bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental determination of Poincaré beam coordinates on a Hybrid order Poincaré sphere
Authors: Bansal Sarvesh , Senthilkumaran P
Published: November 2023

Hybrid order Poincaré sphere (HyOPS) is used to represent Poincaré beams as points on it. The latitude and longitude of the HyOPS represent the size of the Stokes vortex ring and Pancharatnam phase of the Poincaré beam respectively. Although the HyOPS was introduced in 2015, there is no method that allows one to unambiguously determine the coordinates of Poincaré beams on this sphere. In this article, by subjecting the Poincaré beams to angular momentum and polarization transformations using conventional phase and polarizing elements respectively, we demonstrate an experimental method to determine the coordinates of the Poincaré beams on the HyOPS. This method may enable one to study the chirality and circular dichroism in materials and to enable us to segregate them, where both phenomena occur simultaneously.
Cosmic birefringence from the Axiverse
Authors: Gasparotto Silvia , Sfakianakis Evangelos I.
Published: November 2023

We revisit the evidence for CMB birefringence in the context of a rich Axiverse. Using probability density functions (PDFs) for various axion parameters,
such as the mass and axion decay constant, we construct the PDF for the
cosmic birefringence angle and investigate its properties.
By relating the observed value of the birefringence angle to the mean or standard deviation
of the constructed PDF, we constrain the shape of the input PDFs, providing insights
into the statistical distribution of the Axiverse. We focus on three different types of axion
potentials: cosine, quadratic, and asymptotically linear axion monodromy.
Our
analysis showcases the potential of cosmic birefringence in constraining the distribution
of axion parameters and uncovering possible correlations among them.
We additionally offer
predictions for “birefringence tomography”, anticipating future measurements of birefringence from
lower multipoles, and show how it can be used to rule out simpler versions of the Axiverse. Our findings contribute to the
ongoing exploration of the Axiverse and its implications for cosmic birefringence.
High-efficiency continuous-wave Tm-doped fiber laser with a single fiber Bragg grating at 1942 nm
Authors: Yang Chao , Li Xin , Zheng Bowen , Li Yongliang , Ju Youlun
Published: November 2023

We report a continuous-wave Tm-doped fiber (TDF) laser with a single fiber Bragg grating (FBG). The Fresnel effect presenting in the passive fiber end-face and high-reflectivity FBG established the resonator. The peak wavelength of the laser was 1942.25 nm with a spectral linewidth of 194 pm. The maximum output power was 37.5 W, corresponding to a slope efficiency of 63.7% with a beam quality factor of M
2 ∼ 1.51. To the best of our knowledge, this is the highest slope efficiency of a TDF laser pumped by 793 nm laser diode.
Trickle-down strategies: integrating simulations with control loops of autonomous vessels on lab scale
Authors: Baart Fedor , Gijn Max Willem van , Boogmans Bart , Zagonjolli Migena , Zuidwijk Rob , Negenborn Rudy R. , Koningsveld Mark van
Published: November 2023

This study integrates strategic decisions and operational control systems in autonomous shipping. By providing ships with situational information and adding a virtual operator, we show that vessels can make informed choices regarding their route and engine settings. To demonstrate this integration, we developed new components and put these to the test in three lab experiments.

The green routing capability experiment showed the bridge between the control system of the autonomous vessel, operated via Robot Operating System (ROS), to the simulation environment of OpenCLSim. We developed a real-time variant of OpenCLSim and a communication component that could expose the state of the OpenCLSim simulation with the ROS system. This experiment showed that an autonomous vessel could follow a path provided by the simulation.

The green steaming capability experiment showed that the ship could also adapt its speed based on information from the simulations. We developed an additional communication component capable of advising the vessel about its velocity. Together with the green-routing capability, this forms the basis for more complex experiments.

The port layout experiment showed a potential use case of the green-routing and green-steaming capabilities. We created a waypoint layout similar to the port. While a ship is sailing, twelve simulations are computed every five seconds. The scenarios vary in engine order, route choices, resulting in varying emissions, fuel, and cost. We evaluated the impact of different tactics such as green-routing, green-steaming, and full-speed sailing on operational behavior like steering and engine order. Our approach, using a real-time version of a Vessel in the OpenCLSim simulation software, enabled predictive simulations to facilitate the chosen tactic based on a given strategy. Integrating simulations to evaluate the options with the control systems can develop into a valuable tool for optimizing vessel performance and reducing environmental impact in autonomous shipping operations.
Design and Build of an Autonomous Catamaran Urban Cargo Vessel
Authors: Zhang Yan-Yun , Shuai Jiangtao , Billet Jef , Slaets Peter
Published: November 2023

