bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication and characterization of suspended La0.7Sr0.3MnO3 nanofibers for high-sensitive and fast-responsive infrared bolometer
Authors: Paul Nirupam , Vadnala Sudharsan , Bonam Satish , Agrawal Amit , Vanjari Siva R K , Singh Shiv Govind
Published: November 2023

La1−x
Sr
x
MnO3 manganite oxides have shown great potential for infrared (IR) sensing. In this study, La0.7Sr0.3MnO3 (LSMO) nanofibers, synthesized by a simple electrospinning process, are suspended between gold interdigitated electrode (IDE). These electrodes, which acts as a supporting platform for the dangling nanofiber, are microelectromechanical systems based that can be fabricated quickly and economically with fewer fabrication steps. Due to the large surface-area-to-volume ratio, these fibers have outstanding thermo-electrical properties, which puts them in the leagues of materials suitable for IR sensing. Performance-wise these hanging nanofibers belong to a class of promising thermal sensors due to negligible thermal loss. The optoelectrical characterization shows its temperature coefficient of resistance (TCR) is −1.48%K−1, and its electrical resistance follows an inverse square law for distance from the IR source. The fabricated LSMO nanofibers based microbolometer has a significantly low thermal time constant with average thermal response and recovery time of 63 ms and 77 ms, respectively. Furthermore, they show encouraging bolometric properties with thermal conductance, thermal capacitance, voltage responsivity, and thermal noise limited detectivity of 3.6 × 10−3WK−1, 0.2268 × 10−3JK−1
, 1.96 × 105VW−1, and 3.7 × 108cm Hz1/2W−1
respectively. The high voltage responsivity and TCR, commensurate with the ultralow response and recovery time confirm that the fabricated Microbolometer can find industrial applications as thermal sensors.
Investigation on edge defect characteristics and electronic transport characteristics of graphene nano cutting
Authors: Tang Meiling , Yuan Zewei , Sun Jingting , Sun Xiaohan , He Yan , Zhou Xinbo
Published: November 2023

The effects of cutting crystal direction and speed on edge morphology, defects and electron transport characteristics were studied by molecular dynamics from the distribution state of defect atoms, the number of defect atoms, cutting force and radial distribution function. The edge defects of zigzag graphene nanoribbons were extracted, and the difficulty of forming different kinds of defects and the influence of different defects on band gap were studied by density functional theory. The results indicate that cutting graphene along the [010] (zigzag) direction has a smaller variance and smoother cutting. The obtained graphene nanoribbons have fewer defects and good edge quality. And the higher the cutting speed, the fewer defects of the graphene nanoribbons formed, resulting in smaller damage. The typical defects at the edges include 5–8–5 defect (double-vacancy defect), 5–9 SV defect (single-vacancy defect), stone wales (SW) defect, chain defect, crack defect and hole defect. The relationship between the magnitude of forming energy values produced by different defect types is as follows: crack defect > chain defect > SW defect > 5–9 SV defect > 5–8–5 defect > hole defect. Hole defect is the most difficult to form. The band gap width of the cut edge containing defects is smaller than that of the perfect graphene nanoribbon, resulting in the increase of the conductivity of the graphene nanoribbon in the direction of metal characteristics. The presence of defects can open the band gap with of intrinsic graphene.
The effects of illumination on the current conduction mechanisms of the Au/C20H12/n-Si Schottky barrier diode (SBD)
Authors: Bengi Seda
Published: November 2023

Using the I-V characteristics both in the dark and under varied illumination-intensities (50–250 mW.cm−2) by 50 mW.cm−2 steps in the wide range bias-voltage (±5 V), specific fundamental electrical and photo effects parameters of the Au/C20H12/n-Si SBD were examined. Due to the creation of electron–hole pairs and their drift in opposite directions under the influence of an electric field, the value of photocurrent in the reverse bias (Iph) increases when illumination density is increased. The barrier height (ΦB0) tended to decrease due to the increase in photocurrent, while the diode’s ideality factor (n) increased with increasing illumination intensity. Also, the Schottky structure’s open-circuit voltage (Voc), short circuit current (Isc), filling factor (FF), and efficiency (η) were determined to be 0.358 V, 95.5 μA, 33%, and 0.028% under 50 mW.cm−2, respectively. The Rs and Rsh values found using Ohm’s law are a vital function of illumination and voltage which decrease with increasing illumination intensity. Additionally, using the forward bias I-V data and accounting for the bias dependent of the effective barrier height (Φe) and ideality factor n(V) for different illumination intensities, the energy density distribution profile of surface states (Nss) was obtained. According to these results, the organic interlayer consisting of C20H12 is light-sensitive and suitable for optoelectronic devices such as photodetectors and photodiodes.
Primordial stochastic gravitational wave backgrounds from a sharp feature in three-field inflation. Part I. The radiation era
Authors: Aragam Vikas , Paban Sonia , Rosati Robert
Published: November 2023

