bluuebunny/crossref_metadata_2025 huggingface dataset:
An Analytical Approach to Modeling Thin, Pre-Cracked Specimens Using Traction-Separation: A Proof of Concept
Authors: Adly Mohammed A. , Walters Carey L.
Published: August 2024

Cohesive zone and eXtended Finite Element Modeling (xFEM) are promising methods for modeling the propagation of a crack using coarse meshes and hence saving considerable computational time. The Traction Separation Law (TSL) that is needed for such techniques is, however, mostly derived a posteriori using experiments. This prevents its widespread utilization in structures without high costs. For example, in the modeling of a compact tension test, the TSL is known to evolve as the crack grows. Qualitative physical explanations have been offered for this phenomenon. Necking ahead of the crack tip is thought to have a large effect on crack propagation, while the necking behavior in any given element is influenced by both the state of stress acting on it and the structural boundaries around it. However, a method to account for those explanations a priori in the TSL doesn’t exist. Here, TSLs are developed for the elements along the known crack path in a middle crack tension test and implemented as a damage model in Abaqus. They are derived solely from the material properties and the element dimensions, thus excluding the need for inverse engineering based on experiments. This paves the way for more general applications of traction separation laws within the maritime and offshore industry.
Residual Plastic Strain Effects on the Ultimate Capacity for a HSLA Stiffened Panel Subjected to Two Different Cyclic Load Conditions
Authors: Barsotti Beatrice , Gaiotti Marco
Published: August 2024

This paper delves into how plastic deformations accumulate in structures and their effect on the ultimate load strength. More precisely, the study examines how repeated cyclic loads cause plastic deformations, which could have some effects on the ultimate capacity of the structure, in contrast to a continuously rising load. The study suggests a numerical strategy, by means of finite element analyses, to investigate the structural responses of two different load cycle histories and emphasizes differences that arise due to the choice in the material hardening law (model describing material behaviour) like isotropic, kinematic, or the combined Chaboche model.

The researchers focus on a stiffened panel made of high-strength, low-alloy steel subjected to both uniaxial compression and alternating tension-compression cyclic loading. In order to capture the arise of the residual plastic strains, the study employs shell element modelling, while also considering initial imperfections.

The paper discusses how residual displacements magnitude change as the number of load cycles increases under different loading conditions and material hardening models. Ultimately, it analyses how these accumulated plastic deformations influence the ultimate strength, with a particular emphasis on whether different plastic strain inputs from the two load configurations lead to varying outcomes.
An Effective Method for Evaluating the Failure of Wind Turbine Blade Under Various Conditions
Authors: Sheng Fangyuan , Liang Xu , Wang Baoxuan , Liao Haiyan
Published: August 2024

Wind turbine blades are critical components of wind turbines. The behavior of a wind turbine blade when operating involves multi-field coupling, requiring a comprehensive and interdisciplinary understanding of its performance under various design load conditions (DLCs). This paper introduces an efficient algorithm for evaluating the strength failure of all finite elements within the blade components. The algorithm utilizes a distributed load application method. It identifies the maximum failure index value and its corresponding DLC for each individual finite element across all load angles of the load envelope. This novel approach rapidly identifies the primary failure DLC at different locations along the blade’s length. To validate the algorithm, a series of aeroelastic response simulations of a 5MW wind turbine blade are conducted. Then, all load angles in load envelope are thoroughly examined, conduct global failure index assessments based on the Hashin laminate failure theory for the skin’s triaxial ply layer and the shear web’s biaxial ply layer of the blade. In essence, this research offers a rapid and accurate algorithm of identifying potential weaknesses. The algorithm is employed to assess the blade’s vulnerability to strength failure, highlighting its practical value in blade strength failure assessment, ensuring the safety and durability of these critical components.
Rock-Fluid Interactions in a Tight Sandstone Reservoir
Authors: Wang Lianhe , Liu Guangfeng , Jiang Fan , Wang Hengli , Yang Daoyong
Published: August 2024

