2021, 10(2):3-18. DOI: 10.12146/j.issn.2095-3135.20210208001
Abstract:Biochemical indices are important measurands in marine environmental and ecological monitoring. Traditional monitoring methods of biochemical indices usually use chemical reagents and the operation is also time-consumed. Moreover, after a long measurement time, the results cannot accurately reflect the real status of seawater. In this work, four in-situ sensors are investigated based on the optical sensing principles, i.e. the chlorophyll a, chemical oxygen demand (COD), biochemical oxygen demand (BOD), and the underwater plankton imager. The development of the instrument prototypes and buoy-based in-situ trial experiments have been completed and described. During the sea trial, the environment-friendly antifouling paint and mechanical wipers have successfully overcome the biological fouling issues to the sensors, which have been kept operation underwater for more than six months. From the trial experiments, we have collected a large amount of real seawater data and maintenance experience of the equipment. The buoy trial results also reflected the true conditions of the seawater.
2021, 10(2):19-28. DOI: 10.12146/j.issn.2095-3135.20201106001
Abstract:Up till now, the effects of the water adhesion of superhydrophobic coating on its corrosion resistance and antibacterial behaviors are not clear. In this study, superhydrophobic coatings with different water adhesion were successfully fabricated by spraying paints with different percentages of poly (ureaformaldehyde) nanoparticles (PUF NPs) on the Q235 substrate. The electrochemical results showed the lowadhesion superhydrophobic coating with the sliding angle less than 10° exhibited higher charge transfer resistance and lower corrosion current density than the high-adhesion superhydrophobic coating with the sliding angle of 175°. It suggested that the low-adhesion superhydrophobic coatinghad better corrosion resistance compared to the high-adhesion superhydrophobic coating. The crystal violet staining result revealed that the superhydrophobic coatings with high-adhesion and low-adhesion both could significantly restrain the adhesion of P. aeruginosa compared to Q235 substrate, and the superhydrophobic coating with low-adhesion exhibits a more excellent antibacterial capability at the antibacterial rate of 70.3%.
2021, 10(2):29-38. DOI: 10.12146/j.issn.2095-3135.20201121001
Abstract:A reliable recovery system is crucial to marine instruments for effective observations and data acquisitions. The communication beacon between the instrument on the sea and the scientific research ship is a key part of the recovery system. The low-power marine instrument recovery communication beacon designed in this paper is a set of lightweight beacon machines that can be used for marine instrument recovery. The system integrates a global position system (GPS) positioning module and a Lora low-power long-distance communication module. The system can automatically switch to the standby mode while it float up. The system can work continuously for 48 h. Under the low-power standby mode, the theoretical standby time is over 5 years. Once the instrument floats up, the location information can be sent to the nearby ships. The effective communication distance can reach 7 km. The system can bear the pressure up to 9 000 m water depth. Power consumption test and communication test showed that, the proposed instrument has low power consumption, high positioning accuracy, high reliability, and long communication distance.
2021, 10(2):39-49. DOI: 10.12146/j.issn.2095-3135.20201014001
Abstract:Ejector is an important device to improve the efficiency of thermal seawater desalination system. In this work, the internal flow and transport characteristics of a two-stage ejector are investigated via a three-dimensional numerical simulation. The mixing and diffusion processes of ejecting and working fluids are also analyzed to identify the factors related to energy consumption. The simulation results showed that, the maximum velocity of the ejector occurs in the axis direction and the streamline distribution in the nozzle and mixing chamber is uniform. However, one or multiple vortices are generated in the suction chamber, which causes the uneven distribution of streamline. The negative pressure at the entrance of the suction chamber increases firstly, and then decreases with the increasing velocity. The amount of vortex decreases with increasing velocity, which helps to improve the efficiency of ejector. Vortex dissipates faster with increased distance from the central line and the turbulent dissipation increases significantly, which results in a rapid dissipation of vortex.
2021, 10(2):50-62. DOI: 10.12146/j.issn.2095-3135.20201122001
Abstract:To realize safely transportation of the personnel and materials on the marine equipment, a 6-DOF active wave compensation device are researched and analyzed in this work. A complete active wave compensation system is designed, which includes the motion measurement system, control system and the actuator. In the motion measurement system, an adaptive MTi inertial sensors was adopted. And the highpass filter was applied for the measurement of ship motion compensation. In addition, a binocular vision system was designed to inspect the motion of platform at the end. And the convolution neural network was applied to realize the fusion of multiple sensors. The controlling system adopted an active disturbance rejection controller which was adjusted by the neural network to obtain fast response, accurate compensation and anti-interference performance. Actuators based on hydraulically-driven Stewart platform. The MATLAB/Simulink and AMESim were used to establish the co-simulation model of machine, electricity and liquid firstly. Then, performance of the proposed system were analyzed and discussed with a comparison with existing techniques.
