Showing papers in "Marine Technology Society Journal in 2014"

Scientific Operations Combining ROV and AUV in the Trondheim Fjord

Abstract: This paper describes an autonomous underwater vehicle (AUV) and a remotely operated vehicle (ROV) complementing each other on a scientific cruise in the Trondheim Fjord (Norway). The Norwegian University of Science and Technology Applied Underwater Robotics-Laboratory and the Norwegian Defense Research Establishment mobilized for a collaborative cruise with an ROV equipped with video camera, dynamic positioning system, still camera for photographic mosaic, underwater hyperspectral imager (UHI) and inertial measurement unit, and the AUV Hugin HUS with synthetic aperture sonar (SAS) and still camera as main instruments. A multidisciplinary approach was used to set up the operations for using ROV, AUV, SAS, and UHI to document archaeological and biological sites. The cruise was run as an integrated operation processing data online and using collected data actively in the cruise planning and replanning. The AUV presented unparalleled area coverage capacity for mapping and search, while the ROV provided detailed information from the sites. During the cruise, approximately 20 km2 were mapped with high-resolution sensors, and the data were ground-truthed using the ROV. These data provided new information and insight of both biological and archaeological sites.

Application of satellite remote sensing techniques to quantify terminus and ice mélange behavior at helheim glacier, East Greenland

Abstract: Iceberg calving is an efficient mechanism for ice mass loss, and rapidly calving glaciers are often considered to be inherently unstable. However, the physical controls on calving are not well understood. Recent studies hypothesize that the presence of a rigid ice melange (composed of icebergs, bergy bits, and sea ice) can reduce iceberg calving by providing “backstress” to the terminus. To test this hypothesis the authors use remote sensing techniques to construct a time series model of calving rate and size and composition of the adjacent ice melange. The authors describe a semi-automated routine for expediting the digitization process and illustrate the methods for Helheim Glacier, East Greenland, using 2008 data. Ice velocities of the glacier terminus and ice melange are derived with feature-tracking software applied to radar imagery, which is successfully tracked year-round. Object-based image analysis (OBIA) is used to inventory icebergs and sea ice within the ice melange. The authors find that the model successfully identifies the calving rate and ice melange response trends associated with seasonal increases in terminus retreat and advance and shows seasonal trends of ice melange potentially providing seasonal backstress on the glacier terminus.

Glider-Based Passive Acoustic Monitoring in the Arctic

Abstract: Persistently poor weather in the Arctic makes traditional marine mammal research from aircraft and ships difficult, yet collecting information on marine mammal distribution and habitat utilization is vital for understanding the impact of climate change on Arctic ecosystems. Moreover, as industrial use of the Arctic increases with the expansion of the open-water summer season, there is an urgent need to monitor the effects of noise from oil and gas exploration and commercial shipping on marine mammals. During September 2013, the authors deployed a single Slocum glider equipped with a digital acoustic monitoring (DMON) instrument to record and process in situ low-frequency (<5 kHz) audio to characterize marine mammal occurrence and habitat as well as ambient noise in the Chukchi Sea off the northwest coast of Alaska, USA. The DMON was programmed with the low-frequency detection and classification system (LFDCS) to autonomously detect and classify sounds of a variety of Arctic and sub-Arctic marine mammal species. The DMON/LFDCS reported regularly in near real time via Iridium satellite detailed detection data, summary classification information, and spectra of background noise. The spatial distributions of bowhead whale, bearded seal, and walrus call rates were correlated with surface salinity measured by the glider. Bowhead whale and walrus call rates were strongly associated with a warm and salty water mass of Bering Sea origin. With a passive acoustic capability that allows both archival recording and near real-time reporting, the authors envision ocean gliders will become a standard tool for marine mammal and ocean noise research and monitoring in the Arctic.

Testing the Effects of Near-Shore Environmental Variables on Acoustic Detections: Implications on Telemetry Array Design and Data Interpretation

Abstract: Acoustic technology is a common means to study the movements and habitat utilization of aquatic organisms. This study simultaneously assesses the relative importance of a number of major environmental variables affecting the detection range and detection frequency of acoustic tracking technology in near-shore marine environments. Transmitter power output and diel index in order of relative importance were the most influential variables affecting detection range within a temperate reef habitat. Wave height, transmitter power output, and diel index in order of relative importance were the most influential variables affecting detection range within the wash zone. Similar models resulted when examining detection frequency at 100 m within the two habitat types. Attention is also drawn to the selection of transmitter power output based upon the habitat type and environmental conditions of the study site. This study demonstrates the importance of in situ range test studies in array design and interpretation of acoustic telemetry data.

