General Module Function
The advector module combines streamlines capability and a tool for sequential positioning of glyphs along the streamlines trajectory to simulate advection of weightless particles through a vector field (for example, a fluid flow simulation such as modflow). The result is an animation of particle motion, with the particles represented as any EVS geometry (such as a jet or a sphere). The glyphs can scale, deflect or deform according to the velocity vector it passes. At least one of the nodal data components input to advector must be a vector. The direction of travel of streamlines can be specified to be forwards (toward high vector magnitudes) or backwards (toward low vector magnitudes) with respect to the vector field. The input glyphs travel along streamlines (not necessarily visible in the viewer) which are produced by integrating a velocity field using the Runge-Kutte method of specified order with adaptive time steps.
Module Input Ports
advector has three input ports.
Data passed to the first port (the left port) can have a mesh of any type, and must have at least one vector nodal data component. To generate streamlines of scalar data, a module such as gradient must be used to calculate the gradient of a scalar field.
The second port accepts data specifying the starting location of the streamlines. This data is typically generated by the create_grid, slice or isolines modules.
The third port accepts any geometry mesh (glyph, usually read in with the load_glyph module) which will be rendered at each starting point and moved sequentially through the vector field during running of the advector module.
Module Output Ports
advector contains four output ports.
The leftmost port outputs a mesh composed of the original mesh plus the meshes representing the particles.
The second output port creates a new unstructured polyline mesh representing the streamlines, and also contains a nodal data component referencing the velocity component.
The third output creates a renderable version of the glyphs.
The fourth output port sends streamline polylines to the viewer.
Module Control Panel
The control panel for advector is shown in the figure above. Many of the parameters are related to streamline interpolation which is discussed in the streamlines help. Below is a discussion of those parameters unique to advector.
The Run toggle starts or stops advection.
The Cycle toggle starts the advection again at Start Time when End Time is reached.
The Reset Time toggle resets Time to the value of Start Time.
The Direction radio buttons allow the user to specify forward or backward streamlines. Forward streamlines start from the specified starting points and travel to the maximum velocity location. Backward streamlines travel from the specified starting points to the minimum or zero velocity location.
The Scaling Options radio buttons establishes how glyphs are sized based on the data values.
Vector Magnitude sizes the glyphs proportional to the velocity at each node.
Constant Size makes all glyphs the same size.
Log10(Magnitude) scales by the log of the velocity. When velocities span several orders of magnitude working in log space is useful. When selected, an additional parameter is visible:
Magnitude for Zero Size defines the lower clamping velocity that will correspond to a ZERO (0.0) size glyph regardless of "Glyph Scale".
The Advection Time slider and type-in allow you to control the particle animation and also display the progress when Run is selected. The time runs from Start Time to End Time during running of advector.
The Advection Time Step type-in allows you to set the duration of each animation step.
The Glyph Scale slider adjusts the sizes of the glyphs. Default range is 0.0 to 100.00, but the type-in box allow for increasing the range to any value. The default scale of 1.00 is approximately 1/100th the x,y extents of the model.
The End percentile slider allows you to control the automatic scaling of glyphs based on the nth percentile value (versus the maximum 100th%). This addresses datasets where there are only a few nodes with extremely high values (like wells).
The Map Component radio buttons allow the user to color by Velocity, Time or Distance.
The Min Magnitude and Max Magnitude type-ins display the min/max velocities represented in the input field. Changing these values allows the user to reset the min-max values for coloring purposes. NOTE: once you change these values they will not automatically update.
The Z Scale type-in reflects the value of the z exaggeration port.
The Segment per Cell slider is used to set the number of integration steps to be used in each cell (i.e., the number of divisions of the cells) to calculate the streamline. The default is one and the range is 1 to 16.
The Max Segments Total slider is used to set the maximum allowable number of streamline segments that will be completed for each streamline. If the number of segments along a streamline exceeds the max number, the streamline is terminated at the end of the last (max) segment. The default is 15 and the range is 1 to 1000.
The Order slider is used to set the order of the integration. Higher order integration is more accurate, but executes much slower. The default is one and the range is 1 to 4.
The Min Velocity slider and type-in is used to specify the minimum velocity that will be considered in the integration. If the magnitude of the velocity field in a region is less than this minimum value, streamlines will end in that region (or will not be produced if the gradient at a starting point is less than the min). Setting this to a lower value will produce longer streamlines (and typically more). Higher values tend to produce less streamlines and shorter streamlines. If streamlines are not visible on the data set, setting this to a lower value may produce streamlines. The default value is 0.000001.
The Extinction Angle slider is used to specify the maximum allowable angle between successive line segments before integration (streamline generation) should be terminated. The default value is 130 degrees.
The Animation Steps slider controls the incrementation of the glyph stops between the Start Time and the time along the original streamline continuum for each advection step. For example, if the End Time is 10000 and the Animation Steps slider is 10 then there will be ten steps (frames) when the animation is run. The Animation Time Step Type-in box will reflect the time increment based on the slider choice. For the above example (10 steps) the type-in would read 1000.
The Release Cycles slider determines the number of times the particle glyphs will be sent from their release points. This could be thought of as the number of pulses of particle releases. For example, if the End Time is 10000, then a pulse of particles is released at the Start Time and again at 5000.
The End Time slider and type-in reflects the time value along the original streamline at which to halt advection of all particles. The default is 1000.0, but the type-in box allows for increasing the range to any value. Typically with groundwater flow problems (very low velocities) this number needs to be very large to achieve ample travel distance of particles.
Note that adjustments to either the End Time, Animation Steps, or Animation Time Steps will directly affect one or both of the remaining parameters. For example, adjusting the Animation Time Steps in the above example from 1000 to 2000 would increase the End Time from 10000 to 20000.
The Start Time slider reflects the time value along the original streamline continuum at which to start advection. The default is 0.0.
Related Modules
->glyph
© 1994-2018 ctech.com