Underwater Circumstance Research Articles

Clarifying early period hydration process of ultra‐low W/B cementitious composite subjected to underwater circumstance

AbstractAn innovative method is proposed in this study that combines long sequence precision prediction model with experiments to study how early hydration affects ultra‐low water‐binder ratio cementitious composite (ULWBRCC) properties. To be specific, by using heat release and degree of hydration as variables and introducing various temporal models to analyze the early hydration process, the micro‐ and macroscopic properties of specimens at different ages are assessed in detail. The obtained results can be summarized as follows: The long‐sequence accurate time series model can predict the earliest hydration process of underwater ULWBRCC, and the predicted late‐stage hydration pattern matches the experimental results. The underwater environment optimizes ULWBRCC's hydration process and increases its early compressive strength by 19.6%. The hydration of ULWBRCC is predicted using a time series model in the paper, filling the gap of uncertainty in the earliest performance of underwater rapid repair cement‐based composite materials, and the MSE of the Informer is improved by 92.88% compared with other models.

Acoustic notch filter based on self-collimation sonic crystals

Utilizing the self-collimation effect in two-dimensional (2D) sonic crystals (SCs), we have proposed an acoustic notch filter which is composed of two perfect mirrors and a beam splitter. Numerical simulation shows that by properly designing the inside structure of the 2D SC, the self-collimated acoustic waves with a desired frequency can be trapped between the two mirrors, realizing the notch filtering function. Moreover, the frequency and bandwidth of the notch filter can be arbitrarily adjusted by changing the parameters of the internel structure, in a considerably broad band. Potential applications include acoustic communication and acoustic signal processing, especially for underwater circumstances.

Diffraction Neural Network for Multi‐Source Information of Arrival Sensing

AbstractAll‐optical diffractive neural networks (DNNs) based on passive structures have been shown to perform complicated functions by optical acceleration, thus reforming in situ applications requiring digital computing processing. Its stable, compact, and passive features make it suitable for many conventional applications in complex electromagnetic environments. Here, a DNN based on a multilayer passive metasurface array is presented to estimate the information of arrival (IOA) over a wide range of frequency bands and incident angles. Unlike traditional methods, multiple correlated or coherent electromagnetic signals interfere with each other, resulting in difficult separation which is a fundamental obstacle in multi‐source IOA detection. Here, the proposed diffraction system creates separate virtual channels to isolate and process different incoming waves. It recognizes and classifies the beams, focuses them on the output plane divided by the arrival angle and working frequency, and displays the IOA and number of sources in real time at the speed of light. Furthermore, the massive‐parallelism and data‐post‐processing‐free strategy allows for broader applications in harsh environments, such as seismic detection and underwater circumstances.

Bioinspired flexible, breathable, waterproof and self-cleaning iontronic tactile sensors for special underwater sensing applications

Flexible tactile sensors are under high pursuit for wearable healthcare devices. However, challenges still exist in achieving both wearing comfortability through air permeability and hydrophobicity to resist water splash or even to be used in the special underwater circumstance. Inspired by the smart bio-structure of lotus leaf, we develop a flexible, breathable, waterproof and self-cleaning tactile sensor by sandwiching one ionogel electrolyte between two polydopamine (PDA)/MXene/stearic acid (STA) fabric electrodes. The micro-channels in the fabric and the through-holes in the gel endow the sensor with a high air breathability of 723.5 mm s−1 and the STA micro-sheets decorated on the outside surface of the sensor provide hydrophobicity with a large water droplet contact angle of 140.7° for the unique properties of self-cleaning and washability. By taking advantage of the supercapacitive sensing mechanism, the microstructures of MXene nanosheets on microfibers and the using of an interlayer with an internal aperture to initially separate electrodes and electrolyte, an extremely high sensitivity of up to 1677.79 kPa−1 is achieved. Practical sensing applications of the developed flexible sensors worn on different parts of human body for physiological signal monitoring, motion detection and silent information communication through Morse code in the special underwater circumstance are demonstrated.

