bluuebunny/crossref_metadata_2025_split huggingface dataset:
Self‐similar turbulent boundary layer in pressure gradient
Authors: Vigdorovich Igor 
Published: December 2011

AbstractSelf‐similar flows in a turbulent boundary layer when the free‐stream velocity is specified as a power function of longitudinal coordinate are investigated. The self‐similar formulation not only simplifies solving of the problem by reducing the equations of motion to ordinary differential equations but also provides a mean for formulating closure conditions. It is shown that for the class of flows under consideration that depend on three governing parameters the dimensionless mixing length is a function of the normalised distance from the wall and the exponent in the law specifying the free‐stream velocity distribution in the outer region and a universal function of local Reynolds number in the wall region, the latter corollary being true even when the skin friction vanishes. In calculations this function is set to be independent of pressure gradient, which gives the results very close to experimental data.There exist four different self‐similar flow regimes. Each regime is related to its similarity parameter, one of which is the well‐known Clauser equilibrium parameter and the other three are established for the first time. In case of adverse pressure gradient when the exponent lies within certain limits, which depend on Reynolds number, the problem has two solutions with different values of the boundary layer thickness and skin friction, which points out the possibility of hysteresis in near‐separating flow. Separation occurs not at the minimum value of the exponent that corresponds to the strongest adverse pressure gradient but at a higher one whose dependence on Reynolds number is calculated in the paper. The results of the theory are in good agreement with experimental data. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fully implicit time discretization for a free surface flow problem
Authors: Bänsch Eberhard , Weller Stephan 
Published: December 2011

AbstractOne of the challenges in the numerics of free surface flows is the coupling of the flow field to the geometry of the domain. The most simple approach is an explicit decoupling, i.e. computing the flow field with geometrical information of a prior time step and then updating the geometry. This widely used approach leads to a severe CFL condition of the type $\Delta t \le C\sqrt{{\rm We}}\;h^{3 \over 2}$, which may prescribe infinitesimally small time step sizes in the interesting case of a small Weber number (i.e. high surface tension). A semi‐implicit approach utilizing the fact that $x^{n+1} = x^n + \Delta t\, u^{n+1}_{|\Gamma}$, where xk is a parametrization of the capillary boundary Γ, is also available [1]. This approach can be proven to be unconditionally stable but is of first order only. It also suffers from relatively strong numerical dissipation.We present a fully implicit approach using a backward differentiation formula to achieve a time discretization method that is of second order and only minimally dissipative. A numerical example of an oscillating drop showing very low numerical dissipation and second order convergence as well as numerical evidence for the stability of the method is presented. Since the method requires the solution of a highly nonlinear coupled system, possible preconditioners for this system are discussed, including a lower order decoupling. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thin Film Exfoliation in the Zone of Trapped Elastic Wave Localization
Authors: Abramyan Andrey , Indeitsev Dmitriy , Mochalova Yulia , Semenov Boris 
Published: December 2011

AbstractIn modern constructions, thin‐layer coats are often used as protecting or strengthening elements. Deformations of such constructions may cause significant stresses on the interface between the base and the coat because of the difference in their physical mechanical properties, which leads to the destruction or detachment of the cover. The impact of static or shock loads on the emergence and development of delamination in multilayer constructions has been studied fairly well, but much less is known about destructions of this type under nonstationary (vibrational) loads. The interest in the latter is caused by the fact that even small variable actions may cause the localization of oscillations in a neighborhood of inhomogeneities (such as inclusions, defects, construction elements, etc.) [1] (and lead to the emergence and growth of defects, which strongly affects the reliability and functionality of the whole construction. The possibility of the localization of oscillations near initial delamination and the impact of localization on the growth of the delamination are studied and a model for analyzing conditions under which a detachment zone grows or ceases to grow is suggested. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Wave propagation in finite structures due to transient loading with application to pyroshock simulation
Authors: Jüngel Nikolas , Lacher Alexander , von Wagner Utz 
Published: December 2011

