bluuebunny/crossref_metadata_2025 huggingface dataset:
Viscosity Modeling of Solvent-Heavy Oil/Bitumen Systems at High Pressures and Elevated Temperatures
Authors: Hu Bingge , Yang Daoyong
Published: August 2024

This work presents a novel framework for reproducing the measured viscosity of solvent-heavy oil/bitumen systems by integrating the Peng-Robinson equation of state (PR EOS) with binary interaction parameters (BIPs) and modified alpha functions. The oil samples are treated as either as a single pseudocomponent (PC) or multiple PCs. Also, the six most common mixing rules (i.e., Arrhenius’ mixing rule, Cragoe’s mixing rule, double-log mixing rule, Lobe’s mixing rule, power law mixing rule and Shu’s mixing rule) have been evaluated and compared. By adopting the effective density concept, the volume-based power law, weight-based power law, and weight-based Cragoe’s mixing rules reproduce the measured viscosity from 4.3–15000.0 mPa·s within the pressure and temperature range from 1.1 to 10.9 MPa and from 287.9 to 463.4 K. When utilizing one PC, the overall absolute average relative deviation (AARD) for viscosity prediction is found to be 16.0%, 16.5%, and 29.4% for the aforementioned mixing rules. When utilizing four PCs, the AARDs decrease to 13.9%, 14.8%, and 19.3% for the same mixing rules. It is evident that such framework has ability to predict solvent-heavy oil mixture viscosity reasonably accurate under various conditions, while it can be easily incorporated into any reservoir simulators within a given reservoir.
Finite Element Modelling of Residual Stresses in Flexible Pipe Pressure Armor Z Profiles
Authors: Provasi Rodrigo , Toni Fernando Geremias , de Arruda Martins Clovis , Ramos Junior Roberto , Campello George Carneiro , Figueira de Souza Rodolfo , Coser Tiago Brun
Published: August 2024

In the manufacturing of flexible pipes, the pressure armor wires are submitted to successive folding and unfolding processes to achieve its final form. This process results in residual stresses that must be taken into account when calculating the total stresses, they are subjected to in operational situations and in fatigue life calculations. After the manufacturing, the flexible pipe is submitted to the so-called Factory Acceptance Test (FAT), in which a huge internal pressure is applied and then removed. In this latter process, a part of the residual stresses is alleviated, resulting in the residual stress field that must be considered in subsequent mechanical analysis. This paper presents finite element models developed to simulate all the folding and unfolding operations, besides the internal pressure application and removal during the Factory Acceptance Test for Z-shaped pressure armor profiles. This modelling contributes to a more representative manufacturing process, leading to a more assertive stress evaluation.
An Intelligent Failure Data Analysis Framework for Failure Data Management of Wind Turbines
Authors: Li He , Guedes Soares Carlos , Ding Yi
Published: August 2024

This paper proposes an intelligent failure data analysis framework to identify failure features of wind turbines intelligently and automatically, requiring few interactions with analysts. Initially, two operation and maintenance datasets in terms of wind turbine failure and maintenance onshore (LGS-Onshore) and offshore (LGS-Offshore) are introduced. Subsequently, an intelligent failure data analysis model is developed based on Bidirectional Encoder Representations from Transformers and the Conditional Random Field model with the assistance of the proposed adaptive resampling mechanism. The advantage of the proposed framework is validated by the better performance in extracting failure features of wind turbines from the LGS-Onshore and LGS-Offshore datasets. Failure properties of the wind turbines are revealed together with the recommendation for failure prevention actions. Overall, this paper proposes a new concept of failure data analysis and contributes to the operation and maintenance of onshore and offshore wind turbines.
Artificial Intelligence for Cooperative Collision Avoidance of Ships Developed by Multi-Agent Deep Reinforcement Learning
Authors: Yoshioka Hitoshi , Hashimoto Hirotada , Matsuda Akihiko
Published: August 2024

Most ship collisions are caused by human error, making them unpreventable as long as humans operate a ship. Autonomous navigation technology is expected to prevent these accidents. Collision avoidance is a key issue in the realization of autonomous ships. To date, rule- and artificial intelligence (AI)-based collision avoidance algorithms have been studied. However, most of them assumed a simple environment in which other ships maintain their speed and course. During actual navigation in congested waters, safe and efficient collision avoidance are achieved through cooperative maneuvers between ships that obey the COLREGs. To realize cooperative maneuvers of ships, multi-agent deep reinforcement learning was applied to learn collision avoidance maneuvers considering the motions of other ships and COLREGs. Then, the developed multi-agent AI was evaluated with typical one-on-one encounters. The multi-agent AI performed cooperative collision avoidance maneuvers in head-on and crossing situations. Furthermore, the influence of reward setting regarding the degree of compliance with COLREGs on the cooperative collision avoidance was investigated. These results demonstrated that the multi-agent AI was promising for realizing cooperative collision avoidance maneuvers similar to those performed by humans.
Study on the Hydrodynamic Interaction Between Two Floating Bodies of Different Dimensions Undergoing Heave Motion in Regular Waves
Authors: Meng Wei , Li Dan , Kang Zhuang
Published: August 2024