In this work, we present a comprehensive and practical framework to quantify the dynamic characteristics of pore-throat structure together with wettability alterations during a waterflooding process in a tight sandstone reservoir in addition to evaluating the impact of ionic composition and salinity on its performance. Thin section analysis, XRD analysis, SEM tests, PMI and RMI experiments, contact angle measurements, zeta potential tests, and displacement experiments with and without surfactants are integrated. In a reservoir, throats with a radius greater than 0.2 μm are found to control less than 40% of its porosity but contribute over 95% to its permeability. While pore size distribution remains relatively stable, average throat radius with the maximum frequency is decreased from 0.5 μm to 0.3 μm, resulting in a 13.9% decrease in average permeability. Compared to that of using pure brine, adding surfactants reduces the cutoff movable throat radius from 0.033 μm to 0.019 μm, leading to an incremental oil recovery of 4.26%. In a strongly water-wetting formation with its oil filling the center of a pore in the form of oil droplets, the movable water saturation in the two-phase flow zone on the relative permeability curves ranges from 22.5% to 55.1%. At the isotonic point, the water saturation is 43.6%, resulting in a waterflooding oil recovery of 42.1%. Conversely, in a weakly oil-wetting formation with its oil mainly distributing in the form of an oil film, water saturation in the two-phase flow zone varies from 22.3% to 48.1%. At the isotonic point, the water saturation is 38.1%, resulting in a waterflooding oil recovery of 33.2%. Experimental observations demonstrate that low salinity water (LSW) injection expands the electric double layer (EDL) on the oil/brine and rock/brine interfaces, altering the rock wettability; however, the presence of divalent ions in the LSW undermines such wettability alteration. On the other hand, permeability reduction resulting from salinity decrease can be alleviated by introducing divalent ions into the LSW, while continuous injection of monovalent brine reduces the ultimate oil recovery. Alternatively, a mixture of monovalent and divalent ions in LSW is utilized to revive permeability and maintain wettability alteration. Furthermore, an optimized divalent ion concentration is found to be conducive to reducing the cutoff throat radius and achieving a higher oil recovery in a tight sandstone reservoir.
Obstacle Avoidance Nonlinear Model Predictive Controller for Autonomous Surface Vessels With Variable Sampling Time Prediction
Authors: Fernando Eranga , Imtiaz Syed , Ahmed Salim , Murrant Kevin , Gash Robert , Islam Mohammed , Zaman Hasanat
Published: August 2024

This study proposes an innovative nonlinear model predictive control (NMPC) algorithm developed for obstacle avoidance in trajectory tracking of autonomous surface vessels (ASV). The proposed algorithm extends the prediction horizon to enhance situational awareness and enable the controller to calculate the best control actions. The novelty of the proposed algorithm is that it modifies the duration of the prediction by dynamically varying the prediction sampling time. The controller scans along the reference trajectory for potential obstacles and adjusts the prediction sampling time based on the vessel speed and the obstacle size. The simulation results show that the proposed algorithm improves the consistency of the execution time compared to the conventional NMPC and exhibits improved trajectory tracking with less speed variations.
Multi-Objective Optimization of Semi-Submersible Platforms Based on Genetic Algorithm
Authors: Chen Yuchao , Lu Zhen , Wu Xiaofei , Xiao Feng , Tang Minggang , Cheng Xiaoming
Published: August 2024

The main particulars of semi-submersible platforms are the key factor during the design process, which affects the construction cost and hydrodynamic performance. Therefore, it is of great engineering significance to find a design scheme of main particulars that meets the requirements of functional arrangement and construction cost limit and has a relatively good hydrodynamic performance. Aimed at the semi-submersible platform, eight main particulars were selected as input variables to establish the analysis process of grid generation, mass estimation, and hydrodynamic calculation. The hydrodynamic mesh was generated automatically after the parametric modeling of the platform, and the mass and rotational inertia parameters of the platform were obtained through mass estimation. The hydrodynamic performance was calculated by AQWA to obtain the stability, natural periods, and motion RAOs of the platform. Taking a semi-submersible scientific experimental platform as the optimization target, combined with the wave data of the target sea area, the optimization of the main particulars of the platform was carried out based on genetic algorithm. The natural periods and response level of roll, pitch, and heave Motions of the platform were taken as the optimization objectives, and the hydrodynamic performance evaluation function was created through the allocation of the weights of each objective. Meanwhile, with the constraints of the stability and light weight of the platform, the optimization scheme of the main particulars of the platform was obtained, which showed a significant improvement in hydrodynamic performance over the prototype.
An Indirect Measurement Methodology to Identify Fatigue Damage in The Structure of a 2800TEU Container Ship
Authors: Lang Xiao , Zhang Mingyang , Wu Da , Mao Wengang
Published: August 2024

Ships endure fatigue damage from continuous wave-induced stress. The spectral method, despite being a standard assessment tool, is fraught with uncertainties. However, a large segment of today’s maritime vessels abstains from embedding continuous, life-cycle-spanning sensor systems to monitor fatigue damage accumulation. This lacuna precipitates pronounced ambiguities in maintenance prediction, highlighting the urgent need for a rigorously systematic approach to address this knowledge void. To address these issues, this paper introduces a machine learning-based indirect measurement method for evaluating fatigue damage in a 2800TEU container vessel. Utilizing three years of cross-Atlantic voyage data, the study aims to predict fatigue damage more accurately. Our method, which leverages available navigational and environmental data, circumvents the need for intricate sensors. We benchmark our model’s predictions against full-scale measurements and conventional approaches, scrutinizing the accuracy and reliability of each. This indirect strategy not only promises to enhance maritime safety through a more lucid understanding of fatigue accumulation but also supports maintenance planning by estimating long-term fatigue impact. This research posits a simpler yet potentially more efficacious alternative for the surveillance and management of fatigue in maritime vessels.
A Comparison of Wave Directional Spreading Measurements Made With a Spotter Buoy and a Directional Waverider Buoy in Parallel
Authors: Ewans Kevin , Collins Clarence
Published: August 2024

