bluuebunny/crossref_metadata_2025 huggingface dataset:
Particle Flow and Behavior at Bell‐Less Charging of the Blast Furnace
Authors: Yu Yaowei , Saxén Henrik
Published: June 2013

The burden distribution in the upper part of the blast furnace is one of the most important factors controlling the gas flow distribution, and therefore the efficiency of heat and mass transfer and chemical reactions between gas and solids in the process. This work studies burden profiles formed by pellets and coke dumps using experiments and simulation. Comparing results from DEM simulation with findings from a small‐scale experimental system, it is demonstrated that the modeling technique is feasible. The rotation of the chute was found to cause a shift of the particles off from the bottom center line of the chute. In the burden layer formation, coke forms a pile at the intersection of falling trajectory and burden surface, while pellets spread towards the furnace center, simultaneously occupying the space between the larger coke particles after the pellet pile has reached the maximum natural angle. Particles with a high angular velocity were found to be more likely to enter the region close to the furnace wall. It is also shown that reducing the shear modulus of the burden material in the simulation is an efficient method to increase the calculating speed of the DEM without significant effect on the results of the simulation.
Developing a Culture of Assessment in Student Affairs
Authors: Schuh John H.
Published: June 2013

This chapter identifies elements that contribute to developing a culture of assessment in student affairs.
The Role of Geographic Location in the Acquisition Strategies of High‐Technology Firms: Evidence from Computer Networking Equipment Industry
Authors: Yurov Kirill M. , Greenstein Shane M. , Shanley Mark T. , Potter Richard E.
Published: June 2013

The present study focuses on the acquisition strategies of Cisco Systems, a comprehensible representative of high‐technology firms. This investigation has depicted a dynamic picture of acquisition behavior when the geographic location of targets varies. Analysis has revealed that high‐technology firms are more likely to acquire co‐located start‐ups. Our findings suggest that high‐technology firms are more likely to acquire targets who have received an earlier equity investment and whose technologies have been standardized. We have also found partial evidence that supports the argument that high‐technology firms pursue cluster‐based acquisitions. Analysis suggests that access to patents does not matter for start‐up companies located in industry clusters while their counterparts outside these clusters need patents to become acquisition targets. © 2013 Wiley Periodicals, Inc.
Integration Vacuum: Creating Action Space for Global Strategy Implementation in International Acquisitions
Authors: Colman Helene Loe , Grøgaard Birgitte
Published: June 2013

Many multinationals rely on acquisitions when expanding internationally. However, cross‐border integration processes are complex and often result in a looser integration than intended. In this study, we examine the postacquisition process in a multinational seeking global integration of its geographically dispersed organizational units. We find that politicization and ambiguity lead to integration vacuum where top‐down initiatives fail to achieve desired integration outcomes. However, the integration vacuum creates expanded space of action for the acquired firm to initiate unexpected bottom‐up integration. We contribute to the literature on multinationals by illuminating the challenges they face when extending their dominant strategic logic to international acquisitions. Furthermore, we identify the process through which politicization and ambiguity lead to integration vacuum that allows the foreign subsidiary an expanded space of action wherein it can initiate bottom‐up integration efforts. © 2013 Wiley Periodicals, Inc.
The Role of Absorptive Capacity in Acquisition Knowledge Transfer
Authors: Junni Paulina , Sarala Riikka M.
Published: June 2013

This article examines the role of absorptive capacity in acquisitions. We propose that absorptive capacity is an important determinant of acquisition knowledge transfer. Also, we identify antecedents of absorptive capacity in the specific context of acquisitions. These include contextual (national cultural differences), individual (employee withdrawal), and organizational design level (integration process communication, knowledge processing system) antecedents. We test our hypotheses on a sample of domestic and foreign acquisitions conducted by Finnish companies. This study contributes to the acquisition literature by elaborating on the role of absorptive capacity in acquisitions and to the general absorptive capacity literature by highlighting the importance of previously underexplored antecedents and outcomes of absorptive capacity. © 2013 Wiley Periodicals, Inc.
Light‐Touch Integration of Chinese Cross‐Border M&A: The Inﬂuences of Culture and Absorptive Capacity
Authors: Liu Yipeng , Woywode Michael
Published: June 2013

As a major entry mode of global strategy of Chinese MNCs, Chinese cross‐border merger and acquisition (M&A) is still a less understood phenomenon, in particular the post acquisition phase. This study contributes to this rising, important and interesting phenomenon utilizing an explorative research method. By integrating synergy potential, culture influences and the learning perspective, we suggest a multilevel perspective in understanding Chinese cross‐border M&A. A novel post acquisition integration approach, namely light‐touch integration, is investigated, and supported by newly assembled empirical evidence in the context of Chinese M&A in Germany. Light‐touch integration essentially synthesizes the preservation and symbiosis integration approaches due to the contextual characteristics of Chinese cross‐border M&A, such as cultural influences and the learning perspective. Understanding the cultural and learning influences can facilitate and smooth the activities involved in the post acquisition phase. The light‐touch integration approach offers ample opportunities for joint collaborations between and mutual benefits for acquiring firms, acquired targets and third party organizations. © 2013 Wiley Periodicals, Inc.
Principal component analysis of watershed hydrochemical response to forest clearance and its usefulness for chloride mass balance applications
Authors: Guan Huade , Hutson John , Ding Zhenyu , Love Andrew , Simmons Craig T. , Deng Zijuan
Published: June 2013

