Real Sea Environment Research Articles

Preparation and application of the water‐based acrylic self‐polishing resin: Good storage stability, good film‐forming matrix of marine antifouling coatings

AbstractIn order to reduce the release of volatile organic compounds (VOCs), it is of great practical significance to develop water‐based self‐polishing antifouling coatings instead of traditional acrylic self‐polishing antifouling coatings. However, when preparing film forming matrix resin emulsions for water‐based antifouling coatings, the use of emulsifiers in large amounts causes film‐forming defects and poor adhesion. Herein, soap‐free emulsion polymerization is utilized to prepare resin emulsions by copolymerization of hydrophilic monomers, lipophilic monomers and polymerizable hydrophilic ionic monomers. The hydrophilic structure can give the water‐based polymer self‐emulsification function to maintain the stability of the emulsion and can promote the fusion between the latex particles by forming hydrogen bonds and coordination bonds, and its connection with the pigments and fillers in the coating can also promote the excellent film formation of the coating. The experimental results show that the water‐based self‐polishing antifouling resin emulsion has good storage stability and compatibility with the pigments and fillers. The coatings formulated using this emulsion as the film‐forming matrix firmly adhered to substrates and displayed satisfactory antifouling performance even after being exposed to a real sea environment for 18 months. This study presents a simple approach for the development of water‐based resin emulsion with good storage stability and good water‐based self‐polishing marine antifouling coatings.

Steel corrosion and critical chloride content in concrete with calcined kaolinite clay, fly ash, and limestone powder under natural and accelerated marine environments

This study aims to investigate steel corrosion and critical chloride content in concrete with calcined kaolinite clay, fly ash, and limestone powder. The chloride diffusion coefficient and compressive strength of concrete, and weight loss of steel were measured after the specimens were exposed to the tidal zone in a real sea environment for 1 and 2 years. The depassivation time of the embedded steel and the critical chloride content of the concrete under an accelerated marine environment were investigated in the laboratory. The test results revealed that the coefficient of chloride diffusion and critical chloride content of concrete and weight loss of steel decreased with increasing calcined kaolinite clay contents. Although utilizing calcined kaolinite clay in concrete mixtures reduced critical chloride content (0.655% by wt. of binder for OPC and 0.573 to 0.427% by wt. of binder for C15 to C45) because of the lower portlandite content, it caused a longer rebar depassivation time (46 days for OPC and 63 to 237 for C15 to C45). The ternary binder systems of cement, calcined clay, and fly ash demonstrated the best overall performances, i.e., the lowest chloride diffusion coefficient (0.29 ×10−12 m2/s) and the highest compressive strength of the concrete (38.7 MPa), and no weight loss of embedded steel at 2 years of exposure.

Study on the correlation between indoor accelerated corrosion testing of concrete epoxy polysiloxane coating and real-sea environmental testing in the East China Sea

In order to reveal the correlation between the accelerated corrosion test of epoxy polysiloxane coating and the real sea environmental test, the real sea environmental test was carried out in the atmosphere and tidal range area of Zhairuoshan Island in the East China Sea, and the multi-factor coupling test I (Cycle of 7-day xenon lamp aging test + 7-day Wetting-drying test) and test II (Cycle of 7-day xenon lamp aging test + 3-day damp heat test + 4-day salt spray test) were designed with reference to the environment of the East China Sea. The correlation between indoor accelerated corrosion test and real sea environmental test was analyzed by using Grey Relation Analysis, Spearman's rank correlation coefficient and Acceleration factor conversion method. The results show that both the indoor accelerated corrosion test and the real sea environmental test have corrosive effects on the epoxy polysiloxane coating of concrete. In the indoor accelerated corrosion test, it was found that the Wetting-drying test caused the highest loss of light rate. In the real sea environmental test, the loss of light rate of the coating in the atmosphere is higher than that in the tidal area, and the color difference is slightly lower. When the loss of light rate is used as the criterion, the grey correlation coefficient between the multi-factor coupling test I and the tidal range test is 0.63, and the maximum acceleration factor during the test is 5.3, indicating a good correlation between the two tests. Through this study, an effective indoor accelerated corrosion test method with good correlation and acceleration characteristics to the loss of light rate of concrete epoxy polysiloxane coating in a real sea environment was obtained.

