Passive Aeroelastic Tailoring

The Passive Aeroelastic Tailoring (PAT) project was tasked with investigating novel methods to achieve passive aeroelastic tailoring on high aspect ratio wings. The goal of the project was to identify structural designs or topologies that can improve performance and/or reduce structural weight for high-aspect ratio wings. This project considered two unique approaches, which were pursued in parallel: through-thickness topology optimization and composite tow-steering

A Biomechanical Analysis of Bicycle Helmets using FEM

This thesis evaluates, by means of finite element methods the possible head injuries that might occur during an EN 1078 standard impact setting, as well as the energy percentage absorbed by the helmet in the same conditions. In this thesis, the geometry of a commercially available bicycle helmet has been modelled using CATIA. The helmet model geometry has then been meshed with quadrilateral and hexahedral elements using Hypermesh software. The last step of the thesis was performing helmeted head impact simulations using LS-DYNA software. The impacts upon which this thesis is based on are the EN 1078 flat anvil and curbstone anvil shock absorbing capacity tests, which are the EU standards for bicycle helmet safety evaluations. To validate the results, a comparison between the resultant acceleration and impact time between this study and previous studies was made. The EN 1078 flat anvil test has been validated and the set-up for the EN 1078 curbstone anvil test has been deemed correct. The acceleration results deemed the helmet safe by the EN 1078 standard. The head injury criteria assessed for the EN 1078 flat anvil test suggest 50% probability of skull fracture and a 75% concussion probability. A HIC value of 970.2 was obtained, indicating an 88% probability of moderate injury and 49% of serious injury. It was also found that DAI injuries are in the threshold of reaching a 50% probability of occurrence. The head injury criteria assessed for the EN 1078 curbstone anvil test indicates a 50% probability of concussion. A HIC value of 224.2 was obtained, which associates to 7% probability of moderate injury and 3% of serious injury. It was also found that DAI injuries are 11.1 kPa away from the 50% probability threshold. Regarding the additional tests made, the following results were obtained: the PU Foam has little effect on the absorption properties of the helmet and its main use is rider comfort. The importance of the modeling the straps in the simulation is demonstrated, since they keep the head attached to the helmet at all times. Depending on impact speed the helmet can absorb up to 50% of the impact energy. It is proposed that bicycle helmets must be mandatory for all people regardless of age, since the effectiveness of the helmet has also been demonstrated at low impact speeds. An analysis made to the different densities of the EPS Foams showed that in order to achieve a more distributed impact, with a low HIC value and low maximum acceleration it is recommended to use an EPS Foam with a larger density. Curves of injury probability against impact speed were developed showing that minor injuries start to happen at 10 km/h, severe at 15 Km/h and the most extreme injuries at 20 Km/h. The critical value for untreatable damage in the impact is 29.4 Km/h. Even though the effectiveness of the helmet has been proven in this study, it has also been found that at high speeds the cyclist can suffer untreatable damage; therefore, new research on helmets and cyclist safety is required to increase the likelihood of survival. It is proposed to lower the bicycle speed limits to 20 km/h in city shared pathways, and to limit the speed of electric bikes to reach a maximum of 20 km/h without rider input to keep extreme injury modes within reasonable values in the worst-case-scenario impact.Ingeniería Mecánic

Algorithms for meshing smooth surfaces and their volumes

Ph.DDOCTOR OF PHILOSOPH

Between Algorithm and Model: Different Molecular Surface Definitions for the Poisson-Boltzmann based Electrostatic Characterization of Biomolecules in Solution

The definition of a molecular surface which is physically sound and computationally efficient is a very interesting and long standing problem in the implicit solvent continuum modeling of biomolecular systems as well as in the molecular graphics field. In this work, two molecular surfaces are evaluated with respect to their suitability for electrostatic computation as alternatives to the widely used Connolly-Richards surface: the blobby surface, an implicit Gaussian atom centered surface, and the skin surface. As figures of merit, we considered surface differentiability and surface area continuity with respect to atom positions, and the agreement with explicit solvent simulations. Geometric analysis seems to privilege the skin to the blobby surface, and points to an unexpected relationship between the non connectedness of the surface, caused by interstices in the solute volume, and the surface area dependence on atomic centers. In order to assess the ability to reproduce explicit solvent results, specific software tools have been developed to enable the use of the skin surface in Poisson-Boltzmann calculations with the DelPhi solver. Results indicate that the skin and Connolly surfaces have a comparable performance from this last point of view