Application of the simple watershed chloride mass balance (CMB) method over areas of historical forest clearance is highly uncertain because the CMB method requires a steady state assumption, while the beginning, duration, and end of the transient period between preclearance and postclearance steady states is unknown. To address this difficulty, principal component analysis (PCA) with groundwater chemistry data is explored for the Piccadilly Valley in the Mount Lofty Ranges in South Australia, incorporated with hydrological modeling. The results indicate that PCA provides a potentially useful tool to identify postclearance dynamic hydrochemical response. Processes during the postclearance transient period, such as the release of historical soil chloride together with the charge‐balance cations, alter ionic ratios from a steady state condition, which make the hydrochemical signals from the transient processes distinguishable from other processes by PCA. For the studied watershed, the effect of postclearance transient processes accounts for 24% of major‐ion data variance, in comparison to 43% resulting from the effects of precipitation diluting and evapotranspiration concentrating processes. The PC scores associated with the transient processes are shown to be useful for estimating the timing of the postclearance transient, and estimating chloride concentration of groundwater recharge at the preclearance and postclearance steady states, even under conditions where the new steady state has not yet reached or the preclearance hydrochemical signal is lost.
Remanent Si–H Interactions in Late Transition Metal Silane Complexes
Authors: Hauf Christoph , Barquera‐Lozada José E. , Meixner Petra , Eickerling Georg , Altmannshofer Sandra , Stalke Dietmar , Zell Thomas , Schmidt David , Radius Udo , Scherer Wolfgang
Published: June 2013

In general, it is assumed that the reaction between silanes and late transition metal fragments yields silyl hydride species as oxidative addition products. However, the silane complex Ni(iPr2Im)2(SiHMePh2) (iPr2Im = 1, 3‐diisopropylimidazolin‐2‐ylidene) (3a), might represent one of the rare systems where a stable η2‐(Si–H)Ni intermediate of the oxidative addition process has been isolated. Indeed, 3a is characterized by an acute [ang]Si–Ni–H angle of 62.0(2)°, a rather short Si–H bond length of 1.992(6) Å and displays a silicon‐hydride cross peak in Si‐H‐HMQC 2D‐NMR studies. We therefore selected the latter system for a combined experimental and theoretical charge density study to explore the electronic prerequisites which hinder the full completion of the oxidative addition step in transition metal silane complexes and cause the presence of remanent Si–H interactions in these species.
Further Insights into the Role of Temperature in the Synthesis of the Lanthanide(III)‐Pyrazine‐Octacyanotungstate(V) System: an Example of Discrete Materials
Authors: Zhou Hu , Diao Guo‐Wang , Yang Xiao‐Zhen , Yuan Ai‐Hua , Zhang Min , Sun Jing
Published: June 2013

Slow diffusion reactions of Ln3+ (Ln = Ce, Eu, Tb) ions, pyrazine, and the [W(CN)8]3– unit at 0 °C produced three discrete coordination compounds [Ln(H2O)5(CH3CN)2][W(CN)8]·0.5pyrazine·CH3CN·2H2O [Ln = Ce (1), Eu (2)] and [Tb(H2O)6(CH3CN)2][W(CN)8]·pyrazine·2CH3CN·3H2O (3). Single crystal X‐ray diffraction analysis revealed that compounds 1 and 2 are isomorphous and adopt a rare centrosymmetric tetranuclear square unit, while compound 3 exhibits an ion‐pair moiety, in which unique tetramer water clusters (H2O)4 are involved. The presence of different types of hydrogen‐bonding interactions is responsible for the formation of three‐dimensional supramolecular networks. The isolations of compounds 1–3 provide a further insight into the effect of temperatures on constructions and structures of the lanthanide(III)‐pyrazine‐octacyanotungstate(V) system.
Event‐based feedback control of disturbed input‐affine systems
Authors: Stöcker C. , Lunze J.
Published: June 2013

This paper proposes a novel event‐based control method for nonlinear systems that are input‐output linearizable. A method for the design of an event‐based state‐feedback controller is proposed which approximates the disturbance rejection behavior of a continuous state‐feedback system, referred to as reference system, with adjustable accuracy, while simultaneously reducing the feedback communication effort. The event‐based control loop is shown to be input‐to‐state stable. A bound for the deviation between the behavior the event‐based control loop and the reference system is derived. This bound is shown to be a function of the event threshold, which is a design parameter that can be freely chosen. Moreover, the deviation between the outputs of both systems is also proven to be bounded and can be made arbitrarily small by appropriately scaling the event threshold. The minimum time in between consecutive events is shown to be bounded from below by some bound which is explicitly determined. The efficiency of the new control method is demonstrated for a bioreactor example.
Asymptotic modelling and design of some microlayered functionally graded heat conductors
Authors: Woźniak C. , Wa̧growska M. , Szlachetka O.
Published: June 2013