Interfacial Bond Properties of Underwater Concrete Coated with Bisphenol A Epoxy Resins.

This study investigated changes in the interfacial properties of epoxy-coated concrete exposed to various conditions, regarding the epoxy type, coating equipment, and exposure environment and period. The measured coating thickness and pull-off bond strength exhibited diverse trends, depending on the exposure period and conditions. In the real sea (RS) environment, the average bond strengths for bisphenol A (BPA) (E1), BPA with zinc powder (E2), and BPA with cresyl glycidyl ether (E3) were 1.26, 1.93, and 1.92 MPa, respectively. The coating method did not significantly affect the measured coating thickness and strength values. The conventional roller (D1) exhibited the highest thickness variation, with a value of 214.45 μm. The RS condition significantly increased the coating thickness (34% to 158%) compared to the tap water (TW) condition. The exposure conditions had little impact on bond strength except for E3, which showed an increased strength (2.71 MPa) over 7-91 days, especially under RS conditions, while E2 remained constant at approximately 1.82 MPa. This study offers insights into factors influencing marine concrete coating performance and discusses limitations and future work.

Sualtında Birleştirilen AH36 Gemi Sacının Mikro Yapı ve Mekanik Özelliklerinin İncelenmesi

Bu çalışmada, örtülü elektrot ark kaynağı yöntemi ile yerli E6013 rutil elektrotlar (GeKaTec UW E6013) kullanılarak gemi imalat sektöründe; gemilerin gövdesinde ve tankların yapımında yaygın olarak kullanılan AH36 çelik plakaları su altında alın alına birleştirilmiştir. Kaynak işlemleri gerçek deniz ortamında 4 metrelik bir derinlikte uzman sanayi dalgıçları tarafından gerçekleştirilmiştir. Plakalar ilk olarak AWS D3.6 standardının gerekliliklerine uygun olarak tahribatsız muayene testlerine tabi tutulmuştur. Daha sonra su altında birleştirilen kaynaklı plakaların mekanik özelliklerini belirlemek amacıyla sertlik, çentik darbe, eğme ve çekme testleri uygulanmış olup, sonuçlar kaynak bölgesinde meydana gelen mikro yapısal dönüşümlerle birlikte yorumlanmıştır.

Effect of bioluminescence on the performance of an underwater optical wireless communication channel

The performance of an underwater wireless optical communication channel (UWOC) is affected by the ambient noise in the water medium. However, no major studies have estimated the spectral bioluminescence upwelling radiance (BLu) numerically with the inputs of measured bioluminescence potential (BP) in oceanic conditions. This study presents a numerical model to estimate the BLu in open ocean and coastal waters and to investigate the UWOC channel performance in terms of the bit error rate (BER) in presence of bioluminescence using Monte Carlo numerical technique. The simulation results suggested that the BER performance degrades in the presence of bioluminescence and can be improved with a narrower receiver FOV. Further, the impact of bioluminescence on the BER performance of the UWOC system at different operational depths is investigated under typical system specifications (APD/PMT, FOV, and receiver aperture). The simulation results showed that BER at different operational depths is more sensitive in open ocean waters than in coastal turbid water with the bioluminescence signal. The results demonstrate that the PMT improves the UWOC channel performance better than the APD. Besides, these results revealed that the BP stimulation at multiple depths deteriorates the BER performance heavily in comparison to the BP stimulation at single depth in the real sea environment. The results presented in this study provide valuable insights and information for accurate design and development of the UWOC system for the enhanced bioluminescence background noise conditions.

