Sea Trials Research Articles

Measurement of distance and speed between transmitter and receiver using the propagation time of underwater acoustic communication signals with orthogonal signal division multiplexing

This paper proposes a procedure for measuring transmitter–receiver (Tx–Rx) distance using acoustic communication signals to realize communication and positioning underwater with the same signal and device. Specifically, we focus on an underwater acoustic communication using orthogonal signal division multiplexing, where a pilot signal and messages are placed in the time–frequency domain. In this paper, we show that measurements of both Tx–Rx distance and speed are available by utilizing the pilot signal. We conducted a sea trial and evaluated the performance of the proposed method. During the experiment, the Tx–Rx distance was 50–550 m. The obtained results suggest that the proposed method can measure the Tx–Rx distance and speed in a specific environment. The mean absolute error and the standard deviation error of ranging are 4.0 and 2.7 m, respectively, while those of measurement speed are 0.13 and 0.22 m s−1, respectively.

A differential-based method for correcting ultra-short baseline positioning results

The primary factors influencing the positional accuracy of an ultra-short baseline (USBL) system are errors in sound speed, delay, installation deviation, and the bending of sound rays. Premised on the USBL positioning model, an error contribution model including ranging error, delay error, sound speed error and array element installation deviation was constructed. In parallel, an indirect difference correction method with additional coefficients was proposed based on the geometric correlation of the error function model. Specifically, a reference beacon was deployed on the seabed, and differential correction was achieved by directly computing target coordinates, integrating them with the positional data from the reference beacon. The proposed method demonstrated efficacy in mitigating errors associated with gradual variations or pronounced geometric correlations, including discrepancies in sound speed, bending of sound rays, and deviations in the installation of array elements. The correction method was applied to the USBL positioning, and the simulation results show that the proposed method notably enhanced both accuracy and consistency in positioning, particularly in shallow water environments characterised by significant sound speed errors. The sea trial data from the R/V Dayang Yihao in the Western Pacific demonstrate that the proposed method can effectively mitigate the errors induced by sound ray bending in deep-sea environments. The mean absolute error (MAE) and standard deviation (STD) were reduced by 51.3% and 55.3%, respectively, compared with the results of the USBL direct solution.

Research Status of Deep-Sea Polymetallic Nodule Collection Technology

The bottom of the ocean is rich in mineral resources, and deep-sea mining has been a research hotspot in recent years. As a key part of deep-sea mining operation, polymetallic nodule collection technology has been researched in many countries around the world. The distribution of deep-sea polymetallic nodule mining areas and the characteristics of nodules are summarized, which provides a reference for the study of collection technology and the optimization of pick-up device structure. In order to further establish a deep-sea mining collection technology system, the current development status of polymetallic nodule mechanical, mechanical–hydraulic composite and hydraulic collection technologies are summarized, and the analysis shows that hydraulic collection technology has a more promising commercialization prospect. For the hydraulic collection technology, the research progress of suck-up-based collection technology, Coandă-effect-based collection technology, double-row hydraulic collection sluicing technology and other collection technologies are summarized from three aspects: collecting principle, device structure parameter optimization, and sea trial situation, and the key technical problems of hydraulic ore collection are put forward. Through the comparative analysis of the pick-up efficiency, energy consumption, environmental disturbance and other performances of different devices, it is found that the Coandă-effect-based hydraulic collection technology has better comprehensive performance. A structural design evaluation indicator for the collection head of hydraulic collection technology is proposed, and the prospect of further research on hydraulic collection technology is put forward.

Sparus Docking Station: A current aware docking station system for a non‐holonomic AUV

AbstractThis paper presents the design and development of a funnel‐shaped Sparus Docking Station intended for the non‐holonomic torpedo‐shaped Sparus II Autonomous Underwater Vehicle. The Sparus Docking Station is equipped with sensors and batteries, allowing for a stand‐alone long‐term deployment of the vehicle. An inverted Ultra Short Base‐Line system is used to locate the Docking Station as well as to provide long‐term drift‐less vehicle navigation. The Sparus Docking Station is able to observe the ocean currents using a Doppler Velocity Log, being motorized to allow its self‐alignment with the current. Moreover, a docking algorithm accounting for the current is used to guide the robot during the docking maneuver. The paper reports consecutive successful experimental results of the docking maneuver in sea trials in two different countries.

