Boundary Conditions (boundary + condition)

Distribution by Scientific Domains
Distribution within Engineering

Kinds of Boundary Conditions

  • absorbing boundary condition
  • appropriate boundary condition
  • artificial boundary condition
  • different boundary condition
  • dirichlet boundary condition
  • downstream boundary condition
  • essential boundary condition
  • flux boundary condition
  • homogeneous dirichlet boundary condition
  • lateral boundary condition
  • lower boundary condition
  • mixed boundary condition
  • neumann boundary condition
  • non-reflecting boundary condition
  • outflow boundary condition
  • periodic boundary condition
  • radiation boundary condition
  • realistic boundary condition
  • slip boundary condition
  • thermal boundary condition
  • various boundary condition
  • wall boundary condition


  • Selected Abstracts


    CONCENTRATION BOUNDARY CONDITIONS IN THE THEORETICAL ANALYSIS OF CONVECTIVE DRYING PROCESS

    JOURNAL OF FOOD PROCESS ENGINEERING, Issue 5 2007
    AHMET KAYA
    ABSTRACT In the theoretical analysis of convective drying process, two boundary conditions are common for concentration: constant concentration and convection. In this study, these two boundary conditions were comparatively examined by comparing theoretical results obtained with regard to experimental ones. Pumpkin (Cucurbita pepo) was considered as the product to be dried while air was the drying medium. The drying characteristics of pumpkin were determined for various values of drying air parameters, including temperature, velocity and relative humidity. Sorption isotherms of the dried pumpkin were also determined for different temperatures and water activities. The values of the effective moisture diffusivity, Deff, and the convective mass transfer coefficient, hm, were predicted, and these values were found to agree fairly well with those available in the existing literature. PRACTICAL APPLICATIONS Convective drying as well as other drying techniques are used in order to preserve and store agricultural products for longer periods by removing some of their moisture content. Drying is a complicated process involving simultaneous heat and mass transfer under transient conditions. Understanding the heat and mass transfer in the product will help to improve drying process parameters and hence the quality. [source]


    A NUMERICAL APPROACH WITH VARIABLE TEMPERATURE BOUNDARY CONDITIONS TO DETERMINE THE EFFECTIVE HEAT TRANSFER COEFFICIENT VALUES DURING BAKING OF COOKIES

    JOURNAL OF FOOD PROCESS ENGINEERING, Issue 5 2006
    EREN DEMIRKOL
    ABSTRACT The increasing trade of ready-to-eat foods such as cookies highlights an interest in quality defects during baking. Heat (h and thermal diffusivity) and mass (mass transfer and diffusion coefficients) transfer parameters are significant parameters affecting the quality changes. Therefore, it is important to determine these parameters for modeling and process optimization studies. Among these, the h is important, revealing the relationship between the heating medium and product surface. As baking involves a simultaneous heat and mass transfer involving moisture diffusion and heat conduction inside and convective heat and mass transfer outside, a lumped system method may not be an accurate choice to determine the h value. Changes in the product volume and contact heating from bottom of the product also bring extra challenges to the determination of h. Therefore, the objective of this study was to use realistic approaches including simultaneous heat and mass transfer to determine the changes in h. The heffvalues for the bottom and top surface of the cookies were then determined, applying a numerical procedure where the surface temperature changes were the boundary conditions with evaporation on the surface. The hband ht values increased with baking temperature and varied with baking time. The results of this study showed that evaporative mass flux for the top surface, heat flux for the bottom surface and the product's volume changes were significant in the variation of h values. [source]


    Formulation of Boundary Conditions for the Unmagnetized Multi-Ion-Component Plasma Sheath

    CONTRIBUTIONS TO PLASMA PHYSICS, Issue 7-9 2006
    D. Tskhakaya
    Abstract Boundary conditions are derived for the unmagnetized electrostatic multi-ion-component plasma sheath. Analytic results are supported by high-resolution numerical kinetic (particle-in-cell) simulations. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Sheath Physics and Boundary Conditions for Edge Plasmas