This study introduces a novel test bed, named the Maverick, which aims to advance the field of autonomous inland waterborne freight transportation and facilitate its eventual implementation. More specifically, the Maverick focuses on operating in small waterways within urban areas, aligning its application scenario with the European project AVATAR. The hull form of the Maverick was selected to be a catamaran, as it offers several advantages, including a large open deck area, high transverse stability, and excellent maneuverability at low speeds. The Maverick is equipped with two 360-degrees-steerable azimuth thrusters, one at the bow and one at the stern. This configuration makes the Maverick over-actuated, and offers more advanced motion control possibilities compared to conventional rudder-propeller actuated vessels. The Maverick is composed out of modular building blocks combined with a flexible interface, which enables it to accommodate diverse control terminals for future developments. Furthermore, to illustrate the feasibility of the Maverick within an urban context, this study also includes results of several trail tests. The interactive communication framework that was successfully employed in the autonomous sailing experiment is introduced. The Maverick offers a versatile platform for testing and developing a wide range of technologies in situation awareness, autonomous sailing, smart waterway logistics, and other interconnected domains. Therefore, this innovative research vessel can pave the way for the development of a new freight transport mode within European urban areas, contributing valuable experiences to the field.
Multi-functional and Practical Adaptive Collision Avoidance Decision-making System for Autonomous Ships
Authors: Zheng Kang-jie , Zhang Xin-yu , Liu Zhen-sheng , Kwangil Lee , Wang Cheng-bo
Published: November 2023

In the current landscape, autonomous navigation systems face challenges due to incomplete functionality and low integration. They also lack a comprehensive, real-time, and accurate navigation risk assessment, while operating independently from one another. To address these issues, a multi-functional and practical adaptive collision avoidance decision-making system for autonomous ships is developed in this paper. The system primarily relies on the electronic navigational chart (ENC) to effectively display the ship’s navigation situation. It establishes a collision avoidance decision-making model centered around the own ship, offering collision risk analysis, avoidance methods, and optimal timing to ensure safe navigation. The system efficiently integrates and processes multimodal maritime data from various devices, utilizing ontology-based approaches for comprehensive navigation situation understanding, which integration provides invaluable support for intelligent decision-making processes. With a user-friendly interface, excellent portability, and cross-platform interoperability, this system has undergone collaborative efforts and joint debugging with China Shipbuilding Navigation Technology Co., Ltd. during the project’s first and second phases. Notably, the system has been successfully implemented on the “High-performance Integrated Bridge System” platform of China Shipbuilding Navigation, showcasing its potential for advancement from principle prototype development to actual equipment application. By offering accurate collision avoidance decision support, this system significantly contributes to enhancing the safety of ship navigation.
A multi-sensor indoor tracking system for autonomous marine model-scale vehicles
Authors: Ponzini Filippo , Zaccone Raphael , Martelli Michele
Published: November 2023

Attitude estimation is a popular topic in marine engineering and robotics; the position and orientation of a vehicle are required as feedback from several control algorithms to improve autonomous navigation capabilities, such as dynamic positioning, track keeping, and autodocking. Typically, position and heading angles are provided by the Global Positioning System and compass. Usually, during the development and testing, the experiments are performed in a controlled environment, such as an indoor test tank. However, Global Positioning System systems can be unreliable due to non-negligible model scale errors or the absence of line-of-sight with the satellites. This article presents an experimental tracking system setup suitable for indoor testing facilities. In particular, the paper presents a tracking system based on a GigE camera and ArUco markers detection and a LiDAR-based tracking system relying on unsupervised machine learning techniques. The MQTT broker-based publish/subscribe message-queuing protocol allows real-time data communication and sharing. The proposed system was developed, installed, and tested in the COMPASS laboratory (University of Genoa). The two tracking systems’ outcomes have been compared. Eventually, an accuracy analysis was performed by comparing the results to the ground truth in purpose-built experiments. The proposed approach can estimate the degrees of freedom of a self-propelled model-scale vessel in an indoor testing facility without requiring active or powered markers and share the information acquired with multiple entities in real-time at a high frame rate.
Application of the EAST-BL method on a MASS system for Hazard Identification and Risk Assessment
Authors: Ventikos Nikolaos P , Siokouros Panayiotis , Koimtzoglou Alexandros
Published: November 2023

As can be seen through the continuous research on the Marine Autonomous Surface Ships (MASS) in recent years, several positive as well as optimistic results have been emerged, along with several concerns. In particular, the risk analysis process regarding MASS faces many difficulties as the lack of respective data may lead the estimation of probability or frequency to be extremely uncertain or even biased. To this end, the application of risk informed approaches, that are based on the traditional definition of risk, can be quite misleading. This paper presents a methodology for risk assessment on MASS based on the utilisation of the EAST-BL, a system-based methodology that combines the output of three different networks (i.e., task, social and information) for human and non-human agents of a system to identify hazards and the DNV’s framework for risk assessment from the RBAT study. The objective of the paper is to provide insights regarding the application of EAST-BL on MASS as well as the way that system-based methods can be utilised to enhance the hazard identification and risk assessment processes for MASS.
Structured Description of Autonomous Inland Waterway Barge Operations
Authors: Hagaseth Marianne , Meland Per Håkon , Wille Egil
Published: November 2023

