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Verification fly rod, dynamic

Purpose

The purpose of the dynamic rod verification is to verify that calculated and measured rod oscillation frequencies agree.

Furthermore, that the calculated and measured decay of oscillations agree.

Method

The verification procedure for dynamic rod properties is presented below for one specific rod (serving as an example).

The dynamic properties of a fly rod are modeled using:

· The bending stiffness and mass distributions giving the frequencies with which the rod oscillates. During practical casting a fly line is retained to the rod by the guides adding to the effective mass per unit length of the rod (reducing the oscillation frequencies).

· The damping due to air drag and due to the fly line oscillating with the rod. The damping gives the rate of decay of oscillation amplitude.

The distributions for bending stiffness, outer diameter and mass density are presented below:

Note: Mass density incl. the fly line was used in the dynamic verifications below.

The verification of the bending stiffness distribution is explained in “Static verification of fly rod”. The mass distribution was determined by weighing the individual parts of the rod (and the center of mass) and fitting a distribution. The damping due to the fly line oscillating with the rod (and due to internal friction) is modeled using a relaxation time, see Theory

Verification of the dynamical fly rod properties was done as follows:

· The rod handle was fixed in a vice.

· A fly line was held to the rod by the guides.

· Oscillations in the rod were initiated by hand (lowest eigenfrequency).

· The oscillating rod was filmed, and the rod tip positions were measured as the rod tip amplitude decreased with time.

Results

The results are presented below:

Conclusions

· The calculated oscillation frequency agrees with the measured.

· The calculated rate of decay of the rod tip amplitude agrees with the measured.