Spreading a demersal trawl without otter boards: A proof of concept using flexible foils

This manuscript documents an engineering proof of concept. We demonstrate that a deep-water demersal trawl targeting northern shrimp (Pandalus borealis) can be spread without otter boards using nothing more than flexible foils (i.e., kites) mounted near the wings of the trawl. A combination of numerical simulation, physical modeling in a flume tank, and full-scale sea trials were used to optimize the horizontal spreading of the demersal trawl. Spacing between the foils and the angle of attack to the direction of tow were found to be important parameters. To our knowledge this is the first successful attempt to spread a demersal trawl full-scale at-sea using nothing but flexible foils.

A new underwater in-situ microplastics detection system based on micro-Raman spectroscopy: Development and sea trials

In-situ underwater observation for marine microplastics (MPs) study has long been desired but challenged by the difficulty in achieving continuous MPs enrichment and MPs analysis in underwater environments. Herein, a novel underwater system for in-situ detection of MPs was introduced. An innovative design with a filter mesh flipped 180° driven by a stepper motor was adopted to ensure the self-cleaning of the filter mesh and continuous MPs enrichment, reducing the frequency of manual maintenance required for the system. A special-designed optical detection chamber based on micro-Raman spectroscopy featured a 13 × 10 mm imaging field of view and a 50 µm imaging resolution was developed to gather morphology and composition information of MPs. During sea trials, the system successfully detected polypropylene (PP) microplastic and other suspended substances in seawater including microalgae, organic substances, and sands. This study lays the groundwork for future research into underwater in-situ investigation of marine MPs pollution.

A long short term memory network-based, global navigation satellite system/inertial navigation system for unmanned surface vessels

In recent years, research on unmanned surface vessels has entered a new phase, demanding the increased accuracy and reliability of integrated navigation and positioning systems. However, in complex environments, due to intermittent sensor failures or communication limitations, Global Navigation Satellite System (GNSS) signals are unreliable. Various errors that emerge in the system make it impossible to complete the measurement update process of filtering algorithms. This study provides a mechanism for improving the accuracy of combined GNSS/Shipborne Inertial Navigation System (SINS) integrated navigation when a GNSS outage occurs. Firstly, a SINS denoising method combining Complementary Ensemble Empirical Mode Decomposition (CEEMD) and an improved wavelet threshold algorithm is proposed. Secondly, a method based on Long Short-Term Memory (LSTM) network assisted GNSS/SINS integrated navigation is proposed to address the issue of poor information fusion performance when GNSS outages occur. The trained LSTM model is combined with SINS data to predict velocity and position during GNSS outages, providing high-precision velocity and position information. This ensures continuous, high-precision, navigation of unmanned surface vessels. Finally, to confirm the validity of the proposed methodology, a sea trial is performed to compare the different methods, and the results reveal the feasibility and effectiveness of the proposed methodology.

Unmanned sailboat with self-balancing rotating sail based on elastic rope: Modeling, optimization, and sea trials