Studying the Impacts of Local Oceanographic Processes on Adélie Penguin Foraging Ecology

Abstract: The authors are conducting a multi-platform field study to investigate the impact of local physical processes on Adelie penguin foraging ecology in the vicinity of Palmer Deep off Anvers Island, Western Antarctic Peninsula (WAP). Guided by real-time remotely sensed surface current measurements of convergence derived from a network of high-frequency radars (HFRs), the authors adaptively sample the distribution and biomass of phytoplankton and Antarctic krill, which influence Adelie penguin foraging ecology, to understand how local oceanographic processes structure the ecosystem. The recent application of ocean observing and animal telemetry technology over Palmer Deep has led to new understanding and many new questions related to polar ecosystem processes. The HFR coastal surface current mapping network is uniquely equipped to resolve local circulation patterns over Palmer Deep. The surface current measurements enable identification of regions of convergence and divergence in real time. Guided by these maps, the authors' field study adaptively samples the measured convergence and divergence zones within the context of semi-diurnal and diurnal mixed tidal regimes. The in situ sampling includes (a) a mooring deployment, (b) multiple underwater glider deployments, (c) small boat acoustic surveys of Antarctic krill, and (d) penguin ARGOS-linked satellite telemetry and temperature-depth recorders (TDRs). The combination of real-time surface convergence maps with adaptive in situ sampling introduces HFR to the Antarctic in a way that allows for rigorous and efficient testing of the influence of local tidal processes on top predator foraging ecology.

Using Terrain Navigation to Improve Marine Vessel Navigation Systems

Abstract: Terrain navigation has been used extensively by underwater vehicles in the last decade. By comparing bathymetric measurements with a digital terrain model (DTM), one can estimate a global position of a vehicle underwater, where global positioning system (GPS) signals are unavailable. With the increasing threat of GPS signal jammers and spoofers to marine vessels, GPS-independent techniques are becoming more interesting for surface vessels as well. This paper explores the idea and challenges of using terrain navigation to detect GPS spoofing and as a substitute position source during GPS jamming. A robust navigation system is suggested based on a GPS-aided inertial navigation system (INS) augmented by terrain navigation. The INS and terrain navigation system of the HUGIN autonomous underwater vehicle (AUV) was adapted to a surface vessel and tested in two experiments on the coast of Norway in scenarios simulating GPS jamming. The results from the experiments clearly indicate the feasibility of such a system, if a DTM of the area is available and the terrain is well suited for terrain navigation.

Design and Comparison of Constrained MPC With PID Controller for Heave Disturbance Attenuation in Offshore Managed Pressure Drilling Systems

Abstract: This paper presents a constrained finite horizon model predictive control (MPC) scheme for regulation of the annular pressure in a well during managed pressure drilling from a floating vessel subject to heave motion. In addition to the robustness of a controller, how to deal with heave disturbances despite uncertainties in the friction factor and bulk modulus is investigated. The stochastic model describing sea waves in the North Sea is used to simulate the heave disturbances. The results show that the closed-loop simulation without disturbance has a fast regulation response, without any overshoot, and is better than a proportional-integral-derivative controller. The constrained MPC for managed pressure drilling shows further improved disturbance rejection capabilities with measured or predicted heave disturbance. Monte Carlo simulations show that the constrained MPC has a good performance to regulate set point and attenuate the effect of heave disturbance in case of significant uncertainties in the well parameter values.

