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Grid Spacing (grid + spacing)

Distribution by Scientific Domains

Engineering	62%
Earth and Environmental Science	31%

Selected Abstracts

Simulation of nerve bundle activation by simultaneous multipoint extracellular stimulation with surface electrodes

ELECTRONICS & COMMUNICATIONS IN JAPAN, Issue 6 2009
Hirokazu Takahashi
Abstract Neural prostheses for restoring lost functions can benefit from selective activation of nerves. We previously proposed a multipoint gating stimulation, which can selectively activate a desired portion of a nerve bundle, regardless of the density of the electrode. In this paper, we discuss the design of an electrode array and effective strategies to determine the stimulus parameters. Large electrodes were less affected by the relative location of the electrodes and the nodes of Ranvier, suggesting that a rectangular electrode, whose long side along a nerve bundle is longer than the internodal distance (i.e., on the order of 1 mm), would be more effective than a disk electrode. We were able to estimate an appropriate current at each electrode on the basis of a blocking threshold, above which no spike propagation was permitted. For lateral gating stimulation, the gate current should be set above the threshold, while for depthwise gating stimulation, the gate current should be set below the threshold. The spatial resolutions of lateral and depthwise gating stimulation were theoretically estimated to be at least 50 ,m when the grid spacing of the array was 1.2 mm. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 92(6): 31,40, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10064 [source]

Simulating Seepage into Mine Shafts and Tunnels with MODFLOW

GROUND WATER, Issue 3 2010
Jacob Zaidel
In cases when an equivalent porous medium assumption is suitable for simulating groundwater flow in bedrock aquifers, estimation of seepage into underground mine workings (UMWs) can be achieved by specifying MODFLOW drain nodes at the contact between water bearing rock and dewatered mine openings. However, this approach results in significant numerical problems when applied to simulate seepage into an extensive network of UMWs, which often exist at the mine sites. Numerical simulations conducted for individual UMWs, such as a vertical shaft or a horizontal drift, showed that accurate prediction of seepage rates can be achieved by either applying grid spacing that is much finer than the diameter/width of the simulated openings (explicit modeling) or using coarser grid with cell sizes exceeding the characteristic width of shafts or drifts by a factor of 3. Theoretical insight into this phenomenon is presented, based on the so-called well-index theory. It is demonstrated that applying this theory allows to minimize numerical errors associated with MODFLOW simulation of seepage into UMWs on a relatively coarse Cartesian grid. Presented examples include simulated steady-state groundwater flow from homogeneous, heterogeneous, and/or anisotropic rock into a vertical shaft, a horizontal drift/cross-cut, a ramp, two parallel drifts, and a combined system of a vertical shaft connected to a horizontal drift. [source]

Unstructured grid generation using LiDAR data for urban flood inundation modelling

HYDROLOGICAL PROCESSES, Issue 11 2010
Ryota Tsubaki
Abstract Inundation disasters, caused by sudden water level rise or rapid flow, occur frequently in various parts of the world. Such catastrophes strike not only in thinly populated flood plains or farmland but also in highly populated villages or urban areas. Inundation of the populated areas causes severe damage to the economy, injury, and loss of life; therefore, a proper management scheme for the disaster has to be developed. To predict and manage such adversity, an understanding of the dynamic processes of inundation flow is necessary because risk estimation is performed based on inundation flow information. In this study, we developed a comprehensive method to conduct detailed inundation flow simulations for a populated area with quite complex topographical features using LiDAR (Light Detection and Ranging) data. Detailed geospatial information including the location and shape of each building was extracted from the LiDAR data and used for the grid generation. The developed approach can distinguish buildings from vegetation and treat them differently in the flow model. With this method, a fine unstructured grid can be generated representing the complicated urban land features precisely without exhausting labour for data preparation. The accuracy of the generated grid with different grid spacing and grid type is discussed and the optimal range of grid spacing for direct representation of urban topography is investigated. The developed method is applied to the estimation of inundation flows, which occurred in the basin of the Shin-minato River. A detailed inundation flow structure is represented by the flow model, and the flow characteristics with respect to topographic features are discussed. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Higher-resolution convection schemes for flow in porous media on highly distorted unstructured grids

