bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Strain Hardening and the Lode Dependence of the Fracture Strain Locus on Slant Fracture in Charpy V-Notch Impact Testing
Authors: Wong Wei Jun , Walters Carey
Published: August 2024

Ductile fracture in steels relevant to the offshore and maritime industry is often characterized by the occurrence of slant fracture, which is the development of fracture surfaces that are slanted relative to the original surface of the material. The modeling of this phenomenon is important for describing ductility and fracture toughness accurately in ductile fracture simulations. This work uses a consistency model for viscoplasticity with damage softening within a strain-based framework to investigate the effect of variations in strain hardening and Lode dependence on the slant fracture area and impact energy in Charpy tests. The model is first calibrated to uniaxial tensile, single-edge-notched-bending fracture toughness and instrumented Charpy tests performed on an S690QL steel, and then a parametric study varying the strain hardening and the Lode-dependence is performed. It is seen that an increase in the yield-to-tensile-strength ratio (equivalent to a decrease in the strain hardening exponent) leads to a decrease in the impact energy and negligible difference in the percentage slant fracture area when the damage and rate parameters are kept constant. It is found that the Charpy impact energy is not sensitive to the maximum strains in the fracture strain locus and is mainly affected by the minimum strains in the locus. Finally, the rate-dependent consistency plasticity model with a strain-based damage-softening formulation is capable of simulating slant fracture behavior even in cases where the fracture initiation strain is stress-state-independent and constant.
Dynamic Response Analysis for the Monopile Driving Process of Offshore Wind Turbines
Authors: Wang Kang , Hu Haibin , Feng Xiaoxing , Ni Zhonghua , Yan Yan
Published: August 2024

Monopile is used as supporting part of offshore wind turbines (OWTs) and determines its service time. After the construction, dynamic response of monopiles has been extensively studied under external loads, such as seawater corrosion, offshore wind and pile-soil interaction. However, in the monopile driving of large-capacity OWTs, the hammering force and stress peaks increased several times over. Therefore, in this work, two finite element models were established for the monopile driving process, including the bottom-fixed model and spring-friction model. These models were verified by the construction data from engineering. From the comparison, the data in spring-friction model was more consistent with the engineering condition. It overcame the shortcomings of bottom-fixed model. The inclusion of pile-soil interaction allowed for the determination of pile penetration and lateral friction resistance. The simulation results were more accurate and had less error with engineering data. The numerical simulation was expected to provide reference data for studying the fatigue life analysis of the driving monopile.
Multi Modal Mapping of Sea Ice Fields From Remote Shipborne Instrumentation
Authors: Veggeland Oskar G. , Kim Ekaterina , Skjetne Roger
Published: August 2024

We present a standalone instrumentation system designed to create digital multi-modal maps of the sea ice surrounding ships operating in the Arctic. The system contains a 3D LiDAR scanner and an optical camera for remote sensing. Spatial calibration of the sensors enables us to project point clouds onto the optical images, providing RGB values to the 3D map. The presented system can continuously monitor sea ice and build large-scale maps by running a navigation filter to estimate the system trajectory. This is made possible by internal navigational payloads, making the system independent of the vessel on which it is mounted. The ice field maps are validated by reconstructing images and comparing them to synchronized inputs from the optical camera. Qualitative comparisons between the reconstructed and optical images show that the most prominent features of the sea ice are conserved. We also propose a method to track sea ice roughness over large temporal and spatial scales and show how this can automatically detect areas with a high amount of deformed ice.
Analytical and Numerical Study on Drill-String Torsional Vibration Under Weight-On-Bit Fluctuation
Authors: Kaneko Tatsuya , Inoue Tomoya , Wada Ryota , Katsui Tokihiro , Suzuki Hiroyoshi
Published: August 2024

Understanding drill-string dynamics is essential to improving offshore drilling efficiency and preventing accidents. Previous studies have mainly focused on self-excited oscillations due to stick-slip and bit-bounce. However, in deepwater drilling, large weight-on-bit fluctuations due to ship heaving are a major concern that can affect the dynamics in the torsional direction. This paper reports analytical and numerical investigations on the torsional vibration of a drill string under weight-on-bit fluctuation.

First, the analytical solution of a single-mass model showed that forced oscillations are caused by WOB fluctuations, which have not been examined extensively in previous studies. In addition, for the same amplitude of WOB variation, vibration at the heave frequency has a greater effect on torsional vibration than at the axial self-excited frequency. Furthermore, large WOB fluctuations increase the risk of stick-slip and reverse rotation of the drill bit.

