| Unmanned mine is the development direction of coal mining,which is not only the demand for efficient production,but also the need of avoiding mine disaster to achieve intrinsic safety.Currently,the application of unmanned full-mechanized mining face technology has become a hot spot.As follow-up transportation equipment of a direct extension of mining face,the belt conveyor is an important part of full unmanned mine in the future.Will the extending of a running conveyor belt with a specified speed impact on the performance of the whole conveyor? It is a question that must be faced.The core of answer this question is to study the dynamic behavior of the extensible conveyor belt in motion.Based on the finite strain theory of continuum mechanics and the basic knowledge of differential geometry,taking the longitudinally moving conveyor belt supported on two horizontally arranged rollers as the research object,starting with parameterization of the arc length of the curve of the different configurations of the conveyor belt and combining the deformation rate in the arc length direction given by the deformation gradient under the condition of finite deformation,by introducing the St Venant-Kirchhoff constitutive relation and using the divergence of stress field on the conveyor belt,the continuity of the quality of the conveyor belt is integrated with the integral form of Newton's second law to obtain the differential relationship between displacement,tension,arc length and time on the conveyor belt.By using the projection formula between frame vectors of different configuration on the conveyor belt,the non-Euler description items in the differential relation are eliminated,and the finite deformation nonlinear dynamic model of conveyor belt unit in Eulerian description form is obtained.The model shows that there exists a critical value related to dynamic tension under constant speed conditions.When the belt speed is lower than this value,the longitudinal and vertical displacement of the belt is fluctuating.When the belt speed exceeds this threshold,the model will bifurcate.Based on the principle of finite difference,taking the configuration of the catenary as the Cauchy boundary condition,and the velocity and displacement at the end of the unit as Dirichlet boundary conditions,a numerical solution method of the finite deformation nonlinear dynamic model of conveyor belt unit is given.Surrounding the numerical method,a dual-element model is constructed,which can be used to realize the dynamic analysis and numerical simulation of the extensible conveyor belt in motion.The transversal observed displacements,observed tensions and observed configuration of extensible conveyor belt under common working conditions were simulated by the dual-element model.The numerical simulation results shows:1)The increase of span caused by extending can lead to the overall increase of observed tension of the conveyor belt.2)As the extending acceleration increases,the fluctuation of the transversal observed displacement of the extensible conveyor belt at a given point is reduced,that is to say,Faster extending hold the fixed element stabler.3)The observed tension at a given point of a moving extensible conveyor belt is fluctuated,and as the belt speed increases,the median tension value moves upward with an exponential relationship.4)The fluctuation of belt speed will cause continuus tension "polarization" phenomenon,that is,the observed tension is concentrated to two extreme: very large or very small.5)Observed displacement of the moving conveyor belt is fluctuating,and the amplitude of the fluctuation is related to the belt speed.The frequency and amplitude of observed displacement are relatively stable at low speed,and the typical nonlinear characteristic of amplitude appears with the increase of velocity.In order to test the dynamic characteristics of the extensible conveyor belt in motion and check the two-unit model,guided by the universal experimental design theory,based on the experimental principle of "random,repeatable and groupable",taking the "four changes one out"(with variable belt speed,variable belt profile,variable load distribution,variable initial tension,output observed displacement of a given point)as development goal,using the "top-down" development mode,a dynamic characteristic experimental platform of extensible conveyor belt integrated communication control,automatic data acquisition,result recording and condition monitoring with controllable speed,controllable extending,controllable load distribution and controllable initial tension function was developed and set up.On the experiment platform,the experiment of belt dynamic characteristics related to the transversal observed displacement was completed.The rationality of the theoretical model is verified from the perspective of observed displacement. |
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