2021, 10(2):63-74. DOI: 10.12146/j.issn.2095-3135.20201009001
Abstract:With the increasing activities of deep-sea exploration in China, the demand for various transducers, sensors and related products suitable for deep-sea acoustic sensing and testing platforms are also increasing. In this paper, a 20 MPa high-pressure anechoic tank is designed to satisfy the static pressure test within 2 000 meters of water depth, and the acoustic performance test under different water depths can be realized with the additional acoustic metering system. The tank adopts a cylindrical shell, and the covers at both ends are hemispherical. Its inner diameter is 1.5 m and the length at the central axis is 3.0 m. Two flange openings at the top of the tank are provided with a spacing of 1.0 m, which can satisfy the measurement of acoustic devices with a size up to 0.1 m. The water tank is internally equipped with Korean pine made silencing wedges. The wedge has a hollow structure, and the installed cabin has an effective inner diameter of 0.9 m and an effective length of 2.14 m (central axis). The lowest working frequency of acoustic measurement (free field reciprocity method) is designed as 10 kHz. According to the Comsol simulation results, the echo interference from 10 kHz to 58 kHz is larger than 1 dB, which means the measurement should use pulse wave method, and the transmission pulse width does not exceed the shortest sound path difference of 230 μs (sound speed: 1 500 m/s). The echo interference in the frequency band above 58 kHz does not exceed 1dB, which means continuous wave method can be used. Besides, the cabin is equipped with a rotating mechanism and an axial telescopic mechanism, which can meet the measurement requirements of different angles and distances. At the same time, it is equipped with lighting and camera to meet the needs of real-time observation. The anechoic wedge in the middle section of the cabin is designed to be detachable, and the hatch cover at one end is designed to be electrically opened and closed, so it can also meet the static pressure test requirement of large-sized equipment.
2021, 10(2):75-84. DOI: 10.12146/j.issn.2095-3135.20201103001
Abstract:Self-oscillating cavitating jet is a phenomenon in the process of jet flow. The cavitation is produced by the oscillation characteristics of the internal structure of the nozzle. And the cavitation collapses after it is ejected from the nozzle, which enhances the impact force of the water jet. The selfoscillating cavitating jet effect is related to the nozzle structure. Since Helmholtz nozzle has great advantage in enhancing the jet impacting force, this paper investigates the flow fields inside and outside of the Helmholtz nozzle with different structural parameters based on numerical simulation, and this paper mainly analyzes the influence of some key structural parameters, including the outlet diameter, the outlet length,the resonant cavitating length, the resonant cavitating diameter and the target distance, on the cavitating jet performance, and the results can provide a theoretical instruction for the applications like the caviating jet technology in ship cleaning.
2021, 10(2):85-97. DOI: 10.12146/j.issn.2095-3135.20201119003
Abstract:Magnetic resonance wireless power transfer can provide continuous energy for the underwater equipment. Moreover, the energy waves carrying information can also construct a high speed and reliable channel for data communications. Therefore, both the power supply and data transfer bottlenecks are broken. In this paper, an underwater simultaneous wireless information and power transfer (USWIPT) technique is investigated. A prototype based on field programmable gate array (FPGA) was developed, and the frequency-shift keying (FSK) modulation was employed to achieve wireless information and power transfer. While the input power is 20 W, the data rate is about 1 Mbps with low power consumption in the underwater environment. To avoid the channel changes due to the mobility of underwater devices, a support vector machine (SVM) based method was proposed for the signal decoding. Experimental results showed that, the proposed system can work under the high speed transmission and long distance, and the decoding accuracy can reach 99.9%.
2021, 10(2):98-108. DOI: 10.12146/j.issn.2095-3135.20210122001
Abstract:It is very important for near-seabed seismic exploration in deep sea that the pulsed sound source has the merits as following: good performance (sound source level and main frequency) less affected by hydrostatic pressure, long working lifetime and easy to be carried by deep sea platform system. In this paper, a deep-sea pulse sound source is developed based on high-power electromagnetic pulse. The key basic problems such as high-power pulse circuit, discharge current in coil load, electromagnetic force excited by current and plate vibration characteristics (amplitude and frequency) excited by electromagnetic force in air medium are investigated by means of Comsol multi-physical simulation, high-current testing and high-speed imaging. Through the high-speed imaging of the plate vibration under different hydrostatic pressure conditions, it is found that the amplitude of the plate vibration decreased slightly with the increase of hydrostatic pressure, and the vibration frequency is not affected by hydrostatic pressure, thus verifying the technical feasibility of this type of transducer working in deep water.
2021, 10(2):109-121. DOI: 10.12146/j.issn.2095-3135.20201122002
Abstract:In order to ensure the safety of underwater operation, it’s important to monitor the physiological signals of underwater operators in real time. In this article, we have introduced a real-time physiological signals monitoring system of underwater operation. The proposed system consist of three key modules: (1) the photoelectric sensors were used to collect physiological signals to effectively reduce the influence of water on physiological signal data collection, (2) the data were transmitted wirelessly through underwater acoustic communication technology, which can improve the freedom of underwater operators, (3) the physiological, psychological and early warning analysis parts were integrated on the deck unit. By combining the uploaded physiological information data with historical data for statistical analysis and comparison, higher-level early warning information or alarm information can be decided in real-time. The prototype has been developed and experimented underwater, feasibility and reliability of key modules have been verified.