Evaluation of preisach model of hysteresis to model superconductors

The Large Hadron Collider is the world’s largest and most powerful particle accelerator. The project is divided in phases. The first one goes from 2009 until 2020. The second phase will consist of the implementation of upgrades. One of the upgrades is to increase the ratio of collision, the luminosity. This objective is the main of one of the most important projects which is carrying out the upgrades: Hi-Lumi LHC project. Increasing luminosity could be done by using a new material in the superconductor magnets placed at the interaction points: Nb3Sn, instead of NbTi, the one being used right now. Before implementing it many aspects should be analysed. One of them is the induction magnetic field quality. The tool used so far has been ROXIE, software developed at CERN by S. Russenschuck. One of the main features of the programme is the time-transient analysis, which is based on three mathematical models. It is quite precise for fields above 1.5 Tesla. However, they are not very accurate for lower fields. Therefore the aim of this project is to evaluate a more accurate model: Classical Preisach Model of Hysteresis, in order to better analyse induced field quality in the new material Nb3Sn. Resumen: El Gran Colisionador de Hadrones es el mayor acelerador de partículas circular del mundo. Se trata de uno de los mayores proyectos de investigación. La primera fase de funcionamiento comprende desde 2009 a 2020, cuando comenzará la siguiente fase. Durante el primer periodo se han pensado mejoras para que puedan ser implementadas en la segunda fase. Una de ellas es el aumento del ratio de las colisiones entre protones por choque. Este es el principal objetivo de uno de los proyectos que está llevando a cabo las mejoras a ser implementadas en 2020: Hi- Lumi LHC. Se cambiarán los imanes superconductores de NbTi de las dos zonas principales de interacción, y se sustituirán por imanes de Nb3Sn. Esta sustituciónn conlleva un profundo estudio previo. Entre otros, uno de los factores a analizar es la calidad del campo magnético. La herramienta utilizada es el software desarrollado por S. Russenschuck en el CERN llamado ROXIE. Está basado en tres modelos de magnetización, los cuales son precisos para campos mayores de 1.5 T. Sin embargo, no lo son tanto para campos menores. Con este proyecto se pretende evaluar la implementación de un cuarto modelo, el modelo clásico de histéresis de Preisach que permita llevar a cabo un mejor análisis de la calidad del campo inducido por el futuro material a utilizar en algunos de los imanes

Computation of Nonlinear Wave Loads on Floating Structures

Floating wind turbines (FWTs) are proposed as a method to harness the significant wind energy resource in deep water. International research efforts have led to the development of coupled numerical global analysis tools for FWTs in order to understand their behavior under wind and wave actions. The hydrodynamic models in such tools are typically based on first-(and second-)order potential flow theory, sometimes also including Morison s equation. In order to accurately model highly nonlinear waves, their interaction with a floating platform, and obtain estimates of the resulting loads on the structure, a numerical wave tank approach is generally needed. In this thesis, the response of floating structures to nonlinear wave loading is investigated by means of two different numerical approaches: a fully nonlinear Navier-Stokes/VOF solver and a second-order potential flow theory solver. Firstly, the fully nonlinear Navier-Stokes/VOF numerical wave tank, developed within the open-source CFD toolbox OpenFOAMframework (version 1606+), is validated against experimental data for two cases. These comprise the response of a 2D floating box and a 3D floating vertical cylinder. In order to model the motions of the floating structures, together with the generation and absorption of the waves, the interDyMFoam solver, provided by the OpenFOAMlibrary, is extended with the waves2Foam package, developed by Jacobsen at al. (2012). Furthermore, a simple catenary mooring line is implemented for the moored cases. Secondly, a potential flow theory based model of the OC5-semisubmersible floating platform is generated. The frequency-domain analysis is done with the Wadam software and the time-domain simulations with SIMO. This model is validated against measurement data from a 1:50 scale test campaign performed at the MARIN offshore wave basin and the fully nonlinear validated CFD model. Lastly, both numerical models of the OC5-semisubmersible are compared in order to assess the suitability of the diffraction model in two different conditions where nonlinearities are of relevance. The first one involves very long waves, with periods close to 20s, which are likely to take place under swell wave conditions. These may excite the OC5-semisubmersible platform in heave at its natural frequency. The second situation deals with regular waves with increasing steepness. In principle, the fully nonlinear CFD model, if no experimental data is available, is needed to calibrate the diffraction model. However, once the latter is adjusted and validated, results are given at a much lower computational cost. According to the computations throughout this work, when dealing with waves with high steepness and high excitation frequencies, the motions, as well as the peak forces, are properly captured by the diffraction model. However, other local effects of importance for offshore structures, such as wave run-up, or the different components in frequency of the loading, require the use of a fully nonlinear CFD solver. Therefore for preliminary design stages a diffraction model is able to give suitable results regarding the motions and peak inline and vertical forces at a much lower computational cost; however, for detailed design, or optimisation phase stages, where local effects are of relevance, a fully nonlinear CFD model is required

