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Oceanic Engineering, IEEE Journal of

Issue 2 • Date April 2008

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Displaying Results 1 - 20 of 20
  • Table of contents

    Page(s): C1
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    Freely Available from IEEE
  • IEEE Journal of Oceanic Engineering publication information

    Page(s): C2
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  • Editorial: Excellence in Review

    Page(s): 57 - 58
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  • Open-Loop Control of a Multifin Biorobotic Rigid Underwater Vehicle

    Page(s): 59 - 68
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1433 KB) |  | HTML iconHTML  

    This paper presents an open-loop control system for a new experimental vehicle, named the biorobotic autonomous underwater vehicle (BAUV). The rigid cylindrical hull of the vehicle is attached with six strategically located fins to produce forces and moments in all orthogonal directions and axes with minimal redundancy. The fins are penguin-wing inspired and they implement the unsteady high-lift principle found widely in swimming and flying animals. The goal has been to design an underwater vehicle that is highly maneuverable by taking the inspiration from nature where unsteady hydrodynamic principles of lift generation and the phase synchronization of fins are common. We use cycle-averaged experimental data to analyze the hydrodynamic forces and moments produced by a single foil as a function of its kinematic motion parameters. Given this analysis, we describe a method for synthesizing and coordinating the sinusoidal motion of all six foils to produce any desired resultant mean force and moment vectors on the vehicle. The mathematics behind the resulting algorithm is elegant and effective, yielding compact and efficient implementation code. The solution method also considers and accommodates the inherent physical constraints of the foil actuators. We present laboratory experimental results that demonstrate the solution method and the vehicle's resulting high maneuverability. View full abstract»

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  • H_{2} and H_{\infty } Designs for Diving and Course Control of an Autonomous Underwater Vehicle in Presence of Waves

    Page(s): 69 - 88
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    H 2 and H infin designs applied to the diving and course control of an autonomous underwater vehicle (AUV) considering the presence of wave disturbances are described. The six-degrees-of-freedom equations of motion of the vehicle are described as a linear model and divided into three noninteracting (or lightly interacting) subsystems for speed control, steering, and diving. This work is based on the slender form of the Naval Postgraduate School (NPS, Monterey, CA) AUV, considering that the subsystems can be controlled by means of two single-screw propellers, a rudder, port and starboard bow planes, and a stern plane. A model of the AUV dynamics is presented with the first- and the second-order wave force disturbances, i.e., the Froude-Kriloff and diffraction forces. An algorithm of nonlinear regression for the rationalization of the subsurface sea spectrum is provided in this case study. The obtained results are analyzed and evaluated in the frequency domain comparing the controllers performance considering or not the inclusion of the model of waves. View full abstract»

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  • Robust Nonlinear Path-Following Control of an AUV

    Page(s): 89 - 102
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    This paper develops a robust nonlinear controller that asymptotically drives the dynamic model of an autonomous underwater vehicle (AUV) onto a predefined path at a constant forward speed. A kinematic controller is first derived, and extended to cope with vehicle dynamics by resorting to backstepping and Lyapunov-based techniques. Robustness to vehicle parameter uncertainty is addressed by incorporating a hybrid parameter adaptation scheme. The resulting nonlinear adaptive control system is formally shown and it yields asymptotic convergence of the vehicle to the path. Simulations illustrate the performance of the derived controller . View full abstract»

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  • Visually Augmented Navigation for Autonomous Underwater Vehicles

    Page(s): 103 - 122
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    As autonomous underwater vehicles (AUVs) are becoming routinely used in an exploratory context for ocean science, the goal of visually augmented navigation (VAN) is to improve the near-seafloor navigation precision of such vehicles without imposing the burden of having to deploy additional infrastructure. This is in contrast to traditional acoustic long baseline navigation techniques, which require the deployment, calibration, and eventual recovery of a transponder network. To achieve this goal, VAN is formulated within a vision-based simultaneous localization and mapping (SLAM) framework that exploits the systems-level complementary aspects of a camera and strap-down sensor suite. The result is an environmentally based navigation technique robust to the peculiarities of low-overlap underwater imagery. The method employs a view-based representation where camera-derived relative-pose measurements provide spatial constraints, which enforce trajectory consistency and also serve as a mechanism for loop closure, allowing for error growth to be independent of time for revisited imagery. This article outlines the multisensor VAN framework and demonstrates it to have compelling advantages over a purely vision-only approach by: 1) improving the robustness of low-overlap underwater image registration; 2) setting the free gauge scale; and 3) allowing for a disconnected camera-constraint topology. View full abstract»

