bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Investigation of a High-Speed Submerged Cavitating Water Jet Based on Different Turbulence Models
Authors: Zhu Runyu , Zhang Xiaohui , Zhu Haitao , Pan Shize
Published: August 2024

The high-speed submerged cavitating jet can serve as an effective tool for the removal of ship fouling. Numerical simulations can provide guidance for the design of cavitating-jet-based cleaning tools. Turbulence models have a significant impact on the simulation of the unsteady cavitation. To explore effective numerical simulation methods, this study simulates a submerged cavitating jet with various turbulence models, including the SST k-ω model in the Reynolds-Averaged Navier-Stokes (RANS) method and the Stress-Blended Eddy Simulation (SBES) model, Improved Delayed Detached Eddy Simulation (IDDES) model, and IDDES model with Density Correction Method (DCM) in the hybrid RANS-LES method. The Schnerr-Sauer cavitation model is utilized to simulate the cavitation flow. The time-averaged cavity sizes and the shedding frequencies obtained by these models are compared with the data from a famous experiment to evaluate the accuracy of these methods. All hybrid RANS-LES methods successfully capture the jet core and the surrounding cavitation cloud. The SBES model captures abundant details of vortex structures. While the IDDES model tends to underestimate the dense vortex clusters around the shear layer, which can be improved by incorporating the DCM correction. Among these models, SBES is deemed the best as it predicts shedding frequency most accurately.
CO2-Responsive Foam Coupled With Nanoparticles for Enhanced Oil Recovery
Authors: Li Shaopeng , Wang Zhoujie , Li Songyan
Published: August 2024

CO2 foam is widely used in tertiary oil recovery and can increase oil production and reduce greenhouse gas emissions. However, separation of the oil and water phases in the fluid produced by foam flooding is often difficult. CO2-responsive surfactants can control reversible changes in the molecular structure or properties of surfactants through addition of CO2 or N2, thereby turning the foaming ability of solvents either off or on. However, traditional CO2-responsive foam has poor stability, and good results are difficult to achieve in oilfield applications.

In this work, through the use of micro-etching models, the morphological changes and flow properties of foam in porous media were observed. The effectiveness of the C12A-N20 foam in plugging and enhancing recovery in porous media was investigated using sand-packed materials. Finally, the demulsification effects of the foam flooding fluid before and after the N2 addition were compared. The experimental results showed that nanoparticles can effectively inhibit the coalescence of foam and enhance its stability. After the introduction of C12A-N20 foam into the sand-packed mixture, a significant enhancement of 14.1% in oil recovery rate was observed compared to that achieved with the injection of C12A foam, and the demulsification rate of the fluid produced by C12A-N20 foam flooding was greatly improved.
Fully Nonlinear Interaction of Water Waves and a Submerged Cylinder With Wave Breaking Detection and Suppression
Authors: Wu Qihao , Chen Yujing , Zhang Min , Shao Yanlin
Published: August 2024

In this paper, nonlinear interaction of regular water waves propagating over a fixed and submerged circular cylinder is numerically studied. At the structure’s lee side, the free surface profile experiences strong nonlinear deformation where the superharmonic free wave generated can be significant and are superposed on the transmitted wave. The wave profile then becomes asymmetric and skewed and may eventually reach the point of physical wave breaking. The governing equation and boundary conditions of this wave-structure interaction problem is formulated using both the fully nonlinear (FN) and the weak-scatterer (WS) theory. The corresponding boundary value problem (BVP) is numerically solved by the immersed-boundary adaptive harmonic polynomial cell (IB-AHPC) method. In this study, a pragmatic wave-breaking suppression model is incorporated into the original FN IB-AHPC solver.

Both the harmonic free wave amplitudes at the structure’s lee side and the harmonic vertical forces on the cylinder are studied. The simulated harmonic wave amplitudes are compared to other published experiment and theoretical data. In general, good agreement is achieved. The effects of the incorporated wave-breaking suppression model on the simulated results are discussed. In our study, the incorporation of the pragmatic wave-breaking suppression model successfully extends the capabilities of the original FN IB-AHPC solver.
An Experimental Study on the Diffusion Characteristics of Hydrogen by Ventilation System
Authors: Kim Jeong Hwan , Park Soung Woo , Seo Jung Kwan
Published: August 2024