    CONTRIBUTIONS TO PLASMA PHYSICS, Issue 1-3 2004
    R. H. Cohen
    Abstract The boundary conditions of mass, momentum, energy, and charge appropriate for fluid formulations of edge plasmas are surveyed. We re-visit the classic problem of 1-dimensional flow, and note that the "Bohm sheath criterion" is requirement of connectivity of the interior plasma with the external world, not the result of termination of the plasma by a wall. We show that the nature of the interior plasma solution is intrinsically different for ion sources that inject above and below the electron sound speed. We survey the appropriate conditions to apply, and resultant fluxes, for a magnetic field obliquely incident on a wall, including the presence of drifts and radial transport. We discuss the consequences of toroidal asymmetries in wall properties, as well as experimental tests of such effects. Finally, we discuss boundary-condition modifications in the case of rapidly varying plasma conditions. ( 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Area-to-Point Prediction Under Boundary Conditions

    GEOGRAPHICAL ANALYSIS, Issue 4 2008
    E. -H.
    This article proposes a geostatistical solution for area-to-point spatial prediction (downscaling) taking into account boundary effects. Such effects are often poorly considered in downscaling, even though they often have significant impact on the results. The geostatistical approach proposed in this article considers two types of boundary conditions (BC), that is, a Dirichlet-type condition and a Neumann-type condition, while satisfying several critical issues in downscaling: the coherence of predictions, the explicit consideration of support differences, and the assessment of uncertainty regarding the point predictions. An updating algorithm is used to reduce the computational cost of area-to-point prediction under a given BC. In a case study, area-to-point prediction under a Dirichlet-type BC and a Neumann-type BC is illustrated using simulated data, and the resulting predictions and error variances are compared with those obtained without considering such conditions. [source]


    Organizational Politics, Perceived Control, and Work Outcomes: Boundary Conditions on the Effects of Politics,

    JOURNAL OF APPLIED SOCIAL PSYCHOLOGY, Issue 3 2001
    Dennis P. Bozeman
    This investigation examined the moderating influences of perceived control (i. e., personal control and job self-efficacy) on relationships between perceptions of organizational politics and organizational commitment, job satisfaction, intention to turnover, and job stress. Although results failed to support predictions concerning the interaction of perceptions of organizational politics and personal control, some support was found for predictions concerning the interactive influence of perceptions of organizational politics and job self-efficacy on outcomes. Data from 189 hotel managers supported the hypothesized interactive effects of perceptions of organizational politics and job self-efficacy for the outcomes of organizational commitment and job satisfaction. These results suggest that job self-efficacy exacerbates the relationship between perceived politics and certain dysfunctional attitudes. [source]


    ChemInform Abstract: MoV2O2+4 Directs the Formation and Subsequent Linking of Potential Building Blocks under Different Boundary Conditions: A Related Set of Novel Cyclic Polyoxomolybdates.

    CHEMINFORM, Issue 47 2001
    Achim Mueller
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]


    Exact Solution of the Six-Vertex Model with Domain Wall Boundary Conditions: Antiferroelectric Phase

    COMMUNICATIONS ON PURE & APPLIED MATHEMATICS, Issue 6 2010
    Pavel Bleher
    We obtain the large- n asymptotics of the partition function Zn of the six-vertex model with domain wall boundary conditions in the antiferroelectric phase region, with the weights a = sinh(, , t), b = sinh(, + t), c = sinh(2,), |t| < ,. We prove the conjecture of Zinn-Justin, that as n , ,, Zn = C,4(n,)F [1 + O(n,1)], where , and F are given by explicit expressions in , and t, and ,4(z) is the Jacobi theta function. The proof is based on the Riemann-Hilbert approach to the large- n asymptotic expansion of the underlying discrete orthogonal polynomials and on the Deift-Zhou nonlinear steepest-descent method. 2009 Wiley Periodicals, Inc. [source]


    Formulation of Boundary Conditions for the Unmagnetized Multi-Ion-Component Plasma Sheath

    CONTRIBUTIONS TO PLASMA PHYSICS, Issue 7-9 2006
    D. Tskhakaya
    Abstract Boundary conditions are derived for the unmagnetized electrostatic multi-ion-component plasma sheath. Analytic results are supported by high-resolution numerical kinetic (particle-in-cell) simulations. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    On the boundary conditions in slope stability analysis

    INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 11 2003
    Ashok K. Chugh
    Abstract Boundary conditions can affect computed factor of safety results in two- and three-dimensional stability analyses of slopes. Commonly used boundary conditions in two- and three-dimensional slope stability analyses via limit-equilibrium and continuum-mechanics based solution procedures are described. A sample problem is included to illustrate the importance of boundary conditions in slope stability analyses. The sample problem is solved using two- and three-dimensional numerical models commonly used in engineering practice. Copyright 2003 John Wiley & Sons, Ltd. [source]


