Fig. 5 Three-dimensional figure of radiant sound (10 hours)
Fig. 6 Three-dimensional figure of vibration (10 hours)
On the other hand, regarding the vibration, the pattern to indicate the slide of the piston is clearly shown, and it may be said that the vibration is the source of information suitable for understanding the slide condition of the piston ring, etc. Accordingly, it is decided to examine the information on the vibration among the two shown above in this study.
The change in the spectrum of the radiant sound and the vibration in a short time was shown above, and it was examined how the spectrum term changes if the running time is further increased. The below-mentioned results are those obtained during the service after the engine was mounted on the test ship. The data immediately after the engine was mounted to the data in approximately one year and 6 months layer, were used for the analysis. Here, the result after 190 hours, 2300 hours, and 6000 hours are shown in Figs. 7, 8 and 9. As mentioned above, these are the three-dimensional figures of the vibration. In the result of Fig. 7, the vibration by the slide is observed at Points a, b, and c similar to the results of Figs. 4 and 6. However, the condition was slightly changed in Figs. 8 and 9. For example, a high level pattern generated in the range of 70-160° and 250-290° in crank angle of in Fig. 7, (a band-like pattern of not less than 90dB generated over the whole frequency band) is not present as the band-like pattern in Fig. 8 where 2300 hours are elapsed. Besides, the level is not more than 60dB in the higher frequency band (over 15 kHz), which is not indicated by the pattern of the figure. This trend is intensified with the time, and in Fig. 9 where 6000 hours are elapsed, the pattern of not more than 60dB (a white pattern) is spread close to 10kHz in a part of crank angles in Fig. 9. The bow-shaped pattern by the slide shows the trend that the level is dropped as the time is elapsed through it is slight. For example, in Fig. 7, the bow-shaped patterns distributed over higher frequency bands (of not less than 15kHz) are continuous at the level of approximately 100dB or over. However, in Fig. 9, the bow-shaped pattern is reduced in size, and only a part thereof is shown as dots.
As mentioned above, it is observed that the vibration level is changed by and by as the time is elapsed. However, the data is for the normal running condition of the engine, and does not indicate that the engine is in the abnormal condition. In other words, even in the normal running condition, the secular change always works on the engine, and the degree of indication of the secular change is shown in Figs. 7 to 9. Though the factor is natural, the running time of the engine surely affects each member of the engine, and the effect of the abrasion, etc., is indicated more clearly. For the study aiming at the construction of the abnormality monitoring system using the vibration, it is one of the important objects to elucidate the regularity of the vibration which is changed with the running time of the engine.
