Marine Engineering Research Articles

TiO2-hBN nanocomposite coating with excellent wear and corrosion resistance on Ti6Al4V alloy prepared by plasma electrolytic oxidation

Hexagonal boron nitride (hBN) is recognized for its promising application prospects in anti-friction and corrosion resistance due to its self-lubrication and excellent impermeability to gases and liquids. In this study, the TiO2-hBN nanocomposite coatings are prepared via the liquid plasma-assisted particle deposition sintering (LPDS) technology, enabling compact and uniform growth of hBN on the Ti6Al4V surface. Results indicate that the dense and stable plasma at the coating/electrolyte interface facilitates the deposition and sintering of hBN particles, effectively filling surface defects and achieving a coating density of 86.7 %. The friction coefficient of the TiO2-hBN nanocomposite coating significantly decreases from 0.54 (titanium alloy) to 0.28, remaining stable even after 2000 sliding cycles. Compared to the substrate, the wear rate (4.3 × 10−4 mm3N−1 m−1) of nanocomposite coating drops by 70.8 %, which is primarily attributed to the self-lubricating property of hBN, reducing the frictional shear stress. Moreover, the TiO2-hBN nanocomposite coating also has excellent corrosion resistance due to the hBN sheet filling internal defects and inhibiting the corrosion reaction. All these merits render the LPDS technology competitive in expanding the severe service conditions of titanium alloys in aerospace and marine engineering equipment.

Effect of mechanical vibration on microstructure and performance of Fe-based composite coatings fabricated by underwater laser deposition technology

To solve the problem of the uneven composition and poor performance caused by water environment during the underwater laser deposition process, the mechanical vibration assisted underwater laser deposition technology was innovatively proposed, and Fe-based composite layer was successfully prepared. The microstructure, grain type and properties of Fe-based composite layer with and without mechanical vibration were studied and compared. The results showed that the mechanical vibration broke the grain and promoted the formation of more nuclei, which reduced the average grain size by 13.48 %. The solute located in the grain gap was transferred to the liquid molten pool by mechanical vibration, which reduced the Ti content in the intergranular precipitated phase Fe2Ti and made the Fe2Ti from coarse continuous distribution to fine discontinuous distribution. Additionally, the mechanisms of mechanical vibration promoting the performance of the composite were analyzed comprehensively. Compared with the composite without mechanical vibration, the composite with mechanical vibration had good corrosion resistance after 30 days of immersion, and the tribo-corrosion resistance was also improved. With the aid of mechanical vibration, the ultimate tensile strength and elongation of the composite were increased by 11.30 % and 22.08 %, respectively, due to the formation of recrystallized grains, high density high-angle grain boundaries, and fine intergranular precipitate. This study was expected to provide a new way to regulate the microstructure and properties of the underwater laser deposition layer, and promote the application of underwater laser deposition technology in marine engineering equipment.

Report on Marine Engineering Site Visit

Report on Marine Engineering Site Visit

Ti6Al4V alloy with diamond particle-reinforced Cu-based coatings: Microstructure and tribological performance

