Underwater Submarine Research Articles

Numerical Simulation of Bionic Underwater Vehicle Morphology Drag Optimisation and Flow Field Noise Analysis

The study of aquatic organisms’ ectomorphology is important to understanding the mechanisms of efficient swimming and drag reduction in fish. The drag reduction mechanism in fish remains unknown yet is needed for optimising the efficiency of bionic fish. It is thus crucial to conduct drag tests and analyses. In this paper, an optimal dolphin morphological model is constructed taking the beakless porpoise as the research object. A numerical simulation of the dolphin body model is carried out for different combinations of pitch angle and speed adopting computational fluid dynamics, and the flow field noise of the dolphin body model is solved for different speeds using the FW-H equation. When the dolphin model is oriented horizontally, the differential pressure drag accounts for approximately 20–25% of the total drag as airspeed increases. As both the pitch angle and airspeed increase, the differential pressure drag and friction drag decrease with increasing airspeed. Moreover, the acoustic energy is mainly concentrated at low frequencies for both the dolphin and Bluefin-21 models. The dolphin body model has better noise performance than the Bluefin-21 model at the same speed. The optimisation of the external morphology of the bionic underwater submarine and the analysis of the shape drag are thus important for revealing the drag reduction mechanism, reducing noise in the flow field and provide guidance for research on bionic fish.

Localization of Underwater Submarines Based on a Two-Dimensional Trajectory Tracking Model

Localization of Underwater Submarines Based on a Two-Dimensional Trajectory Tracking Model

ADAPTIVE CONTROL OF A SUBMARINE FOR VARIOUS DIVING DEPTHS USING AN EXPONENTIAL

Due to the progress of deep submergence capabilities, a submarine is extensively employed on many sides of marine science. For that reason, it has become necessary to design an effective submarine position controller while achieving a fast and stable mission. An adaptive analytical scheme for the underwater submarine was developed. The main purpose of the adaptive analytical scheme is to provide a powerful analytical controller that can successfully steer the submarine from the current state under the water to the surface of water in a short time. To achieve that, a seventh-term exponential function was proposed to reshape the reference diving depth while maintaining the control variable limitation and satisfying initial and final boundary conditions. The direct search method with two cascade loops was employed to achieve a minimum cost function by determining an appropriate constant of the function and minimum final time. However, using the direct search method can be time-consuming since a number of algebraic operations are executed inside these two loops. Therefore, the curve fitting method was used to fit the set of direct search method data using power functions. Then, at a certain diving depth, the function coefficients were computed based on the final settling time and function constant using the Gaussian elimination method. A nominal numerical simulation of the submarine’s model was implemented using both adaptive analytical and linear controllers.

Ultrafast underwater self-healing piezo-ionic elastomer via dynamic hydrophobic-hydrolytic domains

The development of advanced materials capable of autonomous self-healing and mechanical stimulus sensing in aquatic environments holds great promise for applications in underwater soft electronics, underwater robotics, and water-resistant human-machine interfaces. However, achieving superior autonomous self-healing properties and effective sensing simultaneously in an aquatic environment is rarely feasible. Here, we present an ultrafast underwater molecularly engineered self-healing piezo-ionic elastomer inspired by the cephalopod’s suckers, which possess self-healing properties and mechanosensitive ion channels. Through strategic engineering of hydrophobic C–F groups, hydrolytic boronate ester bonds, and ions, the material achieves outstanding self-healing efficiencies, with speeds of 94.5% (9.1 µm/min) in air and 89.6% (13.3 µm/min) underwater, coupled with remarkable pressure sensitivity (18.1 kPa–1) for sensing performance. Furthermore, integration of this mechanosensitive device into an underwater submarine for signal transmission and light emitting diode modulation demonstrates its potential for underwater robotics and smarter human-machine interactions.

