J. Mar. Sci. Eng., Volume 11, Issue 11 (November 2023) – 174 articles

Mass transfer and phase transition have an important effect on the velocity of bubble migration in deepwater wellbores, and accurate prediction of bubble migration velocity is crucial for calculating the safe shut-in period of deepwater oil and gas wells. Therefore, the effect of bubble dissolution mass transfer and hydrate phase transition on bubble migration behavior in the deepwater environment have attracted extensive attention from researchers in the fields of energy, marine chemistry, and marine engineering safety. In this work, a new model of bubble migration velocity in deepwater is developed, which considers the effect of hydrate phase transition and gas-water bidirectional cross-shell mass transfer during bubble migration. Based on the observation data of bubble migration in deepwater, the reliability of the model in predicting bubble migration velocity is verified. Then, the model is used to calculate and analyze the bubble migration velocity and bubble migration cycle under different initial bubble size, different annular fluid viscosity, and density. The results show that the initial size of bubble and the viscosity of annulus fluid are the main factors affecting the migration velocity of the bubble, but the density of annulus fluid has little effect on the migration velocity of the hydrated bubble and clean bubble. In addition, the migration velocity of the clean bubble gradually increases during the migration process from the bottom to the wellhead, while the migration velocity of the hydrated bubble is divided into a gradually decreasing stage and a slowly increasing stage. The gas consumption and the thickening of hydrate shell in the gradually decreasing stage play a dominant role, and the increase of bubble volume caused by the decrease of pressure in the slowly increasing stage is the most important factor. The formation of the hydrated bubble can significantly reduce the migration velocity of the bubble and effectively prolong the safe shut-in period. This study provides a reference for quantitative description and characterization of complex bubble migration behavior with phase change and mass transfer in deepwater environment. Full article

Among the commonly used ship-stabilizing devices, the fin stabilizer is the most effective. Since the lift force of the conventional fin stabilizer is proportional to the square of the incoming flow velocity, it has a better anti-rolling effect at higher speeds but a poor anti-rolling effect at low speeds and even no effect at zero speed. A combination of modelling analysis, simulation, and a model ship experiment is used in this paper to study the zero-speed roll-reduction control problem of the fin stabilizer. A simulation model of the rolling motion of a polar expedition ship is established. The lift model of the fin stabilizer at zero speed is established using the theory of fluid mechanics. The proportional–integral–differential (PID) controller is selected to control the fin to achieve zero-speed roll reduction. To obtain a better anti-rolling control effect under variable sea conditions, a wavelet neural network (WNN)-based half-period prediction algorithm is adopted to update and adjust PID control parameters in real time. A simulation was carried out, and the effectiveness of the proposed predictive control algorithm is proved. A reduced-scale ship model was established to carry out the water tank experiment, and the results verify the theoretical analysis and simulation. The results also verify the effectiveness of the proposed control strategy. Full article

Sponge assemblages play a significant role in the functioning of the Mediterranean benthic ecosystem. The main goal of this study was to investigate the diversity and distribution of poorly known sponge communities in the mesophotic and deep-sea substrates of the eastern Mediterranean Sea. More than 1500 sponge specimens belonging to 87 taxa were collected from 156 stations during experimental and commercial bottom trawling in the Aegean Sea and the eastern part of the Ionian ecoregion, at depths of between 10 and 800 m. A total of 79 sponge species were found in the Aegean and 40 species in the Ionian Sea. Eight of these species are included in lists of endangered and threatened species, two were newly recorded in the Aegean and six were first recorded in the east Ionian Sea. Both community structure and diversity differed between the two ecoregions. Species richness, biomass, abundance and diversity decreased with increasing depth, while different species dominated, in terms of biomass, abundance and frequency of appearance, in the two ecoregions and the separate depth zones. In contrast with previous investigations, which mostly examined shallow-water sponges, no clear resemblance patterns were observed among the north and south Aegean subareas, probably due to the homogeneity of the deep-sea habitats under investigation. This study, using sampling material from fish stock monitoring programs for the first time, contributed to our knowledge of the largely unknown eastern Mediterranean mesophotic and deep-sea sponge populations, which are subjected to intensive trawling activities. Full article

