bluuebunny/crossref_metadata_2025 huggingface dataset:
Bayesian Updating by Utilization of Bayesian Optimization for Estimation of VIV Load Parameters
Authors: Leira Bernt J. , Andersen Martin L. , Wu Jie , Sævik Svein
Published: August 2024

The purpose of the present paper is to summarize the findings from Bayesian updating methods applied to VIV cross-flow response. The Bayesian updating approach is formulated in terms of a prior statistical model for the quantities of interest (i.e. two parameters entering the VIV load model in the time domain for the present case), and subsequently this statistical model is modified based on a set of available observations. The statistical properties of the observation for a given set of values of the quantities of interest are represented by the so-called likelihood function. By combining the prior model with the likelihood function, the resulting posterior statistical model is obtained.

An experiment with a rigid pendulum subjected to pure cross-flow VIV is analysed. The cross-flow (lift) coefficient and the nondimensional center frequency of the lock-in region are represented as random variables. The following parameter studies are performed: (i) Application of different types of likelihood functions corresponding to different inherent “measurement noise levels” (ii) Introducing the exponent of the Posterior pdf as an objective function rather than the pdf itself (iii) Application of Bayesian optimization (by utilization of Gaussian Process Regression/Kriging) for identification of the extremal point of the objective function. A main objective is to clarify the relationship between the applied Prior model/likelihood function and the so-called Bayesian optimization scheme in order to identify the most likely values of the input parameters for a given set of measured data..
Challenges and Impacts of Severe Slugging Fatigue on SLWR Design
Authors: Vieira dos Santos Junior Joel , Ferreira Senra Stael , Reis Guilherme Paulo Vitor , Massae Hayashi Lucila , Pereira Resende Rodrigo , Gonçalves Moreira Dinis Marcelo , Donni de Sena Bernardo
Published: August 2024

This paper aims to present the impacts of severe slugging over Production SLWR design in a Pre-salt of Santos Basin project. This design criteria of slugging fatigue in steel pipe risers is not frequently used, once subsea systems are, whenever possible, designed to minimize the risk of operating under this regime. However, the subsea layout of some recent projects, with long descending flowlines towards rises basis, increases the risk of occurrence of this phenomenon, mainly under low flow rates, typical of field late life. While hydrodynamic slugging might induce high frequency riser response, severe slugging (terrain induced slug) is characterized by a much lower frequency (but higher amplitude), which leads to a much different riser behavior. Different conditions were assessed, comprising critical scenarios with satellite wells and wells connected to a high-pressure gas/liquid subsea separator (HISEP™), which changes the liquid holdup along the flowline, favoring severe slugging occurrence.

In steel pipe riser design, fatigue represents an important structural failure mode when accounting for all sources of cyclical loads that are expected during operational lifetime, such as: wave-induced motions, both current and heave-induced VIV and, lastly, internal fluid flow loads. This paper will focus on calculating severe slugging damage while performing a comparison among all sources’ percentual contribution to total damage in this studied scenario. This comparison shows that severe slugging heavily contributes to fatigue damage at a specific region located at the Touchdown Zone (TDZ). This critical region suffers mostly from internal fluid weight variation along the riser, which leads to low frequency but high amplitude stress variation.

The OLGA™ dynamic multiphase flow simulator [1] was adopted in order to model the subsea slugging flow and generate the required data for riser analysis, that is, pressure, fluid density, and velocity profiles along the riser pipe, during at least an entire slug cycle, allowing to characterize the fluctuations due to this flow. Afterward, time-domain structural analyses were performed with inhouse Petrobras’ riser analysis software Anflex [2] by having the above-mentioned profiles utilized as input data.

The state of practice for riser slugging fatigue analysis is not yet fully established. Even in guidance with industry standards, different practices and assessment methodologies between operators and projects can be found. It could be observed that uncertainties in reservoir parameters, premises on definition of flow parameters as the multiphase and slugging flow itself, design load cases with respective probabilities of time operation under this regimen and methodology adopted for riser dynamics modeling were crucial, representing Petrobras’ ongoing efforts to establish a robust and safe SLWR riser design.
Unsupervised Machine Learning for Well Log Depth Alignment
Authors: Acharya Sushil , Fabian Karl
Published: August 2024

Depth alignment as a prerequisite for subsurface geology interpretation aims to match signals of two logs from the same well to a common depth scale. Here, three consecutive unsupervised machine-learning techniques are applied to achieve this goal. First, data vectors are reduced through pre-processing with PCA and autoencoder methods, and clustered by K-means with K-means++ initialization. In a second step, corresponding cluster boundaries are identified to globally align lithologic units. This assumes that cluster boundaries represent physical changes in lithology, without direct lithological interpretation. The third step uses cross-correlation to obtain the final log alignment. Additional linear or non-linear interpolation between matching boundaries is sufficient to align well logs. Performance and accuracy of various techniques are compared by visual inspection and manually determined boundaries. Reducing data dimension with an autoencoder and K-means clustering performed best among tested methods. The study suggests that cluster-based methods can automate depth alignment of well logs without human intervention.
Analysis of Installation Time for Floating Offshore Wind Farms
Authors: Hasumi Tomohiro , Yokoi Takeshi , Haneda Ken , Chujo Toshiki , Fujiwara Toshifumi
Published: August 2024