The detection of a primordial stochastic gravitational wave background has the potential to reveal unprecedented insights into the early universe, and possibly into the dynamics of inflation.
Generically, UV-complete inflationary models predict an abundance of light scalars, so any inflationary stochastic background may well be formed in a model with several interacting degrees of freedom.
The stochastic backgrounds possible from two-field inflation have been well-studied in the literature, but it is unclear how similar they are to the possibilities from many-field inflation.
In this work we study stochastic backgrounds from more-than-two field inflation for the first time, focusing on the scalar-induced background produced during the radiation era by a brief turn in three-field space.
We find an analytic expression for the enhancement in the power spectrum as a function of the turn rate and the torsion, and show that unique signatures of three-field dynamics are possible in the primordial power spectrum and gravitational wave spectrum.
We confirm our analytic results with a suite of numerical simulations and find good agreement in the shape and amplitude of the power spectra.
We also comment on the detection prospects in LISA and other future detectors.
We do not expect the moderately large growth of the inflationary perturbations necessary for detection to cause a breakdown of perturbation theory, but this must be verified on a case-by-case basis for specific microphysical models to make a definitive claim.
The Application of 5G Wireless Communication in Maritime Environment
Authors: Wu Jianming , Yang Kun , Zeng Hao , Zhang Shuo , Ding Jianjun , Jiang Xue
Published: November 2023

Recently, 5G wireless communication have been rapidly adopted for maritime applications. As a result, significant progress has been made in the ocean digitalization. 5G features with low latency, high reliability, and a large bandwidth, which satisfies the requirements of maritime applications. Due to significant differences between land and marine radio propagation environments, the maritime communication encounters a large challenge for providing maritime users with reliable data communication service. In order to solve the abovementioned challenge, we designed a maritime 5G terminal and tested it on an unmanned surface vehicle (USV) in the Lanyue Lake of Zhejiang Ocean University. The test data were collected, and the corresponding data analysis are presented, which includes signal strength, signal reception quality, upload and download data rate. The received signal level (RSL) and transmission data rate obtained by the maritime 5G terminals demonstrate great potential of meeting the communication requirements of the maritime users. It is also can be found that the RSL and the data transmission rate of the maritime 5G can be used for the remote control of the unmanned ships, with the signal strength at sea up to -89.45 dBm, and maximum rate up to 226 Mbps.
Comparing Multiple Extended Object Tracking with Point Based Multi Object Tracking for LiDAR in a Maritime Context
Authors: Baerveldt Martin , Hem Audun Gullikstad , Brekke Edmund Førland
Published: November 2023

In this paper, we compare a recently developed multiple extended object tracking method with a point-based tracker for maritime applications by evaluating the methods on both real and simulated LiDAR data. Being able to track other vessels is a key part of maritime situational awareness, and multi-object tracking is well suited to this task. Traditionally, multi-object tracking uses the point approximation to simplify the target tracking problem, meaning that an object is assumed to only generate a single measurement. With recent advances in sensor technology, this approximation is no longer valid. Multiple extended object tracking instead makes use of methods that estimates the extent of a target using all available measurements. However, the target models used in extended object tracking are by necessity more complex. We compare these two approaches on real and simulated LiDAR data, which was gathered by tracking smaller vessels. We find that the extended object method has greater performance on simulated data and experimental data with comparatively little wake clutter. However, on experimental data with more wake clutter, the point-based method outperforms the extended object method since it is less sensitive to the disturbance caused by wake clutter. We can conclude that multiple extended object tracking methods have the potential to be more accurate for LiDAR data, but since the models are more complex, measurement sources need to be modeled correctly.
Study on autonomous ship enhancement by optimizing the object detecting algorithms
Authors: Jiang Xue , Zhang Xinhui , Yang Kun , Zhao Penghui
Published: November 2023

The accuracy and efficiency of object detection is the key technology to spread autonomous driving. In order to address issues such as missed and false detection in traditional target detection algorithms, deep learning technology is used to optimize the ship target detection model as well as the attention mechanisms in this article. Specifically, this paper proposes an improved model based the traditional YOLOv5s algorithm, and a self-created ship dataset is also provided. To refine ship target detection, various attention mechanisms were implemented and compared, including CBAM, ECA, GAM, SimAM, and SK-Net. Through comparative analysis of the effects of these mechanisms, GAM was identified as the optimal choice. The experimental results indicate that the mean average precision (mAP) of detecting ship targets was augmented by 1.0% following the incorporation of GAM. The YOLOv5s-GAM model is therefore deemed as an effective target detection approach in enhancing the safety of ship autopilot, with potential applications in the future.
Evaluation of an autonomous, short sea shipping feeder-loop service through advanced simulations
Authors: Tangstad Espen J. , Mørkrid Odd Erik , Nordahl Håvard , Krause Stefan , Mateienko Denys , Dæhlen Jon Schonhovd , Johanson Kenneth
Published: November 2023

Traditionally, container-freight being shipped from central Europe to the coast of Norway has been transported either by road, or by larger containerships to central ports. For the past 3 years the AEGIS consortium has worked to develop a new, disruptive short sea shipping feeder-loop service based on mother and daughter ships [1]. The hypothesis is that introducing smaller, autonomous, battery-powered vessels into the fjords of Norway would open new business areas, provide access to remote regions, and allow shipping companies to take on cargo that could not previously be transported by water. Such a transport system has the potential of reducing cost, GHG emissions and external costs, while increasing frequency of service and the waterborne cargo volume in Europe. One of the main challenges of the mother-daughter logistic system is how transshipment affects defined key performance indicators (KPIs), especially in terms of cost. For this purpose, the SIMPACT tool [2] was developed in the H2020 projects AEGIS and AUTOSHIP. The tool allows for rapid iterations of maritime logistic systems through discrete event scheduling, and estimation of energy, fuel, emission, and cost.