Second, numerical experiments with the multi-mass model yielded results similar to those of the analytical study. These results show the importance of capturing torsional vibrations caused by fluctuations in the WOB and reducing WOB fluctuations.
Dynamic Responses of a Gravity-Type Fish Cage During Lifting Operations in Waves and Current
Authors: Wen Xueliang , Ong Muk Chen , Cheng Hui
Published: August 2024

Aquaculture has experienced remarkable growth over the past four decades. The utilization of fish cage systems at sea has played a pivotal role in promoting the growth of seafood production. As technology advances, the gravity-type fish cages become more and more popular because of the low capital cost for the industrial-scaled fish farming. The lifting operation of gravity-type fish cages is an important procedure for the harvest and de-lice of the fish. In the present study, the static and dynamic responses of the fish cage before and during the lifting operation are investigated numerically. A Morison model is adopted to calculate the hydrodynamic forces acting on the net ropes of the aquaculture nets and a screen model is used to calculate the hydrodynamic forces acting on the net twines of the aquaculture net. The irregular waves are generated using the JONSWAP wave spectrum. The structure of the aquaculture nets is modelled using an extended position-based dynamics (XPBD) method, which was first used in the cloth dynamics simulations in games. The proposed method is effectively validated against the published experiment data to ensure its accuracy and reliability. The static response of the gravity-type fish cage at various current speeds, and the dynamic responses of the fish cage in irregular waves before and during the lifting operation are analyzed. Results show that in a smooth sea state, the drag force of the fish cage is slightly higher than that in a uniform flow with the same current speed and the fish cage volume sightly decreases, while the deformation of the fish cage is similar. During the lifting operation, the lifting force mainly results from the weight of the sinkers at the bottom of the side net. The maximum tension of the net is located at the net ropes connected to the centre point of the bottom net. Therefore, the structure of the bottom net should be enhanced for safety lifting operations.
Combination of Potential Theory and Morison-Like Viscous Drag Terms in the Hydrodynamic Model of a 12 MW Semi-Submersible Floating Wind Turbine
Authors: Souza Carlos Eduardo Silva de , Fonseca Nuno , Berthelsen Petter Andreas
Published: August 2024

Semi-submersible platforms are widely adopted as support structures for floating wind turbines (FWT). Morison-like, quadratic drag terms are typically used for modelling viscous loads on the platform columns and pontoons, with drag coefficients obtained from model tests. One of the challenges when adopting this modelling approach is to achieve a simultaneous representation of damping effects and viscous excitation. In this paper, a systematic procedure is presented to calibrate the drag coefficients of a semi-submersible platform supporting a 12 MW FWT, based on model test results. First, the pontoon coefficients are calibrated based on the heave and pitch motions. Then, it is assumed that viscous excitation in surge is mainly associated with the upper part of the columns, which are subjected to more significant action of the waves. Thus, the coefficients at this portion of the columns are tuned to retrieve the low-frequency motion components not captured by potential theory alone, while the coefficients at the bottom of the columns are adjusted for achieving the necessary level of damping. The final coefficients are chosen based on comparison between the model test results and multiple combinations of the drag coefficients associated with different components of the platform.
Characteristics of Solid-Liquid Two-Phase Flow in Deep Sea Mining Pipelines
Authors: Li Jianing , Chen Nian-Zhong
Published: August 2024

The technical feasibility of the pipeline hydraulic lifting system has been confirmed through multiple offshore trials and it has been currently the most promising deep-sea mining system. When transporting minerals collected from the deep-sea seabed to the sea surface along with seawater, complex multiphase flow upwelling issues are generated. In this paper, in terms of the open-source Computational Fluid Dynamics (CFD) software OpenFOAM®, a Lagrangian solver coupled the Eulerian and Lagrangian phases is established to simulate the flow of solid-liquid two-phase within a vertical riser. In this model, the discrete phase is solved by using the Discrete Element Method (DEM), and the continuous phase is achieved by solving the Navier-Stokes (RNAS) equations, taking into account the complex particle interaction. The movement of solid particles in turbulent flow is calculated and the distribution of solid particles under different conditions is obtained. The flow characteristics of solid-liquid two-phase flow are obtained from the perspectives of internal flow field distribution. The results demonstrate that the established numerical model for solid-liquid two-phase flow is relatively reliable, and the transported flow velocity has a certain impact on the lifting performance of the riser. This research offers a theoretical basis and practical reference for the future design of pipeline lifting systems.
Formulation of Idealized Structural Unit Method to Perform Progressive Collapse Analyses of Welded Box Girders in Bending
Authors: Lindemann Thomas , Kaeding Patrick
Published: August 2024

The Idealized Structural Unit Method (ISUM) is a simplified but very efficient approach to perform progressive collapse analyses of ship structures. Larger structural units are defined as ISUM-plate elements with idealized material and geometrical nonlinearities, that progressive collapse analyses are performed with reduced numerical efforts compared to nonlinear finite element analyses (FEA). A summary of different generations of the ISUM-plate element formulation is proposed. The newest generation of ISUM is described in detail with respect to its applicability to determine the ultimate strength of welded steel structures. The developed concept to apply welding residual stresses to plates and stiffened plate panels is explained. A combined ISUM-plate/beam-column element model to determine the progressive collapse behavior of welded box girders in four-point bending is proposed. The numerical results are compared to experimental data. For further comparison nonlinear finite element analyses are performed. Details about the FE model and the application of welding related imperfections are given. The ISUM model is used to determine the progressive collapse behavior of a box girder specimen for different load cases of biaxial bending. The influence of lateral pressure acting on the bottom structure on the ultimate strength of the box girder specimen is investigated with ISUM.
A Comprehensive Review of CO2 Corrosion in Oil Well Cement: Mechanisms, Determinants, and Mitigation Strategies
Authors: Zhao Feng , Wang Chengwen , Li Dingye , Chen Zehua
Published: August 2024

