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Sensitivity analysis, modeling of
axial air drag
The purpose of the sensitivity analysis is to determine how the
numerical solution is affected by changes in the constants for calculation of
axial air drag.
Background
The fly line will be subject to shear stresses
in the axial or lengthwise direction as it travels through the air. What is
referred to as boundary layers form in the vicinity of the fly line. The
properties of the boundary layers determine the axial air drag. A fly line
will, in general, move at an angle in the air. The angle will influence the
boundary layer increasing the shear stresses and the drag compared to a
boundary layer developing along a line at zero angle. Here, the air drag is
calculated as a function of the Reynolds number based on experimental data. The
increase in shear stress due to the angle is accounted for approximately.
Hence, there is some uncertainty in the calculation of axial air drag.
Method
The sensitivity of the solution to changes in axial air drag is
analyzed as follows:
·
The 50ft
oh ref. cast is used as reference (drag
constants as for all calculated casts except the one below).
· A solution, denoted “50ft ax drag flyline
+50%”, is calculated with a 50% increased axial air drag as the only
change in relation to the reference cast.
Results
The two solutions are compared in the
animation below (click on image to start animation).
· Increasing the axial air drag by 50%, in relation to the
reference, has a significant impact on the simulated cast.
· It may be concluded that the calculation of axial air drag is an
uncertain aspect of the current simulation model.