ObjectiveTo address the low efficiency of vessel equipment fault diagnosis and the challenges in effective communication with commanders, this study proposes an intelligent solution. This solution employs natural language interaction to rapidly identify fault causes and recommend appropriate maintenance plans. MethodFirst, based on the domain-oriented design concept, an intelligent question answering system was developed by integrating large language models with retrieval-augmented generation technology. Then, a set of document preprocessing methods and comprehensive retrieval strategies were introduced to enhance system performance. Finally, a comprehensive evaluation scheme was devised to thoroughly assess the system.ResultsExperimental results show that by merely using natural language to describe the observed fault symptoms, the system can accurately identify fault causes and provide corresponding maintenance solutions, significantly improving diagnostic efficiency. Compared to basic question answering systems, the optimized system achieved a twofold improvement in ROUGE score, a nearly 30% increase in BERTScore, and a 1.5-fold increase in expert ratings. Additionally, it reduced response time by 95% compared to traditional manual retrieval methods. ConclusionThis offers robust technical support for the rapid restoration of equipment performance on coast guard vessels operating in complex mission environments, effectively enhancing their combat effectiveness and mission execution capabilities.
This paper explores the legal framework surrounding the classification of “other persons” aboard vessels under the Ship Safety Act, particularly in comparison to international maritime conventions such as SOLAS. The term “other persons” has been a source of ambiguity and safety concerns, especially following several maritime accidents, including the 2024 collision near Yeoseodo. In Korea, truck drivers and other non-crew individuals have been permitted to board vessels as “other persons,” often exceeding permissible limits, raising significant safety and regulatory issues. This research examines the inconsistencies between Korea’s Ship Safety Act and international standards, noting that other major maritime nations impose stricter limits and clearer definitions on non-passenger personnel. Recommendations include aligning domestic laws with international conventions by redefining “other persons” and enforcing a stricter cap on non-crew passengers to enhance safety. The paper also addresses the need for categorizing individuals boarding vessels into clearer groups – crew, passengers, industrial personnel, and specialized personnel – to ensure legal clarity and improve compliance with global maritime safety standards. Through a comparative legal analysis, the paper advocates for the adoption of international norms in Korea’s maritime regulations.
To enable early identification of failure risks in ship systems and equipment, a dynamic cloud center of gravity model is developed for real-time system-level health assessment. First, the Functional Analysis System Technique (FAST) was applied to decompose the operational functions and dependencies of the intelligent machinery room system, enabling the structured establishment of a hierarchical evaluation index system. The comprehensive weight is derived through synergistic application of the fuzzy set (FS) theory and entropy weight. This process integrated expert-defined functional boundaries with measurable parameters critical to system performance. Then, an improved cloud center of gravity method based on the Gaussian cloud model and sliding time window method is used for the system’s adaptive health value calculation. The dynamic health model can achieve continuous online assessment and track the further evolution of the system. Finally, the proposed model is applied to the Fuel Oil Supply System (FOSS). The integration of system performance output and disassembly inspection results demonstrates that the method proposed in the article more accurately reflects the true health status changes in the system when mapping health values.
AbstractThis paper optimizes condition‐based replacement policies for a mission‐oriented system. The key challenge in our problem is that the system does not work under a fixed mission type but is subject to an infinite sequence of random types of missions assigned in a Markovian manner, which is realistic in many practical situations. The mission process modulates the deterioration process. Taking advantage of the opportunities when missions are switched, condition monitoring is conducted to support replacement decision‐making. This paper considers two practical scenarios in which the type of the next mission is either available or unavailable at each decision epoch. The objective is to determine the optimal replacement decisions for both scenarios that minimize their long‐run expected average cost rates. The optimization problems are analyzed in the framework of the Markov decision process. The optimal decisions of both scenarios are proven to be of partially monotone control‐limit forms. Near‐optimal policies with multilevel thresholds are provided for more convenient decision‐making. The policy iteration algorithm is modified for efficient optimization. A numerical example is used to demonstrate the feasibility of the proposed approach.
