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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
101

Computational modelling of combined storm surge and wave overtopping of embankments

Jones, David K. January 2012 (has links)
The primary function of seawalls and embankments is to protect against damage and injury caused by flooding. Coastal flooding is caused by combinations of high tides, waves, wind set-up and storm surges driven by low-pressure systems. However with global warming causing sea levels to rise and with increased storminess causing more extreme waves and storm surges, the likelihood of overtopping of seawalls with zero or negative freeboard may well be expected to increase. Researchers using physical and numerical models to develop design formulae have widely investigated wave overtopping of seawalls with positive freeboard. However the design of seawalls with zero or negative freeboard has attracted much less attention, and some variation exists between overtopping discharge calculated with current design formulae. The focus of this thesis is the extreme situation when overtopping caused by storm waves is combined with surge levels above the embankment crest. The local highly accelerative flow over the embankment crest caused by the high surge level will significantly alter the flow at the crest. This is likely to have a highly non-linear effect upon the overtopping waves. In this thesis, the flow is investigated with a 2DV numerical model based on the Reynolds averaged Navier-Stokes (RANS) equations developed by Lin and Liu (1998a). The model describes the flow characteristics of a breaking wave such as the velocities within the wave as well as the turbulence at the seabed boundary layer. As an example of the model’s ability to describe complex hydrodynamic flows, this study investigates its ability to represent the second order mass transport under progressive and standing waves. The model results are compared with available theory and experimental results. This shows that mass transport is successfully predicted, although there is some variation in the magnitude compared to the experimental and theoretical results. To consider the model’s ability to simulate storm surge wave overtopping of embankments, the RANS model has been used to simulate an experimental study conducted by Hughes and Nadal (2009). To examine the success of the model at reproducing the wave generation, transformation and overtopping processes the model results have been compared with the experimental laboratory data. This makes possible a wave-by-wave comparison of overtopping parameters such as discharge, depth and velocity for a storm surge event. Additionally the overtopping discharge predicted by the model is compared with design formulae and the differences in the overtopping discharge calculated with current design formulae are investigated and explained. Finally, the RANS model is used to determine the effect of embankment crest width on the magnitude of the overtopping discharge. Results from RANS model tests are used to provide design guidance in the form of an equation that allows the effect of crest width to be included when evaluating combined discharge at embankments.
102

Mudflow Modeling in the Copiapo Basin, Chile

Valdes-Pineda, Rodrigo, Valdes, Juan B., Garcia-Chevesich, Pablo 28 April 2017 (has links)
Extreme precipitation events that occurred between March 24 and March 26 of 2015 in the region of the Atacama Desert (26-29 degrees S) left around 30000 victims, being one of the biggest events over the past 50 years, with total a cost of reconstruction of about 1.5 billion dollars. The mudflows which increased during the flashflood inundated much of the city of Copiapo and Tierra Amarilla. This manuscript aims to model the mudflow of March 2015 in the Rio Copiapo, specifically in the towns of Copiapo and Tierra Amarilla. The modeling process is performed using the Rapid Mass Movement Simulation Model (RAMMS) that allows modeling the dynamics of the mudflow in two dimensions, only using the topographic features of the modeling domain. Calibration of the model was carried out successfully using data from inundation heights captured around the city after the 2015 event. A detailed analysis of the hydrometeorological event is carried out using satellite images obtained from Multi-satellite Precipitation Analysis (TMPA), and pluviometric and hydrographic data available in the Copiapo River basin. The simulation of the flood is reproduced with maps of inundation heights associated with two modeling scenarios. The maximum flood heights are ultimately used for developing risk maps at both sites. According to our results, the RAMMS model is an appropriate tool for modeling mudflow and mapping flood risk to improve hydrological risk management in arid and semiarid basins of Chile.
103

A Study of the Tradition of Extreme Literature

Chan, Matthew Chi Hei 01 January 2017 (has links)
This thesis endeavours to investigate some of the many ways literary works can engage with the tradition of extremism. In so doing, the author hopes to demonstrate the importance of the tradition as a vessel for understanding the world around and within us. In an effort to show the breadth and endurance of this tradition, this thesis critically analyses selected works by Robert Browning, Harold Pinter, and Frank Bidart in context with various other literary works.
104

FRM AIRCON : What can be done to improve the personal protective equipment for auto body painters?

