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Oceanic Engineering, IEEE Journal of

Issue 4 • Date Oct. 2008

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Displaying Results 1 - 25 of 27
  • Table of contents

    Page(s): C1 - C4
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  • IEEE Journal of Oceanic Engineering publication information

    Page(s): C2
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  • Guest Editorial Special Issue on Sediment Acoustic Processes

    Page(s): 357 - 358
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  • Frequency Dependence of Phase Speed, Group Speed, and Attenuation in Water-Saturated Sand: Laboratory Experiments

    Page(s): 359 - 366
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    Sound propagation in water-saturated sandy sediments was studied under controlled laboratory conditions in the 0.1-1.3 MHz frequency range. In the ??low-frequency domain?? (100-200 kHz), the results obtained were consistent with classical Biot theory, which predicts a positive phase-speed dispersion, but at higher frequencies (f > 500 kHz), a strong negative dispersion of the phase speed was observed, which is in apparent contradiction with the Biot theory predictions. In addition, the attenuation coefficient was found to increase nonlinearly with frequency from 0.5 to 1.3 MHz, whereas Biot theory predicted an almost linear increase of this coefficient. The unexpected behavior of the phase speed and the attenuation coefficient observed in these sandy sediments in the very high-frequency domain may be attributable to scattering by the sand particles, which becomes the predominant mechanism involved when the size of particles is comparable to the wavelength. View full abstract»

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  • Compressional Wave Speed Dispersion and Attenuation in Carbonate Sediments, Kaneohe Bay, Oahu, HI

    Page(s): 367 - 374
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    In situ compressional wave speed and attenuation measurements between 20 and 100 kHz were made at two carbonate sediment sites in Kaneohe Bay, on the windward side of the Hawaiian island of Oahu. Velocities increased with frequency from 1691 to 1708 m/s at a coarse sediment site (HC, porosity=0.45) and from 1579 to 1585 m/s at a fine-grained sediment site (HF, porosity=0.56). Effective attenuation increased with frequency from 15 to 75 dB/m at HC and from 22 to 62 dB/m at HF. Values of sound speed at these sites are within the range of those reported in the literature for silicate sands of the same porosity. Attenuation values of these reef-derived carbonate sands are higher than many of those reported in the literature for silicate sands and they appear to be linearly related to frequency (??=0.65f). Sound-speed and attenuation data were compared to predictions of two sediment geoacoustic models, Biot-Stoll and grain shearing (GS). In both models, two unknown parameters were varied to find best fits at each site to: 1) both attenuation and sound-speed data and 2) sound-speed data only. Both models yielded similar fits, which differ significantly from the measured data. View full abstract»

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  • High-Frequency Sound Reflection by Water-Saturated Sediment Interfaces

    Page(s): 375 - 385
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    Sound reflection by water-saturated sands and glass beads with a flattened surface was studied under controlled laboratory conditions in a wide frequency range, from 200 kHz to 7 MHz. In the ¿low-frequency¿ domain and in the case of medium sand, the reflected sound level was found to be in good agreement with both classical sonar measurements and classical theories of reflection developed for fluid porous media (this reflected level is practically independent of the frequency); as the frequency increases, a large decrease in the reflected level occurs, possibly due to incoherent scattering. In the very high-frequency regime (>3 MHz), the sound level measured was more than 20 dB below the classical level, and it remained constant at higher frequencies. Similar experiments were carried out with coarse sand to study the effect of grain size on the reflection loss. The same behavior with only a frequency shift was observed. These effects were confirmed by repeating the experiments with glass beads of two sizes. The anomalies observed in the reflected levels measured seem to be directly connected to the ratio between the grain size and the wavelength. One of the main conclusions reached in this study was that for very coarse sand and gravels, the effects of the granular structure of the bottom should not be neglected, even at the usual sonar frequencies. View full abstract»

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  • Kirchhoff Approximation for a Cylinder Breaking Through a Plane Surface and the Measured Scattering

