Search

Autonomous underwater vehicles (AUVs) are programmable, robotic vehicles that can drift, drive, or glide through the ocean without real-time control by human operators. AUVs that also can follow a planned trajectory with a chosen depth profile are used for geophysical surveys, subsea pipeline inspection, marine archaeology, and more. Most AUVs are followed by a mother ship that adds significantly to the cost of an AUV mission. One pathway to reduce this need is to develop long-endurance AUVs by improving navigation, autonomy and energy storage. Long-endurance AUVs can open up for more challenging mission types than what is possible today. Fuel cell systems are a key technology for increasing the endurance of AUVs beyond the capability of batteries. However, several challenges exist for underwater operation of fuel cell systems. These are related to storage or generation of hydrogen and oxygen, buoyancy and trim, and the demanding environment of the ambient seawater. Protecting the fuel cell inside a sealed container brings along more challenges related to condensation, cooling and accumulation of inert gases or reactants. This paper elaborates on these technical challenges and describes the solutions that the Norwegian Defence Research Establishment (FFI) has chosen in its development of a fuel cell system for long-endurance AUVs. The reported solutions enabled a 24 h demonstration of FFI's fuel cell system under water. The remaining work towards a prototype sea trial is outlined.

The autonomous under water vehicle (AUV) system uses sensors which have a very important role in this field, even work in very complex environment. In order to improve the reliability of the AUV systems it important to know about the sensor failure diagnostic technology. In this paper two methods has been proposed they are combining phase space reconstruction and extreme learning machine(ELM).They are mostly being used to predict the sensor output in order to achieve the sensor fault diagnosis for AUVS. This stimulation experiments based on sea trial data shows the proposed method can be diagnosed by the sensor faults and recover the signals after the faults occur in a period of time

Underwater cable burying is one of main cable protection methods in the offshore cable installation. In this paper, the performance evaluation of an underwater cable burying robot, named URI-T, through the sea trial is addressed. URI-T, the first heavy-duty underwater robot for cable burying tasks developed in South Korea, is designed to perform burying tasks and maintenance tasks for underwater cables and small-size pipes at the sea bed of 2,500m water depth. URI-T includes water-jetting systems and cable detection sensors for cable burying tasks, and employes mainpulators and tools for cable maintenance tasks. The sea trial at the East Sea having 500m water depth was focused to verify the key performance indices: operation water depth, cable burying depth, cable burying speed, and forward speed. The cable maintenance ability was also examined by carrying out the cable cutting test and the cable gripping test. Moreover, applicability of URI-T is also evaluated by two times of cable burying experiments more than 100m distance. As a result, it was verified not only that URI-T satisfies the target performance indicies, but also that URI-T is applicable for the cable burying construction.

Tidal current energy is a promising renewable energy resource. Full scale tidal current turbines (TCT) have been deployed all over the world. To verify the design methods of large TCTs with high reliability and efficiency, a 600-kW tidal current turbine was designed and tested in this study. This turbine consisted of a two-blade rotor, a low speed ratio gearbox and a medium speed generator. The turbine was grid-connected through a full-rated converter, and its speed was controlled to capture the maximum power. First, to reach high turbine performance, system design details and maximum power point tracking (MPPT) control strategy were considered. Then, the 600-kW turbine was manufactured, and an onshore test was carried out to test power transmission and control performance. The power performance of the blades and control system were further tested in the sea trial carried out in Zhoushan. Good agreement was obtained between theoretical analyses and test results. Finally, to ascertain causes for observed power fluctuations, the power spectral density (PSD) was analyzed; the results indicated that power fluctuations may be due to stream shear.

In this paper, wave-induced motions and loads of a bow flare ship advancing in harsh irregular waves are investigated both numerically and experimentally. A 3D time-domain hydroelasticity theory that includes memory-effect function considering Froude–Krylov nonlinearity is developed to predict ship motions, wave loads and slamming loads in long-crested irregular waves. In the hydroelasticity algorithm, the wave memory effects and forward speed effects are addressed by retardation function method to improve the computing efficiency and provide opportunity for short-term statistical analysis of ship responses in irregular waves. In addition, segmented model tank tests are conducted to experimentally investigate the motions and loads of ship sailing in long-crested irregular waves and also validate the numerical results. To further understand the nonlinear wave loads behavior of ship in short-crested waves, large-scale segmented model sea trials are performed in realistic sea waves. The numerical results and experimental results are systemically analyzed and compared using time series, spectral and probability statistical analysis methods.

We develop the approach to simulate the experiments with surface and underwater vehicles in towing tanks for Reynolds numbers Re, corresponding to sea trials, using discrete injection of polymer additives. The complete dynamic similarity between full-scale and tank tests is possible if both Froude number and Re are equal for a ship and its model. In traditional experiments, the first condition is only satisfied and the viscous and wave resistances are independently studied. The Toms effect is widely used in marine engineering, e.g., to reduce energy cost. In this work, it is applied quite differently. Re is higher and the skin friction coefficient c f is hence less for sea trials than for towing tanks. Injection of polymer additives allows decreasing c f on ship model to full-scale values, providing the complete similarity and reproducing sea trials in that way. We report the selected results of such novel approach that, in particular, include velocity profiles and c f for sea trial, towing tank and pipe experiments, plane boundary layer and 3D flow around propeller, rough and smooth surfaces. The data for full-scale and tank experiments agree well with each other.

The unmanned wave glider (UWG) is a new kind of wave powered unmanned marine vehicle for persistent marine environment monitoring. However, the heading control of UWG is unusual, mainly about the heading control of the surface float body (Float), since it is indirectly actuated and with a large lag of the control response. The adaptive heading control method for the Float with heading information fusion is discussed. The basic and improved arrangement methods of the desired heading of Glider are proposed. Via direct heading control of Glider, the heading control of Float is realized indirectly. Simulation and sea trial results demonstrate that the proposed adaptive heading control method improves the heading control performance of UWG significantly.

