bluuebunny/crossref_metadata_2025 huggingface dataset:
A Problem of Long Period Yaw Motion of an Ultra-Large Floating Offshore Wind Turbine and its Reduction Countermeasure
Authors: Ota Makoto , Murai Motohiko , Otaka Isami , Kondo Shuto
Published: September 2023

In June 2022, the New Energy and Industrial Technology Development Organization (NEDO) of Japan created a 2 trillion yen “Green Innovation Fund” in June 2022. The fund will “develop technologies for wind turbines and floating structures that are suited to Asian weather and ocean conditions for floating wind turbines, which are expected to expand in the medium to long term, and demonstrate the integrated design of wind turbines, floating structures, cables, and other components with a cost level that can compete globally, leading to their social implementation”.

The demonstration of floating wind turbines in actual sea areas in Japan has been conducted off coast of Fukushima Prefecture, off coast of Goto in Nagasaki Prefecture, and in the Hibikinada Sea in Fukuoka Prefecture, where technological accumulation and investigation toward commercialization are being conducted.

While the rated power generation capacity of these demonstration wind turbines is 2–7 MW, the rated power generation capacity envisioned in the above-mentioned fund is 15 MW, and the specifications for the design of floating structures to accommodate ultra-large wind turbines have become more stringent.

As a new issue, it is a relative yaw motion between a nacelle and a tower. The characteristic of such yaw motion has a long period yaw motion, and it is relatively slower than pitch or heave motion but relatively faster as its nacelle tracking motion for catching the wind direction. The effects of reduction of yaw motion and yaw motion speed by a virtual propulsion system attached to the floating structure were qualitatively and quantitatively investigated as countermeasures against the yaw motion problem.
Application of STABLEpipe Method C Assessment to Determine On-Bottom Stability of a Cable Crossing in North Sea Mobile Seabed Conditions
Authors: Jorgensen Jack , Griffiths Terry , McGrath Nicholas , Görmüş Doğukan , Severs Glenn , Thurstan Bryan , Pistani Fabrizio , Ledoux Bart
Published: September 2023

The STABLEpipe JIP produced guidance for the on-bottom stability design of pipelines and cables on mobile or erodible seabeds. This paper describes the first known application of STABLEpipe Method C to assess behaviour of a cable with spatially varying properties (on-bottom weight, external dimensions etc.) to assess the on-bottom stability (OBS) of an offshore windfarm power export cable installed on a mobile seabed in the Dutch sector of the North Sea. The segment assessed is a pipe crossing, clad with a cable protection system (CPS) installed to provide mechanical separation between the cable and pre-existing seabed infrastructure (cable or pipeline). The seabed is sandy, and mobile under ambient conditions. The OBS analysis considers time-varying seabed embedment and seastate evolution to determine whether the crossing section deflects more than a set criteria of +/− 1 m. Field observations of the behaviour of the crossing section are compared to the numerical analysis, providing evidence that the predicted lateral displacements were not exceeded.
A Fast Numerical Model for Evaluating the Stability of a Damaged Ship in Regular Beam Waves
Authors: Duan Jianwen , Ma Ning , Shi Qiqi , Gu Xiechong
Published: September 2023

Damage stability in waves, which reveals highly non-linear and complicated behaviors, is attracting more and more attention recently. In this paper, a fast numerical model for predicting the stability of a damaged ship in regular beam waves is presented and validated by the published model experimental data. The potential flow theory is applied to build the basic model. In the basic model, the flowrate through the breach is calculated through modified Bernoulli’s equation. The compressibility of air and the phenomenon that air escapes from the air pocket in a bubble flow are simply simulated by modified Bernoulli’s equation for compressible fluids and nuclei number density distribution function respectively. The lump mass method is introduced to estimate the sloshing force of floodwater inside the damaged compartment and roll damping is obtained from roll decay experiment of damaged ship. Then the numerical model is applied to the International Towing Tank Conference (ITTC) benchmark model in still water and the frigate hull named DTMB5415 in regular beam waves. Internal water height in the damaged compartment, roll decay of the damaged hull and motion responses in regular waves are calculated and compared with available model experimental data. It is confirmed that the results of the numerical model have a good agreement with the published experimental data.
Modelling of Fibre Rope Mooring for a Floating Offshore Wind Turbine
Authors: Viuff Thomas , Sørum Stian H. , Kvittem Marit I.
Published: September 2023