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  • Thrust Characterization of a Bioinspired Vortex Ring Thruster for Locomotion of Underwater Robots

    Page(s): 123 - 132
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    A new type of thrusting technology, loosely inspired by the locomotion of cephalopods, offers promising low-speed maneuvering capabilities for a new generation of underwater vehicles and robots. The actuators consist of a small cavity with a moving wall on one side and an orifice on the other side. The net effect of periodic movement of the moving wall is the ingestion of low-momentum fluid inside the cavity and then the expulsion of the fluid as a pulsatile jet from the orifice, with no net mass flux. Continuous operation of the actuator results in a synthetic jet. The actuators provide a net positive momentum flux with zero net mass flux. They are compact with no extruding components to negatively impact the vehicle's drag at cruising speed. Parameters controlling the pulsatile jet and its thrust are identified. The thruster was empirically tested for a large range of frequencies and stroke ratios. The thrust characteristics of the device with respect to frequency was seen to converge to a single thrust coefficient. A model was developed to predict the thrust coefficient. The effect of the stroke ratios on the thrust coefficient is investigated. The model accurately predicts the observed thrust coefficient for stroke ratios up to five where the vortex ring pinchoff occurs. The accuracy of the model degrades for stroke ratios above the formation number where part of the expelled jet is pulled back into the cavity. Additionally, these devices have thrust tracking times faster than those reported for typical propellor-type thrusters, and deliver a fully quantized level of thrust. View full abstract»

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  • A Practical Approach to Modeling and Identification of Small Autonomous Surface Craft

    Page(s): 133 - 145
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    This paper discusses the theoretical model of an autonomous surface craft (ASC) with respect to the performance of basic sensors usually available onboard small and relatively low- cost vessels. The aim is to define a practical model and the corresponding identification procedure for simulation, guidance, and control of this class of vehicles. The work is supported by the extended at-sea trials carried out with the autonomous catamaran prototype Charlie2005. View full abstract»

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  • Tracking Large Marine Predators in Three Dimensions: The Real-Time Acoustic Tracking System

    Page(s): 146 - 157
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1626 KB) |  | HTML iconHTML  

    Large marine predators like sharks and whales can have a substantial influence on oceanic ecosystems, and characterizing their interactions with the physical and biological environment is an important goal in marine ecology. Studies of foraging ecology are of particular importance, but sampling prey aggregations encountered by these predators is extremely difficult because of the small spatial scales over which prey aggregations often occur (meters to hundreds of meters). We developed the real-time acoustic tracking system (RATS) to allow large marine predators to be accurately tracked over these small spatial scales to facilitate proximate environmental sampling. The system consists of an array of four free-floating buoys capable of detecting 36-kHz pings emitted by an animal-borne acoustic transmitter. Upon detection, the buoys transmit their position and the arrival time of the ping via a radio modem to a computer on board a nearby ship, and a software program uses differences in arrival times from all of the buoys to estimate the location of the tagged animal. The positions of the tagged animal, buoys, ship, and support boats can be monitored via a graphical user interface to allow proximate environmental sampling and maintenance of the array around the tagged animal. In situ tests indicate that average positional accuracies for a transmitter inside either a four- or three-buoy array (buoys spaced 1-1.75 km apart) are less than 10 m, and that accuracies remain near 10 m for transmitters located up to 500 m away from the edge of the array. The buoys can consistently detect the transmitter up to 1000 m away, but detection rates decrease between 1000 and 2000 m; no detections were obtained beyond 2300 m. Field deployments of the system have demonstrated an unprecedented ability to monitor the movements of baleen whales in real time, allowing a suite of prey and oceanographic observations to be collected within meters to tens of meters of a tagged anim- - al. View full abstract»

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  • Array Modeling of Active Sonar Clutter