The directional spreading is an important characteristic of a sea state. For example, the probability of extreme wave crests occurring within the sea state and the loading on offshore structures are both dependent on the amount of spreading. Accordingly, field measurements of waves that allow quantification of directional spreading provide valuable insight into the directional characteristics of sea states and consequently into wave crest and wave load modelling. Wave buoys that measure three orthogonal component of surface displacement permit directional spreading to be estimated; the Datawell Directional Waverider buoy and the Sofar Spotter buoy are two examples. The Directional Waverider is a 90 cm diameter buoy and has seen widespread use since its introduction some 35 years ago. The Spotter is a recent development, and due its small size, with a diameter of 38 cm, and relatively low-cost, it has become popular solution for wave measurements, particularly in remote regions of the ocean. The Directional Waverider wave measurements are based on its own acceleration measured with onboard accelerometers, whereas the Spotter wave measurements are based on its own velocity measured with GPS. In this paper we compare the relative performance of the Directional Waverider and the Spotter buoys, with particular focus on the directional spreading, using parallel data sets from measurements made at a near shore, 17 m water depth, location in the US Army Corps of Engineer’s field research facility at DUCK, on the east coast of USA.
Numerical Analysis of Overload/Underload Effect on Fatigue Crack Propagation Behavior of AH32 Steel
Authors: Qin Dong , Dai Qiansheng , Xu Geng
Published: August 2024

A numerical analysis has been done to investigate the effects of different overload conditions on crack propagation behavior of AH32 steel. The tensile overload ratios, overload-underload, underload-overload and underload are investigated in this study. The residual stress distribution in the region near the crack tip under different overload ratios and overload conditions are all the results of plastic deformation of the material near the crack tip during fatigue crack propagation, which shows that applying tensile overload postpone the crack growth, while underload promote the crack growth. Furthermore, it is also observed that the crack closure level shows a fast increase with the increase of overload ratio. Finally, the mechanism of residual stress at the crack tip and the mechanism of plastic deformation at the crack tip controlling the transient crack growth behavior under variable amplitude loading are essentially the same.
A Nonlinear Integrable Water-Wave System Model for Gravity and Surface-Tension Waves
Authors: Nabelek Patrik V. , Yim Solomon C.
Published: August 2024

The completely integrable case of the nonlinear Bousinesq abcd system describing 1+1-dimensional weakly nonlinear and weakly nondispersive model for gravity and capillary waves is developed. The case of gravity and surface-tension solutions for the wave elevation and transverse parcel velocity on the surface of the fluid is examined in detail. The total wave energy of the system is written in Hamiltonian canonical variables and can be used to generate the dynamics in this model from a Poisson bracket. The Poisson bracket and dynamics is defined explicitly using the calculus of variations. The energy is the first conservation law obtained immediately from the Hamiltonian formulation. An infinite number of additional conservation laws are derived using a matrix Lax pair formulation of the system. Analytical soliton solutions (a kind of travelling wave) are derived and are combined in nonlinear superposition via the nonlocal dbar dressing method. The forward and inverse scattering transform (IST) for this system is developed and applied to the calculations of analytical multi-soliton solutions, periodic solutions, and undular bore like solutions. The capabilities of this method are demonstrated via various numerical solutions with a variety of boundary conditions. This nonlinear system and other well-known nonlinear wave models such as the KdV equation are compared. Validation of this system for the description of head on collision of solitons in an experimental flume was conducted in 2019 by Redor et. al. is discussed. Potential practical engineering applications of this system are examined and discussed.
Numerical Investigations on the Influence of Stiffness of Floating Collar and Net Cage on the Hydrodynamic Response of a Quadrate Aquaculture Structure in Waves
Authors: Zhang Xueyan , Zhang Xiantao , Wei Handi
Published: August 2024

A method of investigating the hydrodynamic characteristics and deformation of a quadrate gravity fish farm is presented in this paper, which focus on two components: net cage and floating collar. First, lumped mass model and screen model are adopted to simulate the net structure and calculate the hydrodynamic force acting on the net; the discrete-module-beam (DMB) method is applied to analyze the hydroelastic response of the floating collar. And convergence analysis is conducted to determine a reasonable grid division form of the net cage and the floating collar. Then, drag forces of the rigid and flexible circular cylindrical net cage are investigated and show a good agreement with the experimental data, which verifies the accuracy of this numerical simulation method. Given the simplification of the calculation, the explicit coupling method was used to couple the net cage and the floating collar. Finally, the numerical model is used to study three combination forms of the fish farm in waves, which are flexible net cage with elastic floating collar, flexible net cage with rigid floating collar and rigid net cage with elastic floating collar. And calculation results show that the rigidity or elasticity of the floating collar and the rigidity and flexibility of the net has some influence on the motion amplitude and the mooring loads of the fish farm.
Fatigue Performance of Riser Quality Girth Welds: Fracture Mechanics Study of the Slope Transition Point Using DNV’s Girth Weld Database
Authors: Horn Agnes Marie , Johnston Carol
Published: August 2024