Path Replanning Method for an AUV in Natural Hydrothermal Vent Fields: Toward 3D Imaging of a Hydrothermal Chimney

Abstract: Autonomous underwater vehicles (AUVs) can operate without the need for human control or tether cables as long as there is sufficient energy. AUVs have recently been used for seafloor imaging. Visual observation by AUVs provides high-resolution color information of the seafloor. However, conventional observation techniques that follow a prespecified path offer limited coverage because it is impossible for operators to build a suitable path in unknown rough terrain. A flawed prespecified path will produce incomplete observation. If unobserved areas are found during postprocessing, another dive is necessary, which increases the total cost. To overcome this problem, the authors have proposed a path replanning method to realize high-coverage observation in one dive. With this method, the AUV evaluates unobserved areas after the first prespecified observation; if unobserved areas are found, the AUV recreates an appropriate path to cover what was missed. The validity of the proposed method was previously evaluated using an artificial target in a tank and in shallow seas at a depth of approximately 35 m. In this study, the feasibility of the method was validated in a more challenging setting: experimental data were taken from a hydrothermal vent field in Kagoshima Bay, Japan.

Trajectory Clustering by Sampling and Density

Abstract: The trajectory data of moving objects contain huge amounts of information pertaining to traffic flow. It is incredibly important to extract valuable knowledge from this particular kind of data. Trajectory clustering is one of the most widely used approaches to complete this extraction. However, the current practice of trajectory clustering always groups similar subtrajectories that are partitioned from the trajectories; these methods would thus lose important information of the trajectory as a whole. To deal with this problem, this paper introduces a new trajectory-clustering algorithm based on sampling and density, which groups similar traffic movement tracks (car, ship, airplane, etc.) for further analysis of the characteristics of traffic flow. In particular, this paper proposes a novel technique of measuring distances between trajectories using point sampling. This distance measure does not divide the trajectory and thus conserves the integrated knowledge of these trajectories. This trajectory clustering approach is a new adaptation of a density-based clustering algorithm to the trajectories of moving objects. This paper then adopts the entropy theory as the heuristic for selecting the parameter values of this algorithm and the sum of the squared error method for measuring the clustering quality. Experiments on real ship trajectory data have shown that this algorithm is superior to the classical method TRACLUSS in the run time and that this method works well in discovering traffic flow patterns.

Analysis, Fabrication, and Testing of a Liquid Piston Compressor Prototype for an Ocean Compressed Air Energy Storage (OCAES) System

Abstract: Previous work concerning ocean compressed air energy storage (OCAES) systems has revealed the need for an efficient means for compressing air that minimizes the energy lost to heat during the compression process. In this paper, the authors present analysis, simulation, and testing of a tabletop proof-of-concept experiment of a liquid piston compression system coupled with a simulated OCAES system, with special attention given to heat transfer issues. An experimental model of a liquid piston system was built and tested with two different materials, polycarbonate and aluminum alloy, used for the compression chamber. This tabletop liquid piston system was tested in conjunction with a simulated OCAES system, which consisted of a hydrostatic tank connected to a compressed-air source from the wall to mimic the constant hydrostatic pressure at ocean depth experienced by the air stored in an actual OCAES system. Good agreement was found between the experimental and numerical studies and demonstrated that the heat transfer characteristics of a liquid piston compression process are effective in reducing the increase in air temperature that occurs during the compression process. The results also suggest that it may be possible to achieve a near-isothermal process with a fully optimized liquid piston compression system.

Automated Vertical Photography for Detecting Pelagic Species in Multitaxon Aerial Surveys

Abstract: Marine aerial surveys are designed to maximize the potential for detecting target species. Collecting data on different taxa from the same platform is economically advantageous but normally comes at the cost of compromising optimal taxon-specific scanning patterns and survey parameters, in particular altitude. Here, the authors describe simultaneous visual and photographic sampling methods as a proof of concept for detecting large whales and turtles from a single aircraft, despite very different sighting cues. Data were collected for fishing gear, fish, sharks, turtles, seals, dolphins, and whales using two observers and automated vertical photography. The photographic method documented an area directly beneath the aircraft that would otherwise have been obscured from observers. Preliminary density estimates were calculated for five species for which there were sufficient sample sizes from both methods after an initial year of data collection. The photographic method yielded significantly higher mean density estimates for loggerhead turtles, ocean sunfish, and blue sharks (p 0.05), two of the largest species included in the analysis, which are relatively easy to detect by both methods. Although postflight manual processing of photographic data was extensive, this sampling method comes at no additional in-flight effort and obtains high-quality digital documentation of sightings on the trackline. Future directions for this project include automating photographic sighting detections, expanding the area covered by photography, and performing morphometric measurement assessments.