Autonomous and unmanned shipping is revolutionizing the maritime industry by introducing a paradigm shift on how to design the vessels and supporting land-side infrastructure. Currently, there is a lack of formalisms on how to plan for such operations, determining the varying degrees of autonomy and human responsibility, whilst ensuring safety and security. This paper describes fundamental concepts of autonomy in the context of ships. These are then applied in a methodology used to create systematic and structured descriptions for the operation of autonomous ship systems. The examples we use are based on ongoing efforts related to a planned autonomous inland waterway (IWW) barge operation. Finally, we show how the descriptions can be used in conjunction with existing safety and security analysis techniques. Our experience with this methodology is that it allows for a smooth transition from the autonomous ship system design phase to the assessment of the same system using UML notations. We believe that the same methodology can be easily applied to the other use cases and similar systems elsewhere.
The shift toward autonomous European inland waterway shipping: Identifying the gaps in the emerging socio-technical system
Authors: Saha R , Lundh M , MacKinnon S N
Published: November 2023

The introduction of automated solutions for inland waterways shipping supports the European vision for a sustainable and greener shift within maritime management and logistics. Despite increasing investments, impressive technological advancements, and active discussion to solve the regulatory and business model barriers, socio-technical aspects are still less studied in the preparation for the future of autonomous shipping. This study examines stakeholder and technology roles to map the gaps and challenges created in this emerging space using a system theory approach, specifically a recently developed work design system analysis tool named Change Agent Infrastructure (CHAI) analysis [1]. This framework was chosen to better understand the likely changes of the system with the introduction of automated technology and higher degrees of automation and digitalization in the European inland waterways. The analysis identifies that there are multiple receivers of the change and regulatory bodies will also be actors with considerable responsibilities to direct these changes.
Smart Ships and implications in logistics chains a case study in Zeeuws Vlaanderen
Authors: Caballero Rosas A , Verduijn T
Published: November 2023

Autonomous shipping is expected to be gradually adopted in the coming years. While many scientific studies in the field have focused on technological development, recent research has started to explore the effects of this innovation on the cargo transportation industry. This study investigates the economic dynamics that can drive logistics entrepreneurs to adopt teleoperated barges, a specific type of smart shipping. By conducting a case study of cargo transportation between two companies using roundtrips with trucks and barges, the study evaluates a modal shift to intermodal transport and looks into the conditions that are affected if barge teleoperation is implemented. A major conclusion of the study is that the transport distance, the equipment size, and the mix of captain-only tasks versus all the sets of crew tasks affect the expected economic gains that are obtained as a result of implementing smart shipping. In this case, a conventional modal shift to waterborne transport is already economically attractive. When opting to operate a smaller barge, teleoperation becomes preferable when a shore-control captain can only focus on exclusive sailing tasks and when more than one ship is monitored simultaneously.
Vortex filament method 3D analysis of design parameters for counter-rotating axis floating tilted turbine
Authors: Andersson E , Bernhoff H , Goude A
Published: November 2023

The Counter-Rotating Axis Floating Tilted turbine (CRAFT) is a new design for floating off-shore wind power, which utilizes a low center of gravity and allows the tower to tilt to mitigate costs for platforming.

In this study, 3D simulations of the CRAFT have been performed to investigate the effect from the tower’s tilt angle on the aerodynamics of the turbine using a vortex filament method. Due to lack of empirical data of the CRAFT, the method has been benchmark tested against a previous project on a vertical axis wind turbine.

Using this method, the blades’ twist angle has been set to achieve good lift-to-drag ratio along the entire blade. Furthermore, the blades’ chord length has been determined for optimal Tip Speed Ratio (TSR) 6 when the tower is tilted 30 degrees from vertical position.

The CRAFT has been simulated vertically and tilted 15°, 30° and 45°, for TSRs ranging between 4 and 9. The power coefficients (CP
) and normal forces have been determined, and velocity plots are presented to show how the near-wake develops.

The results from this study serves as a basis for further development and design of the CRAFT.
Pile design for X-rotor offshore wind turbine
Authors: Dong Jing , Silva Adriana Correia Da , Muskulus Michael
Published: November 2023

For the foundations of traditional offshore structures in oil and gas industry, the dominant load is in vertical direction. For wind turbines, especially for vertical axis wind turbines, the lateral loads are increased significantly, which makes them the key element of the pile design. The X-rotor offshore wind turbine is a novel concept which is a hybrid of vertical and horizontal axis wind turbines. This paper aims at giving a detailed solution for the pile design of X-rotor type offshore wind turbines based on the existing guidelines and to gain an insight in the influences of the cyclic loads on the pile parameter selection. The pile capacity design and the pile performance design are executed and then the influence of the piles to the natural frequencies of the wind turbine is evaluated.
Start-up Dynamics of Vertical Axis Wind Turbines: A Review
Authors: Lough Jamie , Asim Taimoor , Coull Scott , Marshall Andrew , Islam Sheikh Zahidul , Amber Ityona
Published: November 2023

