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

Hepatic teratoma and peritoneal gliomatosis: a case report

The hepatic teratoma is a very rare entity of which only 25 cases have been published so far. In our case the hepatic teratoma is associated with peritoneal gliomatosis, which is an indicator for an ongoing peritoneal spread of a teratoma. Wall calcifications and the homogeneity as well as the well defined border misled the radiologist to the diagnosis of an echinococcal cyst, which is the most common differential diagnosis, however the hepatic teratoma has to be taking into consideration when dealing with unclear hepatic cysts, although it is very rare

Effect of reader experience on variability, evaluation time and accuracy of coronary plaque detection with computed tomography coronary angiography

Objective: To assess the effect of reader experience on variability, evaluation time and accuracy in the detection of coronary artery plaques with computed tomography coronary angiography (CTCA). Methods: Three independent, blinded readers with three different experience levels twice labelled 50 retrospectively electrocardiography (ECG)-gated contrast-enhanced dual-source CTCA data sets (15 female, age 67.3 ± 10.4years, range 46-86years) indicating the presence or absence of coronary plaques. The evaluation times for the readings were recorded. Intra- and interobserver variability expressed as κ statistics and sensitivity, specificity, and negative and positive predictive values were calculated for plaque detection, with a consensus reading of the three readers taken as the standard of reference. A bootstrap method was applied in the statistical analysis to account for clustering. Results: Significant correlations were found between reader experience and, respectively, evaluation times (r = −0.59, p < 0.05) and intraobserver variability (r = 0.73, p < 0.05). The evaluation time significantly differed among the readers (p < 0.05). The observer variability for plaque detection, compared with the consensus, varied between κ = 0.582 and κ = 0.802. Variability of plaque detection was significantly smaller (p < 0.05) and more accurate (p < 0.05) for the most experienced reader. Conclusion: Reader experience significantly correlated with observer variability, evaluation time and accuracy of coronary plaque detection at CTC

Lung Cancer Screening with Submillisievert Chest CT: Potential Pitfalls of Pulmonary Findings in Different Readers with Various Experience Levels

Purpose To assess the interreader variability of submillisievert CT for lung cancer screening in radiologists with various experience levels. Method Six radiologists with different degrees of clinical experience in radiology (range, 1-15 years), rated 100 submillisievert CT chest studies as either negative screening finding (no nodules, benign nodules, nodules 10 mm). Each radiologist interpreted scans randomly ordered and reading time was recorded. Interobserver agreement was assessed with ak statistic. Reasons for differences in nodule classification were analysed on a case-by-case basis. Reading time was correlated with reader experience using Pearson correlation (r). Results The overall interobserver agreement between all readers was moderate (k = 0.454; p < 0.001). In 57 patients, all radiologists agreed on the differentiation of negative and indeterminate/positive finding. In 64 cases disagreement between readers led to different nodule classification. In 8 cases some readers rated the nodule as benign, whereas others scored the case as positive. Overall, disagreement in nodule classification was mostly due to failure in identification of target lesion (n = 40), different lesion measurement (n = 44) or different classification (n = 26). Mean overall reading time per scan was of 2 min 2 s (range: 7s-7 min 45 s) and correlated with reader-experience (r =-0.824). Conclusions Our study showed substantial interobserver variability for the detection and classification of pulmonary nodules in submillisievert CT. This highlights the importance for careful standardisation of screening programs with the objective of harmonizing efforts of involved radiologists across different institutions by defining and assuring quality standards

Influence of convolution filtering on coronary plaque attenuation values: observations in an ex vivo model of multislice computed tomography coronary angiography

Attenuation variability (measured in Hounsfield Units, HU) of human coronary plaques using multislice computed tomography (MSCT) was evaluated in an ex vivo model with increasing convolution kernels. MSCT was performed in seven ex vivo left coronary arteries sunk into oil followingthe instillation of saline (1/∞) and a 1/50 solution of contrast material (400 mgI/ml iomeprol). Scan parameters were: slices/collimation, 16/0.75 mm; rotation time, 375 ms. Four convolution kernels were used: b30f-smooth, b36f-medium smooth, b46f-medium and b60f-sharp. An experienced radiologist scored for the presence of plaques and measured the attenuation in lumen, calcified and noncalcified plaques and the surrounding oil. The results were compared by the ANOVA test and correlated with Pearson’s test. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. The mean attenuation values were significantly different between the four filters (p < 0.0001) in each structure with both solutions. After clustering for the filter, all of the noncalcified plaque values (20.8 ± 39.1, 14.2 ± 35.8, 14.0 ± 32.0, 3.2 ± 32.4 HU with saline; 74.7 ± 66.6, 68.2 ± 63.3, 66.3 ± 66.5, 48.5 ± 60.0 HU in contrast solution) were significantly different, with the exception of the pair b36f–b46f, for which a moderate-high correlation was generally found. Improved SNRs and CNRs were achieved by b30f and b46f. The use of different convolution filters significantly modifief the attenuation values, while sharper filtering increased the calcified plaque attenuation and reduced the noncalcified plaque attenuation