Sea Environment Research Articles

Evaluation of the Use of M2M-Type NB-IoT and LTE Technologies for Maritime Communication Systems

Abstract The development of IoT (the Internet of Things) wireless transmission opens a new era in communication systems. In the next years, the development and implementation of IoT systems will be very dynamic. It can be seen that the solutions of LTE – NB-IoT (Long Term Evolution – Narrowband IoT) transmission devices are implemented in a wide range of terrestrial solutions, e.g. smart grids. This paper aims to analyse the possibility of the use of NB-IoT technology for maritime communication applications and partially, for some maritime safety solutions, based on signal coverage analysis at sea. An interesting approach is the comparison of the results of NB-IoT coverage to the classic cellular LTE-based communication systems. Proposed solutions are based on the practical implementation of a designed specialised data concentrator with implemented gateway and radio modems, for both NB-IoT technology as well as LTE. In the paper, analyses of radio link budget and propagation loss models for sea environment are presented. The coverage analysis is based on real measurements of the efficiency of transmissions using wireless modems implemented in the developed data concentrator.

Research on the Control Algorithm of Full Sea Heavy Load Proportional Seven-Function Hydraulic Manipulator Based on Load Sensing

Abstract An underwater manipulator is one of the most commonly used tools in offshore operations. In the face of the unknown environment of the deep sea and the uncertainty of the operation target, the underwater manipulator needs good control stability and higher control efficiency to prevent accidents, which puts forward higher requirements for the control of the manipulator. Underwater manipulators often need to work under heavy loads and to perform tasks efficiently under light loads, which is crucial for efficient control under load. In this paper, a control algorithm based on proportion and derivative feedback control for an all sea depth load proportional hydraulic manipulator is proposed. The feasibility and progressiveness of this algorithm are verified by building kinematic and dynamic models, building physical platforms for tests, and building sea trial acceptance.

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.

Key Technologies and Evaluation of a MiniSAR Experimental System for Unmanned Underwater Vehicle Detection

Synthetic aperture radar (SAR) imaging has important application potential in sea environments research, such as submarine detection. It has become one of the most significant research topics in the current SAR imaging field. In order to promote the development and application of SAR imaging technology, a MiniSAR experiment system is designed and developed, which provides a platform for related technology investigation and verification. A flight experiment is then conducted to detect the movement of an unmanned underwater vehicle (UUV) through the wake, which can be captured by SAR. This paper introduces the basic structure and the performance of the experimental system. The key technologies for Doppler frequency estimation and motion compensation, the implementation of the flight experiment, and the image data processing results are given. The imaging performances are evaluated, and the imaging capabilities of the system are verified. The system provides a good experimental verification platform to construct the follow-up SAR imaging dataset of UUV wake and investigate related digital signal processing algorithms.

Effects of seawater on the infiltration behavior of bentonite slurry into sand

As a support fluid, bentonite slurry has been extensively used in slurry shield tunneling to stabilize the tunnel face by forming a low-permeable filter cake. However, the infiltration behavior of bentonite slurry in complex conditions such as when suffering from seawater intrusion has not been fully understood. In order to investigate the infiltration behavior and filter cake formation under seawater intrusion, seawater-based bentonite slurries with increased salt content were prepared to represent different seawater intrusion severities. The rheological properties and physical stability of these slurries were evaluated. A series of infiltration column tests were conducted on two saturated sand beds with different particle sizes. Scanning electron microscope (SEM) was performed to unravel the microstructure of the filter cake. The infiltration column test results show that the low-permeable filter cake can be formed on the fine sand bed regardless of the salt content of the slurry. The salt shortened the time span of the mud spurt and made the filter cake more permeable to water. For the medium sand, the filter cake cannot be formed when the salt content exceeds 1%, because the deterioration of rheological properties of the slurry weakened its rheological blocking effect when infiltrating the sand. Based on the SEM images, it was found that the filter cake under seawater intrusion contained many well-connected inter-agglomerate channels that reduced its sealing quality. The obtained results can provide guidance and reference for the application of bentonite slurry when tunneling in a sea environment.

