SHAO Runzhu, TENG Jinfang, FAN Lin, ZHONG Yongjian, JU Zhenzhou, ZHU Mingmin
The honeycomb at the inner band of a compressor stator and the labyrinth on the disk form a sealed cavity, in which the clearance leakage flow has a key impact on the aerodynamic performance of the axial flow compressor. In this paper, focusing on the first 1.5-stage of a low-speed research compressor, numerical simulations are conducted to compare the impact of honeycomb seal structure and slide wall on the aerodynamic performance of the compressor, as well as the performance changes of honeycomb seal structure under two different labyrinth seal clearance conditions. The performance calculation results show that the isentropic efficiency of the compressor equipped with the 0.2-mm-clearance honeycomb cavity model is slightly lower than that of the slide-wall cavity model, which is attributed to the elevated total temperature rise induced by the leakage flow inside the cavity. Comparative analysis of cavity leakage flow characteristics and detailed flow field investigation indicate that honeycomb structure induces a simultaneous increase in both the cavity leakage flow rate and swirl angle. A strong interaction is observed between the airflow within the cavity and the honeycomb structure, creating a complex vortex flow that significantly elevates the total temperature in both the seal cavity and the honeycomb itself. This temperature elevation ultimately leads to a reduction in compressor efficiency. In contrast, when the zero-clearance honeycomb model is compared with the 0.2-mm-clearance honeycomb model, the decreased total temperature ratio contributes to an improvement in isentropic efficiency. In the zero-clearance model, although the average total temperature of the leakage flow rises owing to the reduced clearance, the compressor efficiency is enhanced by the substantial reduction in leakage flow rate. The findings in this paper clarify the quantitative relationship and influence mechanism of leakage flow under different clearance conditions on the performance of the honeycomb and labyrinth seal structure applied to the compressor stator, which therefore provide certain references for the engineering design of honeycomb seal cavities.
Engineering (General). Civil engineering (General), Chemical engineering
Proton exchange membrane fuel cells (PEMFCs) offer a promising zero-emission power solution for maritime transportation, yet thermal management remains challenging due to localized overheating and non-uniform temperature distribution. To address the trade-off between pressure drop and thermal performance in marine PEMFC cooling plates, this study developed and systematically evaluated six flow channel configurations through CFD simulations. Parametric analysis coupled with orthogonal experimental design was employed to explore the effects of secondary flow channel number (<i>N</i>), angle (<i>α</i>), width (<i>d</i>), and spacing (<i>L</i>). The results demonstrated that Type B (parallel flow with secondary channels) reduced the pressure drop by 28.2% while achieving the highest cooling efficiency coefficient (2.66 × 10<sup>4</sup>) compared to conventional configuration. Range analysis further ranked parameter sensitivity and identified optimal parameter combinations for distinct optimization objectives: thermal performance (<i>N</i> = 7, <i>α</i> = 30°, <i>d</i> = 0.5 mm, and <i>L</i> = 2.5 mm), pressure drop (<i>N</i> = 8, <i>α</i> = 75°, <i>d</i> = 1.5 mm, and <i>L</i> = 2.5 mm), and cooling efficiency (<i>N</i> = 8, <i>α</i> = 90°, <i>d</i> = 1.5 mm, and <i>L</i> = 2.5 mm). These findings provide practical guidelines for designing cooling plates that address thermal-hydraulic requirements in marine PEMFC systems, advancing their viability for maritime propulsion applications.
Raghda Jebbad, Joan Pau Sierra, Xavier Gironella
et al.
This study examines the impact of climate change on wave overtopping discharge (<i>q</i>) at eight Moroccan Mediterranean ports, under climate scenarios SSP2-4.5 and SSP5-8.5, projected to the year 2100. To address inter-model variability and better represent future conditions, wave data from four different models were used. The analysis considers three return periods—1, 5, and 25 years—and includes both central estimates and values from the 90% confidence intervals to assess uncertainty from sea level rise (SLR) and wave projections. Results show that overtopping discharges increase with return period, along with the number of ports affected. At 1 year, two ports exceed tolerable thresholds; at 5 years, three ports are impacted; and at 25 years, nearly all ports face overtopping risks. When varying SLR while holding wave height (<i>Hs</i>) constant, discharge variations remain within one order of magnitude. However, when varying <i>Hs</i> with constant SLR, variations span two to three orders of magnitude. These results suggest that accurate <i>Hs</i> projections are more critical than SLR in estimating overtopping risk, emphasizing the need to reduce wave forecast uncertainty to support climate adaptation strategies.
