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This paper presents the design, test, and experimentation at sea of four JANUS-based services for operationally relevant underwater applications: 1) first contact and language switching; 2) transmission of automatic identification system data to submerged assets; 3) transmission of meteorological and oceanographic data to underwater vessels; and 4) support in distressed submarine operations. On March 24, 2017, JANUS was promulgated as a NATO standard (STANAG 4748) [1], marking the first time that a digital acoustic communications protocol is adopted at international level. JANUS is an open, simple, and robust modulation and coding scheme developed by the NATO STO Centre for Maritime Research and Experimentation, in collaboration with academia and industry. The implementation of the services presented in this paper is based on a standardized protocol and offers the potential to widely increase the safety and efficiency in maritime operations. The objective of this paper is to demonstrate that JANUS can be used in support of maritime operations, potentially increasing their efficiency. Such demonstration is achieved through experimentation at sea of four operationally relevant JANUS-based services. The four JANUS-based services discussed were validated during two different sea trials: REP15-Atlantic and REP16-Atlantic. During those trials, various heterogeneous configurations were considered, including the use of a state-of-the-art diesel-electric submarine, guaranteeing maximum relevance for validation and evaluation of the designed solutions. The collected results demonstrate that JANUS is a viable solution for operationally relevant underwater applications, thus validating the objective of this paper. Additionally, encouraging feedback has been provided by the operational community participating to the trials. The capabilities demonstrated served as an initial proof of concept and will certainly lead to newer requirements and eventually even more functionalities. [ABSTRACT FROM AUTHOR]

This paper presents and investigates a dual-hop mixed radio frequency (RF) and underwater optical communication (UWOC) system. In the proposed system, an unmanned aerial vehicle (UAV) such as drone (S) located at low altitude is transmitting data signal towards the destination (D) which is located under water such as a submarine through a decode and forward (DF) relay (R) mounted on a ship over the sea surface. The data signal is transmitted from the UAV towards the relay located on the ship via RF channel modelled by the Nakagami- $ m$ distributed fading statistics. The relay decodes the received RF data signal and re-transmits it towards the destination via visible light channel modelled by Exponential Generalized Gamma (EGG) distribution. Using the DF relaying protocol, we derive closed form analytical expressions for the outage probability and average bit error rate of the proposed mixed RF-UWOC system. Additionally, UAV optimal altitude analysis has been carried out to find the optimal elevation angle corresponding to the optimal altitude of the UAV where the system performance is maximized. The numerical simulation is carried out to support the performance analysis of the mixed RF-UWOC system and shows the influence of the various channel parameters such as air bubbles, UAV altitude, water salinity variations and scintillation on the end to end performance of the mixed RF-UWOC system. [ABSTRACT FROM AUTHOR]

We consider the problem of maximum-likelihood (ML) direction-of-arrival (DOA) estimation of underwater acoustic signals from ships, submarines, or torpedoes, which contain both sinusoidal and random components, and are called mixed signals in this paper. We model the mixed signals as the mixture of deterministic sinusoidal signals and stochastic Gaussian signals, and derive the ML DOA estimator for the mixed signals under spatially white noise. We compute the asymptotic error covariance matrix of the proposed ML estimator, as well as that of the typical stochastic estimator assuming zero-mean Gaussian signals, for DOA estimation of mixed signals. Our analytical comparison and numerical examples show that the proposed ML estimator, which takes advantage of the sinusoidal components in the mixed signals, improves the DOA estimation accuracy for the mixed signals compared with the typical stochastic estimator assuming zero-mean Gaussian signals. [ABSTRACT FROM AUTHOR]

In this paper, a general formulation of the problem of control of underwater vehicles in full unsteady flow is presented. First, a reduced-order model of the coupled fluid vehicle (CFV) system is developed. The inability to observe fluid motion motivates a fluid compensation control (FCC) approach that compensates for the hydrodynamic loads synthesized from surface measurements. The FCC consists of a tracker, a regulator, and a fluid compensator. A condition is provided that guarantees vehicle stability. The tradeoff between regulation and fluid compensation is also examined. A numerical example of an elliptically shaped vehicle illustrates the results. [ABSTRACT FROM AUTHOR]

In this paper, the problem of minimizing the noise generated by the propeller and the control surfaces of a manned submarine is addressed. Cavitation attached to propeller blades and hydrofoils as well as vortex cavitation occurring at a distance from propeller blades and hydrofoils which is generated by turbulent boundary layers is considered. The main goal is to compute trajectories for different tactically relevant maneuvers that minimize the noise generated by its associated prevalent source. To this end, we consider a constrained, nonlinear, optimal control problem which has a system of 12 nonlinear differential equations as the underlaying state law and a Bolza-type cost function. The control variables are propeller revolutions, deflections of control surfaces, and the rate at which they change. After a suitable change of variables, the existence of a solution for the control problem is proved by using Filippov's theory. The problem is solved numerically with a descent method. A couple of numerical simulations complete our study. [ABSTRACT FROM PUBLISHER]