This paper will present results from a case-study on two different daughter ship concepts. The concepts are evaluated through cost and environmental KPIs presented in [1], in addition to external costs based on the European handbook on the external costs of transport [3].

Results from the case-studies indicate that transport systems including green daughter-vessels have the potential of being cost competitive and would lower externalities compared to the baseline truck transportation system.
VAWT support structure mass sensitivity due to aerodynamic load scaling
Authors: Silva Adriana Correia da , Muskulus Michael
Published: November 2023

The X-rotor wind turbine is an X-shaped hybrid vertical axis wind turbine whose power take-off is done by horizontal axis rotors located at the tip of the lower blades. Based on an initial basic study, the present study developed a preliminary jacket design as the turbine support structure. Steady aerodynamic loads were obtained from an actuator cylinder model and dynamic load simulations including wave loads were performed. The structure was checked according to fatigue damage and maximum yielding for representative site-specific load cases for fatigue and ultimate limit states. Even though the use of a conventional jacket was shown to be feasible for the new turbine concept, the overall mass of the support structure obtained by the higher fidelity model was higher than the initial prediction. The design was driven by the fatigue damage, caused by large cyclical loads on every rotor rotation. The effect of a hypothetical aerodynamic load reduction on the jacket mass was investigated. The developed design methodology was also applied to the design of equivalent jackets after a load reduction of 75% and 50% and the mass of the structure was shown to be sensible, with a respective reduction of 25% and 48%. This result demonstrates that different design strategies that influence the magnitude of the aerodynamic loads (e.g. the control strategy) could lead to a more cost-efficient jacket design.
The influence of journal bearings on the gearbox dynamics of a 5 MW wind turbine drivetrain
Authors: Siddiqui Muhammad Omer , Chodvadiya Ashish , Luo Jingjing
Published: November 2023

In recent years, journal bearings have been replacing roller bearings in wind turbine gearboxes, as they are believed to provide higher reliability compared with roller bearings. However, replacing roller bearings with journal bearings can drastically change the gearbox dynamics. Journal bearings have complex dynamics at different operating speeds, and, as a wind turbine operates at various speeds, it is vital to analyze the gearbox dynamics for the entire speed range. This contribution presents the dynamic response of a wind turbine gearbox when the roller bearings of the high-speed shaft are replaced with journal bearings. This is done by performing a comparative case study using a detailed multibody simulation (MBS) model of a 5 MW reference wind turbine drivetrain. A dynamic model of the journal bearings, developed in Simulink, is dynamically coupled with the 5 MW drivetrain MBS model using co-simulation. The simulation results for the gearbox vibration as well as gear forces are compared with the simulation results of the drivetrain model with roller bearings. The findings from this work will help in clarifying the advantages (or disadvantages) of using journal bearings instead of roller bearings in wind turbine gearboxes.
Open Source High Fidelity Modeling of a Type-5 Wind Turbine Drivetrain
Authors: Hussain Tanveer , Gallego-Calderon Juan , Shafiul Alam S M
Published: November 2023

The increasing integration of renewable energy resources in evolving bulk power system (BPS) is impacting the system inertia. Type-5 wind turbine generation has the potential to behave like a traditional synchronous generator and can help mitigate the impact on system inertia. A hydraulic torque converter (TC) and gearbox with torque limiting feature are integral parts of a Type-5 wind turbine unit. A high fidelity model of Type-5 wind turbine drivetrain is not openly and widely available for grid integration and transient stability studies. This hinders appropriate assessment of Type-5 wind power plant’s contribution to bulk grid resilience. This work develops and validates a TC model based on those generally used in automobile’s transmission system. Moreover, the concept of torsional coupling is leveraged to integrate the TC and gearbox system dynamics. The entire integrated model will be open sourced and publicly available for grid integration studies.
Impact of probe volume and peak detection methods on lidar rotor effective wind speed and turbulence intensity estimations
Authors: Costa F , Peña A , Pettas V , Cheng P
Published: November 2023

