In the last two decades, two major earthquakes have occurred in Japan: the 1995 Kobe earthquake and the 2011 Great East Japan earthquake. In the 2011 Great East Japan earthquake, many bridge structures were destroyed by the tsunamis, but it is interesting to study the ground motion induced damage and also how this earthquake differed from the one in 1995. In this thesis, the seismic response of a bridge designed according to the current Japanese Design Specifications was evaluated when it is subjected to near-field ground motions recorded during the 1995 Kobe earthquake and far-field ground motions recorded during the 2011 Great East Japan earthquake. For this purpose, a series of nonlinear dynamic response analysis was conducted and the seismic performance of the bridge was verified in terms of its displacement and ductility demand. It was found from the dynamic response analysis that the seismic response of the target bridge when subjected to the ground motions from the 2011 Great East Japan earthquake was smaller than during the 1995 Kobe earthquake. Although the ground motions from the 2011 Great East Japan earthquake were very strong, they were not as strong as the ground motions from the 1995 Kobe earthquake. The results obtained in this thesis clarify the validity of the Type I and Type II design ground motions. The target bridge used in this thesis was designed according to the post-1990 design specifications and showed limited nonlinear response when subjected to the different ground motions which shows how efficient the enhancement of the seismic performance of bridges has been since the 1990’s.

No description available.

Full-scale lateral load tests were performed on a pile cap with five backfill conditions: no backfill, densely compacted fine gravel, loosely compacted fine gravel, densely compacted coarse gravel, and loosely compacted coarse gravel. Static loads, applied by hydraulic load actuators, were followed by low-frequency, actuator-driven cyclic loads as well as higher frequency dynamic loads from an eccentric mass shaker. Passive resistance from the backfill significantly increased the lateral capacity of the pile cap. Densely compacted backfill materials contributed about 70% of the total system resistance, whereas loosely compacted backfill materials contributed about 40%. The mobilized passive resistance occurred at displacement-to-height ratios of about 0.04 for the densely compacted gravels, whereas passive resistance in the loosely compacted materials does not fully mobilize until greater displacements are reached. Three methods were used to model the passive resistance of the backfill. Comparisons between calculated and measured responses for the densely compacted backfills indicate that in-situ shear strength test parameters provide reasonable agreement when a log-spiral method is used. Reasonable agreement for the loosely compacted backfills was obtained by either significantly reducing the interface friction angle to near zero or reducing the soil's frictional strength by a factor ranging from 0.65 to 0.85. Cracking, elevation changes, and horizontal strains in the backfill indicate that the looser materials fail differently than their densely compacted counterparts. Under both low frequency cyclic loading and higher frequency shaker loading, the backfill significantly increased the stiffness of the system. Loosely compacted soils approximately doubled the stiffness of the pile cap without backfill and densely compacted materials roughly quadrupled the stiffness of the pile cap. The backfill also affected the damping of the system in both the cyclic and the dynamic cases, with a typical damping ratio of at least 15% being observed for the foundation system.

A Study Of Shock Analysis Using The Finite Element Method Verified With Euler-Bernoulli Beam Theory; Mechanical Effects Due To Pulse Width Variation Of Shock Inputs; And Evaluation Of Shock Response Of A Mixed Flow Fan David Jonathan González Campos For many engineers that use finite element analysis or FEA, it is very important to know how to properly model and obtain accurate solutions for complicated loading conditions such as shock loading. Transient acceleration loads, such as shocks, are not as common as static loads. Analyzing these types of problems is less understood, which is the basis for this study. FEA solutions are verified using classical theory, as well as experimental results. The complex loading combination of shock and high speed rotation is also studied. Ansys and its graphic user interface, Workbench Version 14.5, are the programs used to solve these types of problems. Classical theory and Matlab codes, as well as experimental results, are used to verify finite element solutions for a simple structure, such as a cantilevered beam. The discrepancy of these FEA results is found to be 2.3%. The Full Method and the Mode Superposition Method in Ansys are found to be great solution tools for shock loading conditions, including complex acceleration and force conditions. The Full Method requires less pre-processing but solutions could take days, as opposed to hours, to complete in comparison with the Mode Superposition Method, depending on the 3D Model. The Mode Superposition Method requires more time and input by the user but solves relatively quickly. Furthermore, a new representation of critical pulse width of the shock inputs is presented. Experimental and finite element analyses of a complete mixed flow fan undergoing ballistic shock is also completed; deformation results due to shock loading, combined with rotation and aerodynamic loading, account for 32.3% of the total deformation seen from experimental testing. Solution methods incorporated in Ansys, and validation of FEA results using theory, have great potential implications as powerful tools for engineering students and practicing engineers.

