the hydrogels undergo a reversible volume transformation caused by the absorption or the release of solvent. By using a multiphasic model based on the Theory of Porous Media the chemo‐electro‐mechanical interaction of the different phases can be described. Therefore this model requires a large amount of material parameters, whose determination poses a challenge. To determine the parameters for the mechanical behavior it should be ensured that an interaction of the different phases (solid and fluid) and the surrounding solution bath is realized in order to investigate the viscoelastic behavior of the hydrogel. In the present research, a tensile test is performed to identify the mechanical properties of such stimuli‐responsive hydrogels. Therefore, a specific focus is placed on the dependence of these properties on the solid‐fluid ratio due to the multiphasic composition of this material. The aim of this research is to ameliorate the material equations of the modeling and consequently enhance a prediction of the mechanical behavior.
Efficient phase‐field modelling of fatigue crack propagation
Authors: Seiler Martha , Linse Thomas , Hantschke Peter , Kästner Markus 
Published: November 2019

AbstractFatigue loads come along with high numbers of load cycles which makes the simulation of fatigue fracture computationally very demanding. We present a numerically efficient method which avoids resolving the loading path and instead requires only one increment per load cycle at most. We combine the phase‐field method for fracture with a classic fatigue concept. A local lifetime variable is obtained, which we use to modify the material resistance incrementally in order to consider the progressive weakening of the material. Focussing on ductile material behaviour, we make use of an elasto‐plastic revaluation technique instead of a full plastic material model. The model allows to describe fatigue crack initiation as well as propagation and reproduces Paris behaviour.
What can we learn from information‐entropy about turbulence and Large‐Eddy‐Simulation?
Authors: Engelmann Linus , Wlokas Irenäus , Kempf Andreas M. 
Published: November 2019

AbstractThe Shannon entropy is a rigorous measure of information that can be used to evaluate the properties of information in turbulent flows. In this study, the behavior of the Shannon entropy is investigated for LES of an incompressible turbulent channel flow based on the classical DNS of Moser et al.. The Shannon entropy is calculated from the velocity fluctuation fields and is compared to the turbulent kinetic energy. The quality and resolution of the LES calculations on different grids has been evaluated against DNS results. The Shannon entropy is calculated for velocities and the turbulent viscosity to observe how it behaves and how it is related to the simulation quality and grid resolution.
Challenges and perspectives in brain tissue testing and modeling
Authors: Budday Silvia , Holzapfel Gerhard A. , Steinmann Paul , Kuhl Ellen 
Published: November 2019

AbstractWhile long underestimated, more and more evidence confirms that mechanics play a critical role for brain function and dysfunction. Therefore, computational simulations based on the field equations of nonlinear continuum mechanics can provide important insights into the underlying mechanisms of brain injury and disease. Realistic numerical predictions, however, require models capable of capturing the complex and unique mechanical behavior of this ultrasoft, highly heterogeneous and adaptive tissue. In recent years, contradictory experimental results have retarded progress in this field. Here, we summarize the key characteristics of brain tissue behavior on different length and time scales and propose application‐specific modeling approaches, which are as complex as necessary but as simple as possible. The presented considerations will, on the one hand, facilitate well‐designed future experiments and, on the other hand, help to choose the appropriate constitutive law for a specific application.
Numerical investigations about the use of lattice structures in energy absorbing systems
Authors: Bühring Jannik , Aghdam Nima Jafarzadeh , Mekala Narasimha Rao , Schröder Kai-Uwe 
Published: November 2019

AbstractConventional crash structures normally use areal folding mechanisms to absorb energy. In this work, we show an alternative design concept by using three dimensional lattice structures. The study shows that the cell parameters of bending and tension dominated unit cells have great influences on the specific energy absorption. For bending dominated cells face‐centred cubic cells with vertical struts (f2ccz) and for tensions dominated cells, 3D re‐entrant auxetic structures are used. To investigate the influences of the cell parameters on the energy absorption a numerical parametric study is done.
Tuning of vibration and wave propagation characteristics in pre‐deformed periodic lattice frame structures
Authors: Mellmann Marius , Zhang Chuanzeng 
Published: November 2019