Phytoplankton plays a pivotal role in marine ecosystems and global biogeochemical cycles. Accurate identification and monitoring of phytoplankton are essential for understanding environmental dynamics and climate variations. Despite the significant progress made in automatic phytoplankton identification, current datasets predominantly consist of idealized laboratory images, leading to models that demonstrate persistent limitations in the fine-grained differentiation of phytoplankton species. To achieve high accuracy and transferability for morphologically similar species and diverse ecosystems, we introduce a hybrid dataset by integrating laboratory-based observations with in situ marine environmental data. We evaluate the performance of our dataset on contemporary deep learning models, revealing that CNN-based architectures offer superior stability (85.27% mAcc., 93.76% oAcc.). Multimodal learning facilitates refined phytoplankton recognition through the integration of visual and textual representations, thereby enhancing the model’s semantic comprehension capabilities. We present a fine-tuned visual language model leveraging enhanced textual prompts augmented with expert-annotated morphological descriptions, significantly enhancing visual-semantic alignment and allowing for more accurate and interpretable recognition of closely related species (84.11% mAcc., 94.48% oAcc.). Our research establishes a benchmark dataset that facilitates real-time ecological monitoring and aquatic biodiversity research. Furthermore, it also contributes to the field by enhancing model robustness and transferability to diverse environmental contexts and taxonomically similar species.
To quantitatively assess the storm surge induced by Super Typhoon Doksuri (2023) along the complex coastline of Fujian Province, a high-resolution Finite-Volume Coastal Ocean Model (FVCOM) was developed, driven by a refined Holland–ERA5 hybrid wind field with integrated physical corrections. The hybrid approach retains the spatiotemporal coherence of the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis in the far field, while incorporating explicit inner-core adjustments for quadrant asymmetry, sea-surface-temperature dependency, and bounded decay after landfall. A series of numerical experiments were conducted, including paired tidal-only and full storm-forcing simulations, along with a systematic sensitivity ensemble in which bottom-friction parameters were perturbed and the anomalous (typhoon-related) wind component was scaled by factors ranging from 0.8 to 1.2. Static sea-level rise (SLR) scenarios (+0.3 m, +0.5 m, +1.0 m) were imposed to evaluate their influence on extreme water levels. Storm surge extremes were analyzed using a multi-scale coastal buffer framework, comparing two extreme extraction methods: element-mean followed by time-maximum, and node-maximum then assigned to elements. The model demonstrates high skill in reproducing astronomical tides (Pearson r = 0.979–0.993) and hourly water level series (Pearson r > 0.98) at key validation stations. Results indicate strong spatial heterogeneity in the sensitivity of surge levels to both bottom friction and wind intensity. While total peak water levels rise nearly linearly with SLR, the storm surge component itself exhibits a nonlinear response. The choice of extreme-extraction method significantly influences design values, with the node-based approach yielding peak values 0.8% to 4.5% higher than the cell-averaged method. These findings highlight the importance of using physically motivated adjustments to wind fields, extreme-value analysis across multiple coastal buffer scales, and uncertainty quantification in future SLR-informed coastal risk assessments. By integrating analytical, physics-based inner-core corrections with sensitivity experiments and multi-scale analysis, this study provides an enhanced framework for storm surge modeling suited to engineering and coastal management applications.
