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Doctor of Philosophy / Civil Engineering / Kyle Riding / Pre-stressed concrete is used for manufacturing railroad ties. Air entrainment is used in concrete railroad ties to provide durability in freeze-thaw conditions commonly present in track. Vibration practices in pre-stressed concrete railroad tie plants could contribute to excessive air loss during manufacture and thus poor freeze-thaw resistance. Rheological properties of fresh concrete significantly influence the determination of how much air is lost during vibration. This research attempted to increase understanding of the effect of vibration on air bubble distribution and freeze-thaw resistance of concrete given certain compositions and rheological properties of concrete. The objective was achieved by examining the effect of different admixtures combinations, vibration parameters, and rheological properties on the air void system and freeze-thaw resistance of concrete. This research also proposed a method to measure rheological properties of concrete when vibrated and for concrete mixtures too stiff to measure using conventional rheology measurements. Results showed that delaying the initiation of vibration can cause significant air loss but does not necessarily decrease freeze-thaw performance of concrete. Results also showed that a majority of air loss occurs in the first 30 seconds of vibration. The types of admixtures used in the concrete mixture can significantly affect the air system and freeze-thaw durability of concrete; this effect was shown to be more pronounced in mixtures with low yield stress and plastic viscosity. While the peak vibration acceleration had a mild effect, the frequency and peak velocity of vibration did not seem to have a noticeable effect on the air system and freeze-thaw performance of concrete. Results also showed that rheological properties of stiff mixtures can be estimated by running the rheology test during vibration.

Made available in DSpace on 2018-07-27T17:13:44Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-11-30. Added 1 bitstream(s) on 2018-07-27T17:16:35Z : No. of bitstreams: 1 000888005.pdf: 2314737 bytes, checksum: fe957a04aa48ca32759e7812068c0620 (MD5) / Atualmente as indústrias, as construções civis e centros de pesquisas têm direcionado suas pesquisas visando o controle de vibrações das estruturas através da atenuação das amplitudes de movimento e monitoramento das mesmas pela detecção e localização de falhas oriundas de desgastes ou qualquer outro tipo de irregularidade que altere o comportamento dinâmico e consequentemente sua vida útil. O presente trabalho tem como objetivo a utilização de absorvedores dinâmicos de vibração do tipo lâmina vibrante, modelado por elementos finitos de viga (Euler-Bernoulli), acoplados à uma plataforma, ou superfície retangular modelada por elementos finitos de placa de Kirchhoff que possui um motor em sua superfície. As vibrações são geradas por um desbalanceamento rotativo e a metodologia dos Observadores de Estado é aplicada para detecção e localização de falhas nos parâmetros mais propensos a desgastes ou alterações estruturais. São feitas simulações computacionais com o intuito de ilustrar o comportamento da estrutura e demonstrar os efeitos do acoplamento do absorvedor na estrutura primária / Currently, industries, civil construction and research centers have directed their research aiming at the vibration control of structures by mitigating the range of motion and monitoring by detecting and locating faults arising from wear or any other type of irregularity that can change the dynamic behavior and therefore your life. This study aims to use dynamic vibration absorbers of vibrating blade type, modeled by finite element beam (Euler-Bernoulli), coupled to a platform or rectangular surface modeled by finite element Kirchhoff plate that has a motor on its surface. The vibrations are generated by a rotating imbalance and the methodology of State Observers is applied to detection and localization of failures in the more prone parameters to wear or structural changes. Computational simulations are done with the intention of illustrating the behavior of the structure and to demonstrate the effects of coupling the absorber in the primary structure

