Page 124 - Dynamic Loading and Design of Structures

Page 101

Figure 3.7 Interaction of vortex shedding with galloping excitation.

For an ideal aerofoil there is an analytic solution, conveniently written in complex number
notation (Fung, 1955). The quasi-static solution is a force equivalent to a lift coefficient
(taking the deck width B as the reference dimension) which acts at the quarter-
chord point (B/4 from the upwind edge). For this purpose the apparent instantaneous angle of
incidence (α a) is based on the ratio of the net vertical velocity at the three-quarters-chord point
to the free stream velocity. All forces in harmonic motion (components in phase and in
quadrature of lift and torque associated with both vertical and torsional motions) are then