Hamiltonian formalism of the DNLS equation with nonvanished boundary value

Hamiltonian formalism of the DNLS equation with nonvanishing boundary value is developed by the standard procedure.Comment: 11 page

Three-dimensional micro-siting of a windfarm - A CFD based analysis : A potential wind farm site in Norway, Kylland, has been analysed. An innovative 3D approach for micro-siting the wind turbines is applied together with CFD methods by using the wind farm design tool WindSim

Master's thesis in Renewable energy (ENE500

High Order Solutions and Generalized Darboux Transformations of Derivative Schr\"odinger Equation

By means of certain limit technique, two kinds of generalized Darboux transformations are constructed for the derivative nonlinear Sch\"odinger equation (DNLS). These transformations are shown to lead to two solution formulas for DNLS in terms of determinants. As applications, several different types of high order solutions are calculated for this equation.Comment: 26 pages,5 figure

Evaluation of Hybrid Battery System for Platform Support Vessels

Master's thesis in Offshore structural engineeringIn the last few years, the car industry has developed hybrid battery systems with lower battery price, higher capacity and improved safety. These improvements in performance have led to an increased interest to utilize the technology in marine applications. To satisfy the requirements of redundancy in critical situations vessels are required to run multiple engines at low to medium loads during most of operations in station keeping. Traditional combustion engines are designed to have the optimal level of fuel consumption and lowest emission per kilowatt hour when operating at medium to high loads. This practice therefore represents an overall loss and is unfavorable for environment and fuel consumption. This thesis investigates the effect and viability of applying a Hybrid Battery System (HBS) on a Platform Support Vessel (PSV) by using the battery to optimize the original power system. For the case study, the vessel Viking Energy has been considered. Viking Energy is the first vessel with a HBS approved as a redundant power source in critical operations. The system allows the vessel to reduce the numbers of active engines while ensuring instant available power if required. The remaining active engines are then operating closer to the optimal level, ensuring lower emission and fuel consumption per kilowatt hour. This study analyzes and quantifies the effect in fuel consumption and cost after implementing the HBS to the PSV. It also analyzes the weathers influence of the fuel consumption for the vessel with and without HBS. The study is based on a six-month sample period where the HBS was fully operative. The analysis gave an annual reduction in fuel of 13% comparing the sampling period with historical data given the same time distribution for the vessel. Normalizing both to actual distribution over a three-year operation period gives a calculated reduction of 17% due to more favorable distribution. The difference is mainly due to higher portion of Dynamic Positioning (DP) mode in the historical data. The economical evaluation concluded that the minimum threshold for overall fuel reduction to be 15% for the investment to break even in a ten-year perspective. A vessel is recommended to operate 34% or more of the time in DP or a mode providing similar level of fuel saving to meet an overall reduction of 15%

«They'll just go to Moody's» : Investigating Corporate Credit Rating Updates Using Machine Learning Techniques

Credit Rating Agencies («CRAs») play an important role in the global debt market. They influence the credit spread and thus the borrowing costs for major corporations. An inherent problem is the conflict of interest that arise when the CRAs are paid by issuers. This is not a recent concern, and numerous studies have looked into this and other issues with CRAs. In this master's thesis, we extend this area of research by applying machine learning («ML») models for predicting credit rating updates. For this task, we construct a prediction model using financial ratios, for which we have 20 years of data for two major agencies; Moody's and Fitch. We also include ratings for an investor-paid agency: Egan-Jones. In the model, we change the soft factor in the CRAs' assessment with a new factor that both theoretically and, as will be shown, empirically explain rating updates; trailing stock returns. We apply the XCBoost algorithm to provide more accurate predictions of credit rating updates. Moreover, we analyse SHAP values to interpret different features' contributions to the predictions of rating updates. We evaluate our approach on a dataset of credit ratings in the US and EU and obtain an accuracy of 84.25%. We find that the total return 12 months before the update is the most important when predicting, which suggests stale credit rating updates. Most excitingly, we find that for CRAs with an investor-paid model, the total return three months before the update is the most important when predicting. For the issuer-paid revenue model, twelve months' total stock return turned out to be important: This suggests that investor-paid revenue models are more proactive in updating credit ratings than issuer-paid agencies. The model is applied to the rating downgrade of Wirecard in 2020, which allows for an interesting interpretation of local SHAP values. We also discuss the potential limitations of using ML in credit rating predictions, such as loss of interpretability, unreliable accounting data and the sensitivity of SHAP values.nhhma