It is essential to calculate installation time of a Floating Offshore Wind Farm (FOWF) by summarizing the process based on actual projects to estimate the offshore installation cost more precisely than before. The objective of this paper is to propose an installation time estimation model for FOWF that incorporates installation time for wind turbine mounting and submarine cables by expanding the installation time model of floating offshore wind turbine (FOWT), proposed previously. The results indicate that for the pre-anchoring process, loading time, and total time of pre-installation time per mooring line and tensile testing time per anchor in Japan are about ten, and five times longer, respectively, than those of Europe. As for submarine cables, time for connecting one-side of the riser cable to a floater, and time for trenching cables in Japan are six, and eight times longer, respectively, than the corresponding times in Europe. The reduction of installation time of the anchor-sharing technology is estimated to be 24% assuming a FOWF model. We conclude that a proposed model is validated reproducing the actual offshore installation and provides a common framework of the estimation of installation time of FOWF.
Preliminary Experimental Results of a Temporal Planning-Based System for Autonomous Inspection Using UGV
Authors: Hinostroza M. A. , Lekkas Anastasios M. , de Jonge Christian , Ivar Sagatun Svein , Luteberget Bjørnar , Transeth Aksel
Published: August 2024

Inspection and maintenance (IM) operations in offshore oil & gas platforms involve significant challenges due to the harsh conditions in such remote environments. Therefore, there is a need for robotic solutions that can accomplish IM missions autonomously, a goal that has become more feasible in the last years due to advances in instrumentation, perception and artificial intelligence (AI). In this paper, we present initial experimental results of the Taurob unmanned ground vehicle (UGV) performing autonomous inspection at Equinor’s K-Lab Test Centre, located in Haugesund, Norway. The proposed solution employs the simultaneous task planning (STP) algorithm, introduced by Furelos-Blanco in [1], as a high-level action planner. STP can take into account durative high-level actions, such as “visit a specific location”, “inspect a sensor”, or “take a picture of a specified component” and, in addition, can replan online in case of events such as low battery status, or the need to revisit a location. Communication with the robot is achieved via Equinor’s Integration and Supervisory Control of Autonomous Robots (ISAR) framework, which guarantees a fast and secure wi-fi connection. Two types of experiments were carried out: 1) A basic inspection round, which involves visiting a sequence of predefined waypoints; 2) A replanning scenario, which also takes into account the battery status. Our preliminary tests, where fast and efficient plans were computed and executed in real time, including replanning, showed that connecting the guidance and control system of a UGV with a high-level planner like STP is a promising approach to increased autonomy in IM missions.
Underwater Absorption Performance of a New Rubber-Based Acoustic Absorber Embedded With Composite Scatter
Authors: Wu Guanghua , Han Wei , Li Tianyun , Zhu Xiang
Published: August 2024

The acoustic impedance of rubber matches well with that of water, which makes rubber have a good performance for absorbing underwater noise. However, the effective absorption of underwater low-frequency sound is still a challenge. To solve the problem, a new rubber-based acoustic structure is proposed. Based on the coupling effect between cavity resonance and local resonance, the structure can effectively control the propagation of elastic waves. The absorption coefficient and displacement field distributions of the cavity-type structure, local resonant structure, and the proposed structure are compared to explain the energy loss mechanism. The material parameters of the proposed structure, such as the density of the inner hard core, and elastic modulus of soft rubber and rubber matrix, are changed to investigate the influence of material on absorption performance. In addition, the geometry shape of the cavity is varied, cone cavity and circular truncated cone cavity are introduced to analyze the influence of shape on absorption performance. The results show that the existence of the cavity enlarges the interaction effect between the hard core and soft rubber and increases the displacement of the rubber matrix in the vertical direction. The reduction of the elastic modulus of soft rubber and the increase of density of the hard core can improve the absorption coefficient. The cavity should be designed to be gradient to enhance the coupling effect to dissipate underwater low-frequency noise.
An Experimental Study on Effects of Aerodynamic Damping of a 5MW Semi-Submersible Floating Vertical Axis Wind Turbine
Authors: Jiang Yingying , Cheng Zhengshun , Chen Peng , Liu Lei , Yang Lijun , Xiao Longfei
Published: August 2024

