Improved objective bayesian estimator for a PLP model hierarchically represented subject to competing risks under minimal repair regime

In this paper, we propose a hierarchical statistical model for a single repairable system subject to several failure modes (competing risks). The paper describes how complex engineered systems may be modelled hierarchically by use of Bayesian methods. It is also assumed that repairs are minimal and each failure mode has a power-law intensity. Our proposed model generalizes another one already presented in the literature and continues the study initiated by us in another published paper. Some properties of the new model are discussed. We conduct statistical inference under an objective Bayesian framework. A simulation study is carried out to investigate the efficiency of the proposed methods. Finally, our methodology is illustrated by two practical situations currently addressed in a project under development arising from a partnership between Petrobras and six research institutes

Numerical study of the effect of hydrodynamic blockage in a cavitation tunnel in the flow around a submarine.

O projeto de submarinos é um tema que vem se desenvolvendo há muitos anos. No Brasil, vivemos um momento de pleno avanço na área, sendo encabeçado pela Marinha do Brasil com o desenvolvimento do primeiro submarino de propulsão nuclear brasileiro. No decorrer desse projeto, diversos estudos devem ser desenvolvidos, dentre eles, ensaios com modelos em escala, que serão realizados em um túnel de cavitação. Durante estes experimentos, espera-se que surjam diversas fontes de incerteza, que podem comprometer os resultados obtidos, destacando-se o efeito de blocagem hidrodinâmica. Nesse contexto, esta dissertação apresenta uma investigação do fenômeno de blocagem no modelo de submarino DARPA SUBOFF na seção de testes de um túnel de cavitação. Para isso, simulações tridimensionais de média de Reynolds (RANS) foram realizadas para o modelo de submarino posicionado no túnel (sob blocagem) e sob condição de águas profundas (referência), para diferentes ângulos de ataque e número de Reynolds (Re) constante. Coeficientes de força e momento hidrodinâmicos foram obtidos e os métodos de correção de blocagem clássico e WICS foram empregados para obter fatores que pudessem corrigir esses valores. A eficiência de cada método foi avaliada comparando os valores corrigidos com os de referência. Os resultados mostraram que ambos métodos de correção são eficientes na recuperação de coeficientes de força e momento hidrodinâmicos para razões de blocagem inferiores a 10%, mas ressalvas são feitas quanto à utilização de cada um desses métodos, sendo o método clássico indicado para o estudo de geometrias simples e o método WICS para modelos mais complexos. Paralelamente, a topologia do escoamento ao redor do submarino foi estudada através do método dos pontos críticos, para avaliar se a blocagem hidrodinâmica pode causar alterações nas estruturas presentes no escoamento. A análise topológica permitiu avaliar a evolução nas estruturas do escoamento para os ângulos de ataque e Re simulados. Foram capturadas as linhas de separação no corpo e avaliada sua relação com a tensão de cisalhamento ao longo do casco. A blocagem hidrodinâmica não causou alterações drásticas na topologia do escoamento.The Project of submarines has been in development for years. In Brazil, we are facing a moment of full progress in this area, leaded by the Brazilian Navy with the development of the first submarine with nuclear propulsion in the country. During this project, many studies will be developed, among them, experiments with scaled models, that will be performed in a cavitation tunnel. Throughout these experiments, many sources of uncertainty are expected to arise that may compromise the results obtained, one effect that stands out is the hydrodinamic blockage. In this context, this master\'s thesis presents an investigation of the blockage phenomenon in the submarine model DARPA SUBOFF placed in the test section of a cavitation tunnel. To accomplish this, tridimensional simulations of Reynolds-Averaged Navier Stokes equations (RANS) were performed to the submarine model placed in the tunnel (under blockage) and in deep water condition (reference), to a variety of angles of attack and a constant Reynolds Number (Re). Cofficients of hydrodynamic forces and moment were measured and the classic and WICS correction methods were used to obtain factors that could correct these values. The efficiency of these methods were evaluated comparing the corrected values with the reference ones.The results showed that both correction methods are efficients in the recovery of hydrodynamic forces and moment to blockage ratios below 10%, but reservations are made about the use of each method. The classic method is suggested when simple geometries are tested and the WICS method when more complex models are used. At the same time, the flow topology around the submarine was studied, using the critical point theory, to evaluate if the hydrodynamic blockage can cause changes in the structures in the flow. The topology analysis permited to assess the evolution of structures in the flow to the conditions of angle of attack and Re simulated. Separation lines were captured in the body and their relationship with the shear stress in the hull was evaluated. The hydrodynamic blockage did not cause drastic changes in the flow topology