The paper presents a new method of modelling for certain microlayered heat conductors. So far the main attention related to the modelling of composite materials with deterministic structure was mainly restricted to the periodic composites (Bensoussan, Lions, and Papanicolaou [1]). The main future of the presented approach is that it can be also applied to the class with a non periodic structure. These structures can by referred to as functionally graded in the direction normal to the interfaces between layers. At the same time the non‐homogenous material structure of the composite is slowly varying in this direction. That is why the obtained model equations have functionally but slowly varying coefficients. Moreover, this equations can by applied for designing functionally graded heat conductors with given a priori class of temperature fields.
Comparing sampling strategies for aerodynamic Kriging surrogate models
Authors: Rosenbaum B. , Schulz V.
Published: June 2013

In aerodynamic applications often evaluations of an expensive computer simulation like a CFD solver are needed for a whole range of input parameters. Dense computations to describe the global behavior of an objective function are out of reach due to limited computational resources. Surrogate models like the Kriging method allow an interpolation of collected data and a global approximation. Adaptive sampling strategies can reduce the number of required samples for accurate and efficient surrogate models by automatically identifying critical or too coarse sampled regions of the input domain. We compare different existing sampling strategies as well as new theoretical methods using a dense set of validation data in order to gain a deeper understanding of optimal sample distributions and lower error boundaries.
Thermal expansion of pyrolytic carbon with various textures
Authors: Zhang W. , Li A. , Reznik B. , Deutschmann O.
Published: June 2013

Thermal expansion of differently‐textured pyrolytic carbon matrices (pyrocarbons) of carbon/carbon composites was studied with a high temperature X‐ray diffraction at temperatures ranging from 25°C to 1400°C. The composites were synthesized by chemical vapor infiltration of a carbon fiber felt, using methane as a carbon source. From the linear dependence of the lattice displacement on temperature, coefficients of thermal expansion (CTE) of the pyrocarbons were calculated. One‐dimensional thermal expansion along the (002)‐direction (c‐axis) of the pyrocarbons was found to be proportional to the composite synthesis temperature. A correlation between CTE and pyrocarbon texture was found: low‐textured pyrocarbon with an extinction angle (Ae) of 10° exhibits a smaller CTE of 2.02 × 10‐5 K‐1, whereas high‐textured pyrocarbon with an Ae of 22° exhibits a considerably higher CTE of 2.65 × 10‐5 K‐1. However, CTE of high‐textured pyrocarbon is still smaller than that of graphite, which is 2.9 ×10‐5 K‐1.
Optimal value functions for weakly coupled systems: a posteriori estimates
Authors: Koltai P. , Junge O.
Published: June 2013

We consider weakly coupled LQ optimal control problems and derive estimates on the sensitivity of the optimal value function in dependence of the coupling strength. In order to improve these sensitivity estimates a “coupling adapted” norm is proposed. Our main result is that if a weak coupling suffices to destabilize the closed loop system with the optimal feedback of the uncoupled system then the value function might change drastically with the coupling. As a consequence, it is not reasonable to expect that a weakly coupled system possesses a weakly coupled optimal value function. Also, for a known result on the connection of the separation operator and the stability radius a new and simpler proof is given.
A model for the evolution of laminates in finite‐strain elastoplasticity
Authors: Hackl K. , Heinz S. , Mielke A.
Published: June 2013

We study the time evolution in elastoplasticity within the rate‐independent framework of generalized standard materials. Our particular interest is the formation and the evolution of microstructure. Providing models where existence proofs are possible is a challenging task since the presence of microstructure comes along with a lack of convexity and, hence, compactness arguments cannot be applied to prove the existence of solutions. In order to overcome this problem, we will incorporate information on the microstructure into the internal variable, which is still compatible with generalized standard materials. More precisely, we shall allow for such microstructure that is given by simple or sequential laminates. We will consider a model for the evolution of these laminates and we will prove a theorem on the existence of solutions to any finite sequence of time‐incremental minimization problems. In order to illustrate the mechanical consequences of the theory developed some numerical results, especially dealing with the rotation of laminates, are presented.
On the positivity of solutions of systems of stochastic PDEs
Authors: Cresson J. , Efendiev M. , Sonner Stefanie
Published: June 2013

We study the positivity of solutions of a class of semi‐linear parabolic systems of stochastic partial differential equations by considering random approximations. For the family of random approximations we derive explicit necessary and sufficient conditions such that the solutions preserve positivity. These conditions imply the positivity of the solutions of the stochastic system for both Itô's and Stratonovich's interpretation of stochastic differential equations.
Semiconductor device optimization in the presence of thermal effects
Authors: Drago C.R. , Marheineke N. , Pinnau R.
Published: June 2013