Eriksson, Ruben January 2016 (has links)
The professional auto body painter works in an extreme environment, where the painter faces constant movement, ever-changing working situations and pressure to deliver a flawless paint job: the paint booth. The temperature in the paint booth is high, often around 30˚ Celsius. The floor is very hard, made of metal grid or concrete, and the painter usually has to move around a lot, at least 9 km per day. For this project I chose to focus on the painter’s work footwear as a major part of the personal protective equipment. My goal is to create a new standard in working shoes, specifically made for this environment and context. A comfortable shoe that could withstand heat, paint dust and wear. A shoe that is made for its users: the FRM AIRCON.
105

Does copula beat linearity? : Comparison of copulas and linear correlation in portfolio optimization.

Blom, Joakim, Wargclou, Joakim January 2016 (has links)
Modern portfolio theory (MPT) is an investment theory which was introduced by Harry Markowitz in 1952 and describes how risk averse investors can optimize their portfolios. The objective of MPT is to assemble a portfolio by maximizing the expected return given a level of market risk or minimizing the market risk given an expected return. Although MPT has gained popularity over the years it has also been criticized for several theoretical and empirical shortcomings such as using variance as a measure of risk, measuring the dependence with linear correlation and assuming that returns are normally distributed when in fact empirical data suggests otherwise. When moving away from the assumption that returns are elliptical distributed, for example normally distributed, we can not use linear correlation as a measure of dependence in an accurate way. Copulas are a flexible tool for modeling dependence of random variables and enable us to separate the marginals from any joint distribution in order to extract the dependence structure. The objective of this paper was to examine the applicability of a copula-CVaR framework in portfolio optimization compared to the traditional MPT. Further, we studied how the presence of memory, when calibrating the copulas, affects portfolio optimization. The marginals for the copula based portfolios were constructed using Extreme Value Theory and the market risk was measured by Conditional Value at Risk. We implemented a dynamic investing strategy where the portfolios were optimized on a monthly basis with two different length of rolling calibration windows. The portfolios were backtested during a sample period from 2000-2016 and compared against two benchmarks; Markowitz portfolio based on normally distributed returns and an equally weighted, non optimized portfolio. The results demonstrated that portfolio optimization is often preferred compared to choosing an equally weighted portfolio. However, the results also indicated that the copula based portfolios do not always beat the traditional Markowitz portfolio. Furthermore, the results indicated that the choice of length of calibration window affects the selected portfolios and consequently also the performance. This result was supported both by the performance metrics and the stability of the estimated copula parameters.
106

XTREND: A computer program for estimating trends in the occurrence rate of extreme weather and climate events

Mudelsee, Manfred 05 January 2017 (has links) (PDF)
XTREND consists of the following methodical Parts. Time interval extraction (Part 1) to analyse different parts of a time series; extreme events detection (Part 2) with robust smoothing; magnitude classification (Part 3) by hand; occurrence rate estimation (Part 4) with kernel functions; bootstrap simulations (Part 5) to estimate confidence bands around the occurrence rate. You work interactively with XTREND (parameter adjustment, calculation, graphics) to acquire more intuition for your data. Although, using “normal” data sizes (less than, say, 1000) and modern machines, the computing time seems to be acceptable (less than a few minutes), parameter adjustment should be done carefully to avoid spurious results or, on the other hand, too long computing times. This Report helps you to achieve that. Although it explains the statistical concepts used, this is generally done with less detail, and you should consult the given references (which include some textbooks) for a deeper understanding.
107

Exploring Ultrafast Quantum Dynamics of Electrons by Attosecond Transient Absorption