When two floating bodies work side-by-side, the close spacing between them can cause hydrodynamic interactions, resulting in large wave oscillations in the gap and motions of the two bodies, seriously threatening the safety of the operation. This paper uses a hybrid two-way coupled field-domain decomposition method to establish a numerical wave tank, where the incident wave part is computed explicitly, and the diffraction and radiation parts are solved on a two-way coupled potential-viscous flow field. Further, the overset method is applied to simulate the body motions. The computational method is first validated by simulating the motions of a floating box heaving in regular waves, and the numerical results are compared with experimental data. The hydrodynamic interaction problem of two floating bodies with different principal dimensions undergoing heave motion in regular waves is then studied, and different wave directions and gap widths are considered. The results show that the two bodies move in phase for low-frequency waves, resulting in smaller relative motions between them. On the other hand, under high-frequency wave conditions, the two bodies move in an inverted phase, enlarging the relative motions. Further, when the larger floating body is located upstream, there is a significant shielding effect on the downstream small body.
Analysis of Hydrodynamic Performance and Mooring Dynamic Response of Offshore Dual-Module Floating Photovoltaic Platform
Authors: Wu Fanlei , Zhang Kai , Cheng Xiaoming , Wang Jingxiang , Xie Chunmei , Yu Jun , Gu Yujie
Published: August 2024

Floating photovoltaic (FPV) systems, as an emerging solar photovoltaic technology, have great development prospects. In order to investigate the adaptability of offshore multi-connected floating photovoltaic platforms under specific sea conditions, hydrodynamic performance research was conducted. A frequency domain hydrodynamic performance analysis of the floating photovoltaic platform was performed using the hydrodynamic analysis software AQWA, which includes platform RAOs (Response Amplitude Operators), hydrodynamic interaction characteristics, and shielding effects. Using the hydrodynamic analysis software Orcaflex, a time domain analysis was performed to investigate the influence of hydrodynamic interactions on the motion response of a multi-connected photovoltaic platform under extreme sea conditions. To ensure model consistency between the AQWA and Orcaflex, the platform model was simulated with six degrees of freedom for free decay under time domain analysis. In shallow water environments, the response generated by mooring dynamics cannot be ignored. In order to investigate the effect of mooring dynamics on the platform in shallow water environments, sensitivity analysis was performed for two cases: considering mooring dynamics and not considering mooring dynamics. Finally, the influence of the wave direction on the floating photovoltaic platform was investigated under normal operating sea conditions. The results show that the peaks of the platform RAOs are mainly clustered in the low frequency range. Hydrodynamic interaction on the two-body platform inhibits the platform motion response. Mooring dynamics have little effect on platform motion response in shallow water environments. Waves in the 60° direction exert the greatest force on the mooring chain and should be avoided as much as possible in practical engineering.
Optimization Design of the Jacket Support Structure for Offshore Wind Turbine Using Golden-Sine Dynamic Marine Predator Algorithm
Authors: Han Muxuan , Du Zunfeng , Zhu Haiming , Zhu Haitao , Yang Yuan
Published: August 2024

Jacket support structure is the main support form for bottom fixed offshore wind turbine. Weight optimization is critical importance due to the substantial volume of material used in the components of jacket support structures. A metaheuristic algorithm is a powerful tool that allows many parameters in a structural optimization design to be considered simultaneously. As a nature-inspired metaheuristic algorithm, Golden-Sine dynamic marine predator algorithm (GDMPA) has been proved to be competitive in multi-modal and high-dimension optimization problems. In this study, a type of offshore wind turbine composed of the Offshore Code Comparison Collaboration Continuation (OC4) reference jacket structure and the NREL 5 MW baseline turbine was optimized using GDMPA. The forces applied to the structure are realistic ensuring that the simulations are accurate and realistic. The inner problem which consists of member sizing is solved using a robust and efficient GDMPA. An innovative jacket structure with ultimate strength, stiffness, stability, and natural frequency constraints was optimized. Moreover, ultimate limit state analysis, eigen analysis and fatigue analysis are used to evaluate the optimized structure. The results indicate that the proposed optimization method is an effective way to reduce the weight and stress concentration. The final design is a low mass jacket support structure that fully complies with offshore structural standard requirements for all design limit states, while meeting the fatigue life of the welding points, thus being best suited for long operating life.
The Safety Analysis of a FPSO Temporary Mooring System at Quayside With One Line Failure
Authors: Liang Mingxiao , Wang Chao , Liu Haidong , Teng Yanjun , Yang Shangjun
Published: August 2024

