Annual maintenance is an important measure in ship maintenance reform and is crucial for enhancing ship operational availability and maintaining technical conditions. Currently, the schedule control of annual maintenance projects still relies on traditional management models, which often result in lengthy maintenance cycles. To improve the traditional methods, this paper introduces coefficients for uncertain factors, process location, time elasticity, and resource utilization, based on the Critical Chain Technology (CCT) theory. A calculation method for the project buffer is established, and a schedule control model for annual maintenance projects based on CCT is constructed. The applicability of the model is verified through a case study of an annual maintenance project. The results show that the application of Critical Chain Technology effectively enhances project management, control, and execution capabilities, while significantly shortening the annual maintenance cycle.

In the alignment calculation process for propulsion shafting systems equipped with shaft-mounted generators, the unbalanced magnetic pull (UMP) is often overlooked, leading to deviations and reduced accuracy in the alignment results. To investigate the influence of the UMP of a shaft-mounted generator on the dynamic alignment of a propulsion shafting system, a finite element model for shafting alignment was established based on a simplified modeling principle. Dynamic alignment analyses were conducted under various conditions: without a shaft-mounted generator, with a shaft-mounted generator but without considering UMP, and with a shaft-mounted generator while considering different UMP values. A comparative analysis of the calculation results was performed. The results demonstrate that the UMP of the shaft-mounted generator affects the shaft deflection, stress, and the load on adjacent bearings. The research findings provide valuable guidance and reference for the accurate alignment calculation of propulsion shafting systems equipped with shaft-mounted generators.

On ships using methanol as fuel, the vent mast of the methanol tank is a potential release point for methanol vapor, which may be released during navigation or bunkering operations. As a toxic substance, excessive inhalation of methanol can harm crew health. Classification rules require a minimum distance of 15 meters between the methanol vent mast and non-watertight openings in accommodation areas. Consequently, the vent mast is typically positioned away from accommodation areas during the design phase. However, some smaller vessels may be unable to meet this requirement due to layout constraints. Furthermore, the extent of the influence of methanol vapor released from the vent mast is affected by factors and conditions such as the release rate, ambient wind speed and direction, and the aerodynamic profile of the surrounding structure. Relying solely on the 15-meter spacing requirement is insufficient to determine whether a release from the vent mast during actual operation could lead to personnel exposure to toxic concentrations. Therefore, this study employs computational fluid dynamics (CFD) simulations to analyze gas dispersion from a methanol vent mast located at the bow of a methanol-fueled ship under different wind speeds. The research aims to investigate the extent of the methanol toxic zone and to verify that the hazardous area generated by the vent mast does not endanger crew health.

Accidents involving chemical tankers are often highly hazardous. The operational status of cargo tanks and loading/unloading systems is critical to the safety of these ships during service. This paper reviews 62 accident cases related to the cargo tanks and loading/unloading systems of chemical tankers occurring between 2003 and 2021. A statistical analysis of the accident causes is conducted from four perspectives: accident type, deadweight tonnage of the involved ship, ship age, and the ship's operational status at the time of the accident. This analysis aims to summarize the conditions under which these accidents occur. Thirty-one typical cases are selected for a more detailed examination. The potential risks leading to these accidents are categorized into human factors and non-human factors. Finally, targeted control measures are proposed, including suggestions for chemical tanker rules and standards, as well as recommendations for the management and operational requirements of shipping companies. These measures are intended to provide technical support for enhancing the safety of chemical tanker transportation.

To investigate the patterns of ship detention defects in Port State Control (PSC) inspections and reduce the probability of ship detention, this paper constructs an association rule analysis model for ship detention defects based on an improved Apriori algorithm, considering the characteristics of PSC inspections and ship attributes. Using the PSC inspection data of detained ships from the Tokyo Memorandum of Understanding (Tokyo MOU) between 2018 and 2023 as the research sample, the study first processes the ship attribute data by applying association rule mining technology to perform dimensionality reduction and discrete standardization, thereby forming effective samples for analysis. An improved Apriori algorithm, which incorporates constraints on both antecedent and consequent and introduces the evaluation metric of confidence boost, is employed to conduct an in-depth mining analysis of ship detention defects. Empirical results demonstrate that the improved Apriori algorithm can efficiently screen out significant strong association rules and accurately reveal the patterns of ship detention defects. These patterns can provide an important basis for ship safety risk management and help enhance navigation safety.