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 8 2008
Sadok Lamine
Abstract Higher-resolution schemes are presented for convective flow approximation on highly distorted unstructured grids. The schemes are coupled with continuous full-tensor Darcy-flux approximations. A sequence of non-uniform and distorted grid formulations are developed and compared for a range of unstructured meshes with variable grid spacing. The higher-order schemes are constructed using non-uniform grid slope limiters such that they are stable with a local maximum principle, ensuring that solutions are free of spurious oscillations. Benefits of the resulting schemes are demonstrated for classical test problems in reservoir simulation including cases with full-tensor permeability fields. The test cases involve a range of unstructured grids with variations in grid spacing, orientation and permeability that lead to flow fields that are poorly resolved by standard simulation methods. The higher-order formulations are shown to effectively reduce numerical diffusion, leading to improved resolution of concentration and saturation fronts. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Influence of reaction mechanisms, grid spacing, and inflow conditions on the numerical simulation of lifted supersonic flames

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2010
P. Gerlinger
Abstract The simulation of supersonic combustion requires finite-rate chemistry because chemical and fluid mechanical time scales may be of the same order of magnitude. The size of the chosen reaction mechanism (number of species and reactions involved) has a strong influence on the computational time and thus should be chosen carefully. This paper investigates several hydrogen/air reaction mechanisms frequently used in supersonic combustion. It is shown that at low flight Mach numbers of a supersonic combustion ramjet (scramjet), some kinetic schemes can cause highly erroneous results. Moreover, extremely fine computational grids are required in the lift-off region of supersonic flames to obtain grid-independent solutions. The fully turbulent Mach 2 combustion experiment of Cheng et al. (Comb. Flame 1994; 99: 157,173) is chosen to investigate the influences of different reaction mechanisms, grid spacing, and inflow conditions (contaminations caused by precombustion). A detailed analysis of the experiment will be given and errors of previous simulations are identified. Thus, the paper provides important information for an accurate simulation of the Cheng et al. experiment. The importance of this experiment results from the fact that it is the only supersonic combustion test case where temperature and species fluctuations have been measured simultaneously. Such data are needed for the validation of probability density function methods. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Accuracy analysis of super compact scheme in non-uniform grid with application to parabolized stability equations

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 5 2004
V. Esfahanian
Abstract A brief derivation of the super compact finite difference method (SCFDM) in non-uniform grid points is presented. To investigate the accuracy of the SCFDM in non-uniform grid points the Fourier analysis is performed. The Fourier analysis shows that the grid aspect ratio plays a crucial role in the accuracy of the SCFDM in a non-uniform grid. It is also found that the accuracy of the higher order relations of the SCFDM is more sensitive to grid aspect ratio than the lower order relations. In addition, to obtain a mathematical representation of the accuracy and making clear the role of the aspect ratio in the accuracy of the SCFDM in non-uniform grids, the modified equation approach is used. For the sake of demonstrating the analytical results obtained from the Fourier analysis and the modified equation approach, the super compact finite difference method is applied to solve the Blasius boundary layer and the non-linear parabolized stability equations as numerical examples indicating the difficulty with non-uniform grid spacing using the super compact scheme. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Numerical errors of the volume-of-fluid interface tracking algorithm

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 4 2002
Gregor, erne
Abstract One of the important limitations of the interface tracking algorithms is that they can be used only as long as the local computational grid density allows surface tracking. In a dispersed flow, where the dimensions of the particular fluid parts are comparable or smaller than the grid spacing, several numerical and reconstruction errors become considerable. In this paper the analysis of the interface tracking errors is performed for the volume-of-fluid method with the least squares volume of fluid interface reconstruction algorithm. A few simple two-fluid benchmarks are proposed for the investigation of the interface tracking grid dependence. The expression based on the gradient of the volume fraction variable is introduced for the estimation of the reconstruction correctness and can be used for the activation of an adaptive mesh refinement algorithm. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Sensitivity of the regional climate of East/Southeast Asia to convective parameterizations in the RegCM3 modelling system.

