bluuebunny/crossref_metadata_2025_split huggingface dataset:
POST‐DAMMING FLOW REGIME DEVELOPMENT IN A LARGE LOWLAND RIVER (VOLGA, RUSSIAN FEDERATION): IMPLICATIONS FOR FLOODPLAIN INUNDATION AND FISHERIES
Authors: Górski K. , van den Bosch L. V. , van de Wolfshaar K. E. , Middelkoop H. , Nagelkerke L. A. J. , Filippov O. V. , Zolotarev D. V. , Yakovlev S. V. , Minin A. E. , Winter H. V. , De Leeuw J. J. , Buijse A. D. , Verreth J. A. J. 
Published: March 2011

ABSTRACTPeriodic flooding plays a key role in the ecology of floodplain rivers. Damming of such rivers can disturb flooding patterns and have a negative impact on commercial fish yield. The Volga River, the largest river in Europe, has a regulated flow regime after completion of a cascade of dams. Here, we study effects of damming on long‐term discharge variability and flood pulse characteristics. In addition, we evaluate the effects of the altered flood pulse on floodplain ecosystem functioning and commercial fish yields. Our results indicate that both flood pulse and fish populations of the Volga–Akhtuba floodplain have varied considerably over the past decades. After damming, annual maximum peak discharges have decreased, minimum discharges increased, but average discharges remained similar to pre‐damming conditions. Moreover, because of bed level incision of over 1.5 m, a higher discharge is needed to reach bankfull level and inundate the floodplains. Despite this significantly altered hydrological regime and subsequent morphological changes, current discharge management still provides significant spring flooding. However, commercial fish catches did decrease after damming, both in the main channel and in the floodplain lakes. All catches were dominated by species with a eurytopic flow preference, although catches from the main channel contained more rheophilic species, and floodplain catches contained more limnophilic and phytophilic species. The strong increase of opportunistic gibel carp (Carassius gibelio) around 1985 was apparent in the main channel and the floodplain lakes. Despite the hydrological changes, the decrease in overall catches, and the upsurge of gibel, we found a strong positive effect of flood magnitude in the previous year on commercial fish yield in the floodplain lakes. This suggests that under the current discharge management there still is an increased fish growth and/or survival during high floods and that functioning of the floodplain is at least partly intact. Copyright © 2011 John Wiley & Sons, Ltd.
The use of search‐based optimization techniques to schedule and staff software projects: an approach and an empirical study
Authors: Di Penta Massimiliano , Harman Mark , Antoniol Giuliano 
Published: March 2011

AbstractAllocating resources to a software project and assigning tasks to teams constitute crucial activities that affect project cost and completion time. Finding a solution for such a problem is NP‐hard; this requires managers to be supported by proper tools for performing such an allocation. This paper shows how search‐based optimization techniques can be combined with a queuing simulation model to address these problems. The obtained staff and task allocations aim to minimize the completion time and reduce schedule fragmentation. The proposed approach allows project managers to run multiple simulations, compare results and consider trade‐offs between increasing the staffing level and anticipating the project completion date and between reducing the fragmentation and accepting project delays. The paper presents results from the application of the proposed search‐based project planning approach to data obtained from two large‐scale commercial software maintenance projects. Copyright © 2011 John Wiley & Sons, Ltd.
Numerical validation of a finite element thin‐walled beam model of a composite wind turbine blade
Authors: Cárdenas Diego , Escárpita Alejandro A. , Elizalde Hugo , Aguirre Juan José , Ahuett Horacio , Marzocca Piergiovanni , Probst Oliver 
Published: March 2011

ABSTRACTThis paper presents a numerical validation of a thin‐walled beam (TWB) finite element (FE) model of a realistic wind turbine rotor blade. Based on the theory originally developed by Librescu et al. and later extended to suit FE modelling by Phuong, Lee and others, this computationally efficient yet accurate numerical model is capable of capturing most of the features found in large blades including thin‐walled hollow cross section with variable thickness along the section's contour, inner reinforcements, arbitrary material layup and non‐linear anisotropic fibre‐reinforced composites; the present application is, for the time being, restricted to linearity. This one‐dimensional (1D) FE model allows retaining information of different regions of the blade's shell and therefore approximates the behaviour of more complex three‐dimensional (3D) shell or solid FE models more accurately than typical 1D FE beam models. A 9.2 m rotor blade, previously reported in specialized literature, was chosen as a case study to validate the static and dynamic behaviour predicted by a TWB model against an industry‐standard 3D shell model built in a commercial software tool. Given the geometric and material complexities involved, an excellent agreement was found for static deformation curves, as well as a good prediction of the lowest frequency modes in terms of resonance frequencies, mode shapes and frequency response functions; the highest (sixth) frequency mode shows only a fair agreement as expected for an FE model. It is concluded that despite its simplicity, a TWB FE model is sufficiently accurate to serve as a design tool for the recursive analyses required during design and optimization stages of wind turbines using only readily available computational tools. Copyright © 2011 John Wiley & Sons, Ltd.
Lineare Positionsregelung nichtlinearer mechanischer Systeme
Authors: Müller P. C. 
Published: March 2011