During the Long-Term Glider Mission for Environmental Characterization 2016 sea trial, carried out in the eastern Ligurian Sea (Northwestern Mediterranean Sea), two gliders rated to a maximum depth of 1000 m operated continuously from 3 May 2016–27 June 2016. When possible, glider tracks were synchronized with the contemporaneous footprints of the Jason-2, SARAL/AltiKa and CryoSat-2 altimeters. Temperature and salinity measured by the gliders that were co-localised with the altimeter passages were used to calculate along-track dynamic heights (DH). The latter were then compared with the altimeters’ near real-time absolute dynamic topography (ADT) measurements. ADT and DH values showed very similar, but shifted patterns, suggesting that gliders had sampled the same structures but at different times. Average surface absolute geostrophic velocities at the time of glider transit were used in a novel relocation technique to reposition glider measurements where they would have been at the time of the altimeter passage. The relocation increases the correlation between datasets to a value close to 1 and reduces the RMSE of an order of magnitude, also when the time-difference between measurements was greater than 3 days. The sea level spatial and temporal variability is attributed to the presence of meanders generated by the baroclinic instability of the Liguro- Provencal Current (LPC). These meanders are characterized by a 38 km amplitude and 0.12 m s−1 average propagation speed that are confirmed by the larger scale ocean colour measurements and are in agreement with those previously described in the literature. We found that the presence of LPC meanders in along-track ADT and DH measurements is evidenced by a decrease in sea level when profiles sampled the Modified Atlantic Water, and an increase in sea level when measurements sampled the adjacent waters of Tyrrhenian Sea origin. The relocation technique introduced here is expected to improve future altimetry-glider comparisons, as similar validation experiments were considered possible only when glider and altimetry measurements were near synoptic, and collected up to one day from each other.

In towed sonar systems generally, the array is towed behind a ship using a combination of electro-optic mechanical (EOM) tow cables - negatively buoyant metallic armoured Heavy Cable and neutrally buoyant fibre armoured Light Cable- the former for depth control and latter for depth maintenance. Any failure in these cables can affect the performance of the sensor array and can even result in loss of the towed system to sea. During a series of towed array trials, it was observed that the metallic armoured cable had lost its circularity and became flattened during deployment and retrieval from ship. This may be due to the extreme radial forces acting on the cable while passing through a) rollers located at winch spooler and b) main fairlead comprising of 5 rollers located at aft end of ship, which causes permanent changes in cable’s internal configuration. To verify the cause and study the effects of such flattening on functionality and life of the cable, cyclic load testing studies were carried out after simulating the actual deployment-retrieval conditions as that in the ship. Both indigenously developed and imported cable samples were chosen as test samples for performance comparison. During the tests, it was observed that severe flattening of armour and core cable resulting in failure of electrical & optical lines had occurred in indigenous cable samples. The imported cable samples showed no flatness or failure of lines. Based on the results, steps were taken to improve the radial load bearing capacity of the indigenous cable. Modifications were made in a) core cable sheath material b) core cable sheath thickness & c) armour wire material and an improved indigenous cable was developed, which has withstood all the above tests and is now ready to be inducted to the system for sea trials.

Wave-induced ship motion and load responses are usually investigated on the assumption that the incident waves are long-crested. The realistic sea waves are however short-crested irregular waves. Real practice reveals that the ship motion and load responses induced by short-crested waves are different from those induced by long-crested waves. This paper aims to conduct a comprehensive study on ship motions and loads in different wave fields. For this purpose, comparative studies by small-scale model towing tank test and large-scale model sea trial are conducted to experimentally identify the difference between ship motions and loads in long-crested and short-crested irregular waves. Moreover, the influences of directional spreading function of short-crested waves on ship motions and loads are analyzed by numerical seakeeping calculation. The results and conclusions obtained from this study are of great significance for the further extrapolation and estimation of ship motions and loads in short-crested waves based on long-crested wave response results. Keywords: Short-crested wave, Directional spectrum, Motion and load responses, Seakeeping performance, Hydroelasticity theory

A newly built ship must conduct sea trial to understand its performance including speed, maneuverability and so on. The result of the speed trial is very important for the ship owner, because the ship speed is directly related to profit. In this case, current becomes an important factor because the ship speed is changed by the effect of the current. To remove this effect, International Towing Tank Committee and International Organization for Standardization heve presented procedures of removing this effect. However, these procedures require two or three round–trips against one ship speed. To solve this difficulty, we attempt to estimate herein the current from the ship motion based on successive data assimilation. The proposed method is verified by twin experiments. Consequently, the proposed method is found to estimate the current well.

A comparison between sea trial measurements and full–scale CFD results is presented for two self–propelled ships. Two ships considered in the present study are: a general cargo carrier at Froude number Fn=0.182 and a car carrier at Fn=0.254. For the general cargo carrier, the propeller rotation rate is fixed and the achieved speed and trim are compared to sea trials, while for the car carrier, the propeller rotation rate is adjusted to achieve the 80% MCR. In addition, three grids are used for each ship in order to assess the grid refinement sensitivity. All simulations are performed using the Naval Hydro pack based on foam-extend, a community driven fork of the OpenFOAM software. The results demonstrate the possibility of using high–fidelity numerical methods to directly calculate ship scale flow characteristics, including the effects of free surface, non–linearity, turbulence and the interaction between propeller, hull and the flow field. Keywords: Full scale ship propulsion, Actuator disc, Sea trial validation, Grid sensitivity studies, OpenFOAM

In this short paper, we report some preliminary results on the seabed terrain reconstruction using the two-dimensional (2D) forward-looking sonar. In the underwater pipeline burying project, when the burying machine excavating the trench using the jetting device, the stirred turbid water sharply shorten the visual distance of optical camera. Researchers from Shenyang Institute of Automation, Chinese Academy of Sciences (SIA, CAS) and Korea Institute of Robot and Convergence (KIRO) work together to reconstruct the 3D environment using the acoustic camera. The proposed reconstruction procedure mainly includes two parts: 3D point-cloud extraction for each sonar frame and point-cloud registration. With the former step, the elevation information, which is irreversely lost in the acoustic imaging process, is recovered by the shape-from-shading technology under the Lambert surface assumption. With the latter, a registration method based on symmetrical Kullback-Leibler divergence has been proposed to stitch the point clouds from each sonar image into a panoramic terrain map. The initial experiment results with the sea-trial datasets demonstrate that the proposed method is feasible for the practical underwater engineering.

