http://hdl.handle.net/10397/203 Search the Channel search http://repository.lib.polyu.edu.hk/jspui/simple-search http://hdl.handle.net/10397/5254 Title: Minimization of impulse response using hybrid dynamic vibration absorber<br/><br/>Authors: Cheung, Yanlung; Wong, W. O.; Cheng, L.<br/><br/>Abstract: An active-passive dynamic vibration absorber with acceleration feedback is proposed to minimize the impulse response of a single degree-of-freedom (SDOF) system. It has been proved that the proposed hybrid vibration absorber provides better suppression of the impulse response of a single degree-of-freedom system than the traditional passive vibration absorber. The design parameters are the feedback gain, the tuning frequency ratio, the damping ratio and the mass ratio of the absorber. The effects of these parameters on the vibration absorption of the primary structure are analysed based on the analytical model. Design parameters of both passive and active elements of the HVA are optimized for minimizing the impulse response of the primary system. The proposed control system requires only one feedback signal which can be obtained directly using an accelerometer attached onto the primary mass. The control system may be implemented using an analogue circuit connecting an accelerometer, a power amplifier and an inertial actuator mounted onto the primary system. The control system of the proposed hybrid vibration absorber is much simpler than most of the control systems used on active control of vibration absorber found in the relevant literature. Thu, 01 Dec 2011 00:00:00 GMT http://hdl.handle.net/10397/5253 Title: Modal power flow analysis of a damaged composite plate<br/><br/>Authors: Wong, W. O.; Cheung, Y. L.; Cheng, L.<br/><br/>Abstract: Variation of the modal reactive power distribution of a damaged composite plate is mode led and analyzed both analytically and numerically. Large variation of local reactive power flow in or around the damage region of a plate under resonant vibration is related to the change of strain and kinetic energies in the damage region. Feasibility of damage identification based on the detection of this local variation of modal reactive power flow in a structure is studied. Compared with the damage identification techniques based on the determination of the active power flow in a damaged plate, the proposed method only requires data of a vibration mode shape of the structure and it is easier to apply in practice. Modal power flow of an orthotropic plate with a region of reduced stiffness in the plate is analyzed. Numerical tests show that the proposed method is effective for detection of the damage and the modal power flow is more sensitive 10 the change of plate stiffness than the strain mode shape in the test case. Thu, 01 Dec 2011 00:00:00 GMT http://hdl.handle.net/10397/1828 Title: Robot-assisted wrist training for chronic stroke : a comparison between electromyography (EMG) driven robot and passive motion<br/><br/>Authors: Hu, Xiaoling; Tong, Kai-yu Raymond; Song, Rong; Zheng, X. J.; Lui, Ka-him; Ng, Sheung-mei Shamay; Au-Yeung, Suk-yin Stephanie; Leung, Woon-fong Wallace<br/><br/>Abstract: The motor recovery procedure during robot-assisted wrist rehabilitation for persons after stroke has not been well studied previously. In this work, we carried out acomparative study on the training effects on 10 hemiplegic persons with chronic stroke between a wrist treatment assisted by an electromyography (EMG)-driven robotic system(interactive treatment, n=5, EMG group) and a wrist treatment assisted by a clinical robot system with continuous passive motion (n=5, passive group). Significant decreases (P<0.05) in muscle spasticity were observed at the wrist joint in both the EMG and passive groups; and reduced muscle spasticity at the elbow joint were also obtained in the EMG group (P<0.05). These spasticity decreases were associated with the reduction of EMG activation levels during the training. The EMG-driven robot-assisted training also improved the muscle coordination capability of the persons after stroke. Tue, 01 Jan 2008 00:00:00 GMT http://hdl.handle.net/10397/338 Title: Enhanced multiplexing capacity of low-coherence reflectometric sensors based on a loop topology<br/><br/>Authors: Yuan, Libo; Jin, Wei; Zhou, Limin; Hoo, Y. L.; Demokan, Suleyman<br/><br/>Abstract: A novel scheme for enhancing the multiplexing capacity of low-coherence reflectometric sensors is demonstrated. The scheme is based on connecting the sensing elements in serial in a loop configuration, allowing each of the sensors within the array being interrogated twice from opposite directions. The bi-directional interrogation doubles the multiplexing capacity while maintains the signal to noise ratio. The double interrogation scheme would allow the normal operation of the sensor array even when one end of the transmission fiber were broken, improving the reliability of the sensing system for large-scale structural monitoring. Tue, 01 Jan 2002 00:00:00 GMT