|Title:||Analysis and design of a novel nonlinear vibration isolator and its applications|
|Advisors:||Jing, Xingjian (ME)|
Cheng, Li (ME)
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Mechanical Engineering|
|Pages:||xxviii, 177 pages : illustrations ; 30 cm|
|Abstract:||Vibration is a common physical phenomenon in various engineering systems, which would induce a lot of trouble problems to human beings, precise instruments and civil structures, such as fatigue, discomfort and noise. More and more researches are focusing on structure improvement or passive/semi-active/active control strategies for vibration systems to reduce undesirable responses effectively. In practice, effective and low-cost structures or methods are increasingly needed for better vibration isolation performance in various working environments. In this study, a new isolation platform utilizing n-layer truss structure is investigated to explore the novel design of passive/semi-active/active vibration control/isolation systems and to exploit its potential nonlinear benefits in vibration suppression. Due to the specially designed Scissor-Like Structure (SLS), the equivalent damping and stiffness properties of the system can be adjusted by changing structural parameters and the dynamic response can thus be designed to achieve an excellent performance including satisfying loading capacity, excellent equilibrium stability and high-static-low-dynamic-stiffness (HSLD-stiffness) isolation effect. This work establishes the mathematical model containing equivalent stiffness and damping properties of the nonlinear dynamic system. Theoretical analysis demonstrates the variation of the adjustable structural nonlinearity for different structure parameters and the effect on the isolation performance under different vibration situations. Simulation results with the software ADAMS are conducted which validate the theoretical analysis results and the advantages of the excellent isolation performance are shown in comparison. According to the results of software simulations, a prototype of the SLS isolation platform for vertical direction is manufactured and testing results clearly validate that the excellent isolation and adjustable nonlinear stiffness and damping properties can be realized. The Scissor-Like Structure (SLS) platform is reformed as a two-direction vibration isolation platform by relaxing horizontal motion. Different from existing vibration isolators, an anti-resonant frequency band occurs with this novel isolation platform where the response of the platform is very small. Good isolation performance can be achieved for different base excitations. Also, utilizing the SLSs in existing Quasi-Zero-Stiffness (QZS) systems can realize three-direction zero-stiffness properties. The natural frequencies in three-directions can be adjusted (close) to zero simultaneously while the QZS isolator using SLSs has much better static and dynamic stability than existing QZS isolators using pre-deformation springs in the literature. This scissor-like truss structure has its advantages for vibration suppression and it can potentially be employed in different engineering practices for much better vibration isolation and control for multi-direction vibration isolation.|
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