Floating vertical-axis wind turbines (FVAWTs) offer certain advantages over floating horizontal-axis wind turbines (HAWTs), particularly in terms of the potential to lower the cost of energy. In this study, a 5MW FVAWT concept with three straight blades and a semi-submersible hull deployed in a water depth of 42 m was presented. In addition, the experimental setup is introduced, and calibration tests are also performed to validate the physical model system. The aerodynamic damping in surge and pitch motions was measured by comparing the decay experimental results with and without wind loads. Following this, wind/wave basin model tests with a scale ratio of 1/50 were conducted to explore the effect of aerodynamic damping on the motion characteristics of this turbine concept. Results indicate that aerodynamic damping can suppress the fluctuations of the platform’s surge and pitch motion at their respective resonance frequencies and tends to increase with wind speed at below-rated wind speed. Additionally, surge-induced and pitch-induced aerodynamic damping hardly affect the wave frequency response. Meanwhile, the surge natural frequency is substantially altered due to the wind loads. This study contributes to providing valuable insights into the aerodynamic damping of floating VAWTs.
A Comparison of Optimization Methods Applied to Surrogate-Based Optimization in Wind Farm Yaw Control
Authors: Tu Yu , Zhang Kai , Chen Yaoran , Han Zhaolong , Cao Yong , Zhou Dai
Published: August 2024

In wind farms, wake effects among turbines hinder optimal power generation, making collective yaw control crucial for efficiency. The accurate calculation of power generation for large-scale wind farm is time consuming and computationally expensive. To address this challenge, Surrogate-Based Optimization (SBO) emerges as an effective tool in the yaw optimization. In the design of experiment, wake effects are simulated by Gauss-Curl Hybrid (GCH) model in FLORIS. Based on the limited dataset, SBO utilizes surrogate models to approximate the relationship between yaw angles and total power in the entire design space, enabling a more efficient approach to yaw optimization. The selection of optimization algorithms within the SBO framework becomes pivotal, with the recognition that gradient-free methods excel in scenarios with multiple local minima, while gradient-based methods offer advantages in high-dimensional problems inherent in large-scale wind farms. This paper compares three optimization algorithms — Sequential Least Squares Quadratic Programming (SLSQP), Differential Evolution (DE), and Particle Swarm Optimization (PSO) — in the context of wind farm yaw optimization. Three yaw control case studies are presented, offering a comprehensive comparison of the strengths and limitations of the optimization algorithms. Results show that the gradient-free methods, balancing computational cost and accuracy, stand out as the preferred choice for wind farm yaw optimization. Despite the low-fidelity engineering wake model used in the current study, the SBO framework is also compatible with the higher-fidelity wind turbine models. This capability lays the foundation for optimizing yaw control under more realistic conditions.
Numerical Modelling of Novel Floating Offshore Wind Turbine Concept
Authors: Conway Oisín , Connolly Aengus , Leen Seán
Published: August 2024

This paper describes the numerical modelling of a novel floating offshore wind turbine (FOWT), a next-generation concept which aims to combine the best features of traditional spar and semi-submersible platforms, coupled with a modular design for ease of manufacturing and assembly. The study was conducted as part of Phase IV of OC6 (Offshore Code Comparison Collaboration, Continued, with Correlation and unCertainty), an international research project focused on verifying and validating numerical modelling tools used in the analysis of floating offshore wind systems. In this study, numerical modelling is performed using a mid-fidelity tool which performs fully coupled aero-hydro-servo-elastic simulations in the time domain. The simulation model is based on a full-scale demonstrator version of the FOWT concept hosting a 3.6 MW turbine, which has been deployed offshore and is fully operational since 2021. Results from the numerical model are validated by comparisons with experimental data from a 1:43 Froude-scale test performed in the University of Maine’s Ocean Engineering Laboratory. Beginning with fundamental test cases, including static equilibrium, surge offsets, and free-decay simulations, the scenarios advance in complexity to include wind-only loads, wave-only forces, and a combination of wind and wave conditions. Key parameters of interest include aerodynamic forces, motions of the floating support structure, tower base moments, mooring line tensions, and keel line tensions. Overall, the results show a strong correlation with the empirical data. This paper complements the research work undertaken in OC6 Phase IV, further substantiating its insights into the dynamic responses of floating offshore wind turbines.
Tsunami Actual Water Experience Museums
Authors: Hamada Eigai
Published: August 2024

The NPO Takurou (Chief Director : Eigai Hamada) is planning to construct museums where visitors can learn about how terrifying tsunamis are through actual water demonstrations and about measures to prevent tsunami disasters. The museums will provide actual tsunami-like water flow at a safe height so that visitors can experience the possible effects of tsunamis, such as their legs being directly exposed to rushing water and falling down into the water, so they can see how easy it would be to drown even in shallow water. The museums will also provide information (videos, photos, etc.) of previous tsunami disasters, such as that during the Great East Japan Earthquake and Tsunami of 2011, so that visitors can feel the fear of an actual tsunami. Also, the museums will provide lectures which teach about updated tsunami disaster mitigation measures, how to prevent tsunami disasters, and how to protect residents and their communities from tsunamis.