Lidar simulation techniques are a suitable and increasingly reliable alternative for testing lidar measuring strategies and illustrating their response when combined with modelled wind fields. In this work, two simulation tools are combined to assess the uncertainty in the derivation of the rotor effective wind speed and the wind speed variance from a forward-looking nacelle-mounted continuous wave lidar wind speed estimations. These uncertainties are analysed for a variety of atmospheric turbulence levels and lidar measuring strategies. A synthetic turbulence generator is used to create the reference wind fields. Subsequently, a lidar simulator operated in a continuous-wave mode is used to scan the synthetic wind fields and perform a sensitivity analysis by comparing first- and second-order statistics against reference values. The lidar simulator is enhanced with three Doppler peak detection methods, namely the maximum, the median and the centroid, to extract radial wind speeds from the velocities found within the probe volume. The results show that probe volume and peak detection methods influence the uncertainty of the wind speed variance. The uncertainty in time-averaged and instantaneous rotor effective wind speed estimations is not sensitive to the lidar spatial averaging or peak detection methods investigated. Finally, we saw that the turbulence intensity influences the derived lidar quantities and is the main driver of the variations in rotor effective wind speed uncertainty estimations.
Machine learning for predicting offshore vertical wind profiles
Authors: Rouholahnejad Farkhondeh , Santos Pedro , Hung Lin-Ya , Gottschall Julia
Published: November 2023

The accurate characterization of the vertical wind profile over the sea that covers the rotor swept area of modern wind turbines is a key challenge for wind energy yield calculations. Since offshore wind measurements are scarce, early-phase projects tend to use numerical model outputs before planning a dedicated measurement campaign. This study aims to develop and validate a machine-learning model that can assimilate wind parameters measured at the first level of the meteorological masts as input and provide a wind speed profile covering the rotor swept area of modern turbines that is more accurate than numerical weather prediction models. The methodology is based on a random forest model implemented in the python package Scikit-Learn. Three offshore sites in the North Sea have been selected for this study, namely FINO3, IJmuiden and Nordsee Ost’s (NSO) met mast, which are 100 to 350 km apart. Each site has an instrumented 100-m meteorological mast along with a Doppler wind lidar measuring up to 300 m. The baseline selected for comparison was the Weather Research and Forecast (WRF) model. To assess the accuracy of the random forest model two models were trained at IJmuiden and FINO3 and tested at all three locations. Hence, we examine the model performance at the site of training, the so-called same site approach, as well as new sites, the so-called round robin approach. The same site approach quantifies the model consistency, while the round robin shows the degree of spatial robustness. The results show that the model is consistent, where the model trained and tested at FINO3 showed a mean absolute error (MAE) reduction of 68% compared to WRF. This model is also robust, when applied at IJmuiden, 350 km away with a MAE of 1.2 m/s, 8% improved compared to WRF outputs. This study therefore shows the potential to implement machine-learning methods in the prediction of vertical wind speed profiles over the sea. One potential application for the presented methodology is the extension of wind profiles measured by floating lidar systems to higher heights, where current wind lidar products have low availability and higher associated uncertainties, when measuring at a higher height.
Standalone, Descriptive, and Predictive Digital Twin of an Onshore Wind Farm in Complex Terrain
Authors: Stadtmann Florian , Rasheed Adil , Rasmussen Tore
Published: November 2023

In this work, a digital twin with standalone, descriptive, and predictive capabilities is created for an existing onshore wind farm located in complex terrain. A standalone digital twin is implemented with a virtual-reality-enabled 3D interface using openly available data on the turbines and their environment. Real SCADA data from the wind farm are being used to elevate the digital twin to the descriptive level. The data are complemented with weather forecasts from a microscale model nested into Scandinavian meteorological forecasts, and wind resources are visualized inside the human-machine interface. Finally, the weather data are used to infer predictions on the hourly power production of each turbine and the whole wind farm with a 61 hours forecasting horizon. The digital twin provides a data platform and interface for power predictions with a visual explanation of the prediction, and it serves as a basis for future work on digital twins.
Yaw control strategies for 20 MW multi-rotor systems
Authors: Warner Markus , Eichelmann Tobias , Anselm Rudolf , Störtenbecker Sven , Dalhoff Peter
Published: November 2023

In this paper, the control of an active yaw system for a 20 MW multi-rotor wind turbine system (MRS) is considered. The MRS under investigation consists of five 4 MW turbines in two rows, which are connected to the tower via a space frame. A central yaw bearing at the height of the lower rotors is provided for active yaw. The paper aims to show that active aerodynamic yaw is possible by changing the thrust of certain rotors and should be considered for further research in the field of yawing of an MRS. Two different simulation environments are used in the paper. The MRS is modeled and simulated in Matlab/Simulink. Simulink’s own control modules are used as controllers. In the other simulation approach, the same MRS is modeled and simulated in Bladed and controlled with an external controller based on C++. The use of Bladed and Matlab/Simulink enables the plausibility and verification of the results. Matlab/Simulink is faster based of its simpler models but Bladed is more sophisticated. This paper also briefly presents the state of the art for yaw systems and yaw control of conventional single rotor wind turbines and initial research literature on yaw control of MRS.
A comparative study of laser-arc hybrid welding with arc welding for fabrication of offshore substructures
Authors: Bunaziv I , Ren X , Olden V
Published: November 2023