Hydrogen gas exhibits a broader flammable limit concentration range in comparison to hydrocarbon gas, possesses lower ignition energy and ignition temperature, and manifests a heightened propagation speed of explosive flames. In the eventuality of a hydrogen gas leak, it is noteworthy that the density of hydrogen is lower than that of air, leading to its dispersion into the surrounding atmosphere within an open space. Nevertheless, within a confined environment, the hydrogen gas cloud has the potential to stagnate and accumulate. The presence of an accumulated hydrogen gas cloud elevates the risk substantially, rendering it susceptible to ignition or explosion, even in the presence of a minor ignition source. The purpose of this study is to experimentally investigate diffusion characteristics in response to diverse ventilation methods in the event of hydrogen leaks within the Fuel Gas Supply System (FGSS) room. A FGSS room, representative of the dimensions of an operational hydrogen fuel propulsion ship, was fabricated for the purpose of this investigation. Ventilation capacity was systematically compared and analyzed, taking into consideration variables such as ceiling type, ventilation method, and the length of the ventilation duct. Moreover, the FLACS program was employed for numerical analysis, and a modeling technique for simulating hydrogen leakage diffusion in enclosed spaces was developed through a comprehensive comparison and verification with the experimental findings. The amalgamation of experimental results and the refined numerical approach holds potential utility in informing adjustments to existing International Maritime Organization (IMO) guidelines and the International Code of Safety for Ships using Gases or other Low-flashpoint Fuels (IGF Code).
Dynamic Response Control of 2-D Jacket Structure Using Semi-Active Tuned Liquid Column Damper (TLCD)
Authors: Paul Bapon , Kumar Deepak
Published: August 2024

The jacket structure is a fixed offshore structure. Its natural frequency of vibration is higher than the peak ocean wave frequency. Generally, the response of the jacket structure platform is significantly small in comparison to other floating offshore structures. But, the small response is good enough to generate significant stress at the joint level of jacket members. This is due to the rigid connection between the members at the joint level. In literature also, it’s well-studied that the joint of the jacket structure is vulnerable to stress developed and shows fatigue damage. Further, a reduction in the response of jacket structure using conventional design procedures may have a huge financial burden. So, dynamic response control of such a structure to reduce the effect of fatigue damage at the joint of members is the most economical and practical approach. In this paper, a tuned liquid column damper (TLCD) is used as a passive control device to control the response of the jacket structure. The control in response is achieved by tuning the TLCD at the natural frequency of the Jacket structure. This gives control only at the natural frequency of the structure, but the response at excitation frequency remains unchanged. This way, the total control achieved is not good enough. Further, TLCD is converted to semi-active TLCD by changing the pressure at the column. The fuzzy control algorithm is used to guide the pressure changes in the TLCD column so that optimum control at the natural frequency of the jacket and excitation frequency can be achieved. Further, the robustness of Semi-active TLCD is also shown based on a change in the nature of excitation.
A Tool for Reliability-Based Inspection Planning of Mooring Chains
Authors: Almeida de Rezende Filipe , Videiro Paulo Mauricio , Volnei Sudati Sagrilo Luis , de Oliveira Mauro Costa , dos Santos Gabriel Yudy Matsunaga
Published: August 2024

The safety of offshore floating units highly depends on the platform’s station keeping capability, which is provided by its mooring system. Mooring chain fatigue failures have recently aroused the interest of the technical community in developing new design and monitoring methodologies focused on considering the effects of corrosion degradation in time. The fatigue limit state and the corrosion allowance of mooring chains are safety requirements that need to be verified continuously through mandatory regular inspections. The present work proposes a new efficient reliability-based method for planning future inspections of mooring chains, which combines recently developed fatigue assessment and corrosion methodologies and takes into account the observations of the previous inspections. The risk-based assessment of the mooring system is continuously updated with new inspection data, being a suitable tool for monitoring the current reliability level of the structure. The method is incorporated into a computational tool that monitors the system reliability and drafts future inspection dates based on a sound safety criterion. Additionally, this work presents a case study as an application of the proposed inspection planning method. The results show that the proposed method is able to optimize the number of inspections in all the analyzed scenarios, and it may be used as a relevant tool to help designers and operators in avoiding mooring chain failures.
Underpinning the Value of Buoyant Urbanism: Returning Torrens to the Seas
Authors: Cradduck Lucy M. , Wang Brydon T. , Weinert Kim D.
Published: August 2024

The rise of buoyant urbanism, in the form of floating developments, amphibious architecture, and floating cities; has introduced a new dimension to the traditional understanding of what is ‘real estate’. These innovative forms of development continue to gain prominence and need to be promoted and protected. To engage with the threat of climate change, and the growing incursion of water in our urban spaces, there is a need to ensure appropriate recognition of related property rights and interests. Concurrently, there is a need for valuation of those rights and interests to be linked to a recognised land tenure system to support investment within the Blue Economy. Therefore, our starting point is to develop an international system of recognising, protecting, and articulating the underlying tenure. This paper aims to extend previous research concerning how floating structures are a unique species of property capable of having tenure. However, there are tensions in property law (across common law and civil jurisdictions) concerning these structures, which manifest a rigid view of what is real property. By means of a case study, the solution proposed posits floating structures as a new class of real property within international waters (the global commons). Thereby, if the law understands floating structures as a resource capable of registration akin to real property, the structure itself will be afforded proprietary interests. As the Torrens system of land titling (title by registration) was developed from concepts underlying the registration of vessels, it is now time to return Torrens to the Seas. In doing so, the proposed buoyant urban registration system will be conceived to achieve sustainable use of marine resources under the Blue Economy.
Field Study of Biofouling on the Surface of Synthetic Fiber Ropes in Japanese Coastal Waters and its Influence on the Engineering Characteristics of Hybrid Moorings
Authors: Haneda Ken , Chujo Toshiki , Kojima Ryuji
Published: August 2024

