bluuebunny/crossref_metadata_2025 huggingface dataset:
Failure Rate and Repair Time Analysis of Offshore Wind Turbines
Authors: Guarda Luis Felipe , Terra Leonardo , Ramos Martins Marcelo
Published: September 2023

Offshore wind turbines have several advantages over onshore turbines, such as greater efficiency and the ability to generate greater amounts of energy in a more constant manner. Despite this, the Levelized Cost of Energy of onshore wind turbines is still lower than for offshore wind turbines, and the main reason for this difference comes from the operating and maintenance costs. For this reason, optimize the operating and maintenance costs of offshore wind turbines represents one of the biggest opportunities to improve the offshore wind industry. However, the lack of failure rates and repair times for the new and bigger offshore turbines prevents the feasibility to develop new reliability analysis that could improve the offshore wind turbines costs. To tackle this problem, this work presents a comparison between the 7MW Levenmouth Demonstration Turbine and a theoretical wind turbine obtained from a literature review, contrasting in this way a data-based analysis against the information available in the literature. The obtained results show the feasibility of data-based analysis and Monte Carlo Simulation comparison to failure rates validation and transfer knowledge from the onshore to offshore wind turbine industry.
Large Scale Test of Automatic Tsunami Barrier
Authors: Hamada Eigai
Published: September 2023

The Anti-Tsunami Laboratory (ATL), represented by Eigai Hamada, invented and developed the Anti-Tsunami Door (ATD) as a compact automatic tsunami barrier. In March 2022, ATL tested a large-scale model of a three-stage ATD unit using the Large Wave Flume (a hydraulic test facility) at Oregon State University (OSU) and confirmed its performance: (1) functioning automatically (refer to Figure 4); (2) achieving reasonable wave height reduction, which is approximately 89% of a solid barrier of almost the same height; and (3) demonstrating reasonable strength for a wooden structure under the large-scale model test conditions. Before this test, the Explosion Research Institute (ERI) simulated the wave pressure on a large-scale model ATD unit, because the wave pressure on the ATD unit is expected to be high during the large-scale model test. In this test, ATL measured the wave pressure on the surface of each stage of ATD under post-operation (fully standing) conditions and found that the measured wave pressures are almost same and somewhat higher than those which were simulated previously.
Implementing a Method for Meteorological and Oceanographic Climate and Data Evaluation
Authors: Gullaksen Joannes
Published: September 2023

During the initial phase of the design of an offshore renewable or sustainable energy project, it may prove useful to carry out environmental climate assessment as part of a methodological study to assess the suitability of an offshore renewable energy project. This paper presents description of extreme design mode implemented in a software application designed to support screening of meteorological and oceanographic climates. The method of estimating extreme values is controlled by the availability of data, such as known or unknown probability distributions, maximum wave height, and available time series of sample data. The implementation takes into account both global models and event models in the analysis strategy. The global model strategy describes the long-term variation of the environmental climate in terms of generic distributions, such as marginal distribution models established by adapting the entire dataset from the geographical location using different fitting techniques. In the event model strategy, the extreme value analysis includes selection of data for statistical analysis, sample selection method, model distributions, fitting methods, goodness of fit test and return period values. The criteria for choosing the fitting method are based on minimizing uncertainty and bias in the extreme value estimation, where the test of whether the adaptation method meets the criteria is carried out using a simulation technique. Other important topics, though not covered in this paper, include load analysis, which involves numerical methods for complete models. This application is based on available meteorological and oceanographic data as input to establish climate, estimate design conditions, and select and apply a theory. However, the application can also be used where time series analysis and spectral analysis are already in place. This can have benefits, such as improving the quality of environmental impact analysis.
An Investigation of the Influence of Added Mass on the Ice Loads in Various Sea States
Authors: Jiang Zongyu , Li Fang , Suominen Mikko , Tavakoli Sasan , Kujala Pentti , Hirdaris Spyros
Published: September 2023

Popov et al. (1967) proposed an approach to evaluate the ice loads during ship-ice impact. The approach firstly calculates the reduced mass and velocity of ship-ice system based on the principle of conservation of momentum. Secondly, it predicts the ice loads by assuming that the reduced kinetic energy is absorbed by the work of contact crushing stress. The added mass used at the first stage of Popov approach is estimated with simplified empirical formulas.

This paper attempts to introduce an improved method for the prediction of ice loads by accounting for the influence of the added mass, calculated by potential flow theory, in Popov’s approach. The evaluation of ice loads involves the effects of: 1) ship and ice geometry; 2) waves; and 3) hydrodynamic cross coupling between ship and ice.

