bluuebunny/crossref_metadata_2025_split huggingface dataset:
On a potential‐velocity formulation of incompressible Navier‐Stokes equations
Authors: Marner Florian , Scholle Markus 
Published: December 2014

AbstractComputational fluid dynamics has emerged as an essential investigative tool in nearly every field of technology. Despite a well‐developed mathematical theory and the existence of readily available commercial software codes, computing solutions to the governing equations of fluid motion remains challenging, especially due to the non‐linearity involved. Additionally, in the case of free surface film flows the dynamic boundary condition at the free surface complicates the mathematical treatment notably.Recently, by introduction of an auxiliary potential field, a first integral of the two‐dimensional incompressible Navier‐Stokes equations has been constructed leading to a set of equations, the differential order of which is lower than that of the original equations [1]. A useful application to free surface simulation was found in [2]. Moreover the new formulation is naturally extendible to three dimensions via tensor calculus, involving a non‐unique symmetric tensor potential. The corresponding degrees of freedom can be used in order to achieve a numerically convenient representation. Finally an efficient staggered‐grid finite difference scheme is applied to a Stokes flow problem in a 3D lid‐driven cavity to demonstrate the capabilities of the new approach. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Non‐steady interaction of fluids with free surfaces and rigid bodies
Authors: Keisenberg Tobias , Ostermeyer Georg‐Peter 
Published: December 2014

AbstractInteraction between fluids and rigid bodies is a phenomenon, which occurs for example in floating bearings or turbines. Mostly the focus is on domains with rigid boundaries on every side or defined influx or effusion of fluid over the boundaries.The interaction between fluids with free surfaces and a rigid body were mostly studied under the aspect of stability for steady‐state conditions, e. g. for fluid‐filled centrifuges. A characteristic property is the instability over non‐empty intervalls of angular velocities, so the analysis of non‐steady behaviour is essential to investigate the stability of the drive through these instable domains.A first approach to this topic is the qualitative investigation of a fluid domain with the shallow water theory. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hybrid Solutions for Stationary and Instationary Three‐Dimensional Compressible Navier‐Stokes Layer
Authors: Nastase Adriana 
Published: December 2014

AbstractNew, original hybrid solutions for the three‐dimensional instationary compressible full Navier‐Stokes layer are here proposed. These numerical solutions have also important analytical properties, due to the analytical hybridization and are split, due to the use of the logarithmic density function (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Introduction of an Adaptive Smoothed Particles Hydrodynamics Formulation
Authors: Schnabel Dirk , Müller Alexandra , Eberhard Peter 
Published: December 2014

AbstractIn this work an adaptive Smoothed Particles Hydrodynamics (SPH) formulation is presented which is capable of adjusting the discretization level of a simulation at runtime. In order to increase and decrease the local resolution, the adaptive refinement and coarsening approach introduced in literature was extended to merge a userdefined number of particles at each simulation step. Depending on the simulation different coarsening strategies may be advantageous. Considering for example an SPH formulation for elastic solids, the particles discretizing the continuum experience considerably less disordering than in fluid simulations allowing for an advanced coarsening algorithm which takes each particles refinement history under consideration and preferably merges particles originating from one and the same particle, whereas in SPH for fluids such a strategy would not be reasonable since fluid particles usually experience great relative displacement. Hence different coarsening strategies may be recommended for different simulation scenarios. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical simulation of solutal Rayleigh‐Bénard‐Marangoni convection in a layered two‐phase system
Authors: Köllner Thomas , Boeck Thomas 
Published: December 2014

AbstractWe present a two‐dimensional simulation of solutal Rayleigh‐Bénard‐Maragoni convection in a layered system. In the initial state, the solute concentration is homogeneous in each layer but not in partition equilibrium. Diffusive transfer of solute leads to convective instability. Marangoni convection dominates initially as it operates on a smaller length scale. Rayleigh convection appears later as an instability of the mixed unstably stratified fluid near the interface. Compared to pure Marangoni convection the dynamics is more disordered due to additional flow in the bulk. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of turbulence on the performance of a laboratory scale HAWT
Authors: Al‐Abadi Ali , Ertunc Özgür , Seok Julie , Härtl Michael , Delgado Antonio 
Published: December 2014

