Investigation of the Cavitation Caused by Vibrative Two Concentric or Eccentric Circular Cylinders

Abstract

When two concentric or eccentric circular cylinders vibrate relatively, the phenomenon of cavitation may be caused by a vibratory hydrodynamic pressure set up in a water bounded by two cylinders. The author confirmed this phenomenon using a model with full scale tail shaft diameter and reported in the previous paper.In the present paper, the author shows some results found by the experimental resarch using 3 sets of newly built testing machines. The principal contents of these results are as follows : 1) The approximate empirical formula was derived from the experimental reserch to estimate the critical cavitation frequency. The negative amplitude of vibratory hydrodynamic pressure set up in a water is shown as|hm|= [0.9+1.6 (α/δ] [1+1.9 (e/δ-α) 2] (103·a2/δ) (αω2/g) Where “ω” is the angular frequency of vibration in rad/s, “α” the amplitude of vibration in mm, “a” the radius of inner cylinder in m, “δ” the mean clearance in mm and “g” the accelerlaion of gravity in mm/s2.Using this formula, it is possible to estimate, whether or not cavitation is liable to occur.2) Relations between a vibratory hydrodynamic pressure set up in a water and the cavitation phenomenon were explained using oscillograms showing the vibratory pressure and results of stroboscopic observation with external synchronizer.3) The peculiarites of the cavitation and the erosion damage caused dy such cavitation were explained.4) Using the model test result, one method to avoid cavitation on actual ships was suggested.