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FELISA Sources
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FELISA Source Specification

  The FELISA meshing option also employs sources through which the user may exert the required level of control over the meshing process.  The mechanics for the physical placement of FELISA sources is performed exactly as for the case of VGRID sources, however, the formulation of the sources employed by FELISA is quite different, and thus different quantities must be prescribed by the user.  FELISA employs Nodal, Linear, and Triangle sources which are described below.

1) A Nodal Source enables the control of mesh characteristics about a point in 3D space.

2) A Linear Source enables the control of mesh characteristics about a finite linear segment.

3) A Triangle Source enables the control of mesh characteristics about a closed grouping of three linear segments.

  The sub-panel under the FELISA tab shown to the left provides for selection of the source type as well as the source properties particular to FELISA type sources.  These are invariant for the source type though each is defined for each node which comprises the source.  These source properties are defined in the table below.

Source Property
spacing value at source
Constant Dist
physical distance (radial) away from the source within which the spacing is to be held constant at the value dS
Cell Size
the cell size to be recovered "sufficiently" far from the nodal source
the radial distance at which point the spacing fully transitions from dS to Cell SizeNote that Distance > Constant Dist

  • The user should note that the definition presented above represents a departure from the original formulation of FELISA sources. It has been extended within GridEx in order that the source specification become somewhat more physically intuitive. The user should note, however, that this specification is transparently recast to satisfy the requirements of the FELISA formulation, and subsequent import of sources defined in a previous GridEx session may appear to have been altered from their original specification. The nature of the sources insofar as their influence on the resulting mesh remains unchanged.

The effects of each of the source properties is described below.

The Nodal Source

  The Nodal source is the simplest source and most useful when a desired cell size is required at a point within the domain.  The FELISA nodal source is conceptually simpler than its VGRID counterpart though it it not quite as flexible.

  For a domain having dimensions of 10 x 10 units, a single Nodal source has been placed at the origin with source parameters as specified in the table below.

Constant Dist
Cell Size

  The surface mesh which results is shown to the left.  The rapid change in spacing in the vicinity of the source to that adjacent to the surface boundaries is a result of the limited blending region as determined by Distance - Constant Dist in conjunction with an order magnitude change in the size of the prescribed element size.

The cumulative effect of nodal sources placed at (1,1,0) and (-1,-1,0) can be seen in the mesh to the left.  The source parameters for each are unchanged from the previous example.

The Linear Source

  The Linear source extends the concept of the nodal source as two nodal sources now become linked by a line segment which exerts a continuous influence along its length upon the mesh.  The four parameters identified for the Nodal Source now apply to each termination point of the Linear Source, and they need not be identical.

  The figure to the left shows the influence of a Linear source with nodes positioned at (1,1,0) and (-1,-1,0) with spacing parameters as used above.  There are clear differences (although minor in this particular instance) between this case and the previous due to the nature of the Linear source.

The Triangle Source

The Triangle Source represents a further extension to the Linear source in that a third node is introduced into the definition.  The same four quantities are specified at each node, though again they need not be identical.

  In this example the nodes are positioned at (1.5,1.5,0), (5.0,-5.0,0), and (-1.5,-1.5,0).  A practical application of each of the source types described above is presented in Tutorial I.

Responsible NASA Official: William T. Jones
Site Curator: William T. Jones
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Last Updated: Dec 18, 2001