AbstractPyroshocks are transient motions of a structure caused by e.g. explosion of ordnance devices. Prior to their launching space modules have to be tested for fulfillment of strict requirements concerning the expected acceleration during a space mission. Since, in practical applications, this is still based on empirical knowledge and time consuming testing procedures, an analytical way to face this problem is the modelling of a pyroshock test device for the simulation of mechanical impacts on plates carrying the module to be tested. From the mechanical point of view, the problem is described by the wave propagation in a disk or a plate carrying a point mass and being exposed to a punctual load caused by the impact of a sphere. The displacement field is calculated semi‐analytically by the use of a modal approach, HERTZian contact theory as well as the GALERKIN procedure. In order to systematically determine the optimum setup leading to a desired acceleration signal an evolution strategy is used as well as comparisons with experimental and FEM results have been made. The present procedure allows for a better and faster simulation and predictability of pyroshock tests. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling of Lamb wave propagation in composite plate excited by surface bonded piezoelectrical actuators
Authors: Karmazin Alexander , Kirillova Evgenia , Seemann Wolfgang , Syromyatnikov Pavel 
Published: December 2011

AbstractTransient propagation of Lamb waves in a multilayered infinite composite plate with the arbitrary elastic anisotropy of each layer is considered in this paper. Integral representations of wave fields, an algorithm of computing the Green's matrix of the multilayered medium in Fourier domain and some methods of the Fourier transform inversion are used as basic analytical research instruments. The piezoelectrical transducers frequently used for Lamb wave excitation are modelled in this paper as surface sources with stresses concentrated on the boundaries of actuators. The contribution of each wave mode to a whole amplitude, focusing of Lamb waves and influence of the geometry of the surface source are discussed in this paper by numerical examples. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dusty shock wave interaction – formation of fully dispersed waves and particle focusing effect
Authors: Osiptsov Alexander , Golubkina Irina 
Published: December 2011

AbstractThe problem of regular (symmetric and asymmetric) interaction of plane shock waves in a steady‐state dusty gas flow is considered. For near‐sonic flows with a fairly high particle mass loading, the possibility of the formation of wave structures is revealed, in which either all or only some of the incident or reflected waves degenerate into so‐called fully dispersed waves, i.e. zones in which no discontinuities appear in the parameters of each phase. For stronger shock waves and low particle mass concentration, the effect of aerodynamic particle focusing and the formation of a narrow high‐concentration beam of particles behind the point of the interaction of the waves are detected on the basis of parametric numerical calculations. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Theoretical and Experimental Investigations of Piezoelectrically Excited Travelling Waves in Cylindrical Tubes
Authors: Wallaschek Jörg , Renner Andreas 
Published: December 2011

AbstractFlügge's equations of motion for cylindrical shells are used to analyze the generation of travelling waves in a tube of an ultrasonic travelling wave transport system. The vibration‐shape of a semi‐infinite acrylic tube with structural damping excited by a piezoelectric ring at the end is calculated and the influence of the driving frequency is shown.Starting with an exponential ansatz the frequency dependent wavenumbers can be determined. Three frequency bands with different combinations of imaginary, real and complex wavenumbers can be found. Supposing a semi‐infinite tube with given boundary conditions at the end of excitation the vibrations of the tube can be calculated depending on the frequency. Simulation agrees well with experimental results. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical analyis of turbulent flow in a Coanda ejector
Authors: Alexandru Dumitrache , Florin Frunzulica , Horia Dumitrescu , Octavian Preotu 
Published: December 2011

