Non-Linear modelling of Extreme High-Angle Waves Instability

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Correlation between the pivot node concept and fatigue crack closure

The study of fatigue crack growth has been commonly done by means of bi-dimensional models and assuming a homogeneous behaviour through the thickness. According to the specimen thickness, a state of plane stress or plane strain is presumed. However, recently, it has been shown that thickness effects influence the crack tip behaviour. These works have revealed a series of effects along the thickness with a strong influence on the crack front growth. One of the experimental evidences that can be explained as a direct consequence of these effects is the curvature of the crack. It is observed that when the crack advance, the crack front changes adopting a curved shape, growing faster at the interior than at the exterior. Two mechanisms can explain this effect: the first one is related to the crack closure effect near the surface. The second one, related to the plastic zone size decrement observed in a small region close to the surface, is due to ΔK being smaller near the surface than in the interior. Both mechanisms are difficult to evaluate separately. A series of works were devoted to study these effects. A research line has been focused in the analysis of the stress intensity factor distribution. These works evaluate the finite element model of an Al 2024-T35 compact tension specimen with no plastic wake effect introduced, according to the methodology developed by the authors. The three-dimensional behaviour in the vicinity of the crack front is simulated through numerical analysis with ANSYS code and J-integral method is used to determinate the curves of K evolution along the thickness. The main finding of these studies is that the distribution of K is not homogeneous. The overall values for the whole model accurately agree with the nominal K applied. The K profiles along the thickness are characterized by a series of parameters that allow us to analyze the distribution of K in terms of the expected Knom against variations of geometrical and external factors.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Key aspects in 3D fatigue crack closure numerical modelling

Since long time, fatigue crack closure has been studied by means of finite element models. Initially by bi-dimensional models and recently, due to the higher computational capabilities, the use of three-dimensional models has been extended, providing a wider comprehension of the problem. Starting with the methodology used for 2D cases, a specific methodology for 3D models has been developed. Key parameters affecting the model have been analyzed and recommendations have been established. The numerical accuracy is evaluated in terms of crack closure and opening values. They main issues studied are the material behaviour, the loading cycles and crack growth scheme, the contact simulation, the meshing and the element size at the crack tip and along the thickness, the plastic wake computed and the opening and closure definition considered. This paper summarises the main learning and recommendations from the latest numerical modelling experience of the authors.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Transfer learning for actor-critic methods in Lipschitz Markov decision processes

Aprendizaje por Refuerzo es un paradigma para diseñar agentes artificiales cuando el conocimiento viene exclusivamente de interacción con un ambiente. Dificultades surgen cuando los espacios de estados y acciones son continuos pues los algoritmos clásicos de RL no son factibles ni convergentes. Los enfoques Actor-Critic resuelven dichos problemas al combinar la convergencia de los métodos policy-gradient con el poder representativo de function approximators, en un estimador de baja varianza. Aprendizaje por Transferencia es el paradigma que estudia el problema de transferir experiencia previa de diferentes ambientes cuando el agente encara uno nuevo y desconocido. Su objetivo es desarrollar algoritmos que aceleren el nuevo proceso de aprendizaje aprovechando el conocimiento previo. Avances relativos a TL en RL han emergido en años recientes, pero la mayoría se concentran en transferir información de alto nivel. La continuidad Lipschitziana, una noción más fuerte de continuidad para los elementos del ambiente, puede proveer suficiente información para crear mecanismos de transferencia a nivel de muestras y extender los métodos Actor-Critic. Esta tesis presenta dos de esos mecanismos basados en estimadores ponderados: uno hace una selección optimista de los pesos y otro una selección pesimista. Ambas técnicas son comparadas con un mecanismo de transferencia basado en estimación con Importance Sampling. El enfoque optimista produce buenos resultados en la mayoría de los casos experimentales, mostrándose como una alternativa prometedora sobre aquella con IS y el caso sin transferencia. El enfoque pesimista, en cambio, es demasiado conservativo al seleccionar pesos, y no produce mejoras importantes al caso sin transferencia.Reinforcement Learning is a framework for designing artificial agents when knowledge comes from interaction with an environment only. Difficulties arise when State and action spaces are continuous as dassical RL algorithms are not feasible or convergent. Actor-critic approaches solve these issues by combining the convergence of policy-gradient methods with the representation power of function approximators, in a low variance estimation. Transfer Learning is the paradigm that addresses the problem of transferring past experience from different tasks when the agent is facing a new, unknown one. Its purpose is to develop algorithms that speed-up the new learning process by leveraging the past knowledge. Advances concerning TL in RL have been developed in the recent years, but most of them focus on transfer higher level information like valué functions or policies. The Lipschitz continuity property, a stronger notion of continuity for the elements of the task, can provide enough information to create sample-level transfer mechanisms to extend the Actor-Critic methods. This thesis introduces two such mechanisms based on weighted estimators: one performs an optimistic selection of the weights and the other a pessimistic one. Both techniques are compared with a transfer mechanism based on Importance Sampling estimators. The optimistic approach produces good results in most of the experimental cases, showing itself as a promising alternative over the IS-based one and the no transfer scenario. The pessimistic approach, instead, tends to be too conservative on the selection of the weights, and offers no special improvements with respect to the no transfer scenario.Ingeniero (a) de SistemasPregrad