Acoustic Scattering Characteristics and Geometric Parameter Prediction for Underwater Multiple Targets Arranged in a Linear Pattern

The construction of wind farm pilings, submarine pipelines, and underwater submarines involves multiple cylinders. However, there is currently a lack of economic research on predicting the mechanism and characteristics of mutual coupling of acoustic scattering from multiple cylindrical targets. This study investigates the mechanism and prediction method of acoustic scattering for the structural distribution characteristics of underwater multi-cylindrical targets. A model of a multi-cylindrical target’s two-dimensional acoustic field was established using the finite element method. Numerical calculations were then carried out to elucidate the scattering characteristics of the frequency–angle spectrum in far-field omnidirectional scattering. The simulation of echoes in the time domain explains how echoes propagate and interact with each other, and provides formulas for calculating interference and resonance frequencies. The frequency calculation formula extracts key features from the spectrum, providing a basis for predicting the characteristics of multi-cylindrical targets in terms of scale and spatial position. Measurement experiments were conducted on a double-cylindrical target in a water tank, and the theoretical calculations and experimental data were used to estimate the target’s radius and distance. The actual layout confirms the accuracy of the interference and resonance frequency prediction formulas. This study offers a valuable solution for refined feature extraction and spatial estimation of underwater targets.

RDNN for Classification and Prediction of Rock or Mine in Underwater Acoustics

Mines in the waters are just explosives that detonate upon contact with an object. The underwater submarine must foresee if it will encounter a mine or a rock. Lacking the development of the Ranging Sound Navigation approach, which utilizes particular variables to identify whether a surface or a barrier is made of a mine or rock, finding mines or rocks would have been extremely difficult. In our study, we demonstrate a technique for predicting underwater rocks and mines using SONAR waves. At 60 different angles, SONAR pings are employed to record the various frequencies of submerged objects. To identify whether the object in the ocean is a mine or just a rock, the submarine uses SONAR signals, which transmit sound and receive switchbacks. The mine and rock categories are predicted using the prediction models. To create these prediction models, Supervised Machine Learning Classification methods were employed.

Direct Air-to-Underwater Optical Wireless Communication: Statistical Characterization and Outage Performance

In general, a buoy relay is used to connect the underwater communication to the terrestrial network over a radio or optical wireless communication (OWC) link. The use of relay deployment may pose security and deployment issues. This paper investigates the feasibility of direct air-to-underwater (A2UW) communication from an over-the-sea OWC system to an underwater submarine without deploying a relaying node. We analyze the statistical performance of the direct transmission over the combined channel fading effect of atmospheric turbulence, random fog, air-to-water interface, oceanic turbulence, and pointing errors. We develop novel analytical expressions for the probability density function (PDF) and cumulative distribution function (CDF) of the resultant signal-to-noise ratio (SNR) in terms of bivariate Meijer-G and Fox-H functions. We use the derived statistical results to analyze the system performance by providing exact and asymptotic results of the outage probability in terms of system parameters. We use computer simulations to demonstrate the performance of direct A2UW transmissions compared to the relay-assisted system.

Exploring a Warm Water Inflow Below an Antarctic Ice Shelf

Researchers guided an autonomous underwater submarine to capture the first direct observations of a warm water current flowing in below the Filchner-Ronne Ice Shelf in Antarctica.

Investigation and Numerical Simulation of the Acoustic Target Strength of the Underwater Submarine Vehicle

Modern weapon systems’ survival hinges on their detection capabilities more than anything else. In the active sonar equation, the acoustic target strength is crucial. Under the assumption of plane wave propagation, the standard target strength equation is used to forecast the reradiated intensity for the far field. The ability of a submarine to remain unnoticed while on patrol or accomplishing a mission is its primary defense. Sonar, sometimes known as sound navigation ranging, is a popular method for locating submarines. This is because saltwater effectively absorbs radio frequencies. Sonar technology is used in more than just the commercial fishing business; it is also used in undersea research. The submarine’s designers consider the reflection of acoustic waves to minimize the amount of space required for such reflections. The Target Strength (TS) metric is used to assess the sonar objects’ size. This manuscript explains and demystifies the Benchmark Target Echo Strength Simulation (BeTTSi) benchmark submarine’s TS analysis. This model’s Pressure Acoustic-Boundary Element Model (PA-BEM) interface has been stabilized, and the model itself is pretty huge acoustically.