A potential flow theory model, consisting of a ship and an ice floe, is built to calculate the added mass, wherein the ship is approaching the free-floating ice at a constant speed in random waves. The added mass is subsequently integrated into the Popov approach to evaluate the ice loads. Comparisons of results with those from the conventional Popov prediction reveal that the ice loads are considerably affected by the influence of added mass in waves. Notwithstanding this, ice loads may not be sensitive to hydrodynamic interactions.
Dynamic Response and Damage Assessment of Subsea Pipelines Under Dropped Object Impacts
Authors: Yang Kun , Sha Yanyan , Liu Zhenhui
Published: September 2023

Subsea pipelines transporting crude oil, liquified natural gas and carbon dioxide have been installed offshore for the past decades. However, there are many situations where heavy objects may drop from significant heights over subsea pipelines. These scenarios typically happen during crane operations on platforms, lifting operations from supply vessels, and accidental structural component failure. Such accidents can pose a significant threat to subsea pipelines due to the large mass and velocity of the dropped objects. Therefore, proper analysis and design shall be performed for subsea pipelines under accidental dropped objects impacts. However, present guidelines for the analysis and design of subsea pipelines subjected to dropped object impacts are limited and often based on simplified assumptions. The interaction of the dropped object and the impacted pipeline is often disregarded. In this study, dynamic analyses of subsea pipelines under dropped shipping containers are performed. Finite element models of steel pipelines with and without concrete coating were developed. The structural deformation and damage to both the dropped container and the impacted pipeline are considered. Numerical simulations were performed to investigate the effect of impact angle and pipeline dimensions. The contribution of concrete coating to impact resistance is also discussed. Design considerations were also proposed for dropped object protection of subsea pipelines based on numerical results.
Annotated Guidelines for the Simulation of Floating Offshore Wind Turbines in a Real Environment
Authors: Papi Francesco , Bianchini Alessandro
Published: September 2023

In the case of floating wind turbines (FOWTs), international design standards currently leave a larger degree of freedom to engineers in the specification of the boundary conditions for turbine simulation and certification. This is due to fact that FOWTs are still a young technology, and standards are still evolving. To analyze offshore wind turbines and estimate parameters such as AEP, fatigue and extreme loads, site-specific reference environmental conditions need to be defined. Then, a probabilistic model of the installation site must be built in order to compute lifetime quantities. Finding a trade-off between simulation number and length and good long-term estimation of fatigue and ultimate loads, as well as the selection of relevant loading metrics requires a significant amount of research or experience in the field.

The current work aims at exploiting a procedure that was developed within the H2020 FLOATECH project and made available open source with this study to the scientific community, with the objective of addressing what is required to perform a load and performance evaluation of a FOWT in a real environment. A procedure to obtain environmental conditions if the ones available in the literature do not meet the designer’s needs is first illustrated. Then, the most important parameters that need to be considered when performing an analysis of a FOWT are detailed; taking these into account and their corresponding metrics, a detailed guideline on how to define a suitable list of Design Load Cases (DLCs) is presented, as well as different methods to reduce the number of model evaluations deriving from the DLCs’ list, and thus reduce computational time.
Effects of Controller Dynamics on Aerodynamic Damping of a Semi-Submersible Floating Wind Turbine
Authors: Yang Can , Xiao Longfei , Chen Peng , Cheng Zhengshun
Published: September 2023

Aerodynamic damping is essential in suppressing resonant responses of a floating wind turbine (FWT) under operation conditions. However, aerodynamic damping has not been investigated thoroughly due to its nonlinearity, interaction with floater motions, and effects on controller dynamics. The effects of controller dynamics have been explored in the present study to understand aerodynamic damping better using fully coupled time-domain simulations. The aerodynamic damping in surge and pitch motions are obtained through the comparisons of decay tests with and without wind actions in still water with verification against results from the model tests. Results show that under over-rated wind speed conditions, the blade-pitch controller can affect the aerodynamic damping. In addition, the aerodynamic damping in surge motion is not sensitive to the natural frequencies of the blade-pitch controller. However, the aerodynamic damping in pitch motion has a strong dependence on the controller’s natural frequency. Through reasonably tuning the controller gains, the negative aerodynamic damping effect can be well mitigated. The outcomes of the present study can provide insight into aerodynamic damping and the controller design of FWTs.
Gradient-Based Design Optimization of Fully-Flexible Floating Wind Turbines Using Modal Analysis
Authors: Rohrer Peter J. , Bachynski-Polić Erin E. , Hegseth John Marius
Published: September 2023

A variety of substructure concepts for floating offshore wind have been developed. Design optimization can be used to efficiently explore this design space and guide further work. Previous design optimization studies have been limited by model simplifications, including the assumption of rigid body motions, lack of substructure flexibility, and a focus on a single floating foundation concept. High computational costs of gradient-free optimization methods have limited the number of design variables considered. In this work, gradient-based optimization methods and a frequency-domain modal analysis model based on three-dimensional modeshapes make it possible to consider a more detailed structural model with reasonable computational cost. This work implements a linearized aero-hydro-servo-elastic model of a tension-leg platform wind turbine. The optimization varies sizing parameters and the model computes responses to wind and wave forcing in multiple environmental conditions. The model computes forcing and response in generic modes rather than assuming rigid body motions. Implementation of the model with analytical gradients in OpenMDAO allows for efficient optimization with dozens of design variables. The optimization results show reduction of the objective while satisfying constraints. Furthermore, there is potential for this approach to be adapted to other floating wind turbine substructure designs.
Placing Off-Bottom Cement Plugs: Effects of Density Difference
Authors: Ghazal Abdallah , Karimfazli Ida
Published: September 2023

