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Stochastic Dynamics Research of Vibrating Screen Structure

Author: PengChenYu
Tutor: SuRongHua
School: Liaoning Technical University
Course: Engineering Mechanics
Keywords: vibrating screen mean stiffness stochastic dynamics structural randomparameter exciting force random parameter mean value deviation factor variationfactor variation change rate
CLC: TD452
Type: PhD thesis
Year: 2012
Downloads: 256
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Abstract


Random factors inevitably exist in manufacturing, installation, operation and other sectorsof vibrating screen. In the traditional model, all the relevant parameters of dynamic analysis aredeterministic. The structural damage problems arising in vibrating screen working process aredifficult to explain reasonably by using traditional model. The effect law of dynamiccharacteristics and dynamic response caused by random factors can be revealed by stochasticdynamics model; therefore, the stochastic dynamics analysis for vibrating screen has importanttheoretical significance and practical value. Based on experimental analysis of vibrating screenmechanical properties, combining stochastic dynamics theory with finite element method, thestochastic dynamics model of vibrating screen was built. Considering exciting force randomparameter and structural random parameter, the variation law of dynamic characteristics anddynamic response were studied; the variation change rate was also researched. The maincontents are as follows:1. By experimental analysis of vibrating screen’s rubber spring mechanical properties, thestiffness of rubber spring can be divided into approximate linear region and nonlinear region. Forapproximate linear region, the concept of mean stiffness and its calculation method wasproposed. Using strain energy theory, the nonlinear constitutive equation and nonlinear finiteelement model of rubber spring were built based on five-parameter Mooney-Rivlin strain energyfunction, and the precision is verified. Meanwhile, the linear finite element model was builtaccording to mean stiffness, the simulation precision accords with the result of nonlinear analysismodel, so the linear model can be used as an alternative to nonlinear analysis in the approximatelinear region.2. The dynamic test of vibrating screen structure was carried out, the modal frequency andamplitude in steady working process were got. The results show each modal frequencies werenot coincides with working frequency, resonance phenomenon does not occur.3. Combining stochastic dynamics theory with finite element method, the stochasticdynamics model of vibrating screen was built considering exciting force random parameter andstructural random parameter, the modeling methods and analysis flow chart is given. In order tosolve the key problem in stochastic dynamics modeling, the beam-shell element model was putforward, Using custom section beam element, the actual beam structure was simulated by variable cross section beam; the bolts connection and welded connection were simplified rationalby freedom degrees coupled and constraint equations technology; the exciting force was appliedto structure rational by creating rigid zone. The modal analysis and dynamic response analysis ofvibrating screen structure and major structural parts were made. Comparing with experimentalresults and the traditional solid element model simulation results, the analysis results accuracy ofbeam-shell model is verified.4. The relative mean value deviation factor and variation factor of modal frequency,amplitude and dynamic stress were defined to analyze dynamic variation rules of vibratingscreen quantitatively. In order to quantitatively describe the variation sensitive degree of modalfrequency, amplitude and dynamic stress, separately using relative mean value deviation factorand variation factor of modal frequency, amplitude and dynamic stress as objective function,using variation factor of exciting force random parameter and structural random parameter asindependent variable, the relative mean value deviation factor change rate and variation factorchange rate are offered, which are dimensionless quantity.5. Using stochastic dynamics model, the variation law of modal frequency changing withvariation factor were analyzed when considering structural parameter separate random andcoinstantaneous random. For the vibrating screen studied in this paper, the variation factor ofrubber spring modulus is the main parameter which effecting low-order frequencies variability;the variation factor of steel density is the main parameter which effecting high-order frequenciesvariability. When structural parameters exist variation synchronously, modal frequencyconcentration reduced. Through analysis of frequency ratio, the reasonable range of parametervariation factor was gained. The variation change rate of modal frequency was researched, thevariation sensitive degree of each order frequencies were determined, and variation sensitivedegree sequencing was got.6. The variation law of amplitude and dynamic stress changing with variation factor wereanalyzed when structural parameters exist random. The results show when structural parameterseparate random, in order to ensure screening efficiency and vibrating screen operate smoothly,the reasonable range of rubber spring modulus variation factor and steel density variation factorwere gained. When structural parameters exist variation synchronously, as variation factorreaches critical value, the dynamic stress of partial structure exceed allowable stress, thestructure may be destroyed. From the random point, the results give a reasonable explanation for structural damage in vibrating screen operating process, which the deterministic model can notexplain. The amplitude and dynamic stress variation sensitive degree sequencing was got, in allparameters, steel density variation factor is the most sensitive parameter.7. The variation law of amplitude and dynamic stress changing with variation factor wereanalyzed when exciting force parameters exist random. The exciting force parameters includemass moment, exciting force direction angle and exciting force frequency. The results show theresponse variation factor increased with parameters variation factor rising; the variation factor ofmass moment and exciting force frequency has little effect on relative mean value deviationfactor of amplitude and dynamic stress. The variation factor of exciting force direction angle isthe main parameter which affects response mean value. As the variation factor of exciting forcedirection angle increasing, the difference of amplitude mean value is increased.By variation changing rate analysis, as exciting force parameters exist random, the responsevariation sensitive degree sequencing was got. When variation factor increasing, the sequencingchange. So the parameter of high sensitive needs to draw attention according to analysis results.

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