bluuebunny/crossref_metadata_2025 huggingface dataset:
A Study on Hull Girder Longitudinal Strength Prediction by Adopting the Accurate Plate-Combination Model Based on Load-Shortening Curve
Authors: Yang Hee Yeong , Kim Do Kyun , Cho Nak Kyun , Li Shen
Published: August 2024

In this study, a plate combination model (PC model) was proposed for evaluating the longitudinal strength of the hull girder. There are representative models such as the PSC (Plate-stiffener combination model) and PSS (Plate-stiffener separation model) models for separating the structural components of the midship sections of hull girder. However, both the PSC and PSS models that are subjected to compressive loads have limitations in accurately considering local structural failure mechanisms. To overcome this limitation, the PC model introduced in this study separates all structural components comprising the hull into the concept of plates. Assumptions were made regarding the boundary conditions corresponding to the PC model to account for welding effects and collapse modes. Based on four assumed PC models, the longitudinal strength of the Dow 1/3 frigate model was compared. The results allowed for the selection of the optimised PC model. This study confirmed that CSR-H method could not adequately consider local collapse. The proposed method can be beneficial for the robust design of ship structures.
Numerical Study on Design Optimization of Tension Leg Platform for FOWT Based on Surrogate Model and Multi-Objective Evolutionary Algorithm
Authors: Park Hyo-Jin , Song Zhenhao , Nam Bo Woo , Ha Yoon-Jin , Kim Kyong-Hwan
Published: August 2024

In this study, the tension leg platform (TLP) for floating offshore wind turbines (FOWT) has been numerically optimized to minimize pitch motion and tendon tension responses using a surrogate model and the non-dominated sorting genetic algorithm II (NSGA-II). The target platform comprises a central circular column and three offset square columns with connecting pontoons. Firstly, the input design variables were selected via a sensitivity test, considering the geometrical parameters and specifications of the mooring tendons. Secondly, a large number of sample points were generated considering the constraints, and then the surrogate models were constructed based on the response surface method. Here, frequency-domain hydrodynamic analysis and fully-coupled time-domain simulations for the TLP-type FOWTs have been conducted with the WADAM and OpenFAST programs, respectively. Thirdly, by using the NSGA-II algorithm, the Pareto-optimal solutions for the multi-objective function were derived based on the surrogate model. Finally, the identified optimal solutions were verified by direct simulations, and their performances were compared with the initial design. Significant improvements can be found for the obtained optimized designs in terms of pitch motion or tendon tension responses. From the spectral analysis, it is evident that optimal solutions mainly reduce the wave frequency components of the pitch motion or tendon tension responses.
Analytical Buckling Solution for Steel-Concrete-Steel Sandwich Cylindrical Structures With Non-Uniform Thickness Under Varying External Pressure
Authors: Lin Hung-Chun , Collette Matthew D.
Published: August 2024

This study investigates an analytical global buckling solution for steel-concrete-steel sandwich cylinders, which are proposed to be used as the spar substructure for offshore floating wind turbines. Typically, the spar substructures are composed of steel cylinders with a certain amount of concrete as ballast weight. We propose to transform the conventional all-steel cylindrical spar into a steel-concrete-steel sandwich cylindrical spar, in which the spar structural strength can be potentially increased while providing the required weight. A preliminary estimation shows that the steel-concrete-steel structure can reduce the material cost by about 37% and increase the buckling strength by nearly 18% when comparing these with the original design while considering buckling only. However, the buckling strength evaluated in the preliminary study assumed the model with constant thickness under uniform external pressure, which is not a proper model for spar structures. To estimate the buckling strength realistically, this study will derive the analytical buckling solution for sandwich cylindrical structure with non-uniform thickness under varying external pressure. The classical laminated theory and Rayleigh-Ritz method with appropriate approximation displacement functions are used. The proposed solution is validated with commercial finite element software, ABAQUS, and the results show very good agreement with the simulation.
Numerical Investigation of Vortex-Induced Motions of a Scaled OC4 Floating Offshore Wind Turbine
Authors: Yang Yuxin , Liu Yuanchuan , Li Liang
Published: August 2024

Vortex-induced motion (VIM) is a critical issue for floating structures composed of one or more columns. This phenomenon can excite large oscillatory motions on floating structures, which can severely affect the stability of the structure and the fatigue life of mooring lines. In the present work, the VIM of the OC4 semi-submersible floating offshore wind turbine (FOWT) platform is studied numerically over a wide range of flow velocities by using an open-source Computational Fluid Dynamics (CFD) toolbox OpenFOAM. Comparisons are made between results for models with and without the connecting structures, including delta pontoon and cross braces, to assess their impacts on the platform VIM and the effect the yaw motion is investigated. Results show that the “lock-in” phenomenon in the transverse direction lies within the range of 8 ≤ Vr ≤ 12. By including the connecting structures in modelling the FOWT platform, its transverse motion amplitude is significantly reduced. Analysis reveals that the connecting structures exert considerable negative work on the platform motions and thus effectively mitigate the VIM phenomenon. Meanwhile, when the yaw motion is considered, large motion amplitude is excited in the transverse direction even at Vr ≥ 18, clearly indicating the coupling effects between the transverse and yaw motions. This work will contribute to the understanding of motion responses of FOWTs subjected to environmental loads from current.
Experiment Study of Critical Dynamic Loads for Stiffened Panels Under Axial Impact
Authors: Shi Guijie , Wang Deyu
Published: August 2024

