bluuebunny/crossref_metadata_2025 huggingface dataset:
Tribological behavior of zirconium phosphate‐1,4‐dimethylpiperazine compound as lubricant additives
Authors: Niu Wenxing , Liu Lei , Xu Hong , Dong Jinxiang
Published: December 2018

Zirconium phosphate compound, [C6H16N2]0.5Zr‐(H0.5PO4)2•H2O designated as ZrPO4‐DES8 have been synthesised hydrothermally in the presence of 1,4‐dimethylpiperazine (DMP). In this study, small (0.5‐0.8 μm) and large (8‐10 μm) ZrPO4‐DES8 particles were obtained by varying the amount of H3PO4 in the HF ‐ ZrO2‐P2O5‐DMP‐H2O hydrothermal system. The tribological properties of ZrPO4‐DES8 particles as additives in lithium grease were evaluated by using a ball‐on‐disk reciprocating tribometer under different concentrations, loads, and frequencies. The results illustrated that ZrPO4‐DES8 particles improved the lubricating performance of grease substantially. The small‐sized particles exhibited better and more stable friction reduction and anti‐wear performance than larger ones during sliding. The characterisation of a possible wear mechanism was given by observing the worn surface under a three‐dimensional optical profiler, a scanning electron microscope and energy dispersive X‐ray analysis. The simple synthetic method and superior tribological properties make the ZrPO4‐DES8 become a choice for lubricant additives.
Some transfinite natural sums
Authors: Lipparini Paolo
Published: December 2018

We study a transfinite iteration of the ordinal Hessenberg natural sum obtained by taking suprema at limit stages. We show that such an iterated natural sum differs from the more usual transfinite ordinal sum only for a finite number of iteration steps. The iterated natural sum of a sequence of ordinals can be obtained as a mixed sum (in an order‐theoretical sense) of the ordinals in the sequence; in fact, it is the largest mixed sum which satisfies a finiteness condition. We introduce other infinite natural sums which are invariant under permutations and show that all the sums under consideration coincide in the countable case.
Categoricity and universal classes
Authors: Hyttinen Tapani , Kangas Kaisa
Published: December 2018

Let be a universal class with categorical in a regular with arbitrarily large models, and let be the class of all for which there is such that . We prove that is totally categorical (i.e., ξ‐categorical for all ) and for . This result is partially stronger and partially weaker than a related result due to Vasey. In addition to small differences in our categoricity transfer results, we provide a shorter and simpler proof. In the end we prove the main theorem of this paper: the models of are essentially vector spaces (or trivial, i.e., disintegrated).
Controlled‐Release LCST‐Type Nonwoven Depots via Squeezing‐Out Thermal Response
Authors: Käfer Florian , Vilensky Rita , Vasilyev Gleb , Zussman Eyal , Agarwal Seema
Published: December 2018

A novel thermoresponsive fibrous matrix as controlled release depots upon heating is described. The matrix is composed of electrospun fibers of a lower critical solution temperature (LCST)‐type poly(methacrylamide‐co‐N‐tert‐butylacrylamide‐co‐4‐acryloylbenzophenone) P(MAAm‐NtbAAm‐ABP) copolymer. Spherical particles, simulating depots of drugs, are embedded with liquid‐filled inter‐fiber spaces (pores). On heating above 25 °C up to 45 °C, the nanofibers undergo a contraction of about 40%. This solid deformation is attributed to the LCST transition. Fibrous matrix contraction drives expulsion of depots and water solution stored in the pores of the matrix, as evidenced by in situ observations. The liquid flow in the deformable porous medium demonstrates liquid drainage from the matrix as a function of temperature. Experimental results reveal that 70% of the particles are expelled from the matrix upon heating to 45 °C from room temperature. The presented particles encapsulation and release model system using LCST‐type fibrous matrix can be used as a transdermal patch.
Identification of genes associated with cancer progression and prognosis in lung adenocarcinoma: Analyses based on microarray from Oncomine and The Cancer Genome Atlas databases
Authors: Liu Wei , Ouyang Songyun , Zhou Zhigang , Wang Meng , Wang Tingting , Qi Yu , Zhao Chunling , Chen Kuisheng , Dai Liping
Published: December 2018

Background

Lung adenocarcinoma (LUAD) accounts for approximately 40% of all lung cancer patients. There is an urgent need to understand the mechanisms of cancer progression in LUAD and to identify useful biomarkers to predict prognosis.

Methods

In this study, Oncomine database was used to identify potential genes contributed to cancer progression. Bioinformatics analysis including pathway enrichment and text mining was used to explain the potential roles of identified genes in LUAD. The Cancer Genome Atlas database was used to analyze the association of gene expression with survival result.

Results

Our results indicated that 80 genes were significantly dysregulated in LUAD according to four microarrays covering 356 cases of LUAD and 164 cases of normal lung tissues. Twenty genes were consistently and stably dysregulated by more than twofold. Ten of 20 genes had a relationship with overall survival or disease‐free survival in a cohort of 516 LUAD patients, and 19 genes were associated with tumor stage, gender, age, lymph node, or smoking. Low expression of AGER and high expression of CCNB1 were specifically associated with poor survival.