Quantification of the escapement rate of unwanted fish through a selective device is usually based on catch comparison. This study proposes a new, time efficient method to automatically compare two selective devices by automated counting of fish escapements through each selective device based on video sequences. First, sea trials were conducted to record video sequences of fish escaping a white and black square mesh panel. Then, all of the underwater sequences were automatically analysed by a computer vision software for automated object detection and tracking. Finally, the algorithm was assessed using 150 min of video sequences analysed by humans. We observed that the variability in escapements rate between all the observers on reference video sequences could reach 5%. As the difference in escapements rate between the algorithm and the observers was lower than the variability between observers, the automated approach was validated. The software detected a significant difference in fish escapement rate according to the net colour in the camera field of view: 60% of all fish escaped through the white panel. Our results suggest that net colour influences the escape rates of fish. The colour of the selective device should therefore be investigated further with the aim of increasing their efficiency. Further development of the software could be done to identify species and size of the fish and assess the effectiveness of a selective device by species and size.

Vortex-induced vibration (VIV) resulting lock-in phenomenon which is the vibration frequency of the structure immersed in a fluid is locked in its resonance frequencies within a flow speed range is a potential cause of vibration fatigue and/or singing of the propellers of large merchant ships. A deep learning-based indirect VIV detection algorithm that works by vibration measurement data of a hull structure instead of a propeller during the sea trial phase is proposed in this study. RPM-frequency representations of the vibration signal by stacking the vibration frequency spectrum relative to various propeller RPM's, so-called waterfall chart of 2-dimensional data like an image, are measured and fed into the proposed convolutional neural network (CNN) architecture for VIV detection i.e. VIV frequency and RPM range. To generate the large data set, artificial data looks real, for learning, a method based on the modal superposition method instead of time-consuming fluid-structure interaction analysis is proposed. 10k set data for training, 1k set for hyper-parameter tuning, and 1k set for the test were generated. After the training, it showed a diagnosis success rate of 82% for the test set. To test the proposed VIV detection algorithm, investigations were carried out in a laboratory on a small-scale ship propulsion system designed in such a way that the vortex shedding frequency and the underwater natural frequency match each other. The proposed VIV detection algorithm was tested using the structural vibration signals measured at stationary structures in the air instead of the rotating propeller immersed in water. Lastly, the validity of the proposed algorithm was tested using the structural vibration signal measured at the hull structure of a crude oil carrier in which a propeller singing occurred during her sea trial.

Full scale measurement, model testing and a hybrid CFD method were used to characterize the Underwater Radiated Noise (URN) of a ship at design speed. The CFD method consists of a multiphase Delayed Detached Eddy Simulation and the Ffowcs-Williams Hawkings acoustic analogy. The paper discusses the correlation of the noise spectra with the observed cavitation behavior and compares the measured full scale data with those predicted by the model testing and the CFD method. The comparison shows that the sheet cavity and Tip Vortex Cavitation (TVC) predicted by the model testing are in reasonably good agreement with the full scale observations. The pressure pulses are somewhat higher than the full-scale data. Overall, the predicted URN has a good correlation with the noise spectra obtained from the sea trial. The CFD method shows the potential to resolve turbulence eddy structures in the wake. It captures the dynamic development of sheet cavitation and the collapse and rebound of TVC as observed in the model test and the sea trial, but under-predicts the extent of TVC. The pressure pulses and tonal noise are in close agreement with the respective measured data for the first five orders of blade passing frequency. The method underestimates the broadband noise level in the frequency range 50–112 Hz where the TVC is expected to have an important contribution. The maximum under-prediction in this range is about 28 dB at 72 Hz. At frequencies above 200 Hz, the broadband noise becomes more and more under-predicted with increasing frequency.

Autonomous underwater vehicles (AUVs) are advanced near-bottom platforms that can be used for magnetometric analysis of the seafloor. However, the vehicle itself can cause interference with the magnetic measurements, which need to be corrected. Here, we derive a functional relation between the magnetic measurements and AUV's heading that is based on the composition and causes of an AUV's near-bottom magnetic anomaly. We set up a method to correct tri-axial magnetometer interference caused by the AUV. Magnetic induction intensity is removed using magnetic data collected during the spinning of the AUV. Connatural magnetic field of the AUV is collected and subtracted by using portable magnetometer. The method performs very well during QianlongII AUV experimental tests performed on land and in lake. The method also corrects magnetic data by an autonomous benthic explorer (ABE) AUV and yields good results. The effects of main components of QianlongII AUV on the magnetic measurement results are analyzed and make sure dominating interference produced by the batteries. That is mitigated using a probe extension pole. Furthermore, excellent survey data and satisfactory correction results are obtained during the AUV sea trials. This verifies the efficacy of the proposed method for correcting tri-axial magnetometer interference caused by AUV.

In this paper, seakeeping performance of vessels is comparatively investigated by means of improved 2.5D theoretical calculation, small-scale model towing tank test and large-scale free running model sea trial. This study also provides a scheme of ship vertical motion stabilization technique by using Semi-Submerged Bow (SSB) appendages. Firstly, an improved strip theory based 2.5D theoretical seakeeping algorithm, which considers the viscous flow effects attributed to bow appendages, is developed to estimate ship vertical motion responses in regular waves. Short-term predictions are also made on the basis of spectral analysis theory to predict ship motion responses in irregular waves. Then corresponding small-scale models are made and tested in a laboratory towing tank for both regular and irregular wave conditions to confirm the numerical results. The tank testing results between different ship schemes are also compared to experimentally investigate the effects of SSB and fin on hull vertical motion stabilization. Furthermore, large-scale model sea trials are conducted in coastal waves for a final validation of the ship seakeeping performance in short-crested sea waves. Finally, comparisons of the results by different testing approaches are systematically made and analyzed.

