Sea Test Research Articles

Design and tests of a marine current turbine in low flow velocity

Marine current energy is recognized a promising energy source due to its inherent stability and high predictability. In the past decade, several milestones have been achieved in marine current turbine (MCT) research such as MeyGen and O2. However, compared with high-velocity currents, low velocity currents are more commonly distributed worldwide, which presents new challenges. The demand for low starting velocity and high efficiency necessitates some novel structure in the design of blade, power transmission, etc. To address these issues, taking a 50W MCT as research object, this paper firstly presents the MCT design of a new fan-shaped rotor configuration, a compact non-contact magnetic coupling, a low inertial power train and hollow-cup DC generator for easier starting. Furthermore, to realize the maximum power point tracking (MPPT) and sustainable power supply, the electrical system and its control strategy were designed. The hydrodynamic performance of the fan-shaped rotor was simulated and analyzed using CFD, and a simulation model of the electrical and control systems was constructed and tested to verify the performance. Finally, the tank and sea tests were respectively conducted to validate the performance of proposed MCT. The results indicate that the proposed MCT is capable of starting at velocities around 0.2 m/s and achieving a power coefficient (Cp) exceeding 0.4, making it well-suited for providing a continuous and stable power supply in areas with low flow velocities.

MCLORA: Maritime ad-hoc communication system based on LORA

Maritime communication plays a crucial role in fields such as ocean resource exploration and marine environmental monitoring. Existing maritime communication methods either face challenges in equipment deployment or are limited by high power requirements, making sustained operation difficult. The emergence of LoRa presents an opportunity in this regard, with its characteristics of low power consumption and long communication range, meeting the demands for long-term maritime communication. However, LoRa’s underlying implementation is not open-source, and LoRaWAN itself adopts a star topology, limiting communication between nodes. Therefore, we have devised a communication packet header working at the application layer to enable peer-to-peer communication between nodes. Our on-campus field tests have shown that our system can achieve node-to-node communication, networking functionalities, with a packet delivery rate more than 94%, and max data transmission rate can achieve 1027 bps. In the sea test, the communication rate of our node remained basically around 1035 bps due to the absence of objects blocking the line of sight, and packet delivery rate was more than 96%.The byte error rates of all experiments were less than 0.5%.

Development and Application of a Novel Tsunami Monitoring System Based on Submerged Mooring.

Real-time data transmission and reliable operation are essential for a tsunami monitoring system to provide effective data. In this study, a novel real-time tsunami monitoring system is designed based on a submersible mooring system. This system is equipped with a data acquisition and tsunami wave identification algorithm, which can collect the measured data of the pressure sensor and detect a tsunami wave in real time. It adopts the combination design of underwater inductive coupling transmission and a redundant BeiDou communication device on the water surface to ensure the reliability of real-time data transmission. Compared with traditional tsunami monitoring buoys, it has the advantages of reliable communication, good concealment, high security, and convenient deployment, recovery, and maintenance. The results of laboratory and sea tests show that the system has high reliability of data transmission, stable overall operation of the system, and good application prospects in the field of real-time tsunami monitoring and early warning.

Numerical simulation and experimental study of the dynamic characteristics of a gas turbine rotor system with beam sea and head sea excitation

Vibration analysis is crucial for studying rotor dynamics. The gas turbine rotor system is subjected to complex alternating loads during navigation, resulting in vibrations transmitted to the bearings that alter the system’s dynamic characteristics. Based on the similarity law of the wave resistance test, a hull model was established. Beam sea and head sea tests were conducted in the towing pool to measure the acceleration response at the key positions. A finite element model of the turbine rotor system was established, and the test data were imported into the model after wavelet noise reduction and resampling to calculate the vibration response at the front and rear bearing points. The vibration responses transmitted to different locations and directions caused by beam sea and head sea conditions were analyzed. A comparison and analysis were conducted on the acceleration responses in various locations and directions under beam sea or head sea conditions. The equivalent von Mises stress distribution of the gas turbine rotor system under beam sea and head sea loads was obtained. The vibration transfer model was verified for accuracy and can be used to quickly analyze the vibration response of bearings under wave load transfer. This study provides a theoretical basis and reference for enhancing the stability of the gas turbine rotor system.