The Floating Production Storage and Offloading (FPSO) has a long outfitting period at the dock, which will coincide with the typhoon season. In general, the prediction of temporary mooring system safety does not consider the impact of transient stage of mooring line failure. Instead, the failed mooring line is removed from the mooring system before carrying out the simulation to analysis the mooring safety. However, ignoring the transient stage of mooring line failure will underestimate the damage caused by line failure. In this case, the safety of a temporary mooring system of a large FPSO is investigated in this paper. The failed mooring line is disconnected with the FPSO during the simulate process to achieve the simulation of transient stage. The results of FPSO and mooring system motion response in transient stage and steady state shows that the impact of mooring line failure can be considered as an impact load, which will lead to a rapid increase of the FPSO motion and mooring line tension in transient stage. The underestimated damage of line failure may cause insufficient safety redundancy when design a temporary mooring system for typhoon condition. Thus, with one line failure, the tension of the remaining line in the may exceed the tolerable limit and the mooring system may lose the station keeping ability.
Linear and Nonlinear Pitch Response of a Floating Wind Turbine
Authors: Ma Yueyuan , Cheng Zhengshun , Zhao Wenhua , Wang Shuaishuai , Xiao Longfei , Peng Tao
Published: August 2024

Wave-induced pitch motion of a semi-submersible floating wind turbine (FWT) is of practical significance, particularly in conditions involving shallow and intermediate water depths. These conditions often feature more complex and robust nonlinear wave characteristics, which can potentially trigger pitch resonance more readily. To address this, this study focuses on the analysis of pitch motion for a 5-MW semi-submersible FWT in a water depth of 42 m. A series of experiments are conducted in a large wave basin. The linear and nonlinear pitch responses of a semi-floating wind turbine are examined based on the experimental data. The investigation delves into the pitch response generated by diverse wave loads in both operational and parked wave conditions. Certainly, a well-matched linear correlation can be observed between linear wave loads and linear pitch motion across all wave conditions. The analysis also demonstrates that, in the presence of irregular waves, the nonlinear pitch response, induced by the second-order difference-frequency wave loads and taking place at the pitch natural frequency, becomes increasingly prominent and cannot be disregarded as the wave height grows. The excitation at the second-order difference-frequency holds significant practical implications for offshore operations.
VIV Responses of an Elastic Pipe With Staggered Buoyancy Elements: a Combine CFD and Empirical Time Domain VIV Analysis
Authors: Jiang Fengjian , Wu Jie , Lie Halvor
Published: August 2024

This study examines the influence of buoyancy elements on the VIV responses of a flexible riser using a combined method involving the non-linear time domain VIV prediction program VIVANA-TD and Computational Fluid Dynamics (CFD). Detailed analysis of the flow physics around buoyancy elements was firstly made through visualizations from CFD simulations on a rigid cylinder equipped with staggered buoyancy elements. The CFD results suggest that the vortex shedding behind buoyancy elements is suppressed in the configuration with a diameter ratio 5:1 and a length ratio 1:3, because of the complex wake interactions between the thin cylinder and thick buoyancy elements. This indicates a reduced likelihood of resonance and excitations. Hydrodynamic coefficients respectively for the buoyancy elements and bare cylinder are then derived from forced oscillation CFD simulations, and the values align with above-mentioned flow visualizations, such that buoyancy elements primarily play as a damper in the investigated configuration. These derived hydrodynamic coefficients were further applied in non-linear time domain analysis using VIVANA-TD for a 38m long flexible pipe equipped with buoyancy elements. The results were compared with those from model tests carried out in SINTEF Ocean’s ocean basin, demonstrating promising comparisons.
CFD-Based Consequence Modeling for Jet Fire Release on the LNG Bunkering Ship During Replenishment: Predicting Personnel Injuries and Structural Damage
Authors: Nubli Haris , Jung Dongho , Choi Byung Chul , Sohn Jung Min
Published: August 2024

Liquefied Natural Gas (LNG) remains a popular choice due to its widespread availability. However, LNG, stored in a volatile liquid phase, is susceptible to evaporation and highly flammable, which raises concerns regarding its safe transportation, storage, and utilization. Consequently, accidental releases of this flammable fuel pose potential risks to surrounding structures, including fires and vapor cloud explosions. Furthermore, it is crucial to address the risks to individuals and assets, particularly during bunkering or replenishment processes, which are critical events.

This paper aims to identify the impacts of a jet fire release on both personnel and the ship’s structure during LNG replenishment at an LNG port facility. The study presents a case study involving the use of a Computational Fluid Dynamics (CFD) model to simulate an immediate ignition of fire, employing the OpenFOAM solver. This approach enables the acquisition of a temperature profile within the ship’s structure. Subsequently, a regression tool, Random Forest, was employed to construct the temperature profile. This temperature profile can be utilized to identify potential structural failures. Various regression techniques were also employed for comparison with the Random Forest regression. Additionally, a heat dose profile emitted from the fire was used to estimate the probability of injury in the surrounding area. This paper outlines the entire procedure, encompassing CFD analysis, temperature load mapping, and the assessment of injury probability. The findings and recommendations are comprehensively addressed and discussed.
Impact of Hydrogen Concentration Distribution in Hydrogen-Blended Gas on Fatigue Crack Growth Rate of Pipeline Steels
Authors: Zheng Tingsen , Chen Nian-Zhong
Published: August 2024

