Modelling of radio wave propagation using Finite Element Analysis.

Fourth generation (4G) wireless communication systems are intended to support high data rates which requires careful and accurate modelling of the radio environment. In this thesis, for the first time finite clement based accurate and computationally efficient models of wave propagation in different outdoor and indoor environments has been developed. Three different environments were considered: the troposphere, vegetation and tunnels and wave propagation in these environments were modelled using finite element analysis. Use of finite elements in wave propagation modelling is a novel idea although many propagation models and approaches were used in past. Coverage diagrams, path loss contours and power levels were calculated using developed models in the troposphere, vegetation and tunnels. Results obtained were compared with commercially available software Advanced Refractive Effects Prediction Software (AREPS) to validate the accuracy of the developed approach and it is shown that results were accurate with an accuracy of 3dB. The developed models were very flexible in handling complex geometries and similar analysis can be easily extended to other environments. A fully vectored finite element base propagation model was developed for straight and curved tunnels. An optimum range of values of different electrical parameters for tunnels of different shapes has been derived. The thesis delivered a novel approach to modelling radio channels that provided a fast and accurate solution of radio wave propagation in realistic environments. The results of this thesis will have a great impact in modelling and characterisation of future wireless communication systems

Multiwavelength studies of MHD waves in the solar chromosphere: An overview of recent results

The chromosphere is a thin layer of the solar atmosphere that bridges the relatively cool photosphere and the intensely heated transition region and corona. Compressible and incompressible waves propagating through the chromosphere can supply significant amounts of energy to the interface region and corona. In recent years an abundance of high-resolution observations from state-of-the-art facilities have provided new and exciting ways of disentangling the characteristics of oscillatory phenomena propagating through the dynamic chromosphere. Coupled with rapid advancements in magnetohydrodynamic wave theory, we are now in an ideal position to thoroughly investigate the role waves play in supplying energy to sustain chromospheric and coronal heating. Here, we review the recent progress made in characterising, categorising and interpreting oscillations manifesting in the solar chromosphere, with an impetus placed on their intrinsic energetics.Comment: 48 pages, 25 figures, accepted into Space Science Review

Modeling EMI Resulting from a Signal Via Transition Through Power/Ground Layers

Signal transitioning through layers on vias are very common in multi-layer printed circuit board (PCB) design. For a signal via transitioning through the internal power and ground planes, the return current must switch from one reference plane to another reference plane. The discontinuity of the return current at the via excites the power and ground planes, and results in noise on the power bus that can lead to signal integrity, as well as EMI problems. Numerical methods, such as the finite-difference time-domain (FDTD), Moment of Methods (MoM), and partial element equivalent circuit (PEEC) method, were employed herein to study this problem. The modeled results are supported by measurements. In addition, a common EMI mitigation approach of adding a decoupling capacitor was investigated with the FDTD method

Investigations of Environmental Effects on Freeway Acoustics

abstract: The role of environmental factors that influence atmospheric propagation of sound originating from freeway noise sources is studied with a combination of field experiments and numerical simulations. Acoustic propagation models are developed and adapted for refractive index depending upon meteorological conditions. A high-resolution multi-nested environmental forecasting model forced by coarse global analysis is applied to predict real meteorological profiles at fine scales. These profiles are then used as input for the acoustic models. Numerical methods for producing higher resolution acoustic refractive index fields are proposed. These include spatial and temporal nested meteorological simulations with vertical grid refinement. It is shown that vertical nesting can improve the prediction of finer structures in near-ground temperature and velocity profiles, such as morning temperature inversions and low level jet-like features. Accurate representation of these features is shown to be important for modeling sound refraction phenomena and for enabling accurate noise assessment. Comparisons are made using the acoustic model for predictions with profiles derived from meteorological simulations and from field experiment observations in Phoenix, Arizona. The challenges faced in simulating accurate meteorological profiles at high resolution for sound propagation applications are highlighted and areas for possible improvement are discussed. A detailed evaluation of the environmental forecast is conducted by investigating the Surface Energy Balance (SEB) obtained from observations made with an eddy-covariance flux tower compared with SEB from simulations using several physical parameterizations of urban effects and planetary boundary layer schemes. Diurnal variation in SEB constituent fluxes are examined in relation to surface layer stability and modeled diagnostic variables. Improvement is found when adapting parameterizations for Phoenix with reduced errors in the SEB components. Finer model resolution (to 333 m) is seen to have insignificant ($<1\sigma$) influence on mean absolute percent difference of 30-minute diurnal mean SEB terms. A new method of representing inhomogeneous urban development density derived from observations of impervious surfaces with sub-grid scale resolution is then proposed for mesoscale applications. This method was implemented and evaluated within the environmental modeling framework. Finally, a new semi-implicit scheme based on Leapfrog and a fourth-order implicit time-filter is developed.Dissertation/ThesisDoctoral Dissertation Mechanical Engineering 201

