Ship Signature Research Articles

Numerical simulation of the flow-induced noise of a ducted diaphragm using the Lattice Boltzmann Method

Acoustic discretion is of prime importance for submarines while operating, in order not to be detected. One of the submarine acoustic sources is the noise induced by water flows passing through singularities in pipes ending at the hull, thus radiating acoustic waves in the vessel surroundings. Predicting the noise induced by singularities in pipes is then fundamental to determine the acoustic signature of an underwater ship. Several Computational Aero-Acoustics methods have been implemented in order to predict the sound induced by singularities such as diaphragms and perforated plates. In this study, the Lattice Boltzmann Method (LBM) coupled to Large Eddy Simulation (LES) is used to simulate the flow passing through a diaphragm and to predict the induced noise. The method is first implemented for an airflow in a rectangular duct, with the final objective of being applied to confined water flows encountered in circular or rectangular ducts.

Inference of source signatures of merchant ships in shallow ocean environmentsa).

An ocean acoustics experiment in 2017 near a shipping lane on the New England continental shelf in about 75 m of water provided an opportunity to evaluate a methodology to extract source signatures of merchant ships in a bottom-limited environment. The data of interest are the received acoustic levels during approximately 20 min time intervals centered at the closest position of approach (CPA) time for each channel on two 16-element vertical line arrays. At the CPA ranges, the received levels exhibit a frequency-dependent peak and null structure, which possesses information about the geophysical properties of the seabed, such as the porosity and sediment thickness, and the characterization of the source, such as an effective source depth. The modeled seabed is represented by two sediment layers, parameterized with the viscous grain shearing (VGS) model, which satisfies causality, over a fixed deep layered structure. Inferred estimates of the implicit source levels require averaging an error function over the full 20 min time intervals. Within the 200-700 Hz band, the Wales-Heitmeyer model captures the inferred frequency dependence of the source levels.

Minimization of a ship's magnetic signature under external field conditions using a multi-dipole model

The paper addresses the innovative issue of minimizing the ship's magnetic signature under any external field conditions, i.e., for arbitrary values of ambient field modulus and magnetic inclination. Varying values of the external field, depending on the current geographical location, affect only the induced part of ship's magnetization. A practical problem in minimizing the ship signature is separating permanent magnetization from induced magnetization. When the ship position changes, a signature measurement has to be made under new magnetic field conditions to update the currents in the coils. This is impractical or even difficult to do (due to the need for a measuring ground), so there is a need to predict the ship's magnetization value in arbitrary geographical location conditions based on the reference signature determined on the measuring ground. In particular, the model predicting the signatures at a new geographical location must be able to separate the two types of magnetization, as permanent magnetization is independent of external conditions. In this paper, a FEM model of the vessel is first embedded in an external field and permanent magnetization is simulated using DC coils placed inside the model. Then, using the previously developed rules for data acquisition and determination of model parameters, a multi-dipole model is synthesized in which the induced and permanent parts are separated. The multi-dipole model thus developed has been successfully confronted with the initial model in FEM environment. The separation of permanent and induced magnetization allows the latter to be scaled according to new values of the external field. In the paper, the situation of determining a signature at one geographical position and its projection onto two other positions is analyzed. Having determined the signature with a high degree of accuracy anywhere in the world, it is possible to perform classical signature minimization by determining DC currents in coils placed inside the ship's hull. The paper also analyzes the effectiveness of ship's signature minimization and the influence of ship's course on the signature value. The advantage of the method presented in this paper is an integrated approach to the issue of scaling and minimization of ship magnetic signature, which has not been presented in the literature on such a scale before.