Investigation of the Relationship Between the Yucatan Channel Transport and the Loop Current Area in a Multi-Decadal Numerical Simulation

Abstract: A hypothesis by Maul [1977], stating the rate of change of Loop Current (LC) volume is related to deep Yucatan Channel (YC) transport, is examined and validated with a continuous 54-year simulation of the regional 1/25˚ Gulf of Mexico (GoM) Hybrid Coordinate Ocean Model (HYCOM). The hypothesis states that the imbalance of transport between the upper YC and the Florida Straits controls the rate of change of the LC volume and that the imbalance is compensated by transport through the deep YC. Previous studies have investigated the relationship between deep YC transport and LC area (used as a proxy for the volume). The first attempt by Maul et al. [1985] using a single mooring was unsuccessful in finding a relationship. However, Bunge et al. [2002] using data from the Canek observing program, which deployed 8 moorings across the YC, found a strong relationship between the deep YC transport and the LC area. The data used in Bunge et al. [2002] was for a period of 7.5 months, which is relatively short compared to the time scale of LC variability. A multi-decadal (54 years) HYCOM simulation of the Gulf of Mexico provides long term data to study LC variability and allows one to validate the Maul [1977] theory. Time evolution of the LC between two shedding events can be viewed as a combination of relatively high-frequency (on the order of about 40 days) fluctuations superimposed on a low-frequency trend. The high frequency portions of the modeled variability are shown to be related when the LC-area time derivative and the deep YC transport are compared. The low frequency variability is examined by comparing the LC-area time series with integrated transport in the deep YC, and statistically similar trends are identified. The results support the Maul [1977] theory.%%%%A Thesis submitted to the Department of Earth, Ocean, and Atmospheric Science in partial fulfillment of the requirements for the degree of Master of Science.%%%%Fall Semester, 2013.%%%%August 30, 2013.%%%%Gulf of Mexico, Hycom, Loop Current, Yucatan Channel%%%%Mark A. Bourassa, Professor Directing Thesis; Dmitry S. Dukhovskoy, Committee Member; Steven L. Morey, Committee Member; Eric P. Chassignet, Committee Member; Philip Sura, Committee Member.

Review of Technological Advancements and HSE-Based Safety Model for Deep-Water Human Occupied Vehicles

Abstract: This paper reviews the latest advancements in subsea technologies associated with the safety of deep-water human occupied vehicles. Human occupied submersible operations are required for deep-water activities, such as high-resolution bathymetry, biological and geological surveys, search activities, salvage operations, and engineering support for underwater operations. As this involves direct human presence, the system has to be extremely safe and reliable. Based on applicable International Electrotechnical Commission (IEC) 61508 Standards for health, safety, and environment (HSE), the safety integrity level requirements for the submersible safety systems are estimated. Safety analyses are done on 10 critical submersible safety systems with the assumption that the submersible is utilized for 10 deep-water missions per year. The results of the analyses are compared with the estimated target HSE requirements, and it is found that, with the present technological maturity and safety-centered design, it is possible to meet the required safety integrity levels. By proper maintenance, it is possible to keep the mean time between failures to more than 9 years. The results presented shall serve as a model for designers to arrive at the required trade-off between the capital expenditure, operating expenditure, and required safety levels.

Performance and Stability Analysis for ZJU Glider

Abstract: Underwater gliders provide an effective, low-cost method for sampling the ocean over large spatial and temporal scales. In this paper, we present a series of theoretical analyses to provide guidelines for vehicle design, which are used to develop a coastal 200-m-depth underwater glider known as the Zhejiang University (ZJU) glider. The ZJU glider uses a longitudinally actuated moving mass for pitch control and a rudder for turning control. Computational methods and analytical approaches are chosen to solve the viscous and inviscid terms of glider hydrodynamics, respectively. Steady flight equilibrium analysis gives the varied range of moving mass location for pitch control and varied vehicle volume for buoyancy control. Size analysis investigates the effects of glider geometric parameters on motion performance. For wings-level flight, we describe the variation in the maximum lift-to-drag ratio corresponding to a given vehicle size and speed. For turning motion, we investigate the manner in which the turning performance varies with vertical rudder configuration. Stability analysis determines the relationship between the stability of glider motion and the locations of the glider wings and rudder. Pool trials indicate that the ZJU glider functions well in water and is capable of serving as a sensor platform for ocean sampling.