Sea trials of Sigma wave energy converter – Power and efficiency

Sigma Energy has performed its foremost prototype tests of a scaled wave energy converter (WEC) in a real sea environment. The prototype was a point absorber with a circular buoy, a mechanical power take-off (PTO) system and a counterweight, moored to the seabed as a tension leg platform with three equal tendons. In these extensive experiments, numerous device characteristics were measured and analysed. The paper presents these sea trials, focusing on the power and efficiency of the device. The power has been calculated from the data recorded at 6 locations along the PTO system. In that way, a decay of capture width ratio (CWR) from the one absorbed from the waves to the one delivered to the electrical network was found and analysed. Also, losses of the main elements of the PTO system were defined, calculated and ranked. Optimal sea and loading conditions were indicated, giving the maximal values of the efficiencies. These optimal conditions are physically explained, and the challenges in their prediction are discussed. In addition to the results of numerous 20-min tests, the paper presents the long-term average values of the efficiencies, covering all the tests performed, and accounting for the probabilities of different sea conditions.

Sea trials of Sigma wave energy converter – slacking and snapping of TLP mooring lines

Sigma Energy has performed its foremost prototype tests of scaled wave energy converter in a real sea environment. The prototype was a point absorber with a cylindrical buoy, a mechanical power take-off system with a counterweight, moored to the seabed as a tension leg platform (TLP) with three equal tendons. In these extensive experiments, numerous device characteristics were measured and analysed. The present paper focuses on the dynamic forces in the mooring lines, and some unexpected and rare data obtained. It is well known that TLP tendons are prone to a brief loss of tension (the slacking) and that, after such events, high snapping forces of short duration can arise. Partly by intention, and partly due to underestimation of the dynamical forces, several such slacking-snapping incidents were recorded during the experiments. In some severe storms, the snapping forces were up to six times higher than the tendon pretension. The paper presents several recordings of dynamic forces and platform motion during these critical events. It analysis them, and gives a typical scenario under which they occur. It gives also some theoretical explanations, and numerical predictions of dynamical tendon forces, with their comparison to the experimental results.

Modeling ocean waves and investigation of oceanic wave spectra for wave-to-wire system

The oceanic wave energy is a profuse and sustainable source of clean energy but its enourmous potential is under-exploited. Even though the idea of energy harnessing from oceanic waves is not new, the developments in wave energy conversion technologies are still in an embryonic stage. In most of the studies associated to wave-to-wire systems, oceanic waves are taken as regular waves with a fixed amplitude and a fixed frequency. The main area of focus of the previous studies includes the different conversion stages of the wave-to-wire system, particularly the mechanical, and the electrical conversion stage of the energy and the modeling of oceanic waves for such studies remained neglected in such studies. However, the actual oceanic waves can be presented with the sum of various frequencies to show a specific sea-states with significant wave height and the peak period as the main characterizing parameters. In this study, detailed mathematical modeling of oceanic waves is offered and various wave spectra are investigated for their application in wave-to-wire-based system studies. The best-suited wave spectra are identified parametrically and thereafter it is used for the generation of wave elevation time series in the proposed method presented in this study. The generated time series are appliesd in wave-to-wire systems for the investigation of wave energy conversion devices to mimic the real sea environment. Based on inverse fast Fourier transforms, oceanic wave elevation time series are determined which will be acting as input data for any of the wave energy converters deployed for the capturing of useable energy.

Effects of spanwise length and side-wall boundary condition on plunging breaking waves

A systematic study of the effect of the spanwise length and the sidewall boundary condition of a numerical wave flume (NWF) on direct numerical simulation of a plunging breaking wave is performed. To deal with the topological changes of free surfaces, a high-fidelity numerical model is employed to solve the Navier–Stokes equations together with the volume of fluid function. After verification by two-dimensional (2D) simulations of a plunging breaker on a sloping beach, ten NWFs with different spanwise extents and sidewall boundary conditions are studied. Special attention is devoted to the three-dimensionality of the plunging breaker. Compared with three-dimensional (3D) models, the 2D model accurately reproduces the dynamics of a breaking solitary wave in the early stage, but it is inadequate for the study of the post-breaking process. For a 3D NWF with nonslip sidewall boundary condition, the wave domain can be divided into two regions with different physical properties. In the near-wall region, the nonslip boundary condition on the sidewall plays a crucial role in the wave hydrodynamics, while in the central region, the properties of the breaking wave are similar to those for the periodic boundary condition, which provide a closer representation of the real sea environment. The spanwise length of the NWF plays only a minor role in simulations under the periodic boundary condition. Furthermore, lateral boundaries and spanwise length show more influences on a plunging breaker with larger incident wave steepness. This study provides valuable support for the design of numerical simulations of wave breaking.