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 14 2008
Part 1: Focus on the Korean peninsula
Abstract This study investigates the capability of the regional climate model, RegCM3, to simulate fine-scale regional climate over a narrow peninsula or archipelago. The model is run in one-way double-nested mode with one mother domain and two nested domains. The mother domain encompasses the eastern and southern regions of Asia and adjacent oceans with a grid spacing of 60 km. The first nested domain focuses on the Korean peninsula and the second one covers the Philippine archipelago with a grid spacing of 20 km. The simulation spans a period of 5 years and 1 month, from November 2000 to December 2004. The sensitivity of the two convection schemes, namely, the Grell scheme (Grell) and the MIT-Emanuel scheme (EMU), is studied. Model results obtained with both the Grell and EMU show reasonable performance in capturing the seasonal variation and the spatial characteristics of the East Asian monsoon. However, the Grell simulation appears to have persistent cold and dry biases in the summer season. There is a definite improvement in these model deficiencies by the implementation of EMU. Although the temperature fields in the Grell and EMU simulations are essentially the same in terms of the spatial distribution, the EMU simulation is quantitatively in better agreement with the observed estimates, indicating a substantial reduction in the cold bias. Further, in comparison with the Grell simulation, the EMU simulation shows an improvement in the timing and amplitude of the rain band propagating northward. The spatial distributions of precipitation also have good quality, capturing the localized maxima over Korea. The frequency distributions of daily temperature and precipitation simulated by EMU are closer to observations than those of the Grell simulation. It is found that the convective precipitation derived from different convection parameterizations is a major contributor to the performance of the model in summer. Copyright © 2008 Royal Meteorological Society [source]

Mesoscale precipitation variability in the region of the European Alps during the 20th century

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 9 2002
Jürg Schmidli
Abstract The purpose of this study is to construct and evaluate a new gridded analysis of precipitation that covers the entire region of the European Alps (43.2,48.8 ° N, 3.2,16.2 ° E), resolves the most prominent mesoscale variations (grid spacing 25 km) and extends with a monthly time-resolution over most of the 20th century (1901,90). The analysis is based on a reconstruction using the reduced-space optimal interpolation technique. It combines data from a high-resolution network over a restricted time period (1971,90) with homogeneous centennial records from a sparse sample of stations. The reconstructed fields account for 78% of the total variance in a cross-validation with independent data. The explained variance for individual grid points varies between 60 and 95%, with lower skills over the southern and western parts of the domain. For averages over 100 × 100 km2 subdomains, the explained variance increases to 90,99%. Comparison of the reconstruction with the CRU05 global analysis reveals good agreement with respect to the interannual variations of large subdomain averages (10 000,50 000 km2), some differences in decadal variations, especially for recent decades, and physically more plausible spatial patterns in the present analysis. The new dataset is exploited to depict 20th century precipitation variations and their correlations with the North Atlantic oscillation (NAO). A linear trend analysis (1901,90) reveals an increase of winter precipitation by 20,30% per 100 years in the western part of the Alps, and a decrease of autumn precipitation by 20,40% to the south of the main ridge. Correlations with the NAO index (NAOI) are weak and highly intermittent to the north and weak and more robust to the south of the main Alpine crest, indicating that changes in the NAOI in recent decades are not of primary importance in explaining observed precipitation changes. Copyright © 2002 Royal Meteorological Society [source]

Detection and climatology of fronts in a high-resolution model reanalysis over the Alps