This thesis presents a comparison of added mass modeling techniques that may be used to determine the the vibration response characteristics of ships in water. The mathematical treatment of added mass is reviewed, and a number of numerical approaches are discussed. Experiments to determine the natural frequencies of a ship model in air and in water were performed and were compared with the results obtained from the numerical approaches. It will be shown in this thesis that the use of modal analysis to predict ship vibration responses in water is a satisfactory and less time consuming alternative to a full eigenvalue solution. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Orientador: Gilberto Pechoto de Melo / Banca: Amarildo Tabone Paschoalini / Banca: Fabrício César Lobato de Almeida / Resumo: Atualmente as indústrias, as construções civis e centros de pesquisas têm direcionado suas pesquisas visando o controle de vibrações das estruturas através da atenuação das amplitudes de movimento e monitoramento das mesmas pela detecção e localização de falhas oriundas de desgastes ou qualquer outro tipo de irregularidade que altere o comportamento dinâmico e consequentemente sua vida útil. O presente trabalho tem como objetivo a utilização de absorvedores dinâmicos de vibração do tipo lâmina vibrante, modelado por elementos finitos de viga (Euler-Bernoulli), acoplados à uma plataforma, ou superfície retangular modelada por elementos finitos de placa de Kirchhoff que possui um motor em sua superfície. As vibrações são geradas por um desbalanceamento rotativo e a metodologia dos Observadores de Estado é aplicada para detecção e localização de falhas nos parâmetros mais propensos a desgastes ou alterações estruturais. São feitas simulações computacionais com o intuito de ilustrar o comportamento da estrutura e demonstrar os efeitos do acoplamento do absorvedor na estrutura primária / Abstract: Currently, industries, civil construction and research centers have directed their research aiming at the vibration control of structures by mitigating the range of motion and monitoring by detecting and locating faults arising from wear or any other type of irregularity that can change the dynamic behavior and therefore your life. This study aims to use dynamic vibration absorbers of vibrating blade type, modeled by finite element beam (Euler-Bernoulli), coupled to a platform or rectangular surface modeled by finite element Kirchhoff plate that has a motor on its surface. The vibrations are generated by a rotating imbalance and the methodology of State Observers is applied to detection and localization of failures in the more prone parameters to wear or structural changes. Computational simulations are done with the intention of illustrating the behavior of the structure and to demonstrate the effects of coupling the absorber in the primary structure / Mestre

Recent progress in structural engineering has been marked by the increased use of thin shells as load carrying members. In particular, shells of revolution have been widely utilized in the missile industry whereas shells of arbitrary shape have been incorporated in the architectural design of today's modern buildings. Missile applications have been extensively studied both statically and dynamically. However, architechural applications have generally been limited to the statics problem with little consideration being given to the dynamic behavior of these unique structures.

The present study involved two types of analyses as a part of the investigation leading to the design of a shock absorber providing optimal vibration control and minimum transmissibility. Those two types of analyses were the following.

Freezing rainstorms coupled with moderate winds have often been observed to cause telephone lines and power transmission cables to begin bouncing up and down. This slow frequency high amplitude oscillation, or galloping as it is sometimes called, can build up to large amplitudes before the oscillation either damps out or persists at some constant amplitude. It has been reported by Edwards and Livingston [1] that the amplitude of galloping on transmission lines has been as large as forty feet. Galloping oscillations occur at relatively low frequencies; from .1 to 1 Hz. [1] near the natural frequency of the suspended cable.

Vibration causes problems in many kinds of machinery including fighter aircraft. It can, for example, cause structural fatigue, malfunction in equipment and injuries to humans. The sources of vibration are engines, flow disturbance and separation of external loads, to mention some. To isolate sensitive equipment from the source of vibration it is common to use vibration isolators made of rubber. This master’s thesis is performed at Saab Aeronautics in Linköping at the Department of Environmental Engineering & Thermal Analysis. The subject of the master’s thesis is to develop a methodology for the analysis of vibration isolating systems in aircraft. The work is performed by finite element analysis and laboratory tests using a shaker table. In the finite element analysis, part of the study, a method to condensate the structure to decrease the number of degrees of freedom is studied and used. Nonlinearities are investigated but only linear characteristics are implemented into the f inite element model. Rubber as a material has several non-linear characteristics that depend on the amplitude and frequency of the vibration. For example, the stiffness and damping are amplitude dependent. From laboratory results from tests on a shaker table, the stiffness and damping of the vibration isolators are extracted. To do this, the frequency transfer function is used by identifying eigenmodes and the eigenfrequency to calculate the stiffness and extract the damping by studying the shape of the peak. A finite element model with a condensed structure is used to find the eigenmodes and the eigenfrequencies. By exciting the finite element model the frequency response is also calculated. The tested vibration isolator shows large non-linearity for the stiffness and damping when varying the amplitude of a sinusoidal vibration. Using a condensed structure in finite element is a powerful tool to reduce computational time. If the solution of a simulation or calculation has to be very accurate or if the amplitudes of the vibration vary a lot, the non-linearities must be implemented into the simulation or calculation and accounted for.

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