Fig. 8.2 Structure of Mass Damper System (unit： mm)
Furthermore, theoretical calculation method on the characteristics of combined oscillation of barge and sling frame at sea is deduced. The following matters were made clear. The active damper installed on sling frame is able to reduce the right and left amplitude of sling frame and shackle to about 1/2 〜 1/3. This system is able to use effectively control logic for feedforward mode to counter oscillation with detecting oscillation on the edge of the jib. As a result of water tank tests using crane barge model, it was confirmed that experimental values agreed well with theoretical results, and active damper took the control effect being fit for the aim.
In the tests using real crane barge of Shira-Shima Petroleum Depository, right and left amplitude of sling frame generated about the maximum ±0.5 m at sea. But putting the new damper system in operation, the amplitude decreased to about 1/2 〜 1/3 as the result of the model experiment. It was confirmed that this system had damping effect attaining the goal and was very useful.
8.2 Development of Vibration Control System on Container Crane Girder2)
Mitsubishi Heavy Industries, Ltd. has developed the vibration control system on container crane girder. The outline of container crane is shown in Fig. 8.3. This system reduces horizontal vibration of girder produced with trolley movement by controlling acceleration of its trolley. The feature of this system is simultaneous control of vibration of girder and containers. To attempt this, optimum control theory has been applied.
Fig. 8.3 Outline of Container Crane
By numerical simulations and experiments, it was made clear that vibration control of girder had no influence on antisway control of containers. In this developed system, the maximum amplitude of girder vibration has been decreased to half, vibration does not remain after stopping trolley. The damping constant 0.1 has been achieved from 0.0087 for girder vibration produced at inching motion (this motion means moving the trolley a little to fit a certain position). Therefore, it will be expected that this system will reduce fatigue of structure of the crane affected by girder vibration, disagreeable impression to the operators and so on.
References
1) Ishikawajima-Harima Engineering Review, vol. 37 No. 5 (1997) pp. 349
2) Mitsubishi Juko Giho, Vol. 34 No. 1 (1997.1) pp. 50
[Nobukazu SHIMADA]