Protracted dynamicity of microplastics in the coastal sediment of the Southeast Black Sea

This study provided the first evaluation of microplastic abundance, features, risk assessment, and decade-changing status in sediment along the southeastern Black Sea coast. Sediment samples were collected from thirteen stations in the Southeast Black Sea in 2012 and 2022. >70 % of the detected microplastics had a length of up to 2.5 mm and consisted of fragments and fibers in shape. The average microplastic abundance in the sediment samples was 108 MP/kg. The composition in the sediment (particles/kg) was dominated by polyethylene (PE) (44.9 %), polyethylene terephthalate (PET) (27.2 %), and polypropylene PP (15.2 %). Remarkable results for contamination factors, polymeric risk assessment and contamination risk indices. The sharp rise in MPS highlighted the heavily populated stations and stream discharge locations. The data shed light on anthropogenic and basal microplastic pollution in the Southeast Black Sea, assisting in developing effective policies for preserving and managing the Black Sea environment.

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.

Research on dynamic landing guidance algorithm for the maritime quadrotor

The dynamic landing guidance of the marine quadrotor is composed of trajectory guidance and landing guidance, which can't be completed by the traditional land-based landing guidance method. In addition, complex sea environment will increase the difficulty in dynamic landing guidance such as enhancing the position deviation, which will make the quadrotor unable to land accurately. To address the large trajectory tracking error when the quadrotor is flying, an adaptive step-based line-of-sight (LOS) guidance algorithm is adopted in this work to achieve dynamic three-dimensional (3D) trajectory tracking. The algorithm can not only track the trajectory of the quadrotor in a 3D space based on the position information of the wave glider, but also dynamically adjust the tracking angle and orientation in real time based on the distance and orientation information to improve the tracking accuracy. To address the low accuracy in dynamic positioning of the quadrotor while landing on the wave glider floating body, a visual landing guidance method with fused electromagnetic compensation is used. It can improve accuracy in the dynamic landing guidance of the April Tag visual reference system and reduce the interference from shaking of the wave glider floating body on landing positioning guidance of the quadrotor. The simulation results verify that the proposed algorithm can effectively reduce the trajectory tracking error of the quadrotor and accelerate trajectory convergence. The sea trial experiments prove that the trajectory tracking and landing guidance algorithm adopted in this work can well guide the quadrotor in dynamic and accurate landing on the wave glider floating body, and shorten the time.

Underwater Reverberation Suppression via Attention and Cepstrum Analysis-Guided Network

Active sonar systems are one of the most commonly used acoustic devices for underwater equipment. They use observed signals, which mainly include target echo signals and reverberation, to detect, track, and locate underwater targets. Reverberation is the primary background interference for active sonar systems, especially in shallow sea environments. It is coupled with the target echo signal in both the time and frequency domain, which significantly complicates the extraction and analysis of the target echo signal. To combat the effect of reverberation, an attention and cepstrum analysis-guided network (ACANet) is proposed. The baseline system of the ACANet consists of a one-dimensional (1D) convolutional module and a reconstruction module. These are used to perform nonlinear mapping and to reconstruct clean spectrograms, respectively. Then, since most underwater targets contain multiple highlights, a cepstrum analysis module and a multi-head self-attention module are deployed before the baseline system to improve the reverberation suppression performance for multi-highlight targets. The systematic evaluation demonstrates that the proposed algorithm effectively suppresses the reverberation in observed signals and greatly preserves the highlight structure. Compared with NMF methods, the proposed ACANet no longer requires the target echo signal to be low-rank. Thus, it can better suppress the reverberation in multi-highlight observed signals. Furthermore, it demonstrates superior performance over NMF methods in the task of reverberation suppression for single-highlight observed signals. It creates favorable conditions for underwater platforms, such as unmanned underwater vehicles (UUVs), to carry out underwater target detection and tracking tasks.