Synthetic fibre rope materials such as polyester and nylon are used frequently in the offshore industry due to their low weight and flexible properties. A drawback when utilizing these synthetic fibre rope materials is how to account for their complex, non-linear tension-stretch behaviour, which is a combination of both instant-elastic, visco-elastic, instant-plastic, and visco-plastic (creep) material behaviour. This complex behaviour has previously been simplified as a linear stiffness based on an upper bound or lower bound criterion when performing time domain analyses. These stiffness bounds are based on design tension and platform offset criteria. Today it is recommended to use a bi-linear stiffness curve to include both criteria in one, although the model is still a crude approximation of the real behaviour. Recently, the Syrope JIP has developed a method to account for the non-linear behaviour more accurately, which depends on the mean tension, the load rate, and the load history. This Syrope model is utilized in the present study for mooring system design analyses of a floating offshore wind turbine (FOWT) concept and compared to the previously mentioned methods applied in the industry today. The comparison encompasses both fundamental static and dynamic properties of the concept, as well as design tension based on ultimate limit state (ULS) conditions.
A Simple Estimation Method for Ultimate Strength of Curved Plates Under Axial Compression
Authors: Shiomitsu Daisuke , Ishibashi Kinya , Yanagimoto Fuminori , Fujikubo Masahiko
Published: September 2023

A simple estimation method for ultimate strength of curved plates under axial compression is proposed. Existing estimation methods are mostly empirical based on plastic correction of elastic buckling strength or curve fitting the results of test or nonlinear finite element analysis (NLFEA). For more rational design, it is important to develop a method having more theoretical basis in accordance with physical phenomena including post-buckling behavior, yielding behavior, and effects of initial imperfections and material properties as well as the elastic buckling strength. A series of NLFEA is performed to investigate the buckling and collapse behavior of curved plates under axial compression. Using identified buckling modes and applying the elastic large deflection theory, elastic post-buckling behavior is formulated. The ultimate strength is estimated by checking yielding at specified locations depending on the collapse modes. The proposed method gives the ultimate strength without any iterative calculations. The applicability of the proposed method is demonstrated though a comparison with NLFEA results.
Bayesian Network Modelling of Aero-Mechanical Performance of Wind Turbine
Authors: Dao My Ha , Le Quang Tuyen , Zhao Xiang , Ooi Chin Chun , Luu Trung Pham Duong , Raghavan Nagarajan
Published: September 2023

In this paper, we demonstrate a Bayesian Network (BN) model that returns indicators in terms of range of values and likelihoods of occurrence from the inputs of operating conditions, i.e. inflow wind speed, rotating speed, tilt and pitch angles. The BN could also be used to derive operating conditions (i.e. rotation speed or pitch angle of blade) that maximize the possibility of achieving a desired power output while subject to certain turbine structural conditions.

The BN model is built from a large database of high-fidelity CFD/FEA simulations of a 5MW NREL wind turbine. The abnormality is assumed to be in the form of abnormal deformation and/or stress that are numerically generated by introducing corresponding faults in the blade structure. The database generation, construction and demonstration of the BN model will be presented in the paper.
Design Assessment and Optimization of a Barrier Valve for Subsea Applications
Authors: Ahmadli Mehman , Gjersvik Tor Berge , Sangesland Sigbjørn
Published: September 2023

A subsea Christmas tree is an integral part of the barrier system allowing the controlled production of hydrocarbons while serving to shut in the production in case of an emergency or a need for a planned shut-down. The most important components of the Christmas tree are the barrier valves, most often remotely hydraulically operated, spring-loaded, and fail-safe gate valves.

A primary or wing barrier valve is subjected to full wellhead shut-in pressure when closed. To open such a valve, the valve needs to be forced towards opening overcoming high friction and spring preload forces until the valve opens allowing flow to start and pressure to equalize across the valve. With the coming change to all-electric control systems (AES) dispensing with hydraulics for actuation, it would be highly beneficial to the controls design and power requirements if the operational forces and power required for valve actuation could be reduced.

This paper investigates the possibilities of force and power reduction through the following ways: alternative lower friction coating material and geometrical change of the valve parts. As an alternative coating material polycrystalline diamond compacts (PDC) are analyzed. By geometrical change, we seek a solution whereby only a shorter stem displacement is required before the crack-opening and after the crack-closing phase. The valve is 3D modeled using the same subsea conditions, the model is analyzed using finite element methods.
Energy-Efficient Marine Engine and Dynamic Wing Evaluation Under Laboratory Conditions to Achieve Emission Reduction Targets in Shipping
Authors: Perera Lokukaluge Prasad , Belibassakis Kostas
Published: September 2023

There is a requirement to comply with the forthcoming IMO & EU requirements to reduce ship emissions by at least 40% in 2030 compared to the 2008 levels. Such medium-term emission reduction targets can only be achieved by introducing novel technologies into the shipping industry. The SeaTech H2020 project (seatech2020.eu) introduces two main innovations that can support the same emission reduction objectives. Those innovations consist of integrating an energy-efficient marine combustion engine with a renewable energy recovery device, i.e. dynamic wing. However, these two technologies are not evaluated in an actual environment in a selected ocean-going vessel. On the other hand, various data sets are collected from both innovations and can be used to quantify their energy efficiencies in a data science environment. Furthermore, it is expected that both innovations should interact with each other in the same data science environment as well as in the respective testing platforms, therefore more realistic vessel operational conditions can be introduced. Hence, this study introduces realistic head wave conditions in both innovations, where the dynamic wing creates adequate thrust to push the vessel forward under the same ocean wave conditions. The same thrust and ocean wave conditions have been applied to marine engine testing as the main contribution of this study. Finally, the data sets collected from the engine testing platform under its loading situations for both wave and thrust conditions of the selected ocean-going vessel are presented in this study.
Multiple Model Adaptive Estimation Coupled With Nonlinear Function Approximation and Gaussian Mixture Models for Predicting Fuel Consumption in Marine Engines
Authors: Taghavi Mahmood , Perera Lokukaluge Prasad
Published: September 2023