Integrating Offshore Wind Power and Multiple Oil and Gas Platforms to the Onshore Power Grid Using VSC-HVDC Technology

Abstract: This thesis investigates the possibilities of integrating oil and gas platforms and offshore wind power to the onshore power grid. The main motivation for this is to reduce the large greenhouse gas emissions associated with traditional oil and gas platforms. The oil and gas industry is responsible for 25 % of total greenhouse gas emissions from Norway. The major part of these emissions originates from the power generation on the platforms. By supplying the oil and gas platforms with renewable energy from the onshore power grid in combination with offshore wind power there will be little or no use for power generation on the platforms and greenhouse gas emissions can be greatly reduced. The feasibility of a hypothetical power system in the North Sea consisting of five oil and gas platforms and one offshore wind farm with a common connection to the onshore power grid is studied. The connection to the onshore grid is realized through a High Voltage Direct Current (HVDC) transmissions system based on Voltage Source Converter (VSC) technology The main goal of this thesis is to gain understanding of the system dynamics and the control of VSC-HVDC transmission system, offshore wind power, as well as offshore power systems. A dynamic simulation model of the system and a control system has been developed using SimPowerSystems in MATLAB®/Simulink. In order to save computation time aggregated models are used. The load on the platforms consists of a passive load, a fixed speed induction motor, and a constant power load representing variable speed drives on the platform. The wind farm consists of a wind turbine and a permanent magnet synchronous machine operating at variable speed using a back-to-back VSC. The converters in the VSC-HVSC transmission system and the wind farm are modeled using average models. Simulations are performed on system disturbances that are thought to be critical for the operation of the system. The simulation cases represent large and partly exaggerated disturbances in order to test the limitations of the system. The simulation results showed that the developed control system was able to keep the voltage and frequency variations within the grid code in IEC 61892 even during large disturbances. It was concluded that the system handles variations in the load very well and that the system configuration studied in this thesis is regarded as a feasible way of integrating oil and gas platforms and offshore wind power to the onshore grid. However more detailed studies are recommended including short circuit analysis.

Drag Coefficients of Stock and Stockless Anchors

Abstract: In recent years, collisions between anchors and submarine power cables have attracted increasing research interest because of the rapid growth of offshore wind farms. Since the drag coefficients have not been calculated, conservative values have been assumed and used to simulate collisions. This conservative estimation is likely to result in unnecessarily heavy designs for the protective structures. Therefore, reliable calculations of the drag coefficients are required to reduce the design, manufacture, and installation costs of the protective structures. Here, the authors describe calculations of the drag coefficients of 2,000-kg stock and stockless anchors using numerical flow analyses. The authors show that the drag coefficients of the anchors converge to 1.0 and 0.8, respectively, regardless of the initial velocity and the Reynolds number.

Autonomous year-round sampling and sensing to explore the physical and biological habitability of permanently ice-covered antarctic lakes

Abstract: The lakes of the McMurdo Dry Valleys, Antarctica, are some of the only systems on this planet that are perennially ice-covered and support year-round metabolism. As such, these ecosystems can provide important information on conditions and life in polar regions on Earth and on other icy worlds in the solar system. Working in these extreme environments of the Dry Valleys poses many challenges, particularly with respect to data collection during dark winter months when logistical constraints make fieldwork difficult. In this paper, the authors describe the motivation, design, and challenges for this recently deployed instrumentation in Lake Bonney, a lake that has been the subject of summer research efforts for more than 40 years. The instrumentation deployed includes autonomous water, phytoplankton, and sediment samplers as well as cable-mounted profiling platforms with dissolved gas and fluorometry sensors. Data obtained from these instruments will allow us, for the first time, to define the habitability of this environment during the polar night. The authors include lessons learned during deployment and recommendations for effective instrument operation in these extreme conditions.

