Complex Marine Environment Research Articles

Alkynyl-Based sp 2 Carbon-Conjugated Covalent Organic Frameworks with Enhanced Uranium Extraction from Seawater by Photoinduced Multiple Effects

Biofouling is a major obstacle to the efficient extraction of uranium from seawater due to the numerous marine microorganisms in the ocean. Herein, we report a novel amidoxime (AO) crystalline cova...

An efficient cylindrical coordinate subgrid parabolic equation model for predicting the power distribution and coverage of radar signals in a complex multi‐scale marine environment

An efficient cylindrical coordinate subgrid parabolic equation model is proposed to predict the power distribution and coverage of radar signals in a complex multi-scale marine environment. The model adopts different grid systems for the multi-scale marine environment including flat sea surface, islands, ships and other elements, and realizes the transformation between grids through spatial mesh refinement technology. For the prediction of radio wave propagation in a large area complex environment, the model can balance the calculation efficiency and accuracy, thus effectively reducing the memory requirement and CPU computing time. In addition, combined with digital map and radar equation, the power distribution and coverage of radar signal in complex multi-scale marine environment are calculated. Numerical results verify the correctness and efficiency of the proposed model.

Study of BiOI/BiOIO3 composite photocatalyst for improved sterilization performance of fluorocarbon resin coating (PEVE)

In today's world, in the complex marine environment, various microorganisms can adhere to the hull surface and cause unavoidable damage to the hull structure. Therefore, improving the antimicrobial performance of surface coatings on ships has become a pressing issue. BiOIO3 is a recently discovered photocatalytic material with certain antimicrobial properties. However, its larger band gap and low photo-generated carrier yield limit its further applications. In this work, we prepared BiOIO3, BiOI and BiOI/BiOIO3 composite photocatalysts. The prepared photocatalytic materials are used to improve the sterilization performance of fluorocarbon resin coatings. Under the irradiation of a xenon lamp, sterilization tests were performed with coatings modified with the above materials. The experimental results showed that the sterilization performance of the coatings modified by photocatalyst was substantially improved. Simultaneously, the mechanism of the sterilization performance of coatings modified with composite photocatalysts was also investigated.

Seabed seismic wave simulation by finite difference time domain scheme in marine environment with complex seafloor topography

The studying of the excitation and propagation characteristics of seabed seismic waves in a complex marine environment is of great significance in investigating seafloor physical and mechanical properties and exploring resources. At present, the research of time-domain seabed seismic waves is mostly restricted in a marine environment with horizontal stratification, but the actual geological conditions of seafloor are relatively complex, and the numerical solutions obtained under ideal assumption are quite different from those in an actual complex environment. To master the propagation characteristics of seabed seismic wave in the environment that is closer to the actual one, a complex and long range model including layers of water, soft mud and bedrocks is designed in the paper, where non-horizontal seafloor topography with a dipping and uplifting structure is considered. The staggered-grid finite difference method with 2nd-order accuracy in time and 10th-order accuracy in space is used to simulate the seabed seismic waves under such a complex marine environment. Meanwhile, multi axial perfectly matched layer is used as an artificial boundary condition to ensure the numerical long-term stability in a liquid-solid medium. Considering the dipping structure, the acoustic signals excited by sources at different positions of the model are compared to determine the favorable style of source excitation for Scholte interface wave receiving. Through the time-domain waveform of the calculated acoustic field, the propagation characteristics of the seabed seismic wave in the complex marine environment are analyzed. The results show that the staggered-grid finite difference method with high-order spatial accuracy can improve the dispersion problem in numerical calculation. The multi-axial perfectly matched layer used to replace the traditional perfectly matched layer can solve the instability problem in the numerical simulation of acoustic field in liquid-solid media for a long range. Through the comparison among the acoustic signal amplitudes excited by sources at different positions, a better performance can be achieved when the source-receiver is placed along the updip direction. In such a case, the acoustic signal is stronger, which is more advantageous to receive and analyze the Scholte interface wave. In the complex seabed model with a dipping and uplifting structure, the uplift of seafloor bedrock changes the propagation direction of Scholte wave, which makes it possible to receive Scholte wave at shallower depth.