The fatigue design S-N curves for welded joints include a change in slope to enable fatigue life under variable amplitude loading to be calculated. In in DNV-RP-C203 [1] and BS7608[2] the slope changes from m to m+2, for most of the fatigue Classes for welded joints, this is a change from a slope of m = 3 to m = 5. The slope transition point (STP) is located at 1 × 107 cycles in DNV-RP-C203 but at 5 × 107 cycles in BS7608.

A method was proposed which uses fracture mechanics analysis and a variable amplitude loading spectrum to understand the most suitable location for the STP for girth welds in risers and pipelines. Different positions of the slope transition point (STP) were used in conjunction with two-slope S-N curves in the Miner’s damage sum. By comparing the number of blocks of the histogram applied in both analyses, a suitable position for the slope transition point (STP) in the bilinear S-N curves can be suggested, for the particular VA stress histogram applied. This paper describes the findings related to STP for VA loading for different VA stresses, including recommendations for further work.
Local Structural Response of Stiffened Steel Panels due to Wave Impact: Calculated Responses From Measured Slamming Pressures Vs. Hydroelastic Measurements
Authors: Abrahamsen Bjørn Christian , Hellan Øyvind
Published: August 2024

Design of offshore structures must be designed against wave impacts. The local structural integrity of the stiffened panels is often checked by finite element analysis (FEA). The design critical slamming loads used as input to the FEA is often obtained from model tests in ocean basins or towing tanks. The slamming pressure measurements and corresponding response calculations are not trivial and for practical reasons calculations do not normally account for any hydro-elastic effects, except perhaps added mass. So how accurate are such FEA calculations? This document describes a classical FEA procedure using a constant and uniform added mass. The wave impact pressures used as input to the FE response calculations were measured on a 9 × 5m2 area of a vertical column in SINTEF Ocean’s large wave tank. The FE response calculations are compared with measured responses from hydroelastic wave impacts, where the elastic panel covered the same area as the slamming force panels. The structural response is calculated for the 5 largest extreme total force events out of a total of 19 realizations of a critical sea state. The FE results of the calculations are compared statistically to measured extreme strains from the elastic panels. The FE calculation procedure is found to be conservative since calculated design strain values from FEA are significantly larger than the measured design strain values.
An Overview of the 2021 Tropical Cyclone Features in the Western North Pacific Region
Authors: Zhang Kewei , Meng Wenjian , Liu Haijiang
Published: August 2024

As extreme events are getting more frequent in a changing climate, attention has been paid to the anomalous tropical cyclone (TC) features within a single year. The 2021 TC features in the Western North Pacific (WNP) are analyzed in this study. The result shows that more than half of TCs in 2021 can only reach an intensity of the tropical storm category, and 2021 TCs preferred a northeastward drift direction. August 2021 is identified to be one of the major contributors to these scenarios. Influenced by the strong southwest monsoon in early August 2021, TCs Lupit, Mirinae and Nida kept drifting northeastward since their genesis. Although their tracks were nearly parallel, few interactions among them can be detected due to the instantaneous large mutual distance and low TC intensity. Regarding the relatively low TC intensity in August 2021, it is confirmed that the intensification of TCs Lupit and Mirinae was restrained by the terrain effects along the track, while with the insufficient moisture flux convergence perhaps caused by the adjacent subtropical high, TCs Nida and Omais lacked an environment favorable for the intensification. The present study provides an overview of the TC features in WNP with a special focus on the 2021 August scenario, which could enhance the academic community’s understanding of extreme climate events and provide potential assistance for future disaster prevention and mitigation efforts in coastal areas.
A Numerical Study on Swing Motion of Single Point Mooring Floating Vertical-Axis Wind Turbines With Variable-Pitch Blades
Authors: Fukunaga Yuta , Ikoma Tomoki , Tan Lei
Published: August 2024

Although vertical axis wind turbines have not been introduced into floating offshore wind turbine (FOWT), they have the advantage that the power generation mechanism such as nacelles can be installed in a low location, making it relatively easy to provide static stability to the FOWT and eliminating the need for work at high locations during maintenance. In addition to these advantages, this study examines the effect of the thrust control of a vertical wind turbine on the oscillating motion of a floating structure with several vertical wind turbines equipped with a variable pitch mechanism, which is expected to improve the turbine performance.