Unmanned sailboats use wind energy to assist in propulsion during navigation and are featured by the advantages of clean energy and long endurance, making a hotspot of research on maritime unmanned vehicles. Sails are a core component of unmanned sailboats, and most existing studies on rotating sail have the shortcomings of high energy consumption and load. Therefore, this article proposes a novel method to achieve self-balancing sail rotation based on elastic rope and reduce the energy consumption and load of unmanned sailboats, and establishes a model for the self-balancing rotating sail. We introduced the sum of angular thrust of spherical surface SL as a performance evaluation index for unmanned sailboats, which considers both thrust and navigable range. Based on this index, the mechanical and positional parameters of the model are optimized to obtain the optimal solutions. The performance is increased by 24% after the optimization, and by 76% compared with the sailboat with the fixed sail angle when the same initial sail angle of 38° is adopted. Following the optimal solutions, we develop a prototype of the unmanned sailboat with self-balancing rotating sail. Subsequently, wind turbine experiments are conducted to preliminarily verify the correctness of the model for self-balancing rotating sail and the optimization results. Finally, sea trials are conducted to further verify the performance and seaworthiness of the unmanned sailboat under realistic sea conditions, successfully achieving a 15-day voyage under harsh sea conditions of levels 2 to 4. This study to some extent compensates for the shortcomings of existing studies on rotating sail and provides guidance for subsequent theoretical and engineering research in the field of unmanned sailboats.

Understanding front-rear track effect of seabed mining vehicle and traction performance optimization

The dual-tracked deep-sea mining vehicles used for sea trials generally cannot meet the demands of large-scale manganese nodules production due to their inadequate load bearing and traction performance. Various seabed mining organizations have gradually started four-tracked mining vehicles as seabed traveling ore collection machines to meet the demand for enhanced tractive performance. A notable challenge encountered is the significant front-rear track effect observed when these vehicles navigate soft-cohesive sediments. Addressing this, our study introduces a novel design concept that involves setting the grouser heights with a deviation between the front and rear tracks, coupled with the development of a traction force-slip rate model inspired by this innovative approach. This model facilitates an in-depth analysis of the front-rear track effect, including phenomena such as deep sinkage and an increase in pitch angle experienced by vehicles on soft-cohesive terrains. It is calculated that the front and rear grouser deviation height of only 2 cm can improve the traction force by 21%. Utilizing the multi-body dynamics (MBD) method, we validated the effectiveness of this grouser height adjustment in mitigating front-rear track effects, demonstrating its potential to reduce sinkage by at least 30 mm and pitch angle by at least 0.3 degrees, thereby guiding the optimization strategy. Finally, through optimization simulation, we present optimized track structural parameter sets suitable for three types of seabed pavement, concluding that for soft silty soil, saturated high cohesive soil, and saturated soft sandy soil, the grouser deviation heights should be approximately 5.3, 4.1, and 2.0 cm, respectively. After applying the optimized track structural parameter sets, traction performance evaluation indexes, such as traction force and the traction force-disturbing area ratio, improved by at least 23.4% and 3.3%, respectively. Meanwhile, static sinkage was reduced by at least 21.4% across the three types of pavements.

Nonparametric modeling of a high-speed USV at three speed regions based on Gaussian process regression with a hybrid kernel function

Due to the complexity and variability of the ocean environment, it is difficult for high-speed unmanned surface vehicles (USVs) to construct a unified mathematical model for nonlinear motion under different Froude numbers. In this paper, a nonparametric modeling method for high-speed USVs at three speed regions is presented based on Gaussian process regression with a hybrid kernel function (HKF-GPR). First, the hybrid kernel functions are designed based on the forecasting performance of Gaussian process regression with different single kernel functions (SKF-GPR) using sea trial speed data from the “Jiuhang 750” USV. Second, to better capture the dynamic performance of the USVs, the sea trial speed data are clustered into three speed regions by an improved k-means++ algorithm; these regions are the displacement, semiplanning, and planning regions. Finally, USV modeling and forecasting are performed in the three speed regions using HKF-GPR. The trained model shows good modeling accuracy and forecasting, verifying the effectiveness of the proposed method.

