Modelling the transient response of the Dines anemometer in tropical cyclone winds

The Dines, or pressure-tube, anemometer, consists essentially of a large-diameter pitot tube mounted on a vane, connected to a unique manometer. The manometer consists of an open-bottomed tapered float in a water tank, with the tube from the pitot head feeding into the air space in the float. As the wind speed rises, the pressure inside the float increases and the float rises, moving the recording pen. The Dines anemometer is now obsolete in Australia, having been largely replaced by cup anemometers. Nevertheless, historical records from the instrument are important to understanding the wind risk climate, not least since the two strongest gusts ever recorded in Australia were on Dines instruments (Cyclone Tracy in 1974 and Cyclone Vance in 1999).

The behaviour of cup anemometers in turbulence has been extensively studied, but comparatively little similar work has been done on the Dines, and none recently. This poster will present results from a newly developed physical model of the transient response of the Dines anemometer. Two previously observed resonances are confirmed, and their physical mechanism described. A third low-frequency oscillation, not previously known, is found in the model. Observations that may indicate this oscillation are presented. In addition, it is shown that the instrument may overspeed, albeit for different reasons to cup anemometers.

Further work, in collaboration with the Cyclone Testing Stations at James Cook University and Geosciences Australia, will involve verification and calibration of the physical model by experiments on a remnant functioning Dines instrument, and reinterpretation of the historic gust record.