抄録
The oil damper is a typical example of an all-round structural control device that can cover a wide range of vibration amplitudes from small amplitudes caused by wind disturbances to large amplitudes caused by strong earthquakes. It is well known that the mechanical characteristics of an oil damper installed in a building with a bracing frame is expressed by a Maxwell model, and the energy dissipation capacity or the control effect is limited by the stiffness of the spring element in the model. Because oil dampers can be easily converted to variable type dampers that can control the damping coefficient by solenoid valves, there have been a lot of studies on them since the 1990's. We have carefully studied what can be done by controlling the damping coefficient of the Maxwell model, and came to the conclusion that selecting the maximum or the minimum damping coefficient, or the On/Off switching algorithm, was a sufficient strategy when focusing on the energy dissipation efficiency. We also clarified that a damper controlled by the On/Off switching algorithm can dissipate twice as much vibration energy as a conventional oil damper. Based on our study, we developed a variable oil damper with the On/Off switching algorithm in 2000, and it has been installed in more than 30 high-rise buildings in the subsequent 15 years in Japan. Its excellent control performance beyond that of conventional oil dampers has been verified through vibration tests or observation records.
This paper discusses the possibility of enlarging the energy dissipation capacity of the existing On/Off switching oil damper by introducing an energy recovery system. The proposed device is equipped with an auxiliary oil tank outside of the main cylinder, and the oil flow between the cylinder and the tank can be controlled by control valves. Though conventional oil dampers, including the existing On/Off switching damper, always change all the vibration energy to heat, the proposed device recovers the vibration energy in the auxiliary tank as oil strain energy and reuses it at an optimum timing to enlarge the damper's stroke and thus improves the control efficiency. Its mechanical model is expressed as a four-element model that consists of a Maxwell and a Voigt model in series, and the damping coefficients in the model are switched to the maximum or the minimum based on the states of the control valves. The spring element of the additional Voigt model, which represents the equivalent stiffness of the oil in the auxiliary tank, plays an important role in the model. The change of the mechanical model from the Maxwell to the four-element is the key that enables us to achieve higher efficiency, which can be never realized by controlling the damping coefficient of the Maxwell model.
This paper first presents a basic configuration of the device, and shows how the energy recovery system works according to the control algorithm. Then the control efficiency is evaluated quantitatively based on the four-element model. The control effectiveness for harmonic excitations or earthquakes are examined through a theoretical approach and numerical response analyses, and it is clarified that the energy dissipation capacity or the ability of damping augmentation of the proposed device can be enlarged to four times that of the conventional oil damper for harmonic excitations, and three times for non-stationary earthquake disturbances. It is also pointed out that the control effect of the proposed device can be considered to be the same effect as that of an optimum tuned conventional oil damper with several times larger stiffness. The enhancement effect of the stiffness and tuning-free nature are typical features of the proposed algorithm.