To enhance the reliability and effectiveness of ship magnetic protection capability evaluation, thereby facilitating better magnetic stealth strategy formulation and improved survivability, a study on objective weighting methods for the evaluation indicators of ship magnetic protection capability was conducted. To address the issue of obtaining objective weights for these indicators, the entropy weight method and the Criteria Importance Through Intercriteria Correlation (CRITIC) method were employed for weight assignment. The applicability of these two objective weighting methods in the evaluation of ship magnetic protection capability was analyzed. Furthermore, the impact of variations in the volume of indicator data on both weighting methods was investigated. The research demonstrates that changes in the amount of indicator data have a relatively minor impact on the CRITIC method. As the data volume changes, the maximum average relative error of the weighting results obtained by the CRITIC method is only 2.19%, with a maximum standard deviation of merely 0.002 5. Case analysis indicates that the weighting results of the CRITIC method are more stable than those of the entropy weight method, making it more suitable for the objective weighting of evaluation indicators for ship magnetic protection capability.

The selection of structural materials is a critical aspect in the design of ships operating in polar low-temperature environments. Currently, the requirements of relevant rules from different classification societies exhibit both similarities and differences. The lack of a unified definition for the design temperature poses significant challenges in the selection of hull steels for polar service. Through a systematic review of the rules pertaining to material selection for hull structures in polar low-temperature environments, and based on differences in their foundational principles and definitions of design temperature, these rules can be categorized into three main types: IACS Unified Requirement S6 (UR S6) along with the winterization rules of classification societies, the POLAR CLASS (PC) rules and the rules of the Russian Maritime Register of Shipping (RMRS). This paper conducts a comparative analysis of the differences among these three categories of rules, covering aspects such as the scope of application, design temperature, and steel grade selection. Valuable conclusions and suggestions are summarized, which are expected to provide a reference for the selection of hull steels in polar low-temperature environments.

This study investigates the ultimate strength of container ships under the combined action of vertical and horizontal bending moments. The ultimate strength of three container ships with different specifications is calculated using single-span finite element models, and the influence of loading sequence and path on the results is discussed. A revised failure envelope equation for the ultimate strength of ultra-large container ships under biaxial bending moments is proposed. Using finite element software, the stress-strain characteristics of stiffened panels are obtained, both with and without initial stresses. Based on this, the existing load-end shortening curve for stiffened panels is improved. A simplified incremental iterative method for calculating the hull girder's ultimate strength under biaxial bending moments is then proposed. A comparison between the results from the nonlinear finite element method and those from the proposed method demonstrates that the latter achieves high computational accuracy, along with simplicity of operation and ease of programming. The findings of this research can be applied to the calculation and analysis of the ultimate strength of container ship hull girders under biaxial bending moments.

In the fields of hull structure construction, maintenance, and digital twinning based on digital technology, a reliable positioning method is required to achieve real-time alignment between a ship's digital model and the coordinate system of the physical structure, thereby determining the position of data acquisition points within the hull model's coordinate system. This paper utilizes a lightweight RGB-D camera to acquire image data of the hull structure. Visual feature extraction algorithms are employed to obtain structural features. A method for real-time coordinate alignment between the image data and the 3D model data based on the feature data is proposed, enabling fast and accurate alignment of the image and model coordinate systems. The method first extracts linear features from a prior 3D model of the structure to define the model coordinate system. It then generates corresponding linear features in the 3D reconstruction space from the depth and color images captured by the RGB-D camera. Finally, based on a linear registration algorithm, the fusion of the prior 3D model and the reconstructed model is achieved, enabling the real-time calculation of the positions of the RGB-D camera’s acquisition points within the coordinate system of the structural 3D model.

