bluuebunny/crossref_metadata_2025 huggingface dataset:
A Response Frequency Informed LSTM Model for Ultra-Short-Term Mooring Line Forces Prediction of Floating Wind Turbines
Authors: Chen Peng , Kang Yirou , Zhang Ruihan , Cheng Zhengshun , Deng Shi , Erfort Gareth , Hu Zhiqiang
Published: August 2024

Accurate dynamic response forecasting is pivotal for operational monitoring, maintenance, and dynamic control of floating wind turbines (FWT), ensuring both efficiency and safety in real-world applications. This paper conducts the measured validation and application of the ultra-short-term forecast of a full-scale FWT’s mooring line tension by recurrent neural networks with the frequency decomposition method (RNN-FD). The RNN-FD method is one of the modules of our in-house program DARwind-AI to realize real-time or ultra-short-term forecasting of dynamic response of FWT. Initially, the principles of the RNN-FD method are introduced, including the Long Short-Term Memory (LSTM) encoder-decoder network, wavelet transform applicaiton and frequency decomposition method was demonstrated. Then, the validation of RNN-FD method is carried out using measured data from Hywind Scotland and the results of RNN-FD are promising, with a good agreement observed datasets from 2018 January to July. For instance, the Mean Squared Error (MSE), Mean Absolute Error (MAE), Mean Absolute Percentage Error (MAPE), and One-Nth Largest Error (ONLE) for mooring line forces forecasting at lead times of 60 seconds are 0.0065, 0.063, 0.034 and 0.073, respectively. Conclusively, this innovative methodology, rooted in both traditional engineering principles and artificial intelligence technology, offers promising prospects for real-time FWT monitoring and dynamic control.
Relative Motion Prediction for Integrated Floating Offshore Wind Turbine Installation Scheme Based on Data-Driven
Authors: Ma Can , Zhang Taiyu , Yang Zongyuan , An Yang , Zheng Xiang Yuan , Ren Zhengru
Published: August 2024

With the development of offshore wind power toward deeper seas, innovative installation methods for floating offshore wind turbines (FOWTs) are urgently needed. A novel installation approach involves a specially designed catamaran that carries multiple preassemblies (tower, hub, and blades are mated onshore) to the installation site. The approach separates the construction of foundations and preassembled upper structures. Carrying multiple preassemblies onboard shortens the transportation time, and only one lifting operation shortens the offshore mating time. Due to the complexity of the offshore environment, irregular relative motions occur between the preassemblies and the floating foundation. Larger relative distances between the mating points (lifted preassembly bottom center point and floating foundation top center point) would increase the outcrossing rate during the mating operation. Artificial neural networks are applied to predict the maximum and minimum relative motions between the two mating points during the implementation of mating operations. The installation scheme is simulated in various sea states using Sima, generating datasets for analysis. Statistical motion data (mean value and low-order central moments) for the past period are used as inputs to the neural network to obtain the maximum and minimum relative motion for the coming period. Simulation results show that the prediction model constructed by the back propagation neural network can predict maximum and minimum values of relative motions with acceptable accuracy. The proposed algorithm enables the prediction of potential hazards during the mating operation of the conceptual installation method, facilitating informed decision-making by the crews.
Nonlinear Dynamic Analysis of 2-D Jacket Structure Considering Joint Nonlinearity
Authors: Kumar Ram , Kumar Deepak , Paul Bapon
Published: August 2024

Jacket structures are recognized for their fixed-base design and inherent structural stiffness among the most critical offshore engineering structures. This rigidity, stemming from their solid connection to the foundation, results in a slightly shorter natural time period than their floating structures. Comprising a framework of interconnected tubular members with rigid connections, jacket structures offer durability and stability in the challenging offshore environment. However, the operational performance of these jacket structures is significantly influenced by dynamic forces arising from the random ocean environment. The interaction between the random ocean dynamics and the structural integrity of jacket structures can lead to joint rotations and deformations, introducing nonlinearity into the system. The extent of joint nonlinearity is a critical factor that can intensely affect these offshore structures’ dynamic responses. This comprehensive study extends its focus to involve complete 2D jacket structures by using Finite Element Analysis (FEA) software ABAQUS to model joint behaviour and understand the details of nonlinear dynamic behaviour. The joint modeling approach not only considers the influence of varying angles between members but also accounts for joint level buckling under varying external loading conditions. In the presence of joint buckling, the nonlinear behaviour of the jacket structure changes significantly. This becomes more significant because it may cause significant fatigue damage to the structural joints. The study is focused on understanding the joint buckling and its nature under random ocean waves for a 2D jacket structure. Further, the effect of buckling on the nature of response is studied. This research enhances our understanding of the interaction between structural nonlinear elements (under joint buckling) and dynamic forces, ultimately offering essential information for offshore engineering design, assessment, and safety.
The Effect of Side Girder Distance in Bottom Structure to the Ultimate Strength on Double Hull Tanker
Authors: Muis Alie Muhammad Zubair , Juswan  , Rachman Taufiqur , Mustafa Wahyuddin , Alamsyah  , Rahmadani Elsa Fitria
Published: August 2024

Double bottom structure consists of many elements such as bottom and inner bottom longitudinal, center and side girders, solid and watertight floors and so on. Those elements have dimensions and must be located according to specified distance. The effect of distance has contribution to the deflection or deformation in the local area especially on double bottom. The intersection between longitudinal and transversal elements also gives effect. Therefore, the distance from each installed construction element must be considered more carefully.