Optimal design problems for semiconductor devices with relevant thermal effects can be formulated by help of the energy transport model. In this paper we perform a sensitivity analysis to derive the first‐order necessary condition for the optimization. Exploiting the special structure of the KKT system we use a special variant of the classical Gummel iteration to provide a very fast optimization algorithm. Numerical results for a ballistic diode underline the feasibility of our approach.
A numerical homogenisation method for sandwich plates based on a plate theory with thickness change
Authors: Helfen C. , Diebels S.
Published: June 2013

Nowadays composite plates are widely used, especially in the transport industry. Their importance derives from their relatively low weight and good mechanical properties, but their behaviour is complex and cannot be obtained from a simple mixture rule properly. In the scope of this work, the considered composite plate is composed of a complex assembly of metal layers and carbon fibers reinforced polymers (CFRP) layers. Whereas the CFRP can be considered as anisotropic elastic, the metal layers have an elasto‐plastic material behaviour. In this case, the possibility to use the classical plate theory is excluded, because the classical plate theory can only regard small deformations and linear material behaviour. For this reason, the modelling of the mechanical behaviour of the composite plate is based on a numerical homogenisation. The underlying principle is a numerical multi‐scale consideration of the composite plate: on the one hand, the macroscale is considered as a Finite Element computation of a plate which is following a plate theory including a thickness change, i. e. a seven degrees of freedom approach. On the other hand, the mesoscale is obtained with a three‐dimensional modelling which explicitly takes into account the stacking order and the material behaviour of the different layers. From each integration point of the macroscale, the deformations are projected on the boundaries of a Representative Volume Element (RVE) of the mesoscale. In this scale, a boundary value problem is solved, and the macroscopic forces, moments and shear forces are obtained as resultants from the mesoscopic stresses.
Sparse space‐time Galerkin BEM for the nonstationary heat equation
Authors: Chernov A. , Schwab Ch.
Published: June 2013

We construct and analyze sparse tensorized space‐time Galerkin discretizations for boundary integral equations resulting from the boundary reduction of nonstationary diffusion equations with either Dirichlet or Neumann boundary conditions. The approach is based on biorthogonal multilevel subspace decompositions and a weighted sparse tensor product construction. We compare the convergence behavior of the proposed method to the standard full tensor product discretizations. In particular, we show for the problem of nonstationary heat conduction in a bounded two‐ or three‐dimensional spatial domain that low order sparse space‐time Galerkin schemes are competitive with high order full tensor product discretizations in terms of the asymptotic convergence rate of the Galerkin error in the energy norms, under lower regularity requirements on the solution.
Dirichlet‐transmission problems for pseudodifferential Brinkman operators on Sobolev and Besov spaces associated to Lipschitz domains in Riemannian manifolds
Authors: Kohr M. , Pintea C. , Wendland W.L.
Published: June 2013

In this paper we use a layer potential analysis to show the existence of solutions for a Dirichlet‐transmission problem for pseudodifferential Brinkman operators on Sobolev and Besov spaces associated to Lipschitz domains in compact boundaryless Riemannian manifolds. Compactness and invertibility properties of corresponding layer potential operators on Lp, Sobolev, or Besov scales are also obtained.
Numerical algorithm based on an implicit fully discrete local discontinuous Galerkin method for the time‐fractional KdV‐Burgers‐Kuramoto equation
Authors: Wei L. , He Y. , Yildirim A. , Kumar S.
Published: June 2013

In this paper, an implicit fully discrete local discontinuous Galerkin (LDG) finite element method is considered for solving the time‐fractional KdV‐Burgers‐Kuramoto (KBK) equation. The scheme is based on a finite difference method in time and local discontinuous Galerkin methods in space. We prove that our scheme is unconditional stable and L2 error estimate for the linear case with the convergence rate O(hk+1 + (Δ t)2+ (Δ t)α/2hk+$^{1 \over 2}$). Numerical examples are presented to show the efficiency and accuracy of our scheme.
Elastic buckling of axisymmetric cylindrical shells under axial load using first order shear deformation theory
Authors: Mahboubi Nasrekani F. , Eipakchi H.R.
Published: June 2013

In this paper, the elastic buckling stress of axisymmetric cylindrical shells under uniform axial load is determined analytically by using the first order shear deformation theory. The equilibrium equations are derived by the virtual work principle and then the stability equations are extracted from them. They are systems of differential equations, which are solved analytically by using the perturbation method. The effects of the geometrical properties on the buckling stress are investigated by a parametric study. The results are compared with the finite elements methods.
Dynamics of mechanical systems with nonlinear nonholonomic constraints – III Analysis of motion
Authors: Zeković D.N.
Published: June 2013

The paper analyzes the motion of nonholonomic mechanical systems composed of two particles with imposition of various nonlinear limitations to the velocities of the particles – parallelism of velocities, equality of the intensities of velocities and perpendicularity of velocities. The analysis for such systems includes: equations of constraints, reactions of constraints, i.e. the mode of variations of such constraints, trajectories of the points of the systems, linear integrals for generalized velocities, i.e. cyclical coordinates. It is clearly demonstrated on these models that in the case of nonlinear nonholonomic constraints the Hamiltonian effect, in the general case, has no stationary value. Lastly, the equations of brachistochronic motion of described systems are derived and the brachitochrones of specified points are determined.
Raman microprobe spectrometry of carbon/carbon composites with differently‐textured pyrolytic carbon matrices
Authors: Zhang W. , Reznik B. , Deutschmann O.
Published: June 2013