A novel hybrid swarm intelligence algorithm for solving TSP and desired-path-based online obstacle avoidance strategy for AUV

Aiming at the problem that Ant Colony Optimization (ACO) is subject primarily to the parameters, we propose a hybrid algorithm SOA-ACO-2Opt to optimize the ACO parameter combination through Seagull Optimization Algorithm (SOA) to strengthen ACO’s search capability. To obtain a uniform initial distribution of the ACO parameter combination, we incorporated the Kent Chaos Map (KCM) to randomly initialize the seagull’s position, reducing the tendency of SOA to fall into the local optimum. To avoid slow calculation speed and premature convergence of ACO, we improved the adaptive multi-population mechanism to reduce repeated redundant calculations and used the ϵ−greedy and default strategy, respectively, to update the ants’ position. 2Opt is applied to find shorter paths in each iteration. In addition, when AUV navigates on the planned path, it may encounter obstacles. Therefore, this paper proposes an autonomous obstacle avoidance algorithm based on forward-looking sonar to ensure safety during tasks. SOA-ACO-2Opt is verified against twelve different problems extracted from TSPLIB and compared with some state-of-the-art algorithms. Furthermore, sea trials were carried out for several representative marine engineering applications of TSP and obstacle avoidance. Experimental results show that this work can significantly improve AUV’s work efficiency and intelligence and protect the AUV’s safety.

Simultaneous in-air versus in-water measurements of humpback whale breathing sounds

Humpback whales produce an assortment of sounds ranging from moans and songs to surface-breaching, breathing, and foreflipper flaps. During a sea trial of Northeastern University’s coherent hydrophone array at the Great South Channel in US Northeastern coastal waters, the HF subaperture consisting of 32 hydrophone elements at 0.375 m spacings was deployed vertically with half of the hydrophones in air and the other half submerged underwater on September 6th, 2021. Many instances of humpback whale breathing sounds were recorded over several hours of observation. Visual sightings and video recordings were used to coregister sounds recorded on individual hydrophones of the HF subaperture. Here, we examine and compare the simultaneously recorded humpback whale breathing sound spectra, bandwidth, and duration for in-air versus underwater hydrophones. Whale distances to the vertical HF subaperture could be calculated from curved time of arrival differences due to close proximity of the array. These distances are applied to correct the received underwater sound pressure level for transmission loss and estimate underwater recorded whale breathing sound source level. A consistent broadband dip in the measured underwater sound spectra with null centered at 15 kHz is investigated by propagation modelling, considering both modal interference and attenuation from loud bubbles.

Analysis and Experimental Verification of Improving the EEDI of a Ship using a Thruster Supplied by a Hybrid Power System

Abstract In this study, the authors present a theoretical analysis and experimentally verified methods to improve the Energy Efficiency Design Index (EEDI) of ships. The improvements were studied via the application of an innovative solution of a thruster supplied by a hybrid power system on board a passenger-car ferry. The authors performed sea trials of a ship’s electrical power system supplied by battery packs with diesel generating set power units. The experimental study focused on energy balance and management, which were considered together with related power quality issues. The authors found that the application of an energy storage system to the ferry, such as batteries, with the simultaneous adaption of the operation modes of the electrical power system for current exploitation, significantly improved energy efficiency. Fuel consumption and CO2 emission were reduced, while adequate parameters of electrical power quality were maintained to meet classification standards.

Development and validation of the ASGARD risk score for safe monitoring in asymptomatic nonsevere aortic stenosis.

Current guidelines recommend serial echocardiography at minimum 1-2 year intervals for monitoring patients with nonsevere aortic valve stenosis (AS), which is costly and often clinically inconsequential.We aimed to develop and test whether the biomarker-based ASGARD risk score (Aortic Valve Stenosis Guarded by Amplified Risk Determination) can guide the timing of echocardiograms in asymptomatic patients with nonsevere AS. The development cohort comprised 1,093 of 1,589 (69%) asymptomatic patients with mild-to-moderate AS who remained event-free one year after inclusion into the SEAS trial. Cox regression landmark analyses with a 2-year follow-up identified the model (ASGARD) with the lowest Akaike information criterion for association to AS-related composite outcome (heart failure hospitalization, aortic valve replacement, or cardiovascular death). Fine-Gray analyses provided cumulative event rates by ASGARD score quartiles. The ASGARD score was internally validated in the remaining 496 patients (31%) from the SEAS-cohort and externally in 71 asymptomatic outpatients with nonsevere AS from six Copenhagen hospitals. The ASGARD score comprises updated measurements of heart rate and age- and sex-adjusted N-terminal pro-brain natriuretic peptide upon transaortic maximal velocity (Vmax) from the previous year. The ASGARD score had high predictive accuracy across all cohorts (external validation: area under the curve: 0.74 [95% CI, 0.62-0.86]), and similar to an updated Vmax measurement. An ASGARD score ≤50% was associated with AS-related event rates ≤5% for a minimum of 15 months. The ASGARD score could provide a personalized and safe surveillance alternative to routinely planned echocardiograms, so physicians can prioritize echocardiograms for high-risk patients.

