The ucd streak module is an advanced variation of the ucd_streamlines
module in AVS5. It contains an optional mode where the streamlines
follow the boundary of the flow domain, tracking along the surface,
as long at the velocity field is into the boundary surface, and
are not displayed when they leave the surface. This simulates
oil drop streak lines from exterior flow wind tunnel tests.
The flow is integrated through the 3D boundary elements,
and optional integration step markers can be shown.
Although the streamlines are only displayed at the surface, the
whole interior 3D streamline calculation is taking place,
so this method is quite different from a 2D surface only
particle track algorithm. Any velocity component going into the
boundary surface is projected back inside boundary cell
a small fraction of a cell size away from the boundary,
and another full 3D integration step is performed.
The projection is performed normal to the boundary surface geometry.
The zig-zag markers illustrate the boundary tracking algorithm, and
show the last interior point, the integration step point outside the
domain, the internal projection of cross-over, and the vertices
of the cell face used in the projection.
Additional controls allow the integration to be halted at a
preset number of steps. No options have been removed from
ucd streamlines, however the new boundary following algorithm
and "ribbons" are mutually exclusive.
StreamLine Basics:
The ucd streak module generates colored stream lines or stream
ribbons based on the vector node data in a UCD structure.
The stream lines are generated at selected sample points. For every
time step, ucd streak advances each sample point through space,
based on the interpolated value of the node vectors surrounding the
point. The result is a set of stream lines showing the progress of
massless particles moving under the influence of the vector field at
the nodes of the UCD structure. Stream ribbons behave similarly,
except that their width and rotation also reflect the divergence and
rotation of the flow at each point.
The sample points can be any scatter field. Usually, they come from
two sources: from a sample probe generated by the ucd streak
module; or from arbitrarily-placed points defined by a field generated
interactively by the create geom module.
ucd streak's sample probe places a sample of points at a starting
location in the UCD structure. The number of points is parameter-
controlled. The sample probe's points can be moved around in space
like any other geometry object, using the "virtual trackball"
paradigm. To move the probe, select it by clicking on it, or by
entering the Geometry Viewer and making it the current object.
There are three different modes to initiate the calculation of stream
lines: Immediate, Wait, and Button Up. In Immediate mode, any change
to a parameter or probe displacement will cause stream lines to be
calculated immediately. In Wait mode you must press the Start Streams
button to initiate streaks calculation. This mode is useful when
the streak calculation requires a long time and you want to change
a parameter or move the probe without immediate calculation.
In Button Up mode, you can move probe with the mouse,
keeping the button down.
When you set the probe in a proper position and release the
button, the module will then calculate streaks. This mode can be
useful when the streak calculation requires a long time and you
want to move the probe without immediate calculation.
A UCD structure consists of cells with nodes at their vertices. Each
node may have data associated with it. Ucd streak only works with
structures that have a vector component in their node data, thus it
complains if the input structure has only scalar values at the nodes.
(Scalar components can be converted to vector components with ucd
extract vector.) If the nodes of a structure have more than one 3-
vector component, use the Node Data radio buttons to select which
component to use in calculating the stream lines.
INPUTS
UCD structure (required)
The input structure is in AVS unstructured cell data (UCD)
format. It must have at least one node component which is a 3D
vector, representing the components of a velocity vector.
colormap (required; colormap)
An AVS colormap that is used by ucd streak to associate
colors with vector values. Note that this is a regular AVS
colormap, and not the color field output by ucd contour and ucd
legend.
Data Field (optional, field irregular 3-space float)
ucd streak generates its own data sampling probe that is
manipulated from the geometry viewer module. Optionally, one can
also input a field that defines an arbitrarily-placed set of
sample points. This field is usually created interactively with
the create geom module, but can be saved and reused as an AVS
field.
Upstream Transform (invisible, optional, autoconnect)
When the ucd streak module coexists with the geometry viewer
module in a network, geometry viewer feeds information on how the
point, circle or other sample probe has been moved back to this
input port on the ucd streak module. The two modules connect
automatically, through a data pathway that is normally invisible.
This gives direct mouse manipulation control over ucd
streak's sample probe.
PARAMETERS
Node Data
Selects which of the node's data components to display. A set of
radio buttons shows the label attached to each node data
component. Before the module receives data, the default ", , ..." is displayed. If there are no vector
components of the node data ucd streak complains. If there
are several vector data components, these buttons let you select
which component to use in calculating the stream lines. If there
is no node data in the structure "" is displayed on the
button.
N Segment
Integer dial that controls the density of points in the sample
set.
Sample Style (radio buttons)
Specifies the configuration of points from which stream lines are
drawn: point, line, circle, or plane.
N Steps
Integer dial that specifies the number of time steps for which
stream lines are computed within each cell of the UCD structure.
As the number of time steps increases, so does the accuracy of
the stream lines.
Integration Method
Selects the integration method used to advance sample points
through space: 1st order uses an euler integration method, 2nd
order uses a 2nd order Runge-Kutta method, and 3rd order uses a
3rd order Runge-Kutta method.
Backward (boolean)
If Backward is selected, stream lines are extrapolated in the
opposite direction that the UCD structure's vectors are pointing.
By default this switch is off.
Color Streams (boolean)
If Color Streams is selected, the stream lines are colored based
on the magnitude of the interpolated vectors used to generate the
stream lines. By default this switch is off.
Ribbons (boolean)
A toggle switch that turns on stream ribbons rather than stream
lines. The default is off.
Ribbon Angle (float dial)
This control only appears if Ribbons is selected. It controls
the initial angle at which the ribbon is drawn. By default,
ribbons are drawn with their width parallel to the X axis. The
range is 0 to 360; the default is 0.
Ribbon Width (float dial)
This control only appears if Ribbons is selected. It scales the
width of the ribbon. The range and default shown on the dial is
calculated based on the size of the UCD structure. The default
is 0.1*the maximum dimension of the structure. The minimum is
0.0. The maximum is scaled to be 20 times the default. (Ribbon
width will vary along its length according to the divergence of
the flow at each node.)
Interaction Mode (radio buttons)
Selects a mode to initiate the calculation of stream lines:
Immediate, SWait or Button Up. In Immediate mode, any change to
a parameter or probe displacement will cause stream lines to be
calculated immediately. In Wait mode you must press the Start
Streams button to calculate streaks. In Button Up mode you
can move the probe with the mouse, keeping the mouse button down.
When you set the probe in a proper position and release the
button, the module will calculate streaks.
Start Streams (boolean)
A boolean switch that initiates the calculation of stream lines
in Wait mode. This button allows you to manipulate the sample
probe until you are satisfied with its position, or change other
parameters and only then begin computing stream lines.
OUTPUTS
Stream Lines, Sampling Object (geometry)
ucd streaks outputs two geometries: a set of colored
disjoint lines or ribbons, and the sampling object.