The abandonment protocols of oil and gas wells may vary among regions and countries. Most commonly, however, two or more cement plugs are placed along the well for this purpose. The plugs above the lowermost plug are often referred to as off-bottom. The most used technique to place off-bottom plugs is known as the balanced-plug. Following the Western Canadian practices, wellbores are often flushed with water before the plug placement. A successful placement is achieved when the injected cement slurry accumulates at the target position, over the lighter wellbore fluid. To ensure the long-term integrity of the abandoned wells, the contamination of the injected fluid should be minimized.

We develop a hydrodynamic model of the early stages of placement in a representative two-dimensional domain. In our previous works, we considered a fixed density difference between the two fluids and investigated the effect of the injector size and eccentricity. In this study, we investigate the effect of the density difference on the displacement flow and the quality of the accumulated injected fluid. When the density difference is sufficiently large, the front of the injected fluid accelerates after the onset of injection. When the density difference is sufficiently small, the front velocity reduces to a quasi-steady value after an initial acceleration. A transition in the front velocity between the two extreme cases occurs in a moderate range. Except where the displacement flow does not develop, the injected fluid accumulates when the flow destabilizes below the injector. The preliminary results reveal intermittent mixing of water with the accumulated cement slurry. The quality of the cement slurry changes non-monotonically with the density difference.
Experimental Investigation on Dynamic Responses of Floating-Point Absorber Wave Energy Systems
Authors: Aiswaria K. , Ramakrishnan Balaji
Published: September 2023

Integration of wave energy converters with coastal structures is a promising approach to boost economic power production. For the evaluation of the responses of wave energy devices to waves, it is important to measure their motion during wave tank tests. This paper investigates the dynamic response of floating-point absorber wave energy converter (WEC) devices that are integrated with a chambered breakwater. The main focus is to determine the heave motion of wave energy device models using a Qualisys motion capture system. The model considered for the study is a spherical buoy floating alone and also in a chambered breakwater system.

Experiments are carried out at the Ocean Engineering Laboratory of IIT Bombay and the heave motion of the model under different wave conditions are recorded using the Qualisys motion capture system. The Qualisys cameras track the movement of reflective markers installed on the model with high precision. The data captured by each marker are assembled to calculate the heave motion of the model using the postprocessing software, Qualisys Track Manager. The heave motion measurements of the stand-alone model and integrated with the chambered breakwater model in regular waves are compared to the published data as well as numerical simulation results. The motion of the buoys in irregular waves are then estimated to study the behavior of the WEC bodies and to provide experimental data for further research.
Numerical Study of Wind Loads and Experimental Validation for a FPSO Vessel Model
Authors: Zhang Baili , Dao My Ha , Xing Xiuqing , Lou Jing , Tan Wei Siang , Cui Yongdong , Khoo Boo Cheong
Published: September 2023

FPSO is one of the largest vessels in offshore industry, the complexities of its topside structures pose a big challenge in reliable prediction of wind loads both with CFD modeling and in wind tunnel test. In this study, we have conducted detailed CFD studies of wind flow over a generic FPSO model at both full scale and model scale of 1:400, including the impact of different wind velocities and wind profiles. In the model scale, the simulations are performed at the constant wind velocity of 10m/s and 20m/s, for all wind headings between 0 to 360 degrees with a step of 10 degrees. The calculated wind loads in the form of coefficients of three force components and three moment components are validated against experimental measurements. In addition to the overall wind loads on the FPSO, the static surface pressures at 28 sensor locations were also measured during the wind tunnel test. In general, they are compared well with CFD simulation results. For the full-scale model, the CFD simulations are performed at different design wind speeds, the results confirmed the scalability of wind loads at the model scale. The impact of wind profile shape is addressed in this paper as well.
A Neural Network Approach to Minimize Line Forces in the Survivability of the Point-Absorber Wave Energy Converters
Authors: Shahroozi Zahra , Göteman Malin , Engström Jens
Published: September 2023