A hybrid mooring system with steel chains and synthetic fiber ropes for offshore floating wind turbines is attractive for several reasons, including lower material costs. However, the degradation of synthetic fiber ropes over long-term use has not been fully verified. In this study, the authors focus on the biofouling on the rope. The impact of biofouling on the rope surface includes (1) increasing the line weight of the rope and changing its initial catenary shape, (2) increasing the total diameter of the rope section and changing its dynamic behavior. The authors investigated the biofouling of ropes through a combination of field experiments and numerical simulations to assess its impact on the static and dynamic behavior of mooring lines. Two-year field experiments were conducted at three coastal stations in Japan to clarify the biofouling using different synthetic fiber ropes as specimens. The specification of the specimen was 56 mm in diameter and 1 m in length, made of nylon or polyester. The experiments recorded 83 mm as the maximum biofouling thickness and 100 N/m2 (17.7 N/m) as the weight of the biofouling. Based on the result, numerical simulations were also conducted to clarify the impact of the biofouling on the rope. The results showed that biofouling on the synthetic fiber ropes that make up the catenary mooring had virtually a little effect on the initial catenary shape or tension fluctuations.
A Methodology to Assess Craze Initiation in PVDF Pressure Liners
Authors: Granum Henrik , Holmen Jens Kristian , Bonanni Michele , Al-Zubaidy Majeed , Kirton Peter , Roberts Andrew , Nygård Per , Holmström Jens Petter Henrik , Østby Erling , Hund Jonas , Perillo Giovanni , Johnsen Joakim
Published: August 2024

Crazing has been observed in flexible pipe PVDF pressure sheaths in operation. Whilst no loss of containment has been identified, Baker Hughes and Equinor have collaborated with Enodo and NTNU to investigate the root cause of the mechanism and develop a predictive framework. We developed a methodology involving a combination of finite element (FE) simulations and high-pressure tests to establish a craze capacity curve for the material. A custom polymer material model was implemented in Abaqus and calibrated using various tension and compression tests covering a wide range of stress triaxiality ratios and strain rates. Crazes were generated in circular discs using a custom-built rig for high-pressure testing. Water was used to pressurize one side of the discs up to 2000 bar. The stress and strain state in the discs were varied by changing the disc thickness, disc radius, backing plate geometry, and the applied pressure. We simulated the high-pressure tests and compared the deformed shape of the discs between simulations and tests. Numerous simulations and corresponding tests formed the basis for a material capacity curve predicting the onset of craze formation. The material capacity curve is a function of the applied fluid pressure and the principal strain difference.
On Methodology for a Digital Twin of Ship Propulsion Under Harsh Environmental Conditions
Authors: Purcell Etienne , Nejad Amir R. , Böhm Angelo , Sapp Lina , Lund Jorrid , von Bock und Polach Franz , Nickerson Brendon M. , Bekker Anriëtte , Gilges Markus , Saleh Ahmed , Lehmann Benjamin , Jacobs Georg , Valavi Mostafa , Kranz Tobias
Published: August 2024

The propulsion system of a ship is a critical element for its safety and integrity. Therefore, it must be maintained properly to ensure that a vessel is able to fulfill its primary purpose. The need for maintenance is even more pronounced in ships where extreme environmental conditions, such as ice-covered waters, are expected. This is due to an increase in the magnitude and uncertainty of loads and therewith the increase in possible damages if the propulsion system fails. The use of digital twins is becoming increasingly popular in shipping and can also be used for intelligent maintenance and operation prediction of the propulsion system. This paper proposes the methodology of creating such a digital twin with a specific focus on the required measurement infrastructure, modeling of components, loads, and damage as well as how all of these aspects are combined. The digital twin was created using a polar supply and research vessel, S.A. Agulhas II. Bearings are discussed from the view of high-fidelity simulations and wear modeling. The propeller is modeled as a point mass with the propeller laws for predicting the hydrodynamic torque and thrust. Shaft dynamics are modeled using either a lumped-mass torsional model, a modal model, or a finite element model. Damage of the shaft and the propeller is based on SN-curve fatigue calculations. The motor torque is modeled using an equivalent circuit model while motor damage is modeled by estimating the hottest temperature within the motor windings. Ice-breaking simulations are used as inputs to propeller-ice interaction models to obtain insight into the loads caused by these interactions. The material properties of ice used during simulations are validated using experiments. The need for further validation for low-fidelity models and the need for reduced order modeling or surrogate models for high-fidelity models are discussed. Finally, the implementation of this digital twin is discussed based on the developed model and the found problems that still need to be overcome to increase the technology readiness level.
Damage Localization on Wind Turbine Blades Using Acoustic Emission (AE) Signals and Graph Neural Network (GNN)
Authors: Zhao Zhimin , Chen Nian-Zhong
Published: August 2024