New Measuring and Data Transmission Equipment for Operational Oceanography at the Gelendgik Black Sea Test Site of Institute of Oceanology of the RAS

The design and principles of operation of the bottom multi-modem station MDS-II, located in the coastal zone (depth of location — 25 m) of the northeastern part of the Black Sea at the Gelendzhik Test Site of IO RAS are described. The station is connected to the coastal center by means of a bottom fiber-optic cable, through which power is supplied to the station, and online transmission of measurement data takes place. The station is an underwater server to which one can connect a measuring device and get a real-time access to it, as well as remotely control on its operation. The design of an automatic stationary station for vertical sounding (SSVS) of water column, which is also used at the Gelendzhik Test Site, is also described. This station is installed close to the MDS-II multi-modem station and is connected to one of its modems. The station consists of a bottom electric winch installed on the seabed and a floating module (probe) on a cable line wound around the winch drum. When the command ʺsoundingʺ is given, the cable unwinds and the floating module, equipped with temperature and pressure sensors, floats and measures the water temperature profile from the bottom layer to the sea surface. Then the cable is winding on a drum, and the floating module returns to the bottom layer. A prototype of a new SSVS is being developed, which will allow sounding of the water layer with a thickness of up to 100 m. It will be equipped with a multi-parameter probe that makes joint measurements of hydrophysical and bio-optical parameters.

Underwater weak spectral line extraction scheme based on improved HMM

To address the difficulty of extracting weak spectral lines from signals received by passive sonar, we propose a spectral line extraction scheme based on an improved hidden Markov model (HMM). A new state transition probability based on spectral line features is proposed that solves the problem of state transition probability relying on prior information in traditional HMMs. Using a peak detection algorithm and a parallel processing framework reduces computation. We employ the boxplot method to remove the outliers from the spectral lines caused by strong noise and compensate for them. By improving the forward–backward probability calculation method through a peak penalty factor, we manage adjacent spectral lines prone to be missed by traditional HMMs. Lastly, we use dynamic sliding windows to determine a spectral line’s birth and death. Data verification by simulations and sea tests show that our algorithm extracts spectral lines better and with a smaller error, accurately detects the birth and death of spectral lines, and is faster than traditional HMM algorithms.

Research on Multi-target Tracking Algorithm Based on Track Segment Association

In the process of multi-target tracking, the complex underwater acoustic channel, target model mismatch, target strong maneuvering and other factors are easy to cause track interruption and rerun, which have a bad influence on the situation assessment and tactical decision of the Unmanned sonar system. Aiming at the problem of track interruption, this paper integrates the track adhesion algorithm into the active multi-target tracking algorithm. Simulation results show that the track adhesion algorithm can effectively improve the correct track association rate and track lifetime. By comparing the effect of the new and old methods with the sea test data, the track adhesion can effectively solve the problem of track interruption in the case of target track maneuvering and improve the track life.

Validation and verification of models for setting SONAR system requirements

When determining requirements for a SONAR system as a whole, typically very high-level requirements such as number of detections and total false alarms allowed per unit time must be converted into specific requirements for system components. These requirements may include array requirements like hydrophone count and position. Validation of probability of detection via sea test is fraught with complications, not least of which is environmental uncertainty. As a precursor, it is generally advisable to approach and attempt to validate models for each term in the SONAR equation one at a time. The approaches to validation vary depending on the term and can range in complexity from comparison to analytical solutions, to comparison with alternate available models, up through data collections at sea. Each of these approaches comes with its own challenges and limitations, which are discussed.

Estimating the direction of arrival of spatially spread sources using block-sparse Bayesian learning with an extended dictionary.

Estimating the direction of arrival (DOA) of spatially spread sources is a significant challenge in array signal processing. This work introduces an effective method within the sparse Bayesian framework to tackle this issue. A spatially spread source is modeled using a multi-dimensional Slepian signal subspace that expands the dictionary and results in a block-sparse structured solution. By taking advantage of block-sparse Bayesian learning, parameter estimation becomes feasible. A complex Gaussian posterior is derived under a multi-snapshot block-sparse framework with a complex Gaussian prior and varying noise conditions. The hyperparameters are estimated using the expectation-maximization algorithm. Through numerical tests and sea test data evaluations, the proposed method shows superior energy focusing for spatially spread signals. Under limited snapshots and challenging signal-to-noise ratios, the current method can still offer precise DOA determination for spatially spread sources.

