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The pipe-soil interaction force is a crucial load that ensures the on-bottom stability of submarine pipelines and acts as a vital input parameter for the design of controlled pipeline buckling. It is necessary to precise prediction of soil lateral resistance and sensitivity to environmental parameters. This study developed a numerical simulation technique based on the coupled Euler-Lagrange (CEL) method to systematically analyse the deformation of the pipeline and the soil-pipeline forces on the seabed foundation during service. To validate the numerical method for large lateral displacement of pipe-soil interaction, an experimental approach employing parameter variation was utilized to conduct sensitivity analysis on the environmental parameters. The key parameters affecting soil-pipeline interaction were determined through an analysis of relative variation factors. The research findings demonstrate a satisfactory agreement, with an amplitude difference range of within 15 %, between the numerical simulation technique using the CEL method and the experimental results. This method resolves the issue of non-convergence due to grid distortion under conditions of large displacement, thereby enhancing computational accuracy. Sensitivity analysis shows that the relative variation factors for soil friction angle, initial burial depth, and soil density exceed 50 %, which is notably higher than the elastic modulus, friction coefficient, and Poisson's ratio of the soil. The results of this study enable the prediction of lateral forces in pipe-soil interaction and identification of environmentally sensitive parameters. This study establishes a foundation for calculating pipeline buckling strength in complex environments and holds paramount importance for the design and construction of pipelines to ensure on-bottom stability. [ABSTRACT FROM AUTHOR]

This study analyzes the vibration and stability characteristics of a submarine fluid-conveying pipeline with local variation in stiffness under the influence of external flow fields. Utilizing the absolute nodal coordinate formulation (ANCF), the dynamic equation for the submarine pipeline with local stiffness variation under arbitrary boundary conditions is derived. Through numerical solutions, curves depicting complex frequency variations as a function of the internal flow velocity of the pipeline system are obtained. Additionally, the effects of external flow velocity, geometrical parameters, and local stiffness variation on the vibration and stability characteristics of the submarine pipeline under three different boundary conditions are investigated. Results indicate that the stability of the pipeline system decreases across the three boundary conditions under the influence of the external flow field. Increased external flow velocities lead to further reductions in system stability. Furthermore, as the length-to-diameter ratio increases and the thickness-to-diameter ratio decreases, the first three orders of frequencies of the pipeline gradually diminish. Enhancing local stiffness contributes to improving the stability of the system, whereas reducing local stiffness has the opposite effect. [ABSTRACT FROM AUTHOR]

The water supply pipe system is an important component of the municipal pipe system. However, water supply pipes usually suffer from various defects, such as deposits and infiltrations, which severely affect their performance and result in millions of dollars being wasted on maintenance work. Therefore, timely and effective inspection of water supply pipes is very important. In recent years, automatic detection based on deep learning methods has had the advantages of high efficiency, low cost, and time saving, thus gradually replacing manual inspection for defects in the pipe system. To solve the problem of unclear image acquisition for water supply pipes, this paper proposes a novel automated detection method for water supply pipe defects, mainly involving the use of underwater image enhancement (UIE) algorithms to improve data set image quality, and an attention mechanism was utilized to improve the You Only Look Once X (YOLOX) model for defects detection. Experimental results demonstrate that the improved YOLOX model based on the data set enhanced by underwater image enhancement and attention mechanism achieved an average accuracy [mean average precision (mAP)] value of 92.4% and F1 score of 0.86, which are better than traditional models. Finally, an efficient and accurate automated detection procedure for water supply pipe defects was provided. Practical Applications: The automatic detection method of water supply pipe defects constructed in this research has the following three significant practical advantages: (1) the UIE algorithm is applied to the water supply pipe image, which improves the quality and quantity of the data set; (2) the method combines the improved UIE data set and attention mechanism to promote the efficiency and accuracy of the object detection model; (3) the research provides a novel procedure for the automatic detection work of water supply pipe defects. New attempts have been made in three aspects—the use of underwater pipeline robots for detection, the establishment of a high-quality data set, and the training or prediction of the object detection model for water supply pipe—and good results have been achieved. For these reasons, this method can greatly reduce the workload of construction personnel, and effectively avoid the occurrence of detection error events caused by the misjudgment of technicians. [ABSTRACT FROM AUTHOR]

Recently, the phenomenon of tail-sustained swaying of the 160 km/h EMU in single-track tunnels has gained much attention, especially for the rear-powered vehicle. This phenomenon is investigated from the perspective of aerodynamic fluid–structure coupling vibration in this study. The aerodynamics simulation model of the train in tunnels and the multi-body dynamics model of the rear-powered vehicle were respectively established through the software of XFlow and Simpack, and then the fluid–structure coupling vibration was simulated by using real-time data dynamic exchange between the two models. Moreover, the carbody's vibration acceleration and the aerodynamic loads acting on the carbody under various wheel–rail contact geometrical conditions were discussed. Finally, the train tail swaying in field was tested, and the dominant frequencies were analyzed. The results show that the periodic aerodynamic loads and the frequency locking effect caused by the coupled vibration are the main factors for ride comfort deterioration. The violent vibration caused by fluid–structure coupling is named vortex-induced vibration (VIV) in some industries such as bridge and submarine pipeline. For the vehicle in this work, with the decrease of equivalent conicity in wheel–rail contact, the amplitude of carbody swaying increases owing to the carbody hunting, which enhances the fluid–structure coupling vibration, and further deteriorates the ride comfort. The swaying of the carbody is dominated by the vehicle hunting frequency, and the improvement of vehicle lateral stability can weaken this phenomenon. [ABSTRACT FROM AUTHOR]

AbstractMarine dredged-sediment(DS) is often transported through pipelines, where factors such as the solid volume concentration and transport rate can significantly influence the efficiency of the process. Inadequate selection of transport rates for a given solid volume concentration can lead to substantial energy losses. The pressure loss ΔPL or pressure loss gradient ΔPL/L are critical parameters for assessing energy loss during pipeline transport. In this study, large-scale indoor experiments on DS pipeline transport were conducted to investigate the effects of the cross-sectional mean flow velocity Vavg and solid concentration ϕ on the transport characteristics of DS. The results show that at higher solid volume concentrations, ΔPL/L increases rapidly with the square of Vavg and then plateaus, followed by a linear growth phase. In addition, a linear relationship is observed between lgf and lgVavg when the flow velocity is below critical velocity (Vavg)critical; above (Vavg)critical, the friction factor f stabilizes at f0. Formulas for calculating (Vavg)critical, f0 and ϕ were developed. Additionally, a method for determining the optimal transport velocity of DS at varying volume concentrations was established, enabling the identification of the most efficient flow velocity for DS pipeline transportation across different concentrations.HIGHLIGHTSPipeline model tests were conducted on marine dredged sediments.A formula for predicting pressure loss on the basis of solid concentration was derived.The impact of the solid concentration on the Darcy friction factor was determined.A method for determining the optimal transport velocity was established.Pipeline model tests were conducted on marine dredged sediments.A formula for predicting pressure loss on the basis of solid concentration was derived.The impact of the solid concentration on the Darcy friction factor was determined.A method for determining the optimal transport velocity was established. [ABSTRACT FROM AUTHOR]