Sonic demultiplexer based on self-collimation beams

The self-collimation effect of acoustic waves is a unique acoustic transmission phenomenon in two-dimensional (2D) phononic crystals (PCs), which has broad application prospects in acoustic wave regulation. In this paper, a sonic demultiplexer based on the self-collimation characteristics of 2D PCs is proposed. The sonic demultiplexer, which is composed of three Mach–Zehnder interference structures in 2D PCs, can demultiplex the incident acoustic waves that contain multiple frequencies. Moreover, the frequencies of the incident sound beams can be manipulated by adjusting the internal parameters of the demultiplexer. Potential applications include acoustic communication and acoustic signal processing, especially in underwater circumstances.

Transmission characteristics of linear Gaussian array beams propagating through seawater to air

We examine the transmission characteristics of linear Gaussian array beams (LGABs) propagating through seawater to air considering oceanic and atmospheric turbulences. We derive the expressions of the mean-squared beam width and Rayleigh range of LGABs for the case of both coherent and incoherent combinations using stochastic wave theory and the extended Huygens–Fresnel principle. In addition, the properties of mean-squared beam width versus propagation distance are studied. Furthermore, the characteristics of the Rayleigh range versus the ocean turbulence parameters and beam number as well as the interval distance are investigated. In the seawater–air interface, the Rayleigh range of LGABs is up to three times higher than that of the underwater circumstance. Moreover, the Rayleigh range increases linearly with the increase of interval distance in a turbulent ocean and turbulent atmosphere. It can be concluded that the Rayleigh range is more affected by the rate of dissipation of turbulent kinetic energy and the rate of dissipation of mean-square temperature than by the parameter related to temperature and salinity.

A stochastic nonlinear differential propagation model for underwater acoustic propagation: Theory and solution

• The perturb-coefficient nonlinear propagation equation is derived from the continuity equation, the Euler’s equation and the adiabatic equation. • The physical elements are divided into two types, and the location parameter to present the location-affected elements is designed. The stochastic parameter is designed to model the random-occur physical elements. The small parameters are used to demonstrate the weakly-nonlinear theory. • The initial and boundary conditions are analyzed. The solution existence of the SNDP model is proved. • The operator splitting procedure is proposed to solve the model numerically. The principle of underwater acoustic signal propagation is of vital importance to realize the “digital ocean”. However, underwater circumstances are becoming more complex and multi-factorial because of raising human activities, changing climate, to name a few. For this study, we formulate a mathematical model to describe the complex variation of underwater propagating acoustic signals, and the solving method are presented. Firstly, the perturb-coefficient nonlinear propagation equation is derived based on hydrodynamics and the adiabatic relation between pressure and density. Secondly, physical elements are divided into two types, intrinsic and extrinsic. The expression of the two types are combined with the perturb-coefficient nonlinear propagation equation by location and stochastic parameters to obtain the stochastic nonlinear differential propagation model. Thirdly, initial and boundary conditions are analyzed. The existence theorem for solutions is proved. Finally, the operator splitting procedure is proposed to obtain the solution of the model. Two simulations demonstrate that this model is effective and can be used in multiple circumstances.

Narrow band time–frequency space matched passive detector for underwater signal

Passive target detection under low signal-to-noise ratio is essential in various underwater circumstances, but difficult as lacking of targets’ prior information, special propagation characteristics and effect of background noise. Based on the time–frequency representation, we develop a narrow band time–frequency space matched method. The time–frequency matrix is derived based on the ray theory, the warping expression, and the pooling function. Then the sliding cumulative convolution of the matrix obtains a higher signal to noise ratio output. The likelihood ratio test detector is derived for passive target detection. Analysis and the ocean experiment results show that the proposed approach outperforms other passive detectors.

Bioinspired, Superhydrophobic, and Paper-Based Strain Sensors for Wearable and Underwater Applications.