Intelligent unmanned underwater vehicles (UUVs) fall under two main group categories: the remotely operated vehicles (ROVs), which are characterized by remote operation and presence of a tether cable; and the autonomous underwater vehicles (AUVs), which are characterized by their autonomous behavior and absence of a tether cable. One fundamental issue of the UUV design is the dynamic position control system. This system plays a crucial role together with the sensor architecture in the degree of system autonomy that can be achieved. This paper is concerned with a few issues when dynamically positioning remotely operated underwater vehicles (ROVs). By restricting the operating regime of ROVs to slow velocity requirements we investigate the implementation of a few decentralized control strategies and compare their performance measures, which are assessed by simulating a nonlinear ROV system model for each control strategy. Issues concerning input tracking, disturbance rejection, and plant variations are discussed. Our evaluations consider the use of linear ND feedback and feed forward variants, and a robust nonlinear control strategies applied to a full order, fully coupled, and nonlinear vehicle model. These evaluations consider a vehicle undertaking standard mission activities where the tether cable dynamics, with load estimates obtained from a lumped mass cable model, and the vehicle actuator system are present. We show that much of the performance deterioration may be attributed mainly due to cable inertia. We also verify that the nonlinear robust control strategy does not necessarily allow for better performance over the linear feedback control strategies implemented when vehicle motions are confined to slow velocity profiles. These and other partial results will aid the design of the control system for an underwater vehicle currently under construction. [ABSTRACT FROM AUTHOR]

Multiphase brushless direct current (BLdc) motors with high efficiency and power density are widely used in electric propulsion systems of a wide variety of applications including electric vehicles, submarines, and electric ships. The multiphase motors used in these applications must operate stably without generating large torque ripple in various fault scenarios. In this article, three fault-tolerant control (FTC) methods (minimum double phase, half phase, and multiple phases) are compared with reduce torque ripple by controlling the magnitude and phase angle of healthy phase currents under open-circuit failure. The proposed FTC methods were validated through the hardware-in-the-loop simulation of a 12-phase BLdc motor. [ABSTRACT FROM AUTHOR]

A multiobjective genetic algorithm (MOGA) is used to compare submarine propulsion concepts and seek out tradeoffs in their design. Concepts include the novel integrated electric propulsion (IEP) concept and hybrid steam turbine and electric motor drive. System design and supervisory controllers are optimized under multiple operating conditions to give maximum propulsive efficiency. The advantages of each propulsive topology are compared, along with tradeoffs in their design. The hybrid steam turbine/electric motor drive is found to give superior propulsive efficiency compared with pure mechanical and pure electrical drive topologies. The optimal hybrid drive system design favors a large steam turbine and smaller electric motor, which is utilized during slow cruise speeds and top speed cruising only. Optimization of the supervisory controller simultaneously with the system design is found to give improvements in overall propulsive system efficiency. [ABSTRACT FROM AUTHOR]

This work presents an efficient method for designing submarine cable routes using online seafloor classification based on sidescan sonar scanlines, collected by an autonomous underwater vehicle (AUV). Currently, the cable routes are designed manually by experienced experts. Online seafloor classification and an automated route planning method using an AUV can improve the efficiency of construction of submarine cables. Sidescan sonar is a device commonly used for mapping the seafloor and detecting obstacles. An AUV equipped with a sidescan sonar is used to gather sonar scanlines to perform online seafloor classification and mapping. As the AUV operates, the gathered scanlines are analyzed to classify the seafloor using a probabilistic classifier based on Bayes' theorem with the naïve assumption. Based on the seafloor classification map, a probabilistic roadmap is generated. Then, an A* algorithm is applied to determine appropriate cable routes along the cable corridor, using the following five factors: seafloor classification, bathymetry, steepness of slope, angle of change of course, and cable length. Compared with an existing route planning method, the presented method of using an AUV with automatic decision making algorithm can efficiently support submarine cable construction. The favored route determined by the presented method was as acceptable as the route designed by experts. [ABSTRACT FROM PUBLISHER]

A new real-time underwater object detection method adopting geophysical direct-current resistivity techniques is proposed. Our final goals are real-time detection and tracking of small submarines in water depths less than 100 m, under acoustically noisy conditions. The main features of our method are as follows: 1) a detection line, several kilometers long and semipermanently buried in the seabed, consisting of two current electrodes and multiple potential electrodes; 2) fixed current electrode configurations for high-speed real-time detection of the target object; 3) measurement of extremely low-level electric field signals, made possible by the shielding effect of the conductive seawater overburden; and 4) signals from a moving object such as a submarine are extracted by differential data analysis because the target object passes through the detection area for only a short time compared with the long-term drift change of the electrical properties of seawater. We verify our method and confirm real-time detection feasibility through numerical and physical scale experiments. For this purpose, a dedicated instrument and a background data update algorithm are developed, and a differential data analysis method is used. The background data update algorithm is used for counteracting the time-varying electrical characteristics of seawater. The differential data analysis method is exploited to extract disturbed signals by objects from complex background data. Through numerical experiments, we find that the $x$-coordinate value of a target object corresponds to the position of a peak data point, and this result is consistent with 1:200 downscaled water tank experiments. We also confirm real-time detection feasibility using our instrument through an offshore experiment. We expect that our proposed method will complement conventional detection methods for harbor defense and surveillance systems in acoustically noisy environments. [ABSTRACT FROM PUBLISHER]