Liao, Chen-Ting, Liao, Chen-Ting January 2017 (has links)
Quantum mechanical motion of electrons in atoms and molecules is at the heart of many photophysical and photochemical processes. As the natural timescale of electron dynamics is in the range of femtoseconds or shorter, ultrashort pulses are required to study such phenomena. The ultrashort pulse light-matter interaction at high intensity regime can however dramatically alter the atomic and molecular structures. Our current understanding of such transient electronic modification is far from complete, especially when complicated light-induced couplings are involved. In this dissertation, we investigated how a femtosecond strong-field pulse can control or modify the evolution of atomic or molecular polarization, representing electric dipole excitation in various systems. Extreme ultraviolet (XUV) attosecond pulse trains are used to coherently prepare superposition of excited states in various atomic and molecular systems. A subsequent phase-locked infrared (IR) femtosecond pulse is applied to perturb the dipoles, and transient changes in the transmitted XUV spectra are measured. This scheme is termed as XUV attosecond transient absorption spectroscopy. In the first study, we applied this technique to study the modification of Rydberg states in dilute helium gas. We observed several transient changes to the atomic structure, including the ac Stark shift, laser-induced quantum phase, laser-induced continuum structure, and quantum path interference. When the experiments were extended to the study of a dense helium gas sample, new spectral features in the absorption spectra emerged which cannot be explained by linear optical response models. We found that these absorption features arise from the interplay between the XUV resonant pulse propagation and the IR-imposed phase shift. A unified physical model was also developed to account for various scenarios. Extending our work to argon atoms, we studied how an external infrared field can be used to impulsively control different photo-excitation pathways and the transient absorption lineshape of an otherwise isolated autoionizing state. It is found that by controlling the field polarization of the IR pulse, we can modify the transient absorption line shape from Fano-like to Lorentzian-like profiles. Unlike atoms, in our study of autoionizing states of the oxygen molecule, we observed both positive and negative optical density changes for states with different electronic symmetries. The predictions of two distinct and simplified dipole perturbation models were compared against both the experimental results and a full theoretical calculation in order to understand the origin of the sign of absorption change. We relate this symmetry-dependent sign change to the Fano parameters of static photoabsorption. The same approach was applied to study molecular nitrogen, in which we observed the decay dynamics of IR perturbed doubly-excited Rydberg states with many vibrational progressions. In addition, we also conducted experiments to investigate Rydberg state dynamics of other molecular systems such as carbon dioxide. In summary, we experimentally explored the ephemeral light-induced phenomena associated with excited states of atoms and molecules. These studies provide real-time information on ultrafast electronic processes and provide strategies for direct time-domain control of the light-matter interaction.
108

Análise numérica da influência de chuvas extremas na estabilidade de taludes. / Numerical analysis of influence of extreme rainfall in slope stability.

Zambrana, Veroska Dueñas 13 November 2014 (has links)
Escorregamentos de taludes no Sudeste do Brasil são causados principalmente, pelo efeito da água proveniente das chuvas. Nos últimos anos, vem se incrementando o número de desastres naturais, ao passo são registradas mudanças climáticas, que podem exercer influência na ocorrência de chuvas extremas. Muitas encostas permanecem grande parte do ano com o solo em estado não saturado, porém variações nas condições ambientais podem ocasionar mudanças bruscas da sucção, reduzindo ou até mesmo eliminando-a e gerando pressões neutras positivas. A dissertação apresenta, um estudo sobre a influência das chuvas, consideradas extremas, no processo de infiltração e de este nos eventos de escorregamentos, considerados catastróficos pela sua dimensão, e que causaram prejuízos ambientais, econômicos e sociais no Brasil. Para o estudo foram selecionados dois eventos de escorregamentos translacionais rasos relativamente típicos, considerados catastróficos, um deles aconteceu na região da Serra de Cubatão em janeiro do ano 1985, e o outro na Região Serrana do Rio de Janeiro em janeiro de 2011. Estes dois eventos apresentaram características de precipitações e mecanismos de escorregamentos próprios, que permitem ilustrar os diferentes mecanismos atuantes em cada caso. / Landslide in southeastern Brazil, are mainly caused by the effect of water from rainfall in infiltration process, in recent years has been increasing the number of natural disasters, while climate change that may exercising influence on the occurrence of extreme rainfall are recorded . Many slopes remain a large part of the year with unsaturated soil condition; however, changes in environmental conditions can cause sudden changes of suction, reducing or even deleting it and generate positive pore pressures. This dissertation presents a study about the influence of rainfall, considered extreme in the infiltration process and this one in the events regarded by their size of catastrophic landslides, which caused environmental, economic and social losses in Brazil. For the study were selected two events of shallow translational landslides relatively typical, considered catastrophic, one of them occurred in the Serra de Cubatão region on January 1985 and the other in the mountainous region of Rio de Janeiro on January 2011. Both events exhibit characteristics of rainfall and sliding mechanisms themselves, allowing illustrate the different mechanisms active in each case.
109