    Page(s): 386 - 396
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    When considering the application of quantitative ray theory to the backscattering of sound at grazing incidence by a circular cylinder partially buried in sediment, the analysis is complicated by a transition in the number of reflected rays. For broadside insonification, the number of rays geometrically backscattered may be 0, 1, 2, or 3 depending on the exposure of the cylinder. A formulation for the scattering based on the Kirchhoff approximation is given, which avoids discontinuities associated with transitions in the number of rays. The formulation is tested for the experimentally simpler case of a steel cylinder hung through a free surface with a 30?? grazing angle relative to the air-water interface. Tone burst insonification was used with a wave number radius product ka from 9.6 to 16. The measured dependence of the backscattering on exposure is similar to predictions except for extra features present for a slightly exposed cylinder. The approximation is also supported by comparison with an exact theory for backscattering by a half-exposed rigid cylinder in a flat pressure-release surface. Predictions for the dependence on exposure are also shown for the case of a cylinder emerging from a flat rigid surface. View full abstract»

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  • Evanescent Acoustic Waves From Subcritical Beam Illumination: Laboratory Measurements Near a Liquid–Liquid Interface

    Page(s): 397 - 404
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    Grazing illumination of smooth sediments by acoustical beams generates a rapidly decaying evanescent transmitted wave. One approach to laboratory-based simulation of this process is described in this paper. Immiscible liquids are placed in contact, and the acoustical source is placed in the liquid having the lower sound speed. The orientation of the source transducer (a piezocomposite panel) is adjusted to give subcritical beam illumination. An acoustical field that has a significant evanescent component close to the interface is generated in the second liquid. The second liquid (water) has a lower density than the liquid containing the source of the acoustical beam so that the liquid containing the source is trapped below the simulated sediment (the water). This arrangement is convenient for hydrophone scans of the detailed soundfield in the simulated sediment. Above the center of the illuminated region, close to the interface, the field decays exponentially with a fixed phase. Adjacent to the intensely illuminated region there is a sequence of quasi-nulls associated with the interference of relatively weak evanescent and nonevanescent components of the transmitted wave. Similar features are found to be present in soundfields computed using the OASES, a widely used wave-number-integration-based algorithm. View full abstract»

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  • Array Pattern Synthesis With Robustness Against Manifold Vectors Uncertainty

    Page(s): 405 - 413
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    The directivity pattern of an array is known to degrade in the presence of errors in the array manifolds, with respect to the desired nominal array pattern. This paper describes a new robust pattern synthesis approach to arrays with manifold vectors perturbation. This synthesis technique optimizes the worst case performance by minimizing the worst case sidelobe level while maintaining a distortionless respect to the worst case signal steering vector. The possible values of the manifold are covered by an ellipsoid that describes the uncertainty in terms of errors in element gains and phase angles. The pattern synthesis parameters can be optimally chosen based on known levels of uncertainty in the manifold vectors. Two optimization criteria, l 2 regularization and l 1 regularization, of a robust beamformer are proposed. Both criteria of the robust beamformer problem can be reformulated in a convex form of second-order cone programming, which is computationally tractable. A simple lower bound on the difference between the worse case sidelobe level of the robust beamformer and the sidelobe level of the nominal optimal beamformer with no array manifold uncertainty is derived. This robust approach is applicable to arrays with arbitrary geometry. Its effectiveness is illustrated through its application to a circular hydrophone array. An experiment is performed to measure the manifold vectors uncertainty set of hydrophone arrays. Results of applying the algorithms to both simulated and experimental data are presented and they show good performance of the proposed robust pattern synthesis approach. View full abstract»

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  • Estimating Signal-to-Noise Ratio (SNR)

    Page(s): 414 - 418
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (140 KB) |  | HTML iconHTML  

    In many scientific studies involving evaluation of competing ocean engineering systems or the fundamental limits of system performance it is necessary to compare signal power with noise power; in particular, one needs to estimate the signal-to-noise ratio (SNR). SNR is important in the performance of detection and passive localization, where the bearing to an acoustic source is one parameter to be determined given acoustic signal waveforms received at two hydrophones. We provide a brief explanation of methods to estimate SNR. A discussion is included on the difficulty of this task both in theory and in practice. Simulation results are provided explicitly illustrating the difficulty in obtaining accurate estimates even under ideal conditions. This work has applicability to a wide variety of technical problems including the evaluation of the performance of passive localization techniques of interest to the ocean engineering community. View full abstract»