In an actual seagoing environment, marine structures typically suffer from impact load actions such as bow slamming, ship-ice interactions, and ship-ship collisions. At extreme impact loads, dynamical buckling occurs in the stiffened panels, which is different from the buckling failure in static conditions. It is necessary to investigate the dynamical buckling criteria and failure modes by using experimental methods. In this paper, two sets of marine stiffened panels are designed to separately represent the first buckling on the plating and the stiffener web. Five models are fabricated for each stiffened panel. A drop hammer platform is used and an axial impact load with a series of initial velocities for the hammer is applied at the end of the stiffened panel. The dynamic buckling state is obtained based on the measurement of impact load and the panel deformation. Then, a new evaluation criterion is proposed to predict the critical load for dynamic buckling of the stiffened panels. The predicted critical state is consistent with the changing state of the failure mode for the stiffened panels. The conclusions can be used as a guide for the dynamic buckling evaluation in ship design.
Performance Evaluation of Different Control Algorithms for Torpedo-Shaped AUVs
Authors: Balasubramaniyam Shankruth , Umashankar Shriram , Gurudev Gowsik , Ramanujam Madhavnambi , Somayajula Abhilash , Venkatachalam Sriram
Published: August 2024

This paper compares Linear Quadratic Regulator (LQR) and Proportional Integrative Derivative (PID) control algorithms implemented in an in-house built Autonomous Underwater Vehicle (AUV). The AUV has actuators to control five degrees of freedom and features a non-linear dynamics model established through a Python-based simulation environment. Path following is achieved by employing the Line-of-Sight (LOS) and fully actuated path-following guidance law. The evaluation of the control algorithms is based on the trade-off between effort, endurance, time taken to reach the intended path, overshoot and steady-state error.
Extremum Seeking Control Implementation for Drilling Efficiency
Authors: Ikhlef Mohammed Amine , Bekkevik Sindre , Sahebi Hamed , Gravdal Jan Einar , Sui Dan
Published: August 2024

In the continuously changing environment of drilling operations, the optimization of the Rate of Penetration (ROP) holds significant importance in improving efficiency and minimizing operational expenses. This study introduces a new methodology, referred to as Extremum Seeking Control (ESC) with the aim of implementing sophisticated control and optimization methodologies for real time ROP or mechanical specific energy (MSE) in drilling.

The ESC algorithm is a real-time adaptive control method that does not rely on a model and is capable of adjusting parameters in the presence of unknown system dynamics and mappings between control parameters and an objective function. Extremum searching can be employed as a methodology for addressing static optimization problems and optimizing parameters inside dynamic systems. In this work, this control algorithm is utilized to dynamically modify drilling parameters in real-time. By continuously seeking the optimal combination of factors such as weight on bit (WOB), it enables drilling engineers to maximize ROP while ensuring drilling safety and equipment integrity. This strategy signifies a fundamental change from traditional procedures by providing high accuracy and flexibility in the control of ROP. Moreover, this research examines the application oWith the growing complexity of drilling operations, the incorporation of ESC emerges as a potentially viable approach to address the industry’s need for enhanced efficiency and cost-effectiveness.
Wave Dynamics Run-Up Modelling: Machine Learning Approach
Authors: Vileti Vinicius L. , Ersdal Svein
Published: August 2024

This study proposes an alternative approach to predict wave elevation near multi-column semi-submersible structures by applying machine-learning methods from experimental data.

The most common approach to this problem is to apply linear potential theory numerical programs to calculate the wave elevation close to such marine structures. However, in some cases, the assumptions for the potential theory are no longer valid, leading to a deviation from model test results.

Another possible approach is to solve Navier Stokes Equations Numerically (CFD), which poses a challenge regarding computational power for this kind of stochastic analysis.

This paper details a procedure to apply machine learning to enhance the results by combining potential theory and experimental results for future predictions. Aker Solutions has performed experimental tests with a TLP (Tension Leg Platform) shaped hull under waves while measuring wave elevation on several points around it. These experimental data were treated and combined with potential theory results to compose a machine-learning prediction model.

A frequency domain model was applied, where the experiment data is converted into the frequency domain and combined with the Potential Theory results to train the machine learning model.