One strategy for the survivability of wave energy converters (WECs) is to minimize the extreme forces on the structure by adjusting the system damping. In this paper, a neural network model is developed to predict the peak line force for a 1:30 scaled point-absorber WEC with a linear friction-damping power take-off (PTO). The algorithm trains over the wave tank experimental data and enables an update of the system damping based on the system state (i.e. position, velocity, and acceleration) and information on the incoming waves for the extreme sea states. The results show that the deep neural network (DNN) developed here is relatively fast and able to predict the peak line forces with a correlation of 88% when compared to the true (experimental) data. Then, the optimum damping for survivability purposes is found by minimizing the peak line force. It is shown that the optimum damping varies depending on the system state in each zero up-crossing episode.
Maintaining Constant Export Oil and Gas Rates in Offshore Installations Powered by Fluctuating Wind Energy
Authors: Eyni Leila , Stanko Milan , Schümann Heiner
Published: September 2023

The majority of offshore oil and gas platforms are powered by gas turbines, which are the most significant source of CO2 emissions from offshore oil and gas production. Utilizing offshore wind farms to power processing systems can considerably reduce the total amount of CO2 emitted. However, wind energy has the disadvantage of being intermittent.

This work studies the feasibility of maintaining constant export rates of oil and gas with intermittent power supply and operations of the processing facilities. This is accomplished by utilizing the storage capacity of a large oil tank and variable pressure in an export gas pipeline (line packing and drafting). These methods and the required dimensions are evaluated. This study is based on a case study of an offshore field located on the Norwegian Continental Shelf (NCS).

This study was performed using numerical modeling. The results indicate that the optimal oil tank capacity can be determined for different amounts of fixed desired export oil rates. The required size of the oil tanks is within the range of dimensions commonly used for offshore platforms. Moreover, it has been demonstrated that the export gas rate can be maintained by altering the pressure distribution within a reasonable range.
Optimal Design for the Crashworthiness of the Hull Side Structure Under the Impact of the Raked Bow
Authors: Yu Pengyao , Zhang Chengyu , Zou Runbei , Wang Qiang , Zhang Boran
Published: September 2023

The crashworthiness of hull structures is an important aspect which needs to be considered in the design of hull structures. Serious collision accidents may lead to casualties and economic losses. The raked bow is a common design for many ships, such as supply vessels, merchant vessels, oil ships, and warship. However, many collision studies focused on the structural damage caused by the bulbous bow, and the studies on the collision scene between the raked bow and the hull structure are relatively few. In this paper, the optimal design for the crashworthiness of the hull side structure under the impact of the raked bow is numerically studied. The dynamic collision response between the raked bow and the side structure is simulated by using the explicit finite element method in the commercial software LS_DYNA. Considering the damage and internal energy of the side structure, an objective function is established to describe the hull crashworthiness. The optimization design method for hull structure crashworthiness is established by combining the orthogonal experimental design, BP neural network and genetic algorithm (GA). The samples for training the neural network are determined by using the orthogonal experimental design method. The neural network model for the fast prediction of crashworthiness is established by using BP network and GA-BP network respectively, and it is found the GA-BP network can provide more accurate prediction results. Taking the mass and the scantlings of structural members as constraints, the optimization design of the side structure under the impact of the raked bow is realized.
High Effectiveness of Stays Against H-Mode Vibration of a Main Engine Even With a Foundation Having Reduced Rigidity on a Merchant Ship
Authors: Matsuo Ryo , Yamatoki Shuichi , Onizuka Hiroyuki
Published: September 2023

No rules specifically stipulate the structural foundation of a ship’s main engine from the perspective of resonance vibration. Additionally, a main engine is usually set on a more rigid foundation on land in shop tests conducted by an engine manufacturer. This means that the soundness of the main engine onboard the ship relies on the shipyard accounting for the difference in stiffness of the foundation between land and ship. Furthermore, we would like to adopt a less rigid foundation to reduce the hull weight, so we needed to demonstrate the soundness of the less-rigid foundation. First, we validated a method of estimating the natural frequency of the H-mode vibration of the main engine by comparing the results of finite element analyses with excitation test results for a real ship with a rigid foundation. Second, we calculated the natural frequency for the less-rigid foundation and found that it was not appreciably different when top bracings were used. Third, we clarified quantitatively that the effect of the foundation was less than that of the top bracings on the H-mode vibration using a simple mathematical model. We can therefore adopt the less-rigid foundation for a new merchant ship with effective top bracings.
Energy Extraction of Wave Energy Converter Array Using Anti-Node of Moonpool Resonance
Authors: Tay Zhi Yung , Wan Ling
Published: September 2023

The energy extraction from an array of point absorber wave energy converters (WEC) could be enhanced by deploying the WEC array in confined spaces such as the moonpool. Such a moonpool could be constructed from existing infrastructures such as breakwaters, coastal protection structures or floating platforms. As waves hit on the moonpool of different diameters, the fluid resonance of various frequencies is excited. The energy extraction could be further optimized by placing the multiple WECs at the anti-node of the sloshing modes inside the moonpool. The anti-node could be determined analytically whereas the performance of the WEC array could be computed numerically using the potential theory. A moonpool with an opening is further considered which allows the power enhancement of WECs due to the wave reflection from the wall of the moonpool. This paper shall compare the effectiveness of the sloshing mode on wave energy extraction. The suitable location in the moonpool for the deployment of multiple WECs when the array is deployed in a location of multiple sea states is also investigated. A large array of WECs is then considered in multiple moonpools located in a floating breakwater where the performance of the WECs and the effectiveness of the floating breakwater in attenuating the wave forces are studied.
Dynamic Power Cable Configuration Design for Floating Offshore Wind Turbines Using Gradient-Based Optimization
Authors: Schnepf Anja , Giljarhus Knut Erik Teigen , Johnsen Øyvind , Lopez-Pavon Carlos
Published: September 2023