In recent years, underwater acoustic applications have attracted much attention, for example, for underwater environmental monitoring, underwater exploration, etc. Hydrophones play a particularly important role. Although hydrophone design has been in multifarious application forms, it still needs to consider increasing demand for low-cost, low-consumption, and multiple-function devices, as well as issues around miniaturization, lossless data collection, etc. In this paper, we design a compact underwater acoustic device that has the capability of underwater acoustic signal storage, underwater acoustic signal transmission via the Internet, and decoding based on the direct sequences spread spectrum (DSSS). The key problem is how to implement multiple functions in only one micro-controller unit (MCU). The hardware and software of the proposed multi-function hydrophone are described in detail. In particular, the MCU, the pre-amplifier with gain control, and the analog-to-digital integrated chip are introduced. Moreover, underwater acoustic data storage, underwater acoustic transmission, and the DSSS receiver are depicted in terms of software. The different functions of the hydrophone are verified in sea trial experiments. The results show that the proposed multi-function hydrophone is able to sample underwater acoustic data at high quality. In addition, to demonstrate configurable parameters, the DSSS receiver with different carrier frequencies is provided. The proposed multi-function hydrophone realizes zero bit error rate (BER) when carrier frequency $f_c=9$ kHz, and the BER with ${10}^{-3}$ order of magnitude when carrier frequency $f_c=15.5$ kHz. The results show that the proposed multi-function hydrophone has great potential to explore the ocean. Full article

Three new nematode species belonging to the order Enoplida were discovered in the muddy and sandy sediment along the Shandong peninsula coast of the Yellow Sea during a biodiversity investigation of marine nematodes in the Yellow Sea. They are named Belbolla octobulba sp. nov., Ironella gracilis sp. nov. and Oxystomina longiseta sp. nov. Belbolla octobulba sp. nov. is characterized by having eight pharyngeal bulbs; spicules arcuate, broad and even; gubernaculum with a pair of dorso-caudal apophyses, about a third of the length of spicule; and two winged precloacal supplements. Ironella gracilis sp. nov. differs from known species by body slender, buccal cavity divided into conical vestibulum and cylindrical posterior portion, three sclerotized teeth located in the vestibulum; both circles of outer labial setae and cephalic setae 10 µm apart; elongated spicules weakly arcuate with central strip and cephalate proximal end; gubernaculum conical without apophysis; and a tubular precloacal supplement with a long seta at its anterior end. Oxystomina longiseta sp. nov. can be distinguished from other known species by the relatively long outer labial setae and cephalic setae; arcuate spicules expanded proximally with a median rib; gubernaculum small and oblong; and two unequal precloacal supplementary setae, anterior one short, posterior one very long. Updated keys to eighteen species of Belbolla and keys to four species of Ironella are given. Full article

Mesoscale eddies are a common occurrence in the Kuroshio Extension (KE) that have a major impact on the levels of salinity and heat transport in the Northwest Pacific, the strength of the Kuroshio jet, and the fluctuations of the Kuroshio’s trajectory. In this study, a purely data-driven machine learning model, Temporal Modes-Enhanced Neural Network (TMENN), is proposed to forecast the spatiotemporal variation of mesoscale eddies based on daily sea surface height (SSH) data over a 20-year period (2000–2019) in the Kuroshio Extension. To reduce computational costs and facilitate faster forecasting, raw SSH data are decomposed into spatial modes and temporal modes (principal components, PCs) by empirical orthogonal functions (EOF) analysis, and the first 117 PCs (a total of 8384 PCs), wherein the cumulative variance contribution rate reaches 95%, are selected solely as the predictors of TMENN to train and forecast. Forecasting reconstruction results show that the model can reliably forecast the evolution of the eddy in the KE for about 30 days. Additionally, three classical mesoscale eddy processes are selected to verify the accuracy of the model, namely cold eddy attachment, warm eddy shedding, and attachment, and the results indicate that the model can well capture the evolution process of mesoscale eddies. Full article