To enhance the surface wear resistance of the Ti6Al4V alloy, diamond particles-reinforced Cu-based composite coatings (D500/D1000/D2000 coating: 500/1000/2000 mesh diamond: Cu-based alloy powder = 1:30 (wt%)) were fabricated by vacuum cladding. Cu-based alloys with liquid phase temperatures lower than the phase transition temperature of Ti6Al4V alloys were employed as cladding materials to avoid performance deterioration of Ti6Al4V substrates. The microstructure, mechanical properties, and dry-sliding tribological properties of the Cu-based composite coatings have been investigated systematically. The Cu-based composite coatings are composed of the ductile intermetallic compounds Ti3Sn and SnTi2 as the metal matrix, the hard and brittle intermetallic compounds CuTi, CuTi2, Ti(Cu, Al)2 and CuSn3Ti5, in situ generated TiC and the directly introduced diamond particle as the reinforced phases. In addition, a TiC hard phase protective layer was formed around the diamond particles, which retained the original properties of the diamond. The hardness of diamond particles-reinforced Cu-based composite coatings is much higher than that of the Ti6Al4V. Among them, the D2000 coating possesses the highest microhardness. The average Vickers hardness (HV0.5) on the coating surface and nanoindentation hardness (H) on the coating cross-section (the middle part without diamond particles) of the D2000 coating are 1329.8 HV0.5 and 16.87 GPa), which are 4–5 times higher than that of the Ti6Al4V substrate (333 HV0.5 and 3.37 GPa). Nevertheless, the D2000 coating (wear rate of 50.75 ×10−5 mm3/Nm) demonstrates slightly inferior tribological performance compared to the D500 coating. The wear rate of the latter is approximately 13.37 × 10−5 mm3/Nm, which is only 1/5.6 of the substrate (75.67 ×10−5 mm3/Nm). The larger the diamond particle size, the more the diamond serves as a bearing capacity support point to prevent the hard WC ball from further ploughing into the composite coating, and the better the wear resistance of the coating. Notably, D500 coating with excellent wear resistance has the potential for application in various fields of the machinery industry, marine engineering, and aerospace.

Effect of Trace Rare Earth Element Cerium (Ce) on Microstructure and Mechanical Properties of High Strength Marine Engineering Steel

In this paper, FH460 special steel with rare earth element cerium (Ce) was selected, and the control group without Ce was set up. By changing the content of Ce, the microstructure, phase transition point, and mechanical properties of the test steel were observed to study the effect of trace rare earth element Ce on the microstructure and mechanical properties of high-strength marine engineering steel. The morphology and energy spectrum of inclusions in three kinds of test steels were observed by SEM, and the morphological changes in inclusions in FH460 high-strength marine engineering steel after adding Ce were investigated. The fracture morphology and energy spectrum analysis were carried out by combining the tensile test at room temperature and the gradient low temperature impact toughness test, and the effect of trace Ce on the mechanical properties of the test steel was comprehensively analyzed. The results show that the addition of Ce changes the phase transformation temperature of Ac1 and Ac3, and refines the original microstructure of the test steel. SEM observation showed that the addition of Ce changed the long strip MnS and polygonal irregular Al2O3 inclusions into ellipsoids, which reduced the size of inclusions. The gradient low temperature impact test shows that with the decrease in temperature, the fracture dimple depth of the three test sheets of steel decreases, and the Ce-containing test steel forms a deep dimple centered on rare earth inclusions, which hinders the crack propagation and significantly improves the low temperature impact toughness of the test steel.

Effects of Mo Addition on Microstructure and Corrosion Resistance of Cr25-xCo25Ni25Fe25Mox High-Entropy Alloys via Directed Energy Deposition.

Highly entropy alloys (HEAs) are novel materials that have great potential for application in aerospace and marine engineering due to their superior mechanical properties and benefits over conventional materials. NiCrCoFe, also referred to as Ni-based HEA, has exceptional low-temperature strength and microstructural stability. However, HEAs have limited corrosion resistance in some environments, such as a 3.5 wt% sodium chloride (NaCl) solution. Adding corrosion-resistant elements such as molybdenum (Mo) to HEAs is expected to increase their corrosion resistance in a variety of corrosive environments. Metal additive manufacturing reduces production times compared to casting and eliminates shrinkage issues, making it ideal for producing homogeneous HEA. This study used directed energy deposition (DED) to create Cr25-xCo25Ni25Fe25Mox (x = 0, 5, 10%) HEAs. Tensile strength and potentiodynamic polarization tests were used to assess the materials' mechanical properties and corrosion resistance. The mechanical tests revealed that adding 5% Mo increased yield strength (YS) by 20.1% and ultimate tensile strength (UTS) by 9.5% when compared to 0% Mo. Adding 10% Mo led to a 32.5% increase in YS and a 20.4% increase in UTS. Potentiodynamic polarization tests were used to assess corrosion resistance in a 3.5-weight percent NaCl solution. The results showed that adding Mo significantly increased initial corrosion resistance. The alloy with 5% Mo had a higher corrosion potential (Ecorr) and a lower current density (Icorr) than the alloy with 0% Mo, indicating improved initial corrosion resistance. The alloy containing 10% Mo had the highest corrosion potential and the lowest current density, indicating the slowest corrosion rate and the best initial corrosion resistance. Finally, Cr25-xCo25Ni25Fe25Mox (x = 0, 5, 10%) HEAs produced by DED exhibited excellent mechanical properties and corrosion resistance, which can be attributed to the presence of Mo.