AbstractFür die Regelung nichtlinearer Systeme stehen auf der Basis sehr genauer Systembeschreibungen aufwendige nichtlineare Regelungsverfahren zur Verfügung, die eine Positionsregelung nichtlinearer mechanischer Systeme erlauben. Im allgemeinen sind diese Regelungen jedoch nicht robust gegenüber Parameterungenauigkeiten und nicht modellierten Effekten, die Robustheit muß durch zusätzliche Maßnahmen erreicht werden. Demgegenüber wird in diesem Beitrag die Methode der Nichtlinearitäten‐Schätzung und ‐Kompensation vorgestellt, die effiziente, robuste, lineare Regler zur Positionsregelung zur Verfügung stellt. Das vorgeschlagene Verfahren behandelt nichtlineare, ungenau bekannte oder nicht‐modellierte Effekte nach der Methode der Störgrößenschätzung und ‐aufschaltung. Das Verfahren zeichnet sich durch seine Einfachheit sowohl beim Entwurf als auch bei der Reglerimplementierung aus.
Gleichmäßige (Rundungs‐)Fehlerschranken für Gleitkommaalgorithmen über Datenbereichen
Authors: Krämer W. 
Published: March 2011

AbstractHäufig stellt sich die Frage, wie weit ein auf einem Computer berechnetes Ergebnis vom exakten Ergebnis (berechnet am Körper der reellen Zahlen) entfernt ist. Die hier vorgestellten Sätze erlauben es, für die Gleitkommaauswertung eines vorgegebenen Ausdrucks eine worst‐case Fehlerschranke automatisch mit einem Computer zu berechnen. Die Bestimmung dieser relativen bzw. absoluten Fehlerschranke geschieht a priori. Sie ist gültig, solange die Daten (Parameter, unabhängige Variablen) des Ausdrucks innerhalb der Bereiche (diese können je nach Problemstellung recht groß sein) variieren, die bei der Fehlerabschätzung spezifiziert wurden. Alle Rundungsfehler sowie deren Fortpflanzung und Fehler, die sich aus der Nichtdarstellbarkeit von z. B. transzendenten Konstanten ergeben, werden sicher im Sinne einer worst‐case Fehleranalyse erfaßt.
Contact Laws for Rough Surfaces
Authors: Willner K. 
Published: March 2011

AbstractContact laws for rough surfaces are used to obtain e.g. contact stiffness or contact conductivity. Usually contact laws are derived on the basis of asperity deformation models in conjunction with a stochastic roughness model. As the stochastic parameters depend strongly on the measurement procedure, the obtained contact laws have to be used carefully. Fractal surface parameters can be obtained, which are independent of sampling interval or length, but the resulting contact laws are still dependent on these values.
Parameter Estimation in a Hyperbolic Partial Differential Equation with a Focused Source as Initial Value
Authors: Kowar R. 
Published: March 2011

AbstractWe study the problem of recovering the continuously varying wave speed in the one‐dimensional wave equation with a focused source as initial data. In this paper this inverse problem is transformed into a parameter estimation, problem, which can be solved efficiently. The wave speed can be recalculated by solving an ordinary differential equation of second order where the parameter of the transformed inverse problem enters as a coefficient. We present a regularized finite difference scheme inversion for the stable recovery of the solution of the transformed parameter estimation problem, which combined with the solution of the ordinary differential equation, gives an estimation for the sound speed.
A Linear Viscoelastic Two‐Phase Model for Soft Tissues.: Application to Articular Cartilage
Authors: Ehlers W. , Markert B. 
Published: March 2011