    Page(s): 158 - 170
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    Active sonar systems operating in shallow-water environments often deal with excessive false alarms, generically referred to as clutter, that are more numerous than expected for Rayleigh-distributed reverberation. The clutter probability density function, and therefore the probability of false alarm (P fa), depends on the scattering sources, propagation conditions, sonar system, and signal processing. Clutter statistics are often approximated by the K -distribution where the shape parameter (alpha macr) provides an inverse relationship to P fa with decreases in alpha macr representing an increase in P fa. In this paper, the effect of sonar array processing on clutter statistics is evaluated by first modeling clutter at the hydrophone level and then analyzing the resulting K-distribution shape parameter after conventional beamforming. When the transmit-waveform bandwidth is narrowband with respect to the array processing and propagation consists primarily of low-angle paths, alpha macr was found to be separable into the product of a clutter-source scattering effect, an array processing effect, and a coupled transmit-waveform and propagation effect. The array effect was found to coarsely follow the array beamwidth, although precise evaluation is straightforward given the array beampattern. As might be expected, array design or processing that tends to increase the beamwidth was found to increase alpha macr. Uniform shading was seen to provide a practical, though not exact, lower bound on alpha macr for common array shading functions. For circular arrays with unaliased spatial sampling, an asymptotic beampattern was found to provide a very accurate approximation to alpha macr. These results should be useful in predicting the performance of sonar systems in clutter dominated areas, in the design of arrays and array processing, in the inversion of clutter data for clutter-source scattering parameters, or- - to improve signal processing algorithms aiming to reduce or control clutter-related false alarms. View full abstract»

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  • Design and Capacity Analysis of Cellular-Type Underwater Acoustic Networks

    Page(s): 171 - 181
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    The design of a cellular underwater network is addressed from the viewpoint of determining the cell size and the frequency reuse pattern needed to support a desired number of users operating over a given area within a given system bandwidth. By taking into account the basic laws of underwater acoustic propagation, it is shown that unlike in the terrestrial radio systems, both the cell radius R and the reuse number N must satisfy a set of constraints to constitute an admissible solution (which sometimes may not exist). The region of admissible (R,N) , which defines the possible network topologies, is determined by the user density and the system bandwidth (rho,B) , and by the required signal-to-interference ratio and per-user bandwidth (SIR0,W 0) . The system capacity is defined as the maximal user density rhomax that can be supported within a given bandwidth, and it is derived analytically. Numerical examples are used to illustrate the results. It is shown that capacity-achieving architectures are characterized by N, which grows with rhomax. The capacity, as well as the range of admissible solutions, is heavily influenced by the choice of frequency region to which the bandwidth is allocated. Moving to a higher frequency region than that dictated by signal-to-noise ratio (SNR) maximization improves the SIR and yields a greater capacity. Although higher frequencies demand greater transmission power to span the same distance, they also imply a reduction in the cell size, which, in turn, provides an overall reduction in the transmission power. While complex relationships are involved in system optimization, the analysis presented offers a simple tool for the design of future ocean observation systems based on cellular types of network architecture for wide area coverage. View full abstract»

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  • An Iterative Equalization and Decoding Approach for Underwater Acoustic Communication

    Page(s): 182 - 197
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    In this paper, we present an iterative approach for recovering information sent over a shallow underwater acoustic (UWA) communication channel. The procedure has three main tasks: estimation of channel model parameters (CMPs), channel equalization, and decoding. These tasks are performed cyclicly until the algorithm converges. Information bits are convolutionally encoded, punctured and permuted, mapped into quaternary phase-shift keying (QPSK) symbols, linearly modulated, and transmitted through a downward-refracting ocean waveguide. Training symbols are prepended to the transmitted sequence for initial estimation of CMPs. Our algorithm processes data from a single receive sensor. Data are received on a vertical array and the performance of the algorithm for each sensor in the array is examined. There is negligible Doppler spread in the received data. However, difference between transmitter and receiver clocks as well as slight motion of the receive array produce a nonnegligible compression of the received signals. Consequently, there is observable Doppler ldquoshift.rdquo Nonuniform resampling of the data produces time series we model as the output of a linear time-invariant system. Resampling and CMP estimation are done iteratively, in conjunction with equalization and decoding. The algorithm successfully processes the data to yield few or no information bit errors. View full abstract»