Effect of the Sampling Parameters in FOCV-MPPT Circuits for Fast-Varying EH Sources

The fractional open-circuit voltage (FOCV) method is extensively used in low-power energy harvesting (EH) sources to extract maximum power. For fast-varying EH sources, a fast sampling rate is required. This work theoretically analyzes the influence of the sampling time and period on the harvested power of sinusoidal EH sources. In addition, the circuit limitations to achieve a fast sampling rate are presented and circuits to deal with them proposed and implemented. Furthermore, one of the circuits is based on a novel pseudoFOCV method and achieves the fastest sampling rate. Experimental tests are performed with a 2 Hz, 1 to 3 V sinusoidal source having an output resistance of 127 Ω, and the results are shown to agree with theoretical predictions. It is shown that the harvested power increases with the sampling rate when the sampling time is negligible (sampling 15 times faster than the source frequency extracts around 99% of the maximum), and for fixed sampling times, there is an optimum sampling rate where the harvested power is maximum. The first result is generic and valid for methods other than the FOCV. Tests were also performed with a small-scale wave energy converter placed in a linear shaker emulating a sea environment. Harvested power increases by 25% with respect using a commercial FOCV unit with a low sampling rate.

Pressure treatment has a differential effect on cyanide- and ethanol-induced autofluorescence response in yeast.

Cellular processes associated with biological membranes and multimeric associations exhibit pressure sensitivity. In cellular respiration for example, pressure-regulated respiratory oxidases and cytochromes are found in piezophilic microbes, and pressure reduces oxygen consumption rates in eukaryotes. The presence of piezotolerant obligate aerobic yeasts in deep sea environments further justifies investigating pressure effects on cellular respiratory mechanisms. Ambient pressure analysis of UV-excited autofluorescence signals used for monitoring respiratory metabolism have identified multiple cellular NADH and NADPH conformations, significant because the distribution of conformational forms depends on metabolic conditions. Here, we use UV-excited autofluorescence spectroscopy with the spectral response quantified using phasor analysis to monitor cellular NADH and NADPH conformation in Saccharomyces cerevisiae (baker's yeast) suspensions after 30-minute pressure treatment at up to 11 kpsi (75.8 MPa). Specifically, we investigate the effects of pressure treatment on the autofluorescence response to the additions of cyanide and ethanol (both respiratory inhibitors at ambient pressure). The autofluorescence response to cyanide measured 30 min after pressure release shows a diminished response, while the response to ethanol shows no detectable difference when compared with the response prior to pressure treatment. Conditions for this study are similar to those previously reported to activate transcription factors in yeast due to pressure-induced stress tolerance, suggesting autofluorescence may be useful for assessing mitochondrial functional under induced stress-tolerance conditions.

Discrimination Reef and Non-Reef Environments, Using REE Geochemistry

This research aims to distinguish the reef environment from the non-reef environment. The Oligocene-Miocene-succussion in western Iraq was selected as a case study, represented by the reefal limestone facies of the Anah Formation (Late Oligocene) deposited in reef-back reef environments, dolomitic limestone of the Euphrates Formation (Early Miocene) deposited in open sea environments, and gypsiferous marly limestone of the Fatha Formation (Middle Miocene) deposited in a lagoonal environment. The content of the rare earth elements (REEs) (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Ho, Tm, Yb, Lu, and Y) in reef facies appear to be much lower than of those in the non-reef facies. The open sea facies have a low content of REEs due to being a transitional phase. The facies investigated have ƩREEs lower than the PAAS. The lagoonal facies shows an average ƩREEs higher than the Global Standard of Carbonate Rocks (GSCR), whereas reefal and open sea facies contain lower. The Y/Ho, Y/Dy, and Er/Nd were used as distinctive indicators of facies diagnosis; reefal facies have a high value of Y/Ho, Y/Dy, and Er/Nd as compared to PAAS are higher than1. In contrast, non-reef facies (lagoonal) have a lower value of Y/Ho, and Y/Dy as compared to PAAS is lower than 1, but Er/Nd is higher than 1. While in open sea facies the Y/Ho and Y/Dy have moderate values as compared to PAAS are close to 1, but a high value of Er/Nd as compared to PAAS higher than 1.

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.

A Simple Approach to Estimate the Drag Coefficients of a Submerged Floater.

The calculation of the drag force is a fundamental requirement in the design of any submerged system intended for marine exploration. The calculation can be performed by analytic analysis, numerical modeling, or by a direct calculation performed in a designated testing facility. However, for complex structures and especially those with a non-rigid design, the analytic and numerical analyses are not sufficiently accurate, while the direct calculation is a costly operation. In this paper, we propose a simple approach for how to calculate the drag coefficient in-situ. Aimed specifically at the complex case of elastic objects whose modeling via Computer-Aided Design (CAD) is challenging, our approach evaluates the relation between the object's speed at steady-state and its mass to extract the drag coefficient in any desired direction, the hydro-static force, and, when relevant, also the thruster's force. We demonstrate our approach for the special case of a highly complex elastic-shaped floater that profiles the water column. The analysis of two such floaters in two different sea environments shows accurate evaluation results and supports our claim for robustness. In particular, the simplicity of the approach makes it appealing for any arbitrary shaped object.