The diverse nature of hull components in shipbuilding has created a demand for intelligent robots capable of performing various tasks without pre-teaching or template-based programming. Visual perception of a target’s outline is crucial for path planning in robotic edge grinding and other processes. Providing the target’s outline from point cloud or image data is essential for autonomous programming, requiring a high-performance algorithm to handle large amounts of data in real-time construction while preserving geometric details. The high computational cost of triangulation has hindered real-time industrial applications, prompting efforts to improve efficiency. To address this, a new improvement called Directive Searching has been proposed to enhance search efficiency by directing the search towards the target triangle cell and avoiding redundant searches. Another improvement, Heritable Initial, reduces the search amount by inheriting the start position from the last search. Combining Directive Searching and Heritable Initial into a new method called DSHI has led to a significant efficiency advancement, with a calculation efficiency improvement of nearly 300–3000 times compared to the ordinary Bowyer–Watson method. In terms of outlines extraction, DSHI has improved the extraction efficiency by 4–16 times compared to the ordinary Bowyer–Watson methods, while ensuring stable outlines results, and has also increased the extraction efficiency by 2–4 times compared to PCL. The DSHI method is also applied to actual ship component edge-grinding equipment, and its effect meets the shipbuilding process requirements. It could be inferred that the new method has potential applications in shipbuilding and other industries, offering satisfying efficiency and robustness for tasks such as automatic edge grinding.
Positioning errors introduced by low-precision navigation devices can affect the overall accuracy of a positioning system. To address this issue, this paper proposes a master-slave multi-AUV collaborative navigation method based on hierarchical reinforcement learning. First, a collaborative navigation system is modeled as a discrete semi-Markov process with defined state and action sets and reward functions. Second, trajectory planning is performed using a hierarchical reinforcement learning-based approach combined with the polar Kalman filter to reduce the positioning error of slave AUVs, realizing collaborative navigation in multi-slave AUV scenarios. The proposed collaborative navigation method is analyzed and validated by simulation experiments in terms of the relative distance between the master and slave AUVs and the positioning error of a slave AUV. The research results show that the proposed method can not only successfully reduce the observation and positioning errors of slave AUVs in the collaborative navigation process but can also effectively maintain the relative measurement distance between the master and slave AUVs within an appropriate range.
In this study, the T-matrix method combined with the addition theorems of spherical basis functions is applied to semi-analytically compute the underwater far-field acoustic scattering of a pair of rigid spheroids with arbitrary incident angles. The involvement of the addition theorems renders the multiple scattering fields of each spheroid to be translated into an identical origin. The accuracy and convergence property of the proposed method are verified and validated. The interference of specular reflection wave and Franz wave can be spotted from the oscillations of the form function. Furthermore, the propagation paths of specular reflection and Franz waves are quantitatively analyzed in the time domain with conclusions that the Franz waves reach the observation point subsequent to specular reflection waves and the time interval between these two wave series is equal to the time cost of the Franz waves traveling along the sphere surfaces. Finally, the effects of separation distances, aspect ratios (the ratio of the polar radius to equatorial radius), non-dimensional frequencies, and incidence angles of the plane wave on the far-field acoustic scattering of a pair of rigid spheroids are studied by the T-matrix method.
Unexpected large waves known as freak or rogue waves are a phenomenon emerging in the World Ocean and are causing significant damage to vessels and coastal structures. These waves are often associated with deep-water waves; however, they can also be dangerously close to the shore. The present study is devoted to the numerical modeling of the sea state with parameters close to the ones of the freak wave event that happened in Tillamook Bay, Oregon, on 25 January 2007. Parameters of waves and winds are taken from the description of the event and from the reanalysis model ERA5, which proved to be in good agreement. The Korteweg–de Vries equation is chosen to be the model for the numerical simulation as it is an etalon model for water waves in shallow water with weak nonlinearity and dispersion. Possible scenarios of occurrence of freak waves have been analyzed. Lifetimes of freak waves of different shapes have been estimated.
John A. Theodorou, Vasileios Minasidis, Athina Ziou
et al.