Results show that the machine learning model improves the results for wave elevations when closer to the hull, as those are the cases where the potential theory deviates more. This approach can also be applied to similar problems, such as wave loading and vessel motions.
Influence of Underlying Currents on the Performance of a Taut-Moored Point-Absorber WEC: an Investigation Via High-End Numerical Tools
Authors: Capasso Salvatore , Tagliafierro Bonaventura , Göteman Malin , Martínez-Estévez Iván , Domínguez José M. , Altomare Corrado , Gómez-Gesteira Moncho , Crespo Alejandro J. C. , Viccione Giacomo
Published: August 2024

Site-specific environmental conditions in targeted areas for offshore renewable energy deployment often feature underlying currents. The effects of the latter on wave parameters and overall hydrodynamics modifies the behavior of light offshore structures, such as wave energy converters (WEC), with unforeseen alteration of power yield and structural loads. To address such effects on a taut-moored point-absorber — potentially susceptible to wave and current motion — the high-end numerical framework of DualSPHysics is used, as it leverages the flexibility of the Lagrangian Smoothed Particle Hydrodynamics (SPH) method for simulating fluid-structure interaction and external libraries to take on multibody problem posed by power take-off (PTO) and moored connections. A dedicated numerical wave tank capable of reproducing regular waves propagating over steady uniform currents is used to numerically test the Uppsala University WEC (UUWEC), which consists of a buoy connected to a linear PTO. Clear influence of the current traits is visible in the results regarding the point-absorber motion, power output, and anchoring tension. Remarkably, the sole presence of current can hamper the harvesting capabilities of the device, up to different extents depending on its intensity and relative direction with respect to the wave propagation. Tension patterns, instead, are found to be almost linearly sensitive to current intensity and direction, with beneficial effects produced by opposing currents and vice-versa.
Performance of Wave Absorbing Calculation and Verification for Floating Breakwater
Authors: Ni Xinyun , Wang Qibin , Yu Jun , Ding Jun , Wei Ziyang , Xie Chunmei , Chen Ying , Xu Lingyun , Cheng Xiaoming
Published: August 2024

There are two types of breakwater including fixed and floating. The fixed breakwater is usually used in shallow water sea area, not adapted to deep water area. In deep water area, the floating breakwater is an important type of marine equipment which can improve the work environment conditions effectively. In the course of design for breakwater, the motion responses and wave absorbing performance should be focused importantly. Especially, wave absorbing ability is a key factor for evaluating the performance of breakwater. In this paper, taking the double cylindrical floating breakwater as the research object, the in-house three-dimensional hydroelasticity software THAFTS is used to calculate the motion responses and wave absorbing coefficients of floating breakwater with two different character length, and the effects of length have been analyzed. At the same time, the wave absorbing coefficients at the monitoring points same with model test under different wave period are calculated and compared with model test results. Through the comparison, the calculation results have a good agreement with the model test results, and the breakwater has a good wave absorbing performance when the wave period is less than 6s. The research here offer the reference for further optimization of floating breakwater. And the self-developed software THAFTS can play an important role in performance prediction.
Advancing the Modelica™ Ocean Engineering Toolbox With the Capability to Generate Accurate Wave Excitation Forces
Authors: Menon Ajay , Haider Ali Shahbaz , Bubbar Kush
Published: August 2024

The Ocean Engineering Toolbox (OET) is an open-source, Modelica™ compliant symbolic library capable of simulating the dynamic motions of floating bodies subject to polychromatic, unidirectional waves. This paper presents recent advancements in the OET: (1) the development of custom components to represent the frequency-dependent wave excitation force and (2) significant improvements in the toolbox’s computational performance. While the Modelica language can represent complex cyber-physical systems efficiently, the primary challenges with modeling wave-induced floating bodies are (1) non-compatibility with frequency-dependent variables, (2) lack of hydrodynamic components in the Modelica Standard Library (MSL), and (3) integration with the previous version of the OETv0.1. In the time-domain implementation, surface elevation profiles can now be generated for regular and irregular waves, with three spectral options for polychromatic seas: Pierson-Moskowitz (PM), Bretschneider, and Joint North Sea Wave Project (JONSWAP). Hydrodynamics coefficients are imported using a MATLAB script to process the output from Boundary Element Method (BEM) codes. A novel symbolic implementation of spectral decomposition and interpolation is presented in this work to generate the frequency-dependent excitation force in Modelica. Results from the OET are compared against data generated from WEC-Sim, validating both the wave excitation force and the corresponding system dynamic response for a floating point absorber in heave. These developments lead to superior simulation accuracy and computational performance while expanding the hydrodynamic modeling capabilities of Modelica.
High-Fidelity Simulation Platform for Autonomous Fish Net-Pen Visual Inspection With Unmanned Underwater Vehicles in Offshore Aquaculture
Authors: Tun Thein Than , Huang Loulin , Preece Mark Anthony
Published: August 2024