Measurement, data transfer, modelling, controller systems are the main subjects of interdisciplinary area during prototyping of marine automatic control systems. Experimental parameter identification is an essential step for modelling and control system design are in question for various marine applications. The selection of variables to be measured, type of measurement sensors, type of control algorithms and controller systems, communication, signal conditioning are all important topics for parameter identification and real-time control applications in maritime engineering. The objective of this paper is to present a brief review of these important topics based on our case studies, such as ship roll motion reduction control, optimal trim control of a high speed craft, and dynamic position control of underwater vehicles. These projects involved extensive dynamic modelling, simulation, control algorithm design, real-time implementation and full-scale sea trials. In this paper, the presented methods, and the required characteristics of the marine control systems are demonstrated with the results obtained by the simulation studies and full-scale sea trials. Also, insight into the selection of hardware and software components for mechatronic applications in marine engineering is provided.

Ship owners and classification societies have recently begun to require assessments of the maneuverability of twin-screw ships under machinery failure. Since such an assessment has not yet been previously conducted, its concept and process have not been clearly established. In this paper, we construct a simulation that predicts the maneuverability of a ship under machinery failure and propose a process to conduct IMO maneuvering tests under machinery failure, and this is referred to as single propeller failure, single rudder failure, aligned combination failure, and cross combination failure. A mathematical model for the simulation under normal operating condition is verified, and assumptions are applied to the existing mathematical model to introduce machinery failure. The suggested procedure is followed to verify a mathematical model with these assumptions under machinery failure by conducting sea trials. Finally, numerical simulations for mandatory tests are conducted for the defined failures, and the physical characteristics of each failure are investigated compared to those under normal operating conditions.

To achieve a continuous and accurate navigation solution that avoids interruption, GPS is integrated with dead reckoning techniques such as inertial navigation and speed log. A common approach to obtain a low-cost navigation solution is to utilize a multisensor system consisting of MEMS-based inertial measurement unit (IMU), and the whole system is integrated with GPS. However, these sensors provide significant inherent errors because of their complex error characteristics. Particle filter (PF) is considered as a nonlinear filtering technique to accommodate for arbitrary inertial sensor characteristics and motion dynamics. An adaptive fission PF (AFPF) method is proposed to overcome the shortcoming of sample impoverishment problem and improve particle quality. Moreover, further improvement of the MEMS-based IMU/GPS integration navigation system performance during GPS unavailability is achieved by integrating measurement updates from speed log data. The performance of the proposed GPS/IMU/LOG integration using AFPF is evaluated by sea trial, and results indicate that the AFPF solution outperform three different solutions.

In the paper a modular manoeuvring model of the passenger ferry “Landegode” is built, validated and studied. Global sensitivity analysis based on the variance decomposition is performed to assess the sensitivity of the individual model coefficients on the simulation outcomes. It is found that uncertainty in both hull hydrodynamic coefficients and the steering and interaction coefficients can result in significant uncertainty in the simulation results. The most influential coefficients are defined for the standard IMO manoeuvres. The possibility of identification of “true” values of the coefficients from full scale trials is studied. Such analysis would allow improving empirical predictions of the coefficients. It is found that different combinations of the model coefficients result in similar time-series. This indicates the presence of correlation between the coefficients. Thus, although the identified coefficients can be used for simulations of the ship manoeuvring, it is impossible to identify the single “true” value for each coefficient from these sea trials.

In this paper an investigation of flow noise in sonar applications is presented. Based on a careful identification of the dominant coupling effects, the acoustic noise at the sensor position resulting from the turbulent wall pressure fluctuations is modelled with a system of hydrodynamic, bending and acoustic waves. We describe for the first time an analytical solution of the problem which is based on a biorthogonal system which can be solved in the spectral domain without the usual simplifying assumptions. Finally, it is demonstrated that the analytical solution describes the flow noise generation and propagation mechanisms of the considered sea trials., Comment: 19 pages, 12 figures

This paper described a procedure for predicting the ice loads acting on a hull of an icebreaker that employs a six degrees-of-freedom (6-DOF) inertial measurement system method. Ice loads were calculated using the data measured in full-scale ice sea trials of the Korean ice breaking research vessel (IBRV) ARAON during her Arctic Ocean voyage in 2015. In the measured data, it was found that the sway, roll, and yaw motions were larger than other motions because the ship usually met with pack ice during her voyage. To calculate the maximum ice loads, the center of gravity (COG) approach and the point of impact (POI) approach were used. Ice loads ranged from 1.41 to 4.87 MN when estimated using the COG approach, and from 0.11 to 1.06 MN when estimated using the POI approach. The measured ice loads through the COG and POI approaches were compared with the resultant forces measured using strain gauges.

The cavitation inception speed (CIS) is very important capability for a navy vessel because the underwater radiated noise dramatically increases when cavitation occurs. Therefore, the CIS has been severely restricted and evaluated at sea trial test steps in the shipbuilding process. After a naval vessel is delivered to the navy, CIS can vary according to the propeller and sea state conditions. However, inspection of CIS cannot be performed frequently due to time and expense limitation. Therefore, real time monitoring of CIS is urgently required by navy personnel. In order to inspect CIS with real time monitoring technique, the measuring method detecting fluctuation pressure of the propeller in a ship at sailing state should be developed. In this research, CIS monitoring techniques using acceleration on the hull above the propeller that can measure the fluctuation pressure of the propeller indirectly are suggested and verified experimentally. In addition, the evaluation algorithm of CIS using the kurtosis of the Detection of Envelope Modulation on Noise (DEMON) spectrum is used to determine the CIS quantitatively.

