Tesi sul tema "Flexible structure"
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1
Guy, Nicolas. "Modèle et commande structurés : application aux grandes structures spatiales flexibles". Thesis, Toulouse, ISAE, 2013. http://www.theses.fr/2013ESAE0036/document.
Testo completoAbstract (sommario):
Dans cette thèse, les problématiques de la modélisation et du contrôle robuste de l’attitude des grandes structures spatiales flexibles sont considérées. Afin de satisfaire les performances de pointage requises dans les scénarios des futures missions spatiales, nous proposons d’optimiser directement une loi de commande d’ordre réduit sur un modèle de validation d’ordre élevé et des critères qui exploitent directement la structure du modèle. Ainsi, les travaux de cette thèse sont naturellement divisés en deux parties : une partie relative à l’obtention d’un modèle dynamique judicieusement structuré du véhicule spatial qui servira à l’étape de synthèse ; une seconde partie concernant l’obtention de la loi de commande.Ces travaux sont illustrés sur l’exemple académique du système masses-ressort, qui est la représentation la plus simple d’un système flexible à un degré de liberté. En complément, un cas d’étude sur un satellite géostationnaire est traité pour valider les approches sur un exemple plus réaliste d’une problématique industrielleIn this thesis, modeling and robust attitude control problems of large flexible space structures are considered. To meet the required pointing performance of future space missions scenarios, we propose to directly optimize a reduced order control law on high order model validation and criteria that directly exploit the model structure. Thus, the work of this thesis is naturally divided into two parts : one part on obtaining a wisely structured dynamic model of the spacecraft to be used in the synthesis step, a second part about getting the law control. This work is illustrated on the example of the academic spring-masses system, which is the simplest representation of a one degree of freedom flexible system. In addition, a geostationary satellite study case is processed to validate developed approaches on a more realistic example of an industrial problem
2
O'Connor, Joseph. "Fluid-structure interactions of wall-mounted flexible slender structures". Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/fluidstructure-interactions-of-wallmounted-flexible-slender-structures(1dab2986-b78f-4ff9-9b2e-5d2181cfa009).html.
Testo completoAbstract (sommario):
The fluid-structure interactions of wall-mounted slender structures, such as cilia, filaments, flaps, and flags, play an important role in a broad range of physical processes: from the coherent waving motion of vegetation, to the passive flow control capability of hair-like surface coatings. While these systems are ubiquitous, their coupled nonlinear response exhibits a wide variety of behaviours that is yet to be fully understood, especially when multiple structures are considered. The purpose of this work is to investigate, via numerical simulation, the fluid-structure interactions of arrays of slender structures over a range of input conditions. A direct modelling approach, whereby the individual structures and their dynamics are fully resolved, is realised via a lattice Boltzmann-immersed boundary model, which is coupled to two different structural solvers: an Euler-Bernoulli beam model, and a finite element model. Results are presented for three selected test cases - which build in scale from a single flap in a periodic array, to a small finite array of flaps, and finally to a large finite array - and the key behaviour modes are characterised and quantified. Results show a broad range of behaviours, which depend on the flow conditions and structural properties. In particular, the emergence of coherent waving motions are shown to be closely related to the natural frequency of the array. Furthermore, this behaviour is associated with a lock-in between the natural frequency of the array and the predicted frequency of the fluid instabilities. The original contributions of this work are: the development and application of a numerical tool for direct modelling of large arrays of slender structures; the characterisation of the behaviour of slender structures over a range of input conditions; and the exposition of key behaviour modes of slender structures and their relation to input conditions.
3
Yu, Jianbin. "Flexible reinforced pavement structure-sensitivity analysis". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0015/MQ52682.pdf.
Testo completo
4
Giannopapa, Christina-Grigoria. "Fluid structure interaction in flexible vessels". Thesis, King's College London (University of London), 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413425.
Testo completo
5
Blinn, Bart A. "Flexlab a flexible structure controls test platform". Ohio : Ohio University, 1997. http://www.ohiolink.edu/etd/view.cgi?ohiou1177609627.
Testo completo
6
Aneja, Ashish. "Structure-Property Relationships of Flexible Polyurethane Foams". Diss., Virginia Tech, 2002. http://hdl.handle.net/10919/29887.
Testo completoAbstract (sommario):
This study examined several features of flexible polyurethane foams from a structure-property perspective. A major part of this dissertation addresses the issue of connectivity of the urea phase and its influence on mechanical and viscoelastic properties of flexible polyurethane foams and their plaque counterparts. Lithium salts (LiCl and LiBr) were used as additives to systematically alter the phase separation behavior, and hence the connectivity of the urea phase at different scale lengths. Macro connectivity, or the association of the large scale urea rich aggregates typically observed in flexible polyurethane foams was assessed using SAXS, TEM, and AFM. These techniques showed that including a lithium salt in the foam formulation suppressed the formation of the urea aggregates and thus led to a loss in the macro level connectivity of the urea phase. WAXS and FTIR were used to demonstrate that addition of LiCl or LiBr systematically disrupted the local ordering of the hard segments within the microdomains, i.e., it led to a reduction of micro level connectivity or the regularity in segmental packing of the urea phase. Based on these observations, the interaction of the lithium salt was thought to predominantly occur with the urea hard segments, and this hypothesis was confirmed using quantum mechanical calculations. Another feature of this research investigated model trisegmented polyurethanes based on monofunctional polyols, or "monols", with water-extended toluene diisocyanate (TDI) based hard segments. The formulations of the monol materials were maintained similar to those of flexible polyurethane foams with the exceptions that the conventional polyol was substituted by an oligomeric monofunctional polyether of ca. 1000 g/mol molecular weight. Plaques formed from these model systems were shown to be solid materials even at their relatively low molecular weights of 3000 g/mol and less. AFM phase images, for the first time, revealed the ability of the hard segments to self-assemble and form lath-like percolated structures, resulting in solid plaques, even though the overall volume of the system was known to be dominated by the two terminal liquid-like polyether segments. In another aspect of this research, foams were investigated in which the ratios of the 2,4 and 2,6 TDI isomers were varied. The three commercially available TDI mixtures, i.e., 65:35 2,4/2,6 TDI, 80:20 2,4/2,6 TDI, and 100:0 2,4/2,6 TDI were used. These foams were shown to display marked differences in their cellular structure (SEM), urea aggregation behavior (TEM), and in the hydrogen bonding characteristics of the hard segments (FTIR). Finally, the nanoscale morphology of a series of 'model' segmented polyurethane elastomers, based on 1,4-butanediol extended piperazine based hard segments and poly(tetramethylene oxide) soft segments, was also investigated using AFM. The monodisperse hard segments of these 'model' polyurethanes contained precisely either one, two, three, or four repeating units. Not only did AFM image the microphase separated morphology of these polyurethanes, but it also revealed that the hard domains preferentially oriented with their long axis along the radial direction of the spherulites which they formed.Ph. D.
7
Kaushiva, Bryan D. "Structure-Property Relationships of Flexible Polyurethane Foams". Diss., Virginia Tech, 1999. http://hdl.handle.net/10919/28843.
Testo completoAbstract (sommario):
This study examined several structure-property features of flexible polyurethane foams that are important aspects of foam production. AFM and WAXS were used to demonstrate the existence, for the first time in typical polyurethane foam systems, of lamellae-like polyurea structures ca. 0.2 mm long and ca 5-10 nm across. Aggregations of these lamellae-like hard domains may be the polyurea balls typically observed via TEM. Diethanolamine, a widely used cross-linking agent in molded foams, was shown to disrupt ordering in the polyurea hard domains and alter the interconnectivity of hard domains by preventing the formation of lamellae-like structures. These changes were shown to lead to softening of the foam. Copolymer polyol is frequently applied as reinforcing filler in foams. It was found that a common method of adding this component alters the hard segment/soft segment (HS/SS) ratio, thus increasing the load bearing capacity of the foam. It was observed in this report that at constant HS/SS ratio, the copolymer polyol only increased load bearing under humid conditions. It was also shown that the collapse of the cellular structure of a foam prior to the point of urea precipitation alters the aggregation behavior of the hard domains and alters solid-state properties. Surfactant is thus suggested to play a secondary role in the development of the hard domains by maintaining the cellular structure in the foam as the phase separation occurs and at least until the polyurethane foam has more fully organized hard segment domains. It was found that cure temperature could be manipulated to predictably change interdomain spacings and hydrogen bond development in the polymer. Curing above 100°C was found to lower hard segment content for plaques of the same formulation possibly as a result of water and isocyanate vaporization. Apart from polyurethane materials, structure-property relationships were examined in cast blends based on poly(tetrafluoroethylene) (PTFE) and the terpolymer poly(tetrafluoroethylene-co-vinylidene fluoride-co-hexafluoropropylene) (FKM). This revealed that tensile and dynamic moduli could be predictably altered by controlling the degree of FKM cross-linking or by varying PTFE content in the film. Inducing PTFE fibrillation was found to yield higher modulus films without increasing PTFE content.Ph. D.
