The knowledge about the behavior of cables is substantial in cases of transients or in cases of faults. However, there are only a few models that are tailored to the current requirements for calculations of transient phenomena in three-phase cable systems. These models are based on complex structures. PI-section cable models with simple structures were previously qualified only for calculations in the frequency domain. A new full frequency-dependent cable model to simulate transient phenomena is introduced and validated. The model is based on lumped parameters with cascaded frequency-dependent PI-sections. For the implementation and the integration in simulation tools, it is important to investigate the impact of the PI-section parameters to the accuracy, the stability and the mathematical robustness. In this work, the impact of the frequency dependence of cable parameters, the length distribution and the number of PI-sections on the results of the developed three-phase cable model have been discussed. For simulations in the time domain, two algorithms have been presented to optimize the number of PI-sections based on a specified accuracy.

風力発電システムは、現在世界中で普及しているが、その地上高と立地条件からしばしば落雷の被害を受け、稼働率の低下が問題視されている。本論文は、垂直導体である風力発電タワーにおける雷サージ解析の高精度化、高速化を目的とした垂直導体回路解析モデルの提案、およびその有用性のについて述べるとともに、風力発電所や洋上風車への拡張性についてまとめたものである。 / 博士(工学) / Doctor of Philosophy in Engineering / 同志社大学 / Doshisha University

The pharmaceutical process of dry granulation using roller-compaction (DG/RC) is effectively a non-batch based procedure orientated to deliver a continuous stream of material free of a pre-defined batch-size with reduced plant equipment/scale-up R&D resources and an enhanced work-throughput, particularly suitable for moisture sensitive formulation. The desirable accreditations of DG/RC are many; yet by the nature of a more flexible approach than (i.e. wet-granulation), it must be highly monitored and controlled to accomplish higher-throughput rates and reduced ‘static’ material testing stages. To monitor rapidly and in-line with production, pre-granulated ribbons of RC (which highly correlates to the post milled granulates), terahertz time-domain spectroscopy (TDS) is used to elucidate the key physical attributes of post-compression density and thickness uniformity, key to end-product consistency. Invariably a great number of conditions apply to DG/RC (viz: System design, material characteristics, environmental and unit configuration), although widely regarded as the key processing parameters (PP’s) are roll-pressure and roll-gap [1-4]. The target of the study is to derive a strategy to position TDS as PAT to DG/RC. Two terahertz time-domain TD methods of a conventional transmission setup and reflection (TPI) THz analysis are used on standards of glass slides for verifying the interpretational foundations of the TD methods. Achieving RI/thickness error-discrepancies +2.2 to -0.4% c.f. literature ([150]) values provides foundations to test the solid-fraction ratios of pharma tablets with regard to RI’s being surrogate values to SF/path-length (R2 = 1). Combining transmission principles to the portion of reflected EMR removes the pre-requisite for RI or path-length knowledge, giving +1.5 to +2.4% RI agreement (vs. frequency-domain attained results) thus enabling thickness estimations to be above 95% against physical micrometre judgement in all models. Augmentation of the TD methods, refined in Experimental chapter 2 ,then chiefly focuses on TPI as the principle THz-TD method (as the most ideal tool for PAT) for adopting the RI measures for ribbon uniformity analysis in Experimental chapter 4 in an off-line environment again resulting in RI and thicknesses < 5 % error of known parameters of thickness and further use of RI as a proxy porosity equivalent to gas pycnometry. Elucidated in the work are the limitations encountered with tablets and RC’s, data interpretation of industrial considerations. Experimental chapter 3 diverges from RI to differentiate thickness in-order to assess the FD transmission for non-destructive mechanical assessment. This demonstrates a clear relationship between compaction force and the surrogate value for density, following a linear trend below a certain threshold of force. The ‘threshold’ value is observed for less massive tablets, and concluded is that the mechanistic interplay and permanent (plastic) consolidation is greater in instances where compaction-force increases proportionally with target-fill weights, and thus the various behaviour of MCC to stress.

This thesis describes the generic modeling of a Doubly-Fed Induction Generator (DFIG) based wind turbine. The model can also represent a wind plant with a group of similar wind turbines lumped together. The model is represented as a controlled current source which injects the current needed by the grid to supply the demanded real and reactive power. The DFIG theory is explained in detail as is the rationale for representing it by a regulated current source. The complete model is then developed in the time-domain and phasor domain by the interconnection of various sub-systems, the functions of which have been described in detail. The performance of the model is then tested for steady-state and dynamic operation. The model developed can be used for bulk power system studies and transient stability analysis of the transmission system. This thesis uses as its basis a report written for NREL [1]. / text