Observing in the extreme : British scientific research in the High Alps, c.1815-1880

Smail, Robert January 2013 (has links)
This thesis examines scientific research undertaken by British travellers in the higher regions of the Alps from c.1815 to c.1880. Within this spatial backdrop I study how bodily habits and physical practices were used in the formation of a distinct observational style, how this style was transferred to other individuals and other social groups, and how they could be called upon to legitimate the knowledge produced. Mountain regions provide an ideal space to examine the role of physical practices in the production of scientific knowledge. Difficult geography and unpredictable weather make the Alps a very hostile environment. The period between 1815 (the end of the Napoleonic wars) and 1880 (when 'guideless' climbing was introduced) was a period of considerable change for Alpine research and mountain travel. It was during this period that scientific research was shifted from the lower Alpine valleys towards the higher regions of permanent snow and ice. But before the higher regions could be observed, individuals were first required to learn bodily habits and physical practices. To further these aims this study will the broadly based around the Alpine Club. Formed in 1857, it was the premier authority on high mountain travel. Though knowledge production formed a strong part of its outlook, the Club also contained members intent on pursuing mountain travel for pleasure. As a result the Club placed scientific activities alongside the unique physical skills and the technical experiences of its membership. Members interested in producing scientific research in the higher Alps used the Club to extend participation in observation gathering. To do so they used the Club's rules and regulations, meetings and committee structure as well as its publications to define and articulate how this knowledge should be collected.
110

Dynamic extreme value theory (DEVT): a dynamic approach for obtaining value-at-risk (VaR).

January 2006 (has links)
by Leung Tsun Ip. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (leaves 72-78). / Abstracts in English and Chinese. / Chapter 1. --- Introduction --- p.1 / Chapter 2. --- Literature Review --- p.6 / Chapter 2.1 --- Development of estimation of Value-at-Risk (VaR) --- p.6 / Chapter 2.2 --- Methods to evaluate VaR --- p.9 / Chapter 2.2.1 --- Non-paremetric Method --- p.9 / Chapter 2.2.2 --- Semi-parametric Method --- p.11 / Chapter 2.2.3 --- Parametric Method --- p.12 / Chapter 3. --- Extreme Value Theory (EVT) --- p.16 / Chapter 3.1 --- Introduction of Extreme Value Theory (EVT) --- p.16 / Chapter 3.1.1 --- Block Maxima Approach --- p.18 / Chapter 3.1.2 --- Peaks over Threshold (POT) Approach --- p.21 / Chapter 3.1.3 --- Comparison between Block Maxima and POT Approach --- p.22 / Chapter 3.2 --- Numerical Illustration --- p.23 / Chapter 3.2.1 --- Data --- p.23 / Chapter 3.2.2 --- Diagnosis --- p.24 / Chapter 4. --- Dynamic Extreme Value Theory (DEVT) --- p.29 / Chapter 4.1 --- Theoretical Framework of DEVT --- p.29 / Chapter 4.2 --- Estimation of Parameters --- p.32 / Chapter 4.3 --- Determination of Threshold Level --- p.37 / Chapter 4.4 --- Estimation of zq --- p.44 / Chapter 5. --- Backtesting and Time Aggregation --- p.49 / Chapter 5.1 --- Backtesting DEVT --- p.49 / Chapter 5.2 --- Time Aggregation --- p.55 / Chapter 6. --- Case Study: China Aviation Oil Singapore (CAO) Incident --- p.61 / Chapter 6.1 --- Background Information --- p.61 / Chapter 6.2 --- Data Analysis --- p.63 / Chapter 6.3 --- Suggestion --- p.68 / Chapter 7. --- Discussion --- p.71 / References --- p.72 / Chapter A. --- Appendix --- p.79

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