660 research outputs found
A nonlocal sinusoidal shear deformation beam theory with application to bending, buckling, and vibration of nanobeams
No full textThis paper presents a nonlocal sinusoidal shear deformation beam theory for the bending, buckling, and vibration of nanobeams. The present model is capable of capturing both small scale effect and transverse shear deformation effects of nanobeams, and does not require shear correction factors. Based on the nonlocal differential constitutive relations of Eringen, the equations of motion as well as the boundary conditions of the beam are derived using Hamilton’s principle. Analytical solutions for the deflection, buckling load, and natural frequency are presented for a simply supported beam, and the obtained results are compared with those predicted by the nonlocal Timoshenko beam theory. The comparison firmly establishes that the present beam theory can accurately predict the bending, buckling, and vibration responses of short nanobeams where the small scale and transverse shear deformation effects are significant
Forced vibrations of a Timoshenko beam under the influence of distributed quadratic damping
No full textThe steady-state response of a Timoshenko beam under the unfluence of distributed quadratic damping and a sinusoudal forcing function is considered. The Timoshenko beam equations are solved by the method of characteristics. A numerical example is considered with numerical results given in graphical form.Mechanical Engineering, Department o
The Timoshenko beam with strain rate damping supported by an elastic foundation
No full textThe development of the governing equations for a Timoshenko beam with strain rate damping is presented. Also presented are the governing differential equations for the Shear, Rayleigh and Bernoulli-Euler beams with strain rate damping. The Timoshenko beam with strain rate damping was assumed to be supported by a Winkler-type foundation and subjected to a point load moving with constant velocity. Roots of the steady-state equation are presented as functions of strain rate damping, foundation damping and moving load velocity. The steady-state response of the Rayleigh beam to the moving load is presented for various values of strain rate damping, foundation damping and moving load velocities.Engineering, Cullen College o
Local Structure Studies of for and by Advanced X-ray Absorption Spectroscopy Data Analysis
No full textStrontium titanate is a model quantum paraelectric in which in the region of dominating quantum statistics the ferroelectric instability is inhibited due to nearly complete compensation of the harmonic contribution into ferroelectric soft mode frequency by the zero-point motion contribution. The enhancement of atomic masses by the substitution of O for O decreases the zero-point atomic motion and low-T ferroelectricity in SrTiO is realized. In this study we report on the local structure of Ti in SrTiO and SrTiO by Ti K-edge extended x-ray absorption fine structure measurements in temperature range 6 – 300 K
Interaction curves for vibration and buckling of thin-walled composite box beams under axial loads and end moments
No full textInteraction curves for vibration and buckling of thin-walled composite box beams with arbitrary lay-ups under constant axial loads and equal end moments are presented. This model is based on the classical lamination theory, and accounts for all the structural coupling coming from material anisotropy. The governing differential equations are derived from the Hamilton’s principle. The resulting coupling is referred to as triply flexural–torsional coupled vibration and buckling. A displacement-based one-dimensional finite element model with seven degrees of freedoms per node is developed to solve the problem. Numerical results are obtained for thin-walled composite box beams to investigate the effects of axial force, bending moment, fiber orientation on the buckling loads, buckling moments, natural frequencies and corresponding vibration mode shapes as well as axial-moment–frequency interaction curves
Sistematização da modelagem e simulação dinamica de manipuladores flexiveis
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro TecnologicoEste trabalho trata do desenvolvimento de uma metodologia para a modelagem e simulação de manipuladores contendo ligações e juntas rotacionais flexíveis. Na modelagem são utilizadas as equações de Lagrange. O conjunto de coordenadas generalizadas utilizado é composto de coordenadas que descrevem os grandes deslocamentos de corpo rígido das ligações, e das coordenadas que descrevem os pequenos deslocamentos devido as deformações das ligações. As ligações são discretizadas através de elementos finitos baseados na teoria de vigas de Timoshenko, e a flexibilidade das juntas através de molas torcionais lineares. Para a simulação, foram implementados procedimentos que permitem a obtenção da resposta estática da estrutura para diferentes carregamentos e posições, das freqüências naturais e dos modos de vibração, e a resposta dinâmica no tempo para dadas trajetórias. As informações geradas permitem que o desempenho do projeto estrutural seja avaliado para várias situações de trabalho
Análise do comportamento dinâmico de rotores em eixos bobinados
