Sea Trials Research Articles

Source-Based Disjoint Multipath Routing Protocol for Underwater Acoustic Networks: Protocol Design and Sea Trials

Source-Based Disjoint Multipath Routing Protocol for Underwater Acoustic Networks: Protocol Design and Sea Trials

The role of structural and insulating material in the structure-borne noise propagation of superyachts

The insulation and noise and vibration damping characteristics of complex systems used by humans, such as automobiles, airplanes and ships are becoming increasingly important from the early design stages to ensure an adequate level of comfort. Especially in the naval fields, the design of insulation plans is crucial to prevent the propagation of noise and vibrations on board of megayachts. Since it is quite complex to identify and correctly model the sources due to their deterministic and random nature, during the early design stage, the focus is on insulation rather than reducing the acoustic levels of the sources themselves. In this article, a method for analyzing sea trials on a superyacht will be proposed with the aim of analyzing how much the insulation materials can limit the levels of vibrational energy on board during the path between sources and receivers. A new a descriptor based on harmonic transmission energy through the structure is proposed for path insertion loss experimental identification. In particular, by using spectral analyses and synchronous averaging of sound levels in various areas of the superyacht, it will be possible to study the vibroacoustic insulation of structural materials and their damping coefficient.

A D* orthogonal matching pursuit algorithm for time-varying channel estimation.

Orthogonal matching pursuit (OMP) combined with the A* search algorithm (A*OMP) exhibits robust reconstruction capabilities for synthesizing sparse data and signals, achieving relatively low reconstruction errors and a higher exact recovery ability than conventional OMP. However, A*OMP is only suitable for static channel estimation and cannot be applied to dynamic scenarios. This is because the channel delays for several consecutive orthogonal frequency-division multiplexing blocks per frame are similar and the path gains exhibit temporal correlation. This paper introduces a dynamic OMP approach (D*OMP) that employs a heuristic function of A*OMP and a unique reverse process, enabling sparse solutions to be identified in unknown and changing environments. The proposed method is highly practical for joint channel estimation across multiple blocks. Simulation and sea trial results indicate that D*OMP not only possesses superior channel recovery accuracy, but also has a more efficient channel reconstruction process, outperforming both A*OMP and conventional OMP.

A baseline decomposition ultra-short baseline localization algorithm for arbitrary array structures.

With the rapid development of the marine economy, hydroacoustic positioning technology plays an increasingly important role in marine engineering. The ultra-short baseline (USBL) hydroacoustic positioning system has the advantages of small size, simple operation, and flexible use, and has been widely used. Aiming at the existing USBL acoustic positioning algorithm with low positioning accuracy and complex calculation, a baseline decomposition localization algorithm with arbitrary array structure is proposed. The algorithm is based on the theory of coordinate system transformation, establishes positioning observation equations for each baseline in the base array, and adopts the least squares method to obtain positioning results by selecting different combinations of baselines. The systematic errors of different positioning models themselves are simulated, and then the effects of the three parameter errors, namely, time delay, element coordinates, and sound speed, on the positioning results are analyzed, respectively. Finally, the simulation results and sea trial data show that, compared with the existing algorithms, this algorithm not only simplifies the complicated computation process, but also improves the positioning accuracy and robustness, and has a better application effect.

Velocity Estimation of Passive Target Based on Sparse Bayesian Learning Cross-Spectrum.

To solve the poor performance or even failure of the cross-spectrum (CS) method in hydroacoustic weak-target passive velocimetry, a sparse Bayesian learning cross-spectrum method (SBL-CS), combining phase compensation with sparse Bayesian learning (SBL) is proposed in this paper. Firstly, the cross-correlation sound intensity is taken as the observation quantity and compensates for each frequency point of the cross-spectrum, which enables the alignment of cross-spectrum results at different frequencies. Then, the inter-correlation sound intensity of all frequencies is fused in the iterative estimation of the target velocity, verifying the proposed method's ability to suppress the background noise when performing multi-frequency processing. The simulation results show that the proposed method is still effective in estimating the target velocity when the CS method fails and that the performance of the proposed method is better than the CS method with a decrease in SNR. As verified using the SWellEx-96 sea trial dataset, the RMSE of the proposed method for surface vessel speed measurement is 0.3545 m/s, which is 46.1% less than the traditional CS method, proving the feasibility and effectiveness of the proposed SBL-CS method for the estimation of the radial speed of a passive target.