The importance of high-fidelity simulation in the deployment of Unmanned Underwater Vehicles (UUVs) in offshore aquaculture is evident, driven by a range of crucial factors such as safe deployment in challenging working environments. Such simulations enable thorough testing and refinement of UUV behavior, thereby mitigating safety concerns associated with human workforce exposure to risk. Additionally, the intricate preparations for real-world field trials involving multiple stakeholders require thorough planning. High-fidelity simulations serve a pivotal role as an informed decision-making tool in a cost-efficient way in aligning these diverse stakeholders and in pre-validating the advantages and challenges associated with UUV deployment in uncertain and demanding offshore aquaculture environments. In this paper, a number of existing simulation platforms are reported and using one of them which is built on the Robot Operating System (ROS) in Python, namely UUV simulator, an autonomous fish net-pen visual inspection with the BlueROV2 Heavy Configuration for the Blue Endeavour project (an upcoming first offshore aquaculture firm in New Zealand) of the New Zealand King Salmon company was demonstrated as a use-case study.
Systematic Study on the Drag Reduction Performance of a Microstructure Inspired by Pufferfish
Authors: Hu Shoujun , Li Ruoxin , Yu Kai
Published: August 2024

Due to the nature of migration, pufferfish has excellent underwater drag reduction ability. Apart from its streamline body, some studies showed that the microstructures on its body could also contribute to the drag reduction. In this work, the effects of the microstructure on the surface of pufferfish are numerically simulated. The microstructure features of the pufferfish surface are extracted and simplified. Orthogonal experiments on three levels of height, inclination and spacing of the microstructures are carried out. The simulation scheme and calculation results are verified. The results show that the height of microstructure is the main geometrical parameter affecting its drag reduction performance, and in a certain range, the drag reduction performance of the microstructure increases with the increase of height. The optimal combination of the microstructure for drag reduction is 0.05mm in height, 67.5° in inclination, 0.4mm in spacing.
Fluid-Structure Interaction Analysis of Crescent-Shaped Wingsails
Authors: Zhu Heng , Chernoray Valery , Ringsberg Jonas W. , Yao Hua-Dong , Ramne Bengt
Published: August 2024

The use of wind-assisted ship propulsion is regarded as one of the effective ways to reduce greenhouse gas emissions. This study combines wind tunnel experiments and advanced numerical simulations to investigate the model-scale effects and fluid-structure interaction (FSI) of a wingsail with a crescent-shaped profile. First, a wind tunnel test is carried out to study the aerodynamic loads and flutter of the wingsail. Next, a numerical method for analyzing FSI, fully coupling computational fluid dynamics and finite element analysis, is established. By comparing the experimental and numerical results, the model-scale effect that has an influence on the accuracy of prediction, e.g., laminar-turbulent transition, is discussed. Then, a full-scale FSI simulation based on a simplified solid model was performed to study the flutter and its influence on the propulsive performance. The results indicate that the crescent-shaped profile causes notable periodic oscillations due to strong flow separation, significantly affecting propulsive performance. These insights are crucial for the design and optimization of wingsail structures in enhancing wind-assisted ship propulsion.
Weather Downtime Estimation Using a Simulation Tool
Authors: Mol Arjan , van Goethem Delphine , Smith Timothy
Published: August 2024

Marine operations are heavily influenced by the weather conditions onsite, be it the sea state or other adverse climatic conditions. When the operational limits are breached the works stop and the installation waits for the weather conditions to improve, this is known as weather downtime (WDT). During project preparation, it is essential to accurately quantify the expected downtime when calculating the project budget and schedule. For contractors, the expected WDT is a key input during tender phase of marine installation projects. It determines the most efficient scenario, the project schedule and the choice of equipment, and hence it has a significant impact on the overall budget estimation.

Various methods exist to assess WDT, which differ in the level of detail and complexity that can be considered. The most detailed method is the ‘simulation based on hindcast timeseries’ approach. This paper discusses the in-house developed tool CycleSim, which is one example of a WDT simulation tool. Based on a few example cases, the capabilities of this tool will be demonstrated as well as its added value compared to other methods and tools.

The tool is not only capable of considering complex combinations of basic weather limits (e.g., wind, wave, and current conditions), but it can also deal with more special phenomena such as coupled activities, daylight restrictions, inhibited working periods and flexible waiting windows (i.e., waiting for the tidal current to get below a certain limit). It can not only deliver basic statistical information about the expected project duration for the total offshore installation, including uncertainties (percentiles), but it can also provide planning calendars for each activity of the installation. Finally, it can determine the total expected fuel consumption which can be used to estimate the expected emissions which makes it possible to compare installation methods and choose the most optimal one from a sustainability point of view.
Modeling of Hydroacoustic Noise From Marine Propellers With Tip Vortex Cavitation
Authors: Cheng Zhi , Kashyap Suraj , Smoker Brendan , Burella Giorgio , Jaiman Rajeev
Published: August 2024

