On two distinct Reynolds number regimes of a turbulent square jet

The effects of Reynolds number on both large-scale and small-scale turbulence properties are investigated in a square jet issuing from a square pipe. The detailed velocity fields were measured at five different exit Reynolds numbers of 8 × 10^3 〈 Re 〈 5 × 10^4. It is found that both large-scale properties （e.g,, rates of mean velocity decay and spread） and small-scale properties （e.g., the dimensionless dissipation rate constant A = εL/（u^2）^3/2） are dependent on Re for Re ≤ 3 ×10^4 or Reλ ≤ 190, but virtually become Re-independent with increasing Re or Reλ. In addition, for Reλ 〉 190, the value ofA = εL/（u^2）^3/2 in the present square jet converges to 0.5, which is consistent with the observation in direct numerical simulations of box turbulence, but lower than that in circular jet, plate wake flows, and grid turbulence. The discrepancies in critical Reynolds number and A = εL/（u^2）^3/2 among different turbulent flows most likely result from the flow type and initial conditions.

A palm-like 3D tactile sensor based on liquid-metal triboelectric nanogenerator for underwater robot gripper

The highly sensitive and power efficient tactile sensors can provide grippers with vertical and shear forces from interactions with objects. In an ocean environment with low visual distance and high noise, sea otters can rely on their palms to accurately identify and grasp target objects without damage. Inspired by the structure of the sea otter’s palm, this paper proposes a distributed liquid metal-based three-dimensional biomimetic underwater triboelectric palm-like tactile sensor (UPTS) for feedback-controlled grippers. The device is mainly composed of a flexible shell, a flexible cover, a flexible support, a triboelectric sensing unit and a fixed shell. The force acting on the flexible cover causes the flexible cover and sensing unit to deform, so that the sensing unit undergoes a contact-separation process, thereby generating an electrical signal. UPTS has the capability to identify the magnitude and direction of force, with a direction recognition error angle within 5 degrees. Additionally, it can distinguish the hardness and shape of objects, achieving an accuracy rate of 100% and 99.75% respectively for the tested objects. The results indicate that UPTS can provide force feedback for underwater grippers, thereby assisting the grippers in better completing salvage task.

Highly adaptive and broadband triboelectric energy harvester with stretching silicone rubber strip for variable harmonic frequency vibration

An enormous number of wireless sensing nodes(WSNs)are of great significance for the Internet of Things(IoT).It is tremendously prospective to realize the in-situ power supply of WSNs by harvesting unutilized mechanical vibration energy.A harmonic silicone rubber triboelectric nanogenerator(HSR-TENG)is developed focusing on ubiquitous constant working frequency machinery.The unique design of the strip serving as a flexible resonator realizes both soft contact and high and broadband output.The significant factors influencing the 1^(st)-order vibration mode of the strip are developed for realizing the harmonic frequency adaptation to external vibration.The surface treatment of the strip improves the output performance of HSR-TENG by 49.1%as well as eliminates the adhesion effect.The HSR-TENG is able to achieve a voltage output bandwidth of 19 Hz under a vibration strength of 3.0,showing its broadband capability.The peak power density of 153.9 W/m^(3)is achieved and 12×0.5 W light-emitting diodes(LEDs)are successfully illuminated by the HSR-TENG.It can continuously power a temperature sensor by harvesting the actual compressor vibration energy.In brief,the HSR-TENG provides a promising way for constant frequency vibration energy harvesting,so as to achieve in-situ power supply for the WSNs in the vicinity.

An intelligent self-powered life jacket system integrating multiple triboelectric fiber sensors for drowning rescue

The inherent unpredictability of the maritime environment leads to low rates of survival during accidents.Life jackets serve as a crucial safety measure in underwater environments.Nonetheless,most conventional life jackets lack the capability to monitor the wearer's underwater body movements,impeding their effectiveness in rescue operations.Here,we present an intelligent self-powered life jacket system(SPLJ)composed of a wireless body area sensing network,a set of deep learning analytics,and a human condition detection platform.Six coaxial core-shell structure triboelectric fiber sensors with high sensitivity,stretchability,and flexibility are integrated into this system.Addi-tionally,a portable integrated circuit module is incorporated into the SPLJ to facilitate real-time monitoring of the wearer's movement.Moreover,by leveraging the deep-learning-assisted data analytics and establishing a robust correlation between the wearer's movements and condition,we have developed a comprehensive system for monitoring drowning individuals,achieving an outstanding recognition accuracy of 100%.This groundbreaking work intro-duces a fresh approach to underwater intelligent survival devices,offering promising prospects for advancing underwater smart wearable devices in rescue operations and the development of ocean industry.