Einfluss der Makro-Rauheit auf die Tsunami-Ausbreitung und Überschwemmung an Land: Eine numerische Modellstudie

In tsunami hazard assessment, the vulnerable area is determined using numerical models, which calculate the tsunami propagation and the inundation extent. Large-scale depth-averaged models, e.g. based on non-linear shallow water (NLSW) equations, are commonly applied. In such models, a selected Manning’s coefficient is generally applied to account for the effect of the bottom surface roughness. However, macro-roughness elements (MRE) such as buildings and tree vegetation generally form also part of coastal areas. Using purely empirical Manning’s coefficients to account for such large objects is not physically sound and might result in large uncertainties. To date, there is not generally applicable NLSW model available for adequately considering MRE-induced energy losses during tsunami inundation. This Ph.D. thesis attempts to contribute to a better understanding of the effects of relevant MRE parameters such as shape, size, and arrangement of the MREs on tsunami bore propagation and inundation. In phase 1 of this study, a three-dimensional Reynolds-averaged Navier-Stokes (RANS) model is systematically validated. In phase 2, the RANS model is used in a parameter study to create a database for flow parameters associated to MRE configurations, varying shape, size, height, arrangement, and density of MRE. In phase 3, the most relevant MRE parameters and flow regimes are determined and are carefully formulated so that they are easily obtainable for tsunami modelling. The energy losses are formulated by considering inertia and drag losses in analogy to the Morison equation. In phase 4, the MRE formula is implemented in the NLSW model COMCOT. Finally, the performance of the MRE formula is evaluated by comparing the results with well-documented physical experiments (Park et al., 2013) and with commonly used “equivalent roughness” approaches. The following findings are obtained: (i) In a group of MRE, an upstream zone and an inner zone can be distinguished; (ii) The shape, arrangement angle, relative spacing (ratio between blocked and total cross-section) and relative height (ratio between height of submerged part of MRE and flow depth) are the most relevant parameters; (iii) The MRE model leads to improved results compared to commonly used equivalent roughness models; (iv) The MRE model does not require calibration.In der Tsunami-Gefahrenbewertung wird das gefährdete Gebiet mit Hilfe von numerischen Modellen bestimmt, die u.A. die Überflutungsfläche berechnen. Meist werden großskalige, tiefengemittelte Modelle verwendet, die z.B. auf der nicht-linearen Flachwassergleichung (NLSW) basieren. In diesen Modellen wird meist ein Manning-Beiwert angewandt, um die Bodenrauheit zu berücksichtigen. Jedoch bestehen küstennahe Gebiete in der Regel auch aus sogenannten Makro-Rauheitselementen (MRE) wie Gebäuden und Vegetation. Allein rein empirische Manning-Beiwerte für die Berücksichtigung so großer Hindernisse zu verwenden ist physikalisch nicht korrekt und hat große Modell-Unsicherheiten zur Folge. Derzeit liegt kein NLSW-Modell vor, das MRE-induzierte Energieverluste bei Tsunami-Überflutungen adäquat berücksichtigt. In dieser Doktor-Arbeit wurde versucht zu einem besseren Verständnis relevanter MRE-Parameter, wie z.B. Form, Größe und Anordnung, auf die Tsunami-Ausbreitung und -Überflutung beizutragen. In Phase 1 wurde ein drei-dimensionales Reynolds-gemitteltes Navier-Stokes- (RANS)-Modell systematisch validiert. In Phase 2 wurde das RANS-Modell in einer Parameterstudie angewandt und eine Datenbasis für Fließparameter in Relation zu MRE-Konfigurationen erstellt, die in Form, Größe, Höhe, Anordnung und Dichte der MRE variierten. In Phase 3 wurden die maßgebenden MRE-Parameter ermittelt. Die Parameter wurden sorgfältig gebildet, so dass sie für die Tsunami-Modellierung leicht zu bestimmen bzw. verfügbar sind. Die Energieverluste werden in Analogie zur Morison-Gleichung als Trägheits- und Widerstandsverluste formuliert. In Phase 4 wird die MRE-Formel in das NLSW-Modell COMCOT implementiert. Schließlich wird die Leistungsfähigkeit der MRE-Formel durch den Vergleich der Ergebnisse mit gut dokumentieren Laborexperimenten (Park et al., 2013) und mit zwei der herkömmlichen „äquivalenten Rauheitsansätzen“ bewertet. Die folgenden Erkenntnisse wurden gewonnen: (i) In einer Gruppe von MRE muss zwischen einer Zufluss-seitigen Rand- und einer inneren Zone unterschieden werden. (ii) Die Parameter Form, Anordnungswinkel, relativer Zwischenraum (Verhältnis blockierter zu gesamter Querschnittsfläche) und der relativen Höhe (Verhältnis Höhe (des überfluteten Teils) der MRE zu Fließtiefe) sind maßgebend. (iii) Das MRE-Modell führt im Vergleich zum herkömmlich verwendeten äquivalenten Rauheitsansätzen zu verbesserten Ergebnissen. (iv) Das MRE-Modell benötigt keine Kalibrierung