For visitors who are afraid to experience actual water flow or do not want to watch videos of previous tsunami disasters, medical staff will consult with the visitors and advise them on which exhibits to skip.

These Tsunami Actual Water Experience Museums will be established in two areas in Japan subject to tsunamis (i.e., Kuroshio in Kochi Prefecture and Taro in Miyako in Iwate Prefecture). The planned museums will revitalize the local communities, which are suffering under the threat of tsunamis and whose populations are declining as a result.
Generation of Extreme Waves With Partial Energy Focusing in Random Seas
Authors: Cui Junnan , Feng Xingya , Chen Qunbin
Published: August 2024

In recent years, extreme waves, which appear from nowhere with extremely large wave height in the ocean, have attracted extensive attention and research in academic and engineering fields. A simple linear model proposed by Tromans et al.–NewWave theory[2], has been widely used to explain the occurrence of extreme waves. The NewWave model requires that all frequency components in a random seastate focus at a specific time and location to generate a large wave group, which however is unlikely to happen naturally. In this work, we consider an otherwise more realistic condition where wave energies are only partially focused. Focused wave groups are generated by partial energy focusing using a JONSWAP wave spectrum and their characteristics are studied. The effects of different frequency components and bandwidths on the characteristics of wave groups are investigated. A high order spectral (HOS) model, which is validated by physical experiments, is utilized to simulate the propagation of partial focusing waves. Both second-order and fifth-order simulations are carried out to understand the influence of modulation instability. The nonlinear characteristics of partial focusing waves during its propagation are studied simultaneously. Overall, this work provides some new insights into the mechanism of formation of extreme waves.
Effects of Vertical Distance on Performance and Wake Characteristics of Two Offshore Wind Turbines With Various Lateral Distances
Authors: Li Haolong , Liu Yuanchuan , Chang Shuang
Published: August 2024

Offshore wind turbines are mostly arranged in wind farms in the form of arrays. The aerodynamic performance of downstream wind turbines decreases significantly due to the influence of upstream wind turbine wake. In addition to the streamwise distance, lateral and vertical distances can be imposed for adjacent wind turbines to achieve performance improvement of downstream turbines. In this paper, a large eddy simulation method based on the open source CFD platform OpenFOAM is applied to simulate the turbine blades in conjunction with an actuator line technique. The effect of vertical distance on performance and wake characteristics of two tandem offshore wind turbines in the presence of lateral distance is investigated.

The results show that both lateral and vertical distances can improve the performance of the downstream turbine. When turbines operate at the rated condition, imposing lateral distance improves the power output to a larger extent than raising the hub height of the downstream turbine, although not as much as raising upstream turbine. However, for the above rated condition, the impacts of turbine arrangement on performance improvement of the downstream turbine are opposite to the results obtained for the rated condition, and the increase in rotor power is considerably reduced. Wake characteristics of both turbines are analyzed to support the results.
Experimental Data and Modelling of Cable and Pipe Axial Friction on a Rocky Seabed
Authors: Griffiths Terry , Draper Scott , An Hongwei , Cheng Liang , Fogliani Antonino , White David
Published: August 2024

As part of recent research into the on-bottom stability of subsea pipes and cables on rocky seabeds, a set of physical model tests have been performed investigating the effective lateral and axial friction factors. The lateral friction factor experience led to a new model for the effective friction which scales up the cable-rock interface friction coefficient allowing for the roughness of the rocky surface that the cable moves over.

This paper presents the results of axial friction testing which showed a similar enhancement of friction linked to the roughness of the rock surface in a different way. These test results demonstrated that the axial resistance could also be many times greater than the interface friction force when the characteristic rock particle sizes are comparable to or greater than the cable diameter. This arises from a ‘wedging’ action that leads to inclined contact between the cable and the rock, which causes an increase in the sliding friction. Data and modelling of this behaviour is provided to assist application of these results to design.
Enhancing Offshore Wind Farm Met-Ocean Data Accessibility: A Machine Learning Approach With Satellite-Derived Wave Measurements in the Celtic Sea
Authors: Whistler Sophie , Ashton Ian G. C. , Pillai Ajit C. , Quartly Graham D.
Published: August 2024

Marine operations are a significant expense for offshore wind farms, representing up to one third of total project costs. An improved understanding of the variation of met-ocean conditions across a wind farm site offers the potential to reduce weather downtime and associated costs. This work employs a machine learning approach utilising a surrogate wave model trained on the relationship between the wave conditions at discrete measurement locations to wave conditions across the entire model domain. The surrogate model can then be run with real-time data inputs from the discrete measurement locations to provide a spatial dataset for waves, without the high computational power needed to run the physics-based wave model itself. This new method enhances the accessibility of met-ocean data to allow more informed decision making for the installation, operation, and maintenance of offshore wind farms.