    Matched interface and boundary (MIB) method for the vibration analysis of plates

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 9 2009
    S. N. Yu
    Abstract This paper proposes a novel approach, the matched interface and boundary (MIB) method, for the vibration analysis of rectangular plates with simply supported, clamped and free edges, and their arbitrary combinations. In previous work, the MIB method was developed for three-dimensional elliptic equations with arbitrarily complex material interfaces and geometric shapes. The present work generalizes the MIB method for eigenvalue problems in structural analysis with complex boundary conditions. The MIB method utilizes both uniform and non-uniform Cartesian grids. Fictitious values are utilized to facilitate the central finite difference schemes throughout the entire computational domain. Boundary conditions are enforced with fictitious values,a common practice used in the previous discrete singular convolution algorithm. An essential idea of the MIB method is to repeatedly use the boundary conditions to achieve arbitrarily high-order accuracy. A new feature in the proposed approach is the implementation of the cross derivatives in the free boundary conditions. The proposed method has a banded matrix. Nine different plates, particularly those with free edges and free corners, are employed to validate the proposed method. The performance of the proposed method is compared with that of other established methods. Convergence and comparison studies indicate that the proposed MIB method works very well for the vibration analysis of plates. In particular, modal bending moments and shear forces predicted by the proposed method vanish at boundaries for free edges. Copyright 2008 John Wiley & Sons, Ltd. [source]


    On accurate boundary conditions for a shape sensitivity equation method

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 2 2006
    R. Duvigneau
    Abstract This paper studies the application of the continuous sensitivity equation method (CSEM) for the Navier,Stokes equations in the particular case of shape parameters. Boundary conditions for shape parameters involve flow derivatives at the boundary. Thus, accurate flow gradients are critical to the success of the CSEM. A new approach is presented to extract accurate flow derivatives at the boundary. High order Taylor series expansions are used on layered patches in conjunction with a constrained least-squares procedure to evaluate accurate first and second derivatives of the flow variables at the boundary, required for Dirichlet and Neumann sensitivity boundary conditions. The flow and sensitivity fields are solved using an adaptive finite-element method. The proposed methodology is first verified on a problem with a closed form solution obtained by the Method of Manufactured Solutions. The ability of the proposed method to provide accurate sensitivity fields for realistic problems is then demonstrated. The flow and sensitivity fields for a NACA 0012 airfoil are used for fast evaluation of the nearby flow over an airfoil of different thickness (NACA 0015). Copyright 2005 John Wiley & Sons, Ltd. [source]


    Solution of the hyperbolic mild-slope equation using the finite volume method

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2003
    J. Bokaris
    Abstract A finite volume solver for the 2D depth-integrated harmonic hyperbolic formulation of the mild-slope equation for wave propagation is presented and discussed. The solver is implemented on unstructured triangular meshes and the solution methodology is based upon a Godunov-type second-order finite volume scheme, whereby the numerical fluxes are computed using Roe's flux function. The eigensystem of the mild-slope equations is derived and used for the construction of Roe's matrix. A formulation that updates the unknown variables in time implicitly is presented, which produces a more accurate and reliable scheme than hitherto available. Boundary conditions for different types of boundaries are also derived. The agreement of the computed results with analytical results for a range of wave propagation/transformation problems is very good, and the model is found to be virtually paraxiality-free. Copyright 2003 John Wiley & Sons, Ltd. [source]


    Projected Schur complement method for solving non-symmetric systems arising from a smooth fictitious domain approach

    NUMERICAL LINEAR ALGEBRA WITH APPLICATIONS, Issue 9 2007
    J. Haslinger
    Abstract This paper deals with a fast method for solving large-scale algebraic saddle-point systems arising from fictitious domain formulations of elliptic boundary value problems. A new variant of the fictitious domain approach is analyzed. Boundary conditions are enforced by control variables introduced on an auxiliary boundary located outside the original domain. This approach has a significantly higher convergence rate; however, the algebraic systems resulting from finite element discretizations are typically non-symmetric. The presented method is based on the Schur complement reduction. If the stiffness matrix is singular, the reduced system can be formulated again as another saddle-point problem. Its modification by orthogonal projectors leads to an equation that can be efficiently solved using a projected Krylov subspace method for non-symmetric operators. For this purpose, the projected variant of the BiCGSTAB algorithm is derived from the non-projected one. The behavior of the method is illustrated by examples, in which the BiCGSTAB iterations are accelerated by a multigrid strategy. Copyright 2007 John Wiley & Sons, Ltd. [source]