AbstractThe oncoming wind to horizontal axis wind turbines (HAWT) may change its speed and direction stochastically in time. Hence, turbine blades are exposed to flows both with fluctuating angle of attack and fluctuating yaw angles. The modern wind turbines are reacting to those changes by pitch angle and torque control not only to exploit as much power as possible but also stabilize energy production and prevent any damage of the turbine. However, time scales of wind fluctuations and sudden changes of wind properties can be very short and with very high in amplitude. In the present study we focus on the influence of turbulence on the performance of a HAWT. Main motivation of the investigations is to figure out best strategies for the aerodynamic design of the blades operating under turbulent conditions. A laboratory scale HAWT and a performance measurement set‐up are employed to measure the influence of the oncoming wind. The tests are conducted in the closed loop wind tunnel of our institute. The test section of the tunnel is 1.87 m in width, 1.4 m in height and 2 m in length. The rotor blades are specially designed and optimized for this wind tunnel and the generator used. The turbulence is generated by two static squared mesh grids; fine and coarse one. Hence, two mainly different turbulence scales are obtained. In addition, the distance between the wind‐turbine and the grid is adjusted to have additional sub‐turbulence scales for each grid. The turbulence is nearly isotropic and decays in the flow direction. The developments of Taylor's micro scale (λg) and integral scale (Lg) of the turbulence in the flow direction at various incoming wind velocities (8−16 m/s) are measured. Hence, the facility allows to expose the wind‐turbine to turbulence with various energy and length scale content. Those measurements are conducted with hot‐wire anemometry in the absence of the wind‐turbine. Upstream and downstream turbulence intensities (TI) distributions are measured to give insight on the surrounding free stream and turbine wake interaction and how can different turbulence eddies scales contribute in the influence of the performance of the turbine. Performance measurements are conducted with and without turbulence and the results are compared. The study shows that the higher the turbulence, the more the power extracted by the turbine. This is due to the higher interaction of large eddies with the turbine wake and with the boundary layer, which helps to keeping it attached. Furthermore, higher TI's help in suppressing the tip vortex, thus, reduce turbine tip losses. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hybrid LES‐RANS Modeling of Complex Turbulent Flows
Authors: Breuer Michael , Schmidt Stephan 
Published: December 2014

AbstractThe paper describes a state‐of‐the‐art hybrid LES‐URANS method for the simulation of complex internal and external turbulent flows. Relying on a unified LES‐URANS approach with a soft interface the methodology is designed for wall‐bounded non‐equilibrium flows. The unsteady Reynolds‐averaged Navier‐Stokes (URANS) mode within the hybrid approach is taken into account by an explicit algebraic Reynolds stress model (EARSM), which guarantees an appropriate representation of the anisotropic near‐wall turbulence. All non‐closed terms in the transport equation of the turbulent kinetic energy are modeled by enhanced formulations using the EARSM (production and diffusion term) and the splitting of the dissipation rate into a homogeneous and an inhomogeneous contribution. The former is expressed analytically by a Taylor series expansion of the homogeneous lateral Taylor microscale in the vicinity of the wall guaranteeing the correct asymptotic behavior. The latter is incorporated into the diffusion term. The interface location between the large‐eddy simulation (LES) mode and the URANS mode is determined automatically on‐the‐fly based on the modeled turbulent kinetic energy and the distance to the wall. For transitional (external) flows an additional dynamic transition criterion is applied which determines the laminar and the turbulent flow regimes and is combined with the existing interface criterion. An internal flow over a periodic arrangement of hills and an external flow past a SD7003 airfoil with a laminar separation bubble are taken into account for a detailed evaluation of the method. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Turbulent Entrainment in the Atmospheric Boundary Layer
Authors: Mellado Juan Pedro 
Published: December 2014

AbstractTurbulent entrainment – the process by which turbulence inside of the atmospheric boundary layer entrains air from the free troposphere above it – has been investigated using direct numerical simulations in two configurations, one without a cloud and one with a cloud. With the first configuration, we have learned that the entrainment zone in a convective boundary layer growing into a linearly stratified troposphere is better described in terms of a two‐layer structure, with different characteristic scales associated with each of the two sub‐layers. With the second configuration, we have explained how wind shear across the entrainment zone capping a stratocumulus cloud can render evaporative cooling as important as radiative cooling in driving convective motions. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A mixing‐length model for magnetohydrodynamic flows in channels and ducts with wall‐parallel magnetic field
Authors: Boeck Thomas , Krasnov Dmitry 
Published: December 2014

AbstractA spanwise magnetic field leads to turbulent drag reduction in channel flow of a conducting liquid due to the selective Joule damping of certain flow structures. This effect can be captured by a simple modification of Prandtl's classical mixing‐length idea. The mixing length over which a turbulent fluctuation loses its momentum is not only constrained geometrically but also by magnetic damping. We therefore introduce a magnetic damping length that is proportional to friction velocity and the Joule damping time. The limitation of mixing length is implemented by using the harmonic mean between wall distance and this damping length. By combining this ansatz with the van‐Driest model for turbulent stresses in channel flow we obtain a satisfactory prediction for the mean velocity distribution in magnetohydrodynamic channel flow with spanwise field for different Reynolds and Hartmann numbers. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Friction law for turbulent boundary layers on a flat plate with suction
Authors: Vigdorovich Igor 
Published: December 2014