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico.Este trabalho tem por objetivo analisar, utilizando o método dos elementos finitos, o comportamento dinâmico de rotores em eixos bobinados. Os rotores são formados por um ou dois discos acoplados à um eixo apoiado em mancais flexíveis. Os eixos são, neste caso, fabricados a partir do bobinamento de fibras impregnadas em resina sobre um mandril. Os discos são considerados rígidos e um elemento do tipo viga com módulo equivalente é utilizado para modelar o eixo do rotor. Um modelo de amortecimento interno é introduzido através de um módulo equivalente amortecido. Inicialmente, são determinadas a resposta a uma massa desbalanceada e as zonas de instabilidade para os modos em flexão de rotores apoiados em mancais com diferentes configurações. Nos modos em torção, são determinadas as freqüências naturais e os respectivos fatores de amortecimento, bem como a resposta em freqüência. Os resultados obtidos com o eixo em carbono/epóxi e em vidro/epóxi, mostraram que o ângulo de bobinagem do eixo pode ter forte influência na localização das freqüências naturais, tanto nos modos em flexão quanto em torção. O amortecimento interno, proveniente do material composto, pode reduzir consideravelmente os picos de amplitudes de vibrações, porém pode gerar instabilidade no sistema. E por fim, com o objetivo de ressaltar as vantagens e a flexibilidade oferecidas pelo uso de materiais compostos em rotores, um método de otimização foi utilizado para minimizar picos de amplitude, evitar zonas de instabilidade e determinar a posição ótima das velocidades críticas, tendo como variáveis de projeto o ângulo de bobinagem, as rigidezes dos mancais e a posição do disco no eixo
Damage detections in nonlinear vibrating thermally loaded plates
No full textIn this work, geometrically nonlinear vibrations of fully clamped rectangular plates subjected to thermal changesare used to study the sensitivity of some vibration response parameters to the presence of damage and elevated temperature. The geometrically nonlinear version of the Mindlin plate theory is used to model the plate behaviour.Damage is represented as a stiffness reduction in a small area of the plate. The plates are subjected to harmonicloading leading to large amplitude vibrations and temperature changes. The plate vibration response is obtained by a pseudo-load mode superposition method. The main results are focussed on establishing the influence of damage on the vibration response of the heated and the unheated plates and the change in the time-history diagrams and the Poincaré maps caused by damage and elevated temperature. The damage criterion formulated earlier for nonheated plates, based on analyzing the points in the Poincaré sections of the damaged and healthy plate, is modified and tested for the case of plates additionally subjected to elevated temperatures. The importance of taking into account the actual temperature in the process of damage detection is shown
Lexical Duplicity and Rebranding as Variants of Semantic Shifts
No full textТимошенко Людмила Олеговна, кандидат филологических наук, доцент кафедры иностранных языков гуманитарных факультетов, Башкирский государственный университет (Уфа), [email protected]. Lyudmila O. Timoshenko, PhD, Associate Professor, the Chair of Foreign Languages of Humanitarian
Departments of Bashkir State University (Ufa), [email protected]Статья посвящена актуальной в современном языкознании теме семантических изменений,
деривации и сдвигам в заимствованной лексике. Семантические изменения, или переходы, рассматриваются в рамках лингвистического моделирования. Раскрываются понятия семантической
дублетности и ребрендинга на примерах из английского и французского как ведущих европейских языков в рамках исследования автором лексических соответствий. Обилие лингвистических
терминов, относящихся к сфере семантической деривации, упоминаемых в данной статье, показывает актуальность этой лингвистической проблемы и неоднозначный подход в ее решении.
Все семантические изменения показаны как часть общекогнитивной проблемы передачи смысла
высказывания с точки зрения логики и критерия истинности. Лингвистические проблемы, рассматриваемые в данной статье, носят общекогнитивный и общелогический характер. The article is devoted the topical problem in modern linguistics – the problem of semantic
changes, derivation and shifts in the borrow edlexics. Semantic changes, or shifts are regarded in the
framework of linguistic modelling. The author describes the notions of semantic duplicity and rebranding
on the examples from English and French as the leading European languages, included in the author’s
study of lexical correspondences. The abundance of linguistic terms, denoting the sphere of semantic
derivation, mentioned in the present article, shows the topical character of this linguistic problem
and a multilateral approach in solving it. All the semantic changes, studied by the author, are represented
as a part of the general cognitive problem of transmitting sense, or the purport of the utterance
from the point of view of logic and the criterion of verity. Linguistic problems, described in the present
article, are of general cognitive and general logic character
Static and free vibration of axially loaded functionally graded beams based on the first-order shear deformation theory
No full textThe first-order shear deformation beam theory for static and free vibration of axially loaded rectangular functionally graded beams is developed. In this theory, the improved transverse shear stiffness is derived from the in-plane stress and equilibrium equation and thus, associated shear correction factor is then obtained analytically. Equations of motion are derived from the Hamilton’s principle. Analytical solutions are presented for simply-supported functionally graded beams. The obtained results are compared with the existing solutions to verify the validity of the developed theory. Effects of the power-law index, material contrast and Poisson’s ratio on the displacements, natural frequencies, buckling loads and load–frequency curves as well as corresponding mode shapes are investigated
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