Improving extreme response prediction of a subsea shuttle tanker hovering in ocean current using an alternative highly correlated response signal

A subsea shuttle tanker (SST) is a pioneering underwater submarine specifically designed to economically transport CO2 to smaller hydrocarbon fields. During loading and unloading of the CO2, the SST hovers over the well and experiences extreme heave motions resulting in extreme hydrostatic loading. Sustaining the hydrostatic loading is indispensable as it forms the dominating load and is a driving factor determining the SST hull's collapse design. Furthermore, the SST's extreme surge motion regulates the length of the flowline to evade snap loads. This paper focuses on the problem of determining these extreme positional responses at one location when the aft thruster fails during offloading using data with a shorter time record from another location at the SST. This scenario could be of practical engineering importance when either one of the sensors is malfunctioning or another similar vessel is being designed for the same environmental condition. A 2D planar Simulink model is used to generate the empirical data required for the study.

Underwater Submarine Path Planning Based on Artificial Potential Field Ant Colony Algorithm and Velocity Obstacle Method.

Navigating safely in complex marine environments is a challenge for submarines because proper path planning underwater is difficult. This paper decomposes the submarine path planning problem into global path planning and local dynamic obstacle avoidance. Firstly, an artificial potential field ant colony algorithm (APF-ACO) based on an improved artificial potential field algorithm and improved ant colony algorithm is proposed to solve the problem of submarine underwater global path planning. Compared with the Optimized ACO algorithm proposed based on a similar background, the APF-ACO algorithm has a faster convergence speed and better path planning results. Using an inflection point optimization algorithm greatly reduces the number and length of inflection points in the path. Using the Clothoid curve fitting algorithm to optimize the path results, a smoother and more stable path result is obtained. In addition, this paper uses a three-dimensional dynamic obstacle avoidance algorithm based on the velocity obstacle method. The experimental results show that the algorithm can help submarines to identify threatening dynamic obstacles and avoid collisions effectively. Finally, we experimented with the algorithm in the submarine underwater semi-physical simulation system, and the experimental results verified the effectiveness of the algorithm.

Characteristics of Low-Frequency Acoustic Wave Propagation in Ice-Covered Shallow Water Environment

Mastering the sound propagation law of low-frequency signals in the Arctic is a major frontier basic research demand to improve the level of detection, communication, and navigation technology. It is of practical significance for long-distance sound propagation and underwater target detection in the Arctic Ocean. Therefore, how to establish an effective model to study the characteristics of the acoustic field in the Arctic area has always been a hot topic in polar acoustic research. Aimed at solving this problem, a mathematical polar acoustic field model with an elastic seafloor is developed based on a range-dependent elastic parabolic equation theory. Moreover, this method is applied to study the characteristics of polar sound propagation for the first attempt. The validity and effectiveness of the method and model are verified by the elastic normal mode method. Simultaneously, the propagation characteristics of low-frequency signals are studied in a polar sound field from three aspects, which are seafloor parameters, sea depth, and ice thickness. The results show that the elastic parabolic equation method can be well utilized to the Arctic low-frequency acoustic field. The analysis of the influence factors of the polar sound field reveals the laws of sound transmission loss of low-frequency signals, which is of great significance to provide information prediction for underwater submarine target detection and target recognition.

Numerical investigation of tip-vortex cavitation noise of submarine propellers using hybrid computational hydro-acoustic approach

