Dynamic Characteristics and Fatigue Life Analysis of Hydraulic Direct-Drive Pumping Units

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Summary Hydraulic direct-drive pumping units are known for their high efficiency and energy-saving capabilities. However, existing research predominantly focuses on steady-state analysis, often overlooking the impact of directional reversal shocks on the load-stress-fatigue failure mechanism. To address this, a rigid-flexible coupling dynamic model was developed based on multibody dynamics and fatigue damage accumulation theory, incorporating the nonlinear stiffness of hydraulic cylinders and impact effects during commutation. Analysis of the polished rod load fluctuations indicates that, compared with a sinusoidal velocity curve, an optimized trapezoidal velocity curve reduces maximum velocity by 33.3% while extending the duration of the constant velocity phase. Simulation results reveal the dynamic stress response under varying conditions: The peak equivalent stress of the piston rod increases by 34.3% under extreme conditions compared with rated conditions, with significant stress concentration at the piston/rod interface. Fatigue life predictions, utilizing the rainflow counting method and Miner’s rule, show that the fatigue life of the piston rod under extreme conditions drops to 5.7% of that under rated conditions. These findings quantify the impact of dynamic shocks on equipment durability, providing a theoretical basis for optimizing the design and reliability of hydraulic direct-drive pumping units.

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