Incoherent Shallow-Water Seabed Logging Using Numerical-Model-Based Optimization for the Prediction of Unperturbed UEP Signatures

Underwater electric potential (UEP) ship signatures are evaluated at a test site that provides only incoherent data from electric field sensors placed on the seabed. This paper shows how these data sets can be used to extract significant seabed parameters, which are evaluated by a numerical model combined with an optimization process in the frequency range from 1 Hz up to 100 kHz. This is in contrast to the controlled electromagnetic source technology used by geophysicists, which has to track both phase and amplitude, and, therefore, cannot simply be applied to data from per se stationary systems. Using the aforementioned frequency range within COMSOL Multiphysics (v6.0), the finite-element-based simulation software, a sensitivity analysis of seabed parameter behavior within a seabed depth range from 1 m to 20 m is evaluated for the highest sensitivity for each of the measurable field amplitudes of the locally available sensors. From this, the electrical conductivities of two seabed layers and the depth of the first layer can be extracted using a combination of a genetic algorithm and the Nelder–Mead method. In summary, phase information is not required to characterize the stratified seabed, providing a cost-effective approach to obtaining effective environmental conditions for free-water signature calculations.

Static magnetic signature of a ghost-ship propulsor system as a composite ferromagnetic medium

In this paper, it is shown that the static magnetic signature of a propulsor belonging to a ghost ship, whose hull is made of fiberglass, can be calculated by regarding it as a composite ferromagnetic medium. The calculation of the magnetic signature in the static regime is carried out using finite-element method simulations and according to a simple analytical model based on the concepts of volume averaged magnetization arising from a source magnetic field, volume averaged permeability, surface magnetic charges, and the demagnetization tensor applied to a composite magnetic medium. Using targeted simulations, it is demonstrated that the magnetostatic field of demagnetizing nature forming inside the propulsor almost cancels the contribution of the volume averaged magnetization. From the interplay between the numerical simulations and the analytical model, the elements of the demagnetization tensor in the region filled by the propulsor are locally calculated, and their role in determining the localization effects of the magnetic signature is discussed. By replacing the original ferromagnetic materials with weakly ferromagnetic ones, it is shown that, in the underwater region outside the propulsor, the magnetic signature drop is 64%. This analysis suggests an experimental way to use a simple passive method to minimize the magnetic signature of a propulsor as an alternative to more complex and time-consuming methods, such as the deperming and degaussing methods, widely employed to reduce the magnetic signature of ships and underwater objects in military applications.

Correlating shipping noise on multiple beams

There has been much interest in using transiting surface ships as sources of opportunity for tomography and geo acoustic inversion. In tomography, it would be valuable to increase the ranges at which ship signatures can be processed by measuring times of arrival at the output of beamforming processes, which provide spatial processing gain. This additional gain may enable fainter multipath arrivals to be identified and exploited as additional paths to sample the ocean water column. This seems readily achievable when cross-correlating multiple vertical beams formed on a single vertical line array for example. However, cross-correlating beams from multiple arrays, vertical or horizontal, raises questions. In both cases, different beams may have different Doppler, which is manageable with a correlation process that includes Doppler compensation. But obeserving a ship from different vantage points may be problematic, if the ship signature is due to horizontally displaced noise sources distributed around the ship. We will present results of processing surface ships observed on single and multiple arrays and assess the use of such processing in ambient noise tomography.

Using passive acoustic monitoring to characterize vocal behaviors of sperm whales (Physeter macrocephalus)

Sperm whales (Physeter macrocephalus) have been observed but not well studied in the Monterey Bay National Marine Sanctuary (MBNMS). Vessels transiting through MBNMS may pose a threat to sperm whales and modify their behavior. Knowledge of their activity in relation to vessel presence in MBNMS is largely unknown. In this study, passive acoustic monitoring (PAM) data collected at the Sur Ridge, in close proximity to shipping lanes, are used to characterize vocal and foraging behaviors of sperm whales in relation to vessel transits through MBNMS. PAMGuard automated detectors are used to detect sperm whale clicks and measure inter-pulse intervals with feature-based post-processing to reduce false positives. Probability density functions are used to determine distribution of sperm whale size, sex, and presence in relation to vessel transits. Foraging clicks were positively detected in sequences of bouts from June-August, 2020. Sperm whales observed were adult males. Container ship signatures were observed to cover the same frequency bandwidth as sperm whales with a higher amplitude. This study provides insight on the importance of MBNMS to sperm whales and informs policy makers on potential effects that shipping may have on sperm whale behavior, while providing a novel method to analyze PAM data.