Single Ping Filtering of Multi-Beam Sounding Data Based on Alpha Shapes

AbstractFrom the standpoint of complex marine environments relative to underwater acoustic signal propagation, the application of multi-beam systems for the filtering and processing of multi-beam sounding data is critical. However, currently existing automatic filtering methods estimate data, which involve several calculations and require the respective computer to possess significant processing capabilities. In this study, raw data are measured using an interferometer multi-beam echo sounder, and the characteristics of the noise data are analyzed. The noise data are discontinuous; however, accurate data can be approximated as a continuous distribution. Under the assumption of continuous underwater terrain, in consideration of a circle of the appropriate radius rolling on the terrain profile, the continuous underwater terrain data can be extracted from the raw data by means of the alpha-shapes algorithm. Finally, on the basis of the measured data in a sail trial, the effectiveness of the proposed algorithm is verified.

Unmanned surface vessel obstacle avoidance with prior knowledge‐based reward shaping

AbstractAutonomous obstacle avoidance control of unmanned surface vessels (USVs) in complex marine environments is always fundamental for its scientific search and detection. Traditional methods usually model USV motion and environments in a mathematical way that needs perceptual information. Unfortunately, it is difficult to provide sufficient perceptual information due to complex marine environments, resulting in inaccurate modeling. Reinforcement learning has recently enjoyed increasing popularity in the problem of obstacle avoidance since it can settle problems by partially observable environment information. However, the autonomous USV obstacle avoidance using reinforcement learning is still facing the challenge of designing appropriate reward functions under complex marine environments. To address these issues, we propose a prior knowledge‐based USV reinforcement learning obstacle avoidance algorithm. In this algorithm, an actor‐critic network is used as the main architecture of the algorithm, and prior knowledge‐based reward shaping used to design relevant reward function for USV obstacle avoidance. A standard USV based on a visual sensor is designed, and the state input of the algorithm is through USV's front vision sensor. We conducted simulation experiments and results prove that our algorithm can effectively converge, and USV achieves high velocity and low collision rate in the complex marine environment.

A New Method for Ship Control Valve Overload Protection in Complex Marine Environments

Xie, Y.; Li, C.; Wang, Y., and Dong, Q., 2020. A new method for ship control valve overload protection in complex marine environments. In: Hu, C. and Cai, M. (eds.), Geo-informatics and Oceanography. Journal of Coastal Research, Special Issue No. 105, pp. 228–232. Coconut Creek (Florida), ISSN 0749-0208.The marine environment is complex and always changing, which brings additional load to ship's control valves. When subjected to additional load, the ship's control valves can break or operate abnormally, resulting in valve external leakage, which might lead to a marine environmental disaster. To avoid potential environmental pollution, control valves should have overload protection. To address the shortcomings of traditional valve overload protection methods, an all-electronic overload protection method is proposed. The method is based on the principle that the valve actuator always works to overcome the load torque, and the electromagnetic torque of the actuator motor has a one-to-one correspondence to the valve load. Therefore, calculating the actuator load based on the electromagnetic torque of the motor enables the valve to determine its load. Based on the load, the valve controller's built-in diagnostic program can achieve self-diagnosis and instigate emergency overload protection actions. This all-electronic overload protection has strong anti-interference ability, is not subject to the wear and fatigue of mechanical parts, and has an ability to withstand large loads. The experimental results demonstrate the effectiveness of the proposed overload protection method.

Distributed guidance-based formation control of marine vehicles under switching topology

Because of the limited and unreliable communication topology in complex marine environment, the formation control of marine vehicles under switching topology is investigated in this paper, whereas the most previous works for marine formation focused on the fixed communication topology. In order to simplify the formation control design, a novel distributed guidance system, rather than the traditional distributed control system, is established based on leader-follower strategy only using a portion of communication links. To address the problem of input saturation of marine vehicle, the model predictive control is therefore employed to design the marine formation controller; furthermore, the predictive mechanism allows model predictive control to prevent the constraint violation in advance, which brings advantages against the large inertia of ship motion. Both formation tracking control and formation regulation control are studied herein. For application of formation tracking control of marine vehicles, i.e., the time-varying reference signal, the formation control can be realized under switching topology with the condition that the communication topology contains a directed spanning tree. For application of formation regulation control of marine vehicles, i.e., the constant reference signal, the formation control can be realized under switching topology with a relative milder condition that the union of communication topology contains a directed spanning tree. Multiple simulations are included to show the effectiveness of the presented distributed guidance-based MPC formation controllers.