The objective of the present study is to analyze the ultimate strength caused by the influence of the side girder distance on double bottom of Double Hull Tanker (DHT) for existing and after changing the distance of side girder. The double bottom caused by changing the distance of side girders is analyzed to the ultimate strength of DHT hull girder under hogging and sagging. The analytical method is adopted to analyze the DHT due to the effect of side girder distance to the global structure.

The ultimate strength obtained by analytical method is compared between existing condition and after changing the side girder distance on double bottom. The ultimate strength in terms of the moment-curvature relationship including their behavior is presented in this study.
Structural Response of a Container Ship Against Beam Sea Wave
Authors: Yanagimoto Fuminori , Ishibashi Kinya
Published: August 2024

This study carried out nonlinear finite element analyses of an imaginary container vessel under beam sea wave conditions. Deformation and collapse behaviors of hull structures have been studied using finite element analysis, but many of them focused on the behavior under following and heading wave conditions, evaluating hull girder ultimate strength. Although recent requirements to assess hull structure strength employ beams sea wave, in addition to longitudinal wave, the structural response against beam sea wave has not been paid attention to. In particular, the transverse structures such as side transverse and side shell are supposed to be influenced by the beam wave conditions, but detail analyses of their deformation affected by yielding and buckling have been rarely conducted. A series of nonlinear finite element analyses using a so-called three-hold model of mid region of the container ship were carried out by applying the wave pressure, cargo load and inertia due to ship acceleration, and hull girder moment supposing the time of the maximum roll angle. The results reveal that the side shell undergoes elastic buckling, but the further deflection is suppressed by the neighboring intact side transverse because the compressive displacement of short sides of the side shell panels are constrained by the side transverse. Such behaviors were observed in analyses with different thickness of the side shell and side transverse. Such ‘surrounding’ structure effect might contribute to the hull structural integrity under beam sea waves.
Maneuvering Stability Analysis of a Fouling Autonomous Underwater Vehicle in Horizontal Plane
Authors: Zhang Xiaohui , Huo Jianlong , Xu Qimao , Zhang Meng
Published: August 2024

During the operation of a submerged submarine, its surface will inevitably suffer from fouling, which will affect its hydrodynamic performance. In this paper, the horizontal maneuvering stability of the rough submerged submarine is studied based on the RANS method, where the Defense Advanced Research Projects Agency (DARPA) SUBOFF model developed by the David Taylor Research Centre (DTRC) is taken as the object hull. An appropriate roughness function model proposed by Demirel et al. (2017) for a range of representative coating and fouling conditions is selected to describe the roughness conditions. The hydrodynamics of the smooth SUBOFF model in infinite depth and wide area are calculated, and the validity of the numerical results is verified by the results of the tank test. The hydrodynamic coefficients of translation and rotation of the rough SUBOFF are obtained through the oblique towing tests and the pure yaw tests. According to Routh’s stability criterion, the horizontal maneuvering stability index of rough SUBOFF is obtained. Subsequently, the impact of the roughness height and the distribution position on the horizontal maneuvering stability is analyzed. The results show that when the surface of the submarine is partially covered with deteriorated coating or light slime, the stability index in the horizontal plane decreases by 31.70% for the case of stern one-third of the area fouled only, which is more hazardous than the case of forward one-third of area fouled only (6.23% decrease) or the case of middle one-third of the area fouled only (4.02% decrease). Therefore, minimizing the roughness attached to the stern surface is very beneficial in maintaining the stability of submarines.
Mooring Line Tensions Prediction Based on MLP for Soft Yoke Mooring System
Authors: Li Ying , Zhong Qiyuan , Gan Qiang
Published: August 2024

The soft yoke mooring system is widely used for the floating production storage and offloading (FPSO) in shallow water. However, there were accidents of mooring system being pulled down by the FPSO in field. It is hence necessary to conduct realtime prediction of mooring line tensions. Under complex environmental loads, the coupled effects of the mooring system and floaters lead to nonlinear characteristics of the mooring line tensions. In recent years, scholars explore the application of neural networks to predict mooring line tensions due to the strong nonlinear fitting capacity of neural networks.

