Energy transfer mechanism and performance evaluation of the underwater ultrasonic drilling corer for seabed rock sampling.

To address the problems of high-power consumption, large weight-on-bit, significant disturbance, and difficulties in sealing and waterproofing in the traditional Deep-sea Seafloor Drill, a novel piezoelectric-driven Underwater Ultrasonic Drilling Corer (UUDC) is proposed. Based on piezoelectric drive theory and nonlinear dynamics theory, the energy transfer mechanism of the UUDC is investigated, and its working principle is elucidated, which lays a theoretical foundation for the design and development of its key components. The nonlinear explicit dynamic analysis method is adopted to investigate the interaction mechanisms between the drilling tool and the rock under piezoelectric actuator and free mass actuation. The findings provide guidance for optimizing the dynamic parameters of UUDC and improving the structural design of the drilling tool. A drilling and coring test platform for the UUDC is established, experiments on the mechanical characteristics of drilling and coring are carried out, to verify the feasibility of the design, and evaluate its drilling and coring performance. The experimental results illustrate that the UUDC exerts a maximum drilling force of approximately 7.1 N on the rock, generating a surface stress of up to 2.5 MPa. Under a 5 N weight-on-bit, the device achieves a drilling depth of 20 mm within 2 min, with a coring success rate of 90% and a core recovery of 73.6%. The UUDC prototype efficiently drills into rock under a low weight-on-bit and reliably retrieves cores. It presents strong adaptability to deep-sea environments and compatibility with underwater vehicles, providing an effective solution for seabed rock coring.