The approach has already proven successful with fixed measurement buoys, and work is ongoing to adapt the modelling framework to use satellite-derived wave data as an input. With freely available global coverage, satellite data is a useful complementary data source to wave buoy data. Several Earth Observation satellite missions host radar altimeters that report significant wave height along the satellite’s ground track. The first step towards utilising radar altimeter data with the machine learning framework is assessing the impact of using only significant wave height data as measurement inputs. This paper compares the model outputs from running the model with wave height, period, and direction data, and with wave height data only. The results show that running the model with wave height data only produces a small reduction in the accuracy of output wave predictions in coastal areas.
Time Domain Prediction of Combined CF and IL VIV Responses Under Constant Currents
Authors: Wu Jie , Yin Decao , Lie Halvor , Passano Elizabeth , Baarholm Gro Sagli , Sævik Svein
Published: August 2024

The slender marine structure (e.g., deep water riser systems) subjected to vortex induced vibrations (VIV) can oscillate simultaneously in both cross-flow (CF) and in-line (IL) direction relative to the flow direction. The IL response is important as it may contribute to fatigue damage to the same order of magnitude as the CF responses for high mode responses. A combined CF and IL load model is also required for prediction of VIV responses in more complex flow conditions. The time domain VIV prediction load model has been extended to include an IL VIV load term. The present study aims to validate the latest combined CF and IL load model using laboratory tests and evaluate its limitations. The validation results showed that the averaged spatial and temporal energy transfer process between fluid and structure is sufficiently described by the load model. The time domain VIV load model is able to obtain reasonable prediction of key VIV responses, including curvature, frequency, fatigue damage, higher harmonic responses in both CF and IL directions as well as drag amplification in one single non-linear time domain analysis. This overcomes some of the limitations in the present frequency prediction models.
Mooring System ULS Analysis Based on Empirical QTFs of Wave Drift Loads
Authors: Fonseca Nuno , Tahchiev Galin , Rogne Øyvind Ygre
Published: August 2024

Ultimate limit state (ULS) analysis for the mooring system of floating structures is performed for the most severe seastate conditions. For many structures, horizontal wave drift loads and related slow drift oscillations are simultaneously the environmental component with the largest contribution to the extreme line loads and the component with the largest uncertainty in numerical predictions. It is acknowledged that state-of-the-art hydrodynamic design analysis tools, namely radiation/diffraction potential flow codes, tend to underestimate wave drift loads in severe seastates for floating structures with large waterplane area. This is often the case for floating, production, storage and offloading vessels (FPSOs).

While correction methods have been proposed recently, this paper presents a different approach. The proposal is to use empirical quadratic transfer functions (QTFs) of horizontal wave drift loads directly in the mooring analysis time domain simulations. The empirical QTFs are identified from model test data in severe seastates with current by a second order signal analysis technique known as cross bi-spectral analysis.

The paper describes the method and validates with a case study consisting of a FPSO operating in the North Sea. Standard hydrodynamic analysis tools provide correct first order motions in extreme seastates with current, as compared to model test data. However, it significantly underestimates the wave drift loads and the related low frequency (LF) horizontal vessel motions. Use of empirical QTFs significantly improve the LF motion predictions, both in terms of mean offset and in terms of LF standard deviation and energy spectra. Furthermore, the limitations of Newman’s approximation versus use of full QTFs are highlighted. The later provides a much better phasing of the LF motions and also better prediction of the LF peaks.
Optimization of CO2 Water-Gas Alternating Injection-Production Parameters in Low Permeability Reservoirs
Authors: Tian Leng , Huang Wen-kui , Tang Chuan-yi , Tian Hui , Peng Long , Li Mingliang
Published: August 2024

The reservoir heterogeneity of low permeability reservoir is strong, and it is easy to form fingering phenomenon in the process of continuous water injection or gas injection development. The use of CO2 water-gas alternation technology can not only make full use of the advantages of CO2 flooding, but also effectively reduce the fingering phenomenon and improve the development effect. However, due to the unreasonable injection rate, slug size, gas-water ratio and other parameters, the CO2 breakthrough in the production well is too early or the expected development effect is not achieved. Therefore, it is necessary to study the optimization of CO2 water-gas alternating injection-production parameters in low permeability reservoirs. Based on the actual formation and fluid characteristics of A oilfield, the reservoir numerical simulation method was used to optimize the injection-production parameters of CO2 water-gas alternating flooding in this area. The results show that the development effect is the best when the water injection is first followed by gas injection, the gas injection rate is 0.08 PV / year, the water-gas ratio is 1:2, and the alternating period is 3 months. The recovery rate is 42.15 %. The scheme is 13.67 % higher than the pure water flooding scheme and 4.89 % higher than the pure gas flooding. The research results have certain reference significance for improving the mining effect of A oilfield.
Physics-Informed Neural Networks for Flow-Induced Vibration Prediction of a Subsea Pipeline
Authors: Yin Guang , Janocha Marek Jan , Ong Muk Chen
Published: August 2024

