Hasil untuk "Naval Science"

Pierre Daniel, Guy Claireaux, Nicolas Cormier et al.

The disappearance of the trawler <i>Ravenel</i> in January 1962, resulting in the loss of fifteen men from the Saint-Pierre-and-Miquelon archipelago, has long remained unresolved. This study integrates archival documentation, eyewitness testimony, atmospheric and oceanic reanalyses, and probabilistic drift modelling to reconstruct the circumstances of the loss and to constrain the wreck location. Backward and forward drift simulations were conducted using the MOTHY sea-drift model, incorporating high-resolution tidal dynamics and wind forcing from ERA-20C and ERA5 reanalysis. Results show that uncertainty in debris stranding time exerts a much stronger influence on reconstructed drift paths than uncertainty in stranding location. The discovery of the wreck in May 2025 enabled forward simulations that indicated a most probable sinking time, with ERA5 producing debris stranding times consistent with historical observations. These results confirm the predictive skill of the modelling framework while highlighting remaining uncertainties regarding the sequence of events preceding the sinking.

Changpeng Zhang, Xin Zhao

The integration of advanced wave scattering physics into operational forecast systems like WAVEWATCH III is often hindered by the computational complexity of high-fidelity models. While the diffusion approximation framework of Zhao and Shen (2016) offers a promising alternative to the full Boltzmann equation, its requirement to solve for multiple coupled auxiliary variables (e.g., transmitted and scattered components) presents a significant barrier to practical implementation. To overcome this challenge, this study proposes a novel algorithmic simplification that enhances the model's computational efficiency and tractability. Our key innovation is the introduction of an effective mean action density variable, Neff, formed by combining the transmitted energy and the isotropically redistributed scattered energy. This unification reduces the system's dimensionality, eliminating one prognostic equation and streamlining numerical integration. Validation against benchmark solutions demonstrates that the proposed model accurately captures the directional spreading of wave energy while offering a more computationally efficient pathway. By providing a streamlined and operationally viable framework, this work bridges a critical gap between theoretically rigorous scattering models and the demands of large-scale forecasting.

Qihuan WU, Zhiyu ZHU, Weihan HAO et al.

ObjectivesIn order to ensure the safe and stable operation of a shipboard power system under fault conditions, a dynamic reconfiguration optimization method is proposed that considers time-varying load characteristics.MethodsFirst, considering the topological structure, generation capacity limit, line current, node voltage and other constraints of the shipboard power system, a dynamic reconfiguration optimization strategy is proposed to minimize weight load cutting and voltage deviation. Next, an improved inertial particle swarm optimization algorithm is used to solve the optimization model. Finally, a typical shipboard power system is used as an example to verify the effectiveness of the proposed method.ResultsThe simulation results show that compared with the static reconfiguration method, the dynamic reconfiguration method can reduce the system's voltage deviation by 9.94%, thus significantly improving the quality of the network power supply.ConclusionsThe results of this study can provide references for the reliability design of shipboard power systems.

Alfonso Arrieta-Pastrana, Edwin A. Martínez-Padilla, Modesto Pérez-Sánchez et al.

Currently, hydrodynamic models for bay and estuarine systems involve many parameters that require proper calibration to design coastal structures effectively. However, in coastal regions with limited data availability, the implementation of such models becomes challenging. This research introduces a simplified hydrodynamic methodology designed to analyse the impact of hydraulic control structures in shallow waters. This approach offers a computationally efficient alternative that allows engineers to rapidly evaluate the impact of horizontal and vertical constrictions in shallow waters experiencing wave propagation. A practical application is demonstrated in a one-dimensional channel with a length of 200,000 m and an average depth of 5 m. The only parameter required for calibration in the proposed methodology is bed friction. The three analysed scenarios—longitudinal constriction, plan-view constriction, and the influence of bed friction—demonstrate the model’s sensitivity to these variations, highlighting its reliability as a decision-making tool for coastal engineering projects. Moreover, the comparison of the proposed hydrodynamic simulation methodology at the stabilised tidal inlet structure in Cartagena de Indias, Colombia, demonstrated its ability to reproduce observed water levels accurately, reinforcing its reliability and potential for broader application.

Dhawan Manish, Aditya Joshi, Shyam Madabushi et al.