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  • Multicarrier Communication Over Underwater Acoustic Channels With Nonuniform Doppler Shifts

    Page(s): 198 - 209
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    Underwater acoustic (UWA) channels are wideband in nature due to the small ratio of the carrier frequency to the signal bandwidth, which introduces frequency-dependent Doppler shifts. In this paper, we treat the channel as having a common Doppler scaling factor on all propagation paths, and propose a two-step approach to mitigating the Doppler effect: 1) nonuniform Doppler compensation via resampling that converts a "wideband" problem into a "narrowband" problem and 2) high-resolution uniform compensation of the residual Doppler. We focus on zero-padded orthogonal frequency-division multiplexing (OFDM) to minimize the transmission power. Null subcarriers are used to facilitate Doppler compensation, and pilot subcarriers are used for channel estimation. The receiver is based on block-by-block processing, and does not rely on channel dependence across OFDM blocks; thus, it is suitable for fast-varying UWA channels. The data from two shallow-water experiments near Woods Hole, MA, are used to demonstrate the receiver performance. Excellent performance results are obtained even when the transmitter and the receiver are moving at a relative speed of up to 10 kn, at which the Doppler shifts are greater than the OFDM subcarrier spacing. These results suggest that OFDM is a viable option for high-rate communications over wideband UWA channels with nonuniform Doppler shifts. View full abstract»

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  • Understanding and Interpretations for Mutual Coupling Within Sonar Arrays

    Page(s): 210 - 214
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    In this paper, understanding and interpretations for mutual coupling within sonar arrays are given. Mathematically, our past mutual-coupling understanding of electromagnetic waves is successfully extended to treat acoustic sonar arrays. Physically, new acoustic-wave interpretations are given in this study. Numerical examples converge very fast and show that our mutual-coupling understanding for sonar arrays is very accurate. Our analyses are not only numerically efficient, but also give physical insights into the detailed coupling mechanisms between elements within a sonar array. View full abstract»

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  • A Simplified Subspace Fitting Method for Estimating Shape of a Towed Array

    Page(s): 215 - 223
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    Although the existing array shape estimation methods using reference sources demonstrate good performance, most of the methods require at least two reference sources 2RS in known locations and the reference sources must be in far field. This communication proposes a simplified subspace fitting method that uses only a single reference source 1RS. In the proposed method, the horizontal and vertical positions of each sensor are modeled by applying fixed intersensor spacing and sensor angles, so that the unknown parameters of the cost function are reduced. Furthermore, the Cramer-Rao lower bound (CRLB) is investigated for the proposed method. The results of the numerical experiments indicate that the proposed method is practical for estimating the shape of a towed array. View full abstract»

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  • Sparse Cylindrical Sonar Arrays

    Page(s): 224 - 231
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    Sparse arrays offer a means for reducing the cost and complexity of beamforming systems. Most of the work in the literature has focused on sparse linear arrays with isotropic transducer elements, which simplifies analysis greatly. In this paper, we will focus on multibeam cylindrical arrays using highly directive elements for use in fishery applications, which requires a direction- ally independent imaging performance in the azimuth direction as well as beam steerability in the elevational direction. To populate such an array, we suggest a low periodicity in the azimuth direction of the array, which ensures a (near) directionally independent imaging performance in this direction. At the same time it reduces the complexity of the problem so that a suggested iterative method can find the optimal layout under the given constraints, within reasonable time. The optimality of the constrained solution is verified using a stochastic optimization procedure, with a "loosened" periodicity constraint. Simulations then show that the proposed layout, having low periodicity in the azimuth direction, has a reduced peak sidelobe level compared to the fully sampled array. All of the layouts have been required to support beam steering from -30deg to 0deg in elevation and in all 360deg in azimuth, without deterioration in performance. View full abstract»

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  • Special issue on Non-Rayleigh reverberation and clutter

    Page(s): 232
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    Freely Available from IEEE
  • IEEE Oceanic Engineering Society Information

    Page(s): C3
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    Freely Available from IEEE
  • Blank page [back cover]

    Page(s): C4
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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.

Full Aims & Scope

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