AbstractThe design, optimization and application of periodic materials and structures, such as phononic crystals and structures, are receiving increasing attention in recent years. Such materials and structure can manipulate the characteristics of the elastic and acoustic wave propagation [1]. Thus, it is feasible to create the so‐called band‐gaps, designating certain frequency ranges, in which the propagation of elastic or acoustic waves is prohibited [2]. Accordingly, such structures have many promising applications in sound and vibration insulation as well as wave filters. In this paper, pre‐deformed periodic lattice frame structures for the tuning of the vibration and wave propagation characteristics are investigated.
Effect of uncertain parameters on the deflection of beams
Authors: Reppel Thomas , Korzeniowski Tim Fabian , Weinberg Kerstin 
Published: November 2019

AbstractIn the classical Euler‐Bernoulli cantilever beam theory the deflection w depends on different parameters. On the one hand we have material and geometric parameters, like the Young's Modulus E, the second moment of area I and the length of the beam L. On the other hand there are different loading types like point loads F, distributed loads, or varying loads. All these parameters are usually modeled in a deterministic way. In this contribution we analyze the distribution of the maximum beam deflection of a cantilever beam wmax depending on uncertain parameters. To this end we model the input parameters as random variables (XF, XL, XE) or different random fields (Ei). For the random fields Monte‐Carlo simulations are used to calculate the resulting distribution.
On the transformation laws for the macro to micro transformation
Authors: Jahn Momme , Meywerk Martin 
Published: November 2019

AbstractIn this contribution a transformation from macro‐ to micro‐mechanical quantities is shown. The macro‐scale is treated with the Cosserat‐continuum and is simulated with the Finite‐Element‐Method (FEM), while the body in micro‐scale is simulated with the Discrete‐Element‐Method (DEM). The transformation preserve the mass, the kinetic energy, the momentum, the moment of momentum and the energy of stress, couple stress and volume forces.
On EDP‐convergence for gradient systems with different time scales
Authors: Stephan Artur 
Published: November 2019

AbstractMotivated by the author's work on evolutionary Γ‐convergence of slow‐fast‐reaction systems, we consider a simple evolution equation, an exponential decay which depends very singularly on a small parameter ϵ > 0: the decay rate is proportional to 1/ϵ. Nevertheless the evolution equation can be understood as a gradient system for which structural convergence, the so‐called EDP‐convergence, has been established in recent years. We investigate evolutionary Γ‐convergence based on the energy‐dissipation principle (EDP) for that simple singularly behaving evolution equation.
Numerical Approximation of Heat Transfer on Heterogenous Media
Authors: Scheuermann Tobias M. , Kotyczka Paul , Zanota Marie-Line , Pitault Isabelle , Louati Haithem , Maschke Bernhard 
Published: November 2019

AbstractIn this paper we show the discrete modeling of the heat equation on an open cell metallic foam, exploiting its geometric structure. The topology of the material is described using the incidence matrices of a so called k‐complex. Together with the discrete constitutive equations, a finite‐dimensional model in port‐Hamiltonian form is found.
Phase field modeling of interface effects on cracks in heterogeneous materials
Authors: Kuhn Charlotte , Müller Ralf 
Published: November 2019

AbstractOne of the reasons why the phase field approach has become very popular for modeling fracture processes is that therein the entire evolution of fracture follows from energetic principles without the need for different criteria for crack initiation, nucleation, kinking or branching. Furthermore, these models allow for a straightforward numerical implementation with standard finite elements, since displacement jumps and stress singularities are avoided in these models. Consequently, phase field fracture models are now also used to model and simulate fracture of heterogeneous materials such as composites, where cracks may be arrested, deflected or bifurcated at interfaces between the different components of the composite material, resulting in complicated crack patterns. The crack propagation is not only controlled by the elastic and fracture properties of the bulk phases of the material but also by the properties of the interfaces in between. Thus, it is crucial to take these interface properties into account. Therefore in this work, interfaces are equipped with a fracture energy corresponding to the phase field fracture energy of the bulk phases in order to model the interface fracture properties. In the finite element implementation, the interfaces are modeled by means of surface elements without introducing additional degrees of freedom.
Application of Recurrent Neural Networks in the numerical analysis of reinforced concrete structures considering polymorphic uncertainty
Authors: Leichsenring Ferenc , Fuchs Alexander , Graf Wolfgang , Kaliske Michael 
Published: November 2019