Leakage in submarine oil and gas pipelines can result in financial losses and marine environmental pollution.Timely detecting, analyzing and locating leaks can minimize losses and strengthen pipeline quality control. In this paper, theleak detection system of submarine pipeline in offshore oil jetty projects was studied. By comparing and analyzing existing leakdetection technologies, a practical application solution for the submarine pipeline leak detection system in offshore oil jettyprojects was proposed. The combination of negative pressure wave method and flow balance method can improve the accuracy ofleak detection and reduce false alarm rates, providing a reliable and efficient solution for the project. [ABSTRACT FROM AUTHOR]

Skirted anchors are often used as temporary or permanent anchoring foundations for underwater pipelines and floating platforms. A series of model tests and finite element simulations were conducted to study the bearing capacity of square skirted anchors with different mooring points. Based on the test results, two failure modes of square skirted anchors with different mooring points were analyzed. It was found that, when the mooring point was located at the top of the side skirt, the square skirted anchor was more prone to rotation and had a lower bearing capacity. The numerical method was validated by the model tests. In total, 140 numerical calculation results show that, when the mooring point position (normalized depth of mooring point) h/H = 0.5~0.75 and the load inclination angle θ = 0°~30°, the bearing performance of the square skirted anchor is optimal. As the aspect ratio of the square skirted anchor (H/B) increases from 0.25 to 2.0, the optimal mooring point position h/H moves downward from 0.5 to 0.75. The failure envelopes in the V-H loading space of the square skirted anchor were drawn, and the corresponding fitting equation was obtained. [ABSTRACT FROM AUTHOR]

In the realm of underwater exploration and operations, soft robots exhibit considerable application potential due to their capacity for agile and complex deformations as well as their inherent compliance. These characteristics grant them excellent environmental adaptability and reduce damage to delicate samples and organisms. Nonetheless, existing underwater soft robots are primarily designed to mimic the movements of marine organisms or for specific functions, and little attention is paid to the camouflage ability. To address these challenges, in this study, a reconfigurable transparent soft robot with variable stiffness for underwater operations is presented. The design and fabrication methodology of the robot module is presented, followed by the kinematic analysis and stiffness characterization. Leveraging the proposed robot module, a soft manipulator and a soft gripper are designed for underwater operations. The soft manipulator excels in underwater pipeline detection and obstacle avoidance, while the soft gripper showcases considerable load‐bearing capacity (about 71 times its weight), making it suitable for tasks such as retrieving aquatic biological samples or garbage fishing. The proposed reconfigurable soft robot demonstrates robust camouflage capabilities, high environmental adaptability, and notable versatility, suggesting potential solutions to existing challenges in the field of underwater exploration. [ABSTRACT FROM AUTHOR]

The research work presents a novel voxel-type soft amphibious robot based on an assembly of origami flexiballs. The geometric and elastic constitutive models of the origami flexiball are theoretically established to elucidate its intricate deformation mechanism. Especially, the zero-energy storage phenomenon and the quasi-zero-stiffness characteristic are revealed to prove that the origami flexiball is suitable for serving as soft robotic components. As a proof of concept, fourteen origami flexiballs are interconnected to form a quadruped robot capable of walking or crawling in both underwater and terrestrial environments, including flat surfaces and sandy terrain. Its adaptability across multiple environments is enhanced by the origami polyhedra-inspired hollow structure, which naturally adjusts to underwater conditions such as hydrostatic pressure and currents, improving stability and performance. Other advantages of the voxel-type soft amphibious quadruped robot include its ease of manufacture using 3D printing with accessible soft elastic materials, ensuring rapid and cost-effective fabrication. We anticipate its potentially versatile applications, including underwater pipeline inspections, offshore maintenance, seabed exploration, ecological monitoring, and marine sample collection. By leveraging metamaterial features embodied in the origami polyhedra, the presented voxel-type soft robot exemplifies an innovative approach to achieving complex functionalities in soft robotics. [ABSTRACT FROM AUTHOR]

Pipe-soil interactions are a crucial consideration in the realization of shallow-embedded pipelines' in situ stability, and the choice of pipe-soil interaction model is correlated with the distinction between "light" and "heavy" pipe motion patterns. Based on the difference in the motion pattern of a shallow-embedded pipeline in sandy soil after a breakout, a numerical model of pipe-soil interaction is constructed. The influencing factors of different motion patterns are studied, while taking into account the shear expansion or shrinkage characteristics of sand. Accordingly, a method of discriminating pipeline motion patterns is proposed. The results show that the motion pattern of a shallow-embedded pipeline in sandy soil depends on the relative weight of the pipe and soil bearing capacity, that the smaller the embedment, the easier the "heavy pipe" motion pattern appears, and that the critical pipe weight required for "heavy pipe" motion increases with initial sand density and pipeline embedment depth. This paper outlines the different motion patterns of pipelines during breakout stage in sandy soil. A numerical model that can consider the mechanical response of sand in pipe-soil interaction is established, and the factors influencing the light and heavy pipe motion patterns of submarine pipelines are analysed. Based on the numerical results, the empirical and theoretical formulas for assessing the critical pipe weight in sand are proposed. These formulas offer a basis for distinguishing between the "light pipe" and "heavy pipe" motion patterns of shallow-embedded pipes in sand. [ABSTRACT FROM AUTHOR]

The study investigates the impact of drag forces on underwater pipeline structures at junctions where diameter changes occur, utilizing three-dimensional numerical simulations to analyze flow patterns around dual-step cylinders at a Reynolds number of 5000. The numerical model is validated against benchmark studies for a plain circular cylinder at heating condition, demonstrating strong agreement. Subsequently, cylinder temperatures were varied to assess their influence on drag force. The study further explores the effect of varying the aspect ratio L/D from 1 to 3 on drag reduction. Analysis of the flow structures is conducted, focusing on vortex patterns, velocity fields, and force coefficients surrounding the cylinders. Additionally, streamwise and crosswise velocities are analyzed at different sectional planes of the step cylinder. Results indicate that the drag force diminishes with increasing aspect ratio, correlating with formation length (Lf). At lower aspect ratios, step-induced vortices migrate toward the wall, while at higher aspect ratios, they drift midway. This research provides insights for designing stepped diameter cylinder systems in the subcritical regime, contributing to optimized underwater pipeline structures. [ABSTRACT FROM AUTHOR]

