Novel DEMON Spectra Analysis Techniques and Empirical Knowledge Based Reference Criterion for Acoustic Signal Classification

This paper presents some novel methods to estimate a vessel’s number of shafts, course, speed and classify it using the underwater acoustic noise it generates. A classification framework as well as a set of reference parameters for comparison are put forth. Identifying marine traffic in surroundings is an important task for vessels in an open sea. Vessels in vicinity can be identified using their signatures. One of the typical signatures emitted by a vessel is its acoustic measurements. The raw sonar data consisting of the acoustic signatures is generally observed manually by sonar operators for suggesting class of query vessel. The valuable information that can be extracted from the recorded acoustic signature includes shaft revolutions per minute (SRPM), number of blades (NOB), number of shafts, course and speed etc. Expert sonar operators use their empirical knowledge to estimate a vessel’s SRPM and NOB. Based on this information vessel classification is performed. Empirical knowledge comes with experience, and the manual process is prone to human error. To make the process systematic, calculation of the parameters of the received acoustic samples can be visually analyzed using Detection of Envelope Modulation on Noise (DEMON) spectra. Reported research mostly focuses on SRPM and NOB. Parameters such as number of shafts and vessel course and speed can effectively aid the vessel classification process. This paper makes three novel contributions in this area. Firstly, some novel DEMON spectra analysis techniques are proposed to estimate a water vessel’s number of shafts, speed, and relative course. Secondly, this paper presents a classification framework that uses the features extracted from DEMON spectra and compares them with a reference set. Thirdly, a novel set of reference parameters are provided that aid classification into categories of large merchant ship type 1, large merchant ship type 2, large merchant ship type 3, medium merchant ship, oiler, car carrier, cruise ship, fishing boat and fishing trawler. The proposed analysis and classification techniques were assessed through trials with 877 real acoustic signatures recorded under varying conditions of ship’s speed and sea state. The classification trials revealed a high accuracy of 94.7%

A systematic experimental approach to cavitation noise prediction of marine propellers

PhD ThesisMinimization of propeller cavitation noise is best achieved through accurate and reliable pre-dictions at an early design stage. The effect of cavitation and particularly the dynamics of cav-itation on URN is rather complex to understand and the current state of the art does not offer a plausible cavitation noise prediction method which can be implemented within the propeller design spiral. Within this framework, the aim of the present thesis is to enhance the understand-ing of the propeller cavitation noise by conducting detailed systematic cavitation tunnel tests to investigate the main propeller design parameters and operating conditions and to scrutinize their impact on propeller Radiated Noise Levels (RNL). The resulting experimental data are also utilized to compile a database that enables engineering a novel noise prediction method to be developed and used at preliminary design stage, using standard series approach. A holistic approach to cavitation noise has been adopted through experimental investigations into oblique flow effects on propeller noise and by conducting full scale and model scale noise experiments of a research vessel. These have been used to evaluate the capabilities of the adopted standard series based experimental prediction methodology. The accumulated knowledge based on prior experiments has been utilized to design standard series propeller test campaign. Experiments using members of Meridian standard propeller se-ries were tested both in an open water condition and also behind systematically varied wake inflows. Initially, a small subset of the Meridian standard propeller series was chosen, with loading conditions derived from in-service, ocean-going vessels. The resulting measured noise data were extrapolated to full-scale based on the powering information of these vessels to com-pare with average shipping noise data. Finally, a larger subset of the propeller series was tested systematically to compile a database of propeller cavitation noise and for the development of noise prediction software

An investigation on the vibroacoustic behavior of systems in similitude

Similitude theory allows engineers to establish the necessary conditions to design a scaled - up or down - model of a full-scale prototype structure. In recent years, the research on similitude methods, which allow to design the models and establish similitude conditions and scaling laws, has grown so that many obstacles associated with full-scale testing, such as cost and setup, may be overcome. This thesis aims at, on the one hand, expanding the possibilities of similitude methods by means of their application to new structural configurations; on the other hand, at the investigation of new approaches. Therefore, similitude conditions and scaling laws of thin aluminium plates with clamped-free-clamped-free boundary conditions, first, and aluminium foam sandwich plates with simply supported and free-free boundary conditions, then, are derived. Particularly, two sets of conditions are derived for the sandwich plates: the first by expliciting all the geometrical and material properties, the second by combining some parameters into just one with physical meaning, that is, the bending stiffness. These conditions and laws are successively validated by means of dynamic experimental tests, in which reconstructions of the natural frequencies and the velocity response of the prototype are attempted. Also the prediction of the radiated acoustic power is performed for the sandwich plates. All the tests highlight that these laws do not work fine when the models are distorted, i.e., when the similitude conditions are not satisfied. Therefore, the potentialities of machine learning are investigated and used to establish degrees of correlation between similar systems, without invoking governing equations and/or solution schemes. In particular, artificial neural networks are used in order to predict the dynamic characteristics, first, and the scaling parameters, then, of beams, as test (since they do not exhibit distorted models), and plates. In the latter case, the predictions of the artificial neural networks are validated by the results provided by the experimental tests. The networks prove to be robust to noise, very helpful in predicting the response characteristics, and identifying the model type. Finally, the similitude methods are used as a tool for supporting, and eventually validating, noisy experimental measurements, not for predicting the prototype behavior. In this way, they can help to understand if a set of measurements is reliable or not. Therefore, the sandwich plates are analysed with digital image correlation cameras. Then, with the help of an algorithm for blind source separation, the force spectra and velocity responses are reconstructed. It is demonstrated that the similitude results are coherent with the quality of the experimental measurements, since the curves overlap when the spatial patterns are recognizable. Instead, when the displacement field is too polluted by noise, the reconstruction exhibits discrepancies. This proves that the application of similitude methods should not be underestimated, especially in the light of the expanding range of approaches which can extract important information from noisy observations

