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Flow Calculations (flow + calculation)
Selected AbstractsComputation of locational and hourly maximum output of a distributed generator connected to a distribution feederELECTRICAL ENGINEERING IN JAPAN, Issue 2 2009Yasuhiro Hayashi Abstract Recently, the total number of distributed generation such as photovoltaic generation systems and wind turbine generation systems connected to a distribution network has drastically increased. Distributed generation using renewable energy can reduce the distribution loss and emission of CO2. However, the distribution network with the distributed generators must be operated while maintaining the reliability of the power supply and power quality. In this paper, the authors propose a computational method to determine the maximum output of a distributed generator under operational constraints [(1) voltage limit, (2) line current capacity, and (3) no reverse flow to bank] at arbitrary connection points and hourly periods. In the proposed method, a three-phase iterative load flow calculation is applied to evaluate the above operational constraints. The three-phase iterative load flow calculation has two simple procedures: (Procedure 1) addition of load currents from the terminal node of the feeder to root one, and (Procedure 2) subtraction of voltage drop from the root node of the feeder to terminal one. In order to check the validity of the proposed method, numerical simulations are performed for a distribution system model. Furthermore, the characteristics of locational and hourly maximum output of a distributed generator connected to a distribution feeder are analyzed using several numerical examples. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(2): 38,47, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20610 [source] An updated interactive boundary layer method for high Reynolds number flowsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2006F. Álvarez Abstract The quasi-simultaneous interactive boundary layer (IBL) method is improved with the iterative correction of an inviscid operator. The updated interactive boundary layer method (UIBL) presented in this work, uses the Hess,Smith panel method (HSPM) as an inviscid operator to update the outer flow calculation and the inviscid velocity in the interaction law (IL). The discretization of the Hilbert integral (HI) from the original method is modified to reduce the error introduced by the calculation of the HI in a restricted domain. The method is tested on a flat plate with a small indentation for two-dimensional, steady, incompressible and laminar flow. The UIBL method is capable to predict the flow separation and reattachment with good accuracy. The accuracy of the results is competitive with the numerical solution of the Navier,Stokes equations (NSE). Copyright © 2005 John Wiley & Sons, Ltd. [source] Integration of on-the-fly kinetic reduction with multidimensional CFDAICHE JOURNAL, Issue 5 2010Kaiyuan He Abstract A reduction approach for coupling complex kinetics with engine computational fluid dynamics (CFD) code has been developed. An on-the-fly reduction scheme was used to reduce the reaction mechanism dynamically during the reactive flow calculation in order to couple comprehensive chemistry with flow simulations in each computational cell. KIVA-3V code is used as the CFD framework and CHEMKIN is employed to formulate chemistry, hydrodynamics and transport. Mechanism reduction was achieved by applying element flux analysis on-the-fly in the context of the multidimensional CFD calculation. The results show that incorporating the on-the-fly reduction approach in CFD code enables the simulation of ignition and combustion process accurately compared with detailed simulations. Both species and time-dependant information can be provided by the current model with significantly reduced CPU time. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Experimental study of fire compartment with door opening and roof openingFIRE AND MATERIALS, Issue 5 2005E. H. Yii Abstract A series of reduced-scale experimental fires was conducted to study the characteristics of fire induced vent flows in a reduced-scale post-flashover fire compartment with a door opening and a roof opening. The fire source was a heptane pool fire near the wall furthest from the door vent. In the study, the roof vent opening area was systematically varied between experiments and the characteristics of vent flows through the door opening are presented as a function of the roof vent opening area. The experimental results show that the mass flow rate of air into the compartment increases linearly as the size of roof vent opening increases. Analytical vent flow calculations based on the hydrostatic pressure difference between two quiescent environments are presented for a post-flashover fire compartment with both horizontal and vertical openings. The calculated results are in good agreement with the experimental measurements. Copyright © 2005 John Wiley & Sons, Ltd. [source] Moho undulations beneath Tibet from GRACE-integrated gravity dataGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2007Young