Carbon capture, utilization and storage (CCUS) is the main technique for carbon neutrality. This emerging technology has been developed to capture CO2 and store it in underground formations, such as aquifers or depleted gas or oil reservoirs. The corrosion of oil well cement by CO2 is a significant challenge which this technology faces. CO2 dissolves in the formation liquid phase to form an acidic fluid that interacts with various components in oil well G cement. As the corrosion progresses, the cement’s mechanical integrity diminishes, permeability escalates, and overall properties degrade. Factors like temperature, pressure, and the inherent properties of the cement significantly influence this reaction process. Over recent years, numerous investigations have delved into the CO2-cement interaction, leading to the innovation of myriad techniques aimed at mitigating this concern. Employing oil well cement, distinguished by its diminished porosity, decreased permeability, and attenuated alkalinity, represents a globally recognized strategy for augmenting CO2 corrosion resistance. Pozzolanic substances and film-forming barrier materials are extensively documented in literature as CO2-resistance potent agents. This paper offers a review of previous research works, encompassing the corrosion mechanism of oil well cement by CO2, various factors affecting CO2 corrosion, and CO2-resistant cement techniques.
Enhancing the Resolution of Large-Scale Sea-Ice Models Through Synthesising Satellite Imagery and Discrete-Element Modelling
Authors: Tsarau Andrei , Lu Wenjun , Lubbad Raed
Published: August 2024

Deformation is a fundamental aspect of sea-ice behaviour, playing a crucial role in the overall dynamics of polar regions. Sea ice deforms as it moves and changes shape in response to external forces and internal stresses. This may lead to the formation of specific narrow deformation structures, including cracks, elongated openings (leads), pressure ridges and shear zones, all of which are important for safety and navigation in polar regions. Cracks and leads also influence the exchange of heat and gases between the ocean and the atmosphere, affecting climate patterns and ecosystems.

Satellite sensors may provide data on local sea-ice conditions, including leads and other deformation features, at high spatial resolution. However, the temporal resolution of these data is often insufficient as it is limited by the satellite’s revisit time and may also be affected by weather conditions. Sea-ice models may be used with various spatial and temporal resolutions. Nevertheless, modelling the dynamics of sea ice, including floes of various sizes and narrow deformation features, using traditional (continuum) models is challenging because of their coarse grids, especially near coastlines and islands. Models based on the Discrete-Element Method (DEM), on the other hand, can resolve the dynamics of individual floes of any sizes and, therefore, are well-suited for modelling the behaviour of sea ice at small scales.

Using high-resolution satellite imagery along with oceanographic reanalysis data and large-scale ice drift predictions to initialise and force a DEM model, we have shown that this model can reproduce short-term ice drift and deformation patterns within a 100-by-100 km2 area near Arctic islands. However, further development of the DEM towards explicit ice fracture, accompanied by upgrades to ocean-current models, may be necessary, especially for long-term simulations (over 24 hours). The present model resolves elements of sea ice on scales of 50 m to 100 kilometres, including floes and leads, and, therefore, can be useful, e.g., in ice navigation and climate studies. To demonstrate a possible application example, we explored the possibility of using this DEM model for assessing routes for ship navigation through ice-covered waters.
Digital Twin-Driven Optimal Design of Connector Stiffness for Floating Multi-Modular Structures - An Application for Floating Solar Energy Harvest
Authors: Nguyen Dong Trong , Sølvberg Stian Hansen , Aas-Hansen Trine
Published: August 2024

This paper proposes an optimization framework for connector stiffness design for multi-modular floating structures, designed for offshore floating solar in open seas. The framework integrates an optimization scheme with a digital twin. An early-phase digital twin was developed to assess the structure’s response to waves as a basis for evaluating a connector stiffness parameter that mitigates environmental effects. An objective function considers module motions and internal connector loads, offering flexibility in tuning based on priorities. Bayesian optimization was adopted to find the global optimal connector stiffness, utilizing Gaussian Process regression. This method is suitable for optimizing objective functions that are expensive to evaluate, e.g. resource-intensive simulations of the response of the large multi-modular structure. The optimization process was validated and verified through model-scaled experiments and simulations in regular waves with different wave periods. In conclusion, the proposed framework demonstrates the capability to find optimal stiffnesses for different sea states, mitigating environmental effects on multi-modular structures. Future work will concentrate on improving the digital twin fidelity, reducing simulation time and developing an optimal control algorithm to enhance overall multi-modular structure performance in real-time.
The Influence of Slot Design and Biofouling on the Hydrodynamics and Dissolved Oxygen Exchange Through a Finfish Open Ocean Aquaculture Structure
Authors: Nguyen Duc , Wakes Sarah , Vennell Ross , Paing Si Thu , Rhone Scott , Kregting Louise , Black Suzy , Janssen Gerard
Published: August 2024