The coupled time-domain model of FPSO and soft yoke mooring system is established and sensitivity analyses are conducted to identify input parameters. Accordingly, a series of numerical analyses are carried out to extract the datasets for prediction. A multilayer perceptron (MLP) neural network model is established to predict the maximum mooring line tensions of the soft yoke mooring system in Bohai Sea in this work. The results demonstrate that the model is applicable for predicting the mooring tensions in short term sea states.
Rate of Penetration Optimization With Data Analytics Using Dynamic Trend Analysis
Authors: Ochije Uchenna Blesseth , Gravdal Jan Einar , Sahebi Hamed , Sui Dan
Published: August 2024

In drilling operations, optimizing the rate of penetration (ROP) remains a complex challenge due to the multifaceted interplay of dynamic drilling parameters and inherent uncertainties in subsurface formation properties. This study introduces a pioneering approach to ROP optimization through the implementation of a Moving Window Trend Analysis (MWTA) technique. The MWTA method enables real-time extraction and classification of ROP trends, providing drillers with crucial insights for enhanced decision-making and control to improve drilling efficiency and optimize drilling performance.

The MWTA method overcomes the modeling and optimization challenges by processing real-time ROP data streams, swiftly identifying fluctuations, and categorizing them into stationary, falling, or rising trends for further ROP control. This approach enables drilling engineers to promptly detect changes in ROP and make informed decisions for improved control and optimization. The complete workflow of ROP optimization with trend and dynamics analysis is presented. The simulation, validation, and testing of the efficacy of the MWTA is conducted in a high-fidelity drilling simulation environment. This simulator incorporates high-fidelity models, including multiphase flow, transient Torque & Drag, cuttings transport, drill string mechanics, and near-well formation flow and temperature interaction. Simulated real-time drilling data is streamed from the simulator, enabling the MWTA algorithm to work on the intricate relationship between ROP and drilling parameters, such as Weight on Bit (WOB), drilling mud flow rate, and Rotary Speed (RPM). The approach used in MWTA not only promises increased drilling efficiency and cost reduction but also advances safety standards, making it a compelling solution for modern drilling operations. The integration of the MWTA into real-time drilling data analytics represents a significant step toward achieving optimal ROP and enhanced decision-making capabilities in the drilling industry. This paper showcases the potential for data-driven ROP optimization, furthering the industry’s pursuit of efficient and cost-effective drilling operations.
Sandwich Pipe: Technical Viability in Subsea Gas Pipelines
Authors: Paz Claudio Moura , Gaigneux Anne-Laure , Sant’Anna do Nascimento Leonardo , Lourenço de Souza Marcelo Igor , Estefen Segen Farid
Published: August 2024

The exploration and advancement of subsea technology, especially in gas pipelines, has always necessitated innovative solutions. This study evaluates the potential of sandwich pipes for such applications, advocating for their technical and economical benefits over traditional single-walled pipes. To substantiate these claims, full-scale prototypes of the sandwich pipes were manufactured. These were tested at the reputable Subsea Technology Laboratory (COPPE/UFRJ). The assessment criteria were based on collapse and propagation buckling, and the installation feasibility was considered using the Reel-Lay method. This rigorous testing regimen facilitated a detailed numerical-experimental analysis. The primary goal was to fine-tune and calibrate a tool capable of accurately simulating the structural behavior of the sandwich pipe. This tool harnesses the capabilities of the finite element method within the ABAQUS software. Further, following a validation process, the study ventured into an intricate lateral buckling analysis. Here, the focus was the displacement-controlled local buckling limit state (DCC), emphasizing the pipe-soil interaction in the pre-salt region’s clay soil of the Brazilian coast. The findings were promising. The observed longitudinal strains fully complied with standards set by DNV-ST-F101 (Submarine pipeline systems) and DNV-RP-F110 (Global buckling of submarine pipelines). They remained below the critical 0.4% threshold. A comparative analysis was presented as the study culminated, emphasizing the sandwich pipe’s structural resistance to collapse and cost benefits over its single-walled counterpart.
Directional Wave Spectrum Estimation Using Ship Motion Data by Improved CGAN With Physics Guided
Authors: Li Xin , Ma Ning , Shi Qiqi , Gu Xiechong
Published: August 2024

The measurement of directional wave spectrum in the ocean is a crucial but challenging task. By regarding the ship as a substantial wave buoy, it is reasonable and convenient to measure the directional wave spectrum based on the ship’s motion without additional sensor cost. Given the intricacies of characterizing the relationships between wave and ship motions with precision, this study employs the Improved Conditional Generative Adversarial Net (Improved CGAN) for stable and efficient model learning to achieve the mapping of ship motions to wave characteristics within the frequency domain. A framework is introduced to enhance the model’s performance and ensure a meaningful physical interpretation by training neural network architectures with physics-based knowledge, considering factors such as energy consistency and non-negativity of wave spectra for learning physically consistent solutions. Study compares the performance of Improved CGAN without physics guided, Improved CGAN with physics guided, and direct mapping of machine learning model on the ITTC spectrum for learning and estimation. The generalization ability of the models is investigated through the zero-sample estimation of the JONSWAP-type wave spectra. Results show that by achieving consistency in energy, Improved CGAN with physics guided has good performance in terms of estimation error, stability. A single physics indicator guides the model better than two, which may prevent conflicts. On single peak spectrum similar to the ITTC wave spectrum, Improved CGAN with physics guided exhibits great generalization ability. On the spectrum with significant differences in energy shapes, it can also maintain energy consistency, enhancing stability in HS estimation and more precisely identifying mean wave direction.
NextFloat: Light Is Beautiful, Use of Lattice Structure in Floating Wind
Authors: Cahay Marc , Milde Lucy
Published: August 2024