In this study, the thrust calculated using double multiple stream tube model was added as an external force to the equation of motion of the floating body to simulate the swing motion of the floating body. The moving position of the floating body also differs depending on the pitch control angle, suggesting that the floating body can be moved to any position in the future with appropriate control.
Vortex-Induced Motion of a Novel Mono-Column FPSO in Waves and Currents
Authors: Gu Jian , Zhao Zhanhua , Yin Yan , Fan Yali , Han Xiangxi
Published: August 2024

The mono-column FPSO platform has recently attracted more attention from researchers due to its advantage of stability in waves and currents relative to the traditional Spar platform with the larger draft. However, the heave motion of the mono-column platform becomes a concomitant disadvantage for this type of platform. The submersible appendix is usually designed to suppress the heave motion of the platform, which could interrupt the flow patterns around the column. The vortex-induced motion (VIM) of the platform could be much different from the original column or Spar platform. The present article initially investigates the VIM performances of a novel mono-column FPSO with a heave suppression structure. The performance is studied numerically in the case of both currents only and currents with waves, respectively. The dependency of mesh and time step are observed to validate the numerical model. The characteristics of inflow and cross-flow responses are analyzed comprehensively. Further, the influence of waves is found limited to the overall responses of vortex-induced motion in the given cases. The present article is significant to the design of the novel mono-column FPSO platform and provides references for further study of vortex-induced motion.
An Attention-Based Deep Learning Model for Phase-Resolved Wave Prediction
Authors: Chen Jialun , Gunawan David , Zhao Wenhua , Taylor Paul H. , Chen Yunzhuo , Milne Ian A.
Published: August 2024

Phase-resolved wave prediction capability, even if only over two wave periods in advance, is of value for optimal control of wave energy converters (WECs), resulting in a dramatic increase in power generation efficiency. Previous studies on wave-by-wave predictions have shown that an Artificial Neural Network (ANN) model can outperform the traditional linear wave theory-based model in terms of both prediction accuracy and prediction horizon when using synthetic wave data. However, the prediction performance of ANN models is significantly reduced by the varying wave conditions and buoy positions that occur in the field. To overcome these limitations, a novel wave prediction method is developed based on the neural network with an attention mechanism. This study validates the new model using wave data measured at sea. The model utilizes past time histories of three Sofar Spotter wave buoys at upwave locations to predict a Datawell Waverider-4 at a downwave location. The results show that the attention-based neural network model is capable of capturing the slow variation in the displacement of the buoys, which significantly reduces the prediction error compared to a standard ANN model.
Numerical Simulation of Concurrent Flexural and Crushing Failure of Level Ice
Authors: Mokhtari Mojtaba , Kim Ekaterina , Amdahl Jørgen
Published: August 2024

This study presents a novel approach for simulating the concurrent flexural and crushing failure of level ice when interacting with sloping structures. The mechanical behaviour of ice is simulated by a nonlinear viscoelastic constitutive model with progressive damage, accounting for microstructural evolution and phase transitions in polycrystalline ice under compression. The constitutive model, scripted in Fortran, has been validated against laboratory-scale physical tests.

To simulate the flexural failure of ice, the ice domain is first discretized with hexahedral finite elements that do not share nodes with their neighbouring counterparts in the in-plane directions. Then, a cohesive contact model with a traction-separation law and damage evolution is implemented to define cohesive interaction behaviour at the vertical interface of adjacent elements. This model, based on a Discrete Finite Element Method (DFEM), allows for the computation of multiple crack initiations and propagations, effectively simulating ice fragmentation into rubble. Therefore, the proposed ice model eliminates the need for predetermining ice breaking length, a notable limitation in prior studies that utilized the cohesive zone method.

To validate the ice model, a numerical model of an ice-breaking cone mounted on a jacket structure in the Bohai Sea interacting with drifting level ice is developed. Good agreement between the numerical results and the field measurements is achieved, which demonstrates the effectiveness of the proposed ice model.
Extreme Wave Run-Up Loads on Monopile Appurtenances: A Practical Guide
Authors: Bermejo Jimenez Ana , Skourup Jesper , Lykke Andersen Thomas , Garborg Karsten , Ankerstjerne Rolland Louise
Published: August 2024

Monopiles are often the preferred foundation concept for an offshore wind turbine. The interaction between extreme waves and the large diameter monopile will in some cases result in a vertical jet of water uprush on the monopile (i.e., wave run-up) which subsequently may lead to large slamming loads on monopile appurtenances like the external working platform.

Extreme wave run-up interaction with an external working platform is often an area of concern during the design phase of an offshore wind project as an overly conservative assessment of the run-up loads may lead to unneeded costs in material and an increased project carbon footprint. An insufficient assessment of the run-up loads may lead to structural failure of the appurtenances and subsequent costly maintenance and repair works, further exacerbated by possibly difficult access to the damaged platform.

The practical process in the assessment of wave run-up on monopiles and associated loads on appurtenances can be a challenge to the designer due to lack of guidance on this topic in governing standards. The designer may then have to rely on several sources of available literature and must assess and include the effect of associated uncertainties like: Adjustment to site specific environmental conditions, unclear or unconcise terminology in the literature, lack of model test results representing the actual geometry and limited knowledge of spatial and temporal run-up load distribution on the appurtenances.