AbstractThe task of this study is to investigate the influence of various geometric parameters and pressure ratios on the Coanda ejector performance. For numerically investigations we use an implicit formulation of the compressible Reynolds‐average Navier‐Stokes equations (RANS) for axisymmetric flow with a shear stress transport k − ω (SST model) turbulence model. The numerically results was obtained for a total pressure range 1‐5 Bars, imposed at the reservoir inlet. The effect of various factors, such as, the pressure ratio, primary nozzle and ejector configurations on the system performance has been evaluated based on defined performance parameters. The numerical results have been compared with theoretical and experimental results for a given Coanda ejector configuration. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Motion of a Ferrofluid in a Periodic Magnetic Field due to Surface Deformation
Authors: Popp Jana , Zeidis Igor , Zimmermann Klaus , Böhm Valter , Gärtner Ralf 
Published: December 2011

AbstractThe article considers a plane flow of an incompressible, viscous magnetizable fluid. Cause of the flow is an alternating magnetic field, which consequently affects the free surface to periodical deformation. The proof of a peristaltic material transport is desired. The STOKES approximation for creeping flows and the two‐dimensional continuity equation serve for governing equations. The methods used include power series expansion with regard to the small ratio of ε perturbed and unperturbed fraction of the magnetic field. The analytical result is discussed with regard to functional parameters. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of supersonic flow in Oswatitsch inlet configuration
Authors: Vuković Danijel , Matijašević Dubravko , Vrdoljak Milan 
Published: December 2011

AbstractThe aim of this work is a study of the flow parameters relevant for the Oswatitsch intake configuration. Geometry of the cone and inlet are equivalent to those on MiG‐21bis fighter aircraft. Supersonic flow parameters for a channeled cone were studied at two different operational Mach numbers. Center body cone is movable along longitudinal axis and analysis is focused on specific positions for supersonic flight regimes. To study the problem, numerical model of axisymmetric two‐dimensional Euler flow is applied. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stability of solutions to Cauchy problem on linear approximation and branching equation in the root subspace
Authors: Trenogin Vladilen , Kim‐Tyan Luiza , Loginov Boris 
Published: December 2011

AbstractStability of solutions to Cauchy problem on linear approximation for differential equation in Banach space E with degenerate linearization is studied from viewpoint of branching equation in the root subspace. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Parameter estimation for DAE models in a multiple experiment context
Authors: Kircheis Robert , Körkel Stefan 
Published: December 2011

AbstractParameter estimation for PDE models is a recent topic of our research. After discretization in space we get a system of DAEs. We here present the techniques we use (e.g., Multiple Shooting, generalized Gauss‐Newton) to fit the parameters. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Locally Optimal Block Preconditioned Conjugate Gradient Method for Hierarchical Matrices
Authors: Benner Peter , Mach Thomas 
Published: December 2011

AbstractWe present a method of almost linear complexity to approximate some (inner) eigenvalues of symmetric self‐adjoint integral or differential operators. Using ℋ‐arithmetic the discretisation of the operator leads to a large hierarchical (ℋ‐) matrix M. We assume that M is symmetric, positive definite. Then we compute the smallest eigenvalues by the locally optimal block preconditioned conjugate gradient method (LOBPCG), which has been extensively investigated by Knyazev and Neymeyr.Hierarchical matrices were introduced by W. Hackbusch in 1998. They are data‐sparse and require only O(nlog2 n) storage. There is an approximative inverse, besides other matrix operations, within the set of ℋ‐matrices, which can be computed in linear‐polylogarithmic complexity. We will use the approximative inverse as preconditioner in the LOBPCG method.Further we combine the LOBPCG method with the folded spectrum method to compute inner eigenvalues of M. This is equivalent to the application of LOBPCG to the matrix Mμ = (M − μI)2. The matrix Mμ is symmetric, positive definite, too.Numerical experiments illustrate the behavior of the suggested approach. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimal control of hydroforming processes
Authors: Koller Daniela , Ulbrich Stefan 
Published: December 2011

