Studies of the Phenomena of Waving Plants (“HONAMI”) Caused by Wind

Abstract

Phenomena of waving plants and vibration of individual plant are regarded to be both caused by behaviors of turbulons contained in the surface wind just at the plants height. Turbulons are divided into two classes of the coupling frictictional ones and the larger ones. The former is further subdivided into the predominant corresponding to the earlier mixing length concept, the intermediate to which the well known second similarity hypothesis of turbulence is applicable and the smallest to which the first similarity hypothesis is applicable.The predominant turbulon is fed energy from the shearing mean wind field and simultaneously provides the same amount of energy to the intermediate, and the energy distribution among the intermediate turbulons is represented by the so-called -5/3 power law of the turbulon energy spectra.The Lagrangian description of turbulon spectrum is applied to the waving plants phenomena, in which the progressing plants waving is compared to the non-lift balloons floating over the plants, and the Lagrangian spectrum of turbulence is presented asF(n/n0)=2/π1/1+(n+n0)2, where n denotes the life-frequency of turbulon and n0 does approximately that of the predominant turbulon and/or waving plants. The life-time of the predominant waving plants over rice fields is estimated to decrease with increasing wind velocity and to attain a constant value of about 1.5sec at and beyond the critical wind velocity (over ca. 5.5m/sec at 2m height).The vibration of individual plants is regarded to be due to the successive passage of turbulons in the surface wind. Since under a condition of wind velocity below the critical the fluctuations in displacement (or the amplitude of plant vibration) is represented in terms of the wind force or wind pressure fluctuations, the spectral function of wind pressure fluctuations is suggested to be applicable to the plants vibration as follows:F(N/N0)=20/9(N/N0)3/{1+(N/N0)2}8/6, where N0 corresponds approximately to the passage-frequency of the predominant turbulon.The plants vibration is divided also into the predominant, the intermediate and the smallest vibration. The smallest vibration is considered to be caused by turbulons of the passage-time just same as the period of natural vibration of plants. At and beyond the critical wind velocity, periods of the predominant and of the smallest vibration coincide with each other and the above spectral function cannot be applied, but the line spectrum of vibration is expected to predominate at the period of natural vibration of plants.No practical observations have yet been available to be compared to the theoretical results.