Laser-arc hybrid welding (LAHW) is an efficient and promising joining method for offshore structures made from metallic alloys. Under a high-power laser output, a keyhole is formed that efficiently melts a metal and provides high penetration depths compared to shallow and wide welds made by conventional arc welding, thus it requires much less time for production. A significant reduction in welding time leads to a substantial reduction of welding consumables and electricity use. Higher gap bridging ability can be achieved and tolerances for plate preparation is reduced when an arc is added to a laser beam. This work explicitly presents and compares different welding methods and their efficiency in application for offshore windmill substructures. According to a preliminary calculation, LAHW may reduce welding time by 10–20 times depending on process parameters and up to 15 times lower consumables usage. It was identified that the highest costs in welding is the filler wire followed by a shielding gas and electricity. This leads to high efficiency of LAHW in term of sustainability and reduction of CO2 emissions in general compared to well-established arc welding. However, the narrow and deep welds made by LAHW may suffer from high hardness in the root area, inhomogeneous filler metal mixing, which may lead to poor microstructure, cracking and porosity. This requires an extensive research work on the process optimization and understanding the underlying physics to provide sound welds which must comply with the international standards.
Effect of body motion on the wave loads computed with CFD on the INO-WINDMOOR floater
Authors: Califano A , Berthelsen P A , Magalhaes Duque Da Fonseca N M
Published: November 2023

CFD simulations were carried out on the 1:40 model of the INO WINDMOOR floater in regular waves to extract hydrodynamic loads, both on the structure, the single columns and sections from each column. Three different approaches for the platform motion were used, (i) fixed, i.e., restrained from motion, (ii) prescribed, i.e., forcing the floater to follow the motion recorded during model tests and (iii) 6 DOF, i.e., allowing the floater to move according to external forces from waves and anchor lines. The obtained results show the effect of the free surface on the local drag forces at sections with different submergences, which are important to include when modelling the motion with simplified methods based on pre-computed force coefficients. A comparison of the surge force shows that the amplitudes of the loads obtained with moving platform are reduced compared to the corresponding fixed case. The mean total surge force computed on the single columns and the whole platform show small quantitative differences between the different methods. The motion responses of the platform for surge and heave obtained with CFD are in fair agreement with the experiments.
Lidar-based virtual load sensors for mooring lines using artificial neural networks
Authors: Gräfe Moritz , Özinan Umut , Cheng Po Wen
Published: November 2023

Floating offshore wind turbines are equipped with a variety of sensors, which are measuring data, valuable for the control and monitoring of the turbine. However, reliable measurements are difficult or costly for some physical quantities. This includes load estimates for mooring lines and fairleads. In this study, we investigate an approach using wind speed measurements from a forward-looking nacelle-based lidar as inputs to long short-term memory networks to estimate fairlead tensions. Nacelle-based lidar wind speed measurements on floating offshore wind turbines are influenced by platform motions, in particular by the rotational pitch displacement and the surge displacement of the floater. Therefore, the lidar wind speed measurement contains information about the dynamic behavior of the floater. In turn, the floater’s dynamics determine the fair lead loads. Thus in this study, we directly use the lidar-measured line of sight (LOS) wind speeds to estimate mooring line tensions. The model training data is obtained using the aero-elastic wind turbine simulation tool openFAST in combination with the numerical lidar simulation framework ViConDAR. Results show, that lidar-based virtual load sensors can reproduce mean fairlead tension as well as low-frequency fluctuations, with varying accuracy dependant on the combination of input features. For the model which is only using LOS wind speed measurements as input a normalized root mean squared error of 0.55 was obtained.
Development of a risk analysis model for the installation of offshore wind farms
Authors: Munoz N Garcia , Lange AK , Kaczenski J , Wiggert M
Published: November 2023

The installation of offshore wind farms represents a major driver of offshore wind energy costs due to the high level of associated risks. Substantial cost reduction potential can be realized if these risks are effectively identified and controlled, preventing project delays and financial damages. Therefore, we propose a new method to identify, analyse and evaluate installation risks for use in project planning. This paper provides an in-depth walkthrough of the steps involved in the development of a simulation-based quantitative risk analysis model. At the example of a turbine installation case study, project plan-related risks are identified and quantified by conducting a literature review and expert interviews. The corresponding risk likelihoods and consequences are modelled with probability distributions to simulate their impact on total project duration. Using Monte Carlo simulation, the distribution of results is statistically evaluated to derive the expected project delay caused by the analysed risks as well as reference values for optimistic and pessimistic scenarios. Regarding the underlying model assumptions, the most significant risks (e.g. supply chain failure) are identified and examined in a sensitivity analysis. The developed model can serve as a basis for developing more reliable schedule estimations and contribute to minimizing installation delays and costs.
Quick assessment of semi-submersible floating offshore wind turbines under misaligned wind, wind-wave and swell-wave loading
Authors: van der Spek J B , Maljaars N , Shen Q , Grammatikopoulos A
Published: November 2023