Conclusion

Our findings implicate AGER and CCNB1 might be potential biomarkers for diagnosis and prognosis targets for LUAD.
Advocates address need to reframe discussion on guns, MI
Authors: Canady Valerie A.
Published: December 2018

While the media may have some think that the link between gun deaths and mental illness is through homicide, it is actually suicide, observed the director of public policy for Mental Health America (MHA) of Wisconsin during a Dec. 12 webinar.
Distal nerve transfer from the median nerve lumbrical fibers to the distal ulnar nerve motor branches in the palm: An anatomical cadaveric study
Authors: Colonna Michele R. , Pino Davide , Battiston Bruno , d'Alcontres Francesco Stagno , Natsis Konstantinos , Bassetto Franco , Papadopulos Nikolaos A. , Tiengo Cesare , Geuna Stefano
Published: December 2018

Background

The aim of the current study is to investigate the first and second lumbrical nerves as potential fibers donors to the deep motor branch of the ulnar nerve to avoid intrinsic atrophy in high ulnar nerve injuries.

Methods

Sixteen fresh frozen cadaveric hands were dissected, the radial lumbrical nerves accessed, and a coaptation, either in reverse end‐to‐side or in double end‐to‐side through a bridge nerve graft, was created to the deep motor branch of ulnar nerve.

Semithin sections were taken from samples of donor and recipient nerves for qualitative (nerve architecture) and quantitative studies (fiber count and donor/recipient ratio).

Results

The first lumbrical showed a robust trunk and a superior axon density (9,126.50 ± 2,923.41 axons/mm2) to the ulnar motor branch (7,506.50 ± 1,137.50 axons/mm2 distal to the opponens tunnel and 7,947.75 ± 1,741.24 axons/mm2 before its terminal branching); the ulnar motor branch showed a higher axon number (2,633.51 ± 410.00 distal to the opponens tunnel and 2,345.75 ± 2,101.56 before its terminal branching) than the first lumbrical (1,410.56 ± 823.89); section areas occupied by axons were higher in proximal (0.20 ± 0.16) and distal (0.26 ± 0.20) ulnar samples than the first lumbrical (0.17 ± 0.16).

Donor/recipient ratio first lumbrical/deep motor branch of the ulnar nerve were 1:1.86 (distal to the opponens tunnel) and 1:1.67 (at its terminal branching); data about the second lumbrical were ruled out because of bias.

Conclusions

A transfer from the first lumbrical nerve to the deep motor branch of the ulnar nerve in palm is suitable to avoid intrinsic atrophy.
Reconstruction of laryngopharyngectomy defects: Comparison between the supraclavicular artery island flap, the radial forearm flap, and the anterolateral thigh flap
Authors: Reiter Maximilian , Baumeister Philipp
Published: December 2018

Objectives

The purpose of this study was to evaluate the application of the supraclavicular artery island flap (SCAIF) for the reconstruction of laryngopharyngectomy defects in comparison with reconstructions with the anterolateral thigh flap (ALT) and the radial forearm flap (RFF).

Patients and methods

A retrospective study was performed. We compared indications for surgery, reconstructive techniques, operative time, time of hospitalization, and complication rates between patients treated with SCAIF, RFF and ALT following laryngopharyngectomy. Seventy‐seven patients were included, 18 underwent reconstruction with SCAIF (23%), 36 with RFF (47%), and 22 with ALT (29%). Seventy‐five laryngopharyngectomies (97%) were performed due to oncologic indications, 27 patients (35%) had been treated with prior radiotherapy. Fifty‐seven defects (74%) were partial defects, whereas 20 (26%) were circumferential.

Results

No statistical differences in operative time between the groups (298 min ± 53 [SCAIF] vs 301 min ± 54 [ALT] vs 302 min ± 47 [RFF]; P = .806) were observed. Preoperative radiation was found to be an independent risk factor for flap loss (P < .001), the development of fistula (P = .032), and pharyngeal stenosis (P = .034) in our cohort. Nevertheless, no differences between the different groups were detected (fistula rate: 11% [SCAIF] vs 14% [ALT] vs 11% [RFF]; P = .944, stenosis rate: 11% [SCAIF] vs 14% [ALT] vs16% [RFF]; P = .874, gastric tube dependency: 28% [SCAIF] vs 23% [ALT] vs16% [RFF]; P = .590).

Conclusion

The SCAIF is an equivalent alternative compared to well‐established techniques, such as the RFF and the ALT regarding reconstruction of defects after laryngopharyngectomy.
Quasistatic frictional thermo‐piezoelectric contact problem
Authors: Benaissa Hicham , Benkhira El‐Hassan , Fakhar Rachid , Hachlaf Abdelhadi
Published: December 2018

We consider here a mathematical model describing the bilateral frictional contact between a thermo‐piezoelectric body and a thermally conductive foundation. We model the behavior of the material with a linear thermo‐electro‐elastic constitutive law. The process is assumed to be quasistatic and the contact is modeled with a nonlocal version of Coulomb's dry friction law, in which the frictional heat generated in the process, is taken into account. We drive a variational formulation of the problem and establish the existence of its weak solution.
Delayed perturbation of Mittag‐Leffler functions and their applications to fractional linear delay differential equations
Authors: Mahmudov Nazim I.
Published: December 2018