Expanding seawater carbon dioxide and methane measuring capabilities with a Seaglider

Abstract. Warming, ocean acidification, and deoxygenation are increasingly putting pressure on marine ecosystems. At the same time, thawing permafrost and decomposing hydrates in Arctic shelf seas may release large amounts of methane (CH4) into the water column, which could accelerate local ocean acidification and contribute to climate change. The key parameters to observing and understanding these complex processes and feedback mechanisms are vastly undersampled throughout the oceans. We developed carbon dioxide (CO2) and CH4 gliders, including standard operational procedures, with the goal that CO2 and CH4 measurements will become more common for glider operations. The Seagliders with integrated Contros HydroC CO2 or CH4 sensors also include conductivity, temperature, depth, oxygen, chlorophyll a, backscatter, and fluorescent dissolved organic matter sensors. Communication via satellite allows for near-real-time data transmission, sensor adjustments, and adaptive sampling. Several sea trials with the CO2 Seaglider in the Gulf of Alaska and data evaluation with discrete water and underway samples suggest nearly “weather-quality” CO2 data as defined by the Global Ocean Acidification Network. A winter mission in Resurrection Bay, Alaska, provided the first insights into the water column inorganic carbon dynamics during this otherwise undersampled season. The CH4 Seaglider passed its flight trials in Resurrection Bay but needs to be tested during a field mission in an area with CH4 concentrations beyond background noise. Both sensing systems are available to the science community through the industry partners (Advanced Offshore Operations and -4H-JENA engineering GmbH) of this project.

A fast temporal multiple sparse Bayesian learning-based channel estimation method for time-varying underwater acoustic OFDM systems

In this paper, a fast temporal multiple sparse Bayesian learning (FTMSBL)-based channel estimation method for underwater acoustic (UWA) orthogonal frequency division multiplexing (OFDM) systems is proposed, which is optimized using the fast marginalized likelihood maximization method. The algorithm fully uses the consistent sparse structure and time-domain correlation properties of channels to improve the reconstruction performance and computational efficiency, offering better performance and higher computational efficiency than the traditional Bayesian learning algorithms. At the same time, the FTMSBL algorithm does not require computing the inverse of large matrices and consumes very little storage resources in the operation, making it suitable for hardware implementation. Simulation and sea trial results show that the FTMSBL-based underwater channel estimation algorithm achieves higher channel estimation accuracy than the orthogonal matching tracking algorithm, and the system bit error rate (BER) is significantly reduced; specifically, the FTMSBL algorithm can achieve optimal performance in strong time-dependent channels.

Evaluation of the powering extrapolation of a ship with a gate rudder system, including ageing and fouling effects

This paper is based on the evaluation results of the calm water powering extrapolation of a 90-m general cargo vessel, originally built with a conventional rudder system (CRS) and later retrofitted with an innovative energy-saving device (ESD) known as the Gate Rudder System® (GRS), as part of the EU H2020 Project GATERS. The power estimation of the vessel was conducted using an adapted extrapolation procedure based on the scaled model tests of the vessel in a towing tank, validated by the three sets of sea trials. The first sea trial was performed when the ship was new, while the latter two were conducted during the project timeline, before and after the GRS retrofit. This paper aims to adapt the ITTC-78 power extrapolation method to predict the power performance of a ship retrofitted with the GRS for the first time in the maritime industry. Within this framework, the specific objectives of the paper are to describe and validate the proposed method using relevant power-speed data of the GATERS project target vessel (M/V ERGE) initially equipped with the CRS and later replaced by the retrofit GRS to achieve the project objective. Due to the real-world circumstances of retrofitting a 13-year-old ship with a novel energy-saving device, investigating the effects of ageing, hull roughness, and fouling has also become one of the key objectives of the paper. The findings demonstrate the ageing effect on the target ship's powering performance after retrofitting with GRS, highlighting the need for special consideration of power extrapolation alongside the hull fouling effects. The paper also demonstrates that the GRS is an emerging ESD, as a retrofit beside newly built ships with GRS, which improved the powering performance of the project target vessel, achieving a remarkable 25% power saving based on the comparative full-scale sea trials.

Performance Evaluation of Hybrid Propulsion System on Fast Patrol Boat

This paper presents a performance evaluation of a hybrid propulsion system applied to a fast patrol boat. The study aims to analyze the efficiency, fuel consumption, and overall operational effectiveness of the hybrid system compared to conventional propulsion methods. A combination of electric motors and diesel engines is utilized in the hybrid setup, allowing for optimized energy use in varying operational conditions. The performance of the system was evaluated through simulation and sea trials, focusing on key metrics such as speed, endurance, maneuverability, and emission reduction. Results indicate that the hybrid system offers significant advantages in terms of fuel savings and reduced environmental impact, particularly during low-speed or patrol operations. This research provides valuable insights into the practical benefits and challenges of implementing hybrid propulsion systems in maritime security operations.

