How to Set Up Unsteady Flow

  1. Load a Metadata file (*.vdf file) into VAPOR.
  2. In the Basic Flow Settings:
    1. Specify "Unsteady" as the flow type
    2. Specify three variables for the unsteady (e.g. velocity) field
    3. Specify the "Unsteady Integration Direction" as either "Forward" or "Backward".  Seeds will be advected in the specified direction by integrating the unsteady field either forwards or backwards in time.
    4. Specify the "Unsteady field scale factor".  (Normally with WRF datasets this factor is 1.) This depends on the space and time scales that were used when the data was generated.  It is the product: (spatial-correction-factor)*(time-correction-factor), where:
      • (time-correction-factor) is the number of simulation time units (e.g. seconds) per vapor (.vdf) time step. If the user times are correctly specified in the metadata (vdf file) then this factor should be 1.
      • (spatial-correction-factor) is the ratio of the full domain size in VAPOR (see the VAPOR region panel) to the actual user domain extents that were used in the simulation. If the data extents in the metadata (vdf file) are correctly specified to the actual user coordinates, then this factor should be 1.
  3. Set up flow seeding as follows:
    1. Decide whether to use a random rake, nonrandom rake, or a list of seeds, as the starting seeds for the field lines to be advected.
    2. Under the "Unsteady Flow Time Settings", specify the time steps when the seed points are to be injected into the flow, using the three values labeled "Seed time start, end, increment".  These determine an increasing sequence of integers evenly spaced in time, of the form: a, a+b, a+2b,...,a+kb, where a is the "Seed Time Start", b is the "increment" and the largest injection time, a+kb, is no greater than the "Seed Time End".  If the seeds are from a seed list, and the seed time is nonnegative, then that seed is only injected at its specified time step.
    3. In the Unsteady Flow Time Settings:
      1. Set the "Unsteady samples per time step" to be the number of separate positions along a path line that will be displayed in the interval from one time step to the next.  Increase this to get a smoother path line.
      2. “Display interval min, max” determines the portion of each path that is displayed at a given time.  If T is the current time step (as specified in the Animation Panel), then the portion of the flow line from T+min to T+max will be displayed.  For example:
        •  To see the entire path line at once, make min very negative and max very positive (e.g. -1000 and +1000).
        • To see the path line evolve (grow) over time, with the unsteady integration = forward, set min to be very negative (e.g. min = -1000) and set max = 0. The animation panel can later be used to animate the path line evolution.
    4. If the unsteady field data is not available at every time step, you must specify the time steps that will be sampled, using the "Unsteady Flow Time Settings".  By default, every time step is sampled from beginning to end, using values in "Time step sample start, end, increment".  Check the optional "Use time step list" to specify an arbitrary set of time steps that will be sampled.

    Nonuniform random seed placement:
        If you are using the “Random Rake” for seed placement, the distribution of random seeds can be biased by a field magnitude using bias settings in the "Flow Seeding Settings".    As you increase the bias (above 0), the seeds are chosen at larger field magnitude values, approaching the maximum field magnitude within the rake bounds.  Bias values below zero result in seeds to be distributed with field magnitudes nearer zero.  The three variables labeled "Seed Distrib. Field" identify the vector field whose magnitude is used to determine the seed distribution.
     
    Color and opacity settings
        By default, path lines have a constant color and opacity.   Using the Color/Opacity mapping, you can make the color and opacity depend on any of the following:
    When one of these mappings is selected, be sure to specify the color (or opacity) map endpoints to include the range of values to be mapped.  Then use the color editor or the opacity editor to specify the color or opacity at specific points along that range.