Análisis comparativo de teorías para rotores en vuelo axial ascendente

En el estudio de las actuaciones de rotores en vuelo axial son muchas las teorías utilizadas para modelar el comportamiento de estos. Así, el presente trabajo se enfoca en el estudio del vuelo axial ascensional de un rotor de helicóptero, considerando diversas teorías que van desde las más sencillas a las más complejas. El desarrollo de las teorías se realizará de forma incremental en complejidad, comenzando con teorías muy básicas las cuales permiten comprender ideas generales del comportamiento del rotor. Estas teorías serán cruciales para etapas iniciales del desarrollo de un proyecto de diseño, donde únicamente valores rápidos y estimados son requeridos. A medida que se avanza en el desarrollo, se introducirán teorías más complejas, las cuales permiten un modelado local del problema, modelando fenomenología compleja y permitiendo valores de las variables de interés mucho más cercanos a los esperados en la realidad. Estos valores son necesarios cuando la precisión toma mayor importancia, especialmente en etapas más avanzadas del proceso de diseño. El aspecto clave de todo este desarrollo reside en la comparativa de las diferentes teorías a estudiar, identificando puntos fuertes y débiles de cada una de ellas, regímenes de aplicación, etc. De esta forma, dada la necesidad de realizar un dimensionado de un rotor en una situación particular, se tengan las herramientas necesarias para poder saber qué metodología ofrece mejores resultados, en precisión y tiempo de cálculo. Finalmente, se pretende realizar un estudio de detalle de la distribución de fuerzas generadas en las palas del rotor con la teoría más avanzada a modelar, donde podrán identificarse las zonas de mayor carga aerodinámica, así como la distribución de velocidades en el rotor de forma local.In the study of rotor performances in axial flight, there are many theories used to model their behavior. Thus, this work focuses on the study of the ascending axial flight of a helicopter rotor, considering various theories ranging from the simplest to the most complex. The development of these theories will be carried out incrementally in complexity, starting with very basic theories that allow for a general understanding of rotor behavior. These theories will be crucial for the initial stages of design projects, where only quick and estimated values are required. As the development progresses, more complex theories will be introduced, allowing for local modeling of the problem, and capturing intricate phenomena, thereby providing values of variables of interest much closer to real-world expectations. These values are necessary when precision becomes more critical, especially in later stages of the design process. The key aspect of this entire development lies in the comparison of the different theories under study, identifying their strengths, weaknesses, applicable regimes, etc. Thus, when sizing a rotor for a specific situation, one will have the necessary tools to determine which methodology offers better results in terms of accuracy and calculation time. Eventually, a detailed study of the distribution of forces generated on the rotor blades will be conducted using the most advanced theory to be modeled. This study will help identify areas of higher aerodynamic load and the local distribution of velocities in the rotor.Universidad de Sevilla. Máster en Ingeniería Aeronáutic

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century