A new class of trigonometric B-Spline Curves

We construct one-frequency trigonometric spline curves with a de Boor-like algorithm for evaluation and analyze their shape-preserving properties. The convergence to quadratic B-spline curves is also analyzed. A fundamental tool is the concept of the normalized B-basis, which has optimal shape-preserving properties and good symmetric properties

AutoGraff: towards a computational understanding of graffiti writing and related art forms.

The aim of this thesis is to develop a system that generates letters and pictures with a style that is immediately recognizable as graffiti art or calligraphy. The proposed system can be used similarly to, and in tight integration with, conventional computer-aided geometric design tools and can be used to generate synthetic graffiti content for urban environments in games and in movies, and to guide robotic or fabrication systems that can materialise the output of the system with physical drawing media. The thesis is divided into two main parts. The first part describes a set of stroke primitives, building blocks that can be combined to generate different designs that resemble graffiti or calligraphy. These primitives mimic the process typically used to design graffiti letters and exploit well known principles of motor control to model the way in which an artist moves when incrementally tracing stylised letter forms. The second part demonstrates how these stroke primitives can be automatically recovered from input geometry defined in vector form, such as the digitised traces of writing made by a user, or the glyph outlines in a font. This procedure converts the input geometry into a seed that can be transformed into a variety of calligraphic and graffiti stylisations, which depend on parametric variations of the strokes

Transporte transmembranar de aniões por moléculas sintéticas: uma investigação por métodos de modelação molecular