Ship acceleration manoeuvre is important in terms of safety and engine performance. Head seaways are one of the most challenging conditions for the ship propulsion. A detailed simulation of the propulsion system's transient response during dynamic acceleration in harsh conditions can result in a thorough investigation of the engine performance, a better management of control system and the monitoring of engine limiters application in real conditions. For the overall propulsion system performance assessment during ship acceleration, a computational tool has been developed that consists of a number of sub-systems for the simulation of engine, turbocharger, propeller components and their interaction. The developed tool has been first validated against available shop and sea trials data and subsequently it has been tested for the simulation of propulsion system performance during acceleration in dynamic conditions. Based on the simulation results, a sensitivity analysis has been performed for the investigation of the governor control unit limiters that apply on the engine during acceleration. As a result, the effect of engine governor limiters on the overall engine and hydrodynamic performance of the ship during acceleration is quantified and discussed.

Both Backward Bent Duct Buoy (BBDB) and Japanese “Mighty Whale” are offshore floating Oscillating Water Column (OWC) type wave power devices. The investment of “Mighty Whale” is comparatively huge and its wave-to-wire efficiency is about 5.3%. Based on the reports of model experiments and over-3-year sea trials of “Mighty Whale”, recent progress of air turbines and the studies of BBDB and air turbine in Guangzhou Institute of Energy Conversion (GIEC), Chinese Academy of Sciences (CAS), the cost-performance ratio of wave power boat based on the BBDB principle is evaluated. According to the RMB purchasing power in 2014, if the incident wave power density is 16 kW/m, the boat lifespan is 15 years, and the air turbine efficiency is high enough to make the wave-to-wire conversion efficiency reach 30%, the cost of electricity generated by this boat can drop to below 1 CNY/kWh. If the incident wave density or the wave-to-wire efficiency is higher, this cost will decrease further. And, the mobility of the self-propelled wave power boat solves the underwater residue problem caused by the complex mooring of traditional wave energy converter; also, it helps the wave power boat in moving to a port to avoid typhoons and adjusting to the wave direction. Therefore, the BBDB wave power boat technology has broad prospects for developments.

This paper presents the experimental testing of an intermediate guidance level for Unmanned Surface Vehicles (USV). The work aims to deal with specific requirements when the execution of survey operations is performed. The necessities in terms of path coverage can be different throughout the mission and the possibility to take them into account in the mission plan, thereby obtaining an appropriate and feasible path plan, constitutes an enhancing capability. In order to tackle the mission requirements, four different turn types are defined. The computed path is constituted by a sequence of straight-lines and circular arcs, hence allowing the use of existing path following methods. An architecture consisting of a payload computer and the unmanned surface vehicle C-Worker 5 by ASV Global Ltd, connected through a Robot Operating System (ROS) network and a radio datalink, has been implemented to execute sea trials and experimentally validate the proposed guidance. Experimental results are presented and the cross track error measurements as well as the percentage of covered path are considered in the analysis.

Wave driven robots (WDRs) are a new type of autonomous ocean observation platform driven by wave energy. This paper is concerned with the multi-body yawing filter problem of the WDR. The adaptive multi-body yawing filter (AMF) of WDR was presented by considering the driven principle of the yawing motions of the submerged glider (glider) and the float body (float). The linearized yawing response models of the glider and the float were derived. The adaptive amending method of the dynamic response coefficients (DRCs) of the glider and the float were proposed. On this basis, the AMF of WDR was developed within the extended Kalman filter (EKF) framework. The AMF method utilized input and output (I/O) data to extract model information and is independent of the accurate mechanism model of the system. Numerical simulations of step steering and continuous steering under nominal model and the model with parameter perturbation were performed. The sea trial was conducted and the filtering results of the actual sensor data by AMF, EKF and tracking differentiator (TD) were presented. The proposed AMF method was found to be with good performance in suppressing noise and tracking speed.

Bycatch of protected species, particularly small cetaceans, in gillnets is a worldwide concern. One hypothesis for this is that echolocating cetaceans entangle because they do not perceive conventional gillnets as impenetrable barriers, owing to the gillnet’s faint echo. A gillnet modified for improved acoustical visibility was tested in a first pilot trial in a commercial gillnet fishery targeting turbot (Scophthalmus maeoticus) on the Turkish Black Sea coast. This study is the first demonstration of the viability of using a gillnet equipped with small acrylic glass spheres to reduce bycatch of harbor porpoises in a commercial fishery and provides the basis for full-scale sea trials of the gear in commercial fisheries through a power analysis. In these pilot experiments, the focus lied on the handling of the gear and identification of requirements for a full-scale trial, but results include promising bycatch data for an endangered echolocating marine mammal (Phocoena phocoena) and no reduction in catch efficiency of a bottom-dwelling, vulnerable species (Raja clavata).

This paper describes an open and extensive validation study carried out by the Specialist Committee on Ships in Operation at Sea (SOS) of the International Towing Tank Conference (ITTC) on the newly developed SHOPERA-NTUA-NTU-MARIC (SNNM) wave-added resistance prediction method. The SNNM method aims at a simple, fast and transparent determination of the added resistance in regular waves of arbitrary encounter directions, even when the hull geometry is not available. Prior to the validation study, a series of acceptance criteria for the new method were specified by the committee. Contributions of 1,477 added resistance experimental data samples from 8 institutions were collected, analyzed and cross-checked with satisfactory outcome, which finally led to the inclusion of the new method into the ITTC recommended sea trial procedure as an important progress. Some aspects of concerns are discussed in detail and further work in the future is recommended.

With the outstanding performance of unmanned surface vehicles (USVs) in maritime missions with scientific and commercial applications, increasing numbers of ships have begun to carry USVs to perform tasks. For the autonomous recovery of a USV along a preset trajectory to the docking station under various sea conditions, we propose a new navigation strategy with dual-attention-based optical terminal guidance. Monocular vision systems with creatively designed identification light sources are mounted on the docking station and USV, respectively. Thus, the azimuth angle, heading angle and relative distance between the docking station and the USV can be accurately measured. This method achieves centimeter-level homing accuracy and a 0.1-degree angle measurement error. A tracking control algorithm based on a line-of-sight method is suggested , and the control quantity of the USV is directly generated. Sea trials were conducted under various weather conditions to validate the proposed algorithm. This method provides reliable USV guidance to the docking station with a stern ramp from the maximum capture distance of approximately 100 meters. The proposed dual-attention method provides convenient implementation and transplantation to various unmanned platforms.