In this paper, we propose a delayed perturbation of Mittag‐Leffler type matrix function, which is an extension of the classical Mittag‐Leffler type matrix function and delayed Mittag‐Leffler type matrix function. With the help of the delayed perturbation of Mittag‐Leffler type matrix function, we give an explicit formula of solutions to linear nonhomogeneous fractional delay differential equations.
Practical application of 1H benchtop NMR spectroscopy for the characterization of a nonaqueous phase liquid from a contaminated environment
Authors: Fallaise Darcy , Balkwill Tweedie Hannah , Konzuk Julie , Cheyne Carol , Mack E. Erin , Longstaffe James G.
Published: December 2018

Nonaqueous phase liquids (NAPLs) located at the surface of the water table and/or below the water table are often a significant source for groundwater contamination near current or former commercial/industrial facilities. Due to the complex and long history of many industrial sites, these NAPLs often contain a complex mixture of contaminants and as such can be difficult to fully characterize using conventional analytical methods. Remediation and risk assessment activities at sites containing NAPLs may, subsequently, be hindered as the contamination profile may not be fully understood. This paper demonstrates the application of bench‐scale 1H nuclear magnetic resonance (NMR) spectroscopy as a practical tool to assist with the characterization of complex NAPLs. Here, a NAPL collected from a contaminated site situated near a former chemical manufacturing facility was analyzed using a combination of one‐dimensional (1D) 1H NMR spectroscopy and two‐dimensional (2D) 1H J‐resolved spectroscopy (JRES). It is shown that 1D NMR experiments are useful in the rapid identification of the classes of compounds present, whereas 2D JRES NMR experiments are useful in identifying specific compounds. The use of benchtop NMR spectroscopy as a simple and cost effective tool to assist in the analysis of contaminated sites may help improve the practical characterization of many heavily contaminated sites and facilitate improved risk assessments and remedial strategies.
Modeling binary alloy solidification by a random projection method
Authors: Carpy Sabrina , Mathis Hélène
Published: December 2018

This paper addresses the numerical modeling of the solidification of a binary alloy that obeys a liquidus–solidus phase diagram. In order to capture the moving melting front, we introduce a Lagrange projection scheme based on a random sampling projection. Using a finite volume formulation, we define accurate numerical fluxes for the temperature and concentration fields which guarantee the sharp treatment of the boundary conditions at the moving front, especially the jump of the concentration according to the liquidus–solidus diagram. We provide some numerical illustrations which assess the good behavior of the method: maximum principle, stability under CFL condition, numerical convergence toward self‐similar solutions, ability to handle two melting fronts.
An analysis of the Robert–Asselin time filter for the correction of nonphysical acoustics in an artificial compression method
Authors: DeCaria Victor , Layton William , McLaughlin Michael
Published: December 2018

Artificial compression methods create nonphysical acoustic waves. Time filters, often used in geophysical fluid dynamics, are shown in this paper to selectively damp these acoustics. We analyze the stability of a two‐step artificial compression method with the Robert–Asselin (RA) time filter, and provide tests delineating the filter's positive effects on both stability and accuracy.
Thermo‐viscoelastic fiber‐reinforced continua simulated by variational‐based higher‐order energy‐momentum schemes
Authors: Groß Michael , Dietzsch Julian , Bartelt Matthias
Published: December 2018

In this paper, novel higher‐order accurate energy‐momentum schemes are presented, emanating from a discrete mixed principle of virtual power. These time‐stepping schemes are designed for simulating an uni‐directional fiber‐reinforced material, considered as transversely isotropic nonlinear continua. The matrix material is considered as an isotropic thermo‐viscoelastic material and the fibers behave thermoelastic. The higher‐order accurate energy‐momentum schemes preserve each balance law of the continuous problem also in the discrete setting, independent of the chosen time step size and the prescribed Neumann and Dirichlet boundary conditions. Therefore, the implemented time step size control with the iteration number as target function does not influence the preservation properties of the time‐stepping schemes. The balance laws are also preserved together with different time scales in the mechanical, thermal and viscous time evolution (different shape functions in time).
Identification of a nonlinear spring and damper characteristics of a motorcycle suspension using test ride data
Authors: Lauß Thomas , Sterl Dominik , Oberpeilsteiner Stefan , Steiner Wolfgang
Published: December 2018

During test rides of motorcycles modifications are made to the suspension. In order to quantify those changes, the nonlinear spring and damper characteristics must be determined. This is usually done on a test bench. However, measurements on a test bench are closely related to high costs and high time exposure. Hence, a parameter identification after a test run, formulated as an optimization task, seems to be an auspicious approach. For this purpose a cost function is defined, which is minimized by considering the dynamics of the system. The strength of the contribution is the efficient gradient computation using the adjoint variable approach. In order to approximate the nonlinear spring and damper characteristics cubic splines are used. The values of the spline functions at specified grid points (knots) are adjusted such that the deviation between simulation and measurement is minimal.
Polyconvexity inspired frameworks and structure‐preserving integrators for multi‐field problems
Authors: Franke Marlon , Janz Alexander , Schiebl Mark , Ortigosa Rogelio , Betsch Peter
Published: December 2018