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  • Reverberation Suppression Using Wideband Doppler-Sensitive Pulses

    Page(s): 419 - 433
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    The influence of transmitted waveforms on the signal-to-reverberation ratio (SRR) of a low-frequency active sonar is analyzed both theoretically and experimentally. Reverberation experiments have been conducted during a sea trial in a littoral water environment in October 1999. The aim of the trials was to compare the performance of three classes of waveforms: standard hyperbolic frequency-modulated (HFM) waveforms, continuous waveforms (CWs), and innovative pulse trains of linear frequency-modulated (PTFM) waveforms. Transmissions were combined (CW/PTFM train) or intermitted (HFM) to compare the performance of the three classes in (exactly) the same environment. Experimental results in highly reverberant environment illustrated that PTFM pulses allow a reduction in reverberation power greater than 10 dB over the standard detection pulses for slowly moving targets. The results are in agreement with theoretical predictions. View full abstract»

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  • Superellipse Fitting for the Recovery and Classification of Mine-Like Shapes in Sidescan Sonar Images

    Page(s): 434 - 444
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (6241 KB) |  | HTML iconHTML  

    Mine-like object classification from sidescan sonar images is of great interest for mine counter measure (MCM) operations. Because the shadow cast by an object is often the most distinct feature of a sidescan image, a standard procedure is to perform classification based on features extracted from the shadow. The classification can then be performed by extracting features from the shadow and comparing this to training data to determine the object. In this paper, a superellipse fitting approach to classifying mine-like objects in sidescan sonar images is presented. Superellipses provide a compact and efficient way of representing different mine-like shapes. Through variation of a simple parameter of the superellipse function different shapes such as ellipses, rhomboids, and rectangles can be easily generated. This paper proposes a classification of the shape based directly on a parameter of the superellipse known as the squareness parameter. The first step in this procedure extracts the contour of the shadow given by an unsupervised Markovian segmentation algorithm. Afterwards, a superellipse is fitted by minimizing the Euclidean distance between points on the shadow contour and the superellipse. As the term being minimized is nonlinear, a closed-form solution is not available. Hence, the parameters of the superellipse are estimated by the Nelder-Mead simplex technique. The method was then applied to sidescan data to assess its ability to recover and classify objects. This resulted in a recovery rate of 70% (34 of the 48 mine-like objects) and a classification rate of better than 80% (39 of the 48 mine-like objects). View full abstract»

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  • Whale Entanglements With Submarine Telecommunication Cables

    Page(s): 445 - 450
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    Before 1955-1966, 16 instances of whale entanglement with submarine telegraphic cables were reported in the scientific literature. Here we present new information, derived from global cable fault databases, that reveals an absence of whale entanglements since 1959. This cessation coincided with the transition from telegraphic to coaxial telecommunication cables followed by the change to fiber-optic systems in the 1980s. We propose that entanglements ceased in response to advances in cable design, marine surveying, and cable laying techniques. These changes involved the following: 1) development of torque-balanced cables that were less prone to self-coiling, 2) laying armored cables under slight tension to minimize suspensions and loops, and laying low-torque, nonarmored cables with minimum slack to follow the seabed topography, 3) avoidance of rough topography where suspensions may develop, 4) burial of cables below the seabed on the continental shelf and upper slope to protect against shipping and fishing activities, and 5) use of fault repair procedures that reduce cable slack. View full abstract»

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  • A Shallow-Water Reverberation Model Based on Perturbation Theory

