bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interaction between inner and outer layer in drag‐reduced turbulent flows
Authors: Cormier Marion , Gatti Davide , Frohnapfel Bettina 
Published: October 2016

AbstractEffects of wall‐based skin‐friction drag reduction strategies on the statistical properties of large‐scale motions in moderate Reynolds number turbulent flows have been investigated by exploiting Direct Numerical Simulation of turbulent channels. To educe large scales, a new efficient parallel distributed memory algorithm has been implemented which delivers data‐driven modes of increasing characteristic lengthscales: the Fast and Adaptive Bidimensional Empirical Mode Decomposition (FABEMD). The influence of wall‐based skin friction reduction on large scales is studied by comparing single point statistics, such as r.m.s. fluctuations, and two‐point statistics, as cross‐correlation functions in controlled and uncontrolled channel flow fields at constant friction Reynolds number. The traditional way of observing large‐scale footprinting at the wall, as cross‐correlation of the streamwise velocity components at different wall distances, has been found to be unreliable when comparing drag‐reduced flows, due to the arbitrary choice of a reference plane in the logarithmic layer. A more sound way of observing the footprinting via the correlation of the streamwise velocity with the friction velocity is addressed and shows an increase of the footprinting in drag‐reduced flows. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transportation of dry fine powders by coordinated friction manipulation
Authors: Dunst Paul , Bornmann Peter , Hemsel Tobias , Littmann Walter , Sextro Walter 
Published: October 2016

AbstractThe transportation of dry fine powders is an emerging technologic task, as in biotechnology, pharmaceutical or coatings industry particle sizes of processed powders are getting smaller and smaller. Fine powders are primarily defined by the fact that adhesive and cohesive forces outweigh the weight forces. This leads to mostly unwanted agglomeration (clumping) and adhesion to surfaces, what makes it more difficult to use conventional conveyor systems (e. g. pneumatic or vibratory conveyors) for transport. A rather new method for transporting these fine powders is based on ultrasonic vibrations, which are used to reduce friction and adhesion between powder and the substrate. One very effective set‐up consists of a pipe, which vibrates harmoniously in axial direction at low frequency combined with a pulsed radial high frequency vibration. The high frequency vibration accelerates the particles perpendicular to the surface of the pipe, which in average leads to lower normal and thereby smaller friction force. With coordinated friction manipulation the powder acceleration can be varied so that the powder may be greatly accelerated and only slightly decelerated in each excitation period of the low frequency axial vibration of the pipe. The amount of powder flow is adjustable by vibration amplitudes, frequencies, and pulse rate, which makes the device versatile for comparable high volume and fine dosing using one setup. Within this contribution an experimental set‐up consisting of a pipe, a solenoid actuator for axial vibration and a piezoelectric actuator for the radial high frequency vibration is described. An analytical model is shown, that simulates the powder velocity. Finally, simulation results are validated by experimental data for different driving parameters such as amplitude of low frequency vibration, pipe material and inclination angle. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Enhancement of adjoint topology optimization by approximated L1‐regularization for promotion of sparse distributed control
Authors: Gerdes Anne , Hinze Michael , Rung Thomas 
Published: October 2016

AbstractAn L1‐penalty term is inserted in the cost functional of an optimal control problem in order to promote a sparse distribution of the control variable. The non‐differentiable L1‐regularization term is approximated by differentiable Huber functions. The approach is validated by generic fluid‐dynamic test cases and applied to a cabin air outlet of an aircraft. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Existence of undercompressive weak solutions to the Euler equations
Authors: Kabil Buğra 
Published: October 2016

AbstractWe prove the local existence of an undercompressive hydrodynamical shock to the isothermal Euler equations with a non‐monotone pressure function. This nonlinear problem will be formulated as an abstract hyperbolic initial boundary value problem. The existence of a weak solution to a linearized version of the problem is shown with the use of Riesz theorem. Using the results of the linear system yields by an iteration scheme (local in time) well‐posedness of the nonlinear problem. The system of equations is obtained by modeling the motion of sharp liquid‐vapor interfaces including configurational forces as well as surface tension. The considered non‐viscous Van der Waals fluid is compressible and allows phase transitions. The propagating phase boundary is controlled by a modified version of the Rankine‐Hugoniot jump condition obtained by the Young‐Laplace law. Entropy dissipation at the interface is precisely described by a kinetic relation. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Minimization of asymptotic energy of Müller's functional endowed with local nonlinear lower‐order term
Authors: Raguž Andrija 
Published: October 2016