The microstructure of carbon/carbon composites obtained by chemical vapor infiltration of carbon‐fiber felts was studied comparatively by means of Raman spectroscopy, polarized light microscopy (PLM), scanning electron microscopy (SEM), and X‐ray diffraction. The matrices, which are homogeneously textured according to PLM, exhibit pronounced spatial structural gradients at the sub‐μm scale if investigated by means of Raman microprobe spectrometry. The Raman and SEM observations demonstrate that the high‐temperature treatment correlates with the increasing development of the graphitic ordering in low‐ and high‐textured pyrolytic carbon matrices.
A multi‐time stepping integration method for the ultrasound heating problem
Authors: Shevchenko I. , Kaltenbacher M. , Wohlmuth B.
Published: June 2013

A two‐dimensional thermo‐acoustic problem consisting of the Pennes bioheat transfer model and a nonlinear wave equation with a temperature dependent speed of sound is considered. The large discrepancy in time scales of the wave propagation and the heat conduction processes requires a multi‐time stepping method allowing to solve both equations on different time scales. However, the standard approach considers a sequential solution process without any error control. We propose a multi‐time stepping scheme based on a fixed‐point approach resulting in a thermo‐acoustic coupling controlled by a stopping criterion. Furthermore, in most high‐intensity focused ultrasound applications the problem has to deal with absorbing boundary conditions (ABCs) in a bounded region. The use of a Lagrange multiplier based technique allows us to efficiently incorporate the second order Engquist–Majda ABC into the weak formulation of the original problem. The efficiency and robustness of the proposed multi‐time stepping method as well as improved accuracy compared to the widely used standard scheme for modeling high‐intensity focused ultrasound is demonstrated through a series of numerical examples which are typical for ultrasound heating.
On the use of sampling surfaces method for solution of 3D elasticity problems for thick shells
Authors: Kulikov G.M. , Plotnikova S.V.
Published: June 2013

This paper presents a simple and effective method of solving the 3D elasticity problems for thick shells. It is based on the new concept of sampling surfaces (S‐surfaces) inside the shell body. According to this concept, we introduce N not equally located S‐surfaces parallel to the midsurface and choose displacements of these surfaces as basic shell unknowns. Such choice allows one to represent the governing equations of the proposed higher order shell model in a very compact form and to solve the 3D static problems for thick plates and shells efficiently.
Exact solutions of the 2‐D frictional sliding contact problem of electrically insulated triangular and cylindrical punches on piezoelectric materials
Authors: Zhou Y.‐T. , Lee K.Y.
Published: June 2013

The present paper performs an exact electro‐mechanical contact analysis for piezoelectric materials under a frictional sliding triangular or cylindrical punch. The Coulomb frictional law is used inside the contact region. Appropriate fundamental solutions that can lead to real solutions of electro‐mechanical quantities are derived for real and complex eigenvalues. A second kind singular integral equation of Cauchy type is obtained for the stated problem, whose exact solution can be found by using the excellent properties of Jacobi Polynomials. Closed‐form expressions of stress components and electrical displacement are obtained, which provide benchmark solutions for examining the frictional contact behaviors of piezoelectric materials. Numeric results are presented. The influences of the friction coefficient on the contact region, stress components and electric displacement are detailed.
Exact solution for boundary layer flow of Casson fluid over a permeable stretching/shrinking sheet
Authors: Bhattacharyya K. , Hayat T. , Alsaedi A.
Published: June 2013

In this investigation, the steady boundary layer flow of Casson fluid over a porous stretching/shrinking sheet is studied. The governing equations are transformed using similarity transformations and then solved analytically. In both stretching and shrinking sheet cases, the closed form exact solutions are obtained. The solution is always unique for stretching sheet case. On the other hand, in shrinking sheet case, the solution may exist or may not and if exists it may be unique or may be of dual nature; these all depend on the value of Casson parameter and wall mass transfer parameter. Also, the analysis reveals that for steady flow of Casson fluid stronger mass suction is needed.
Homogenization of thermoelasticity processes in composite materials with periodic structure of heterogeneities
Authors: Savatorova V.L. , Talonov A.V. , Vlasov A.N.
Published: June 2013

The majority of processes in composite materials involve a wide range of scales. Because of the scale disparity in multi scale problem, it's often impossible to resolve the effect of small scales directly. In this paper we perform multi scale modeling in order to analyze properties of composite materials with periodical structure under temperature and stresses influence. Each component has its own thermal and mechanical (elastic) properties. We replace differential equations with rapidly oscillating coefficients by homogenized equations having effective parameters, incorporating multi scale structure and properties of any component. The influence of any component's properties and of the layer thickness on the effective properties of whole sample has been studied. We perform comparison of results, obtained with and without account for thermostresses.
Modelling strain localization by cohesive/overlapping zones in tension/compression: Brittleness size effects and scaling in material properties
Authors: Carpinteri A. , Paggi M.
Published: June 2013