AbstractA universal friction law for turbulent boundary layers on a flat plate with suction is established. Experimental skin‐friction distributions obtained for various suction factors and Reynolds numbers are described in similarity variables by a single universal curve. The law is valid for the entire range of suction velocities from zero one till the limiting values corresponding to asymptotic‐suction boundary layers. The analysis is not based on any particular turbulence model. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Simulation of Bubbles in Shear Flow
Authors: Anderl Daniela , Bauer Martin , Rauh Cornelia , Rüde Ulrich , Delgado Antonio 
Published: December 2014

AbstractTo gain a basic understanding of foam flow, as it can be found e.g. in transport of aerated food, simulation tools can help to provide better insight. Shearing of the bubbles appears in different flow geometries and is for a bubble assembly not captured analytically. Also experimentally, those flow fields are hard to observe so that simulations are the method of choice.Our method to simulate foams uses a volume of fluid approach that is based on the free surface algorithm by Körner et al. [1]. Different from classical multiphase methods, only the liquid phase is simulated and special boundary conditions at the liquid‐gas interface account for the gas phase. With this approach high density ratios, e.g. in water‐air systems, are easier to realize than in other methods. High density ratios are even necessary to physically justify the model, where the dynamics of the lighter phase are partially neglected. This method is integrated in the Lattice Boltzmann software framework waLBerla [3] (widely applicable Lattice Boltzmann solver from Erlangen†) that can be used on massively parallel computers and thus allows to simulate even large bubble assemblies.As first validation, single bubbles are sheared with different capillary numbers and the simulation results are compared to literature [2] and show good agreement. The next step is shearing a bubble assembly which is arranged like a dense sphere packing. In order to investigate the geometrical configuration of the assembly and its impact on the behavior during a shear deformation, the bubble assembly is rotated with different angles with respect to the shear direction. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Rising bubble simulations using lattice Boltzmann method coupled with level set interface capturing
Authors: Safi Mohammad Amin , Turek Stefan 
Published: December 2014

AbstractA multiphase Lattice Boltzmann (LB) scheme coupled with a level set interface capturing module is used for the simulation of multiphase flows, and in particular, rising bubbles under moderate and high density and viscosity ratios. We employ a consistent, robust discretization of the pressure forces which enables us to preserve stability and accuracy. The accuracy of the present scheme is shown to be competitive with that of the benchmark data from the finite element solutions in [3]. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Explosive‐crystallization waves in thin amorphous layers on heat conducting substrates with thermal contact resistance
Authors: Buchner Christoph , Schneider Wilhelm 
Published: December 2014

AbstractA model for explosive crystallization in a thin amorphous layer on a heat conducting substrate is presented. Rate equations are used to describe the kinetics of the homogeneous amorphous‐crystalline transition. Heat conduction into the substrate and thermal contact resistance at the interface between layer and substrate are taken into account.The whole process is examined as a wave of invariant shape in a moving frame of reference. A coupled system of an integro‐differential equation and ordinary differential equations is obtained and solved numerically. The propagation velocity of the wave is obtained as an eigenvalue of the system of equations. Some representative solutions are shown. Crystallization‐wave velocities are compared with experimental values for explosive crystallization in germanium. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electromagnetic flow control in liquid metals using Lorentz force techniques
Authors: Dubovikova Nataliia , Karcher Christian , Kolesnikov Yuri 
Published: December 2014

AbstractFlow measurement and flow control in opaque and aggressive liquids such as metal melts are challenging tasks in industrial fluid mechanics. Optical measurement techniques as well as submerging probes or control units cannot be applied in case of highly severe environment; hence, contactless electromagnetic methods are of interest for practical flow control because of relatively high electrical conductivity of investigated materials. In this paper we present working principle and experimental results of two such contactless techniques. First, time‐of‐flight Lorentz force velocimetry (LFV), which allows to determine the flow rate of liquid metal without information about any fluid properties or magnetic field magnitude by cross‐correlation of two Lorentz force signals. Secondly, Lorentz torque velocimetry (LTV) ‐ a technique, which uses an electromagnetic pump with a torque sensor connected to the pump's shaft. In the methods so‐called Lorentz force [1] is measured, which has electromagnetic nature and is proportional to velocity and flow rate of conductive liquid. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The relaxed micromorphic continuum model
Authors: Ghiba Ionel‐Dumitrel , Neff Patrizio , Madeo Angela 
Published: December 2014