Digital twin type models can be developed for physical systems that are complex nonlinear a system of systems (SoS). However, such models are usually difficult to represent by linear equations. Therefore, an adequate linearization technique should be introduced. Therefore, linear models as digital twins can be interpreted easily and need much less computational power when applied to various industrial applications. On the other hand, a linearization approach can increase the respective system-model errors and impose significant constraints on the models of SoS, i.e., since linear models can be applicable only in limited operating regions. This research study aims to combine positive characteristics of both linear and nonlinear modelling into a digital twin development framework by having the properties of linear digital twin models locally while the model framework is covering the whole operating region of the SoS. An industrial application of marine engines as an SoS is considered for this study, where the respective models have been used to predict engine fuel consumption.

For this purpose, firstly, a dataset is selected from a marine engine of a selected ocean-going vessel. Then, several localized linear operational regions of the respective data set are identified using an unsupervised data-driven technique, i.e., on the engine propeller combinator diagram. For developing the localized models: firstly, the Gaussian Mixture Models method is used to cluster the data points into different operational regions of the engine propeller combinator diagram. Then, a nonlinear model of the relationship between features is developed in each cluster using the polynomial regression approach. Then, these models are combined using the Multiple Model Adaptive Estimation (MMAE) method to create an overall model for the marine engine as an SoS. The same model is utilized to predict the respective fuel consumption based on engine operational conditions.
Numerical Modelling of the Performance of Floating Fish Pen in Harsh Environmental Conditions
Authors: Nasyrlayev Nazhmiddin , Dyson Ashley , Kefayati Gholamreza , Tolooiyan Ali
Published: September 2023

The growing demand for high-quality protein sources, coupled with technological advancements, has recently created the need, and facilitated opportunities for offshore aquaculture in high-energy areas. Although based on experience gained through many years of practice in low-energy areas, aquaculture companies prefer to use traditional fish pens in high-energy regions, the short- and long-term performance of the pen and mooring components in harsh environments are not well studied. In this study, a numerical model of a slender fish pen is created in the Finite Element (FE) environment to study the pen’s response to harsh environmental loads, including currents and waves. To assess the reliability of the FE model, a validation exercise was conducted for both current-only and combined current and wave conditions, which led to good agreement between the published data and the modelling conducted in this study. The model is then employed in total of 1440 simulations to analyze various pen arrangements with different angles of attack of waves and currents concerning a range of current intensity and wave height. Further consideration is given to the performance of pens at high current velocity and wave height (e.g., 2 m/s and 3 m) while observing the volumetric changes of the pen and distribution of the tension load in mooring lines.
Hydrodynamic Forces of Subsea Small-Diameter Pipeline in a Deep/Wide Trench
Authors: Liu Zinan , Cheng Liang , Ren Chengjiao , Griffiths Terry , Tong Feifei
Published: September 2023

Accurate predictions of the hydrodynamic forces on a pipeline or cable in a trench are of both fundamental and practical significance. Existing design guidance (DNV-RP-F109) enables forces to be estimated based on a simplified model of a pipeline in a trapezoidal trench with very limited dependence of hydrodynamic forces on incoming flow and some trench geometry parameters, such as the slope of the trench θ, the trench-width-to-pipeline-diameter ratio W* and the trench-height-to-pipeline-diameter ratio H*. The present study conducts a series of two-dimensional (2-D) and three-dimensional (3-D) direct numerical simulations of steady flow past a pipeline placed at the bottom of a smooth trench over a range of trench configurations (θ = 0°–30°, W* = 3–20 and H* = 1–20). The pipeline Reynolds numbers vary from 500 to 3900 based on incoming steady flow velocity and pipeline diameter, meaning that these results are a preliminary investigation of the problem rather than representing typical pipeline/cable/trench/ flow conditions. This paper explores the dependence of trench configurations on flow characteristics and hydrodynamic forces.
Sea Trials of Multiple Heterogenous Cruising AUVs and ASV With Basic Formation Control
Authors: Sato Takumi , Kim Kangsoo , Sasano Masahiko , Okamoto Akihiro , Inaba Shogo , Kondo Satoshi , Matsumoto Hiroshi , Murashima Takashi , Fujiwara Toshifumi , Osawa Hiroyuki
Published: September 2023