Background: Outcomes of Veno-Venous extracoporeal membrane oxygenation during resource limited settings of SARS-nCOV2 pandemic from a denovo ECMO centre. Methods: Adult patients with age more than 18 years on VV-ECMO were evaluated on the duration of the onset of symptoms to hospital admissions (direct or referred); mechanical ventilation; time to initiate ECMO, Murray score, PaCO2, and PaO2/FiO2 ratio; associated organ injury; duration of intensive care unit; hospital stay; and mortality. Results: From 01 Jun 2020 to 30 May 2022, eight patients were placed on VV-ECMO. The mean age of cannulation was 46 years. Two (25%) patients were health-care workers. The mean Murray score, PaCO2, and the PaO2/FiO2 ratio were 3.375, 72.5 mmHg, and 65.98, respectively. The average time to initiate ECMO was 8.375 days from the time of admission, with an average duration of ECMO of 16.375 days. One (12.5%) survived the intervention and was discharged uneventfully. Conclusions: Delayed initiation of VV-ECMO in severe SARS-nCoV2 acute respiratory distress syndrome may result in higher mortality and worse outcomes.

Konstantinos Psaraftis, Klimis S. Ntalianis, Nikos E. Mastorakis

Carpooling services are increasingly popular due to their potential for reducing fares, shortening travel times, and increasing driver income. However, despite the efforts of many carpooling recommendation systems to balance the often conflicting objectives of drivers and passengers, there remains significant room for improvement in effectively managing these objectives. To address this challenge, a novel quality of experience-oriented, eco-friendly taxi-ride recommendation system called QE-Ride is proposed. This system optimizes taxi selection for passengers by evaluating factors such as time delay tolerance, preferred vehicle capacity, fare reduction preferences, tolerance for additional driving distance, as well as preferences for driver safety, eco-friendliness, and the past ratings of both drivers and co-travelers. For drivers, QE-Ride considers their preferred vehicle capacity, interest in profit maximization, and passengers&#x2019; past ratings. The effectiveness of QE-Ride was validated using GPS trace data from 10,357 taxicabs, demonstrating the system&#x2019;s ability to align with both drivers&#x2019; and passengers&#x2019; incentives while accounting for real-time traffic conditions. The results indicate that QE-Ride outperforms existing systems in key areas, including reducing total mileage, lowering passenger fares, and increasing driver profits. By introducing a balanced approach that considers eco-friendliness, safety, and other critical factors, QE-Ride offers a promising enhancement to the overall carpooling experience, making it a standout tool in the domain of ride-sharing services.

Jialun LIU, Zhilin DONG, Shijie LI et al.

ObjectiveAiming at the problem of the autonomous berthing control of tugboats, this study focuses on the application of a target tracking control strategy based on virtual leadership. MethodsFirst, the autonomous berthing process of the tugboat is transformed into the target tracking control process of the virtual tugboat and actual tugboat. A kinematics model of the berthing system is then designed. Considering special environmental interference in the berthing scenario, the backstepping method and sliding mode control method are used to design an autonomous berthing controller for an azimuth stern drive tugboat. Three different sliding mode surfaces are provided and the stability is verified by the Lyapunov function. Finally, a simulation test is used to verify the control effect through the berthing trajectory, speed error and distance error. ResultsThe simulation results show that the designed tugboat autonomous berthing control strategy and controller have a good effect in the tugboat autonomous berthing scenario and good performance in the face of uncertain disturbances of the system. ConclusionsThe control strategy and berthing controller designed in this paper have good applicability and robustness. The autonomous berthing control of tugboats is realized from a new angle, providing a new direction for subsequent research on the berthing control of tugboats.

Rahmawati Rahmawati, Yushinta Aristina Sanjaya, Sri Alam Syah Lihan Candra Asih et al.

Fishery resources are a good source of food for human health. The fisheries sector plays a role in food security, not only as a complement but also plays a role in fulfilling food, nutrition, and protein sources, as well as people's income. Food security is closely related to the continuity of fish supply to meet people's needs. In this study the method used was survey method with the type of research used was descriptive research with a quantitative approach and data collection techniques in this study by conducting a survey using a questionnaire. The low consumption of fish in the community is caused by a lack of public knowledge about information on the nutritional content and benefits of consuming fish. The survey results stated that 89.3% of the respondents already knew the benefits of fish and the remaining 10.7% did not know the benefits of fish. As much as 85.4% of the people of Jombang District, East Java, get fish by buying it themselves at traditional markets with 80.6% liking fresh fish products and 19.4% liking processed fish products. As many as 79.6% of the people of Jombang District, East Java consider the quality of fish before buying fish; 45.6% stated that the ease of obtaining fish was their consideration in buying fish; and 50.5% stated price as their consideration in buying fish. As many as 83.5% of respondents stated that there was no difference in fish consumption patterns before and after the pandemic era. After the pandemic, people's frquency in consuming fish has increased, although not significantly. This is possibly due to the start of a sense of public awareness of the body's nutritional needs after the pandemic era.