Design Options For Low Cost, Low Power Microsatellite Based SAR.

This research aims at providing a system design that reduces the mass and cost of spaceborne Synthetic Aperture Radar (SAR) missions by a factor of two compared to current (TecSAR - 300 kg, ~ £ 127 M) or planned (NovaSAR-S — 400 kg, ~ £ 50 M) mission. This would enable the cost of a SAR constellation to approach that of the current optical constellation such as Disaster Monitoring Constellation (DMC). This research has identified that the mission cost can be reduced significantly by: focusing on a narrow range of applications (forestry and disasters monitoring); ensuring the final design has a compact stowage volume, which facilitates a shared launch; and building the payload around available platforms, rather than the platform around the payload. The central idea of the research has been to operate the SAR at a low instantaneous power level—a practical proposition for a micro-satellite based SAR. The use of a simple parabolic reflector with a single horn at L-band means that a single, reliable and efficient Solid State Power Amplifier (SSPA) can be used to lower the overall system cost, and to minimise the impact on the spacecraft power system. A detailed analysis of basic pulsed (~ 5 - 10 % duty cycle) and Continuous Wave (CW) SAR (100 % duty cycle) payloads has shown their inability to fit directly into existing microsatellite buses without involving major changes, or employing more than one platform. To circumvent the problems of pulsed and CW techniques, two approaches have been formulated. The first shows that a CW SAR can be implemented in a mono-static way with a single antenna on a single platform. In this technique, the SAR works in an Interrupted CW (ICW) mode, but these interruptions introduce periodic gaps in the raw data. On processing, these gapped data result in artefacts in the reconstructed images. By applying data based statistical estimation techniques to “fill in the gaps” in the simulated raw SAR data, this research has shown the possibility of minimising the effects of these artefacts. However, once the same techniques are applied to the real SAR data (in this case derived from RADARSAT-1), the artefacts are shown to be problematic. Because of this the ICW SAR design technique it is—set aside. The second shows that an extended chirp mode pulsed (ECMP) SAR (~ 20 - 54 % duty cycle) can be designed with a lowered peak power level which enables a single SSPA to feed a parabolic Cassegrain antenna. The detailed analysis shows the feasibility of developing a microsatellite based SAR design at a comparable price to those of optical missions

The 1999 Center for Simulation of Dynamic Response in Materials Annual Technical Report

Introduction: This annual report describes research accomplishments for FY 99 of the Center for Simulation of Dynamic Response of Materials. The Center is constructing a virtual shock physics facility in which the full three dimensional response of a variety of target materials can be computed for a wide range of compressive, ten- sional, and shear loadings, including those produced by detonation of energetic materials. The goals are to facilitate computation of a variety of experiments in which strong shock and detonation waves are made to impinge on targets consisting of various combinations of materials, compute the subsequent dy- namic response of the target materials, and validate these computations against experimental data