Abstract

Underwater images play a critical role in underwater exploration and related tasks. However, due to light attenuation and other underwater factors, underwater images often suffer from color distortion and low contrast, which to some extent limit the efficiency and safety of underwater exploration. To meticulously address these issues and enhance the accuracy and reliability of underwater exploration, this paper proposes a multi-task underwater image enhancement method based on Retinex theory. This method divides the underwater image enhancement task into several sub-tasks, including image decomposition, color correction, detail reconstruction, and illumination adjustment. Specialized sub-networks— DecomNet, DecolorNet, and DelightNet—are designed to specifically address these problems, thereby alleviating color distortion, enhancing image details, and improving contrast. Experiments conducted on several publicly underwater image datasets indicate that the quality of underwater images is significantly improved after enhancement with the proposed method, compared to other representative underwater image processing techniques. For example, on the real-world dataset Underwater Image Enhancement Benchmark, the MSE, Structural Similarity Index Measure, and Peak signal-to-noise ratio scores achieved were 453.480, 0.901, and 25.145, respectively. This study holds significant implications for underwater exploration, with potential applications in the fields of marine research and underwater archaeology.OPEN ACCESS Received: 03/11/2024 Accepted: 27/12/2024 Published: 20/04/2025

Abstract

Climate change demands innovative renewable energy solutions, with wind energy emerging as a key resource. Vertical-axis wind turbines (VAWTs) are particularly suited for low-speed, turbulent wind environments due to their ability to capture wind from all directions. However, VAWTs face aerodynamic difficulties, especially at the downwind, where problems like negative torque and decreased efficiency are frequent. This study explores a novel solution for enhancing VAWT performance by incorporating an inner cylindrical deflector aimed at optimizing airflow around the blades. Using computational fluid dynamics (CFD) simulations, the study focuses on a three-bladed H-type VAWT with an airfoil profile of NACA0018 at a turbine diameter of 1 m. The simulations begin by evaluating a bare turbine arrangement, which shows negative torque beginning at an azimuth angle of about 165 degrees onwards. When a cylindrical deflector of different diameters is introduced, the torque coefficient and overall performance are greatly enhanced by a 0.3-meter diameter. The cylindrical deflector’s effectiveness is demonstrated by the 15% increase in power coefficient C pthat results from its inclusion. These results highlight how an inner cylindrical deflector could be a useful addition to VAWTs, resolving significant inefficiencies while preserving a positive angle of attack. This strategy offers a way forward for more effective VAWT designs in renewable energy systems in addition to increasing energy output. To enhance the efficiency of vertical-axis wind turbines (VAWTs) for both urban and rural applications, future research could investigate different configurations and empirically confirm these findings.OPEN ACCESS Received: 21/01/2025 Accepted: 10/03/2025 Published: 20/04/2025