    Page(s): 451 - 461
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    A shallow-water reverberation model is developed based on Bass perturbation theory. The key component for shallow-water reverberation modeling, the modal backscattering matrix (MBSM), has been investigated and the explicit analytic expressions of the MBSM both for the scattering due to interface roughness and due to sediment volume inhomogeneities are derived. For rough interface scattering, it is shown that the angular dependence and the frequency dependence of the MBSM can be separated: the angular dependence is given by sin2(?m P/2)sin2(?nP/2), where ?m is the modal grazing angle and P is a bottom parameter related to the bottom reflection phase shift, and the frequency dependence is given by k0 4-n, where n depends on the power spectrum of the roughness, for instance, n = 3 for Goff-Jordan spectrum. The difference between the scattering due to sediment volume inhomogeneities and the scattering due to rough interface is that there is an extra factor contributed by the vertical correlation and the exponential attenuation of the modal function weighting on the vertical direction in the sediment medium. This extra factor has some important impacts: (1) there will be, in general, a coupled angular-frequency behavior, (2) the angular pattern will decrease more rapidly at small grazing angle area, and (3) the angular pattern is no longer separable. It is shown that only for a ?thin? layer (or low frequency), the scattering due to volume inhomogeneities will have a similar behavior as the scattering due to rough interface. The significant feature of the angular pattern for both kinds of scattering is a marked departure from Lambert's law at small grazing angle area. The explicit analytic expression of the MBSM, and the differences between the two kinds of bottom scattering, given in this paper, provide the opportunity for a comprehensive model-data comparison and a better understanding of the - - scattering mechanism. View full abstract»

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  • An Efficient Normal Mode Solution to Wave Propagation Prediction

    Page(s): 462 - 476
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    In this paper, an overview of a normal mode method of solving the Helmholtz wave equation to describe the underwater sound field for a fixed-point source in a plane multilayered medium is presented. The mode functions are well-defined at all depths of the medium as they are continuous across turning points of the separated depth-dependent differential equation. Comparisons of model results to a limited number of measured data sets and benchmark propagation codes are presented. View full abstract»

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  • Anisotropy of the Wavefront Distortion for Acoustic Pulse Propagation Through Ocean Sound-Speed Fluctuations: A Ray Perspective

    Page(s): 477 - 488
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    Observations of broadband sound propagation through the deep ocean, rich in sound-speed inhomogeneities, show that the double accordion acoustic wavefront pattern expected from model predictions without inhomogeneities is remarkably stable. This stability is found for propagation ranges up to 5000 km for acoustic frequencies of 28-84 Hz, and up to 1200-km range for 250 Hz. While the observed wavefront pattern is stable, the acoustic intensity along the wavefront is not. Furthermore, significant vertical extension of turning point caustics has been observed. This line of evidence suggests that the scattering is anisotropic in the sense that it is primarily along the wavefront, rather than across it. In addition, ray and parabolic equation simulations of acoustic propagation through ocean internal waves obeying the Garrett-Munk (GM) internal wave spectrum reinforce this notion of the anisotropy of the wavefront distortion. This paper presents a ray-based physical model for this phenomenon based on small angle forward scattering and provides analytic formulas to predict the wavefront distortions caused by ocean internal waves and other ocean processes. Further applications include out-of vertical-plane scattering and wavefront healing near seamounts or islands. View full abstract»

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  • Distributed Space–Time Cooperative Schemes for Underwater Acoustic Communications

    Page(s): 489 - 501
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    In resource limited, large scale underwater sensor networks, cooperative communication over multiple hops offers opportunities to save power. Intermediate nodes between source and destination act as cooperative relays. Herein, protocols coupled with space-time block code (STBC) strategies are proposed and analyzed for distributed cooperative communication. Amplify-and-forward-type protocols are considered, in which intermediate relays do not attempt to decode the information. The Alamouti-based cooperative scheme proposed by Hua (2003) for flat-fading channels is generalized to work in the presence of multipath, thus addressing a main characteristic of underwater acoustic channels. A time-reversal distributed space-time block code (TR-DSTBC) is proposed, which extends the dual-antenna TR-STBC (time-reversal space-time block code) approach from Lindskog and Paulraj (2000) to a cooperative communication scenario for signaling in multipath. It is first shown that, just as in the dual-antenna STBC case, TR along with the orthogonality of the DSTBC essentially allows for decoupling of the vector intersymbol interference (ISI) detection problem into separate scalar problems, and thus yields strong performance (compared with single-hop communication) and with substantially reduced complexity over nonorthogonal schemes. Furthermore, a performance analysis of the proposed scheme is carried out to provide insight on the performance gains, which are further confirmed via numerical results based on computer simulations and field data experiments. View full abstract»

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  • Efficient Channel-Estimation-Based Multiuser Detection for Underwater CDMA Systems