    An improved study of real-time fluid simulation on GPU

    COMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 3-4 2004
    Enhua Wu
    Abstract Taking advantage of the parallelism and programmability of GPU, we solve the fluid dynamics problem completely on GPU. Different from previous methods, the whole computation is accelerated in our method by packing the scalar and vector variables into four channels of texels. In order to be adaptive to the arbitrary boundary conditions, we group the grid nodes into different types according to their positions relative to obstacles and search the node that determines the value of the current node. Then we compute the texture coordinates offsets according to the type of the boundary condition of each node to determine the corresponding variables and achieve the interaction of flows with obstacles set freely by users. The test results prove the efficiency of our method and exhibit the potential of GPU for general-purpose computations. Copyright 2004 John Wiley & Sons, Ltd. [source]


    Column restraint in post-tensioned self-centering moment frames

    EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 7 2010
    Chung-Che Chou
    Abstract Gaps between beam-to-column interfaces in a post-tensioned (PT) self-centering frame with more than one column are constrained by columns, which causes beam compression force different from the applied PT force. This study proposes an analytical method for evaluating column bending stiffness and beam compression force by modeling column deformation according to gap-openings at all stories. The predicted compression forces in the beams are validated by a cyclic analysis of a three-story PT frame and by cyclic tests of a full-scale, two-bay by first-story PT frame, which represents a substructure of the three-story PT frame. The proposed method shows that compared with the strand tensile force, the beam compression force is increased at the 1st story but is decreased at the 2nd and 3rd stories due to column deformation compatibility. The PT frame tests show that the proposed method reasonably predicts beam compression force and strand force and that the beam compression force is 2 and 60% larger than the strand force with respect to a minor restraint and a pin-supported boundary condition, respectively, at the tops of the columns. Therefore, the earlier method using a pin-supported boundary condition at upper story columns represents an upper bound of the effect and is shown to be overly conservative for cases where a structure responds primarily in its first mode. The proposed method allows for more accurate prediction of the column restraint effects for structures that respond in a pre-determined mode shape which is more typical of low and mid-rise structures. Copyright 2009 John Wiley & Sons, Ltd. [source]


    Response of unbounded soil in scaled boundary finite-element method

    EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 1 2002
    John P. Wolf
    Abstract The scaled boundary finite-element method is a powerful semi-analytical computational procedure to calculate the dynamic stiffness of the unbounded soil at the structure,soil interface. This permits the analysis of dynamic soil,structure interaction using the substructure method. The response in the neighbouring soil can also be determined analytically. The method is extended to calculate numerically the response throughout the unbounded soil including the far field. The three-dimensional vector-wave equation of elasto-dynamics is addressed. The radiation condition at infinity is satisfied exactly. By solving an eigenvalue problem, the high-frequency limit of the dynamic stiffness is constructed to be positive definite. However, a direct determination using impedances is also possible. Solving two first-order ordinary differential equations numerically permits the radiation condition and the boundary condition of the structure,soil interface to be satisfied sequentially, leading to the displacements in the unbounded soil. A generalization to viscoelastic material using the correspondence principle is straightforward. Alternatively, the displacements can also be calculated analytically in the far field. Good agreement of displacements along the free surface and below a prism foundation embedded in a half-space with the results of the boundary-element method is observed. Copyright 2001 John Wiley & Sons, Ltd. [source]


    Development of equine upper airway fluid mechanics model for Thoroughbred racehorses

