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Departure Points (departure + point)

Distribution by Scientific Domains
Engineering40%

Selected Abstracts

Treatment of vector equations in deep-atmosphere, semi-Lagrangian models.

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 647 2010
I: Momentum equation
Abstract Application of the semi-Lagrangian method to the vector momentum equation in orthogonal curvilinear systems is considered, with emphasis on spherical and spheroidal coordinates for deep-atmosphere models (in which the shallow-atmosphere approximation is not made). In spherical coordinates, a certain rotation matrix allows vector components at semi-Lagrangian departure points to be expressed in the required component forms at the corresponding arrival points. This rotation matrix also allows the unit vector triad at the arrival point to be expressed in terms of the unit vector triad at the departure point. The resulting formalisation of the momentum equation applies to timesteps of arbitrary length, and in the limit of infinitesimal timestep it delivers the familiar Eulerian components. Extension of the rotation matrix technique to more general orthogonal curvilinear systems is remarkably straightforward, thus demonstrating the versatility of the semi-Lagrangian method. Explicit forms are given for systems having longitude as one coordinate and general orthogonal coordinates in the meridional plane, and in particular these forms are applicable to both confocal oblate spheroidal and similar oblate spheroidal systems. A specific factorisation of the rotation matrix in the spherical polar case involves three matrices, one of which represents rotation of the unit vector triad along a great circle arc; the non-Euclidean, shallow-atmosphere approximation of the total rotation matrix results when the great circle rotation matrix is replaced by the identity matrix (but the other two matrices involved in the factorisation are kept intact). This shallow-atmosphere rotation matrix agrees with that used by ECMWF and Météo-France. © Crown Copyright 2010. Published by John Wiley & Sons, Ltd. [source]

Traffic flow continuum modeling by hypersingular boundary integral equations

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2010
Luis M. Romero
Abstract The quantity of data necessary in order to study traffic in dense urban areas through a traffic network, and the large volume of information that is provided as a result, causes managerial difficulties for the said model. A study of this kind is expensive and complex, with many sources of error connected to each step carried out. A simplification like the continuous medium is a reasonable approximation and, for certain dimensions of the actual problem, may be an alternative to be kept in mind. The hypotheses of the continuous model introduce errors comparable to those associated with geometric inaccuracies in the transport network, with the grouping of hundreds of streets in one same type of link and therefore having the same functional characteristics, with the centralization of all journey departure points and destinations in discrete centroids and with the uncertainty produced by a huge origin/destination matrix that is quickly phased out, etc. In the course of this work, a new model for characterizing traffic in dense network cities as a continuous medium, the diffusion,advection model, is put forward. The model is approached by means of the boundary element method, which has the fundamental characteristic of only requiring the contour of the problem to be discretized, thereby reducing the complexity and need for information into one order versus other more widespread methods, such as finite differences and the finite element method. On the other hand, the boundary elements method tends to give a more complex mathematical formulation. In order to validate the proposed technique, three examples in their fullest form are resolved with a known analytic solution. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Semi-Lagrangian advection on a spherical geodesic grid

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 2 2007
Maria Francesca Carfora
Abstract A simple and efficient numerical method for solving the advection equation on the spherical surface is presented. To overcome the well-known ,pole problem' related to the polar singularity of spherical coordinates, the space discretization is performed on a geodesic grid derived by a uniform triangulation of the sphere; the time discretization uses a semi-Lagrangian approach. These two choices, efficiently combined in a substepping procedure, allow us to easily determine the departure points of the characteristic lines, avoiding any computationally expensive tree-search. Moreover, suitable interpolation procedures on such geodesic grid are presented and compared. The performance of the method in terms of accuracy and efficiency is assessed on two standard test cases: solid-body rotation and a deformation flow. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Treatment of vector equations in deep-atmosphere, semi-Lagrangian models.

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 647 2010
I: Momentum equation
Abstract Application of the semi-Lagrangian method to the vector momentum equation in orthogonal curvilinear systems is considered, with emphasis on spherical and spheroidal coordinates for deep-atmosphere models (in which the shallow-atmosphere approximation is not made). In spherical coordinates, a certain rotation matrix allows vector components at semi-Lagrangian departure points to be expressed in the required component forms at the corresponding arrival points. This rotation matrix also allows the unit vector triad at the arrival point to be expressed in terms of the unit vector triad at the departure point. The resulting formalisation of the momentum equation applies to timesteps of arbitrary length, and in the limit of infinitesimal timestep it delivers the familiar Eulerian components. Extension of the rotation matrix technique to more general orthogonal curvilinear systems is remarkably straightforward, thus demonstrating the versatility of the semi-Lagrangian method. Explicit forms are given for systems having longitude as one coordinate and general orthogonal coordinates in the meridional plane, and in particular these forms are applicable to both confocal oblate spheroidal and similar oblate spheroidal systems. A specific factorisation of the rotation matrix in the spherical polar case involves three matrices, one of which represents rotation of the unit vector triad along a great circle arc; the non-Euclidean, shallow-atmosphere approximation of the total rotation matrix results when the great circle rotation matrix is replaced by the identity matrix (but the other two matrices involved in the factorisation are kept intact). This shallow-atmosphere rotation matrix agrees with that used by ECMWF and Météo-France. © Crown Copyright 2010. Published by John Wiley & Sons, Ltd. [source]

Pathways to the Enabling State: Changing Modes of Social Provision in Western Australian Community Services

AUSTRALIAN JOURNAL OF PUBLIC ADMINISTRATION, Issue 4 2000
Wendy Earles
This investigation of reform of Western Australian community services problematises assumptions about the enabling state. The investigation is distinctive by virtue of its attention to the departure points as well as the destinations in pathways of policy change and its unpacking of three modes of public provision into their three constituent policy elements (funder-provider mix; the nature of agreements between policy actors; and the type of funding relationships). We find first that government had long adopted some aspects of the model of governance associated with the enabling state. Second, we find some path dependency in policy change towards marketisation. Third, we find highly nuanced policy outcomes combining government exploitation of its authority, market innovations and the maintenance of basic network features of the programs. [source]