Fig. 11 Diesel Propulsion Plant
Fig. 12 Measured waveform of vibratory acceleration
It is noted that the extraordinary vibration described here is the phenomenon which generally occurs in the shafting having gear trains with light gear load, and consideration is required in designing the shafting with reduction gear trains.
6. CONCLUSION
In such system as has a reduction gear supported by the plane bearing which connects to the torsional vibratory shafting, there often appears unstable phenomena and extraordinary vibration.
In order to clarify the conditions and the mechanism of this extraordinary vibration and also to show the conditions to avoid it in designing the gearing system, the simplified torsional vibration model considering self-exciting vibration of the bearing oil film is proposed. By this simplified model, unstable conditions and factors are clearly proved with the characteristic equations, the computer simulation and also the analysis based on the assumption of the steady oil whirl.
The unstable area of the shafting with reduction gear expands when the self-exciting vibration of the bearing couples with the torsional vibration. Further, the unstable phenomena appear in such low rpm range as is inexplicable by the theory of the oil whirl phenomena. This unstable area is closely related to the torsional vibration of the system and mainly dominated by the natural frequency of the said vibration.
The severe fluctuation is reproduced only when both gear backlash and oil film is taken into consideration around the boundary line between the stable and unstable area. This is caused by such phenomena that the stable area is not fixed but varies with the spring constant depending on the amplitude of the vibration in such non-linear vibration with backlash.
The simple method of the assumption of the steady oil whirl gives the approximate criterion of unstable boundary line, which meets well the unstable area obtained by the characteristic equation. This give the designer an indication in designing the reduction gear that pinion rpm should be below 2 times of the natural circular frequency of the torsional vibration of the shafting.
The extraordinary vibration is the phenomenon which generally occurs in the shafting having gear trains including diesel propulsion plant with light gear load, and consideration is required in designing the shafting with reduction gear trains.
References
[1] M. Matsuda, etc. "Non-linear Torsional Vibration Analysis for Geared slow Speed Diesel Propulsion Shafting with Fixed Pitch Propeller" Bulletin of the M. E. S. J., vol. 19, No. 8, (1984), p597
[2] M Matsuda, "A Study of Chattering Problems on a Gearing System in Marine Practice", Chinese SNAME, (1987), p1
[3] Tsuda "A Reasoning about Reduction Gear Noise of a Main Propulsion Turbine Plant", Bulletin of the M.E.S.J., vol. 18, No. 12. (1983), 989
[4] M. Matsuda "Studies on Non-linear Torsional Vibration of Marine Steam Turbine Propulsion Shafting", Bulletin of the M. E. S. J., vol.26, No. 1, (1998), p32
