This project studies the dynamic response of a composite floor system to excitations from moving fork-lift trucks. The floor system analysed is a system of precast and partially prestressed double-tee elements with a cast in-situ topping. Currently, there are concerns whether the vibrations caused by fork-lift trucks might exceed acceptable limits due to an ongoing trend towards structures of higher slenderness. This study investigates the mechanical background of the excitation and the current design of the floor system. The study is divided into three major chapters: <strong>Dynamic fork-lift truck model</strong> A dynamic load model of a fork-lift truck is developed which can be used in the analytical verification of the vibration serviceability of structures. The model is based on tests performed on four fork-lift trucks in various configurations. The tests are analysed for the spectrum of accelerations. The analysis results in a simple two-degree-of-freedom model. Its only variables are velocity and time. All other values are constant throughout a simulation and depend on the geometry of the specific fork-lift truck and its payload. The frequencies and phase delays are constants and they are verified as eigen-frequencies of a three-degree-of-freedom model. <strong>FE-simulation of vibrations of a composite floor system</strong> The fork-lift truck model is applied to a three-dimensional model of a composite floor system. The finiteelement model is developed to simulate the construction process of the composite floor system and its influence on the in-service properties of the structure. As part of this work a preliminary investigation of the damping potential of the joint between precast and cast in-situ concrete is undertaken. A linear time-step analysis of the structure is performed and the nodal accelerations are analysed for their magnitude, dependence on the excitation and frequency content. <strong>Field test</strong> In order to verify the FE-model of the floor system and the results of the dynamic analysis a field test was undertaken: a floor system was monitored under service conditions. The field data comprise the accelerations of the floor and the forklift truck and the position of the truck relative to the points of measurement. A comparison of the field data and the simulation results proves the validity of both the dynamic fork-lift truck model and the FE-model of the floor system.

Este trabalho trata da análise dinâmica bidimensional de treliças de aço e pórticos de concreto armado, onde estudam-se os efeitos da não-linearidade física desses materiais e os efeitos da não-linearidade geométrica de tais estruturas. Neste contexto, define-se a equação geral que descreve o comportamento de estruturas discretizadas por elementos finitos, utilizando-se o Princípio dos Trabalhos Virtuais para estruturas em movimento. Para a integração temporal dessa equação, utiliza-se um método implícito de integração numérica, onde adota-se um processo previsor-corretor com auxílio das equações generalizadas de Newmark. Na análise da não-linearidade geométrica, define-se o campo de deformações através de uma função quadrática dos deslocamentos, que ocorrem ao longo de cada elemento finito, sendo que para treliças planas consideram-se todas as parcelas provenientes de tal relação e para pórticos planos desprezam-se os termos que contém produtos de parcelas de ordem superior. Para descrever a posição de equilíbrio do sistema estrutural ao longo do processo de integração numérica, utiliza-se a formulação Lagrangeana atualizada que resulta na dedução das matrizes de rigidez incrementais secante e tangente. Com relação à não-linearidade física do aço, elabora-se uma modelagem numérica através da utilização de um diagrama tensão x deformação bilinear, destacando-se os modelos cinemático, isotrópico e independente. Já para a não-linearidade física do concreto armado, elabora-se uma modelagem numérica através da utilização dos modelos propostos pelo CEB e pelo ACI, onde corrige-se o valor do momento de inércia em função do grau de fissuração do elemento. Estas modelagens contemplam, também, o comportamento para carregamento cíclico e sua inversão. Para finalizar, apresentam-se com posterior análises qualitativa e quantitativa dos resultados. / This work deals with the two-dimensional dynamic analysis of steel trusses and reinforced concrete frames. The physical non-linear effects of these materials as well as the geometrical non-linearity of such structures are studied. In this context, a general equation that describes the behaviour of structures approximated by finite elements is defined, using the Virtual Works Principle for structures in movement. In order to integrate this differential equation along the time an implicit procedure is adopted based on the predictor-corrector process taking into account the Newmark\'s generalised equations. For the geometrical non-linear analysis, the deformation field is defined by assuming displacements approximated along each finite element by quadratic shape functions. All terms resulting from that assumption are taken into account for the plane trusses, while for plane frame, terms representing higher order products are neglected. In order to describe the equilibrium position of the structural system, during the numeric integration process, the updated Lagrangean formulation is used to give the secant and tangent incremental stiffness matrices. Regarding the steel non-linear physical behaviour, a numerical procedure is achieved based on a bilinear stress-strain curve that is able to describe kinematic, isotropic and independent responses. For the reinforced concrete physical non-linear behaviour the well known CEB and ACI models were taken to derive and implement the numeric process. In this case, the moment of inertia is corrected according to the element level of cracking. These models also consider the material behaviour when cyclic loads are applied causing stress sign inversion. Finally, numeric examples are presented to illustrate the quality and accuracy of obtained results.