Flow-induced vibration (FIV) is a common phenomenon in ocean engineering for subsea structures with circular-shaped cross sections. A large amount of computational resources or experimental efforts are required to predict or measure the complicated motions and flow field surrounding a circular cylinder undergoing VIV. Physics-informed neural networks (PINNs) are powerful deep learning techniques for solving governing partial differential equations (PDEs) of dynamic systems as an alternative to complex numerical methods. In the present study, a framework is built employing PINNs for solving the Navier-Stokes equations to predict flows past an FIV cylinder by using sparsely distributed spatiotemporal data inside the domain. The training process involves minimizing the supervised loss of flow data at these sparse points and the residuals of the governing PDEs. For the training of the PINN model, a moving frame around an FIV cylinder is used to collect the training flow data from two-dimensional direct numerical simulation results at a low Reynolds number. The structural displacements of the cylinder are also implemented in the residuals of the equations of the developed PINN. The performance of the PINN is evaluated by comparing the predicted contours of the surrounding flow velocities with the training data. The hydrodynamic forces prediction is achieved using the PINN-obtained flow field predictions combined with the force partitioning method.
Comparative Study of Mooring Type Effect On Offloading Operability of Near-Shore FLNG With Side-By-Side Moored LNG Carrier in Shallow Water Depth
Authors: Kim Mun Sung , Kim Bo Hee , Yuck Rae Hyoung , Lee Yong Chul , Heo Jae Kyung
Published: August 2024

Recently, the FLNG projects have been developed for the LNG production at near shore field with shallow water depth. For the permanent mooring of FLNG in this field, several mooring types such as Jetty, Yoke, fixed structure (strut) and spread mooring are considered up to now. In the development of near shore (NS) FLNG projects, one of the key issue is safe ship-to-ship (STS) offloading operation for the transfer of LNG cargo to shuttle LNG carrier through marine loading arm (MLA) with side-by-side (SBS) mooring arrangement. In this paper, a numerical comparison of the side-by-side offloading operability of NS FLNG with the different mooring system is performed for the near shore site.

In order to perform the comparison, two permanent mooring types for the fixed structure (strut) mooring and spread mooring system are designed for NS FLNG. For comprehensive SBS offloading operation comparison, numerical two-body motion simulation is carried out in frequency- and time-domain. As an environmental condition, the benign sea, such as North America or East/South Asia wind, wave and current data is applied for the study.

Based on numerical simulation results, offloading operability of near shore FLNG during STS operation, dynamic loads acting on the mooring lines and fenders as well as relative motion are compared. Generally, the maximum line tension, fender force and relative motions are under the limit criteria, however, the responses of SBS line tension are not similar in both cases. Throughout the comparative study, it is found that the offloading operability of NS FLNG is affected by the different mooring system types. In addition, there are needs of further study for precise hydrodynamic analysis for damping in sloped shallow water depth.
Efficient Design of Floating Offshore Wind Turbines
Authors: Sablok Anil , Koo Bonjun , Miliante Thiago
Published: August 2024

The offshore wind industry trend is towards larger floating wind turbines to lower the Levelized Cost of Energy (LCOE). It is more difficult to design, install, and maintain them. The challenges related to a large floating wind turbine design and analysis are to model and analyze in the time domain the fully coupled system that includes flexible turbine tower dynamics, rotor dynamics, and floating platform dynamics. Floating Offshore Wind Turbine (FOWT) analysis and design require more design load cases than oil and gas platforms due to the various wind turbine operating conditions. This takes a very long time and extends the engineering schedule significantly. To reduce time and make the design process efficient and accurate, a more automated design process and tools are required along with using High Performance Computing (HPC) resources.

The improved processes and tools developed for oil and gas production platforms have been improved and adapted to the design and analysis of FOWT for quick investigation of different design parameters and select an optimum design satisfying all the design criteria upfront and minimizing required design iterations which are normally not possible in a FOWT project due to long analysis and design time. Global response and improved structural analysis methodology compatible with HPC are used for efficient analysis and design of FOWT and associated mooring. The results show that the design cycle time is not only significantly reduced, but the estimation of full lifetime estimation of platform performance and energy production is more accurate. The tools developed can also be used as a digital twin for quick estimation of performance and conditioning.
A Novel Drag Anchor Design for Enhanced Penetrability and Holding Capacity
Authors: Zhang Youhu , Li Shuzhao , Wang Xiangyu , Wu Chuheng , Guo Peng , Lei Di
Published: August 2024

