Real Marine Environment Research Articles

Correlation between the Compressive, Tensile Strength of Old Concrete under Marine Environment and Prediction of Long-Term Strength

Compressive strength and tensile strength are important mechanical properties of concrete. The long-term strength of concrete under real service environment is an important parameter when evaluating existing buildings, which should also be properly considered in structural design. In this study, the relationship between compressive and splitting tensile strength of old concrete existing for long period under marine environment was investigated. At a deserted harbour, concrete cores samples were drilled by pairs in site. For each pair of samples, the two cores were drilled from the adjacent location and conducted to compressive, splitting tensile test, respectively. 48 compressive and splitting tensile strengths were finally obtained. From the test results, tensile strength presents general uptrend with compressive strength, and the two parameters are well positively correlated. Exponential model generally recommended by building codes or literatures is still capable of describing the relationship between compressive and tensile strength of old deteriorated concrete, when function parameters are properly determined. Based on statistical theory and the experimental result of this study, a method for predicting long-term tensile strength of concrete is developed and an example is given, which may provide a potential way to estimate long-term concrete strength under real marine environment.

Inversion of seabed attenuation by using single mode extracted by warping transform

Seabed is an important part of the marine environment and it has a significant influence on sound propagation. Considering the fact that geoacoustic parameters are directly acquired with difficulty and complexity, a lot of researchers have focused on the inversion of them. The seabed attenuation coefficient is insensitivity to the matching field. However it has great effects on the transmission loss, mode amplitude ratios, etc. It can be inverted from measurements of these quantities. In this paper, we present an inversion scheme based on warping transform technique for estimating the seabed attenuation coefficient. It utilizes an equivalent seabed model which is constructed by using a prior and posterior knowledge. The dispersion characteristics of normal modes can be observed using the time-frequency analysis of the explosive signal recorded. The dispersion curve can be used to invert the seabed sound speed and density. The results presented by other scholars in the same circle are cited in this paper that focuses on how to obtain the seabed attenuation. Warping transform technique is used to separate and extract the normal modes. The main advantage of warping transform is that it can transform the time-frequency spectrogram into linear relationship which makes it easier to extract the normal modes. The feature of this paper lies in determining the distance normalized normal mode transmission loss. If the depths of receiving hydrophone and the explosion source are constant, the plot of normalized normal mode transmission loss versus distance is a straight line from the normal modes theory, which can be used to obtain the attenuation factor of real part of pressure. Then the seabed attenuation coefficient of the shallow water acoustic model can be calculated. In order to verify the effectiveness of this method, the warping transformation technology is used to separate and extract the first three modes from the simulated Gaussian pulse signal which is obtained in a simulated environment which is similar to the real marine environment. The extracted results are completely consistent with the numerical results. After that, the impulsive signal data collected in the Yellow Sea are analyzed according to the scheme process, and the relationship between the seabed attenuation and frequency is =0.581fk1.86(dB/m) in a range from 150 Hz to 550 Hz. The results are in good agreement with those obtained by other scholars in the same circle. On the other hand, the inversion results of seabed attenuation from different modes can be used for comparison at the same frequency, which can be a good support for the result.

Radar-based collision avoidance for unmanned surface vehicles

Unmanned surface vehicles (USVs) have become a focus of research because of their extensive applications. To ensure safety and reliability and to perform complex tasks autonomously, USVs are required to possess accurate perception of the environment and effective collision avoidance capabilities. To achieve these, investigation into realtime marine radar target detection and autonomous collision avoidance technologies is required, aiming at solving the problems of noise jamming, uneven brightness, target loss, and blind areas in marine radar images. These technologies should also satisfy the requirements of real-time and reliability related to high navigation speeds of USVs. Therefore, this study developed an embedded collision avoidance system based on the marine radar, investigated a highly real-time target detection method which contains adaptive smoothing algorithm and robust segmentation algorithm, developed a stable and reliable dynamic local environment model to ensure the safety of USV navigation, and constructed a collision avoidance algorithm based on velocity obstacle (V-obstacle) which adjusts the USV’s heading and speed in real-time. Sea trials results in multi-obstacle avoidance firstly demonstrate the effectiveness and efficiency of the proposed avoidance system, and then verify its great adaptability and relative stability when a USV sailing in a real and complex marine environment. The obtained results will improve the intelligent level of USV and guarantee the safety of USV independent sailing.