Data conversion between ship CAD software and hull prescriptive design software is a crucial step in achieving model-based integrated 3D digital design. This paper investigates the requirements and technical pathways for bidirectional data conversion between Smart3D (S3D) and the hull prescriptive design software Mars2000 (Mars). A secondary development of the S3D software was conducted using the VB.NET language. The tool extracts data related to plating, compartments, and longitudinal stiffener connection nodes at transverse section positions from the full ship model through longitudinal range traversal and filtering. Based on custom rules, the extracted data is converted according to the Mars modeling method, and a Mars model file is exported. Subsequently, by comparing files, the tool identifies modifications made in the optimized Mars model and automatically updates the S3D model accordingly. Tests and validations performed on a 114,000 DWT oil tanker demonstrate that the bidirectional data conversion between S3D and Mars is accurate and efficient. The time required for model conversion using the tool is approximately 1/20 of the time needed for manual modeling, and the model update time is reduced to about half of the manual modification time.

As proposed in the revised MSC.1/Circ.1533 (2016), evacuation analysis should be performed to evaluate escape routes at an early stage of ship design. Accordingly, this paper introduces how to apply the evacuation analysis method to guide the general arrangement design of passenger ships in the early design stage. The study deeply analyzes the mutual influence between the evacuation analysis method and the general arrangement design, focusing on three decisive parameters of the total evacuation time. These include the influence of vertical spatial division on the staircase passage time (tstair), the influence of deck horizontal layout on the deck movement time (tdeck), and the influence of crowding and queuing on the flow time (tF). Incorporating evacuation analysis in the early stage of passenger ship design aims to achieve rational planning of the ship's escape routes. This approach helps to avoid excessive sacrifice of the general arrangement space and effectively prevents major subsequent modifications, while meeting the performance requirements of the evacuation analysis. An overview of existing domestic research reveals that most studies remain at a superficial level. Therefore, efforts in evacuation analysis research should be gradually increased to lay a foundation for the independent research and development of high-end passenger ships in China.

To accurately assess the overall energy efficiency of cruise ships and propose optimization strategies, it is necessary to establish calculation formulas for evaluating the energy efficiency of various onboard systems, combined with actual ship data analysis to reveal the characteristics of energy consumption distribution. This paper first constructs a typical model of the energy-consuming systems on a cruise ship, including the propulsion system, electrical system, and thermal system. Then, based on the first law of thermodynamics, corresponding calculation formulas and methods for the energy consumption, work output, and energy loss of each system are established. A comprehensive voyage calculation and analysis for a medium-sized luxury cruise ship is conducted. The analysis of the results reveals that the energy consumption of equipment and systems related to passenger services accounts for a high proportion, approximately 50% of the ship's total energy consumption. This finding shows a significant discrepancy from the simplified approach used in the International Maritime Organization (IMO)'s Energy Efficiency Design Index (EEDI) calculation for luxury cruise ships, where the auxiliary engine power is treated as a fixed percentage (about 5%) of the main engine power. The results of this study provide a methodological foundation for assessing the overall energy efficiency of cruise ships, lay the groundwork for proposing future revisions to the IMO's energy efficiency assessment methodology for cruise ships, and offer insights for optimizing the energy efficiency design of new cruise ships and retrofitting existing ones.

