The efficient swimming of fish is closely linked to their unique body morphology. This study seeks to explore the impact of body morphology on hydrodynamic performance through numerical analysis. Initially, the investigation focuses on carangiform swimmers with varying thicknesses, denoted by the thickness coefficient ψ. Key performance indicators such as vortices, velocity, pressure, thrust, and energy consumption are analyzed. The findings reveal a notable phenomenon of vortex deflection in self-propelled studies, which is affected by the interplay between initial vortices and flow conditions. Specifically, the carangiform swimmer with ψ = 1.4 exhibits the highest thrust but also the greatest energy consumption. In contrast, the swimmer with ψ = 0.8 demonstrates the best acceleration and steady swimming speeds with moderate energy usage. This paper provides new insights into how body morphology influences self-propulsion in aquatic environments.

When designing the internals of robotic fish, variations in the internal arrangements of power and control systems cause differences in external morphological structures, particularly the positions of maximum thickness. These differences considerably affect swimming performance. This study examines the impact of the topological structure of self-propelled fish-like swimmers on hydrodynamic performance using fluid–structure interaction techniques. Fish-like swimmers with maximum thickness closest to the head exhibit optimal swimming performance, characterized by modest energy consumption for fast-response acceleration during the starting phase and higher swimming velocity for high-speed travel during steady swimming. As the maximum thickness moves toward the middle, acceleration performance significantly weakens and swimming speed decreases, although maximum energy consumption is relatively reduced. This study will provide a notable reference for the morphological design of underwater robotic fish.

A circular expanding duct features an increasing cross-sectional area that tends to excite higher-order modes at low frequencies, thereby affecting the performance of acoustic devices. Studying the acoustic propagation characteristics of circularly expanding ducts is thus crucial for optimal design and noise control. Traditional prediction methods do not adequately account for three-dimensional wave effects inside a duct. This study investigates the sound attenuation performance of various circular expanding ducts in the frequency range of 10–2500 Hz using the three-dimensional finite element method in combination with acoustic theory. The results show that the geometric expansion of the duct changes the wavefront shapes of transmitted sound waves, causing varying degrees of wavefront distortion. Behind the expanding region, these distorted wavefronts interfere with each other to varying extents, affecting the transmission loss (TL) of the duct. When the length of the expanding section is shorter, the average attenuation is generally higher. However, at specific frequencies (e.g., 2100 Hz), a longer expanding section may enhance sound attenuation by exciting more resonant modes. As the expansion ratio of the cross-sectional area increases, wavefront distortion and modal resonance become more pronounced, leading to increased average attenuation and the appearance of more peaks in the TL curve. In addition, the incidence of higher-order modes induces complex modal coupling and interference, significantly reducing the average sound attenuation of the duct. This study provides theoretical foundations and reference values for optimizing the design of circular expanding ducts to improve acoustic performance.

The impact-freezing phenomenon of supercooled saline droplets on cold surfaces poses a serious threat to the operational stability and structural integrity of offshore wind turbines. Compared to freshwater droplets, numerical models for analyzing the impact-freezing behavior of saline droplets typically involve complex physical mechanisms, resulting in high computational costs. This study employs a simplified two-dimensional axisymmetric numerical model that integrates the Volume of Fluid (VOF) method with the enthalpy–porosity approach, enabling rapid analysis of the saline droplet impact-freezing process under marine environmental conditions. The model is validated by comparing the spreading factor curve of saline droplets with a salinity of 35‰ against existing experimental data. Results show that the salinity corresponding to the peak relative deviation shifts with varying impact parameters, depending on the competition between impact dynamics and solidification. Furthermore, the maximum spreading factor decreases with increasing supercooling degree and contact angle but increases with higher Weber number. These findings provide useful correction parameters for improving existing droplet motion and icing prediction models.