The present paper is a state‐of‐the‐art review of the research carried out at the Politecnico di Torino during the last two decades on the modelling of strain localization. Introducing the elementary cohesive/overlapping models in tension/compression, it will be shown that it is possible to get a deep insight into the ductile‐to‐brittle transition and into the scaling of the material properties usually detected when testing quasi‐brittle material specimens or structures at different size‐scales.
High‐order finite elements compared to low‐order mixed element formulations
Authors: Netz T. , Düster A. , Hartmann S.
Published: June 2013

High‐order finite elements are commonly compared with linear element formulations showing that, in terms of the relation between computational time and achievable accuracy, linear element formulations are inferior to high‐order elements. On the other hand, the finite element community follows the h‐version approach due to its simplicity in implementation. This article compares high‐order finite elements based on hierarchic shape functions with low‐order mixed element formulations using finite strain hyperelasticity. These comparisons are conducted from the point of view of both accuracy and efficiency as well as highly deformed structures. It also investigates improvements to minimize the overall computational effort such as parallelizing the element assemblage procedure, choosing a starting vector estimator for Newton's method, and investigating the Newton‐Chord method. The advantages and disadvantages of both finite element approaches are also discussed.
Photoelastic‐numerical treatment of Beltrami‐Michell boundary value problems
Authors: Rezini D. , Tamine T.
Published: June 2013

One of the main challenges of using photoelasticity has always been its complexity to determining all stress components, for it provides an unfinished solution. Indeed, the use of the Beltrami‐Michell Boundary Value Problem remains of practical interest for the study of the stress‐separation, when complemented by the photoelasticity analysis to acquire the Dirichlet conditions. The synergy of both is enhanced with the use of Finite Difference Method to work out a photoelastic‐numerical hybrid method for stress analysis under plane conditions. On the other hand, while for photoelasticity specially, annular disks under diametral compressive load are usually used as standard models allowing to check the performance of any developed method; because theoretical solutions exist. A comprehensive study has been carried out to show the photoelastic‐numerical method in order to investigate the in‐plane stress distribution using isochromatic values only on the boundaries of an annular object subjected to diametral compression. Compared with a reference work, the obtained results are more than concluding. The method is fast in the analysis for a low cost.
Hysteresis models and gravity fingering in porous media
Authors: Rätz A. , Schweizer B.
Published: June 2013

We study flow problems in unsaturated porous media. Our main interest is the gravity driven penetration of a dry material, a situation in which fingering effects can be observed experimentally and numerically. The flow is described by either a Richards or a two‐phase model. The important modelling aspect regards the capillary pressure relation which can include static hysteresis and dynamic corrections. We report on analytical existence and instability results for the corresponding models and present numerical calculations. We show that fingering effects can be observed in various models and discuss the importance of the static hysteresis term.
Model reduction of an elastic crankshaft for elastic multibody simulations
Authors: Nowakowski C. , Kürschner P. , Eberhard P. , Benner P.
Published: June 2013

System analysis and optimization of combustion engines and engine components are increasingly supported by digital simulations. In the simulation process of combustion engines multi physics simulations are used. As an example, in the simulation of a crank drive the mechanical subsystem is coupled to a hydrodynamic subsystem. As far as the modeling of the mechanical subsystems is concerned, elastic multibody systems are frequently used. During the simulation many equations must be solved simultaneously, the hydrodynamic equations as well as the equations of motion of each body in the elastic multibody system. Since the discretization of the elastic bodies, e.g with the help of the finite element method, introduces a large number of elastic degrees of freedom, an efficient simulation of the system becomes difficult. The linear model reduction of the elastic degrees of freedom is a key step for using flexible bodies in multibody systems and turning simulations more efficient from a computational point of view. In recent years, a variety of new reduction methods alongside the traditional techniques were developed in applied mathematics. Some of these methods are reviewed and compared for reducing the equations of motion of an elastic body used in multibody systems. The special focus of this work is on balanced truncation model order reduction, which is a singular value based reduction technique using the Gramian matrices of the system. We investigate a version of this method that is adapted to the structure of a special class of second order dynamical systems which is important for the particular application discussed here. The simulation of a crank drive with a flexible crankshaft is taken as technically relevant example. The results are compared to other methods like Krylov approaches or modal reduction.
Numerical investigation of 1D continuum dynamical models of discrete chain
Authors: Andrianov I.V. , Starushenko G.A. , Weichert D.
Published: June 2013