The methods to achieve large-scale and long-distance hydrogen transport are primarily to blend hydrogen with another gas, such as natural gas. Due to the significant difference of the densities of hydrogen and those of other gases, the distribution of hydrogen-blended gas becomes uneven during pipeline transportation. Mechanical properties of pipeline steels are normally degraded due to the internal hydrogen environment, and thus fatigue and fracture of pipelines that transport hydrogen-blended gases are likely to occur. This paper aims to investigate the impact of the heterogeneous hydrogen volume fraction of hydrogen-blended gas on the hydrogen induced fatigue crack growth rate of pipeline steels using the cyclic cohesive zone model (CCZM). A dynamic surface hydrogen concentration is used to simulate the heterogeneous hydrogen volume fraction of hydrogen-blended gas during transportation. In the CCZM, not only the degradation of cohesive strength but also the degradation of accumulated cohesive length is considered to incorporate the impact of hydrogen embrittlement (HE) on the fatigue crack growth. The predicted results are compared with the fatigue crack growth rate where the hydrogen volume fraction is constant and the most prone locations in pipeline steels where HE may occur are discussed. The results tend to provide a valuable reference for future designs of hydrogen-blended gas pipelines.
The Sympathetic Implosion of Multiple Titanium Alloy Spheres Under Various Inductive Conditions
Authors: Zheng Jiancai , Li Mingyi , He Tengwu , Zhao Min
Published: August 2024

When a pressure hull implodes in the deep-sea environment, it generates a shock wave that propagates at an exceptionally high speed and releases immense energy accumulated due to ultra-high pressure differences. The phenomenon can potentially induce a chain-type implosion of nearby pressure hulls, posing a significant threat to the reliability and safety of the entire underwater vehicle. Therefore, this study aims to investigate the effect of sympathetic implosion between two titanium alloy spheres under different inducing conditions. Firstly, a self-developed numerical method for three-phase fluid-structure interaction involving compressible multiphase flow is implemented based on an open-source solver. This method ensures the conservation properties and accurately captures and tracks gas-liquid interfaces during simulations. Subsequently, the differences in impulse pressure are compared when sphere I implodes due to local impacts or large geometric defects. Furthermore, the sympathetic implosion phenomena and failure mechanisms are extensively discussed under two inducing conditions, including damage characteristics observed in deformed structures, high-speed movement of compressed fluids, and evolution and balance of energy during fluid-structure interactions. The results demonstrate that when the sympathetic implosion occurs due to the local impact, sphere II fractures under the combined effect of the shock wave, expanding bubble, and structural fragments from sphere I. However, sphere II fractures primarily due to dynamic pressure difference when the larger geometric defect induces the sympathetic implosion. Moreover, when the sympathetic implosion is caused by local impact, there is a greater release of energy through shock waves and a higher absorption of energy through structural plastic strain.
Designing for the Animal: Reimagining Offshore Fish Structures
Authors: Black Suzanne , Vennell Ross , Kregting Louise , Moran Damian , Cook Denham , Janssen Gerard
Published: August 2024

The offshore marine environment has the potential to play a significant role in meeting the projected global demand for high quality protein from finfish aquaculture. However, moving aquaculture structures to open ocean locations poses technical and engineering challenges due to increased environmental loads from larger waves and current velocities. Several global initiatives are exploring this opportunity, but none is tackling the ambitious goal of developing soft-structure, mobile solutions. Our aim is to re-imagine the entire approach to finfish aquaculture by considering the key variables, temperature, water motion and husbandry, to understand the requirements for optimal fish wellbeing and growth. This knowledge will enable the design and future implementation of radically new Mobile Aquaculture Production Systems (MAPS). These systems will be flexible, mobile enclosures, readily customizable to support optimal conditions throughout the fish grow-out production cycle, addressing the design challenges for growing, transporting and harvesting fish offshore. The long-term goal is to create an optimal culture system for fish that supports fish wellbeing and growth while enabling increased production, reduced capital outlay and operating costs in a novel, scalable, low-impact, sustainable aquaculture system.
Non-Contact Dynamic Testing of a Next-Generation Helical Crossflow Tidal Turbine Foil Using a Laser Scanning Vibrometer
Authors: Munaweera Thanthirige Tenis Ranjan , Flanagan Michael , Kennedy Ciaran , Jiang Yadong , Fakhari Vahid , Bachour Carlos , Courade Clement , Cronin Patrick , Dillon Conor , McEntee Jarlath , Flanagan Tomas , Goggins Jamie , Finnegan William
Published: August 2024