8
Aditya, Riza. "Secure electronic voting with flexible ballot structure". Thesis, Queensland University of Technology, 2005. https://eprints.qut.edu.au/16156/1/Riza_Aditya_Thesis.pdf.
Testo completoAbstract (sommario):
Voting is a fundamental decision making instrument in any consensus-based society. It is employed in various applications from student body elections, reality television shows, shareholder meetings, to national elections. With the motivation of better eciency, scalability, speed, and lower cost, voting is currently shifting from paper-based to the use of electronic medium. This is while aiming to achieve better security, such that voting result reflects true opinions of the voters. Our research focuses on the study of cryptographic voting protocols accommodating a flexible ballot structure as a foundation for building a secure electronic voting system with acceptable voting results. In particular, we search for a solution suitable for the preferential voting system employed in the Australian Federal Election. The outcomes of the research include: improvements and applications of batch proof and verication theorems and techniques, a proposed alternative homomorphic encryption based voting scheme, a proposed Extended Binary Mixing Gate (EBMG) mix-network scheme, a new threshold randomisation technique to achieve receipt-freeness property in voting, and the application of cryptographic voting protocol for preferential voting. The threats and corresponding requirements for a secure secret-ballot voting scheme are rst discussed. There are significant security concerns about the conduct of electronic voting, and it is essential that the voting results re ect the true opinions of the voters - especially in political elections. We examine and extend batch processing proofs and verifications theorems and proposed applications of the theorems useful for voting. Many instances of similar operations can be processed in a single instance using a batch technique based on one of the batch theorems. As the proofs and verications provide formal assurances that the voting process is secure, batch processing offers great efficiency improvements while retaining the security required in a real-world implementation of the protocol. The two main approaches in cryptographic voting protocols, homomorphic encryption based voting and mix-network based voting, are both studied in this research. An alternative homomorphic voting scheme using multiplicative homomorphism property, and a number of novel mix-network schemes are proposed. It is shown that compared to the mix-network approach, homomorphic encryption schemes are not scalable for straight-forward adaptation of preferential systems. One important requirement of secret-ballot voting is receipt-freeness. A randomisation technique to achieve receipt-freeness in voting is examined and applied in an ecient and practical voting scheme employing an optimistic mix-network. A more general technique using threshold randomisation is also proposed. Combination of the primitives, both the homomorphic encryption and mixnetwork approach, yields a hybrid approach producing a secure and ecient secret-ballot voting scheme accommodating a exible ballot structure. The resulting solution oers a promising foundation for secure and practical secret-ballot electronic voting accommodating any type of counting system.
9
Aditya, Riza. "Secure Electronic Voting with Flexible Ballot Structure". Queensland University of Technology, 2005. http://eprints.qut.edu.au/16156/.
Testo completoAbstract (sommario):
Voting is a fundamental decision making instrument in any consensus-based society. It is employed in various applications from student body elections, reality television shows, shareholder meetings, to national elections. With the motivation of better eciency, scalability, speed, and lower cost, voting is currently shifting from paper-based to the use of electronic medium. This is while aiming to achieve better security, such that voting result reflects true opinions of the voters. Our research focuses on the study of cryptographic voting protocols accommodating a flexible ballot structure as a foundation for building a secure electronic voting system with acceptable voting results. In particular, we search for a solution suitable for the preferential voting system employed in the Australian Federal Election. The outcomes of the research include: improvements and applications of batch proof and verication theorems and techniques, a proposed alternative homomorphic encryption based voting scheme, a proposed Extended Binary Mixing Gate (EBMG) mix-network scheme, a new threshold randomisation technique to achieve receipt-freeness property in voting, and the application of cryptographic voting protocol for preferential voting. The threats and corresponding requirements for a secure secret-ballot voting scheme are rst discussed. There are significant security concerns about the conduct of electronic voting, and it is essential that the voting results re ect the true opinions of the voters - especially in political elections. We examine and extend batch processing proofs and verifications theorems and proposed applications of the theorems useful for voting. Many instances of similar operations can be processed in a single instance using a batch technique based on one of the batch theorems. As the proofs and verications provide formal assurances that the voting process is secure, batch processing offers great efficiency improvements while retaining the security required in a real-world implementation of the protocol. The two main approaches in cryptographic voting protocols, homomorphic encryption based voting and mix-network based voting, are both studied in this research. An alternative homomorphic voting scheme using multiplicative homomorphism property, and a number of novel mix-network schemes are proposed. It is shown that compared to the mix-network approach, homomorphic encryption schemes are not scalable for straight-forward adaptation of preferential systems. One important requirement of secret-ballot voting is receipt-freeness. A randomisation technique to achieve receipt-freeness in voting is examined and applied in an ecient and practical voting scheme employing an optimistic mix-network. A more general technique using threshold randomisation is also proposed. Combination of the primitives, both the homomorphic encryption and mixnetwork approach, yields a hybrid approach producing a secure and ecient secret-ballot voting scheme accommodating a exible ballot structure. The resulting solution oers a promising foundation for secure and practical secret-ballot electronic voting accommodating any type of counting system.
10
Thompson, Hugh Patrick George. "Extending crystal structure prediction methods towards flexible molecules". Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708949.
Testo completo
11
Paraz, Florine. "Oscillation d'une plaque flexible dans un écoulement". Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4327/document.
Testo completoAbstract (sommario):
La physique de nage d’une nageoire caudale flexible est étudiée expérimentalement grâce à une plaque flexible immergée dans un écoulement uniforme. Le bord d’attaque est forcé par un mouvement harmonique, tandis que le bord de fuite répond passivement au forçage. Une résonance en amplitude dans la réponse est mise en évidence et révèle une forte interaction entre les fréquences naturelles de la plaque et celles du forçage. Les résultats expérimentaux suggèrent un rôle non trivial de l’amplitude de forçage, qui souligne le rôle des non linéarités dans ce problème. Pour avoir une meilleure compréhension de l'origine de ces non linéarités, un modèle analytique faiblement non linéaire a été développé. Nous supposons une plaque d'épaisseur nulle immergée dans un écoulement potentiel, sujette à une force de traînée résistive. La déflection de la plaque a ensuite été décomposée en un mode rigide, mimant le forçage en pilonnement et en modes propres de flexion d’une poutre dans le vide. Les prédictions de la réponse en amplitude et en fréquence du système forcé sont alors calculées. Les fréquences de résonances, ainsi que l’enveloppe de la déflection, sont en bon accord avec les résultats expérimentaux. Les performances du système, mesurées à travers la poussée générée, est également correctement prédite par la modélisation. L’accord entre les expériences et le modèle est étendu à une étude trouvée dans la littérature. Une optimisation analytique a été conduite et étendue à l’application de la bio-robotiqueThe physics of the swimming with a flexible caudal fin is studied experimentally by the means of an elastic plate immersed in a uniform water flow. The leading edge of the plate is forced into a harmonic motion, while its trailing edge responds passively to this actuation. A resonance response in amplitude is demonstrated, revealing a strong interaction between the natural frequencies of the plate and the forcing frequencies. Experimental results suggest a non-trivial role of the forcing amplitude, emphasizing the role of non linearities in this problem. To gain better insight into the origin of these non linearities, a weakly non linear model is developed. We model a quasi two-dimensional plate of zero thickness immersed in a potential flow and subject to a resistive drag-like force. The plate deflection is then decomposed into a forcing heaving mode and natural flexural modes. Predictions of the response in amplitude and frequency to a heave forcing system are then calculated. The frequencies of the resonances, as well as the shapes of the deflection, match the experimental results. The performance of the system measured through the generated thrust, is well predicted by the modelling. The experimental and modelling results presented here show (very) good agreement with the literature. Finally, an analytical optimization is undertaken and potential applications to bio-robotic are suggested
12
Suckley, Daniel R. "The structure Development High-Resilience Flexible Polyurethane Foam". Thesis, University of Manchester, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.518440.