Vertical Axis Wind Turbines (VAWTs) are becoming increasingly popular for wind power extraction due to their simpler design, lower manufacturing and maintenance costs. The omni-directionality of these power generating machines make them more suitable for operation both under lower wind speeds and highly transient winds. The key wind power extraction component of VAWTs is their rotor, which is conventionally either Drag-based or Lift-based, with the latter being more widely studied in the published literature due to its higher power coefficient compared to its counterpart. The lift-based rotor comprises of aerodynamically profiled blades, while the drag-based rotor comprises of thin cup-shaped blades. The start-up of both these types of VAWT rotors has been an area of active research in the last decade. These studies have been conducted using numerical and experimental methods focusing on key parameters related to the start-up dynamics of VAWTs. Many of these research studies complement each other’s findings, however, there are also a number of aspects where there are disagreements and/or significant knowledge gaps that need to be highlighted in order to accelerate scientific efforts strategically. In the present study, we aim to address these challenges through a thorough and critical review of the published literature on VAWTs’ start-up dynamics, leading towards the identification of key knowledge gaps.
Direct drive double fed wind generator
Authors: Ostović Vlado
Published: November 2023

An electric machine topology characterized by single tooth winding in both stator and rotor is presented. The proposed machine is capable of operating as a direct drive double fed wind generator (DDDF, D3F), because it requires no gearbox. A wind turbine drive built around a D3F generator is cheaper to manufacture, requires less maintenance and has a higher energy yield than its conventional counterparts. The all tooth wound generator of a D3F turbine has a superb volume utilisation and lower stator I2R losses due to its extremely short end windings, efficient cooling and reduced active length. Both stator and rotor of a D3F generator can be manufactured in segments, which simplifies its assembly and transportation to the site, and makes its production cheaper.
Aero-structural coupled optimization of a rotor blade for an upscaled 25 MW reference wind turbine
Authors: Werthen Edgar , Ribnitzky Daniel , Zerbst David , Kühn Martin , Hühne Christian
Published: November 2023

One major challenge of the wind turbine industry is the reduction of the levelized cost of energy (LCoE) while following the strong demand for a higher annual energy production (AEP). To meet these goals, larger wind turbine sizes are required. The common method of upscaling existing wind turbine designs comes along with the problem of faster growing blade masses and costs compared to the AEP. Investigations in new technologies to improve the structural efficiency of larger blades can be supported by aero-structural coupled optimizations. The present work introduces a two-step aero-structural coupled design process to capture the multi-disciplinary trade-offs between costs and AEP, aiming at minimizing LCoE for a 25 MW wind turbine. In a first step, a preliminary aero-structural optimisation is carried out using simplified and fast methods. The output is then refined with respect to additional design criteria with an advanced optimization process, including an aero-servo-elastic coupled loads analysis. The process is applied to a 25 MW blade, upscaled from the IEA 15 MW reference wind tubine. Based on the results of an utilization analysis, the structural design is adapted, and a stiffness optimization is performed. The optimum airfoil positions are identified to reduce the amount of material while limiting losses in the aerodynamic performance. The obtained blade designs facilitate a consistent AEP compared to the upscaled reference design. A mass reduction of 35% could be achieved, which results in a reduced LCoE of 1.7% compared to the purely upscaled blade design.
An assessment of electrolyser portfolio for offshore hydrogen production considering its key properties – efficiency, ramp rate and capacity
Authors: Andreae E , You S , Bindner H W , Petersen M
Published: November 2023

Wind-electrolyser systems that produce green hydrogen – including hydrogen-generating offshore energy hubs – have received a lot of attention. The electrolyser capacity in such systems can be arranged in different configurations by varying the location setup of the electrolysers. The setup influences not only the dynamic performance of electrolysers but also the system economics. This paper analyses the differences in the dynamic performance of electrolysers in a centralised and decentralised setup from a technical and economic perspective, when the target is to produce as much renewable hydrogen as possible using today’s electrolyser technology. The economic effects of scaling for various wind turbines under different wind conditions are incorporated in the analysis.