Due to growing marine ecological concerns, there is an acute industrial need to significantly reduce the underwater radiated noise (URN) from marine propellers during ship operations. In this regard, high-fidelity fluid flow and hydroacoustic models are required for understanding the propeller noise generation and propagation in the ocean environment. Using high-fidelity CFD modeling, the present work aims to study the cavitating turbulent flow of a full-scale marine propeller and explore the physical mechanism underpinning the underwater radiated noise. We employ the standard dynamic large eddy simulation for the turbulent wake flow and the Schnerr-Sauer cavitation model, while the Ffowcs-Williams-Hawkings acoustic analogy is considered for the hydroacoustic modeling. For the current investigation, we consider a well-known Potsdam Propeller Test Case to analyze the turbulent cavitating flow and the associated hydroacoustic emissions. To begin, the modeling framework is validated using the available experimental data, and distinctive double-helical tip vortex cavitation and its qualitative patterns along the vortex trajectory are captured. In comparison to the non-cavitating condition, the pressure distribution on the propeller surface is more disordered for the cavitating condition, which is further reflected by a relatively stronger power of both low-frequency tonal peaks and high-frequency broadband components in the spectrum of thrust generation. Specifically, the generation of cavitation leads to the enhancement of the monopole noise source and the breakdown of cavitation bubbles as well as vortex structures in the turbulent wake. Furthermore, the tonal noise with the frequency corresponding to the harmonics of blade passing frequency is also enhanced. Generally speaking, the generation of cavitation structures enhances the hydroacoustics energy of URN at all orientations, especially in the downstream direction with sound pressure level increasing up to 20 dB.
Mooring Optimization of Floating Offshore Wind Turbines Using Genetic Algorithm
Authors: do Vale Machado Lucas , Shadman Milad , Amiri Mojtaba Maali , Estefen Segen Farid
Published: August 2024

Most global wind resources are found in water depths exceeding 60 meters, where using bottom-mounted structures is challenging and costly. Thus, increased the studies on floating offshore wind turbine (FOWT) solutions characterized by complex dynamics between the floating structures and turbines. Nowadays, one key challenge is designing optimum mooring arrangements for large-scale FOWT.

A meta-heuristic solution is recommended to solve a complex optimization problem, such as the mooring arrangement of a floating wind turbine. Among these, the Evolutionary Algorithms (EA) use mechanisms inspired by biological evolution. Genetic Algorithm (GA) is a multi-objective search and optimization algorithm based on the concept of Darwin’s theory of evolution, and it belongs to the class of Evolutionary Algorithms. It combines the idea of survival of the fittest with randomized information exchange.

Based on the literature, multi-objective optimization algorithms, such as the GA, are commonly used with hydrostatic and frequency-domain models, which are less accurate than a time-domain model for optimization purposes of FOWT.

This work addresses the optimization of the mooring system of a FOWT using time-domain simulations in OpenFAST. An in-house code is developed to handle calculations on OpenFAST and apply GA to find the optimal mooring arrangements for specific design variables meeting predefined multi-objectives, respecting all specific constraints for the FOWT. Finally, the optimized arrangements are checked against Ultimate Limit State (ULS) and Accidental Limit State (ALS), performed for the mooring system in damaged condition.

The developed optimization process is applied to the UMaine VolturnUS-S semisubmersible platform to maximize power quality and minimize the costs of the lines.
Numerical Study on the Characteristics of Bow-Flare and Stern Asymmetric Slamming for Container Ships
Authors: Lu Lin , Ren Huilong , Li Hui
Published: August 2024

The large bow flare and flat stern of container ships can result in a significant slamming phenomenon. Asymmetric slamming often occurs in oblique waves. The slamming can lead to ship vibration, reduced speed, and direct structural damage in severe cases. However, the prediction of slamming loads remains a challenge due to the highly nonlinear characteristics of the free surface and the physical surface conditions. This paper aims to provide a deeper analysis of the mechanisms of the oblique water entry process of the bow and stern of container ships. A numerical model of the two dimensional (2D) section is established using the open-source software OpenFOAM, incorporating the Volume of Fluid (VOF) method to solve the water-air phase flow. The free surface flow, slamming forces and the distribution of slamming pressures along the section were obtained. The numerical model is validated against available experimental data from the literature and the accuracy of the algorithm is discussed. The differences in slamming characteristics resulting from various shape features of the bow and stern is explored. Additionally. the comprehensive effects of geometric asymmetry during water entry are investigated by systematically altering the section’s roll angle. This study is expected to provide a reliable algorithmic framework for coupling slamming loads with the ship motion in the future.
An Experimental Study of Roll Damping Using a Pendulum-Based System
Authors: Xi Kemeng , Milne Ian , Draper Scott , Chen Lifen
Published: August 2024