Towards Skeleton based Reconstruction : From Projective Skeletonization to Canal Surface Estimation

International audienceWe present a novel approach to reconstruct a 3D object from images corresponding to two different viewpoints: we estimate the skeleton of the object instead of its surface. The originality of the method is to be able to reconstruct a tubular object with a limited number of input images. Unlike classical reconstruction methods, like multi-view stereo or more recently structure-from-motion, this approach does not rely on interest points but estimates the topology of the object and derives its surface. Our contribution are twofold. First, given two perspective images of the 3D shape, the projection of the skeleton is computed in 2D. Secondly the 3D skeleton is reconstructed from the two projections using triangulation and matching. A mesh is finally derived for each skeleton branch

Caractérisation de la projection du squelette d'une surface canal 3D : Application à la reconstruction 3D à partir de deux images

International audienceNous présentons dans cet article une nouvelle approche pour reconstruire un objet 3D à partir de deux images de celui-ci. L'originalité de notre approche vient du fait que nous n'estimons pas directement la surface de l'objet 3D mais son squelette. Ce travail s'appuie sur les deux contributions suivantes. Premièrement, nous décrivons la relation existant entre un squelette 3D et sa projection, orthographique ou perspective, sur un plan image. Ensuite, nous montrons comment retrouver le squelette 3D à partir de deux de ses projections. Contrairement aux méthodes de reconstruction 3D classiques qui génèrent un nuage de points sans maillage, cette approche a pour avantage de reconstruire aussi la topologie de l'objet, c'est-à-dire d'en retrouver un maillage sans traitement annexe. Nous traitons ici des objets représentables par un squelette 3D curviligne et nous supposons aussi que les points de vue sont calibrés

A Guide to Additive Manufacturing

This open access book gives both a theoretical and practical overview of several important aspects of additive manufacturing (AM). It is written in an educative style to enable the reader to understand and apply the material. It begins with an introduction to AM technologies and the general workflow, as well as an overview of the current standards within AM. In the following chapter, a more in-depth description is given of design optimization and simulation for AM in polymers and metals, including practical guidelines for topology optimization and the use of lattice structures. Special attention is also given to the economics of AM and when the technology offers a benefit compared to conventional manufacturing processes. This is followed by a chapter with practical insights into how AM materials and processing parameters are developed for both material extrusion and powder bed fusion. The final chapter describes functionally graded AM in various materials and technologies. Throughout the book, a large number of industrial applications are described to exemplify the benefits of AM

Study of Finite Elements-based reliability and maintenance algorithmic methodologies analysis applied to aircraft structures and design optimization

This thesis presents the development of a research methodology oriented to the analysis of an aircraft structure in terms of operational reliability and maintainability requirements regarding its airworthiness. The study has been focused on modern commercial aircraft models, carrying out a market research and model selection according to different criteria. The study then develops a practical implementation consisting of the design approach of the aircraft airframe and main structural components for its subsequent numerical analysis and simulation. The numerical simulations will be computed by application of the Finite Elements Method on the main structural systems of the aircraft and establishment of boundary conditions. These simulations will allow the development of a computational study on linear, non-linear, and transient simulations of static loads, buckling, modal analysis, temperature, fatigue and thermal stress of individual structures and full assembly in different conditions. Finally, these results will be assessed and exported to a Matlab code which will compute an algorithmic methodology in order to approach the operational reliability and safety of the aircraft in the studied conditions. The thesis will conclude with a review of airworthiness regulations a proposal of research paths and further development of the methodology implemented

SHAPE DEFORMATION FOR OBJECTS OF GREATLY DISSIMILAR SHAPES WITH SMOOTH MANIFOLD

Ph.DDOCTOR OF PHILOSOPH