Accurately localizing the source of early structural damage on wind turbine blades poses a challenge for constructing acoustic emission (AE) based structural health monitoring (SHM) systems. Existing damage localization methods struggle to extract and utilize the intricate connections inherent in the AE signals. A novel method for localizing structural damage zone on wind turbine blades based on AE and graph neural networks (GNN) is proposed in this paper. First, the AE signals are converted into graph structure data in non-Euclidean space combined with time-frequency analysis. Then, the Euclidean distance between the features of each pair of nodes is calculated to determine the connectivity of the graph. The information of the neighboring nodes in the graph is aggregated using the message passing paradigm, which can not only make effective use of the node features, but also excavate the deeper intrinsic connection of the AE signals. The proposed method can easily localize structural damage on wind turbine blades with the assistance of the established graph. Another novelty of the proposed method is its ability to locate damage for wind turbine blade with high accuracy using only one AE sensor. This not only simplifies the sensor setup but also leads to significant cost reduction. The effectiveness of the proposed method is validated using an experimental dataset collected from a segment of a wind turbine blade. The results demonstrate the superior performance and high accuracy of the proposed method.
Experimental Investigation on the Current Suppression Performance of a Plate-Net Complex Mounted Beneath a Floating Breakwater
Authors: Gu Jian , Ni Xinyun , Cheng Yong , Bu Shuxia , Kuang Xiaofeng
Published: August 2024

Suppression of currents is crucial for aquaculture and coastal engineering structures like aquaculture platforms and floating breakwaters. There have been many remarkable studies on current integration in the flow channel, mostly aiming to reduce the turbulence intensity. Meanwhile, the investigation into current suppression is relatively scarce, especially in the case of floating structures. In the present article, a novel plate-net complex is investigated experimentally, mounted beneath a floating breakwater to mitigate the current and wave simultaneously. The dependency of suppression efficiency is investigated on the flow speed, the height ratio of the plate, the solidity ratio of the net, and the motion of the floating breakwater, respectively, through model tests in a recirculating flume. A velocimeter matrix is designed to measure the flow velocity upstream and downstream of the floating breakwater simultaneously. According to the analysis, the dependency of the average current reduction ratio is found on the current speed of incoming flow, height ratio, solidity ratio and the motion of the floating breakwater. Meanwhile, the significance of the solidity ratio of the net is less than that of the height ratio of the plate on the suppression efficiency. The experimental results demonstrate the effectiveness of the plate-net complex in current suppression and provide significant references for the design and optimization of the floating breakwater.
Study on Weather Vane Effect of a Single-Point Mooring Floating Offshore Wind Turbine
Authors: Chen Jiahao , Gao Yifan , Wang Kai
Published: August 2024

Affected by extreme loads, structural fatigue and other factors in marine environment, yaw system failures of offshore wind turbines are frequent, making floating wind turbines operation and maintenance costs high. Regarding this issue, it is an effective solution to combine single-point mooring system with floating offshore wind turbines. However, dynamic response characteristics of a single-point mooring floating offshore wind turbine (SPM-FOWT), especially the weather vane effect under misaligned wind, wave and current coexisting condition, are still unknown. In this paper, a high-precision downwind type SPM-FOWT simulation model is constructed by the in-house aero-hydro-elastic-servo coupling software for floating offshore wind turbines, and the contributions from wind, wave, and current loads on the wind tracking performance of a SPM-FOWT are also investigated. It is found that the angle to the wind of the SPM-FOWT is usually biased, which is affected by the comprehensive influence of wind, wave and current direction. In addition, It is found that the horizontal arrangement position of the single-point mooring turret has a significant effect on the weather vane effect of a SPM-FOWT.
Reliability Analysis of Ro-Ro Vessel Movable Vehicle Ramps Under Vehicle Moving Load
Authors: Tao Shuo , Zhu Ling , Liang Qiyu , Zhang Qiying
Published: August 2024

In the design of roll-on/roll-off ship structures, movable vehicle ramps serve as a bridge connecting different decks and are typically subjected to various moving vehicles. However, the loads carried by the ramp during its operation often vary from the design loads considered in the design phase. Due to the uncertainty of vehicle loads and the structural materials, it is of significant importance to assess the reliability of the movable vehicle ramp structure. To investigate the structural reliability of the movable vehicle ramp structure under vehicle moving loads, the weight of the vehicle, the moving speed, and the thickness of the top plate of the ramp were selected as random variables. Based on numerical results, the limit state equation of the movable vehicle ramp structure was obtained by the Box-Behnken design response surface method. Then, the structural reliability index was calculated by the checking point (JC) method, and the influence of each variable on the structural reliability of the movable ramp was derived through sensitivity analysis. Finally, the structural optimization of the plate thickness was carried out according to the reliability analysis, which is significance guidance for the optimization of the movable ramp design.
Effect of Seawater Immersion on the Steel Plate Reinforced With Fiber-Reinforced Composites
Authors: Matsuo Tsuyoshi , Sakurai Akio , Yanagimoto Fuminori , Ishibashi Kinya
Published: August 2024

