Página 1 dos resultados de 19 itens digitais encontrados em 0.050 segundos

‣ Density-Profile Processes Describing Biological Signaling Networks: Almost Sure Convergence to Deterministic Trajectories

FERNANDEZ, Roberto; FONTES, Luiz R.; NEVES, E. Jordao
Fonte: SPRINGER Publicador: SPRINGER
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
27.457822%
We introduce jump processes in R(k), called density-profile processes, to model biological signaling networks. Our modeling setup describes the macroscopic evolution of a finite-size spin-flip model with k types of spins with arbitrary number of internal states interacting through a non-reversible stochastic dynamics. We are mostly interested on the multi-dimensional empirical-magnetization vector in the thermodynamic limit, and prove that, within arbitrary finite time-intervals, its path converges almost surely to a deterministic trajectory determined by a first-order (non-linear) differential equation with explicit bounds on the distance between the stochastic and deterministic trajectories. As parameters of the spin-flip dynamics change, the associated dynamical system may go through bifurcations, associated to phase transitions in the statistical mechanical setting. We present a simple example of spin-flip stochastic model, associated to a synthetic biology model known as repressilator, which leads to a dynamical system with Hopf and pitchfork bifurcations. Depending on the parameter values, the magnetization random path can either converge to a unique stable fixed point, converge to one of a pair of stable fixed points, or asymptotically evolve close to a deterministic orbit in Rk. We also discuss a simple signaling pathway related to cancer research...

‣ Desenvolvimento de um sistema de transmissão mecânica baseado em engrenagens cônicas e faciais

Bianchi, Kleber Eduardo
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Tese de Doutorado Formato: application/pdf
Português
Relevância na Pesquisa
38.352954%
O presente trabalho foi desenvolvido com o intuito de propor um sistema de transmissão mecânica baseado em engrenagens cônicas e faciais, de razões de velocidades escalonadas, para uso industrial e no setor da mobilidade. Em virtude do grande desenvolvimento das transmissões compostas por engrenagens faciais nos últimos anos, implementado por centros de pesquisa da área e por indústrias do setor aeronáutico, um dos objetivos deste trabalho foi estender o campo de aplicação dessas engrenagens para outros campos da engenharia. Inicialmente, mostra-se um estudo dos principais tipos de transmissões mecânicas presentes na indústria e, principalmente, no setor da mobilidade; área em que, usualmente, encontram-se os requisitos mais elevados de operação. Além disso, foi realizada uma revisão bibliográfica abordando tópicos importantes relacionados às engrenagens em geral e, mais especificamente, às transmissões cônicas e faciais. Esta revisão serviu de base para a implementação dos algoritmos para modelagem das engrenagens do sistema proposto. Para validar o conceito, um protótipo foi construído e testado, tendo como principal objetivo a comprovação da viabilidade e eficácia do sistema proposto, tanto na transmissão do movimento como na alteração da razão de velocidades. Realizados os testes...

‣ Modelagem numerica de problemas de dominios acoplados para aplicação em microsistemas eletromecanicos; Coupled field problems numerical modeling for microelectromechanical systems

Cornelis Joannes van der Poel Filho
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 25/02/2005 Português
Relevância na Pesquisa
38.164421%
Microsistemas eletromecânicos geralmente têm seu princípio de funcionamento baseado na interação entre dois ou mais campos físicos. Para seu projeto são necessárias ferramentas de simulação multi-domínios. Este trabalho visa estudar o fenômeno de acoplamento eletromecânico em microsistemas e construir uma ferramenta de simulação numérica para este tipo de problema. São apresentados métodos de análise estática, modal e transiente baseados em modelos de elementos finitos e de ordem reduzida. Na análise estática cada domínio é resolvido separadamente. Foi mostrado um método de transferência das forças eletrostáticas para o domínio mecânico e proposto e testado um esquema de atualização da malha elétrica. Para a análise dinâmica transiente foi implementado um método de Newmark adaptado de forma a considerar os efeitos do acoplamento eletromecânico. Outro método de análise dinâmica apresentado é baseado numa estratégia de perturbação do sistema em equilíbrio em conjunto com a resolução de um problema de autovalor / autovetor. O método de perturbação fornece diretamente as freqüências naturais de vibração do sistema acoplado. A técnica de redução de ordem apresentada é baseada numa projeção de Galerkin da equação diferencial governante utilizando como funções de base os modos empíricos do sistema dinâmico. Um programa computacional para modelagem numérica multi-domínios com solução particionada para o acoplamento eletromecânico foi proposto e implementado. O código computacional...