In pursuit of more efficient load-bearing solutions for ship deck panels of Very Large Crude Carriers exposed to vertical hull girder bending forces, laser-welded web-core sandwich panels are considered as an alternative to conventional stiffened panels. The primary goal is to identify a lighter steel sandwich structure capable of matching the ultimate strength of conventional counterparts. Utilizing non-linear finite element analysis, the ultimate strength of conventional decks subjected to uniaxial compression is assessed. Attention is then shifted to laser-welded sandwich panels, with a detailed examination of how various design parameters influence their performance. Specifically, four key design aspects of unidirectional vertical webs, including face thickness, web thickness, web height, and web spacing, are optimized to strike a balance between weight and strength through structural optimization techniques combined with the response surface method. Ultimately, a comparison is drawn between the ultimate strength of these innovative steel sandwich panels and their conventional, stiffened counterparts. The findings reveal that web-core sandwich panels, when employed as an alternative, result in a notable reduction in hull weight, thereby showcasing the potential for a more efficient and sustainable approach in the maritime industry. Full article

This research investigates cavitation around a marine propeller, employing computational fluid dynamic (CFD) solvers, including an incompressible, isothermal compressible, and fully compressible flow. The investigation commenced with simulations utilizing an incompressible flow solver, subsequently extending to the two compressible flow solvers. In the compressible flow, there is a close interrelation between density, pressure, and temperature, which significantly influences cavitation dynamics. To verify computational methods, verification tests were conducted for leading-edge cavitating flows over a two-dimensional (2D)-modified NACA66 hydrofoil section at various cavitation numbers. The computational results were validated against the experimental data, with the solvers’ capability to predict cavitation forming the basis for comparison. The results demonstrate consistent predictions among the solvers; however, the fully compressible flow solver demonstrated a superior performance in capturing re-entrant jets and accurately modeling cavity closure regions. Furthermore, the fully compressible flow solver precisely estimated propeller hydrodynamic performance, yielding results closely aligned with experimental observations. Full article

Some structures in the harbour environment need to be inspected regularly. However, these scenarios present a major challenge for the accurate estimation of a vehicle’s position and subsequent recognition of similar images. In these scenarios, visibility can be poor, making place recognition a difficult task as the visual appearance of a local feature can be compromised. Under these operating conditions, imaging sonars are a promising solution. The quality of the captured images is affected by some factors but they do not suffer from haze, which is an advantage. Therefore, a purely acoustic approach for unsupervised recognition of similar images based on forward-looking sonar (FLS) data is proposed to solve the perception problems in harbour facilities. To simplify the variation of environment parameters and sensor configurations, and given the need for online data for these applications, a harbour scenario was recreated using the Stonefish simulator. Therefore, experiments were conducted with preconfigured user trajectories to simulate inspections in the vicinity of structures. The place recognition approach performs better than the results obtained from optical images. The proposed method provides a good compromise in terms of distinctiveness, achieving 87.5% recall considering appropriate constraints and assumptions for this task given its impact on navigation success. That is, it is based on a similarity threshold of 0.3 and 12 consistent features to consider only effective loops. The behaviour of FLS is the same regardless of the environment conditions and thus this work opens new horizons for the use of these sensors as a great aid for underwater perception, namely, to avoid degradation of navigation performance in muddy conditions. Full article

Amphipods are an important group of invertebrates in marine ecosystems due to their high abundance and diversity. As an essential part of the marine food web, amphipods play a vital role in nutrient recycling and provide large amounts of detritus-derived fine-particulate organic matter for other invertebrates. Although the importance of gut microbiota and the necessity to consider them has been increasingly recognized, the gut microbial community and diversity of amphipods have not been well studied. Here, we comparatively studied the gut microbiota of diverse amphipod species inhabiting from coastal to hadopelagic zones. The results showed that four phyla, including Proteobacteria, Firmicutes, Bacteroidota, and Actinobacteriota, occupied more than 90% of the total microbes in the studied amphipod guts, with Firmicutes being dominant in the hadal amphipods. The gut microbiome of amphipods from the hadal zone displayed the lowest richness, lowest diversity, and shared few microorganisms with the surrounding seawater compared to others. Amphipods in different inhabiting regions have discriminant taxa for their gut microbial communities. Taken together, amphipod gut microbiota was affected by both biological and abiotic factors, yet these factors are not independent. This article provides us with a further understanding of the structure and characteristics of the gut microbiota of invertebrate organisms. Full article

