Granular damping is a passive vibration control method that has attracted considerable attention in mechanical and structural vibration reduction. To reveal the energy dissipation mechanism of granular dampers under sinusoidal excitation, this study develops a numerical model of a granular damper based on the discrete element method (DEM). First, two damper construction methods—using particle elements and clump elements—are compared, and the clump element approach is selected to construct the damper. The friction coefficient and normal critical damping ratio are then calibrated using the Hertz contact model and single-particle bounce experiments. On this basis, a forced vibration system with a virtual spring is established, and numerical simulations are carried out under three sinusoidal excitation conditions: 0.4 cm-15 Hz, 1.0 cm-15 Hz, and 0.4 cm-45 Hz. The damping mechanism is analyzed from an energy perspective, with discussion of the impact force, displacement, and velocity responses. The results show that the damping particles accelerate the system’s approach to steady-state vibration. Energy dissipation occurs mainly during collisions between the damping particles and the inner wall of the damper, and collision dissipation is greater than friction dissipation. When the particles detach from the wall, the inter-particle forces are very small, and the energy dissipation is negligible. The particle–wall impact force exhibits a multi-peak profile, and the force–time ratio increases with excitation intensity. These findings deepen the understanding of granular damping mechanisms and provide a reference for the design and optimization of granular dampers.

Severe drill-string–wellbore friction during slide drilling limits axial-load transfer and reduces drilling efficiency in extended-reach horizontal wells. To investigate the mechanical response of a horizontal drill string under axial vibration, a three-dimensional geometrically nonlinear finite element model was developed in Abaqus/Explicit. The model incorporates a previously validated dynamic friction formulation and directly accounts for deformation-dependent drill-string–wellbore contact, allowing the coupled effects of axial vibration, friction, load transfer, and lateral deformation to be captured. Numerical results show that axial vibration markedly alters the spatial and temporal distributions of axial force and sliding velocity. Periodic modulation and reversal of axial velocity induce synchronous reversal of the friction force, which constitutes the dominant friction-reduction mechanism under the investigated conditions. The reduced effective friction improves axial-load transfer, increases WOB, and produces a more continuous drilling response, although larger WOB fluctuations are introduced. The vibration effect attenuates with propagation distance, indicating a spatially limited effective range of the axial oscillation tool. Under high axial compression, buckling increases drill-string–wellbore contact and deteriorates load-transfer efficiency. Axial vibration further reduces the externally applied compressive load required to reach sinusoidal and helical buckling, with a maximum reduction of approximately 12.9% in the investigated cases. These results provide a mechanical basis for balancing friction reduction, dynamic bottom-hole loading, load-transfer improvement, and drill-string stability in the application of axial oscillation tools, thereby helping to improve drilling energy efficiency and enhance the development capabilities of unconventional oil and gas resources.