Computer-intensive coupled time-domain simulations are used by both academia and industry to capture the nonlinear behavior of floating offshore wind turbines. To assist in pre-design and optimization, computationally efficient methods such as frequency-domain methods are required. However, state-of-the-art frequency-domain methods consider simplified cases which do not represent operational design cases of industry projects. This paper compares the effectiveness of a frequency-domain method based on Response Amplitudes of Floating Turbines (developed by the NREL) to time-domain simulations carried out in BHawC-OrcaFlex by Siemens Gamesa Renewable Energy. The load cases are part of IEC Design Load Case 1.2 (fatigue in normal power production) and are selected from an industry project. Reasonable agreement is found for the pitch/roll rigid body modes around rated wind speed. However, the mean response and dynamic response is overestimated by the frequency-domain method due to underestimation of the mooring stiffness and the underestimation of hydrodynamic damping. For the estimation of the fore-aft and side-to-side bending moment, main differences are identified due to the absence of the tower bending, excitation due to rotor rotation and second-order wave forcing in the frequency-domain method. The results show the need for extending the frequency-domain method with tower bending and rotor rotation as degrees of freedom.
Rational Simplification of High Fidelity Wind Turbine Models Used for Mooring Analysis
Authors: Kvittem Marit I , Fredriksen Arnt G , Souza Carlos S de , Hanssen Finn-Christian W
Published: November 2023

This study investigates the use of simplified turbine modelling in analysis of a soft mooring system (horizontal plane periods > 250 s). Two simplified turbine models are developed, tested and compared to a high fidelity turbine model in a case study of the INO WINDMOOR 12 MW FOWT with a soft mooring system. The chosen simplified modelling strategies are a drag disc model, a de-coupled approach where the aerodynamic loads are pre-calculated in a fixed turbine simulation and a model with reduced degrees-of-freedom. Corrections to the pre-calculated force model is also developed and compared. The results show that the pre-calculated force approach gives better comparisons to the full model than the drag disc model, and that applying a controller correction to account for the wind turbine controller’s response to floater motions improves the predicted response.
A passively self-adjusting floating wind farm layout to increase the energy production: a sensitivity analysis
Authors: Mahfouz Mohammad Youssef , Cheng Po Wen
Published: November 2023

Offshore wind farm layout design techniques and methodologies currently focus on fixed bottom offshore wind turbines. As more floating wind farm (FWFs) are planned, new methodologies for FWF layout design and optimization are required to consider the different attributes between fixed bottom and floating offshore wind turbines (FOWTs). One main difference is the ability of FOWTs to move in the horizontal plane (surge and sway motions). In our work in [1], we showed that the motions of the FOWTs in the horizontal plane represent an opportunity which can be used to increase the FWF’s annual energy production (AEP). We can passively control the motions of the FOWTs in a FWF according to the incoming wind direction, moving the downwind turbines out of the wake of upwind ones. Since the horizontal motions of a FOWT are governed by the mooring system design (MSD) attached to it, this passive control can be done by designing a customized mooring system (MS) for every FOWT in the farm. In this work we build on our work in [1], as we carry out a sensitivity analysis to check the effect of the farm size and the wind rose on the methodology we introduced. The results show that the percentage increase of energy production due to passively relocating the FOWT is sensitive to the FWF size. Very small FWFs will gain less energy by relocating the FOWTs. Moreover, we show that even with a more uni-directional wind rose relocating the FOWTs in a FWF remains beneficial.
Layout and yaw optimisation of an offshore wind farm through analytical modelling
Authors: Sukhman D , Lück S , Göing J , Bartl J , Hansen T , Stenfelt G , Friedrichs J
Published: November 2023

In this work, a computational tool for analytical large scale modelling of offshore wind farms is presented. Using Horns Rev 1 as a reference baseline, an optimal layout and yaw angle setting for one wind direction based on aerodynamic considerations is proposed. Based on a wake model presented by Qian & Ishihara, flow velocities as well as turbulence intensities are predicted when several wake flows are superimposed. Subsequently, the aerodynamic performance of the wind turbines is calculated. The proposed tool shows good agreement with measurement and LES data. The influence of performance-driving parameters, namely turbine spacing, ambient turbulence intensity and yaw angle are investigated. The axial spacing and ambient turbulence are identified as the most significant factors. Based on these results, the proposed optimal layout solution suggests a higher power yield of up to 57 %, while the optimal yaw angles found in this work show a power increase of over 6% compared to the baseline layout.
Wind tunnel hardware-in-the-loop experiments about the global response of a 15 MW floating wind turbine
Authors: Fontanella A. , Facchinetti A. , Belloli M.
Published: November 2023