In this study, we investigated the hydrodynamic characteristics of marine aquaculture net cages used for farming silver salmon (Oncorhynchus kisutch). Two sets of experiments were conducted: model-scale testing, which was used to measure the drag force and deformation of a model net cage at different current velocities, and full-scale testing, which involved a sea trial at a silver salmon farm site. In the sea trial, an acoustic wave and current meter was deployed to record the current velocities around the net cage, and the cage deformation was estimated from the several vertical positions of net using 13 depth sensors. The precision of estimating the cage deformation using only the depth information was evaluated by comparing the estimated cage deformation with that determined from the images in model-scale testing. Comparing the model-scale and full-scale testing results showed that only the bottom netting was found to be deformed under lower water currents. The trends observed for the drag force, cage deformation, and cross-section area estimated from the depth data in full-scale testing were generally consistent with those converted from the model-scale testing using Tauti's similarity law. However, the drag force values of a full-scale net cage converted from the model-scale testing were higher than those estimated from the depth data in the full-scale testing. In contrast, the converted cross-sectional areas from model-scale testing were smaller than the estimated values in full-scale testing. In future, the cage deformation should be examined under higher current velocities, and the drag force should be measured in the full-scale testing to validate the results of the model-scale testing and the hydrodynamic model.

Underwater navigation is a challenging topic in the field of underwater exploration. Accurate and effective underwater navigation is necessary in applications such as 3D seafloor topography scanning, cable laying, deep-sea resource survey and wreck salvage. However, underwater navigation becomes difficult due to the variability and complexity of underwater environment. In the deep-sea environment, the ultra-short baseline positioning system (USBL) is very unstable, and the flying abnormal points and signal loss often occur. To solve these problems, this paper proposes a two-step filtering scheme combined with doppler velocity log (DVL). The first step is to construct a rough Monte Carlo particle filter (MPF) model for the autonomous underwater vehicle (AUV) position, and then select candidate particles with the strategy of minimizing the local backward dead reckoning (DR) errors. In the second step, the results of the first step are further smoothed and optimized using the weighted extended Kalman filter (WEKF). Finally, the robustness and practicability of the proposed method are verified by the multiple data obtained from several sea trials in the South-West Indian Ocean. The results also show that the integrated navigation framework is superior to single navigation method and other traditional filtering methods. The best balance between accuracy and computational cost is achieved.

This paper proposes a control architecture of autonomous underwater vehicle (AUV) for coverage mission in irregular region (CMIR) with an improved task planner. The CMIR control architecture is structured in four layers: perception layer, reactive layer, decision making layer and execution layer. To improve the task planner in decision making layer of control architecture, we adopted convex partitioning method and Success-History Based Adaptive Differential Evolution Algorithm (SHADE) including linear population size reduction (L-SHADE) as the computing engine, which make CMIR control architecture more suitable to coverage problems. Through statistical analysis, we obtained a set of optimized control parameters. Simulation experiments were carried out, three task planners were compared in terms of convergence speed, optimized path length and computing time consumption. The results show that the coverage efficiency of the task planner based on L-SHADE is higher than that of task planner based on particle swarm optimization (PSO) and differential evolution (DE). Sea trial was performed with Sailfish-AUV, which proved that the CMIR control architecture is feasible in actual marine environment.

Underwater glider is becoming an increasingly important tool for exploring the ocean. As the underwater tasks become more challenging, it puts forward higher requirements for the endurance of electric underwater gliders. This paper proposes an operation principle for the underwater glider jointly driven by the ocean thermal energy and the electrical energy, which has the advantages of both electric underwater glider and thermal underwater glider. Based on the proposed operation principle, a universal energy consumption model and sailing range equation suitable for the electric, thermal and hybrid propulsion underwater gliders are established. Taking the sailing range, sailing range difference and sailing range ratio as the evaluation indexes, the effects of configuration parameters and navigation parameters on the endurance of three underwater gliders are analyzed. The results show that the endurance and endurance advantage of hybrid propulsion underwater glider can be improved with greater volume change rate of phase change material (PCM), heavier energy carrier and smaller average power of the task sensor, and its high performance can also be maintained with a weight ratio of PCM close to the critical value. Meanwhile, it is beneficial to obtaining stronger endurance for the hybrid propulsion glider during its operation by setting larger diving depth as well as smaller gliding angle and volume change of oil within the design range. Finally, the hybrid propulsion prototype and Petrel-II electric underwater glider are deployed to carry out the comparative sea trial, which verifies the correctness of sailing range equation and the availability of prototype. The results show that the hybrid propulsion underwater glider has a better energy consumption economy than the electric underwater glider.

In light of the proposal of the International Civil Aviation Organization and International Maritime Organization joint working group on harmonization of aeronautical and maritime search and rescue (ICAO/IMO JWG-SAR) 27th meeting, which points out that the current International Aviation and Maritime Search and Rescue (IAMSAR) standard man overboard (MOB) maneuvers may not be suitable for very large carriers, the authors briefly summarize the research on the MOB recovery maneuvers in recent years and conduct an investigation on the serviceability of these maneuvers by a series of full-scale sea trials. The sea trial results indicate that the standardized recovery maneuvers are serviceable to the employed oil/chemical tanker. However, similar to the simulation results obtained in the previous studies, there is a deviation in the Scharnov turn.