AbstractHydrated soft tissues such as articular cartilage can be considered as porous materials consisting of an organic solid matrix saturated by a pore‐fluid. These types of biological tissues exhibit significant viscoelastic behaviour because of flow‐dependent fluid‐solid interaction and flow‐independent viscoelastic skeleton properties. To describe this complex behaviour, a linear viscoelastic two‐phase model based on the macroscopic Theory of Porous Media is presented. The required linear viscoelastic constitutive law is given in differential form deduced from rheological considerations. Numerical examples within the finite element method show the applicability of the presented model. Furthermore, they reveal the influence of the flow‐independent viscoelasticity of the solid skeleton on the general behaviour of hydrated soft tissues, for example on articular cartilage.
Selfexcitation of a MDF‐System with Coulomb friction, varying normal forces and impacts
Authors: Engleder T. 
Published: March 2011

AbstractThe investigation is focused on nonlinear oscillations of a beam structure with unilateral contact to a sliding surface. Analytical solutions for each state (stack, slip, free oscillation, impact) are used to reduce the non‐smoothness of the system to an algebraic task. The numerical results are compared with experimental data.
Simulation nichtlinearer hydraulischer Steuersysteme
Authors: Borchsenius F. , Pfeiffer F. 
Published: March 2011

AbstractEs wird eine neuartige Methode zur Simulation hydraulischer Steuersysteme vorgestellt. Bei herkömmlichen Methoden zur Simulation von hydraulischen Steuersystemen werden die Komponenten durch elastische Verbindungselemente miteinander gekoppelt. Damit erhalten die Bewegungsgleichungen eine einfache Struktur ‐ sie sind jedoch für kleine Baugrößen der Komponenten steif. Besser geeignet ist ein Modell mit starren Koppelelementen wobei die hydraulischen Komponenten durch Zwangsbedingungen gekoppelt sind. Elemente mit einseitiger Kraftübertragung, z.B. Rückschlagventile, werden durch Komplementaritätsbedingungen erfasst. Das Verfahren wird an einem einfachen Beispiel angewendet.
A Time Adaptiv Finite‐Element Procedure Applied to Creep and Relaxation Processes
Authors: Hartmann S. 
Published: March 2011

AbstractIn this paper we interpret the finite‐element method applied to constitutive models with internal variables as the solution of differential algebraic equations (DAE). With this interpretation we can utilize Diagonal Implicit Runge‐Kutta methods (DIRK) as well as a corresponding step‐size control and a special solution technique for block‐structured systems of equations. This proceeding doesn't affect already developed FE‐implementations which are based on the Backward Euler method. Furthermore, the meaning of the consistent tangent operator becomes more obvious. The paper ends with some examples in creep and relaxation tests, where step size control should always be used conditioned by the different time scales.
Self‐excited vibration of a rotor supported on journal bearings with flexibly mounted bushes
Authors: Starczewski Z. 
Published: March 2011

AbstractThe paper is concerned with dynamics of a rigid rotor supported on journal bearings having flexibly mounted bushes. In the analysis equations of motion of the journal as well as the bush center have been derived. The system has been examined with respect to self‐excited vibration resulting from interactions between the journal and bush through the oil film layer. Effect of structural parameters of the system (bearing gap, stiffness of the elastic mounting, masses of the elements) on critical rotation speed at which self‐excitation appears has been discussed. Appropriate diagrams and concluding remarks have been included.
Zur Simulation von Toroidreibradgetrieben
Authors: Bork H. , Pfeiffer F. 
Published: March 2011

AbstractReibradgetriebe sind eine alternative zu stufenlosen Umschlingungsgetrieben und bieten sich vor allem für den Einsatz in hinterradgetriebenen PKW der höheren Leistungsklasse an. Durch die physikalische Modellierung der Komponenten eines Reibradgetriebes soll dessen dynamisches Verhalten nachgebildet werden. In diesem Beitrag wird das mechanische Ersatzmodell, die Kontaktpunktbestimmung und die Kraftübertragung im Kontakt vorgestellt.
Finite element modeling of orthotropic material behaviour in pneumatic membranes
Authors: Raible T. , Reese S. , Wriggers P. 
Published: March 2011