The RI.P.R.O.VA.RE. Project for the Regeneration of Inland Areas: A Focus on the Ufita Area in the Campania Region (Italy)

The depopulation of inland areas has reached very high levels in recent years. Among the actions to enhance these areas, the Strategia Nazionale Aree Interne (SNAI) was established in Italy in 2012, which proposed a delimitation of inland territories in light of criteria and indicators related to the distance of small towns from major urban poles. In doing so, SNAI gave less weight to some critical issues and potentialities that are considered, in many cases, particularly significant. In light of these considerations, this paper presents the results of a research project developed by three University Departments of Southern Italy that are in continuity with the activities carried out by SNAI. This project, entitled Re-inhabiting Countries. Operational Strategies for the Valorisation and Resilience of Inland Areas (RI.P.R.O.VA.RE), lasted 22 months, ending in 2022. Funded by the Ministry of the Environment and Protection of Land and Sea, it provided a theoretical–methodological contribution to the implementation of the National Sustainable Development Strategy, as well as operational tools to promote sustainable and resilient development processes. The paper focuses, in particular, on the results achieved in one of the selected focus areas, namely the Ufita valley in the Campania region of Southern Italy.

Inversion of shallow seabed structure and geoacoustic parameters with waveguide characteristic impedance based on Bayesian approach

Underwater acoustic technology is essential for ocean observation, exploration and exploitation, and its development is based on an accurate predication of underwater acoustic wave propagation. In shallow sea environments, the geoacoustic parameters, such as the seabed structure, the sound speeds, the densities, and the sound speed attenuations in seabed layers, would significantly affect the acoustic wave propagation characteristics. To obtain more accurate inversion results for these parameters, this study presents an inversion method using the waveguide characteristic impedance based on the Bayesian approach. In the inversion, the vertical waveguide characteristic impedance, which is the ratio of the pressure over the vertical particle velocity, is set as the matching object. The nonlinear Bayesian theory is used to invert the above geoacoustic parameters and analysis the uncertainty of the inversion results. The numerical studies and the sea experiment processing haven shown the validity of this inversion method. The numerical studies also proved that the vertical waveguide characteristic impedance is more sensitive to the geoacoustic parameters than that of single acoustic pressure or single vertical particle velocity, and the error of simulation inversion is within 3%. The sea experiment processing showed that the seabed layered structure and geoacoustic parameters can be accurately determined by this method. The root mean square between the vertical waveguide characteristic impedance and the measured impedance is 0.38dB, and the inversion results accurately represent the seabed characteristics in the experimental sea area.

Modelling parametric uncertainty in large-scale stratigraphic simulations

We combine forward stratigraphic models with a suite of uncertainty quantification and stochastic model calibration algorithms for the characterization of sedimentary successions in large scale systems. The analysis focuses on the information value provided by a probabilistic approach in the modelling of large-scale sedimentary basins. Stratigraphic forward models (SFMs) require a large number of input parameters usually affected by uncertainty. Thus, model calibration requires considerable time both in terms of human and computational resources, an issue currently limiting the applications of SFMs. Our work tackles this issue through the combination of sensitivity analysis, model reduction techniques and machine learning-based optimization algorithms. We first employ a two-step parameter screening procedure to identify relevant parameters and their assumed probability distributions. After selecting a restricted set of important parameters these are calibrated against available information, i.e., the depth of interpreted stratigraphic surfaces. Because of the large costs associated with SFM simulations, probability distributions of model parameters and outputs are obtained through a data driven reduced complexity model. Our study demonstrates the numerical approaches by considering a portion of the Porcupine Basin, Ireland. Results of the analysis are postprocessed to assess (i) the uncertainty and practical identifiability of model parameters given a set of observations, (ii) spatial distribution of lithologies. We analyse here the occurrences of sand bodies pinching against the continental slope, these systems likely resulting from gravity driven processes in deep sea environment.