Differences in electrolyser efficiency, start-stop, ramping, operation range and scale are modelled, and the models are applied to a case study depicting an offshore energy hub. Using a representative wind profile of fluctuating conditions and considering identical electrolyser ramping and efficiency for the same turbine configuration, the analysis shows that the single electrolyser solution (centralised), where the electrolyser is sited at a substation, gives a better levelized cost of hydrogen than the alternative setup (decentralised) with multiple in-turbine electrolysers.
Resilience to storm conditions of power systems with large dependencies on offshore wind
Authors: Forsberg S , Thomas K , Bergkvist M , Göteman M
Published: November 2023

The ongoing transition towards large installations of offshore wind and the electrification of the transport sector and other critical infrastructures introduce new vulnerabilities to the society. Large dependencies of power production from offshore wind are expected in the next decades, but there are large knowledge gaps regarding the power production reliability under severe weather conditions. Simultaneously, weather extremes may increase in frequency and intensity, driven by climate change. In this paper we investigate the resilience of a power system subject to a hurricane event. The power system is based on the IEEE39-bus New England system but with different scenarios for increasing penetration of offshore wind. We find that an offshore wind penetration level of 30% or less results in a power system resilient to hurricane events, with no need for load disconnection. However, when increased to 40% offshore wind penetration, 650 MW corresponding to 10% of the total load demand gets disconnected during the storm peak. With a penetration of 50% offshore wind, the disconnected load ranges from 2.2 GW of load corresponding to 1/3 of the total load demand, to a total power system blackout.
Overview of the potential of floating wind in Europe based on met-ocean data derived from the ERA5-dataset
Authors: Messmer Thomas , Ran Xiaoming , Benifla Victor , Lutz Marco , Adam Frank , Bachynski-Polić Erin E. , Hölling Michael
Published: November 2023

This paper provides an overview of the potential of floating wind in Europe. Wind and wave data from the ERA5 dataset as well as bathymetry data are analysed to identify regions suitable for floating wind deployment. The most promising areas are quantified according to different characteristics (wind resource, bathymetry, distance to the coast). The wind resource is quantified in terms of averaged wind velocity and wind availability at 100 m height above sea level. The results show the great potential of Ireland, Iceland, Norway and the United Kingdom. Indeed, a large part of the seas of these countries is located in water depths between 60 and 1000 meters and has a very high wind resource despite stronger wave conditions than in other countries. In addition, Spain, France, Sweden, Finland and Greece all exhibit good potential.
Triple-lidar measurements of wind across a virtual rotor plane over a sea surface
Authors: Nafisifard M , Jakobsen J B , Snæbjörnsson J T , Sjöholm M , Mann J
Published: November 2023

An improved understanding of the spatiotemporal characteristics of the wind velocity field above the sea surface will benefit the design of modern offshore wind turbines. This study examines wind velocity data recorded on a bow-tie-like measurement pattern, approximately covering a rotor area diameter of about 70 m. The measurement data are obtained by triple continuous-wave Doppler lidars (short-range WindScanners). Two of the instruments are installed on a stable platform in the form of a suspension bridge deck, whereas the third is stationed on the ground nearby. Data from sonic anemometers installed above the bridge deck are used to validate the wind characteristics observed by the lidars. The lidar measurement data are explored in terms of wind flow mapping, mean flow characteristics and co-coherences. The results demonstrate the difference between the co-coherence at lateral and vertical separations and also differences from the coherence model in the IEC standard. The results further show the potential of lidar measurements to provide new insight into mean wind flow and turbulence characteristics applicable for offshore wind turbine design.
Operational Expenditure Modelling of the X-Rotor Offshore Wind turbine concept: Sensitivity of Key Modelling Assumptions
Authors: Anderson Fraser , Carroll James , Leithead William
Published: November 2023

The focus of this paper is operational expenditure modelling of the novel X-Rotor offshore wind turbine concept. The X-Rotor presents significant opportunities for operational expenditure reduction. There are, however, numerous uncertainties associated with modelling of those costs. Namely; failure rates for a novel concept are difficult to quantify, and the design of the concept is still being refined. These uncertainties may be addressed via simple sensitivity analyses. Here, three such sensitivity analyses are presented: one focusing on the main bearing failure rate, one on the generator failure rate, and one exploring the provision of redundancy via the operational strategy of secondary rotors. The main bearing failure rate had a particularly significant impact on operations and maintenance costs, accounting for approximately 22% of costs under baseline assumptions. The generator was less impactful as a cost driver, accounting for approximately 10% of costs under baseline assumptions. Lastly, assuming the X-Rotor could operate at 50% capacity upon failure of one of the secondary rotors decreases the operational expenditure by 8% compared to full turbine unavailability.
On the Sensitivity of Wind Turbine Failure Rate Estimates to Failure Definitions
Authors: Anderson F , Dawid R , McMillan D , Cava D García
Published: November 2023