AbstractWe solve a minimization problem associated to a generalization of the Müller functional studied in the paper G. Alberti, S. Müller: A new approach to variational problems with multiple scales, Comm. Pure Appl. Math. 54, 761–825 (2001), whereby the lower order term
∫10a(s)v2(s)ds
(involving a primitive of the mass density function,
v = v(s),
and the weight function
a = a(s))
is replaced by
∫10a(s, v(s), v′(s))v2(s)ds
(where a belongs to a suitable Carathéodory class). We calculate the rescaled asymptotic energy of the functional as small parameter epsilon tends to zero. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of the Flow of Magnetoelastic Materials
Authors: Benešová Barbora , Forster Johannes , García‐Cervera Carlos , Liu Chun , Schlömerkemper Anja 
Published: October 2016

AbstractWe consider evolutionary models for magnetoelastic materials. The PDEs modeling the flow of the material were derived from variational principles in a continuum mechanical setting.In this article, we discuss the existence of weak solutions for two models, one with gradient flow type dynamics on the magnetic variable and in the other the dynamics of the magnetization is described by the Landau‐Lifshitz‐Gilbert equation. We highlight the main differences of the proofs in the two cases. © 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The sum of squared logarithms inequality in arbitrary dimensions
Authors: Borisov Lev , Neff Patrizio , Sra Suvrit , Thiel Christian 
Published: October 2016

AbstractWe prove the sum of squared logarithms inequality (SSLI) which states that for nonnegative vectors x, y ∈ ℝn whose elementary symmetric polynomials satisfy
ek(x) ≤ ek(y) (for 1 ≤ k < n)
and
en(x) = en(y)
, the inequality
∑i(log xi)2 ≤ ∑i(log yi)2
holds. Our proof of this inequality follows by a suitable extension to the complex plane. In particular, we show that the function
f : M ⊆ ℂn → ℝ with f(z) = ∑i(log zi)2
has nonnegative partial derivatives with respect to the elementary symmetric polynomials of z. We conclude by providing applications and wider connections of the SSLI. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A linear elastic Fuzzy Finite Element Method with two fuzzy input parameters
Authors: Dridger Alex , Caylak Ismail , Mahnken Rolf 
Published: October 2016

AbstractThis work employs a fuzzy finite element method (FFEM) in order to characterize the non‐statistical properties based on the possibility theory [2]. A linear elastic body with fuzzy input material parameters Young's modulus
$\tilde{E}$
and Poisson's ratio
$\tilde{\nu}$
is studied. To this end, the fuzzy parameters are represented by possibility distributions generated from sparse experimental data. A computational approach involving the α‐level discretization technique [4] is used in order to calculate the possibility of the system response. Finally, our method is applied in a numerical example. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
SFEM for rubber‐like materials at large deformations
Authors: Penner Eduard , Caylak Ismail , Nörenberg Nicole , Mahnken Rolf 
Published: October 2016

AbstractThis paper investigates the uncertainty of hyper‐elastic model, by random material parameters as stochastic variables. For its stochastic discretization a polynomial chaos (PC) is used to expand the coefficients into deterministic and stochastic parts. Then, from experimental data in combination with artificial data for elastomers the distribution of the force‐displacement curves are obtained. In the numerical example the PC‐based Stochastic Finite Element Method (SFEM) and the deterministic parameter identification are used for generation of the distribution of Ogden's material parameters. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Solution of the suicide substrate kinetics with an O'Malley/Hoppensteadt approximation of a higher order
Authors: Feist Bernd 
Published: October 2016

AbstractSolving singularly perturbed initial‐value problems with an two scale approach, the O’Malley/Hoppensteadt approximation (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Plastic limit analysis and optimum design of structures for uncertain conditions.
Authors: Movahedi Rad Majid 
Published: October 2016

AbstractAt the application of the plastic analysis and design methods the control of the plastic behaviour of the structures is an important requirement. Since the plastic limit analysis provides no information about the magnitude of the plastic deformations and residual displacements accumulated before the adaptation of the structure, therefore complementary strain energy of the residual forces could be considered an overall measure of the plastic performance of structures and the plastic deformations should be controlled by introducing a bound for magnitude of this energy. If the design uncertainties (manufacturing, strength, geometrical) are expressed by the calculation of the complementary strain energy of the residual forces a reliability based extended plastic limit design problem is formed. In this research, due to the uncertainties the bound for the complementary strain energy of the residual forces is given randomly and a general approach to evaluate the limit load capacity of structures for uncertain conditions is presented. The aim of this study is to evaluate limit load capacity of structures with limited residual strain energy on the probabilistically given conditions. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Tuning of mass dampers for preventing brittle fracture by employing teaching learning based optimization
Authors: Nigdeli Sinan Melih , Bekdas Gebrail 
Published: October 2016