A hull-pendulum system is introduced to investigate the roll damping of a hull through roll decay. Compared to conventional roll decay tests, this method can reduce the decay of the KC number (roll amplitude) and more conveniently allows for a range of oscillatory frequencies to be investigated. Further, the setup allows for roll damping experiments with low mechanical friction and at low cost. The study primarily focuses on flow separation and vortex shedding. Two types of sharp bilges were investigated: a square bilge and a round bilge equipped with a bilge keel. The results demonstrate that, in most of the scenarios studied, the roll damping coefficient is proportional to the roll amplitude, which aligns with the assumption and prediction of the Ikeda method. However, for bilge keel configurations, the roll damping coefficient decreases rapidly at ϕ ≤ 2°. These findings are consistent with the prediction of isolated edge theory that the roll damping coefficient is proportional to KC2/3 in the case of the bilge keel with ϕ ≤ 2°. For ϕ > 2°, the isolated edge theory suggests that the damping coefficient, effectively reverting to that of a square edge, should be proportional to KC, as corroborated by experimental observations.
Analysis of Implosion Protection Effect of Ceramic and Titanium Alloy Hollow Spheres Wound With Carbon Fiber
Authors: Zhang Xinyu , Zhao Min , Ge Tong
Published: August 2024

As an important part of deep-sea submersibles, once a catastrophic implosion occurs, the pressure-resistant structure will pose a huge threat to the vitality of deep-sea equipment. Therefore, it is necessary to conduct relevant research on implosion protection. In this work, we selected ceramic and titanium alloy hollow spheres as deep-sea flotation devices, and formed a composite pressure-resistant structure with both lightweight and implosion protection advantages by winding carbon fiber outside them. Based on the open-source solver OpenRadioss, the arbitrary Lagrangian-Eulerian method is used to simulate the implosion process of composite hollow spheres. Firstly, the feasibility of the numerical method is verified by comparing with the relevant experiment. Secondly, the response analysis of the two composite hollow spheres is carried out. The 3D Hashin criterion, the maximum principal stress criterion and the Johnson-Cook failure criterion are used to describe the failure of carbon fiber reinforced polymer (CFRP), ceramic and titanium alloy respectively. By comparing the flow field response and structural collapse form, the influence of outer winding carbon fiber on the implosion characteristics of ceramic brittle material hollow spheres and titanium alloy ductile material hollow spheres is discussed. The failure modes of hollow spheres with different lining materials are summarized, and the advantages of this scheme in lightweight and implosion protection are highlighted. In summary, this work not only clarifies the mechanism of implosion, analyzes the structural response, and proposes implosion protection measures, but also provides a reference for the material selection and design of deep-sea equipment structures.
Research on a Fast Resistance Performance Prediction Method for SUBOFF Model Based on Physics-Informed Neural Networks (PINNs)
Authors: Wu Yuliang , Han Fenglei , Peng Xiao , Gao Liangtian , Zhao Yiming , Zhang Jiawei
Published: August 2024

Physics-Informed Neural Networks (PINNs) represent a novel intelligent algorithm for solving partial differential equations (PDEs), which has been partially validated in solving Navier-Stokes equations. However, numerous challenges remain in the application of PINNs to the calculation of hydrodynamic performance of ships.

This paper utilizes discrete solutions of the Navier-Stokes (N-S) equations obtained via the Finite Volume Method (FVM) and Reynolds Averaged Navier-Stokes (RANS) approach of the CFD method for training PINNs to directly solve flow field information. This approach achieves a solution with approximate accuracy to that based on the CFD method, but with significantly reduced time consumption. The development of this algorithm could offer a novel perspective for calculating the hydrodynamic performance of ships.

The study focuses on the DARPA SUBOFF-B model, using field information obtained at specific speeds through the CFD method, including pressure and velocity fields, as the training set to train the neural parameters within PINNs. This enables the PINNs model to predict the flow field information around the hull and calculate the hull resistance through integration. The results predicted by the PINNs method are compared and analyzed against those calculated via the CFD method, Shows the comparison of the predicted results of the hull surface pressure field, as well as the relative error of the predicted total resistance., thereby proving the feasibility of the method.
A Journey Towards Safer and Faster Drilling: Real-Time Advisory With Digital Twins and AI
Authors: Gu Chunwei , Xu Tong , Lye Jen , Ødegård Sven Inge , Cao Jie
Published: August 2024

The oil and gas industry has undergone remarkable advancements in embracing digital transformation, revolutionizing its operations, and unlocking many new opportunities. This paper presents the journey of digital transformation toward achieving safer and faster drilling operations within CNOOC. Specifically, the focus will be on implementing drilling advisory systems and their diverse applications in enhancing efficiency, cost reduction, safety improvement, and operational optimization.

