To investigate dependencies in the magnitudes of a waving ear on mean wind speed, field observations were carried out over a barley filed in the ripe stage. Fluctuating displacements derived from HONAMI were measured using a newly designed 2-dimension strain sensor. The velocity fields were measured by a sonic anemometer-thermometer.
A coherently waving phenomena of HONAMI appeared and was evaluated by the fluctuating displacements of a single ear of the stand. Dividing a time series of the fluctuating displacement into five typical bands of frequency by use of an analog filter, it was shown that there are two dominants of 0.5-Hz and below 0.1-Hz in the original. The bands were from a natural frequency and a gustness of wind respectively. Comparing the amplitudes, the natural frequency contributed remakably to the original fluctuation of HONAMI.
Magnitudes of an instantaneous ear-displacement, which represents 0.5-0.6-Hz of frequency, varied with increments of the mean wind speed within a range of 2.6-4.4-m/s. Except for this range, the dependency between the amplitude and the wind speed was not clear.
Instantaneous changes in lateral displacements and velocity fluctuations were quite similar except for the component of higher frequencies. Under such circumstances, an ear-displacement will appear to infulence strongly the aero-dynamical properties of the canopy boundary layer.
The force per unit length acts on a waving ear generates by a relative velocity of u-dx/dt. Here, u is the mean wind speed, and dx is the displacement of an ear from its mean position during dt. Using this concept, drug force was evaluated under two criteria for leeward ear-moving and ear-standing. Under the windy conditions, the force loaded on an waving ear reduced by 10% against the standing criterion with dx=0. On the other hand, the reduction rate became small down to 4% of the standing criterion under the condition of weak wind.