In case of onshore structures such as bridges and elevated roads, repairs and reinforcements by carbon fiber reinforced plastics (CFRPs) have been in practical use for the damaged or deteriorated parts. However, in the other case of maritime structures, ship hulls and offshore structures are operated under conditions exposed to salt water and repeated cycles of drying and wetting, which is an even more severe corrosive environment than onshore structures. Furthermore, during repairs and constructions, it is necessary to suspend operation and usage, and it is undesirable to take a long time in the environment such as waves and wind. Therefore, it is necessary to minimize and simplify the working time required for repairs as much as possible.

CFRP strand sheets are reinforcement materials made by processing carbon fiber strands impregnated with resin into a blind-like shape, and they excel in workability as the impregnation of adhesive resin is fast during the adhesive construction to steel materials. If this repair and reinforcement method using CFRP strand sheets can be applied to ship hulls and marine structures, rapid repairs by manpower or operating machine are possible, leading to improved operational efficiency.

In this study, the degree of corrosive degradation caused by seawater immersion when CFRP strand sheets are used as reinforcements is verified experimentally, and the applicability of CFRP repair and reinforcement to ship hulls and offshore structures is investigated.
Study on Wave Scattering by Inverse T-Type Bottom-Standing Breakwater
Authors: Sharma Priya , De Soumen , Gayen Rupanwita
Published: August 2024

In the present study, the scattering of normal incident wave by (i) single and (ii) dual inverse T-type bottom standing breakwaters are analyzed under the assumption of linearized water wave theory. The objective of the current study is to compare the effectiveness of the two breakwater configurations and to provide some useful results for engineering design and application. To address the physical problem, we employ Havelock’s expansion methodology and Galerkin’s approximation technique. We utilize multi-term Galerkin approximations that incorporate ultraspherical Gegenbauer polynomial to solve the integral equations that arises in the mathematical analysis. This study demonstrates how to encounter the singularity by using ultra-spherical Gegenbauer polynomial as basis function with suitable weight. To understand how the profile geometry can affect the performance of the bottom standing inverse T-type breakwater’s main dimensions, including its profile height and width, is conducted on several hydrodynamic quantities of interests such as reflection, transmission coefficient and horizontal drift force. The numerical estimates are first validated against the data of existing studies in the literature, computed and graphically discussed for a variety of structural conditions, including the height and width of breakwater submergence. The effectiveness of both single and dual breakwaters can be assessed by examining wave reflection and horizontal drift forces, as evident in the graphical representations. This theoretical framework not only offers a promising method for addressing wave interaction with bottom-standing in-verse T-type breakwater model but also serves as a dependable reference point for complex numerical solutions of integral equations.
Assessment of the Group Behavior of Torpedo Anchors Through Finite Element Modelling
Authors: Kronemberger Lopes Guilherme , Mendes de Sousa José Renato , Carre de Oliveira Allan , Guerreiro Basilio Costa Genzani Rachel
Published: August 2024

In Brazilian offshore fields, torpedo anchors are extensively used in deep-water mooring systems. These anchors are known to be cost-effective and capable of withstanding high vertical loads. Despite their successful usage in the offshore industry, the increasing loads imposed by the mooring systems in ultra-deepwater applications demand higher anchor holding capacities. In this scenario, a possible solution is to consider a group of torpedo anchors, which has not been investigated. Hence, this article uses a three-dimensional nonlinear finite element model to present a numerical study on the group behavior of typical torpedo anchors embedded in a purely cohesive isotropic soil. In this model, the soil is simulated with solid elements representing its nonlinear behavior and the large deformations involved. The torpedo anchors are also modeled in detail with solid elements.

Moreover, the anchor-soil interaction is addressed with contact finite elements that allow relative sliding with friction between the surfaces in contact. Several analyses are conducted to understand the response of this type of anchor when installed in groups. The research addresses some essential features in group analysis, such as anchor spacing, connection between the anchors, and soil-structure interaction. Additionally, the results are compared with those from a single anchor installed in the same conditions to highlight the torpedo anchor group efficiency.
Development and Validation of Real-Time Hybrid Model Testing Framework for Aerodynamic Simulation of Floating Wind Turbines
Authors: Yao Tiancheng , Cai Weikai , Wang Yipin , Zhao Yongsheng , Wang Jin
Published: August 2024