The renewable energy sector is strategically focused on mitigating risks associated with tidal energy converters to lower the cost of tidal energy to allow it to become a significant contributor to the renewable energy mix. In this study, dynamic testing was used to assess the structural performance of a next-generation helical crossflow tidal turbine foil made with carbon fibre prepreg composite material. Utilizing a Laser Scanning Vibrometer (LSV) expedites testing and data processing. A 5-metre foil prototype underwent dynamic testing in accordance with DNVGL-ST-0164 and IEC DTS 62600-3 standards. Two dynamic testing setups, with and without an unbalanced rotating mass system, were conducted before and after a series of static and fatigue tests. The research highlights the impact of altering tidal turbine system mass on dynamic response, offering crucial insights for designers. This study establishes the groundwork for a standardized LSV testing protocol for small to large scale tidal turbines, contributing to the optimization of next generation designs and performance. Ultimately, it paves the way for more efficient and sustainable marine energy solutions in the future.
Model Tests of a 12 by 18 Floating Solar Array Under Regular Wave Conditions
Authors: Jiang Zhiyu , Dai Jian , Saettone Simone , Souto-Iglesias Antonio
Published: August 2024

Floating solar has appeared as an emerging technology in the global renewable energy portfolio. Although several floating solar concepts have been proposed in the past, most of them are well-suited for deployment in inland or near-shore water bodies with benign environmental conditions. To address the need for sustainable and cost-effective floating solar energy production in offshore areas, a novel modular floating photovoltaic concept suitable for offshore environmental conditions has very recently been proposed in (Jiang et al. 2023). The concept proposes the use of semi-submersible floats for individual modules and crisscrossed rope connections to join neighbouring modules. Based on the conceptual design, this paper presents the experimental investigation of a 12 by 18 array with 216 floats in regular waves under both operational and survival conditions. First, we describe the model test set-up, the physical models of the simplified floats, the environmental conditions, and the sensor instrumentation and measurement. Then, selected time histories of the array motions are analysed. It is observed that the tested large array has good motion performance with limited wave overtopping. Finally, limitations of and lessons learned from the model tests are summarised. This paper paves the way for the next-stage research and development of the floating solar concept for harsh offshore conditions.
CFD Evaluation of the Self-Starting of a Vertical-Axis Wave Turbine and the Related Flow and Load Characteristics
Authors: Yan Deguang , Yang Yingchen , Ge Zhongfu
Published: August 2024

The research and application of marine renewable energy have received much attention due to its potential to generate power with less emissions than traditional sources. Among various types of wave energy converters (WECs), research is still in its infancy for Vertical-Axis Wave Turbines. While the concept has been well adopted in the wind energy industry, the use of this technology for wave energy harvesting could meet challenges due to the reciprocal motion of surface waves. When previously tested, the wave turbine design showed promising spin-up and sustained rotation of the rotor in regular waves. This test encouraged detailed assessment of the self-starting process of the rotor in the present work.

For numerical simulation, a Computational Fluid Dynamics (CFD) model following the Reynolds-Averaged Navier-Stokes framework was established. The model took various aspects into account, such as the influence of the numerical waves, the highly unsteady initial self-starting process, and the appropriate gridding strategy needed to suit a wide range of rotational speeds from near-zero to the quasi-steady, terminal speed of the rotor. The CFD model was applied to reveal detailed characteristics of the flow field and to evaluate the sensitivity of the self-starting process to different inertial properties and damping coefficients of the rotor. The simulation showed that the inertial properties of the rotor would only affect the efficiency of the self-starting process. In contrast, the damping coefficient could have a profound effect on the attained steady-state rotational speed, which has strong implication for the design of power-take-off.

The methodology established in the present work will be invaluable for design optimization as the self-starting process is an important stage of the device operating in an ever-changing environment. The methodology is also transferrable to other types of renewable energy devices that are equipped with a self-started rotor.
Role of Front Splitter Plate Gap on the Flow-Induced Vibrations of a Circular Cylinder
Authors: Tandon Ishan , Kanna Rohan , Joshi Vaibhav
Published: August 2024

In engineering applications, we frequently encounter flow around circular cylinder-type geometries, such as in cooling pipes for heat exchangers, risers and pipelines in oil and gas extraction, storage silos, and buildings in civil engineering. It is widely known that unsteady flow past a bluff body causes alternate vortex shedding and subsequent fluctuating lift and drag forces, resulting in structural damage. It becomes increasingly important to suppress these oscillations to prevent shortening the structure’s lifespan. Amongst various passive suppression devices studied previously, the addition of rigid splitter plates along the horizontal centre-line of the cylinder both upstream and downstream has been found to be quite effective in mitigating transverse vibration. This study aims to understand the previously unexplored effect of varying the upstream gap on suppressing flow-induced vibrations. To accomplish this, the optimization of the gap (g) between the cylinder of diameter D and the trailing edge of the front splitter plate in the range of 0 to 5D has been explored. A two-dimensional stabilized Petrov-Galerkin variational formulation is used to solve the Navier-Stokes equations on an arbitrary Lagrangian-Eulerian moving mesh framework to investigate the response at a low Reynolds number of 120 for reduced velocities of 3–12. The plate length is kept equal to the diameter of the cylinder, and the system is free to oscillate in the streamline and crossflow directions under a low damping ratio of 0.01 and a mass ratio of 6.9. The results of this study will provide valuable insight and aid the development of passive suppression devices for deep-sea structures.
Experimental Study on the Dynamic Responses of a Novel 10 MW Floating Offshore Wind Turbine Integrated With a Fish Cage
Authors: Zhang Sheng , Zheng Xiang Yuan , Zhang Xiangyu , Lei Yu , Liu Yue , Jiang Yucong , Qian Kehao , Li Xin
Published: August 2024