‣ Assessment of the mechanical microstructure of masonry clay brick by nanoindentation

Krakowiak, Konrad J.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Tese de Doutorado
Publicado em 14/04/2011 Português
Relevância na Pesquisa
38.785264%
Tese de doutoramento em Engenharia Civil; The work presented in this thesis aims to implement the recent advances in the material science into the field of structural clay products applied to masonry constructions. The experimental analysis carried out by the author is focused on the detailed description of the heterogeneous microstructure of the fired clay brick, as a function of its composition and processing conditions. Multi-field methods of investigation have been combined, from standard mechanical tests carried out on bulk material on the macro-scale to novel nanoindentation techniques, which infers the mechanical properties of the solids on the nanoand micro-scales. Moreover, the complex interplay between the different components of this heterogeneous solid is traced with Scanning Electron Microscopy methods or Mercury Intrusion Porosimetry. The existing hierarchical ordering of fired brick microstructure is framed in the multi-level model, where the building blocks are classified and described with reference to the type of morphology present and mechanical characteristics. The statistical indentation method, originally developed for cement based materials is extended to the field of structural ceramics. Such an experimental analysis of mechanical phase properties is carried out with the aid of Gaussian Mixture Modeling...

‣ Characterization of a Multi-element Clinical HIFU System Using Acoustic Holography and Nonlinear Modeling

Kreider, Wayne; Yuldashev, Petr V.; Sapozhnikov, Oleg A.; Farr, Navid; Partanen, Ari; Bailey, Michael R.; Khokhlova, Vera A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/2013 Português
Relevância na Pesquisa
27.882205%
High-intensity focused ultrasound (HIFU) is a treatment modality that relies on the delivery of acoustic energy to remote tissue sites to induce thermal and/or mechanical tissue ablation. To ensure the safety and efficacy of this medical technology, standard approaches are needed for accurately characterizing the acoustic pressures generated by clinical ultrasound sources under operating conditions. Characterization of HIFU fields is complicated by nonlinear wave propagation and the complexity of phased-array transducers. Previous work has described aspects of an approach that combines measurements and modeling, and here we demonstrate this approach for a clinical phased array transducer. First, low-amplitude hydrophone measurements were performed in water over a scan plane between the array and the focus. Second, these measurements were used to holographically reconstruct the surface vibrations of the transducer and to set a boundary condition for a 3-D acoustic propagation model. Finally, nonlinear simulations of the acoustic field were carried out over a range of source power levels. Simulation results were compared to pressure waveforms measured directly by hydrophone at both low and high power levels, demonstrating that details of the acoustic field including shock formation are quantitatively predicted.

‣ Using CellML with OpenCMISS to Simulate Multi-Scale Physiology

Nickerson, David P.; Ladd, David; Hussan, Jagir R.; Safaei, Soroush; Suresh, Vinod; Hunter, Peter J.; Bradley, Christopher P.
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Publicado em 05/01/2015 Português
Relevância na Pesquisa
28.515637%
OpenCMISS is an open-source modeling environment aimed, in particular, at the solution of bioengineering problems. OpenCMISS consists of two main parts: a computational library (OpenCMISS-Iron) and a field manipulation and visualization library (OpenCMISS-Zinc). OpenCMISS is designed for the solution of coupled multi-scale, multi-physics problems in a general-purpose parallel environment. CellML is an XML format designed to encode biophysically based systems of ordinary differential equations and both linear and non-linear algebraic equations. A primary design goal of CellML is to allow mathematical models to be encoded in a modular and reusable format to aid reproducibility and interoperability of modeling studies. In OpenCMISS, we make use of CellML models to enable users to configure various aspects of their multi-scale physiological models. This avoids the need for users to be familiar with the OpenCMISS internal code in order to perform customized computational experiments. Examples of this are: cellular electrophysiology models embedded in tissue electrical propagation models; material constitutive relationships for mechanical growth and deformation simulations; time-varying boundary conditions for various problem domains; and fluid constitutive relationships and lumped-parameter models. In this paper...