The National Maritime Research Institute (NMRI), in collaboration with the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), is conducting research and development of seafloor observation technology using multiple autonomous underwater vehicles (AUVs) and one autonomous surface vehicle (ASV) under the 2nd SIP project “Innovative Technology for Deep Sea Resource Exploration.” A group of heterogeneous AUVs with different design concepts may have to be controlled when operating multiple AUVs simultaneously. In this study, we developed a basic formation control system that enables various AUV control with minimal software and hardware modifications to ASV and AUVs and successfully tested it in actual sea conditions. Four AUVs and one ASV from different manufacturers were used in the sea trials. The basic formation control system kept all AUVs within acoustic communication range and successfully acquired seafloor topographic data. The tests demonstrated the capability of basic formation control with heterogeneously navigated AUVs. This paper reports and summarizes the test results of those basic formation control tests.
A Numerical Simulation Tool of Ship Navigation in Ice Under Various Ice Conditions
Authors: Li Fang , Kujala Pentti
Published: September 2023

The performance of ships going through ice-covered water is a main focus of the design of such ships. Estimation of ships’ ice-going performance has been a challenging task for decades due to the complexity in the modelling of ship-ice interaction process. To date, empirical formulae have been the mostly used method in ship design practice. Over the last decade, numerical simulation has emerged as an alternative technique for the evaluation of ships’ ice-going performance. A ship-operation-in-ice simulator has been developed at Aalto University during the past few years. The simulator supports diversified operation senarios such as going straight ahead or turning in level ice, navigation through narrow ice channel, breaking out of channel, as well as going through compressive ice channel. The simulator is designed as a Matlab Application with user interface and as well support running through scripting. It requires light computation and can be executed with a normal PC within a relatively short time. This paper introduces its overall structure, modelling techniques and associated functionality. Examples of various operation scenarios are given to illustrate the functionality of the simulator. Comparisons with model scale tests and full-scale measurements are provided to demonstrate the validity of the simulator. Finally, the planned further development is described.
Wave-Induced Dynamic Seabed Response Around a Submerged Breakwater With Dynamic Permeability
Authors: Li Zhengxu , Jeng Dong-Sheng
Published: September 2023

In this paper, an integrated numerical model with Open-FOAM for the wave-breakwater-seabed interactions problem is presented. Unlike previous studies available in the literature, the present model adopts Biot’s u-p approximation and considers dynamic seabed permeability, which is a function of pore-fluid pressures in the seabed. The proposed model is verified against the existing experimental data. The numerical examples show that dynamic permeability has a significant effect on wave-induced dynamic soil responses, which will cause a deeper and wider liquefaction zone compared with the conventional models with constant permeability. Ignoring the effects of dynamic permeability could significantly impact the transient seabed liquefaction depth and the stability of offshore structures.
A Framework for Defining Risk-Based Inspection Plans for Subsea Equipment
Authors: Schleder Adriana M. , Maturana Marcos C. , Ramos Martins Marcelo , F. F. Frutuoso e Melo Paulo , Barros Leonardo de Oliveira , Orlowski Rene Thiago Capelari
Published: September 2023

Cost and risk optimization is a central issue in the offshore Oil and Gas sector, and risk-based approaches has been more and more employed to assist the segment in the concretization of that goal. In this sense, the use of Risk Based Inspection by the oil industry has increased. The inspection procedure aims mitigating the uncertainty related to the asset degradation state, enabling a better quantification of the actual damage, and, consequently, increasing the accuracy of remaining life projections. However, the costs involved in offshore subsea inspections are considerable. Therefore, the optimization of inspection plans plays a crucial role in the definition of an asset management program economically balanced. To perform an efficient optimization, it is important not only obtain an effective optimization algorithm but also achieve a high quality of the information used as input. In other words, an adequate definition of the risk indexes used is necessary, as well as the entire process used to quantify them. In this context, this paper presents a framework for obtaining the optimized inspection plans, starting from the assessment of the risk associated with the failure modes, moving on through the process of defining risk indices and, finally, presenting the optimization process itself. In this way, the framework proposed presents all the phases necessary to obtain optimized inspection plans, including the stage of preparation for the optimization process. Finally, the application of the proposed framework is illustrated by the elaboration of the inspection plans for a subsea manifold.
Numerical Simulation of the Wave-Induced Drift of Disc-Shaped Floating Plastic Debris
Authors: Westerkamp Diederik , Rakotonirina Andriarimina Daniel , Sainte-Rose Bruno , van den Bremer Ton
Published: September 2023