Power cables transmit the electric energy generated by offshore wind turbines to consumers on land and at sea. The power cables usually lie statically on the seabed to prevent them from moving and being damaged. Since floating offshore wind turbines (FOWTs) are positioned using mooring systems, their power cables are placed from a hang-off location at the floater through the water to the seabed. In this dynamic section, they must withstand environmental loads and the loads induced by the FOWT motions. A minimized power cable length is crucial for low transmission losses during operation, which is a priority during the design of the overall configuration. This work presents a dynamic power cable configuration modeling approach using gradient-based optimization. The applied method is Sequential Least Squares Programming (SLSQP). Its applicability is shown in the example optimization of a tethered lazy-wave dynamic power cable configuration connected to a spar-FOWT. The optimization method is applied with two and three design variables. Steady-state analyses with extreme environmental loads are performed at each iteration, considering three distinct loading directions. The resulting optimized power cable configurations have a shorter cable length than the initial configurations. Dynamic analyses of the optimized configuration show that it satisfies the design limits.
Thermo-Mechanical Assessment and Challenges of Mero 1 HPHT Flowlines
Authors: Jebali Adel , Solano Rafael F. , Scultori Marcio , Novel Matthieu , Valer Carlos , Mustiere Olivier
Published: September 2023

This paper discusses the thermo-mechanical design challenges of rigid mechanically lined pipe (MLP) flowlines installed in the Mero field located in ultra-deep waters of the Santos Basin, offshore Brazil.

The Mero 1 project includes rigid MLP pipeline systems which operate under high temperature and high internal pressure (HTHP) for oil (PROD) and water alternating gas (WAG) service. The pipelines are unburied with fully restrained anchoring systems at both ends: A suction pile is used at the well side (PLET) and a compliant in-line anchoring system (with torpedo piles) is used at the transition riser flowline (TRF) side connecting to a steel lazy wave riser (SLWR). The severe operational conditions (HPHT) include permanent and transient flow regime with several predicted shutdown/start-up cycles during design life. This induces large compressive axial forces in the pipe and requires mitigation by controlling the lateral buckling response. The pipeline walking as well as the lateral ratcheting are also verified due to the high number of operational cycles.

The thermo-mechanical design of lateral buckling and walking has reached a certain level of maturity over the last years, particularly with steel sleepers as main triggering concept (buckling mitigation). However the particularities of the Mero 1 field required the development of a complex engineering solution to control the buckle formation and flowline end loads at pipeline end termination (PLET) and transition riser-flowline (TRF) locations to acceptable levels.

The overall thermo-mechanical design strategy is further complicated by the compliant anchoring system and interaction between the rigid flowline and SLWR. This system is designed in such way to allow for dynamic load transfer from SLWR to the flowline through chain slack control at the TRF connection. The complicated path of the MLP flowline, involving curves, crossings with other lines (umbilical, flexible, rigid), combined with this anchoring system has a significant impact on the pipeline behavior. This requires a fit-for-purpose engineering solution not normally found in similar field developments.

The paper addresses the strategy and challenges encountered to develop a feasible solution through the steps of thermo-mechanical design carried out as per field-specific specifications, DNV-RP-F110, and Safebuck JIP recommendations.
NextFloat: Disrupting Floating Wind
Authors: Cahay Marc , Mahmoudi Hedy
Published: September 2023

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 FOWTs 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-CL5-2021-D3-03) started in November 2022. NextFloat will engineer and build an innovative weathervanning FOWT concept that will be deployed and operated on the Mistral test site in the South of France near Marseille. The unit will be a 6 MW version of the PivotBuoy currently deployed by X1-Wind on the PLOCAN site in the Canary Islands.