Docking an unmanned underwater vehicle (UUV) with a submerged submarine in littoral waters in high sea states requires more dexterity than either the submarine or streamlined UUV possess. The proposed solution uses an automated active dock to correct for transverse relative motion between the vehicles. Acoustic, electromagnetic, and optical sensors provide position sensing redundancy in unpredictable conditions. The concept is being evaluated by building and testing individual components to characterize their performance, errors, and limitations, and then simulating the system to establish its viability at low cost. [ABSTRACT FROM PUBLISHER]

Launching gliders from a submarine torpedo tube is of special interest for military operations. This is not currently possible because the wing span needed to achieve a good gliding performance is twice the standard diameter of submarine torpedo tubes. To fit lifting surfaces into small and nonconventional volumes in missiles and unmanned aerial vehicles (UAVs), retractable, compliant, and inflatable wings have been proposed by some researchers. Unfortunately, applying these solutions to underwater gliders would result in complicated wing devices or would require substantial modification to the vehicle. Lowering the wing aspect ratio while keeping constant the initial wing surface would be easier to implement, however, this would substantially degrade glider lifting performance. A possible alternative is the use of ring wings. This study investigates the hydrodynamic properties of a glider equipped with a ring wing specifically designed to fit into a torpedo tube. Specifically, a panel method is employed to compute the lift, induced drag and moment coefficient of a glider with different wing configurations. Modeled results are first compared with experimental data in the case of a glider with standard wing configuration. This study is performed on the Slocum glider due to the availability of experimental data. A numerical study is made of the Slocum glider equipped with a low aspect wing and with a ring wing. Results confirm the degradation of lifting performance of the low aspect ratio configuration. On the other hand, numerical results predict that similar gliding performance can be achieved with a Slocum glider equipped with a ring wing sized to fit the vehicle into a torpedo tube. Results encourage follow-up experimentation of these close lifting surfaces in underwater glider technology. [ABSTRACT FROM AUTHOR]

The principles of a new method for reduction of self-noise in sonar systems are presented, together with corroborative experimental data taken from both surface ships and submarines. The technique is one of towing or streaming one or more hydrophones, called Towflex Hydrophones. The self-noise reduction observed in such Towflex units is due to several contributing factors. In the first place, the many structure-borne vibration paths feeding energy into the hydrophones are virtually eliminated, except for the cable itself. Because of the flexible construction, the transmission of cable vibration, in turn, is also reduced substantially since the fluid-filled flexible tubing discourages transmission of vibrations to the hydrophone elements. Moreover, the hydrodynamic flow around the hydrophones is at all times nearly axisymmetric and the hydrophones stream stably at speeds up to 30 knots with a minimum of flow noise. Additionally, the sensitive elements in Towflex hydrophones are so designed as to respond only to acoustic pressure and to cancel vibration and acceleration inputs. The net result is a hydrophone array system of remarkably low self-noise. In tests of Towflex units streaming from the sail of the submarine ALBACORE noise reductions of as much as 20 to 40 dB were observed when compared to the hull-mounted unit of conventional design located below the Towflex unit. The levels observed with the Towflex hydrophone on ALBACORE are 2 to 12 dB lower than those measured by USNUSL for the BQR-2 installations on other submarines, depending on operating conditions. This difference represents a detection range improvement of as much as a factor of four. When towed as little as 200 yards astern of the converted seaplane tender J. WILLARD GIBBS, noise levels approximately 10 dB above sea-state 1 ambient and some 20 dB below the ship noise level expected for a omni-directional hydrophone were found, because of pattern discrimination against the noise from the towing... [ABSTRACT FROM AUTHOR]

Towed-array research and development over 86 years is examined from the inventions of Dr. H. C. Hayes during World War I to multiple arrays towed by oil exploration ships in 2003. Time lines of the effort over the years are presented for array applications to military surface ships, submarines, and for oil exploration efforts. Military surface ship towed-array systems from the Hayes electric eel effort to the SQR-14, SURTASS, ETASS, and APL/Johns Hopkins dual towed arrays are reviewed. Submarine towed-array programs from the early 1960s to today are described and a prediction of future towed-array development is presented. [ABSTRACT FROM AUTHOR]

An electromagnetic model of the floating antenna used by submarines for LORAN-C radionavigation and very low frequency (VLF) communications is proposed. We present a description of the floating antenna and analyze its electric characteristics. The current in the horizontal wire induced by the lateral wave is then computed and we suggest a model that yields to a nonrational transfer function. A parameter estimation algorithm based on parallel-extended Kalman filters is then proposed and validated on real data. [ABSTRACT FROM AUTHOR]