Effect of Sampling Rate in Sea Trial Tests on the Estimation of Hydrodynamic Parameters for a Nonlinear Ship Manoeuvring Model

This paper explores the impact of sampling rates during sea trials on the estimation of hydrodynamic parameters in a nonlinear manoeuvring model. Sea trials were carried out using an offshore patrol vessel and test data were collected. A nonlinear manoeuvring model is introduced to characterise the ship’s manoeuvring motion, and the truncated least squares support vector machine is employed to estimate nondimensional hydrodynamic coefficients and their corresponding uncertainties using the 25°–25° zigzag test. To assess the influence of the sampling rates, the training set is resampled offline with 14 sampling rates, ranging from 0.2 Hz to 5 Hz, encompassing a rate 10 times the highest frequency component of the signal of interest. The results show that the higher sampling rate can significantly diminish the parameter uncertainty. To obtain a robust estimation of linear and nonlinear hydrodynamic coefficients, the sampling rate should be higher than 10 times the highest frequency component of the signal of interest, and 3–5 Hz is recommended for the case in this paper. The validation is also carried out, which indicates that the proposed truncated least square support vector machine can provide a robust parameter estimation.

An equivalent modeling method of the umbilical hydraulic characteristics and the simulator for the umbilical

This paper proposed an equivalent model for the hydraulic characteristics of the umbilical with hydraulic resistance, hydraulic inductance and hydraulic capacitance. Based on the model, an umbilical simulator is designed for subsea control model tests. The simulation of the pressurizing and relieving, and production master valve opening and closing are conducted through SimulationX. The simulator's performances are verified through the sea trials. In the umbilical simulator, the slender pipe, the accumulator, and the hydraulic motor and flywheel can be employed as the hydraulic resistance, hydraulic capacitance and inductance, respectively. Their sequence affects the simulator's performances and the best sequence is capacitance-inductance-resistance. The simulation results of the simulator and the umbilical are analyzed and compared. The pressurizing and relieving times of the umbilical are 529s and 192s, while that of the simulator are 572s and 165s. The opening and closing times of the umbilical are 4.4s and 8.3s, while that of the simulator are 4.8s and 8.2s. The sea trials show that the errors for the simulator of the pressurizing time, the production master valve opening and closing time are 11.12%, 11.62% and 7.89%, respectively.

Doppler and Channel Estimation Using Superimposed Linear Frequency Modulation Preamble Signal for Underwater Acoustic Communication

Due to the relative motion between transmitters and receivers and the multipath characteristic of wideband underwater acoustic channels, Doppler and channel estimations are of great significance for an underwater acoustic (UWA) communication system. In this paper, a preamble signal based on superimposed linear frequency modulation (LFM) signals is first designed. Based on the designed preamble signal, a real-time Doppler factor estimation algorithm is proposed. The relative correlation peak shift of two LFM signals in the designed preamble signal is utilized to estimate the Doppler factor. Moreover, an enhanced channel estimation algorithm, the correlation-peak-search-based improved orthogonal matching pursuit (CPS-IOMP) algorithm, is also proposed. In the CPS-IOMP algorithm, the excellent autocorrelation characteristic of the designed preamble signal is used to estimate the channel sparsity and multipath delays, which are utilized to construct the simplified dictionary matrix. The simulation and sea trial data analysis results validated the designed preamble, the proposed Doppler estimation algorithm, and the channel estimation algorithm. The performance of the proposed Doppler factor estimation is better than that of the block estimation algorithm. Compared with the original OMP algorithm with known channel sparsity, the proposed CPS-IOMP algorithm achieves a similar estimation accuracy with a smaller computational complexity, as well as requiring no prior knowledge about the channel sparsity.