SONG Chuanming, DU Qinjun, LI Cunhe, LUO Yonggang

Aimed at the joint vibration problem caused by the load change of humanoid flexible joint, a torque compensation control method based on state observer is proposed. By controlling the motor to output a torque increment equivalent to the disturbance torque, the joint torque can quickly balance the load torque and shorten the oscillation process of the elastic element passively adapting to the load change. A state observer for estimating load disturbance torque and motor speed is designed, whose convergence is proved by the Lyapunov function. The control structure of the drive system based on the proportional integral-intergral proportional (PI-IP) speed regulator is established, and the observer output feedforward link is added to the speed regulator to improve the anti-interference ability of the system. The simulation results show that compared with proportional integral differential (PID) control and joint force feedback proportional differential (PD) control, the proposed method can restore the motor speed to stability within 0.6 s after load change and realize joint vibration suppression within 1 s. Besides, the joint speed adjustment time is shortened by about 1.8 s and 0.9 s respectively, which effectively improves the dynamic adjustment ability of the system. Finally, the effectiveness of the proposed method was verified by experiments on an integrated flexible joint testing platform.

Hongchu Yu, Xinyu Bai, Jingxian Liu

With the rapid development of the global economy and trade, the number of ships serving ports in China is increasing continuously. Port traffic is becoming busier, and ship behavior is more complex and changeable. The analysis of ship behavior patterns in port waters has become an urgent problem to improve the efficiency and safety of port areas. In this paper, through the full integration of ship trajectory and port geographic information, the behavior chain of a single ship across the whole process of entering and exiting the port is identified. The traffic complexities and dynamics can be further analyzed by grouping the movement patterns of large ships. Based on graph theory, the port areas can be described as a transportation network in which functional areas are nodes and fairways between different areas are edges. The traffic can be analyzed through the network structure characteristics, such as node degree, node weight, and edge weight, and by their similarities and differences. This methodology provides a quantitative analysis for exploring the behavior patterns of large ships as well as the various traffic complexities. A case study in Tianjin Port has been conducted to verify the proposed model. The results show that it can accurately analyze a ship behavior’s regularity, occasion, and correlation. It provides a theoretical reference for the port to schedule and formulate emergency plans.

Chen Zhuang, Hongbo Zhao, Yuli He et al.

High-precision positioning methods have drawn great attention in recent years due to the rapid development of smart vehicles as well as automatics driving technology. The Real-Time Kinematic (RTK) technique is a mature tool to achieve centimeter-level positioning accuracy in open-sky areas. However, the users who drive under dense urban conditions are always confronted with harsh global navigation satellite system (GNSS) environments. Skyscrapers and overpasses block the signals and reduce the number of visible satellites, making it difficult to achieve continuous and precise positioning. Considering that the road is relatively smooth in most urban areas, vehicles are expected to travel on the same plane when they are close to each other. The road plane information is a promising candidate to enhance the performance of the RTK method in constrained environments. In this paper, we propose a plane-constrained RTK (PCRTK) method using the positioning information from cooperative vehicles. In a vehicle-to-vehicle (V2V) network, the positions of cooperative vehicles are used to fit a road plane for the target vehicle. The parameters of the plane fitting are treated as new measurements to enhance the performance of the float estimator. The relationship between the plane parameters and the state of the estimator is derived in our study. To validate the performance of the proposed method, several experiments with a four-vehicle fleet were carried out in open-sky areas and dense urban areas in Beijing, China. Simulations and experimental results show that the proposed method can take advantage of the plane constraint and obtain more accurate positioning results compared to the traditional RTK method.

Gabriele Boscolo Palo, Manfredi Di Lorenzo, Salvatore Gancitano et al.

Elasmobranchs are among the marine species more threatened by overfishing. Their conservation is often impaired by the lack of knowledge of species’ life history traits. We filled knowledge gaps on age and growth of two threatened smooth-hound sharks (<i>Mustelus mustelus</i>, <i>Mm</i>; <i>Mustelus punctulatus</i>, <i>Mp</i>) in the central Mediterranean Sea, combining standard vertebrae analysis with growth increment data from a tagging survey. Our data revealed that the two species grow at a faster rate than previously estimated using vertebrae reading only. The maximum age/size found was higher for <i>Mm</i> (16 years, 170 cm TL) than <i>Mp</i> (8 years, 120 cm TL), the first species attaining larger size-at-age than the second one. <i>Mp</i> reaches maturity at earlier ages (A₅₀ 3 years for both females and males) than <i>Mm</i> (A₅₀ females: 4 years; males: 3 years). The use of the tag-recapture method to validate the growth rate, firstly derived by sectioned vertebrae readings, highlighted the presence of false check marks. The new estimates of growth and longevity have important implications for the assessment of natural mortality, productivity, and stock resilience to fishing pressure which, combined with the high site fidelity highlighted by tagging data, may have crucial implications for the conservation of these two threatened sharks in the Mediterranean Sea.