Effects of Reaction Parameters on the Geometry and Crystallinity of Hydrothermally Synthesized ZnO Nanorods for Bio-Fouling Applications

In this present work, we have successfully synthesized vertical aligned ZnO nanorod arrays (ZnO NRs) on conductive stainless-steel substrate. These ZnO NRs were obtained by using a low temperature, low cost, and eco-friendly hydrothermal approach. The effect of the sol-gel deposited ZnO seed layer on the vertical alignment ZnO NRs has been thoroughly studied. Characterizations of the seed layer and the as-obtained nanorods were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), high-resolution transmission electron microscopy (HR-TEM), and water contact angles (WCA) measurement. SEM analysis shows that these nanorods were grown with a high uniformity and density over the entire substrate. TEM and XRD studies confirmed the hexagonal wurtzite structure of ZnO nanorods. Finally, field immersion tests using the optimized samples were conducted in a coastal sea environment to study biofouling settlement. To the best of our knowledge, there are few articles that investigate the influence of the seed layer deposited on stainless steel on the formation of vertically aligned nanorods for antifouling applications. The novelty of this work is manifested by optimizing the ZnO seed layer to obtain either thick or fine ZnO nanorods (NRs). Moreover, another novelty of this study is the use of the hydrothermal deposition of ZnO NRs on stainless steel for biofouling to replace paints in marine applications.

A cross-scale hygro-mechanical coupling model for hollow glass bead/resin composite materials

Hollow glass bead/resin composite materials are now mainly used in the deep sea submersibles. They are also targeted for application in aviation, aerospace and military applications in the future because of their good material properties, such as low density and high compressive strength. However, there is a coupling relationship between the stress and hygroscopicity in their water absorption process. This reduce the safety of structures produced by hollow glass bead/resin composite materials, especially the underwater and deep-sea structures. In this paper, a hygro-mechanical coupling model and its simplified model for hollow glass bead/resin composites are proposed based on Fick’s second law. A number of experiments are conducted to validate these two models. Comparisons of the predictions of these two models with experimental data show good agreement. The distribution and variation of the stress, water absorption and diffusion coefficient of the composite during the water absorption process were studied. The relationship between the deviation and the water absorption in the simplified model has been given. These results can guide the engineering application of hollow glass bead/resin composite materials, especially in deep sea environments.

The Neolithic Culture and Paleogeographic Environment Evolution in the Eastern Jianghuai Area

According to previous studies, the Lixiahe area in the east of the Jianghuai River was an alternate environment of land and sea in the middle Holocene, and it was not until the late Holocene that the eastern Jianghuai completely became a terrestrial environment. However, recent archaeological studies have found that the extensive Neolithic sites in the Lixiahe area have recorded the rich human activities and cultural connotations of the prehistoric civilization in the Middle Holocene. In this paper, the Gangxi section of Jianhu Lake, Jiangsu Province (GX2) was selected and pollen analysis was fulfilled, then the geomorphic evolution process of the study area from sea to land was investigated according to the palynological assemblages and algae fossils of brackish water, semi-saline water, fresh water and terrestrial in the section strata. During the period of 8500–3800 cal. BP, GX2 was affected by multiple factors such as sea surface fluctuation, ocean flow and sediment deposition carried by seagoing rivers. Since 5800 cal. BP, the area east of the Grand Canal between the Yangtze River and the Huaihe River, and the west of the Yangzhai town, Funing–Longgang town, Yancheng–Dagang town and Yancheng–west of the Dongtai–Hai’an line, have become a terrestrial environment. After the eastern Jianghuai became a land, the Liangzhu culture (5300–4300 cal. BP) in the Taihu Lake basin in the south wing of the Yangtze River delta expanded to the eastern Jianghuai area, and the Longshan culture and Yueshi culture in the Haidai area in the north also migrated south to the eastern Jianghuai area. Admittedly, the main reason in the process of Neolithic cultural development is the internal motivation that the ancient ancestors struggled with nature and pushed forward the continuous development of civilizations. However, our study explains the palaeogeographical origin of Neolithic culture in the eastern and coastal areas of Jianghuai in the middle Holocene, and meanwhile, provides an example for the man–land relationship research on Neolithic culture.