Joint User-Subcarrier Pairing and Power Allocation for Uplink ACO-OFDM-NOMA Underwater Visible Light Communication Systems

Underwater visible light communication (UVLC) is a promising technique to provide high-speed data transmission in the water. Since it is quite difficult to supply power to the underwater devices in the complex and severe marine environment, energy consumption would be a main consideration in the practical deployment of UVLC system. In this article, we investigate an asymmetric clipped optical orthogonal frequency division multiplexing and non-orthogonal multiple access (ACO-OFDM-NOMA) scheme for the uplink UVLC system to realize energy saving and support massive device connectivity. A mixed integer nonlinear programming problem of jointly optimizing the user-subcarrier pairing and power allocation is formulated to maximize the system utility. To tackle this problem, we propose a low-complexity iterative algorithm to obtain an optimal solution. Simulation results verify that the proposed algorithm converges quickly, and the uplink ACO-OFDM-NOMA system using the proposed algorithm has better utility compared to the uplink ACO-OFDM-NOMA system using the greedy algorithm and the traditional uplink ACO-OFDM access (ACO-OFDMA) system.

Ultra-wideband underwater acoustic transducer with a gradient impedance matching layer

In complex marine environments, high-efficiency, wideband and high-frequency transducers can improve the imaging resolution of sonar systems and there is an urgent need for the detection and identification of seafloor landforms. The bandwidth expansion of the traditional transducer is usually achieved by using a single or multiple uniformly matching layers, but it cannot meet the ultra-wideband performance requirement of the transducer in water because it fails to achieve an optimal acoustic impedance transition. Based on theoretical analysis of sound transmission, analytical calculation, and finite element simulation, an acoustic gradient impedance matching layer transducer is studied. We propose an acoustic gradient impedance matching layer material that largely compensates for this shortcoming. This gradient matching layer material has the characteristic that the acoustic impedance decreases in the direction of thickness according to an exponential law z(x)=z1e2αx. It is implemented by filling the specific binary mixture into the conical cavities structure produced by 3D accurately printing. Experimental testing results show that the transducer's transmitting voltage response bandwidth (−3dB) reaches 110%.

Secondary Marine Aerosol Plays a Dominant Role over Primary Sea Spray Aerosol in Cloud Formation.

Marine aerosols play a critical role in impacting our climate by seeding clouds over the oceans. Despite decades of research, key questions remain regarding how ocean biological activity changes the composition and cloud-forming ability of marine aerosols. This uncertainty largely stems from an inability to independently determine the cloud-forming potential of primary versus secondary marine aerosols in complex marine environments. Here, we present results from a unique 6-day mesocosm experiment where we isolated and studied the cloud-forming potential of primary and secondary marine aerosols over the course of a phytoplankton bloom. The results from this controlled laboratory approach can finally explain the long-observed changes in the hygroscopic properties of marine aerosols observed in previous field studies. We find that secondary marine aerosols, consisting of sulfate, ammonium, and organic species, correlate with phytoplankton biomass (i.e., chlorophyll-a concentrations), whereas primary sea spray aerosol does not. Importantly, the measured CCN activity (κapp = 0.59 ± 0.04) of the resulting secondary marine aerosol matches the values observed in previous field studies, suggesting secondary marine aerosols play the dominant role in affecting marine cloud properties. Given these findings, future studies must address the physical, chemical, and biological factors controlling the emissions of volatile organic compounds that form secondary marine aerosol, with the goal of improving model predictions of ocean biology on atmospheric chemistry, clouds, and climate.

Durable super-hydrophobic PDMS@SiO2@WS2 sponge for efficient oil/water separation in complex marine environment

The robust and eco-friendly super-hydrophobic sponge with remarkable performances has been potential adsorption material for the treatment of offshore oil spills. In this work, the durable PDMS@SiO2@WS2 sponge was fabricated via a green and facile one-step dipping method. The mixed tungsten disulfide (WS2) microparticles and hydrophobic SiO2 nanoparticles were immobilized on the sponge by non-toxic polydimethylsiloxane (PDMS) glue tier, which featured the hierarchical structure and extreme water repellency with the water contact angle of 158.8±1.4°. The obtained PDMS@SiO2@WS2 sponge exhibits high oil adsorption capacity with 12-112 times of its own weight, and oil/water selectivity with separation efficiency over 99.85%. Notably, when subjected to the complex marine environment including high temperature, corrosive condition, insolation, and strong wind and waves, the modified sponge can maintain sable super-hydrophobicity with water contact angle over 150°. Moreover, it possesses superior mechanical stability for sustainable reusability and oil recovery. The sponge fabricated by non-toxic modifiers along with its sable super-hydrophobicity in complex marine environment makes it a potential material for practical applications.