The present study investigates through an integrated survey, for the first time in Greek shellfish market, the marketing distribution towards a new edible shellfish product that of the non-indigenous pearl oyster <i>Pinctada imbricata radiata</i>. The survey conducted through personal interviews on sector entrepreneurs/staff of the supply (i.e., shellfish producers, wholesalers, fishmongers, owners of restaurants). Internet-based quantitative research was also conducted to explore the market supply of the pearl oyster covering all nine regional units of Greece. The market for pearl oyster seems to be there as a substitute of the major commercial species in seasons of shortages. There is a specimen mislabeling throughout Greece, thus, extraction of significant information about the market supply of pearl oyster is deficient. Further knowledge on the bivalve shellfish value chain is needed, to define how the wild and the farmed species (mussels) interact in the market and in the distribution channels, toward a product-easy to use in the supply chain and friendly to the consumer. Findings also raises additional concerns as a priority for conservation, and the current practices do not satisfy the Common Fisheries Policy in terms of traceability.
Propeller-induced longitudinal vibration resonance in marine propulsion shafting systems causes great harm to the hull structure and is the primary source of shipboard noise. Integrating a friction damper with designed parameters into thrust bearings can prevent these issues. To investigate the performance of the damper-integrated thrust bearing in longitudinal vibration transmission control, an experimental and theoretical study is carried out in a laboratory-assembled test rig, which consists of components similar to the existing marine propulsion system. We developed a prototype of a thrust bearing designed with a friction-damping generation that allows switching from two supporting states, i.e., damper-connected and damper-disconnected states. Furthermore, a nonlinear analysis method for friction dampers is proposed. By this method, the way in which the friction damper changes the dynamic characteristics of the shafting system is analyzed. Based on the test rig, the acceleration frequency response function (AFRF) of the thrust bearing with and without a friction damper is measured. By comparison, the effectiveness of the friction damper is proved. The experimental results show that the friction damper suppresses the shafting longitudinal vibration response in a broadband frequency range and also confirms the stability of the damping effect, which does not change with the shafting rotational speed or static thrust from the propeller.
Confined environments increase psychological stress and lead to health problems such as abnormal mood and rhythm disruption. However, the mechanism by which confined environments impact health has remained unclear. Significant correlations have been reported between psychological stress and changes in gut microbiota. Therefore, we investigated the effect of a confined environment on the composition of the gut microbiota by 16s rDNA high-throughput sequencing, and analyzed the correlation between gut microbiota and health indicators such as uric acid (UA), sleep, and mood. We found that the gut microbiota of the subjects clustered into two enterotypes (Bi and Bla), and that the groups differed significantly. There were notable differences in the abundances of genera such as Bifidobacterium, Dorea, Ruminococcus_torques_group, Ruminococcus_gnavus_group, Klebsiella, and UCG-002 (p < 0.05). A confined environment significantly impacted the subjects’ health indicators. We also observed differences in how the subjects of the two enterotypes adapted to the confined environment. The Bi group showed no significant differences in health indicators before and after confinement; however, the Bla group experienced several health problems after confinement, such as increased UA, anxiety, and constipation, and lack of sleep. Redundancy analysis (RDA) showed that UA, RBC, mood, and other health problems were significantly correlated with the structure of the gut microbiota. We concluded that genera such as UCG-002, Ruminococcus, CAG352, and Ruminococcus_torques_group increased vulnerability to confined environments, resulting in abnormal health conditions. We found that the differences in the adaptability of individuals to confined environments were closely related to the composition of their gut microbiota.
AbstractThis paper studies a combined replenishment and warehouse size planning problem. A firm (3PW user) decides the replenishment quantities over a finite planning horizon to satisfy the time‐varying demands of a product. The firm has no warehouse and contracts with a third‐party warehousing (3PW) provider for storage space over the planning horizon. In the warehousing contract, the planning horizon is partitioned into a number of sessions, and each session also consists of multiple periods. The firm decides a stationary base storage size (BSS) of each session and has an opportunity to adjust the BSS at the beginning of each session. The firm also has the option to rent additional storage size beyond the BSS by paying higher rental cost in each individual period. We explore structural properties and develop a strongly polynomial‐time algorithm by applying geometric techniques to solve the firm's replenishment and warehouse sizing problem. We also conduct numerical experiments and provide important insights into the 3PW user's decisions and the 3PW contract design.