This study presents a wind turbine reliability analysis at the turbine and assembly level. It is concerned with the uncertainties associated with data-processing for wind turbine failure rate figures. These uncertainties are prominent in discussions of failure data in the literature. In particular, the influence of different failure definitions on failure rate estimates are investigated. The baseline estimate is 9.06 failures per turbine per year. This figure changes significantly when introducing a lower downtime limit, repair limit or limit on time between subsequent downtimes of the same turbine for a downtime event to be considered a failure. It changes significantly depending on which maintenance actions are categorised as corrective and by what data points represent an intervention. From the one dataset analysed here, results show derived failure rates ranging from below 1 failures per turbine per year to over 10 failures per turbine per year using failure definitions which have previously been used in the literature. When restricting failures to those that can be attributed to a particular assembly, the failure rate estimate reduces to 7.47 failures per turbine per year. Assemblies that fail the most are the frequency converter (at around 1 failures per turbine per year) and the cooling system (at around 0.9 failure per turbine per year). The gearbox, blades, yaw system and hydraulic group were the next most frequently failing assemblies.
Multi Rotor Wind Turbine Systems: An Exploration of Failure Rates and Failure Classification
Authors: McMorland Jade , Khisraw Abdullah , Dalhoff Peter , Störtenbecker Sven , Jamieson Peter
Published: November 2023

The Multi-Rotor System (MRS) is a proposed solution to the increasing costs associated with the manufacture and maintenance of large single-rotor wind turbines. The MRS consists of many small rotors that can capture the same amount of energy as a large turbine but with the added benefits of standardization, reduced system loads, and improved reliability due to the redundancy of components and smaller size. However, modelling the operation and maintenance (O&M) of the MRS presents several challenges, including a lack of available failure data. This work aims to determine, what failure rate reduction, can MRS be competitive with equivalent single-rotor wind farms, using existing single-rotor turbine data as a baseline. The key failure components are identified through the use of a cost-based comparison parameter. Statistical and theoretical approaches are then used to analyse the impact of fatigue on failure rates for downscaled turbines, to determine if the required reduction in failure rate is feasible. Using a case study, the sensitivity of availability, operational expenditure, and lost revenue to failure rates is also determined.
Effect of leading-edge erosion on the performance of offshore horizontal axis wind turbine using BEM method
Authors: Mian H H , Siddiqui M S , Yang L , Keprate A , Badar A W
Published: November 2023

This research focuses on the effect of leading-edge erosion on the performance of wind turbines, specifically the GE1.5XLE horizontal axis wind turbine. The blade element momentum (BEM) method is used to predict the performance of the eroded blade configurations, and the open-source code QBLADE is used for simulation. The importance of including the effects of blade erosion in the design phase is highlighted, as it can optimize turbine performance and ensure operational efficiency. The high blade tip velocity in large rotors, which can reach 90-110 m/s, makes them susceptible to sand and rain erosion, which can significantly affect the turbine’s performance. The research compares the performance of clean and eroded blade configurations, with different levels of leading-edge erosion as percentages of the chord (0.5%, 1.0%, 1.5%, and 2.0%). The results show that the worst-case scenario of 2.0% leading-edge erosion reduced the lift-to-drag ratio of an airfoil by 65% and reduced the power output by 20%. The low-fidelity analysis methodology presented in this research is fast and can be easily implemented in the early design phase of wind turbines to predict the effect of leading-edge blade erosion. This allows for cost-effective and efficient design solutions that take into account the effects of erosion on wind turbine performance. The research provides valuable insights for the wind energy industry to improve the reliability and performance of wind turbines.
Investigation of the effect of prescribed coupled motions on the power production of a floating offshore wind turbine
Authors: Ramponi R , Amaral R , Viré A
Published: November 2023

Floating offshore wind turbines are subjected to platform motions that modify the local velocity experienced by the rotor. This work analyzes how variations in the platform motions affect the aerodynamic power of a floating wind turbine. Idealized wind conditions and rigid wind turbine are considered. The platform motions are prescribed by the user and the coupled motions considered are pitch-surge, pitch-yaw and surge-yaw. The main novelties of the work consist in the fact that multiple motions are prescribed simultaneously, including yaw, and that the prescribed motions present a difference in phase. In absence of wind turbine controller, the pitch-surge coupling shows significant increase in average power production with respect to fixed conditions when either the amplitude or frequency are increased. This gain is maximum when surge and pitch are in phase, and is almost zero in phase opposition. The presence of the controller reverses the behavior and introduces a loss in average power along with increasing amplitudes. Phase shift analysis is particularly interesting in the surge and pitch cases: the controller introduces an upper limit in power, and phase opposition is now desirable. The yaw degree of freedom is shown to be of secondary importance in every condition.
Economic feasibility study for continued operation of German offshore wind farms
Authors: Walgern Julia , Baumgärtner David , Fricke Johannes , Requate Niklas , Kolios Athanasios , Dörenkämper Martin , Meyer Tobias , Vollmer Lukas
Published: November 2023