Wave-induced vertical bending moment (VBM) and horizontal bending moment (HBM) on a large-scale segmented model with a box-type backbone beam in short-crested irregular seas are systematically analyzed using sea trial measurement data. New insights into the relationship between nonlinear VBM and HBM of the ship sailing in short-crested sea waves are explored and presented. The results indicate that the HBM significantly contributes to the total sectional loads when the ship is sailing in a seaway and the HBM has a strong correlation with VBM in both magnitude and tendency. Therefore, design loads of HBM and the corresponding lateral structural strength issues should also be concerned in addition to VBM at the ship design phase.

The form-changeable boats have received much attention due to its far-ranging applicability, strong combat capability and the low operating cost. This paper constructs a variable-structure boat whose mainhull is planing hull form and twin retractable deep-V side-hulls are placed on both sides of the mainhull, aims at assessing its seakeeping performance in the monomer-form state (MFS) and the trimaran-form state (TFS) by model tests, numerical simulation and sea trials. Regular head wave tests were conducted at volume Froude numbers (Fr∇) ranging from 0.44 to 2.67 for the MFS and TFS models. Verification and validation of the CFD method were performed, the influences of side-hull draft on the seakeeping of TFS model under different wave configurations were analysed. Sea trials of the full-scale vessel (USV) in irregular sea were also carried out at the design velocities. The results show that the TFS has different effects on motion responses and vertical accelerations of the model at different speeds and wavelengths, the applicable range of side-hulls with gain effect is in the diaplacement and semi-planing stage, and the maximum velocity is suggested not to exceed Fr∇ = 2.22. For the USV at Fr∇ = 1.33, the TFS mainly cut down its roll in irregular head sea, followed by following and beam sea; when the Fr∇ increases to 1.78, the roll gain declines, but the pitch gains more, the better side-hull draft ratios are 1.0 and 0.67, corresponding to the above two design speeds, respectively.

Most sea trials of large merchant ships are carried out with the filling ballast water in cargo, and the trial environment may involve mild waves as well. It causes the ship to undergo a coupling effect between external wave excitation and internal sloshing motion, and an understanding of such coupling is important to analyze the components of the total resistance measured in sea trials. In this study, a blunt modified Wigley equipped with two inner tanks is selected to observe its hydrodynamic responses under head waves, using both experimental measurement and numerical computations. Ship is considered to have a forward motion at the Froude number of 0.2, and three filling conditions varying from low filling to high filling have been arranged for two inner tanks. For validation, numerical computation is performed based on the three-dimensional Rankine panel method with the linearized boundary value problems. Both seakeeping and internal sloshing flow are analyzed using the linear potential theory. The validation presents a sufficient agreement between experimental measurement and numerical results with or without the sloshing effect, and both two methods have shown that the sloshing coupling effect is generally insignificant for present ship model. However, when the wave encounter frequency becomes very close to the tank natural frequency, the medium filling tanks generate a strong coupling effect which can restrain ship motion responses as well as added resistance.

This study proposes a path planning method based on behavioral decision-making (PPM-BBD). An optimized path is planned for autonomous underwater vehicle (AUV) to save energy during the diving process. The key idea is to apply success-history based adaptive differential evolution algorithm including linear population size reduction (L-SHADE) to the optimization of energy. In addition, motion constraints are considered during the diving process to ensure that the path points are reachable. We take the sequence of motion angles as the population, and propose an angle modification strategy to apply to the population evolution process, so that the angle sequence remains in the space of feasible solutions. The modification strategy lays a theoretical foundation for the application of L-SHADE in this path planning problem. The performance of PPM-BBD is evaluated on data from simulation test. The most suitable control parameters are determined through simulation experiments. The effects of PPM-BBD with L-SHADE and five types of DE are compared. The experimental evaluation was performed through sea trials in Tuandao Bay, Qingdao, China. Results show that PPM-BBD saves at least 9% energy compared to the other algorithms. It is concluded that it is workable to obtain a reachable path with optimized energy consumption during diving process.

The oscillating buoy wave energy converter (OBWEC) is a popular and widely used wave energy converter (WEC) due to the simplicity of its structure and its strong adaptability. In this paper, the “Haiyuan No. 1″ OBWEC is taken as the research object, in which the buoys adopt heave mode of motion. In order to further enhance the hydrodynamic performance of the buoys, an improved scheme with longitudinal swing motion is proposed through theoretical analysis for the buoy. A 2D numerical wave tank (NWT) model based on the RANS equation is established by using CFD software. The numerical model is applied to compare and analyze the hydrodynamic performance differences of the buoy under two different motion forms: heaving and longitudinal swing, and the consistency of the numerical results is validated by the experimental data under regular waves. Finally, the irregular wave data obtained during the sea trial of the “Haiyuan No. 1″ OBWEC is used to numerically simulate the two buoys. The results show that the buoy with longitudinal swing motion is more effective in improving the hydrodynamic performance compared to the buoy with heave motion, in both regular and irregular waves. The conclusions of this paper can serve as a guide to improve the design of the hydrodynamic performance of the buoy.

Deep-water or open sea area developments bring technology challenges to offshore pipeline installation safeties. With low oil price, offshore contractors endure considerable pressure and struggle to provide cost-effective services. To achieve safe operations with higher efficiencies, it is essential to acquire better understanding of pipeline conditions in-process, which benefits operation planning and decision making. Offshore operational window and pipeline fatigue damage significantly depends on vessel motions. Current engineering practices generally predict motions through metocean and hydrodynamics based numerical simulations. This approach is useful but naturally leads itself to prediction uncertainties, which are most likely conservatism. With deep-water and open sea application, the uncertainties may become underestimations of key parameters due to possibly insufficient metocean data and inapplicable hydrodynamic methods. Subsequently, a real-time offshore pipeline installation monitoring system has been developed to predict realistic pipeline behavior by adoption of real-time operation parameters including vessel motions. A sea-trial for the system has been conducted on a pipelay project in 2016. As an alternative treatment to pipeline installation planning and decision making, the system has been proven capable of accurate simulations and additional functions such as touch point monitoring and fatigue tracking.