METEOROLOGICAL APPLICATIONS, Issue 1 2010
J. Jenkner
Abstract The identification of low-level thermal fronts is particularly challenging in high-resolution model fields over complex terrain. Firstly, direct model output often contains numerical noise which spuriously influences the high-frequency variability of thermal parameters. Secondly, the boundary layer interferes via convection and consequently leaves its thermal marks on low levels. Here, an automated objective method for the detection of frontal lines is introduced which is designed to be insusceptible to consequences of small grid spacings. To this end, existing algorithms are readopted and combined in a novel way. The overall technique subdivides into a basic detection of fronts and a supplemental division into local fronts and synoptic fronts. The fundamental parts of the detection are: (1) a smoothing of the initial fields, (2) a definition of the frontal strength, and, (3) a localisation with the thermal front parameter. The local fronts are identified by means of a classification of open and closed thermal contours. The resulting data comprise the spatial outline of the frontal structures in a binary field as well as their type and movement. The novel methodology is applied to a 3 year high-resolution reanalysis over central Europe computed with the COSMO model using a grid spacing of 7 km. Grid-point based climatologies are derived for the Alpine region. Frequencies of occurrence and characteristics of motion are analysed for different frontal types. The novel climatology also provides quantitative evidence of dynamical properties such as the retardation of cold fronts ahead of mountains and the dissolution of warm fronts over mountains. Copyright © 2009 Royal Meteorological Society [source]

A cloud-resolving regional simulation of tropical cyclone formation

ATMOSPHERIC SCIENCE LETTERS, Issue 1 2002
Jordan G. Powers
Abstract The development of Tropical Cyclone Diana (1984) is simulated with a mesoscale model using 1.2 km grid spacing over a regional-scale (>1000 km) domain in the first known experiment of this kind. With only a synoptic-scale disturbance in the initial conditions, the model first develops a mesoscale convective system along a remnant frontal zone, which yields a mesoscale vortex. After a period of quiescence, banded convection organizes about the vortex from isolated, grid-resolved cells, with the system becoming warm-core and intensifying into Tropical Storm Diana. Copyright © 2002 Royal Meteorological Society. [source]

From grid cells to place cells: A mathematical model

HIPPOCAMPUS, Issue 12 2006
Trygve Solstad
Abstract Anatomical connectivity and recent neurophysiological results imply that grid cells in the medial entorhinal cortex are the principal cortical inputs to place cells in the hippocampus. The authors propose a model in which place fields of hippocampal pyramidal cells are formed by linear summation of appropriately weighted inputs from entorhinal grid cells. Single confined place fields could be formed by summing input from a modest number (10,50) of grid cells with relatively similar grid phases, diverse grid orientations, and a biologically plausible range of grid spacings. When the spatial phase variation in the grid-cell input was higher, multiple, and irregularly spaced firing fields were formed. These observations point to a number of possible constraints in the organization of functional connections between grid cells and place cells. © 2006 Wiley-Liss, Inc. [source]

Finite volume method with zonal-embedded grids for cylindrical coordinates

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2006
Yong Kweon Suh
Abstract A zonal-embedded-grid technique has been developed for computation of the two-dimensional Navier,Stokes equations with cylindrical coordinates. As is well known, the conventional regular grid system gives very small grid spacings in the azimuthal direction so it requires a very small time step for a stable numerical solution when the explicit method is used. The fundamental idea of the zonal-embedded-grid technique is that the number of azimuthal grids can be made small near the origin of the coordinates so that the grid size is more uniformly distributed over the domain than with the conventional regular-grid system. The code developed using this technique combined with the explicit, finite-volume method was then applied to calculation of the asymmetric swirl flows and Lamb's multi-polar vortex flows within a full circle and the spin-up flows within a semi-circle. It was shown that the zonal-embedded grids allow a time step far larger than the conventional regular grids. For the case of the Lamb's multi-polar vortex flows, the code was validated by comparing the calculated results with the exact solutions. For the case of the semi-circle spin-up flows, the experimental results were used for the verification. It was seen that the numerical results were in good agreement with the experimental results both qualitatively and quantitatively. Copyright © 2006 John Wiley & Sons, Ltd. [source]