Testo completo
13
Daily, David J. "Fluid-Structure Interactions with Flexible and Rigid Bodies". BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/3791.
Testo completoAbstract (sommario):
Fluid structure interactions occur to some extent in nearly every type of fluid flow. Understanding how structures interact with fluids and visa-versa is of vital importance in many engineering applications. The purpose of this research is to explore how fluids interact with flexible and rigid structures. A computational model was used to model the fluid structure interactions of vibrating synthetic vocal folds. The model simulated the coupling of the fluid and solid domains using a fluid-structure interface boundary condition. The fluid domain used a slightly compressible flow solver to allow for the possibility of acoustic coupling with the subglottal geometry and vibration of the vocal fold model. As the subglottis lengthened, the frequency of vibration decreased until a new acoustic mode could form in the subglottis. Synthetic aperture particle image velocimetry (SAPIV) is a three-dimensional particle tracking technique. SAPIV was used to image the jet of air that emerges from vibrating human vocal folds (glottal jet) during phonation. The three-dimensional reconstruction of the glottal jet found faint evidence of flow characteristics seen in previous research, such as axis-switching, but did not have sufficient resolution to detect small features. SAPIV was further applied to reconstruct the smaller flow characteristics of the glottal jet of vibrating synthetic vocal folds. Two- and four-layer synthetic vocal fold models were used to determine how the glottal jet from the synthetic models compared to the glottal jet from excised human vocal folds. The two- and four-layer models clearly exhibited axis-switching which has been seen in other 3D analyses of the glottal jet. Cavitation in a quiescent fluid can break a rigid structure such as a glass bottle. A new cavitation number was derived to include acceleration and pressure head at cavitation onset. A cavitation stick was used to validate the cavitation number by filling it with different depths and hitting the stick to cause fluid cavitation. Acceleration was measured using an accelerometer and cavitation bubbles were detected using a high-speed camera. Cavitation in an accelerating fluid occurred at a cavitation number of 1.
14
Akkala, James Marcus. "Flow structure and performance of a flexible plunging airfoil". Thesis, University of Iowa, 2013. https://ir.uiowa.edu/etd/2433.
Testo completoAbstract (sommario):
An investigation was performed with the intent of characterizing the effect of flexibility on a plunging airfoil, over a parameter space applicable to birds and flapping MAVs. The kinematics of the motion was determined using of a high speed camera, and the deformations and strains involved in the motion were examined. The vortex dynamics associated with the plunging motion were mapped out using particle image velocimetry (PIV), and categorized according to the behavior of the leading edge vortex (LEV). The development and shedding process of the LEVs was also studied, along with their flow trajectories. Results of the flexible airfoils were compared to similar cases performed with a rigid airfoil, so as to determine the effects caused by flexibility. Aerodynamic loads of the airfoils were also measured using a force sensor, and the recorded thrust, lift and power coefficients were analyzed for dependencies, as was the overall propulsive efficiency. Thrust and power coefficients were found to scale with the Strouhal number defined by the trialing edge amplitude, causing the data of the flexible airfoils to collapse down to a single curve. The lift coefficient was likewise found to scale with trailing edge Strouhal number; however, its data tended to collapse down to a linear relationship. On the other hand, the wake classification and the propulsive efficiency were more successfully scaled by the reduced frequency of the motion. The circulation of the LEV was determined in each case and the resulting data was scaled using a parameter developed for this specific study, which provided significant collapse of the data throughout the entire parameter space tested.
15
Aioun, F. "Commande robuste d'une structure flexible garantissant des performances optimales". Paris 11, 1993. http://www.theses.fr/1993PA112200.
Testo completoAbstract (sommario):
Le controle actif des vibrations dans les structures flexibles fait l'objet de recherches dans de nombreux domaines d'application (astronautique, robotique). Son principe consiste a attenuer, au moyen de sources de vibrations, l'amplitude des vibrations perturbatrices, en des points particuliers de la structure ou sont positionnes des capteurs. Pour cela, le regulateur doit: 1) garantir la stabilite robuste du systeme en boucle fermee vis-a-vis des dynamiques negligees et des incertitudes parametriques (frequences propres non amorties, facteurs d'amortissement des modes); 2) realiser l'attenuation de vibrations sinusoidales non stationnaires dans le temps (excitation de la structure par des machines tournantes, dont le regime de fonctionnement varie); 3) etre obtenu par une methode de synthese bien conditionnee numeriquement meme lorsque l'ordre du modele est eleve. Pour repondre a ces specifications, cette these presente, dans le cas d'un systeme monovariable d'ordre reduit egal a 10 (attenuation en un point de la structure), des methodes de synthese basees sur le theoreme du faible gain ou le critere de nyquist (synthese h#, q-synthese, -synthese) qui permettent l'optimisation des performances pour des contraintes de robustesse de la stabilite fixees. Les regulateurs obtenus par ces approches sont d'ordre eleve (30 a 50) mais cet ordre peut etre fortement reduit en supprimant les etats peu observables ou commandables (20). L'extension au cas des systemes d'ordre eleve est envisagee par une approche, basee sur un decouplage frequentiel des regulateurs (methode des regulateurs emboites) qui ne donne pas des resultats satisfaisants en simulation (performances insuffisantes)
16
Hui, Shirley. "FlexSADRA: Flexible Structural Alignment using a Dimensionality Reduction Approach". Thesis, University of Waterloo, 2005. http://hdl.handle.net/10012/1173.
Testo completoAbstract (sommario):
A topic of research that is frequently studied in Structural Biology is the problem of determining the degree of similarity between two protein structures. The most common solution is to perform a three dimensional structural alignment on the two structures. Rigid structural alignment algorithms have been developed in the past to accomplish this but treat the protein molecules as immutable structures. Since protein structures can bend and flex, rigid algorithms do not yield accurate results and as a result, flexible structural alignment algorithms have been developed. The problem with these algorithms is that the protein structures are represented using thousands of atomic coordinate variables. This results in a great computational burden due to the large number of degrees of freedom required to account for the flexibility. Past research in dimensionality reduction techniques has shown that a linear dimensionality reduction technique called Principal Component Analysis (PCA) is well suited for high dimensionality reduction. This thesis introduces a new flexible structural alignment algorithm called FlexSADRA, which uses PCA to perform flexible structural alignments. Test results show that FlexSADRA determines better alignments than rigid structural alignment algorithms. Unlike existing rigid and flexible algorithms, FlexSADRA addresses the problem in a significantly lower dimensionality problem space and assesses not only the structural fit but the structural feasibility of the final alignment.
17
Warnakulasuriya, Hapuhennedige Surangith. "Soil structure interaction of buried pipes". Thesis, University of East London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286607.
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18
Algarra, Nicolas Pierre. "Pénétration d'une fibre flexible dans un milieu granulaire dense". Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066500/document.
