Dissertations / Theses: 'Flexible structures'

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Guy, Nicolas. "Modèle et commande structurés : application aux grandes structures spatiales flexibles." Thesis, Toulouse, ISAE, 2013. http://www.theses.fr/2013ESAE0036/document.

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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 industrielle
In 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

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Montgomery, Darcy Thomas. "Milling of flexible structures." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/29689.

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Current manufacturing research aims at increasing productivity by optimal selection of process parameters. This is accomplished by understanding the fundamental physics of individual manufacturing processes. In this thesis, peripheral milling of very flexible cantilevered plates is studied. The static and dynamic deflections of the plate under periodic milling forces are modelled. A new dynamic cutting force model is developed which considers five discrete zones of relative motion between the tool and the workpiece. The kinematics of both milling and vibratory motions are modelled, which is an original research contribution in this area. It is shown that the penetration of the tool into the workpiece during vibratory cutting has a strong influence on the damping and stiffness characteristics of the milling process. A structural model of a discontinuous cantilevered plate is determined using the finite element method. A reduced order structural model at the tool-workpiece contact zone is implemented for discrete time response analysis of the plate under cutting force excitations during milling. The closed loop dynamic behaviour of the system is modelled and taken into account in the analysis. Simulations of plate machining are compared with experimental results. A model of the surface finish generation mechanism is deduced from the analysis and experimental results. Applications of this research include peripheral milling of integral jet engine impellers, computer disk drives and other flexible mechanical components.
Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate

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Villarreal, Seth. "EXAMINING FLEXIBLE BIOLOGICAL STRUCTURES." Case Western Reserve University School of Graduate Studies / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=case1414772850.

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Lee, Seung-Yoon. "Geometrically exact modeling and nonlinear mechanics of highly flexible structures /." free to MU campus, to others for purchase, 2002. http://wwwlib.umi.com/cr/mo/fullcit?p3074421.

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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.

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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.

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Pimm, Andrew James. "Analysis of flexible fabric structures." Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/12162/.

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This thesis is primarily aimed at carrying out analysis of Energy Bags, reinforced fabric bags used for subsea compressed air energy storage. Subsea compressed air energy storage is a completely new method of large-scale energy storage designed to be integrated with direct-compression offshore wind turbines and wave energy converters. Energy Bags are impermeable bags anchored to the seabed at significant depths (e.g. 500m) in which high pressure air, compressed by specially designed wind turbines and wave energy converters, is stored at pressures roughly equal to the hydrostatic pressure of the surrounding water. Energy Bags do not need to be particularly strong because most of the reaction to the pressure load is provided by the surrounding water, and high energy densities are available at such depths as 500m. This thesis investigates the deformed shapes of Energy Bags and studies optimal designs. Three analysis methods are developed which vary in their complexity, ease of use, and accuracy. First, a system of coupled ordinary differential equations (ODEs) is derived which describes the deformed shape of an axisymmetric Energy Bag. This model is later used in an optimisation study to find the shapes of bag which minimise the cost of materials (reinforcement, fabric, and ballast) per unit of energy stored. Circumferential reinforcement, hanging masses from the inside of the bag (which it was hoped would lower the total cost) and fill level are all included as variables in the optimisation, and it is found that for reasonable materials costs an Energy Bag could cost less than £10,000/MWh when anchored at 500m. This compares favourably with all other methods of large-scale energy storage. However, the bags used in the optimisation study have wide bases, which will require sealing against the seabed (unless water is to be allowed into the bags). Problems are encountered when trying to use the ODE method to find the shapes of partially inflated bags, and it is generally not very easy to use. Next, we carry out finite element analysis (FEA) of an axisymmetric Energy Bag using cable elements. This is much more user-friendly and flexible than the ODE method. Partially inflated bag shapes are found, and pressure-volume curves are presented which show the almost isobaric performance of an Energy Bag. It is found that material mass limits the extent to which the bag can be deflated before it becomes unstable. The axisymmetric FEA is used to study bags with much more realistic circumferential reinforcement than the ODE method, and we also look at bags with an unsealed base, which allow water in through the base as they deflate. A three-dimensional FEA tool is presented which models an Energy Bag as a cable-reinforced membrane using cable and membrane elements, and special measures had to be taken to deal with wrinkling. We assume that the bag is rotationally symmetric, comprising a number of symmetric lobes. The 3D FEA is used to find the stress distribution in the membrane of the bag, however a converged solution cannot always be found. It is not certain why this is the case but it is anticipated that it is because deformed bags are not always rotationally symmetric. The 3D FEA could also be used to model other membrane structures such as balloons, parachutes, roofs and sails, as well as nets. The standard cutting patterns for lobes in lobed balloons are analysed, and a new cutting pattern known as the Constant Tension lobe is generated. This is an extension of the Constant Radius lobe and takes into account the pressure gradient found in both air and water, minimising waste material. The Constant Tension lobe is particularly appropriate for Energy Bags because of the large pressure gradient in water. The Ultra High Performance Vessel architecture is also presented, upon which the design of the prototype Energy Bags is based. The fabric structure of an Ultra High Performance Vessel comprises only two sheets of fabric (rather than many separate lobes welded together), and tendon shortening and “bellows” serve to ensure that there is no meridional stress in the fabric. An analytical optimisation is used to show that the zero pressure bag that minimises cost of materials per unit of energy stored has equal costs of reinforcement and membrane. The axisymmetric FEA is also used to find the optimum bag size and maximum fill level for a bag which comes down to a single point at the base (as opposed to a wide base bag). Finally, testing of two 1.8m diameter superpressure Energy Bags has been commenced during the course of this work, and the prototypes and test rig are documented in this thesis. The prototypes were manufactured for us by Thin Red Line Aerospace Ltd., a Canadian manufacturer of deployable fabric structures for use in space. They are being cycled back-to-back in order to prove the concept, assess the performance of an Energy Bag over time, and identify any problems that need to be addressed. One of the bags had a few small leaks from the moment it was first inflated, but the other has remained airtight to date. It was found that if an Energy Bag is to be airtight, special attention must be paid to the welds at the seams and the sealing around the airline fittings.