Tropical cyclones (TCs) exert a significant influence on the upper ocean, leading to sea surface temperature (SST) changes on a global scale. However, TC-induced SST responses exhibit considerable variability in the northern Indian Ocean (NIO), and the general understanding of these responses remains limited. This paper investigates the SST changes caused by 96 TCs over an 18-year period in the NIO. Through a composite analysis utilizing satellite SST data, a comprehensive study is conducted to examine the relationship between TC characteristics, including wind speed and translation speed, and the associated SST changes. The overall findings reveal that within a radius of 300 km from the TC center, SST decreases were observed at 1702 (86%) locations, with an average SST response to TC of −0.46 °C and a maximum decrease of −2.07 °C. The most significant reduction in SST typically occurred two days after the passage of TCs, followed by a gradual recovery period exceeding 15 days for the SSTs to return to their initial values. Consistent with findings in other ocean basins, stronger and slower-moving TCs induced more substantial cooling effects. Conversely, at 279 (14%) locations, particularly associated with TCs of weaker intensities, SST increases were observed following the TC passage. Notably, 140 of these locations were situated at low latitudes, specifically between 8° N and 15° N. This study provides a quantitative analysis of the comprehensive SST response to TCs in the NIO. Full article

Polymetallic nodules and polymetallic sulfides are currently the major mineral resources found on the seabed. The motivation behind deep-sea mining arises from the pursuit of valuable metals, driven by both economic and geopolitical considerations. However, before mining can be authorized, it is crucial to understand the microbial adaptation and biomineralization process related to heavy metals in deep-sea environments. To search for potential candidate materials for bioremediation in deep-sea environment, two strains with high resistance to manganese and the ability to form rhodochrosite precipitates were isolated from the deep-sea polymetallic nodule areas and hydrothermal polymetallic sulfide areas. Genomic analysis revealed that the strains employed various effective survival strategies, such as motility, chemotaxis, biofilm formation, metal redox, and transporters, to adapt to heavy metal environments. The bacterial strains Ery5 and Ery15 promote the formation of carbonate crystals by creating an excessively alkaline environment and releasing extracellular polymeric substances (EPSs). Furthermore, strains Ery5 and Ery15 were identified using polyphasic taxonomy methods and proposed as a new species belonging to the genus Croceicoccus. This study presents potential candidates for bioremediation in deep-sea environments. Full article

Online monitoring of mooring system response for the FPSO platform in any operational condition is so far challenging for machine learning (ML). This paper presents a new dynamic NARX ANN model for time series of mooring tension and a static MLP model for the offset chart prediction of a taut-leg moored FPSO with different working scenarios. A novel method for supervised feature selection of the dataset was applied to determine the most influential design features. Additionally, a design of experiments (DOE) technique was implemented for test matrix creation, simulation, database generation, and supervised selection characteristics in ML. The DOE analysis revealed that the mooring configuration, platform loading condition, and environmental loads alter the platform’s six-degree-of-freedom motion response patterns. These input data were used to predict the mooring tension and the offset chart of the floater. The results include the fair values of statistical error for mooring tension (R² = 0.8–0.98, E ≈ 1.3–5.7%, RMSE ≈ 6–66 kN) and platform offset (E ≈ 0.1–1 m) prediction when testing the trained models with unseen data representing new operational conditions. Faster convergence can be achieved by adding non-numeric (string) input values to dataset numeric features. Supervised feature selection of the dataset is a step forward in ML to improve prediction accuracy. Full article

Macroalgae, playing a crucial role in coastal marine ecosystems, are subject to multiple environmental challenges due to tidal and seasonal alterations. In this work, we investigated the physiological responses of Pyropia yezoensis to ocean acidification (ambient CO₂ (AC: 400 μatm) and elevated CO₂ (HC: 1000 μatm)) under changing salinity (20, 30 psu) and light intensities (50, 100 μmol photons m⁻² s⁻¹) by measuring the growth, pigment content, chlorophyll fluorescence, and soluble sugar content. The key results are the following: (1) P. yezoensis exhibited better growth under normal salinity (30 psu) compared to hyposaline conditions (20 psu). (2) Intermediate light intensity increased phycoerythrin content, ultimately enhancing thalli growth without significant changes to the contents of chlorophyll a and carotenoids. (3) Ocean acidification alleviated hyposaline stress by enhancing pigment production in P. yezoensis only at a salinity of 20 psu, highlighting the complex interplay of these environmental factors. These findings indicate that higher light intensities and elevated pCO₂ levels could mitigate the stress caused by low salinity. Full article