Since the Hywind Demo project, the first Floating Offshore Wind Turbine (FOWT) of 2.3 MW installed 12 km offshore Karmøy island, South West of Norway by Equinor in 2009, up to the ongoing Hywind Tampen floating wind farm composed of 11 units of 8.6 MW to provide electricity for the Snorre and Gullfaks oil and gas fields in the Norwegian North Sea, most of the FOWT deployed are spread moored to the seabed and use upwind 3 bladed turbines.

Some other small scale prototypes using catenary or tension legs, spread or single point moorings, single or multi-turbine configurations and upwind or downwind turbines were also tested during this period in a variety of environments.

The NextFloat project (European Commission Grant Agreement n°101084300 under Horizon Europe program) has started in November 2022. NextFloat will engineer and build an innovative weathervanning concept of FOWT that will be deployed and operate on the Mistral test site in the South of France near Marseille. The unit will be a 6 MW version of the PivotBuoy previously deployed by X1-Wind on the PLOCAN site in the Canary Islands.

This innovative platform concept specifically developed by X1-Wind for floating offshore environments in deep waters combines the advantages of a semi-submersible and TLP through its single-point mooring (SPM, called PivotBuoy®). The result is a downwind tripod-like platform that self-aligns passively with the wind allowing an efficient structural design eliminating also the traditional tower (which suffer high bending moments at its base and is very sensitive to 1P/3P excitations). Substantially lighter, the downwind tripod structure is a more easier and scalable design than the SPAR, semi or barge existing technologies. Furthermore, the use of lattice structure for the tripod legs allows a high weight saving of more than 1000 tons compared to the typical tower structure for the future 20MW+ turbines. Those benefits will be detailed in the publication including a comparison with tower solution based on structural calculation of stresses usage ratios and natural periods.
Pull-Out Capacity of Suction Anchors Considering Trench Effect: A Numerical Study
Authors: Zhang Min-Hao , Fu Yong , Yin Zhen-Yu
Published: August 2024

With the increasing utilization of suction anchors in mooring systems, field surveys have observed seabed trenches near suction anchors caused by anchor chain motion and soil erosion. The presence of these trenches significantly reduces the pull-out capacity of suction anchors, emphasizing the need for attention. This study investigates the impact of seabed trenches on the undrained pull-out capacity of suction anchors at an optimal padeye depth through a series of finite element analyses. Rectangular cross section trenches are considered in this study. The effects of trench size, trench distance, trench shape and local scour on reducing the pull-out capacity of suction anchors are systematically examined. Furthermore, we present an optimal design approach for suction anchors considering seabed trenches that addressed two aspects: (a) determining whether higher pull-out capacity can be achieved by relocating the anchor padeye to a shallower depth and reducing trench depth; and (b) identifying the optimal anchor aspect ratio considering material cost and seabed trench conditions. These analyses provide valuable insights for practical design considerations when dealing with trench-related issues encountered by suction anchors.
Full-Field Strain Estimation From Measured Accelerations of Offshore Wind Turbine Support Structures
Authors: Guo Jianxun , Li Yanchen , Wu Xinyan , Tian Zhe , Liu Fushun
Published: August 2024

The strain history of an offshore wind turbine (OWT) during its operational phase is an essential parameter for assessing safety and estimating its remaining lifespan. In this context, a strain estimation scheme is proposed in this paper, which uses the measured acceleration to estimate the strain state of the OWT support structure. The proposed method relies on the adaptive displacement reconstruction technique in conjunction with the evolutionary orthogonal based response expansion method, which is implemented as an in-house code in numerical software. A mapping process is achieved to obtain full-field strain in the numerical space from measured acceleration in the physical space of the OWT support structures. The advantage of this approach is that it solely depends on the measured acceleration and structural geometry, without requiring measured displacement, strain or modal information. To assess the validity of the proposed method, physical experiments under cyclic loading were carried out on a scaled wind turbine model equipped with acceleration, laser displacement and Fiber Bragg Grating sensors as reference measurements. The results demonstrate that the proposed method could accurately predict the dynamic strain of the wind turbine support structures, while an excellent agreement between the estimated strain and the measured response from the Fiber Bragg Grating is observed, which provides valuable insights for the development of a strain monitoring system applicable to the OWT.
The Influence of Jacket Orientation on Integral Horizontal Forces For a Large 3-Legged Jacket Under Collinear Wave-Current Impact
Authors: Wynants Mareile , Schendel Alexander , Welzel Mario , Kerpen Nils , Schlurmann Torsten
Published: August 2024