With a large number of wind farms already deployed in German waters and aiming to achieve a minimum of 70 GW of offshore wind capacity by 2045, investigating the potential for extended operation of existing assets is an important task. This paper documents the development of a life cycle cost/revenue framework capable of incorporating CAPEX and OPEX related elements, revenue factors, and deployment location specific aspects, in order to support decisions on the business case for continued operation beyond the nominal service life. The framework called ELSA (Economic Life cycle Simulation and Assessment) is applied to a cumulative scenario which classifies all existing offshore wind farms in Germany with respect to size and key dimensions. Outcomes of the analysis support the case for extended operation, while highlighting the importance of wake effects to AEP, the magnitude and variability of O&M costs and finally the influence of CAPEX and financial modelling.
Surrogate based sensitivity analysis and uncertainty quantification of floating wind turbine mooring systems
Authors: Dighe Vinit V. , Peeringa Johan , Hermans Koen , Swamy Siddharth Krishna , Bulder Bernard , Savenije Feike
Published: November 2023

A Floater module containing several empirical parameters has been added to the TNO’s Cost model in order to include the analysis of floating wind turbine support structures and mooring systems. It is of our interest to know which model parameters within the Floater module contribute most significantly to the mooring system costs and ultimately to the levelized cost of energy (LCOE). The strategy employed relies on constructing a surrogate model (based on Kriging), which is then used to perform global sensitivity analysis. For the scenarios studied here, it was found that the model parameter related to the mooring line breaking load coefficient remained the most sensitive to the capital expenditure (CapEx) cost, while the model parameter related to the failure event cost for mooring line repair remained most sensitive to the operational expenditure (OpEx) cost. Additionally, the study aimed at expanding the deterministic Cost model to systematically account for stochastic model parameter inputs in order to reduce modelling uncertainties and contribute towards more reliable mooring line designs.
Quantifying the effect of rock armour scour protection on eigenfrequencies of a monopile supported OHVS
Authors: Winkler K. , Weil M. , Sastre Jurado C. , Stuyts B. , Weijtjens W. , Devriendt C.
Published: November 2023

It is common practice to install scour protection systems during the construction of offshore wind farms. This is because the guidelines allow for a more optimal structural design, as the potential effects of scouring may be ignored. However, multiple sources, as well as measurements, suggest that there is an additional gain in stiffness which is not being taken into account by current guidelines. Scour protection has the ability to provide extra foundational stiffness to the monopile, which results in higher natural eigenfrequencies and mode shapes. In this paper the focus will be on an offshore high voltage station (OHVS) located in the North Sea and the impact of a rubble riprap scour protection on the foundational stiffness of the structure. Furthermore, a proposal is made on how to take these effects into account when calculating for design. This site was equipped with a mobile measurement system containing a multi-axial accelerometer, which was active in a period both before and after installation of the scour protection rock armour layer. In case of similar environmental circumstances, the eigenfrequencies of the OHVS were noticeably higher after the scour protection was installed, thus substantiating the claim of increased foundational stiffness. To perform numerical studies on the impact of the scour protection system on structural dynamics, an OHVS support structure finite element model was built. As no formally agreed upon formulation to include scour protection exists, two possible methods are proposed. One is adding a global accretion layer to model the scour protection as an additional soil layer. The other calculates an overburden pressure due to the scour protection weight, which translates to the stiffening of the upper soil layers of the foundation. Both methods have their own strengths and weaknesses, but more research on different locations and offshore structures is needed to formalize the definitive description for modelling scour protection.
Application of CFD on VIM of semi-submersible FOWT: A Case Study
Authors: Jiang Fengjian , Yin Decao , Califano Andrea , Berthelsen Petter Andreas
Published: November 2023

This study examines the Vortex Induced Motions (VIM) of the INO WINDMOOR 12 MW semi-submersible Floating Offshore Wind Turbine (FOWT) platform using three-dimensional Computational Fluid Dynamics (CFD). The results from both model- and full-scale simulations are presented. The model scale results reveal varying VIM performances at different current headings, with detailed flow visualizations and analyses of hydrodynamic loads on FOWT components providing insights into the underlying wake interaction scenarios. One simulation shows bifurcated VIM, where regular motions are intermittently interrupted due to simultaneous suppression of vortex shedding on all FOWT columns. Preliminary full-scale CFD results suggest a strong scale effect. The paper concludes with a discussion on how CFD simulation can be more effectively used in VIM research.
A study of the towing characteristics of a semi-submersible floating offshore wind platform
Authors: Ramachandran R. C. , Otter A. , Serraris JJ , Ridder EJ de , Desmond C. , Murphy J.
Published: November 2023

A robust pipeline of floating wind energy has emerged with a general trend of projects becoming larger, further from shore, and placed in increasingly energetic seas. The installation process for these farms involves the pre-assembly of components onshore or in sheltered waters before towing the platform to the operational location using tugs. It can be expected that such marine operations will be repeated in reverse at the time of decommissioning. The cost and safety of these operations will be influenced by the tugs used, towing speed, the local metocean conditions, the platform/turbine characteristics and other factors. This paper investigates the hydrodynamic characteristics of a large semi-submersible floating offshore wind turbine (FOWT) under tow. The motions of the FOWT are analysed using a numerical tool and validated using a towing test. A framework is proposed for the assessment of FOWT towing operations. Various limiting factors have been identified and the hydrodynamic performance of the system has been evaluated using the framework.
Mitigation of assembly constraints for floating offshore wind turbines using discrete event simulation
Authors: Smith B Moverley , Ongley J , Angeloudis A , Thies P R
Published: November 2023