Anastasia Patera, Zoi Pataki, Dimitra Kitsiou

Marine spatial planning (MSP) has been established as the appropriate policy framework to study and resolve conflicts that arise among various activities. A pre-requisite for the successful implementation of MSP is the availability of efficient tools to support decision-makers and enhance stakeholders’ engagement. In this paper, a webGIS application is proposed that is able to assess the intensity of conflicts among marine activities; the area of the Cyclades in the Aegean Sea was used as a case study. The webGIS application allows the visualization of existing activities, the delineation of conflicting activities, the detection of areas where multiple conflicts co-exist, and the delineation of areas of conflicts based on specific criteria. The webGIS application is available via a user-friendly interface as well as allowing interaction with users by providing them the opportunity to comment on the results and/or exchange ideas with other users of various groups; therefore, the participatory process, a creative stage in MSP, is further supported. The usefulness of such tools in coastal and marine planning and the decision-making process are further discussed.

Haichao Wang, Guorun Yang, Wei Kang et al.

Electrified ports using medium-voltage DC (MVDC) renewable energy microgrids require current-fed dc/dc converters in application scenarios such as battery or ultracapacitor charging units and hydrogen production systems. This paper designs a three-level phase-shift full-bridge (TL-PSFB) converter that interfaces with the MVDC microgrid. Its operation in the current source mode requires a wide output voltage range and small output current ripple. Firstly, the dual-output TL-PSFB topology is introduced, and the principle of phase-shift pulse width modulation (PS-PWM) is presented. Secondly, the principle of the traditional constant-conduction-duty-cycle (CCDC) strategy is analyzed. Then, a minimum-output-current-ripple (MOCR) strategy is proposed by analyzing the relationship between output current ripple, conducting-duty cycle, and phase-shift duty cycle, and a constant current control combined with the MOCR strategy is designed. The output current ripple of the MOCR strategy is smaller than that of the CCDC strategy in a full range of operating conditions. Under the same output current ripple design index, the value and loss of the filter inductor can be reduced with the MOCR strategy. In addition, the MOCR strategy can widen the output voltage regulation range and increase the bus voltage utilization without causing significant changes to the total harmonic distortion (THD) of primary voltage. Finally, experimental results verify the correctness of the theoretical analysis.

Kaichuan Sun, Fei Meng, Yubo Tian

As an image processing method, underwater image enhancement (UIE) plays an important role in the field of underwater resource detection and engineering research. Currently, the convolutional neural network (CNN)- and Transformer-based methods are the mainstream methods for UIE. However, CNNs usually use pooling to expand the receptive field, which may lead to information loss that is not conducive to feature extraction and analysis. At the same time, edge blurring can easily occur in enhanced images obtained by the existing methods. To address this issue, this paper proposes a framework that combines CNN and Transformer, employs the wavelet transform and inverse wavelet transform for encoding and decoding, and progressively embeds the edge information on the raw image in the encoding process. Specifically, first, features of the raw image and its edge detection image are extracted step by step using the convolution module and the residual dense attention module, respectively, to obtain mixed feature maps of different resolutions. Next, the residual structure Swin Transformer group is used to extract global features. Then, the resulting feature map and the encoder’s hybrid feature map are used for high-resolution feature map reconstruction by the decoder. The experimental results show that the proposed method can achieve an excellent effect in edge information protection and visual reconstruction of images. In addition, the effectiveness of each component of the proposed model is verified by ablation experiments.

Muhammad Umair, Muhammad Shahbaz Khan, Fawad Ahmed et al.