AbstractThe realistic modelling of structures is fundamental for their numerical simulation and is mainly characterized by the physical approach and the consideration of the available data by an adequate uncertainty description. The key idea in the contribution at hand is the consideration of polymorphic uncertainty in the numerical structural analysis and in the mechanical modelling for reinforced concrete structures, which are characterized by a combination of heterogeneous concrete and different types of reinforcement (e.g. steel bars or woven carbon fibres). Typically, the reinforcement is determined by another length scale compared to the overall structural size. The formulation and development of a computational homogenization approach, considering the different homogeneous and heterogeneous characteristics of a macroscopic structure, are essential for a realistic numerical computation. In recent years, focal point of research was on structural analysis considering uncertain material or geometry parameters. Probabilistic approaches are dominating the uncertainty consideration currently, although they are associated with specific disadvantages and limitations. In this contribution, a generalized uncertainty model is utilized in order to take variability, impression as well as inaccuracy, vagueness and incompleteness into account. This allows a separated evaluation of the influence for each uncertainty source on the results. Therefore, polymorphic uncertainty models are applied and developed by combining aleatoric and epistemic uncertainty descriptions, resulting e.g. in the formulation of the uncertainty model “fuzzy probability based randomness”. The information of the different length scales is considered to be uncertain, e.g. the geometry or the material properties of a representative volume element (RVE) at the meso scale. Subsequently, the uncertainty of a macro structure is derived from uncertain results on the meso structure. In the contribution, a parametrized RVE for concrete structures, including cement phase as well as aggregates, is presented. Various material parameters are considered as uncertain, which results in uncertain effective quantities. Assuming, that an uncertain quantity is substitutable by a combination of a representative measure and multiple uncertainty characterizing measures, an approximation of both type of quantities by a recurrent neural network is carried out. The surrogate models are utilized as constitutive description in a numerical structural analysis on macro level, providing uncertain structural responses.
Development of a novel damage approach on the microstructure for modeling woven ceramic matrix composites
Authors: Reuvers Marie-Christine , Rezaei Shahed , Brepols Tim , Reese Stefanie 
Published: November 2019

AbstractCeramic Matrix Composites (CMC) overcome limitations associated with classical technical ceramics e.g. low fracture toughness and brittle failure under mechanical or thermomechanical loading [1]. Their high temperature stability and low weight makes them attractive for use in various fields, especially aerospace industry, where they improve engine efficiency compared to metal components. However current CMCs lack well established material property design databases for a reliable use in critical aerospace structures. Demonstrating the durability of this relatively new class of materials is the challenge to face and therefore the failure mechanisms need to be investigated further. This contribution deals with the successive development of a woven representative volume element (RVE) for arbitrary CMCs. In contrast to previously developed continuum mechanical or laminate theory based modeling approaches, the introduced model combines various damage formulations. The fiber bridging effect, resulting from the weak interface bond of matrix and reinforcement, is governed by the use of cohesive zone (CZ) elements [2]. Whereas the matrix damage is represented using a continuum mechanical approach [3].
Hierarchical Parcel‐Swapping: An efficient mixing model for turbulent reactive flows
Authors: Starick Tommy , Schmidt Heiko 
Published: November 2019

AbstractHierarchical Parcel‐Swapping (HiPS) developed by A.R. Kerstein [J. Stat. Phys. 153, 142‐161 (2013)] is a computationally efficient and novel model for the effects of turbulence on time‐evolving, diffusive scalar fields. The characteristic feature of HiPS is the interpretation of the one‐dimensional flow domain or a state space as a binary tree structure. Every tree level corresponds to a specific length and time scale, which is based on a turbulence inertial range scaling. The state variables reside at the base of the tree and are interpreted as fluid parcels. The effects of turbulent advection are represented by stochastic swaps of sub‐trees at rates determined by turbulent time scales associated with the sub‐trees. The mixing of adjacent fluid parcels is done at rates consistent with the prevailing diffusion time scales. In this work, we investigate the influence of turbulent time scale variations on an isothermal series‐parallel reaction scheme. The production of a desired chemical species is evaluated by means of a defined selectivity and is strongly affected by the underlying mixing time scales.
Estimated number of adult survivors of childhood cancer in United States with cancer‐predisposing germline variants
Authors: Wilson Carmen L. , Wang Zhaoming , Liu Qi , Ehrhardt Matthew J. , Mostafavi Roya , Easton John , Mulder Heather , Hedges Dale J. , Wang Shuoguo , Rusch Michael , Edmonson Michael , Levy Shawn , Lanctot Jennifer Q. , Currie Kelsey , Lear Matthew , Patel Aman , Sapkota Yadav , Brooke Russell J. , Moon Wonjong , Chang Ti‐Cheng , Chen Wenan , Kesserwan Chimene A. , Wu Gang , Nichols Kim E. , Hudson Melissa M. , Zhang Jinghui , Robison Leslie L. , Yasui Yutaka 
Published: November 2019