    EQUINE VETERINARY JOURNAL, Issue 3 2008
    V. RAKESH
    Summary Reason for performing study: Computational fluid dynamics (CFD) models provide the means to evaluate airflow in the upper airways without requiring in vivo experiments. Hypothesis: The physiological conditions of a Thoroughbred racehorse's upper airway during exercise could be simulated. Methods: Computed tomography scanned images of a 3-year-old intact male Thoroughbred racehorse cadaver were used to simulate in vivo geometry. Airway pressure traces from a live Thoroughbred horse, during exercise was used to set the boundary condition. Fluid-flow equations were solved for turbulent flow in the airway during inspiratory and expiratory phases. The wall pressure turbulent kinetic energy and velocity distributions were studied at different cross-sections along the airway. This provided insight into the general flow pattern and helped identify regions susceptible to dynamic collapse. Results: The airflow velocity and static tracheal pressure were comparable to data of horses exercising on a high-speed treadmill reported in recent literature. The cross-sectional area of the fully dilated rima glottidis was 7% greater than the trachea. During inspiration, the area of highest turbulence (i.e. kinetic energy) was in the larynx, the rostral aspect of the nasopharynx was subjected to the most negative wall pressure and the highest airflow velocity is more caudal on the ventral aspect of the nasopharynx (i.e. the soft palate). During exhalation, the area of highest turbulence was in the rostral and mid-nasopharynx, the maximum positive pressure was observed at the caudal aspect of the soft palate and the highest airflow velocity at the front of the nasopharynx. Conclusions and clinical relevance: In the equine upper airway collapsible area, the floor of the rostral aspect of the nasopharynx is subjected to the most significant collapsing pressure with high average turbulent kinetic during inhalation, which may lead to palatal instability and explain the high prevalence of dorsal displacement of the soft palate (DDSP) in racehorses. Maximal abduction of the arytenoid cartilage may not be needed for optimal performance, since the trachea cross-sectional area is 7% smaller than the rima glottidis. [source]


    Non-equilibrium water flow characterized by means of upward infiltration experiments

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2001

    Summary Upward infiltration experiments under tension were used to demonstrate the presence of non-equilibrium flow in soils, the phenomenon that has important implications for the accelerated movement of fertilizers, pesticides, non-aqueous liquids, and other pollutants. Data obtained from these experiments were analysed using the single-porosity Richards equation, as well as a variably saturated, dual-porosity model and a dual-permeability model for characterizing non-equilibrium water flow. The laboratory experiments were carried out on 0.10-m-long soil cores having an internal diameter of 0.10 m. Constant pressure heads of ,0.10 and ,0.01 m were used as the lower boundary condition. Each infiltration was followed by a single-rate evaporation experiment to re-establish initial conditions, and to obtain the drying soil hydraulic properties. Pressure heads inside the cores were measured using five tensiometers, while evaporative water loss from the top was determined by weighing the soil samples. The data were analysed to estimate parameters using a technique that combined a numerical solution of the governing flow equation (as implemented in a modified version of the Hydrus-1D software) with a Marquardt,Levenberg optimization. The objective function for the parameter estimation was defined in terms of pressure head readings, the cumulative infiltration rate, and the final total water volume in the core during upward infiltration. The final total water volume was used, as well as the pressure head readings during the evaporation part. Analysis of flow responses obtained during the infiltration experiment demonstrated significant non-equilibrium flow. This behaviour could be well characterized using a model of physical non-equilibrium that divides the medium into inter- and intra-aggregate pores with first-order transfer of water between the two systems. The analysis also demonstrated the importance of hysteresis. [source]


    Full-scale study on combustion characteristics of an upholstered chair under different boundary conditions,Part 1: Ignition at the seat center

    FIRE AND MATERIALS, Issue 6 2009
    Q. Y. Xie
    Abstract The objective of this work is to investigate the effects of boundary conditions on the combustion characteristic of combustible items in a room. A series of full-scale experiments were carried out in the ISO 9705 fire test room with an upholstered chair at four typical locations, i.e. at the middle of side wall, at the center of the room with the seat toward the door, at the center of the room with the seat toward inside of the room, at the room corner, respectively. Ignition was achieved through a BS No.7 wooden crib at the geometric center of the seat surface for each test. Besides the heat release rate (HRR), four thermocouple trees were placed around the chair to monitor detailed temperature distributions during the combustion process of an upholstered chair. The results indicated that the boundary conditions had some effects on the combustion behavior of a chair in a room. It was shown that there were clearly two main peak HRRs for the cases of a chair being clung to the side wall or at the corner. However, there was only one main peak HRR when the chair was placed at the center of the room, either outwards or inwards. In addition, the results of the two cases of chairs being at the center indicate that the maximum HRR (about 829,kW) for the chair seat toward the door was relatively larger than the maximum HRR (about 641,kW) for the chair seat toward inside of the room. It was suggested that the special complex structure of a chair was also a considerable factor for the effect of boundary conditions on the combustion behavior of a chair in an enclosure. Furthermore, the measured temperature distributions around the chair also illustrated the effects of boundary condition on the combustion behavior of a chair in a room. It was suggested that although HRR was one of the most important fire parameters, HRR mainly represented the comprehensive fire behavior of a combustible item. In order to develop more suitable room fire dynamic models, more detailed information such as the surrounding temperature distributions measured by the thermocouple trees are useful. Copyright 2009 John Wiley & Sons, Ltd. [source]