Drag anchor is an appealing anchoring solution for a variety of floating structures due to its high holding capacity ratios and relatively low cost for installation. The holding capacity of a drag anchor is to a large extent dictated by the penetration depth achieved during installation. In hard soils, such as sand and stiff clay, the penetration depth of the drag anchor is often limited to about one fluke length due to the large soil resistance encountered on the shank. In this paper, a novel single-shank anchor design that greatly reduces the soil resistance on the shank is proposed in the hope of improving its penetration depth and consequently the holding capacity. To verify the design assumption, a series of three-dimensional finite element simulations using the Coupled Eulerian-Lagrangian method are carried out. The results of the analyses in both sand and clay soils demonstrate superior penetrability and considerably improved holding capacity of the proposed single-shank anchor design.
Numerical Investigation on the Hydrodynamic Performance of High-Speed Displacement Vessel With Transom Hull Vane
Authors: Soma Gouthama Chary , R. Vijayakumar
Published: August 2024

A numerical analysis of the hydrodynamic performance of high-speed displacement vessels with and without Hull Vane (HV) is presented in the paper. A Hull Vane is an energy-saving device that is transversely fastened to the vessel’s transom bottom. The pressure differential is the primary reason for the vessel’s decreased pressure drag and trim. The Finite Volume approach employing a standard mesh was used to analyze the hull model utilizing a Hull Vane with various spans. Heave and pitch are the two degrees of freedom taken into account. The high-speed displacement vessel with and without a Hull Vane is subjected to model tests in calm water in the Department of Ocean Engineering’s current towing tank facility at the Indian Institute of Technology, Madras. The effects of span (Length of the HV has been discussed in this paper. The vessel’s performance is significantly influenced by the length of the Hull Vane and limited condition for span has been obtained. The study demonstrates a greater trim reduction due to the lift force produced by the hull vane at the stern of the vessel. The overall resistance coefficient has been decreased to 7%.
A Hybrid Deep Learning Approach to Predict Dynamic Mooring Tension of a Wave Energy Converter
Authors: Xu Sheng , Wang Shan , Guedes Soares Carlos
Published: August 2024

Enhancing the precision of short-term mooring tension prediction holds the key to bolstering safety measures within marine operations. In this study, a hybrid model which takes the advantages of convolutional neural networks (CNN) and gated recurrent units (GRU) is developed to predict dynamic mooring tension time series of a wave energy converter. The datasets used to train the hybrid model were collected from model tests conducted in a wave flume. The hybrid model is trained using motion responses of a wave energy converter. The study explores and discusses the impact of various factors on the performance of the hybrid GRU model, including the number of neurons, the choice of optimizer, and the number of dully connected layers. Optimal model parameters are determined through an assessment of error indexes. Once the optimum GRU model is determined, a hybrid model which consists of the CNN and the optimum model is proposed for predicting mooring tensions. To evaluate the effectiveness of the hybrid model, a comparison is made between its performance in dynamic mooring tension prediction and that of GRU. This research offers highlights the substantial potential of the proposed method in predicting mooring tensions for other offshore floating structures.
The SPAR Model: A New Paradigm for Multivariate Extremes. Application to Joint Distributions of Metocean Variables
Authors: Mackay E. B. L. , Murphy-Barltrop C. J. R. , Jonathan P.
Published: August 2024

This paper presents the application of a new multivariate extreme value model for the estimation of metocean variables. The model requires fewer assumptions about the forms of the margins and dependence structure compared to existing approaches, and provides a flexible and rigorous framework for modelling multi-variate extremes. The method involves a transformation of variables to polar coordinates. The tail of the radial variable is then modelled using the generalised Pareto distribution, with parameters conditional on angle, providing a natural extension of uni-variate theory to multivariate problems. The resulting model is referred to as the semi-parametric angular-radial (SPAR) model. We consider the estimation of the joint distributions of (1) wave height and wave period, and (2) wave height and wind speed. We show that the SPAR model provides a good fit to the observations in terms of both the marginal distributions and dependence structures. The use of the SPAR model for estimating long-term extreme responses of offshore structures is discussed, using some simple response functions for floating structures and an offshore wind turbine with monopile foundation. We show that the SPAR model is able to accurately reproduce response distributions, and provides a realistic quantification of uncertainty.
Comprehensive Evaluation and Optimization of Multilateral-Well Aquifer Thermal Energy Storage Systems
Authors: Li Shuang , Song Xianzhi , Wang Gaosheng , Yi Junlin
Published: August 2024

Aquifer thermal energy storage (ATES) has proven to be an effective way to mitigate energy production and supply issues. Drilling branching holes from traditional vertical wells can enhance the injection and production capacity of the ATES system. There are many influencing parameters and evaluation indexes of ATES system with multilateral wells. It is necessary to conduct a comprehensive analysis of the system performance. Therefore, a three-dimensional numerical model of fluid flow and heat transfer for the multilateral-well ATES system is built with COMSOL and verified with experimental data. Then, the multilevel orthogonal tests are carried out to analyze 6 factors with 5 values. The grey correlation method is used to compare the influence of key parameters on energy utilization coefficient and coefficient of performance (COP) of hot well. The results show that there are great differences in the order of parameter correlation degree under different indicators. So this study determines the weights of four evaluation indicators based on the Analytic Hierarchy Process (AHP). The optimal scheme is selected from 25 orthogonal experiments by fuzzy comprehensive evaluation. The optimization method established in this study can comprehensively evaluate the operating performance of multilateral-well ATES system and provide reference for its reasonable design.
Round-Trip Between Two Ports: Autonomous Operation of a Container Feeder Vessel
Authors: Cozijn J. L. , de Kruif B. J. , van Daalen E. F. G. , Iavicoli G.
Published: August 2024