A novel float-type device for wave energy power generation, designed specifically for offshore wave environments, is introduced as an innovative technology in wave energy utilization. Herein, we present the design concept, structural composition, and energy conversion process of the device, and conduct mathematical modeling and theoretical research on its kinematic and dynamic characteristics. At the same time, we use a numerical wave pool based on the STAR-CCM+ boundary wave making method and damping dissipation method to analyze the motion response and output power of the wave energy generator in a five-order Stokes wave environment within one wave cycle and the entire operating cycle. Finally, in order to develop the best design strategy, we study the effect of changing the structural parameters of the power generation device on the hydrodynamic performance of the device. Full article

In this study, we investigate a terminal sliding mode control (TSMC) system combined with predefined-time and prescribed-performance control methods for an unmanned planing hull (UPH) system in the presence of a control input delay at the heading axis and a porpoising motion due to pitching-moment disturbance. A second-order TSMC system is adopted to bypass the unstable heading-angle response of the conventional first-order TSMC system caused by the control input delay of the hydraulic rudder actuator system. Next, predefined-time and prescribed-performance control methods are proposed to enhance the disturbance rejection performance of an uncertain UPH. The results of sequential comparative simulations show that the disturbance rejection performance of the proposed hybrid disturbance rejector using both the predefined-time and prescribed-performance control methods for a porpoising motion is superior to those of conventional controller systems without introducing disturbance observers. Full article

Anchorage failure of a suction anchor is more likely to occur in low-strength muddy clay. This paper focuses on the failure behaviors of suction anchors and muddy clay stress responses. The centrifugal model test was used to study the loading processes of suction anchors with various pulling angles. Firstly, the multi-stage developing process of anchoring force was analyzed according to the test results. Numerical modeling was used to validate the test results. The displacement of the suction anchor and muddy clay soil were analyzed using the numerical results. Then, the numerical and testing results were compared to analyze the horizontal soil pressure responses around the suction anchors. It was found that the change in loading direction affected the distribution and development of soil stress. The horizontal soil resistance played a crucial role in improving the bearing capacity. The soil stress variation and anchor displacement revealed that the suction anchors exhibited multi-attitude coupling movement during the inclined pulling. The vertical pulling suction anchor showed shear–slip failure behaviors, while the inclined pulling suction anchors showed compression–shear–slip coupling failure behaviors. The results of this study provide insight into the interaction mechanism between suction anchors and muddy clay, serving as a reference for the design and application of suction anchors. Full article

Floating breakwaters have recently been generating increasing interest as a vital means to provide shelter and protect the ever-increasing number of structures deployed at sea. Notwithstanding the novel ideas being put forward, to date, floating breakwater deployment has been limited to inshore and shallow water areas. The scale of such structures has been restricted to the smaller spectrum. Furthermore, whilst some concepts to integrate floating breakwaters with other offshore systems have been proposed to benefit from cost-sharing strategies, studies related to floating breakwaters integrating energy storage are lacking in the open literature. The present research investigates the wave attenuating and dynamic performance of a large-scale floating breakwater in deep seas with a hydro-pneumatic energy storage system also integrated within the structure. This article highlights the arising need for floating breakwaters and sheds light on the present-day technological status of floating wave breakers. It then lays the ground for the proposed, novel floating breakwater concept that aims to address the current knowledge gaps in this field of study. The simulation results generated from numerical modelling via the potential flow solver ANSYS^® AQWA™ have been promising, connoting that the addition of hydro-pneumatic energy storage to a floating breakwater will not lead to a degradation in the dynamic performance or wave breaking efficiency of the floating structure. Full article