This work describes a new wind tunnel hybrid experiment investigating the aerodynamics and the global response of a 15 MW floating wind turbine. The floater motion is realized with a 6-degrees-of-freedom robotic platform controlled with a hardware-in-the-loop system, in which aerodynamic forces developed by the turbine model are the input of a numerical simulation of the floater dynamics, hydrodynamic excitation, and mooring. It is shown that accuracy of the aerodynamic force feedback from the wind turbine is critical to reproduce the floating wind turbine motion, and measurement of aerodynamic loads is more uncertain in case of pitch motion that movement in the other directions. Free decay tests show that damping of platform surge, pitch, and yaw modes is increased with wind and operating wind turbine compared to the no wind case. The effect of aerodynamic loads on the platform response with stochastic waves is small in the wave frequency range, whereas response of the surge mode is increased with wind.
Validation of a panel method with full-scale FOWT measurements and verification with engineering models
Authors: Netzband Stefan , Schulz Christian W , Özinan Umut , Adam Raphaël , Choisnet Thomas , Cheng Po Wen , Abdel-Maksoud Moustafa
Published: November 2023

The present paper gives insights into the verification of different models of the Floatgen demonstrator by BW Ideol. This floating offshore wind turbine (FOWT) is based on a barge type-floater with moonpool. The moonpool shall dampen the platform’s motion and is challenging to model due to the increased complexity of the hydrodynamic behaviour. For the verification purposes, the results of two engineering methods (OrcaFlex, OpenFAST) equipped with frequency-dependent hydrodynamic solver and the nonlinear time-domain boundary element method panMARE are compared. The OrcaFlex model designed by BW Ideol is regarded as a reference because of a preceding calibration with measurement data. All models show fairly good agreement in most cases. Only in heave there are significant differences between engineering and the nonlinear models which is caused by different modelling of the moonpool hydrodynamics. In addition, a hybrid simulation approach with prescribed motion and constrained wind field based on motion sensors and LIDAR measurements on the Floatgen demonstrator was applied for an aerodynamic and load validation of panMARE. The validation shows good agreement based on time-domain comparison regarding the tower top loads and turbine operation.
The Impact of Unsteadiness on the Aerodynamic Loads of a Floating Offshore Wind Turbine
Authors: Schulz Christian W. , Özinan Umut , Netzband Stefan , Cheng Po Wen , Abdel-Maksoud Moustafa
Published: November 2023

The role of unsteadiness in the aerodynamics of Floating Offshore Wind Turbines (FOWT) remains a subject of discussion among the research community. Therefore, it must be investigated whether and to what extent transient aerodynamic phenomena impact the loads of a wind turbine rotor undergoing motions in unsteady winds. The study of transient aerodynamic phenomena is closely linked to the question of whether the modern Blade Element Momentum Theory (BEMT) methods can be considered reliable for the simulation of FOWTs. In this work, investigations are carried out to identify the relevant transient aerodynamic phenomena and quantify their effects on the torque and thrust of the Floatgen wind turbine. A free-wake panel method is utilised to identify and quantify transient parts of the load response to a set of simplified unsteady scenarios: a wind gust, a harmonic surge motion and a rotor speed oscillation. Transient contributions to the load behaviour of the wind turbine can be identified in all scenarios under consideration. In addition, the ability of a state-of-the-art BEMT method to model the identified transient contributions is evaluated. While an agreement of the qualitative impact of the transient aerodynamic phenomena at moderate motion frequencies is found, a contradicting behaviour of the simulation models becomes apparent at high motion frequencies. This indicates the presence of a transient, three-dimensional wake effect that cannot be reproduced by the common unsteady corrections for BEMT methods.
Validation of a potential flow-based numerical model for engineering design of Floating Offshore Wind Turbine foundations
Authors: Tomaselli P D , Jensen B
Published: November 2023

Designers apply numerical models for scrutinizing the complex response of Floating Offshore Wind Turbine (FOWT) foundations to environmental conditions at sea. This paper presents a numerical model for predicting the wave-induced motions of FOWT foundations. The model combines two solvers, one for generating the forcing wave field and the other for computing the foundation response based on Potential Flow Theory. With its robustness and relatively low computational demand, the proposed model aims to assist the initial exploratory stages of the FOWT design process. A validation of the proposed model against a laboratory experimental campaign is presented. The performance of the model is investigated, with highlighting the role of second-order hydrodynamic effects such as viscous damping and slow-drift.
A control-oriented model for floating wind turbine stability and performance analysis
Authors: Pegalajar-Jurado Antonio , Lio Alan W.H.
Published: November 2023

A well-designed floating turbine controller should lead to small power fluctuations while keeping the system stable. Floating wind turbines can experience instability when operating above rated wind speed, due to the blade pitch controller. This phenomenon, known as negative aerodynamic damping, is the reason why a controller needs to be re-designed for floating applications. One solution is to de-tune the blade pitch controller and make it slower than the floater pitch motion. This solution, although simple, reduces the controller’s ability to react to changes in the inflow and results in large power fluctuations. A more sophisticated approach involves an additional loop feeding back the fore-aft nacelle velocity to the blade pitch or generator torque. The choice of gains, however, is not trivial. This work proposes a control-oriented model derived from first principles to investigate different controller configurations in terms of both stability and turbine performance. The linear model with seven degrees of freedom (six rigid-body motions and drivetrain) is formulated analytically and coupled with the controller. The linear formulation allows us to investigate stability via eigenvalue analysis and performance via frequency-domain response, thus bypassing the need for time-domain simulations. Parametric studies with thousands of different controller configurations can be completed in a matter of minutes.
Thermoelectric properties of metashale geopolymer mortar doped with graphite powder
Authors: Hotěk Petr , Fiala Lukáš , Černý Robert
Published: November 2023