Amidst the backdrop of the European “Green Deal,” mandating climate neutrality by 2050, the expansion of offshore wind energy in the German North Sea gains increasing significance. The projected trend in offshore wind energy turbines (OWTs) towards exceeding 20 MW, with hub heights surpassing 240 m and rotor diameters over 300 m, demands a concomitant shift in substructure design. Jacket-type substructures, tailored for sites with larger water depths, are expected to increase individual pile diameters or overall structural density to bear the new, markedly increased top loads. These Offshore Megastructures present a new approach to traditional slender structures. This study investigates the impact of individual and combined wave and current conditions on a 3-legged jacket-type Offshore Megastructure in a 1/140 scale laboratory study. The structure, a simplified iteration designed to support a > 20 MW OWT, was mounted to a load cell for monitoring integral horizontal loads. Testing encompassed current-only, wave-only, and combined wave-current scenarios in both following and opposing configurations. Reference tests without structure, with a monopile, and tests with the jacket structure oriented at 0°, 15° and 30° were executed. Findings illustrate an influence of both wave steepness and jacket orientation on the integral horizontal forces. This relation changes in dependency of the presence and orientation of a superimposed current for values of wave steepness H/L > 0.01.
An Efficient HOS-SPH-BEM Coupling Method for Wave-Structure Interaction Problems
Authors: Xie Chunmei , Yang Juncheng , Sun Pengnan , Ni Xinyun , Wang Qibin , Ye Yonglin
Published: August 2024

In this paper, a potential-viscous coupling method based on Xie’s HOS (Boundary Element Method)-SPH (Smoothed Particle Hydrodynamics) coupling method is proposed by introducing the BEM (Boundary Element Method). The domain decomposition model is adopted with the HOS method generating the incident waves, the BEM propagating the radiation and diffraction waves in the far field, and the SPH method used in the near field around the structure for simulating the wave breaking and nonlinear wave-structure interaction. Therefore, the whole coupling method can be divided into two parts: one-way coupling of HOS-SPH (which has been studied in Xie et al.’s paper) and two-way coupling of SPH-BEM. Similar to Xie et al.’s, Grid2Grid is used to connect the HOS and SPH, meanwhile the velocity and pressure transformation between SPH and BEM is achieved by a linear blending scheme. This coupling method combines the advantage of the potential methods in generating and propagating waves quickly and accurately and the SPH method in adopting the strong nonlinear free surface problems. The numerical results of the HOS, SPH, BEM and SPH-BEM coupling methods are validated by calculating regular and irregular waves. The accuracy of the whole coupling method was verified through the interaction between a two-dimensional freak wave and a three-degree of freedom floating body. Compared with experiment data, the HOS-SPH-BEM coupling method can effectively improve computational efficiency and extensively reduce numerical dissipation. It removes the reflected waves in Xie’s HOS-SPH coupling method.
Numerical Studies on Dynamic Responses of Honeycomb Sandwich Plate Under Slamming Loadings
Authors: Liao Yong , Guo Kailing , Zhu Ling , Yang Weixiang , Dai Shaoling
Published: August 2024

When ships travel with high speed in rough sea, the hull may be subjected to impact loading from water, and the phenomenon of slamming will appear. It may produce large slamming force which can lead to severe damages on the local structures of the ship, sometimes may cause accident. The honeycomb sandwich structure is one kind of lightweight structures, and possesses excellent performance on energy absorption. Hence honeycomb sandwich structure has great application prospect in impact protection.

In this paper, based on Arbitrary Lagrangian-Eulerian (ALE) method, the fluid-solid interaction numerical simulation model on aluminum honeycomb sandwich plates (AHSPs) is established, and the characteristics of slamming loads and structural responses are analyzed. Meanwhile, the accuracy of the numerical simulation has been verified by comparing the slamming pressure and permanent deflection of the numerical simulation with those of the slamming experiment. Based on the numerical method, the influence of the μ (face sheet thickness ratio) on slamming load and dynamic structural responses is investigated. The relationship between slamming pressure, structural responses and energy absorption with μ is analyzed. Results show that, with the increase of μ, the deformation of the front sheet and the honeycomb decrease gradually, while the deformation of the back sheet increases gradually. In terms of energy absorption, as μ increases, the front sheet increases gradually, while the back sheet and the honeycomb decrease gradually. Besides, the peak value of slamming pressure increases linearly with the increase of μ. Therefore, the proper decrease of μ can reduce the plastic deformation of AHSPs. The studies in this paper can provide reference for the design of ship structures suffering from slamming loads and improve the structural safety.
A Modular Steel Gravity Foundation (MSGF) for TLP Floating Offshore Wind Turbine (FOWT) Tendon
Authors: Periyaiah Rathinam , Huang Edward , Tang Zhaoxiang , Erten Mustafa , Tavassoli Moe
Published: August 2024