Development of a full ocean depth hydraulic manipulator with heavy-duty capacity

The underwater manipulator is a versatile tool commonly used for various underwater operations. In this study, we developed a heavy-duty hydraulic manipulator capable of operating at full ocean depth. The overall system design integrates both the mechanical structure and the electric control system. The master arm controls the slave arm by transmitting control signals to the controller and valve box. The structural design of the elbow and wrist joints has been optimized to enhance the manipulator's underwater performance and operational range. Laboratory tests demonstrated the manipulator’s excellent response consistency and tracking capability across a wide range of motion. During sea trials in the Mariana Trench, the manned submersible Fendouzhe successfully deployed the manipulator, showcasing its exceptional ability to complete complex tasks.

A 500 kW hydrogen fuel cell-powered vessel: From concept to sailing

This paper presents the “Three Gorges Hydrogen Boat No. 1”, a novel green hydrogen-powered vessel that has been successfully delivered and is currently sailing. This vessel, integrated with a hydrogen production and bunkering station at its dedicated dock, achieves zero-carbon emissions. It stores 240 kg of 35 MPa gaseous hydrogen and has a fuel cell system rated at 500 kW. We analysed the engineering details of the marine hydrogen system, including hydrogen bunkering, storage, supply, fuel cell, and the hybrid power system with lithium-ion batteries. In the first bunkering trial, the vessel was safely refuelled with 200 kg of gaseous hydrogen in 156 min via a bunkering station 13 m above the water surface. The maximum hydrogen pressure and temperature recorded during bunkering were 35.05 MPa and 39.04 °C, respectively, demonstrating safe and reliable shore-to-ship bunkering. For the sea trial, the marine hydrogen system operated successfully during a 3-h voyage, achieving a maximum speed of 28.15 km/h (15.2 knots) at rated propulsion power. The vessel exhibited minimal noise and vibration, and its dynamic response met load change requirements. To prevent rapid load changes to the fuel cells, 68 s were used to reach 483 kW from startup, and 62 s from 480 kW to zero. The successful bunkering and operation of this hydrogen-powered vessel demonstrates the feasibility of zero-carbon emission maritime transport. However, four lessons were identified concerning bunkering speed, hydrogen cylinder leakage, hydrogen pressure regulator malfunctions, and fuel cell room space. The novelty of this work lies in the practical demonstration of a fully operational, hydrogen-powered maritime vessel achieving zero emissions, encompassing its design, building, operation, and lessons learned. These parameters and findings can be used as a baseline for further engineering research.

Wideband beam domain sparse Bayesian learning passive focusing localisation algorithm

AbstractTo address the challenges of large‐aperture sonar systems passive localisation, this paper proposes the application of sparse Bayesian learning (SBL) for passive target localisation in the wideband beam domain. The proposed algorithm aims to overcome the issues of massive computational requirements for two‐dimensional SBL scanning and increased localisation errors due to interference energy leakage. The wideband beam domain SBL focusing localisation algorithm is developed by constructing an azimuth‐range two‐dimensional transformation matrix to preprocess array data, which effectively reduces the computational load of SBL processing while suppressing strong interference energy leakage in passive sonar operating environments, thus improving the range resolution and parameter estimation accuracy of focusing localisation. Simulation and sea trial data analyses demonstrate the feasibility of the proposed algorithm, with results indicating its superior performance compared to existing algorithms.

A robust iterative algorithm for SINS/USBL integrated navigation based on dual hydrophone differential model

Aiming at the complex underwater environment which leads to large measurement errors and outliers in ultrashort baseline, a robust iterative Kalman filtering algorithm based on the differential model of dual hydrophones is proposed in this paper. Firstly, to achieve accurate navigation under large initial misalignment angles, the algorithm builds an inertial navigation error equation based on the right invariant error definition of Lie groups. Then a dual hydrophone differential model is proposed based on SINS/USBL tightly coupled. It successfully improves the accuracy of integrated navigation and significantly mitigating the issue of SINS/USBL positioning accuracy degradation caused by USBL slant distance noise that grows with distance. Finally, a robust iterative Kalman filter based on the dual hydrophone differential model is proposed to counter the threat to the vehicle’s safe operation and the accuracy loss caused by outliers. The algorithm’s superiority and effectiveness are verified through simulation and sea trial.

