bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractNonaqueous 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.
Thermo‐viscoelastic fiber‐reinforced continua simulated by variational‐based higher‐order energy‐momentum schemes
Authors: Groß Michael , Dietzsch Julian , Bartelt Matthias 
Published: December 2018

AbstractIn 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

AbstractDuring 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

AbstractA 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

AbstractSymmetry 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

AbstractThe 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

AbstractIndustrial 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

AbstractIn 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

AbstractFlows 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

AbstractSome 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

AbstractIn 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

AbstractSo 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.
Domain decomposition applied to the thermal model of selective beam melting processes
Authors: Soldner Dominic , Steinmann Paul , Mergheim Julia 
Published: December 2018

AbstractThe 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

AbstractA 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

AbstractIt 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

AbstractIn 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

AbstractThe 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

AbstractThe 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

AbstractMaterials 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

AbstractNowadays 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

AbstractThis 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.