Floating plastic debris poses a significant threat to the health of the world’s oceans and ecosystems. Understanding the pathways of floating marine litter is crucial in designing effective solutions to mitigate this problem. The Ocean Cleanup aims to build simple but reliable numerical models to better predict plastic accumulation zones. In this context, a Lagrangian point-particle model has been developed that can help better understand wave-induced drift. The continuous and the discrete phase are coupled in a one-way fashion using a micro-scale Euler-Lagrange approach. The Maxey-Riley equation is modified to account for disc-shaped objects, variable submergence, and two-directional drag correlation. By comparing our numerical predictions with experimental work, we demonstrate that floating discs can experience up to 73% increased wave-induced drift compared to Stokes drift. We show that the non-Lagrangian behaviour of objects is mainly dependent on the water-plastic density ratio and its size compared to the wavelength. Two key physical mechanisms contributing to increased drift effects are investigated, both related to the particle’s variable submergence. Finally, we provide an overview of the computational limitations and the model sensitivities that can help to improve the accuracy of numerical wave-induced drift predictions.
Upheaval Buckling Analysis of the Large Deformation of Unbonded Flexible Pipe Under Cyclic Pressure and Temperature Loadings
Authors: Liu Jian , Zhu Linfa , Tan Zhimin , Roberts Andrew , Murray Sean , Trousdale Euan , Patrocinio Juliana , Casanovas Revilla Clara , Lopes de Castro Mario Augusto
Published: September 2023

The upheaval buckling (UHB) behaviour of buried unbonded flexible pipes governs the cost of mitigation measurement in terms of material and installation. The traditional industry approach to mitigate UHB risk of flexible pipes is to design them to stay in place, which is inherited from rigid pipelines technology where a catastrophic buckling can be triggered by small perturbations within material elastic region. On the other hand, unbonded flexible pipes of multiple layer construction are designed to accommodate large pipe deformation without compromising their structural integrity. By allowing large upwards movement of flexible pipes within the soil cover, an alternative UHB analysis design approach will present a better reality compared with the stay in place design approach.

The present paper investigates the large deformation characteristics of flexible pipe interacting with soil cover beyond its mobilization displacement, i.e., post-buckling behaviour. The paper also explores a method to account for the effects of potential cyclic pressure/temperature loadings where the pipe reversible displacement might be resisted by ‘fill in’ material. The study will use finite element analysis method. Sensitivity studies are performed to investigate the impact of different pressure loading history during the pipe service life on the final pipe deformation configuration and its UHB risk of breaching soil cover. A comparison is also made to the traditional stay in place mitigation approach to demonstrate the improvement, for example, the volume of rock dump, without violating both the pipe functional requirements and structural integrity.
Application of Different Methods to Determine the Ultimate Strength of Ships in Bending
Authors: Lindemann Thomas , La Ferlita Alessandro , Di Nardo Emanuel , Kaeding Patrick
Published: September 2023

Displacement controlled nonlinear finite element analyses are performed to determine the ultimate strength of three different vessel types in vertical bending. Parametric finite element models are proposed for a bulk carrier, double hull VLCC and for a container vessel. The influence of different model parameters on the collapse behavior is shown for sagging and hogging condition. The influence of initial imperfections of the stiffeners and the attached plating due to welding is taken into account. The results are validated for all different ships against Smith’s method. An inhouse code has been developed following the Common Structural Rules (CSR) proposed by the International Association of Classification Societies (IACS). The Smith’s method based results of intact and damaged ships in vertical bending have been used to train a Deep Neural Network (DNN) as machine learning approach. The applied network architecture is composed of two layers with a high-level number of activation units. The applicability of DNN to predict rapidly the ultimate strength of ships in vertical bending is demonstrated exemplarily for the same bulk carrier, double hull VLCC and the container vessel. Furthermore, DNN is used to determine the shift of the neutral axis for the different vessels.
Performance Analysis and Optimization of a Wave Energy-Based Zero-Liquid-Discharge Hybrid Desalination System
Authors: Glosson Gabriel , Filho Faete , Chen Jinbo , Abdel-Salam Tarek , Duba Kurabachew
Published: September 2023

The demand for freshwater is increasing globally, particularly in areas with limited water resources. Desalination, the process of removing salt and other minerals from seawater, is one solution that can help meet this demand. However, traditional desalination methods can be energy-intensive and generate significant amounts of waste. To help address these issues, a hybrid wave-to-water desalination system that combines reverse osmosis (RO) with supercritical water desalination (SCWD) can be used to produce freshwater from seawater. SCWD is used to treat the brine produced by RO, while the RO system produces fresh water at a lower energy cost. The system utilizes a wave energy converter (WEC) to harness the energy of ocean waves to power the desalination process by using the motion of waves to directly pressurize the seawater feeding into the RO system. Using ocean waves as an energy source makes the system renewable and reduces the carbon footprint of the desalination process. This paper presents a numerical model of a small-scale zero-waste desalination system powered by off-grid renewable energy along with a sensitivity analysis to determine the optimal configuration of key parameters of the system. An oscillating surge wave energy converter (OSWEC) was selected for the current study to directly pressurize the ocean water to meet the minimum pressure requirement of the RO. The numerical model of the water desalination system was developed using MATLAB-Simulink. WEC-Sim was used to develop the wave energy converter subsystem. A sensitivity analysis was conducted using an irregular wave pattern with a wave height of 0.117 m and a period of 1.68 s to determine the optimal combination of the power take-off (PTO) volumetric displacement, accumulator size, and RO membrane type for the system. Results showed that the type of RO membrane and the PTO volumetric displacement had a much larger impact on the water production rate than the accumulator volume.
A Novel Numerical Model for Computing the Global Response and Fatigue of a Steel Catenary Riser Based on Absolute Nodal Coordinate Formulation
Authors: Hou Jing , Jia Lusheng , Liu Yi , Wang Dejun , Jia Xu , Zhang Cheng
Published: September 2023

