The dynamics of mine hoist catenaries.

[摘要] The dynamic analysis of catenary vibration of mine hoist ropes on South African mines isexamined. This research has been preceded by studies in the mining industry, which havelaid the foundation fot the definition of design guidelines of hoist systems to avoid catenaryvibrations or rope whip. These guidelines are based on a classical linear analysis of a tautstring, and in essence rely on ensuring that the frequency of excitation at the winder drumdue to the coilingmechanism, does not coincide with the linear transverse natural frequencyof the taut catenary. Such an approach neglects the nonlinear coupling between the lateralcatenary motion and the longitudinal systern response. Although previous research suggested the possibility of autoparametric coupling between the catenary and vertical rope,this was not developed further on a theoretical level.. The possibility of such behaviour isdefined by considering the equations of motion of the coupled system.A design methodology is developed for determining the parameters of a mine hoist systernso as to avoid rope whip. The methodology accounts for the nonlinear coupling betweenthe catenary and longitudinal system. In order to implement the proposed methodology,two phases of the analysis are developed. In the first phase the stability of the linear steadystate motion is examined in the context of the nonlinear equations of motion, by applyinga harmonic balance method. The stability analysis defines regions of secondary resonance,where it is shown that such regions may arise at sum and difference combinations of thelinear lateral and longitudinal natural frequencies due to autoparametric excitation. Priorto this research, this phenomenon had not been appreciated in the context of the mine hoistsystem. A laboratory experiment was conducted to confirm the existence of these regionsexperimentally. In reality, the system is non-stationary since the dynamic characteristics ofthe system change during the winding cycle, and hence the steady state stability analysis canonly describe potential regions of nonlinear interaction on a qualitative basis. The secondphase of the analysis deals with a non-linear numerical simulation of the hoist system, whichaccounts for the non-stationary nature of the systems dynamic characteristics, and includestransient excitations induced during the wind.The methodology developed is assessed by considering the Kloof mine rope system, whererope whip was observed. This study demonstrates that although an appreciation of thesteady state system characteristics is useful, the stability analysis alone is not sufficient.It is necessary to account for the non-stationary aspects of the winding cycle if a realisticinterpretation of the observed behavlcur is to be achieved. To compliment this study, amotion analysis system was developed to record catenary response on an existing mine hoistinstallation. Such data has not been recorded before. This data provides direct evidence ofthe autoparametric nature of the coupled catenary/vertical rope system.

[发布机构] University of the Witwatersrand