Browsing by Subject "Resonance"
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Item Analysis and Simulation of Mechanical Trains Driven by Variable Frequency Drive Systems(2012-02-14) Han, XuInduction motors and Variable Frequency Drives (VFDs) are widely used in industry to drive machinery trains. However, some mechanical trains driven by VFD-motor systems have encountered torsional vibration problems. This vibration can induce large stresses on shafts and couplings, and reduce the lifetime of these mechanical parts. Long before the designed lifetime, the mechanical train may encounter failure. This thesis focuses on VFDs with voltage source rectifiers for squirrel-cage induction motors of open-loop Volts/Hertz and closed-loop Field Oriented Control (FOC). First, the torsional vibration problems induced by VFDs are introduced. Then, the mathematical model for a squirrel-cage induction motor is given. Two common control methods used in VFD are discussed - open-loop Volts/Hertz and closed-loop FOC. SimPowerSystems and SimMechanics are used as the modeling software for electrical systems and mechanical systems respectively. Based on the models and software, two interface methods are provided for modeling the coupled system. A simple system is tested to verify the interface methods. The study of open-loop Volts/Hertz control method is performed. The closed-form of electromagnetic torque sideband frequency due to Pulse Width Modulation is given. A torsional resonance case is illustrated. The effects of non-ideal power switches are studied, which shows little in uence on the system response but which uses little energy consumption. A study of a non-ideal DC bus indicates that a DC bus voltage ripple can also induce a big torsional vibration. Next, the study of the closed-loop FOC control method is presented. Simulation for a complete VFD machinery train is performed. With the recti er and DC bus dynamic braking, the system shows a better performance than the ideal-DC bus case. Lastly, a parametric study of the FOC controller is performed. The effects of primary parameters are discussed. The results indicate that some control parameters (i.e. speed ramps, proportional gain in speed PI controller) are also responsible for the mechanical torsional vibration.Item Item Initial guess and optimization strategies for multi-body space trajectories with application to free return trajectories to near-Earth asteroids(2014-08) Bradley, Nicholas Ethan; Russell, Ryan Paul, 1976-; Ocampo, CesarThis concept of calculating, optimizing, and utilizing a trajectory known as a ``Free Return Trajectory" to facilitate spacecraft rendezvous with Near-Earth Asteroids is presented in this dissertation. A Free Return Trajectory may be defined as a trajectory that begins and ends near the same point, relative to some central body, without performing any deterministic velocity maneuvers (i.e., no maneuvers are planned in a theoretical sense for the nominal mission to proceed). Free Return Trajectories have been utilized previously for other purposes in astrodynamics, but they have not been previously applied to the problem of Near-Earth Asteroid rendezvous. Presented here is a series of descriptions, algorithms, and results related to trajectory initial guess calculation and optimal trajectory convergence. First, Earth-centered Free Return Trajectories are described in a general manner, and these trajectories are classified into several families based on common characteristics. Next, these trajectories are used to automatically generate initial conditions in the three-body problem for the purpose of Near-Earth Asteroid rendezvous. For several bodies of interest, example initial conditions are automatically generated, and are subsequently converged, resulting in feasible, locally-optimal, round-trip trajectories to Near-Earth Asteroids utilizing Free Return Trajectories. Subsequently, a study is performed on using an unpowered flyby of the Moon to lower the overall DV cost for a nominal round-trip voyage to a Near-Earth Asteroid. Using the Moon is shown to appreciably decrease the overall mission cost. In creating the formulation and algorithms for the Lunar flyby problem, an initial guess routine for generic planetary and lunar flyby tours was developed. This continuation algorithm is presented next, and details a novel process by which ballistic trajectories in a simplistic two-body force model may be iteratively converged in progressively more realistic dynamical models until a final converged ballistic trajectory is found in a full-ephemeris, full-dynamics model. This procedure is useful for constructing interplanetary transfers and moon tours in a realistic dynamical framework; an interplanetary and an inter-moon example are both shown. To summarize, the material in this dissertation consists of: novel algorithms to compute Free Return Trajectories, and application of the concept to Near-Earth Asteroid rendezvous; demonstration of cost-savings by using a Lunar flyby; and a novel routine to transfer trajectories from a simplistic model to a more realistic dynamical representation.Item Investigation of internal resonance of a three-degree-of-freedom system under random excitation(Texas Tech University, 1989-05) Ekwaro-Osire, StephenA three-degree-of-freedom system, with cubic nonlinearity, was investigated. The system consists of two masses attached by nonlinear springs and linear dampers. The lower mass was excited, through similar attachment elements, by a random excitation. The excitation was assumed to be narrow band white noise. Since the statistical moments of this nonlinear system responding to random excitation are governed by an infinite hierarchy of equations, truncation or closure schemes are necessary to approximately compute the important lower order moments. For this research, the Gaussian closure scheme and the non- Gaussian closure scheme were used. The non-Gaussian closure scheme was in the cumulant neglect sense, whereby only the cumulants up to the sixth order were considered. The mean-square response was the main system statistical property used to investigate the system behavior. The system response was investigated in the vicinity of the combination resonance conditions. The results obtained by the two methods were compared on the basis of the prediction of the system response around the combination resonance condition. An effort was made to account for the differences of the system prediction as achieved from the respective closure schemes.Item Investigation of internal resonance of a three-degree-of-freedom system under random excitation(Texas Tech University, 1989-05) Ekwaro-Osire, StephenA three-degree-of-freedom system, with cubic nonlinearity, was