Impact of hydrate spatial heterogeneity on gas permeability in hydrate-bearing sediments

The permeability characteristic of hydrate-bearing sediments (HBSs) is an essential factor for assessing the exploiting potential of target area. The two trial tests in the South China Sea have demonstrated the production feasibility of clayey hydrate reservoirs, and further clarifying main controlling factors of the permeability characteristic is an essential prerequisite for commercial development. However, the current studies mainly focus on homogeneous HBSs with different saturations and porosities, ignoring the natural spatial heterogeneity of hydrate since the sedimentary and accumulation history. In this study, spatial heterogeneous hydrate (0–23.1%) was generated in montmorillonite specimens, and effective stress (1–5 MPa) was applied. The results show that 1) HBSs permeability with heterogeneity hydrate occurrence presents an exponential-like relationship with saturation. 2) Heterogeneous hydrate occurrence would reduce the permeability sensitivity to saturation. 3) The permeability of heterogeneous HBSs decreases in a power function trend with increasing effective stress. 4) The heterogeneity reduces compression effect and decreases permeability damage rate. 5) Increasing hydrate spatial heterogeneity would decrease HBSs permeability.

Development and evaluations of the broadband ocean bottom seismometer (Yardbird-BB OBS) in Taiwan

This study focuses on developing and evaluating the broadband ocean bottom seismometer (Yardbird-BB OBS) in Taiwan. The Yardbird-BB OBS is a crucial instrument for recording seismic signals in deep-sea environments. Rigorous testing ensures optimal performance and data recording capabilities. Following assembly, the Yardbird-BB OBS undergoes a 3–6 month deployment test in the deep sea, capturing seismic signals worldwide. Data from 2016 and 2017 deployments in the Okinawa Trough analyze significant seismic events, including a magnitude 7.8 earthquake in New Zealand and a magnitude 6.3 earthquake from a North Korean nuclear test. Waveform analysis, focusing on tele-seismic events and waveform quality, assesses the OBS’s performance, highlighting successful automatic leveling adjustment. These high-quality recordings benefit research, aiding the study of plate tectonics, crustal age estimation, seafloor ambient noise determination, and earthquake location accuracy improvement. The study also details methods for verifying instrumental self-noise, dynamic range, digitization sensitivity, linearity error, clock drift, and data logger power consumption. Calibration procedures and evaluation methods provide insights into Yardbird-BB OBS performance characteristics, contributing to its understanding and enhancement for effective long-term underwater data recording and valuable scientific research.

New Measuring and Data Transmission Equipment for Operational Oceanography at the Gelendgik Black Sea Test Site of the Shirshov Institute of Oceanology, Russian Academy of Sciences

New Measuring and Data Transmission Equipment for Operational Oceanography at the Gelendgik Black Sea Test Site of the Shirshov Institute of Oceanology, Russian Academy of Sciences

Vibration energy harvesting from an unmanned surface vehicle: Concept design, open sea tests and harvester optimization

With the growing worldwide attention to marine environment protection, marine resource exploration, and so on, unmanned surface vehicles (USVs) have become one of the critical mobile marine observation equipment. However, USVs generally rely on limited onboard batteries to provide electricity, and thus, they have low endurance and poor load capacity. The lack of a long-term power supply is currently a great challenge for the further application and development of USVs. Harvesting energy from the working environment of USVs is a promising solution to address that problem. To demonstrate the possibility of this scheme, a physical prototype of a novel USV with a built-in vibration energy harvester has been fabricated and tested in an open sea for the first time. Moreover, a full-coupled mathematical model is developed to further optimize the power performance of the USV based on the Taguchi method. Experimental results show that this prototype can generate a maximum instantaneous electric power of 277.71 mW, 112.95 mW and 101.27 mW when the USV is in a status of towage, propulsive and free-floating, respectively. Simulation results present that the optimized USV can achieve a mean electric power of 246.14 mW, which is improved by 49.88% compared with the unoptimized results of the developed prototype.