Steel catenary risers (SCRs) are widely used in ocean engineering, whose dynamic performance is particularly critical to the safe operation of offshore oil and gas development. In order to fully consider the nonlinear factors of SCRs, a novel numerical model has been established based on the absolute nodal coordinate formulation (ANCF) in this paper. The position and slope coordinates are used in global framework to avoid coordinate transformation, and the accurate geometric relationship is introduced to describe the geometric nonlinearity of structural deformation. A hysteretic riser-soil interaction model is applied to simulate the nonlinear seabed force while the Morrison equation is used to compute the nonlinear current and wave forces. The overall static and dynamic equilibrium equations, deduced by the principle of virtual work, are numerically solved by Newton-Raphson and Newmark-β methods, respectively. The proposed model is compared with the software OrcaFlex in the numerical simulation for a typical SCR, following by a discussion on the response characteristics of the SCR. The model is proved to reliable to evaluate the dynamic performance and fatigue damage of SCRs, which can further support their engineering designs.
Spatial Distribution Characteristics of Ice Pressure Loads Under Turning Operations in Level Ice
Authors: Ge Yuhui , Ding Shifeng , Liu Renwei , Wang Aimin
Published: September 2023

There is variability in the degree of danger encountered by different hull areas when turning in level ice, so predicting the trend of load characteristics with turning angle in advance can improve navigation safety. In this paper, we use a well-developed numerical simulation method, A more reasonable turning condition was selected, and the Weibull distribution is used to describe the numerical results. The collision probability of ice pressure along the hull area under different turning angles are analyzed by probabilistic statistical methods, and the trend of ice pressure peak with angle at typical positions is studied to reveal the intrinsic relationship between ice pressure load characteristics and turning angles.The results showed that the collision mainly occurred in the inner midship at the beginning of the turn, and gradually shifted to the bow and the shoulder area as the turning angle increased; when the turning angle tended to be horizontal or vertical with the sea ice, the collision probability in the outer midship increased.
Investigation on Layout Optimization of Helical Strakes on Marine Riser
Authors: Deng Pengqian , Fu Shixiao , Zhang Mengmeng , Ren Haojie , Xu Yuwang , Sun Tongxiao
Published: September 2023

Helical strakes have been widely used in ocean engineering to suppress vortex-induced vibrations (VIV) of risers. To reveal the optimal layout scheme of helical strakes in engineering, a prediction method base on the non-iterative frequency domain is applied to investigate the VIV responses of risers with different strake coverage rates in this paper. On this basis, the multi-objective optimization algorithm is further used to obtain the optimal layout scheme of helical strakes in engineering. Comparisons between the prediction result and the experimental result under uniform flow are conducted to verify the feasibility and reliability of the prediction method. Results show that the coverage rate and position of strakes have a great influence on the fatigue damage rate and the total drag of the riser undergoing VIV, and it is not always optimal to cover helical strakes from the top of the riser.
Experimental Investigation on Response of Ship Rolling Motion Coupled With Liquid Sloshing
Authors: Wang Yunhe , Jiang Shengchao , Zhou Tongming
Published: September 2023

Ship motion coupled with sloshing of three partially filled prismatic tanks is analyzed experimentally in a towing tank. The results show that the sloshing can increase the natural period of ship motion and another peak caused by the sloshing inside the tanks can be seen at a lower period. In addition, anti-rolling effect under low filling conditions and enhanced-rolling effect under high filling conditions are observed, depending on the dominant force, namely, the hydrostatic force and the hydrodynamic force for different filling depths. The internal sloshing flow is able to generate the restoring moment and overturning moment at both low-filling conditions and high-filling conditions, respectively, leading to the suppressed and enhanced effect on ship rolling responses. It is also found that if the filling depths of the three tanks are not the same, the ship rolling motion will be reduced significantly, especially at the resonant period of ship rolling motion.
Predicting the As-Laid Embedment of Surface-Laid Pipelines and Cables in Sand Wave Regions
Authors: Hou Zhechen , Bransby Fraser , Watson Phil , White David , Ballard Jean-Christophe , Delvosal Pierre , Denis Raphael , Low Han Eng
Published: September 2023