A Sea-Sky Line Detection Method for Unmanned Surface Vehicles Based on Gradient Saliency.

Special features in real marine environments such as cloud clutter, sea glint and weather conditions always result in various kinds of interference in optical images, which make it very difficult for unmanned surface vehicles (USVs) to detect the sea-sky line (SSL) accurately. To solve this problem a saliency-based SSL detection method is proposed. Through the computation of gradient saliency the line features of SSL are enhanced effectively, while other interference factors are relatively suppressed, and line support regions are obtained by a region growing method on gradient orientation. The SSL identification is achieved according to region contrast, line segment length and orientation features, and optimal state estimation of SSL detection is implemented by introducing a cubature Kalman filter (CKF). In the end, the proposed method is tested on a benchmark dataset from the “XL” USV in a real marine environment, and the experimental results demonstrate that the proposed method is significantly superior to other state-of-the-art methods in terms of accuracy rate and real-time performance, and its accuracy and stability are effectively improved by the CKF.

Laplace-domain waveform modeling and inversion for the 3D acoustic–elastic coupled media

Laplace-domain waveform inversion reconstructs long-wavelength subsurface models by using the zero-frequency component of damped seismic signals. Despite the computational advantages of Laplace-domain waveform inversion over conventional frequency-domain waveform inversion, an acoustic assumption and an iterative matrix solver have been used to invert 3D marine datasets to mitigate the intensive computing cost. In this study, we develop a Laplace-domain waveform modeling and inversion algorithm for 3D acoustic–elastic coupled media by using a parallel sparse direct solver library (MUltifrontal Massively Parallel Solver, MUMPS). We precisely simulate a real marine environment by coupling the 3D acoustic and elastic wave equations with the proper boundary condition at the fluid-solid interface. In addition, we can extract the elastic properties of the Earth below the sea bottom from the recorded acoustic pressure datasets. As a matrix solver, the parallel sparse direct solver is used to factorize the non-symmetric impedance matrix in a distributed memory architecture and rapidly solve the wave field for a number of shots by using the lower and upper matrix factors. Using both synthetic datasets and real datasets obtained by a 3D wide azimuth survey, the long-wavelength component of the P-wave and S-wave velocity models is reconstructed and the proposed modeling and inversion algorithm are verified. A cluster of 80CPU cores is used for this study.

Monitoring of the Long-term Performance of Stainless Steel Reinforcement in Saline Environments

The aim of the present work is to evaluate the corrosion behaviour of different types of stainless steel reinforcement and to determine their suitability for the use in a chloride contaminated concrete environment. Electrochemical impedance spectroscopy (EIS) measurements were performed on steel reinforcement specimens in a simulated concrete pore solution containing chlorides. The concrete specimens, with embedded electrical resistance (ER) probes for corrosion monitoring, were subjected to cyclic wetting-drying. Reinforced concrete columns with ER probes and coupled multi-electrodes for the measurement of partial currents were exposed to a real marine environment. Traditional stainless steel reinforcement in chloride contaminated environment behaves significantly better than carbon steel. Austenitic low-Ni stainless steel showed similar corrosion resistance to that of the traditional stainless steels, whereas ferritic stainless steel was found to be unsuitable for use in such environments. ER probes and coupled multi-electrodes were shown to be promising methods for corrosion monitoring in concrete.