CFD-Modified Potential Simulation on Seakeeping Performance of a Barge

This study proposes a computational fluid dynamics (CFD)-modified potential (CMP) model. This hybrid model uses linear potential theory with a corrected damping ratio obtained from CFD simulations to analyze the seakeeping performance of a small vessel. According to the analysis procedure of the proposed model, a motion analysis, including the prediction of the roll and pitch damping ratio of a small barge, was conducted; to verify reliability; the results were compared to those of an experiment performed in a physical tank. The relative errors in the experiment for peak amplitude in the roll motion response amplitude operators (RAOs) using the CMP model were relatively small, whereas those obtained from only the potential analysis were large errors in all three conventionally used roll-damping ratios. In addition, the computational time consumed by the CMP model was longer than that consumed by the potential theory but faster than the full CFD simulation for all wave conditions. Subsequently, based on the motion analysis results, the seakeeping performance was evaluated in a real sea environment, and the results on the single significant amplitude (SSA) were discussed through comparison with the results of the potential analysis and experiment.

Application of functional polymer materials for marine anti-fouling

Marine organisms adsorb and grow on the surface of underwater facilities. This process, known as fouling, has a detrimental impact on marine shipping and development. Currently, in order to prevent marine biofouling, the most efficient and economical method is the application of antifouling coatings that synthesized by a diverse of different functional polymer materials. For this reason, this research will introduce the progress in five types of functional polymer materials, which are polymers with catechol groups, polysulfide-based polymers, polymer quaternary ammonium salts, hydrogels and silicone resin. Due to different functional groups properties as well as mechanisms of action, they have their own advantages in the application of antifouling coatings. Meanwhile, the future trend of antifouling coatings development and their application in real sea environment are prospected.

Design of an Optimal Testbed for Acoustic Tags: Test Case for Marine Megafauna

Underwater acoustic technologies are a key component for exploring the behavior of marine fauna such as sea turtles, sharks, and seals. The animals are marked with acoustic devices (tags) that periodically emit signals encoding the device’s ID along with sensor data such as depth, temperature, or the dominant acceleration axis - data that is collected by a network of deployed receivers. In this work, we aim to optimize the locations of receivers for best tracking of acoustically tagged marine fauna, and provide a test case with tags suitable for megafauna tracking. The outcomes of such tracking allows the evaluation of the animals’ motion patterns, their hours of activity, and their social interactions. In particular, we focus on how to determine the receivers’ deployment positions to maximize the coverage area in which the tagged animals can be tracked. For example, an overly-condensed deployment may not allow accurate tracking, whereas a sparse one, may lead to a small coverage area due to too few detections. We formalize the question of where to best deploy the receivers as a non-convex constraint optimization problem that takes into account the local environment and the specifications of the tags, and offer a sub-optimal, low-complexity solution that can be applied to large testbeds. Numerical investigation for three stimulated sea environments shows that our proposed method is able to increase the localization coverage area by 30%, and results from a test case experiment demonstrate similar performance in a real sea environment. We share the implementation of our work to help researchers set up their own acoustic observatory.

