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
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.
spacing value at source
physical distance (radial) away from the source within which the
spacing is to be held constant at the value dS
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 Size. Note 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.
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
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.
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.
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.
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
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.