‣ Reduced-order modeling of MEMS using modal basis functions; Reduced-order modeling of microelectromechanical systems using modal basis functions

Varghese, Mathew, 1973-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 93 leaves; 7295972 bytes; 7295731 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
28.169512%
The field of MEMS has matured significantly over the last two decades increasing in both complexity and level of integration. To keep up with the demands placed by these changes requires the development of computer-aided design and modeling tools (CAD/CAM) that enable designers to reduce the time and cost it takes to produce working prototypes. An ideal scenario is one in which a designer is able to quickly model and simulate an entire microsystem - sensors, actuators and electronics -- with the certainty that their results will match that of physical prototypes. This vision of design requires the existence of system level models of MEMS devices that can capture the complex non-linear coupling between multiple physical domains, yet be sufficiently fast and compact in form to insert into a system dynamics simulator. In this thesis I explore techniques of automatically constructing such models from meshed representations of device geometry. These dynamical models are known as "reduced-order" models or "macromodels." They are characterized by few degrees of freedom (DOF), and a small set of state equations. Our process for constructing macromodels is built upon two well-established methodologies - normal mode superposition and Lagrangian mechanics. This is referred to as the "CHURN process" and was originally developed by Gabbay et al. to create models of electromechanical devices with two electrodes under conditions satisfying linear mechanics.; (cont.) In this thesis I significantly extend this process to model multi-port magnetostatic devices...

‣ Methodology for the evaluation of natural ventilation in buildings using a reduced-scale air model

Walker, Christine E. (Christine Elaine)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 211 p.
Português
Relevância na Pesquisa
17.712068%
Commercial office buildings predominantly are designed to be ventilated and cooled using mechanical systems. In temperate climates, passive ventilation and cooling techniques can be utilized to reduce energy consumption while maintaining occupant comfort using natural ventilation. However, current modeling techniques have limitations and assumptions that reduce their effectiveness in predicting internal building performance. There are few tools to predict the thermal performance of and resulting airflow patterns in naturally ventilated office buildings accurately. This thesis presents three significant contributions for the evaluation of natural ventilation in buildings: * A methodology for assessing the performance of naturally ventilated buildings through a reduced-scale air model was developed based on dimensional analysis and similitude criteria. Buoyancy, wind, and combined ventilation strategies for a multi-zoned commercial office building with an open floor plan layout were evaluated using the reduced-scale model. * Guidelines were established for monitoring natural ventilated buildings as a means to evaluate their operation, based on field measurements of a prototype building were established. * A framework for evaluating current techniques for modeling airflow patterns in naturally ventilated buildings was developed...

‣ Estudo de metodologias para análise numérica do campo de temperatura no processo de soldagem MIG em chapas de aço inoxidável AISI 304L

Farias, Rodrigo Martins; Teixeira, Paulo Roberto de Freitas; Araújo, Douglas Bezerra de
Fonte: Universidade Federal do Rio Grande Publicador: Universidade Federal do Rio Grande
Tipo: Conferência ou Objeto de Conferência
Português
Relevância na Pesquisa
17.457822%
Os processos de soldagem em chapas envolvem fenômenos físicos e químicos muito complexos e, por isso, difíceis de serem modelados matematicamente. Embora os efeitos termo-mecânico-metalúrgico acoplados sejam importantes, na maioria dos casos são encontrados bons resultados considerando modelos numéricos baseados nas equações da transferência de calor e nas que governam o comportamento estrutural das chapas. De modo geral, o campo térmico é independente do estrutural, permitindo que as soluções sejam realizadas em sequência (térmicoestrutural), sem necessidade de acoplamento. As análises mais adequadas dos processos de soldagem com deposição de material usam a técnica denominada de “element birth and death”, a qual considera a ativação dos elementos pertencentes ao cordão de uma malha de elementos finitos a medida que a fonte de calor se movimenta. Neste trabalho, são apresentadas análises numéricas de soldagem de topo multipasse, com chanfro em V, de chapas de aço inoxidável AISI 304L através do processo MIG convencional. As chapas possuem 9,6 mm de espessura, 200 mm de comprimento e 50 mm de largura. As simulações numéricas são realizadas no software Ansys Multiphysics®, considerando os fenômenos de convecção e radiação...