The paper presents the objectives, the key challenges, the project design basis and the different innovations to be studied. It also highlights how this platform can be more suitable for the future 14MW+ turbines.
Demonstration of a Standalone, Descriptive, and Predictive Digital Twin of a Floating Offshore Wind Turbine
Authors: Stadtmann Florian , Wassertheurer Henrik Andreas Gusdal , Rasheed Adil
Published: September 2023

Digital Twins bring several benefits for planning, operation, and maintenance of remote offshore assets. In this work, we explain the digital twin concept and the capability level scale in the context of wind energy. Furthermore, we demonstrate a standalone digital twin, a descriptive digital twin, and a prescriptive digital twin of an operational floating offshore wind turbine. The standalone digital twin consists of the virtual representation of the wind turbine and its operating environment. While at this level the digital twin does not evolve with the physical turbine, it can be used during the planning-, design-, and construction phases. At the next level, the descriptive digital twin is built upon the standalone digital twin by enhancing the latter with real data from the turbine. All the data is visualized in virtual reality for informed decision-making. Besides being used for data bundling and visualization, the descriptive digital twin forms the basis for diagnostic, predictive, prescriptive, and autonomous tools. A predictive digital twin is created through the use of weather forecasts, neural networks, and transfer learning. Finally, digital twin technology is discussed in a much wider context of ocean engineering.
Gimbal Joint Riser – A Novel Concept: Experimental Hydrodynamic Coefficients
Authors: Ramiro Amorim Andre , Oliveira Ribeiro Felipe , Klim Gomes Rodrigo , Asgari Peyman , Do Nascimento Carvalhal Rodrigo , Rezende Diezel Alexandre
Published: September 2023

Gimbal Joint (GJ) is a device designed to connect the upper and lower parts of a steel riser in a free-hanging system. The mechanism consists of a flexible conduit, inside a structure that is made of several hinged connection elements, making the whole system work as an articulation. Hydrodynamic properties of GJ are recognized as an uncertainty source due to its novelty and very specific geometry. Recently, an experimental campaign of a model scale size — 1:9 — has been performed as a part of technology qualification programme.

The forced oscillation tests focused on obtaining drag and hydrodynamic inertia coefficients of the GJ, as a recommended practice to estimate hydrodynamic coefficients of complex bodies. As an oscillating porous body, the hydrodynamic coefficients shall be assessed in terms of the Keulegan Carpenter number, at different flow regimes corresponding to varying Reynolds number.

The focus of this paper is to present and discuss the hydrodynamic coefficients obtained in the forced oscillation tests. A discussion about the correlated effect of the model porosity and KC (Keulegan-Carpenter number) compared to Sarpkaya’s experiment from the literature is also presented. Results indicate that porosity changes significantly the hydrodynamic coefficients, providing that standard industry coefficients, normally used in dynamic analysis, shall not be used when GJ is part of the system.
Echo State Networks for Surface Current Forecasting in a Port Access Channel
Authors: Marino Moreno Felipe , Fialho Coelho Jefferson , Sproesser Mathias Marlon , Rodrigues de Barros Marcel , Fabricio Deberaldini Netto Caio , Palmiro de Freitas Lucas , Dottori Marcelo , Gagliardi Cozman Fábio , Helena Reali Costa Anna , Satoshi Gomi Edson , Aoun Tannuri Eduardo
Published: September 2023

This work employs Echo State Networks (ESN) to improve one day ahead forecasts of water currents in a port access channel entrance, with the aim to provide a more accurate method that can be used to alert the port authority about unsafe conditions for navigation in the near future. For this task Leaky integrator Echo State Networks (LiESNs) are applied to predict one day ahead currents in the Santos channel, Brazil; The method has been trained with data obtained from an Acoustic Doppler Current Profiler installed in the channel, with data available between the years of 2019–2020. Results have been compared with the Santos Operational Forecasting System (SOFS), a numerical model already in use for the same region. Experiments show that the LiESN outperforms the numerical model by the metrics of Index of Agreement (0.922 versus 0.812) and RMSE (0.152 ms−1 versus 0.220 ms−1).
Numerical Simulation of Motion Responses of a Cabin-Suspended Catamaran in Head Waves
Authors: Han Jialin , Kitazawa Daisuke , Murai Motohiko
Published: September 2023

In this study, the motion responses of a suspension catamaran in head waves are presented using numerical calculation and experimental validation. The cabin-suspended ship has 9 degree-of-freedom, as the heave, pitch, and roll motion of the cabin can be separated from that of the twin-hull through a suspension unit. The suspension unit consists of four compression springs and linkages to guide the motion. The hydrodynamic coefficients and the wave exciting force/moments of the twin-hull were calculated using a potential flow solver named OrcaWave. A method was proposed to approximate the wave exciting force/moments at an advancing speed using the wave exciting force/moments at zero speed. The study analyzed the motion response of the ship at different damping coefficients and spring constants. The results show that motion reduction of the cabin by tuning only the spring constant and damping coefficient is limited, and different pairs of spring constant and damping coefficient would be needed for different wave encounter frequencies. The study provides valuable insights for the design of suspension ships to reduce motion responses in head waves.
Development of an IPM Tool for Subsea System Design Considering Lifetime Production/Injection Performance
Authors: Wang Yuxi , Hong Cheng , Estefen Segen F.
Published: September 2023

