A study of vortex ring generation by a circular disc with its application in bionic investigation

Numerical simulation on a vortex ring generated by an impulsive started disc is studied. Commercial CFD software is used for the numerical simulation. Modelling results are compared with previous experimental data. The circulation, vortex core position and symmetric breaking time are discussed at two different velocities. Results show that a larger velocity leads to a greater vortex ring circulation, a shorter developing time for occurring asymmetry phase comparing with a smaller velocity

A novel method for two-dimensional physical modelling of a vessel's rudder wake using flowing soap films

Flowing soap films have been used in recent years as an apparatus to study natural phenomena encountered within fluid dynamics, such as the movement of flexible bodies within a flow field [1]. The apparatus consists of a water/soap solution which is suspended between two threads and allowed to flow from a raised position. This creates a thin sheet of flowing liquid into which static or moving bodies can be placed. This thin film may be considered to be two dimensional as it is typically 105 – 106 wider than it is thick [2]. The water/soap solution results in a thin water layer covered by a soap surfactant. When photographed under a monochromatic light source, the movement of the surfactant on the film can be clearly visualised. The primary aim of the research was to investigate the applicability of flowing soap films to the field of Naval Architecture for use as a tool for the qualitative assessment of hullforms. The following questions were investigated: - Can the wake from a ship be adequately modelled using flowing soap films? - How does twin rudder positioning/spacing affect this modelled wake? - Can the wires supporting the flowing soap film be used to model a system boundary, such as the sea surface or bottom? - Can the forces acting on bodies inserted into the soap flow be readily measured

Optimising floating wind turbine layouts with wake modelling and reinforcement learning

With 80% of offshore wind resources located at depths greater than 60m, beyond the reach of fixed-bottom turbines, the focus is increasingly on floating offshore wind technologies. This shift towards larger turbines and rotor diameters introduces complex interactions with environmental variables, which traditional simulation methods struggle to model accurately and efficiently. Our research aims to explore the application of machine learning techniques to predict and optimise the layouts of floating offshore wind farms, considering specific turbine characteristics and geographical constraints. This research will enhance our ability to design optimal layouts for floating wind farms, leading to more sustainable solutions supporting global renewable energy targets and promoting environmental stewardship

A colour preference technique to evaluate acrylamide-induced toxicity in zebrafish

The zebrafish has become a commonly used vertebrate model for toxicity assessment, of particular relevance to the study of toxic effects on the visual system because of the structural similarities shared by zebrafish and human retinae. In this article we present a colour preference-based technique that, by assessing the functionality of photoreceptors, can be used to evaluate the effects of toxicity on behaviour. A digital camera was used to record the locomotor behaviour of individual zebrafish swimming in a water tank consisting of two compartments separated by an opaque perforated wall through which the fish could pass. The colour of the lighting in each compartment could be altered independently (producing distinct but connected environments of white, red or blue) to allow association of the zebrafish's swimming behaviour with its colour preference. The functionality of the photoreceptors was evaluated based on the ability of the zebrafish to sense the different colours and to swim between the compartments. The zebrafish tracking was carried out using our algorithm developed with MATLAB. We found that zebrafish preferred blue illumination to white, and white illumination to red. Acute treatment with acrylamide (2 mM for 36 h) resulted in a marked reduction in locomotion and a concomitant loss of colour-preferential swimming behaviour. Histopathological examination of acrylamide-treated zebrafish eyes showed that acrylamide exposure had caused retinal damage. The colour preference tracking technique has applications in the assessment of neurodegenerative disorders, as a method for preclinical appraisal of drug efficacy and for behavioural evaluation of toxicity

Double doppler shift theory on water waves generated by the translating and oscillating source

Paper deals with the development of double Doppler shift theory and application of double Doppler shift theory on the prediction of water waves generated by a translating and oscillating source

Response of a flexible filament in a flowing soap film subject to a forced vibration

The interactions between flexible plates and fluids are important physical phenomena. A flag in wind is one of the most simplified and classical models for studying the problem. In this paper, we investigated the response of a flag in flow with an externally forced vibration by using flexible filaments and soap film. Experiments show that for a filament that is either in oscillation or stationary, the external forced vibration leads to its oscillation. A synchronization phenomenon occurs in the experiments. A small perturbation leads to a large response of flapping amplitude in response. The insight provided here is helpful to the applications in the flow control, energy harvesting, and bionic propulsion areas