Testo completoAbstract (sommario):
Nous étudions de manière expérimentale un cas d’interaction fluide/structure entre une fibre élastique et un milieu granulaire dense proche du jamming. Dans notre dispositif expérimental horinzontal, un milieu granulaire bidimensionnel, aléatoire et dense est en interaction avec une fibre élastique encastrée. L'extrémité encastrée de cette fibre est en translation par rapport aux grains tandis que son extrémité libre fait initialement face au flux de grains dans une géométrie de pénétration, avant de se défléchir par interaction avec les grains. Les paramètres de contrôle de notre système sont la compacité du milieu granulaire, la longueur et la rigidité de la fibre. Notre dispositif nous permet de mesurer la déformée de la fibre, les efforts que les grains exercent sur la fibre, notamment la force de traînée et de suivre les réorganisation du milieu granulaire. Sous certaines conditions expérimentales, nous avons observé que ce système présente plusieurs régimes d'évolution. A faible et à forte déflexions de la fibre, le système connaît une évolution stochastique, liée à la nature aléatoire du milieu granulaire : respectivement de petites fluctuations de la fibre autour de sa position d'équilibre et des événements brusques de balayage de la fibre en flexion associés à des avalanches granulaires. La transition entre ces deux régimes est associée à une brisure de symétrie qui affecte tant la fibre que le milieu granulaire. Dans une première partie, nous étudions comment la déflexion de la fibre est influencée par les paramètres de contrôle, en particulier par l'écart au jamming. Dans une seconde partie, nous montrons qu'une asymétrie de densité se développe dans le milieu granulaire lorsque la fibre est suffisamment défléchie. Dans une troisième partie, nous tentons de comprendre l'évolution des forces mesurées à l'aide de simulations numériques de l'Elastica sur une poutre sous chargement. Enfin, nous proposons un modèle de compaction des grains par la fibre qui est en bon accord avec l'évolution expérimentale du système. Une application de cette thèse est la compréhension des mécanismes de pénétration d'une racine ou d'une tige dans un sol granulaireWe study experimentally a fluid/structure interaction between an elastic fiber and a dense granular medium near the jamming transition. In our horizontal setup, a bidimensionnal and dense random packing is interacting with a clamped elastic fiber. The clamped end of the fiber is in translation relative to the the grains while the free end faces initially the grain flux in a penetration geometry before being deflected by grain/fiber interactions. The control parameters of our system are the packing fraction of the medium, the length and the rigidity of the fiber. Our setup allows us to measure the deflected shape of the fiber, the forces exerted by the grains on the fiber (including the drag force) and to follow the reorganizations of the granular medium. Under some experimental conditions, we observed that this system exhibits several regimes of evolution. For low and large fiber deflections, the system evolves stochastically as a consequence of the random nature of the granular medium : respectively small fluctuations of the fiber around its equilibrium position and sudden events of unlozding of the fiber in flexion associated to granular avalanches. The transition between those two regimes is associated with a symmetry breaking that affects the granular medium as well as the fiber. In a first part, we study how the fiber deflection is influenced by the control parameters, particularly by the distance to jamming. In a second part, we show that a packing fraction asymmetry appears in the granular medium when the fiber is deflected enough. In a third part, we try to understand the evolution of the measured forces using numerical simulations of the Elastica on a constrained beam. Finally, we propose a model of compaction of the grains by the fiber that is in a good aggreement with the experimental evolution of the system. An application of this thesis is the understanding of the mechanisms involved in the penetration of a root or a beam in a granular soil
19
Kerr, Murray. "Robust control of an articulating flexible structure using MIMO QFT /". [St. Lucia, Qld.], 2004. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe17449.pdf.
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20
Mao, Zhu. "Comparison of shape reconstruction strategies in a complex flexible structure". Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2008. http://wwwlib.umi.com/cr/ucsd/fullcit?p1450351.
Testo completoAbstract (sommario):
Thesis (M.S.)--University of California, San Diego, 2008.Title from first page of PDF file (viewed April 28, 2008). Available via ProQuest Digital Dissertations. Includes bibliographical references (p. 53-55).
21
Lin, Yeong Ching. "Controlling a large flexible structure to mimic a rigid one". Diss., The University of Arizona, 1990. http://hdl.handle.net/10150/185155.
Testo completoAbstract (sommario):
Analytical and experimental comparisons are presented for two control laws used in a laboratory structure designed to simulate large space structures. The proposed control laws are based on minimizing the amount of energy imparted to the flexible modes during the maneuver. Structure modeling and various control techniques are discussed. In the proposed modeling procedure, the finite element method is used to describe the equations of motion for a given structure. The main objective of the analysis is to determine optimal actuator locations and the command forces to the actuators such that the structure will follow a desired trajectory while minimizing the internal energy to the flexible modes. The numerical simulations are verified experimentally using a digital implementation of the control laws. Critical issues related to experimental implementation are discussed. A closed-loop control system design which will take care of nonlinearities and uncertain inputs is included in this dissertation.
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Schwellnus, Adrian. "Linear-Rational Term Structure Models With Flexible Level-Dependent Volatility". Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29215.
Testo completoAbstract (sommario):
The Linear-Rational Framework for the modelling of interest rates is a framework which allows for the addition of spanned and unspanned factors, while maintaining a lower bound on rates and tractable valuation of interest rate derivatives, particularly swaptions. The advantages of having all these properties are significant. This dissertation presents the Linear-Rational Framework, and specializes the factor process to a class of diffusion models which allows for the degree of state dependence of volatility to be estimated. This dissertation then finds that the estimated state dependent volatility structure is significantly different to that of typical models, where it is set it a priori. The effect the added degree of freedom has on the model implied swaption skew is then analysed.
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De, Greef Aline. "Towards medical flexible instruments: a contribution to the study of flexible fluidic actuators". Doctoral thesis, Universite Libre de Bruxelles, 2010. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210073.
Testo completoAbstract (sommario):
The medical community has expressed a need for flexible medical instruments. Hence, this work investigates the possibility to use "flexible fluidic actuators" to develop such flexible instruments. These actuators are driven by fluid, i.e. gas or liquid, and present a flexible structure, i.e. an elastically deformable and/or inflatable structure. Different aspects of the study of these actuators have been tackled in the present work:• A literature review of these actuators has been established. It has allowed to identify the different types of motion that these actuators can develop as well as the design principles underlying. This review can help to develop flexible instruments based on flexible fluidic actuators.
• A test bench has been developed to characterize the flexible fluidic actuators.
• A interesting measuring concept has been implemented and experimentally validated on a specific flexible fluidic actuator (the "Pneumatic Balloon Actuator", PBA). Ac- cording to this principle, the measurements of the pressure and of the volume of fluid supplied to the actuator allow to determine the displacement of the actuator and the force it develops. This means being able to determine the displacement of a flexible fluidic actuator and the force it develops without using a displacement sensor or a force sensor. This principle is interesting for medical applications inside the human body, for which measuring the force applied by the organs to the surgical tools remains a problem.
The study of this principle paves the way for a lot of future works such as the implemen- tation and the testing of this principle on more complex structures or in a control loop in order to control the displacement of the actuator (or the force it develops) without using a displacement or a force sensor.
• A 2D-model of the PBA has been established and has helped to better understand the physics underlying the behaviour of this actuator.
• A miniaturization work has been performed on a particular kind of flexible fluidic actu- ator: the Pleated Pneumatic Artificial Muscle (PPAM). This miniaturization study has been made on this type of actuator because, according to theoretical models, minia- turized PPAMs, whose dimensions are small enough to be inserted into MIS medical instruments, could be able to develop the forces required to allow the instruments to perform most surgical actions. The achieved miniaturized muscles have a design similar to that of the third generation PPAMs developed at the VUB and present a total length of about 90 mm and an outer diameter at rest of about 15 mm. One of the developed miniaturized PPAMs has been pressurized at p = 1 bar and it was able to develop a pulling force F = 100 N while producing a contraction of 4 %.
Propositions have been made regarding a further miniaturization of the muscles.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished
24
Lelong, Alexandra. "Etude expérimentale du comportement hydroélastique d'une structure flexible pour différents régimes d'écoulement". Thesis, Brest, 2016. http://www.theses.fr/2016BRES0048/document.
Testo completoAbstract (sommario):
Cette thèse vise à analyser expérimentalement une structure flexible et légère dans différents régimes d’écoulement, dont le régime cavitant. Un protocole expérimental a donc été mis en place afin de caractériser le comportement hydroélastique d’un profil NACA 0015 en polyoxyméthylène (POM) et de le comparer à un profil en acier inoxydable considéré comme « rigide ». Des mesures en écoulement subcavitant ont été réalisées : chargement hydrodynamique, contraintes, déformées statiques, réponse vibratoire et champ de vitesse ont été mesurés pour les deux matériaux. Enfin, une analyse vibratoire a été menée en écoulement cavitant. Ces mesures nous ont permis de constater que les déformées statiques du profil flexible sont similaires aux déformations observées sur une poutre encastrée : la flexion est la déformation principale et la torsion est faible. Toutefois les performances du profil flexible sont moins bonnes que pour un profil rigide : la portance diminue tandis que la traînée augmente. D’autre part, il apparaît que la dynamique du profil est contrôlée par l’écoulement. En effet, lorsque l’incidence du profil est proche de l’angle de décrochage, une fréquence liée au détachement tourbillonnaire apparaît sur les spectres de vibration des profils. Elle conduit à une réduction des fréquences propres liées à la flexion : si l’influence de cette fréquence sur le profil rigide reste faible à basse vitesse, sa proximité avec la fréquence propre du profil flexible conduit à un lock-in. Celui-ci se produit également en écoulement cavitant : lorsque la poche de cavitation devient instable, sa fréquence d’oscillation devient très énergétique et prend le contrôle de la dynamique du profil flexible. Le lock-in prend fin quand une supercavitation se développe autour du profil. Il conduit à une augmentation de la masse ajoutée au profil alors qu’elle devrait diminuer en présence de vapeur d’eauThis work deals with an experimental analysis of a flexible and light lifting profile for various flow conditions, including cavitation. An experimental protocol was set up to study a flexible NACA 0015 made of polyoxymethylene (POM) and compare its behaviour with a foil made of steel, which is considered as rigid. The forces, strains, stresses and vibrations of the foils were measured, as well as the velocity field. Moreover, a vibratory analysis was performed in cavitating flow. The flexible foil behaves like a built-in beam : the deformations corresponds to predictions from the beam theory, with high bending and low twisting. These deformations imply lower lift and higher drag compared to the rigid foil. The vortex shedding frequency appears on the vibration spectra near stall. It increases with flow velocity and leads to a decrease of the natural bending frequency. But flexibility involves lower natural frequencies : the first bending frequency of the flexible foil is 3.5 times lower than the rigid one. This allows lock-in between the first bending frequency of the flexible foil and the vortex shedding frequency. Lock-in occurs in cavitating flows too : when cavitation becomes unstable, it oscillates with a frequency close to the bending natural frequency of the flexible foil. This lock-in ends when the cavitation number is low enough, what leads to a decrease of the cavitation oscillation frequency. In those conditions, the added mass of the flexible foil does not decrease with the cavitation number as the added mass of the rigid foil
25
Carstoiu, Benjamin Jean. "Material Fluidity: Sense - Will - Form, Alexandria, Virginia Maritime Museum". Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/30834.