Ship noise quantification of fisheries vessels on the Great Lakes

Prey fish abundances in the Great Lakes are a driver for several agencies’ commitments to the Council of Lake Committees to support fisheries management. These management decisions have profound economic and social impacts within the Great Lakes region. Fisheries estimates done by echosounders or trawling may be biased due to the propagated noise from large fisheries vessels. In the first two years of a four-year collaborative study, crewed fisheries vessels and uncrewed Saildrone vessels were used to compare abundance estimates between “loud” and “quiet” vessels. To quantify the effects of ship noise on prey fish abundance estimates, a mobile ship noise measurement system was designed and deployed to measure radiated acoustic signatures of several ships in the Great Lakes. This talk will discuss the deployment of a mobile underwater acoustic test range and show results of ship noise measurements from the first two years of the program. In addition, plans for future data generation, analysis, and comparison between crewed and autonomous systems will be discussed and an overview of the effects of ship noise on fish avoidance will be discussed in the proceeding talk.

A strategy for evaluating micro-doppler signature and motion parameter of ship over time-varying sea surface

ABSTRACT The micro-Doppler (m-D) signature can describe the motion state and structure of the target in detail. It can be considered as an effective method for ship target detection and recognition in the marine environment. In this paper, an effective strategy is proposed to simulate the m-D signature and extract the ship’s motion parameters on the time-varying sea surface. For this purpose, a ship target micro-motion model based on six degrees of freedom is first established. Then, the public domain strip (PDSTRIP) method is used to realize real-time estimation of ship motion. Next, a high-precision electromagnetic scattering model is used to generate radar echoes of a ship on the rough sea. Finally, the m-D signature can be acquired and analysed based on the obtained radar echo. The numerical results show that the instantaneous frequency and motion parameters can be estimated well from the m-D signature. At the same time, the proposed model can also be used to calibrate the Inverse Synthetic Aperture Radar (ISAR) of ship targets in the marine environment.

Quantifying ship noise bias in fish abundance estimates in the Great Lakes

Prey fish abundances in the Great Lakes are a driver for several agencies commitments to the Council of Lake Committees to support fisheries management. These management decisions have profound economic and social impacts within the Great Lakes region. Fisheries estimates done by echosounders or trawling may be biased due to the propagated noise from large fisheries vessels. In the first year of a four year collaborative study, crewed fisheries vessels and uncrewed Saildrone vessels were used to compare abundance estimates between “loud” and “quiet” vessels. In order to quantify the effects of ship noise on prey fish abundance estimates, a mobile ship noise measurement system was designed and deployed to measure radiated acoustic signatures of several ships in the Great Lakes. This talk will discuss the deployment of a mobile underwater acoustic test range, and show initial results of ship noise measurements from the first year of the program. In addition, an overview of the echosounder abundance results will be given along with plans for future data generation, analysis, and comparison between crewed and autonomous systems.

Converter Design for High Temperature Superconductive Degaussing Coils

Detection of the magnetic signature of ships can be avoided by using a degaussing system; a set of on-board copper coils that compensates for the magnetic signature. High temperature superconductors (HTS) are currently investigated as a replacement for copper degaussing coils. By using HTS, we have to deal with higher currents and therefore with higher power supply losses. Also, large current leads are needed which introduces extra losses. This paper investigates different possible solutions to minimize these losses. Four H-bridge-based MOSFET topologies are presented that were designed to reduce the power supply and current lead losses. The first topology uses an H-bridge configuration so that the degaussing current can freewheel through the low-resistance MOSFETs. The second topology places the H-bridge inside the cryostat so that the current leads can be made smaller. The third topology includes a smoothing capacitor in the cryostat so that the current leads and input current are even smaller. The fourth topology uses a transformer so that the current leads can be eliminated. Measurements were done to determine the MOSFETs and capacitor performance in liquid nitrogen. The simulated losses of the four topologies are compared to determine the most energy-efficient option for supplying current to the HTS coils. It was found that by submerging multiple parallel MOSFETs in liquid nitrogen, the on-state resistance is decreased and the current supply can be made more efficient. Also, by placing a smoothing capacitor inside the cryostat, the current lead losses can be minimized significantly. The benefits of using a transformer do not outweigh the transformer losses.