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Vlajic, Nicholas A. "Dynamics of slender, flexible structures." Thesis, University of Maryland, College Park, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3628601.

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Dynamics of slender beam-like structures subjected to rotational motions is studied experimentally, numerically, and analytically within this dissertation. As the aspect ratio of beam-like structures is increased (i.e., as the structures become slender), the structure can undergo large elastic deformations, and in addition, the torsional and lateral motions can be strongly coupled. Two different paradigms of rotor systems are constructed and used to investigate coupled torsional-lateral motions in slender rotating structures. The first rotor model is a modified version of the classical Jeffcott rotor, which accounts for torsional vibrations and stator contact. Analysis and simulations indicate that torsional vibrations are unlikely to exist during forward synchronous whirling, and reveal the presence of phenomena with high-frequency content, such as centrifugal stiffening and smoothening, during backward whirling. The second rotor model is a nonlinear distributed-parameter system that has been derived with the intent of capturing dynamics observed in an experimental apparatus with slender, rotating structures. Nonlinear oscillations observed in the experiments contain response components at frequencies other than the drive speed, a feature that is also captured by predictions obtained from the distributed-parameter model. Further analysis of the governing partial-differential equations yields insights into the origins (e.g., nonlinear gyroscopic coupling and frictional forces) of the nonlinear response components observed in the spectrum of the torsion response. Slender structures are often subject to large deformations with pre-stress and curvature, which can drastically alter the natural frequencies and mode shapes when in operation. Here, a geometrically exact beam formulation based on the Cosserat theory of rods is outlined in order to predict the static configuration, natural frequencies, and mode shapes of slender structures with large pre-stress and curvature. The modeling and analysis are validated with experiments as well as comparisons with a nonlinear finite element formulation. The predictions for the first eight natural frequencies are found to be in excellent agreement with the corresponding experimentally determined values. The findings of this dissertation work have a broad range of applications across different length scales, including drill strings, space tethers, deployable structures, cable supported structures (e.g., bridges and mooring cables), DNA strands, and sutures for non-invasive surgery to name a few.

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Orr, John. "Flexible formwork for concrete structures." Thesis, University of Bath, 2012. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.566135.

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Concrete, our most widely used construction material, is a fluid that offers the opportunity to economically create structures of almost any geometry. Yet this unique fluidity is seldom capitalised on, with concrete instead being cast into rigid prismatic moulds to create high material use structures with large carbon footprints. Our rate of concrete consumption means that cement manufacture alone is estimated to account for some 5% of global Carbon Dioxide emissions. This dissertation shows that by replacing conventional orthogonal moulds with a flexible system comprised primarily of high strength, low cost fabric sheets, the fluidity of concrete can be utilised to create structurally optimised concrete structures. Flexible formwork therefore has the potential to facilitate the change in design and construction philosophy that will be required for a move towards a less material intensive, more sustainable, construction industry. Optimisation and design processes developed in this thesis show that material savings of up to 40% are possible in flexibly formed concrete beams. Full scale structural testing of these processes is undertaken to verify the flexural and shear behaviours of non-prismatic elements. This is supported by further experimental and theoretical investigations into the durability of concrete cast in a permeable, flexible mould. Detailed analysis is provided alongside practical guidance for designers. Coupled with innovation in design and analysis techniques, flexible formwork is shown to provide a globally accessible method for the construction of low carbon, materially efficient and architecturally interesting concrete structures. Recognising the impact construction has on the environment, design philosophies centred around the need to put material where it is required are becoming increasingly desirable. This can now be achieved by replacing rigid formworks with systems comprised of flexible sheets of fabric. This is a step change in the way we think about our new concrete structures.

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Hoberg, Theresa B. (Theresa Blinn). "Capillary flows in flexible structures." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/81604.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 73-75).
Interactions between capillary and elastic effects are relevant to a variety of applications, from micro- and nano-scale manufacturing to biological systems. In this thesis, we investigate capillary flows in extremely flexible, millimeter-scale cylindrical elastic tubes. We demonstrate that surface tension can cause sufficiently flexible tubes to collapse and coalesce spontaneously through non-axisymmetric buckling, and develop criteria for the initial deformation and complete collapse of a circular tube under capillary pressure. Experimental results are presented for capillary rise and evaporation of a liquid in a flexible tube. Several regimes are seen for the equilibrium state of a flexible tube under capillary pressure, and deformations of the tube walls are measured in different regimes and compared with a shell theory model. Good agreement is found between experiments and theory overall. Analysis and experimental results show that despite the complex and non-axisymmetric deformed shapes of cylindrical structures, the elastocapillary length used in previous literature for flat plates and sheets can also apply for flexible tubes, if the tube radius is used as the characteristic length scale.
by Theresa B. Hoberg.
S.M.

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Cui, Yuefeng. "Adaptive multistable flexible composite structures." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/25513.

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A composite laminate with unsymmetric layup may exhibit two distinct stable configurations at room temperature due to the residual thermal stresses imparted during curing. This bistability leads unsymmetric composite laminates to be good candidates for adaptive flexible structures in particular for the fields of aerospace and aircraft. To extend the application potential of bistable composite laminates, the multistable behaviour of continuous compound composite surfaces are investigated. Two connection approaches are presented in this research. By tailoring the asymmetric bistability of indi- vidual composite elements, continuous surfaces composed of series-connected bistable composite shells demonstrate a high degree of multistability. This model can be developed to design longer composite surfaces possessing more stable shapes. In addition, a high degree of multistability is achieved by connecting square composite elements in a tessellated feature. By reducing the interactions between adjacent elements, a tessellated surface composed of n bistable elements shows a theoretical maximum 2n stable shapes. Finally, potential applications of highly multistable composite surfaces are introduced. The proposed multistable designs improve the flexible functionality of the adaptive structures.

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Ward, Christina C. "Attitude control of flexible structures." Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA240520.