    Page(s): 502 - 512
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    Motivated by finding reduced complexity versions of the maximum-likelihood (ML) detector for highly distorted underwater channels, a multiuser detection (MUD) algorithm for joint data detection and channel estimation based on the cyclic coordinate descent method is proposed. Assuming that the data symbols are available, they are used to estimate the channel responses, which, in turn, are used to refine the symbol estimates. Adaptive estimation is performed using minimum mean square error as the overall optimization criterion. The receiver is implemented in a multichannel configuration, which provides the array processing gain necessary for many of the underwater acoustic channels. The complexity of the detection algorithm is linear in the number of receive elements and it does not depend on the modulation level of the transmitted signals. The algorithm has been tested using real data obtained over a 2-km shallow-water channel in a 20-kHz band, demonstrating good results. View full abstract»

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  • Characterization of the Beam-Spread Function for Underwater Wireless Optical Communications Links

    Page(s): 513 - 521
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    Optical links are currently being considered for high-bandwidth underwater communications at short ranges (<100 m). To predict the performance of these links, a firm understanding of how the inherent optical properties of water affect the encoded optical signal is needed. Of particular interest is the impact of scattering due to particulates. Typically, the link loss is computed using the beam attenuation coefficient, which describes the attenuation of nonscattered light due to absorption and scattering. This approach is insufficient, as it neglects the contribution of scattered light to the total received signal. Given the dynamic nature of underwater platforms, as well as the dynamic nature of the environment itself, knowledge of the angular dependence of forward-scattered light is imperative for determining pointing and tracking requirements as well as overall signal to noise. In this work, the theory necessary to describe spatial spreading of an optical beam in the presence of scattering agents underwater is reviewed. This theory is then applied to a performance prediction model that is validated via laboratory experiments. Finally, the model is used to study the impact of spatial spreading on an underwater optical link. View full abstract»

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  • Path Planning of Autonomous Underwater Vehicles for Adaptive Sampling Using Mixed Integer Linear Programming

    Page(s): 522 - 537
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    The goal of adaptive sampling in the ocean is to predict the types and locations of additional ocean measurements that would be most useful to collect. Quantitatively, what is most useful is defined by an objective function and the goal is then to optimize this objective under the constraints of the available observing network. Examples of objectives are better oceanic understanding, to improve forecast quality, or to sample regions of high interest. This work provides a new path-planning scheme for the adaptive sampling problem. We define the path-planning problem in terms of an optimization framework and propose a method based on mixed integer linear programming (MILP). The mathematical goal is to find the vehicle path that maximizes the line integral of the uncertainty of field estimates along this path. Sampling this path can improve the accuracy of the field estimates the most. While achieving this objective, several constraints must be satisfied and are implemented. They relate to vehicle motion, intervehicle coordination, communication, collision avoidance, etc. The MILP formulation is quite powerful to handle different problem constraints and flexible enough to allow easy extensions of the problem. The formulation covers single- and multiple-vehicle cases as well as single- and multiple-day formulations. The need for a multiple-day formulation arises when the ocean sampling mission is optimized for several days ahead. We first introduce the details of the formulation, then elaborate on the objective function and constraints, and finally, present a varied set of examples to illustrate the applicability of the proposed method. View full abstract»

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  • Investigation of Normal Force and Moment Coefficients for an AUV at Nonlinear Angle of Attack and Sideslip Range

    Page(s): 538 - 549
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    This paper presents a comparative study of computational fluid dynamics (CFD) and analytical and semiempirical (ASE) methods applied to the prediction of the normal force and moment coefficients of an autonomous underwater vehicle (AUV). Both methods are applied to the bare hull of the vehicle and to the body-hydroplane combination. The results are validated through experiments in a towing tank. It is shown that the CFD approach allows for a good prediction of the coefficients over the range of angles of attack considered. In contrast with the traditional ASE formulations used in naval and aircraft fields, an improved methodology is introduced that takes advantage of the qualitative information obtained from CFD flow visualizations. View full abstract»

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  • Docking Control System for a 54-cm-Diameter (21-in) AUV

    Page(s): 550 - 562
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    The Monterey Bay Aquarium Research Institute (MBARI, Moss Landing, CA) has developed a 54-cm-diameter (21-in) docking AUV and companion docking station. This program resulted in four consecutive successful autonomous homing and docking events in the open ocean, which included downloading data, uploading a new mission plan, recharging the battery, and complete power cycling of the AUV. We describe the design, simulation, and at-sea test of the homing and docking control system. View full abstract»