The current study examines the influence of a new design of open ocean aquaculture (OOA) finfish structure and environmental and physical factors on the hydrodynamics and dissolved oxygen (DO) exchange using Computational Fluid Dynamics (CFD). The structure is a 1,500 m3 square cross-section cylinder with mesh placed at the front and back of the body. There are slots on the body of the structure with densities varying between 0% (i.e. no slots) and 12%. Both parallel and perpendicular to the flow direction slots are examined. Biofouling is simulated using a flow reduction ratio through the mesh that varies between 5% and 50%. Fish density is 15 kg.m−3 and water temperature is 15°C with current speed scenarios of 0.1, 0.05 and 0.01 ms−1. We found that increasing the flow reduction ratio through the mesh to simulate biofouling effects results in a decrease of DO inside the structure. For example, flow reduction through the mesh increases from 15% to 50% resulting in the healthy volume fraction inside the structure (i.e. DO > 70% saturated DO) decreases from 0.22 to 0.15, when current speed is 0.01 ms−1. Increasing slot density facilitates flow ventilation through the structure and increases DO inside the structure. Increase of current speed results in an increase of DO inside the structure. For example, the healthy volume fraction increases from 0.19 to 1.0 when the current speed increases from 0.01 to 0.1 ms−1. Overall, we found that CFD modeling is a useful tool to explore the complex relationship between novel OOA structure designs (e.g. various slot densities on the body of structure) and environmental and physical factors (e.g. blockage mesh effects, current speed) on the hydrodynamics and DO exchange.
Hydrodynamic Characteristics of Heave Plates in Shallow Water Using Forced Oscillation
Authors: Li Haoran , Zheng Jinhai , Zhang Jisheng , Xue Mi-An , Yang Chen
Published: August 2024

Heave plates which are widely attached at the base of columns of offshore floating wind turbines (OFWTs) can effectively reduce the resonance oscillations and improve the stability of OFWTs by providing additional added mass and damping. These hydrodynamic forces are strongly affected by the proximity of boundaries in shallow water. In the present work, the variations of added mass and damping coefficients as the heave plate moves a flat and stepped terrain are investigated. A column with a single solid circular heave plate is simulated in a numerical wave tank using forced oscillation tests. The added mass and damping coefficients are determined by fitting time series of the calculated force to Morison’s equation with a least squares procedure. The damping coefficients of heave plate increase with the decreasing water depth in the flat terrain (up to 60% compared to the coefficient in deep water). Similar conclusions are found when the length of stepped terrain is not less than the diameter of heave plate. However, the damping coefficients of heave plate significantly increase in the condition that the length of stepped terrain is smaller than the diameter of heave plate (up to 80% compared to the coefficient in the flat terrain).
Hydrodynamic Characteristic of the “ChangJiangKou II” Wreck Salvage: A Coupled Time Domain Model
Authors: Wang Yiting , Wang Lei
Published: August 2024

This paper reports an integral salvage solution for an ancient vessel “Chang Jiang Kou II” wreck salvage. To ensure the safety of the whole salvage operation and reduce the damage to the historical relic, especially in the off-bottom and lifting process, a novel coupled time-domain model is developed to evaluate the safety of the moored salvage system in Yangtze River. The wreck-soil interaction module, lifting module and mooring module are coupled into the conventional potential flow time domain numerical simulation code. The finite element method, potential flow method and lumped mass method are adopted and integrated for considering the influence of the wreck-soil interaction, lifting and mooring system. The coupled model is preliminary validated by similar mature software in our previous study and is further validated by a model-scale experiment in present paper. The safety assessment is quantitatively conducted by using a three-parameters safety assessment methodology. Case studies with different sea states are numerically performed and quantitatively assessed. The results of the numerical simulation and experiments found that there is a special breakout phenomenon, where the displacements increase abruptly, and uneven distributions of the lifting tensions are observed. The outcome of present coupled model can give an important reference in real salvage operation.
Development of Hanwha Ocean Liquefied CO2 Carrier
Authors: Jun In-Jae , Koh Teuk-Jin , Kang Byoung-Chul
Published: August 2024