At present, the International Maritime Organization (IMO) has issued interim guidelines for the direct stability assessment of surf-riding and broaching for the second-generation intact stability criteria. Accurately and efficiently predicting surf-riding and broaching remains a key problem to be solved for the direct stability assessment of surf-riding and broaching. Therefore, a six-degree-of-freedom(6DOF) coupled mathematical model is established in this paper. Firstly, the four-degree-of-freedom(4DOF) coupled equations of surge–sway–roll–yaw motions are built based on the traditional MMG maneuvering mathematical model by considering Froude–Krylov forces, diffraction forces and restoring forces, and the heave and pitch are approximately calculated by iteratively solving improved static equilibrium equations in real-time, effectively solving the divergence problem in direct time-domain seakeeping calculations of high-speed ships in stern-quartering waves. Secondly, the hydrodynamic lift forces due to the coexistence of wave particle velocity and ship forward velocity are taken into account in the propeller-thrust and rudder-force models. In addition, the real-time emersion of twin rudders in waves is considered in the rudder-force models. At the same time, the free-running model experiments with a ONR tumblehome vessel are carried out in stern-quartering waves, and the pure loss of stability and broaching motions are observed. Finally, comparative validations between the calculations and the experiments of surf-riding and broaching in stern-quartering waves are carried out, and the effects of the ship speed, the instantaneous wetted surface of the hull, rudder exposure, heave and pitch motions on predicting surf-riding and broaching motions are investigated. The computation results show that the established 6DOF mathematical model has enough accuracy to be used for the direct stability assessment of the surf-riding and broaching failure modes.
The precise prediction of ship fuel consumption (SFC) not only serves to enhance energy efficiency to benefit shipping enterprises but also to provide quantitative foundations to aid in carbon emission reduction and ecological environment protection. On the other hand, SFC-related data represent typical multi-source characteristics and heterogeneous features, which lead to several methodological issues (e.g., feature alignment and feature fusion) in SFC prediction. Therefore, this paper proposes a dual-attention parallel network named DAPNet to solve the above issues. Firstly, we design a parallel network structure containing two kinds of long short-term memory (LSTM) and improved temporal convolutional networks (TCNs) for time-series analysis tasks so that different source data can be applied to suitable networks. Secondly, a local attention mechanism is included in each single parallel network so as to improve the ability of feature alignment from different-scale training data. Finally, global attention is employed for the fusion of all parallel networks, which can enrich representation features and simultaneously enhance the performance of SFC prediction. In experiments, DAPNet is compared with 10 methods, including baseline and attention models. The comparison results show that DAPNet and several of its variants obtain the highest accuracy in SFC prediction.
Numerous studies have been conducted to minimize material costs and improve efficiency, one of which involves using the genetic algorithm (GA) for material selection. Although the GA provides the best solution, it is computationally intensive. To mitigate this issue, a simple method was proposed. The stiffened plate, a primary component of ship structure, was chosen as the optimization model for this study, with the objective of minimizing material costs using the proposed simple method. Two design variables, plate thickness (<i>t</i>) and plate material type (<i>m</i>), were selected with specific constraints. The simple method was used to determine the appropriate plate material types to reduce material costs. Additionally, size optimization was conducted using stress equations to produce the optimal thickness. The results showed that this method significantly reduced the computational time and material cost of the ship structure.
The traditional construction methods involving carrying, distributing, recycling, positioning support, state monitoring, and energy supply for autonomous undersea vehicles (AUVs) via a specific support mothership are relatively expensive as well as low in efficiency. Therefore, various scientific research and engineering institutions have begun to study the use of unmanned surface vessels (USVs) for carrying AUVs and providing the necessary technical support. Automatic recovery technology for AUVs is crucial. Accordingly, the development of AUV recovery technology is first introduced herein. Then, AUV autonomous recovery methods based on USV platforms are summarized, including surface slide type, surface cabin dock type, and underwater docking station type. Finally, the key technologies of AUV autonomous recovery are analyzed, including the design of USV-integrated launch and recovery systems, AUV guidance capture devices, and cross-media collaborative control. Thus, this study aims to provide research ideas for breaking through key technologies, develop integrated surface unmanned platforms for AUV operational support and guarantee of AUV operation, improve AUV operational efficiency, and reduce construction risks and cost.