With the growing global emphasis on environmental protection and sustainable development, the shipping industry is facing severe pressure to reduce emissions and save energy. As a clean and renewable energy source, wind energy demonstrates significant potential in the field of ship auxiliary propulsion. This paper takes the KVLCC2 ship as the research object and establishes a three-degree-of-freedom mathematical model for ship motion. The thrust and moment generated by a specific type of sail on the hull in a wind field are introduced as additional terms into the model, enabling the simulation of the sail-assisted ship's motion under wind conditions. Simulation studies on the turning and zigzag motions of the sail-assisted ship reveal that the sail has a significant impact on the ship's maneuverability. Under a wind speed of 8 m/s, the sail increases the ship's turning drift distance by 38.4 m (accounting for 12% of the ship's length) while also increasing the ship's speed during the turning process by 28.1%. In zigzag motion, the sail increases the ship's overshoot angle, particularly during upwind turns, where the second overshoot angle increases from 18.4° to 25.7°. Under beam wind conditions (±90°), the sail induces an asymmetric effect on the ship's steering. The auxiliary effect of the sail is more pronounced during downwind steering, whereas upwind steering requires an increase in the rudder angle for compensation.

The deep-sea green intelligent technology test vessel “WEI LAI” is designed primarily for tasks including the pilot testing of green intelligent technologies, surface support for deep-sea equipment, and comprehensive marine scientific surveys. It features a rational overall layout, strong retrofitting and reconfiguration capability, flexible equipment integration, excellent maneuverability, a high degree of intelligence, and powerful testing capabilities. It serves as a crucial cornerstone for supporting the intelligent upgrading and green development of key systems and equipment and for promoting the transformation and industrialization of scientific and technological achievements. This paper briefly describes the functional orientation of the "WEI LAI" vessel and analyzes its design requirements from the aspects of functional diversification, whole-vessel modularization, and system intelligence. It then presents the overall schemes for the ship type and general arrangement, modular retrofitting design, and key systems, including the power redundancy and hybrid propulsion system, intelligent information system, integrated platform for intelligent and dynamic testing, power system sea trial verification platform, dynamic testing system, and test collaborative control system. This paper can provide references for the development of special test vessels for marine equipment.

Polar research vessels demand increasingly greater endurance due to their special scientific research missions. A marine plant factory solution is proposed to address the problem of vegetable shortage for long-endurance polar research vessels, ensuring continuous supply of vegetables. The applied research of plant factory technologies for polar research vessels is conducted by discussing the key technologies, environmental control requirements and type selection of marine plant factories. A design method for the plant factory on long-endurance polar research vessels is then presented to provide references for ship designers.

The wheelhouse windows will be iced by seawater droplet and climatic conditions such as rain and snow for vessels operating in extreme cold environments. It will obstruct the view from the wheelhouse and thus threaten the navigation safety, making the deicing design for the wheelhouse windows critically important. Aiming at optimizing the deicing effect of the wheelhouse windows under extreme cold environments, it studies the causes of icing on the surface of the wheelhouse windows. Using this as input conditions, the electric heating deicing of the wheelhouse windows are numerically simulated and analyzed to provide the deicing effect of different electric heating powers under different external ambient temperatures. An electric heating deicing solution is finally proposed for the wheelhouse windows under extreme cold environments.

A ship interior outfitting design system using virtual simulation technology is developed to address the limitations of the traditional ship interior outfitting design system, including lack of intuitiveness, poor interaction and long design iteration cycles. 3ds Max has been used for 3D modeling, and the realism of the model and the real-time nature of the system are considered through refined modeling and optimization processing. A virtual environment based on the Unreal Engine 4 is established to complete the model import, material allocation, collision setup and lighting optimization, together with efficient connection to a MySQL database through C++ plug-ins. The system integrates the functions of resource management, dynamic adjustment of design schemes and perceptual engineering evaluation, and develops diversified interactive logic through blueprint technology to improve the user experience. The test results show that the system can accurately present the three-dimensional model and material effects of the interior outfitting design, realize the function of real-time interaction and perceptual engineering evaluation, thereby meeting the basic requirements of ship interior outfitting design. Users can intuitively adjust design schemes and obtain visualized evaluation feedback through the system. The system has good intuitiveness and operability, enhancing the presentation quality of the design scheme and user experience. It provides an innovative solution for the ship interior outfitting design.