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Thesis (M.S. in Astronautical Engineering)--Naval Postgraduate School, September 1990.
Thesis Advisor(s): Agrawal, Brij N. Second Reader: Titus, Harold. "September 1990." Description based on title screen as viewed on December 17, 2009. DTIC Identifier(s): Attitude Control Systems, Flexible Structures, Spacecraft, Structural Response, Resonant Frequency, Experimental Design, Model Tests, Active Control, Gifts Computer Program, Dynamic Response, Computerized Simulation, Control Theory, Modal Analysis, Laboratory Tests, Theses. Author(s) subject terms: Attitude Control, Flexible Structures. Includes bibliographical references (p. 52). Also available in print.

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Bennighof, Jeffrey Kent. "Modeling and control of flexible structures." Diss., Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/49982.

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This dissertation is concerned with some topics in the modeling and control of large flexible structures. In the finite element convergence toward the natural modes and frequencies of a structure, it is found that two mechanisms limiting the accuracy of higher modes are, first, a decrease in the number of active degrees of freedom for higher mode approximations due to orthogonality constraints, and, second, the fact that lower computed, rather than actual, eigenfunctions appear in the orthogonality constraints, so that inaccuracy in lower modes inhibits convergence to higher modes. Refining the elements using the hierarchical p-version proves to be far superior to refining the mesh, as demonstrated by numerical examples. In the third chapter, a method is presented for solving the algebraic eigenvalue problem for a structure, which combines attractive features of the subspace iteration method and the component-mode synthesis methods. Reduced substructure models are generated automatically and coupled exactly to form a reduced structure model, whose eigensolution is used to refine the substructure models. Convergence is much faster than in the subspace iteration method, as demonstrated by numerical examples. In the fourth chapter, the effectiveness of modal control (IMSC) and direct feedback control, in which the actuator force depends only on the local velocity and displacement, are investigated for suppressing traveling waves on a string and on a beam, both with slight material damping. Direct feedback proves superior for the string, as more modes must be controlled than can be handled by modal control with a limited number of actuators, but inferior for the beam, as effort is wasted suppressing motion in higher modes where damping is pervasive, while modal control focuses effort on those lower modes which need to be controlled. The optimal vibration control for a distributed system subjected to persistent excitation is not available, so a two-part control is proposed in chapter five for suppressing the motion of a distributed system with a moving support. The first part cancels the moving support's excitation to an optimal extent, and the second is a direct velocity feedback control. A numerical example demonstrates the effectiveness of this control method.
Ph. D.
incomplete_metadata

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Carlsson, Martin. "Design and Testing of Flexible Aircraft Structures." Doctoral thesis, KTH, Aeronautical and Vehicle Engineering, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3761.

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Methods for structural design, control, and testing offlexible aircraft structures are considered. Focus is onnonconventional aircraft con- figurations and control concepts.The interaction between analysis and testing is a central topicand all studies include validation testing and comparisonbetween computational and experimental results.

The first part of the thesis is concerned with the designand testing of an aeroelastic wind-tunnel model representing aBlended Wing Body (BWB) aircraft. The investigations show thata somewhat simplified wind-tunnel model design concept isuseful and efficient for the type of investigations considered.Also, the studies indicate that well established numericaltools are capable of predicting the aeroelastic behavior of theBWB aircraft with reasonable accuracy. Accurate prediction ofthe control surface aerodynamics is however found to bedifficult.

A new aerodynamic boundary element method for aeroelastictimedomain simulations and its experimental validation arepresented. The properties of the method are compared totraditional methods as well as to experimental results. Thestudy indicates that the method is capable of efficient andaccurate aeroelastic simulations.

Next, a method for tailoring a structure with respect to itsaeroelastic behavior is presented. The method is based onnumerical optimization techniques and developed for efficientdesign of aeroelastic wind-tunnel models with prescribed staticand dynamic aeroelastic properties. Experimental validationshows that the design method is useful in practice and that itprovides a more efficient handling of the dynamic aeroelasticproperties compared to previous methods.

Finally, the use of multiple control surfaces andaeroelastic effects for efficient roll maneuvering isconsidered. The idea is to design a controller that takesadvantage of the elasticity of the structure for performancebenefits. By use of optimization methods in combination with afairly simple control system, good maneuvering performance isobtained with minimal control effort. Validation testing usinga flexible wind-tunnel model and a real-time control systemshows that the control strategy is successful in practice.Keywords: aeroelasticity, active aeroelastic structures,aeroelastic tailoring, control, structural optimization,wind-tunnel testing.

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Akpan, Unyime Okon. "Dynamics of flexible mobile manipulator structures." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ31515.pdf.

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Heinze, Sebastian. "Aeroelastic Concepts for Flexible Aircraft Structures." Doctoral thesis, Stockholm : Farkost och flyg Aeronautics and Vehicle Engineering, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4419.

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Heinze, Sebastian. "Aeroelastic Concepts for Flexible Wing Structures." Licentiate thesis, Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-244.

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ALMEIDA, PRISCILLA OLIVEIRA DE. "DYNAMIC OF ONE-DIMENSIONAL FLEXIBLE STRUCTURES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2006. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=9232@1.

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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Nesse trabalho, calcula-se a dinâmica de sistemas contínuos unidimensionais. Problemas de barras e vigas com diferentes condições de contorno e condições intermediárias são tratados no contexto da formulação fraca para que seja aplicado o Método de Elementos Finitos; e então seja possível calcular as aproximações das freqüências naturais e dos modos de vibração do sistema. Uma vez conhecidos os modos (exata ou aproximadamente), constrói-se um modelo reduzido de equações diferenciais ordinárias e, então, calcula-se a dinâmica do sistema. Essa dissertação propõe um material didático a ser utilizado no curso de Vibrações, com o intuito de auxiliar os alunos de graduação no estudo de sistemas contínuos, através do desenvolvimento da formulação fraca e aplicação do MEF.
In this work, the dynamic of one-dimensional continuum systems is calculated. Problems of bars and beams with different boundary and intermediate conditions are treated in the context of weak formulation, so the Finite Element Method (FEM) can be applied; and it is possible to calculate the approximation of natural frequencies and vibration modes of the system. Once the modes are known (exactly or approximately), a reduced-model of ordinary differential equations is constructed and the dynamic of the system is calculated. This essay proposes a didactic material to be used at the Vibration course, with the purpose to help undergraduate students in the studies of continuum systems, through the development of the weak formulation and the application of the FEM.