Experimental results of the cooperative operation of autonomous surface vehicles navigating in complex marine environment

Experimental results are presented of the cooperative operation of two maritime autonomous surface vehicles (ASVs) executing a pre-defined task in a complex marine environment. The ASVs are equipped with algorithms for motion-planning, path-following and motion control, where the motion-planning algorithm is based in the angle-guidance fast marching square method, the path-planning module is based in the vector-field path-following method and the controller is a PID. The ASVs are two self-propelled models of 2.5 m and 3.2 m length instrumented with several sensors, actuators and communication unit, such as, inertial measurement units, Global positioning system, anemometers, accelerometers, inclinometers, DC motors and Wi-Fi communication. To monitor and command the ASVs, a real-time program was coded in LabVIEW 2018®. Finally, in order to validate the developed system, experimental tests were carried out in an open-door pool with low wind conditions, and from these experiments good capabilities of the system were found.

Correction of water column height variation on 2D grid high-resolution seismic data using dGPS based methodology

Variations in the physical properties of water column usually impede exact water column height correction on high-resolution seismic data, especially when the data are collected in shallow marine environments. Changes in water column properties can be attributed to variation in tides and currents, wind-generated swells, long and short amplitude wave-fronts, or variation in salinity and water temperature. Likewise, the proper motion of the vessel complicates the determinability of the water column height. This study provides a less time-consuming and precise differential Global Positioning System based methodology that can be applied to most types of high-resolution seismic data in order to significantly improve the tracking and quality of deduced geological interpretations on smaller depth scales. The methodology was tested on geophysical profiles obtained from the German sector of the North Sea. The focus here was to identify, distinguish and classify various sub-surface sedimentary structures in a stratigraphically highly complex shallow marine environment on decimeter small-scale. After applying the correction to the profiles, the sea floor, in general, occurs 1.1 to 3.4 m (mean of 2.2 m) deeper than the uncorrected profiles and is consistent with the sea floor from published tide corrected bathymetry data. The corrected seismic profiles were used in plotting the depth of the base of Holocene channel structures and to define their gradients. The applied correction methodology was also crucial in glacial and post-glacial valley features distinction, across profile correlation and establishing structural and stratigraphic framework of the study area.

The effect of rolling motion on flow resistance and heat transfer in narrow rectangular channel under natural circulation

With the increase demand for energy for ocean development, small reactors with natural circulation as the normal operating conditions are increasingly becoming an important energy supply option. The complex marine environment, such as fluctuations in the flow rate of coolant in nuclear reactor due to wind and waves, affects the flow resistance and heat transfer characteristic of the coolant, threatening the safety of the reactor. The current study performs one-dimensional and three-dimensional code coupling method to analyze the effect on flow resistance and heat transfer in a narrow rectangular channel under rolling condition. In addition to the influence of flow pulsation which has been considered universally by past studies, it was found that transverse mixed convection caused by external force fields, and boundary layer acceleration caused by the ununiform distribution of cross-section pressure, also have an impact on flow resistance and heat transfer. Unlike the flow pulsation, which has no effect on the time-average flow resistance and heat transfer, the transverse mixed convection increases the time-average flow resistance while also enhances the time-averaged heat transfer. Boundary layer acceleration occurs at lower Reynold number (Re≈800), and results in a steep increase in flow resistance, while the effect on heat transfer is not so significant. The relative strength of the three effects is impacted by the rolling parameters maximum rolling angle θ0 and period t0. The flow pulsation effect increases with increasing θ0 and decreasing period, while the mixed convection effect increases with increasing θ0.

Finite Element Analysis for the Stability of Marine Winch System

Li, S. and Liu, Y., 2020. Finite element analysis for the stability of marine winch system. In: Al-Tarawneh, O. and Megahed, A. (eds.), Recent Developments of Port, Marine, and Ocean Engineering. Journal of Coastal Research, Special Issue No. 110, pp. 175–178. Coconut Creek (Florida), ISSN 0749-0208.The marine winch system is the core of marine towing. The stability of this system is of great significance to the stability and safety of complex marine environments and offshore platforms. Based on the design and analysis of the marine winch system, this paper performs a simulation analysis for the strength and stiffness of the drum of the winch system using the ANSYS finite element software. Also, it explores the active heave compensation function of this system. The research results show that the stability of the marine winch system is controlled by the main drive system, rolling gear train and cable routing system; after analyzing the drum of the marine winch system by ANSYS finite element analysis software, it's found that the overall strength of the mechanical drum meets the requirements, and the maximum stress value on the surface of the marine winch mechanical drum was 159.48MPa. The research findings provide a theoretical basis for the stability design of large marine winch systems.

