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Tip vortex cavitation (TVC) stands as a primary source of underwater radiated noise, garnering significant attention in the relevant fields due to its early manifestation in propellers and broad frequency spectrum. Although some meaningful experimental and numerical research concerning TVC noise has been implemented, a comprehensive understanding of TVC noise properties still remains elusive. This study delves into the acoustic characteristics of TVC through cavitation experiments of hydrofoil and jet pump and signal processing tools, including frequency-domain analysis, time-frequency representation, and signal demodulation. Comparative analysis between static and dynamic states of the test hydrofoil and the test jet pump reveals several insights into TVC noise. First, the acoustic characteristics of TVC primarily encompass multiple low-frequency characteristic peaks below 300 Hz alongside an overall increase in the high-frequency domain. Second, the oscillating hydrofoil at a cavitation number of 2.00 exhibits two distinct frequency bands caused by cavity volume variation and cavity resonance of TVC at 190–280 and 360–400 Hz, which shift toward the lower frequency region with larger TVC sizes. Finally, the periodic oscillation of hydrofoil or the rotational motion of impeller induces a modulation effect on TVC noise, with spectral correlation (SC) identifying two dominant carrier bands within 100–400 Hz. [ABSTRACT FROM AUTHOR]

A sustainable power source is more and more important in modern society. Ocean wave energy is a very promising renewable energy source, and it is widely distributed worldwide. But, it is difficult to develop efficiently due to various limitations of the traditional electromagnetic generator. In recent years, the newly developed triboelectric nanogenerator (TENG) provides an excellent way to convert water wave energy into electrical energy, which is mainly based on the coupling between triboelectrification and electrostatic induction. In this paper, a review is given for recent advances in using the TENG technology harvesting water wave energy. We first introduce the four most fundamental modes of TENG, based on which a range of wave energy harvesting devices have been demonstrated. Then, these applications’ structure and performance optimizations are discussed. Besides, the connection methods between TENG units are also summarized. Finally, it also outlines the development prospects and challenges of technology.

Horizontal axis tidal turbines (HATTs) working in a complex flow environment will encounter unsteady streamwise flow conditions that affect their power generation and structural loads, where power fluctuations determine the quality of electricity generation, directly affecting the grid and reliability of the power transmission system; fatigue loads affect various structures and mechanical components of the turbine, directly determining the lifespan and reliability of the turbine. To gain insight into the generation mechanism and distribution of these excitations, a large eddy simulation is employed to analyze the inflow turbulence and unsteady forces excitations by a three-blade HATT. A spectral synthesizer was used to generate incoming turbulence flow. The strip method was applied on the HATT by dividing the blade into 20 strips. The thrust received by each strip and the flow velocity upstream and downstream of the blade's root, middle, and tip were monitored. The distribution of unsteady loads on the blades was analyzed, as well as the relationship between flow velocity upstream and downstream of the blade and the unsteady characteristics of the blades. The simulation results show that the unsteady hydrodynamic fluctuations of the HATT blades reach up to 57.44% under a turbulent intensity of 10%. Through intuitive analysis of flow separation on the suction surface of the blade at various moments under a low tip speed ratio, we can comprehend the variations in inflow velocity and flow separation on the blade surface. Analyzing the distribution of blade load from root to tip reveals that the maximum load values are concentrated in the 14th–16th strips, corresponding to the region from 0.7R to 0.8R. Moreover, the middle and tip sections of the blades predominantly contribute to the harmonics of the 3BPF (blade passing frequency) and broadband, with the middle section making a greater contribution. The tip section primarily contributes to harmonics above 3BPF. This research want to makes a valuable contribution to the comprehensive understanding of turbulence-induced exciting forces and the practical engineering design of HATT. [ABSTRACT FROM AUTHOR]