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Acikgoz, Mehmet Sinan. "Seismic assessment of flexible rocking structures." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708891.

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Feghali, Habib Labib. "Seismic performance of flexible concrete structures /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.

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Hong, Tony. "Time-delayed control of flexible space structures." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq35189.pdf.

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Barsky, Michael Frederick. "Holographic sensing for control of flexible structures." Diss., This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-09162005-115002/.

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Stricher, Alain. "Tolérancement flexible d'assemblages de grandes structures aéronautiques." Phd thesis, École normale supérieure de Cachan - ENS Cachan, 2013. http://tel.archives-ouvertes.fr/tel-00824579.

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Comme son nom l'indique, le tolérancement flexible a pour objectif de tenir compte de la souplesse des pièces dans un processus de tolérancement. Il permet d'évaluer les défauts géométriques admissibles par des critères aussi bien géométriques que mécaniques. Ces travaux abordent en premier lieu l'élaboration de modèles adéquats permettant de prédire le comportement mécanique d'un assemblage de grandes pièces relativement souples lorsqu'elles sont sujettes à des défauts géométriques issues du procédé de fabrication. Une méthode a alors été proposée pour y implémenter des variations géométriques aléatoires réalistes vis-à-vis de ces hypothétiques défauts géométriques. Pour simuler les opérations d'assemblage, le phénomène de contact unilatéral et les variations de rigidité dues aux variabilités géométriques ont été prises en compte. En fonction de ces hypothèses, les stratégies d'analyse de tolérance avec Monte Carlo ou la méthode des coefficients d'influence ont été comparées afin de choisir celle minimisant les coûts de calcul tout en conservant la justesse des résultats. Finalement, ces travaux s'achèvent sur une étude de cas industriel : un treillis supportant des équipements sous le plancher du fuselage d'un Airbus A350.

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Tsakalotos, Orestis I. "Active control of flexible structures and manipulators." Thesis, University of Newcastle Upon Tyne, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316255.

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Hong, Chinsuk. "Active control of resiliently-mounted flexible structures." Thesis, University of Southampton, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.420248.

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Blackwood, Gary H. (Gary Howard). "Active vibration isolation for controlled flexible structures." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/12204.

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Saeed, Najmadeen. "Prestress and deformation control in flexible structures." Thesis, Cardiff University, 2014. http://orca.cf.ac.uk/69777/.

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A direct method for controlling nodal displacements and/or internal bar forces has been developed for prestressable structural assemblies including complex elements (“macro-elements”, e.g. the pantographic element), involving Matrix Condensation. The method is aimed at static shape control of geometrically sensitive structures. The dissertation discusses identification of the most effective bars for actuation, without incurring violation in bar forces, and also with objective of minimal number of actuators or minimum actuation. The method can also be used for adjustment of bar forces to either reduce instances of high forces or increase low forces (e.g. in a cable nearing slack). The techniques of controlling nodal displacement, bar force and simultaneously nodal displacement and bar force for a structure made of non-complex elements have been verified by experiments on the physical model of a cable-stayed bridge. Likewise the technique of joint displacement controlling of structures constructed from complex structural elements, has been also been confirmed by experiments on the physical model of an aerofoil shaped morphing pantographic structure. Overall, experimental results agree well with theoretical prediction. This dissertation also concerns with morphing structures, e.g. as applied in the aerospace industry. A morphing aerofoil structure capable of variable geometry was developed, which was shown to be able to cater for the different aerodynamic requirements at different stages of flight. In this thesis, two suitable morphing aerofoil structures were made of curved pantographic units. Results show that the configuration with a large number of small pantograph elements exhibits a wider range of Lift Coefficient (CL) and Drag Coefficient (CD) than achievable by the first, and also by the standard NACA2415 aerofoil with flaps. In addition, it was found that the morphing aerofoil can decrease the drag by more than 18%, especially in the early stages of morphing. Finally, two useful and relatively simple methods have been presented in this dissertation which provide a direct method for calculating required morphing shape displacements and calculating set of length actuations for bar assembly to adjust shape imperfection. Keywords: Static shape control, Prestress control, Displacement control, Actuator placement, Force Method, Pantographic unit, Morphing structure, Morphing aerofoil, NACA aerofoil, Aerodynamic characteristics.

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Stemple, Timothy J. "Dynamics and Control of Flexible Multibody Structures." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30407.

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The goal of this study is to present a method for deriving equations of motion capable of modeling the controlled motion of an open loop multibody structure comprised of an arbitrary number of rigid bodies and slender beams. The procedure presented here for deriving equations of motion for flexible multibody systems is carried out by means of the Principle of Virtual Work (often referred to in the dynamics literature as d'Alembert's Principle). We first consider the motion of a general flexible body relative to the inertial space, and then derive specific formulas for both rigid bodies and slender beams. Next, we make a small motions assumption, with the end result being equations for a Rayleigh beam, which include terms which account for the axial motion, due to bending, of points on the beam central axis. This process includes a novel application of the exponential form of an orthogonal matrix, which is ideally suited for truncation. Then, the generalized coordinates and quasi-velocities used in the mathematical model, including those needed in the spatial discretization process of the beam equations are discussed. Furthermore, we develop a new set of recursive relations used to compute the inertial motion of a body in terms of the generalized coordinates and quasi-velocities. This research was motivated by the desire to model the controlled motion of a flexible space robot, and consequently, we use the multibody dynamics equations to simulate the motion of such a structure, providing a demonstration of the computer program. For this particular example we make use of a new sequence of shape functions, first used by Meirovitch and Stemple to model a two dimensional building frame subjected to earthquake excitations.
Ph. D.

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Blinn, Bart A. "Flexlab a flexible structure controls test platform." Ohio : Ohio University, 1997. http://www.ohiolink.edu/etd/view.cgi?ohiou1177609627.