This experimental work is to study the dynamic responses of a novel floating offshore wind turbine integrated with a fish cage (FOWT-FC) under wave and wind loads and to provide a benchmark for the establishment of numerical simulations. A series of model tests of scale 1:30 have been carried out in the ocean basin at Tsinghua Shenzhen International Graduate School (SIGS). This paper provides a detailed description of the experimental setup, including the design, fabrication, calibration and identification of the model, type and arrangement of the sensors. The 6 degrees of freedom (DOFs) displacements of cage, the accelerations at tower top and base and other responses are collected and analyzed. The displacement response amplitude operators (RAOs) are obtained through white noise wave tests, manifesting the excellent seakeeping performance of FOWT-FC. Besides, all responses in the operational and non-operational load cases are below the code limits. A group of controlled experiments are set up to investigate the effect of wind on dynamic responses, and several findings are discovered. In general, wind loads increase low-frequency responses, but have little effect on wave-frequency responses. Moreover, the low-frequency growths under turbulent wind are more significant than those under steady wind. Besides, the turbulent wind enhances the high-frequency responses at around tower’s 1st-mode vibration frequency. Whether under the action of random waves alone or combined wave-wind, the cage’s motions are predominantly controlled by low-frequency and wave-frequency responses, while hardly influenced by high-frequency excitations. The blades’ 3P excitation is not observed in the cage motion spectra, but found in the tower acceleration spectra. Also interestingly, the tower top acceleration has more pronounced spectral contents at high frequencies than the tower base acceleration does. On the contrary, the tower base acceleration has more pronounced spectral contents at low frequencies than the tower top acceleration does. These low frequencies are sourced from the wind loads and difference-frequency hydrodynamic loads.
Free Roll Decay of FPSO and FLNG Hulls With Bilge Keels Through Experimental Tests and CFD Simulations
Authors: Kim Joo-Sung , Choi Yong-Ho , Han Solyoung , Yuck Raehyoung
Published: August 2024

The objective of present paper is to assess the roll damping characteristics of FLNGs and FPSOs. The roll damping characteristics are examined through the three prediction methods; 1) Ikeda’s empirical method, 2) experimental tests and 3) CFD simulations. Practically, design variables that can be adjusted to reduce the roll motion include only the bilge radius and the height of bilge keel. In the present paper, a parametric study has been made considering various combinations of bilge radius and bilge keel height.

The three prediction methods constantly show that the roll damping of FLNG and FPSO hulls considered in the present paper increases with increasing bilge keel height and decreasing bilge radius. Using experimental and simulation data with systematic variation of bilge radius and bilge keel height, it is shown that the roll damping can be correlated with a function bbk/bbk_max0.8. Using this relationship, a design guideline is proposed to simultaneously optimize the roll damping performance, the structural integrity of bilge design and the constructability related to bilge design of the hull form of FPSOs and FLNGs.
An Autonomous Ship Formation Method Based on Virtual Physical System
Authors: Ding Ming , Wang Lei , Wang Yiting
Published: August 2024

The current ship autonomous formation algorithm directly or indirectly designates the specific position of each ship in the formation, which leads problems such as large communication volume, inability to formation according to the proximity principle, and difficulty in expanding the number of ships, etc.. With the expansion of formation scale, these problems will be more significant, so the research of new formation strategy is imperative. Inspired by the rules of nature and artificial potential field method, this study proposes an autonomous formation method that can automatically select the appropriate position according to the actual situation without specifying the specific position of the ship in the formation: the Virtual Wall Method, which solves the problems above. The effectiveness of this algorithm is verified by the simulation of static, dynamic, rotation, scaling and obstacle avoidance of the ship formation. The Virtual Wall Method is applicable to both first- and second-order systems and has significant advantages in large-scale formation of ships.
Diagnostic Digital Twin for Anomaly Detection in Floating Offshore Wind Energy
Authors: Stadtmann Florian , Rasheed Adil
Published: August 2024

The demand for condition-based and predictive maintenance is rising across industries, especially for remote, high-value, and high-risk assets. In this article, the diagnostic digital twin concept is introduced, discussed, and implemented for a floating offshore turbine. A diagnostic digital twin is a virtual representation of an asset that combines real-time data and models to monitor damage, detect anomalies, and diagnose failures, thereby enabling condition-based and predictive maintenance. By applying diagnostic digital twins to offshore assets, unexpected failures can be alleviated, but the implementation can prove challenging. Here, a diagnostic digital twin is implemented for an operational floating offshore wind turbine. The asset is monitored through measurements. Unsupervised learning methods are employed to build a normal operation model, detect anomalies, and provide a fault diagnosis. Warnings and diagnoses are sent through text messages, and a more detailed diagnosis can be accessed in a virtual reality interface. The diagnostic digital twin successfully detected an anomaly with high confidence hours before a failure occurred. The paper concludes by discussing diagnostic digital twins in the broader context of offshore engineering. The presented approach can be generalized to other offshore assets to improve maintenance and increase the lifetime, efficiency, and sustainability of offshore assets.
Characteristics of Organic Carbon Distributions in Tidal Wetland of the Yangtze River Estuary
Authors: Chen Shizhe , Lou Sha , Yang Zhongyuan , Liu Shuguang
Published: August 2024