This paper proposes an offshore, unmanned auto-leveling sea-surface drifting platform, with a compact size of 0.7 m in diameter, used for obtaining air-sea interface environmental parameters. The platform was designed based on the parallel mechanism with limited degrees of freedom. The mechanical structure, control system hardware, and software of the principal prototype are introduced. A ground-based device was developed to simulate wave disturbance, based on which the static and dynamic simulation experiments were carried out. Experimental results show that the auto-leveling system can achieve real-time leveling against the angle deviation induced by waves, with a leveling accuracy of 0.2° in a simulated wave with an angle of 12°, which meets the requirements of observation equipment.
Diana María Quintana-Saavedra, Rafael Ricardo Torres-Parra, Richard Guzmán-Martínez
et al.
This paper proposes a comprehensive methodology for the management of submerged cultural heritage sites despite their worldwide location. The methodology is applied to four colonial shipwrecks located in Cartagena de Indias Bay (Colombia), two of them in the Inner Bay and two in the Bocachica sector. Five criteria are used and scored from 1 (indicating a low risk for the wreck) to 5 (high risk). The sum of the scores obtained at each criterion ranges from 5 to 25, and when the value obtained is higher than 15, management action is required. Five criteria were analyzed; (i) The historical criterion is based on the antiquity of the wreck. The ones investigated in this paper are associated with the Battle of Cartagena de Indias (A.D. 1741), having been submerged for ~280 years (all wrecks obtained a score of 3); (ii) The geographical criterion concerns the depth at which the wreck is located, which determines its accessibility. In Cartagena Bay, wrecks are situated at a water depth between 15.6 and 29.7 m (all wrecks were scored 4); (iii) The shipwreck condition criterion indicates the level of preservation, including organic and inorganic material, distinguishing among wooden hulls, ballast stones, and cannons. Obtained scores were 4 and 3 for the wrecks, respectively, located in the Inner Bay and in the Bocachica sector. (iv) The oceanographic criterion, linked to chemical and biological conditions of the water column, influences wreck conservation. All wrecks investigated scored 5. (v) The socioeconomic criterion indicates the multiple maritime and cultural activities presently taking place that might affect the wreck. In Cartagena Bay, all wrecks were scored 4. According to the total score obtained (20—Inner Bay and 19—Bocachica sector), guidelines for shipwreck conservation of cultural heritage in Cartagena Bay are proposed.
The effects of yaw angle on wake characteristics of a stationary square cylinder were investigated in terms of the hydrodynamic forces, the vortex shedding frequency, and the vortical structures using direct numerical simulations (DNS) at a Reynolds number of 1000. In total, four yaw angles, namely, α = 0°, 15°, 30°, and 45°, were considered. The three-dimensional (3D) Navier–Stokes equations were solved directly using the finite volume method in OpenFOAM. It was found that the first-order statistics of the drag coefficient and the Strouhal number satisfied the independence principle (IP) closely. However, the second-order statistics of the drag and lift coefficients deviated apparently from the IP for α ≥ 25°. The iso-surfaces of the spanwise vorticity gradually disorganized and the magnitudes of the spanwise vorticity contour decreased as the yaw angle α was increased from 0° to 45°. By contrast, the streamwise vorticity iso-surfaces were found to become more organized and the magnitudes of the spanwise velocity contour became larger as a result of the increase in yaw angle, indicating the impairment of the quasi-two-dimensionality and the enhancement of the three-dimensionality of the wake flow. Extensive comparisons were also made with previous DNS results for a yawed circular cylinder, and both similarities and differences between these two kinds of cylinder wakes are discussed.
The dynamics of the installation process of marine risers subjected to shoal/deep seawater is studied. The riser is assumed to be a cantilevered Euler‒Bernoulli beam. The upper end of the riser is clamped on the vessel or the drilling platform. The lower end of the riser is connected to the Blowout Preventer Stack (BOPs) and Lower Marine Risers Package (LMRP). The lateral fluid forces induced by the sea wave and sea current are introduced into the governing equations of motion. The lateral displacement and stress distributions of the riser are obtained by solving the governing equation of the riser via Galerkin’s discretisation scheme and a fourth-order Runge‒Kutta algorithm. The results indicate that the riser exhibits different behaviours under various depths because of the different distributions of the flow velocity ranging from the sea surface to the seabed. In the case of shoal water, the dynamics of the riser are dominated by the sea wave, while in the case of deep water it is affected mainly by the sea current velocity and sea surface wind velocity.