There is currently a growing demand for flexible strain sensors with high performance and water repellency for various applications such as human motion monitoring, sweat or humidity detection, and certain underwater tests. Among these strain sensors, paper-based ones have attracted increasing attention because they coincide with the future development trend of environment-friendly electronic products. However, paper-based electronics are easy to fail when they encounter water and are thus unable to be applied to humid or underwater circumstances. Herein, based on a strategy of coupling bionics inspired by lotus leaf and scorpion, which exhibit superhydrophobic characteristics and ultrasensitive vibration-sensing capacity, respectively, a paper-based strain sensor with high sensitivity and water repellency is successfully fabricated. As a result, the strain sensor exhibits a gauge factor of 263.34, a high strain resolution (0.098%), a fast response time (78 ms), excellent stability over 12,000 cycles, and a water contact angle of 164°. Owing to the bioinspired structures and function mechanisms, the paper-based strain sensor is suitable to not only serve as regular wearable electronics to monitor human motions in real-time but also to detect subtle underwater vibrations, demonstrating its great potential for numerous applications like wearable electronics, water environmental protection, and underwater robots.

A direct ethylene glycol fuel cell stack as air-independent power sources for underwater and outer space applications

A passive direct ethylene glycol fuel cell stack is developed and tested, in which each single cell consists of an alkaline Pd-based anode, an acid Au-based cathode, and a cation exchange membrane. Experimentally, at the optimal reactant-feeding concentrations of 5.0 M EG and 9.0 M KOH as anolyte and 4.0 M H2O2 and 1.0 M H2SO4 as catholyte, this passive stack yields an open-circuit voltage of 3.0 V, a maximum current of 860 mA, and a peak power of 1178 mW at room temperature, which exhibits a two-time higher peak power density (24.5 mW cm−2) than a passive stack using the same type of fuel but the air as oxidant (12 mW cm−2). The impressive improvement can be ascribed to the faster hydrogen peroxide reduction reaction due to its two-electron transfer process rather than a four-electron process. In addition, the effects of feeding concentrations of reactants in both anolyte and catholyte on the stack performance are studied. Finally, the present passive stack is applied to power an electric fan for around 3 h under the mimetic underwater circumstance, demonstrating that this passive stack is a promising power source for airtight situations, such as underwater and outer space.

Research on underwater flux cored arc cutting mechanism based on simulation of kerf formation

As an efficient underwater cutting method, flux cored arc cutting is not clear in its mechanism because it is difficult to directly observe the process. In this paper, we studied the mechanism of flux cored arc cutting in air first. The impact of cutting parameters was studied by cutting workpiece’s edge and observing it with a high-speed camera system. Secondly, a sandwich structure was designed to observe the underwater cutting process. The characteristics of air and underwater cutting were analyzed and compared, and it showed that the arc moved up and down while moving forward with the cutting torch in both circumstances. Based on the arc movement characteristics and the underwater circumstance, a numerical simulation of the underwater cutting process was conducted. The simulation results showed that different cutting parameters led to different cutting mode and kerf forming. The numerical results of temperature distribution and kerf shape were consistent to the experimental data, which revealed the cutting mechanism. This work is significant for further process optimization and cutting automation.

Ionic Electroactive Polymers Used in Bionic Robots: A Review

Ionic electroactive polymers (IEAPs) are a category of intelligent soft materials exhibiting large displacement under electric excitation, based on inner ion or solvent transport. Due to their unique advantages such as flexibility, low driving voltage, large bending displacement and aquatic-environment adaptability, IEAPs have been documented as very promising actuators for the applications in bionic robots. This review presents an analysis to the current research status of IEAPs exploited in bionic robots. According to the specific bionic parts, those robots are divided into four classes: imitation of fins, limbs, joints and trunks. Their dimension, weight, voltage amplitude, frequency and maximum speed were summarized to show the optimum design range. The results show that the approach velocity of the current robots were higher (> 35 mm·s-1) when the robot weighted 60 g–180 g and the body was 90 mm–130 mm long. For voltage from 1 V–3 V and frequencies from 0.7 Hz–1.2 Hz, the speed was relatively higher (> 35 mm·s-1). To some extent, the maximum speed decreases when the area of the IEAP material used in bionic robot increases. For underwater circumstances, IEAP materials are most suitable for designing bionic robots swimming with Body and/or Caudal Fin (BCF). This review provides important guidance for the design of IEAP bionic robots.