In general, Tension Leg Platform (TLP) demonstrates exceptional dynamic behavior with very low displacements and almost no vertical / rotational motions. Its lightweight structure and simple geometry lend themselves to simplifying fabrication / integration processes and competitive Levelized Cost of Energy (LCOE) levels. Furthermore, the much smaller footprint of TLP mooring compared to other alternatives like Semis or Spars allows for better accommodation for fishing and shipping lanes. However, the major cost driver for the TLP as an option of foundation system for Floating Offshore Wind Turbine (FOWT) is the cost of tendon systems and its installation, including the tendon foundation. The TLP with simplified installation method of Modular Steel Gravity Foundation (MSGF) and Tendon presented in this paper will make the TLP option much more competitive and reduce the overall LCOE.

The MSGF as TLP FOWT Tendon foundation is an innovative method of installing the traditional gravity base foundation. The proposed modular solution offers a simple, noiseless, and environmentally friendly installation process. It requires a simple decommissioning process without the need to mobilize a high day-rate installation vessel. It is suitable for all types of seabed soil conditions since the design can be adjusted to suit any support ground condition, and its components can be sized and designed within the handling capacity of locally available installation vessels. The above uniqueness of the MSGF foundation option results in a significant reduction in the installation schedule and cost of a FOWT. This paper contains the MSGF configuration and sizing for TLP with pontoon Extension (ETLP) tendon for the US west coast 15MW FOWT, including the design load conditions and design loads. It also provides details of foundation modules and the sequences of module fabrications, transportation, and installation. Additionally, this paper includes the execution plan for foundation installation, addressing the local supply chain and logistics, as well as providing a high-level cost estimate. This study finds that the MSGF option for ETLP FOWT reduces the foundation component level LCOE significantly compared to the traditional pile foundation.
Preliminary Numerical Assessment of Marine Turbines With Rigid Blades Using Low Reynolds Approach
Authors: Paredes Rubén J. , Zambrano Paul S. , Marin-Lopez Jose R. , Jasak Hrvoje
Published: August 2024

Tidal turbines with morphing blades could increases the mean time to failure of turbine blades and drive trains by mitigating power and loads fluctuations associated with the larger scales of the turbulent tidal stream flow. However, the numerical modeling of this fluid-structure interaction problem would require expensive high performance computing infrastructure to obtain results in a reasonable time. In order to develop this analysis capability, the goal of the present work is to identify the numerical setup details in OpenFOAM framework to assess the performance of the Oxford tidal turbine with rigid blades. For this, thrust and torque predictions were used to assess the performance of this turbine considering the steady inflow condition of with a rotor tip-speed ratio of 5.82 and turbulence intensity of 3.1%. For the near-wall treatment, a κ-ω SST turbulence model with low Reynolds number approach was used. Thrust and torque predictions using a grid with element size of 1.5%D in the turbine region have and error of 0.5% and 14.8% respectively. Also, a 1/15 power law velocity profile was assumed to assess its effect on load fluctuations. Further, a reduced order model will eventually be implemented to capture blade deformation and reduce load fluctuations.
A Preliminary Experimental Study of a Dual-Function Slotted Barrier Integrated With an Oscillating Water Column for Wave Energy Extraction and Shore Protection
Authors: Huang Zhenhua , Walker Mayah , Reyes Clint C. M. , Cross Patrick
Published: August 2024

Wave energy conversion is a promising technology to provide renewable energy, but its commercialization is limited mainly due to high initial investment and maintenance cost. One way to improve the economic feasibility of wave energy utilization is to integrate wave-energy converters (WECs) into shore-protection structures to form dual-function structures, which have the capability to harness wave energy for electricity generation and provide coastal protection. Among different types of existing WECs, oscillating water columns (OWCs) have the power takeoff (PTO) system out of water, which greatly reduces the influence of befouling on PTO performance and lowers maintenance cost. This study introduces a dual-function design by integrating an OWC-type WEC with a bottom sitting slotted barrier. For these types of dual-function structures, the main design objectives are to achieve the designed transmission coefficient, maximize the wave power extraction, and minimize the wave loading on the structure. In this study, we present preliminary results of an experimental study of the proposed dual-function structure in a small wave flume equipped with a piston-type wave generator. In the experiment, a circular orifice at the top of the pneumatic chamber was utilized to emulate the PTO system. Wave power extraction was measured using a differential pressure sensor. Wave loading on the structure was measured using a single-axis force balance. The focus of this study is to observe the effects of tide level and the porosity of the slotted barrier on the wave power extraction, wave transmission and wave loading under different wave conditions. Two slotted barriers and two water depths were studied. Main results reported include reflection, transmission and energy loss coefficients, wave power extraction efficiency, and wave loading.
Reinforcement Learning Driven Ship Biofouling Cleaning Strategy Optimization Considering Carbon Emission
Authors: Wei Qikun , Cheng Jianda , Xiang Gong , Liu Yan
Published: August 2024