Globally, there is a surge in offshore wind farms, with Floating Offshore Wind Turbines (FOWTs) becoming the focal point of research and industry investment. To ensure the accuracy of the numerical model and the operation safety of FOWTs, it is crucial to conduct model test. This will provide a comprehensive understanding of the complex structural behavior of FOWTs under the combined influence of wind and wave loads. However, the process is complicated due to Reynolds-Froude scaling incompatibilities. The reproduction of aerodynamic loads of FOWTs in wave basin model tests is complex because the aerodynamic loads are dominated by Reynolds similarity. To address this issue, various strategies have been employed, including the use of a tuned actuator disk or a redesigned rotor to achieve the correct scaled thrust at low Reynolds numbers. However, these methods only ensure the similarity of mean thrust under some certain wind velocities, while some important properties of floating wind turbine are still out of reach, such as aerodynamic damping and wind turbine control strategy. In this paper, a Real-Time Hybrid Testing (RTHT) framework is introduced to integrate aerodynamic thrust during wave basin model tests. The feasibility and fidelity of the proposed RTHT framework are verified by using a Pitch-mode Modeling System (PMMS) of FOWT so that the construction and commission of RTHT framework could be conducted on land and modified. The PMMS can accurately simulate the aerodynamic load, inertial load, and hydrostatic restoring moment of a FOWT. Additionally, the RTHT system is calibrated and enhanced by examine the correlation between experimental measurements and simulation results. The results indicate that the proposed RTHT framework, based on PMMS, can effectively reproduces the aerodynamic load of FOWT under different wind conditions and control regimes in a low latency.
Evaluation of Motion-Vibration Couples for Semi-Submersible Offshore Floating Wind Turbines
Authors: Xu Kai , Liu Qiang , Zhao Zhixin , Liu Fushun
Published: August 2024

The structural reliability design of floating offshore wind turbines (FOWT) relies on the analyzable and integrated coupled dynamics mechanisms. As the FOWT consisting of complex rigid-flexible coupled substructures is subjected to severe wind, wave and current loads, both accurate and quantitative evaluations of the coupled dynamic performance are challenging. Taking into account these factors, the model of the aero-hydro-servo-elastic FOWT system including a tower with a torsional degree-of-freedom (DOF) has been developed to quantitatively analyze the coupled dynamics. As the Kane method has the ability to efficiently analyze the performances of complex rigid-flexible systems, it has been implemented in the established model. To evaluate the motion-vibration effect of such model, the comparison responses between the rigid and rigid-flexible FOWT structures have been investigated. Results have shown that the sway response of the rigid-flexible FOWT, also called the motion-vibration coupled model, has been reduced by 12.63% as compared with that of the fully rigid FOWT under the steady state wind of 5 m/s and wave height of 1.2 m. Moreover, the discrepancy of the coupled responses for the heave and yaw calculated between two models has almost varied linearly with the environmental loads. Summarily, the present work provides analytical formations for the accurate modeling and quantitative evaluation of coupling effects for the FOWTs subject to harsh marine environments.
Application of Idealized Structural Unit Method to Determine the Ultimate Strength of Ship Model in Bending
Authors: Lindemann Thomas , La Ferlita Alessandro , Kaeding Patrick
Published: August 2024

The Idealized Structural Unit Method (ISUM) is applied to perform progressive collapse analyses for a 1/3-scaled frigate model in bending. For the load case of pure vertical bending (sagging), the ISUM results are validated against experimental data. The ISUM model is explained in detail taking into account the initial imperfections of stiffeners and the attached plating. In particular, the effect of welding residual stresses on the ultimate hull girder strength is discussed. Displacement controlled nonlinear analyses are performed by using the full Newton-Raphson scheme an incremental iterative solution approach. Furthermore, Smith’s method is applied to determine the progressive collapse behavior the 1/3-scaled frigate model in bending. Smith’s method based calculations are performed under consideration of scantlings and rule based load-end shortening curves of all structural components. Both simplified approaches are applied to determine the progressive collapse behavior of the frigate model in vertical, horizontal and biaxial bending. For the ISUM model the effect of welding residual stress on the ultimate hull girder strength is also proposed for the different load cases.
Effect of Axial Density Distribution in Liquid–Solid Flow in Pipes on the Jumper for Deep Sea Mining
Authors: Takano Satoru , Yamamoto Marcio , Masanobu Sotaro
Published: August 2024

Subsea minerals have been found in the deep water within Japan’s exclusive economic zone. However, the development of subsea minerals has not reached the commercialization stage because many technical issues still need to be addressed.