Rational conceptual design is a formidable task to ensure feasible and economic operation along offshore oil field development lifecycle. An integrated production modeling (IPM) approach has to be adopted at the conceptual design stage since it enables the assessment of the spatio-temporal interaction between the subsea pipeline network and the reservoir. This work reports the development of an computer-aided IPM tool to facilitate effective subsea scenario comparison and selection considering the lifecycle performance of both the production system and the injection system. Three performance indicators are used for scenario comparison and selection, namely, NPV, recovery rate, and wax-free index. A case study demonstrates the application of the IPM tool in assessing the effect of subsea water separation, for both green field design and brown field revitalization purposes. The developed IPM tool allows the production engineer to focus on the subsea configuration itself since production performance of each candidate scenario is effectively evaluated from autonomous simulation results under the same development logic.
Research on Lost Circulation Diagnosis Model Based on SMOTE-Tomek and Stacking Ensemble Learning
Authors: Han Liang , Song Xianzhi , Zhang Haolin , Lv Zehao , Zhou Detao , Zhu Zhaopeng , Yao Xuezhe , Zhang Rui
Published: September 2023

Lost circulation is one of the common risks in the drilling process, accurate and efficient lost circulation risk diagnosis is very important to ensure drilling safety. The risk diagnosis method based on machine learning has high efficiency and strong robustness, and is receiving more and more attention. However, the class imbalance of lost circulation/normal sample size seriously limits the performance of the machine learning model. Moreover, the stability and generalization of the intelligent model built using single algorithms are limited. To solve the above problems, SMOTE-Tomek algorithm is used to process the lost circulation dataset with unbalanced structure. And then random forest (RF), extreme gradient boosting (XGBoost) and support vector classification (SVC) are used to build the Stacking ensemble learning diagnosis model. Finally, the effects of the ensemble learning model and the single algorithm models are compared. The research results show that SMOTE-Tomek algorithm can effectively improve the diagnostic performance of the model for the risk of lost circulation, and the Stacking ensemble learning model has the best diagnostic effect, with its accuracy rate (96.40%), recall rate (92.74%), and missed alarm rate (7.26%) superior to the single algorithm model. This study is of great significance to ensure drilling safety and provide auxiliary reference for on-site control personnel.
Numerical Investigation of Internal Flow Effect on the Cross-Flow Vortex-Induced Vibration
Authors: Zhao Guixin , Meng Shuai
Published: September 2023

To examine the internal flow effect (IFE) on the vortex-induced vibration (VIV) of a flexible marine riser in the subcritical internal flow region, the cross-flow (CF) VIV of the riser with single-phase internal flows is investigated employing a semi-empirical hydrodynamic force model. The governing equation can be established based on Hamilton Principle and solved by finite element method. A MATLAB code has been developed and it has been validated for IFE and VIV respectively. The numerical simulations of a flexible riser are carried out with different internal flow velocities and internal flow densities. The IFE on CF VIV is investigated by analyzing the dominant mode, dominant frequency and displacement response of the riser. It has demonstrated that with the increase of internal flow velocity and density, (1) the dominant mode of VIV can transfer to a higher order, accompanied by a jump increase of the dominant frequency; (2) the increase or decrease of the root mean square displacement of VIV depends on whether the dominant frequency approaches or departs from the vortex shedding frequency; (3) the travelling wave characteristics of VIV can be enhanced.
Comparison Between Experiments and Simulations for a Ship Maneuvering in Waves
Authors: Ramachandran Krishnavelu , Borsutkar Visharad , Somayajula Abhilash Sharma
Published: September 2023

The current regulations of the International Maritime Organization (IMO) aims to increase the reduction of carbon dioxide (CO2) emissions from shipping by providing mandates to improve the Energy Efficiency Design Index (EEDI) of new ships. This has prompted newer vessels to be equipped with low-powered engines as compared to the previous vessels of similar size. However, the low power may potentially cause some vessels to be ill-equipped to maneuver effectively in the presence of waves. Although, traditionally turning characteristics of a vessel is considered in calm waters, in light of the new regulations it is important to consider course-changing ability in waves during the design process. This study aims to compare the maneuvering simulations and experiments of a scaled KRISO container ship (KCS) in calm water and in regular waves. The MMG standard method was developed by the Maneuvering Mathematical Group (MMG) which was organized by the Japan Society of Naval Architects and Ocean Engineers. This model is used to simulate the motions of the vessel in still water. A potential flow theory-based MDLHydroD software is used for calculating second-order wave drift forces and these drift forces are added to the MMG model. The simulations are compared with free-running model tests in both calm water conditions and in regular waves.
Seabed Proximity Effect on Free Spanning Pipelines: the FIST JIP
Authors: Caruso Mário , Sutherland James
Published: September 2023

Natural free spans occur in offshore pipelines when its stiffness prevents it from following the contours of the seabed., typically either due to the seabed contour or an erosion process after the pipe is laid. Free spans may be subjected to vortex induced vibrations that can lead to rapid accumulation of fatigue damage. Most offshore pipelines free spans occur in the proximity of the seabed. The influence of the seabed proximity on the hydrodynamic behaviour of the system is dictated by the span gap. When the seabed proximity significantly affects the flow around the pipeline in free span, the span may be considered a small gap span. When assessing VIV in small gap spans, current practice is to either nearly ignore the effect from proximity or to ignore VIV based on a critical gap approach. Previous research on crossflow VIV showed that both approaches are limited.