Building materials with favorable thermoelectric properties can become a supplementary source of clean energy due to their ability to convert waste heat into electric energy. Depending on the thermoelectric conversion effectivity defined by the Seebeck coefficient, constructions made of these materials can serve as civil engineering energy harvesters. Since the conversion effectivity of common calcium(alumino)silicates (cementitious materials, geopolymers) is low, doping with electrically conductive admixtures is a crucial step to handle the issue. The paper is focused on the design of metashale mortar doped with graphite powder (3 wt.%), determination of its common material properties, as well as experimental determination of thermoelectric properties. The maximum thermoelectric voltage (161.65 mV, ΔT = 130 °C), Seebeck coefficient (538 μV K-1), and figure of merit (∼ 10-9) revealed significantly better thermoelectric performance than cement pastes or alkali-activated slags doped with multi-walled carbon nanotubes and if of promising thermoelectric conversion potential.
Physical properties of alkali activated aluminosilicates based on low-reactivity ceramics in room temperature conditions
Authors: Keppert M , Pommer V , Šádková K , Vejmelková E , Černý R
Published: November 2023

Alkali activated aluminosilicates (AAA), or geopolymers, are widely studied materials because they are supposed to become a more sustainable alternative to materials based on Portland cement, such is especially concrete. AAA materials are generally produced by activation of an aluminosilicate precursor by an alkaline solution – usually solution of sodium silicate and sodium hydroxide. The capability of the prepared material to be used as construction material is commonly evaluated by means of its compressive strength. The present paper aims to broaden the AAA materials characterization to other physical properties such are porosity and thermal conductivity, since these measures are closely related to the engineering performance of the material. The waste ceramic dust was used as precursor while the solution of potassium silicate was an activator. The relationships between the above listed physical properties and obviously on the material composition were searched.
Deterioration of basalt-based reinforcement in corrosive environments: experimental monitoring and mathematical models
Authors: Kočí V , Keppert M , Černý R.
Published: November 2023

The basalt-based reinforcing elements are considered as alternative to conventional steel-based reinforcing elements (rebars, wires). The motivation to use basalt-based elements (fibers, composite bars, meshes etc.) is better corrosion resistance of basalt fibers especially in sea-water environment, compared to carbon steel. Nevertheless, it does not mean that basalt fibers are 100% corrosion resistant. The basalt fibers are produced from silicate melt of proper composition, i.e. the basalt fibers are vulnerable to both acid and alkaline hydrolysis, as well as other silicates do. When basalt fibers are used as reinforcement in concrete, the alkaline hydrolysis will become an important issue. The present paper deals with experimental observation of basalt fibers in alkaline environment of Simulated Pore Solution. The fibers deterioration was monitored by their mass loss and SEM microscopy. Jander’s model was used to describe mathematically the kinetics of the fibers alkaline hydrolysis. The results revealed that a corrosion products layer is formed on the fibers surface in this environment. The composition of this layer corresponds to N-A-S-H and C-A-S-H phases known from alkali-activated aluminosilicates or hydrated Portland cement.
Evaluation of transient measurements of thermophysical parameters using Finite Elements Method.
Authors: Malinarič S
Published: November 2023

The transient plane source (TPS) method was used to measure the thermal diffusivity and conductivity of silica glass and polymethyl methacrylate (PMMA). The results were evaluated by an analytical model and also by a numerical model created by the finite elements method (FEM). The results of both models and both materials were compared, and the difference was less than 0.4%.
Study of the illite-kaolinite-CaCO3 mixtures during firing
Authors: Mikušová D , Húlan T , Lukáč F , Csáki Š , Trník A
Published: November 2023

The raw materials used in traditional ceramics include highly plastic clay minerals such as illite or kaolinite. Non-plastic materials are usually added to the mixtures, which affect their workability and sintering process. The formation of a new crystalline phase (e.g. anorthite) is often observed in mixtures that contain a large amount of CaO. The improvement of final properties of ceramic materials is attributed to the formation of anorthite. The aim of this paper is to study the firing of anorthite ceramics in the system illite-kaolinite-CaCO3. Four sets of samples with different illite:kaolinite ratio (8:2, 6:4, 4:6, 2:8), and with a constant addition of CaCO3 are produced. The samples were subjected to the thermal and structural analyses. A significant mass loss is observed for all studied samples during the process of dehydroxylation and decomposition of CaCO3. An exothermic peak around 950 °C, which is connected with the formation of anorthite, is observed during differential thermal analysis. Above this temperature, no significant length changes are recorded. The presence of anorthite is confirmed by XRD analysis. The most formation of anorthite is observed in the illite-kaolinite sample with ratio 8:2.