The COVID-19 outbreak began in December 2019 and has dreadfully affected our lives since then. More than three million lives have been engulfed by this newest member of the corona virus family. With the emergence of continuously mutating variants of this virus, it is still indispensable to successfully diagnose the virus at early stages. Although the primary technique for the diagnosis is the PCR test, the non-contact methods utilizing the chest radiographs and CT scans are always preferred. Artificial intelligence, in this regard, plays an essential role in the early and accurate detection of COVID-19 using pulmonary images. In this research, a transfer learning technique with fine tuning was utilized for the detection and classification of COVID-19. Four pre-trained models i.e., VGG16, DenseNet-121, ResNet-50, and MobileNet were used. The aforementioned deep neural networks were trained using the dataset (available on Kaggle) of 7232 (COVID-19 and normal) chest X-ray images. An indigenous dataset of 450 chest X-ray images of Pakistani patients was collected and used for testing and prediction purposes. Various important parameters, e.g., recall, specificity, F1-score, precision, loss graphs, and confusion matrices were calculated to validate the accuracy of the models. The achieved accuracies of VGG16, ResNet-50, DenseNet-121, and MobileNet are 83.27%, 92.48%, 96.49%, and 96.48%, respectively. In order to display feature maps that depict the decomposition process of an input image into various filters, a visualization of the intermediate activations is performed. Finally, the Grad-CAM technique was applied to create class-specific heatmap images in order to highlight the features extracted in the X-ray images. Various optimizers were used for error minimization purposes. DenseNet-121 outperformed the other three models in terms of both accuracy and prediction.

Pengyao Yu, Muk Chen Ong, Hui Li

The impact between the wave and the bottom of a high-speed vessel is often simplified as water-entry problems of wedges. Most investigations focus on the water entry of two dimensional (2D) wedges. The effects of added mass and structural damping are still not fully investigated. By combining the normal mode method, the hydrodynamic impact model of rigid wedges and the potential flow theory, a dynamic model for predicting the response of a three dimensional (3D) wedge impacting on water with a constant velocity is established in this paper. The present model can selectively consider the effects of the added mass and the structural damping. The present method has been validated through comparisons with results of published literatures and commercial software. It is found that the added mass can increase the stress response before the flow separation, and reduce the vibration frequency after the flow separation. Due to the effect of the added mass, the stress response of some positions after the flow separation is even higher than that before the flow separation. The structural damping has a negligible effect on the stress before the flow separation, but it can reduce vibration stress after the flow separation.

Chang-Li Yu, Zhan-Tao Chen, Chao Chen et al.

Comprehensive consideration regarding influence mechanisms of initial imperfections on ultimate strength of spherical shells is taken to satisfy requirement of deep-sea structural design. The feasibility of innovative numerical procedure that combines welding simulation and non-linear buckling analysis is verified by a good agreement to experimental and theoretical results. Spherical shells with a series of wall thicknesses to radius ratios are studied. Residual stress and deformations from welding process are investigated separately. Variant influence mechanisms are discovered. Residual stress is demonstrated to be influential to stress field and buckling behavior but not to the ultimate strength. Deformations are proved to have a significant impact on ultimate strength. When central angles are less than critical value, concave magnitudes reduce ultimate strengths linearly. However, deformations with central angles above critical value are of much greater harm. Less imperfection susceptibility is found in spherical shells with larger wall thicknesses to radius ratios.

FANG Xiongbing

Many cognominal parts exist in JT models exported by FORAN V70 R2.0 software, and this leads to an increase in time consumption and the space analysis results becoming hard to process when using clearance analysis software to perform distance computing for such JT models. Aiming at this problem, an algorithm for merging component nodes is put forward based on investigating the assembly configuration and inherent information (i.e. geometric and material information) of JT models created by FORAN. The method is composed of four steps:coordinate transformation, model node renaming, node geometric data transferring and material attribute processing. Finally, the proposed method is implemented by C++ and JT Open Toolkit. The results show that the new JT models generated by the proposed method are comprised of only one assembly node, and they preserve the intrinsic information of the original JT models. Its validity is illustrated by a great deal of examples, and the content of the worked JT models are reduced by about 7% to 20%.

Chang-Li Yu, Ji-Cai Feng, Ke Chen

This paper concentrated on the ultimate uniaxial compressive strength of stiffened panel with opening under lateral load and also studied the design-oriented formulae. For this purpose, three series of well executed experiments on longitudinal stiffened panel with rectangular opening subjected to the combined load have been selected as test models. The finite element analysis package, ABAQUS, is used for simulation with considering the large elasticplastic deflection behavior of stiffened panels. The feasibility of the numerical procedure is verified by a good agreement of experimental results and numerical results. More cases studies are executed employing nonlinear finite element method to analyze the influence of design variables on the ultimate strength of stiffened panel with opening under combined pressure. Based on data, two design formulae corresponding to different opening types are fitted, and accuracy of them is illustrated to demonstrate that they could be applied to basic design of practical engineering structure.