Operating in the depth-varying oceanic environment, the buoyancy of deep-sea underwater gliders (UGs) will change with depth due to pressure hull deformation and seawater density variation. As the buoyancy variation caused by these two factors is of the same order of magnitude as the nominal net buoyancy, hull deformation and seawater density variation will accordingly affect the dynamic behaviors of deep-sea UGs. In this paper, a full dynamic model was established using Newton-Euler method for a deep-sea UG, PETREL-II. The hull deformation and seawater density variation, fitted as the functions of depth, are considered in the model. Comparisons of results obtained by sea trials, the full dynamic model and the simpler dynamic model without considering hull deformation and seawater density variation showed that the proposed full dynamic model can more truly reflect dynamic behaviors of the glider. Comparisons of simulation results for the full and simpler dynamic models showed hull deformation and seawater density variation have great effect on pitch angle and velocity of the gliders. Through analysis of motion control strategy, a buoyancy compensation scheme was proposed to reduce the negative effect of hull deformation and seawater density variation, and was validated to be effective by sea trials.

To reduce deployment and maintenance costs, a novel wave energy converter (WEC) is proposed for mooring-less sensor buoys. The design concept is based on a small size WEC capable of harvesting wave energy without mooring, which can reduce the installation cost. The proposed wave energy converter consists of a submerged and a floating body, and the submerged body is a self-rectifying wave-induced turbine that uses the rise and fall of waves to turn a rotor. The rotor of the turbine has flap-type blades, which allows a self-rectifying rotation with rising and falling of waves. In this paper, the dynamics of the system is modeled by hydrodynamic equations, and simulations are carried out based on the dynamic model to determine the optimal design parameters of the system. In addition, the power generation in regular and irregular wave conditions and efficiency in irregular waves of the system are estimated. To verify the results of the simulation, a prototype of the system is implemented and tested in a sea trial. The results demonstrate the feasibility of the proposed wave energy converter.

This paper describes a new maximum power point tracking (MPPT) algorithm developed to control a wave energy converter (WEC) in random seas. This algorithm, named the cycling MPPT algorithm, is compared to a perturb and observe algorithm described in numerous literature. Both algorithms were initially tested during 2012 ocean tests of the half-scale prototype Wave Energy Technology – New Zealand (WET-NZ) WEC off the Oregon coast. During these sea trials the perturb and observe algorithm failed to provide effective control of the WET-NZ, while the cycling algorithm was observed to give effective control. More complete investigations were later carried out using MATLAB-Simulink simulations of an autonomous WEC (AWEC) being developed at Oregon State University. The results of the AWEC simulations also showed the cycling algorithm provided better control than the perturb and observe algorithm. The operation of the cycling algorithm was fully characterized during the AWEC simulations and these results are presented.

In order to optimize the utilization of the kinetic energy derived from the hydrostatic energy to collect more sediment core, the paper focus on the analysis and the modeling of the percussion coring of a hydrostatic seafloor sediment corer, including the modeling of the stress wave traveling along the tube and the construction of the dynamic model of the tube-sediment system. The hydrostatic corer is feature by using both the hydrostatic energy of the seawater and gravity potential energy to collect the sediment in a percussive way. The analysis results reveal the under-sampling phenomenon of the corer which was observed and confirmed by the sea trial. To weaken the under-sampling and improve the utilization of the hydrostatic energy, several effective factors have been studied through the dynamic model and the results shows that the large inner diameter of the tube and the high mechanical impedance of the cushion and the increase of the single percussion energy and the adequate area ratio of the tube can considerably weaken the under-sampling and improve the recovery ratio. The modeling method and analysis results can provide some instructive information for the design and improvement of the percussive seafloor sediment corer.

This paper compares the skill of two algorithms that enable real-time estimation of the directional wave spectra exciting a ship from its measured motions. One algorithm consists of a nonlinear optimization of a parametric or non-parametric spectral model and the other is a Kalman filter based observer. Sea trials have been conducted on an oceanographic vessel that was instrumented with a six degree of freedom fiber optic gyro, complemented with a rate gyro, several accelerometers, a dedicated GPS receiver and a bow mounted down-looking wave radar with motion compensation. The two algorithms are applied to the measured data and a discussion is provided on their skill to recover the properties of existing sea states.

Shanghai University has developed an unmanned survey vehicle (USV) named JingHai-I. The mission of JingHai-I is to work as a test bed USV for the development and validation of various algorithms. One main innovation of the USV is the capability to achieve hydrographic surveying and charting in nearshore shallow waters. The highly resistant overturning ability and low draft (0.43 m) enables the USV to move safely in shallow waters. Moreover, the USV can sail on a setting track and automatically avoid obstacles. This paper presents a review of our research work on the development of the USV, with a performance evaluation by a series of tests. In addition, the system design and implementation of the USV is detailed in the introduction. In order to get better control effects, a numerical model for the USV was built and a GPC-PID cascade controller was proposed, which combines generalized predictive control and PID control. A series of test results and discussions of the results are presented. Compared with the actual sea trial test data, the results show that the USV offers good maneuverability.

Cavitating ship propellers are known to be the dominant noise source contributing significantly to the underwater radiated noise (URN) level. Innovative measurement methods using on-board devices need to be further investigated as they offer a serious alternative to traditional methods in terms of cost-efficiency and practicality. This exploratory study combined simultaneous on- and off-board noise and vibration measurements with cavitation views captured by digital photography and high speed cameras.Comprehensive full-scale trials were conducted on Newcastle University’s research vessel, The Princess Royal, in the framework of the FP7-EU project SONIC. On-board data were captured from multiple measurement systems (including. hull pressure sensors, accelerometers, optical devices, shaft strain gauges) provided by SONIC project partners CETENA, Wärtsilä , University of Southampton and Newcastle University. A new semi-empirical correlation method based on cavitating propeller pressure fluctuation and the URN level was established. Results offer clear evidence of successfully estimating URN with on-board measurements up to the middle frequency region where the blade passing fundamental and low harmonic frequencies occur. These illuminating insights reported in this paper provide valuable benchmark sea trial data in full scale.