On August 5, 2010 the U.S. Department of Energy (DOE) has designated the Center for Ocean Energy Technology (COET) at Florida Atlantic University (FAU) as a national center for ocean energy research and development of prototypes for open-ocean power generation. Maintenance on ocean-based machinery can be very costly. To avoid unnecessary maintenance it is necessary to monitor the condition of each machine in order to predict problems. This kind of prognostic health monitoring (PHM) requires a condition-based maintenance (CBM) system that supports diagnostic and prognostic analysis of large amounts of data. Research in this field led to the creation of ISO13374 and the development of a standard open-architecture for machine condition monitoring. This thesis explores an implementation of such a system for ocean-based machinery using this framework and current open-standard technologies. / by Mark Bowren. / Thesis (M.S.C.S.)--Florida Atlantic University, 2012. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2012. Mode of access: World Wide Web.

In the field of machine prognostics, vibration analysis is a proven method for detecting and diagnosing bearing faults in rotating machines. One popular method for interpreting vibration signals is envelope demodulation, which allows a technician to clearly identify an impulsive fault source and its severity. However incipient faults -faults in early stages - are masked by in-band noise, which can make the associated impulses difficult to detect and interpret. In this thesis, Wavelet De-Noising (WDN) is implemented after envelope-demodulation to improve accuracy of bearing fault diagnostics. This contrasts the typical approach of de-noising as a preprocessing step. When manually measuring time-domain impulse amplitudes, the algorithm shows varying improvements in Signal-to-Noise Ratio (SNR) relative to background vibrational noise. A frequency-domain measure of SNR agrees with this result. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection

The design of bridge structures to resist explosive loads has become more of a concern to the engineering community. This thesis proposes a method to evaluate the effects of conventional blast loads on a two span continuous composite steel girder bridge system. The bridge design is based on AASHTO LRFD method. Resistance capacities of bridge deck and composite steel girder are calculated according to AASHTO specifications. Equivalent blast pressures on the bridge components are obtained. Response and performance of concrete deck, steel girders, and supporting piers are evaluated under typical blast loads. The blast induced force in the bridge components are computed in the static analyses for varying amounts of TNT. The blast effects in the supporting pier are determined using both static and dynamic analyses. Further research needs to be done in the dynamic analysis of the bridge system subjected to blast loads. / by Fang Zhou. / Thesis (M.S.C.S.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.

On August 5, 2010 the U.S. Department of Energy (DOE) has designated the Center for Ocean Energy Technology (COET) at Florida Atlantic University (FAU) as a national center for ocean energy research and development. Their focus is the research and development of open-ocean current systems and associated infrastructure needed to development and testing prototypes. The generation of power is achieved by using a specialized electric generator with a rotor called a turbine. As with all machines, the turbines will need maintenance and replacement as they near the end of their lifecycle. This prognostic health monitoring (PHM) requires data to be collected, stored, and analyzed in order to maximize the lifespan, reduce downtime and predict when failure is eminent. This thesis explores the use of a data gateway which will separate high level software with low level hardware including sensors and actuators. The gateway will v standardize and store the data collected from various sensors with different speeds, formats, and interfaces allowing an easy and uniform transition to a database system for analysis. / by Joseph. Gundel. / Thesis (M.S.C.S.)--Florida Atlantic University, 2012. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2012. Mode of access: World Wide Web.

Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Dept. of Ocean Engineering. / Includes bibliographical references. / by J. Kim Vandiver. / Ph.D.

Uncertainty propagation in engineering mechanics and dynamics is a highly challenging problem that requires development of analytical/numerical techniques for determining the stochastic response of complex engineering systems. In this regard, although Monte Carlo simulation (MCS) has been the most versatile technique for addressing the above problem, it can become computationally daunting when faced with high-dimensional systems or with computing very low probability events. Thus, there is a demand for pursuing more computationally efficient methodologies. Further, most structural systems are likely to exhibit nonlinear and time-varying behavior when subjected to extreme events such as severe earthquake, wind and sea wave excitations. In such cases, a reliable identification approach is behavior and for assessing its reliability. Current work addresses two research themes in the field of stochastic engineering dynamics related to the above challenges. In the first part of the dissertation, the recently developedWiener Path Integral (WPI) technique for determining the joint response probability density function (PDF) of nonlinear systems subject to Gaussian white noise excitation is generalized herein to account for non-white, non-Gaussian, and non-stationary excitation processes. Specifically, modeling the excitation process as the output of a filter equation with Gaussian white noise as its input, it is possible to define an augmented response vector process to be considered in the WPI solution technique. A significant advantage relates to the fact that the technique is still applicable even for arbitrary excitation power spectrum forms. In such cases, it is shown that the use of a filter approximation facilitates the implementation of the WPI technique in a straightforward manner, without compromising its accuracy necessarily. Further, in addition to dynamical systems subject to stochastic excitation, the technique can also account for a special class of engineering mechanics problems where the media properties are modeled as non-Gaussian and non-homogeneous stochastic fields. Several numerical examples pertaining to both single- and multi-degree-of freedom systems are considered, including a marine structural system exposed to flow-induced non-white excitation, as well as a beam with a non-Gaussian and non-homogeneous Young’s modulus. Comparisons with MCS data demonstrate the accuracy of the technique. In the second part of the dissertation, a novel multiple-input/single-output (MISO) system identification technique is developed for parameter identification of nonlinear time-variant multi-degree-of-freedom oscillators with fractional derivative terms subject to incomplete non-stationary data. The technique utilizes a representation of the nonlinear restoring forces as a set of parallel linear subsystems. In this regard, the oscillator is transformed into an equivalent MISO system in the wavelet domain. Next, a recently developed L1-norm minimization procedure based on compressive sampling theory is applied for determining the wavelet coefficients of the available incomplete non-stationary input-output (excitation-response) data. Finally, these wavelet coefficients are utilized to determine appropriately defined time- and frequency-dependent wavelet based frequency response functions and related oscillator parameters. A nonlinear time-variant system with fractional derivative elements is used as a numerical example to demonstrate the reliability of the technique even in cases of noise corrupted and incomplete data.

Numerical models are pervasive tools in science and engineering for simulation, design, and assessment of physical systems. In structural engineering, finite element (FE) models are extensively used to predict responses and estimate risk for built structures. While FE models attempt to exactly replicate the physics of their corresponding structures, discrepancies always exist between measured and model output responses. Discrepancies are related to aleatoric uncertainties, such as measurement noise, and epistemic uncertainties, such as modeling errors. Epistemic uncertainties indicate that the FE model may not fully represent the built structure, greatly limiting its utility for simulation and structural assessment. Model updating is used to reduce error between measurement and model-output responses through adjustment of uncertain FE model parameters, typically using data from structural vibration studies. However, the model updating problem is often ill-posed with more unknown parameters than available data, such that parameters cannot be uniquely inferred from the data. This dissertation focuses on two approaches to remedy ill-posedness in FE model updating: parametrization and regularization. Parametrization produces a reduced set of updating parameters to estimate, thereby improving posedness. An ideal parametrization should incorporate model uncertainties, effectively reduce errors, and use as few parameters as possible. This is a challenging task since a large number of candidate parametrizations are available in any model updating problem. To ameliorate this, three new parametrization techniques are proposed: improved parameter clustering with residual-based weighting, singular vector decomposition-based parametrization, and incremental reparametrization. All of these methods utilize local system sensitivity information, providing effective reduced-order parametrizations which incorporate FE model uncertainties. The other focus of this dissertation is regularization, which improves posedness by providing additional constraints on the updating problem, such as a minimum-norm parameter solution constraint. Optimal regularization is proposed for use in model updating to provide an optimal balance between residual reduction and parameter change minimization. This approach links computationally-efficient deterministic model updating with asymptotic Bayesian inference to provide regularization based on maximal model evidence. Estimates are also provided for uncertainties and model evidence, along with an interesting measure of parameter efficiency.