Yes / A dynamic response analysis model of a Class E2 converter for wireless power transfer applications is presented. The converter operates at 200 kHz and consists of an induction link with its primary coil driven by a class E inverter and the secondary coil with a voltage-driven class E synchronous rectifier. A seventh-order linear time invariant state-space model is used to obtain the eigenvalues of the system for the four modes resulting from the operation of the converter switches. A participation factor for the four modes is used to find the actual operating point dominant poles for the system response. A dynamic analysis is carried out to investigate the effect of changing the separation distance between the two coils, based on converter performance and the changes required of some circuit parameters to achieve optimum efficiency and stability. The results show good performance in terms of efficiency (90–98%) and maintenance of constant output voltage with dynamic change of capacitance in the inverter. An experiment with coils of the dimension of 53 × 43 × 6 mm3 operating at a resonance frequency of 200 kHz, was created to verify the proposed mathematical model and both were found to be in excellent agreement.

No description available.

The otolith organs are commonly modeled as a system consisting of three distinct elements, a viscous endolymph fluid in contact with a rigid otoconial layer that is attached to the skull by a viscoelastic gel layer. However, in this model the gel layer is considered as a bi-layered viscoelastic solid and is modeled as a simple Kelvin-Voigt material. The governing differential equations of motion are derived and nondimensionalized yielding - three non-dimensional parameters: nondimensional viscosity, nondimensional elasticity and nondimensional density. These non-dimensional parameters are derived from experimental research. The shear stresses acting at the interface of the viscoelastic bi-layered gel are nondimensionalized and equated. The governing differential equations are then solved using finite difference techniques on a digital computer for a step-change in velocity and a constant acceleration stimulus. The results indicate that the inclusion of a viscoleastic bi-layered gel is essential for the model to produce greater otoconial layer deflections that are consistent with physiologic displacements. Future mathematical modeling of the otolith organs should include the effects of a viscoelastic bi-layered gel, as this is a major contributor to system damping and response and increased otoconial layer deflections. / Master of Science

The purpose of this research is to study a new type of vibration isolator, utilizing the post-buckled stiffness of elastic struts (or columns). The advantage of the post-buckled state is that ideally it can support more static load with a relatively small static deflection than traditional vibration isolators such as springs or rubber mounts, but can also exhibit a low axial stiffness when dynamic excitation is introduced. Three models consisting of buckled or pre-bent struts serving as vibration isolators which support a rigid bar are examined in this research. The three cases studied are 1) two buckled struts supporting a symmetric rigid bar, 2) two buckled struts supporting an asymmetric rigid bar, and 3) two pairs of buckled struts with a bonded filler supporting a symmetric rigid bar. The models are subjected to a harmonic excitation at the base, and external damping is included. The struts in all cases are modeled as an elastica, and the boundary conditions are clamped/clamped for all cases. Because the purpose of the struts is to reduce unwanted vibrations, determining the displacement transmissibility of the system is the main goal of this research. Transmissibility versus frequency plots are generated for all cases, with varying parameters such as stiffness, damping, and location of center of mass, to determine how they affect the behavior of the struts. Models that produce a large range of frequencies at which the transmissibility is well below unity are the most effective. Vibration shapes are also determined for certain frequencies so that the physical behavior of the system can be studied. / Master of Science