The Role of English Pop Songs in Listening Skills Learning among Maritime Students

Effective listening is important for seafarers, but often overlooked in English language teaching. Listening skills are often overshadowed by grammar and writing instruction. To address this problem, researchers and educators are exploring innovative approach in improving listening comprehension, including the use of pop songs as a potential tool to help the students. This study aims to investigate engineering students’ perceptions towards the use of English pop songs in listening exercises and assessing the effectiveness of this approach in improving their listening comprehensions, especially in Maritime English subject. This study employs a descriptive qualitative approach and using two instruments to gather the data. The first one is a questionnaire to gather data on students’ perceptions, attitudes, and experiences related to using English pop songs for listening improvement. Focus group discussion is conducted to dig deeper into students’ perspective and gather qualitative data. The respondents of the study are twenty students from the fourth-semester in Marine Engineering Program at Akademi Maritim Nusantara Cilacap. The questionnaire revealed positive perceptions toward the use of pop songs for vocabulary enrichment, pronunciation practice, and overall listening comprehension. However, the respondents also identified challenges related to different English accents that they hear in the songs. Moreover, focus group discussion emphasized the enjoyment and the motivation the respondents experience in their lessons compare to traditional listening materials. To conclude this study, the finding suggests a positive perception from the students that the use of English pop songs help them improve their listening skills.

Design, preparation, and performance of marine resource-based alkali-activated cementitious materials

The construction of islands and reefs and marine engineering cannot depend on cementitious materials, and how to utilize marine resources to prepare cementitious materials is the key to realizing the convenient construction of marine engineering. In this paper, starting from the necessary composition for the formation of gels, the effects of different activation methods on their activities were investigated by utilizing coral and diatomite as calcium and silicon sources, respectively. The study results show that using calcined coral to activate calcined diatomite resulted in a 28 days strength of up to 2.89 MPa, but it was not processable. The precursor with volcanic ash can be prepared by co-calcining coral and diatomite under lower temperature conditions, and its calcination temperature needs to be no less than 800 °C. In addition, characterization by XRD, FTIR, SEM and BET showed that increasing the calcination temperature helps to form more active substances with volcanic ash, such as CaO, CaSiO3, and Ca2SiO4, which can improve the compressive strength of alkali-activated materials prepared from them. The highest strength growth rate of 3.03 % and 28 days compressive strength of 10.80 MPa were obtained when the co-calcined temperature was 850 °C. The results of this study can provide some reference for the development of marine resource-based cementitious materials.

The influence of ultrasonic vibration on micro-arc oxidation behaviour of manganese aluminium bronze

As a promising material for marine engineering, the insufficient corrosion resistance of manganese aluminium bronze (MAB) alloy when exposed to the marine environment may limit its application. In the present work, micro-arc oxidation (MAO) of MAB alloy was conducted in an aluminate-based electrolyte with the influence of ultrasonic vibration (UV) examined. A porous ceramic film has been successfully produced on MAB via MAO, which exhibits dramatic increases in both film thickness and compactness after the introduction of UV. As a result, the ceramic film produced by ultrasound-assisted MAO (UMAO) exhibits an enhanced corrosion resistance relative to that via MAO, which also possesses a desired antifouling capability. Hence, the present work illustrates the influence of UV on the MAO behaviour of non-valve alloys and, more importantly, provides theoretical guidance for related surface modification strategies in marine engineering.