Application of the monitoring and early warning system for internal solitary waves: Take the second natural gas hydrates production test in the South China Sea as an example

Internal solitary waves (ISWs) contain great energy and have the characteristics of emergency and concealment. To avoid their damage to offshore engineering, a new generation of monitoring and early warning system for ISWs was developed using technologies of double buoys monitoring, intelligent real-time data transmission, and automatic software identification. The system was applied to the second natural gas hydrates (NGHs) production test in the Shenhu Area, South China Sea (SCS) and successfully provided the early warning of ISWs for 173 days (from October 2019 to April 2020). The abrupt changes in the thrust force of the drilling platform under the attack of ISWs were consistent with the early warning information, proving the reliability of this system. A total of 93 ISWs were detected around the drilling platform. Most of them occurred during the spring tides in October–December 2019 and April 2020, while few of them occurred in winter. As suggested by the theoretical model, the full-depth structure of ISWs was a typical current profile of mode-1, and the velocities of wave-induced currents can reach 80 cm/s and 30 cm/s, respectively, in the upper ocean and near the seabed. The ISWs may be primarily generated from the interactions between the topography and semidiurnal tides in the Luzon Strait, and then propagate westward to the drilling platform. This study could serve as an important reference for the early warning of ISWs for offshore engineering construction in the future.©2023 China Geology Editorial Office.

Advanced Marine Antifouling Hydrogels Based on 7-Amino-4-methylcoumarin Fluorescence Driven by Rare-Earth Phosphorescence.

At present, there are very few reports on the combination of phosphorescence and fluorescence in the field of pollution prevention. A composite antibacterial agent was designed to store energy by using the phosphorescence effect of rare earth oxides, emit light at night, and stimulate 7-amino-4-methylcoumarin to produce fluorescence and prevent algae from adhering. When complexed with PVA, it exhibited excellent characteristics as an all-weather autocatalytic phosphorescence-fluorescence antifouling hydrogel. The rare earth phosphorescent powder was prepared in a high-temperature tube furnace, coated with SiO2 on the surface for waterproofing, and then grafted with 7-amino-4-methylcoumarin to obtain a composite antibacterial agent with a phosphorescence-fluorescence effect. The composite antibacterial agent was added with PVA to obtain a hydrogel, which exhibited bactericidal rates of more than 99.98% against both Gram-positive and Gram-negative bacteria after 48 h. The results of fluorescence staining showed that the coverage rate of dead bacteria reached 41.6% after 24 h. The tensile strength of the antifouling hydrogel is up to 1.49 MPa, which is strong enough for real marine environments. Moreover, the algae coverage area of the composite hydrogel under natural light was only 2.7%, representing a 10-fold reduction compared with the control. The antifouling hydrogel has good antipollution and algae suppression performance, which is due to the fact that the rare earth phosphorescent powder when exposed to sunlight can provide a light source to stimulate 7-amino-4-methylcoumarin fluorescence at night and thereby prevent algae adhesion. After testing in the marine field and the real sea test when wrapped in a fishing net, the excellent antifouling performance was demonstrated. The functional hydrogel has great application potential in the protection of seawater-exposed structures, such as bridges and bay ports.

Research on dynamic response prediction of semi-submersible wind turbine platform in real sea test model based on machine learning

The motion response of floating offshore wind turbine (FOWT) platform is closely related to its safety, and model test is the most direct method to fully study its dynamic characteristic behavior. In this paper the dynamic response of intermediate-scale physical semi-submersible FOWT model test under real sea environmental loads is studied and compared with the numerical model dynamic response, demonstrating that some limitations of small-scale physical model tests can be overcome, such as the catenary effect of mooring lines. It is found that the nonlinear dynamic characteristics of the physical model under actual marine environmental loads can be captured by the numerical model, which can improve the fidelity of model test data for semi-submersible FOWT structures in the existing literature. The dynamic response database of semi-submersible FOWT under complex wind, wave and current loads was established by using a numerical model with high accuracy, and was used in the prediction research of different machine learning algorithm models such as Genetic Algorithm optimization Back Propagation neural network (GA-BP), Support Vector Machine (SVM) and Gaussian Process (GP). The research shows that the relationship between the environmental load and the dynamic response of FOWT can be established by using the machine learning model, in which the number of samples has a significant impact on the prediction of the mooring line tension, and the research on the three algorithm models shows that GP performs significantly better than GA-BP and SVM in predicting the mean value of surge, pitch and mooring line force. For the dynamic response prediction of mooring line tension, GP model can get better results. In the future, this method will become an important method to predict and monitor the dynamic response of FOWT.

