Research On Nonlinear Torsional Vibration Dynamics Behaviors Of Strip Rolling Mill’s Multi-dof Main Drive Systems

Recent years, strip rolling mill develops in the directions of large-scale, modern andhigh speed gradually. Along with the overall equipment level of rolling mill of continuousimprovement, specifications of the rolling mill’s drive system like high stability, highaccuracy and high dynamic performance are requested. However the torsional abnormalinstability phenomenon of the rolling mill’s drive system occur frequently has become animportant factor restricting the production and quality of products. In this dissertation, themulti-degree-of-freedom of torsional vibration nonlinear dynamic models of drive systemof rolling mill were established. The instability mechanics of the torsional vibration of thedrive system under the effect of the electrical disturbance, structure parameters, complexload and other aspects are revealed in the nature of nonlinearity. The combined effect ofmultiple factors on the torsional vibration of the rolling mill’s drive system in theinstability mechanism of dynamic response, bifurcation, chaos dynamics and other aspectsare analyzed, which provide theoretical basis with the rolling mill’s drive system forstructure optimization design and fault prevention and treatment.Considering the nonlinear factors of the rolling mill such as structure clearance,motor torque disturbance, nonlinear friction, shaft angle and tension fluctuation,3modelsof the multi-degree-of-freedom of nonlinear torsional vibration of rolling mill’s drivesystem were established based on the principle of generalized Lagrange, which provides atheoretical model for the precise analysis of torsional vibration characteristics of striprolling mill’s drive system.The method of Modified Lindstedt-Poincare was employed to obtain the analyticalsolutions of the nonlinear system with clearance under loaded friction of rolling and outdisturbance excitation. The bifurcation equation of the system is deduced by the modifiedLindstedt-Poincare combined with the multiple scales method. The main resonanceamplitude-frequency characteristic equation of the multi-degree-of-freedom nonlineartorsional vibration system with joint parametric was obtained by solving the dynamicalequation using the multi-scale method. And super-harmonic resonance, sub-harmonic resonance, and combination resonance amplitude-frequency characteristic equations of thenonlinear torsional vibration system with both joint parametric and tension fluctuationwere obtained also by the multi-scale method.The characteristics of bifurcation of the nonlinear system with clearance wereanalyzed by means of singularity theory, respectively, and different topological structureof solution is obtained under different parameters and obtaining the variation area ofparameters under which the rolling mill could vibrate stably. And the amplitude-frequencycharacteristic curves exhibited the influence of various parameters on the stability of thesystem. With the numerical simulation method, the main resonance amplitude-frequencycurves of the nonlinear torsional vibration system with joint parametric were obtained andthe super-harmonic resonance, sub-harmonic resonance, and combination resonanceamplitude-frequency characteristic curves of the nonlinear torsional vibration system withboth joint parametric and tension fluctuation were obtained, too.The heteroclinic orbit of the multi-degree-of-freedom nonlinear torsional vibrationdynamic system which constrained joint parametrically excited was obtained by usingMelnikov’s method. The global bifurcation and chaotic dynamics of the torsional vibrationmodel were analyzed by the numerical simulation, and the conditions for the appearanceof periodic motion, periodic doubling motion and chaotic motion were obtained, whichprovides some theoretical guidance and reference for the future research on dynamicbehavior of strip mill nonlinear torsional vibration.