A new approach for the design of energy‐momentum (EM) consistent time integrators for nonlinear coupled problems is proposed. Polyconvexity inspired internal or Helmholtz free energy functions are obtained by using the rediscovered tensor cross product (see [1]) which is basically applied on the cofactor and the determinant of the right Cauchy‐Green strain tensor and greatly simplifies the algebra (see [1,2]). On this basis multi‐field problems concerning non‐linear thermo‐elastodynamics (see [3]) and electro‐elastodynamics (see [4]) are considered. For the former a temperature based weak form is employed which facilitates the design of a structure‐preserving time‐stepping scheme for coupled thermo‐elastic problems. For the latter a four‐field internal energy‐based dynamic formulation is applied. In both cases, the polyconvexity‐based framework facilitates the design of EM consistent time integrators. In particular algorithmic stress formulas are employed which show a remarkably simple structure when compared to traditional, elaborate projection‐based formulas. The spatial discretisation relies on finite element interpolations for the unknown fields. Eventually, the superior robustness of the proposed formulations is shown in two numerical examples.
Symmetry Groups and the Observability of PDEs
Authors: Kolar Bernd , Schöberl Markus
Published: December 2018

Symmetry groups of PDEs allow to transform solutions continuously into other solutions. In this contribution, we use symmetry groups for studying the observability of systems of nonlinear PDEs with input and output. Based on a differential‐geometric representation of the system, we present conditions for the existence of special symmetry groups that do not change the trajectories of the input and the output. If such a symmetry group exists, the system cannot be observable.
On an Invariance Principle for the Solution Space of the Differential Riccati Equation
Authors: Behr Maximilian , Benner Peter , Heiland Jan
Published: December 2018

The differential Riccati equation appears in different fields of applied mathematics like control theory and systems theory. For large‐scale systems the numerical solution comes with a large amount of storage requirements. This motivates the use of Krylov subspace and projection based methods [1–3].

In the present paper we apply an invariance theorem for ODEs to the differential Riccati Equation. We show that the solution is contained in a Krylov like subspace and extend our results to certain time‐varying cases.
Product integration method for simulation of radial effects in dry spinning processes
Authors: Wieland Manuel , Arne Walter , Feßler Robert , Marheineke Nicole , Wegener Raimund
Published: December 2018

Industrial dry spinning processes are crucially determined by the interaction of the spun fibers with the surrounding airflow as well as the radial effects of the fiber quantities due to solvent evaporation. To achieve computability for a large number of fibers the numerical simulation of the latter has to be very efficient. We present a suitable solution algorithm based on the product integration method. Thereby, accuracy and stability of the underlying quadrature formulas are discussed.
An extended exponentiated Hencky energy for transverse isotropy
Authors: von Hoegen Markus , Schröder Jörg , Neff Patrizio
Published: December 2018

In this contribution we aim to formally extend the promising exponentiated Hencky strain‐energy to transversely isotropic problems. This is facilitated by using additional anisotropic logarithmic strain invariants. The potential of the logarithmic‐strain driven material response is studied for a numerical example associated to arterial wall mechanics in order to draw a comparison to a more classical material formulation based on the right Cauchy‐Green tensor.
Weak shock reflection in steady transonic dense gas flow
Authors: Kluwick A. , Cox E. A.
Published: December 2018

Flows of dense gases may exhibit a number of phenomena which are impossible in the case of perfect gases and thus are of considerable theoretical interest. These include, among others, the formation of rarefaction shock waves which accelerate rather than decelerate the gas and a substantial increase of the lower critical Mach number. As a consequence there is no danger of flow separation if rarefaction shocks interact with boundary layers in high Reynolds number flow. Experimental work is needed to clarify whether these phenomena predicted by theory can be realised in a technical environment and be used to increase the efficiency of turbomachines in Organic Rankine Cycles for decentralised power plants in low popularised areas. Special interest here is for steady transonic flow. The present work is intended to support such experimental efforts. As a first step the most simple but canonical case of slightly supersonic flow past compression/compression ramps was considered in Kluwick & Cox [1]. The present study is intended to complete the understanding of such flows by investigating the reflection problem arising from the presence of an opposing solid wall in confined geometries.
Solid‐shell formulations based on reduced integration – investigations of anisotropic material behaviour at large deformations
Authors: Barfusz Oliver , Smeenk Randy , Reese Stefanie
Published: December 2018

Some years ago, a family of continuum finite elements based on reduced integration (e.g. [1], [2]) was investigated. Many engineering problems with isotropic material behaviour were considered and these elements showed accurate results while being more efficient than similar three‐dimensional formulations based on full integration. The objective of the present contribution is to extend the analysis to layered structures with anisotropic material behaviour undergoing large deformations. Here, we follow an ansatz which is similar to so called equivalent single layer theories, i.e., we model the inhomogeneous material as a continuum using solely one solid‐shell element over the thickness. Therefore, we introduce an additional mapping procedure which enables both, the usage of a certain quadrature rule within each layer of the composite and the consideration of layers with different thickness. A benchmark problem from the literature shows that the new developed ingredient within the solid‐shell concept leads to accurate results in terms of the global response of anisotropic structures at large deformations.
On a geometrically exact Euler‐Bernoulli beam element
Authors: Maassen Sascha , da Costa e Silva Cátia , de Mattos Pimenta Paulo , Schröder Jörg
Published: December 2018