The aim of the present paper is to describe a complete methodology for assessment of wave run-up on monopiles and associated loads on appurtenances. The methodology, which will serve as a practical guide, is based on a collection of existing methods with new analysis to consider the pressure distribution on modern asymmetric grated platforms. This was based on experiences gained and challenges encountered during a detail design project of a monopile foundation for an offshore wind turbine in extreme environmental conditions. The sensitivity of the run-up assessment related to the design input (water depth, wave height and period, associated water level and current conditions) is discussed by considering a matrix with various environmental input combinations representing extreme environmental conditions.
Effects of Temperature and Water on the Fatigue Performance of Composite Materials and Steel-Composite Bonded Interfaces
Authors: Karpenko Olena , Egilsson Sigurdur , Moreira Arouche Marcio , Pavlović Marko
Published: August 2024

This work investigates the effect of temperatures and salt water exposure on the fatigue performance of Glass Fibre-polymer Composite and composite-to-steel interfaces. Four-point end notched flexure tests are employed to gauge interface fracture behavior under the fatigue loading, along with cyclic tensile tests for material assessment. A digital image correlation system is employed to track the progressive crack development on the steel-composite interface, while an extensometer paired with thermocouples are integrated in the fatigue testing of the composite material. As the result the fatigue crack propagation behavior and material fatigue performance are compared between reference and temperature/moisture exposed specimens.
Non-Stationary Equivalent Storm Model for Long-Term Statistics of Ocean Storms
Authors: Laface Valentina , Arena Felice , Bitner-Gregersen Elzbieta
Published: August 2024

In the last decade many researchers focused on the study of non-stationary pattern of climatic variables., It is well established that marine signals e.g., significant wave height or sea water level exhibit a long-term trend due to climate change. The classical approach for the estimation of extreme values analyses may not be enough reliable. The need to account for non-stationarity has involved the development of non-stationary extreme value analysis (NS-EVA) approaches. The main idea is to modify the classical extreme value analysis approach by using non-stationary distributions instead of the stationary ones. Non-stationary probability distributions are analogue to the stationary ones, but their parameters are time dependent. The time dependency may involve all or some of the distribution parameters which may be expressed in different ways. In this paper, this basic concept is applied to develop a non-stationary Equivalent Storm Model (ESM) using the concept of Equivalent Triangular Storm (ETS). The ESM approach is a semi-analytical approach based on the statistic equivalence between actual and an associated simplified storm characterized by a standardized storm shape which leads to the equivalence of wave risk between actual storm sequence and simplified storm sequence at a given site. Due to the equality of wave risk between actual and simplified storm sequences, the problem of calculating return period of sea storm with assigned characteristics can be managed analytically referring to the standardized storm shape, providing very simple analytical formulae dependent on the significant wave height probability distribution and on a duration-intensity regression function at the considered site. The non-stationary ESM is achieved by substituting these two stationary functions with time dependent ones in a similar way as NS-EVA does. A data analysis is proposed to elucidate the differences on significant wave height return values estimation between stationary and non-stationary ESM approach due to non-stationarity of significant wave height and storm duration.
Recognition of Surface Corrosion Morphology on Coastal Engineering Structures Using Machine Vision Technology
Authors: Yu Qifeng , Han Yudong
Published: August 2024

The harsh marine atmospheric conditions, including high temperatures, humidity, and salt spray, prevalent in the coastal areas of Hainan, pose a significant challenge to the durability of ground facilities and equipment, often resulting in corrosion and functional degradation. Hence, accurate monitoring of corrosion is paramount for maintaining coastal engineering structures. This study leveraged data from the Chinese National Center for Materials Corrosion and Protection Science to extract corrosion morphology features using image analysis techniques. Subsequently, a corrosion identification model was developed using machine learning algorithms. The model’s accuracy was validated through various evaluation metrics. The research outcomes have practical applications in the maintenance and management of coastal engineering structures by providing automatic corrosion morphology recognition. This enables maintenance personnel to promptly undertake repair measures, thereby reducing maintenance costs and enhancing structural sustainability.
An Investigation of Winter Navigation and Icebreaker Needs in the Ice-Infested Water: The Gulf of Finland and the Gulf of Riga
Authors: Lu Liangliang , Kondratenko Aleksandr , Kulkarni Ketki , Li Fang , Kujala Pentti , Musharraf Mashrura
Published: August 2024