An improved genetic collision avoidance algorithm is proposed in this study to address the problem that Autonomous Surface Vehicles (ASV) need to comply with the collision avoidance rules at sea in congested sea areas. Firstly, a collision risk index model for ASV safe encounters is established taking into account the international rules for collision avoidance. The ASV collision risk index and the distance of safe encounters are taken as boundary values of the correlation membership function of the collision risk index model to calculate the optimal heading of ASV in real-time. Secondly, the genetic coding, fitness function, and basic parameters of the genetic algorithm are designed to construct the collision avoidance decision system. Finally, the simulation of collision avoidance between ASV and several obstacle vessels is performed, including the simulation of three collision avoidance states head-on situation, crossing situation, and overtaking situation. The results show that the proposed intelligent genetic algorithm considering the rules of collision avoidance at sea can effectively avoid multiple other vessels in different situations.
A numerical study was conducted to characterize the probability and intensity of storm surge hazards in Canada’s western Arctic. The utility of the European Centre for Medium-Range Weather Forecasts Reanalysis 5th Generation (ERA5) dataset to force numerical simulations of storm surges was explored. Fifty historical storm surge events that were captured on a tide gauge near Tuktoyaktuk, Northwest Territories, were simulated using a two-dimensional (depth-averaged) hydrodynamic model accounting for the influence of sea ice on air-sea momentum transfer. The extent of sea ice and the duration of the ice season has been reducing in the Arctic region, which may contribute to increasing risk from storm surge-driven hazards. Comparisons between winter storm events under present-day ice concentrations and future open-water scenarios revealed that the decline in ice cover has potential to result in storm surges that are up to three times higher. The numerical model was also used to hindcast a significant surge event that was not recorded by the tide gauge, but for which driftwood lines along the coast provided insights to the high-water marks. Compared to measurements at proximate meteorological stations, the ERA5 reanalysis dataset provided reasonable estimates of atmospheric pressure but did not accurately capture peak wind speeds during storm surge events. By adjusting the wind drag coefficients to compensate, reasonably accurate predictions of storm surges were attained for most of the simulated events. The extreme value probability distributions (i.e., return periods and values) of the storm surges were significantly altered when events absent from the tide gauge record were included in the frequency analysis, demonstrating the value of non-conventional data sources, such as driftwood line surveys, in supporting coastal hazard assessments in remote regions.
Houari Hussein, Kadda Boumediene, Samir Belhenniche
et al.
The objective of the current paper is to study the flow around Seiun Maru Highly Skewed (HSP) marine propeller by assessment of blade forces and moments under non-cavitating case. The calculations are performed in open water (steady case) and non-uniform ship wake (Unsteady case). The governing equations based on Reynolds Averaged Navier-Stokes Equation (RANSE) are solved using Finite Volume Method. Ansys Fluent 14.0 is used to implement the simulation. For the steady case, Moving Reference Frame (MRF) is selected while sliding mesh technique is adopted for the unsteady case. Calculated open water performances in terms of thrust and torque coefficients fit very well with experimental data for a wide range of advance ratio. In the unsteady calculations, axial velocities, deduced from the nominal wake, are introduced in the Ansys fluent code. To locate suitably the non-uniform wake in the propeller front plane, three positions of inlet wake have been taken into account to determine their effects on the accuracy of the results. Obtained results show that computed performances are improved compared to panel method when the inlet is close to the propeller.
