A particle/drogue coverage is used for visualization post-processing. The feature points and arc nodes/vertices define the seed locations for generating an animation of particles flowing through a hydrodynamic current. The particles are simulated as massless objects or "drogues" floating in the flow field. SMS computes the paths these particles would follow when driven by the currents of the flow field using numerical integration.
This coverage must be defined before selecting the drogue option when setting up a film loop.
When displaying the resulting animation, the particles may be displayed in a color based on the current velocity of the particle or the distance the particle has traveled. ti is also possible to specify the length of the tail behind the particle (in units of time). Therefore, a longer particle tail indicates a generally faster moving particle.
Drogue plot animations are different from flow trace animations in that the distances traveled by each drogue represents the actual physical speed of the flow field.
- Residence time calculations. One of the most useful applications of drogue plots is to approximate residence time of a basin or other subregion of a hydrodynamic domain. In order to approximate this:
- Distribute a fairly large number of drogue seed points inside the basin (or sub domain) of interest).
- Generate a drogue plot film loop of the time range of interest. (Currently the hydrodynamic solution must include enough time steps to span the residence time in question. If this is not the case, additional time steps should be added to the data set either by rerunning the simulation for a longer time period or duplicating time steps).
- Review the number of particles still in the basin (or subdomain) at various time intervals. The percentage of particles, and their position give an indication of overall concentration and local concentration in the basin.
- General visualization of flow field.
- “Gas Flow Visualization for Combustion Analysis”, Energy and Fuels, Vol. 7, No. 6, 1993, pp. 891-896. Zundel, A.K., Saito, T., Owen, S.J., Sederberg, T.W., Christiansen, H.N. 
SMS – Surface-water Modeling System
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