The world has seen a rapid transition to a lower carbon future. As part of the global move, the marine field has been making effort to achieve a sustainable development. Ship biofouling adds resistance during navigation which not only increases cost of shipping operation but also weakens the competitiveness of vessels in terms of carbon reduction and efficiency improvement. Ship biofouling cleaning is an indispensable maintenance task in the life-cycle of ships. The fouling cleaning creates additional expenses and impacts schedules of shipping operation. Therefore, an appropriate strategy based on biofouling conditions is essential for cost optimization. This paper establishes a multi-state biofouling growth model based on Markov chain and solves the optimal strategy by reinforcement learning. An illustration case of a container ship is presented for verification. The proposed method is effective and efficient to support state-based decision making of stakeholders for reducing cost and carbon emissions.
Three-Dimensional Vortex-Induced Vibrations of Catenary Risers Under Sheared Flows at Different Incidence Angles
Authors: Ma Bowen , Srinil Narakorn
Published: August 2024

Marine risers may experience a complex vortex-induced vibration (VIV) owing to the enhanced nonlinear effects from structural curved shapes versus sheared flows. Many studies have focused on VIV of straight risers in sheared flows or curved risers in uniform flows. In this study, a numerical prediction model is advanced to investigate the multidirectional VIV of a catenary riser subjected to linearly sheared flow. The prediction model is described by equations of three-dimensional responses of the catenary riser coupled with the spatially distributed nonlinear wake oscillators calibrated against experimentally observed VIV responses of curved cylinders. Hydrodynamic lift and drag forces are mathematically modelled based on fluid-structural variables accounting for effects of space-varying riser local inclinations, vortex excitation frequencies and relative flow-cylinder velocities following the Independence Principle. The coupled VIV system is discretized in space by a second order finite difference scheme and integrated in time. To validate the model, simulations are performed based on a flexible curved cylinder under the concave sheared flow and compared with experimental results in the literature. By varying the relative directions between the riser equilibrium and the incoming flow in planar and non-planar configurations, VIV responses of a long flexible catenary riser in a uniform free stream flow versus a linearly sheared flow are compared and analysed in terms of amplitudes, resonant frequencies, lock-in conditions, and energy transfer mechanisms under perpendicular, convex and concave flows. Typical VIV features are captured alongside travelling wave responses, modulated amplitudes and frequency switching caused by sheared flows. Overall results highlight the influence of sheared flows on multidirectional VIV features.
Three-Dimensional Flow Around a Span Shoulder of a Pipeline/Cable: Insight From Experiments Combined With Numerical Modelling
Authors: Zhang Bingchang , An Hongwei , Draper Scott , Jiang Hongyi , Cheng Liang , Zhao Xu
Published: August 2024

Current-induced three-dimensional (3-D) scour below offshore pipelines and cables (P/Cs) is a concern in both the offshore oil and gas industry and the offshore renewable energy industry. This 3-D scour phenomenon can lead to elongation of free spans and control the time scale of self-burial. Thus, much experimental research has focused on span elongation due to 3-D scour. However, due to limitations in measurement techniques, especially in accurately assessing the flow structure in the gap, the scour propagation mechanism is not well understood. In this study, scour propagation below a pipe in steady current was investigated experimentally, and the 3-D flow around a span shoulder was further studied using a 3-D numerical RANS model. The experimental results and numerical simulations show that the scour propagation may be attributed to two processes: erosion induced by 3-D flow on the upstream side of the span shoulder, and spanwise avalanching (or sand sliding) towards the scour hole on the downstream side of the span shoulder. The numerical results indicate that the flow is highly three-dimensional at the scour front; a spiral flow forms upstream side of the scour front with the maximum spanwise flow velocity reaching 0.32Ūa under the pipe.
Cyclically Buckling/Plastic Collapse Behavior of Deck Beam-Column Obtained by Fluid-Structure Interaction Analysis for Floating Structure in Waves
Authors: Imai Nao , Toh Kimihiro , Yanagihara Daisuke
Published: August 2024