Radar Technology

In this book “Radar Technology”, the chapters are divided into four main topic areas: Topic area 1: “Radar Systems” consists of chapters which treat whole radar systems, environment and target functional chain. Topic area 2: “Radar Applications” shows various applications of radar systems, including meteorological radars, ground penetrating radars and glaciology. Topic area 3: “Radar Functional Chain and Signal Processing” describes several aspects of the radar signal processing. From parameter extraction, target detection over tracking and classification technologies. Topic area 4: “Radar Subsystems and Components” consists of design technology of radar subsystem components like antenna design or waveform design

Near real-time detection of low-frequency baleen whale calls from an autonomous surface vehicle: implementation, evaluation, and remaining challenges

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Baumgartner, M. F., Ball, K., Partan, J., Pelletier, L., Bonnell, J., Hotchkin, C., Corkeron, P. J., & Van Parijs, S. M. Near real-time detection of low-frequency baleen whale calls from an autonomous surface vehicle: implementation, evaluation, and remaining challenges. Journal of the Acoustical Society of America, 149(5), (2021): 2950-2962, https://doi.org/10.1121/10.0004817.Mitigation of threats posed to marine mammals by human activities can be greatly improved with a better understanding of animal occurrence in real time. Recent advancements have enabled low-power passive acoustic systems to be integrated into long-endurance autonomous platforms for persistent near real-time monitoring of marine mammals via the sounds they produce. Here, the integration of a passive acoustic instrument capable of real-time detection and classification of low-frequency (LF) tonal sounds with a Liquid Robotics wave glider is reported. The goal of the integration was to enable monitoring of LF calls produced by baleen whales over periods of several months. Mechanical noises produced by the platform were significantly reduced by lubricating moving parts with polytetrafluoroethylene, incorporating rubber and springs to decelerate moving parts and shock mounting hydrophones. Flow noise was reduced with the development of a 21-element hydrophone array. Surface noise produced by breaking waves was not mitigated despite experimentation with baffles. Compared to a well-characterized moored passive acoustic monitoring buoy, the system greatly underestimated the occurrence of sei, fin, and North Atlantic right whales during a 37-d deployment, and therefore is not suitable in its current configuration for use in scientific or management applications for these species at this time.Funding for this project was provided by the Environmental Security Technology Certification Program of the U.S. Department of Defense and the U.S. Navy's Living Marine Resources Program

Automatic Detectors for Underwater Soundscape Measurements

Environmental impact regulations require that marine industrial operators quantify their contribution to underwater noise scenes. Automation of such assessments becomes feasible with the successful categorisation of sounds into broader classes based on source types – biological, anthropogenic and physical. Previous approaches to passive acoustic monitoring have mostly been limited to a few specific sources of interest. In this study, source-independent signal detectors are developed and a framework is presented for the automatic categorisation of underwater sounds into the aforementioned classes

New Perspectives on Wave Energy Converter Control

This work examines some of the fundamental problems behind the control of wave energy converters (WECs). Several new perspectives are presented to aid the understanding of the problem and the interpretation of the literature. The first of these is a group of methods for classifying control of WECs. One way to classify control is to consider the stage of power transfer from the wave to the final energy carrier. Consideration of power transfer can also be used to classify WECs into families. This approach makes it possible to classify all WECs, including those that had previously eluded classification. It also relates the equations of motion of different classes of WECs to a generalised equation of motion. This in turn clarifies why some types of control are suited to some WECs, but not others. These classification systems are used to demarcate the boundary for the theoretical work that follows. The theory applies to WECs with governing equations of motion that are linear, and to control systems that are linear, aim to maximise power, and which regulate the PTO stage of power flow. Another important perspective is the new wet and dry oscillator paradigm, which is used to differentiate between frequency domain modelling and a commonly used technique, monochromatic modelling. This distinction is necessary background for many of the new ideas discussed. It is used to resolve an ongoing debate in wave energy research: whether frequency domain modelling can be applied to cases that are not monochromatic. It is the key to an extension to the theory of capture width, a widely used performance indicator. This distinction is also the rationale behind an improved method of presenting frequency domain results: the frequency responses due to both monochromatic and polychromatic forcing are represented on the same graph. These responses are different because the optimal control problem is acausal, a topic that is also discussed in depth. This visual tool is used to investigate and confirm various ideas about the control of WECs, and to demonstrate how the newly redefined capture width encapsulates the essential control problem of WECs. The optimal control problem is said to be acausal because information about the future is required to achieve optimal control. Another vantage point offered is that of the duration of the prediction interval required for optimal control. This is given by a new parameter emerging from this work, which has been termed the premonition time. The premonition time depends on the amount of knowledge required, which is determined by the geometry of the WEC, and the amount of information available, which is largely determined by the bandwidth of the sea state. The new perspectives introduced are the various systems of classification, the wet and dry oscillator paradigm, the presentation of monochromatic and polychromatic results on the same axes, premonition time, and the revised theory on capture width. These are all used to discuss the interrelationship between WEC geometry, the control strategy and the sea-state. The opportunities for, and limitations of, the use of intelligent control techniques such as artificial neural networks are discussed. The potential contribution of various control strategies and associated design principles is explored. This discussion culminates in a series of recommendations for control strategies that are suited to each class of WEC, and for the areas of research that have the potential to bring about the greatest reductions in the cost of harnessing energy from sea waves