AbstractA new material formulation to describe nonlinear hyperelastic orthotropic behaviour of composite membranes at finite strains is presented in this article. To provide numerically efficient calculations, a reduced integration scheme avoiding locking and hourglass instabilities is used. Restrictions concerning material parameters are discussed, and material parameters are adapted to experimental data. Numerical calculations are used to demonstrate the potential of the approach to inflated rubber matrix membranes applications.
Comments on objective rates of 2nd order, symmetric Eulerian tensors
Authors: Meyers A. T. M. , Chiesse P. S. , Xiao H. , Bruhns O. T. 
Published: March 2011

AbstractIt is shown that objective rates of objective and symmetric second order Eulerian tensors should be corotational when one restricts to a single Euclidean vector space. As a consequence, when we equalize the objective strain rate and the deformation rate, only the Hencky strain is a mathematically consistent strain measure; and only the logarithmic rate is an admissible strain rate.
On the Calculation of Plastic Spin in a Model of Crystal Plasticity Based on Symmetric Tensors
Authors: Schmidt M. O. , Hackl K. 
Published: March 2011

AbstractIn a model of anisotropic plasticity based on symmetric tensors the plastic spin is not determined by the principle of maximum plastic dissipation. The spin can be derived by introducing additional kinematic relations and applying a generalized inverse based on a minimum principle. A procedure specialized for the case of crystal plasticity is shown.
Shortest Curves for Vehicles on Surfaces of Celestial Bodies
Authors: Bittner L. 
Published: March 2011

AbstractThe classical problem, to find the shortest line connecting two given points of a given surface, does not take account of 1) obstacles, i. e. forbidden regions (islands, icebergs, foreign territories a. s. o.) through which the curve must not run, 2) alterations of the shape of the surface in the course of time (tides, tectonic displacements a. s. o.), 3) the fact that the length of the curve, described by a vehicle moving on the surface, has eventually to be measured with respect to a primary inertial coordinate system emitting the control signals. The surface system may change its position relating to the primary system.
Optimal design of steel barrelled shells
Authors: Blachut J. 
Published: March 2011

AbstractThe Simulated Annealing, SA, technique is applied to maximize the magnitude of external hydrostatic pressure for bowed out shells for which, the shape of the meridian is sought. A global maximum offers a 40% increase in load carrying capacity over the mass equivalent cylindrical shell of the same mass whilst the SA heuristic proves to be computationally affordable.
Effiziente semi‐analytische Gradientenberechnung in der Strukturoptimierung
Authors: Hörnlein H. R. E. M. 
Published: March 2011

AbstractBei der Lösung von Strukturoptimierungsaufgaben werden fast immer Gradientenverfahren der Mathematischen Optimierung eingesetzt. Die Bereitstellung der ersten Ableitungen beansprucht den größten Teil der Gesamtrechenzeit. Der Erfolg der Optimierung hängt aber auch von der numerischen Genauigkeit der Ableitungen ab. Hier wird auf einen entscheidenden Nachteil der favorisierten semi‐analytischen Sensitivitätsanalyse aufmerksam gemacht, gleich‐zeitig wird aber gezeigt wie dieser Nachteil zu beheben ist.
Optimization of Composite Laminates under Uniaxial Tension with Respect to the Free‐Edge Effect
Authors: Lindemann J. , Becker W. 
Published: March 2011

AbstractHigh interlaminar stresses in the vicinity of free edges of composite laminates can result in laminate failure by free‐edge delamination. In the current work it is shown in which way the interlaminar normal stress component is reduced by means of structural optimization resulting in laminate configurations with a minor risk of delamination.
Optimal layouts of structural components considering fatigue strength
Authors: Rottler A. , Eschenauer H. A. 
Published: March 2011

AbstractDesigning complete systems or system components, it is of vital importance for the manufacturers nowadays to optimally fulfil the ever increasing demands pertaining to safety, durability, reduction of energy consumption, noise reduction, improvement of comfort, accuracy, etc. This, for instance, applies to all types of traffic and transportation systems like rail vehicles, automobiles, airplanes, and ships.
A nonoverlapping DDM for the nonstationary Navier‐Stokes problem
Authors: Müller Lars , Lube Gert 
Published: March 2011

AbstractWe consider the nonstationary incompressible Navier‐Stokes problem in a bounded domain. A semidiscretization in time followed by a linearization procedure lead to Oseen type problems. For an efficient solution we take advantage of a nonoverlapping domain decomposition method (DDM) with interface conditions of Robin type. Strong convergence of the DDM‐iterations to the Oseen solution can be proven. Furthermore we apply an a‐posteriori estimate which controls the error on the subdomains in terms of the jumps of the velocity across the interface. This may serve as a stopping criterion and gives some information how to choose a free parameter appearing in the interface condition. A stabilized FEM is used to derive a discrete version of the DDM and requires a modification of the method.
Implementing Global Masters into Parallel Condensation
Authors: Pelzer Andreas , Hofferek Birgit , Voss Heinrich 
Published: March 2011

