4,455 research outputs found

    Analysis of potential helicopter vibration reduction concepts

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    Results of analytical investigations to develop, understand, and evaluate potential helicopter vibration reduction concepts are presented in the following areas: identification of the fundamental sources of vibratory loads, blade design for low vibration, application of design optimization techniques, active higher harmonic control, blade appended aeromechanical devices, and the prediction of vibratory airloads. Primary sources of vibration are identified for a selected four-bladed articulated rotor operating in high speed level flight. The application of analytical design procedures and optimization techniques are shown to have the potential for establishing reduced vibration blade designs through variations in blade mass and stiffness distributions, and chordwise center-of-gravity location

    Model-Based Development and Evaluation of Control for Complex Multi-Domain Systems: Attitude Control for a Quadrotor UAV

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    A Cyber-Physical System (CPS) incorporates sensing, actuating, computing and communicative capabilities, which are often combined to control the system. The development of CPSs poses a challenge, since the complexity of the physical system dynamics must be taken into account when designing the control application. The physical system dynamics are often defined within mechanical and electrical engineering domains, with the control application residing in software and control engineering domains. Therefore, such a system can be considered multi-domain.With the constant increase in the complexity of such systems, caused by technological advances in all domains, new ways of approaching multi-domain system development are needed. One methodology, which excels in complexity management, is model-based development. Multidomain systems require collaborative modeling, where the physical system dynamics are captured in the Continuous Time (CT) modeling domain and the digital control is captured in the Discrete Event (DE) modeling domain.This thesis demonstrates how an extended CT-first model-based development approach can be applied to a complex multi-domain system. A collaborative model of a quadrotor Unmanned Aerial Vehicle (UAV) has been constructed and used to develop an attitude controller based on Model Predictive Control (MPC). The MPC controller has been compared to an existing open source Proportional Integral Derivative (PID) attitude controller.This thesis contributes to the discipline of model-based development with a methodological extension to the CT-first approach, which extends the conventional approach by expanding the physical modeling process into three consecutive steps. An evaluation of the extension is presented, describing how and when the extended methodology provides increased value

    Modern Approaches To Quality Control

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    Rapid advance have been made in the last decade in the quality control procedures and techniques, most of the existing books try to cover specific techniques with all of their details. The aim of this book is to demonstrate quality control processes in a variety of areas, ranging from pharmaceutical and medical fields to construction engineering and data quality. A wide range of techniques and procedures have been covered

    Flight control systems properties and problems, volume 1

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    This volume contains a delineation of fundamental and mechanization-specific flight control characteristics and problems gleaned from many sources and spanning a period of over two decades. It is organized to present and discuss first some fundamental, generic problems of closed-loop flight control systems involving numerator characteristics (quadratic dipoles, non-minimum phase roots, and intentionally introduced zeros). Next the principal elements of the largely mechanical primary flight control system are reviewed with particular emphasis on the influence of nonlinearities. The characteristics and problems of augmentation (damping, stability, and feel) system mechanizations are then dealt with. The particular idiosyncracies of automatic control actuation and command augmentation schemes are stressed, because they constitute the major interfaces with the primary flight control system and an often highly variable vehicle response

    Motion analysis report

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    Human motion analysis is the task of converting actual human movements into computer readable data. Such movement information may be obtained though active or passive sensing methods. Active methods include physical measuring devices such as goniometers on joints of the body, force plates, and manually operated sensors such as a Cybex dynamometer. Passive sensing de-couples the position measuring device from actual human contact. Passive sensors include Selspot scanning systems (since there is no mechanical connection between the subject's attached LEDs and the infrared sensing cameras), sonic (spark-based) three-dimensional digitizers, Polhemus six-dimensional tracking systems, and image processing systems based on multiple views and photogrammetric calculations

    Development, modeling, and simulation of a nano aerial vehicle using empirical data

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    The ultimate goals of this study were to use experimental data to estimate the flight capabilities of a flapping wing nano aerial vehicle (NAV), estimate the power required to provide such flight, and develop a controller approach for future use in the design of this aircraft. The experimental data is a collection of measurements of the normal force on a flapping wing taken in stationary water, and was used to develop empirical coefficient derivatives for use in the dynamic modeling of the NAV --Abstract, page iii

    Energy transfer and localization in molecular crystals

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    With the aim of developing new technologies for the detection and defeat of energetic materials, this collection of work was focused on using simulations to characterize materials at extremes of temperature, pressure and radiation. Each branch of the work here is collected by which material response is potentially used as the detectable signal. Where the chemical response is of interest, this work will explore the possibility of non-statistical chemical reactions in condensed-phase energetic materials via reactive molecular dynamics (MD) simulations. We characterize the response of three unique high energy density molecular crystals to different means of energy input: electric fields of various frequencies (100 − 4000cm−1) and strengths, and direct heating at various rates. It was found that non-equilibrium states can be created for short timescales when the energy input targets specific vibrations through the electric fields, and that equilibration eventually occurs even when the insults remain present. Interestingly, for strong fields these relaxation timescales are comparable to those of the initial chemical decomposition of the molecules. On similar timescales, we have studied the relaxation process of shock compressed molecules. Details of how energy localization, either from these vibrational or mechanical insults, affects the preferred uni- or multi-molecular reactions are discussed. These results provide insight into non-equilibrium or coherent initiation of chemistry in the condensed phase that would be of interest in fields ranging from catalysis to explosives. Without initiating reactions, the thermal response of a material subject to a mechanical stimulus can be used to inform on the chemical characteristics. Here MD simulations are performed to study how energy from an acoustic wave is localized in a composite material of a polymer and molecular crystal. Insight is provided on how the interface between these to materials will affect which component absorbs and localizes this insult energy. Furthermore these results provide an explanation to anomalous experimental results that subject similar composites to acoustic insults. In parallel efforts for the detection and defeat of explosives, we study the scattering of electromagnetic waves in anisotropic energetic materials. Nonlinear light-matter interactions in molecular crystals result in frequency-conversion and polarization changes. Applied electromagnetic fields of moderate intensity can induce these nonlinear effects without triggering chemical decomposition, offering a mechanism for non-ionizing identification of explosives. We use molecular dynamics simulations to compute such two-dimensional THz spectra for planar slabs made of PETN and ammonium nitrate. We discuss third-harmonic generation and polarization-conversion processes in such materials. These observed far-field spectral features of the reflected or transmitted light may serve as an alternative tool for stand-off explosive detection

    Development of the US3D Code for Advanced Compressible and Reacting Flow Simulations

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    Aerothermodynamics and hypersonic flows involve complex multi-disciplinary physics, including finite-rate gas-phase kinetics, finite-rate internal energy relaxation, gas-surface interactions with finite-rate oxidation and sublimation, transition to turbulence, large-scale unsteadiness, shock-boundary layer interactions, fluid-structure interactions, and thermal protection system ablation and thermal response. Many of the flows have a large range of length and time scales, requiring large computational grids, implicit time integration, and large solution run times. The University of Minnesota NASA US3D code was designed for the simulation of these complex, highly-coupled flows. It has many of the features of the well-established DPLR code, but uses unstructured grids and has many advanced numerical capabilities and physical models for multi-physics problems. The main capabilities of the code are described, the physical modeling approaches are discussed, the different types of numerical flux functions and time integration approaches are outlined, and the parallelization strategy is overviewed. Comparisons between US3D and the NASA DPLR code are presented, and several advanced simulations are presented to illustrate some of novel features of the code
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