When slurry pumps are used for lifting seafloor massive sulfides, internal flow in pipes becomes liquid-solid flow. The slurry pump is connected to seafloor production tools by a jumper so that the seafloor production tools can move to collect subsea minerals. To operate the production system safely, simulating the behavior of the jumper is necessary. There is axial density distribution in internal flows in the jumper because of the slip velocity between liquid velocity and solid velocity, and simulating the behavior of the jumper with consideration of density distribution is essential. Thus, we simulated the behavior of the jumper with consideration of density distribution by lumped mass model. We calculated the density distribution at each delivered concentration by equations of hindered settling velocity of solid particles and mixture velocity. The calculated results were compared with experimental results to validate the lumped mass model. The experimental apparatus had a flexible hose of 38 mm in internal diameter, and we used alumina beads of 4 mm in diameter. The comparison showed the behavior by considering density distribution and that with the homogeneous flow which has the uniform density of internal flows. Their comparison showed that the calculated results considering density distribution were more consistent with experimental results than those with the homogeneous flow. In calculating the behavior of the jumper with liquid-solid internal flow, it was important to consider the density distribution.
Prediction of Global Whipping Responses on a Large Cruise Ship Under Unknown Sea States Using an LSTM Based Encoder-Decoder Model
Authors: Liu Ruixiang , Li Hui , Ong Muk Chen , Zou Jian
Published: August 2024

Global whipping responses, characterized by high-frequency vibration components on the hull girder, are typically induced by stern and bow slamming loads. These responses contribute to an increase in vertical bending moments, making their accurate prediction crucial for ship safety. In this study, we build upon our prior work to establish an encoder-decoder model based on Long Short-Term Memory (LSTM), designed to predict whipping responses under varying sea states. The model is trained on a comprehensive dataset, which includes motion data and vertical bending moment history of a large cruise ship under various sea states. This dataset is established via numerical simulation, ensuring a wide range of scenarios for the model to learn from. The efficacy of the LSTM encoder-decoder model in capturing global whipping responses is initially verified under a single sea state case. This step confirms the model’s ability to accurately predict vertical bending moments under known conditions. Subsequently, the model’s performance under unknown sea states is examined. Given that the distribution of training data significantly influences the model’s performance under unknown sea states, a data mixing strategy is employed during the training process in this scenario. The results indicate that the LSTM encoder-decoder model effectively captures whipping responses. Furthermore, the data mixing strategy significantly improves prediction accuracy under unknown sea states, demonstrating the potential of this approach in enhancing ship safety.
Analysis of the Linear Hydroelastic Response of Flexible Floating Solar Devices
Authors: Douteau Louis , Castillo Florian , Gupta Salabh , Ikhennicheu Maria , Gilloteaux Jean-Christophe
Published: August 2024

This paper introduces a numerical model based on generalized modes and linear deflection modes superposition dedicated to the simulation of the dynamic behavior of flexible floating solar concepts. Deflection modes, derived from a Finite Element Method solver, are used as inputs for a linear potential flow solver, enabling the calculation of diffraction and radiation coefficients. These coefficients are then incorporated into a time-domain model, considering deflection modes as additional degrees of freedom.. Verification work considering a generic flexible barge sourced from the literature shows satisfactory results. An application to the simulation of a flexible FPV platform demonstrates a robust estimation of dynamic motions and deflections within the platform.
Investigation on Flow-Induced Rotation of Coupled Double Cylinders Arranged in Tandem
Authors: Feng Weipeng , Yang Xu , Yan Xiang , Li Lingfan
Published: August 2024

The flow-induced rotation of coupled double cylinders in tandem has rarely been investigated in existing studies. In this paper, the theoretical basis of flow-induced rotation was established, the experimental setup was established and verified. Based on the test data, the flow-induced rotation characteristics of coupled double cylinders arranged in tandem were investigated. The study aims to provide reference for the design of the flow-induced vibration energy conversion equipment. The main conclusions can be summarized as follows: The oscillation response of coupled double cylinders arranged in tandem is vortex-induced vibration (VIV). When the spacing ratio of coupled double cylinders is 4.0, the amplitude is low and a “re-growth zone” is observed in the lower branch of VIV. When the spacing ratio is 6.0, the amplitude is high, and the maximum arc length ratio (A*) is 0.92. When the spacing ratio is 8.0, the lock-in range is wide. The effect of system stiffness (K) on flow-induced rotation response is not sensitive. The width of lock-in range is similar under different stiffness, while the desynchronization and the frequency response in the non-locked range are significantly different. The maximum arc length ratio is 0.98, which occurs at K = 1400N/m.
Laboratory Investigations on Oscillatory Seabed Responses and Scour Around a Pipeline Under Wave-Current Loading
Authors: Xu Yue , Cui Lin , Jeng Dong-Sheng , Sun Ke , Chen Bing
Published: August 2024