Evidence for non-Rayleigh characteristics in ship underwater acoustic signatures.

This work examines ship underwater acoustic signature amplitude statistics and statistical distributions and explores the hypothesis that ship signatures exhibit amplitude fluctuations that are different from Rayleigh-distributed ambient ocean noise. Signature measurements from a small oceanographic ship conducting a variety of maneuvers are examined, focusing on those conditions where propeller cavitation and broadband signal modulation occur, specifically during maximum speed runs and turning maneuvers. A key difference for a ship signature is the amplitude modulation generated by propeller cavitation, and this is found to be associated with super-Rayleigh signal characteristics. Cyclostationary processing techniques are used to estimate propeller shaft- and blade-rate modulation. Under conditions of clearly observable propeller modulation, time-series statistics scintillation index and skewness showed values significantly in excess of Rayleigh-distributed values. Ship signature amplitude probability density functions were found to be better matched by a K-distribution model with small shape factor, indicating clearly non-Rayleigh behavior. Evidence for a secondary, high-amplitude, lognormally distributed sound generation mechanism was observed during maximum helm turns.

Correlation of deep seabed structure with waveguide invariant β in ±∞ regime

An examination of the received spectrogram levels of merchant ship recordings has identified an important acoustic feature at the very-low frequencies (VLF). The data were recorded on vertical line arrays deployed in the New England Mudpatch during the Seabed Characterization Experiment 2017 in about 75 m of water. The VLF feature occurs when the group velocities of modes 1 and 2 are equal at a frequency f = F. The average value of F from about twenty ship signatures observed in the Mudpatch is about 24.5 Hz. Generally, the observation of this VLF feature is a result of βmn( F) = infinity where βmn is the waveguide invariant for modes n and m. The sign of the waveguide invariant is determined by the sign of the difference between the phase speeds at F. Also, we predict what F would be in two areas south of the Mudpatch, including a second smaller Mudpatch in about 125 m of water and an area near the slope in about 250 m of water where the sediment is reported to be sand over multiple layers of softer sediments. Finally, F is predicted on the Atlantis II seamount with a limestone seabed in about 1650 m of water.

The Ship Signature Licensing System


 
 
 Vessel registration is a registration of ownership rights to a ship. A vessel that has been registered can be used as collateral for debt by means of a mortgage imposition on the vessel, it can also be subject to other property rights. The stages and conditions for registering ships in Indonesia are based on the Regulation of the Minister of Transportation Number PM 39 of 2017. Applications are submitted to ship registrar officials, accompanied by various documents. Information is also required from the applicant demonstrating that the ship is an Indonesian ship according to the 311 Commercial Code. Further documents are required for determination of the nationality of the ship. Based on the request, and provided all documentation is verified and all requirements met, the harbormaster (a ship registrar official) will make a registration deed and the ship owner will be given the first copy of the registration certificate.
 Keywords: Licensing, Registration Letter, Ship
 
 

Efficient Generation of Artificial Training DB for Ship Detection Using Satellite SAR Images

In this paper, we propose an effective scheme to generate artificial training database (DB) to mitigate the deficiency in the amount of training DB for ship detection using satellite synthetic aperture radar (SAR) images. In the proposed scheme, SAR signatures of ship targets are first obtained from two different types of image: 1) KOMPSAT-5 images with automatic identification system (AIS) information and 2) simulated SAR images which are acquired using electromagnetic numerical analysis (EMNA). Then, the ship signatures are combined with sea clutter models to generate realistic SAR patches. For overall ship detection tasks (i.e., training and testing), the oriented bounding box (OBB) concept was adopted to appropriately represent slender ship targets in SAR images. When compared with the rash collection of a large number of real SAR images, the proposed scheme is more efficient in terms of cost and time. Experimental results demonstrated that the proposed method can considerably aid in increasing the ship detection capacity of deep learning models. Thus, it is expected that the proposed scheme can be usefully exploited to solve the lack of the amount of training DB.

