Optimization of mounting positions and supporting structures of building services equipment for vibration control

Abstract

Building services equipment such as chillers, pumps, air compressors, generators, and electric motors are installed in modern buildings. These kinds of vibratory equipment produce low frequency noise and vibration that is a serious environmental problem because of its negative effect on human health, well-being, and living quality. Therefore, to improve acoustical environment, a lot of efforts are required to reduce noise and vibration of building services equipment. It is known that mounting positions of building services equipment and geometrical parameters of supporting structures have influence on the amount of structure-borne sound power transmitted to the supporting structures and as a result influence the levels of low frequency noise and vibration. This thesis addressed the problem of optimizing mounting positions of building services equipment and geometrical parameters of supporting structures. The aims are therefore to develop optimization strategies for mounting positions and supporting structures; to propose active and passive control systems for the suppression of structure-borne sound power transmission and to obtain a better understanding of structure-borne sound power transmission of vibratory equipment. Firstly, an investigation of the optimum mounting positions for a vibratory building services equipment on a floor is presented. The criteria for selecting the optimum mounting positions are the minimum structure-borne sound power transmission and the minimum rotational velocity of the vibratory equipment. The results indicate that a vibratory equipment should be symmetrically installed on diagonal lines of the floor. A study of the optimum mounting positions of two coherent motors on a floor is also presented. Secondly, a study of the structure-borne sound power transmission from two coherent vibratory equipment to a supporting structure is presented. A design framework of supporting structure optimization strategy that targeted on minimizing the structure-borne sound power transmission from two coherent vibratory equipment to a supporting structure is proposed. A steel-made periodical supporting structure with two coherent fans installed are investigated. Experiments are conducted to obtain the source characteristics (source mobility and free velocity) of the two coherent fans. Parametric finite element analysis models and a genetic algorithm are utilized in the optimization strategy. The results show that the proposed design framework is sufficiently capable of optimizing a supporting structure. Thirdly, a theoretical study of an inertial actuator connected to an accelerometer by a local feedback loop for vibration control on a two-stage vibration isolation system with time-varying excitation sources is presented. The results reveal that the optimum mounting positions of the inertial actuator varied with frequencies. Therefore, a control system based on monitoring rotational frequencies of the excitations, real-time measurement of a cost function, and automatically searching the optimum mounting position of the inertial actuator is proposed. A linear motor is proposed to move the mounting position of the inertial actuator according to the optimization result solved by the control system. Finally, the band gap properties of periodic structures on the vibration control of a two-stage vibration isolation system are investigated by using the transfer matrix method. To maximize the power transmissibility of the two-stage vibration isolation system, a geometrical parameters optimization strategy by using the genetic algorithm is proposed. The fitness function is the power flow of the flexible floor in the two-stage vibration isolation system. The numerical results demonstrate that stop band regions of the optimum periodic structure contained all the harmonic frequencies of the force excitation. The proposed optimization approach has potential use for the development of vibration isolation systems for vibratory equipment.