Active Vibration Control of Frame Smart Structures by New Approach

In this paper, new approach is presented for controlling the structural vibrations. In spite of previous methods, which are used mathematical concepts, the proposed active control technique is based on structural dynamics theories in which multi actuators and sensors are utilized. Each actuator force is modeled as an equivalent viscous damper so that several lower vibration modes are damped critically. This subject is achieved by simple mathematical formulation. First, the proposed multi actuators control method is formulated based on structural dynamics theories. Then the sensors and actuator's locations are determined by simple algorithm. For numerical verification of the proposed technique, the displacement's variations of a five-story shear building, excited by seismic load (Elcentro Earthquake), are evaluated. This study shows that the proposed method has suitable efficiency for reducing structural vibrations. According to the results, the maximum shift in the structure of the upper floors 5 degrees of freedom are reduced by 70%.Smart structures are systems that can teach and protect themselves against the external excitation such as wind and earthquake. Analyzing and designing of smart structures is based on set of sciences including materials science, applied mechanics, electronics, bio-mechanics and structural dynamics. In this procedure, maintaining the structural performance against the external hazards is very important issue called control system. Many studies have been performed in the field of structural control. These methods can be categorized into three groups i.e. passive, semi-active and active procedures (Akutagawa et al. 2004). Due to the simplicity, low cost of assembly and no need to the external power, the passive control systems are numerous.
However, the constant control feature makes these systems fail during the earthquakes.
In other words, these systems are designed to work only for a certain excitation and limited frequency bound.
The passive control system tries to remove the kinetic energy from the structure.
Because of the mentioned constraints in passive algorithms, active control is highly regarded systems to cope with the earthquake. These techniques have suitable efficiency in different excitation so that they could exactly sense and adopt the structural vibrations. To achieve this goal, each active control method is constructed based on algorithm, which verifying its efficiency and accuracy. The application of such systems began in 1989.In these systems an external power source is required so that this applied force is affected the structural equilibrium equation. This applied force may lead to instable vibrations if the active control algorithm is not suitable.
Hence, the complexity, the calculations volume, the instability risk and the uncertainty factor are some difficulties arise from active control systems.
It should be noted that, good performance of active methods depends on some parameters such as the reliable algorithm and the suitable positions for both sensors and actuators
(Guclu et al. 2008; Chen et al. 2001;Rudinger et al.2007; Hoang et al.2008).
The common active control algorithms have been listed in Table 1, followd by the main idea used in each method (Datta et al.2003).