In this work, a geometrically exact, fully nonlinear Euler‐Bernoulli beam formulation is presented. Herewith a special case of Timoshenko rod models, discussed in various publications such as [2] or [4], is considered. Following the basic assumptions of transversal shear rigidity and plane cross sections, the formulation is based on displacements, their derivatives and a torsional rotation angle, in order to cover finite deformations and rotations. A straight reference configuration is considered, whereas the possibility for initially curved configurations is discussed in [1]. Within the Euler‐Bernoulli theory a cross section undergoes ridged body translation and rotation. While the translation is described by the motion of the beam axis only, the rotation is accounted within a rotational field, see e.g. [3]. In the present formulation, the rotational field is parametrized by the rotation tensor based on Rodrigues formula, which yields a simple update scheme as shown in [5], and is the first of its kind for Euler‐Bernoulli beam models. Using this parametrization an ansatz is presented, that allows for consistent connection of structural members, even in cases of physical discontinuities. On the element level C1 continuous Hermite polynomials are used to interpolate the displacements an their derivatives, while a Lagrangian interpolation scheme is chosen for the torsional rotation. A numerical Benchmark problems is presented to demonstrate the performance of the finite element formulation.
An ℋ2 ⊗ ℒ2‐Optimal Model Order Reduction Approach for Parametric Linear Time‐Invariant Systems
Authors: Hund Manuela , Mlinarić Petar , Saak Jens
Published: December 2018

So far, ℋ2 ⊗ ℒ2‐optimal model order reduction (MOR) of linear time‐invariant systems, preserving the affine parameter dependence, was only considered for special cases by Baur et al in 2011. In this contribution, we present necessary conditions for an ℋ2 ⊗ ℒ2‐optimal parametric reduced order model, for general affine parametric systems resembling the special case investigated by Baur et al.
Calibrations in families for minimal networks
Authors: Carioni Marcello , Pluda Alessandra
Published: December 2018

We define the calibrations in families for minimal Steiner networks and we explain through an example its convenience with respect to the “classical” notions of calibrations for the Steiner Problem.
Domain decomposition applied to the thermal model of selective beam melting processes
Authors: Soldner Dominic , Steinmann Paul , Mergheim Julia
Published: December 2018

The utilization of additive manufacturing enables the realization of rather complex part geometries. In the context of powder bed‐based selective beam melting processes, parts are built in a layer‐by‐layer fashion by locally fusing powdered material using either a laser or electron beam. The simulation of powder bed‐based additive manufacturing processes for both, polymers as well as metals, is usually a computationally expensive task. This is especially due to the different involved time and length scales, highly non‐linear material behaviour and dynamic growth of the simulation domain. Hence, several numerical methods are ought to be combined in order to reduce the associated computational cost. Therefore we employ adaptivity in the spatial and temporal domain. This allows to have locally refined regions that are currently exposed to the beam, while coarsening the discretization in areas that are currently not exposed to the beam. In addition the path of the heat input is integrated in time, which renders a line heat input model. Furthermore, domain decomposition (Multi‐Time‐Stepping) is applied to account for the different requirements regarding the temporal discretization of different parts of the considered domain. This renders a time integration scheme with distinct time step sizes for different partitions of the domain.
Singularity‐free dislocation continuum theory for anisotropic crystals
Authors: Lazar Markus , Po Giacomo
Published: December 2018

A non‐singular theory of three‐dimensional dislocations is derived from a particular version of Mindlin's anisotropic strain gradient elasticity theory of form II. Using the anisotropic gradient elasticity theory, we give the non‐singular fields produced by arbitrary dislocation loops in anisotropic solids. In particular, we present the anisotropic versions of the Burgers displacement equation with solid angle, the Mura‐Willis equation for the elastic distortion, the Peach‐Koehler stress equation, the Blin equation for the interaction energy and the Peach‐Koehler force.
Goal‐oriented adaptivity for parameter identification in linear micromorphic elasticity
Authors: Ju Xiaozhe , Mahnken Rolf
Published: December 2018

It is well‐known that the classical Cauchy‐Boltzmann continuum, in spite of its simplicity, has its limitations, e.g. on the simulation of strain localization phenomena or size effects. For a remedy, one may resort to the so‐called generalized continuum theories, see e.g. [2] and references therein. Amongst others, we consider a class of higher order continua, namely the micromorphic continua, where the kinematics are enriched by means of a microstructure undergoing an affine micro deformation. As a drawback, the enriched kinematics lead to additional constitutive equations, increasing the number of material parameters, and therefore making the parameter identification procedure more involved. Here, the parameter identification is viewed as an inverse problem minimizing a least‐square function, see also [3] for a micropolar continuum. For simplicity, we restrict ourselves to a small strain theory. The increasing number of the degrees of freedom and the material parameters clearly motivates an application of adaptive methods. For an application on the direct micromorphic problems, we refer to [5]. Here for the inverse micromorphic problems, we follow the general ansatz by [1] for goal‐oriented error estimation and adaptivity, with which we control the spatial discretization errors of the finite element method. For illustration, numerical examples are presented.
Computing solution‐compensation spaces using an enhanced Fourier‐Motzkin algorithm
Authors: Vogt Marc Eric , Duddeck Fabian , Harbrecht Helmut , Stutz Florian , Wahle Martin , Zimmermann Markus
Published: December 2018