Predicting the as-laid embedment of surface-laid pipelines and cables is important for estimating their in-service response. To date, design approaches have only considered flat seabed conditions. The as-laid embedment is estimated using vertical ‘lay down’ seabed springs that are calculated allowing for the pipeline geometry and weight as well as its interaction with the seabed during the dynamic lay process. This paper addresses the important and different case where pipelines and cables are laid on a seabed with bedform features (e.g. sand waves, mega ripples or ripples). The measured as-laid embedment for a pipeline installed within a region of sand waves on the North West Shelf of Australia is examined and compared with numerical simulations of the lay process. Good agreement with the field embedment is obtained for both flat and sand wave zones. However, this is achieved using soil springs that are around 10 times softer than prescribed by current recommended practice. This is attributed to the neglect of dynamic lay effects in design guidance for sands and the high compressibility of carbonate soils. The field data and the simulations both show that the pipe embedment varies throughout each sand wave. The maximum embedment near the sand wave peak is greater by a factor of up to 5 compared to the minimum embedment found near the sand wave trough. The embedment profile is phase-shifted from the sand wave profile by 10–20% of the sand wave length.
A Coupled Fluid-Structure Model for Estimation of Hydraulic Forces on the Tool-Joints
Authors: Volpi Lucas P. , Cayeux Eric , Wiggo Time Rune
Published: September 2023

Most models employed for fluid forces in drill-string dynamics are of reduced order. The simplified nature of these models often fails to describe complex behaviour of the fluid force, in particular when the drill-string movement is non-trivial or even when non-Newtonian behaviour is predominant. In this work, the fluid forces are estimated by modelling the dynamic of the drilling fluid for both Newtonian and non-Newtonian fluids, and compared with reduced order models. To achieve it, the lattice Boltzmann method is implemented to solve the fluid model, while prescribed movements are set for the tool-joint. With the obtained fields, the forces are calculated and compared with recurrent models. Finally, it is observed that some models are capable of describing the interaction as long as the dynamic of the tool-joint is simple. In the presence of other trajectories — e.g.: bouncing and chaotic — the models fail to describe the details of the dynamic.
A Methodology for Tuning of Computational Vessel Models Utilizing Wave Measurements From X-Band Marine Radar and Wave Buoy
Authors: Radhakrishnan Gowtham , Leira Bernt J. , Gao Zhen , Sævik Svein , Kaasen Karl E. , Christakos Konstantinos , Dirdal Johann A.
Published: September 2023

Accurate estimation of the wave field and subsequent vessel response prediction are vital for making crucial judgments on the safe and timely execution of marine operations. Decision support systems based on the Response-Based Decision-Making (RBDM) methodology are still in the early stages due to the challenges in addressing the uncertainties in the environmental conditions and vessel computational models. Therefore, this study offers a model tuning technique that utilizes the waves measured from an onboard X-band wave radar, wave buoy, and simultaneously measured vessel motions using an Inertial Measurement Unit (IMU), for applications in RBDM. For this purpose, full-scale wave and vessel response measurements were conducted using the NTNU research vessel Gunnerus on the west coast of Norway. The on-site directional wave spectra are obtained by processing the backscattered radar images using existing inversion schemes. Furthermore, the directional wave spectra are also derived from the nearby wave buoy measurements using the Maximum Entropy Method (MEM). The influential system variables in the vessel model that induce maximum variation to the response Quantities of Interest (QoIs) are quantitatively identified using probabilistic sensitivity indices. Out of the 31 system variables, only 14 were considered influential and subsequently tuned by minimizing the error between the measured and simulated response spectra. Heave, roll, and pitch modes were tuned and results exhibit superior agreement with the measured response spectra.
Long-Term Corrosion of Parked and Abandoned Offshore Steel Pipelines
Authors: Melchers Robert E.
Published: September 2023

Internal corrosion of steel pipelines before use, or temporarily taken out of use, and ‘parked’ on the seafloor for some time (months), suspended from operation or ‘abandoned’ for extensive period of time continues to be an issue for offshore operators and regulators. This is irrespective of whether the pipes are gas or oil production or water injection pipelines. Severe pitting corrosion, sometimes observed at the 6 o’clock position, conventionally often is assumed the result of microbiologically influenced corrosion (MIC), particularly if coupled with high bacterial concentrations in the rusts. Dosing with biocides is not always effective and increasingly is considered environmentally undesirable. This paper provides a brief overview of the fundamental requirements for long-term corrosion under low oxygen and essentially stagnant environmental conditions. It shows that any severe internal corrosion at the 6 o’clock position has similarities to that sometimes observed for water injection pipelines and likely the result of under-deposit corrosion resulting from the deposition of rusts and other debris. MIC may contribute providing there is availability of necessary nutrients. Generally similar issues apply for the external and interior corrosion of abandoned pipelines. Avenues for further research and development are outlined, including for pipelines proposed to be abandoned.
Rapid Residual Strength Assessment of Degraded Mooring Chains Using an FEA Based Response Surface Modelling Tool
Authors: Gunn David , Dimopoulos Simon , Carra Chris
Published: September 2023

Design of moorings with chain sections typically assume a level of uniform through-life corrosion and wear. The associated reduction in strength is, in simplistic terms, estimated by assuming a smaller as-new chain diameter.