AbstractThe dynamic analysis of structures leads to very large generalized eigenvalue problems. Their number of unknowns can be reduced to a manageable size by condensation methods which can be parallelized by combining it with substructuring. In this note we implement global masters into the parallel condensation process.
Splitting techniques for the Navier‐Stokes equations
Authors: Haschke H. , Heinrichs W. 
Published: March 2011

AbstractA pseudo spectral approximation for the Navier‐Stokes equations is presented. After considering the unsteady Stokes equations we use the Uzawa algorithm to decouple the spectral system into Helmholtz equations for the velocity components and an equation with the Pseudo‐Laplacian for the pressure. In order to avoid spurious modes the pressure is approximated with polynomials of one degree lower than the velocity on staggered grids. For the time discretization a high order backward differentiation scheme for the intermediate velocity is combined with a high order extrapolant for the pressure.
Experimental and Numerical Investigation of the Oblique Shock Wave/Turbulent Boundary Layer Interaction at M=5
Authors: Fedorova N. N. , Fedorchenko I. A. , Schülein E. 
Published: March 2011

AbstractThe results of the joint experimental investigations and numerical simulations of hypersonic separated flows are presented. The computed and experimental results are compared with respect to surface pressure, skin friction and Stanton numbers distributions as well as the integral boundary layer parameters and the mean gas‐dynamic profiles.
Large Eddy Simulation of a Counterflow Configuration
Authors: Kempf A. , Forkel H. , Chen J.‐Y. , Sadiki A. , Janicka J. 
Published: March 2011

AbstractThe aim of the present work is to extend the possibilities of predicting turbulent activity and mixing in counterflow burners. Such burners are well suited for the calibration and validation of combustion models. Because of their geometry, they allow simulations to be performed in only one dimension of space. This safes much computation time, rendering for example the simulation of detailed chemistry possible. Here, a three dimensional LES is applied without considering chemical reactions. Sub‐grid fluctuations are modeled according to Smagorinsky. The model constant is determined dynamically by the well known Germano approach.
Simulation of Condensation Processes in Turbines including Impurity Effects
Authors: Winkler G. , Heiler M. , Schnerr G. H. 
Published: March 2011

AbstractCondensation processes are important for many technical applications such as in transsonic low pressure steam turbines. Impurities like dust particles or chemical deposits significantly affect the condensation process. Depending on the expansion rate the condensate formation is controlled by homogeneous or heterogeneous nucleation. Technical steam for example, used in power processes, typically consists of several impurities, which change due to lower expansion rates the condensation behaviour, so that a large fraction of the condensate mass is formed heterogeneously. Numerical parameter variations in the nozzle BA‐1 were performed to study as how to the number of particles influences the condensation onset and the total amount of formed condensate mass. In comparison to the homogeneous case, a smaller supersaturation is reached if heterogeneous condensation dominates. The condensation occurs close to the equilibrium state and reduces losses caused by the pure non‐equilibrium process.
Gas/Liquid Two‐Phase Flow under Low Gravity Conditions
Authors: Wölk G. , Dreyer M. , Rath H. J. 
Published: March 2011

AbstractA novel flow pattern map is developed based on five dimensionless parameters. The transition region from dispersed bubble to slug flow, from slug to frothy slug/annular flow and from frothy slug/annular to annular flow is presented and good agreement between theory and experimental data from the literature is obtained.
Modeling Rule-Based Item Generation
Authors: Geerlings Hanneke , Glas Cees A. W. , van der Linden Wim J. 
Published: March 2011

AbstractAn application of a hierarchical IRT model for items in families generated through the application of different combinations of design rules is discussed. Within the families, the items are assumed to differ only in surface features. The parameters of the model are estimated in a Bayesian framework, using a data-augmented Gibbs sampler. An obvious application of the model is computerized algorithmic item generation. Such algorithms have the potential to increase the cost-effectiveness of item generation as well as the flexibility of item administration. The model is applied to data from a non-verbal intelligence test created using design rules. In addition, results from a simulation study conducted to evaluate parameter recovery are presented.