Ion transport across cell membranes, via protein membrane channels, is crucial in several biological processes. Thus, the malfunctioning of this complex cellular machinery is linked with several channelopathies, such as cystic fibrosis (CF), associated with the deficient chloride transport through the CFTR channel. As present treatments only aim to manage the disease’s symptoms, alternative treatments are needed, such as channel replacement therapies. Over the last decades, this fact has motivated the development of synthetic anion transporters able to recognise and later promote the passive anion transport in lipid vesicles or even in CF cell models. However, the design of small drug-like transporters is still not straightforward and depends on an intricate equilibrium between the transporters’ binding affinity and lipophilicity. In this context, this thesis interfaces between the supramolecular, medicinal and computational fields of Chemistry. The theoretical investigations reported in this thesis consisted on quantum calculations together with molecular dynamics simulations based on classical force fields. The following series of molecules were investigated: two series of tripodal molecules (chapters II and V), a series of decalin-based transporters (chapter III) and four series of squaramide-based compounds (chapter IV). The structural and energetic insights allowed to understand, at the atomistic level, the interaction of synthetic molecules with membrane models as well as the anion transport mechanisms. The molecular dynamics simulations of passive diffusion were carried out with chloride complexes placed either in the water phase or inside the phospholipid bilayer, allowing the investigation of the transporters’ ability to permeate the water/lipid interface and to diffuse within the highly packed bilayer medium. Moreover, the assessment of the electrostatic surface potential of the transporters yielded insights that generally correlate well with anion binding constants. In chapters IV and V, constrained molecular dynamics simulations with linear squaramides and fluorinated tripodal derivatives are reported, respectively. These simulations allowed to estimate the free energy barriers associated with the translocation of these two series of molecules across the membrane model, with the reconstruction of the potential of mean force along the bilayer normal. The energetic barriers assessed for both series of molecules agree well with their lipophilicities and experimental anion transport data. Furthermore, a simulation reported in chapter V shows, for the first time, a neutral transporter facilitating the translocation of chloride across a phospholipid bilayer. Within the scope of supramolecular Chemistry, chapter VI reports the development of force field parameters for chalcogen bonding interactions. These bonding interaction, as well as halogen bonds, can also be used for the recognition and transmembrane transport of anions, becoming potential alternatives to the ubiquitous hydrogen bonds studied in the previous chapters.O transporte de aniões através de membranas celulares, com recurso a canais proteicos, é fundamental em vários processos biológicos. Assim, o funcionamento deficiente desta complexa maquinaria celular está relacionado com o aparecimento de várias canalopatias como a Fibrose Cística (FC), associada ao transporte deficiente de cloreto através do canal CFTR. Os tratamentos atuais para esta doença apenas minoram os seus sintomas, sendo necessário desenvolver tratamentos alternativos, como, por exemplo, as terapias de substituição de canal. Este facto, ao longo das últimas décadas, tem motivado o desenvolvimento de moléculas capazes de procederem ao reconhecimento e, posteriormente, ao transporte passivo de aniões em vesículas lipídicas e em modelos celulares de FC. No entanto, uma molécula com atividade de transporte depende de um delicado equilíbrio entre sua a lipofilia e a afinidade para o anião. Neste contexto, esta tese situa-se na interface entre Química supramolecular, medicinal e computacional. Os estudos teóricos que aqui se reportam consistiram em cálculos de mecânica quântica conjugados com simulações de dinâmica molecular baseados em campos de forças clássicos. Foram investigadas duas séries de moléculas trípodes (capítulos II e V), uma de transportadores derivados de decalina (capítulo III), e quatro séries de esquaramidas (capítulo IV). Os resultados estruturais e energéticos obtidos contribuíram para compreender, ao nível atómico, a interação destas moléculas com modelos de membranas, bem como dos respetivos mecanismos de transporte de aniões. As simulações de dinâmica molecular de difusão passiva foram realizadas com os complexos de cloreto colocados na fase aquosa ou dentro da bicamada fosfolipídica, permitindo o estudo da capacidade de um transportador permear a interface água/lípido e de se difundir no meio altamente empacotado da bicamada. Por outro lado, a avaliação da distribuição do potencial electroestático na superfície eletrónica das moléculas correlaciona-se com as suas constantes de associação com aniões. Nos capítulos IV e V descrevem-se também simulações de dinâmica molecular constrangidas, realizadas com esquaramidas lineares e derivados trípodes fluorinados, respetivamente. Estas simulações permitiram a estimativa das barreiras de energia livre associadas à difusão destas duas séries de moléculas através do modelo de membrana por reconstrução do potencial de força média ao longo da normal à bicamada. As barreiras energéticas para estas duas séries de moléculas são consistentes com os dados experimentais de transporte e lipofilia. Adicionalmente, uma simulação reportada no capítulo V mostra, pela primeira vez, um transportador neutro a facilitar o transporte de cloreto através de uma bicamada fosfolipídica. No âmbito da Química supramolecular, no capítulo VI reporta-se o desenvolvimento de parâmetros de campo de forças para ligações de calcogénio. Estas ligações, tal como as ligações de halogénio, também permitem o reconhecimento e transporte transmembranar de aniões, surgindo como potenciais alternativas às ligações de hidrogénio convencionais estudadas nos capítulos anteriores.Mais ainda, os estudos apresentados nesta tese foram realizados com recursos computacionais adquiridos sob o projeto P2020-PTDC/QEQ-SUP/4283/2014, financiado pela FCT e pelo Fundo Europeu de Desenvolvimento Regional (FEDER) através do COMPETE 2020 − Programa Operacional Competitividade e Internacionalização.Programa Doutoral em Biomedicin

Advances on Mechanics, Design Engineering and Manufacturing III

This open access book gathers contributions presented at the International Joint Conference on Mechanics, Design Engineering and Advanced Manufacturing (JCM 2020), held as a web conference on June 2–4, 2020. It reports on cutting-edge topics in product design and manufacturing, such as industrial methods for integrated product and process design; innovative design; and computer-aided design. Further topics covered include virtual simulation and reverse engineering; additive manufacturing; product manufacturing; engineering methods in medicine and education; representation techniques; and nautical, aeronautics and aerospace design and modeling. The book is organized into four main parts, reflecting the focus and primary themes of the conference. The contributions presented here not only provide researchers, engineers and experts in a range of industrial engineering subfields with extensive information to support their daily work; they are also intended to stimulate new research directions, advanced applications of the methods discussed and future interdisciplinary collaborations

Collision-free path planning for robots using B-splines and simulated annealing

This thesis describes a technique to obtain an optimal collision-free path for an automated guided vehicle (AGV) and/or robot in two and three dimensions by synthesizing a B-spline curve under geometric and intrinsic constraints. The problem is formulated as a combinatorial optimization problem and solved by using simulated annealing. A two-link planar manipulator is included to show that the B-spline curve can also be synthesized by adding kinematic characteristics of the robot. A cost function, which includes obstacle proximity, excessive arc length, uneven parametric distribution and, possibly, link proximity costs, is developed for the simulated annealing algorithm. Three possible cases for the orientation of the moving object are explored: (a) fixed orientation, (b) orientation as another independent variable, and (c) orientation given by the slope of the curve. To demonstrate the robustness of the technique, several examples are presented. Objects are modeled as ellipsoid type shapes. The procedure to obtain the describing parameters of the ellipsoid is also presented