In this paper, a series of preliminary experimental data for wave (current)-induced hydrodynamics, pore-water pressure and scour around an exposed pipeline is presented. Unlike previous studies, the combined action of waves and currents is considered in this study. Wave flume experiments were conducted to investigate the temporal and spatial variations of pore-water pressures and seepage, as well as the development of scour around a pipeline. The experimental results indicate that the seabed response caused by the combined action of waves and currents are significantly different from those caused by wave load alone. It was found that the amplitudes of pore-water pressures increase, while the attenuation of pore-water pressures slows down under the large wave height with a large current. Additionally, the amplitude of seepage force under the combined action of wave and current is significantly greater than that under wave-only action, which subsequently affects the scour process around the pipeline. As the current velocity increases, the equilibrium scour depth increases, and the time to reach the equilibrium depth is also longer. Moreover, under the action of wave and current, the maximum scouring depth is more significantly affected by the high current velocity.
Experimental Investigation of Hybrid Smart Brine With Phosphate and Hexameta-Phosphate in Enhancing Oil Recovery From Carbonates
Authors: Murad Abdul Majid , Qi Chuangchuang , Haroun Mohamed , Al Kobaisi Mohammed , Rahman Md Motiur
Published: August 2024

Smart water flooding (SWF) has become an enhanced oil recovery (EOR) technique in field applications, as it provides better microscopic displacement efficiency in a relatively economic and environmentally friendly manner compared to other EOR techniques. The ionic composition, the key parameter that affects SWF performance in carbonates, has been extensively investigated to understand the EOR mechanism. The most widely accepted mechanism is that the ion exchange between injected brine and reservoir rock causes wettability alteration towards more water wet, leading to an improvement in oil recovery. Nevertheless, a consistent understanding and explanation of the geochemistry of how specific ions affect EOR performance has yet to emerge.

In this study, hybrid smart brine formulations were developed by spiking seawater with specific amounts of phosphate and hexametaphosphate (HMP) and their potential to increase oil recovery from carbonate core plugs were asseessed. Interfacial tension (IFT) measurements were performed for various smart brines with crude oil. In addition, brine compatibility analysis was conducted to study the potential of salt precipitation due to interactions between injected water and formation water, and the ability of the smart brines to create emulsions was assessed. A series of core flooding experiments was conducted to evaluate the ability of smart brines to increase oil recovery. Amott-Harvey/USBM wettability analysis was conducted to select smart brines and study their effect on wettability. Zeta potential measurements were conducted to capture the possible electric double-layer expansion.

It was concluded that excessive spiking with HMP led to precipitation and the optimal concentration was determined. Moreover, wettability analysis indicated that HMP is a stronger wettability modifying agent than phosphate, while phosphate performed better in reducing the IFT than HMP. Core flooding experiments demonstrated that creating a hybrid smart brine containing both phosphate and HMP has combined advantages. In addition, none of the studied smart brines generated an emulsion. Zeta potential measurements showed that flooded samples exhibited less negative values than aged samples, indicating the release of trapped oil. This study demonstrates the potential of increasing oil recovery from carbonate core plugs and can help to understand the impact of phosphate and HMP on EOR performance.
Numerical Hydrodynamic Investigations of a Multi-Pile-Supported Aquacultural Structure
Authors: Wang Hanbin , Zhang Xueyan , Zhang Xiantao , Li Xin , Tian Xinliang
Published: August 2024

With the continuous consumption of natural resources in the ocean, aquaculture has become a new focus in various countries and fish farming structures have developed rapidly in last decades in both nearshore and offshore regions. However, the hydrodynamic characteristics of structures which integrated aquacultural nets and other marine structures together remain unclear. Monopile-based structures are common types of fixed-bottom structures at offshore sea areas with shallow water depths where are rich in wind energy, oil and fishery resources. In order to improve the utilization efficiency of offshore structures, a multi-pile-supported aquacultural structure is proposed in the study which consists of net panels and monopiles. In this paper, a new coupling method which combined discrete-module-beam (DMB) method and lumped mass method with Screen model is proposed to obtain the hydrodynamic responses of monopiles and nets in the integrated aquacultural structure. A series of numerical calculations are carried out to investigate the hydrodynamic characteristics of pile-net structures under different regular wave conditions. The influence of net panels on the hydrodynamic characteristics of monopiles are measured and discussed. It is found that the influence of net panels on the hydrodynamic characteristics of current model is negligible. Overall, the results of this study can be used as a basis for future design and optimization of similar integrated marine structures.
Laboratory Experiments on Statistics of Shoaling Finite Amplitude Waves
Authors: Mendes Saulo , He Yuchen , Chauhan Kapil , Chabchoub Amin , Kasparian Jérôme
Published: August 2024

The formation, growth and increase in the frequency of extreme waves over the coast has been consistently observed and reproduced in laboratory experiments in recent years. On the other hand, as soon as waves reach the surfzone, a new regime comes into play where sub-Gaussian wave statistics dominate, as described by Glukhovskiy-type of height distributions. Dealing with a wave field transitioning from steady-state to out-of-equilibrium conditions due to a steep shoal, available theories can model the rogue wave amplification near shallow water regimes before the surf zone. Nevertheless, theoretical work to date has also been limited to small amplitude waves, thus, far from a wave breaking regime. To connect these two regimes (prior to and post the surf zone), we experimentally probe inhomogeneous finite amplitude wave fields that overlap both.