‣ Micro-macro Modeling of Advanced Materials by Hybrid Finite Element Method

Cao, Changyong
Fonte: Universidade Nacional da Austrália Publicador: Universidade Nacional da Austrália
Tipo: Thesis (PhD); Doctor of Philosophy (PhD)
Português
Relevância na Pesquisa
38.01538%
Advanced composite materials are increasingly used in a variety of fields due to their desirable properties. The use of these advanced materials in different applications requires a thorough understanding of the effect of their complex microstructures and the effect of the operating environment on the materials. This requires an efficient, robust and powerful tool that is able to predict the behavior of composites under a variety of loading conditions. This research addresses this problem and develops a new convenient numerical method and framework for users to perform such analyses of composites. In this thesis, the hybrid fundamental solution based finite element method (HFS-FEM) is developed and applied to model composite materials across microscale and macroscale and from single field to multi-field. The basic idea and detailed formulations of the HFS-FEM for elasticity and potential problems are first presented. Then this method is extended to solve general three-dimensional (3D) elasticity problems with body forces and to model anisotropic materials encountered in composite analysis. Standard tests for proposed elements are carried out to assess their performance. Further, an efficient numerical homogenization method based on HFS-FEM is applied to predict the macroscopic elasticity properties and thermal conductivity of heterogeneous composites in micromechanical analysis. The effect of material parameters...

‣ Getting the details of fuel rod simulation in reactor safety analysis right: performance of the code coupling DYN3D-TRANSURANUS for RIA

HOLT Lars; ROHDE Ulrich; SEIDL Markus; SCHUBERT Arndt; VAN UFFELEN Paul; MACIAN-JUAN Rafael
Fonte: German Nuclear Society Publicador: German Nuclear Society
Tipo: Contributions to Conferences Formato: CD-ROM
Português
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17.457822%
Over the last decades the importance of fuel-specific processes for safety analysis has grown, due to an increase of discharge burn-up for more efficient use of nuclear fuels. This results in a high burn-up structure (HBS) characterized by a decrease of the original grain size to ~0.1 - 0.2 μm, high concentration of pores with a diameter ~0.5 - 1 μm and depletion of fission gas from the matrix. It is known that the HBS can have an important effect on the fuel behavior during design basis accidents (DBA). For example, pellet cladding mechanical interaction (PCMI) can be observed under reactivity initiated accident (RIA) conditions, which can lead to fuel rod failure and in later stages to interaction between fuel and coolant. To analyze the behavior of high burn-up fuel in detail several experimental projects had begun, e.g. High Burnup Rim Project and the OECD/NEA Cabri Water Loop Project. Nevertheless, most of the reactor dynamics codes, thermal hydraulics system codes and sub-channel thermal hydraulics codes still include a simplified fuel behavior model. Thence licensing calculations concerning fuel rod performance are so far done in a conservative manner. However, today multi-physics code systems are more and more state-of-the-art thanks to hard- and software. For advanced safety analysis...

‣ Modelagem mecânica e investigação numérica de escoamentos de fluidos SMD empregando um método multi-campos de galerkin mínimos-quadrados

Santos, Daniel Dall'Onder dos
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Dissertação Formato: application/pdf
Português
Relevância na Pesquisa
78.330293%
A maioria dos líquidos encontrados na natureza são não-Newtonianos e o estudo do seu comportamento tem uma importância significante em diferentes áreas da engenharia. Entre eles, uma larga classe de materiais que exibem pequena ou nenhuma deformação quando sujeitos a um nível de tensões inferiores a uma tensão limite de escoamento – chamado de comportamento viscoplástico. A presente Dissertação tem como objetivo o estudo numérico de escoamentos bidimensionais em regime permanente de fluidos viscoplásticos não-lineares em uma cavidade forçada. O modelo mecânico é definido pelas equações de conservação de massa e de balanço de momentum acopladas ao modelo viscoplástico recentemente introduzido por Souza Mendes e Dutra – SMD – e é aproximado por um método de elementos finitos multi-campos estabilizado baseado na metodologia de Galerkin mínimos-quadrados que possui como variáveis primais os campos de tensão-extra, velocidade e pressão. As condições de compatibilidade entre os subespaços de elementos finitos para tensão-extra-velocidade e velocidade-pressão são violadas, permitindo assim a utilização de interpolações de igual ordem. O método estabilizado foi implementado no código de elementos finitos para fluidos não-Newtonianos em desenvolvimento no Laboratório de Mecânica dos Fluidos Aplicada e Computacional (LAMAC) da UFRGS. Em diversos trabalhos encontrados na literatura...

