Improving the mechanized logging safety on steep slopes through the analysis of dynamic behavior of harvester rope anchor systems

Mechanized logging on steep slopes using forestry machines equipped with winch-rope anchor systems to ensure equipment stability and safe operation is becoming increasingly popular. The parameters that characterize the dynamic behavior of both the harvester and the rope anchor system are crucial to the operational efficiency of the anchor system. The purpose of this study is to create a comprehensive mathematical 12-mass model for the dynamic system “harvester - manipulator - anchor system - natural anchor - log - soil”. The developed model combines all the key components of the system and enables assessment of their mutual influence on the quantitative parameters of the dynamic processes occurring in the system. The model includes 34 generalized coordinates that describe the displacement of the center of mass of each component of the harvester during its operations for felling trees and moving logs to the laying place. To construct a system of equations of motion characterizing the dynamics of the simulated system, an approach based on Lagrange equations of the 2nd kind was used. The model allows for analyzing the influence of the harvester’s design and operating parameters, and of the physical and mechanical properties of the ground, on the harvester load with a manipulator and on the structural elements of the anchor system. To demonstrate the model’s functionality, a specific 6-wheeled harvester weighing 20 tons was chosen as the study object while operating on slopes with a steepness ranging from 50% to 100%. The variable inertial loads on the manipulator from the displaced log cause oscillations in the tensile force of the anchor rope. The maximum values of the force in the studied range of slope steepness increased from 19 kN to 72 kN, while the average values increased from 16 kN to 65 kN, with an increase of oscillation in the range 6-14 kN. The oscillation frequency remains constant throughout the log’s motion, as it is determined by the geometric dimensions of the structural elements in the simulated dynamic system.