There is a large and increasing pipeline of floating offshore wind projects with total global floating offshore wind capacity projected to grow year on year by, on average, between 59 and 104 % in the 2020s. This will lead to competition for infrastructure resources, in particular, port facilities for the construction and marshalling of the floating foundations and turbines. It is likely that multiple ports will need to be combined to provide the necessary fabrication capacity for a floating offshore wind farm of commercial scale. To enable an efficient and coordinated utilisation of multiple fabrication ports, it is crucial to understand the likely duration of different assembly and construction activities at different locations. However, at present this task is difficult to perform using top-down estimation models, as commercial-scale floating offshore wind farms comprising many tens of units have not been built to date. In this work we present a methodology, based on discrete event simulation (DES) and time series analysis, to produce an explicit simulation-based estimate of assembly activity durations, which are sensitive to setting specific factors. Three example case studies are outlined to demonstrate the ability to capture the variation in activity duration due to resource availability, and the season and location of activity. The methodology will be of use to project planners as it can be used at an early stage in the project life-cycle to appraise and adopt different construction strategies.
Effects of negative shear on loads for a 15 MW offshore wind turbine during low-level jet events
Authors: Ahmed Fahim Masud , Paskyabi Mostafa Bakhoday
Published: November 2023

Wind turbines are more often interacting with the negative shear region of a low-level jet due to increasing turbine sizes. However, the effects of negative shear on wind turbines are not sufficiently studied, particularly for offshore wind applications. In this paper, we studied the effects of negative shear on wind turbine loading. This was done using user-defined wind profiles and a model chain. The model chain consisted of a turbulence generator and a wake modelling tool coupled to an aero-hydro-servo-elastic engineering tool. We observed significant variations in the structural loading in the case of low-level jets. We also observed changes in the power spectral density estimates. Additionally, we briefly examined the wake recovery distance.
Design and costs benefits of shared anchors and shared mooring lines of floating wind turbines at farm level
Authors: Chemineau M , Castillo F , Mechinaud L , Arramounet V , Gilloteaux J C
Published: November 2023

This paper focuses on innovative mooring layouts using shared anchors and shared mooring lines. Three studies with the ActiveFloat semi-submersible floater supporting a 15MW wind turbine are presented. Those include two studies of shared anchors layouts, with a semi-taut mooring system at a deep-water site subjected to extreme conditions (Morro Bay) and a catenary mooring at a moderate water depth with gentle environment (Gran Canaria). The third study focuses on shared mooring layout at Morro Bay. The mooring system at this site is semi-taut, made of polyester, with chain close to the sea surface and the anchors. At Gran Canaria, ActiveFloat is featured with a catenary mooring system made of chain lines. Both sites are subjected to irregular sea states and turbulent wind. Time domain simulations in ULS are performed using OrcaFlex models that combine potential flow theory and Morison drag coefficients. Aerodynamic load time series are applied at the tower top. Results show that shared anchor layouts are technically feasible but do not improve the mooring system procurement costs due to the spacing constraint between each turbine. Sharing mooring lines at farm level seems more promising and could help reduce costs, due to the decrease in amount of material use.
Investigation of the influence of sinusoidal internal waves on a SPAR buoy structure
Authors: Maertens Vivien , Blenkinsopp Chris , Milewski Paul
Published: November 2023

Offshore wind has a great potential as a competitive source of renewable energy, especially in deep waters where wind speeds are more consistent and fewer restrictions apply for running large wind turbines. Previous analyses of Floating Offshore Wind Turbines (FOWTs) mostly considered obvious sources of loading: surface waves, currents, wind and mooring. However, in some deep-water locations, internal waves can occur and these have been shown to significantly affect floating structures. Since the hydrodynamic response of an FOWT governs the structure’s general stability, the aim of this research is to investigate the impact of sinusoidal internal waves on the platform motion of a free-floating SPAR-type cylinder. A potential flow model and Morison’s equation are applied numerically to calculate the forces acting on a free-floating cylinder in an oscillating flow. The commercial Finite Element Analysis software OrcaFlex is verified by the potential flow model of the oscillating flow and is then used to mimic sinusoidal internal waves acting on a free-floating cylinder in a stratified flow. Three different internal wave amplitudes and peak velocities are analysed, and the nine resulting cases are investigated for the oscillating and stratified flow each. It has been found that the pitch rotations of the SPAR cylinder were small (< 0.1°) in all cases and can likely be disregarded. The surge displacements of the free-floating cylinder were substantial in both oscillating and stratified flows, with maximum surge magnitudes of 423m and 120m, respectively. Therefore, significant additional mooring loads due to internal waves could be sustained by SPAR-type FOWTs.