This paper optimizes the scheme of side-by-side mooring operation for a special SWATH. Through numerical simulation and model tests, we analyze relative motions, mooring line tensions, and fender loads between the SWATH and single-body ship, aiming to guide the side-by-side mooring operation. The results show that the displacement difference of SWATH significantly affects the horizontal motion of the barge and the motion of SWATH itself. Changes in wave direction have a notable impact on the horizontal motion of both ships. Under the same relative motion, short mooring lines and fenders bear large loads. Therefore, it is recommended to select optimal wave directions (e.g., head seas) and loading states for operations. Beam seas (90°) pose the highest risk due to excessive fender compression. The research provides references for the design and optimization of side-by-side operations between SWATH and ships.

Numerical simulation on the static and dynamic characteristics of the rigid base has been conducted based on finite element analysis (FEA) to verify the reliability and safety of the rigid base of the designed marine diesel generator set. The modeling of the components and BOM assembly is completed by using the NX11.0 software integrated in the Teamcenter platform, according to the schematic diagram of the rigid base from the selected design. After simplifying the component features, the BOM assembly is imported into FEA software for static and dynamic modal simulations of the rigid base. The calculation results show that the static strength and stiffness of the designed rigid base meet the operational requirements, and the first six natural frequencies are much higher than the external excitation frequency. There will be no resonance phenomena, and the dynamic strength and the stiffness of the structure are reliable, verifying the rationality of the selected design. It allows for the early evaluation and prediction of the reliability and safety of the structural performance of the rigid base. It provides theoretical support for subsequent product processing and manufacturing and offers direction for further optimization of the product design.

Communication, positioning and navigation (CPN, referred to as “communication and navigation” in Chinese, where “positioning” is integrated into “navigation”) are crucial for all marine vehicles, and it is more essential for under-ice vehicles operating in polar regions. As human beings step into the polar regions with higher latitude and larger depth, underwater vehicles are more active in under-ice scientific surveys. However, compared to open-water environments at lower latitude regions, the under-ice CPN in polar regions is very special and the relevant CPN technologies also face unique challenges. Hence, the development of under-ice CPN technologies in polar regions also differs from that in other regions. This study reviews the current status and challenges of under-ice CPN technologies in polar regions and provides a prospect for their future developments.

The length-to-breadth ratio ( L/ B) of a heavy icebreaker is generally between 4~5. The applicability of conventional calculation formulae for calculating wave loads on hull girder is limited. The characteristics of heavy icebreakers hull lines differ significantly from those of vessels designed for open waters. Numerical methods are consequently required to study the characteristics of wave loads on hull girder. A time-domain Rankine source method accounting for speed is employed to predict the wave loads on hull girder by using the hydrodynamic software WASIM. Both the long-term values of linear wave loads and the direct calculation results of nonlinear wave loads are obtained. Comparisons are then made among the long-term linear wave loads (after nonlinear correction), the directly calculated nonlinear wave loads and the standard values. The results show that the long-term linear vertical wave bending moment is approximately 1.4 times the standard linear value, and the long-term linear vertical wave shear force is 1.9 times that of the standard linear values, owing to the unique hull lines of heavy icebreakers. It is indicated that the standard formulae cannot provide a reasonable evaluation of the wave loads on the hull girder for these vessels. From a practical engineering design perspective, the long-term linear vertical wave loads (after non-linear correction) at a speed of 5 knots are adopted as the design wave loads of the hull girder for the evaluation of the overall strength of the hull structure. The non-linear effect of the sagging wave bending moment is significant, resulting in special consideration of the structural buckling of long superstructures during the check of the longitudinal strength of the hull under sagging condition.

Extrusion between the side structure and the level ice is one of the most common scenarios encountered by polar ships. It is of great significance for the design and operation of polar ships to explore the mechanism of the extrusion between the level ice and the broadside. A numerical simulation model of the interaction between the level ice and the broadside is established by using the discrete element method in the current study. The rationality of the numerical model is verified based on the results of a model test on the ice loads during the broadside extrusion conducted in an indoor ice tank. The influence of the variation of the angle between the level ice drift direction and the ship's heading on the ice loads during the broadside extrusion is studied and analyzed based on established numerical model of the extrusion between the level ice and the broadside. The mechanism of the broadside extrusion and the distribution law of nonlinear ice loads are discussed. It can provide technical support for predicting ice loads and structural responses in the scenario involving the extrusion between the level ice and the broadside.