This paper is devoted to the numerical analysis of the various continuum models of a 1D discrete media. Namely, we consider intermediate, quasi‐continuum, and improved quasi‐continuum models. The analysis of various receptions of continualization in a linear case is carried out. For this purpose, we consider the solution in the form of a traveling wave caused by the initial perturbation. The solution is obtained by Fourier transformation inverted numerically. Then we compare solutions of discrete and continuum models for wave velocity. Numerical calculations show that all the above described nonlocal theories qualitatively equally well describe the propagation of waves in a discrete media. The disadvantage of intermediate continuum model is the high order of differential equation. For finite chain this leads to the need for the formulation of boundary conditions that do not follow naturally from the source of the problem. The quasi‐continuum approximation yields results practically identical with those obtained on the basis of improved quasi‐continuum approximation. The most accurate approximation of a discrete medium gives improved quasi‐continuum approximation. The advantage of improved quasi‐continuum approximation is manifested in those cases where you need to describe the high modes of oscillation of the discrete finite chain.
Scattering of plane acoustic waves by a circular semi‐infinite pipe with a rigid end face placed axially in an infinite circular duct
Authors: Yanaz Çınar Ö.
Published: June 2013

In this paper, the propagation of acoustic waves along a duct system, where a semi‐infinite circular rigid pipe with a rigid end face is placed axially inside an infinite circular rigid pipe is analyzed rigorously. First, direct Fourier transform is applied and the problem is reduced into the solution of a modified Wiener‐Hopf equation of the second type from which the reflection and transmission coefficients are determined. Then the bifurcated circular waveguide problem is solved by applying direct Fourier transform again to reduce the problem into the solution of a Wiener‐Hopf equation and the resulting transfer coefficients are taken into account when applying the building block method. Building block method is one of the scattering matrix techniques where reflection and transmission characteristics of each discontinuity in a duct are first determined independently and then taken into account as scattering matrices in order to analyze the original problem. At the end of the analysis, numerical results are presented comparing two approaches of formulation and illustrating the effects of the radii of the pipes and frequency.
Sharp conditions of global existence for second‐order derivative nonlinear Schrödinger equations with combined power‐type nonlinearities
Authors: Xu Runzhang , Xu Chuang
Published: June 2013

We undertake a comprehensive study of the Cauchy problem of a class of second‐order derivative nonlinear Schrödinger equations with combined power‐type nonlinearities. Using the potential theory and the concavity method, we construct a variational problem and two invariant manifolds. Furthermore, we give sharp conditions of global existence and blowup.
Prandtl‐Tomlinson model: History and applications in friction, plasticity, and nanotechnologies
Authors: Popov V.L. , Gray J.A.T.
Published: June 2013

One of the most popular models widely used in nanotribology as the basis for many investigations of frictional mechanisms on the atomic scale is the so‐called Tomlinson model consisting of a point mass driven over a periodic potential. The name “Tomlinson model” is, however, historically incorrect: The paper by Tomlinson from the year 1929 which is often cited in this context did not, in fact, contain the model known as the “Tomlinson model” and suggests, instead, an adhesive contribution to friction. In reality, it was Ludwig Prandtl who suggested this model in 1928 to describe the plastic deformation in crystals and dry friction. Staying in line with some other researchers, we call this model the “Prandtl‐Tomlinson model,” although the model could simply and rightly be dubbed the “Prandtl model.” The original paper by Ludwig Prandtl was written in German and was not accessible for a long time for the largest part of the international tribological community. The present paper is a historical introduction to the English translation of the classical paper by Ludwig Prandtl. It gives a short review of the model as well as its properties, applications, and extensions from the contemporary viewpoint.
Simulation of the abrasive flow machining process
Authors: Schmitt J. , Diebels S.
Published: June 2013

During the last decade the abrasive flow machining process became an accepted technique to smooth and to round inner edges in badly contactable regions of complex geometries, e.g. grooves in rails of common rail systems. The process is based on the flow of a highly viscous silicone oil which is charged by abrasive particles. This leads to an efficient rounding of the egdes. In the present article a material model for the non‐Newtonian behaviour of the abrasive paste is proposed, the material parameters are identified according to experiments and, finally, a simulation of the abrasive flow machining process is presented based on a model implementation in the software package COMSOL Multiphysics®.
From fractal media to continuum mechanics
Authors: Ostoja‐Starzewski M. , Li J. , Joumaa H. , Demmie P.N.
Published: June 2013

This paper presents an overview of modeling fractal media by continuum mechanics using the method of dimensional regularization. The basis of this method is to express the balance laws for fractal media in terms of fractional integrals and, then, convert them to integer‐order integrals in conventional (Euclidean) space. Following an account of this method, we develop balance laws of fractal media (continuity, linear and angular momenta, energy, and second law) and discuss wave equations in several settings (1d and 3d wave motions, fractal Timoshenko beam, and elastodynamics under finite strains). We then discuss extremum and variational principles, fracture mechanics, and equations of turbulent flow in fractal media. In all the cases, the derived equations for fractal media depend explicitly on fractal dimensions and reduce to conventional forms for continuous media with Euclidean geometries upon setting the dimensions to integers. We also point out relations and potential extensions of dimensional regularization to other models of microscopically heterogeneous physical systems.
Global well‐posedness of the aggregation equation with supercritical dissipation in Besov spaces
Authors: Wu G. , Zhang Q.
Published: June 2013

