Real Time Delay Control for Lower Frequency Waves in a Test Basin and its Verification by Short-Time Fourier Transform Technique〔含討論〕

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This paper describes a real time, delay time control method for lower frequency waves in a test basin. In doing wave tolerance experiments by irregular waves in a test basin, we have a problem : higher frequency waves can't reach a test target even when lower frequency waves approach it. Wave boards generate a number of frequency component waves simultaneously, however higher and lower frequency waves propagate separately due to the dispersion relation. A given wave spectrum must affect a test body from the beginning of a test to obtain valid test results. The authors have developed a real time control algorithm to solve this problem. The developed algorithm is based on an idea : delay time control for lower frequency waves. Irregular waves are realized by the summation of a finite number of sinusoidal waves with single frequencies to generate them. The representative frequencies of generated spectrum are known variables. Therefore the time to reach a test target for each frequency component wave can be calculated. The start time for generation of each frequency component wave is set at the time which is conversely calculated from the time to reach a test target. Consequently all frequency component waves can reach a target at the same time. The authors have obtained good experimental results of this algorithm. Moreover, using the short-time Fourier transform technique, the validity of the proposed method is verified.