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Liu, Wei. "Vibration control of large scale flexible structures using magnetorheological dampers." Link to electronic thesis, 2005. http://www.wpi.edu/Pubs/ETD/Available/etd-031005-105004/.

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Genari, Helói Francico Gentil. "Damage-Tolerant Modal Control Methods for Flexible Structures." Thesis, Paris, ENSAM, 2016. http://www.theses.fr/2016ENAM0032/document.

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Les structures intelligentes sont de plus en plus présentes dans différentes industries et notamment dans les domaines de l'aéronautique et du génie civil. Ces structures sont dotées de fonctions qui leur permettent d'interagir avec leur environnement, d'adapter leurs caractéristiques structurelles (raideur, amortissement, viscosité, etc.) selon les besoins ou de surveiller leur état de santé ou « SHM » (Structural Health Monitoring). Aujourd’hui, les performances des méthodes de contrôle actif peuvent être considérablement dégradées lors de l’apparition d’endommagement. Le contrôle actif tolérant aux dommages ou « DTAC » (Damage Tolerant Active Control) est un champ de recherche récent qui s'intéresse à l'élaboration d'approches intégrées pour réduire les vibrations tout en surveillant l'intégrité de la structure, en identifiant les éventuels dommages, et en reconfigurant la loi de commande.Cette thèse apporte une contribution au DTAC en proposant une approche originale basée sur la norme H∞ modale . Les méthodes proposées se focalisent principalement sur le cas où plusieurs actionneurs et capteurs piézoélectriques non-collocalisés sont utilisés pour atténuer les vibrations des structures endommagées. Le manuscrit comprend quatre parties principales. Le chapitre 2 présente des rappels sur la commande H∞ et sur sa solution sous optimale obtenue par une approche par inégalité matricielle ou « LMI » (Linear Matrix Inequality), sur lesquels s’appuient les développements proposés dans ce travail. Le chapitre 3 décrit la norme H∞ modale introduite pour le contrôle actif des vibrations. Cette commande présente une sélectivité modale élevée, permettant ainsi de se concentrer sur les effets du dommage tout en bénéficiant des propriétés de robustesse qu'offre la commande H∞ vis-à-vis du spillover et des variations de paramètres. Une nouvelle stratégie de rejet des vibrations est proposée au chapitre 4. C'est une approche dite préventive où une prise en compte lors de l'élaboration de la commande H∞ modale, des zones fortement contraintes de la structure, où le risque d’endommagement est élevé est réalisée. Un algorithme SHM est proposé afin d'évaluer la sévérité du dommage pour chaque mode. Le chapitre 5 propose une nouvelle approche modale à double boucle de commande pour faire face à des endommagements imprévisibles. Un premier correcteur est conçu dans ce but pour satisfaire les contraintes de performance et de robustesse sur la structure saine, tandis que le second a pour objectif de conserver un contrôle satisfaisant quand un dommage survient. La loi de commande s'appuie sur un observateur d’état et d'un algorithme SHM pour reconfigurer en ligne le correcteur. Toutes les approches DTAC proposées sont testées en utilisant des simulations (analytiques et éléments finis) et/ou des expérimentations sur des structures intelligentes
Smart structures have increasingly become present in different industry applications and particularly in the fields of aeronautics and civil engineering. These structures have features that allow interactions with the environment, adapting their characteristics according to the needs (stiffness, damping, viscosity, etc.), monitoring their health or controlling their vibrations. Today smart structure active control methods do not respond appropriately to damage, despite the capacity of external disturbances good rejection. Damage-tolerant active control (DTAC) is a recent research area that aims to develop integrated approaches to reduce the vibrations while monitoring the integrity of the structure, identifying damage occurrence and reconfiguring the control law of the adopted active vibration control method.This thesis contributes to DTAC area, proposing a novel modal control framework and some applying strategies. Developed methods focus in non-collocated flexible structures, where multiples piezoelectric sensors and actuators are used to attenuate damaged structure vibration. The chapters present four main topics and the conclusions. Chapter 2 reviews the regular suboptimal H∞ problem and its respective solution based on the linear matrix inequality (LMI) approach, which is a fundamental tool for the development of subsequent topics. Chapter 3 introduces the modal H∞-norm based method for vibration control, which reveals high modal selectivity, allowing control energy concentration on damage effects and presenting robustness to spillover and parameter variation. A new control strategy is developed in Chapter 4, taking into account existing knowledge about the structure stressed regions with high probability of damage occurrence, leading to specific requirements in the modal H∞ controller design. A structural health monitoring (SHM) technique assesses each damaged mode behavior, which is used to design a preventive controller. Chapter 5 presents a novel modal double-loop control methodology to deal with the unpredictability of damage, nevertheless ensuring a good compromise between robustness and performance to both healthy and damaged structures. For this purpose, the first loop modal controller is designed to comply with regular requirements for the healthy structure behavior, and the second loop controller is reconfigured aiming to ensure satisfactory performance and robustness when and if damage occurs, based on a state-tracking observer and an SHM technique to adapt the controller online. In all these chapters, simulated (analytical and finite elements based) and/or experimental aluminum structures are used to examine the proposed methodology under the respective control strategies. The last chapter subsumes the achieved results for each different approach described in the previous chapters

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Liu, Wei Lin. "Integrated and flexible ultrasonic transducers for structural health monitoring on aircraft structures." Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=97155.