Tailbeat perturbations improve swimming efficiency in self-propelled flapping foils

Recent studies have shown that superimposing rhythmic perturbations to oscillating tailbeats could simultaneously enhance both the thrust and efficiency (Lehn et al., Phys. Rev. Fluids, vol. 2, 2017, p. 023101; Chao et al., PNAS Nexus, vol. 3, 2024, p. 073). However, these investigations were conducted with a tethered flapping foil, overlooking the self-propulsion intrinsic to real swimming fish. Here, we investigate how the high-frequency, low-amplitude superimposed rhythmic perturbations impact the self-propelled pitching and heaving swimming of a rigid foil. The swimming-speed-based Reynolds number ranges from 1400 to 2700 in our study, depending on superimposed perturbations and swimming modes. Numerical results reveal that perturbations significantly increase swimming speeds in both pitching and heaving motions, while enhancing efficiency exclusively in the heaving motion. Further derived scaling laws elucidate the relationships of perturbations with speeds, power costs and efficiency, respectively. These findings not only hypothesise the potential advantages of perturbations in biological systems, but also inspire designs and controls in biomimetic propulsion and manoeuvring within aquatic environments

Rapid validation of water wave metamaterials in a desktop-scale wave measurement system

Metamaterials have a unique ability to manipulate wave phenomena beyond their natural capabilities, and they have shown great promise in electromagnetic and acoustic wave control. However, their exploration in hydrodynamics remains limited. This article introduces a novel desktop-scale wave measurement system, specifically designed for the rapid prototyping and validation of water wave metamaterials. By utilizing 3D printing, the system accelerates the transition from theoretical designs to practical testing, offering a versatile and user-friendly platform. This is further enhanced by a synchronized stereo-camera setup and advanced data processing algorithms, enabling precise measurement and reconstruction of water wave behavior. Our experimental results demonstrate the system’s effectiveness in capturing intricate interactions between engineered structures and water waves. This significantly advances rapid prototyping for water wave metamaterial research, underscoring the system’s potential to catalyze further innovation in this emerging field

Effect of leading and secondary vortices on the propulsion performance of an undulating swimmer in the periodic vortex street

Aquatic animals have evolved diverse swimming techniques. They have demonstrated abilities to harness energy from vortices, particularly the Kármán vortex street, resulting in enhanced thrust. However, gaps remain in comprehensively understanding the factors influencing this increased thrust and the specific hydrodynamic characteristics involved. In this study, we studied an undulating foil downstream a circular cylinder to further understand the flow control mechanism involved in optimizing energy capture from hydrodynamic disturbances. We utilised numerical simulations with a moving adaptive mesh in laminar flow. We found that the leading vortex and secondary vortex at the foil's leading edge, originating from the Kármán vortex, played a crucial role in thrust enhancement. The undulating foil was more efficient in capturing energy from the Kármán vortex street than a stationary foil. When the foil was nearer to the cylinder, the energy capture was more evident, leading to intricate vortex patterns and easier leading vortex and secondary vortex generation. The foil's lift initially rose with closer proximity but decreased with increased distance. Our results showed that for minimal drag and optimal lift, the cylindrical body's position is closely tied to the interaction between the Kármán vortex street and the undulating foil. These insights can be applied in applications of designing efficient propulsion systems for underwater vehicles and optimising energy harnessing mechanisms in marine environments

Rapid and continuous regulating adhesion strength by mechanical micro-vibration

Controlled tuning of interface adhesion is crucial to a broad range of applications, such as space technology, micro-fabrication, flexible electronics, robotics, and bio-integrated devices. Here, we show a robust and predictable method to continuously regulate interface adhesion by exciting the mechanical micro-vibration in the adhesive system perpendicular to the contact plane. An analytic model reveals the underlying mechanism of adhesion hysteresis and dynamic instability. For a typical PDMS-glass adhesion system, the apparent adhesion strength can be enhanced by 77 times or weakened to 0. Notably, the resulting adhesion switching timescale is comparable to that of geckos (15 ms), and such rapid adhesion switching can be repeated for more than 2×10^7 vibration cycles without any noticeable degradation in the adhesion performance. Our method is independent of surface microstructures and does not require a preload, representing a simple and practical way to design and control surface adhesion in relevant applications