Experimental demonstration on long-range time-reversal multiple-input/multiple-output underwater acoustic communication over tens of kbps in 12.5 km range

In this paper, the adaptive time reversal (ATR) technique combined with a single channel decision feedback equalizer (DFE) is applied to an at-sea experiment of the underwater acoustic multiple-input/multiple-output (MIMO) communication utilizing the signal bandwidth of 4.5–8.5 kHz over the distance of 12.5 km. This paper focuses on the demonstration of the effectiveness of the spatial division multiplexing MIMO using ATR-DFE schemes in time-varying real sea environment, and how much the communication rate could be achieved, with changing the signal parameters. We report that the communication quality is dependent on the duration from the channel probing for ATR process to signal reception, and we found that the output signal-to-noise ratio of the demodulated results highly correlated to the temporal coherence of the acoustic channel. Finally, the relationship between the effective data rate and the bit error rate is evaluated. As a result, the achievable data rate in the experiment of this study would be a remarkable considering the distance of the communication.

Marine environment induced failure of FRP composites used in maritime transport

Fiber reinforced polymer (FRP) composites are being extensively considered for construction of ships and marine structures. Due to harsh environmental operational conditions, failure prediction of such structures is an imperative in this industry sector. This paper presents the final results of a 2-year research of real marine environment induced changes of mechanical properties in FRP composites.Realistic environmental input parameters for structural modeling of marine structures are crucial and can be obtained by conducting tests in real sea environment for prolonged periods, as opposed to usual accelerated laboratory experiments. In this research, samples of epoxy/glass and polyester/glass with various fiber layout configurations have been submerged under the sea for periods of 6, 12 and 24 months. An analysis of mass changes, marine microbiology growth, tensile strength and morphological structures of the coupons was performed and compared with samples exposed to room environment.All samples exhibited an increase in mass due to seawater absorption and microorganism growth in the organic resins (matrix). The tensile strength loss variation through the periods of submersion showed a correlation with the fiber layout configuration. The results of optical and scanning electron microscopical investigation indicated significant matrix morphological changes primarily due to salt crystal formation and the impact of sea microorganisms embedding in and attaching to the resin.The outcome of this research will be the basis for a set of realistic input parameters for a failure analysis numerical tool currently in development that can be applied for life-time behavior predictions of marine structures.

Deep learning method for 3-DOF motion prediction of unmanned surface vehicles based on real sea maneuverability test

Motion prediction in a real sea area is a relatively difficult problem due to the lack of reliable measurement of the environment and an accurate model of ship motion under external disturbance. A deep learning method is applied in this study for the modeling of 3-DOF motion prediction under a real sea environment with the influence of currents and waves. The network with angle feature and the network with trigonometric feature are validated for the identification of the influence of the environment regarding winds, waves, and currents, in which the selection of activation function is further discussed. The developed method is validated by learning the data generated through the turning test of JARI-USV in a real sea area in Rizhao, Shandong. Analysis on the turning radius and the drift distance of the integrated track shows maximum relative errors of 5.44% and 9.09%, and the derived drift angle has a maximum absolute error of 4.84°. The prediction results verify the ability of the designed network to capture the environment influence on ship motion, as well as the turning feature of the ship itself from the maneuvering test data in a real sea trial.

Failure analysis of FRP composites exposed to real marine environment

Fiber reinforced polymer (FRP) composites find ever growing application possibilities in marine structures. Due to harsh environmental operational conditions, failure prediction of such structures is an imperative in this industry sector. For this reason, samples of epoxy/glass and polyester/glass with various fiber layout configurations have been submerged under the sea for prolonged periods (6 and 12 months). On contrary to usual accelerated laboratory experiments, these type of tests in real sea environment and for prolonged periods are rarely done. They are useful to obtain more realistic environmental input parameters for structural modeling of marine structures. Changes in mass, marine microbiology growth, tensile strength and morphological structures were analyzed after submersion and compared with samples exposed to room environment. All samples exhibited an increase in mass due to seawater absorption and microorganism growth in the organic resins used as matrix materials. The dynamic and level of decrease in tensile strength showed dependency on the fiber layout configuration. Optical and scanning electron microscopical investigation showed significant matrix morphological changes primarily due to salt crystal formation and the impact of sea microorganisms embedding in the resin. Results of this experimental work will be used as realistic input parameters for subsequent failure analysis numerical tool that can be applied for life-time behavior predictions of marine structures.