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  • Synchronization of Animal-Inspired Multiple High-Lift Fins in an Underwater Vehicle Using Olivo–Cerebellar Dynamics

    Page(s): 563 - 578
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    The development of neuroscience-based control methodologies and their integration with the high-lift unsteady hydrodynamics of control surfaces inspired by swimming and flying animals are the subjects of this paper. A biology-inspired rigid autonomous undersea vehicle called the biorobotic autonomous undersea vehicle (BAUV) has been developed at the Naval Undersea Warfare Center (NUWC), Newport, RI. The BAUV is equipped with six simultaneously rolling and pitching fins for generating large unsteady control forces for performing agile maneuvers. First, as an exploratory example, we introduce the van der Pol oscillator as an oscillatory controller for the BAUV and we describe experiments performed to examine the fin forces (thrust and lift) and electric power requirement, and to demonstrate the effectiveness of the oscillator's limit cycle property for disturbance rejection effectiveness. We then describe a BAUV control system that includes six inferior-olive (IO) neuron models for control of the pitch and roll motion of the six foils. These IO neurons exhibit limit cycle oscillation (LCO). For control of the BAUV, these IO neurons must oscillate in synchronism with specific relative phases. We present here four feedback linearizing control systems of varying complexity for control of the relative phases of the IO neurons. It is shown that each of the IO control systems accomplishes asymptotic regulation of the phases and thus enables the foils to produce the required control forces. The first controller has a global synchronization property, but the remaining controllers accomplish local synchronization. We present simulation results for tracking piecewise, time-varying phase angle commands as well as experimental results for control of the BAUV by IO neurons. The results show that with appropriate phasing of the fins, an optimal graceful gait of the BAUV is achieved where no untoward force or moment is present. An analog hardware version of the local controller wit- - h a cluster of six IO neurons has also been built, which allows five of the signals to rapidly synchronize to the reference, with or without prescribed phase shift, much like in the simulations. The designed controllers can be used in any platform or multivariate BAUV-like system requiring fast, accurate phase control. Laboratory test results for the phase synchronization of two servomotors (roll and pitch) using the designed analog hardware controller are also shown. View full abstract»

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  • Guidance of Underwater Vehicles With Cable Tug Perturbations Under Fixed and Adaptive Control Systems

    Page(s): 579 - 598
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    This paper is concerned with the study of guidance of underwater vehicles subject to cable perturbations due to action of currents and harmonic waves. The general case involves a variable cable length that is usually deployed during vehicle tactics. Control situations are considered, namely, trajectory tracking and position regulation when the reference trajectory for the vehicle is given beforehand. To this end, a control system is designed with adaptive features. A great effort is made in this paper for modeling the cable dynamics in a quasi-stationary state. This model can serve the operator to compensate for the perturbation automatically during teleoperation. Moreover, in the adaptive systems, the perturbation is filtered automatically without having to embed the cable model in the controller design. Effects of the cable perturbation on the control system in adaptive and fixed systems are analyzed comparatively. Proofs of convergence to the tracking error to a residual set are given rigorously in the framework of total stability. The features of the controlled behavior are illustrated by numerical simulations in a case study in six degrees of freedom. View full abstract»

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  • List of Reviewers

    Page(s): 599 - 600
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    Freely Available from IEEE

Aims & Scope

The IEEE Journal of Oceanic Engineering (ISSN 0364-9059) is published quarterly by the IEEE Oceanic Engineering Society (IEEE OES). The scope of the Journal is the field of interest of the IEEE OES, which encompasses all aspects of science, engineering, and technology that address research, development, and operations pertaining to all bodies of water. This includes the creation of new capabilities and technologies from concept design through prototypes, testing, and operational systems to sense, explore, understand, develop, use, and responsibly manage natural resources.

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Meet Our Editors

Editor-in-Chief
N. Ross Chapman
School of Earth & Ocean Sciences
University of Victoria
3800 Finnerty Road
Victoria, BC V8P 5C2 Canada
chapman@uvic.ca