Abstract
The fundamental analysis and optimization (minimization) of dynamic loads in elastic elements (ropes) of load lifting mechanisms of cranes used in urban development is carried out. The basis of the analysis and methodology of optimization of motion modes of the mentioned mechanisms is the approach implemented in the classical calculus of variations, namely: the integral functional is minimized, which reflects undesirable properties of the mechanical system. Optimized modes of motion of the crane load lifting mechanism, which is represented in the paper by a mechanical system with a linear function of the position of its elements (the load on the rope and the drive mechanism). The significant influence of motion modes of exactly drive mechanisms on dynamic loads in elastic elements (ropes) of the load lifting mechanism of a city-building crane is shown. Usually separate typical modes of motion optimize only one certain property of the specified mechanism. In many practical cases, it is necessary to select modes of motion that optimize a set of properties of a machine or mechanism (respectively, a crane or a load lifting mechanism of a city-building crane). It is for the selection of such modes of motion of machines and mechanisms that dynamic criteria for their evaluation are needed. All existing criteria for evaluating machines and mechanisms can be conditionally divided into two classes: 1) positional (maximum values of kinematic characteristics of links, dynamic loads, amplitudes and frequencies of oscillations, dynamics coefficients, etc.); 2) integral (rms values of kinematic characteristics of links and dynamic loads, energy costs, etc.). In the work the fundamental analysis of the mentioned criteria is carried out and it is shown that for estimation of motion modes of hoisting machines, as well as mechanisms of cargo lifting cranes (boom, bridge, gantry, city cranes) it is necessary to use integral criteria, because they are the ones that estimate motion during the whole cycle. Integral criteria for evaluating urban construction cranes and load lifting mechanisms are presented, which fully reflect their dynamic properties, motion characteristics and, in particular, minimize dynamic loads on elastic elements (ropes). The results obtained in this study can be further used to clarify and improve the existing engineering methods of calculation of hoisting cranes used in urban planning, as well as their load lifting mechanisms, both at the design stages and in the modes of proper operation.
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