This research aims at understanding the conditions that lead to reaction initiation of polymer-bonded explosives (PBXs) as they undergo mechanical and thermal processes subsequent to impact. To analyze this issue, a cohesive finite element method (CFEM) based finite deformation framework is developed and used to quantify the thermomechanical response of PBXs at the microstructure level. This framework incorporates the effects of large deformation, thermomechanical coupling, failure in the forms of micro-cracks in both bulk constituents and along grain/matrix interfaces, and frictional heating. A novel criterion for the ignition of heterogeneous energetic materials under impact loading is developed, which is used to quantify the critical impact velocity, critical time to ignition, and critical input work at ignition for non-shock conditions as functions of microstructure of granular HMX and PBX. A threshold relation between impact velocity and critical input energy at ignition for non-shock loading is developed, involving an energy cutoff and permitting the effects of microstructure and loading to be accounted for. Finally, a novel approach for computationally predicting and quantifying the stochasticity of the ignition process in energetic materials is developed, allowing prediction of the critical time to ignition and the critical impact velocity below which no ignition occurs based on basic material properties and microstructure attributes. Results are cast in the form of the Weibull distribution and used to establish microstructure-ignition behavior relations.

As forças devidas ao vento variam espacial e temporalmente e consequentemente provocam esforços de torção em edifícios. A magnitude desses esforços depende basicamente da forma do edifício, de sua altura e estrutura, da influência da vizinhança e da direção do vento. As normas técnicas geralmente negligenciam a importância da torção. A versão atual da norma brasileira de forças devidas ao vento (NBR 6123) não possui uma abordagem aplicável para modos de vibração torcionais. Verificando a falta de recomendações da norma brasileira a respeito dos efeitos dinâmicos da torção em edifícios, este trabalho apresenta uma metodologia para a estimativa do momento torçor devido ao vento, a qual contempla tanto a parcela média quanto a parcela flutuante da solicitação. Para sua calibração utilizaram-se dados de 19 edifícios altos ensaiados no túnel de vento do Laboratório de Aerodinâmica das Construções com o método High Frequency Pressure Integration (HFPI), bem como dados da literatura técnica. A análise dos resultados mostrou que as excentricidades das forças de arrasto para cálculo do momento torçor apresentadas na NBR 6123 são adequadas na estimativa dos efeitos estáticos para edificações com efeitos de vizinhança mas tendem a subestimar a solicitação nos casos sem efeito de vizinhança. Assim, propuseram-se novos valores de excentricidades baseadas na análise da base de dados. Finalmente, apresentou-se uma metodologia para estimativa dos momentos torçores estáticos equivalentes, a qual foi comparada com os valores fornecidos pelo HFPI e constatou-se que a proposta fornece valores adequados. / Wind loads change spatially and temporally consequently they induce torsional moments on buildings. These moments are affected by building shape and structure, by interfering effects of nearby buildings and wind direction. The importance of torsional loads is usually neglected by most codes. Indeed, dynamic torsional response is not presented on current Brazilian Wind Loads Code (NBR 6123). Therefore, a procedure to determine torsional dynamic response of buildings subjected to turbulent wind action is proposed. Experimental data of 19 buildings are used to improve the reliability of proposed procedure. These experimental tests were performed in boundary layer wind tunnel of Aerodynamic Laboratory using the High Frequency Pressure Integration (HFPI) technique. About torsional loads, results have shown that drag forces eccentricities present on the NBR 6123 are reliable when neighboring effects are considered, but they underestimate torsion when neighboring effects are not considered. New eccentricities values are proposed. Finally, a procedure to estimate the torsional static equivalent moment is presented and it agrees well with HFPI results. The average relative error between the results determined by the proposed formulae and the experimental data obtained by the HFPI shows the reliability and applicability of the proposed formulation to the design of isolated and nonisolated buildings.