The interest in carbon neutrality is growing around the world as human faces the climate crisis caused mainly by greenhouse gas emission. The methodologies for carbon reduction are being introduced in every industry and carbon reduction through Carbon Capture Utilization & Storage (hereafter “CCUS”) is being recognized as one of the most feasible carbon reduction plan at the moment. CCUS is defined as a system of technologies that intergrates three stages: CO2 capture, transportation and utilization & geological storage. The transportation sector is a major part in CCUS value chain to link the capture sector and utilization & storage sector. Transportation methods of trucks, trains, pipelines, ships, etc. are being considered in the CCUS value chain and pipelines and ships are applicable in ocean transportation field. As the transportation distance of CCUS projects under development becomes longer and the total transportation volume is increased, ocean transportation using a dedicated liquefied CO2 (LCO2) carrier is expected to play a key role in carbon transportation of CCUS chain. In these market trends, Hanwha Ocean began developing a new vessel that can transfer liquid CO2 safely. This paper is to introduce the design development of Hanwha Ocean LCO2 carrier such as ship & cargo tank design, tank material, CHS (Cargo Handling System) test facility, etc.
Monte Carlo Dropout Based Active Learning for Deep Learning in Structural Simulation
Authors: Jiang Chunhao , Chen Nian-Zhong , Zhao Zhimin
Published: August 2024

In recent years, deep learning (DL) has been widely used in the realm of maritime technology and engineering, particularly in the domain of structural simulation. However, one of the significant challenges in this context is the requirement for extensive training data, which is cost-prohibitive. To mitigate the expensive cost of generating training data, an active learning (AL) model is proposed to reduce the required number of labeled samples for deep learning. Within this active learning model, a predefined acquisition function is used to query an unlabeled sample pool. It focuses on selecting highly informative samples for labeling and subsequent inclusion into the training dataset. The predefined oracle in the proposed active learning model is developed based on the Monte Carlo dropout technique, which is used to quantify the aleatory uncertainty and epistemic uncertainty inherent in the deep learning model. Consequently, samples characterized by maximal uncertainty are identified and subsequently integrated into the training dataset. A comparative study with random sampling is conducted to demonstrate the effectiveness and advantage of the proposed active learning model. This model can be generalized to improve other deep learning models used in the maritime technology and engineering domain, as it offers a computationally efficient way of sampling additional data.
Global Response Performance of HDPE Based Offshore Floating Solar Farm by Using Beam-Floater Model
Authors: Gavin Surjadi Frederick , Bakti Farid Putra , Jin Chungkuk , Simamora Pandu Kristian Prayoga
Published: August 2024

This study investigates the hydrodynamic and structural behavior of floating photovoltaics (FPV) equipped with floaters made of high-density polyethylene (HDPE) in marine environments. A comprehensive time-domain dynamics simulation of coupled FPV is executed to analyze the interactions among floaters, connectors, mooring lines, and PV modules. The HDPE floater is represented by a 6-degree-of-freedom (6DOF) non-diffracting buoy, interconnected by beam elements to capture elastic behavior. The PV module is positioned on the floater and modeled as a wing component with consideration for wind drag and lift forces. Multiple mooring lines, strategically placed on all sides of the FPV, serve the purpose of station-keeping. The study evaluates the tension in mooring lines and the bending moments of floaters using statistical values, response amplitude operators (RAOs), time histories, and spectra. The findings indicate that low-frequency excitation emerges as a pivotal factor influencing structural dynamics, primarily due to significant flexibility. The proposed design demonstrates superior performance in low-sea states.
Time-Varying Model for Scour Evolution Around Pile Foundations in Clay Soils
Authors: Zhao Pei-Qing , Wang Shun-Yi , Qi Wen-Gang , Gao Fu-Ping
Published: August 2024

The determination of the equilibrium value and time-dependent development of the scour depth around pile foundations has been a fundamental concern in hydraulic and coastal engineering. While significant progress has been made in understanding local scour around pile foundations in non-cohesive soils in recent years, the study of scour in clay soils remains less developed. Traditional methods for predicting scour in non-cohesive soils have been inappropriately applied to clay soils. Therefore, there is a pressing need to establish an accurate prediction model for scour depth in clay soils to enhance foundation designs. Current formulas for predicting scour development in clay soils around pile foundations are often empirical fittings to experimental data, making them susceptible to data ranges and scale effects. To fill this gap, a time-varying model for the evolution of scour around pile foundations in clay soils under a steady flow is proposed in this paper. This model utilizes a scaling expression for shear stress based on the phenomenological theory of turbulence (PTT) and integrates a general sediment transport model with sediment mass conservation principles to derive an ordinary differential equation (ODE) representing temporal variations in scour depth. By comprehensively considering all dimensional parameters affecting the scouring process, the model overcomes scale issues. The proposed model’s predictions closely align with previously observed scour depth development curves, demonstrating its effectiveness.
The Effect of Boundary Condition on Predicting the Thrust Loss of Azimuth Thruster in Ship-Type Offshore Structures
Authors: Woo Jaehong , Song Gisu , Kim Joo-Sung
Published: August 2024

