SUMMARYA recently developed hybrid mass damper (HMD) system and its application to a 36-storey high-rise building with a bi-axial eccentricity, located in Tokyo, are presented. This new HMD system utilizes a gear-type pendulum and a linear actuator. Here, the gear-type pendulum is employed to make the natural period of the auxiliary mass comparatively long while minimizing the height of the device, and the linear actuator, on the other hand, ensures smooth and noiseless operation of the system. There are several special features in the control method as well; two HMD systems are applied to control the transverse-torsional coupled vibration of the building, and also variable gain feedback (VGF) control technique has been developed to fully utilize the capacity of the HMD system from weaker to stronger external excitations.Free vibration tests as well as control of wind vibrations of the building induced by the Typhoon 9810 in 1998 were used to verify the performance of the control system. It was found that the maximum and the root-mean-square acceleration responses of the building were reduced to 63 per cent and 47 per cent of the corresponding uncontrolled accelerations. Finally, the control performance of the system was conÿrmed.
Fluidelastic instability (FEI) remains the most important vibration mechanism in steam generators. Fluidelastic instability of an array of tubes thought to be mainly occurred in the cross-flow direction. In the present day, some researchers reported possibility of occurrence of fluidelastic instability in the in-flow direction. However, the phenomenon of the in-plane FEI has not been well recognized compared to the transverse FEI.
In this study, air flow tests using cantilevered straight cylinder array of tubes in triangular configuration were conducted. It is confirmed that the in-flow FEI could be occurred and the critical flow velocity in the in-flow direction is larger than that of in the cross flow direction. Furthermore, the relationship between P/D of an array of tubes and the critical flow velocity in the in-flow direction was also investigated.
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