Preparation and characterization of polypropylene fiber-grafted polybutylmethacrylate as oil sorbent

Polypropylene fiber-grafted polybutylmethacrylate (PP-g-PBMA), a new oil absorbent, was prepared by suspension polymerization using butyl methacrylate as monomer, benzoyl peroxide (BPO) as initiator, and N,N′-methylenebisacrylamide as cross-linker. The effects of monomer concentration, initiator concentration, and cross-linker dosage on the oil absorbency were studied. The results revealed that the pseudo-second-order kinetics model fitted well with the experimental results. The sorption isotherms studies indicated that the equilibrium process was well described by the Freundlich isotherm model. The structures of polypropylene fiber (PP) and PP-g-PBMA were characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), N2 adsorption–desorption, contact-angle (CA) measurements, and differential thermogravimetric analysis. The results of FTIR and SEM show that PBMA was successfully grafted onto PP fiber substrate. The maximum oil sorption capacity of PP-g-PBMA for toluene, diesel, soybean oil, and lubricating oil can reach 18.65, 25.74, 33.56, and 38.90 g/g, respectively. In order to simulate real marine environment, the oil sorption capacities of PP-g-PBMA at different stirring speed values, temperatures, and salinity were investigated. Furthermore, PP-g-PBMA can be reused and recycled more than eight times. It can be concluded that PP-g-PBMA with low-cost and high oil sorption capacity could be used for removal of oil spill.

Local reactive obstacle avoidance approach for high-speed unmanned surface vehicle

Unmanned surface vehicles (USVs) are important autonomous marine robots that have been extensively studied and gradually applied. However, the autonomy of USVs is still restricted by the performance of autonomous navigation technology. At present, various local obstacle avoidance algorithms have been proposed for USVs. However, the majority of algorithm results have only been verified by simulations, with only a few demonstrated by low-speed USVs (≤5 knots) in the sea. Therefore, the issues of obstacle avoidance for high-speed USVs in complicated obstacles environments have to be studied. This paper presents a novel general local reactive obstacle avoidance algorithm for high-speed USVs. In this algorithm, the direction steady-state model and the translational velocity model are proposed for the base normal motion and base motion control characteristics of high-speed vessels. During navigation, USV motion depends on the guidance angle and guidance translational velocity. The validity of the proposed algorithm is verified by experiments in simulations and sea trials on a high-speed USV (≥20 knots) in real marine environments. Results show that the algorithm adapts to the characteristics of high-speed USVs and can guide high-speed USVs (≥20 knots) in realizing safe navigation in real marine environments.

Corrosion rate of carbon steel under synergistic effect of seawater parameters including pH, temperature, and salinity in turbulent condition

AbstractThe variation of AISI 1045 carbon steel corrosion rate in seawater is investigated under the simultaneous effect of marine parameters in both stagnant and turbulent conditions. The combined effect of salinity, velocity, pH, and temperature is studied using two-by-two graphical curves, while each parameter is applied at three levels. The possible influence of simultaneously acting factors on each considering parameter is experimentally studied and explained using theoretical basis. This paper offers an advantage of considering the simultaneous effect of parameters instead of individual ones, which simulate the experimental media close to the real in-site marine environment where all the affecting factors act in a combined manner. The most innovation of this study is two-by-two investigation of combined action of effective parameters on corrosion rate, which is much more comprehensive and detailed compared to previous researches. Every parameter is considered at three ranges and all the possible interactions with other factors are taken into account. It is proven that the effect of considered parameters on the rate of corrosion is the function of other simultaneously acting factors. The role of fluid velocity condition and also the reaction polarization status is found to be pronounced.

Electrochemical measurements of cathodic protection for reinforced concrete piles in a marine environment using embedded corrosion monitoring sensors

This study developed a sensor to monitor the corrosion of reinforced concrete structures. Concrete pile specimens with embedded sensors were used to obtain data on corrosion and cathodic protection for bridge columns in a real marine environment. Corrosion potential, cathodic protection current density, concrete resistivity, and the degree of depolarization potential were measured with the embedded sensors in concrete pile specimens. The cathodic protection (CP) state was accurately monitored by sensors installed in underwater, tidal, splash, and atmospheric zones. The protection potential measurements confirmed that the CP by Zn-mesh sacrificial anode was fairly effective in the marine pile environment. The protection current densities in the tidal, splash zones were 2–3 times higher than those in underwater and atmospheric zones. The concrete resistivity in the tidal and splash zones was decreased through the installation of both mortar-embedded Zn-mesh (sacrificial anode) and outside an FRP jacket (cover). Considering the CP, the cathodic prevention was more effective than cathodic protection.