Long-term study on the mechanical properties of the ITZ in coral aggregate concrete and its impact on material durability

The rich coral reef resources on the island make coral aggregate concrete (CAC) widely applied in marine engineering construction. This study extensively investigates the mechanical properties of the interfacial transition zone (ITZ) within CAC and its consequential influence on the overall mechanical performance of concrete. This article uses the interface bonding strength method, microscopic hardness technology, and X -ray diffraction (XRD) test. It is found that the performance of ITZ is critical to the overall performance of CAC. Optimizing the formation of cement paste and regulating the generation of hydrophilic products can significantly enhance the interface strength and durability of concrete. Our findings demonstrate a clear mathematical correlation between the splitting tensile strength of interface bonding and the microhardness value of the ITZ, offering a novel theoretical framework and practical approach for concrete structure design. The characteristics of hydrophilic products within the ITZ, such as the orientation and dimensions of CH crystals, directly influence the intricate properties of concrete. Therefore, in the process of concrete preparation and construction, attention should be paid to the control and optimization of these micro-structural parameters.

Maritime ISAR detection and tracking algorithm for multiple maneuvering extended vessels in heavy-tailed clutter using SK-MM-Sub-RMM-MB-TBD filter

Multiple extended objects tracking (EOT) tasks play an important role in computer vision and engineering applications of artificial intelligence. In particular, nonlinear marine object imaging and tracking has received an increasing amount of attention due to its enormous application potential in the field of marine engineering, Autonomous Underwater Vehicles, and Remotely Operated Vehicles. Under high sea state, ship-EOTs perform complex maneuvering movements due to strong disturbances such as sea winds and sea waves. In this paper, we exploit emergent maneuvering EOTs (M-EOTs) methodologies in heavy-tailed clutter. We propose a M-EOT procedure in real-time scenario based on the popular multi-Bernoulli (MB)-TBD filter in maritime inverse synthetic aperture radar (ISAR) systems, and in particular, we describe the extended ship target state through the random matrices model (RMM). In RMM, scatter centers are distributed symmetrically around the M-EOT's centroid. However, in ship M-EOT scenario, the distribution over the whole object is not symmetrical, but distributed and skewed in some portions while a target maneuvers. To solve this problem, a novel robustness observation model is represented by using skewed (SK) non-symmetrically normal distribution and multiple model (MM) MB-TBD with more than one ellipse. Simulation and experimental results illustrate that the proposed SK-MM-Sub-RMM-MB-TBD filter outperforms the existing filters for M-EOTs.

Innovative load identification with Res-UNet: Integrating phase space reconstruction and physics-informed deep learning

This study developed a specialized load identification model for a specific ocean platform that integrates advanced deep learning techniques with the unique physical characteristics of marine engineering. Key achievements include high-dimensional mapping of data features using phase space reconstruction (PSR) techniques to enhance the predictive capacity of the model through chaos system theory; optimization of ResNet and UNet deep learning networks with attention mechanisms to boost performance; calculation of stiffness, mass, and damping matrices using finite element software; establishment of corresponding state-space equations; and integration of structural dynamics equations with the deep learning network loss function to significantly improve load identification accuracy. In addition, proprietary structural equations for ocean platform structures were developed, underscoring the uniqueness and applicability of the algorithm. The proposed physics-informed Res-UNet model exhibited excellent performance in identifying both periodic and random loads. These improvements were validated through training with finite element simulated data and subsequent experimental applications, demonstrating the effectiveness of the proposed innovative methods.

System Structural Error Analysis in Binocular Vision Measurement Systems

A binocular stereo vision measurement system is widely used in fields such as industrial inspection and marine engineering due to its high accuracy, low cost, and ease of deployment. An unreasonable structural design can lead to difficulties in image matching and inaccuracies in depth computation during subsequent processing, thereby limiting the system’s performance and applicability. This paper establishes a systemic error analysis model to enable the validation of changes in structural parameters on the performance of the binocular vision measurement. Specifically, the impact of structural parameters such as baseline distance and object distance on measurement error is analyzed. Extensive experiments reveal that when the ratio of baseline length to object distance is between 1 and 1.5, and the angle between the baseline and the optical axis is between 30 and 40 degrees, the system measurement error is minimized. The experimental conclusions provide guidance for subsequent measurement system research and parameter design.