The icebreaker needs to adjust the ship's longitudinal attitude to accomplish icebreaking during missions. To accomplish the rapid longitudinal adjustment of the ship, a multi-medium method is adopted to complete the ballast/deballast process for the fore and aft tanks. The ballast process is based on a hybrid method using ballast pumps and gravity flooding, while the deballast process is based on a hybrid method using ballast pumps and air compressors. For the ship's ballast/deballast system, a network model for the longitudinal attitude adjustment is established based on the designed multi-medium ballast/deballast method, considering both the fore and aft tanks. Simulation analysis shows that compared with the pure ballast pumps, the multi-medium method increases the ballast process speed by 4% and the deballast process speed by 25.6%. The multi-medium ballast/deballast method can greatly shorten the time required for rapid longitudinal attitude adjustment for icebreakers, thereby enhancing their operation flexibility.

With the continuous development of Arctic resources, the risk of collision between polar ships and level ice is increasing. Different icebreaking methods will have different effects on the hull structure under variable ice thickness. At present, the judgment of icebreaking methods is mainly based on the icebreaking levels in polar ship specifications. It is difficult to study the maximum icebreaking thickness and the speed of different icebreaking methods without classifying the icebreaking levels. The equation between the propulsion force and speed is therefore derived based on the force balance relationship. A method for judging the icebreaking method of polar ships is proposed by combining with the safety design of hull structure strength. The maximum cruising ability of the continuous icebreaking for a polar icebreaking transport ship has been determined. The reliability of the determination of the icebreaking method is verified by comparing with the model experimental results. The speed range for continuous icebreaking and impact icebreaking methods has been divided under different ice thickness conditions. It provides theoretical support for the icebreaking design and navigation of polar ships.

With the promotion of carbon peak and carbon neutrality strategy, offshore wind power is developing towards deep waters, facing server challenges of strong winds and waves. Traditional personnel transportation methods have significant safety hazards in harsh sea conditions, seriously restricting the high-quality development of project construction. It is therefore necessary to explore new methods for offshore resource support under complex sea conditions. Based on the fractal characteristics of waves, a fractal-wave compensation adaptive algorithm is proposed by combining with the active wave compensation and adaptive principles. An adaptive compensation trestle model is then established on the basis of this algorithm. The adaptive operation and maintenance ship is transformed through the installation of adaptive compensation trestles. Compared with the traditional operation and maintenance ship, the adaptive operation and maintenance ship transformed from an offshore wind power maintenance ship in the South China Sea can effectively solve the safety issues of personnel boarding. At the same time, the utilization rate of the sea window is increased by 3.5 times, the efficiency of the transfer personnel is increased by 3.3 times, and the comprehensive economic benefit is increased by 10.3%. The adaptive operation and maintenance ships have significant advantages in operations under complex sea conditions. It can provide resource support for subsequent deep-sea offshore wind power projects.

Zooplankton nets are fundamental tools for biological oceanography, and their sampling quality directly affects the evaluation accuracy of species composition and ecological function. The technical evolution of zooplankton nets from early vertical hauls to modern multi-net platforms (such as MOCNESS and Multinet) has been reviewed to highlight significant advancements in mechanical control, telemetry, and depth-resolved sampling. It analyzes the complementary role of non-contact technologies, such as optics, acoustic, and environment DNA, to traditional nets, emphasizing the continuing necessity of net sampling in species identification and data verification. It is further proposed that the future development of zooplankton nets should integrate sensing systems, artificial intelligence, and sample-preservation technologies to develop a “smart net” system for efficient, low-bias and quantitative sampling of meso- and macro-zooplankton.