Effects of hydrolyzable comonomer and cross-linking on anti-biofouling terpolymer coatings

Antifouling coatings based on the cross-linked terpolymer chains made of methyl methacrylate (MMA), the hydrolyzable tributylsilyl methacrylate (TBSM) or triisopropylsilyl methacrylate (TIPSM) and acrylic acid (AA) were developed. By varying the hydrolyzable monomer content and the cross-linking degree, a set of such prepared coatings were evaluated in terms of their degradation rate, swelling degree, contact angle and antifouling properties. After immersed in seawater, such coatings quickly self-generate a thin and swollen hydrogel layer at the water-contacting surface due to the hydrolysis of the hydrolyzable groups on the surface. Further hydrolysis leads to a gradual degradation and self-peeling of this hydrogel layer. Their antifouling properties were evaluated by both the adsorption of fluorescence-labeled bovine serum albumin and the field-testing in a real marine environment. Our results reveal that it is such a layer-by-layer hydrogel formation and self-peeling process that leads to an excellent antifouling property. Therefore, it is vitally important to delicately balance the hydrogel formation and the self-peeling rate to achieve the best antifouling of such a coating by carefully choosing a proper cross-linking degree and a suitable content and type of the hydrolyzable comonomer.

Novel hybrid anti-biofouling coatings with a self-peeling and self-generated micro-structured soft and dynamic surface.

We prepared hybrid antifouling coatings with a self-generated topographical microgel surface by mixing small surface-functionalized microgels with a self-peeling resin and a poly-functional cross-linking agent (axiridine). The microgels were prepared by copolymerizing acrylamide (AAm) and methacrylic acid (MAA). The resin is a random terpolymer made of methyl methacrylate (MMA), acrylic acid (AA) and triisopropylsilyl methacrylate (TIPSM). During the coating process, the microgels and terpolymer chains are cross-linked together to form a hard thin film. After it is immersed into sea water, the microgels dispersed and embedded on the film surface are swollen, generating small and soft bumps, and at the same time, the hydrolysis of TIPSM makes the surface layer hydrophilic, forming a thin layer of soft hydrogel. A combination of these two effects leads to a soft and dynamic topographical surface layer with many well-structured microgel bumps. Such a soft and dynamic surface is self-generating; namely, the hydrolysis of TIPSM eventually makes the terpolymer chains on the surface soluble so that a thin layer of them is gradually dissolved and washed away and the inner layer is further exposed to sea water. Here, both the self-peeling and topographically structured surface by small microgel bumps lead to antifouling properties. To test such a novel idea, we prepared a set of coatings with different microgel and TIPSM contents and evaluated their antifouling properties in a real marine environment. We found some optimal composition at which the coatings showed excellent antifouling properties in the field tests. Moreover, adding the microgels reduces the amount of expensive TIPSM required so that the coatings become more cost-effective, which is vitally important for industrial applications.

On mapping seafloor mineral deposits with central loop transient electromagnetics

Electromagnetic methods are commonly employed in exploration for land-based mineral deposits. A suite of airborne, land, and borehole electromagnetic techniques consisting of different coil and dipole configurations have been developed over the last few decades for this purpose. In contrast, although the commercial value of marine mineral deposits has been recognized for decades, the development of suitable marine electromagnetic methods for mineral exploration at sea is still in its infancy. One particularly interesting electromagnetic method, which could be used to image a mineral deposit on the ocean floor, is the central loop configuration. Central loop systems consist of concentric transmitting and receiving loops of wire. While these types of systems are frequently used in land-based or airborne surveys, to our knowledge neither system has been used for marine mineral exploration. The advantages of using central loop systems at sea are twofold: (1) simplified navigation, because the transmitter and receiver are concentric, and (2) simplified operation because only one compact unit must be deployed. We produced layered seafloor type curves for two particular types of central loop methods: the in-loop and coincident loop configurations. In particular, we consider models inspired by real marine mineral exploration scenarios consisting of overburdens 0 to 5 m thick overlying a conductive ore body 5 to 30 m thick. Modeling and resolution analyses showed that, using a [Formula: see text] transmitting loop with 20 A of current, these two configurations are useful tools to determine the overburden depth to a conductive ore deposit and its thickness. In the most extreme case, absolute voltage errors on the order of 10 nV are required to resolve the base of a 30 m thick ore deposit. Whether such noise floors can be achieved in real marine environments remains to be seen.