An Underwater Stereo Matching Method: Exploiting Segment-Based Method Traits without Specific Segment Operations

Stereo matching technology, enabling the acquisition of three-dimensional data, holds profound implications for marine engineering. In underwater images, irregular object surfaces and the absence of texture information make it difficult for stereo matching algorithms that rely on discrete disparity values to accurately capture the 3D details of underwater targets. This paper proposes a stereo method based on an energy function of Markov random field (MRF) with 3D labels to fit the inclined plane of underwater objects. Through the integration of a cross-based patch alignment approach with two label optimization stages, the proposed method demonstrates features akin to segment-based stereo matching methods, enabling it to handle images with sparse textures effectively. Through experiments conducted on both simulated UW-Middlebury datasets and real deteriorated underwater images, our method demonstrates superiority compared to classical or state-of-the-art methods by analyzing the acquired disparity maps and observing the three-dimensional reconstruction of the underwater target.

A Liquid Metal-Based Temperature-Responsive Low-Toxic Smart Coating for Anti-Biofouling Applications in Marine Engineering.

Titanium alloys have been widely used in marine engineering fields. However, because of high biocompatibility, they are vulnerable to biofouling. In this work, based on the micro-arc oxidation technology and spontaneous galvanic replacement reaction, a temperature-responsive low-toxic smart coating consisting of liquid metal particles is designed to control the release of Ga3+, Cu2+, and Cu1+ ions in different temperatures. This technology can ensure the full release of active ingredients within the target temperature range, intelligently maintaining the excellent anti-biofouling performance, while saving active ingredients. After being immersed in culture media with Sulfate-Reducing Bacteria (SRB) for 14 days at 10, 20, and 30°C, at the optimal activity temperature of 30°C for SRB, the best sample releases the highest amounts of Ga3+, Cu2+, and Cu1+ ions, demonstrating a 99.9% bactericidal rate. When the temperature decreases to 10°C, the activity level of SRB is very low, and the smart coating can also reduce the released ions correspondingly, still with a 97.3% bactericidal rate. The remarkable anti-biofouling performance is attributed to the physical damage and lethal ions interaction. Furthermore, the best sample exhibits good corrosion resistance. This work presents a design route for smart anti-biofouling coatings for temperature-responsive.

Real-Time Prediction of Multi-Degree-of-Freedom Ship Motion and Resting Periods Using LSTM Networks

This study presents a novel real-time prediction technique for multi-degree-of-freedom ship motion and resting periods utilizing Long Short-Term Memory (LSTM) networks. The primary objective is to enhance the safety and efficiency of shipborne helicopter landings by accurately predicting heave, pitch, and roll data over an 8 s forecast horizon. The proposed method utilizes the LSTM network’s capability to model complex nonlinear time series while employing the User Datagram Protocol (UDP) to ensure efficient data transmission. The model’s performance was validated using real-world ship motion data collected across various sea states, achieving a maximum prediction error of less than 15%. The findings indicate that the LSTM-based model provides reliable predictions of ship resting periods, which are crucial for safe helicopter operations in adverse sea conditions. This method’s capability to provide real-time predictions with minimal computational overhead highlights its potential for broader applications in marine engineering. Future research should explore integrating multi-model fusion techniques to enhance the model’s adaptability to rapidly changing sea conditions and improve the prediction accuracy.

Dynamic Characteristics Analysis of the DI-SO Cylindrical Spur Gear System Based on Meshing Conditions