Assessment of the gate rudder system on the cavitation and underwater radiated noise characteristics of a containership

Predictions of model tests and numerical studies (Sasaki et al., 2016), both at model- and full-scale, as well as results of the recent sea trials, have demonstrated that the Gate Rudder System (GRS), a novel energy-saving device, increases propulsive efficiency and reduces fuel consumption of a ship. Despite detailed investigations into the impact of the GRS on powering performance and manoeuvring, studies on its effect on cavitation phenomena and underwater radiated noise (URN) are limited. In this study, the effects of the GRS on cavitation and URN were investigated experimentally and compared to a conventional rudder system (CRS). Cavitation observations and URN measurements were conducted on sister ships -one with the CRS, SAKURA, and the other with the GRS, SHIGENOBU- at Istanbul Technical University Cavitation Tunnel (ITUKAT). A wooden ship model was built to be used in resistance and propulsion tests and then truncated due to the cavitation tunnel's test section length limitation of 5.5 m. Numerical studies were performed for both the original and truncated models at model- and full-scale to assess their wake characteristics. The nominal wake distributions along the CRS and GRS propeller planes were measured using a Laser Doppler Velocimetry (LDV) system. The test results supported the findings of the sea trials, showing that the GRS significantly reduces URN levels by up to 10 dB at high-frequencies, compared to the CRS, due to its effect on propeller loading and cavitation phenomenon.

Lidar-Based Obstacle Detection and Path Prediction for Unmanned Surface Vehicles

Abstract Unmanned Surface Vehicles (USVs) represent an advanced technology with a wide range of applications in maritime contexts, and they offer a promising alternative to manned systems, particularly for the provision of services such as riverbed mapping. Furthermore, the use of USVs in combination with other robotic systems, such as flying drones, remotely operated underwater vehicles (ROVs) and autonomous underwater vehicles (AUVs), opens up innovative ways to inspect and monitor maritime infrastructure. However, the use of these systems in dynamic environments, such as ports or shipping lanes, requires a high degree of adaptability and precision in navigation to manoeuvre safely between other traffic participants and obstacles to prevent collisions. To address this problem, USVs require sophisticated perception systems for the precise detection and classification of nearby objects. Leveraging Light Detection and Ranging (LiDAR) technology, which is renowned for its efficacy in obstacle avoidance in robotics, this paper outlines the adaptation of a LiDAR sensor for USVs. The proposed pipeline enables the detection of other moving vessels and the accurate determination of their positions and trajectories up to 150 m from the USV. This paper introduces an obstacle detection system and validates it within a port setting. A methodical approach to LiDAR data preprocessing, clustering, and point cloud extraction will be outlined. Furthermore, it explores the application of an Unscented Kalman Filter (UKF) for the projection of motion paths of identified entities. This advanced form of data analysis provides the ability to predict the future position and path of potential obstacles, optimize decision-making for autonomous navigation algorithms and significantly improve the safety of USV operations. The pipeline is tested experimentally in sea trials by enacting five different scenarios that USV may encounter in a port setting. The results of the pipeline’s tracking capabilities are compared to the ground truth data collected by the tracked vessel and plotted to visualize the error.

The challenge of harvesting common sole (Solea solea) in highly selective trawl fisheries

Common sole (Solea solea) is an economically important species in several European trawl fisheries, yet little is known about the size selective properties of codends used in bottom trawl fisheries targeting sole. This study presents results from a sea trial conducted in the inner Danish waters where common sole is fished in a seasonal trawl fishery using a 90 mm diamond mesh codend with a mandatory large mesh escape panel. To improve understanding of the selectivity in this gear, we in addition tested a plain 90 mm diamond mesh codend without an escape panel. This combination of codend mesh size and large mesh escape panel is part of an ambitious management plan aimed at eliminating bycatch of cod (Gadus morhua) in trawl fisheries in the inner Danish waters. In the fishery for common sole, we found a severe mismatch between gear regulations and minimum conservation reference size of the target species. The outcome is a highly inefficient fishery in which only 22 % (CI: 18–27 %) by weight of the marketable sole is retained in the 90 mm diamond mesh codend. Further, we estimated that 25 % (CI: 16–35 %) of the sole entering the codend would contact the mandatory escape panel and escape, resulting in a total loss of 83 % (CI: 79–87 %) of marketable sole through the mandatory gear. The inefficiency in this fishery demonstrates the need for other means than gear specifications to regulate this type of fishery.