ObjectivesThe hydrodynamic performance of three-dimensional hydrofoils with different shapes is studied in order to find the optimal hydrofoil geometry.Methods NACA 0012 hydrofoil model with different aspect ratios, tip ratios, forward-swept and back-swept shapes are used to simulated the flow field of the hydrofoil with multi-DOF coupling motion based on the NUMECA Fine/Marine solver. The reliability of the numerical method is validated by comparison with the experimental results and analysis of grid independence.ResultsThe results show that a hydrofoil with a larger aspect ratio has better performance. By comparing the results of hydrofoils with the same aspect ratio and different tip ratios, it is found that tip ratio causes performance degradation. By comparing the results of forward-swept, back-swept and trapezoidal hydrofoils with the same tip ratio, it is found that the performance of the back-swept hydrofoil is optimal, and the shape of the trailing edge has great influence on hydrofoil performance.ConclusionsThis study obtains certain optimal geometrical parameters of flapping foil propulsors, and achieves greater understanding of the characteristics of wake vortex structures.
Zhen-hua Wang, Zhen-hua Wang, Xiao-gang Bao
et al.
Lack of vascularization is directly associated with refractory wound healing in diabetes mellitus (DM). Enrichment of endothelial precursor cells (EPCs) is a promising but challenging approach for the treatment of diabetic wounds. Herein, we investigate the action of nicotinamide riboside (NR) on EPC function for improved healing of diabetic wounds. Db/db mice that were treated with NR-supplemented food (400 mg/kg/d) for 12 weeks exhibited higher wound healing rates and angiogenesis than untreated db/db mice. In agreement with this phenotype, NR supplementation significantly increased the number of blood EPCs and bone marrow (BM)-derived EPCs of db/db mice, as well as the tube formation and adhesion functions of BM-EPCs. Furthermore, NR-supplemented BM-EPCs showed higher expression of sirtuin 1 (Sirt1), phosphorylated adenosine monophosphate–activated protein kinase (p-AMPK), and lower expression of acetylated peroxisome proliferator–activated receptor γ coactivator (PGC-1α) than BM-EPCs isolated from untreated db/db mice. Knockdown of Sirt1 in BM-EPCs significantly abolished the tube formation and adhesion function of NR as well as the expression of p-AMPK and deacetylated PGC-1a. Inhibition of AMPK abolished the NR-regulated EPC function but had no effect on Sirt1 expression, demonstrating that NR enhances EPC function through the Sirt1-AMPK pathway. Overall, this study demonstrates that the oral uptake of NR enhances the EPC function to promote diabetic wound healing, indicating that NR supplementation might be a promising strategy to prevent the progression of diabetic complications.
Ira B. Schwartz, Victoria Edwards, Sayomi Kamimoto
et al.
Dynamical emergent patterns of swarms are now fairly well established in nature and include flocking and rotational states. Recently, there has been great interest in engineering and physics to create artificial self-propelled agents that communicate over a network and operate with simple rules, with the goal of creating emergent self-organizing swarm patterns. In this paper, we show that when communicating networks have range dependent delays, rotational states, which are typically periodic, undergo a bifurcation and create swarm dynamics on a torus. The observed bifurcation yields additional frequencies into the dynamics, which may lead to quasi-periodic behavior of the swarm.
Xujian Lyu*, Dongdong Tang, Yanmin Guan and Jianglong Sun 1School of Energy and Power Engineering, Nanjing University of Science and Technology, Nanjing 210 094, P R China 2School of Naval Architecture and Ocean Engineering, Jiangsu University of Science and Technology, Zhenjiang 212 003, P R China 3School of Naval Architecture and Ocean Engineering, Huazhong University of Science and Technology, Wuhan 430 074, P R China