In complex system design, design variables can be divided into two groups, early‐ and late‐decision variables. Early‐decision variables are equipped with tolerance regions which are specified during the early stages of the development process. Tolerance is necessary to account for changes of design variable values due to later and therefore unknown, design restrictions. In this sense, early‐decision variables are subject to lack‐of‐knowledge uncertainty. Tolerance regions for early‐decision variables can be significantly increased by the use of late‐decision variables. The latter are not equipped with tolerance regions and, by contrast, have to be arbitrarily well adjustable within their design intervals. The values of late‐decision variables are chosen in a later development phase when further design restrictions are known. Late‐decision variables then may compensate for the choice of early‐decision variables. Solution‐compensation spaces are regions of early‐ and late‐decision variables where for all values of early‐decision variables values for late‐decision variables from their associated intervals exist such that all design requirements are satisfied.

A new approach to compute solution‐compensation spaces for linear systems is introduced. It is based on an enhanced Fourier‐Motzkin‐Elimination algorithm which uses H‐redundancy removal. The new algorithm is applied to a design problem from vehicle dynamics and we show that it outperforms the so‐called basic projection algorithm presented in [7].
Sparsity pattern extraction for assembly of KKT‐like matrices in multibody dynamics
Authors: Hofmeister Benedikt , Gebhardt Cristian Guillermo , Hente Christian , Rolfes Raimund
Published: December 2018

The implicit dynamic solution of multibody and finite element simulations with kinematic constraints requires the assembly of KKT‐like matrices, which are constant in structure, but unsymmetric in the most general case. Basically, the numerical solution is computed by means of a Newton‐Raphson iterative scheme and applying a direct sparse solver in this context demands a reordering step prior to the actual iterative solution procedure. This means that the sparsity pattern of the KKT structure has to be known in advance for all possible configurations and loading situations that are going to be employed along each stand along simulation step.

In this contribution, we present a scheme, in which the sparsity pattern is extracted dynamically from the assembly code of KKT‐like matrices. The underlying sparse scheme is transparent to the element and constraint iteration matrix assembly. This is enabled by exploiting the structure and order of events during the element matrix assembly. The proposed strategy is implemented with an object‐oriented programming style in a modern Fortran 2008 environment.
On the Identification of the Contact Parameters of the Discrete Element Method for Complex Particle Ensembles
Authors: Hoormazdi Golnaz , Hackl Klaus
Published: December 2018

The Discrete Element Method (DEM) is a particle‐based approach, which is applied in a wide range of engineering fields. One problem of the DEM is the identification of the required input parameters that govern the material behavior. In this study, we develop an analytical prediction based on an energy minimization approach relating the macroscopic elastic parameters to the microscopic contact parameters. In order to validate these relations, a series of confined and unconfined compression tests are performed by PFC3D. A more complex version of materials containing a mixture of different types of particle ensembles are used to study the effect of bonding and grain shape on the elastic properties of the materials. This study covered both solid (bonded) and granular (unbonded) materials.
Phase field modeling of brittle fracture in materials with anisotropic fracture resistance
Authors: Schreiber Christoph , Kuhn Charlotte , Müller Ralf
Published: December 2018

Materials which reveal a directionality in terms of the fracture resistance motivate the integration of anisotropic behavior within approaches for crack growth simulations. Within a variational phase field model for fracture, this kind of anisotropy is included by the enhancement of the non‐local part of the crack energy functional. Results of a numerical crack path simulation are presented and discussed to illustrate the properties of the applied model.
Applied Mechanics on Docking Sequences
Authors: Weltzien Charlott
Published: December 2018

Nowadays many shipyards have their own floating docks for both new buildings and repairs. In view of all the challenging projects these days, many yards have to produce designs which are close to or even beyond the structural limits of their docking facilities. This paper presents a first principle based method to calculate the key numeric values to extend the scope of application of floating docks and platforms.
A fuzzy‐stochastic model for transversely fiber reinforced plastics
Authors: Caylak Ismail , Penner Eduard , Dridger Alex , Mahnken Rolf
Published: December 2018

This work is directed to aleatoric and epistemic uncertainties in the framework of constitutive modeling, which are taken into account by stochastic and fuzzy analysis. The stochastic part of material parameters are expanded with the multivariate polynomial chaos expansion, where for epistemic uncertainty the polynomial chaos coefficients are defined as design variables, which are modeled as fuzzy sets. The resulting min‐max optimization problem for the fuzzy analysis is approximated by α‐level discretization. A numerical example for the hybrid fuzzy‐stochastic analysis of material parameters is concerned with two different uncertain approximations to demonstrate the versatility of the proposed formulation.
On the hot spots of quantum trees
Authors: Kennedy James , Rohleder Jonathan
Published: December 2018