Application of Self-Polishing Copolymer and Tin-Free Nanotechnology Paint for Ships

During a ship’s voyage, it is difficult to maintain its hull, and prolonged exposure to seawater can lead to the attachment of marine organisms, which can negatively impact the ship’s speed. The original self-polishing copolymer was a tributyltin-containing paint used for applying two layers of protective coating onto a ship’s bottom plate. According to International Maritime Organization (abbreviated as IMO) regulations, users are no longer allowed to use paints containing tributyltin. Therefore, manufacturers have developed a tributyltin-free paint, known as tin-free nanotechnology paint, which can be used as a replacement for the base coat on ship bottom plates. This study involves the use of a self-polishing copolymer spray and tin-free nanotechnology paint. A model coated with these two types of paint will be observed underwater to study the growth of marine organisms. Additionally, fuel consumption will be analyzed through underwater inspections and sea trials. Based on the experimental data, it is known that tin-free nanotechnology paint can significantly reduce the need for repairs in factories and greatly decrease maintenance costs when compared to self-polishing copolymers.

Numerical Simulation and On-Site Measurement of Dynamic Response of Flexible Marine Aquaculture Cages

Flexible cages are widely used in marine aquaculture, yet their mechanical features in extreme seas are still unclear. This study proposes a numerical algorithm to solve the coupled response of the multiple cage systems. The net and mooring lines are modeled using the lumped-mass model, while the flexible floating collar system is assessed with the large-deformation FEM model, and the two models are coupled through an iterative scheme. Sea trials are conducted, and the motion of the cage is obtained using an image processing technique, which validates the numerical algorithm. Using the proposed numerical algorithm, a series of simulations are performed to investigate the response of flexible cages in extreme seas. Motions, line tensions, and structural sectional forces are studied, and the effects of factors such as the wavelength of incident waves and the diameter of collar pipes are investigated.

Off-Grid Underwater Acoustic Source Direction-of-Arrival Estimation Method Based on Iterative Empirical Mode Decomposition Interval Threshold.

To solve the problem that the hydrophone arrays are disturbed by ocean noise when collecting signals in shallow seas, resulting in reduced accuracy and resolution of target orientation estimation, a direction-of-arrival (DOA) estimation algorithm based on iterative EMD interval thresholding (EMD-IIT) and off-grid sparse Bayesian learning is proposed. Firstly, the noisy signal acquired by the hydrophone array is denoised by the EMD-IIT algorithm. Secondly, the singular value decomposition is performed on the denoised signal, and then an off-grid sparse reconstruction model is established. Finally, the maximum a posteriori probability of the target signal is obtained by the Bayesian learning algorithm, and the DOA estimate of the target is derived to achieve the orientation estimation of the target. Simulation analysis and sea trial data results show that the algorithm achieves a resolution probability of 100% at an azimuthal separation of 8° between adjacent signal sources. At a low signal-to-noise ratio of -9 dB, the resolution probability reaches 100%. Compared with the conventional MUSIC-like and OGSBI-SVD algorithms, this algorithm can effectively eliminate noise interference and provides better performance in terms of localization accuracy, algorithm runtime, and algorithm robustness.

Experimental assessment of hull, propeller, and the gate rudder system interaction in calm water and oblique waves

This study focuses on the experimental assessment of the EU H2020 Innovation Action project GATERS' target ship, a 7241 DWT multi-purpose dry cargo ship (M/V ERGE), scaled to 1/27.1, in calm water and oblique wave (at a yaw angle of the ship model) conditions. M/V ERGE was initially built with a Conventional Rudder System (CRS) in 2010 but was later retrofitted with a newly introduced energy-saving device, the Gate Rudder System (GRS), in 2023 as part of the GATERS project. In this project, the interaction of the GRS with the hull and propeller was investigated using model tests of the vessel in the Kelvin Hydrodynamics Laboratory's (KHL) towing tank at the University of Strathclyde (UoS) and compared to the CRS. The main objectives of these tests were threefold. While they aimed to make experimental contributions toward the establishment of the best procedure for estimating the powering prediction of a ship with the GRS, they also aimed to investigate the hull, propeller and rudder interaction for the CRS and GRS configurations. In addition, a set of comparative pilot tests were conducted in waves to explore the effect of the oblique waves on the vessel's performance with the CRS and GRS. The resistance and self-propulsion tests were performed for both the CRS and GRS configurations, and performance predictions based on the model tests were compared with sea trials. Furthermore, tests at a yaw angle of the ship model were conducted to evaluate the effect of waves on the vessel's performance with the CRS and GRS, simulating the in-service conditions of commercial ships. These tests were conducted in regular waves with the hull at a yaw angle to simulate oblique wave conditions, with a wave height of 1.25 m in full scale (corresponding to moderate breeze, Beaufort 4) for a range of wavelengths. Numerical analyses were performed to obtain the full-scale propeller open water characteristics. The paper demonstrates the superior interaction of the GRS with the hull and propeller in both conditions compared to the CRS configuration, even improving its contribution to the vessel's performance in oblique waves.