Due to the coupling effects of runoff and tidal currents, the carbon cycle process of tidal wetlands in the Yangtze River estuary is extensively influenced by both hydrodynamic and environmental factors. In this study, samples of particulate organic carbon (POC) and dissolved organic carbon (DOC) in water, and total organic carbon (TOC) in surface sediments were taken at sites Sanjiagang (SJG) and Nanhui (NH) along the Yangtze River estuary (YRE) in December 2022 to investigate the tidal variation of organic carbon distributions. The results showed that the concentrations of organic carbon, including POC, DOC and TOC were higher at SJG than at NH. According to the Pearson correlation analysis, the concentrations of POC and TOC were positively correlated at NH, and tidal elevation had a positive effect on TOC concentrations. Organic carbon concentrations and water physicochemical properties (salinity, dissolved oxygen, temperature, turbidity and pH) had strong relevance. Results in this paper can provide a scientific basis for the assessment of regional and global carbon balance in coastal wetlands.
Numerical Modeling of Bismuth-Based Plugs for Well Plug and Abandonment
Authors: Jaculli Marcelo Anunciação , Hmadeh Lewaa , Sangesland Sigbjørn , Elahifar Behzad
Published: August 2024

Plugging and abandonment of wells is a fundamental operation within the oil and gas industry, which has gained more focus recently due to safety and environmental concerns. Downhole plugs must withstand extreme pressure and temperature conditions and, in some cases, corrosive environments. Ensuring good sealability is of utmost importance considering the long-lasting perspective of P&A. The usage of plugs made of bismuth alloys is a recent technology that has been vouched as an improvement over traditional cement solutions, especially in terms of resistance to pressure, corrosion, and leakage. Bismuth has the unique characteristic of expanding upon solidification, a phenomenon that has been the main driver for suggesting it as a potential barrier material. Furthermore, creep and aging effects become relevant since the plug is placed in temperatures that could reach close to the melting point of its alloy. This paper comprehensively assesses the necessary modeling steps for characterizing the eutectic bismuth-tin alloy appropriately in commercial finite element analysis software considering the aforementioned phenomena, including a comparison with laboratory tests. Simulations are carried out to test this plug model under different downhole scenarios. Results show that the resistance of the plug to pressure diminishes when the downhole temperature increases, although the exhibited resistances seem to suffice field applications. These conclusions are intended to support bismuth in its qualification as an accepted barrier material.
Experimental Study on the Influence of Seepage on Sediment Initiation Under Steady and Oscillatory Flows
Authors: Zhang Yuhuan , Cui Lin , Zhai Hualing , Jeng Dong-Sheng
Published: August 2024

Sediment incipient motion is a crucial stage in the erosion process, making it imperative to study its mechanism. Seepage can significantly alter hydrodynamic forces around soil particles near seabed surfaces and affect erosion processes. Most previous studies ignored the effect of seepage by assuming the seabed surface as impermeable. Some studies attempted to clarify the effect of seepage force on sediment initiation theoretically, but quantitative analysis through laboratory tests is necessary. In this study, an in-house designed Erosion-Seepage System (ESS) is used to simulate the erosion process with seepage under either steady or oscillatory flow. Through the designed ESS, the erosion rate and seepage can be directly determined and their relationship can be established. The experimental results show that the upward seepage reduces the initial shear stress of the sandy bed under a steady flow. Furthermore, the upward seepage under an oscillatory flow also results in a reduction of the shear stress amplitude required for the motion of the sediment as well as an increase in the erosion rate. In addition, the erosion rate becomes more pronounced for large seepage.
Design and Optimisation of Parallel Hybrid Converter Connected With LCL Filter for Offshore Wind System
Authors: Li Ning , Finney Stephen , Judge Paul D. , Zhang Yixiao , Ng Eddie Yin Kwee
Published: August 2024