Use of AUVs to Inform Management of Deep-Sea Corals

Abstract: Nationalandinternationalobligationstoprotectvulnerablespecies,communities,habitats, and ecosystems (VSCHEs) require greater attention as human uses extendto deeper water. These obligations increase the need for improved understanding ofthe distribution and abundance of VSCHEs to develop management actions. Datafromlow-speedvehiclesthatoperateattheseafloor(e.g.,remotelyoperatedvehicles,camerasleds)predominate.These“lowandslow”approaches,whileprovidinghigh-resolution data, do not operate at the scale required for management. We suggestautonomous underwater vehicles (AUVs) flown at relatively high altitude and highspeed over the seafloor as a “high and fast” approach to survey areas at the scalefisheriesandotheractivitiesoperate.WeusedREMUS6000AUVstocollectpresencedataforVSCHEsinarapidassessmentonPhysaliaSeamount.AUVswereprogrammed to collect digital images, side-scan sonar (120/410 kHz), and envi-ronmental parameters and could navigate a 40° slope. Our preliminary results ofthis approach, predicated on the assumption that coarse taxonomic resolution isadequate for management needs, indicates AUVs can be effective tools for largearea surveys in short time periods.Keywords: imaging, sonar, vulnerable species, seamount, assessment

Underwater Color Image Enhancement Using Combining Schemes

Abstract: Underwater color image processing has received considerable attention in the last few decades for underwater image-based observation. In this article, a novel underwater image enhancement approach using combining schemes is presented. This study aims to improve color correction under nonuniform illumination conditions. The objective of this approach is threefold. First, to correct nonuniform illumination and enhance contrast in the image, homomorphic filtering is used. Second, the color contrast of an image is equalized by a contrast stretching algorithm in red, green and blue (RGB) color space. Finally, the noise amplified after the previous two steps is suppressed by using wavelet domain denoising based on threshold processing. The comparison of experimental results shows that the proposed approach of underwater image enhancement can correct the color imbalance and is especially suitable for processing underwater color images that have nonuniform lighting.

Xuelong Navigation in Fast Ice Near the Zhongshan Station, Antarctica

Abstract: Navigation in polar sea regions requires special attention to the sea ice condition because it is a major barrier for an icebreaker to break the drift ice or fast ice, allowing the vessel to keep moving forward. The advancement of remote sensing imagery provides an effective means to classify and identify various features, including different types of sea ice. Hence, it permits fuel and time saving for the entire voyage, especially when drift ice or fast ice becomes a barrier for the icebreaker. In this study, the authors exploit the potential usage of high-resolution synthetic aperture radar (SAR) imageries from Radarsat-2 to identify sea ice conditions for precise navigation of China’s icebreaker vessel (Xuelong) during the 29th Chinese Antarctic Research Expedition in December 2012. Different features on the fast ice were identified from horizontal-transmit and horizontal-receive polarized imagery. The potential usage of SAR imagery for precise navigation was confirmed by an expert witness on the Xuelong vessel at that time. The final voyage route has validated our analysis of fast ice and navigation of the Xuelong vessel. The predicted regions for unloading locations were also found to be matching well with the actual vessel unloading locations after the final voyage route.

Measuring Turbulent Dissipation Rates Beneath an Antarctic Ice Shelf

Abstract: Microstructure shear, temperature, and conductivity observations from a tethered profiler have been made beneath George VI Ice Shelf to examine processes driving vertical heat flux in the oceanic turbulent boundary layer. Such measurements at the ice-ocean interface within the cavity of an ice shelf are unprecedented, requiring the deployment of a profiler through 400-m deep access boreholes. The authors describe the drilling technique developed for this purpose, which involves using a brush to widen the deepest section of the borehole, and as evidence that this novel technique can be successful, they present shear and thermal variance spectra from the profiler. These spectra indicate that dissipation rates of turbulent kinetic energy, from which heat flux can be calculated, can be resolved beneath an ice shelf as well as they can be in open water.

Arctic communication challenges

Abstract: The vast geographic distances and the economic importance of activities in remote areas like the Arctic demand new innovative radio-based solutions. There are numerous unsolved research challenges pertaining to (broadband) radio communication coverage and satellite navigation reliability throughout the large region composed of the Norwegian Exclusive Economic Zone and the Arctic waters. This paper outlines these challenges and the current situation, in addition to identifying future systems capable of mitigating the crucial lack of adequate electronic communications infrastructure in the High North.