Nezha‐IV: A hybrid aerial underwater vehicle in real ocean environments

AbstractHybrid aerial underwater vehicles (HAUVs) that are capable of autonomously operating in both the aerial and underwater environments with repeated rapid transitions have received great interest in recent years. Current HAUV prototypes cannot fully cope with the unstructured, harsh, and hazardous ocean environments considering the high‐pressure and the strong hydrodynamic perturbations. This work reports on the HAUV, Nezha‐IV, with all basic functions validated in a real ocean environment. Nezha‐IV has four aerial propellers and eight underwater thrusters. It is not only capable of maneuvering delicately during flight and underwater but can also perform dynamic transitions under rough sea conditions. We present the design, construction, control, and oceanic testing of Nezha‐IV and demonstrate reliability and robustness, especially during the transition phases. Performance estimation and results gathered from tests in the South China Sea show that Nezha‐IV can operate at various depths ranging from 0 to 50 m at a velocity of 1 kt for 22 min and hover in the air for 15 min or cruise at a velocity of 10 m/s for 7.2 km in 12 min. This project contributes to the field of HAUV with (i) a HAUV capable of dynamic locomotion with high stability in both media and during transitions; (ii) identification of challenges during water–air transition in harsh sea conditions, and a reliable transition strategy that helps the development of fully autonomous HAUVs; (iii) a modular, foldable, and impact‐resistant HAUV structure; (iv) vehicle's capability proved by extensive tests in dynamic ocean environment.

Biological chorusing and fish calls in Bermuda

A series of sea tests and long term passive acoustics monitoring studies have been conducted in Bermuda from 2020–2023. Observations of biological choruses and individual fish call events from sensors in deep water off the flank of the Bermuda Atoll, and alongside shallow sub-tropical reefs, will be discussed. We find striking similarities between sub-tropical Atlantic reefs in Bermuda with documented trends in tropical coral reef soundscapes studies in Hawaii and the tropical Pacific. This observation suggests that evening chorusing and patterns in reef sound and fish calls are potentially pervasive across large portions of the world’s oceans. Deep water calls that appear to be associated with large fish such as groupers were observed on the atoll flank. Evening chorusing at change of light is commonly observed on tropical reefs and also persistent on Bermuda’s sub-tropical reefs. Evening biological chorusing is also evident at deep water sights, indicating that this may not be a strictly littoral biological soundscape feature.

An Effectiveness Analysis for the Multi-Factor Accelerated Test of a Copper-Free Self-Polishing Antifouling Coating

In order to eliminate or slow down the corrosion of various marine facilities, it has become a necessary choice to develop and use effective antifouling coatings for the development of marine equipment. This paper takes the newly developed copper-free, self-polishing, antifouling coating (CSAFC) as its research object, studies the performance changes in the exudation rate, adhesion, and abrasion rate by conducting a multi-factor accelerated test (MFAT) in the laboratory and a real sea test (RST), analyzes the correlation and acceleration multiplier in the two test environments, and provides a reference for the research on the relevant performance of this material. Firstly, it introduces the importance of antifouling coatings for modern maritime business, the importance of conducting accelerated tests in the laboratory, and explains the current test methods; secondly, it analyzes and fits the performance changes in materials such as the exudation rate, adhesion, and abrasion rate in different environments, and determines the main failure factors; finally, the correlation and acceleration multiplier are calculated using the Spearman rank correlation coefficient method (SRCCM) and acceleration factor method (AFM). The result shows that this MFAT has a good correlation and acceleration effect relative to the RST.

Improved Adaptive Finch Clustering Sonar Segmentation Algorithm Based on Data Distribution and Posterior Probability

This study proposes a side-scan sonar target detection technique for CPU or low-performance GPU to meet the requirement of underwater target detection. To rectify the gray distribution of the original side scan sonar data, enhance picture segmentation, and supply the data distribution probability for the clustering algorithm, the methodology uses a classic image processing technique that is GPU-friendly. The modified adaptive Finch clustering technique is used to segment the image and remove image voids after assessing the processed image attributes. The posterior information is then used to apply a classification label to each pixel. The characteristics of the connected region are analyzed in the data playback of the Tuandao experiment in accordance with the imaging principle of side-scan sonar and the original shape and size characteristics of the target. The predicted target results are combined with the AUV navigation information to obtain the predicted target longitude and latitude information, which is then sent to the AUV master control system to guide the next plan. The Jiaozhou Bay sea test results demonstrate that the traditional target detection algorithm put forth in this paper can be integrated into a low-performance GPU to detect targets and locate them. The detection accuracy and speed exhibit strong performance, and real-time autonomous sonar detection is made possible.