Where inspections show chain links to have localised material loss the resultant reduction in strength is harder to account for as it is dependent on the volume, shape and location of the loss. Discard criteria found in design standards are necessarily conservative as they must encompass the most damaging combinations of size, shape, and location of material loss. As a result, operators have turned to Finite Element Analysis (FEA) to directly assess the effect of localised chain material loss. Whilst this approach has been shown to be effective it incurs significant computational cost and is time consuming and expensive when compared to the application of these simple discard criteria.

The Corroded Chain Analysis and Structural Evaluation (CCASE) tool has been developed to leverage the benefits of FEA while reducing significantly the time and cost associated with a chain anomaly assessment, providing a rapid prediction of the degraded chain’s residual strength within minutes.

CCASE utilises the results of FEA conducted previously for the Chain FEARS JIP as well as newly performed FEA for pitting, seabed, hawsepipe, and interlink wear anomalies to generate a Response Surface Model (RSM) of Break Load Prediction. The geometry of the degraded chain links is input into CCASE via a point cloud file typically obtainable by surface or subsea photogrammetry scanning methods. These chains are then characterised by the tool, relative to an idealised chain link, at a number of cross sections around the geometry. These characteristic parameters, when used with the Response Surface Model (RSM), predict the break load of the degraded chain link.

The CCASE tool was able to predict the break load of test degradation geometries, independent of those used to develop the RSM, to within approximately 5% of the break load predicted by the FEA approach for the cases tested and within a similar margin for two cases involving real-world degraded chain pulled to destruction on a test rig.

CCASE can thus be used to perform rapid, cost effective engineering assessments of chain anomalies in place of traditional conservative discard criteria. This gives an operator a clearer decision path to continue to monitor chain anomalies or commit to expensive replacement works.
The Study of the Wave Attenuation Performance of Triple Plates Interacting With a Solitary Wave
Authors: Wen Chang-Qing , Wu Jing-Ping
Published: September 2023

In order to explore measures to reduce tsunami wave height, this paper uses solitary waves instead of tsunamis, numerically simulates the interaction between triple rigid flat plate model and solitary waves, and analyzes the effects of the dipped depth, plate spacing and tilt angle on the transmission coefficient. The triple rigid plates are the same scale and remain unchanged. The relationship between plate length L and water depth h is L/h = 0.4; the vertical distance d from the lower end to the water surface is used to change the position of the plate in the water. Triple plates is in the equal space S arrangement. Based on the Fluent software platform, a two-dimensional numerical wave flume is constructed, and the piston-type solitary wave generation method based on Goring is used to simulate the physical solitary wave. Firstly, a solitary wave is numerically constructed at different truncation velocities R, and compared with the solitary wave height of the analytical solution and the experimental results, the numerical simulation parameters such as the truncation velocity R with sufficient accuracy are determined. Then, under the same water depth h and solitary wave height H, the propagation of solitary waves in triple plates under 9 kinds of relative dipped depth d/h, 16 kinds of relative spacings S/λ and 15 kinds of tilt angles is numerically simulated, the transmission coefficient Ct of the model is calculated, and the effects of the relative dipped depth, relative spacings and tilt angles of the plates on the transmission coefficient Ct are analyzed. The results show that the transmission coefficient decreases first and then increases with the increase of the relative dipped depth d/h, and there is an optimal relative dipped depth d/h. The transmission coefficient decreases monotonically with the increase of the relative spacings S/λ, and tends to be flat. When relative dipped depth d/h = 0.13 and the relative spacings S/λ = 6.69%, the transmission coefficient is the smallest at the tilt angle of 75°.
Tribological Performance of Nylon-6/Oyster Shell Composites
Authors: Ambika Harikumar Akshay Krishna , Heitzmann Michael Tobias , Basnayake Asanka , Khakbaz Hadis , Martin Darren
Published: September 2023

Polyamide-6 (PA6), an engineering thermoplastic polymer widely used in tribological and structural application due to its low-cost, manufacturing ease and better performance. PA6 exhibits high strength, high modulus, abrasion resistance and can be manufactured via injection moulding technique. Wear and mechanical performance of PA6 reinforced with oyster shell powder at different filler contents were investigated in this paper. Raw oyster shell was sourced from the local supplier and series of steps have been performed to manufacture the composite material as shown in Figure 1.

Tensile and wear tests were carried out on the injection moulded composite specimens. Addition of oyster shell has positivity influenced the tensile strength and modulus of PA6 polymer material and increased with increasing filler content. Strain at break has significantly dropped by the addition of oyster shell filler and decreased with increasing filler content. Composite materials have shown a higher wear rate compared to the pure polymer.