    A unified continuum representation of post-seismic relaxation mechanisms: semi-analytic models of afterslip, poroelastic rebound and viscoelastic flow

    GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2010
    Sylvain Barbot
    SUMMARY We present a unified continuum mechanics representation of the mechanisms believed to be commonly involved in post-seismic transients such as viscoelasticity, fault creep and poroelasticity. The time-dependent relaxation that follows an earthquake, or any other static stress perturbation, is considered in a framework of a generalized viscoelastoplastic rheology whereby some inelastic strain relaxes a physical quantity in the material. The relaxed quantity is the deviatoric stress in case of viscoelastic relaxation, the shear stress in case of creep on a fault plane and the trace of the stress tensor in case of poroelastic rebound. In this framework, the instantaneous velocity field satisfies the linear inhomogeneous Navier's equation with sources parametrized as equivalent body forces and surface tractions. We evaluate the velocity field using the Fourier-domain Green's function for an elastic half-space with surface buoyancy boundary condition. The accuracy of the proposed method is demonstrated by comparisons with finite-element simulations of viscoelastic relaxation following strike-slip and dip-slip ruptures for linear and power-law rheologies. We also present comparisons with analytic solutions for afterslip driven by coseismic stress changes. Finally, we demonstrate that the proposed method can be used to model time-dependent poroelastic rebound by adopting a viscoelastic rheology with bulk viscosity and work hardening. The proposed method allows one to model post-seismic transients that involve multiple mechanisms (afterslip, poroelastic rebound, ductile flow) with an account for the effects of gravity, non-linear rheologies and arbitrary spatial variations in inelastic properties of rocks (e.g. the effective viscosity, rate-and-state frictional parameters and poroelastic properties). [source]


    Human modification of the landscape and surface climate in the next fifty years

    GLOBAL CHANGE BIOLOGY, Issue 5 2002
    R. S. Defries
    Abstract Human modification of the landscape potentially affects exchanges of energy and water between the terrestrial biosphere and the atmosphere. This study develops a possible scenario for land cover in the year 2050 based on results from the IMAGE 2 (Integrated Model to Assess the Greenhouse Effect) model, which projects land-cover changes in response to demographic and economic activity. We use the land-cover scenario as a surface boundary condition in a biophysically-based land-surface model coupled to a general circulation model for a 15-years simulation with prescribed sea surface temperature and compare with a control run using current land cover. To assess the sensitivity of climate to anthropogenic land-cover change relative to the sensitivity to decadal-scale interannual variations in vegetation density, we also carry out two additional simulations using observed normalized difference vegetation index (NDVI) from relatively low (1982,83) and high (1989,90) years to describe the seasonal phenology of the vegetation. In the past several centuries, large-scale land-cover change occurred primarily in temperate latitudes through conversion of forests and grassland to highly productive cropland and pasture. Several studies in the literature indicate that past changes in surface climate resulting from this conversion had a cooling effect owing to changes in vegetation morphology (increased albedo). In contrast, this study indicates that future land-cover change, likely to occur predominantly in the tropics and subtropics, has a warming effect governed by physiological rather than morphological mechanisms. The physiological mechanism is to reduce carbon assimilation and consequently latent relative to sensible heat flux resulting in surface temperature increases up to 2 C and drier hydrologic conditions in locations where land cover was altered in the experiment. In addition, in contrast to an observed decrease in diurnal temperature range (DTR) over land expected with greenhouse warming, results here suggest that future land-cover conversion in tropics could increase the DTR resulting from decreased evaporative cooling during the daytime. For grid cells with altered land cover, the sensitivity of surface temperature to future anthropogenic land-cover change is generally within the range induced by decadal-scale interannual variability in vegetation density in temperate latitudes but up to 1.5 C warmer in the tropics. [source]