With climate change, the ice cover in the Arctic and subArctic regions is likely to change relatively quickly. The Baltic Sea is a region with much maritime traffic and meanwhile some parts are covered by ice during wintertime. Icebreakers are usually needed in this region to assist the traffic in ice. However, icebreakers are a limited and expensive resource, and the number of vessels waiting for assistance often outnumbers the available icebreakers. Therefore, whether the current icebreaker strategy needs to change under the impact of the changing ice environment is important. This paper aims to establish a wintertime traffic simulation model with icebreaker assistance for an ice-infested area, i.e., the Gulf of Finland and the Gulf of Riga to see the possible trend. The model is developed with traffic data, ice data and icebreaker information, etc. With the model developed, investigations are conducted by varying different parameters to estimate their effect on the system. This way, the icebreaker needs under different future winter scenarios can be estimated with appropriate system behavior indicators calculated. The results show that the different winter scenarios have quite different icebreaker needs and system behaviors.
Analysis of Higher Harmonic Loads on a Fixed Truncated Vertical Cylinder
Authors: Chen Junru , Feng Xingya , Li Ye
Published: August 2024

Understanding the characteristics of the nonlinear extreme waves loading has both scientific and economic benefits of the offshore structures design. This paper investigates the higher-harmonic loads on a fixed truncated vertical circular cylinder under the action of nonlinear focused waves. This is the concern of the excitation force on the foundation of the cylindrical floating wind turbines in extreme waves. In order to analyse the higher-harmonic loads, focused wave groups are generated by a fully nonlinear potential flow model based on the assumption of a “Stokes-type” nonlinear harmonic structure. A general phase-based harmonic decomposition method is employed for the higher-harmonic hydrodynamic loading on a fixed structure in water waves of moderate steepness. The local wave elevations around the structure are also visualized and compared with the pure wave elevations for the first three harmonics in order to reveal the local dynamics driving higher harmonic loads. The results show that the higher-harmonic load components satisfy the nonlinear harmonic structure of the Stokes expansion. Accordingly, higher-harmonic loads of a focused wave group on the fixed truncated vertical circular cylinder can be estimated by a simple mathematical model with the linear component. The simple estimation results are compared with both the experimental data and the analytical solutions to validate the accuracy.
Diving Into Subsea Decommissioning: the Challenge of an Economic Approach Beyond Costs Model
Authors: Santos Thauan , Santos Luan , Fontainha Tharcisio , Infante Carlos Eduardo , Grangeia Carol , Nascimento Annyeli , Cordon Marco , Tosto Giovanna , Ivo Marcelo
Published: August 2024

This article aims to identify national and international studies and practical experiences in the economic analysis related to subsea decommissioning, in order to identify the best alternatives applied to the Brazilian case. Since the country has a schedule of offshore structures to be decommissioned in the coming decades, studies are needed to support public policymakers by proposing sustainable strategies in line with international standards and practices. To this end, the methodology initially used a literature review based on bibliometric analysis, using scientific publications available on the Scopus and Web of Science databases. Lastly, the article highlights the importance of the multi-criteria analysis to define decommissioning alternatives considering not only economic results, but other perspectives, such as social, environmental, and waste. As the main results, the research identifies the lack of literature and the sectoral limitations of current best practices worldwide. The main reasons for those limitations are the disparity of projects and technological and regional characteristics, and consequently difficulties for costs measurements and benchmarking; lack of professional capabilities on sustainable subsea decommissioning, limited availability of studies, and fragmented regulatory approach on this matter.
Barge Maneuvering Using a Fleet of Autonomous Surface Vessels: Simulations and Experiments
Authors: M. de Andrade Emerson , Fernandes Antonio C. , Sales Junior Joel S.
Published: August 2024

In recent years, there has been a growing trend in the use of autonomous surface vessels for various everyday tasks. These vessels’ capabilities include, for instance, monitoring water quality, surveillance, passenger transportation, and underwater mapping. However, overcoming the challenge of using autonomous surface vessels to transport larger vessels and floating structures is not an easy task, requiring a multidisciplinary approach. In our study, we delve into the potential of employing six autonomous surface vessels to transport a non-self-propelled rectangular barge. Our methodology is based on numerical and experimental tests. In the first part, we prepare our simulations using the 3D Gazebo Simulator and the Robot Operating System (ROS), where we build models for both the barge and the autonomous surface vessels (ASVs). These vessels maneuver using a non-linear approach, taking into account the characteristics of each floating object to calculate the forces and moments during the simulations. To proceed with the transportation of the barge, we implement a PID controller and a thrust-allocation algorithm. Then, we build reduced-scale models to carry out experimental tests in the visualization tank at the Laboratory of Waves and Current (LOC/COPPE/UFRJ). Finally, our combined numerical and experimental findings confirm the viability of using a fleet of autonomous surface vessels and our proposed approach for barge transportation.
Early Lost Circulation Monitoring Using a Hybrid CNN-LSTM Model
Authors: Wu Liwei , Han Liang , Li Gensheng , Song Xianzhi , Zhang Qilong , Zhang Rui , Zhang Ziyue
Published: August 2024