Parametric instabilities in magnetized multicomponent plasmas

This paper investigates the excitation of various natural modes in a magnetized bi-ion or dusty plasma. The excitation is provided by parametrically pumping the magnetic field. Here two ion-like species are allowed to be fully mobile. This generalizes our previous work where the second heavy species was taken to be stationary. Their collection of charge from the background neutral plasma modifies the dispersion properties of the pump and excited waves. The introduction of an extra mobile species adds extra modes to both these types of waves. We firstly investigate the pump wave in detail, in the case where the background magnetic field is perpendicular to the direction of propagation of the pump wave. Then we derive the dispersion equation relating the pump to the excited wave for modes propagating parallel to the background magnetic field. It is found that there are a total of twelve resonant interactions allowed, whose various growth rates are calculated and discussed.Comment: Published in May 2004; this is a late submission to the archive. 14 pages, 8 figure

Zakharov simulation study of spectral features of on-demand Langmuir turbulence in an inhomogeneous plasma

We have performed a simulation study of Langmuir turbulence in the Earth's ionosphere by means of a Zakharov model with parameters relevant for the F layer. The model includes dissipative terms to model collisions and Landau damping of the electrons and ions, and a linear density profile, which models the ionospheric plasma inhomogeneity whose length scale is of the order 10--100 km. The injection of energy into the system is modeled by a constant source term in the Zakharov equation. Langmuir turbulence is excited ``on-demand'' in controlled ionospheric modification experiments where the energy is provided by an HF radio beam injected into the overhead ionospheric plasma. The ensuing turbulence can be studied with radars and in the form of secondary radiation recorded by ground-based receivers. We have analyzed spectral signatures of the turbulence for different sets of parameters and different altitudes relative to the turning point of the linear Langmuir mode where the Langmuir frequency equals the local plasma frequency. By a parametric analysis, we have derived a simple scaling law, which links the spectral width of the turbulent frequency spectrum to the physical parameters in the ionosphere. The scaling law provides a quantitative relation between the physical parameters (temperatures, electron number density, ionospheric length scale, etc.) and the observed frequency spectrum. This law may be useful for interpreting experimental results.Comment: 7 pages, 8 figure

HF wave propagation and induced ionospheric turbulence in the magnetic equatorial region

The propagation and excitation of Artificial Ionospheric Turbulence (AIT) in the magnetic equatorial region by high frequency (HF) electromagnetic (EM) waves injected into the overhead ionospheric layer is examined. EM waves with ordinary (O) mode polarization reach the critical layer only if their incidence angle is within the Spitze cone. Near the critical layer the wave electric field is linearly polarized and directed parallel to the magnetic field lines. For large enough amplitudes, the O mode becomes unstable to the 4-wave oscillating two-stream instability (OTSI) and the 3-wave parametric decay instability (PDI) driving large amplitude Langmuir and ion acoustic waves. The interaction between the induced Langmuir turbulence and electrons located within the 50-100 km wide transmitter heating cone at an altitude of 230 km can potentially accelerate the electrons along the magnetic field to several tens to a few hundreds of eV, far beyond the thresholds for optical emissions and ionization of the neutral gas. It could furthermore result in generation of shear Alfvén waves such as have been recently observed in laboratory experiments at the UCLA Large Plasma Device (LAPD)

Invariant imbedding theory of mode conversion in inhomogeneous plasmas. II. Mode conversion in cold, magnetized plasmas with perpendicular inhomogeneity

A new version of the invariant imbedding theory for the propagation of coupled waves in inhomogeneous media is applied to the mode conversion of high frequency electromagnetic waves into electrostatic modes in cold, magnetized and stratified plasmas. The cases where the external magnetic field is applied perpendicularly to the direction of inhomogeneity and the electron density profile is linear are considered. Extensive and numerically exact results for the mode conversion coefficients, the reflectances and the wave electric and magnetic field profiles inside the inhomogeneous plasma are obtained. The dependences of mode conversion phenomena on the magnitude of the external magnetic field, the incident angle and the wave frequency are explored in detail.Comment: 11 figures, to be published in Physics of Plasma

Geometric aspects of HF driven Langmuir turbulence in the ionosphere

International audienceThe geometric aspects of HF-generated Langmuir turbulence in the ionosphere and its detection by radars are theoretically discussed in a broad approach, including local modelling (damped and driven Zakharov system), basic parametric instabilities, polarization and strength of the driving electric field, and radar configurations. Selected examples of numerical results from the local model are presented and discussed in relation to recent experiments, with emphasis on recent experiments at the EISCAT facilities. Anisotropic aspects of the cavitation process in the magnetized plasma are exhibited. Basic processes of cascades and cavitation are by now well identified in these experiments, but a few problems of the detailed agreement between theory and experiments are pointed out