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Aluminium alloy is a commonly used material in the superstructure of naval vessels. This alloy is prone to sensitisation when exposed to the marine environment for an extended period, which leads to the formation of stress corrosion cracks. Because welding is unsuitable for repairing sensitised aluminium alloy with cracks, this study used carbon-fibre-reinforced plastic (CFRP) patches for repair. The repair effect of CFRP patches was examined through experiments and numerical simulation to clarify the mechanical properties of cracked aluminium alloy repaired with CFRP patches. The experimental results revealed that the tensile strength of cracked aluminium alloy was increased by 40% after its repair with a CFRP patch, and the obtained tensile strength was higher than the yielding strength of this alloy. With regard to numerical simulation, this study employed the extended finite-element method (XFEM) and traction-separation law to simulate crack propagation in cracked aluminium alloy and the bonding strength at the repair interface. The numerical simulation results were consistent with the experimental results, which confirmed that the established numerical model accurately captures the failure trends and ultimate strength of cracked aluminium alloy repaired with a CFRP patch. Future researchers can use the numerical simulation method established in this study to predict the effectiveness of using CFRP patches in the repair of naval vessel superstructures.

Purpose This paper aims to design a novel isolation system based on natural rubber (NR), polyurethane (PU), and Sorbothane for protecting a sensitive article kept within a naval vessel container (NVC) from a shock load. Methods First, NVC is analyzed using the MATLAB tool as an analytical model with two degrees of freedom, wherein the elastomer’s isolation system is modeled by nonlinear stiffness up to third-order and linear damping. The genetic algorithm determines optimal values of stiffness and damping parameters to minimize simultaneously both the maximum shock transfer to the sensitive article and the maximum deformation of the isolation system. Furthermore, the NVC’s 3D finite element model (FEM) is created in ABAQUS and exposed to the transverse shock load to perform an in-depth dynamic analysis of the isolation system. In the 3D FEM, the nonlinear elastic and time-dependent properties of the considered materials are defined based on test data using appropriate hyperelastic and viscoelastic models, respectively. Results The 3D FEM results show that three isolators with lengths of 170 mm, 75 mm, and 500 mm each for NR, PU, and Sorbothane materials, respectively, are optimal. The NVC’s 3D simulation results for the optimal design of NR, PU, and Sorbothane isolators closely match the analytical model’s optimized results. Conclusions Moreover, the shock is reduced by 98.26%, 98.29%, and 98.49%, respectively, for NR, PU, and Sorbothane isolators with the maximum deformation of isolators below 10 mm, demonstrating the high effectiveness of the proposed design in shock mitigation.

This study introduces a BiGMM-HMM Integration Framework designed to improve predictive maintenance strategies for naval vessel propulsion systems, addressing the need for efficient and reliable operation in marine engineering applications. The framework effectively manages multimodal sensor data by leveraging a unique combination of Gaussian Mixture Models (GMMs) and Hidden Markov Models (HMMs) in a bidirectional architecture. It analyses the dynamic interactions between sensors and subsystems. Two preprocessing methods are evaluated: Method 1 focuses on subsystem interactions, employing divergence-based root cause analysis to identify key sensor variables by clustering of sensors and subsystems. In contrast, Method 2 processes the entire dataset directly. Experimental results demonstrate that Method 1 outperforms Method 2, achieving an accuracy of 91%, precision of 94%, recall of 91%, and an F1-score of 91%, compared to 87%, 90%, 87%, and 88% for Method 2, respectively. These findings underscore the role of feature selection, clustering, and dimensionality reduction in predictive analytics for marine systems. Utilizing two GMMs—one for label inference and another for transition and emission probabilities—the framework captures the multimodal characteristics of propulsion system data, resulting in improved health state prediction. Applied to a naval propulsion system dataset, this approach provides actionable insights into optimizing maintenance by understanding sensor interdependencies and subsystem interactions, offering substantial advancements in marine engineering operations through more effective maintenance strategies.

In this paper, we analyze the radar cross section (RCS) of an integrated mast and present the optimized mast shape for RCS reduction. The RCS is simulated using commercial electromagnetic (EM) software based on the shooting and bouncing rays (SBR) method and the diffraction fields at the edges are also considered. Threat frequencies, threat regions and cardinal points are first defined considering the operational environments of a naval vessel. We calculate and analyze the RCS of the integrated mast in terms of the threat frequencies, the shapes of the integrated mast and the direction and polarization of the incident waves. The shape of the integrated mast is optimized based on the shaping technique. The optimized mast has low RCS properties in the primary threat sectors except for the exceptional angle regions.