Gurney flaps can enhance the hydrodynamic efficiency of airfoils, and they are currently used in several applications, including racing cars and wind turbines. However, there is a lack of studies in the literature on the application of Gurney flaps on the Horizontal Axis Ocean Current Turbine (HAOCT). The influence of Gurney flaps on the hydrodynamic efficiency of the HAOCT is evaluated through numerical analysis. The effect of the Gurney flaps on the turbine is evaluated after the validation of the utilized numerical method is completed using the wind tunnel experimental data of the two-dimensional NACA 63415 airfoil and the water tunnel experimental data of the NACA 638xx series rotor on the clean blade. By calculating the velocity and pressure fields of the 2D airfoil by CFD, it was possible to analyze the lift improvement with the addition of the Gurney flaps by evaluating the pressure difference between the pressure surface and the negative pressure surface, and the drag improvement was due to the Gurney flaps obstructing the chordal flow of the fluid in the wake. For the 2D NACA-63415 airfoil, the drag coefficient increases with the increase in the head angle, while the lift coefficient increases and then decreases. The flap height divided by the local chord length of the Gurney flaps is 0.01, and the lift-to-drag ratio is the highest when the head angle is 4°. For the NACA-638xx turbine, the addition of Gurney flaps significantly increases the axial thrust coefficient. At lower tip speed ratios, the effect of the Gurney flaps on the rotor’s power coefficient is limited, with the greatest increase in the power coefficient at a tip speed ratio of 6 and a decrease in the power coefficient increase as the tip speed ratio increases. Increasing the height of the Gurney flaps can increase the peak power coefficient, but the power performance decreases at high tip speed ratios. The Gurney flaps distributed at the root of the rotor have less effect on the power performance. A 0.4 local radius spread of the Gurney flaps increases the peak turbine power coefficient by only 0.34%, while full-length Gurney flaps can increase the peaked blade power coefficient by 10.68%, indicating that Gurney flaps can be used to design a new HAOCT. Full article

To reduce air pollution worldwide, regulations on exhaust gas emissions from ships are becoming increasingly stringent. One fuel that is being considered as an alternative to replace the heavy fuel oil used in existing ship engines and thereby reduce harmful emissions, such as NO_x, SO_x, and greenhouse gases, is sulfur-free liquefied petroleum gas (LPG). To assess the viability of this alternative, it is necessary to understand propane reactivity, the main component of LPG, and develop after-treatment devices applicable to LPG engines. This research evaluated the performance of three prototype Pd-based three-way catalysts (TWCs) with varying Pd loadings (6.5, 4.1, and 1.4 g/L), focusing on their effectiveness concerning propane reactivity in LPG engines. For the fresh samples, catalysts with 4.1 g/L Pd demonstrated performance that was comparable to, or even surpassed, those containing 6.5 g/L Pd. Notably, the temperature of 50% conversion (T₅₀) for NO and C₃H₈ in the fresh Pd-4.1 was lower by 14 °C and 10 °C, respectively, compared to the fresh Pd-6.5 sample, despite having 37% less precious-metal loading. However, after hydrothermal aging at 900 °C for 100 h, the performance of the 4.1 g/L Pd catalyst significantly deteriorated, exhibiting lower efficiency than the 6.5 g/L Pd catalyst. The study also delved into various probe reactions, including the water–gas shift and propane steam reforming. Advanced analytical techniques, such as N₂ physisorption and scanning transmission electron microscopy, were employed to elucidate the texture and structural characteristics of the catalyst, providing a comprehensive understanding of its behavior and potential applications. Through this research, within the efforts of the maritime sector to address challenges posed by emission regulations and rising costs associated with precious metals, this study has the potential to contribute to the development of cost-effective emission control solutions. Full article

This study assessed the impact of intensive human activities on organic matter (OM) and heavy metal cycles in Shihwa Lake, South Korea. Sediment oxygen demand (SOD), benthic nutrient flux (BNF), and benthic heavy metal flux were estimated using in situ benthic chambers. The combined analysis of sediment trap and SOD showed that the vertical supply of OM was a major controlling factor for benthic respiration. The BNF accounted for 35–144% and 32–184% of the N and P required, respectively, for primary production (PP) in the water column. The higher SOD may have also accelerated the release of Mn, Fe, Co, and Ni from the sediment. Benthic fluxes of Cr, As, Cd, Pb, Cu, and Zn were highest near the industrial complex, with ranges of 1.3 ± 0.9, 6.4 ± 4.9, 0.2 ± 0.1, 0.5 ± 0.4, 7.7 ± 1.4, and 452 ± 133 μmol m⁻² d⁻¹, respectively. Mn, Fe, Co, As, Pb, Ni, and Cu contributed more than 10% of the sediment to the current standing stock at Shihwa Lake. Full article