Ground-Penetrating Radar (GPR) is a non-destructive electromagnetic investigative tool used in many applications across the fields of engineering and geophysics. The propagation of electromagnetic waves in lossy materials is complex and over the past 20 years, the computational modelling of GPR has developed to improve our understanding of this phenomenon. This research focuses on the development of accurate numerical models of widely-used, high-frequency commercial GPR antennas. High-frequency, highresolution GPR antennas are mainly used in civil engineering for the evaluation of structural features in concrete i. e., the location of rebars, conduits, voids and cracking. These types of target are typically located close to the surface and their responses can be coupled with the direct wave of the antenna. Most numerical simulations of GPR only include a simple excitation model, such as an infinitesimal dipole, which does not represent the actual antenna. By omitting the real antenna from the model, simulations cannot accurately replicate the amplitudes and waveshapes of real GPR responses. Numerical models of a 1.5 GHz Geophysical Survey Systems, Inc. (GSSI) antenna and a 1.2 GHz MALÅ GeoScience (MALÅ) antenna have been developed. The geometry of antennas is often complex with many fine features that must be captured in the numerical models. To visualise this level of detail in 3d, software was developed to link Paraview—an open source visualisation application which uses the Visualisation Toolkit (VTK)—with GprMax3D—electromagnetic simulation software based on the Finite-Difference Time-Domain (FDTD) method. Certain component values from the real antennas that were required for the models could not be readily determined due to commercial sensitivity. Values for these unknown parameters were found by implementing an optimisation technique known as Taguchi’s method. The metric used to initially assess the accuracy of the antenna models was a cross-corellation of the crosstalk responses from the models with the crosstalk responses measured from the real antennas. A 98 % match between modelled and real crosstalk responses was achieved. Further validation of the antenna models was undertaken using a series of laboratory experiments where oil-in-water (O/W) emulsions were created to simulate the electrical properties of real materials. The emulsions provided homogeneous liquids with controllable permittivity and conductivity and enabled different types of targets, typically encountered with GPR, to be tested. The laboratory setup was replicated in simulations which included the antenna models and an excellent agreement was shown between the measured and modelled data. The models reproduced both the amplitude and waveshape of the real responses whilst B-scans showed that the models were also accurately capturing effects, such as masking, present in the real data. It was shown that to achieve this accuracy, the real permittivity and conductivity profiles of materials must be correctly modelled. The validated antenna models were then used to investigate the radiation dynamics of GPR antennas. It was found that the shape and directivity of theoretically predicted far-field radiation patterns differ significantly from real antenna patterns. Being able to understand and visualise in 3d the antenna patterns of real GPR antennas, over realistic materials containing typical targets, is extremely important for antenna design and also from a practical user perspective.

Theoretical and experimental plasmonics is a growing field as a method to create near fields at sub-wavelength distances. In this thesis, a finite-difference time-domain method is used to simulate electromagnetic waves onto a thin film that present of nickel nanorods with sharp apexes. The absorbed, transmitted, and reflected fields were shown to depend linearly on silver film thickness and nanotip length. The electric field is visualized along the tip to show strong charge density along the base of the tip’s apex and how that density changes for wavelength, metal, and source tilt. Lastly, the study shows gold film on the nanotip apex provides the largest enhancement of the electric field for the wavelengths 532, 572, and 633 nm.

Photoconductive antenna (PCA) array based THz near-field imager incorporating Hadamard multiplexing method is developed in this work. By using a 2 × 2 dipole antenna array as the THz transmitter, the system signal-to-noise ratio (SNR) is demonstrated to be improved by a factor of 2 as the theory predicts. Additionally, a 2-D scanning of a metallic structure on a THz-transparent substrate (with a total scanning area of 1 × 1 mm2) is experimentally implemented. Correlation coefficient estimation is made afterwards to quantify the reconstructed image quality.

O método de Ibrahim no Domínio do Tempo (ITD) é considerado um dos métodos clássicos de identificação de parâmetros modais de estruturas. As maiores vantagens da sua aplicação residem na identificação de modos muito próximos com boa precisão, em uma faixa relativamente larga de freqüências, além do número reduzido de equipamentos requeridos para a realização de ensaios experimentais. Neste trabalho foi realizada uma aplicação do método ITD no processo de identificação das freqüências naturais, dos fatores de amortecimento e dos modos de vibrar de uma placa quadrada de alumínio, engastada em um dos lados e livre nos demais. Este modelo experimental apresenta alta densidade modal e a análise foi realizada em uma faixa de freqüências de 0 a 1600 Hz através de um ensaio de impacto. Para produzir um conjunto consistente de resultados é necessário utilizar um modelo sobredeterminado para o sistema em estudo. O resultado desta análise, porém, apresenta modos computacionais que devem ser eliminados. Para tanto, foram utilizados dois índices de confiança para qualificar os resultados, sendo estes o Fator de Confiança Modal (MCF) e a Colinearidade de Fase Modal Ponderada (MPCW). Os modos que apresentaram melhores índices de confiança são considerados o resultado final do processo de identificação. / The Ibrahim Time Domain (ITD) method is considered one of the classical modal parameter identification techniques. The greatest advantages of the ITD application consist of the precise identification of closely spaced modes within a wide range of frequencies and the small amount of equipment required to accomplish experimental testing. In this work, the ITD method was applied in the process of identification of natural frequencies, damping factors and mode shapes of a cantilever aluminium plate. High modal density was detected on the experimental model and the analysis was performed on a frequency range from 0 to 1600 Hz by means of impulse testing. However, an oversized model of the test structure must be used, so that a consistent set of results can be achieved. The results, nevertheless, present computational modes that must be removed from the model. Two confidence factors were used to qualify the results, namely the Modal Confidence Factor (MCF) and the Modal Phase Collinearity - Weighted (MPCW). The modes that presented higher confidence factor values were considered as the final result of the identification process.

