Optimierung von Wellenkraftanlagen mit oszillierender Wassersäule: eine numerische Studie

This PhD research aims at the study of the combined effect of the structure geometry and of the damping applied by a non-linear turbine (i.e., an impulse turbine) on the performance of a fixed Oscillating Water Column (OWC) device for harvesting wave energy. The improved knowledge base regarding the still not well-understood optimal OWC geometry and the optimal turbine damping, specifically for moderate wave climates such as in the Mediterranean Sea, contributes to fill one of the current gaps of knowledge. Moreover, the scale effect induced by neglecting the air compressibility in modelling OWC devices at small-scale is evaluated, and correction factors for the results from small-scale laboratory testing of OWC devices as well as for the results of incompressible numerical models are provided, thus contributing to fill a further recognized knowledge gap. Further, a conceptual model allowing to predict the capture width ratio of the OWC based on the geometrical parameters (e.g. chamber width and front wall draught), the damping applied by the turbine and the incident wave conditions is proposed. The proposed conceptual model might be applied as a design tool in the process of the OWC device optimization. The research methodology is based on numerical modelling supported by small-scale laboratory experiments performed by Crema et al. (2016) and further experiments from the literature, which are used to better understand the involved processes and to validate the Computational Fluid Dynamics models. A comparative analysis of the results from the validated CFD codes applied at full-scale (1:1) and three smaller scales (1:25, 1:10 and 1:5) is performed in order to assess the errors induced by neglecting the effect of air compressibility for each scale and to derive the aforementioned correction factors which are valid for the range of considered flow regime in terms of the Mach number (Ma=0.05-0.15). Indeed, for the air pressure levels considered in the simulations (up to 350 Pa at model scale 1:50), the effect of neglecting the air compressibility results in an overestimation up to about 15% for the air pressure in the OWC chamber and the subsequent air volume flux, but less than 10% for the capture width ratio. This overestimation increases with increasing pressure levels.In dieser Dissertation wird die kombinierte Auswirkung der Strukturgeometrie und der, durch eine nichtlineare Turbine (z.B. Gleichdruckturbine), aufgebrachten Dämpfung im Hinblick auf die Leistungsfähigkeit einer Wellenenergieanlage untersucht. Der hier betrachtete Prozess der Energieerzeugung basiert auf einer fest installierten, oszillierenden Wassersäule (Oscillating Water Column, OWC). Fortgeschrittenes Grundwissens erlaubt sowohl Fragestellungen bezüglich der idealen OWC-Geometrie als auch nach einer optimalen Turbinendämpfung neu zu betrachten. Dies ist insbesondere für moderate Seegangsverhältnisse, wie im Mittelmeer zu beobachten, von Bedeutung und trägt dazu bei gegenwärtige Wissenslücken zu schließen. Darüber hinaus werden Maßstabseffekte, welche durch die Vernachlässigung der Luftkompressibilität bei der kleinmaßstäblichen Modellierung von OWC-Anlagen induziert werden, ausgewertet. Des Weiteren werden Korrekturfaktoren festgelegt, welche sowohl auf Labortestergebnisse von OWC-Anlagen im Kleinmaßstab als auch auf die Ergebnisse inkompressibler, numerischer Modelle angewendet werden können. Somit kann eine weitere, anerkannte Wissenslücke geschlossen werden. Außerdem wird ein Konzeptmodell vorgestellt, welches die Bestimmung des Einlauf-Breiten-Verhältnisses der OWC (capture width ratio) auf Grundlager geometrischer Parameter ermöglicht. Die Forschungsmethodik basiert auf numerischer Modellierung, unterstützt durch die kleinmaßstäblichen Laborversuche von Crema et al. (2016) und weiteren, der Fachliteratur entnommenen Experimenten. Diese dienen einer besseren Verständlichkeit der beteiligten Prozesse und gewährleisten die Validierung der Computational Fluid Dynamics (CFD) Modelle. Zur Beurteilung der Fehler, welche infolge der Vernachlässigung der Luftkompressibilität (für jede Skala) entstehen, sowie der bereits erwähnten Korrekturfaktoren (Gültigkeit für den betrachteten Bereich der Durchflussregelung in Bezug auf Mach-Zahlbereich von 0,05 bis 0,15) wird eine vergleichende Ergebnisanalyse der validierten CDF-Codes sowohl vollskalig (1:1) als auch kleinskalig (1:25, 1:10 und 1:5) durchgeführt. Die, in den Simulationen, berücksichtigten Luftdruckniveaus (bis zu 350 Pa im Modellmaßstab von 1:50) in Verbindung mit einer Vernachlässigung der Luftkompressibilität führen zu einer Überschätzung des Luftdrucks in der OWC-Kammer und des nachfolgenden Volumenstroms von bis zu 15%. Die Überschätzung des Einlauf-Breiten-Verhältnis beträgt lediglich 10%