In this paper, we study the supercritical aggregation equation. We prove the global well‐posedness for small initial data lying in Besov spaces and the local well‐posedness for arbitrary initial data. The Fourier localization technique and the Littlewood‐Paley theory are the main tools used in the proof.
A note on the carbuncle phenomenon in shallow water simulations
Authors: Kemm F.
Published: June 2013

A classic problem in gas dynamics simulation is the occurrence of the carbuncle phenomenon, a breakdown of discrete shock profiles. We show that for high Froude number, this also occurs in shallow water simulations. Numerical evidence is given that commonly accepted cures developed for the numerics of gas dynamics should also work for shallow water flows.
Finite element modeling of Kirchhoff‐Love shells as smooth material surfaces
Authors: Vetyukov Yu.
Published: June 2013

We consider large deformations of curved thin shells in the framework of a classical Kirchhoff‐Love theory for material surfaces. The geometry of the element is approximated via the position vector and its derivatives with respect to the material coordinates at the four nodes, and C1 continuity of the surface over the interfaces between the elements is guaranteed. Theoretical background provides certainty concerning the boundary conditions, the range of applicability of the model, extensions to multi‐field problems, etc. Robust convergence and accuracy of the resulting simple numerical scheme is demonstrated by the analysis of benchmark problems in comparison with other solutions.
Layer potential analysis for a Dirichlet‐transmission problem in Lipschitz domains in ℝn
Authors: Fericean D. , Wendland W.L.
Published: June 2013

In this paper we obtain the existence and uniqueness in some Sobolev and Lp spaces for a Dirichlet‐transmission problem for the Stokes and Brinkman equations on Lipschitz domains in ℝn, n > 3. In the particular case n = 3 this problem describes the Stokes flow of a viscous incompressible fluid past a porous particle and in presence of a solid core. The flow within the porous particle is described by the Brinkman equation. In order to obtain the desired existence and uniqueness result, we use an indirect boundary integral formulation based on the layer potential theory for both Brinkman and Stokes equations. Some special cases, which refer to the Stokes flow past a porous particle with large permeability, respectively low permeability, are also analyzed.
Refined modeling of composite plates with in‐plane heterogeneity
Authors: Lee C.‐Y. , Yu W. , Hodges D.H.
Published: June 2013

This article is concerned with the mechanical behavior of heterogeneous composite plates with elastic moduli and layered geometries varying through the thickness direction and periodically along the in‐plane directions. By using the concept of decomposition of the rotation tensor, we first formulate the three‐dimensional elastic problem in an intrinsic form for application to the geometrically nonlinear problem. The variational asymptotic method is then exercised, leading to simultaneous homogenization and dimensional reduction to construct an effective and simple model suitable for plates with in‐plane periodicity. In particular, having obtained the refinement terms up to the second order, we develop a refined plate model, namely a generalized Reissner‐Mindlin model that is capable of capturing the transverse shear deformations. In order to deal with realistic and complex plate geometries and constituent materials efficiently and conveniently, the proposed model is implemented into a single unified formulation suitable for incorporation into a commercial analysis package. Numerical results computed herein for a few examples are compared to similar results available in the literature to demonstrate the application and performance of the present model.
Adaptive fuzzy sliding mode control of a chaotic pendulum with noisy signals
Authors: Bessa W.M. , de Paula A.S. , Savi M.A.
Published: June 2013

Chaotic response is related to a dense set of unstable periodic orbits (UPOs) and the system often visits the neighborhood of each one of them. Moreover, chaos has sensitive dependence to initial conditions, which implies that the system evolution may be altered by small perturbations. Chaos control is based on the richness of chaotic behavior and may be understood as the use of tiny perturbations for the stabilization of an UPO enclosed in a chaotic attractor. It makes this kind of behavior to be desirable in a variety of applications, since one of these UPOs can provide better performance than others in a particular situation. In this work, an adaptive fuzzy sliding mode controller is combined with the close return method for the stabilization of UPOs in a chaotic pendulum. The adaptive fuzzy inference system is embedded in a smooth sliding mode controller to cope with both structured and unstructured uncertainties. Since noise contamination is unavoidable in experimental data acquisition, this work also investigates the effect of noisy signals on the used control law, verifying their influence on the system stabilization and on the required control action. Numerical results are presented in order to illustrate the ability of the proposed control scheme to track UPOs even in the presence of modeling inaccuracies and noisy input signals.
On the bending of plates in the electromagnetic theory of microstretch elasticity
Authors: Galeş C. , Baroiu N.
Published: June 2013

This paper deals with the electromagnetic theory of microstretch elasticity. The full dynamic theory, which describes the interaction of electromagnetic fields with piezoelectric bodies, called piezoelectromagnetism, is considered. First, we derive the equations governing the bending theory of thin piezoelectromagnetic microstretch plates. Then, the boundary‐initial value problem is formulated and a uniqueness result is presented. Finally, the effects of a concentrated charge density in an infinite plate are studied.