Lost circulation is one of the most common issues affecting drilling safety, known for its sudden occurrence. Traditional expert diagnosis methods heavily rely on expert experience, exhibiting a high degree of subjectivity and lag. Conventional machine learning approaches struggle to fully capture the spatial and temporal variations within the multidimensional data of lost circulation, leading to insufficient accuracy. To address the challenge, this paper proposes an early intelligent monitoring hybrid model for lost circulation by concatenating Convolutional Neural Network (CNN) and Long Short-Term Memory Neural Network (LSTM). Initially, sliding window method is employed to structure historical data of lost circulation into time series samples. Subsequently, these time series samples are input into one-dimensional CNN network to extract spatial feature vectors. Following this, the extracted feature vectors are input into LSTM network to uncover temporal feature information. Finally, the Softmax function is applied at the network’s output layer for classification. The proposed model is tested on real dataset of lost circulation. The results show that the performance of this hybrid model is superior to traditional machine learning models, with accuracy of 94%, missed alarm rate of 4%, and false alarm rate of 8% on the test set. Compared with expert diagnosis, hybrid model can detect lost circulation risk earlier and significantly improve monitoring timeliness. This study is of great significance for ensuring drilling safety and improving drilling efficiency.
Comprehensive Hydrodynamic Performance Evaluations of Representative Atlantic Canadian Fishing Vessels
Authors: Islam Mohammed , Akinturk Ayhan , Faramarzifar Ali
Published: August 2024

Domestic vessel designs are generally aimed at satisfying certain operational specifications, not targeting optimized fuel consumption, greenhouse gas (GHG) emissions or Underwater Radiated Noise (URN) generation. This can be observed in Canadian domestic vessels, as Canada encompasses vast maritime terrain and a long history of shipping and fishing industry. The situation may be more challenging for Canadian fishing vessels, primarily constructed to satisfy economic needs that meet the minimum jurisdictional requirements. The high length/beam ratio, deep hull shape, off-the-shelf propeller and rudder and other hull appendages are often selected to maximize the profit/capacity and with insufficient attention to their impacts on the hydrodynamic performance, stability and the GHG and URN emission aspects. The impact of the not-well-designed propeller, rudder, and hull shape and appendages on various performance indices such as fuel consumption and greenhouse gas (GHG) emissions (powering performance), manoeuvring, seakeeping and URN emissions are poorly understood.

The primary objective of this research is to gain insights into existing designs of Canadian fishing vessels’ hull, propeller, rudder and appendage systems to improve understanding of the hydrodynamic interactions and the resulting impacts on performance efficiencies, GHG and URN emissions. As the first step in achieving this objective, the research team has selected and physically modelled a representative Atlantic Canadian fishing vessel at a suitable scale. The team utilized both physical and numerical modelling tools and techniques to conduct the investigations on the hydrodynamic performance evaluations of the fishing vessel model at realistic operating conditions in terms of bare and appended hull resistance, powering predictions using self-propulsion tests, free running manoeuvring and seakeeping performance. This paper presents the preliminary results of the physical and numerical modelling campaign, specifically investigations of the effects of a hull appendage known as a keel cooler. This work improves understanding of the interactions between the vessel, propeller, rudder, and hull appendages regarding hydrodynamic, dynamic stability and GHG and URN emissions performance.
Combining Drilling Condition Analysis With Unsupervised Time Series Models for Kick Monitoring
Authors: Zhou Detao , Zhu Zhaopeng , Li Gensheng , Song Xianzhi , Han Liang , Li Qihao , Zhou Chenzhan
Published: August 2024

With the continuous development of petroleum exploration and production technology and the increasing complexity of geological conditions, the problem of narrow-margin safe drilling has become a major challenge in the field of petroleum exploration and development. Kick is also one of the high-frequency, high-hazard accidents in drilling. To reduce drilling costs and improve drilling safety, it is crucial to accurately monitor kicks and prevent their further development. A method for monitoring kick, based on the variation of logging parameters, currently exists. However, it does not take into account the impact of abnormal conditions such as pump stoppages on the outlet flow rate and the total volume of drilling fluid in the tank, which can lead to false alarms. In order to improve the accuracy of risk identification and reduce the false alarm rate, a kick monitoring method is proposed that combines drilling conditions with an unsupervised Bidirectional Long Short-Term Memory Autoencoder (BiLSTM-AE). This model simultaneously considers past and future information through forward and backward propagation, effectively extracting temporal features from sequences using bidirectional information. The proposed method was tested using kick monitoring data from 3 wells. The experimental results indicate that the recognition accuracy of the kick intelligent monitoring model based on BiLSTM-AE is 88.85%, surpassing other existing intelligent monitoring models. When combined with abnormal conditions such as pump stoppages, the model’s false alarm rate is reduced by 9.33%.

This research can provide a theoretical foundation and important technical reference for accurate kick risk monitoring, especially in conditions where kick risk data labels are lacking. Moreover, it holds significant potential for practical field applications.