‣ Magnetic machines and power electronics for power MEMS applications

Das, Sauparna, 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 323 p.; 16921694 bytes; 16936400 bytes; application/pdf; application/pdf
Português
Relevância na Pesquisa
17.457822%
This thesis presents the modeling, design, and characterization of microfabricated, surface-wound, permanent-magnet (PM) generators, and their power electronics, for use in Watt-level Power MEMS applications such as a microscale gas turbine engine. The generators are three-phase, axial-flux, synchronous machines, comprising a rotor with an annular PM and ferromagnetic core, and a stator with multi-turn surface windings on a soft magnetic substrate. The fabrication of the PM generators, as well as the development of their high-speed spinning rotor test stand, was carried out by collaborators at the Georgia Institute of Technology. The machines are modeled by analytically solving 2D magneto-quasistatic Maxwell's Equations as a function of radius and then integrating the field solutions over the radial span of the machine to determine the open-circuit voltage, torque and losses in the stator core. The model provides a computationally fast method to determine power and efficiency of an axial-air-gap PM machine as a function of geometry, speed and material properties. Both passive and active power electronics have been built and tested. The passive power electronics consist of a three-phase transformer and diode bridge rectifier.; (cont.) The active power electronics consist of a switch-mode rectifier based on the boost semi-bridge topology which is used to convert the unregulated AC generator voltages to a regulated 12 V DC without the need for rotor position/speed or stator terminal current/voltage sensing. At the rotational speed of 300...

‣ Modelagem mecânica e investigação numérica dos efeitos elásticos e viscosos em escoamentos inerciais de fluidos não newtonianos

Santos, Daniel Dall'Onder dos
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Tese de Doutorado Formato: application/pdf
Português
Relevância na Pesquisa
68.50643%
A maioria dos líquidos encontrados na natureza são não newtonianos e o estudo do seu comportamento reológico tem uma importância significante em diferentes áreas da engenharia. Entre eles, existe uma classe de fluidos que exibem pequena deformação aparente quando sujeitos a um nível de tensões inferior a uma tensão limite de escoamento, referido como comportamento viscoplástico. Nesta classe de materiais, alguns apresentam também comportamento elástico quando submetidos a baixas taxas de cisalhamento. A presente Tese tem como objetivo o estudo numérico de escoamentos bidimensionais em regime permanente de fluidos elasto-viscoplásticos através de uma expansão-contração planar. O modelo mecânico é definido pelas equações de conservação de massa e de balanço de momentum acopladas ao modelo elasto-viscoplástico proposto nesta Tese. Esta modelagem é aproximada por um método de elementos finitos multi-campos estabilizado baseado na metodologia de Galerkin mínimos-quadrados que possui como variáveis primais os campos de tensão extra polimérica, velocidade e pressão. As condições de compatibilidade entre os sub-espaços de elementos finitos para tensão extra-velocidade e velocidade-pressão são violadas...

‣ A Reconnecting Flux Rope Dynamo

Baggaley, Andrew W.; Barenghi, Carlo F.; Shukurov, Anvar; Subramanian, Kandaswamy
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
27.457822%
We develop a new model of the fluctuation dynamo in which the magnetic field is confined in thin flux ropes advected by a multi-scale flow modeling turbulence. Magnetic dissipation occurs only via reconnection of the flux ropes. We investigate the kinetic energy release into heat, mediated by the dynamo action, both in our model and by solving the induction equation with the same flow. We find that a flux rope dynamo is an order of magnitude more efficient at converting mechanical energy into heat. The probability density of the magnetic energy release in reconnections has a power-law form with the slope -3, consistent with the Solar corona heating by nanoflares.; Comment: 10 pages, 4 figures