The stability of navigation in waves is crucial for ships, and the effect of the waves on navigation stability is complicated. Hence, the LSTM neural network technique is applied to predict the course changing of a ship in different wave conditions, where K-means clustering analysis is used for the category of the ship’s navigation data to improve the quality of the database. In this paper, the effect of the initial database obtained by the K-means clustering analysis on prediction accuracy is studied first. Then, different input features are used to establish the database to train the neural network, and the influence of the database by different input features on the accuracy of the navigation prediction is discussed and analyzed. Finally, multi-task learning is used to make the neural network better predict the navigation in various wave conditions. Using the improved neural network model, the course of an autopilot ship in waves is predicted, and the results show that the current database and the neural network model are accurate enough for the course prediction of the autopilot ship in waves. Full article

The excavation of the ocean has led to the submersion of numerous autonomous vehicles and sensors. Hence, there is a growing need for multi-user underwater acoustic communication. On the other hand, due to the limited bandwidth of the underwater acoustic channel, downlink non-orthogonal multiple access (NOMA) is one of the fundamental pieces of technology for solving the problem of limited bandwidth, and it is expected to be beneficial for many modern wireless underwater acoustic applications. NOMA downlink underwater acoustic communication (UWA) is accomplished by broadcasting data symbols from a source station to several users, which uses superimposed coding with variable power levels to enable detection through successive interference cancellation (SIC) receivers. Nevertheless, comprehensive information of the channel condition and channel state information (CSI) are both essential for SIC receivers, but they can be difficult to obtain, particularly in an underwater environment. To address this critical issue, this research proposes downlink underwater acoustic communication using a deep neural network utilizing a 1D convolution neural network (CNN). Two cases are considered for the proposed system in the first case: in the first case, two users with different power levels and distances from the transmitter employ BPSK and QPSK modulations to support multi-user communication, while, in the second case, three users employ BPSK modulation. Users far from the base station receive the most power. The base station uses superimposed coding. The BELLHOP ray-tracing algorithm is utilized to generate the training dataset with user depth and range modifications. For training the model, a composite signal passes through the samples of the UWA channel and is fed to the model along with labels. The DNN receiver learns the characteristic of the UWA channel and does not depend on CSI. The testing CIR is used to evaluate the trained model. The results are compared to the traditional SIC receiver. The DNN-based DL NOMA underwater acoustic receiver outperformed the SIC receiver in terms of BER in simulation results for all the modulation orders. Full article

To improve the accuracy of solving the Poisson equation and the efficiency of handling complex boundary shapes in the particle method, this paper proposes a Local Regular-distributed Background Particles (LRBP) as an alternative to traditional boundary handling methods. This method avoids the trouble of arranging virtual particles by introducing background particles, making it suitable for problems with complex boundary shapes. In addition, based on the framework of the weak form Poisson equation, the boundary conditions are easily applied, and the calculations are more accurate. Furthermore, this method allows for different interpolation methods inside and outside the boundary, providing flexibility and versatility. These characteristics are well demonstrated in the validation examples, which indicate its potential to solve complex flow problems. Full article

In order to reduce the offshore wind power operation and maintenance vessel motion induced by severe sea states, a suitable stabilizer with the ship based on linear quadratic regulator strategy is proposed in this paper. First of all, the dynamics of the ship motion model are established to study the longitudinal control system. The six degrees of freedom nonlinear motion model and nonlinear coupled longitudinal motion (heave and pitch) model are described in detail in this paper. Secondly, this work presents matching suitability between the T-foil and the operation and maintenance vessel. Therefore, the most suitable installation position and the optimum strut’s height of T-foil are determined by meshing the ship hull model, setting the water channel, and a series of corresponding computer fluid dynamic simulation. Following that, the linear quadratic regulator controller is studied with active longitudinal control system based on the suitable T-foil. Furthermore, a longitudinal control system is built, including free vessel module and the suitable T-foil stabilizer-based proposed controller module. Finally, the simulation results indicate that the designed T-foil and the longitudinal control system are feasible and effective to ensure the heave and pitch motion reduction based on the proposed controller. Full article

The Volume of Fluid (VOF) method is used in two-phase fluid flow problems of ship hydrodynamic calculations, to capture the motion and distribution of the gas–liquid free surface. To ensure solution stability and accuracy, numerical simulations typically require separate mesh refinement for the free surface or a reduced time step, resulting in a significant increase in solution time. This study aims to compare the drag and vessel attitude change calculations of the VOF implicit multi-step method with the traditional single-step method, and to verify the feasibility of the method in the numerical prediction of ship resistance and flow field analysis. The results show that an implicit multi-step method with a reasonable number of internal iterations could obtain results close to those of the single-step method with a reduced time step, and the error in trim angle was relatively large, about 2%, but the solving time was only about half that of the latter. The method could also capture the shape and location of waves on the hull, especially in the vicinity of the ship, while the distribution of the waves in the far field differed from those in the experiments to some extent. Full article