Effect of Time-Real Marine Environment Exposure on the Mechanical Behavior of FRP Composites

Fiber reinforced polymer (FRP) composites coupons were exposed to real sea environment to assess the influence on the mechanical behavior of composite materials used in the construction of marine structures. Real-life sea environment conditions were opted for instead of the more common simulated and laboratory versions of seawater in the attempt to obtain more realistic structural modeling environmental input design parameters for marine structures. Exposure was performed over prolonged time span instead of the usual accelerated tests. Epoxy and polyester resins, reinforced with glass fibers in three fiber layout configurations, were used to manufacture standardized tensile testing coupons. Mass changes due to seawater absorption, microorganism growth, changes in tensile strength (standard tensile tests), and surface morphology of the coupons were evaluated after 6- and 12-month long periods of submersion in the sea in the Rijeka bay, Croatia. All specimens showed mass increase due to water absorption and growth of attached algae and sea microorganisms. Various levels of reduction in tensile strength, depending on the fiber layout configurations, were observed. Significant changes in the matrix material structure were noticed, effectively producing “voids”. Based on these results, sustainability of FRP composites in marine environment is addressed and discussed.

A Study on the Selective Guidance Scheme for Remote/Autonomous Retrieval of Underwater Platform

The path guidance method is one of important technologies for autonomous navigation system. The localization errors in structured environments may bring about the path-following error; it can be caused the underwater platform such as AUV collision with a structure and the path generation failure. In this paper, the selective guidance method is proposed to solve these guidance problems. The suggested method optionally used both the LOS guidance and steering control in direction of cross-track error. Generally, the AUV used the LOS guidance method for steering control. However, the AUV conducts the steering control in direction of cross-track error if the path error is bigger than threshold value (turning radius of AUV). The proposed method was verified by comparing with the conventional LOS guidance method at real sea environment, and it showed the satisfactory path-following performance near the underwater structure.

Active Sonar Target Classification with Power-Normalized Cepstral Coefficients and Convolutional Neural Network

Detection and classification of unidentified underwater targets maneuvering in complex underwater environments are critical for active sonar systems. In previous studies, many detection methods were applied to separate targets from the clutter using signals that exceed a preset threshold determined by the sonar console operator. This is because the high signal-to-noise ratio target has enough feature vector components to separate. However, in a real environment, the signal-to-noise ratio of the received target does not always exceed the threshold. Therefore, a target detection algorithm for various target signal-to-noise ratio environments is required; strong clutter energy can lead to false detection, while weak target signals reduce the probability of detection. It also uses long pulse repetition intervals for long-range detection and high ambient noise, requiring classification processing for each ping without accumulating pings. In this study, a target classification algorithm is proposed that can be applied to signals in real underwater environments above the noise level without a threshold set by the sonar console operator, and the classification performance of the algorithm is verified. The active sonar for long-range target detection has low-resolution data; thus, feature vector extraction algorithms are required. Feature vectors are extracted from the experimental data using Power-Normalized Cepstral Coefficients for target classification. Feature vectors are also extracted with Mel-Frequency Cepstral Coefficients and compared with the proposed algorithm. A convolutional neural network was employed as the classifier. In addition, the proposed algorithm is to be compared with the result of target classification using a spectrogram and convolutional neural network. Experimental data were obtained using a hull-mounted active sonar system operating on a Korean naval ship in the East Sea of South Korea and a real maneuvering underwater target. From the experimental data with 29 pings, we extracted 361 target and 3351 clutter data. It is difficult to collect real underwater target data from the real sea environment. Therefore, the number of target data was increased using the data augmentation technique. Eighty percent of the data was used for training and the rest was used for testing. Accuracy value curves and classification rate tables are presented for performance analysis and discussion. Results showed that the proposed algorithm has a higher classification rate than Mel-Frequency Cepstral Coefficients without affecting the target classification by the signal level. Additionally, the obtained results showed that target classification is possible within one ping data without any ping accumulation.