The speed control of a pipeline inspection gauge (PIG) directly affects the quality of the comprehensive inspection of submarine pipelines. However, the mechanism of the gas flow behavior in a pipeline under the influence of a pig speed control valve is not well understood. In this study, the driving differential pressure of a pig was modeled based on the building block method and numerical simulations. For the first time, the influence of the pressure and flow rate of the gas in a pipeline on the torque of the speed control valve opening process was studied. The results show that when the opening angle of the speed control valve increased from 4.5° to 22°, the gas differential pressure reduced from 1325 to 73 kPa, realizing a 94.5% pressure reduction. In addition, the torque of the bypass valve increased from 7.7 to 2470 Nm during the closing process. The pressure and flow rate increases were directly correlated with increased torque. The established experimental system for torque measurement confirmed the numerical analysis results. By clarifying the law of torque variation, this study provides theoretical guidance for the structural design and control scheme of a pig speed control unit. [ABSTRACT FROM AUTHOR]

Over the past few years, there has been an increased focus on offshore pipeline safety due to the development of offshore oil and gas resources. Both onshore and offshore pipelines may face significant geological hazards resulting from active faults. Pre-excavated soil can be used as backfill for trenches to prevent major pipeline deformations. Since these backfill materials have been heavily remolded, they are softer than the native soil. Therefore, the difference in shear strength between the backfill and native ground may have an effect on the interaction between the pipeline and the backfill. In this paper, the pipeline–backfill–trench interaction is investigated using a hybrid beam–spring model. The P-Y curves obtained from CEL analysis are incorporated into a 3D beam–spring model to analyze the pipeline's response to lateral strike-slip faults. Additionally, the nonlinearity of pipeline materials is considered to study pipeline failure modes under strike-slip fault movements. A series of parametric studies were conducted to explore the effects of fault intersection angle, pipe diameter, buried depth of the pipe, and soil conditions on the failure modes of buckling pipelines. The developed method can be used to analyze and assess pipeline–backfill–trench interaction when subjected to strike-slip fault displacements. [ABSTRACT FROM AUTHOR]

This study aims to investigate the mechanical response of a submarine concrete pipeline under wave action in shallow waters, taking into account factors such as the compressibility of pores and the permeability of the seabed. The control equation of the elliptical cosine wave theory is adopted to simulate the action of waves. In order to simulate the interaction between the solid skeleton and pore fluid, the concept of a "porous medium" is used to establish the transient seepage control equation. Utilizing the stress and displacement conditions at the interface of the ideal fluid media, porous media, and concrete pipeline, the numerical solutions for the internal force and pore pressure of the concrete pipeline buried in a semi-infinite thickness seabed were obtained; meanwhile, the effects of changes in the gas content in pore water and changes in the seabed permeability coefficient on a concrete pipeline were analyzed. The numerical calculation results show that, with the increase in the gas content in the pore water, the amplitude of the pore pressure on the pipeline surface decreases, and both the horizontal and vertical forces acting on the pipeline decrease; the amplitude of the pore pressure on the pipeline surface increases with the increase in seabed permeability and decreases with the enhancement of seabed permeability anisotropy; the improvement of the seabed permeability or enhancement of the permeability anisotropy can increase the horizontal force acting on the pipeline. This study provides a reference for the stability evaluation of submarine concrete pipelines under wave action in shallow water areas. [ABSTRACT FROM AUTHOR]

In response to China's dual carbon call, the petroleum industry is committed to green transformation, promoting the energy green revolution, focusing on domestic offshore CO2 -enriched oil and gas reservoirs, and carrying out offshore platform carbon capture, utilization, and storage–enhanced oil recovery (CCUS-EOR) pilot projects. CO2 continuously displaces crude oil while being injected into deep-sea oil and gas reservoirs for carbon sequestration, achieving an increase in oil recovery and residual oil recovery. However, the implementation of offshore CCUS-EOR technology relies on the safe transportation of supercritical CO2 pipelines. Due to the unique physical and chemical properties of supercritical CO2 , the safe transportation of supercritical CO2 pipelines faces multiple threats. This paper focuses on the current status of safe transportation technology for supercritical CO2 pipelines on offshore platforms, and summarizes multiple operational challenges, including obtaining high CO2 gas sources, high construction costs of pipelines, complex phase change of media, and internal and external corrosion of pipelines. The risk factors for failure of supercritical CO2 pipelines on offshore platforms were systematically identified, and the mechanism of leakage hazards of supercritical CO2 pipelines was determined. Based on the six-step cycle of pipeline integrity management, a targeted integrity management method for supercritical CO2 pipelines on offshore platforms is proposed, providing reference for improving the safety transportation technology system of supercritical CO2 pipelines on offshore platforms. [ABSTRACT FROM AUTHOR]

The development of flow assurance technology in submarine pipelines affects the safety, efficiency, and economy of deepwater natural gas development. In this study, in order to accurately predict the hydrate formation risk in deepwater submarine pipelines, a novel mathematical prediction model of hydrate formation risk has been established. The model has been applied and sensitivity analysis of typical factors has been carried out. The model prediction results show that: (1) Due to the low temperature of the seabed, hydrate formation region (HFR) often exists in submarine pipelines. (2) When other conditions are constant, hydrate formation region increases with the decrease in seawater temperature. (3) When other conditions are constant, the temperature drop, and the length of hydrate formation region decrease with the increase of gas transmission rate. (4) When other conditions are constant, the temperature drop, and the length of hydrate formation region decreases with the increase of gas transport temperature. (5) Reasonable setting of gas transmission temperature and gas transmission rate can help to reduce the hydrate risk and consumption of inhibitors during submarine natural gas transmission. Highlights: The hydrate risk prediction model for submarine pipeline is established. The model has been applied in submarine pipeline natural gas transmission. The T-P distribution characteristics in submarine pipeline are analyzed. The hydrate formation region in submarine pipeline is determined. [ABSTRACT FROM AUTHOR]