With the continuous advancement of decarbonization in the maritime industry, especially after MEPC 80 setting the goal of achieving net-zero emissions by 2050, the application of low-carbon/zero-carbon fuels has become a major focus. The large-scale adoption of energy sources such as liquid ammonia, liquid hydrogen, green methanol, and LNG is gradually accelerating. Nuclear energy, as a clean energy source, is also of increasing interest to the maritime industry. With the development of fourth-generation small modular reactor (SMR) technology, the inherent safety attributes of reactors have been enhanced while reducing the risk of radiation leakage, making nuclear energy a possible propulsion method for large commercial vessels. Starting from the decarbonization needs of the maritime industry, the current use of nuclear energy as a marine propulsion method has been introduced with a focus on the recent technological developments of fourth-generation SMRs. It particularly analyzes their development potential as marine small reactors and proposes key factors that should be considered for their application onboard ships. It focuses on the unique application advantages of molten salt reactors (MSRs), especially thorium-based solid-fueled MSRs, for civilian ships. It also analyzes and prospects the application of SMRs in Suezmax oil tankers, ultra-large container ships, and floating power generation platforms. It can provide theoretical support and references for subsequent engineering applications of nuclear power in ships.

As a strategic national asset ensuring the security of China’s energy resources, the summer extreme heat environmental condition and complex air flow composition of the ocean drilling vessels have become one of the key challenges in the design and construction. By establishing the balance formula of air volume inside a galley, this study sorts and analyzes the airflow parameters such as air conditioner air supply, air intake outside and inside the cabin and air mechanical exhaust. Based on the cooling capacity calculation method for fresh air conditioners specified in ISO 9943:2009, and incorporating personnel comfort requirements, this study proposes a solution for adjusting air conditioning cooling capacity parameters under extreme heat conditions exceeding standard environmental design specifications. Using an ocean drilling vessel as a case study, calculations were performed to develop recommended cooling capacity parameters for such extreme conditions on this vessel. This provides a reference for engineers to clarify air flow composition in complex cabins and to select appropriate cooling equipment under extreme heat environments.

Ropes are critical components for mooring ships and offshore floating structures under periodic axial loads. To investigate the tensile properties and stiffness characteristics of deep-sea mooring polyester ropes, they are categorized into three stages: preloading, initial installation, and aging. Initially, the tensile properties of the ropes under static loads are examined, quantifying strain and reversible elongation rates at each stage and comparing mechanical properties of polyester ropes with those of nylon ropes. Subsequently, creep coefficient solution tests under varying tensions are designed, establishing a quasi-static stiffness empirical equation with consideration of the rope creep coefficients. Experiments have shown that the mooring ropes still undergo reversible elongation after unloading, and sufficient break-in period of the ropes can reduce their inherent deformation and increase their structural stability. Static stiffness of the ropes increases with loading time and force until it reaches a constant value. Polyester ropes have greater stiffness, smaller deformation and more stable structure than nylon ropes, making them more suitable for deep-sea mooring. The findings enable comprehensive analysis of rope stiffness evolution throughout its service life, thereby offering references for reasonable design of deep-sea taut-line mooring systems.

High-precision localization of pipeline damage using acoustic emission technology in the marine environment remains challenging. A hybrid path optimization-based localization method for structural damage source localization is proposed. First, the short-time Fourier transform (STFT) maps acoustic signals into the time-frequency domain, with K-means cluster grouping signals to separate different damage sources. Subsequently, the ROTH dual-weighted cross-correlation algorithm is employed to accurately estimate the time difference of acoustic wave arrivals at sensors under strong noise conditions, extracting temporal characteristics of the acoustic waves. Next, an initial propagation path is generated via the Rapidly-exploring Random Tree (RRT) algorithm, and further optimized through an improved D* dynamic path optimization algorithm to determine the optimal propagation path. Finally, acoustic emission source locations are calculated by using hyperbolic equations and weighted least squares based on geometric localization methods. Experimental results demonstrate that this method can accurately locate the structural damage source in complex environments, significantly outperforming traditional approaches.