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The scattering of surface waves by structures intersecting liquid surfaces is fundamental in fluid mechanics, with prior studies exploring gravity, capillary and capillary–gravity wave interactions. This paper develops a semi-analytical framework for capillary–gravity wave scattering by a fixed, horizontally placed, semi-immersed cylindrical barrier. Assuming linearised potential flow, the problem is formulated with differential equations, conformal mapping and Fourier transforms, resulting in a compound integral equation framework solved numerically via the Nyström method. An effective-slip dynamic contact line model accounting for viscous dissipation links contact line velocity to deviations from equilibrium contact angles, with fixed and free contact lines of no dissipation as limiting cases. The framework computes transmission and reflection coefficients as functions of the Bond number, slip coefficient and barrier radius, validating energy conservation and confirming a$$90^\circ$$phase difference between transmission and reflection in specific limits. A closed-form solution for scattering by an infinitesimal barrier, derived using Fourier transforms, reveals spatial symmetry in the diffracted field, reduced transmission transitioning from gravity to capillary waves and peak contact line dissipation when the slip coefficient matches the capillary wave phase speed. This dissipation, linked to impedance matching at the contact lines, persists across a range of barrier sizes. These results advance theoretical insights into surface-tension-dominated fluid mechanics, offering a robust theoretical framework for analysing wave scattering and comparison with future experimental and numerical studies. 

Hand clapping, a ubiquitous human behavior, serves diverse daily-life purposes. Despite prior research, a comprehensive understanding of its physical mechanisms remains elusive. To bridge this gap, we integrate human data, parametric experiments, finite-element simulations, and theoretical frameworks to investigate the acoustic properties of clapping sound and their connections with the fluid flow and soft matter collision. Motion-audio synchronization reveals the flow-excitation nature of the hand cavity resonance. The classical Helmholtz resonator model, incorporating occasional pipe standing wave contributions for finger grooves, reliably predicts clapping sound frequencies across various real and engineered hand configurations. Material elasticity, coupled with the dynamic collision process, has minor effects on the sound frequency but a major impact on the temporal evolution of the sound signals, as reflected by the quality factors of resonance. Both spatial and dynamic factors for sound intensity are examined. We establish a quadratic scaling relationship between hand cavity gauge pressure and clapping speed, elucidating the positive correlation between faster claps and louder sounds. Our work advances the knowledge of hand-clapping acoustics and offers insights into sound signal synthesis, processing, and recognition. Furthermore, these findings may facilitate low-cost acoustical diagnostics in architecture and enhance rhythmic sound patterns in music and language education. 

The scattering of surface waves by structures intersecting a liquid surface has long been a focus in fluid dynamics due to its theoretical and practical implications. Historically, theoretical studies on this problem have predominantly employed idealized assumptions such as infinitesimally thin barriers, which do not fully represent real-world conditions. This project aims to extend the study by numerically investigating the scattering by a cylindrical barrier intersecting the liquid surface through a pinned contact line. Detailed numerical simulations of potential flow coupled with the surface elevation dynamics were conducted to analyze the interactions between the wave and the barrier. Parameters such as wave frequency and barrier radius were varied to examine their effects on the scattering. The results highlight how the barrier's dimensionless size and the Bond number influence the scattering, with notable findings on the dependency of the scattering efficiency on these parameters. The study elucidates the role of contact lines and barrier size in modifying the scattering and presents a comprehensive view of the scattering across different parameter ranges. 

The wetting phenomenon at three-phase boundaries (solid, liquid, and gas) affects capillary-gravity wave scattering from barriers, but there is a lack of experimental data and comparison with simulations. The scattering is affected by surface tension and the contact lines at the three-phase boundary. When the solid surface conditions vary, the contact angle and the shape of the meniscus generated by the wetting effect change accordingly. It is possible to measure the influence of the wetting effect on the scattering by coating the barrier surface to be hydrophobic or hydrophilic. Our previous work focused on how the scattering is affected by the portion of the barrier immersed under the water surface with a pinned contact line. In this study, we will coat the barrier surface to experimentally measure how the wetting with different coatings affect the scattering. A comparison of the experimental measurements with numerical simulations of potential flow of the waves will be potentially included. 

Contact lines at a three-phase boundary (solid, liquid and air) play an essential role in the dynamics of the free surface of liquids in surface-tension-dominated fluids. While previous studies on the contact line effect have mainly focused on frequency and damping of standing wave modes in capillary dynamics, our study focuses on the contact line effect on capillary-gravity wave scattering from barriers. Models have predicted the contact line effects on capillary-gravity wave scattering from a barrier in ideal fluid configurations, but the lack of experimental data has hindered the progress. This research presents an experimental study that utilizes an acoustic approach to measure variations of the scattering with the barrier depth, barrier width, and surface wave frequency. Our study provides both evidence and quantitative measurements of the contact line effect on capillary-gravity wave scattering in realistic fluid configurations.