A new study by DNV analyzes the potential for hydrogen export from Sweden, Finland, and the Baltic states to Germany and Central Europe. The study examines the production potential, costs, and benefits of developing an H2 network in the region. It also compares different pipeline routes for large-scale hydrogen export. The study highlights the importance of establishing stable partnerships for hydrogen import chains to ensure a stable supply in Europe. [Extracted from the article]

Local site conditions may pose a significant influence on the seismic responses of submarine pipelines by altering both the offshore motion propagation and soil‐structure interaction (SSI). This paper aims to provide an in‐depth understanding of the influence regularity of local site conditions on the seismic performance of free‐spanning submarine pipelines (FSSPs). For this purpose, a suite of underwater shaking table tests were performed to investigate the seismic responses of FSSP subjected to the offshore spatial motions at three site categories. Response comparison factor (χR.ij${\chi }_{R.ij}$) is defined to quantify the structural response discrepancies caused by the seismic inputs at different sites. The test results indicate that responses of the studied model FSSP gradually increase as spatial offshore motions at softer soil sites are employed as inputs; and the values of χR.ij${\chi }_{R.ij}$ vary with a maximum magnitude of up to 40%–60% for different response indices when the site soil changes from fine sand to clay. Subsequently, the corresponding numerical simulations are carried out to reproduce the seismic responses of the test model. The experimental and numerical results meet a good agreement, indicating that the developed numerical modeling method can accurately predict the seismic responses of FSSPs. Following this verified modeling method and using the p‐y approach to address the SSI effect, fragility surfaces of the studied FSSP are derived in terms of PGA and site parameter VS30${V}_{S30}$ (shear‐wave velocity in the top 30 m of the soil profile) via probabilistic seismic demand analyses. The impact of local site conditions on the seismic performance of the FSSP is quantitatively examined by comparing the fragility curves corresponding to various VS30${V}_{S30}$. Furthermore, a fast seismic damage assessment method is proposed for efficiently evaluating the performance of FSSPs buried in various offshore soil conditions. This approach proves beneficial for designers and decision‐makers, enabling accurate estimation of seismic damage and facilitating the implementation of post‐earthquake maintenance measures for FSSPs. [ABSTRACT FROM AUTHOR]

This research aims to investigate the effects of seawater parameters like salinity, pH, and temperature on the external corrosion behaviour and microhardness of offshore oil and gas carbon steel pipes. The immersion tests were performed for 28 days following ASTM G-1 standards, simulating controlled artificial marine environments with varying pH levels, salinities, and temperatures. Besides, Field emission scanning electron microscopy (FESEM) analysis is performed to study the corrosion morphology. Additionally, a Vickers microhardness tester was used for microhardness analysis. The results revealed that an increase in salinity from 33.18 to 61.10 ppt can reduce the corrosion rate by 28%. In contrast, variations in seawater pH have a significant effect on corrosion rate, with a pH decrease from 8.50 to 7 causing a 42.54% increase in corrosion rate. However, the temperature of seawater was found to be the most prominent parameter, resulting in a 76.13% increase in corrosion rate and a 10.99% reduction in the microhardness of offshore pipelines. Moreover, the response surface methodology (RSM) modelling is used to determine the optimal seawater parameters for carbon steel pipes. Furthermore, the desirability factor for these parameters was 0.999, and the experimental validation displays a good agreement with predicted model values, with around 4.65% error for corrosion rate and 1.36% error for microhardness. [ABSTRACT FROM AUTHOR]

Naphthenic acid corrosion is a well-recognized factor contributing to corrosion in the construction of offshore industry pipelines. To mitigate the corrosive effects, minor quantities of alloying elements are introduced into the steel. This research specifically explores the corrosion effects arising from immersing low-carbon steel, specifically A333 Grade 6, in a naphthenic acid solution. Various weight percentages of niobium were incorporated, and the resulting properties were observed. It was noted that the addition of 2% niobium in low-carbon steel exhibited the least mass loss and a lower corrosion rate after a 12 h immersion in naphthenic acid. Microstructural analysis using scanning electron microscopy (SEM) revealed small white particles, indicating the presence of oil sediment residue, along with corrosion pits. Following the addition of 2% niobium, the occurrence of corrosion pits markedly decreased, and only minor voids were observed. Additionally, the chemical composition analysis using energy-dispersive X-Ray analysis (EDX) showed that the black spot exhibited the highest percentage of carbon, resembling high corrosion attack. Meanwhile, the whitish regions with low carbon content indicated the lowest corrosion attack. The results demonstrated that the addition of 2% niobium yielded optimal properties for justifying corrosion effects. Therefore, low-carbon steel with a 2% niobium addition can be regarded as a superior corrosion-resistant material for offshore platform pipeline applications. [ABSTRACT FROM AUTHOR]

Article 58 of the United Nations Convention on the Law of the Sea (UNCLOS) addresses the rights and obligations of States in the exclusive economic zones (EEZ) of other States. It guarantees third-party States the freedom of navigation, the laying of submarine cables and pipelines, and other internationally lawful uses of the sea related to these activities. However, these rights must be exercised in accordance with the laws and regulations of the coastal State and the UNCLOS itself. The jurisprudential analysis of this article reveals various interpretations, often influenced by distinct national contexts and interests. Disputes related to the EEZ mainly focus on issues of maritime delimitation, the exploitation of natural resources, and the protection of the marine environment. West African countries, rich in marine resources, have diverse positions depending on their economic, security, and environmental interests. Some favor a strict application of their sovereign rights to maximize economic benefits and resource sustainability, while others advocate for regional cooperation to manage potential conflicts and strengthen maritime security. In summary, Article 58 of UNCLOS is essential for balancing the interests of coastal States and third-party States in the EEZ while allowing for the harmonious management of maritime resources and maritime security. [ABSTRACT FROM AUTHOR]

Continuous monitoring of Underwater Pipelines Temperature (UPT) is crucial for identifying and understanding various issues with oil pipeline operations. In this study, we propose a novel optical temperature sensor based on an apodized Fiber Bragg Grating (FBG) to measure variations in UPT. The choice of coating material and optimized grating profile significantly impacts the construction of the FBG sensor's head. Therefore, we conducted a comparative study of various coating materials to enhance the temperature sensitivity of the FBG and applied various apodized profiles to achieve high reflectivity, minimal sidelobes, and narrow bandwidth. Our comparative analysis reveals that the proposed sensor with optimal parameters demonstrates a temperature sensitivity of 168 pm/°C within the temperature range of 20 °C to 50 °C (i.e. ten times the commercial sensor) and a strain sensitivity of 12 pm/µɛ within the strain range of - 0.0015 µɛ to 0.0015 µɛ. The performance of the proposed PTFE-Coated temperature sensor is validated against commercial temperature sensors, indicating high temperature sensitivity. Consequently, we designed a multi-sensor simulation model incorporating the proposed sensor, and our observations indicate its effectiveness for underwater pipeline temperature monitoring. [ABSTRACT FROM AUTHOR]

