3.2 Fully Dynamic.

The fully dynamic approach is different from the Quasi-static in that the deflections are no longer directly related to the load, but are such that the damping at that limit cycle deflection will absorb per cycle the energy which the wind will supply per cycle.

This state of affairs can occur for one of three reasons: the first is the result of the fluctuating nature of the wind speed, this is called "Buffeting". Only when a natural frequency of the member corresponds to high energy in the spectrum of loading might this lead to sufficient deflection to become fully-dynamic. This has therefor been considered in Section 3.1.1 as part of Quasi-Static loading, and in most of the mildly-dynamic approach in Section 3.3.

The second reason is that the particular shape generates an oscillatory flow pattern about it even in a uniform steady stream of air. These types of flow have been discussed in Section 2.1.4. Because the oscillation is wind generated, it usually occurs at a frequency which is wind speed related. It also usually occurs, in practice, in combination with buffeting.. Also in this category are those members with curved rather than sharp edged corners (see Section 2.1.3) or those which have two possible flow patterns around them (see Section 2.1.4.2). The change over might be of a switching nature (a bank of tubes in a cooler, see sections 2.1.4.2 and 3.2.8), or there might be a transition from Laminar to Turbulent flow which is wind...