bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.