The leakage from submarine gas pipelines presents a significant threat to marine ecological environments. Bubble plumes can be formed when gas escapes, which can give rise to the distinctive fountain phenomenon by interacting with the water surface. It is imperative to understand the factors that influence the physical dimensions and temporal characteristics of the resulting fountain to elucidate the formation mechanism of this phenomenon. Gas leakage experiments under various conditions are conducted to investigate the dynamic characteristics of the fountain in the study. The findings reveal the following: The initial kinetic energy of the escaping gas varies significantly under different leakage scenarios, resulting in the positive correlation between the maximum fountain height and width, as well as the leakage pressure and diameter of the leakage hole. Then, the analysis of dimensional indicates that the dynamic equilibrium of the bubbles is intricately tied to both the Froude number (Fr) and Reynolds number (Re). Notably, the effect of leakage pressure on Fr and Re follows similar patterns. However, the trends of Fr and Re values across varying leak hole diameters are opposite. At last, the frequency analysis of the time series data related to the fountain height demonstrates that higher leakage pressure and larger leak hole diameters result in an increase in both the main frequency and bandwidth. The research results offer valuable insights for evaluating the impact of gas leakage intensity on the marine environment by analyzing the size parameters of fountain. [ABSTRACT FROM AUTHOR]

Marine pipeline vibration condition monitoring is a critical and challenging issue, on account of the complex marine environment, while powering the required monitoring sensors remains problematic. This study introduces a vibration sensor based on a ball triboelectric nanogenerator (B-TENG) for marine pipelines condition monitoring. The B-TENG consists of an acrylic cube, polyester rope, aluminum electrodes, and PTFE ball, which converts vibration signals into electrical signals without the need for an external energy supply. The experimental results show that B-TENG can accurately monitor the frequency, amplitude, and direction of vibration in the range of 1–5 Hz with a small error of 0.67%, 4.4%, and 5%, and an accuracy of 0.1 Hz, 0.97 V/mm, and 1.5°, respectively. The hermetically sealed B-TENG can monitor vibration in underwater environments. Therefore, the B-TENG can be used as a cost-effective, self-powered, highly accurate vibration sensor for marine pipeline monitoring. [ABSTRACT FROM AUTHOR]

Green hydrogen production through electrochemical overall water splitting has suffered from sluggish oxygen evolution reaction (OER) kinetics, inferior conversion efficiency, and high cost. Herein, ultrafine PtIr clusters are synthesized via an electrodeposition method and decorated on the Co3O4 nanoflowers assembled by nanowires (PtIr‐Co3O4). The encouraging performances in electrochemical OER and hydrogen evolution reaction (HER) are achieved over the PtIr‐Co3O4 catalyst, with the overpotentials as low as 410 and 237 mV at 100 mA cm−2, respectively, outperforming the commercial IrO2 and Pt/C catalysts. Due to the ultralow loading of PtIr clusters, the PtIr‐Co3O4 catalyst exhibits 1270 A gIr−1 for OER at the overpotential of 400 mV. Our detailed analyses also show that the strong interactions between the ultrafine PtIr clusters and the Co3O4 nanoflowers enable the PtIr‐Co3O4 catalyst to afford 10 mA cm−2 for the overall water splitting at the potential of 1.57 V, accompanied by high durability for 100 h. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study to model the thermal-induced pipeline buckling–soil interaction as a demonstration of the feasibility of modeling global buckling using an effective stress remeshing and interpolation technique with a small strain (RITSS) approach in 3D. The numerical results are compared with a previously published large-scale laboratory test, centrifuge, and numerical models. The influence of embedment depth, pipe weight, and pipe–soil interface roughness on the global pipe–soil response is investigated. The current study unveiled some of the key behaviors of partially embedded and buried pipes during thermal expansion. First, the expansion-induced displacements comprise vertical and lateral displacements. Heavy pipes dive deeper into the soil, whereas lightweight pipes rise above their initial position as they move laterally for partially embedded and buried pipes. Furthermore, expansion-induced displacements become insignificant as the burial depth increases. The soil in front of the buried pipe flows up and above to its rear end as the expansion-induced displacements increase. Moreover, lateral buckling occurs in buried pipes even though the lateral out-of-straightness of the pipe is within the recommended limit set by the Det Norske Veritas (DNV) guideline. Finally, the pipe–soil interface roughness significantly influences the undrained lateral resistance for partially embedded pipes. [ABSTRACT FROM AUTHOR]

This study employs a statistical regression technique to investigate the maximum displacement, stress, and natural vibration frequencies of a submarine pipeline subjected to hydrodynamic wave forces. Eighteen pipeline models are designed, varying in wall thickness from 10 mm to 30 mm and diameter from 500 mm to 1000 mm. The hydrodynamic drag and inertia forces are performed by using the Morison equation. Computer-aided Finite Element Analysis is employed to simulate the complex interactions between the fluid and structure in 18 pipelines. Multiple Regression technique is used to evaluate the reliability metrics, considering uncertainties in geometrical properties affecting pipeline performance. Full Quadratic models are developed for expressing more effective and concise mathematical equations. Analysis of Variance (ANOVA) is performed to determine the adequacy of the model in representing the observed data. The Coefficient of Determination (R2), Mean Square Error (MSE), and Mean Absolute Error (MAE) are calculated to assess the equation's predictive accuracy and reliability. The results confirm the suitability of the suggested regression technique for analyzing the relationships between predictor variables and the response variable. [ABSTRACT FROM AUTHOR]