Laplace–Fourier-Domain Waveform Inversion for Fluid–Solid Media

Full waveform inversion algorithms are widely used in the construction of subsurface velocity models. In the following study, we propose a Laplace–Fourier-domain waveform inversion algorithm that uses both Laplace-domain and Fourier-domain wavefields to achieve the reconstruction of subsurface velocity models. Although research on the Laplace–Fourier-domain waveform inversion has been published recently that study is limited to fluid media. Because the geophysical targets of marine seismic exploration are usually located within solid media, waveform inversion that is approximated to acoustic media is limited to the treatment of properly identified submarine geophysical features. In this study, we propose a full waveform inversion algorithm for isotropic fluid–solid media with irregular submarine topography comparable to a real marine environment. From the fluid–solid system, we obtained P and S wave velocity models from the pressure data alone. We also suggested strategies for choosing complex frequency bands constructed of frequencies and Laplace coefficients to improve the resolution of the restored velocity structures. For verification, we applied our Laplace–Fourier-domain waveform inversion for fluid–solid media to synthetic data that were reconstructed for fluid–solid media. Through this inversion test, we successfully restored reasonable velocity structures. Furthermore, we successfully extended our algorithm to a field data set.

Corrosion of Steel Bars in Autoclaved Concrete Pile Containing γ-2CaO·SiO2 with an Accelerated Carbonation Curing Submerged in the Real Marine Environment

This paper presents a set of the investigation of corrosion of steel bars in autoclaved concrete pile containing γ-2CaO·SiO2 (γ-C2S) with carbonation curing. OPC, γ-C2S, and fine silica powder were used as the binders; the replacement ratio of OPC by γ-C2S was 0%, 40%, and 80% by mass. Autoclaved concrete pile after carbonation was submerged in real marine environment at Kurihama Bay for two years. After immersion, visual observation of steel bars was conducted to confirm the corrosion state of steel inside the concrete pile. Furthermore, to evaluate the corrosion of steel bars - weight loss, corrosion current density, and anodic polarization curve were measured ; various corrosion substances also were measured to evaluate the permeability of corrosion factors. In addition, cement past sample with same mixed proportion and curing condition was made for explaining the permeable characteristics of corrosion substances. As the results, the steel bars in the 80% γ-C2S replacement ratio did not corrode while steel bars in the other mixed proportions had corroded. The weight loss of steel bar in the 80% γ-C2S replacement ratio after carbonation reduced by 39% and corrosion current density reduced more than 95% compared with the 0% γ-C2S replacement ratio. Furthermore, the corrosion substances in concrete pile - carbonation depth, total chloride ion content, and oxygen diffusion rate, reduced significantly at the 80% replacement ratio of γ-C2S. Based on the overall results of this study, we suggest that, when using γ-C2S with an autoclave curing, accelerated carbonation curing is able to do to densify the concrete surface preventing the steel from corrosion for the long-term exposure.

Simulation of sacrificial anode protection for steel platform using boundary element method

In the present paper, an offshore platform model dealing with sacrificial anode protection was simulated using boundary element method. The potential and current density were calculated, and the distribution trend of the data was analyzed. To evaluate the computation results, proper physical model was built in a given dimension. The physical platform model was placed in a marine environment modeling tank that was designed to simulate the real marine environment with seawater, and the calculation data were compared with those from laboratory experimental work. This study showed that the boundary element method is a powerful tool for the sacrificial anode protection of marine structures.

Research on FRP-Reinforced Concrete Exposure Test

The paper makes an analysis of the selected location and feasibility of the exposure test ground in the real marine environment, and the endurance test of the FRP- reinforced concrete built-up beam has been carried out on the exposure test ground. After 6 month and 12 month’s exposure test, the beams' mechanic performance and the chloride ion content in different depths have been determined. The results show that after the exposure test, the beams' ultimate capacity has been greatly decreased to a certain extent, and the FRP board can effectively prevent chloride from penetrating.