Computation of Nonlinear Wave Loads on Floating Structures

Floating wind turbines (FWTs) are proposed as a method to harness the significant wind energy resource in deep water. International research efforts have led to the development of coupled numerical global analysis tools for FWTs in order to understand their behavior under wind and wave actions. The hydrodynamic models in such tools are typically based on first-(and second-)order potential flow theory, sometimes also including Morison’s equation. In order to accurately model highly nonlinear waves, their interaction with a floating platform, and obtain estimates of the resulting loads on the structure, a numerical wave tank approach is generally needed.In this thesis, the response of floating structures to nonlinear wave loading is investigated by means of two different numerical approaches: a fully nonlinear Navier-Stokes/VOF solver and a second-order potential flow theory solver. Firstly, the fully nonlinear Navier-Stokes/VOF numerical wave tank, developed within the open-source CFD toolbox OpenFOAM, is validated against experimental data for two cases. These comprise the response of a 2D floating box and a 3D floating vertical cylinder. In order to model the motions of the floating structures, together with the generation and absorption of the waves, the interDyMFoam solver, provided by the OpenFOAM library, is extended with the waves2Foam package, developed by Jacobsen et al. (2012). Furthermore, a simple catenary mooring line is implemented for the moored cases. Secondly, a potential flow theory based model of the OC5-semisubmersible floating platform is generated. The frequency-domain analysis is done with the Wadam software and the time-domain simulations with SIMO. This model is validated against measurement data from a 1:50 scale test campaign performed at the MARIN offshore wave basin and the fully nonlinear validated CFD model. Lastly, both numerical models of the OC5-semisubmersible are compared in order to assess the suitability of the diffraction model in two different conditions where nonlinearities are of relevance. The first one involves very long waves, with periods close to 20s, which are likely to take place under swell wave conditions. These may excite the OC5-semisubmersible platform in heave at its natural frequency. The second situation deals with regular waves with increasing steepness.In principle, the fully nonlinear CFD model, if no experimental data is available, is needed to calibrate the diffraction model. However, once the latter is adjusted and validated, results are given at a much lower computational cost. According to the computations throughout this work, when dealing with waves with high steepness and high excitation frequencies, the motions, as well as the peak forces, are properly captured by the diffraction model. However, other local effects of importance for offshore structures, such as wave run-up, or the different components in frequency of the loading, require the use of a fully nonlinear CFD solver. Therefore for preliminary design stages a diffraction model is able to give suitable results regarding the motions and peak inline and vertical forces at a much lower computational cost; however, for detailed design, or optimisation phase stages, where local effects are of relevance, a fully nonlinear CFD model is required.European Wind Energy Masters (EWEM

Morphological tuning of plasmonic silver nanostars by controlling the nanoparticle growth mechanism: Application in the SERS detection of the amyloid marker Congo Red

12 pags., 8 figs., 2 tabs., app.Silver nanostars (AgNS) have promising applications in spectroscopic, theranostic and sensing applications. In this work we have tuned the morphology of AgNS by the modification of the experimental fabrication conditions. Silver nanostars were fabricated by following a two-step process that involves the use of two different chemical reducers: neutral hydroxylamine (HA), employed as primary chemical reducer, and citrate (CIT), in a second reduction step. The key experimental parameters which were modified in this work were the [HA]/[Ag] ratio (R), the [HA]/[CIT] ratio (R) and the time between reductions or elapsed time (T), which also determines a factor of the highest importance: the ratio between the Ag concentrations existing at the beginning of each reduction process (R). The growth mechanisms followed by Ag nanostars to reach their final size and shape determined different growth pathways which were identified in this work as well, as deduced by the analysis derived from the transmission electron micoroscopic (TEM) images and the extinction spectra from the resulting plasmons. The SERS effectiveness of the resulting substrates was analyzed by using thiophenol (TP) as molecular probe, and a correlation between morphology and SERS intensification factor was deduced. The experimental parameters leading to the highest SERS enhancement were identified. Finally, these Ag nanostars were probed in the sensitive detection of Congo Red, an amyloid marker dye usually employed in the detection of amyloid fibrils related to Alzheimer diseases.Ministerio de Economía y Competitividad (MINECO, grant FIS2014-52212-R).Peer Reviewe