    A new global biome reconstruction and data-model comparison for the Middle Pliocene

    GLOBAL ECOLOGY, Issue 3 2008
    U. Salzmann
    ABSTRACT Aim, To produce a robust, comprehensive global biome reconstruction for the Middle Pliocene (c. 3.6,2.6 Ma), which is based on an internally consistent palaeobotanical data set and a state-of-the-art coupled climate,vegetation model. The reconstruction gives a more rigorous picture of climate and environmental change during the Middle Pliocene and provides a new boundary condition for future general circulation model (GCM) studies. Location, Global. Methods, Compilation of Middle Pliocene vegetation data from 202 marine and terrestrial sites into the comprehensive GIS data base TEVIS (Tertiary Environmental Information System). Translation into an internally consistent classification scheme using 28 biomes. Comparison and synthesis of vegetation reconstruction from palaeodata with the outputs of the mechanistically based BIOME4 model forced by climatology derived from the HadAM3 GCM. Results, The model results compare favourably with available palaeodata and highlight the importance of employing vegetation,climate feedbacks and the anomaly method in biome models. Both the vegetation reconstruction from palaeobotanical data and the BIOME4 prediction indicate a general warmer and moister climate for the Middle Pliocene. Evergreen taiga as well as temperate forest and grassland shifted northward, resulting in much reduced tundra vegetation. Warm-temperate forests (with subtropical taxa) spread in mid and eastern Europe and tropical savannas and woodland expanded in Africa and Australia at the expense of deserts. Discrepancies which occurred between data reconstruction and model simulation can be related to: (1) poor spatial model resolution and data coverage; (2) uncertainties in delimiting biomes using climate parameters; or (3) uncertainties in model physics and/or geological boundary conditions. Main conclusions, The new global biome reconstruction combines vegetation reconstruction from palaeobotanical proxies with model simulations. It is an important contribution to the further understanding of climate and vegetation changes during the Middle Pliocene warm interval and will enhance our knowledge about how vegetation may change in the future. [source]


    Uniform Head in Horizontal and Vertical Wells

    GROUND WATER, Issue 1 2006
    David R. Steward
    The steady-state head within a fully penetrating well may be estimated by evaluating the Thiem equation at the radius of the well. A method is presented here to extend results from the Thiem equation to horizontal wells and to partially penetrating wells. The particular model used in this investigation is based upon the analytic element method; it accurately reproduces a boundary condition of uniform head along the cylindrical surface at the perforated face of the well. This model is exercised over a representative range of parameters including the well's length, radius, and pumping rate, and the aquifer's hydraulic conductivity and thickness. Results are presented in a set of figures and tables that compare the well's drawdown to the drawdown that would have been obtained using the Thiem solution with the same pumping rate and radius. A methodology is presented to estimate the head within a horizontal or partially penetrating well by adding a correction term to results that can be readily obtained from computer models of vertical fully penetrating wells. This approach may also be used to contrast the differences in head between horizontal and vertical wells of various lengths, radii, and placement elevations. [source]


    Multilayer Analytic Element Modeling of Radial Collector Wells

    GROUND WATER, Issue 6 2005
    Mark Bakker
    A new multilayer approach is presented for the modeling of ground water flow to radial collector wells. The approach allows for the inclusion of all aspects of the unique boundary condition along the lateral arms of a collector well, including skin effect and internal friction losses due to flow in the arms. The hydraulic conductivity may differ between horizontal layers within the aquifer, and vertical anisotropy can be taken into account. The approach is based on the multilayer analytic element method, such that regional flow and local three-dimensional detail may be simulated simultaneously and accurately within one regional model. Horizontal flow inside a layer is computed analytically, while vertical flow is approximated with a standard finite-difference scheme. Results obtained with the proposed approach compare well to results obtained with three-dimensional analytic element solutions for flow in unconfined aquifers. The presented approach may be applied to predict the yield of a collector well in a regional setting and to compute the origin and residence time, and thus the quality, of water pumped by the collector well. As an example, the addition of three lateral arms to a collector well that already has three laterals is investigated. The new arms are added at an elevation of 2 m above the existing laterals. The yield increase of the collector well is computed as a function of the lengths of the three new arms. [source]