Highly adaptive triboelectric tactile sensor on the foot of autonomous wall-climbing robots for detecting the adhesion state and avoiding the hazard

Due to the excellent maneuverability and obstacle crossing of legged robots,it is possible for an autonomous legged wallclimbing robots to replace manual inspection of ship exterior panels.However,when the magnetic adsorption legged wallclimbing robot steps on the convex point or convex line of the wall,or even when the robot missteps,the robot is likely to detach from the ferromagnetic wall.Therefore,this paper proposes a tactile sensor for the legged magnetic adsorption wall-climbing robot to detect the magnetic adsorption state and improve the safety of the autonomous crawling of the robot.The tactile sensor mainly comprises a three-dimensional(3D)-printed shell,a tactile slider,and three isometric sensing units,with an optimized geometry.The experiment shows that the triboelectric tactile sensor can monitor the sliding depth of the tactile slider and control the light-emitting device(LED)signal light.In addition,in the demonstration experiment of detecting the adsorption state of the robot's foot,the triboelectric tactile sensor has strong adaptability to various ferromagnetic wall surfaces.Finally,this study establishes a robot gait control system to verify the feedback control ability of the triboelectric tactile sensor.The results show that the robot equipped with the triboelectric tactile sensor can recognize the dangerous area on the crawling wall and autonomously avoid the risk.Therefore,the proposed triboelectric tactile sensor has great potential in realizing the tactile sensing ability of robots and enhancing the safety and intelligent inspection of ultra-large vessels.

A humidity resistant and high performance triboelectric nanogenerator enabled by vortex-induced vibration for scavenging wind energy

Wind energy is a promising renewable energy source for a low-carbon society.This study is to develop a fully packaged vortexinduced vibration triboelectric nanogenerator(VIV-TENG)for scavenging wind energy.The VIV-TENG consists of a wind vane,internal power generation unit,an external frame,four springs,a square cylinder and a circular turntable.The internal power generation unit consists of polytetrafluoroethylene(PTFE)balls,a honeycomb frame and two copper electrodes.Different from most of the previous wind energy harvesting TENGs,the bouncing PTFE balls are fully packaged in the square cylinder.The distinct design separates the process of contact electrification from the external environment,and at the same time avoids the frictional wear of the ordinary wind energy harvesting TENGs.The corresponding VIV parameters are investigated to evaluate their influence on the vibration behaviors and the energy output.Resonant state of the VIV-TENG corresponds to the high output performance from the VIV-TENG.The distinct,robust structure ensures the full-packaged VIV-TENG can harvest wind energy from arbitrary directions and even in undesirable weather conditions.The study proposes a novel TENG configuration for harvesting wind energy and the VIV-TENG proves promising powering micro-electro-mechanical appliances.

A bio-inspired and self-powered triboelectric tactile sensor for underwater vehicle perception

Marine mammals relying on tactile perception for hunting are able to achieve a remarkably high prey capture rate without visual or acoustic perception.Here,a self-powered triboelectric palm-like tactile sensor(TPTS)is designed to build a tactile perceptual system for underwater vehicles.It is enabled by a three-dimensional structure that mimics the leathery,granular texture in the palms of sea otters,whose inner neural architecture provides additional clues indicating the importance of tactile information.With the assistance of palm structure and triboelectric nanogenerator technology,the proposed TPTS has the ability to detect and distinguish normal and shear external load in real-time and approximate the external stimulation area,especially not affected by the touch frequency,that is,it can maintain stable performance under high-frequency contact.The results show that the TPTS is a promising tool for integration into grippers mounted on underwater vehicles to complete numerous underwater tasks.

Deep-Learning-Assisted Underwater 3D Tactile Tensegrity

The growth of underwater robotic applications in ocean exploration and research has created an urgent need for effective tactile sensing.Here,we propose an underwater 3-dimensional tactile tensegrity(U3DTT)based on soft self-powered triboelectric nanogenerators and deep-learning-assisted data analytics.This device can measure and distinguish the magnitude,location,and orientation of perturbations in real time from both flow field and interaction with obstacles and provide collision protection for underwater vehicles operation.It is enabled by the structure that mimics terrestrial animals’musculoskeletal systems composed of both stiff bones and stretchable muscles.Moreover,when successfully integrated with underwater vehicles,the U3DTT shows advantages of multiple degrees of freedom in its shape modes,an ultrahigh sensitivity,and fast response times with a low cost and conformability.The real-time 3-dimensional pose of the U3DTT has been predicted with an average root-mean-square error of 0.76 in a water pool,indicating that this developed U3DTT is a promising technology in vehicles with tactile feedback.

A Triboelectric-Based Artificial Whisker for Reactive Obstacle Avoidance and Local Mapping

Since designing efficient tactile sensors for autonomous robots is still a challenge,this paper proposes a perceptual system based on a bioinspired triboelectric whisker sensor(TWS)that is aimed at reactive obstacle avoidance and local mapping in unknown environments.The proposed TWS is based on a triboelectric nanogenerator(TENG)and mimics the structure of rat whisker follicles.It operates to generate an output voltage via triboelectrification and electrostatic induction between the PTFE pellet and copper films(0.3 mm thickness),where a forced whisker shaft displaces a PTFE pellet(10 mm diameter).With the help of a biologically inspired structural design,the artificial whisker sensor can sense the contact position and approximate the external stimulation area,particularly in a dark environment.To highlight this sensor’s applicability and scalability,we demonstrate different functions,such as controlling LED lights,reactive obstacle avoidance,and local mapping of autonomous surface vehicles.The results show that the proposed TWS can be used as a tactile sensor for reactive obstacle avoidance and local mapping in robotics.