Experimental study of spray from wave impact

Overtopping plumes from wave impact is relevant to coastal defence for overtopping analysis of sea walls, levees, and gates. Improved insight into this phenomenon will further enhance the prediction of wave overtopping and its induced hazard, e.g., erosion, saltwater ingress, and a hindrance to traffic. A series of small-scale experiments have been carried out in the WaterLab at TU Delft to characterize the droplets formed by wave impacts. Focused waves were generated by the piston-type wavemaker to control the wave breaking point on the wall, which allowed the creation of different types of wave impact. Impacts were investigated respectively: non-breaking, flip-through, and air pocket. After the wave impact, all the stages of the plume formation were filmed using a high-speed camera at a frame rate of 500fps. In this study, the spray sheet breakup and droplet formation are investigated. A simple approach to estimate the maximum spray height is proposed, which can be used for the splash type overtopping in the future.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Hydraulic Structures and Flood Ris

Low-frequency dynamic wake meandering: comparison of FAST.Farm and DIWA software tools

Most of the global dynamic response models used today for the design of wind turbines are based on the aero-hydro-servo-elastic analysis of one single turbine. However, research on bottom- fixed offshore wind turbines has shown that interactions among turbines in a farm influence both the power production and the structural loading. Furthermore, floating wind turbines (FWTs) are sensitive to low-frequency variations, and therefore to wake meandering perturbations. In the current work, we use the Dynamic Wake Meandering (DWM) model as implemented in DIWA and FAST.Farm, to study the low-frequency content of the meandering at a target turbine placed 8 diameters downstream. At frequencies in the range of the natural frequencies of rigid body motions of semisubmersible floaters, the two models yield different results. These differences are seen for every wind speed and wind turbine model, even though they decrease as the wind speed increases. The observed differences may affect low-frequency motions and consequently mooring system design

Low-frequency dynamic wake meandering: comparison of FAST.Farm and DIWA software tools

Most of the global dynamic response models used today for the design of wind turbines are based on the aero-hydro-servo-elastic analysis of one single turbine. However, research on bottom- fixed offshore wind turbines has shown that interactions among turbines in a farm influence both the power production and the structural loading. Furthermore, floating wind turbines (FWTs) are sensitive to low-frequency variations, and therefore to wake meandering perturbations. In the current work, we use the Dynamic Wake Meandering (DWM) model as implemented in DIWA and FAST.Farm, to study the low-frequency content of the meandering at a target turbine placed 8 diameters downstream. At frequencies in the range of the natural frequencies of rigid body motions of semisubmersible floaters, the two models yield different results. These differences are seen for every wind speed and wind turbine model, even though they decrease as the wind speed increases. The observed differences may affect low-frequency motions and consequently mooring system design

Validation of the dynamic wake meandering model against large eddy simulation for horizontal and vertical steering of wind turbine wakes

This work focuses on the validation of the dynamic wake meandering (DWM) model against large eddy simulation (LES). The wake deficit, mean deflection, and meandering under different wind turbine misalignment angles in yaw and tilt, for the IEA 15MW wind turbine, for two turbulent inflows with different shear and turbulence intensities are compared. Simulation results indicate that the DWM model as implemented in FAST.Farm shows very good agreement with the LES (VFS-Wind) data when predicting the time-averaged horizontal and vertical wake, especially at x > 6D and for cases with positive tilt angles (> 6deg). The wake dynamics captured by the DWM model include the large-eddy-induced wake meandering at low Strouhal number (St < 0.1). Additionally, the wake oscillation induced by the shear layer at St approx. 0.27 is captured only by LES. The mean and standard deviation of the wake deflection, as computed by the DWM, are sensitive to the size of the polar grid used to calculate the spatial-averaged velocity with which the wake planes meander. The power output of a turbine in the wake of a wind turbine in free-wind deflected by a yaw angle gamma = 30deg is almost doubled compared to the fully-waked condition

Low-frequency dynamic wake meandering: comparison of FAST.Farm and DIWA software tools

Most of the global dynamic response models used today for the design of wind turbines are based on the aero-hydro-servo-elastic analysis of one single turbine. However, research on bottom- fixed offshore wind turbines has shown that interactions among turbines in a farm influence both the power production and the structural loading. Furthermore, floating wind turbines (FWTs) are sensitive to low-frequency variations, and therefore to wake meandering perturbations. In the current work, we use the Dynamic Wake Meandering (DWM) model as implemented in DIWA and FAST.Farm, to study the low-frequency content of the meandering at a target turbine placed 8 diameters downstream. At frequencies in the range of the natural frequencies of rigid body motions of semisubmersible floaters, the two models yield different results. These differences are seen for every wind speed and wind turbine model, even though they decrease as the wind speed increases. The observed differences may affect low-frequency motions and consequently mooring system design.publishedVersio