Numerical study on the effects of a semi-free and non-uniform flexible filament in different vortex streets

The variable flexibility of a fish body is believed to play a significant role in improving swimming performance.To explore the effect of non-uniform flexibility on the motion performance of fish under biologically relevant conditions,we set up three different flexible distribution modes for a semi-free filament and compared the motion performance of different flexible distribution modes through numerical simulations.The filament is located in the wake of the front flapping foil;it can swing adaptively in the lateral direction according to the flow situation of the surrounding fluid and finally reach a stable position.The results show that the motion state of the filament will alter with a change in the flexibility of the filament,from moving in the vortex street to moving on the side of the vortex street.In the Bénard-von Kármán(BvK)vortex streets,the drag coefficient of the filament increases as the flexibility of the filament increases,and the value of the drag coefficient is at a minimum when the flexibility of the filament increases linearly along the length of the filament.Further investigation indicates that at 85%–90%of the filament length(starting from the leading edge),the flexibility of the filament begins to increase significantly,and the filament can obtain its best propulsion performance.The results of this work provide new insights into the role of non-uniform flexibility during the process of fish movement and provide a valuable reference for the design of bionic underwater vehicles.

Effect of different bending shapes on thermal properties of flexible light-emitting diode filament

Heat dissipation is an important part of light-emitting diode(LED)filament research and has aroused constant concern.In this paper,we studied the thermal performance of flexible LED filament by numerical simulation and through experiment.The heat dissipation characteristics of spring-like structure flexible LED filament were computed by finite volume method,and it was found that the chip junction temperature was closely related to the pitch and the bending radius.The effect of inclination angle of lighting LED filament was discussed because it is relevant to the spring-like structure flexible LED filament in geometry.The results demonstrated that the temperature of the filament increases as the inclination angle improves.

Self-propelled swimming of a flexible fllament driven by coupled plunging and pitching motions

This paper numerically investigates the self-propelled swimming of a flexible filament driven by coupled pitching and plunging motions at the leading edge.The influences of bending rigidity and some actuation parameters(including the phase offset between pitching and plunging,and the amplitudes of pitching and plunging motions)on the swimming performance are explored.It is found that with increasing rigidity,the swimming style gradually transits from the undulatory mode to the oscillatory mode.The plunging-pitching actuation is found to be superior to the plunging-only actuation,in the sense that it prevents the decrease of speed at high rigidity and achieves a higher efficiency across a wide range of rigidity.The comparison of the body kinematics with those of animal swimmers,and the classification of the wake structures are discussed.The results of this study provide some novel insights for the bio-inspired design of autonomous underwater vehicles.

Ultra‑High Sensitivity Anisotropic Piezoelectric Sensors for Structural Health Monitoring and Robotic Perception

Monitoring minuscule mechanical signals,both in magnitude and direction,is imperative in many application scenarios,e.g.,structural health monitoring and robotic sensing systems.However,the piezoelectric sensor struggles to satisfy the requirements for directional recognition due to the limited piezoelectric coefficient matrix,and achieving sensitivity for detecting micrometer-scale deformations is also challenging.Herein,we develop a vector sensor composed of lead zirconate titanate-electronic grade glass fiber composite filaments with oriented arrangement,capable of detecting minute anisotropic deformations.The as-prepared vector sensor can identify the deformation directions even when subjected to an unprecedented nominal strain of 0.06%,thereby enabling its utility in accurately discerning the 5μm-height wrinkles in thin films and in monitoring human pulse waves.The ultra-high sensitivity is attributed to the formation of porous ferroelectret and the efficient load transfer efficiency of continuous lead zirconate titanate phase.Additionally,when integrated with machine learning techniques,the sensor’s capability to recognize multi-signals enables it to differentiate between 10 types of fine textures with 100%accuracy.The structural design in piezoelectric devices enables a more comprehensive perception of mechanical stimuli,offering a novel perspective for enhancing recognition accuracy.