Minimal Time Route for Wind-Assisted Ships

Abstract: As a result of a global call for energy-saving and emission-reduction strategies as well as an urgent need to reduce the shipping cost of transoceanic crossings, this paper proposes a route that minimizes the time for such crossings and provides technical support to efficiently utilize wind power based on existing research for wind-assisted ships. To begin, the ocean winds around the ship route were analyzed, and the different influences on traditional ships and wind-assisted ships were listed for various wind speeds and directions. The number of waypoints of a route was subsequently calculated, and a model of the optimal ship route was then built based on the fixed power output of the main marine engine. A solution algorithm based on simulated annealing was then presented to determine the optimal wind-assisted ship routes by minimizing the travel time. Finally, a 76,000-DWT wind-assisted cargo ship was designated as the experimental ship, and the optimization model and its algorithm were simulated to generate an optimized wind-assisted route. The simulation indicated that the speed of a ship equipped with wind propulsion increases, which significantly reduces the travel time and fuel costs over the optimized route, despite the increased distance of this route. Thus, the route optimization algorithm designed in this study can be applied to optimize the routes for wind-assisted ships and theoretically guide further studies of wind-assisted projects.

Quarter Circular Breakwater: Prediction of Transmission Using Multiple Regression and Artificial Neural Network

Abstract: The physical model study of coastal structures is a nonlinear process influenced by innumerable parameters. As a result of a lack of definite systems, intricacies, and high costs involved in the physical models, a simple mathematical tool is needed to predict wave transmission through quarter circular breakwater (QBW). QBW is a state-of-the-art breakwater essentially based on the exploitation of the concepts of semicircular breakwater. This paper discusses the use of soft computing tools such as MATLAB-based multiple regression (MR) and artificial neural network (ANN) to predict the wave transmission coefficient of QBW. To assess the accuracy of the proposed model and its ability to forecast, correlation coefficient and mean squared error are availed. On comparing the results obtained from MR and ANN, it is concluded that ANN gives more accurate results and can be used as a powerful tool for the modeling of hydrodynamic breakwater transmission through QBW. It serves as a viable alternative to the conventional physical model to simulate the hydrodynamic transmission performance of QBW.

Hybrid underwater glider for underwater docking: modeling and performance evaluation

Abstract: The development of a novel type of hybrid underwater glider that combines the advantages of buoyancy-driven gliders and propeller-driven autonomous underwater vehicles has recently received considerable interest. However, few studies have considered a hybrid glider with docking capability, which would expand the glider's applications. This study presents a hybrid glider with a rotatable thruster for realizing underwater docking. A tailored dynamic model of the hybrid glider is derived, and the motion performance is evaluated by simulations and experimental tests. A comparison between the experiments and simulations shows that results are in agreement, thus indicating the feasibility of the dynamic model and the accuracy of the hydrodynamic coefficients. In addition, the hybrid glider open-loop docking tests validate the feasibility of the mechanical docking system. Moreover, the experimental tests also validate the glider's different functions and indicate that the hybrid glider with rotatable thruster has high maneuverability even at low speeds. Thus, this type of hybrid glider can be used for underwater docking.

A Study of the Algorithms for the Detection of Tsunami Using an Ocean Bottom Pressure Recorder

Abstract: The National Institute of Ocean Technology (NIOT), an autonomous organization under the Ministry of Earth Sciences, government of India, is engaged in developing and installing systems for tsunami detection and reporting. This involves high-precision bottom pressure recorders (BPRs) installed on the ocean floor, which can detect water level changes in the order of a few centimeters. Data are logged and recorded subsea by instruments located close to the BPRs. The detection of abnormal changes in the water level is required for detecting a tsunami event. This paper describes algorithms incorporated in most BPRs for detecting a tsunami by predictive methods such as Newton’s Extrapolation and Kalman predictor techniques. The most widely used tsunami detection algorithm is based on Newton’s extrapolation. The tsunami detection technique based on the Kalman prediction algorithm developed by NIOT can be an alternative for the existing technique. This paper describes both the algorithms and analyzes their effectiveness during tsunami event detection using MATLAB software. It is found that the Kalman algorithm has a better detection performance over the Newton extrapolation technique for tsunami wave amplitudes up to 300 mm. The Newton extrapolation technique has a better detection performance for tsunami wave duration of less than 10 min. For tsunami wave durations greater than 10 min, the Kalman algorithm has a better detection performance. As the wave durations of most of the recorded tsunamis are greater than 10 min, the Kalman algorithm could be a viable substitute for tsunami detection.