AbstractPurposeTo estimate the absolute number of adult survivors of childhood cancer in the U.S. population who carry a pathogenic or likely pathogenic variant in a cancer predisposition gene.MethodsUsing the Surveillance, Epidemiology, and End Results (SEER) Program, we estimated the number of childhood cancer survivors on December 31, 2016 for each childhood cancer diagnosis, multiplied this by the proportion of carriers of pathogenic/likely pathogenic variants in the St. Jude Lifetime Cohort (SJLIFE) study, and projected the resulting number onto the U.S. population.ResultsBased on genome sequence data, 11.8% of 2450 SJLIFE participants carry a pathogenic/likely pathogenic variant in one of 156 cancer predisposition genes. Given this information, we estimate that 21 800 adult survivors of childhood cancer in the United States carry a pathogenic/likely pathogenic variant in one of these genes. The highest estimated absolute number of variant carriers are among survivors of central nervous system tumors (n = 4300), particularly astrocytoma (n = 1800) and other gliomas (n = 1700), acute lymphoblastic leukemia (n = 4300), and retinoblastoma (n = 3500). The most frequently mutated genes are RB1 (n = 3000), NF1 (n = 2300), and BRCA2 (n = 800).ConclusionGiven the increasing number of childhood cancer survivors in the United States, clinicians should counsel survivors regarding their potential genetic risk, consider referral for genetic counseling and testing, and, as appropriate, implement syndrome‐specific cancer surveillance or risk‐reducing measures.
The association of mediastinal mass in the formation of thrombi in pediatric patients with non‐lymphoblastic lymphomas
Authors: Gartrell Jessica , Kaste Sue C. , Sandlund John T. , Flerlage Jamie , Zhou Yinmei , Cheng Cheng , Estepp Jeremie , Metzger Monika L. 
Published: November 2019

AbstractBackgroundChildren diagnosed with cancer are at a significantly higher risk of developing a thrombotic event (TE) compared with the general population. The rarity of these events makes it difficult to discern the specific risk factors; however, age, sex, presence of central venous lines, inherited thrombophilia, and mediastinal mass may play a role. The primary aim of this study is to identify prognostic characteristics of children diagnosed with non‐lymphoblastic lymphomas associated with a greater risk of developing a TE early on in their disease, with an increased focus on mediastinal mass characteristics.MethodsRetrospective chart review of pediatric patients diagnosed with non‐lymphoblastic lymphoma between 2004 and 2014 at St. Jude Children's Research Hospital.ResultsTE occurred in 8.5% (n = 28/330) of individuals at a median of 21 days from the diagnosis of a non‐lymphoblastic lymphoma, with 60% of TEs occurring within 30 days of diagnosis. Of the variables evaluated, only presence of a peripherally inserted central catheter (odds ratio [OR]: 3.14 [95% CI: 1.24‐7.98; P = 0.02]) and degree of superior vena cava (SVC) compression of > 25% increased the odds of developing a TE (OR: 2.2 [95% CI: 1.01‐4.93; P = 0.048]).ConclusionPediatric patients with non‐lymphoblastic lymphoma are at increased risk of developing TEs. In contrast to previous studies, the presence of a mediastinal mass alone was not associated with a higher risk of TE, but individuals with a mediastinal mass with 25% or greater degree of SVC compression were more likely to develop a TE. This finding highlights a high‐risk group of children who may benefit from prophylactic anticoagulation.