AbstractWe formulate a relaxed linear elastic micromorphic continuum model with symmetric Cauchy force‐stresses and curvature contribution depending only on the micro‐dislocation tensor. We prove that the new relaxed micromorphic model supports well‐posedness results. Relations with other theories are also pointed out. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Rank‐one convexity and polyconvexity of Hencky‐type energies
Authors: Neff Patrizio , Ghiba Ionel‐Dumitrel , Lankeit Johannes , Martin Robert 
Published: December 2014

AbstractWe investigate a family of isotropic volumetric‐isochorically decoupled strain energies based on the Hencky‐logarithmic (true, natural) strain tensor log U. The main result of this note is that for n = 2 the considered energies are rank‐one convex for suitable values of two material parameters. We also conjecture that there are values of the material parameters such that the corresponding energies are polyconvex. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Uniqueness Aspects of Semi‐Discretized Navier‐Stokes Equations
Authors: Zanger Florian 
Published: December 2014

AbstractWe consider the Navier‐Stokes equations on a time interval [0, T) in the weak formulation given by

Here we assume
ν > 0, G ⊂ ℝ3 open, bounded with
C2,1
boundary,
f ∈ L2 (0, T, L2), and
u0 ∈ V, where V
is the closure of
C∞0,σ in (H10, ‖∇ ·‖) and (·, ·)
denotes the scalar product in L2. The above equations for
u ∈ L2(0, T, V ∩ H2) with ∂tu ∈ L2 (0, T, L2 )
can be semi‐discretized with respect to time in different ways. The existence of solutions to the resulting schemes can be shown with the Galerkin method provided the viscous term is not treated fully explicitly. In the case of linear schemes, uniqueness can easily be proven with the Lax‐Milgram lemma. However, schemes that are implicit in both factors of the convective term seem to cause difficulties with respect to uniqueness, even for arbitrary small step sizes. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stochastic Approaches of Nonlinear Model‐Based Simulations for Vibratory Compaction Process
Authors: Debeleac Carmen , Nastac Silviu 
Published: December 2014

AbstractThe paper presents a basic approach regarding nonlinear models intended for computational dynamics of vibratory compaction process in order to evaluate the consolidation level. Taking into account the complex rheology of terrains and the relative variable dynamic load in time for each point inside the working area, a stochastic approach both of the material characteristics, and of the excitatory charges have been appropriate. Numerical simulations has developed based on nonlinear models containing conservative and complex dissipative rheological elements, which include two main groups of stochastic data as follows: terrain characteristics from preconditioning experimental tests, and vibratory actions from analytical approaches supposing the soil‐drum contact area and the number of dynamic load transitions over this area. Simulation results dignify small variances between the real and computed terrain responses, comparative with the case supposing full determinist parameters. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the preliminary design of axial fans: extending the validity of the flow assumptions over the whole hydraulic characteristic and improvement of modeling
Authors: Semel Matthias , Willinger Bettina , Grilliat Julien , Delgado Antonio 
Published: December 2014

AbstractIn order to carry out a preliminary axial fan design, established assumptions are made onto the flow structure within the fan at the design point. As an example the very common hypothesis of radial equilibrium, states that the radial velocity component downstream the fan is zero, and that the flow in this area is axisymmetric. With the help of this hypothesis, the flow is idealized in order to draw quantitative conclusions. The present communication aims at extending these assumptions on the whole flow regime in order to help fan designers to reduce the try‐and‐error cycle number. An analytical formulation for axial fan velocity distributions at design and off design conditions is proposed for an arbitrary work distribution. It is shown that the total pressure characteristics can be described by means of hyperbola and straight line. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of AR and ARMA processes in structural health monitoring.
Authors: Alexander Ostermann , Spielberger Georg 
Published: December 2014

AbstractIn this short note we discuss the application of AR and ARMA processes in structural health monitoring with output only data. We highlight the advantages of both types of processes for different purposes. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Comparison of Optimization Methods for Process Parameters Identification in Forming Technology
Authors: Rozgi` c Marco , Stiemer Marcus 
Published: December 2014

AbstractThe SAND formulation known from structural and topology optimization is applied to a forming problem arising from certain technological forming processes. The SAND approach is compared to a well known and widely used method on a model problem within the scope of linear elasticity. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimization of sit to stand motions of elderly people for the design and control of physical assistive devices
Authors: Mombaur Katja 
Published: December 2014

AbstractSit to stand motions represent a big challenge for many elderly people even if other types of motions such as walking can still be achieved with less problems. It is therefore important to gain a deeper understanding of this type of motions and provide strategies to perform sit to stand transfers even in the presence of different pathologies and joint weaknesses. In this paper we present a numerical study of sit to stand motions based on mechanical multibody models and optimal control techniques. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)