For various offshore structures including ship types such as drillship, Wind Turbine Installation Vessel (WTIV), Floating Production Storage and Off-loading (FPSO), and Floating Liquefied Natural Gas (FLNG), the dynamic positioning (DP) is a fundamental function. For effective DP operation, the special propulsor, for example, azimuth thruster was chosen in general. It is well known that several azimuth thrusters are installed in offshore structures, the thrust loss might be induced by various interaction phenomena. In this study, the influence of boundary conditions is mainly examined for predicting thrust loss on numerical simulation. WTIV and FPSO were chosen as a target vessel, respectively. Two different types of boundaries were defined. The first consideration is that the boundary condition was assigned with the direction of the azimuth angle of the thruster whereas it is fixed regardless azimuth angle of the thruster. The predicted thrust loss according to these boundary conditions showed a difference and this is originated from the current load of the vessel. The current load on the ship depends on the ship type, draft, and inflow direction, the magnitude of the current load is affected by those conditions. Since the current load might be induced unintentionally in numerical simulation, the boundary condition is important to obtain a realistic thrust loss.
Numerical Study of Motion Responses of a New Combined Floating Wind Turbine and Wave Energy Converters
Authors: Lu Shunhang , He Fang , Cai Yuanlang , Yang Xiaolong , Zhang Guanglei
Published: August 2024

Improving power generation efficiency and reducing development costs is one of the main challenges for the floating offshore wind turbine (FOWT). A similar set of challenges is encountered in wave energy converter (WEC) systems. In response, this paper proposes a novel hybrid concept that combines FOWT and oscillating water columns (OWC) to capitalize on their respective advantages, as substantiated through a comprehensive numerical comparison with a purely FOWT system. The hybrid concept’s advantages are underscored by a rigorous analysis that incorporates wave-induced loads on the semi-submersible floating foundation and OWC using the potential theory, encompassing the 1st and 2nd order excitation forces as well as radiating added mass and damping, all integrated within the AQWA code. Viscous effects are approximated via the empirical Morison equation. Furthermore, the aerodynamic impact of the turbine blades is meticulously simulated using the blade element momentum method within the FAST code. Pitch and Nacelle horizontal acceleration of system are identified as the primary criterion for illustrating the advantages of the hybrid concept. In addition, this paper conducts a comparative study that explores the impact of sizing OWC in hybrid systems, shedding light on the potential for optimizing system motion performance and improving cost efficiency while maintaining constant structural weight. The paper culminates in a proposed arrangement plan, serving as a fundamental reference for the design of future offshore wind turbine systems.
Dynamic Analysis of a Novel Floating Wind Turbine and Fish Cage Combined System
Authors: Chen Feng , Li Jinghui , Deng Shi , Liu Xuping , Zhang Fafu
Published: August 2024

In recent years, the combined floating offshore wind turbine and fish cage has garnered significant attention as a novel form of clean energy infrastructure. In this study, a novel combined floating offshore wind turbine and fish cage structure was proposed. A three-dimensional diffraction/radiation analysis was performed in the frequency-domain using the WADAM program to compute hydrodynamic coefficients, such as added mass, radiation damping, first-order wave exciting forces, wave drift force coefficients, and motion. Additionally, second-order difference-frequency wave forces were calculated using the Newman approximation method. Time domain analysis was carried out using ORCAFLEX. The results of frequency domain analysis, including hydrodynamic coefficients (potential added mass and damping), transfer functions of the 1st and 2nd order wave loads. were substituted into the time domain model. In the ORCAFLEX program, full coupled motion analysis was conducted for wind-wave-current operation and extreme environmental conditions of the combined system. For the wind loads, a decoupled analysis method was applied, with the wind turbine tower base loads as input loads for the lower floating foundation. The analysis also included an assessment of the global motion, accelerations, and heel angles for the semi-submersible platform. The results indicate that the floating offshore wind turbine meets the requirements with a maximum inclination of less than 9 deg under extreme conditions, the maximum inclination in the operation condition meets the requirement less than 5 deg. the maximum acceleration in the extreme condition meets the requirement less than 0.6 g. The maximum acceleration in the operation condition meets the requirement less than 0.3 g. There is no green water phenomenon on the floating wind turbine system. The novel combined system exhibits favorable motion performance and can serve as a reference for engineering practice.
Position Loss Incidents on DP Class 3 Mobile Offshore Drilling Units on the Norwegian Continental Shelf
Authors: Chen Haibo , Reinås Lorents , Garlid Stian , Nygård Bjørn , Hasund Nils
Published: August 2024

This paper presents a study to collect and analyze position loss incidents on dynamically positioned (DP) mobile offshore drilling units (MODUs) on the Norwegian Continental Shelf (NCS). These MODUs are of DP class 3 according to the requirements from the Norwegian Petroleum Safety Authority (PSA) and perform offshore operations with major accident risk potentials if position loss occurs. A definition of position loss is formulated in this study with considerations of capability and excursion. A method for position loss incident data collection and analyses is developed. Twenty-six (26) DP class 3 MODUs have worked on the NCS from 2000 to 2022. Among them, 31 position loss incidents were reported. Position loss incidents and associated DP operational time data are collected and estimated from multiple public sources and several databases in Equinor. Position loss scenarios and their common patterns of event development are analyzed. A historical frequency of position loss for DP class 3 MODUs on the NCS is derived, and uncertainties are discussed. The results in this paper provide useful knowledge of position loss incidents and insight into the safety of DP operations on MODUs on the NCS.
Study on Failure Modes and Ultimate Strength of Stiffened Panels in Large Cruise Ships
Authors: Zhang Zheng , Wu Haolong , Liu Xiang , Deng Hui , Gan Jin , Wu Weiguo
Published: August 2024