Multi-Objective structural optimization of repairs of blisk blades

Modern manufacturing technologies offer multiple options to extend the service life of expensive jet engine components through repairs. In this context, the repair processes of blade-integrated disks (blisks) are of particular interest, as the complex design makes replacement of this part very costly. However, currently, repairs of blisks are mainly done manually and repair design decisions still rely on the expertise of maintenance technicians. From a scientific perspective, these subjective, experience-based decisions are a major drawback, as today’s computational methods allow for systematic analysis and evaluation of design alternatives. The present doctoral thesis contributes to the decision-making process related to the repair of blisk blades by blending and patching by providing an engineering optimization framework and simulation routines for structural assessment of different repair designs. First, an object-oriented optimization framework is developed that is ideally suited to address engineering optimization problems such as blisk repair optimization. The design of the software architecture is chosen to achieve a high degree of flexibility and modularity. In particular, the framework provides a unified interface for global and local derivative-free optimization algorithms and custom engineering optimization problems. Thereby, optimization of single- as well as multi-objective problems is supported. The broad applicability of the framework in engineering optimization is demonstrated using examples from wind energy research. Furthermore, the optimization framework forms a suitable environment for structural multi-objective optimization of blend and patch repairs. The second part of this thesis is devoted to the application of the optimization framework to blend repairs of a compressor blisk. The geometry of the removed blade part and the resulting blend is parameterized by three geometric design variables. The two objectives of the optimization correspond to two modal criteria, because especially the vibration behavior of blades is affected by this kind of geometric modification. To check if frequency requirements are harmed by the repair the first objective reflects the deviation of the natural frequencies of the repaired blade to the natural frequencies of the nominal blade. The second objective considers resonance conditions by evaluating the proximity of natural frequencies to excitation frequencies. Pareto optimal repair designs are found by solving the derived optimization problem using appropriate structural mechanics models of a blade sector and employing the developed optimization framework. By analyzing the optimal blend shapes for two different damage patterns, it is shown that the characteristics of Pareto frontiers, like the occurrence of discontinuities, are damage-specific. Therefore, it is concluded that design decisions on blend repairs have to be made on a case-by-case basis. The third part of this thesis is concerned with the multi-objective optimization of patch repairs. While blend repairs change the blade geometry, patch repairs restore the original blade contour. In terms of structural integrity, the most significant modification due to patching is hence associated with the welding process to join patch and blade. The remaining residual stresses, affect the strength of the repaired blade, are therefore the most critical aspect of patch repairs. Utilizing the engineering optimization framework and the parametric simulation model, a multi-objective optimization problem is solved considering the length of the weld and the fatigue strength of the repaired blade. In addition to fatigue strength properties, the weld length is selected as an optimization goal, since the manufacturing effort of the high-tech repair is of practical importance. Pareto optimal repair designs are presented for a damage pattern at the leading edge. The optimization results are further complemented by subsequent thermal and mechanical simulations of the welding and heat treatment process. Different patch geometries are classified from the Pareto optimal solutions. Depending on the preferences in terms of weld length and the High-Cycle Fatigue strength of different load cases, short or long patches are to be used. In addition, the results show that some potential patch designs are not optimal in any case, and therefore can be completely excluded. Finally, the benefits of the unified interface of the engineering optimization framework are emphasized. Different optimization settings of a patch repair optimization are presented and compared utilizing the hypervolume metric. Concluding remarks on the potential of computational methods for improved repair design and an outlook on future maintenance of blisks complete this work.DFG/SFB 871/119 193 472./E

Mechanical Engineering

The book substantially offers the latest progresses about the important topics of the "Mechanical Engineering" to readers. It includes twenty-eight excellent studies prepared using state-of-art methodologies by professional researchers from different countries. The sections in the book comprise of the following titles: power transmission system, manufacturing processes and system analysis, thermo-fluid systems, simulations and computer applications, and new approaches in mechanical engineering education and organization systems