SUMMARYAn algorithm to calculate direct velocity feedback gain with limited number of sensors is developed in a simple way such that a certain performance index is minimized according to QN control method. If a limited number of velocity outputs can be measured, full velocity responses of the whole structure can be interpolated based on the mode shapes. By deÿning the performance index function as a combination of the structure's velocity responses and control forces only, feedback gain can be determined according to QN control method with the external excitation being taken into account throughout the entire algorithm. Control forces are then regulated by the time-invariant feedback gain matrix. The e ective location of the active control devices for a building structure subjected to intermediate-storey excitation has been determined to be in the three oors adjacent to the vibration source. Hence for the purpose of this paper, only the optimal placement of sensors is veriÿed. It is shown in this paper that if the dynamic behaviour of the structure is well described by a mathematical model, su cient response reduction e ect can be achieved according to the new DVFC algorithm, and the degradation of control performance due to time delay can also be veriÿed.

SUMMARYIn order to investigate ways of reducing vibrations of building structures subjected to excitation acting on intermediate storey, active vibration controls are conducted with active control devices installed on di!erent #oors of the structure, and the e!ective location of control devices is also investigated. In this paper, we propose a new &Discrete-Optimizing Control Method' for vibration control. The control forces are determined analytically which makes the &discrete-index function' minimum. Through numerical simulation, the Discrete-Optimizing Control Method is proved to be an e!ective control method. The response reduction e!ects are the best when the control devices are concentrated on the adjacent three #oors of the vibration source.

SUMMARYIt has been proved in the authors' latest paper that the e!ective location of active control devices for building vibration caused by periodic excitation acting on intermediate story is the adjacent three #oors to the vibration source. However, in terms of the Discrete-Optimizing control method, the control forces are on-line calculated step-by-step and time-delay must exist. The degradation of control e!ect caused by time-delay can not be avoided. In this paper, QN control method is proposed in order to resolve this practical problem.Since the external excitations which the building structure would experience are supposed to be periodic to some degree, Quasi-Newton method is applied into the close-loop Linear}Quadratic optimal control method and the new control method is called the &QN control method'. In this new control method, instead of solving the Riccati equation, the feedback gain matrix is determined by optimizing the quadratic performance index of the structure with the Quasi-Newton method, one of the most commonly used minimization of functions. The new control law can easily be implemented for time-delay problems, the degradation can be greatly improved with compensated feedback gain matrix. As a result, the QN control method is proved to be an e$cient method to determine the feedback gain matrix.

An automatic control system of the electrode's position during whole process of steel-making based on real-time control is presented in this paper, which is adapted for LF steel-making stove. The voltage between electrode and molten steel is measured accurately, which is used to calculate the accurate distance of the electrode and molten steel, during whole process of steel-making. The original position is memorized when the anodes descend to the molten steel, and the electrodes move upwards suitably when the cathode begin to make electric arc that achieves the best control distance. The whole process of steel-making would complete and the molten steel would purify. The problem of carburet of molten steel would guarantee the quality of steel production by using the control system.