In response to the demand for structural lightweight design in large cruise ships, the geometric parameters of the materials used in their construction differ significantly from those used in traditional vessels. Traditional empirical formulas offer limited accuracy in assessing the ultimate strength of stiffened panels. As a result, there is a need to investigate the impact of failure modes on the ultimate load-carrying capacity of such stiffened panels and to propose a predictive method for evaluating their ultimate load-carrying capacity. To explore the influence of failure modes on the ultimate strength of stiffened panels, and to propose a method for predicting the ultimate strength of stiffened panels. Using the nonlinear finite element method, the model of a typical hull stiffened panel is analyzed. Considering the two main influencing factors of reinforcement slenderness ratio and deck slenderness ratio, the failure mechanism of the stiffened panel is analyzed, and the influence rules of the deck slenderness ratio and reinforcement compliance on the ultimate strength of the stiffened panel under different failure modes are clarified, and different failure modes are proposed. Empirical formulas for the ultimate load-carrying capacity of stiffened panels under failure modes. When the slenderness ratio of the deck is constant, with the increase of the slenderness ratio of the reinforcement, the failure mode of the stiffened panel changes from the local buckling of the panel and the reinforcement to the local buckling of the panel, and finally to the overall beam-column of the stiffened panel buckling. When the panel width is low, the failure mode of the stiffened panel will change from beam-column buckling to panel buckling with the increase of the reinforcement height, and when the panel width is large, the failure mode of the stiffened panel with different reinforcement heights Both are panel buckling. At the same time, under different failure modes, the load-displacement curves of the stiffened panels also show different trends. The quantitative relationship between the slenderness ratio of the stiffener and the slenderness ratio of the deck will lead to different failure modes of the stiffened panels. At this point, the impact of these two factors on the ultimate strength of the stiffened panels will diverge. During the design phase, it is imperative to align the stiffness of the reinforcement with that of the deck, thus preventing a scenario where material utilization becomes excessively inefficient.
Research on Failure Modes Converting Method and Identification Method of Autonomous Navigation Equipments Based on Knowledge Graphs
Authors: Kang Jichuan , Zhang Weijie , Zhang Zizhao , Li Mingxin
Published: August 2024

To solve the problem of insufficient real data of autonomous navigation equipment, this paper extracts the failure causes of equipment by constructing a knowledge graph and converting human errors into equipment errors. Firstly, this paper searches relevant websites to obtain the collision accident investigation reports as source data. Web crawlers are applied to get the report that compliance with keywords is efficient. After conversion and filtering operations, the target files are filtered out and they are then transformed into structured data. Text annotation is introduced to process data for entity extraction and relation extraction, and to get an exact data set. A knowledge graph in terms of failure modes of normal vessels is established based on the extracting results, which serves as a knowledge base to support the subsequent work. This step takes failure cases in plain text form and organizes them into a structured, visual form that can be easily retrieved to summarize the main human errors of conventional ships’ collisions. A convert model is created to convert human errors to device errors of autonomous vessels. Typical failure modes identification of the autonomous navigation equipment is performed through FMEA to clarify the critical components and their potential failure modes.
The Field Test of a Shallow-Water Mooring System for FOWT Using Nylon Synthetic Fiber Ropes
Authors: Kamizawa Ken , Yoshimoto Haruki , Chujo Toshiki
Published: August 2024

Japan Marine United Corporation (JMU) are currently developing substructures and mooring systems for floating offshore wind turbines (FOWT) With the cooperation of National Maritime Research Institute. Cost reduction technology is very important for the large-scale commercialization of FOWTs, and a low-cost mooring system as well as a floating foundation are required.

Among these, mooring systems using nylon ropes have been attracting attention in recent years because they can reduce mooring costs in shallow waters. However, nylon rope has little experience in mooring large offshore structures. Therefore, there is insufficient durability data of nylon ropes under actual sea conditions.

The authors conducted a field test of a mooring system using nylon ropes in shallow water to verify the durability of nylon ropes. The 1/9th scale semi-submersible floating structure designed for FOWT is moored, and the mooring system consists of two taut mooring lines and two catenary mooring lines, totaling four lines, was set up at a depth of about 20 m off Akita Prefecture in Japan for about one-year test. This paper introduces the field tests conducted and presents the results of the comparison between the design and measured values, as well as the results of the evaluation of the durability of the nylon rope.
The Spatiotemporal Distribution of Heavy Metals and Their Response to Physicochemical Parameters of Water Quality in the Yangtze River Estuary
Authors: Zou Yuwen , Lou Sha , Zhang Zhirui , Liu Shuguang , Zhou Feng
Published: August 2024