AbstractWe consider an optimal control problem for sheet metal hydroforming. As a first step derivative free optimization algorithms are used to control the time dependent blank holder force and the fluid pressure, which are typical control variables. Our goal is to obtain a desired final configuration. We present numerical examples for 2D and 3D ABAQUS simulations for the hydroforming process of complexly curved sheet metals with bifurcated cross‐sections. Since a single ABAQUS simulation takes a long time, optimization algorithms based on reduced models are under investigation. The reduced order model is based on a Galerkin solver for the elastoplasticity problem. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Gyroscopic Stabilization of 2nd‐Order‐Systems with Indefinite Damping
Authors: Damm Tobias , Homeyer Jan 
Published: December 2011

AbstractWe consider the gyroscopic stabilization of the unstable system ẍ + D ẋ + Kx = 0 with positive definite stiffness matrix K. The indefinite damping matrix D is responsible for the instability of the system. The modelling of sliding bearings can lead to negative damping, see [6]. A gyroscopic stabilization of an unstable mechanical system with indefinite damping matrix was investigated in [4] in the case of matrix order n = 2 using the Routh‐Hurwitz criterion. The question was raised whether an unstable system can be stabilized by adding a gyroscopic term Gẋ with a suitable skew‐symmetric matrix G = −GT. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Stream Function Approach to Optical Flow with Applications to Fluid Transport Dynamics
Authors: Luttman Aaron , Bollt Erik , Basnayake Ranil , Kramer Sean 
Published: December 2011

AbstractOptical flow is one of the classical problems in computer vision, but it has recently also been adapted to applications from other fields, such as fluid mechanics and dynamical systems. If the goal is to analyze the dynamics of system whose evolution is governed by a flow field that is the gradient of a potential function – which describes many flows in fluid dynamics – it is natural to approach the optical flow problem by reconstructing the potential function, also called the stream function, rather than reconstructing the components of the flow directly. This alternate approach allows one to impose scientific priors, via regularization, directly on the flow itself rather than on its components independently. We demonstrate the stream function formulation of optical flow and its application to reconstructing an oceanic fluid flow driven by satellite measurements. It is also shown how these flow fields can be used to analyze mixing and mass transport in the fluid system being imaged. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Separation of Edges in X‐Ray Images by Microlocal Analysis
Authors: Storath Martin 
Published: December 2011

AbstractIn many x‐ray images, we find crossing structures, for example the rib bones of a thorax image. Hence, many edges in such images intersect with other edges. We propose a new algorithm, which simultaneously detects and separates such crossing edges. We prove the functionality of the algorithm under the geometric assumption that the edges possess different orientations at the points of intersection. To this end, we model edges as singularities of distributions with a submanifold structure and define the edge orientation to be the orientation of the corresponding singularity in the sense of microlocal analysis. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The application of the Ehrlich‐Aberth method to structured polynomial eigenvalue problems
Authors: Noferini Vanni 
Published: December 2011

AbstractAn algorithm for the application of the Ehrlich‐Aberth method to polynomial eigenvalue problems (PEPs) is proposed. The computational complexity of the algorithm is only quadratic with respect to the degree of the polynomial, where customary matrix methods have cubic complexity. For the case of some structured PEPs a strategy is given in order to exploit the structure and obtain the induced coupling in the spectrum. Numerical experiments are provided for the particular case of even/odd PEPs. This communication is based on joint work with Dario A. Bini and Luca Gemignani. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thiourethane thermoset coatings from bio‐based thiols
Authors: Yan Jingling , Ariyasivam Sharonie , Weerasinghe Dimuthu , He Jie , Chisholm Bret , Chen Zhigang , Webster Dean 
Published: December 2011