Testo completoAbstract (sommario):
The goal of my thesis was to produce a building that lives in the spirit of water -
a universal substance that senses and responds to the will of the environment around it. Similar to water, the maritime museum adapts its form to external forces while borrowing and redistributing energy throughout an internal cohesive structure. The building serves as an instrument of measurement, etching the pattern of the tides in the night sky and measuring its own shifting form in relation to the moon - its form, constantly reformulates itself, and is analogous to the ebb and flow of progress in history of maritime navigation.
Located on North Union Street in Alexandria, Virginia, the building is anchored to the edge of the Potomac, taking full advantage of the endless source of energy that the river provides. The building's form derives itself from the interaction between structure and water. It borrows from the paradoxical behavior of water: the tendency to alternate between platonic spherical forms which occur through internal forces and the unraveling of the sphere in response to gravitational external forces applied to it.
The building's circular lighthouse on the northern end serves as a symbolic focal point as well as a central repository for the energy gathered by its two wings. The east wing closest to the water unravels in response to the 4 foot rise and drop of the tides, and borrows that energy to continually recreate an architecture in the image of itself. The west wing of the enclosed portion of the museum serves as a barrier and helps contain the water that is to be released through the lighthouse.
The lighthouse also forms a symbolic focal point for the city where light for navigation towards the waterfront, provides a point for people, boats and water to come together. During low tide, a gush of water is released through the lighthouse's inner vortex, as a waterwheel harnesses the lunar energy it is released as a single beam of a light into the sky with surplus energy stored for future use. The interplay between static form and dynamic form creates a building that is both anchored to earth and free to react to the spirit of the movement of the water.Master of Architecture
26
Harrington, William Burke. "Experimental verification of an optimal linear controller for a flexible structure". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA305316.
Testo completoAbstract (sommario):
Thesis (Degree of Aeronautical Astronautical Engineer) Naval Postgraduate School, December 1995."December 1995." Thesis advisor(s): B.N. Agrawal. Includes bibliographical references. Also available online.
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Gatzhammer, Bernhard [Verfasser]. "Efficient and Flexible Partitioned Simulation of Fluid-Structure Interactions / Bernhard Gatzhammer". München : Verlag Dr. Hut, 2015. http://d-nb.info/1067708928/34.
Testo completo
28
Firthriyah, Nural Hidayati. "Structure Development and Properties of Flexible Polyurethane Foam-Layered Silicate Nanocomposites". Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.503646.
Testo completo
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Castellanos, Diana C. "Analysis and design of a flexible structure for benchmaking robust controllers". Honors in the Major Thesis, University of Central Florida, 1993. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/111.
Testo completoAbstract (sommario):
This item is only available in print in the UCF Libraries. If this is your Honors Thesis, you can help us make it available online for use by researchers around the world by following the instructions on the distribution consent form at http://library.ucf.edu/Systems/DigitalInitiatives/DigitalCollections/InternetDistributionConsentAgreementForm.pdf You may also contact the project coordinator, Kerri Bottorff, at kerri.bottorff@ucf.edu for more information.Bachelors
Engineering
Computer Engineering
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Chaudhari, Devendra. "Experiments on the vibration control of a flexible structure using FPGA". Thesis, California State University, Long Beach, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10014956.
Testo completoAbstract (sommario):
The goal of this project is to develop, implement and test experimentally a state-feedback controller for the vibration control of a flexible structure, using an Active Mass Damper (AMD). Based on a previously developed model of the structure, a state-feedback controller with full observer has been implemented in the LabView (Laboratory Virtual Instrument Engineering Workshop) computational environment using the myRIO FPGA board (Field Programmable Gate Array). Experimental results show that the controller improves the structural response significantly by reducing the amplitude and duration of the response when the structure is subject to random earthquake-like excitations.
31
Reichard, Karl Martin. "Distributed-effect modal domain optical fiber senors for flexible structure control". Diss., Virginia Tech, 1991. http://hdl.handle.net/10919/39420.
Testo completo
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Wynn, Robert H. "The control of flexible structure vibrations using a cantilevered adaptive truss". Diss., Virginia Tech, 1990. http://hdl.handle.net/10919/39949.
Testo completo
33
Chun, Sangeon. "Nonlinear Fluid-Structure Interaction in a Flexible Shelter under Blast Loading". Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/29849.
Testo completoAbstract (sommario):
Recently, numerous flexible structures have been employed in various fields of industry. Loading conditions sustained by these flexible structures are often not described well enough for engineering analyses even though these conditions are important. Here, a flexible tent with an interior Collective Protection System, which is subjected to an explosion, is analyzed. The tent protects personnel from biological and chemical agents with a pressurized liner inside the tent as an environmental barrier. Field tests showed unexpected damage to the liner, and most of the damage occurred on tent's leeward side.
To solve this problem, various tests and analyses have been performed, involving material characteristics of the liner, canvas, and zip seals, modeling of the blast loading over the tent and inside the tent, and structural response of the tent to the blast loading as collaborative research works with others. It was found that the blast loading and the structural response can not be analyzed separately due to the interaction between the flexible structure and the dynamic pressure loading. In this dissertation, the dynamic loadings imposed on both the interior and the exterior sides of the tent structure due to the airblasts and the resulting dynamic responses were studied. First, the blast loadings were obtained by a newly proposed theoretical method of analytical/empirical models which was developed into a FORTRAN program. Then, a numerical method of an iterative Fluid-Structure Interaction using Computational Fluid Dynamics and Computational Structural Dynamics was employed to simulate the blast wave propagation inside and outside the flexible structure and to calculate the dynamic loads on it.
All the results were compared with the field test data conducted by the Air Force Research Laboratory. The experimental pressure data were gathered from pressure gauges attached to the tent surfaces at different locations. The comparison showed that the proposed methods can be a good design tool to analyze the loading conditions for rigid or flexible structures under explosive loads. In particular, the causes of the failure of the liner on the leeward were explained. Also, the results showed that the effect of fluid-structure interaction should be considered in the pressure load calculation on the structure where the structural deflection rate can influence the solution of the flow field surrounding the structure.Ph. D.
34
Liu, Yanan. "Dynamics of flexible and Brownian filaments in viscous flow". Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCC196/document.