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Fatigue crack initiating from fastener holes in aluminum plates is a typical damagefrequently found on modern aircraft structures. Requirements for life extension of agingaircraft fleets and reduced maintenance costs have been accelerating the developments ofstructural health monitoring (SHM) technologies. This thesis considers the active sensingapproach of SHM that involves the integrated ultrasonic transducer (IUT) and the flexibleultrasonic transducer (FUT). The main component of IUT and FUT was piezoelectriclead-zirconate-titanate composite films which were fabricated using the sol-gel spraytechnique. The crack growth monitoring capability of the IUT and FUT was successfullydemonstrated on aluminum plates with fatigue cracks. The artificial damages on analuminum test article representing aircraft structural complexity were also detected by theFUT array bonded on both planar and curved surfaces. Finally, the design and fabricationof miniature angle beam wedges having low spurious noise are presented. The fatiguecrack on an aluminum thin plate was detected using the FUT bonded onto such anglebeam wedges.
Les fissures dues à la fatigue du métal initiées aux trous de fixation dans lesplaques d'aluminium sont des problèmes communs dans les avions modernes. De plus,l'utilisation d'avions de plus en plus âgés et le besoin de réduire leurs coûts d'entretien àaccélérer le développement de la technologie de la surveillance de la santé structurelle(SSS) de ces derniers. Ce mémoire considère l'approche active de la SSS en incorporantla capacité des capteurs intégrés ultrasonores (CIU) et des capteurs flexibles ultrasonores(CFU). L'ingrédient principal des CIU et CFU est des films à base de plomb-zirconatetitanatequi sont fabriqués à partir de la technique sol-gel. La capacité des CIU et CFU àsurveiller la croissance des fissures sur des plaques d'aluminium fissurées par fatigue futdémontrée avec succès. Les défauts artificiels mis dans des échantillons de plaquesd'aluminium représentant la complexité structurelle furent également détectés par unematrice de CFU collée sur des surfaces plane et courbe. Finalement, la conception et lafabrication de coins d'angles miniatures ayant comme caractéristiques de faibles bruitsparasites sont présentées. Les fissures par fatigue sur de minces plaques d'aluminiumfurent détectées en utilisant les CFU collés sur de tels coins.

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Rodriguez, Jesus. "Modeling of complex systems using nonlinear, flexible multibody dynamics." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/12344.

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Ramanathan, Suresh. "Dynamics characterization of highly flexible beams using a 3D motion analysis system /." free to MU campus, to others for purchase, 2004. http://wwwlib.umi.com/cr/mo/fullcit?p1426096.

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Santos, Antônio José Boness dos. "Mecanical and numerical models to unidimensional flexible structures." Laboratório Nacional de Computação Científica, 2007. http://www.lncc.br/tdmc/tde_busca/arquivo.php?codArquivo=143.

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Apresentamos um modelo matemático geral, baseado na teoria de Cosserat para estruturas flexíveis unidimensionais, em regime de deslocamentos finitos e sujeitas a restrições unilaterais. Ao modelo geral agregamos a hipótese de inextensibilidade e, desprezando os efeitos do cisalhamento e das forças inerciais, formulamos o problema variacionalmente tanto na forma cinemática quanto em Lagrangiano Aumentado. Para esta última formulação, construímos aproximações por elementos finitos de Galerkin e utilizamos um algoritmo do tipo Uzawa para a solução do problema aproximado. Apresentamos estudos numéricos com o intuito de avaliar a formulação, validar o algoritmo de solução e exemplificar possíveis aplicações práticas do modelo. Buscando viabilizar uma análise numérica, realizamos uma linearização consistente do modelo geral apresentado anteriormente, produzindo um modelo em regime de pequenos deslocamentos e deformações, descrito no espaço tridimensional. Para este problema, introduzimos uma aproximação por elementos finitos mistos estabilizados, adicionando à formulação de Galerkin formas residuais de mínimos quadrados provenientes das equações de equilíbrio. Provamos que esta formulação atende às condições suficientes para existência e unicidade de solução, independente da esbeltez da estrutura. Apresentamos estimativas de erro indicando taxas de convergência e resultados numéricos comprovando tais taxas. Apresentamos algumas aplicações dos modelos ao estudo de estabilidade de dutos aquecidos e enterrados, na análise da estabilidade de armaduras de risers e umbilicais e, na área biológica, apontamos as possibilidades de suas utilizações na modelagem de moléculas de ADN.

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Zee, Robert E. "Control of flexible space structures with localized modes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ27758.pdf.

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Bravo, Rafael. "Vibration control of flexible structures using smart materials." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0034/NQ66256.pdf.

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Howard, Carl. "Active isolation of machinery vibration from flexible structures." Title page, abstract and table of contents only, 1999. http://web4.library.adelaide.edu.au/theses/09PH/09phh8478.pdf.

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Thesis (Ph. D.)--University of Adelaide, Dept. of Mechanical Engineering, 1999?
Copy 2 does not have a CD-ROM. Includes bibliographical references (p. 317-330). Also available in an electronic version.

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38

Whorton, Mark S. (Mark Stephen). "High performance, robust control of flexible space structures." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/12502.

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毛生根 and Shenggen Mao. "Symplectic analysis of flexible structures by finite elements." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B3123754X.

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Mantikas, Nikolaos. "Dynamics of large flexible multibody structures in space." Thesis, University of Southampton, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396146.

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PINTO, OSVALDO CASERES. "ACTIVE NONLINEAR CONTROL OF VIBRATIONS IN FLEXIBLE STRUCTURES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1999. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=1886@1.