The residual buoyancy of vessels after damage has a fundamental role in their survivability and it is implemented through adequate ship internal subdivision. Traditionally the number and the position of transverse watertight bulkheads are selected for most ships early in the design phase by means of the “floodable length curve” coupled with the concept of “margin line”. However, for naval vessels, it is more and more common during the acquisition process to explore a wide domain of feasible ships, identified with the assistance of automated processes and assessed also in terms of capabilities, among which is survivability. The generation and the comparison of a considerable number of different ship configurations is very time consuming. Therefore recourse to a parametric expression of the floodable length curve is considered to be a very efficient approach and would thus enable characterisation of the ship, in terms of survivability performance. In this paper such an approach is presented, using an offshore patrol vessel (OPV) as the case study.

Currently, in order for the Chinese naval forces to achieve strategic transformation and move towards the deep blue sea, there is an urgent need to enhance the capabilities of far-sea operations. Most naval ships in various countries use gas turbines as the power source, and the bearings supporting the transmission shafts of gas turbines are the key components restricting their performance. This paper conducts research on the tilting pad journal bearings in gas turbines and proposes a conversion method between the oil film pressure at the bearing measuring point and the maximum pressure of the pad.

Turkey's policies often appear at odds with its position in NATO and the broad direction of its allies. These polices become less mysterious when it is understood that Turkey's strategic imperatives are driven by its unique position as gatekeeper to the Black Sea and the dynamics introduced by the tiered rights granted by the Montreaux Convention.

Composite materials are a combination of two or more types of materials used to enhance the mechanical and structural properties of engineering products. When fibers are mixed in the polymeric matrix, the composite material is known as fiber-reinforced polymer (FRP). FRP materials are widely used in structural applications related to defense, automotive, aerospace, and sports-based industries. These materials are used in producing lightweight components with high tensile strength and rigidity. The fiber component in fiber-reinforced polymers provides the desired strength-to-weight ratio; however, the polymer portion costs less, and the process of making the matrix is quite straightforward. There is a high demand in industrial sectors, such as defense and military, aerospace, automotive, biomedical and sports, to manufacture these fiber-reinforced polymers using 3D printing and additive manufacturing technologies. FRP composites are used in diversified applications such as military vehicles, shelters, war fighting safety equipment, fighter aircrafts, naval ships, and submarine structures. Techniques to fabricate composite materials, degrade the weight-to-strength ratio and the tensile strength of the components, and they can play a critical role towards the service life of the components. Fused deposition modeling (FDM) is a technique for 3D printing that allows layered fabrication of parts using thermoplastic composites. Complex shape and geometry with enhanced mechanical properties can be obtained using this technique. This paper highlights the limitations in the development of FRPs and challenges associated with their mechanical properties. The future prospects of carbon fiber (CF) and polymeric matrixes are also mentioned in this study. The study also highlights different areas requiring further investigation in FDM-assisted 3D printing. The available literature on FRP composites is focused only on describing the properties of the product and the potential applications for it. It has been observed that scientific knowledge has gaps when it comes to predicting the performance of FRP composite parts fabricated under 3D printing (FDM) techniques. The mechanical properties of 3D-printed FRPs were studied so that a correlation between the 3D printing method could be established. This review paper will be helpful for researchers, scientists, manufacturers, etc., working in the area of FDM-assisted 3D printing of FRPs.

The paint industry constitutes a fundamental part of the entire industrial landscape. The primary role of paint is to preserve and protect a product from external sources such as weathering, vegetation, and rust. The maritime sector is particularly sensitive to this issue, as fouling on the hull can lead to a 40% increase in resistance, resulting in higher fuel consumption and the potential transportation of invasive species from one ecosystem to another. Paints used for ships have the characteristic of releasing biocides, primarily represented by copper and zinc, inhibiting life forms from adhering to the hull but at the same time causing a gradual “poisoning” of the ecosystem. For these reasons, new types of paints that exploit the principle of anti-adhesion rather than the release of biocides are being studied. This paper presents and characterizes epoxy-based surfaces with EPO-TQ, HDTMS, and PFOTES through experimental tests. Laboratory tests have highlighted the hydrophobicity level of each surface by evaluating the recovery time of a droplet impacting it and the final wetting angle. It has been demonstrated that among the three, the PFTOS surface exhibits the best performance and has the potential to be used as a surface/paint for naval vessels.