Testo completoAbstract (sommario):
La dynamique de filaments flexibles individuels en écoulement visqueux est une étape essentielle pour comprendre et contrôler la rhéologie de nombreux fluides complexes. Cette dynamique sous-tend également une multitude de processus biophysiques allant de la propulsion des micro-organismes aux écoulements intracellulaires. Cette thèse présente des expériences systématiques permettant d’étudier la dynamique de filaments flexibles browniens dans un écoulement visqueux. Nous avons choisi d’utiliser un biopolymère, l’actine, comme système modèle de filaments. Sa longueur typique varie de 1 à 100 μm, il est flexible à ces échelles avec une longueur de persistance de l’ordre de 20μm, à cause de ses petites dimensions, il est soumis aux forces Browniennes avec des fluctuations en flexion, et enfin il peut être marqué en fluorescence. Nous utilisons des dispositifs microfluidiques associés à des systèmes de contrôle d’écoulements, un microscope optique équipé́ avec une platine motorisée pour réaliser des expériences contrôlées permettant de suivre la dynamique des filaments d’actine dans un écoulement de cisaillement pur et dans un écoulement élongationnel. Pour les expériences en cisaillement pur, des simulations reproduisant les conditions expérimentales ont aussi été́ menées en utilisant la théorie des poutres inextensibles d’Euler-Bernoulli et la théorie non locale des corps élancés en présence de fluctuations Browniennes et sont en accord quantitatif avec les résultats expérimentaux. Nous montrons que la dynamique des filaments dans ce système est principalement régie par le nombre élasto-visqueux, nombre sans dimension comparant les forces de trainée visqueuses aux forces de flexion élastiques, les fluctuations thermiques ne jouant qu’un rôle secondaire. Nous présentons une caractérisation complète des différents modes de déformation subies par le filament pendant une rotation ainsi que des transitions entre les différents modes. Dans la géométrie élongationnelle, nous avons choisi un canal hyperbolique optimisé pour permettre de longs temps de résidence sous taux de déformation constant. Nous avons observé́ directement la suppression des fluctuations transverse dans la partie extensionnelle tandis que nous observons, dans la partie compressive la formation de structures hélocoïdales tridimensionnelles après le flambage du filament. Pour finir, ce manuscrit de thèse décrit des développements expérimentaux permettant de fabriquer des suspensions de filaments d’actine relativement monodisperse en taille ainsi que des résultats préliminaires sur des effets rhéofluidifiants. Au bilan, les résultats présentes dans ce manuscrit pose les premières pierres de travaux futurs en direction de l’étude de la dynamique de ces filaments dans des écoulements plus complexes comme des écoulements de Poiseuille ou oscillants. Ils permettent aussi d’envisager des études sur le lien entre déformations de particules et propriétés des suspensions diluées d’objets flexibles et Brownien, lien encore peu étudié du point de vue expérimentalThe dynamics of individual flexible filament in a viscous flow is the key to deciphering the rheolog- ical behavior of many complex fluids and soft materials. It also underlies a wealth of biophysical processes from flagellar propulsion to intracellular streaming. This thesis presents systematic exper- iments to investigate the dynamics of flexible and Brownian filaments in viscous flows. Biopolymer actin has been chosen to be our experimental model filament: its typical length can be varied from 1 to 100 μm, it is flexible at these dimensions with a persistence length in the order of 20μm, it is Brow- nian due to its small diameter with bending fluctuations and it can be labelled by fluorescent dye. Microfluidic channels and flow control systems are combined to optical microscope with automated stage to carry out well-controlled experiments on the diverse dynamics of actin filaments in shear flow and pure straining flow. In shear flow, simulations matching the experimental conditions have also been performed using inextensible Euler-Bernoulli beam theory and non-local slender body hy- drodynamics in the presence of thermal fluctuations and agree quantitatively with the experimental results. We demonstrate that filament dynamics in this flow geometry is primarily governed by a dimension- less elasto-viscous number comparing viscous forces to elastic forces with thermal fluctuations only playing a secondary role. We present a complete characterization of the different modes of defor- mation undergone by the filament while rotating as well as of the transitions between these different modes. In pure straining flow, we opt to use an optimized hyperbolic channel to allow long resi- dence time at constant strain rate to be applied. We directly observe the suppression of transverse fluctuations in the extensional part of the hyperbolic channel while we observe, in the compressive part of the flow, the formation of three dimensional helical structures subsequent to the initial buck- ling of the filament. Finally, this thesis manuscript also reports on experimental developments to fabricate suspensions of actin filament with a narrow distribution of lengths and on preliminary re- sults on shear-thinning effects. All together the results presented here pave the way of future studies towards the understanding of filament dynamics in more complex flows, as Poiseuille flows or oscil- latory flows, as well as towards establishing the link between filament deformations and rheological response in dilute suspensions of flexible Brownian filaments, which remains nearly unexplored from an experimental point of view
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Cole, Robert Edward. "Numerical Modeling of Air Cushion Vehicle Flexible Seals". Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/83828.
Testo completoAbstract (sommario):
Air cushion vehicle flexible seals operate in a complex and chaotic environment dominated by fluid-structure interaction. An efficient means to explore interdependencies between various governing parameters that affect performance is through high fidelity numerical simulation. As previous numerical efforts have employed separate iterative partitioned solvers, or have implemented simplified physics, the approaches have been complex, computationally expensive, or of limited utility. This research effort performs numerical simulations to verify and validate the commercial multi-physics tool STAR-CCM+ as a stand-alone partitioned approach for fluid-structure interaction problems with or without a free surface. A dimensional analysis is first conducted to identify potential non-dimensional forms of parameters related to seal resistance. Then, an implicit, Reynolds-averaged Navier-Stokes finite volume fluid solver is coupled to an implicit, nonlinear finite element structural solver to successfully replicate benchmark results for an elastic beam in unsteady laminar flow. To validate the implementation as a seal parameter exploratory tool, a planer bow seal model is developed and results are obtained for various cushion pressures and inflow speeds. Previous numerical and experimental results for deflection and resistance are compared, showing good agreement. An uncertainty analysis for inflow velocity reveals an inversely proportional resistance dependency. Using Abaqus/Explicit, methodologies are also developed for a two-way, loosely coupled explicit approach to large deformation fluid-structure interaction problems, with and without a free surface. Following numerous verification and validation problems, Abaqus is ultimately abandoned due to the inability to converge the fluid pressure field and achieve steady state. This work is a stepping stone for future researchers having interests in ACV seal design and other large deformation, fluid-structure interaction problems. By modeling all necessary physics within a verified and validated stand-alone approach, a designer's ability to comprehensively investigate seal geometries and interactions has never been more promising.Ph. D.
36
Madani, Kermani Seyed Hossein. "Application of immersed boundary method to flexible riser problem". Thesis, Brunel University, 2014. http://bura.brunel.ac.uk/handle/2438/9605.
Testo completoAbstract (sommario):
In the recent decades the Fluid-Structure Interaction (FSI) problem has been of great interest to many researchers and a variety of methods have been proposed for its numerical simulation. As FSI simulation is a multi-discipline and a multi-physics problem, its full simulation consists of many details and sub-procedures. On the other hand, reliable FSI simulations are required in various applications ranging from hemo-dynamics and structural engineering to aero-elasticity. In hemo-dynamics an incompressible fluid is coupled with a flexible structure with similar density (e.g. blood in arteries). In aero-elasticity a compressible fluid interacts with a stiff structure (e.g. aircraft wing) or an incompressible flow is coupled with a very light structure (e.g. Parachute or sail), whereas in some other engineering applications an incompressible flow interacts with a flexible structure with large displacement (e.g. oil risers in offshore industries). Therefore, various FSI models are employed to simulate a variety of different applications. An initial vital step to conduct an accurate FSI simulation is to perform a study of the physics of the problem which would be the main criterion on which the full FSI simulation procedure will then be based. In this thesis, interaction of an incompressible fluid flow at low Reynolds number with a flexible circular cylinder in two dimensions has been studied in detail using some of the latest published methods in the literature. The elements of procedures have been chosen in a way to allow further development to simulate the interaction of an incompressible fluid flow with a flexible oil riser with large displacement in three dimensions in future. To achieve this goal, a partitioned approach has been adopted to enable the use of existing structural codes together with an Immersed Boundary (IB) method which would allow the modelling of large displacements. A direct forcing approach, interpolation / reconstruction, type of IB is used to enforce the moving boundary condition and to create sharp interfaces with the possibility of modelling in three dimensions. This provides an advantage over the IB continuous forcing approach which creates a diffused boundary. And also is considered as a preferred method over the cut cell approach which is very complex in three dimensions with moving boundaries. Different reconstruction methods from the literature have been compared with the newly proposed method. The fluid governing equation is solved only in the fluid domain using a Cartesian grid and an Eulerian approach while the structural analysis was performed using Lagrangian methods. This method avoids the creation of secondary fluid domains inside the solid boundary which occurs in some of the IB methods. In the IB methods forces from the Eulerian flow field are transferred onto the Lagrangian marker points on the solid boundary and the displacement and velocities of the moving boundary are interpolated in the flow domain to enforce no-slip boundary conditions. Various coupling methods from the literature were selected and improved to allow modelling the interface and to transfer the data between fluid and structure. In addition, as an alternative method to simulate FSI for a single object in the fluid flow as suggested in the literature, the moving frame of reference method has been applied for the first time in this thesis to simulate Fluid-Structure interaction using an IB reconstruction approach. The flow around a cylinder in two dimensions was selected as a benchmark to validate the simulation results as there are many experimental and analytical results presented in the literature for this specific case.