<b>[Objectives]</b> Due to the limitation of the existing fabrication technology, the sensitivity of hydrophones at different frequency is not exactly the same. Most of the acquisition equipment can only convert acoustic waves to electrical signals by setting up a fixed reference sensitivity,which will lead to the deviation between measured signal and actual signal,so it is necessary to improve the accuracy of the measured signal by amplitude correction. An amplitude correction method of signals measured by hydrophone based on filter design was proposed in this paper to convert the amplitude correction into Finite Impulse Response(FIR)filter design problem.<b>[Methods]</b> Firstly,the filter coefficients that meet the amplitude correction characteristics were designed by the second-order cone programming method. Then, the measured signal is filtered in time domain to achieve amplitude correction.<b>[Results]</b> The processing results show that the relative error of corrected signals decreases with the length of the filter. When the length of the filter is 257,the relative error of the corrected signal is only 0.3%.<b>[Conclusions]</b> The method overcomes the defect of time accumulation required by block processing of Fast Fourier Transform (FFT),and obtains continuous and accurate corrected signals only by using time-domain filter,which has the advantages of good real-time capability,small relative error and low computational cost.
The purpose of the paper is to create a method for studying nonlocal stability in the mean and in the mean square of the ship, positioned on the beam of an intensive wind–waves mode, which is based on the use of the correlation theory of random functions close to continuous Markov processes. With the help of this method and the integral formula of event probability, a method for determining the reliability indicator of the ship in respect of the existing wind–waves excitations of the operating area is formed. An example of investigating the nonlinear motion of the ship, determining its local and nonlocal stability in the first approximation of the theory of considered random functions, is given. Such approximation uses correlation theory with models of acting excitations represented by the generalised derivatives of the Wiener process. Moreover, special attention is paid to reflecting the connection of the proposed methods for investigating the ship stability under constantly acting random excitations with the traditional methods of studying ship stability at small and large inclinations. The established connection defines the proposed methods as a development of the traditional methods of ship stability deterministic theory during the transition to its formation in the class of random functions, with the addition to these methods of the missing link of determining the level of reliability of ships towards the acting wind–waves excitations of the operation area.
In this study, the Reynolds-averaged Navier⁻Stokes (RANS) method and a model experimental test in a towing tank are used to investigate the unsteady hydrodynamic performance of <i>L</i>-type podded propulsion under different oblique flow angles and advance coefficients. The results show that the load of the operative propeller increases with oblique flow angle and the bracket adds resistance to the pod due to the impact of water flow, leading to a reduced propeller thrust coefficient with increased oblique flow angle. Under a high advance coefficient, the speed of increase of the pressure effect is higher than that of the viscosity effect, and the propeller efficiency increases with the oblique flow angle. The nonuniformity of the inflow results in varying degrees of asymmetry in the horizontal and vertical distributions of the propeller blade pressure. Under high oblique flow angle, relatively strong interference effects are seen between venting vortexes and the cabin after blades, leading to a disorderly venting vortex system after the blade. The numerical simulation results are in good agreement with the experimental values. The study findings provide a foundation for further research on <i>L</i>-type podded propulsors.
Generalised reviews of RNA interference (RNAi) in invertebrates, and for use in aquaculture, have taken for granted that RNAi pathways operate in molluscs, but inspection of such reviews show little specific evidence of such activity in molluscs. This review was to understand what specific research had been conducted on RNAi in molluscs, particularly with regard to aquaculture. There were questions of whether RNAi in molluscs functions similarly to the paradigm established for most eukaryotes or, alternatively, was it more similar to the ecdozoa and how RNAi may relate to disease control in aquaculture? RNAi in molluscs appears to have been only investigated in about 14 species, mostly as a gene silencing phenomenon. We can infer that microRNAs including let-7 are functional in molluscs. The genes/proteins involved in the actual RNAi pathways have only been rudimentarily investigated, so how homologous the genes and proteins are to other metazoa is unknown. Furthermore, how many different genes for each activity in the RNAi pathway are also unknown? The cephalopods have been greatly overlooked with only a single RNAi gene-silencing study found. The long dsRNA-linked interferon pathways seem to be present in molluscs, unlike some other invertebrates and could be used to reduce disease states in aquaculture. In particular, interferon regulatory factor genes have been found in molluscs of aquacultural importance such as Crassostrea, Mytilus, Pinctada and Haliotis. Two possible aquaculture scenarios are discussed, zoonotic norovirus and ostreid herpesvirus 1 to illustrate the possibilities. The entire field of RNAi in molluscs looks ripe for scientific exploitation and practical application.