Research On Dynamic Modeling And Dynamic Properties Of Rubber Isolator

Isolators were one indispensable part of APU (auxiliary power unit) for an aircraft. Rubberisolators were installed in APU systems to isolate the vibration transmission between APU and theaircraft for APU operating safety. It is necessary to study the rubber isolator’s dynamic characteristicsfor meeting to need advanced aircraft development. In this paper, dynamic characteristics of the APUrubber isolator are studied for rubber material with strong nonlinear dynamic characteristics, whichprovides basis and reference for rubber isolator’s theoretical research and engineering applications.The main contents and innovations were researched as following:(1) A nonlinear dynamic five-parameter fractional derivative model of rubber isolator waspresented about the frequency and amplitude parallel connection: the former were described withfive-parameter fractional derivative and the latter were described with friction force respectively.Quantitative results were given by numerical simulation. Simulation and experimental results showedthat the model fit well with test results and could describ much better dynamic characteristics of theAPU rubber isolator in a wide frequency range. The influence of model parameters for dynamicstiffness was also studied in the paper so as to provid theoretical basis for design and applicayion ofrubber isolator. The proposed five-parameter fractional derivative model possessed academicinnovation value.(2) A nonlinear dynamics constitutive model of isolator’s rubber material was established makinguse of five-parameter fractional derivative. Constitutive model parameters were obtained by fitting theexperimental results. Nonlinear dynamics finite element equations about the rubber isolator wereestablished with this model. These equations were solved by iteration according to reasonablesimplification and features of the fractional derivative factors. The influence of model parametersabout dynamic response characteristics of the isolator was analyzed with simulating. The results byexperimental verification showed that the finite element equations could predict much better thedynamic characteristics of the isolators. Characteristics of the nonlinear viscoelastic material weregrasped making use of influence analysis of model parameters for dynamic response of the isolator,and theory analytical basis was provided effectively for rubber design and application of isolator. Theproposed nonlinear dynamics constitutive model and finite element equations possessed academicinnovation value.(3) Nonlinear dynamics finite element equations of the rubber isolator-mass system were established. Influence of the transmiting characteristics of axial and radial directions were analyzedabout constitutive model parameters and structural parameters, and the design method of the isolatorwere given. Experimental results showed that dynamic characteristics of the rubber isolator could bepredicted well making use of finite element equations and the numerical method. Nonlinearcharacteristics can be grasped, and dynamic response of complex structure system containing therubber isolator can be predicted making use of influence analysis of model parameters abouttransmiting characteristics of the isolator-mass system. The theoretical basis was provided for designmethod and installation layout of the APU system isolator, which possessed an important engineeringvalue.(4) The limitations were analyzed about linear fractional derivative model on analyzing impactvibration. The nonlinear fractional derivative dynamics model was presented about the rubber isolatorunder impact exciting. Two different nonlinear fractional derivative models were studied and were fitwith results of experimental data basing on the impact exciting: the first model was assumed asnonlinear in the coefficient about fractional derivatives factor; and the second model in the derivativefactor. Acceleration response characteristics under impact exciting were studied about the rubberisolator-mass system, and response characteristics are analyzed about various parameters effecting ondecay rate and response frequency of the rubber isolator with numerical simulations. The resultsshowed that the nonlinear fractional derivative model proposed in the paper could fit the experimentaldata better, and the dynamic characteristics under impact exciting could be described accurately with afewer parameters comparing with traditional dynamic model. The nonlinear fractional derivativemodel possessed academic innovation value in theory.In conclusion, nonlinear dynamics model, nonlinear constitutive model and nonlinear finiteelement equations of the rubber isolator, dynamic characteristics of the isolator-mass system andnonlinear fractional derivative model were studied systematically in the paper. The results possessedimportant significance for to conduct the rubbe isolator design and application in the theoretical andengineering.