    Numerical and experimental investigation of heat and mass transfer in unsaturated porous media with low convective drying intensity

    HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 5 2008
    Tao Lu
    Abstract The heat and mass transfer in an unsaturated wet cylindrical bed packed with quartz particles was investigated theoretically and experimentally for relatively low convective drying rates. The medium was dried by blowing dry air over the top of the porous bed which was insulated by impermeable, adiabatic material on the bottom and sides. Local thermodynamic equilibrium was assumed in the mathematical model describing the multi-phase flow in the unsaturated porous medium using the energy and mass conservation equations for heat and mass transfer during the drying. The drying model included convection and capillary transport of the moisture, and convection and diffusion of the gas. The wet and dry regions were coupled with a dynamic boundary condition at the evaporation front. The numerical results indicated that the drying process could be divided into three periods: the initial temperature rise period, the constant drying rate period, and the reduced drying rate period. The numerical results agreed well with the experimental data, verifying that the mathematical model can evaluate the drying performance of porous media for low drying rates. 2008 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(5): 290,312, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20205 [source]


    A study on thermal conductivity of a quasi-ordered liquid layer on a solid substrate

    HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 7 2007
    Xiao-Yan Shi
    Abstract In the present paper, a study on thermal conductivity of a quasi-ordered liquid layer on a solid surface was performed by molecular dynamic simulation. Results showed that the motion of the molecules and their radial distribution function in the quasi-ordered liquid layer were similar to those of solid molecules. By using the Green,Kubo formula, the thermal conductivity of the layer was calculated. It was found that it increased with the increase of the parameters of ordering. The size effect and the influence of the boundary condition were also discussed. 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 36(7): 429,434, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20171 [source]


    DNS of turbulent heat transfer in a channel flow with a varying streamwise thermal boundary condition

    HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 4 2006
    Yohji Seki
    Abstract Direct numerical simulation (DNS) was performed for the turbulent heat transfer in a channel flow. In the present study, the effect of the thermal boundary condition was examined. DNS was carried out for varying streamwise thermal boundary conditions (Re, = 180) with Pr = 0.71 to obtain statistical mean temperatures, temperature variances, budget terms, and time scale ratios. The results obtained indicate that the time scale ratio varies along the stream direction. 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(4): 265,278, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20114 [source]


    Analytical approach with Laplace transform to the inverse problem of one-dimensional heat conduction transfer: Application to second and third boundary conditions

    HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 1 2003
    Masanori Monde
    Abstract An analytical method using Laplace transformation has been developed for one-dimensional heat conduction. This method succeeded in explicitly deriving the analytical solution by which the surface temperature for the first kind of boundary condition can be well predicted. The analytical solutions for the surface temperature and heat flux are applied to the second and third of the boundary conditions. These solutions are also found to estimate the corresponding surface conditions with a high degree of accuracy when the surface conditions smoothly change. On the other hand, when these conditions erratically change such as the first derivative of temperature with time, the accuracy of the estimation becomes slightly less than that for a smooth condition. This trend in the estimation is similar irrespective of any kind of boundary condition. 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 32(1): 29,41, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10069 [source]


    Errors of kinematic wave and diffusion wave approximations for time-independent flows with infiltration and momentum exchange included

    HYDROLOGICAL PROCESSES, Issue 9 2005
    V. P. Singh
    Abstract Error equations for kinematic wave and diffusion wave approximations were derived for time-independent flows on infiltrating planes and channels under one upstream boundary and two downstream boundary conditions: zero flow at the upstream boundary, and critical flow depth and zero depth gradient at the downstream boundary. These equations specify error in the flow hydrograph as a function of space. The diffusion wave approximation was found to be in excellent agreement with the dynamic wave approximation, with errors below 2% for values of KF (e.g. KF , 75), where K is the kinematic wave number and F is the Froude number. Even for small values of KF (e.g. KF = 25), the errors were typically less than 3%. The accuracy of the diffusive approximation was greatly influenced by the downstream boundary condition. For critical flow depth downstream boundary condition, the error of the kinematic wave approximation was found to be less than 10% for KF , 75 and greater than 20% for smaller values of KF. This error increased with strong downstream boundary control. The analytical solution of the diffusion wave approximation is adequate only for small values of K. Copyright 2005 John Wiley & Sons, Ltd. [source]