We show that any second eigenfunction of the Laplacian with standard vertex conditions on a metric tree graph attains its extremal values only at degree one vertices, and give an example where these vertices do not realise the diameter of the graph.
Stabilization of a Time‐Dependent Discrete Adjoint Solver for Chaotic Incompressible Flows
Authors: Warnakulasuriya Suneth , Andre Michael , Wüchner Roland , Bletzinger Kai‐Uwe
Published: December 2018

Following the growth of computational fluid dynamics in engineering applications, adjoint methods for sensitivity analysis are being applied to an increasing range of industrial problems. In recent years, growth in computational power has led to widespread use of high‐fidelity, time‐resolved techniques, such as large‐eddy simulation, for applications, including bluff‐body aerodynamics, where time‐averaged equations may be less reliable. The solution of time‐dependent adjoint equations, however, becomes unstable in time as the Reynolds number increases and the flow becomes chaotic. The source of this instability has been explained by analysis of the system's Lyapunov exponents and several solutions have been proposed in the literature based on least‐squares shadowing. Currently, such techniques impose a higher computational cost compared to classical adjoint methods and may become infeasible when the number of unstable Lyapunov exponents is large. In this work, we explore a more recently proposed approach, which balances the adjoint energy source term with added artificial dissipation. The stability of this approach is investigated for a discrete adjoint solver based on the time‐dependent incompressible Navier‐Stokes equations. The accuracy of the resulting shape sensitivities is analyzed using a linear regression technique for the flow around a circular cylinder.
Finite element investigations on the cyclic behavior of shape memory alloys
Authors: Waimann Johanna , Hackl Klaus , Junker Philipp
Published: December 2018

Shape memory alloys show the effect of functional fatigue under cyclically loading. This fatigue comes along with a decrease of the stress plateaus in the characteristic hysteresis curve which is also accompanied by an accumulated permanent strain. Cyclic experiments detected that a formation of dislocations trigger a stabilization of martensite and thus, are responsible for this kind of functional degradation. Our model takes into account the inelastic behavior by splitting the phase transformation from austenite to martensite into a reversible and an irreversible process. In addition to that, we include an orientation distribution function to account –in a numerically very advantageous way– for the shape memory alloy's polycrystalline structure, see [3]. After presenting the material model [6], we comment on the implementation into a finite element framework. Starting with the simulation of a cyclically loaded wire, we close with the geometrically more ambitious and application‐oriented example of a clamping ring as already presented in [7].
Data‐driven approach to elastic problems
Authors: Korzeniowski Tim Fabian , Weinberg Kerstin
Published: December 2018

Recently Kirchdoerfer and Ortiz proposed a new computing paradigm, called data‐driven computing [1]. It is a new approach to overcome uncertainties in the modeling process of the material law. The aim of this work is to compare the solutions of the data‐driven method with classical finite element solutions and an analytic solution. A simple elastic problem is considered and solutions of all methods are presented.
Coupled mass interactions in plant tissues under frost conditions
Authors: Eurich Lukas , Wagner Arndt , Ehlers Wolfgang
Published: December 2018

Frost‐hardy plant tissues have developed strategies to cope with frost events without damage. This is a very interesting feature with regard to technical applications in construction industry, where frost damage is still a major concern. This contribution introduces a biologically inspired macroscopic modelling approach based on the Theory of Porous Media (TPM) to describe the coupled thermo‐hydro‐mechanical processes in plant tissues. The focus is, in particular, on the mass interactions within the plant tissue under frost conditions, which are the ice formation in the intercellular space and the dehydration of the tissue cells, which is a crucial property for frost‐resistance. A numerical example illustrates the coupling of these mass interactions.
New biaxially loaded specimens for the material parameter identification of ductile damage
Authors: Gerke Steffen , Schmidt Marco , Brünig Michael
Published: December 2018

The paper deals with new biaxial experiments to study the damage and fracture behavior of ductile sheet metal. For this purpose the H‐specimen has been specially designed and is subjected to different proportional loadings within this context.

The stress state dependent damage and fracture behavior can be described by a phenomenological continuum damage and fracture model which is briefly presented. In continuation results of new biaxial experiments are given which facilitate the study of different damage mechanisms in a well controlled way. The proposed H‐specimen is applied for shear–tension as well as for shear–compression load cases and can be used to evaluate the corresponding continuum damage model. Furthermore a perspective to future work is given.
Double‐stage optimization of truss and frame structures
Authors: Keller Alexander , Muench Ingo , Wagner Werner
Published: December 2018

Comprehensive optimization of truss and frame structures is intended to optimize all aspects of a structure: the topology, shape and size of members. However, simultaneous optimization of all mentioned aspects increases the complexity of the problem and leads to high demands for the used optimization algorithm. We propose to decompose the optimization task and to use specialized algorithms for each stage of the process. First, a phase field model evolves the topology as basic design. Then, we use an interface to set up a simplified beam model, where connection topologies and nodal positions as well as cross sections are simultaneous optimization parameters of the Evolutionary Algorithm.
On a least‐squares finite element formulation for sea ice dynamics
Authors: Schröder Jörg , Nisters Carina , Ricken Tim
Published: December 2018