Parallel hybrid converters utilise partially rated Silicon Carbide (SiC) Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) based converters as active filters or partial power transfer for slower switching Silicon (Si) Insulated-Gate Bipolar Transistor (IGBT) based converters. This allows the effective SiC MOSFET switching frequency of the overall converter to be significantly increased, reducing the requirement for external filters and increasing the converter’s current control bandwidth, without relying on a wholly SiC MOSFET-based approach in the same topology. In the practical network system, the transformer and capacitor are usually adopted as Inductor-Capacitor-Inductor (LCL) filters after the converter. This paper investigated the potential performance of Parallel Hybrid Converter (PHC) topology with the LCL filter and also designed the component parameters for this topology, including the IGBT and SiC impedance. The parallel direct current supply for both converters also opens up the potential for partial-load efficiency improvements. A long-horizon finite step model predictive current controller is implemented as the control system, which allows significant flexibility in the converter’s operation, compared with direct space vector control and fractional power control. The results validate that the parallel hybrid converter with an LCL filter could achieve the grid-current total harmonic distortion (THD) below 3% with IGBT bridge frequencies in 2 kHz. The stability performance in dynamic situations, including system fault and harmonic injection, is also verified.
A Modern Data-Driven Approach for Accurately Assessing Wave-Induced Loads and Responses of Ships Using AIS and Weather Data
Authors: George Jagite , Aarsnes Lars Holterud , Storhaug Gaute
Published: August 2024

Prescriptive load formulations used during the design process for most ships are based on a presumed design environment. For standard ships, the strength evaluation is performed according to the North Atlantic design environment, while the fatigue design may be verified according to the Worldwide environment. However, it is well-known that some ships operate globally, while others operate in specific areas, being subjected to different environmental conditions than assumed during the design phase. Therefore, the prescriptive loads from design may not be relevant for the actual operation of certain ships. Consequently, within the last decade, significant attention has been given to digital twin models and hull monitoring systems, where the hull structure utilization (e.g., strength and fatigue) is continuously assessed by combining structural models with actual encountered weather conditions. Setting up advanced digital twin models and running the analyses takes time and effort, preventing such models from being used operationally on a large scale. Aiming to reduce the risks and increase the profitability of ships, as well as to make structural health monitoring solutions more accessible, an effective innovative hull condition monitoring system is proposed by combining advanced data-driven techniques with hindcast weather data. This paper presents the novel method developed for accurately approximating the wave-induced loads and responses for all ships without complex hydrodynamic models. The solution makes accurate predictive and preventive maintenance accessible for all.
Strain Capability Analysis of Metallurgically Clad Pipe With Girth Welds Under Combined Loads
Authors: Yang Renjie , He Yangye , Zhang Yu , Duan Menglan
Published: August 2024

Metallurgically Clad Pipes (MCP) have a strong bond between the outer pipe and the liner, effectively avoiding the separation failure of Mechanically Lined Pipes (MLPs). The girth weld position in an MCP becomes the weakest point of the entire pipeline. In this study, a three-dimensional bimetallic model with a girth weld is established, considering factors such as weld reinforcements, weld bottom width, weld groove angle, misalignment value, heat-affected zone width, and material properties of the girth weld and heat-affected zone. The influence of different working internal pressures and bending moments on the load-bearing and strain capacity of MCP under combined loads is investigated. With the increase of working internal pressure, stress concentration and plastic deformation occur in the heat-affected zone of the metallurgical clad pipe with girth welds. The stress level at the weld location is relatively low. An appropriate working internal pressure can effectively improve the load-bearing capacity of MCP, which allows it to withstand larger bending loads. Increasing the bending moment, the stress at the girth weld and heat-affected zone significantly increases, resulting in plastic deformation and a decrease in the overall load-bearing capacity of the pipeline. Considering pipe failure, the bending moment within the combined loads assumes the most critical role. It is concluded that for the MCP under combined loads, the overall stress level is lower at the girth weld, while the heat-affected zone experiences higher stress which may become the main location of failure. The present research results can provide a theoretical basis for the design, manufacturing, and safety assessment of MCP.
Multi-Surrogate Model Aided Bow Optimization of River and Coastal Connection Ship
Authors: Zheng Long , Yan Shikuan , Chen Xinyu , Kun Ban , Chen Shunhuai
Published: August 2024

In the simulation-based ship design, performance evaluation plays a crucial role. However, the process of evaluating the hydrodynamic performance of a ship can be both time-consuming and expensive, especially when relying on high-fidelity computational fluid dynamics (CFD) methods. To address this issue, this paper constructs an approach to hull form optimization design based on a multi-surrogate model. The study focuses on the bow optimization of River and Coastal Connection Ship. Two classic surrogate models are utilized to compare the multi-surrogate model’s approximation capabilities in four test functions. The numerical experimental results demonstrate that the multi-surrogate model exhibits superior forecast accuracy and robustness compared to the other models. Furthermore, a simulation-based optimization design model for the resistance performance of river and coastal connection ships is established, utilizing the aforementioned surrogate model and solved through an evolutionary algorithm. The result indicates that the multi-surrogate model facilitates the attainment of improved optimization design results. The optimization of the bow shape of the river and coastal connection ship through the multi-surrogate model effectively enhances the resistance performance of the target vessel. The proposed approach offers a more efficient and cost-effective method for evaluating the hydrodynamic performance of ships and optimizing their hull forms. The use of a multi-surrogate model significantly reduces the computational cost of the optimization process, while also improving the accuracy and robustness of the results.