Hong Shin SUMMARY Knowledge of the variation of crustal thickness is essential in many applications, such as forward dynamic modelling, numerical heat flow calculations, seismologic applications and geohistory reconstructions. We present a 3-D model of the Moho undulations over the entire Tibetan plateau derived from gravity inversion. The gravity field has been obtained by using the Gravity Recovery and Climate Experiment (GRACE) potential field development which has been integrated with terrestrial data, and is presently the best available in the studied area. For the effective use of the global geopotential model that has no height information of observation stations, upward continuation is applied. The Moho model is characterized by a sequence of troughs and ridges with a semi-regular pattern, which could reflect the continent,continent collision between the Indian and Eurasian plates. The three deep Moho belts (troughs) and shallow Moho belts (ridges) between them are clearly found to have an E,W directional trend parallel to the border of the plateau and tectonic lines, while variation of the directionality is observed in central to southeast Tibet. To describe the distinctive shape of the Moho troughs beneath Tibet, we introduce the term, ,Moho ranges'. The most interesting aspects of the Moho ranges are (1) that they run in parallel with the border and tectonic sutures of the plateau, (2) that the distances between ranges are found at regular distances of about 330 km except in northeast Tibet and (3) that the splitting of the ranges into two branches is found as the distance between them is increasing. From our study, we conclude that the distinctive undulations of the Tibetan Moho have been formed by buckling in a compressional environment, superimposed on the regional increase in crustal thickness. According to our analysis, the GRACE satellite-only data turns out to have good enough resolution for being used to determine the very deep Moho beneath Tibet. Our Moho model is the first one that covers the entire plateau. [source] Laminar and turbulent flow calculations through a model human upper airway using unstructured meshesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 12 2007P. Nithiarasu Abstract In this paper, numerical investigation of airflow through a human upper airway is presented using an unstructured-based characteristic-based split (CBS) scheme. The CBS scheme used in the present study employs a fully explicit matrix-free solution procedure along with artificial compressibility. A one equation Spalrat,Allmaras (SA) turbulence model is employed to study low and moderate Reynolds number flows. A detailed discussion of the qualitative and quantitative results is presented. The results show a strong influence of the Reynolds number on the flow pattern and quantities of interest, pressure drop and wall shear stress. It is also apparent that SA model can be employed on unstructured meshes to predict the steady flow with good accuracy. Thus, the novelties of the present paper are: use of the unstructured mesh-based solution algorithm and the successful application of the SA model to a typical human upper airway. Copyright © 2006 John Wiley & Sons, Ltd. [source] Comparison of three second-order accurate reconstruction schemes for 2D Euler and Navier,Stokes compressible flows on unstructured gridsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 5 2001N. P. C. Marques Abstract This paper reports an intercomparison of three second-order accurate reconstruction schemes to predict 2D steady-state compressible Euler and Navier,Stokes flows on unstructured meshes. The schemes comprise one monotone slope limiter (Barth and Jespersen, A1AA Paper 89-0366, 1989) and two approximately monotone methods: the slope limiter due to Venkatakrishnan and a data-dependent weighting least-squares procedure (Gooch, Journal of Computational Physics, 1997; 133:6,17). In addition to the 1D scalar wave problem, comparisons were performed under two inviscid test cases: a supersonic 10° ramp and a supersonic bump; and two viscous laminar compressible flow cases: the Blasius boundary layer and a double-throated nozzle. The data-dependent oscillatory behaviour is found to be dependent on a user-supplied constant. The three schemes are compared in terms of accuracy and computational efficiency. The results show that the data-dependent procedure always returns a numerical steady-state solution, more accurate than the ones returned by the slope limiters. Its use for Navier,Stokes flow calculations is recommended. Copyright © 2001 John Wiley & Sons, Ltd. [source] On the geometric conservation law in transient flow calculations on deforming domainsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2006Ch. Förster Abstract This note revisits the derivation of the ALE form of the incompressible Navier,Stokes equations in order to retain insight into the nature of geometric conservation. It is shown that the flow equations can be written such that time derivatives of integrals over moving domains are avoided prior to discretization. The geometric conservation law is