In this study, the hybrid computational hydro-acoustics (CHA) method is applied to predict hydrodynamic noise due to tip vortex cavitation (TVC) of underwater submarine propellers. The hybrid CHA approach consists of two sequential methods: Delayed Detached Eddy Simulation (DDES) technique with adaptive mesh refinement method and the Ffowcs Williams and Hawkings (FW–H) equation. The former is utilized for accurate prediction of TVC of underwater propellers, and the latter is used for efficient prediction of hydro-acoustic pressure due to cavitating flow. The target submarine and propeller are the DARPA suboff submarine and two high skew propellers with skew angles of 17 and 38°. The propellers are designed to investigate the effects of skew angle on TVC and its noise. The corresponding experiments are performed in the Large Cavitation Tunnel (LCT) of the Korea Research Institute of Ships and Ocean Engineering (KRISO). The two preliminary simulations are carried out to confirm the close reproduction of the experimental conditions in the main simulations. First, the flow through the LCT test section is simulated to confirm the accurate reproduction of the wall boundary layer. Its validity is confirmed by comparing the predicted boundary layer profiles with the measured results. Second, the flow over the DARPA suboff submarine without a propeller in the LCT test section is simulated to confirm the accurate prediction of the inflow distortion originating from the boundary layer flow of the submarine body. Its validity is also confirmed by comparing the predicted nominal wake field with the measured one. After the close reproduction of these two effects is confirmed, the cavitating flow of the propellers installed to the DARPA suboff submarine body is simulated by using the DDES technique combined with adaptive mesh refinement, and the TVC noise is predicted by applying the quadrupole-corrected FW-H equation to the surfaces enclosing the propellers. The predicted TVC of the propeller closely follows the measured one. The numerical and experimental results capture the TVC induced by the wake flows due to the submarine body's rudders and sail. The predicted hydro-acoustic pressure spectra due to the propellers' cavitating flow also show excellent agreements with the predicted ones. Besides, both the numerical and experimental results confirm that the lower noise is generated by the propeller with a higher skew angle.

Remote hydroacoustic-infrasonic detection and characterization of Anak Krakatau eruptive activity leading to, during, and following the December 2018 flank collapse and tsunami

A climactic eruption phase on December 22, 2018, triggered the collapse of the southwest flank and summit of Anak Krakatau stratovolcano, generating a tsunami which struck the coastlines of Sumatra and Java. We employ a selection of remote moored hydroacoustic (H08S, 3307 km; H01W, 3720 km) and infrasonic (IS06, 1156 km; IS07, 3475 km; IS52, 3638 km) stations of the International Monitoring System (IMS) to investigate eruptive activity preceding, during, and after the climactic eruption phase. We observe 6 months of co-eruptive intermittent infrasound at IS06 and powerful infrasound from the climactic eruption on IS06 and IS52. The climactic eruption phase was not detected hydroacoustically, but we observe a ~ 12-day swarm of hydroacoustic signals beginning 24 days before the flank collapse event that we attribute to sustained submarine eruptive activity at Anak Krakatau. We perform hydroacoustic waveform and envelope multiplet analysis to assess event similarity during the hydroacoustic swarm. Hydroacoustic waveforms are not well-correlated, but envelopes with a main pulse duration of ~ 20-s are correlated, with 88.7% of 247 events grouping into two multiplets using a threshold correlation coefficient of 0.75. The repetitive envelopes indicate a repetitive impulsive volcanic process, either underwater submarine explosions or volcanic earthquakes in the solid Earth coupled to the water column from the Sunda Shelf. This study further underscores the potential of remote acoustic technology for detecting and characterizing eruptions at submarine or partially submerged volcanoes.

Primjena B-splajna na identifi kaciju jednadžbi kretanja plovnih objekata

The paper presents the possibilities of using B-splines to determine a mathematical model in the form of linear differential equations describing the change of the motion parameters of floating objects depending on the values of the control signals. The elaborated identification system is a collection of algorithms including: approximation of input and output signals, optimal selection of differential equation coefficients and model verification. The basic spline functions were used to approximate the values of the input and output signals. The developed method was illustrated by an example of identification of underwater submarine motion equations describing the change in draft depth and trim angle depending on the difference between buoyancy force and ship’s weight.

Resistance and flow field of a submarine in a density stratified fluid

The research on resistance and wake of an underwater submarine in density-stratified fluid is very necessary. To study the hydrodynamic performances of an underwater submarine navigating in density-stratified fluid, a CFD model is established based on RANS equations, combined with the Realizable k - ε turbulence and Euler multiphase flow models. Meanwhile, the VOF method is used for capturing the interface. At first, the established CFD model is validated by comparing with experimental results. Thereafter, the resistance and flow field of a full-scale SUBOFF model in density-stratified and uniform fluids with different forward speeds, submerged positions and fluid densities are investigated. The results show that the forward speed and submerged depth significantly affect the hydrodynamic performances of the submarine. However, the density of the lower layer and the distance of submarine above the internal surface both have little effect. The influence of the density stratification on the resistance increases as the forward speed becomes faster and the position becomes closer to the free surface. The pattern of the internal wave when submarine navigates under the internal interface is obviously different from that when submarine navigates above the internal interface. In general, the pattern of the internal wave changes more slowly than that of the free surface.