Numerical simulation of boiling two-phase flow in the subchannel under static state and rolling motion

The design and operation of the offshore floating reactor cannot follow those of the land-based reactor affected by the complex marine environment. This study investigated subcooled flow boiling in the subchannel under static state and rolling motion numerically. Clear interfaces between the vapor and liquid phases are obtained.The numerical result of void fraction deviates from the experimental value by 11.9% at a given elevation. The transverse flow fields and phase-distributions are centrosymmetric under static state. The vapor only exists near the rod surfaces under static state, which is in the shape of “H”. Under rolling motion, flow fields and phase distributions vary periodically with time and the positions of the subchannel, which are significantly different from static state. At the same elevation, the time-averaged void fraction under roll motion is slightly higher than that under static state.

A review on development of offshore wind energy conversion system

Wind energy conversion system, aiming to convert mechanical energy of air flow into electrical energy has been widely concerned in recent decades. According to the installation sites, the wind energy conversion system can be divided into land-based wind conversion system and offshore wind energy conversion (OWEC) system. Compared to land-based wind energy technology, although OWEC started later, it has attracted more attentions due to its significant advantages in sufficient wind energy, low wind shear, high power output and low land occupancy rate. In this paper, the principle of wind energy conversion and the development status of offshore wind power in the world are briefly introduced at first. And then, the advantages and disadvantages of several offshore wind energy device (OWED), such as horizontal axis OWED, vertical axis OWED and cross axis OWED are compared. Subsequently, several major constraints, such as complex marine environment, deep-sea power transmission and expensive cost of equipment installation faced by offshore wind conversion technology are presented and comprehensively analysed. Finally, based on the summary and analysis of some emerging technologies and the current situation of offshore wind energy utilization, the development trend of offshore wind power is envisioned. In the future, it is expected to witness multi-energy complementary, key component optimization and intelligent control strategy for smooth energy generation of offshore wind power systems.

Parallel Three-Branch Correlation Filters for Complex Marine Environmental Object Tracking Based on a Confidence Mechanism.

Marine object tracking is critical for search and rescue activities in the complex marine environment. However, the complex marine environment poses a huge challenge to the effect of tracking, such as the variability of light, the impact of sea waves, the occlusion of other ships, etc. Under these complex marine environmental factors, how to design an efficient dynamic visual tracker to make the results accurate, real time and robust is particularly important. The parallel three-branch correlation filters for complex marine environmental object tracking based on a confidence mechanism is proposed by us. The proposed tracker first detects the appearance change and position change of the object by constructing parallel three-branch correlation filters, which enhances the robustness of the correlation filter model. Through the weighted fusion of response maps, the center position of the object is accurately located. Secondly, the Gaussian-triangle joint distribution is used to replace the original Gaussian distribution in the training phase. Finally, a verification mechanism of confidence metric is embedded in the filter update section to analyze the tracking effect of the current frame, and to update the filter sample from verification result. Thus, a more accurate correlation filter is trained to prevent model drift and achieve a good tracking effect. We found that the effect of various interferences on the filter is effectively reduced by comparing with other trackers. The experiments prove that the proposed tracker can play an outstanding role in the complex marine environment.

The Construction of Sound Speed Field Based on Back Propagation Neural Network in the Global Ocean

The sound speed is a key parameter that affects the underwater acoustic positioning and navigation. Aiming at the high-precision construction of sound speed field in the complex marine environment, this paper proposes a sound speed field model based on back propagation neural network (BPNN) by considering the correlation of learning samples. The method firstly uses measured ocean parameters to construct the temperature and salinity field. Then the spatial position, the temperature and the salinity information are used to construct the global ocean sound speed field based on the back propagation neural network algorithm. During the processing, the learning samples of back propagation neural network are selected based on the correlation between sound speed and distance. The proposed algorithm is validated by the global Argo data as well as compared with the spatial interpolation and the empirical orthogonal function (EOF) algorithm. The results demonstrate that the average root mean squares of the BPNN considering the correlation of learning samples is 0.352 m/s compared to the 1.527 m/s of EOF construction and the 2.661 m/s of spatial interpolation, with an improvement of 76.9% and 86.8%. Therefore, the proposed algorithm can improve the construction accuracy of sound speed field in the complex marine environment.