The real-time drilling advisory system relies on cutting-edge technologies such as digital twins and artificial intelligence (AI) to operate effectively. A drilling digital twin is a digital replica of the physical well throughout the entire drilling life cycle. Its functionality stems from dynamic hydraulic, thermal, and mechanical modelling that accurately simulates drilling operations. Driven by real-time data, the digital twin facilitates automated monitoring, forward-looking analysis, and predictive insights. To create diagnostics of drilling events in advance, the advisory system employs model-based reasoning, an AI inference method. Continuously updated with real-time data streamed from the rig, the digital twin promptly generates diagnostic messages, identifying risks or issuing warnings based on predictive analysis and forecasting. In conclusion, the real-time advisory system empowers drilling engineering by enabling enhanced operational efficiency, safety, and sustainability, while driving significant cost reductions and fostering opportunities for growth and innovation.
Combined EFD and CFD Approach for Full Scale Ship Resistance Predictions Using the Form Factor
Authors: Quintuña María , Horn Peter , Zhang Junheng , Sprenger Florian
Published: August 2024

In this study, a comparison of the experimental full scale ship resistance extrapolation procedure using the ITTC’78 power prediction method with a newly proposed hybrid EFD/CFD approach has been performed for two benchmark ship hull geometries. For both hulls, resistance tests have been performed in the towing tank of HSVA at model scale. From these tests, experimental form factors have been determined according to Prohaska’s approach. In addition, CFD simulations have been performed to determine a new numerical flat plate friction line as well as the frictional resistance for both hulls by double body CFD simulations in model and full scale. Based on these simulations, numerical form factors according to Hughes have been derived. Two different turbulence models, the k-ω standard and the k-ω SST, have been used to obtain the flat plate frictional resistance curve. It has been found that the mean difference between the numerical form factors obtained for model and full scale CFD simulations is 10.4% using the ITTC’57 correlation line. When using the newly established numerical friction line based on the k-ω SST model, this mean difference is reduced to mean 6.4%. Based on the results, full scale resistance predictions were performed based on the different form factors that have been derived following the ITTC’78 method. Since no data from sea trials is available, the full scale resistance predictions for the two ship hulls were compared with the results of full scale CFD simulations. It was found that the extrapolation based on the form factor derived from the numerical friction line using the k-ω SST shows a 3.1% deviation from the full scale CFD results, while a deviation of 7.1% was observed for the form factor based on the ITTC’57 line.
Numerical Simulation of Ascending Motion of Polymetallic Nodules for Hydraulic Lifting of Vertical Pipes
Authors: Liu Yajiao , Dou Peilin , Li Xiu
Published: August 2024

Deep-sea polymetallic nodule hydraulic lifting program belongs to the particle fluid complex system of solid-liquid two-phase flow problems, most of the previous research for low-density, small-sized particles, for high-density, large-sized particles of the research is mostly carried out in the net water free-fall problem .In this paper, the solid-liquid two-phase flow of seawater with polymetallic nodules was numerically calculated using the CFD-DEM semi-analytical method in the context of deep-sea mining polymetallic combined with hydraulic lifting. The effect on the particle rise process was investigated for several cases, such as the particle fluid density ratio of 1:2, different pipe diameters with particle size ratios of (2∼10), different pipe Reynolds numbers (400∼2000; lifting velocities of 2∼10m/s), and different initial positions of the particles. The accuracy of the computational model is also verified by comparing the infinite-boundary free-fall experiments with the results of the literature by Lei Liu and Horowitz M. The results are summarized as follows. Through numerical simulation, five subdivided types of particle ascent trajectories were obtained; Different Reynolds numbers and particle size ratios also have an impact on the upward trend of particles, while changes in initial position have little effect on the upward velocity of particles.
Evaluation of Mooring Line Degradation in Floating Offshore Wind Turbines: A Comprehensive Analysis of Corrosion and Fatigue Under Environmental Impacts
Authors: Beer Theresa Marie , Karpenko Olena , Collu Maurizio , Coraddu Andrea
Published: August 2024

As the demand for renewable energy grows, floating offshore wind turbines have become crucial, especially in deep water areas where traditional structures are impractical. These turbines need station keeping systems, which often consist in catenary mooring lines, making their durability vital against extreme weather conditions. While direct monitoring of these lines would be preferable, it is often unpractical due to high costs and maintenance. This research presents a new method to evaluate the degradation of mooring lines. The study investigates fatigue and corrosion behavior along the mooring lines by simulating environmental impacts, considering varied forces and weather patterns. Considering seawater’s oxygen and temperature, a distinct corrosion model is merged with fatigue performance predictions based on DNV standards. Mooring line loading conditions derived from environmental factors are then incorporated into a finite element model, assessing various load cases and corrosion’s role in line degradation. This comprehensive model examines the combined effects of corrosion (in particular, pitting corrosion) and fatigue, including hydrostatic pressure and out-of-plane bending on the performance of the mooring line chain in the offshore environment. The methodology’s validation relies on previous research and mooring line operational data.
The Bearing Capacity of Torpedo Anchor in Clay Under Inclined Loading of Mooring Chain
Authors: Tang Chao , Wu Xiaoni , Shu Jian , Chen Jinjian , Wang Teng
Published: August 2024