Submarine pipelines have become integral for transporting resources and drinking water across large bodies. Therefore, ensuring the stability and reliability of these submarine pipelines is crucial. Incorporating climate change impacts into the design of marine structures is paramount to assure their lifetime safety and serviceability. Deterministic design methods may not fully consider the uncertainties and risks related to climate change compared to risk-based design models. The latter approach considers the future risks and uncertainties linked to climate and environmental changes, thus ensuring infrastructure sustainability. This study pioneers a Hybrid 3D Hydrodynamic Monte Carlo Simulation (HMCS) Model to improve the reliability-based design of submarine pipelines, incorporating the effects of climate change. Current design approaches may follow deterministic methods, which may not systematically account for climate change's comprehensive uncertainties and risks. Similarly, traditional design codes often follow a deterministic approach, lacking in the comprehensive integration of dynamic environmental factors such as wind, waves, currents, and geotechnical conditions, and may not adequately handle the uncertainties, including the long-term effects of climate change. Nowadays, most countries are developing new design codes to modify the risk levels for climate change's effects, such as sea-level rises, changes in precipitation, or changes in the frequency/intensity of winds/storms/waves in coastal and marine designs. Our model may help these efforts by integrating a comprehensive risk-based approach, utilizing a 3D hydrodynamic model to correlate diverse environmental factors through Monte Carlo Simulations (MCS). The hybrid model can promise the sustainability of marine infrastructure by adapting to future environmental changes and uncertainties. Including such advanced methodologies in the design, codes are encouraged to reinforce the resilience of maritime structures in the climate change era. The present design codes should inevitably be reviewed according to climate change effects, and the hybrid risk-based design model proposed in this research should be included in codes to ensure the reliability of maritime structures. The HMCS model represents a significant advancement over existing risk models by incorporating comprehensive environmental factors, utilizing advanced simulation techniques, and explicitly addressing the impacts of climate change. This innovative approach ensures the development of more resilient and sustainable maritime infrastructure capable of withstanding future environmental uncertainties. [ABSTRACT FROM AUTHOR]

Sediment erosion around submarine pipelines is a popular topic, widely investigated in both ocean and submarine-pipeline engineering. In this paper, the incompressible smoothed-particle hydrodynamics (ISPH) method is modified for simulation of local scouring process around the submarine pipeline under the action of unidirectional flow. The erosion model is based on the Clear Water Particle–Turbid Water Particle–Critical Shear Stress (CWP-TWP-CSS) concept, and a sand–water two-phase model is proposed to deal with the sediment-entrained flow. The results of the numerical simulation are compared with the experimental data to verify the accuracy and applicability of the numerical model. The scouring process around the pipeline is investigated under different conditions, i.e., pipeline diameters, gap ratios, and flow velocities. The ISPH model is further used to study the flow characteristics of the scour pits around the submarine pipeline and the influence of the vortices on the maximum scour depth, to provide a theoretical basis for the stability design of submarine pipelines. [ABSTRACT FROM AUTHOR]

The high contrast degraded underwater images often demand extensive pre-processing to attain reliable information for object detection and pipeline tracking. The prototype system developed employs CLAHE, a variant of adaptive histogram equalization, with an adaptive clip limit based on entropy. To yield an enhanced image, CLAHE is applied to the L* channel alone, resulting in improved L- CLAHE and better results. Validation of the improved L-CLAHE method is carried out using real-life underwater images captured using DTG2 Pro ROV from Kochi backwaters based on PSNR, SSIM, EPI, and PFOM quality measures and outperforms the conventional histogram equalization and adaptive histogram equalization techniques. These images are subjected to intensification and filtering for further enhancement as well as object detection and pipeline tracking applications. The proposed algorithm is compared with CLAHE, MSRCR, and L-CIF methods. The improved L-CIF algorithm has a high entropy value compared to the existing algorithms while the EME metric has been evaluated close to unity indicating the improved performance of the fast-guided filter. The method developed also helps in improving the average pixel intensity of the input images. [ABSTRACT FROM AUTHOR]

In this article, we propose a shape optimization pipeline for propeller blades, applied to naval applications. The geometrical features of a blade are exploited to parametrize it, allowing to obtain deformed blades by perturbating their parameters. The optimization is performed using a genetic algorithm that exploits the computational speed‐up of reduced order models to maximize the efficiency of a given propeller. A standard offline–online procedure is exploited to construct the reduced‐order model. In an expensive offline phase, the full order model, which reproduces an open water test, is set up in the open‐source software OpenFOAM and the same full order setting is used to run the CFD simulations for all the deformed propellers. The collected high‐fidelity snapshots and the deformed parameters are used in the online stage to build the nonintrusive reduced‐order model. This article provides a proof of concept of the pipeline proposed, where the optimized propeller improves the efficiency of the original propeller. [ABSTRACT FROM AUTHOR]

As the global market develops for green hydrogen and ammonia derived from renewable electricity, the bulk transmission of hydrogen and ammonia from production areas to demand-intensive consumption areas will increase. Repurposing existing infrastructure may be economically and technically feasible, but increases in supply and demand will necessitate new developments. Bulk transmission of hydrogen and ammonia may be effected by dedicated pipelines or liquefied fuel tankers. Transmission of electricity using HVDC lines to directly power electrolysers producing hydrogen near the demand markets is another option. This paper presents and validates detailed cost models for newly-built dedicated offshore transmission methods for green hydrogen and ammonia and carries out a techno-economic comparison over a range of transmission distances and production volumes. New pipelines are economical for short distances, while new HVDC interconnectors are suited to medium-large transmission capacities over a wide range of distances, and liquefied gas tankers are best for long distances. [Display omitted] • Future hydrogen and ammonia markets will require new-build long-distance transmission. • Energy may be transmitted in dedicated pipelines, liquid tankers or by HVDC lines. • Levelised cost of transmission depends on the transferred quantity and the distance. • Pipelines are the best option over short distances for hydrogen and ammonia. • HVDC has lowest cost for medium distances, tankers are suitable for long distances. [ABSTRACT FROM AUTHOR]

Numerous T-junction circular channels are used in the pipeline system of marine dynamic platforms. Unlike terrestrial conditions, the fluid inside the channels experiences additional inertial forces due to rolling motion, leading to complex and variable fluid mixing characteristics within T-junction pipes. The flow and pressure drop characteristics were investigated inside the T-junction pipe under rolling motion conditions, including the average value, the fluctuation value, and the instantaneous value. The working fluid is considered as the de-ionized water. The inlet Reynolds number of the main pipe ranges from 2110 to 25 320, and the flow rate ratio is from 1 to 20. The rolling time and angle are 5–15 s and 0°–15°, respectively. The range of rolling Reynolds number is 0–3520. The results indicate that the influence of the rolling motion on the flow and pressure drop characteristics inside the T-junction pipe depends on the inertial force of the fluid itself. When the inertial force of the fluid itself is large, the influence of the rolling motion on the flow parameters will be weakened. The rolling motion has a greater impact on the branch than on the main pipe. Predictive relationships for flow rates and pressure loss coefficients are established under the stationary and rolling conditions, respectively, with a fitting error of less than 10%. In addition, the boundary that ignores the influence of rolling motion on flow fluctuations and the criteria for identifying fluid backflow are also proposed. [ABSTRACT FROM AUTHOR]