Fluid-structure interaction analysis applying ICFD solver incorporated in ANSYS LS-DYNA is applied to rigid motion of a floating box and hydro-elastic motion of a slender floating beam in waves, and the fundamental validity is confirmed comparing with the past test results and theoretical solutions. A structure with a slender beam-column in the deck is assumed to be floated in waves. The cyclically buckling/plastic collapse behavior of the deck and the overall bending response of the whole structure are examined through the fluid-structure interaction analysis varying the slenderness ratio of the deck. As a result, it is found that both the tensile and compressive load-carrying capacities of the deck are reduced with an increase in the number of wave encounters and this tendency becomes remarkable in the slenderer deck. The reduction of the compressive capacity especially depends on the residual deflection of the buckled deck. Regarding the bending moment acted on the whole structure, the maximum hogging moment is obtained just when the tensile axial force of the deck attains the peak. However, the sagging moment continuously increases even after the compressive force attains the peak because the intact bottom part can be subjected to a further moment. The overall bending deformation of the whole structure is influenced by the reduction of the load-carrying capacity of the deck after the peak.
A Study on Dimensionality Reduction Technique-Based Wave Estimation Using the Motion Response Spectra of the Advancing Ship
Authors: Ko Donghyeong , Nam Bo Woo , Choi Ju Hyuck
Published: August 2024

This study introduces a new hybrid method, named the two-step method, for estimating the wave spectrum of an advancing ship. Among the various wave estimation approaches based on the wave-buoy analogy, the two-step method, rooted in the brute force algorithm, utilizes parametric main wave heading direction and spreading strength. The method follows a stepwise approach, initially detecting the wave heading and subsequently estimating wave height and period based on the pre-detected wave heading direction. In the first step, pseudo data is generated through numerical simulation and combined with real motion data to create a high-dimensional feature space. The feature values extracted from the motion response spectra demonstrate distinct characteristics, where the magnitudes vary gradually with changes in wave direction as the wave heading develops, influenced by forward speed and hull form. Utilizing the nonlinear dimensionality reduction technique t-SNE, these feature values facilitate the visualization of wave heading clustering levels in the dataset. Additionally, the graph-based semi-supervised learning algorithm, label propagation, is employed to estimate the wave heading using simulation data. In the second step, wave height and period are estimated using the modified brute force algorithm based on the pre-detected wave heading. The accuracy of the proposed method was validated by comparing it with model test results, demonstrating enhanced performance compared to the original approach. It is expected that the proposed method could efficiently detect the wave spectrum and the main wave heading.
Calculation of Force-Coefficients of a Wind Propulsion System for a 4 DOF Velocity / Power Prediction Program
Authors: Oettle Johannes , Krüger Stefan
Published: August 2024

In this paper, a method to calculate the force coefficients of a wind propulsion system consisting of single wind propulsion elements is presented. With this method it is possible to calculate the forces of the whole system using measured or calculated force coefficients of single elements, without knowledge of the section shape of the wind propulsion elements. The single elements are modelled as horseshoe vortices to calculate the interaction inbetween the elements. This method is based on potential theory in order to quickly obtain sufficiently accurate force coefficients, which are necessary for velocity respectively power prediction programs. These programs balances the forces acting on the ship to evaluate the performance of the wind ship or wind assisted ship in an early design stage. Calculations of wind propulsion systems consisting of five and six curved rectangular plates are presented and compared with wind tunnel measurements. These calculations demonstrate adequate accuracy, particularly in the domain of small angles of attack, which is of interest for wind-assisted ships.
An Optimal Adaptive Bias RBF Controller for Dynamic Positioning Vessels
Authors: Ye Yutu , Wang Yiting , Wang Lei
Published: August 2024

To improve the performance of tracking control for dynamically positioned (DP) vessels, this paper presents the design and implementation of an adaptive robust backstepping controller without using model parameters in the presence of unknown time-varying disturbances. The bias radial basis function neural networks (RBFNN) are employed to compensate for the uncertainties and disturbances of ship dynamics. The introduction of bias term of RBFNN helps to avoid the designing of additional integrator of backstepping. The output of the RBFNN can be non-zero when the inputs of the RBFNN deviate significantly from the center points because of the bias term, which improves the robustness of the adaptive RBFNN controller. The reference trajectories of this paper are generated by linear quadratic regulator (LQR) to diminish the overshoot and save the energy consumption. The system matrices used in LQR are identified through the data-driven technique. Uniform boundedness of the closed-loop system is proved by the Lyapunov stability theory. Simulation results illustrates the performance of suggested control scheme.
Towards Integrated Asset Modelling With Intermittent Green Power
Authors: Roli Ole-André , Skogestad Jan Ole , Persia Cosimo , Nybø Roar , Schümann Heiner , Bergmo Per Eirik Strand
Published: August 2024

The introduction of offshore wind turbines and shore-based electrification on the Norwegian Continental Shelf is a source of green energy, replacing gas-powered turbines. However, while the phase-out of offshore gas turbines will reduce CO2 emissions from offshore installations, the fluctuating electricity price and availability of wind power pose challenges for the oil and gas production on the installations. In the framework of Integrated Asset Modelling (IAM), we are studying how higher flexibility in the energy demand of the production system can alleviate this issue and reduce CO2 emissions without affecting production adversely. In this paper we give an overview of findings and challenges in applying IAM to CO2 emissions and work on cloud solutions that can help facilitate dissemination and uptake of research findings in the oil and gas industry.