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Kourmoulis, Panayiotis Konstantinos. "Parallel processing in the simulation and control of flexible beam structure systems". Thesis, University of Sheffield, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359846.
Testo completo
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Jiang, Jian Hua M. Eng Massachusetts Institute of Technology. "Performance evaluation of innovative toggle brace damper for flexible structure seismic upgrade". Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/99602.
Testo completoAbstract (sommario):
Thesis: M. Eng., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 72-73).
Amplifying the motion of viscous dampers has been recognized as an effective solution to mitigate structural response to wind and seismic excitation. Motion amplification devices are designed to amplify a small interstory drift to intensify the stroke of the dampers attached. The efficiency of such devices relies on their geometric configurations in addition to the stiffness of the support elements. This thesis focuses on the seismic performance evaluation of the toggle brace frame configuration employed for seismic upgrade. In order to carry out a performance evaluation of the toggle brace damper, a practical approach to performance-based earthquake engineering (PBEE) is presented in this study. The approach considers the seismic hazard, structural response, resulting damage, and repair costs associated with restoring the building to its original condition using a fully probabilistic analysis. The procedure is organized to be consistent with conventional building designs, construction, and analysis practices so that it can be readily incorporated into a design process. A nine-story moment frame located in downtown Los Angeles based on pre-Northridge design code is subjected to PBEE evaluation in this study. The performance of the structural frame is assessed by conducting a non-linear dynamic time history analysis in both cases, with and without the inclusion of the toggle brace damper. The results and comparisons are detailed in the chapters of this thesis.
by Jian Hua Jiang.
M. Eng.
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Olivier, Mathieu. "A fluid-structure interaction partitioned algorithm applied to flexible flapping wing propulsion". Doctoral thesis, Université Laval, 2014. http://hdl.handle.net/20.500.11794/25395.
Testo completoAbstract (sommario):
Cette thèse concerne l’étude des ailes oscillantes flexibles et des méthodes numériques qui s’y rattachent. De ce fait, la thèse est divisée en deux parties. La première contribution concerne le développement d’un algorithme de couplage fluide-structure qui prend en charge les interactions entre un solide élastique en grands déplacements et un fluide incompressible. L’algorithme est basé sur une approche partitionnée et permet d’utiliser des codes numériques de mécanique des fluides et de mécanique des solides existants. L’utilisation d’un terme de compressibilité artificiel dans l’équation de continuité du fluide combinée à des choix algorithmiques judicieux permet d’utiliser cette méthode de couplage efficacement avec un code de mécanique des fluides utilisant une méthode de projection de type SIMPLE ou PISO. La seconde contribution est l’étude de l’effet de flexibilité des ailes sur le vol à ailes battantes. Deux principaux régimes de vol sont mis en évidence concernant la déformation de l’aile : déformation causée par la pression et déformation causée par l’inertie. Les effets de ces régimes sur la topologie de l’écoulement et sur les performance de l’aile en propulsion sont discutés. Il est montré que les cas avec des déformations causées par la pression présentent généralement des efficacités plus élevées avec une flexibilité modérée. Il en est de même pour la force de poussée lorsque l’amplitude de tangage est faible. D’autre part, lorsque les déformations sont causées par l’inertie, les performances de l’aile sont généralement réduites. Certains cas montrent une augmentation marginale des performances lorsque le synchronisme des déformations est optimal, mais ces cas représentent davantage une exception que la norme. Il est également démontré que la flexibilité peut être utilisée comme mécanisme de tangage passif tout en conservant des performances intéressantes. Enfin, un modèle d’aile oscillante flexible non contraint est présenté. Il est démontré que le mouvement de déviation observé dans la nature est une conséquence d’un phénomène aérodynamique de mise en drapeau.This thesis concerns the study of flexible flapping wings and the related numerical methods. It thus contains two distinct themes. The first contribution is the implementation of an efficient fluid-structure interaction algorithm that handles the interaction of an elastic solid undergoing large displacement with an incompressible fluid. The algorithm is based on the partitioned approach and allows state-of-the-art fluid and structural solvers to be used. Stabilization with artificial compressibility in the fluid continuity equation along with judicious algorithmic choices make the method suitable to be used with SIMPLE or PISO projection fluid solvers. The second contribution is the study of the effects of wing flexibility in flapping flight. The different regimes, namely inertia-driven and pressure-driven wing deformations are presented along with their effects on the topology of the flow and, eventually, on the performance of the flapping wing in propulsion regime. It is found that pressure-driven deformations can increase the thrust efficiency if a suitable amount of flexibility is used. Thrust increases are also observed when small pitching amplitude cases are considered. On the other hand, inertia-driven deformations generally deteriorate aerodynamic performances of flapping wings unless meticulous timing is respected, making them less practical. It is also shown that wing flexibility can act as a passive pitching mechanism while keeping decent thrust and efficiency. Lastly, a freely-moving flexible flapping wing model is presented. It is shown that the deviation motion found in natural flyers is a consequence of a feathering mechanism.
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Liu, Ding. "On intrinsically live structure and deadlock control of generalized Petri nets modeling flexible manufacturing systems". Thesis, Paris, CNAM, 2015. http://www.theses.fr/2015CNAM1004/document.
Testo completoAbstract (sommario):
Nos travaux portent sur l'analyse des systèmes de production automatisée à l'aide de réseaux de Petri. Le problème posé est de savoir si un système peut se bloquer complètement ou partiellement et si besoin de calculer un contrôleur garantissant son bon fonctionnement. Les systèmes de production se modélisent naturellement à l'aide d'une sous-classe des réseaux de Petri, les S3PRs. Ce modèle a été très largement étudie par le passe conduisant à des méthodes basées uniquement sur la structure du modèle. Dans ce travail, nous généralisons ces travaux aux modèles des WS3PR, une extension des S3PR ou la réalisation d'une active nécessite non par une ressource mais plusieurs ressources d'un même type et pour lesquels nous proposons des techniques originales combinant des éléments de Théorie des graphes et de théorie des nombres, améliorant même les méthodes du passe sur le modèle simple des S3PR.On présente une caractérisation fine de la vivacité d'un tel modèle basée la notion d'attente circulaire. Une attente circulaire peut être vue comme une composante connexe du sous graphe réduit aux transitions et aux places ressources du modèle. Puis nous démontrons que la non vivacité d'un WS3PR est équivalente a l'existence d' ≪ un blocage circulaire dans une attente circulaire ≫. Ce résultat généralise finement la caractérisation de la vivacité d'un S3PR. Apres avoir introduit la notion de ≪ circuits du graphe de ressources ≫ (WSDC), on construit une méthode de contrôle de ces verrous garantissant la vivacité du modèle d'autant plus efficace qu'une méthode de décomposition du réseau est proposée. Enfin, une traduction de traduit la condition de vivacité des WS3PR sous la forme d'un programme linéaire en nombres entiers est établie et des expérimentations ont démontré l'intérêt de la méthode pour contrôle de systèmes l'allocation des ressourcesAs an indispensable component of contemporary advanced manufacturing systems, flexible manufacturing systems (FMSs) possess flexibility and agility that traditional manufacturing systems lack. An FMS usually consists of picking and placing robots, machining centers, logistic systems, and advanced control systems. Some of them can be recognized as its shared resources, which result in its flexibility but may lead to its deadlocks. As a classic problem in resource allocation systems, deadlocks may arise in a fully automated FMS and bring about a series of disturbing issues, from degraded and deteriorated system productivity and performance to low utilization of some critical and expensive resources and even long system downtime. Therefore, the analysis of and solution to deadlock problems are imperative for both a theoretical investigation and practical application of FMSs. Deadlock-freedom means that concurrent produc-tion processes in an FMS will never stagnate. Furthermore, liveness, another significant behavioral property, means that every production process can always be finished. Liveness implies deadlock-freedom, but not vice versa. The liveness-enforcement is a higher requirement than deadlock-freedom.From the perspective of the behavioral logic, the thesis focuses on the intrinsicallylive structures and deadlock control of generalized Petri nets modeling flexible manufacturing systems. Being different from the existing siphon-based methods, a concept of intrinsically live structures becomes the starting point to design, analyze, and optimize a series of novel deadlock control and liveness-enforcing methods in the work.The characteristics and essence of intrinsically live structures are identified and derived from subclasses of generalized Petri nets modeling FMSs with complex resource usage styles. In addition, the numerical relationship between initial markings and weights of connecting arcs is investigated and used to design restrictions that ensure the intrinsical liveness of global or local structures.With the structural theory, graph theory, and number theory, the thesis work achieves the goals of deadlock control and liveness-enforcement.The proposed methods are superior over the traditional siphon-based oneswith a lower computational complexity (or a higher computational efficiency),a lower structural complexity, and a better behavioral permissiveness of the controlled system
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Gomes, Jorge Miguel Pereira [Verfasser], e Franz [Akademischer Betreuer] Durst. "Fluid-structure interaction-induced oscillation of flexible structures in uniform flows. / Jorge Miguel Pereira Gomes. Betreuer: Franz Durst". Erlangen : Universitätsbibliothek der Universität Erlangen-Nürnberg, 2012. http://d-nb.info/1024406776/34.