Thus, a joint industry project to study proximity effects in free spans in scour trenches, the FIST JIP, was formed. FIST JIP performed extensive test program focused on in-line VIV near seabed, with and without scoured trenches, to document the proximity effects. This paper presents the experimental work from FIST JIP and a suggestion to incorporate its results to better account for seabed proximity.
A Mesh Convergence Study for Low Frequency Second Order Wave Forces on Floating Bodies
Authors: Pan Zhiyuan , Kim Taeyoung , Heo Jaekyung
Published: September 2023

The second-order wave excitation forces acting on offshore floating structures are much more sensitive to mesh quality than linear forces when using the boundary element method to solve potential flow problems. This paper demonstrates the importance of mesh refinement near the waterline and sharp corners for mean drift forces, as well as low-frequency components in bi-chromatic wave conditions. To achieve better local panel refinement, a stretching factor is introduced to the Cosine spacing formulation used in meshing for the potential flow solver. This approach yields an economical and effective mesh for second-order analyses. An optimal mesh for a bottom-fixed cylinder is identified by comparing the horizontal mean drift force from numerical results against analytical values. Off-body kinematics near the cylinder are also studied as a basis for the mid-field formulation. A truncated floating cylinder is used to test the mid-field formulation applied for the vertical drift force. It is found that the drift force calculated by the pressure integration method matches well with the result obtained by the mid-field formulation when the sharp corner at the bottom is properly refined. Two ship models are then used to test the meshing strategy towards the waterline for second-order forces using both the near-field and mid-field methods. Recommendations are provided for meshing strategies on wetted hulls for boundary element method codes applied to low frequency second-order problems.
Preliminary Investigation of Ocean Wave Refraction Using an Array of Wave Energy Converters
Authors: Sergiienko Nataliia , Tuck William , Cannard Patrick , Georgiadis Mikaela , Capper Benjamin , Schultz Jesse , Cleggett James , Cazzolato Benjamin
Published: September 2023

Coastal erosion and its management cause significant economic, social, and environmental impacts on Australia. Current methods of controlling coastal erosion are expensive and are frequently damaged during severe weather events. However, recent studies have identified the potential for Wave Energy Converters (WECs) to provide a solution to this problem. WECs can extract energy from ocean waves and attenuate the wave field propagating towards the shore. The aim of this project is to determine whether arrays of WECs can not only reduce the magnitude of the propagated wave but also change its direction, thereby creating more favourable nearshore conditions.

The study is conducted using small-scale experiments in a wave flume using an array of ten oscillating water columns (OWC). The OWCs are placed perpendicular to the incoming wave and equally spaced across the width of the wave flume. The OWCs are constructed using L-shaped pipes of 60-mm diameter, and the natural frequency of each OWC is tuned using different horizontal pipe extensions, which ultimately change the mass of water within the OWC. The damping is tuned using end-caps with different orifice diameters. Each OWC is equipped with a pressure sensor to measure the differential air pressure inside the OWC air chamber. The downstream wave field is characterised using a row of 6 resistive wave gauges located at a distance of 2 m from the wave array. The study is conducted using regular waves with a wave frequency of 1 Hz. The preliminary results demonstrate that the array of OWCs can change the direction of the incoming wave by several degrees.
Fatigue Crack Propagation Prediction for Pipeline Steel Under Gaseous Hydrogen Environment
Authors: Zheng Tingsen , Chen Nian-Zhong
Published: September 2023

Hydrogen embrittlement (HE) refers to the irreversible damage caused by hydrogen diffused in the metal lattice with the metal material itself or other chemical elements in the matrix, which may lead to fatigue failure. Therefore, for safety reasons, it is of great significance to investigate the impact of HE on the fatigue strength of pipeline steel under gaseous hydrogen environment. Cyclic cohesive zone model (CCZM) is one of the potential methods for simulating the hydrogen assisted crack (HAC). A fatigue crack propagation simulation for API X52 pipeline steel based on a modified CCZM under gaseous hydrogen environment is performed in this paper. The modified CCZM is proposed where not only the degradation of cohesive strength but also the degradation of accumulated cohesive length is considered in order to clarify the impact of HE on the fatigue crack propagation. The degradation of cohesive strength and that of accumulated cohesive length is expressed with piece-wise linear relationships. The results of simulation are then compared with test results to demonstrate the capability of the proposed CCZM. The proposed model tends to provide a useful reference for further research on the simulation for HAC by CCZM.