The dual-input single-output (DI-SO) cylindrical spur gear system possesses advantages such as high load-carrying capacity, precise transmission, and low energy loss. It is increasingly becoming a core component of power transmission systems in maritime vessels, aerospace, marine engineering, and construction machinery. In practical operation, the stability of the DI-SO cylindrical spur gear system is influenced by complex excitations. These excitations lead to nonlinear vibration, meshing instability, and noise, which affect the performance and reliability of the entire equipment. Hence, the dynamic performance of the DI-SO cylindrical spur gear system is thoroughly investigated in this research. The impact of excitations and nonlinear factors on the dynamic characteristics was investigated comprehensively. A comparative analysis of the gear system was conducted by establishing a bending–torsional coupling vibration analysis model under synchronous and asynchronous meshing conditions. Nonlinear factors such as periodic time-varying meshing stiffness, meshing damping, friction coefficient, friction arms, load sharing ratio, comprehensive transmission error, and backlash were considered in the proposed model. Then, the effect laws of excitations and nonlinear factors such as meshing frequency, driving load fluctuation, backlash, and comprehensive transmission error were analyzed. The results indicate that the dynamic characteristics exhibited staged stable and unstable states under different meshing frequencies and meshing conditions. At the medium-frequency meshing stage (0.96 × 104~1.78 × 104 Hz), alternating phenomena of multi-periodic, quasi-periodic, and chaotic motion states were observed. Moreover, the root mean square value (RMS) of the dynamic transmission error (DTE) in the asynchronized gear system was generally higher than that in the synchronized gear system. It was found that selecting the appropriate meshing condition could effectively reduce the amplitude of the DTE. Additionally, the dynamic performance could be significantly improved by adjusting control parameters such as driving load fluctuation (0~179 N), backlash (0.8 × 10−4~0.9 × 10−4 m), and comprehensive transmission error (7.9 × 10−4~9.4 × 10−4 m). The research results provide a theoretical guidance for the design and optimization of the DI-SO cylindrical spur gear system.

Enhancement of mechanical properties in coral concrete via seawater and sea-sand: Experimental insights into the use of dual plastic fibers

The South China Sea contains many coral reefs, and there is a lot of discussion about the best way to dispose of them. Finding ways to use these materials effectively in marine engineering could help address the shortage of natural aggregates in coastal engineering. One potential solution is using coral concrete, which offers cost-effective and enhanced properties. A type of coral fiber concrete using sea sand is created by combining coral rock, sea sand, seawater, PVA fiber, and PP fiber. The findings indicate that by utilizing the optimal ratio of the two fibers (3 kg PVA + 1 kg PP and 2 kg PVA + 2 kg PP), the cubic and axial compressive strength of the new concrete can be increased by 10 % and 20 %, respectively compared to ordinary coral concrete. Furthermore, incorporating these fibers can also reduce axial displacement, resulting in an elastic modulus that is 30–50 % higher than non-fiber variants while enhancing axial toughness. Finally, this study examines stress-strain curves at three different stages through analysis of macroscopic and microscopic failure mechanisms. It was found that there exists a correlation exceeding 0.9 between two mathematical models and measured stress-strain curves from this study. The effective use of composite plastic fiber significantly enhances concrete material performance while providing valuable data support for marine economic facilities construction.

Computational Fluid Dynamics Modeling and Experiments of Two-Phase Flows

Two-phase flows are prevalent in natural phenomena, as well as a wide range of marine engineering and industrial applications [...]

Discrete Element Study on Mechanical Properties of MICP-Treated Sand under Triaxial Compression

Microbial-induced calcium carbonate precipitation (MICP) has attracted much attention as a promising technology for soil improvement in the infrastructures of marine engineering. This paper introduces a novel numerical sample preparation technique for MICP-treated sand, with particular attention paid to the distribution patterns of calcium carbonate, including contact cementing, bridging, and grain coating. The effect of calcium carbonate content (CCC) on the deformation and failure mechanism is studied at macroscopic and granular scales. The findings show that a small amount of calcium carbonate can quickly increase the strength of sand. The strength improvement and deformation control of MICP technology are better than those of traditional compaction treatment. As the calcium carbonate content increases, the mechanical coordination number of the sand also increases, indicating a more stable microstructure of the sand phase. In the contact bonding mode, initial failure occurs as shear failure between sand and calcium carbonate. In the bridge mode, initial failure manifests as shear failure between calcium carbonate particles. In the coating mode, initial failure occurs as tensile failure between sand and calcium carbonate. Calcium carbonate contributes to a reduction in both sliding and rolling movements among sand particles.