This study proposes a novel fuzzy programming optimization model for tugboat scheduling, directly considering multiple berthing bases, time windows, and operational uncertainties. The uncertainties in the required number of tugboats, the earliest start time, the latest start time, the processing time, and the start and end locations of each task are directly captured in the proposed fuzzy optimization model. The objective of the presented formulation is to minimize the total cost of fuel and delays. According to the characteristics of the problem, a Grey Wolf Optimization algorithm based on random probability encoding and custom genetic operators is proposed. The proposed algorithm, LINGO, the canonical Grey Wolf Optimization algorithm, and particle swarm optimization were used to compare and analyze the results of several examples. The results validate the efficiency of the proposed algorithm against the alternative exact and metaheuristics methods. Moreover, the findings from the conducted sensitivity analysis show the applicability of the developed fuzzy programming model for different confidence interval levels. Full article

This work addresses the effects of blade tip-rake reformation on the performance of marine propellers using a low-cost potential-based vortex-lattice method (VLM) and the high fidelity artificial compressibility CFD-RANS solver MaPFlow. The primary focus lies on determining whether the low-cost VLM, in conjunction with a multidimensional parametric model for the tip-rake and pitch/camber distributions, can produce a propeller geometry with improved efficiency. Due to the availability of experimental and numerical data, the NSRDC 4381-82 propellers were selected as reference geometries. Torque minimization serves as the objective function in the gradient-based optimization procedure under a thrust constraint, which translates into efficiency enhancement at the selected design advance ratio. The optimized 4381 propeller yields a +1.1% improvement in efficiency based on CFD-RANS, whereas for the modified skewed 4382 propeller, the efficiency gain is +0.5%. The performance enhancement is also evident at a region near the design advance ratio. The results suggest that the exploitation of low-cost VLM solvers can significantly reduce the CFD simulations required in the optimization process and thus can be effectively used for the design of propellers with tip-rake reformation. Full article

Fish eggs have a wide range of predators. However, observing these predators is challenging, as is identifying fish eggs based on morphological traits. In this study, we observed hydroids, which are sessile organisms, consuming pelagic fish eggs. We conducted cytochrome c oxidase I (COI) metabarcoding to identify both the predator and the prey species. Massive COI reads were de novo assembled and nine representative sequences were constructed. The predator, identified from the representative sequences and its morphological features, was determined as Ectopleura crocea. The fish eggs that had been preyed upon belonged to two species: Sillago japonica and Parajulis poecilepterus. Additionally, four arthropod species (Labidocera rotunda, Oithona similis, Paracalanus parvus, and Pseudevadne tergestina) were consumed, and their morphological traits could not be observed, due to digestion. COI metabarcoding was an effective tool for studying the feeding activity of these small predators. Full article

In the context of climate change with frequent natural disasters, disaster risk assessment can provide great help for related risk decision-making. Based on the theory of loss expectation, this paper presents a quantitative method to assess typhoon disaster risk. Among them, the probability of typhoon occurrence is calculated by fitting the optimal structure function of the sample to the joint distribution of wave height, water increment and wind speed. Then, the loss expectation is expressed as the product of typhoon occurrence probability and loss utility, which is used to quantify the loss result of a typhoon disaster. Using the loss utility theory, the risk grade chart is drawn with the direct economic loss rate and the proportion of the affected population as indicators. The results show that the absolute loss value considering the loss utility is slightly higher than the loss value of the quantitative algorithm by 2% to 25%, indicating that the new model reflects the social group’s aversion to typhoon disaster risk. As can be seen from the risk level zoning map, the highest combined risk level typhoons are Prapiroon 0606 and Chanthu 1003, with a risk level of Category 5. The typhoon comprehensive risk level before 2011 was ≥3, and the typhoon comprehensive risk level from 2012 to 2015 was ≤3. The evaluation model has certain feasibility and practicability, and the results can provide a basis and reference for typhoon risk assessment and decision-making. Full article