AbstractThree bio‐based thiols were synthesized via the thermal thiol‐ene reactions between sucrose soya ester (SSE) and multifunctional thiols; then, thiourethane coatings were produced from these thiols and their coating properties were studied. A series of high bio‐renewable content thiol oligomers were synthesized according to the previously reported thermal thiol‐ene reaction. Fourier transform infrared spectra (FTIR) confirmed the complete consumption of the double bonds in SSE, and gel permeation chromatography confirmed the formation of high‐molecular‐weight oligomers. The viscosity of these oligomers remained low due to their compact and branched structures. Thermoset thiourethane coatings were prepared from these thiol oligomers and polyisocyanate trimer resins with dibutyltin diacetate as the catalyst. FTIR spectra confirmed the formation of the thiourethane group. However, coatings based on isophorone diisocyanate (IPDI) polyisocyanate resin showed a lower degree of cure because of the decreased resin mobility due to the rigid cyclohexane ring. Generally, all the coatings showed good adhesion to aluminum panels, and had high gloss. However, they exhibited low tensile strength, modulus and chemical resistance due to the flexibility of the fatty acid chain. Coatings based on more rigid IPDI‐based polyisocyanate showed higher Tg, hardness and direct impact resistance compared with the hexamethylene‐diisocyanate (HDI) based polyisocyanate counterparts. Thermogravimetric analysis results showed that coatings based on mercaptanized soybean oil have better thermal stability than those from di‐pentene dimercaptan or glycol di‐3‐mercaptopropionate. Two Tg values were found by both differential scanning calorimetry and dynamic mechanical thermal analysis of thiourethanes from HDI‐based polyisocyanate and di‐pentene dimercaptan or glycol di‐3‐mercaptopropionate based oligomers due to phase separation resulting from the poor compatibility between HDI‐based polyisocyanate and the respective oligomers. Copyright © 2011 Society of Chemical Industry
Strong resistance of poly (ethylene glycol) based L‐tyrosine polyurethanes to protein adsorption and cell adhesion
Authors: Yang Jui‐Chen , Zhao Chao , Hsieh I‐Fan , Subramanian Senthilram , Liu Lingyun , Cheng Gang , Li Lingyan , Cheng Stephen Z. D. , Zheng Jie 
Published: December 2011

AbstractBiofouling that involves protein adsorption, cell and bacteria adhesion, and biofilm formation between a surface and biological entities is a great challenge for biomedical and industry applications. In this work, L‐tyrosine‐derived polyurethanes (L‐polyurethane) with different molecular weights of poly(ethylene glycol) (PEG) were synthesized, characterized and coated on gold surfaces using spin‐coating. The non‐fouling activity of different L‐polyurethane films was evaluated by protein adsorption and cell adhesion. Surface plasmon resonance and cell assay results demonstrate that the PEG content in these L‐polyurethanes contributes excellent resistance to protein adsorption and cell attachments. This work provides alternative and effective biomaterials for potential applications in blood‐contacting devices. Copyright © 2011 Society of Chemical Industry
Thermal properties of poly(dimethyl siloxane) nanocomposite filled with silicon carbide and multiwall carbon nanotubes
Authors: Hong Jinho , Choi Hyun Seok , Lee Kyung Sub , Shim Sang Eun 
Published: December 2011

AbstractSilicon carbide was incorporated in poly(dimethyl siloxane) (PDMS) in combination with multiwall carbon nanotubes (MWCNTs) to improve the thermal conduction behavior. The amount of silicon carbide was increased from 0 to 150 phr and the amount of MWCNTs was increased from 0 to 8 phr at a fixed amount of silicon carbide (150 phr). The thermal conductivity of the PDMS composite was increased with increasing amount of the MWCNTs and fine dispersibility of the incorporated MWCNTs was achieved without pretreatment. The rheological properties of the PDMS composites incorporating silicon carbide and MWCNTs were investigated and the activation energy of the composites was calculated during thermal decomposition using the Horowitz‐Metzger method. Importantly, unexpected thermal decomposition behavior as indicated by the reduction in activation energy from 361.63 to 194.18 kJ mol−1, namely acceleration of decomposition of the PDMS matrix caused by MWCNTs, was observed for the first time. Copyright © 2011 Society of Chemical Industry