UBathy: a new approach for bathymetric inversion from video imagery

A new approach to infer the bathymetry from coastal video monitoring systems is presented. The methodology uses principal component analysis of the Hilbert transform of video images to obtain the components of the wave propagation field and their corresponding frequency and wavenumber. Incident and reflected constituents and subharmonics components are also found. Local water depth is then successfully estimated through wave dispersion relationship. The method is first applied to monochromatic and polychromatic synthetic wave trains propagated using linear wave theory over an alongshore uniform bathymetry in order to analyze the influence of different parameters on the results. To assess the ability of the approach to infer the bathymetry under more realistic conditions and to explore the influence of other parameters, nonlinear wave propagation is also performed using a fully nonlinear Boussinesq-type model over a complex bathymetry. In the synthetic cases, the relative root mean square error obtained in bathymetry recovery (for water depths 0.75m¿h¿8.0m) ranges from ~1% to ~3% for infinitesimal-amplitude wave cases (monochromatic or polychromatic) to ~15% in the most complex case (nonlinear polychromatic waves). Finally, the new methodology is satisfactorily validated through a real field site video.Postprint (published version

Obtaining directional wave characteristics in front of nearshore field sites

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Implementación de un plan de prevención de riesgos mecánicos en industrias Palugi Ibarra - Ecuador

Implementar un plan de prevención de riesgos mecánicos en “Industrias Palugi”, identificando, evaluando y controlando técnica y objetivamente el factor de riesgo para la prevención de accidentes laborales.El presente estudio se realizó en la planta de producción de la empresa Industrias Palugi, dedicada a la elaboración de alimentos “Granola”, en vista de que la empresa se encuentra catalogada en un nivel de riesgo medio, se inició un análisis de la situación actual en cuanto a Seguridad Industrial, mediante el levantamiento de procesos, identificación, evaluación, medición y control de riesgos a los que está expuesto el talento humano. Como parte inicial se identificaron los puestos de trabajo, los riesgos existentes y la cantidad de personas expuestas, esto con el fin de realizar una evaluación efectiva que permita determinar el nivel de riesgo al cual están expuestos los trabajadores, para así mediante manuales, reglamentos, procedimientos, aplicar medidas preventivas adecuadas y que abarquen el número total de puestos y personas expuestas a los riesgos. La evaluación realizada permitió identificar la necesidad de elaborar un plan de prevención de riesgos mecánicos en industrias Palugi a más de integrar un manual de mantenimiento mecánico preventivo, el cual contiene lineamientos que permiten disminuir el impacto de los factores de riesgo mecánicos de la empresa. Para la implementación de las medidas preventivas, conforme a la magnitud del riesgo se las aplico en: la fuente, el medio de transmisión, el trabajador y los complementos. Elaborando procedimientos técnicos que permiten la implementación de las medidas preventivas frente a los riesgos identificados en la empresa. Para finalizar esta implementación, se realizó una comparación de la situación identificada, como situación actual implementada en cuanto a la seguridad Industrial, logrando constatar el cumplimiento de parámetros establecidos por las entidades de control vigentes en cuanto a Seguridad y Salud Laboral.Ingenierí