introduced into the equations and the resulting formulation is discretized in time and space without loss of stability and accuracy compared to the fixed grid version. There is no need for temporal averaging remaining. The formulation applies equally to different time integration schemes within a finite element context. Copyright © 2005 John Wiley & Sons, Ltd. [source] Parallel adaptive refinement for unsteady flow calculations on 3D unstructured grids,INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 1 2004Jacob Waltz Abstract A parallel adaptive refinement algorithm for three-dimensional unstructured grids is presented. The algorithm is based on an hierarchical h -refinement/derefinement scheme for tetrahedral elements. The algorithm has been fully parallelized for shared-memory platforms via a domain decomposition of the mesh at the algebraic level. The effectiveness of the procedure is demonstrated with applications which involve unsteady compressible fluid flow. A parallel speedup study of the algorithm also is included. Published in 2004 by John Wiley & Sons, Ltd. [source] Three-dimensional incompressible flow calculations using the characteristic based split (CBS) schemeINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2004P. Nithiarasu Abstract In this paper, the characteristic based split scheme is employed for the solution of three-dimensional incompressible viscous flow problems on unstructured meshes. Many algorithm related issues are discussed. Fully explicit and semiimplicit forms of the scheme are explained and employed in the calculation of both isothermal and nonisothermal incompressible flows simulation. The extension of the scheme to porous medium flows is also demonstrated with relevant examples. Copyright © 2004 John Wiley & Sons, Ltd. [source] Omnidirectional Vision and Inertial Clues for Robot NavigationJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 1 2004Irem Stratmann The structural features inherent in the visual motion field of a mobile robot contain useful clues about its navigation. The combination of these visual clues and additional inertial sensor information may allow reliable detection of the navigation direction for a mobile robot and also the independent motion that might be present in the 3D scene. The motion field, which is the 2D projection of the 3D scene variations induced by the camera-robot system, is estimated through optical flow calculations. The singular points of the global optical flow field of omnidirectional image sequences indicate the translational direction of the robot as well as the deviation from its planned path. It is also possible to detect motion patterns of near obstacles or independently moving objects of the scene. In this paper, we introduce the analysis of the intrinsic features of the omnidirectional motion fields, in combination with gyroscopical information, and give some examples of this preliminary analysis. © 2004 Wiley Periodicals, Inc. [source] Dimensionierung von Vakuumwasserhaltungen im tertiären FeinsandBAUTECHNIK, Issue 7 2004Peter-Michael Mayer Dr.-Ing. Der Entwurf umfangreicher Vakuumwasserhaltungen ist aufgrund fehlender allgemeingültiger analytischer Berechnungsverfahren bisher auf Abschätzungen und Erfahrungen angewiesen. Vorliegende Untersuchungen zeigen exemplarisch für eine 80 m lange und 37 m breite Spundwandbaugrube im tertiären Feinsand, wie mittels räumlicher Finite-Element-Modelle die erforderliche Anzahl und Tiefe von Vakuumtiefbrunnen zur Grundwasserabsenkung berechnet werden kann. Die Auswirkungen von Schichtanisotropien bzw. lokaler Bereiche mit hoher Durchlässigkeit auf das erreichte Absenkziel und die geförderten Pumpmengen werden aufgezeigt. Darüberhinaus wird auch der Wasserdruck auf die Spundwand analysiert. Die Bedeutung zeitabhängiger Strömungsberechnungen wird durch die Verbindung von Aushub und Wasserhaltung deutlich und kann durch instationäre Betrachtungen erfaßt werden. Der Vergleich von in-situ-Messungen und Berechnungsergebnissen zeigt die Leistungsfähigkeit, aber auch die Grenzen numerischer Strömungsmodelle bei der Abschätzung des Ausführungsrisikos und möglicher wirtschaftlicher Optimierungen. Dimensioning of vacuum dewaterings in tertiary fine sand. Because of outstanding valid analytical solutions, the study of extensive dewatering depends actually only on estimations and experiences. This paper show, for a 80 m long and 37 m large excavation in fine sand, how to calculate the requested number and depth of vacuum deep well for the lowering of the groundwater level by Finite-Element-Models. The effects of anisotropic layer and layer with local ranges with high porosity for the achieved lowering and pumping capacity have been showed. Additionally the water pressure on sheet pile wall was also analyzed. The significance of transient flow calculations becomes clearly by the connection of excavation and dewatering. The comparison of in-situ measurements and results of calculations shows the performance but also the limits of the numerical flow models on the estimation of the execution risks and possible improvement on dewatering process. [source] | ||||||||||