A case study on chemical defense based on quorum sensing: antibacterial activity of sponge-associated bacterium Pseudoalteromonas sp. NJ6-3-1 induced by quorum sensing mechanisms

A case study to investigate the relationship between antibacterial activity and quorum sensing mechanisms was carried out on a sponge-associated bacterium with remarkable biological activities: Pseudoalteromonas sp. NJ6-3-1. The dependence of active substance production on cell density was studied under various growth conditions. Bacteria NJ6-3-1 was found to start producing antibacterial compounds only when cell density reached the threshold value of OD630 = 0.4. To simulate the competitive real marine environment, NJ6-3-1 at low cell density (OD630 value below the required threshold value) was co-cultured with the terrestrial bacterium Staphylococcus aureus. Antibacterial activity assays indicated the existence of some signal molecules in the metabolites of S. aureus that could induce NJ6-3-1 to produce antibacterial substances even at low cell density. Three diketopiperazines (DKPs) as metabolites and potential autoinducers of NJ6-3-1 were synthesized and co-cultured with low density NJ6-3-1. The antibacterial activity assay showed that one of these DKPs—cyclo-(l-Phe-l-Val)—was the autoinducer and could indeed induce NJ6-3-1 to produce antibacterial substances under low cell density. Our results thus provide preliminary support to the hypothesis that the antibacterial activity of NJ6-3-1 is controlled by the quorum sensing system in both an intra-species and an inter-species manner.

Water repellent surface impregnation for extension of service life of reinforced concrete structures in marine environments: The role of cracks

Abstract The enhancement of long-term durability of marine structures is a matter of interest to many researchers. The study presented in this paper examines the effectiveness of a water reducer and chloride barrier surface impregnation of the concrete cover of reinforced concrete (RC) structures, exposed to a marine environment. Specific focuses is on how surface cracks created (1) before impregnation and (2) after impregnation, affect the effectiveness of the surface treatment. The experiments are conducted in an environment which is as close as possible to the real humid subtropical marine environment. A series of reinforced concrete (RC) prisms and concrete cylinders, each treated with various commercial surface impregnation agents, were exposed to cyclic sea water shower under an outdoor environment to accelerate the dry/wet cycles for 1 year. Six types of surface impregnation agents, including four types of silane-based water repellent agents and two types of sodium silicate-based pore blockers (water–glass) were applied. Three types of RC prisms were prepared to simulate the different cracking possibilities, which may occur in surface impregnated concrete structures, during their service life. No cracks were introduced in the first prism group, while cracks were introduced before and after surface impregnation, in the second and third groups, respectively. The time-dependent water absorption of all specimens was monitored during exposure to the dry/wet cycles. Finally the specimens were split open to measure the penetration depths of the surface impregnation agents and the chloride penetration profiles. The areas with corrosion evident in the steel reinforcement in the RC prisms were also measured. Sodium silicate-based pore blockers were found to be inefficient in preventing chloride penetration of concrete under simulated marine exposures. The long-term efficiency of water repellent agents used for surface impregnation was found to be highly dependent on the type of agent and whether impregnation was carried out before or after crack formation.

Spatiotemporal complexity of a ratio-dependent predator-prey system

In this paper, we investigate the emergence of a ratio-dependent predator-prey system with Michaelis-Menten-type functional response and reaction diffusion. We obtain the conditions of Hopf, Turing, and wave bifurcation in a spatial domain. Furthermore, we present a theoretical analysis of evolutionary processes that involves organisms distribution and their interaction of spatially distributed population with local diffusion. The results of numerical simulations reveal that the typical dynamics of population density variation is the formation of isolated groups, i.e., stripelike or spotted or coexistence of both. Our study shows that the spatially extended model has not only more complex dynamic patterns in the space, but also chaos and spiral waves. It may help us better understand the dynamics of an aquatic community in a real marine environment.