As estruturas, particularmente na engenharia civil, podem apresentar ruína quando atingem sua capacidade resistente ou quando perdem sua estabilidade, sendo, portanto atribuição básica do engenheiro de estruturas o estudo de ambas as situações. A instabilidade de uma estrutura pode surgir de dois modos, a saber: por ocorrência de uma bifurcação de equilíbrio ou por ocorrência de um ponto limite, também conhecido por snap-through, onde o aumento do carregamento provoca uma diminuição da rigidez da estrutura, até que esta se anula no ponto limite (REIS; CAMOTIM, 2012). Estruturas como arcos, treliças e calotas esféricas abatidas, presentes em grandes coberturas, são tipos de estruturas que podem apresentar esta instabilidade, em que há a passagem dinâmica da estrutura para uma configuração de equilíbrio afastada e estável, saltando para essa configuração pós-crítica envolvendo grandes deslocamentos e inversão da curvatura. Se, no entanto, o carregamento é dinâmico, como, por exemplo, harmônico, a resposta do sistema adquire uma grande riqueza de possíveis comportamentos, em função da amplitude e frequência desse carregamento. As respostas podem resultar vibrações periódicas de vários períodos diferentes, quase periódicas, caóticas etc. Este trabalho tem como objetivo fazer um estudo da estabilidade estática e dinâmica do problema da treliça simples de duas barras (treliça de Von Mises) e do arco abatido senoidal, de comportamento elástico linear, com o estabelecimento das equações de equilíbrio na configuração deformada, i.e., levando em conta a não linearidade geométrica. A avaliação da resposta, bem como a caracterização de sua estabilidade, se dará pela apresentação das cargas críticas de instabilidade do sistema perfeito, exibição do comportamento de pós-instabilidade e, com a integração numérica do modelo matemático, o estudo geométrico dado pelos planos de fase, mapas de Poincaré, diagramas de bifurcação e fronteira de estabilidade. / Structures, particularly in civil engineering, can ruin when they reach their strength capacity or when they lose their stability. So, it is the basic assignment of the structural engineer to study both situations. The instability of a structure can arise in two ways, namely: by the occurrence of bifurcation of equilibrium or by the occurrence of a snap-through, where an increase of the loading causes a decrease in structure stiffness, until the stiffness is annulled in the limit point (REIS, CAMOTIM, 2012). Structures such as arches, trusses and domes, present in large roofs, are types of structures that may present this kind of instability, in which there is the dynamic passage of the structure to a far away stable equilibrium configuration, jumping to this post-critical configuration involving large displacements and reversal of the curvature. If, however, the load is dynamic, such as harmonic, the response of the system acquires a great wealth of possible behaviors, depending on the amplitude and frequency of this loading. The responses may result in periodic vibrations of several different periods, almost periodic, chaotic, etc. This work intends to study the static and the dynamic stability of the Von Mises truss and the shallow arc of linear elastic behavior, with the establishment of the equilibrium equations in the deformed configuration, i.e., taking into account the geometric non-linearity. The evaluation of the response, as well as the characterization of its stability, will be done by numerical integration of the mathematical model and geometric study of the phase planes, Poincaré maps, bifurcation diagrams and stability border.