The temperature distribution around the offshore burial pipeline is an important factor affecting its safety design and economic operation. The traditional test method cannot obtain the continuous temperature distribution of soil owing to the constraints of placing measurement sensors in soil. The transparent soil model test is an alternative method to realize the visualization research of soil temperature. In this paper, a relationship between the temperature of transparent soil and pixel intensity was first established. Then, the transparent soil test and numerical simulation, considering the natural convection, were carried out to study the temperature distribution around the submarine pipeline during start-up and stable operation. The influence of buried depth and pipeline diameter was analyzed. The results suggest that the continuous temperature distribution can be obtained visually by using a transparent soil test, and the observed heating zone of influence extended to a radial distance of 2.6 pipe diameters. The numerical analysis results show that the influence zone of the temperature of pipeline is a distance of four pipeline diameters at a temperature difference of 45 °C. The buried depth and pipeline diameter have little influence on the influence zone. In addition, the contour curves of soil temperature around the pipeline with different diameter are similar in shape. With the decrease in the buried depth of pipeline, the temperature gradient of soil around the pipeline decreases, which is caused by the natural convection. [ABSTRACT FROM AUTHOR]

The pipeline system is widely used in marine engineering, and the formation mechanism and flow patterns of two-phase slug flows are of great significance for the optimal design of and vibration prevention in a complex pipeline system. Aiming at the above problems, this paper proposes a modeling and solving method for gas-liquid slug flows. First, a VOF-PLIC-based coupling gas-liquid slug flow transport model is conducted. Second, to reduce the fuzzy boundary between the gas-liquid coupling interfaces, an artificial compression term is added to the transport equations, and the formation and evolution mechanism of severe slugging flow in piping systems is investigated. The pressure pulsation and gas content characteristics of the gas-liquid coupling process are explored. Research results found that the slugging phenomenon occurs at the gas-liquid interface, where liquid slugging frequency reaches its peak. The pipeline system has prominent periodic characteristics of the slugging phenomenon, and the period decreases when the gas-phase converted speed rises; pressure fluctuation amplitude increases, and the gas-phase velocity change is the inducing factor for the drastic change of pressure fluctuation. The research results can offer theoretical references for optimal designs of and vibration prevention in marine pipeline systems. [ABSTRACT FROM AUTHOR]

Engineers need to know properties of shallow marine sediments to build piers, pipelines and even offshore windfarms. We present a method for estimating the density, P velocity and thickness of these sediments. The traveltime inversion of primary and multiple reflections enables their semiquantitative estimation in marine surveys when using a minimal acquisition system such as a monochannel Boomer. Picking errors, ambient noise and interfering events lead to significant errors in the estimates. Similar, albeit milder, instabilities occur when inverting the signal amplitudes to determine the reflectivity of the layer interfaces. In this paper, we introduce a coupling between the separate inversion of amplitudes and traveltimes to obtain a better Earth model. The P velocity shows up in two stable terms provided by the separate inversions: the acoustic impedance of shallow sediments (through the amplitudes) and the transit time across the sediment layer (through the traveltimes). We couple the two inversion engines by imposing a smoothness condition on velocity and density and thickness of the layer while keeping the impedance and traveltime constant. We thus exploit the ambiguity of the solution to introduce geological criteria and reduce the noise contribution. We validated the proposed method with synthetic and real data. [ABSTRACT FROM AUTHOR]

Underwater pipelines are exposed to harsh environments, including high salinity, multi-modal vortex corrosion, and severe wave interference. Their safety is essential for the development and transportation of marine energy. Therefore, real-time safety monitoring of long-distance energy pipelines is of great strategic importance for ensuring the safety of life and property and energy security. With the rapid development of energy development, the corrosion and leakage mechanisms of natural gas pipelines, as well as their identification and early warning, have become the focus of attention. Optical fiber sensing technology has been applied to various energy safety monitoring fields. However, the mechanism of sound source fluctuations in pipeline leakage and the mutual coupling mechanism between distributed optical fiber sensing technology and leakage sound waves are not yet clear. This paper establishes a model based on sound wave propagation and leakage noise response, derives a quadratic fitting relationship between pipeline pressure fluctuations and leakage orifices and a relationship between leakage noise source standard deviation and orifices, and proposes a complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) permutation entropy underwater natural gas pipeline leakage signal recognition method based on distributed optical fiber acoustic sensing technology. The results of theoretical analysis are verified by experiments. It shows that the signal processing method of CEEMDAN permutation entropy is superior to traditional noise reduction methods, which can better preserve the features of the original signal; the radial basis function (RBF) neural network model can accurately identify four different leakage features with an accuracy of 88.15%, and its recognition stability and generalization ability are superior to convolutional neural network, backpropagation, and random forest. Therefore, the research results of this paper provide a new method for safety monitoring in the application of energy pipeline transportation engineering, and expand the potential application scenarios of distributed acoustic sensing sensor systems and RBF neural networks. [ABSTRACT FROM AUTHOR]

In recent years, the surge in marine activities has increased the frequency of submarine pipeline failures. Detecting and identifying the buried conditions of submarine pipelines has become critical. Sub-bottom profilers (SBPs) are widely employed for pipeline detection, yet manual data interpretation hampers efficiency. The present study proposes an automated detection method for submarine pipelines using deep learning models. The approach enhances the YOLOv5s model by integrating Squeeze and Excitation Networks (SE-Net) and S2-MLPv2 attention modules into the backbone network structure. The Slicing Aided Hyper Inference (SAHI) module is subsequently introduced to recognize original large-image data. Experimental results conducted in the Yellow Sea region demonstrate that the refined model achieves a precision of 82.5%, recall of 99.2%, and harmonic mean (F1 score) of 90.0% on actual submarine pipeline data detected using an SBP. These results demonstrate the efficiency of the proposed method and applicability in real-world scenarios. [ABSTRACT FROM AUTHOR]

Offshore oil and gas resources play a crucial role in supplementing the energy needs of human society. The crisscrossing subsea pipeline network, which serves as vital infrastructure for the storage and transportation of offshore oil and gas, requires regular inspection and maintenance to ensure safe operation and prevent ecological pollution. In-line inspection (ILI) techniques have been widely used in the detection and inspection of potential hazards within the pipeline network. This paper offers an overview of ILI techniques used in subsea pipelines, examining their advantages, limitations, applicable scenarios, and performance. It aims to provide valuable insights for the selection of ILI technologies in engineering and may be beneficial for those involved in pipeline integrity management and planning. [ABSTRACT FROM AUTHOR]