Occupation and working outcomes during the Coronavirus Pandemic

Using data from the recent SHARE COVID-19 survey and additional information collected in the previous waves of SHARE, we explore the effects of occupation’s characteristics on two outcomes: (i) the probability of work interruptions during the pandemic, coupled with the length of such interruptions and (ii) the probability of switching to homeworking during the lockdown. In order to assess how job features affected the likelihood of having experienced work interruptions or shifted to teleworking, we define six occupation categories by classifying the ISCO job titles according to two criteria: the safety level of the occupation and the essential (unessential) nature of the good or service provided. We find that characteristics of the occupation are major determinants of the probability of experiencing work interruptions and determine the length of such interruptions. Working from home also largely depends on the features of the job, even controlling for many other covariates at the individual level. In addition, we show that labour market outcomes of women, self-employed and less educated workers are negatively affected by the pandemic to a much larger extent than men

15 What is the future of (remote) work?

Among the individuals who worked continuously since the start of the COVID-19 pandemic, around 22% of men and 30% of women were working remotely in both waves of the SHARE Corona survey. Only 10% of the workers in our sample were initially working remotely, and then moved back to their usual workplace. Remote work adoption varied depending on the technical feasibility of performing a job remotel

Concentração de fluoreto na água do setor abastecido pela Estação de Tratamento de Água de Bauru, SP

OBJECTIVE: to analyze the fluoride concentration in the public water supply at the area supplied by the Water Treatment Station of Bauru and classify the samples as acceptable or unacceptable according to the fluoride concentration. MATERIAL AND METHODS: samples were collected from 30 areas at two periods, October 2002 and March 2003. The fluoride concentration in the samples was determined in duplicate, using an ion sensitive electrode (Orion 9609) connected to a potentiometer (Procyon, model 720). Samples with fluoride concentration ranging from 0.55 to 0.84 mg F/L were considered acceptable, and those whose concentration was outside this range as unacceptable. Data were analyzed by descriptive statistics. RESULTS: the fluoride concentration of the water samples varied between 0.31 and 2.01 mg F/L. Nearly 56% of the samples were classified as acceptable. CONCLUSION: the variations in fluoride concentration at the area supplied by the Water Treatment Station reinforce the need of constant monitoring for maintenance of adequate fluoride levels in the public water supply.OBJETIVO: Analisar a concentração de fluoreto da água de abastecimento público do setor abastecido pela Estação de Tratamento de Água de Bauru e classificar as amostras em aceitáveis ou inaceitáveis de acordo com a concentração de flúor. MATERIAL E MÉTODOS: Foram coletadas 238 amostras de 30 bairros em duas etapas, Outubro de 2002 e Março de 2003. A concentração de fluoreto presente nas amostras foi determinada em duplicata, utilizando-se o eletrodo íon sensível (Orion 9609), acoplado ao potenciômetro (Procyon, modelo 720). As amostras com concentração de flúor variando entre 0,55 e 0,84 mg F/L foram consideradas como aceitáveis e aquelas cuja concentração estava fora do intervalo, como inaceitáveis. Os dados foram analisados por meio de estatística descritiva. RESULTADOS: A concentração de fluoreto das amostras de água variou entre 0,31 e 2,01 mg F/L, sendo que cerca de 56% das amostras foram classificadas como aceitáveis. CONCLUSÃO: A variação na concentração de fluoreto do setor abastecido pela ETA reforça a importância de um monitoramento constante da fluoretação para a manutenção dos níveis adequados de fluoreto na água de abastecimento

Fluoride concentrations in industrialized beverages consumed by children in the city of Bauru, Brazil

The increasing consumption of juices, soft drinks and teas among children has increased significantly fluoride ingestion at the age range of risk for development of dental fluorosis. Objective: The purpose of this study was to evaluate fluoride concentrations in some brands of industrialized beverages consumed by children in the city of Bauru, SP, Brazil. Material and Methods: 98 brands of beverages were analyzed, divided into 3 lots, comprising 36, 32 and 30 brands, respectively, for the first, second and third lots. Fluoride concentrations were determined by HMDS-facilitated diffusion, using a fluoride ion-specific electrode (Orion 9409). Results: Fluoride concentrations ranged between 0.04 and 1.76 µg F/mL. It was observed a wide variation in fluoride concentrations among the different brands, as well as the different lots of the same brand. There was no information on fluoride concentrations on the labels of any product. Conclusions: Some of the products analyzed could contribute significantly to the total fluoride intake and, thus, be important risk factors for development of dental fluorosis, which indicates the need of controlling the production of these beverages with respect to fluoride concentration