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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
FUNDAÇÃO UNIVERSIDADE DO RIO GRANDE
Neste trabalho estuda-se uma estratégia para o controle ativo não-linear de estruturas flexíveis submetidas a carregamentos dinâmicos. O algoritmo de controle é deduzido com base na teoria de controle ótimo não-linear com realimentação de estado, utilizando uma representação tensorial. Desenvolve-se as equações polinomiais de controle para diferentes ordens, partindo-se do controle linear clássico até um controle não-linear de quinta ordem. A estratégia é particularizada para aplicação em sistemas com um grau de liberdade que apresentem não-linearidades quadráticas e cúbicas, que podem representar, de forma aproximada, a maioria dos elementos estruturais encontrados nas Engenharias Civil e Mecânica, tais como vigas, arcos, placas e cascas. Determina-se analiticamente os coeficientes de ganhos até a terceira ordem, e utiliza-se os mesmos para estudar o feito das forças de controle sobre a não- linearidade e estabilidade do sistema. Vários exemplos numéricos de aplicação são apresentados, utilizando-se diferentes tipos de excitação. Uma atenção especial é dedicada a sistemas caracterizados pela coexistência de dois vales potenciais, um deles correspondente a uma posição de equilíbrio pós- flambagem. A influência do sistema de controle sobre a carga de escape é estudada. O efeito do retardo na aplicação das forças de controle é analisado tanto numericamente como analiticamente, utilizando-se o método das múltiplas escalas para desenvolver expressões que permitem encontrar situações críticas de retardo. Como exemplo de aplicação prática, estuda-se o problema de uma viga flambada submetida a um carregamento dinâmico lateral.
The present thesis studies a strategy for the active non- linear control of dynamically loaded flexible structures. The control method is based on the non-linear optimal control theory using state feedback and the solution of the non-linear optimal control problem is obtained by representing system non-linearities and performance indices by power series with the help of algebraic tensor theory. General polynomial representations of the non-linear control law are obtained up to the fifth order. This methodology is applied to systems with quadratic and cubic nonlinearities, capable of representing most of the elements usually used in civil and mechanical engineering structures, such as beams, plates, shells and arcs. Control gains up to the third order are analytically derived and the effect of the control forces on the system is studied. Special emphasis is placed on systems susceptible to chaotic vibrations, escape from a potential well and dynamic jumps. Several examples are provided to illustrate the control approach. Strongly nonlinear systems subjected to free vibration, simple harmonic excitations, impact and ground acceleration are tested. The variation of the dynamic buckling load with the degree of the control algorithms is studied for the problem of structures with two potential wells, one of them corresponding to a post-buckling equilibrium position. The effect of time delay on controlled systems is studied analytically and numerically. The studied methodology is also applied to control the oscillations of simply supported buckled beams, in order to mitigate the effects of dynamic loading on the vibration amplitudes and prevent dangerous instability phenomena.
En este trabajo estudia se una estrategia para el control activo no-lineal de extructuras flexibles sometidas la cargas dinámicas. EL algoritmo de control es deduzido con base en la teoría de control ótimo no lineal con realimentación de estado, utilizando una representación tensorial. Se dearrollan las ecuaciones polinomiales de control para diferentes órdenes, desde el control lineal clásico hasta el control no lineal de quinta orden. Se particulariza la estrategia para la aplicación en sistemas con un grado de liberdad que presenten no linealidades cuadráticas y cúbicas, que pueden representar, de forma aproximada, la mayoría de los elementos extructurales encontrados en las Ingenierías Civil y Mecánica, tales como vigas, arcos y placas. Se determinan analiticamente los coeficientes de ganancias hasta tercer orden, y se utilizan los mismos para estudiar las fuerzas de control sobre la no linealidad y estabilidad del sistema. Varios ejemplos numéricos de aplicación son presentados, utilizando diferentes tipos de excitación. Atención especial se le dedica a los sistemas caracterizados por la coexistencia de dos vales potenciales, uno de ellos correspondiendo a una posición de equilibrio posflameado. Se estudia también la influencia del sistema de control sobre la carga de escape. EL efecto de retardo en la aplicación de las fuerzas de control se anlaiza tanto numérica como analíticamente, utilizando el método de las múltiples escalas para dearrollar expresiones que permiten encontrar situaciones críticas de retardo. Como ejemplo de aplicación práctica, se estudia el problema de una viga flameada sometida a una carga dinámica lateral.

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PECIN, THIAGO GALINDO. "EVALUATION OF TORNADO LOADS OVER FLEXIBLE FRAMED STRUCTURES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2006. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=8952@1.

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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
A consideração dos efeitos da incidência de tornados sobre estruturas é prática corrente em vários países, principalmente no que diz respeito a instalações industriais sensíveis, nas quais as conseqüências de uma eventual ocorrência de tal fenômeno são de maior risco. No Brasil, a despeito de múltiplos registros em algumas regiões ao longo dos últimos anos, tais estudos são ainda incipientes. Objetiva-se, em particular, a avaliação de efeitos mecânicos de tornados sobre sistemas estruturais. Para isso, utiliza-se o modelo de campo de vento proposto por Wen (1975), baseado na solução qualitativa de Kuo (1971), e três modelos de pórticos tridimensionais, de alturas 20, 60 e 100 m. Através de ensaios numéricos, apresentam-se as respostas estática, cinemática e dinâmica dessas estruturas quando atingidas pelo tornado modelado. Análise comparativa entre os efeitos de inércia e arrasto é feita e é proposto um espectro de resposta cinemática a tornados. Os efeitos globais são também avaliados, a fim de se inferirem informações gerais sobre os efeitos mecânicos do fenômeno sobre sistemas estruturais. Comparações com a norma brasileira de vento são apresentadas e a simplificação de se considerar a estrutura como ponto material perante o sinistro é avaliada.
The consideration of the effects of the incidence of tornadoes on structures is common in many countries, mainly in sensible industrial installations, in which the consequences of an eventual occurrence of such phenomenon are of large risk. In Brazil, in spite of multiple registers in some regions during the last couple of years, such studies are still incipient. A methodology for the evaluation of tornado mechanical effects on structural systems is presented. For this, the wind field model proposed by Wen (1975), based on the qualitative solution of Kuo (1971) is used, and three models of 3-D framed structures, 20, 60 and 100 m high, are analyzed. Through numerical tests, the static and dynamic response of these structures to a sampling tornado are evaluated and analyzed. Comparative analysis of the inertia and drag effects is made and a tornadic response spectrum is presented. Global effects are also evaluated, in order to infer general information on the mechanical actions of the phenomenon on structural systems. Comparisons with the Brazilian wind code provisions are presented and the simplification of considering the structure as a material point during the analysis is criticized.

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RIOS, GABRIEL EMILIANO BARRIENTOS. "NONLINEAR DYNAMICS OF FLEXIBLE STRUCTURES WITH LARGE DEFORMATION." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1997. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=19770@1.