The in-pipe robot is the most commonly used technique in offshore pipelines. The use of rubber sealing discs is important for in-pipe robots to ensure that the robots are moved by fluid pressures inside offshore pipelines. This paper focuses on the measuring and modeling of the wax–oil gel-breaking process at the soft frictional area between sealing discs and the pipe wall. In this study, a detailed characterization of the gel-scraping process and in situ probing portable microscopy are performed. Two contributions are made in this study. First, a direct observation of wax–oil deposition breaking is employed to detect the minute changes at the in-pipe robot. Second, we find that a simple function is possible to describe the relationship between the wax contents and dewaxing efficiency, in which the debris material removal ratio (DRR) is discussed. Thus, the gel deposition-breaking phenomena are quite different under the influence of rubber sealing discs. This result is further confirmed by the real contact ratio measurements. It is important to research the sealing disc further and apply it more in the petroleum industry, especially in in-pipe robots for deepwater pipeline systems. [ABSTRACT FROM AUTHOR]

It is an important function of submarine pipeline flow assurance system to monitor undesirable gas-liquid flow patterns in pipeline in real time, and release early warning ahead of the formation of these flow patterns. In order to tackle the problem of existing method that requires a large training set, and A method of self-adaptive early warning of transition to unstable regime is developed based on transient experiment of gas-liquid two-phase flow performed on a 150-m-long laboratorial pipeline-riser system. The responses of different differential pressure signals were investigated first, so as to pick out the optimum ones used for early warning. Then, the long-short time memory (LSTM) neural network combined with empirical mode decomposition (EMD) was adopted to judge transient condition. In the next step, a series of EMD-LSTM models were trained in order to predict whether undesirable flow pattern would occur, and the warning would be released if the result was 'yes'. Within the range of experiments, all transient cases were correctly judged. The principles of proposed method were then tested and verified by data from a longer laboratorial pipeline-riser system and an offshore oil field, indicating good adaptability of the method. • Indicators (signals) for early warning of undesirable flow patterns are selected. • Two levels of judging process are setup to meet the defense-in-depth principle. • Long-time flow parameters are predicted by LSTM neural network. • The method does not need a trained flow pattern recognition model. • The principles of the method are verified by laboratorial and field data. [ABSTRACT FROM AUTHOR]

Offshore pipelines of different diameters are often seen in piggyback arrangements in close proximity. Under the effects of external flows, the pipelines may experience vibration. Reliable prediction of the vibration amplitudes is important for the design and operation of these structures. In the present study, the effect of the position angle (α) and gap ratio (G/D) of a piggyback pipeline on the amplitude of 1DOF vortex-induced vibration (VIV) was investigated experimentally in a wind tunnel. The diameter ratio d/D of the two cylinders was 0.5. Five position angles, namely, α = 0°, 45°, 90°, 135°, and 180°, and six gap ratios at each angle, G/D = 0, 0.1, 0.2, 0.3, 0.4, 0.5, were tested. It was found that both α and G/D affected the amplitude of vibrations significantly. For all gap ratios, the amplitude of vibrations increased from α = 0° to α = 90° and then decreased to a minimum value around α = 135°. The maximum amplitude occurred around α = 90° when G/D = 0, and the minimum occurred around α = 135°, when G/D = 0.2–0.3. At other position angles, the vibration amplitude was less sensitive to G/D, especially when the latter was between 0.1 and 0.4. These results verified those obtained using numerical methods and are invaluable to engineers when designing offshore piggyback pipelines. [ABSTRACT FROM AUTHOR]

The construction of wind farm pilings, submarine pipelines, and underwater submarines involves multiple cylinders. However, there is currently a lack of economic research on predicting the mechanism and characteristics of mutual coupling of acoustic scattering from multiple cylindrical targets. This study investigates the mechanism and prediction method of acoustic scattering for the structural distribution characteristics of underwater multi-cylindrical targets. A model of a multi-cylindrical target's two-dimensional acoustic field was established using the finite element method. Numerical calculations were then carried out to elucidate the scattering characteristics of the frequency–angle spectrum in far-field omnidirectional scattering. The simulation of echoes in the time domain explains how echoes propagate and interact with each other, and provides formulas for calculating interference and resonance frequencies. The frequency calculation formula extracts key features from the spectrum, providing a basis for predicting the characteristics of multi-cylindrical targets in terms of scale and spatial position. Measurement experiments were conducted on a double-cylindrical target in a water tank, and the theoretical calculations and experimental data were used to estimate the target's radius and distance. The actual layout confirms the accuracy of the interference and resonance frequency prediction formulas. This study offers a valuable solution for refined feature extraction and spatial estimation of underwater targets. [ABSTRACT FROM AUTHOR]

The micromechanical mechanism of pipe instability under lateral force actions on sloping sandy seabeds is unclear. This study investigated the effects of slope angle and instability direction (upslope or downslope) on pipe–soil interaction instability for freely laid and anti-rolling pipes using coupled discrete element method and finite element method (DEM–FEM) simulations. The numerical results were analyzed at both macro- and microscales and compared with the experimental results. The findings revealed that the ultimate drag force on anti-rolling pipes increased with slope angle and was significantly larger than that on freely laid pipes for both downslope and upslope instabilities. Additionally, the rotation-induced upward traction force was proved to be the essential reason for the smaller soil deformation around freely laid pipes. Moreover, the shape differences in the motion trajectories of pipes were successfully explained by variations in the soil supporting force distributions under different slope conditions. Additionally, synchronous movement between the pipe and adjacent particles was identified as the underlying mechanism for the reduced particle collision and shear wear on pipe surfaces under a high interface coefficient. Furthermore, an investigation of particle-scale behaviors revealed conclusive mechanistic patterns of pipe–soil interaction instability under different slope conditions. This study could be useful for the design of pipelines in marine pipeline engineering. [ABSTRACT FROM AUTHOR]

The propagation of shallow-water waves may cause liquefaction of the seabed, thereby reducing its support capacity for pipelines and potentially leading to pipeline settlement or deformation. To ensure the stability of buried pipelines, it is crucial to consider the excess pore pressure induced by irregular waves thoroughly. This paper presents the findings of an experimental study on excess pore pressure caused by irregular waves on a sandy seabed. A series of two-dimensional wave flume experiments investigated the excess pore pressure generated by irregular waves. Based on the experimental results, this study examined the influences of irregular wave characteristics and pipeline proximity on excess pore pressure. Using test data, the signal analysis method was employed to categorize different modes of excess pore-water pressure growth into two types and explore the mechanism underlying pore pressure development under the influence of irregular waves. [ABSTRACT FROM AUTHOR]