Optimal Relay Node Placement and Flow Allocation in Underwater Acoustic Sensor Networks

In recent years, underwater acoustic sensor networks (UASNs) have attracted widespread attention in academia. Prolonging the network lifetime is a crucial issue for UASNs. Compared with traditional wireless sensor networks (WSNs), stringent energy becomes more critical in UASNs because the battery equipped at sensor nodes has the limited amount of energy and it is much more difficult to replace or recharge in underwater circumstance. This fact motivates us to pursue the solutions to reduce power consumption by using relay nodes and flow allocation mechanism in order to extend the network lifetime. In this paper, the issues of relay node placement and the flow allocation have been considered as a joint problem and are formulated into an integer nonlinear programming problem, which is node placement-hard in general. To solve the problem efficiently, this paper proposes a novel heuristic scheme for UASNs, which works based on a 3-D architecture. The proposed scheme consists of three algorithms, named as Alternative Flow and Relay-node Adjustment as a whole. Extensive simulation experiments demonstrate that the proposed scheme offers a simple yet attractive solution to the problem.

RC잠수함을 이용한 해상풍력하부구조 모니터링 융합시스템

모형잠수함, 중계부 및 제어부를 포함하는 수중 탐사 장치. 모형잠수함이 촬영한 영상정보를 중계부를 통해 전송한다. 모형잠수함의 자세 및 속도를 제어하는 제어신호 또한 중계부를 통해 제어 한다, 모형잠수함은 수중환경을 촬영하여 영상을 중계부로 전송하고, 중계부는 제어신호를 수신하여 수중에서 자세 및 속도를 제어한다, 중계부는 부표에 결합되어 수면에서 부유하고 제어부와 모형잠수함 사이에서 영상신호와 제어신호를 중계하되, 제어부와는 무선통신을 수행한다. 모형잠수함과는 유도선을 통해 유선통신을 수행하는 것으로 부표에 설치된 중계부와 모형잠수함 간을 유선통신으로 연결함으로써 모형잠수함에 대한 분실의 위험 없이 원활하게 수중 탐사를 수행할 수 있다. 또한 중계부와 제어부 간을 무선통신으로 연결함으로써 수중탐사를 쉽고 용이하게 수행할 수 있다. 이런 모형잠수함과 무선통신 및 제어를 결합한 융합기술을 구현하였다. The image information acquired by a model submarine is transmitted through the repeater. The control signal of a position for submarine and its speed is also controlled by the repeater. Shooting images of underwater circumstances are transmitted to the repeater where the received signal controls a position and speed of underwater submarine. This repeater is combined by a buoy that is floating on the surface to relay the signal of image as well as control between a control unit and a submarine whereas the repeater communicates wirelessly with a control unit. Due to wire communication between the repeater and the submarine, the underwater exploration can be smoothly carried out without a risk of loss of a model submarine. Also, connecting to the repeater and control unit wirelessly makes it possible to conduct easily the underwater exploration. The convergence technology that combines a wireless communication and a control as well as a model submarine is designed.

Effects of hyperbaric nitrogen-induced narcosis on response-selection processes

Certain underwater circumstances carry risk of inert gas narcosis. Impairment of sensorimotor information processing due to narcosis, induced by normobaric nitrous oxide or high partial nitrogen pressure, has been broadly evidenced, by a lengthening of the reaction time (RT). However, the locus of this effect remains a matter of debate. We examined whether inert gas narcosis affects the response-selection stage of sensorimotor information processing. We compared an air normobaric condition with a hyperbaric condition in which 10 subjects were subjected to 6 absolute atmospheres of 8.33% O2 Nitrox. In both conditions, subjects performed a between-hand choice-RT task in which we explicitly manipulated the stimulus–response association rule. The effect of this manipulation (which is supposed to affect response-selection processes) was modified by inert gas narcosis. It is concluded, therefore, that response selection processes are among the loci involved in the effect of inert gas narcosis on information processing.

Algorithm for Imaging Sonar Target Detection based on Geometry Characteristic and SVM

The attack from small speedboat and underwater robot is becoming more and more serious. And most powerful countries have installed underwater surveillance systems to protect port, ship, seashore depository and anchorage. The detection technology of underwater target is the most important technology in the process of surveillance. In order to take good advantage of the target’s geometry characteristic and classification function of SVM(Support Vector Machine), an algorithm for imaging sonar target detection based on geometry characteristic and SVM is proposed in the paper. The experiment results are presented and show that this algorithm is in high detection rate under complex underwater circumstance.