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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
É apresentado o modelo não-linear de barras proposto por Simo para o estudo do comportamento dinâmico de estruturas espaciais. A formulação das equações do movimento é feita em um sistema inercial de modo a simplificar o operador de inércia e o material é considerado como elástico linear. Carregamos não – conservativos são considerados de modo que a integração das equações é feita na forma fraca. As partes flexíveis, que são necessariamente estruturas unidimensionais, são descritas por um modelo de barras que generaliza os modelos clássicos de Euler-Bernouilli e de Timoshenko. Implementa-se um programa computacional baseado nesta teoria na linguagem Matlab. O modelo de barras discretiza-se espacialmente usando elementos finitos e integra-se o sistema de equações resultante linearizado usando o método de Newton-Raphson, associado ao esquema de integração de Newmark. Incorpora-se os efeitos de amortecimento interno e cargas seguidoras, assim como elementos lineares quadráticos. Se incorpora à programação o tratamento de juntas esféricas através do método de multiplicadores de Lagrange, que permitem estudar alguns tipos de sistemas de multicorpos flexíveis. O programa é testadopor uma série de exemplos e comparações com resultados clássicos para mostrar a sua versatilidade e também as limitações dos modelos clássicos. Também se apresenta o modelo usado no programa computacional SAMCEF, e mostra-se a potencialidade deste programa em base a uma série de exemplos que incluem problemas de flexibilidade e choque em sistemas multicorpos.
It is presented a theory to treat multibody problems with rigid or flexible parts that treats the overall motion and the deformations in the same way using na inertial reference frame. The essential part of the model is the treatment of nonlinear rods that are flexible parts of the multibody systems. A code was construcetd in the platform MATBLAB and it was widely tested thorough comparisons with results found in the literature that acted as benchmark problems. The results are very good.

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44

Yung, Jeremy Hoyt 1971. "Gain scheduling for geometrically nonlinear flexible space structures." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/16838.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, February 2002.
Includes bibliographical references (p. 181-185).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
A gain-scheduling approach for the control of geometrically nonlinear structures is developed. The objective is to improve performance over current linear design techniques that are applied to the same control problem. The approach is applicable to a variety of structures that have complex dynamics with slow variations such as flexible robotic arms and space structures with gimballing solar arrays. The modeling approach is motivated by the lack of in situ test data available for design of 0-g controllers. A Linear Fractional form allows the nonlinear and uncertain aspects of the structure to be modeled independently. The geometric nonlinearity is modeled using a feedback description of structural coupling. The uncertainty model is based on a physical parameter description, so that an experimentally identified 1-g parametric uncertainty model can be extrapolated to 0-g. The control approach is motivated by the success of linear control design synthesis and analysis techniques for space structures. Graphical heuristics for linear control design using Linear Quadratic Gaussian (LQG) and Sensitivity Weighted LQG techniques are introduced. A procedure to realize reduced-order gain-scheduled controllers from a family of linear state-space controllers is developed. A nonlinear analysis framework suitable for the slow variations of geometrically nonlinear structures is also presented. The realization procedure and nonlinear analysis is combined with the graphical linear design heuristics to form an iterative gain scheduled design process. The complete gain scheduling approach is applied to the MIT/MACE-II experiment flown on the International Space Station. Gain scheduled controller designs are shown to provide improved performance and robustness over a Multiple Model linear controllerdesign.
by Jeremy Hoyt Yung.
Ph.D.

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45

Blaurock, Carl Allen. "Modeling of geometrically nonlinear flexible structures for control." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10090.

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46

Gangadharan, Sathya N. "Statistical system identification of structures with flexible joints." Diss., Virginia Tech, 1990. http://hdl.handle.net/10919/39890.

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The flexibility of welded joints is an important issue in design of car bodies. Two generic, 3-D, design-oriented models (simple and complex) are developed to represent the compliant behavior of multibranch flexible joints. The simple model consists of torsional springs restraining the relative rotation of the joint branches in the three planes, while all branches are assumed to be rigidly connected in translation. Coupling between motions in different planes is neglected. The complex model accounts for such coupling. A statistical system identification method is proposed for inferring the model parameters from the static response of the structure. The method is demonstrated by applying it to a simple cube frame structure and a car body. Finally, the two models are compared in terms of their ability to predict static response.
Ph. D.

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Jones, Stephen H. "Parameter robust reduced-order control of flexible structures." Diss., Virginia Tech, 1991. http://hdl.handle.net/10919/29264.

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This thesis generalizes the concept of internal feedback loop modeling, due to Tahk and Speyer, to arrive at two new LQG-based methods of parameter robust control. One component of the robustness procedure, common to both methods, is the application of an auxiliary cost functional penalty to desensitize the system to variations in selected parameters of the state-space model. The other component consists of the formulation of a fictitious noise model to accommodate the effect of these parameter variations. The "frequency-domain method" utilizes knowledge of the system dynamics to create a frequency-shaped noise model with a power spectrum that approximates the frequency content of unknown error signals in the system due to parameter uncertainties. This design method requires augmentation of additional dynamics to the plant, which results in higher-dimensional full-order controllers. However, the controller design computations are identical to those of a standard LQG problem. The "time-domain method" emulates the same error signals by means of a multiplicative white noise model which reflects the time-domain behavior of those signals. The resulting robust controller is of the same order as the standard LQG controller, although the design involves a more complex computational algorithm. The application of multiplicative white noise to the system model requires the solution of a system of four coupled equations - two modified Riccati equations and two modified Lyapunov equations. In addition, the optimal projection equations are applied to both robustness methods to reduce the controller order with minimal loss in performance. Comparisons are drawn between these and related robust control methods, and it is shown that the relative effectiveness of such methods is problem dependent. Parameter sensitivity analysis is carried out on a simply supported plate model subject to external disturbances. The appropriate robust controller is selected, and it is found to stabilize the plate with little sacrifice in performance.
Ph. D.

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48

Dohrmann, Clark. "Stability analysis and modeling of rotating flexible structures /." The Ohio State University, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487777901660729.

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Eghbali, Amir. "Contributions to Flexible Multirate Digital Signal Processing Structures." Licentiate thesis, Linköping : Department of Electrical Engineering, Linköping University, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-17182.

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Mao, Shenggen. "Symplectic analysis of flexible structures by finite elements /." Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19471154.

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Dissertations / Theses on the topic 'Flexible structures'

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