Experimental and numerical study of stratified viscous-oil/water flow

O escoamento estratificado óleo-água é de grande interesse para a indústria de petróleo, pois é comumente observado em oleodutos e poços direcionais. Nos últimos anos, diversos trabalhos surgiram com o intuito de analisar esse tipo de escoamento, seja através de dados experimentais ou de modelos numéricos. Contudo poucos deles focam suas análises no escoamento de líquidos com alta razão de viscosidade. Outro ponto importante é o fato que fenômenos dinâmicos comuns nesse escoamento, como a formação de ondas interfaciais e entranhamento de gotas são difíceis de modelar e motivo de estudo recorrente na área. Nesse contexto, este trabalho avalia o escoamento estratificado de óleo viscoso e água através de três abordagens distintas e complementares: experimentos, modelagem unidimensional e modelagem tridimensional utilizando técnicas de CFD. Os dados experimentais são utilizados para a validação e fechamento de correlações usadas nos modelos numéricos. A modelagem unidimensional baseia-se em um modelo da literatura, desenvolvido para escoamentos estratificados ondulados e adiciona a ele efeitos do entranhamento, através de alterações na equação de quantidade de movimento e nas propriedades médias dos fluidos. As simulações em CFD, com a técnica \"Volume-of-fluid (VOF)\", tentam capturar os fenômenos dinâmicos associados a escoamentos estratificados ondulados e com mistura na interface e determinar parâmetros locais do escoamento, que não podem ser obtidos através da modelagem unidimensional simplificada. Através dos dados experimentais foi possível levantar dados de distribuição de fases, fração volumétrica, perda de carga, características interfaciais e fatores de entranhamento. Os resultados dos modelos indicam vantagem na utilização de CFD frente ao modelo unidimensional para escoamentos estratificados liso e ondulado, principalmente utilizando simulações de grandes escalas para a turbulência. Para o padrão estratificado com mistura na interface, tanto o modelo em CFD quanto a modelagem unidimensional padrão mostraram-se incapazes em capturar todas as nuances do escoamento, contudo o novo modelo unidimensional proposto mostra bons resultados para a análise desse padrão de escoamento e é uma modelagem promissora que precisa ser testada mais a fundo.The petroleum industry is highly interested in stratified oil-water flows, because they are common in pipelines and directional wells. In the past few years, many studies were developed to analyze this type of flow, through experiments or numerical modeling. However, just a few of these are focused in the flow of liquids with high viscosity ratio. Another important point is the fact that several dynamic phenomena of this type of flow, such as interfacial waves or droplet entrainment, are difficult to model and hence subject of many studies. In this context, this project evaluates the stratified viscous-oil/water flow using three different and complementary approaches: experiments, one-dimensional and three-dimensional modeling using CFD techniques. The experimental data is used to validate and to provide closure correlations used in the numerical models. The one-dimensional model proposed is based in one from the literature, developed to stratified wavy flows. The effects of entrainment are added to the model through changes in the momentum equation and in the mean properties of the fluids. The CFD simulations, using Volume-of-fluid (VOF) try to reproduce the dynamics associated with stratified flows and determine local parameters of the flow that can not be obtained through the simplified one-dimensional models. With the experimental data it was possible to define values of phases distribution, volumetric fractions, pressure drop, interfacial features and entrainment factor. The models\' results show an advantage in using CFD in comparison with the one-dimensional model to stratified smooth and wavy flows, especially using large eddy simulations for turbulence. When evaluating the stratified flow with mixture at the interface, both CFD and the one-dimensional model were unable to properly represent the flow, however the new proposed one-dimensional model showed good results in the analysis of this flow pattern and it is a promising tool that needs to be further evaluated

ATLANTIC BIRD TRAITS: a data set of bird morphological traits from the Atlantic forests of South America