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Chalvet, Vincent. "Conception, réalisation et commande d'un microrobot numérique, planaire, non-redondant et en technologie MEMS". Phd thesis, Université de Franche-Comté, 2013. http://tel.archives-ouvertes.fr/tel-00913321.
Testo completoAbstract (sommario):
Le développement récent en micro- et nano-technologies (dans des domaines tels que l'horlogerie, l'électronique, l'optique, le biomédical, . . .) a créé un fort besoin concernant des systèmes capables de manipuler et d'assembler des objets de plus en plus petits. La conception de stations robotisées, capables de manipuler des micro-objets, s'est multipliée à travers le monde, faisant intervenir des actionneurs de haute résolution adaptés au micromonde, ainsi que de nombreux capteurs. Ce mémoire ouvre une nouvelle voie pour le développement de robots de micromanipulation. Il présente la conception, la modélisation, la fabrication et la commande d'un nouveau concept de microrobot, le DiMiBot (Digital MicroroBot). Il s'agit du premier microrobot numérique - inspiré de l'électronique numérique - qui fait intervenir des actionneurs binaires pour générer un déplacement discret d'une grande précision sans nécessiter de capteur (en boucle ouverte). Ces actionneurs binaires extrêmement répétables et robustes (les modules bistables), assurent chacun un déplacement précis de 25 μm. Ils sont associés de manière monolithique à une architecture robotique parallèle flexible, assurant la génération d'un espace de travail discret, dont les 2N (N est le nombre de modules bistables utilisés au sein du DiMiBot) positions distincts atteignables sont parfaitement stables, répétables et robustes mécaniquement. Elles sont réparties de manière homogène dans un carré de10,5 μm de côté. La microfabrication du premier prototype de microrobot numérique en silicium - faisant suite à un dimensionnement minutieux en éléments finis - a été réalisé au sein de la salle blanche MIMENTO de l'institut FEMTO-ST. Ce DiMiBot possédant 4 modules bistables assure une résolution de 3,5 μm pour une répétable de chacune des 16 positions atteignables de 90 nm.
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Naito, J., Z. Y. Tan, M. Shikida, M. Hirota e K. Sato. "Characteristics of On-Wall In-Tube Flexible Thermal Flow Sensor at Wrap Pipe Condition". IEEE, 2007. http://hdl.handle.net/2237/9560.
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Yi, Tianyi. "Experimental Investigation and Numerical Simulation of an Unreinforced Masonry Structure with Flexible Diaphragms". Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5149.
Testo completoAbstract (sommario):
Unreinforced masonry (URM) construction, which has been widely used in the United States, presents a large threat to life safety and regional economic development because of its poor seismic resistance. In this research, the nonlinear seismic properties of URM structures were investigated via a quasi-static test of a full-scale two-story URM building and associated analytical and numerical studies.
The tests of the 24ft. by 24ft. in plan 22ft. high URM building revealed that the damage was characterized by (1) the formation of large discrete cracks in the masonry walls and (2) the rocking and sliding of URM piers. Both of these results were consistent with the predictions based on individual component properties obtained in previous research. However, the tests also revealed significant global behavior phenomena, including flange effects, overturning moment effects, and the formation of different effective piers in a perforated wall. This global behavior greatly affected the response of the URM building tested.
In order to understand the nonlinear behavior of the test structure, a series of analytical studies were conducted. First, at the material level, a mechanical key model was proposed to describe the failure of URM assemblages under a biaxial state of stress. Second, at the component level, an effective pier model was developed to illustrate the mixed failure modes of a URM pier and its nonlinear force-deformation relationship. Third, at the structure level, a nonlinear pushover model was built using the mechanical models at the material and component levels to describe the nonlinear properties of a URM building. This nonlinear pushover model and a three-dimensional finite element model were employed to analyze the test structure. Both gave results in good agreement with the test data. Improvements to current provisions for the evaluation of existing masonry structures were proposed.
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Sato, Kazuo, Mitsuhiro Shikida, Hirotaka Hida e Jeong Il Lee. "Microfabricated 3D Flexible Tactile Sensor with Table-shaped Structure for Intelligent Robot Fingers". IEEE, 2011. http://hdl.handle.net/2237/14445.
Testo completo
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Michelsons, A. M. "Turin between Fordism and flexible specialization : industrial structure and social change, 1970-85". Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233971.
Testo completoAbstract (sommario):
Turin has long been a town in which almost all economic activities were finalized to the mass production of cars, while the choices of its economic developments depended on those of the car firm, Fiat. In the 1950s and 1960s, both Turinese industry and labour market were tightly organised by Fiat in a pyramid-like structure, at the top of which were the car company and its workers respectively. Fiat's efforts to 'rationalize' and control the local labour and components market were not accompanied by a similar strategy towards social structure. Fiat limited itself to supporting the conservative political parties in office in Turin, which were able to gain a stable consensus by Tuninese petty bourgeoisis, but were not far-sighted enough to try to integrate the immigrant workers through a policy of reforms and services. This turned out in a very conflictual pattern of industrial relations in the late 1960s. Thus, the economic crisis which hit the mass-production firms worldwide in the mid-1970s had particularly negative effects on Fiat, due to bitter industrial relations within the plants. Elsewhere, as the large mass-production firms did not recover from the crisis, the segmentation of product markets and the availability of the new electronically-based technologies, which allow a greater flexibility together with high levels of productivity, fostered the emergence of a new competitive model of industrial organization: flexible specialization. These very market and technological conditions, interacting with the local social dynamics, also helped a wide reorganization of Turinese industry which ceased to depend strictly on Fiat's choices and orders. At the same time, the social structure of Turin became much more differentiated and the strategies of social actors proved to be no longer as linked to Fiat's decisions as in the past. Instead, throughout the 1970s Fiat was unable to respond to the new conditions of competition and to undertake a deep process of restructuring, due to the unpreparedness of its own management and to the strict unions' control over its moves. Only once the unions had been defeated in 1980, Fiat was able to take the lead among European car makers in a few years in terms of sales, technology and market strategy. My dissertation tries, therefore, to answer to the following questions: how did it happen? And how did the mentioned endogenous and exogenous factors influence Fiat's strategy? How is the Turinese model of industrial organization at the present, and what is Fiat's role in it?
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Newman, Scott M. "Active damping control of a flexible space structure using piezoelectric sensors and actuators". Thesis, Monterey, California. Naval Postgraduate School, 1992. http://hdl.handle.net/10945/23517.
Testo completoAbstract (sommario):
Approved for public release; distribution is unlimitedThis thesis details the experimental analysis of an active damping control technique applied to the Naval Postgraduate School's Flexible Spacecraft Simulator using piezoceramic sensors and actuators. The mass property of the flexible arm is varied to study the frequency effects on the Positive Position Feedback (PPF) algorithm. Multi-modal dynamics response is analytically studied using a finite-element model of a cantilevered beam while under the influence of three different control laws: a basic law derived rom the Lyapunov Stability Theorem, PPF and Strain Rate Feedback (SRF). The advantages and disadvantages of using PPF and SRF for active damping control are discussed.
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Herman, Deborah Ann. "Discrete and continuous dynamics modeling of a mass moving on a flexible structure". Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/42526.
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YU, YU-CONG, e 余裕琮. "Variable structure control of large-scale flexible structures". Thesis, 1988. http://ndltd.ncl.edu.tw/handle/67816930879393486046.
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Kanchanasaratool, Narongsak. "Control of flexible structure". Phd thesis, 2003. http://hdl.handle.net/1885/148681.
Testo completo