Heavy metals present a significant risk to the safety of water environments and aquatic ecosystems due to their resistance to degradation and high levels of toxicity. Field investigations were conducted in this study in Yangtze River Estuary in July, 2021 and February, 2022. Seven sampling locations were selected at Liu He Kou (LHK), Shi Dong Kou (SDK), Wu Song Kou (WSK), Zhu Yuan (ZY), San Jia Gang (SJG), Chao Yang Nong Chang (CYNC), Da Zhi He (DZH). Fourteen sediment samples and fourteen water samples were collected. The heavy metal concentrations (Cr, Ni, Cu, Pb, Zn, Cd) and physicochemical parameters of water quality including Temperature (Temp), pH, Oxygen redox potential (ORP), Dissolved oxygen (DO), Electrical conductivity (EC), Electrical resistivity (RES), Total dissolved solids (TDS), Salinity (SAL) and turbidity (NTU) were investigated. The concentrations of most heavy metals were higher in July compared to February, and exhibited spatial heterogeneity. Principal component analysis (PCA) was used to determine the sources of heavy metals. Steel industry wastewater, domestic and industrial sewage, shipping and vessel emissions were the main sources of heavy metals. Spearman correlation analysis identified Temp, pH, and DO as the key physicochemical parameters of water quality, exhibiting the strongest correlation with heavy metal concentrations in sediment and water samples. These results can provide scientific basis and guidance for the water environmental management of the Yangtze River estuary, making a significant contribution to the protection of water quality and health in this region.
Load Mapping Algorithm of Submerged Floating Tunnels Under Different Wave Conditions
Authors: Liao Haiyan , Wang Baoxuan , Sheng Fangyuan , Liang Xu
Published: August 2024

The submerged floating tunnel is a new type of traffic structure that can cross the deep as well as long channels. Most of the current studies on submerged floating tunnels are based on highly simplified beam models. Although the use of beam element modeling is convenient for analysis, the beam model of submerged floating tunnels is limited to longitudinal. In order to design the sections reasonably, it is required to provide information about the member forces in the transverse direction. So, it needs to conduct a more detailed three-dimensional finite element analysis of the submerged floating tunnels’ structure system under the action of waves and currents. This paper proposes a set of load mapping algorithms for submerged floating tunnels, which maps the load from the beam finite element model to the shell finite element model, to analyze the three-dimensional structure of submerged floating tunnels in the time domain. In this study, it is the first time to realize full load mapping in the field of submerged floating tunnels. According to the load mapping algorithm, this paper calculates the response of a submerged floating tunnel under different wave conditions, which provides a reference for the actual design of submerged floating tunnels.
Computer Simulation of Laboratory Experiments With Two-Phase Slug Flow Induced Oscillations on a Submerged Flexible Catenary Pipe
Authors: Cesar de Oliveira Trigo Caio , Kazuyuki Morooka Celso , Nascimento Bordalo Sergio , Yamamoto Marcio
Published: August 2024

Experiments were conducted for the oscillations of a submersed suspended flexible pipe ex]cited by the internal two-phase slug flow of liquid and gas. Computer simulations were carried out with proprietary numerical tools to evaluate suitable modeling methods for pipe oscillations. The experiment was conducted with a pipe set in a catenary configuration inside a two meters deep water tank. Water and air were injected into the pipe at its bottom end with various flow rate combinations, forming horizontal slug flow patterns. The slug two-phase flow generated intermittent loads on the pipe promoting its oscillation. At the same time, cameras monitored the dynamic response of the pipe. Processing the video images frames generated time-history records of the movement of the pipe. In this paper, computer simulations were performed to determine the frequencies and amplitudes of the pipe oscillations, which were compared to those from the experiment. A proper scaling up of experimental results with the support of computer simulations should be helpful for the analysis and design of suspended risers employed in offshore petroleum platforms carrying up oil and gas from petroleum reservoir wells to floating production facilities.
A Numerical Investigation on Collapse Modes of Stiffened Plates Under Combined Dynamic Loads
Authors: Guo Guangyu , Cui Jinju , Wang Deyu
Published: August 2024

In actual navigation environments, hull structures are subjected to multiple combined loads, in many cases, such as hogging and slamming, transient and impactive load components occur frequently. Accordingly, the collapse behavior and ultimate strength of ship structures under combined dynamic load cases have received considerable interest. As the basic member of ship structures, stiffened plates contribute to the loading capacity and the ultimate strength of the hull structure. Thus, it is necessary to further investigate the mechanical properties and ultimate strengths of stiffened plates subjected to combined dynamic loads, including lateral pressure, longitudinal load and transversal compression. In this study, a series of numerical models of stiffened plates are designed according to recommendations of ISSC. Then, with the help of nonlinear finite element method (NFEM), the structural responses and deformation behaviors of stiffened plates subjected to combined dynamic in-plane and out-of-plane loads are simulated. With the help of NFEM, the collapse modes of the stiffened plates under combined dynamic loading cases are researched, and a further explanation of the structural response of stiffened plates under combined dynamic load cases is derived.