Study On Dynamic Properties Of SALiM Isolator

In the fields of vibration isolation for heavy equipment engineers are not satisfied with the existing isolation technologies which leaves much to be desired, such as small static load capability, lack of thorough understanding of working mechanism, difficult maintenance process, gas leakage, unstable performance and so on. This work is funded by the"Study on Dynamic Mechanism of Hybrid Liquid Medium"of Natural Science Foundation of China (grant number: 10772080) and the "Study of a High Performance Isolator" (Approval No.: BCXJ06-05) of Nanjing University of Aeronautics and Astronautics, Ph.D. Innovation Fund project. This paper proposes a new type of nonlinear isolator which is based on Solid And Liquid Mixture (SALiM). The SALiM mixture consists of incompressible liquid and a number of compressible elastic solid elements. When under shock or vibration, the incompressible liquid can instantly pass the pressure on to all the solid elements in the container of the isolator, which causes all the solid elements compressed and deformed simultaneously. As a result it could greatly absorb and dissipate the energy of vibrations and shocks. According to information retrieval, this subject is a completely new research.Based on the analyses of the functions and basic requirements of the various components of SALiM and structures of solid elements, this work chooses the hollow rubber spheres as solid elements and uses nonlinear continuum mechanics theory to analyze the relationship between force and deformation of elements undergo finite deformation, the nonlinear stiffness and the dynamic model of the system are studied. In the aspect of experiment modeling,the model of nonlinear elastic restoring force and Dahl model which is used to describe friction damping are combined to build the identification model, the model can reflect asymmetric characteristic of system response. The theoretical dynamic model of SALiM system is used to solve the main resonance frequency response equation by multi-scale method. The main resonance stability is analyzed and the conditions of the vibration isolation system at 1/2 sub-harmonic resonance are defined by the multi-scale method. The responses and shock isolation performance of SALiM shock absorber are studied, and the buffer effects influenced by the isolation parameters are analyzed. And then, the properties of SALiM shock absorber are tested by the impact experiment. In the other experiments of SALiM isolator, the nonlinear stiffness of the isolator is tested by quasi-static experiment of MTS, which are compared with theoretical results. The measured FRF by the sweep measurement verify the system has a nonlinear soft spring characteristics. The performance of SALiM isolator is estimated by measurement of the vibration level difference. With numerical method of precise integration, the super-harmonic, sub-harmonic resonances of the system are analyzed. The frequency characteristics of the energy transmissibility which reflects the performance of nonlinear vibration isolation system are calculated. At last the isolation performance influenced by 1/2 sub-harmonic resonance of the system is analyzed.The results show that the elastic restoring force of SALiM isolator is a nonlinear function containing once term, quadratic term and cube term of piston displacement. The theoretic stiffness and dynamic model indicate a good agreement with the measured data. The SALiM isolator has softening spring characteristics and unsymmetrical responses. The excellent performances of SALiM isolator are described by the energy transmissibility curves. The tested vibration level differences achieve 15dB in the frequency scopes of research. It is suitable for the heavy equipment with low natural frequencies. The results show that the properties of isolation go down if the sub-harmonic resonance of isolation system occurrs. Thereby, the sub-harmonic resonances of isolation system should keep from happening as the design of nonlinear isolation system.