Cathodic Protection Modeling of a Covered and Uncovered Steel Immersed in Seawater: Corrosion Characterization

As underwater structure, ships are protected by a suitable cathodic protection system to prevent and reduce significantly corrosion phenomenon. This protective system, called Impressed Current Cathodic Protection (ICCP), creates an underwater electrical current. Then, this current generates an electromagnetic field also referred as electrical signature that could be detectable by sensors [1-2]. Therefore, this work refers to the electrochemical characterization of the materials used in naval framework in addition to a better comprehension of the corrosion phenomenon. The final goal is to predict electrical signatures of ships under different corrosion conditions as illustrated on figure 1: Electrical fields induce by natural corrosion or ICCP. These predictions will be done by including the obtained models of material in numerical simulation tools based on the boundary element method.In a first time, polarization laws of different materials present on the immersed hull and electrically connected are obtained: the hull material (coated and uncoated), the propeller material and zinc for sacrificial anodes to complete the cathodic protection system. One part of this project is to be able to model the metal/electrolyte interface in different operating conditions: speed, temperature, polarization state, ageing of the coating and galvanic coupling between the different metals. The second part of this project is to integrate these laboratory data in simulation tools to optimize it. In these simulation tools, the hull is discretized by a surface mesh. Each element of the mesh is being associated to local polarization laws obtained during the laboratory test. Then laboratory models and simulation tools will be tested at a bigger scale on a mockup.To achieve these goals, it’s important to understand what happens physically at the interface and modeling the different corrosion phenomena which take place at the interface. To model the interface experimentally, Electrical Equivalent Circuits are used. These Electrical Equivalent Circuits, commonly called EEC, are deduced considering physical phenomenon happening at the interface by fitting Electrochemical Impedance Spectroscopy (EIS) data. To complete EIS investigations and confirm the different models, potentiodynamic curves and Scanning Electron Microscopy with EDX analyses were also performed.From the first results, Electrical Equivalent Circuits (EEC) of the metallic interface behavior (hull) are proposed for different polarizations conditions: anodic, corrosion potential and cathodic (ICCP potential: -0,8 VECS) in order to understand more deeply the corrosion phenomenon following the polarization state of the steel. In complement EEC investigations will be made under different temperatures and in electrolyte dynamic conditions (thanks to a rotating electrode) for hull steel samples at corrosion potential. The propeller material will also be characterized following speed influence of the solution and temperature. Simultaneously painted hull steel is also investigated in regards to temperature, polarization state and mechanical ageing. Transition state (ICCP turn on/off) and galvanic coupling between propeller and hull materials coated or not will be investigated to complete elementary investigations. Painted hull steel samples give equivalent result whatever experimental conditions. Indeed freshly painted hull steel samples show an almost pure capacitance behavior if we refer to the (Loveday et al.; 2004) [1] work’s suggesting a strong protective behavior of freshly painted sample. To model this behavior a simple Randle circuit,which only take into account the impedance of the paint, is used. The impact of mechanical defects will be presented to simulate paint degradation and investigate evolution of polarization law. In case of uncoated hull steel, EEC are more complex and change following the polarization and experimental conditions. In all cases, a deposit is formed but its nature and protective behavior change with polarization: a formation of calcareous deposit under cathodic polarization and corrosion products deposit under anodic polarization. That requires in consequence to include additional impedances in the EEC modeling: impedance of a deposit or diffusion impedance for example. Temperature variation and dynamic conditions influence also the kinetic of the different interfacial phenomena. Simultaneously some results of simulation obtain with the use of this first result give encouraging results with good correlations between data obtain in at laboratory scale and simulations. (C Rannou and JL Coulomd; 2008 ) : Optimization of the cathodic protection system of military ships with respect to the double constraint:cathodic protection and electromagnetic silencing ; HAL ; MARELEC 2006; Amesterdam; Netherlands; 2004 (A.Guibert ) : Diagnostique de corrosion et prédiction de signature électromagnétique de structures sous-marines sous protection cathodique ; Science de l’ingénieur ; Institut National Polytechnique de Grenoble-INPG ; HAL ; 2009 (Loveday et al.; 2004) : Evaluation of organic Coatings with Electrochemical Impedance Spectroscopy, part 2; Gamy Instruments; JCT Coating tech; 2004 Figure 1

