The Analysis Setup Tab shown below contains the following analysis control parameters and options:
- Integration Time Step: This is one of the more difficult parameters to determine. The rule of thumb is
that if you get consistent answers by dividing the time step in two, then the larger time step is appropriate for use.
The only caution here is that if you get a divergent solution (the projectile yaw rate and yaw increase dramatically
in the bore), the time step is likely too large. You can also get into trouble if the time step is too small; aside
from the solution taking an inordinate amount of time, the solution may diverge also.
I recommend starting with a time step of 0.0001 milli-seconds.
- Print Step Option, Number of Print Steps, Start/Stop: These options affect the output display.
There are a maximum of 150 output print steps. These steps are divided in equal increments of time or distance between
the selected start and stop times or distances, depending upon your selection. The Print Stop Distance/Time are
defaulted to the maximum values in the forcing function.
- Analysis Type: This can be either Single or Statistical. I recommend that you start each project with a
single analysis. This will give you confidence that the model is working correctly and the answers are useful. The
single analysis also gives you output relative to the stresses in the projectile – useful during design. The Statistical
analysis is very useful in determining the expected dispersion from a projectile/tube.
- Number of Iterations: This only applies to a Statistical analysis. It is the number of iterations or the
Statistical sample size upon which the results will be determined. The initial conditions are randomized creating different
initial orientations. For many cases, this number could be as small as 50 or as large as 500. The best approach is to start
with 50 iterations and then examine the Projectile Cumulative Average Exit Resultant plots under the Plotted Results Tab. The
proper amount of iterations is achieved when the cumulative average line has "leveled-out". Note that each parameter
(yaw, yaw rate, cross vel, cross accel) may
"level-out" at different numbers of iterations; you want all of them to "level-out".
- Distance to Obturator: This is the distance from the tube coordinate system origin to the obturator at the
start of the forcing function.
- Muzzle Velocity and Spin: The muzzle velocity for this projectile is 1700 m/s and the spin at the muzzle is zero.
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