Scientists have long been trying to understand why the Neotropical region holds the highest diversity of birds on Earth. Recently, there has been increased interest in morphological variation between and within species, and in how climate, topography, and anthropogenic pressures may explain and affect phenotypic variation. Because morphological data are not always available for many species at the local or regional scale, we are limited in our understanding of intra- and interspecies spatial morphological variation. Here, we present the ATLANTIC BIRD TRAITS, a data set that includes measurements of up to 44 morphological traits in 67,197 bird records from 2,790 populations distributed throughout the Atlantic forests of South America. This data set comprises information, compiled over two centuries (1820–2018), for 711 bird species, which represent 80% of all known bird diversity in the Atlantic Forest. Among the most commonly reported traits are sex (n = 65,717), age (n = 63,852), body mass (n = 58,768), flight molt presence (n = 44,941), molt presence (n = 44,847), body molt presence (n = 44,606), tail length (n = 43,005), reproductive stage (n = 42,588), bill length (n = 37,409), body length (n = 28,394), right wing length (n = 21,950), tarsus length (n = 20,342), and wing length (n = 18,071). The most frequently recorded species are Chiroxiphia caudata (n = 1,837), Turdus albicollis (n = 1,658), Trichothraupis melanops (n = 1,468), Turdus leucomelas (n = 1,436), and Basileuterus culicivorus (n = 1,384). The species recorded in the greatest number of sampling localities are Basileuterus culicivorus (n = 243), Trichothraupis melanops (n = 242), Chiroxiphia caudata (n = 210), Platyrinchus mystaceus (n = 208), and Turdus rufiventris (n = 191). ATLANTIC BIRD TRAITS (ABT) is the most comprehensive data set on measurements of bird morphological traits found in a biodiversity hotspot; it provides data for basic and applied research at multiple scales, from individual to community, and from the local to the macroecological perspectives. No copyright or proprietary restrictions are associated with the use of this data set. Please cite this data paper when the data are used in publications or teaching and educational activities. © 2019 The Authors. Ecology © 2019 The Ecological Society of Americ

ATLANTIC BIRD TRAITS

Scientists have long been trying to understand why the Neotropical region holds the highest diversity of birds on Earth. Recently, there has been increased interest in morphological variation between and within species, and in how climate, topography, and anthropogenic pressures may explain and affect phenotypic variation. Because morphological data are not always available for many species at the local or regional scale, we are limited in our understanding of intra- and interspecies spatial morphological variation. Here, we present the ATLANTIC BIRD TRAITS, a data set that includes measurements of up to 44 morphological traits in 67,197 bird records from 2,790 populations distributed throughout the Atlantic forests of South America. This data set comprises information, compiled over two centuries (1820–2018), for 711 bird species, which represent 80% of all known bird diversity in the Atlantic Forest. Among the most commonly reported traits are sex (n = 65,717), age (n = 63,852), body mass (n = 58,768), flight molt presence (n = 44,941), molt presence (n = 44,847), body molt presence (n = 44,606), tail length (n = 43,005), reproductive stage (n = 42,588), bill length (n = 37,409), body length (n = 28,394), right wing length (n = 21,950), tarsus length (n = 20,342), and wing length (n = 18,071). The most frequently recorded species are Chiroxiphia caudata (n = 1,837), Turdus albicollis (n = 1,658), Trichothraupis melanops (n = 1,468), Turdus leucomelas (n = 1,436), and Basileuterus culicivorus (n = 1,384). The species recorded in the greatest number of sampling localities are Basileuterus culicivorus (n = 243), Trichothraupis melanops (n = 242), Chiroxiphia caudata (n = 210), Platyrinchus mystaceus (n = 208), and Turdus rufiventris (n = 191). ATLANTIC BIRD TRAITS (ABT) is the most comprehensive data set on measurements of bird morphological traits found in a biodiversity hotspot; it provides data for basic and applied research at multiple scales, from individual to community, and from the local to the macroecological perspectives. No copyright or proprietary restrictions are associated with the use of this data set. Please cite this data paper when the data are used in publications or teaching and educational activities. © 2019 The Authors. Ecology © 2019 The Ecological Society of Americ