‣ Phase field modeling of nonlinear material behavior

Pellegrini, Yves-Patrick; Denoual, Christophe; Truskinovsky, Lev
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
27.77192%
Materials that undergo internal transformations are usually described in solid mechanics by multi-well energy functions that account for both elastic and transformational behavior. In order to separate the two effects, physicists use instead phase-field-type theories where conventional linear elastic strain is quadratically coupled to an additional field that describes the evolution of the reference state and solely accounts for nonlinearity. In this paper we propose a systematic method allowing one to split the non-convex energy into harmonic and nonharmonic parts and to convert a nonconvex mechanical problem into a partially linearized phase-field problem. The main ideas are illustrated using the simplest framework of the Peierls-Nabarro dislocation model.; Comment: 12 pages, 4 figures. v1: as submitted. v2: as published (conclusion added, unessential part of appendix removed, minor typesetting revisions). To appear in: K. Hackl (ed.), Proceedings of the IUTAM Symposium on Variational Concepts with Applications to the Mechanics of Materials, September 22-26, 2008, Bochum. (Springer-Verlag, 2010 presumably)

‣ Atomistic-to-Continuum Multiscale Modeling with Long-Range Electrostatic Interactions in Ionic Solids

Marshall, Jason; Dayal, Kaushik
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 09/10/2013 Português
Relevância na Pesquisa
27.62796%
We present a multiscale atomistic-to-continuum method for ionic crystals with defects. Defects often play a central role in ionic and electronic solids, not only to limit reliability, but more importantly to enable the functionalities that make these materials of critical importance. Examples include solid electrolytes that conduct current through the motion of charged point defects, and complex oxide ferroelectrics that display multifunctionality through the motion of domain wall defects. Therefore, it is important to understand the structure of defects and their response to electrical and mechanical fields. A central hurdle, however, is that interactions in ionic solids include both short-range atomic interactions as well as long-range electrostatic interactions. Existing atomistic-to-continuum multi-scale methods, such as the Quasicontinuum method, are applicable only when the atomic interactions are short-range. In addition, empirical reductions of quantum mechanics to density functional models are unable to capture key phenomena of interest in these materials. To address this open problem, we develop a multiscale atomistic method to coarse-grain the long-range electrical interactions in ionic crystals with defects. In these settings...

‣ Multiscale Modeling of Polymer Gels-Chemo-Electric Model versus Discrete Element Model

Wallmersperger, Thomas; Wittel, Falk K.; D'Ottavio, Michele; Kröplin, Bernd
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/09/2015 Português
Relevância na Pesquisa
37.870269%
Polyelectrolyte gels are a very attractive class of actuation materials with remarkable electronic and mechanical properties with a great similarity to biological contractile tissues. They consist of a polymer network with ionizable groups and a liquid phase with mobile ions. Absorption and delivery of solvent lead to a large change of volume. This mechanism can be triggered by chemical (change of salt concentration or pH of solution surrounding the gel), electrical, thermal or optical stimuli. Due to this capability, these gels can be used as actuators for technical applications, where large swelling and shrinkage is desired. In the present work chemically stimulated polymer gels in a solution bath are investigated. To adequately describe the different complicated phenomena occurring in these gels, they can be modeled on different scales. Therefore, models based on the statistical theory and porous media theory, as well as a coupled multi-field model and a discrete element formulation are derived and employed. In this paper, the coupled multi-field model and the discrete element model for chemical stimulation of a polymer gel film with and without domain deformation are employed. Based on these results, the presented formulations are compared and conclusions on their applicability in engineering practice are finally drawn.

‣ Behavior modeling for hybrid robotic systems

Rawal, Chetan
Fonte: University of Delaware Publicador: University of Delaware
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
27.457822%
Herbert G. Tanner; The behavior of a certain class of hybrid robotic systems can be expressed using formal languages. In this work, we show how languages can be generated from discrete abstractions of such hybrid systems; that these languages are regular; and they belong to the star free (SF) class of the Sub-regular hierarchy. Planning and control of hybrid systems is typically difficult due to the computational cost involved in predicting the system’s future states, since the states can take infinite values while evolving along the trajectories of continuous dynamics. A discrete abstraction of the hybrid system can reduce these values to a finite number, thereby fascilitating the solution to the reachability problem. Abstraction enables us to focus on planning the system’s overall behavior through controller sequences observed in the abstract system, instead of dealing with the dynamics associated with each controller. The constraints between controllers enable or disable their temporal sequencing. Similarity of these constraints with those found in formal language theory, allows us to express controller sequences as strings of symbols forming a formal language. A formal language analysis of hybrid systems provides an approach for automatic planning and control design synthesis in single and multi-agent robotic systems. The class of hybrid systems considered in this work have convergent continuous dynamics with parameterized attractors. We model a robot as a hybrid system...