An in-situ portable pore-water sampler for evaluating the vertical distribution in the sediment interface

The characteristics of chemical elements in marine pore-water are significant for investigating and evaluating the marine sediment environment (especially vertical distribution characteristics, etc.). Therefore, sampling high-quality pore-water is necessary for marine scientific research. This paper proposes an in-situ portable pore-water sampler that utilizes the compression spring structure, allowing the potential energy generated by the spring to be converted into kinetic energy for the sampling process. The sampler requires no other power and can be portable for marine pore-water sampling. We first described the sampler’s mechanical design, which can obtain one sediment-overlying water and three sediment pore-water samples at different depth profiles. Secondly, to judge the force state of the power spring, we designed laboratory experiments and simulation tests based on COMSOL Multiphysics to analyze the force during the working process of power springs. Finally, we deployed the sampler offshore in Zhoushan Islands for actual sampling, and we tested and compared the in-situ samples with the centrifugal samples to analyze the vertical distribution of chemical elements. The successful sea trials verified the reasonableness of the mechanical design, theoretical calculation and experimental analysis of the sampler. Furthermore, we will continue to optimize the sampler and apply it more widely.

A deep-sea in-situ chemical laboratory for cabled seafloor observatories

A deep-sea in-situ chemical laboratory (DICL) is proposed for new insight into ocean chemical evolution. The DICL integrates a deep-sea in-situ anion analyzer (DIAA) and several chemical sensors connected to cabled seafloor observatories via a science instrument interface module (SIIM). It can measure the concentrations of seawater anions (e.g., Fˉ, Clˉ, Brˉ, NO3ˉ, SO4 2ˉ, PO4 3ˉ), chlorophyll-a, dissolved oxygen, and methane, as well as pH value. The system operation status can be monitored remotely on the shore, and the science data can be acquired in real-time. After water pressure tests and shallow sea trials, the DICL was tested in the Monterey Accelerated Research System (MARS) deep-sea observatory and collected high-resolution time-series chemical parameters. The experimental results demonstrated that the DICL's mechatronics integration design is reasonable and feasible.

Motion states identification of underwater glider based on complex networks and graph convolutional networks

Underwater glider (UG) plays an important role in ocean observation and exploration for a more efficient and deeper understanding of complex ocean environment. Timely identifying the motion states of UG is conducive for timely attitude adjustment and detection of potential anomalies, thereby improving the working reliability of UG. Combining limited penetrable visibility graph (LPVG) and graph convolutional networks (GCN) with self-attention mechanisms, we propose a novel method for motion states identification of UG, which is called as visibility graph and self-attention mechanism-based graph convolutional network (VGSA-GCN). Based on the actual sea trial data of UG, we chose the attitude angle signals of motion states related sensors collected by the control system of UG as the research object and constructed complex networks based on the LPVG method from pitch angle, roll angle, and heading angle data in diving and climbing states. Then, we build a self-attention mechanism-based GCN framework and classify the graphs under different motion states constructed by a complex network. Compared with support vector machines, convolutional neural network, and GCN without self-attention pooling layer, the proposed VGSA-GCN method can more accurately distinguish the diving and climbing states of UG. Subsequently, we analyze the variation of the transitivity coefficient corresponding to these two motion states. The results suggest that the coordination of the various sensors in the attitude adjustment unit during diving becomes closer and more efficient, which corresponds to the higher network measure of the diving state compared to the climbing state.