For the design of a horizontal-axis tidal current turbine with adaptive variable-pitch blades, both numerical simulations and physical model experiments were used to study the hydrodynamic performance of symmetrical airfoil blades based on backward swept models. According to the lift–drag ratio of symmetrical airfoils, variable airfoil sections were selected for each part of the blade in the spanwise direction. Then, three kinds of blades were designed by using different swept-back models from wind turbines. A rotation model with a multi-reference frame was employed to conduct a three-dimensional steady numerical simulation of the turbine model based on the CFD method. The axial thrust and energy-capturing efficiency under different tip speed ratios, as well as the corresponding starting torque under different flow rates, were analyzed. The simulation results indicate that model 2 has optimal start-up performance, and model 3 has the largest power coefficient. The thrust coefficient of model 1 is the smallest. In all, model 2 has better comprehensive performance. The experiments of model 2 show that it has suitable hydrodynamic performance to capture bidirectional energy via passively variable pitch. This research provides an important solution for the design and optimization of horizontal-axis turbines to harvest bidirectional tidal current energy.

This study introduces a novel switchable energy harvesting composite generator (SEHCG), a groundbreaking solution that integrates a triboelectric nanogenerator (TENG) with an electromagnetic generator (EMG) via a magnetic-spring coupling mechanism. The core mechanism enables automatic switching between TENG (low-speed) and EMG (high-speed) modes, using a 0.5-mm-diameter compression spring, with switching thresholds ranging from 0.181 to 0.212 m s⁻¹. SEHCG captures energy at ultralow flows (≥0.072 m s⁻¹) via the TENG operation. Compared with conventional EMGs, SEHCG dramatically widens the effective flow range by overcoming the low-speed barrier, providing a viable solution for low-velocity marine current energy harvesting.

To address dependence on external power and the limited capability of conventional hydroelectric units to detect low-amplitude vibrations, this work introduces a self-contained, highly accurate monitoring device. The design incorporates a magnetically levitated configuration, with triboelectric films placed on both the upper and lower faces of the floating magnet. Under minor oscillations, magnetic repulsion increases the relative displacement between the friction layers, producing a substantial voltage that permits low-level vibration sensing. A surrounding induction coil responds to the levitated pole’s vertical motion; this motion intersects the magnetic flux, generating a current that provides stable energy for wireless data transmission. Experimental outcomes confirm a detection limit of 0.1 mm. At an amplitude of 1 mm and a load of 1000 Ω, the system achieves a maximum output of 9 mW and a power density of 1.587 W/m², ensuring reliable power. This configuration provides a new pathway for monitoring vibrations in hydroelectric turbine generators.

This study presents a novel self-adaptive marine current power generation system capable of operating efficiently across a wide range of flow velocities. The key innovations include an adaptive variable-solidity rotor and a non-contact magnetic speed-increasing dynamic seal. The rotor employs foldable blades that enable passive solidity regulation in response to varying inflow conditions. At low flow velocities, the blades remain deployed, increasing rotor solidity and reducing the required startup flow velocity. Water tank experiments indicate that the minimum startup velocity of the variable-solidity rotor is 0.217 m/s, which represents a 38% reduction compared to a conventional rotor. At high flow velocities, the blades fold under increased hydrodynamic loading, thereby reducing the effective solidity and suppressing torque growth to provide overload protection. The power transmission module incorporates a non-contact magnetic speed-increasing dynamic seal, which ensures underwater dynamic sealing of the main shaft while simultaneously increasing the rotational speed of the driven shaft. Motor-driven bench tests demonstrate that when the active shaft speed remains below the cut-off threshold, a stable speed-increasing ratio of 2:1 is maintained, enabling effective speed amplification and torque transmission. Once the active shaft speed exceeds the cut-off threshold, the driven shaft automatically stalls, thereby preventing motor overload. Overall, this work provides an effective solution for enhancing the operational adaptability and transmission reliability of marine current energy conversion systems under variable flow conditions.