舶用シーチェスト構造の励振力に関する実験

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A box-shaped cavity open to the surface of a solid body at times generates the acoustic resonance or structural oscillation when a fluid flows uniformly and at high speed over and past the opening. Recently there have been episodes of sea-chests in some of high-speed ships generating heavy structural oscillations, to prompt many researches to the exploration of exciting force that causes such oscillations. It is well known that the oscillations are excited by vortices produced in way of the sea-chest's opening. Just what characteristics the exciting force has, however, still remains unknown. To identify the characteristics of the exciting force, the authors carried out a series of exploratory tests by exposing models of the sea-chest to air flows in a Gottingen wind tunnel. The sea-chest models were each fitted with a circular oscillatory diaphragm in one side wall. First, frequencies and amplitudes of pressure fluctuations caused by vortices in way of the sea-chest's opening were measured. Then, the sea-chest's oscillatory diaphragm was excited into oscillation at a constant amplitude by means of vibration exciter, and frequencies and amplitudes of pressure fluctuations thereby produced were measured together with the phase difference between the pressure fluctuation and diaphragm oscillation. The wind tunnel test results revealed that the principal Strouhal number was about 0.6 and that its 2nd, 3rd and 4th components would also exist at the same time. Also, the measurements taken while the oscillatory diaphragm was in the forced vibration revealed the presence of intermittent self-exciting force between dimensionless frequencies of 0.4 and 1.7. The region of these dimensionless frequencies involving such an intermittent self-exciting force was found to closely match that spotted in the actual ship sea-chest measurement data. The authors found that some modification to the shape of the sea-chest's opening could successfully eliminate such a self-exciting force.
社団法人日本船舶海洋工学会の論文

舶用シーチェスト構造の励振力に関する実験

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