Feasibility Analysis of Magnetic Navigation for Vehicles.

Magnetic navigation is a promising positioning technique for scenarios where a global navigation satellite system (GNSS) is unavailable, such as for underwater submarines and aircraft in space. For ground scenarios, it faces more challenges, since the magnetic distribution suffers interference from surrounding objects such as buildings, bridges, and vehicles. It is natural to think how feasible it is to apply magnetic matching positioning to vehicles. In this paper, a theoretic distribution model is proposed to analyze the magnetic field around objects such as buildings, bridges, and vehicles. According to the experiments, it is shown that the proposed model matches the experimental data well. In addition, a comprehensive indicator metric is defined in this paper to describe the feasibility of the magnetic matching method based on the statistical characteristics of magnetic maps. The best length of matching window, anti-noise performance, and pre-comparison of positioning accuracy in different regions can be easily derived using the proposed comprehensive indicator metric. Finally, the metric is verified through a drive test using different building densities.

Research on Probability of Detection of Submarine Time Limit Based on Continuous Time within Finite Region

The sonar detection of underwater submarines in a certain sea area was modeled by using the sonar in the sea area. The problem of continuous detection time of underwater large random targets was studied based on the fixed detection points. According to the characteristics of the target’s motion, this paper puts forward the research method of detecting the probability of finding the time limit of the random moving target by fixed point detection, establishes the random constant velocity target distribution model under the target initial position distribution, uses this model to carry on the duration. The effective probing time and the redundant probing time exist in the probing and continuous probing times. The probabilistic trend of the probing probability under the probing limit time decreases with the increase of the distance between the probing point and the distribution center. The effective probing time length increases with the probing point The distance from the center generally increases, but there is no linear rule.

The Numerical Investigation of Optical Error Compensation for Dynamic Target by FSM in Photoelectric Mast

In this paper, firstly, based on the basic control equations of fluid mechanics, the effects of the fluid on force and vortex induced vibration around underwater submarine model are studied and discussed, employing the finite volume method by hierarchy grids. Secondly, the structural characteristics, transfer functions and control strategies of Steering Mirror Fast (FSM) are analyzed and obtained. The disturbance of moment also has been resolved to optical axis coordinate system. Finally, take the optical model of submarine as the research background, the effects of the FSM on the stability improvement of photoelectric tracking system are discussed. The results show that the disturbance of submarine moments mainly origin from the vortex induced vibration. The dynamic target tracking error could be suppressed. This research explores vortex induced vibration control in optical filter. Therefore, it holds certain scientific significance and practical value.

Application of a Winch-type Towed Acoustic Sensor to a Wave-powered Unmanned Surface Vehicle

Although many countries have focused on anti-submarine warfare for several decades, underwater submarines can hardly be detected by current assets such as patrol aircraft, surface ships and fixed underwater surveillance systems. Due to the difficult conditions of the oceanic environment and the relative quietness of submarines, existing acoustic surveillance platforms are not able to fully cover their mission areas. To fill in the gaps, a winch-type towed acoustic sensor system was developed and integrated into a wave-powered unmanned surface vehicle by the Korea Institute of Ocean Science and Technology. In June 2015, sea trial tests were conducted to verify maneuvering, acoustic signal detection, and communication capabilities. During the maneuvering test, the wave-powered glider successfully moved along programmed waypoints. Despite towing the acoustic sensor system, only 20% of initial electricity was consumed in 20 days. The acoustic sensor was lowered to depths of 100–150 m by the winch system, and received signals from an acoustic simulator lowered to depths of 50–100 m by RV Jangmok. Simulated submarine noises that were refracted downward could be clearly received and classified by the hydrophone system, from distances of 2–8 km, while it was being towed silently and deeply. In addition, an optical camera provided high-resolution images of surface vessels, allowing integration with acoustic detection of underwater objects. In conclusion, this new platform using a deeply towed hydrophone system is worthy of consideration as an underwater surveillance asset. Future work is required to strengthen inter-asset communication and obstacle avoidance, and to overcome strong currents to make this technology a reliable part of the underwater surveillance network.