Esta tese apresenta o desenvolvimento de um método de elementos de contorno (BEM) no domínio do tempo baseado em fontes de Rankine para analise linear de comportamento no mar de sistemas oceânicos. O método e formulado por dois problemas de valor inicial de contorno definidos para os potenciais de velocidade e aceleração, sendo este ultimo utilizado para calcular de maneira acurada a derivada temporal do potencial de velocidades. Testes de verificação são realizados para a solução dos problemas de difração, radiação e de corpo livre para flutuar. Uma vez verificada, a ferramenta e aplicada em dois problemas multicorpos considerados no estado-da-arte em termos de modelagem hidrodinâmica utilizando BEM. O primeiro trata do problema envolvendo duas embarcações atracadas a contrabordo. Este é um caso no qual os códigos baseados na teoria de escoamento potencial são conhecidos por apresentarem dificuldades na determinação das soluções, tendendo a superestimar as elevações de onda no vão entre as embarcações e a apresentar problemas de convergência numérica associados a efeitos ressonantes de onda. O problema e tratado por meio do método de damping lid e a convergência das series temporais e investigada avaliando diferentes níveis de amortecimento. Os resultados são comparados com dados experimentais. O segundo problema se refere a analise de sistemas multicorpos com grandes deslocamentos relativos. Neste problema, ferramentas no domínio da frequência nao podem ser utilizadas, por considerarem apenas malhas fixas. Deste modo, o presente método e estendido para considerar um gerador de malhas de paineis e um algoritmo de interpolação de ordem alta no laco de tempo do código, possibilitando a mudança de posições relativas entre os corpos durante a simulação. Os resultados são comparados com dados de experimentos executados especificamente para fins de verificação do código, apresentando uma boa concordância. De acordo com o conhecimento do autor, esta e a primeira vez que certas questões relativas a modelagem numérica destes dois problemas multicorpos são relatadas na literatura especializada em hidrodinâmica computacional. / The development of a time domain boundary elements method (BEM) based on Rankine\'s sources for linear seakeeping analysis of offshore systems is here addressed. The method is formulated by means of two Initial Boundary Value Problems defined for the velocity and acceleration potentials, the latter being used to ensure an accurate calculation of the time derivatives of the velocity potential. Verification tests for solving the difraction, radiation and free floating problems are presented. Once verified, the code is applied for two complex multi-body problems considered to be in the state-of-the-art for hydrodynamic modelling using BEM. The first is the seakeeping problem of two ships arranged in side-by-side, a problem in which all potential flow codes are known to have a poor performance, tending to provide unrealistic high wave elevations in the gap between the vessels and to present numerical convergence problems associated to resonant effects. The problem is here addressed by means of a damping lid method and the convergence of the time series with different damping levels is investigated. Results are compared to data measured in an experimental campaign. The second problem refers to the analysis of multi-body systems composed of bodies undergoing large relative displacements. This is a case that cannot be properly analyzed by frequency domain codes, since they only consider fixed meshes. For this application, the present numerical method is extended to consider a panel mesh generator in the time loop of the code, enabling the change of body relative positions during the computations. Furthermore, a higher order interpolation algorithm designed to recover the solutions of a previous time-step was also implemented, enabling the calculations to progress with reasonable accuracy in time. The numerical results are compared to data of experimental tests designed and executed for verification of the code, and presented a very good agreement. To the author\'s knowledge, this is the first time that certain issues concerning the numerical modelling of these two complex multi-body problems are reported in the literature specialized in hydrodynamic computations.

The Finite Difference Time Domain (FDTD) Method has been a powerful tool in numerical simulation of electromagnetic (EM) problems for decades. In recent years, it has also been applied to biomedical research to investigate the interaction between EM waves and biological tissues. In Wireless Body Area Networks (WBANs) studies, to better understand the localization problem within the body, an accurate source/receiver model must be investigated. However, the traditional source models in FDTD involve effective volume and may cause error in near field arbitrary direction. This thesis reviews the basic mathematical and numerical foundation of the Finite Difference Time Domain method and the material properties needed when modeling a human body in FDTD. Then Coincident Phase Centers (CPCs) point sources models have been introduced which provide nearly the same accuracy at the distances as small as 3 unit cells from the phase center. Simultaneously, this model outperforms the usual sources in the near field when an arbitrary direction of the electric or magnetic dipole moment is required.