Lead-lag dampers are present in most rotor systems to provide the desired level of damping for all flight conditions. These dampers are critical components of the rotor system, and the performance of semi-active Coulomb-friction-based lead-lag dampers is examined for the UH-60 aircraft. The concept of adaptive damping, or “damping on demand,” is discussed for both ground resonance and forward flight. The concept of selective damping is also assessed, and shown to face many challenges. In rotorcraft flight dynamics, optimized warping twist change is a potentially enabling technology to improve overall rotorcraft performance. Research efforts in recent years have led to the application of active materials for rotorcraft blade actuation. An innovative concept is proposed wherein the typically closed section blade is cut open to create a torsionally compliant structure that acts as its own amplification device; deformation of the blade is dynamically controlled by out-of-plane warping. Full-blade warping is shown to have the potential for great design flexibility. Recent advances in rotorcraft blade design have also focused on variable-camber airfoils, particularly concepts involving “truss-core” configurations. One promising concept is the use of hexagonal chiral lattice structures in continuously deformable helicopter blades. The static behavior of passive and active chiral networks using piezoelectric actuation strategies is investigated, including under typical aerodynamic load levels. The analysis is then extended to the dynamic response of active chiral networks in unsteady aerodynamic environments.

Orientador: Katia Lucchesi Cavalca Dedini / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-24T00:13:00Z (GMT). No. of bitstreams: 1 Galera_Larissa_M.pdf: 7841610 bytes, checksum: b4caff2b3c8de6cf54d4ef086fd47585 (MD5) Previous issue date: 2013 / Resumo: A análise dinâmica de rotores visa prever o comportamento e identificar desvios caracterizados por meio das respostas dinâmicas do conjunto, fornecendo indicadores de mau funcionamento ou diagnóstico de falhas, e minimizando os riscos de paradas imprevistas no sistema. O estudo dinâmico de máquinas rotativas deve ser realizado considerando a interação entre os componentes envolvidos na sua construção, como por exemplo, rotores, eixos, mancais, selos de fluxo e estruturas de suporte. Os selos de fluxo causam forças de reação que podem ser representadas por coeficientes dinâmicos. Este componente é o principal responsável por diferenças entre um modelo usando apenas eixo-mancal e a vibração real do sistema, como por exemplo, em bombas centrífugas. Dentro deste contexto, este trabalho tem por objetivo a determinação dos coeficientes dinâmicos de três tipos de selos planos, sendo eles: cilíndrico, cônico e escalonado, os quais serão integrados ao modelo global de sistemas rotativos, de modo a tornar a análise do conjunto girante mais completa. A análise dos selos de fluxo será realizada utilizando o método de volumes finitos para determinar a distribuição de velocidade circunferencial e de pressão ao longo do selo, que caracterizam as forças de reação. Estas, por sua vez, podem ser representadas em coeficientes de rigidez, amortecimento e inércia. Além disso, será verificada a influência de diversos parâmetros geométricos e operacionais nestes coeficientes. A inserção dos coeficientes dinâmicos dos selos planos e a análise do conjunto girante, a partir do pacote computacional Rotortest®, permitirá verificar a influência desses tipos de selos no sistema rotativo, analisando como este elemento modifica as características do conjunto e como acopla o eixo à fundação / Abstract: The dynamic analysis of rotors aims to predict its behavior and identify deviations characterized by the dynamic response of the set, providing malfunction indications or failure diagnosis, and minimizing the risk of having unexpected halts on the system. The dynamic study of rotating machines must be conducted by taking in account the interactions between the components involved in its construction, such as rotors, shafts, bearings, fluid seals, and support structures. The fluid seals cause reaction-forces, which can be represented for dynamic coefficients. This component is mainly responsible for the differences between a model using only a rotor-bearing and the actual vibration of the set, for example in centrifugal pumps. In this context, this work aims the determination of the dynamic coefficients of three types of plain seals, namely: straight, tapered, and stepped seals, which will be integrated with the global model of rotating systems, in order to make the analysis of the rotating set more complete. The fluid seals analysis will be accomplished through the finite volume method in order to determine the circumferential velocity and pressure distribution along the seal, which characterizes the reaction forces. Those can be, in turn, represented by stiffness, damping, and inertia coefficients. Besides, it will be verified the influence of several geometric and operational parameters on these coefficients. The insertion of the dynamic coefficients of plain seals and the analysis of the rotating set in the computational package Rotortest®, will verify the influence of these seals on the rotating system, analyzing how this element modify the set's characteristics and the coupling of the shaft to the foundation / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestra em Engenharia Mecânica

Indiana University-Purdue University Indianapolis (IUPUI) / A constant-volume combustor is used to investigate the ignition initiated by a traversing jet of reactive hot gas, in support of combustion engine applications that include novel wave-rotor constant-volume combustion gas turbines and pre-chamber IC engines. The hot-jet ignition constant-volume combustor rig at the Combustion and Propulsion Research Laboratory at the Purdue School of Engineering and Technology at Indiana University-Purdue University Indianapolis (IUPUI) was used for this study. Lean premixed combustible mixture in a rectangular cuboid constant-volume combustor is ignited by a hot-jet traversing at different fixed speeds. The hot jet is issued via a converging nozzle from a cylindrical pre-chamber where partially combusted products of combustion are produced by spark- igniting a rich ethylene-air mixture. The main constant-volume combustor (CVC) chamber uses methane-air, hydrogen-methane-air and ethylene-air mixtures in the lean equivalence ratio range of 0.8 to 0.4. Ignition delay times and ignitability of these combustible mixtures as affected by jet traverse speed, equivalence ratio, and fuel type are investigated in this study.