AbstractIn design of reinforced concrete structures, a ductile design is needed, because the brittle fracture is sudden. Also, the energy absorbed by the structure is effective for ductile structures during earthquake excitations. In design regulations, especially for vertical supporters such as columns, the shear force and axial force capacity is limited, although the strength of the members is not at the limits. For that reason, the shear forces of structures excited by earthquakes can be reduced by adding a tuned mass damper (TMD), but TMD must be optimized and it must not be heavy. If the mass of the TMD is not optimized, the ductile behaviour constraint about the axial force capacity cannot be provided. The compressive strength of the concrete is a measure for the effective application of a TMD to a reinforced concrete structure. Since the mass is limited by the design constraint, the other design variables of TMD such as period and damping ratio are optimized. Using the formulas for frequency and damping ratio related to a preselected mass may not be sufficient and a precise optimum solution for preventing brittle fracture. Metaheuristic methods can be used by using a specific limit. In this study, Teaching Learning Based Optimization (TLBO) is employed to find optimum TMD parameters. Several earthquake excitations were used in the optimization process. A three storey RC frame structures with different compressive strength of concrete is investigated. Three stopping criteria have been used in the proposed methodology. The first criterion is the reduction of the maxi‐mum shear force value for the most critical excitation to the ductile behaviour limit. The second criterion is the reduction of the ratio of maximum first storey displacements of structure with and without TMD. This value is reduced under a user defined value, but the user defined value can be entered as zero. This value can be iteratively increased for minimization. The last criterion is the reduction of the acceleration transfer function of the structure. The proposed method is feasible on finding optimum TMD ensuring ductility conditions. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
FEM Shakedown of uncertain structures by chance constrained programming
Authors: Tran Ngoc Trinh , Tran Thanh Ngoc , Matthies H. G. , Stavroulakis G. E. , Staat M. 
Published: October 2016

AbstractWe present a new primal‐dual numerical algorithm of the shakedown problem under uncertainty in which the material strength is considered as a normally distributed random variable. Using chance constrained programming, we obtain deterministic equivalent formulations based on upper bound and lower bound theorems which are dual to each other. The proposed algorithm is tested in numerical examples which are applied to civil engineering structures. The obtained solutions show good performance. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Positive Definiteness of Cokriging Covariance Matrices
Authors: Sauerbrei Anna , Zimmermann Ralf 
Published: October 2016

AbstractVariable‐fidelity modeling (VFM), sometimes also termed multi‐fidelity modeling, refers to the utilization of two or more data layers of different accuracy in order to construct an inexpensive emulator of a given numerical high‐fidelity model. In practical applications, this situation arises when simulators of different accuracy for the same physical process are given and it is assumed that many low‐fidelity sample points are affordable, but the high‐fidelity model is extremely costly to assess. More precisely, the VFM objective is to construct a predictor function, which interpolates the primary sample data but is driven by the trend indicated by the secondary data. In view of the computational effort, the objective is to use as few high‐fidelity sample points as possible to achieve a desired level of accuracy.A widely used VFM method is Cokriging. The technique yields the best linear unbiased estimator based on the given data, taking spatial correlation into account. One way to model spatial correlation is via positive definite correlation kernels that yield positive definite correlation matrices for distinct input sample points.In this contribution, we will address the positive definiteness of Cokriging correlation matrices which is necessary for the method but not granted, due to the modeling of the cross‐correlations. We discuss both the cases of distinct and coincident low‐ and high‐fidelity sample points. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
C1‐continuous time integration based on cubic Hermite interpolation
Authors: Mergel Janine C. , Sauer Roger A. , Ober‐Blöbaum Sina 
Published: October 2016

AbstractWe discuss a C1‐continuous time integration method based on piecewise cubic Hermite approximation. This method, denoted as p2‐scheme, belongs to a class of one‐step integration methods derived recently [1]. It exhibits a convergence rate of order four and shows properties similar to variational integrators, such as an excellent long‐term energy preservation. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Adaptive FEM and a posteriori error control for stationary coupled bulk‐surface PDEs
Authors: Eigel Martin , Müller Rüdiger 
Published: October 2016

AbstractWe consider a system of two coupled elliptic equations, one defined on a bulk domain and the other one on the boundary surface. The numerical error of the finite element solution can be controlled by a residual a posteriori error estimator which takes into account the approximation errors due to the discretisation in space as well as the polyhedral approximation of the surface. The estimators naturally lead to refinement indicators for an adaptive algorithm to control the overall error. Numerical experiments illustrate the performance of the a posteriori error estimator and the adaptive algorithm. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On accuracy and efficiency of the CESE‐method of C. S. Chang for one‐dimensional unstaedy flow computation
Authors: Niessner Herbert 
Published: October 2016

AbstractAbout twenty years ago a NASA‐group around S. C. Chang began to develop a method using space‐time domains as elements for unstaedy flow computation. There are two kinds of elements. One within which the linearized form of the underlying differential equation is satisfied and one whithin which space‐time flux is conserved. Therefore the method is called conservation‐element solution‐element or shortly CESE. Applied to one‐dimensional flow equations we show conditions under which the method in the version of Jerez et al. [1] is‐ second order accurate and ‐ more efficient than Lax‐Wendroff type methods.(© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High order time discretisation methods for incompressible Navier–Stokes equations
Authors: Rang Joachim 
Published: October 2016