Neural-Network-Based Classification of Commercial Ships From Multi-Influence Passive Signatures

Monitoring the underwater environment is important for maritime security, marine conservation, and mine countermeasures. With developments in computation and artificial intelligence, it is increasingly important to measure and classify underwater ship signatures. In this work, we design an artificial neural network that classifies commercial ships based on their multi-influence signature. In total, 103 ship passages were included in the considered data set, with signatures recorded as the ship crossed a line of passive underwater sensors. The multi-influence signature was formed by feature-level sensor fusion of the hydroacoustic signature, the underwater electric potential, and the static and alternating magnetic signatures. Ships were classified according to size, or type, as broadcast on the AIS. With feature-level fusion, the neural network will optimize the relationship between different types of signatures, emphasizing features with greater predictive power. At the same time, weak features, even if not independently adequate for classification, can add information that improves accuracy further. The developed neural network achieved a classification accuracy of 87.4% when classifying according to size. With augmented data to balance the classes, 85.0% classification accuracy was achieved when classifying according to ship type. This is a large improvement on the found classification accuracy when using only hydroacoustic or electromagnetic signatures. This article verifies the value of feature-level sensor fusion in classification, and provides guidance on classifier design depending on the exact ship classification task.

Multi-attribute concept design procedure of a generic naval vessel

This paper presents a multi-attribute concept design procedure of a generic naval vessel. The procedure generates a set of Pareto optimal design solutions of up to corvette size vessels. It is composed of the self-balanced concept design model and of the search for the Pareto optimal design solutions. The self-balanced concept design model generates a set of balanced designs of required displacement, deck area, and internal volume, respectively, solving the naval architecture-related problems. The Pareto optimal search performs the multi-attribute evaluations of design solutions and identification of Pareto optimal set. The design variables are related to the ship’s form parameters and to the tactical and technical characteristics of the ship, such as selected options of armament, cruising range, autonomy, materials, propulsion, and the ship signatures, respectively. The selected design attributes are ship life cycle cost and the overall measure of effectiveness (OMOE). The procedure is codded in the form of the software named “Monako PRB”. The procedure is verified by performing the series of tests on the module level as well as on the global level. The final results were compared to the parameters of the existing ships. The results were satisfactory and proved the feasibility and reliability of the presented procedure.

HF radar signatures of ship and submarine wakes

Radars operating in the HF band have been widely used to detect and track surface ships from their skin echoes; indeed, in many cases this has been the primary mission of the radar. Yet vessels moving on and through the ocean create a family of disturbances collectively referred to as the wake, though a number of different mechanisms and phenomena are involved. It is therefore of interest to explore the possibility of detecting the wake echo and exploiting it as far as possible. In this study, the author presents an analysis of this problem and shows that there is indeed a characteristic signature associated with the Kelvin wake and this contains retrievable information relevant to target discrimination and classification.

Container ship source level and directionality measurements

Underwater radiated noise from container ships was measured opportunistically from multiple spatial aspects to estimate directionality and signature source levels. Transiting ships were tracked via the Automatic Identification System in a shipping lane while acoustic pressure was measured at the ships’ keel and beam aspects. Port and starboard beam aspects were 15, 30, and 45 deg in compliance with ship noise measurements standards [ANSI/ASA S12.64 (2009) and ISO 17208-1 (2016)]. Source levels were derived with a spherical propagation (surface-affected) or a modified Lloyd’s mirror model to account for interference from surface reflections (surface-corrected). Ship source depths were estimated from spectral differences between measurements at different beam aspects. In addition, recordings were made at a ∼10 deg starboard aspect and utilized to measure and compare signatures of MAERSK G-class container ships before and after the ships were equipped with new propellers as part of MAERSK’s $100+ million Radical Retrofit Program.