Torpedo anchors represent a promisingly innovative anchorage foundation for deep water applications due to their efficient and economical installation. During installation, a significant length of mooring chain was embedded into the seabed alongside the torpedo anchor. This interaction between the chain and the soil alters the strength characteristics of the clay, and also affect the loading angle at the padeye during pullout. As a result, the bearing capacity of the torpedo anchor is influenced by the movement of the chain. However, existing numerical studies lack a comprehensive understanding of the pullout performance of torpedo anchors, particularly in considering the presence of mooring chains. This study endeavors to investigate the pullout capacity of torpedo anchors in clay, accounting for the effect of the mooring chain attached to the padeye, utilizing the large deformation finite element method (LDFE). The elastic-perfectly plastic material model, adhering to the modified Tresca yield criterion, was employed. Verification of the model’s accuracy and effectiveness was conducted through centrifuge test results. The influence of the mooring chain and loading angle on the pullout capacity were investigated. The findings indicate that the discrepancy in the bearing capacity of torpedo anchors, with and without considering the mooring chain, increases from 3% to 38.4% as the loading angle rises from 0° to 75°. Conversely, for vertical loading, the difference decreases to 7%. Based on the numerical analysis, normalized V-H envelopes were provided. This work contributes valuable insights into the capacity of torpedo anchors.
Time-Harmonic Ship Waves From the Perspective of an Earth-Fixed Observer
Authors: Chen Xiaobo , Liang Hui
Published: August 2024

Time-harmonic flows around a ship advancing in waves are usually described in the coordinate system moving with the ship’s average speed. Within this moving reference system, detailed descriptions of ship waves have been made in many previous studies. Recent works in [1, 2] revealed that essential physical features such as different wave systems and their wavelengths, cusp angles, phase, and group velocities, are directly related to wavenumber curves determined by the dispersion relation on the mathematical Fourier plane. Insightful physical results have been achieved and applied in developing numerical tools to predict ship seakeeping. However, the description of time-harmonic ship waves in the Earth-fixed coordinate system is missing although a few studies exist on steady ship waves like that in [3, 4] It is not trivial to transform results in the moving coordinate system to the fixed coordinate system. Much caution is needed to obtain consistently the phase and group velocities which are closely associated with wave crestlines. In the present study, after summarising classical results in the moving coordinate system, detailed analyses of time-harmonic ship waves in the Earth-fixed coordinate system are presented with numerical illustrations. The results obtained in both coordinate systems are believed to be useful in the prediction of ambient waves due to the passage of ships.
Escarpment Crossing Design and Analyses of Large Diameter Offshore Pipelines
Authors: Qi Xinhai , Kvist Orjan , Chen Jian , Duan Gang , Ren Lan , Wang Howard , Lan Jundong
Published: August 2024

Subsea pipeline design for escarpment crossings proves complicated and time-consuming, primarily attributable to the excessive plastic strains encountered at the overbend and the extraordinary fatigue damage over long spans, exacerbated by the steep seabed conditions.

Due to substantial uncertainties, the design approach for pipeline escarpment crossings leans towards conservatism by limiting pipeline bending moment/strain and span length. Consequently, the implementation of mitigation measures becomes a common necessity. In pursuit of a straightforward and cost-effective crossing design, this paper offers a comprehensive insight into the in-place behavior of large diameter pipeline crossing over escarpments.

This study investigates a 24-in gas export pipeline in an African field from a water depth of 25m to 250m. The pipeline strength assessment employs the displacement-controlled condition (DCC) at the escarpment top and load-controlled condition (LCC) for the remaining pipeline, aligning with DNV offshore pipeline design standards. The numerical model, utilizing Abaqus elbow elements, simulates the S-lay, pre-commissioning, and operating processes. The mitigations of the strain and DCC utilization are then examined. This involves optimizing pipeline route, wall thickness, lay tension, and crossing protection.
Seismic Vulnerability Analysis of Pile Foundations in Liquefiable Sites
Authors: Tao Xiaosan , Wang Zhekai , Tan Huiming
Published: August 2024

Pile foundations of structures like offshore wind farms and bridges are often located in potentially liquefiable sites. In order to study the seismic vulnerability of pile foundations in liquefiable sites and analyze the seismic response of pile foundation structures in such conditions, a numerical model of pile foundations was established using OpenSees platform. Subsequently, by conducting nonlinear time history analysis using representative seismic waves, seismic vulnerability curves for various components were plotted with the peak ground acceleration (PGA) as a parameter. The results indicate that the failure probability of the piers is related to both PGA and the damage state. A higher PGA leads to a higher failure probability of the piers. With a constant PGA, the more severe the damage state of the piers, the lower the failure probability. As PGA increases from 0.1g to 0.5g, the probability of slight and moderate damage states of the piers shows a rapid increase, indicating a significant response of the piers to the change in seismic intensity from 0.1g to 0.5g, making them highly susceptible to damage during this stage. As for the vulnerability curve under complete damage state, the damage probability starts to change only after PGA reaches 0.5g, and the magnitude of change is small. When PGA reaches 0.8g, the damage exceedance probability is also less than 10%, demonstrating the structural safety.