AbstractIn this paper we solve incompressible Navier–Stokes equations with higher order time integration schemes such as Radau‐IIA and Lobatto‐IIIC methods. We compare the results with 4th order DIRK and ROW methods to show the advantages of higher order time integration methods. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A discontinuous method for oil‐water flow in heterogeneous porous media
Authors: Bürger Raimund , Kumar Sarvesh , Kenettinkara Sudarshan Kumar , Ruiz‐Baier Ricardo 
Published: October 2016

AbstractAn oil‐water flow‐transport problem in a heterogeneous porous medium (HPM), given by the Brinkman model coupled with a fractional flow formulation, is solved numerically by a discontinuous finite volume element (DFVE) method coupled with a Runge‐Kutta Discontinuous Galerkin (RKDG) scheme. A new (original) numerical example is presented. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Relaxing the CFL condition for the wave equation on adaptive meshes
Authors: Peterseim Daniel , Schedensack Mira 
Published: October 2016

AbstractThe Courant‐Friedrichs‐Lewy (CFL) condition guarantees the stability of the popular explicit leapfrog method for the wave equation. However, it limits the choice of the time step size to be bounded by the minimal mesh size in the spatial finite element mesh. This essentially prohibits any sort of adaptive mesh refinement that would be required to reveal optimal convergence rates on domains with re‐entrant corners. A simple subspace projection step inspired by numerical homogenisation can remove the critical time step restriction so that the CFL condition and approximation properties are balanced in an optimal way, even in the presence of spatial singularities. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A semi‐smooth NEWTON method for dynamic multifield plasticity
Authors: Schröder Bettina , Kuhl Detlef 
Published: October 2016

AbstractIn the present paper a multifield approach towards isotropic dynamic small strain elastoplasticity is depicted. Its solution procedure is based on a semi‐smooth NEWTON method coupled to a higher order accurate time integration scheme in the context of the finite element method. The appearing interactions are partly analyzed by means of an axisymmetric example. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A discontinuous Galerkin Finite Element Method for linear elasticity using a mixed integration scheme to circumvent shear‐locking
Authors: Steiner Tobias , Wriggers Peter , Loehnert Stefan 
Published: October 2016

AbstractShear‐locking is a significant problem when using the Finite Element Method (FEM) with standard lower order Langrangian shape functions. To avoid this effect we introduce the discontinuous Galerkin Finite Element Method (dG‐FEM) for linear elasticity. In addition to a standard integration scheme for the dG‐FEM we develop a mixed integration scheme and compare both with established finite elements using a bending dominated benchmark. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On finite discrete operators and equations
Authors: Vasilyev Alexander , Vasilyev Vladimir 
Published: October 2016

AbstractFor discrete operators generated by Calderon–Zygmund kernels we consider certain finite‐dimensional approximations. We compare an initial discrete operator with its finite‐dimensional analogue and obtain invertibility conditions and approximation rate. The error estimate for approximate finite‐dimensional solution of corresponding equation is given also for a special right‐hand side. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Adaptive space‐time boundary element methods for the wave equation
Authors: Zank Marco , Steinbach Olaf 
Published: October 2016

AbstractFor the solution of the wave equation a space‐time energetic boundary integral formulation is used. The resulting single layer boundary integral equation is discretised by a conforming ansatz space on the lateral boundary. To derive an adaptive scheme an a posteriori error estimator based on the representation formula is used. Finally, numerical examples for a one‐dimensional spatial domain are presented. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimal control of time discrete two‐phase flow governed by a diffuse interface model
Authors: Garcke Harald , Hinze Michael , Kahle Christian 
Published: October 2016

AbstractWe present results on optimal control of two‐phase flows. The fluid is modeled by a thermodynamically consistent diffuse interface model and allows to treat fluids of different densities and viscosities. In earlier work we proposed an energy stable time discretization for this model that we now employ to derive existence of optimal controls for a time discrete optimal control problem. The control aim is to obtain a desired distribution of the two phases in the system. For this we investigate three control actions. We use tangential Dirichlet boundary control and distributed control. We further consider the inverse problem of finding an initial distribution such that the evolution over a given time horizon starting from this value is close to a desired distribution. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A sharp regularization error estimate for bang‐bang solutions for an iterative Bregman regularization method for optimal control problems
Authors: Pörner Frank 
Published: October 2016

AbstractIn the present work, we present numerical results for an iterative method for solving an optimal control problem with inequality contraints. The method is based on generalized Bregman distances. Under a combination of a source condition and a regularity condition on the active sets convergence results are presented. Furthermore we show by numerical examples that the provided a‐priori estimate is sharp in the bang‐bang case. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)