MARIN is a partner in the EU funded research project MOSES (“AutoMated Vessels and Supply Chain Optimisation for Sustainable Short SEa Shipping”). MARIN has designed an innovative container feeder vessel, including solutions for zero emission propulsion. The autonomous operation of this vessel was investigated using a two-step approach.

First, a time-domain simulation model of the ship was made. Algorithms for vehicle control and autonomous operation were designed, implemented and tested. The time-domain model included a large sea area with two ports (Mykonos and Piraeus) and an accurate model of the container feeder vessel, including all necessary sensors and actuators. The round-trip between two ports consists of several different sections, such as docking and undocking, port manoeuvring and transit in open sea. Each section required different capabilities of the ship, which were defined using operational states in a state machine.

Second, the simulated ship was replaced by a scale 1:17 physical model, while the software for autonomous control remained the same. The model was completely wireless, with its own on-board power supply. Measured signals were transferred to the basin carriage using a Wi-Fi connection. The scale model, during one of the experiments in the basin, is shown in the photograph in Figure 1. In the model basin, a schematic port was modelled, as the start and end point of its journeys. The ship model was able to successfully perform round-trips through the basin, including autonomous docking and undocking.
Retrofitting Propeller Procedure for a Hydrogen Fueled Offshore Support Vessel
Authors: Tadros Mina , Xu Yunxin , Das Tapas K. , Shi Weichao
Published: August 2024

With new technologies bringing drastic changes to ship design, existing vessels are facing challenges to accommodate the revolutionary changes for a cleaner future. This paper presents the retrofitting study applied to the propulsion system of an offshore support vessel to be fueled by hydrogen, which shows suitability to operate coastal vessels.

Redesign of the vessel’s propulsion system has been conducted. First, the ship resistance is computed using the computational fluid dynamics (CFD) method. The results show a good agreement with the data exported from the experimental tests and the computed results from empirical formulas. Then, based on the resistance calculation, the propeller is redesigned to improve its performance without any modifications in the main prime mover and the gearbox. The results show a significant improvement in the propeller performance as well as ship operating conditions compared to the existing propeller.

The findings of this study contribute to the ongoing TransShip II project, which is applied to the Prince Madog research vessel to achieve zero emission levels in the maritime industry. This kind of retrofitting procedure will promote energy-efficient designs in further ships to reduce the amount of fuel consumption and exhaust emissions compared to the performance of the existing vessels.
Level of Service Evaluation Method for Waterways Based on Vessel Displacement
Authors: Liu Yihua , Wang Menglin , Li Mengting
Published: August 2024

The level of service (LOS) of a waterway is an important evaluation index to measure the planning effect and operation quality of waterway facilities. However, the research on LOS from the perspective of vessel characteristics and vessel traffic flow operating conditions has yet to be mentioned. In this paper, based on vessel displacement, proposing a method to use the theory of redefined parameters of water traffic flow characteristics to analyze the data of ship navigation information of the waterway, establishing an evaluation system using vessel displacement as an indicator, and to formulate a waterway service level evaluation standard for the water transport version. The method was applied to process and analyze the data in the waters of the NanCao Channel of the Yangtze River, the results show that the method can more accurately determine LOS and truly reflect the operation quality of the waterway infrastructure. Therefore, the method can not only guide vessel drivers to choose areas with higher comfort for navigation but also provide a decision-making basis and critical parameters for the waterway management department.
Analytical method for studying acoustic fields radiated by general spherical sound sources in thermoviscous fluids
Authors: Zhang Yong-Bin , Liang Meng-Hui , Zheng Chang-Jun , Zhang Xiao-Zheng , Wang Shuai , Bi Chuan-Xing
Published: August 2024

The study of acoustic radiation from spherical sound sources plays a crucial role in understanding the thermoviscous effects in practical acoustic problems. However, finding a general solution of acoustic radiation from spherical sound sources in thermoviscous fluids remains a formidable challenge. To advance this issue, an analytical method is developed in this paper to calculate the acoustic field radiated by spherical sound sources with the isothermal boundary condition and arbitrary velocity boundary condition. The developed method is utilized to present the solutions of the acoustic field generated by an oscillating sphere and a general spherical sound source, and the accuracy and validity of these solutions are verified through analytical and numerical methods.