In this contribution a mixed least‐squares finite element method (LSFEM) for the modeling of sea ice motion including a viscous‐plastic (VP) sea ice rheology is investigated. The simulation of sea ice motion goes back to the findings in Hibler III [4], where a numerical model for the simulation of sea ice circulation and thickness evolution over a seasonal cycle is introduced. Both the ice thickness and ice concentration distribution are explicitly described on the basis of evolution equations. Recent research in this field is devoted to finite element formulations based on the Galerkin variational approach. Here, special focus lies on the stabilization of the numerically complex scheme. It is therefore desirable to establish a least‐squares formulation to overcome possible numerical drawbacks. The least‐squares variational approach is well established in finite element formulations in the branch of fluid mechanics, see [2], [3] and [6], for instance. A great advantage of the method is its applicability to first‐order systems, such that it results in stable and robust formulations also for not self‐adjoint operators like in the Navier‐Stokes equations, for instance. A box test case, see [7], is investigated for the least‐squares formulation.
Restrictions in phase field modeling of brittle fracture
Authors: Strobl Michael , Seelig Thomas
Published: December 2018

A key feature of phase field approaches to fracture is the relatively simple structure of the method. However, current approaches inevitably exhibit some limitations which do not seem to be obvious and are therefore neglected in many investigations. The assumption of isotropic stiffness degradation by a scalar phase field parameter does not capture the anisotropy introduced by a crack and severely restricts the scope of application. Widely used tension‐compression splits violate the specific conditions at cracks like traction free crack surfaces and, in addition, introduce mesh orientation dependency. Accurate approximation of the surface (fracture) energy is another important requirement which is discussed for a non‐vanishing internal length ℓ.
An adaptive FE2 method for the thermomechanical behaviour of a SMA‐Fiber matrix composite
Authors: Praster Maximilian , Klinkel Sven
Published: December 2018

This contribution deals with the multiscale analysis of a reinforced matrix with shape‐memory‐alloys (SMA). The complicated micro‐structure permits a full discretized macro‐structure, due to that an FE2 approach is used. Unlike classic materials, the SMA has more complex behavior with a high‐temperature dependency in the loading and unloading case. The micro‐structure of the macroscopic problem consists of a linear‐elastic matrix and a random fiber distribution. The stress response of the composite depends non‐linearly on the deformation, the fiber orientation and the temperature. Due to the non‐linear behavior of the fiber a nested homogenized is employed at each integration point. This results in the so‐called FE2 method. One disadvantage of the FE2 method is the high computational effort by solving the boundary value problem (BVP) in every integration point and every iteration step. This motivates the present work to introduce an indicator, which determines whether an accompanying homogenization is needed. Due to the temperature dependency, on the macro‐scale, a coupled thermo‐mechanical problem is solved. In the first homogenization step, the BVP of the RVE is solved with Neumann Boundary conditions. This leads to an overestimation of the strains. The SMA will remain linear elastic until the phase transition condition is reached. The formulation is similar to the classical yield condition of elasto‐plastic materials, however, here a strain instead a stress creteria is used. From the phase transition condition, the temperature dependent indicator is defined and formulated as a limit strain for the linear behavior of the SMA‐fibers. The accompanying homogenization is firstly needed when the limit strain is reached.
External boundary value problems in the quasi static theory of thermoelasticity for materials with triple voids
Authors: Svanadze Merab
Published: December 2018

In this paper the quasi static linear theory of thermoelasticity for materials with triple voids is considered. Basic external boundary value problems (BVPs) of steady vibrations are formulated. The uniqueness and existence theorems for regular (classical) solutions of these BVPs are established.
A normalization concept for smart material actuation by the example of hydrogels
Authors: Ehrenhofer Adrian , Wallmersperger Thomas
Published: December 2018

For passive (classical) materials, stress and strain are used to extract the material behavior from the sample behavior in a tensile test. In analogy, the actuation behavior of active (smart) materials can be normalized. In the present research, we show the normalization using the example of hydrogels that react with a volume change (swelling and deswelling) when exposed to stimulus‐changes like temperature, chemical concentrations, pH or light intensity changes. The normalized behavior can then be implemented with the Temperature‐Expansion‐Model which is based on the analogy of active behavior with thermal expansion. This allows the simulation of arbitrary active structures and the extraction of the sensitivity measure to a stimulus.
First Steps Towards the Direct Micro‐Macro Simulation of Reinforced Concrete Under Impact Loading
Authors: Tamsen Erik , Weber Wolfang , Balzani Daniel
Published: December 2018

This contribution presents a micro‐macro formulation for impact loading based on kinematic admissibility and the principle of multiscale virtual power, which allows for an energetically consistent scale‐bridging taking into account inertia forces at the microscale. Necessary constraints are discussed, a consistent formulation for the macroscopic tangent modulus for dynamic loading is presented and applied to a simple numerical example.