investigated. The system consists of two masses attached by nonlinear springs and linear dampers. The lower mass was excited, through similar attachment elements, by a random excitation. The excitation was assimied to be narrow band white noise. Since the statistical moments of this nonlinear system responding to random excitation are governed by an infinite hierarchy of equations, truncation or closure schemes are necessary to approximately compute the important lower order moments. For this research, the Gaussian closure scheme and the non- Gaussian closure scheme were used. The non-Gaussian closure scheme was in the cumulant neglect sense, whereby only the cumulants up to the sixth order were considered. The mean-square response was the main system statistical property used to investigate the system behavior. The system response was investigated in the vicinity of the combination resonance conditions. The results obtained by the two methods were compared on the basis of the prediction of the system response around the combination resonance condition. An effort was made to account for the differences of the system prediction as achieved from the respective closure schemes.Item Linear and autoparametric modal analysis of aeroelastic structural systems(Texas Tech University, 1984-05) Woodall, Tommy DaleThis investigation deals with the linear modal analysis and autoparametric interaction of aeroelastic systems such as an airplane fuselage and wing with fuel storage. The mathematical modeling is derived by applying Lagrange's equations taking into consideration the Christoffel symbol of the first kind to account for the nonlinear coupling of the system coordinates, velocities, and accelerations. The linear modal analysis will be obtained by considering the linear, conservative portion of the equations of motion. The normal mode frequencies and the associated mode shapes are obtained in terms of the system parameters. The main objective of the linear analysis is to explore the critical regions of autoparametric (or internal) resonance conditions, £kiwi=0 (where ki are integers and wi are the normal mode frequencies). The results show that for certain system parameters the condition of internal resonance is satisfied. The dynamic behavior of the structure in the neighborhood of internal resonance conditions is obtained by considering the nonlinear coupling of the normal modes. The asymptotic approximation technique due to Struble is employed. Three groups of internal and normal resonance conditions are obtained from the secular terms of the first-order perturbational equations. The transient and steady-state responses cure obtained numerically by using the IBM Continuous System Modeling Program (CSMP) with double precision Milne integration. The transient response shows a build up in the interacted modes to a level which exceeds the steady-state response. In addition, the excited mode is suppressed by virtue of the nonlinear feedback of other modes. Under certain conditions, the steady-state response is derived analytically. It is concluded that the nonlinear modal analysis reveals certain types of response characteristics which cannot be interpreted within the framework of the linear theory of small oscillations.Item Methodology for characterizing electric power system response and locating the energized capacitor banks using conventional power quality data(2007-05) Hur, Kyeon, 1973-; Santoso, SuryaItem Methodology for characterizing electric power system response and locating the energized capacitor banks using conventional power quality data(2007) Hur, Kyeon; Santoso, SuryaA relatively small harmonic current with frequencies near or at the power system parallel resonant frequencies could excite the power system into a resonance condition. While a capacitor bank is not the root cause of the condition, it facilitates and helps cause the problem. This is because when the capacitor bank is energized, the system resonant frequency could shift closer to existing harmonic frequencies produced by nonlinear loads. Therefore, the objective of this dissertation is to quantify the power system characteristics corresponding to the parallel resonant frequencies and system damping. Additionally, since a capacitor bank actively facilitates the resonance condition, the relative or exact location of the involved bank must be determined. This dissertation first presents a practical and accurate methodology to estimate system parallel resonant frequencies by performing spectral analysis of the voltage and current transient data immediately after the capacitor bank switching. The proposed method is also robust in that the accuracy of the resulting estimates is not affected by prevalent harmonics in the system. This dissertation provides two efficient algorithms for estimating the system damping parameters using the Hilbert and analytic wavelet transforms. These algorithms take advantage of the principle of an asymptotic or weaklymodulated signal, for which the signal phase varies much more rapidly than the amplitude. The zero-input voltage response or free response of the capacitor bank energizing can be categorized into these asymptotic signals, and one can assign a unique time-varying amplitude with the system damping information and phase pair by building analytic signals. System model reduction theory also allows us to interpret or quantify this damping as an effective X/R ratio. This dissertation defines two fundamental signatures of shunt capacitor bank energizing. It demonstrates that these two signatures can be utilized to accurately determine the relative location of an energized capacitor bank whether it is upstream or downstream from the monitoring location. This dissertation also presents an efficient and accurate methodology for finding the exact location of an energized capacitor bank. Once a PQ monitor is found to be upstream from the capacitor bank by the relative location finding algorithm, the proposed algorithm can further determine the exact location of the switched capacitor bank by estimating the distance between the PQ monitor and the energized capacitor bank. Thus, one can pinpoint the energized capacitor bank causing the resonance.Item Numerical Study On A SPAR Type Floating Offshore Wind Turbine Using COUPLE-FAST Code(2015-03-03) Peng, ChengFloating offshore wind turbine (FOWT) attracts more and more attention for harnessing wind power over the surface of relatively deep ocean water, where steady and strong wind occurs. Although it has been shown that the knowledge gained from the development of floating platforms for oil and gas production is helpful for the development of FOWTs, it alone is insufficient for understanding dynamic interactions between the supporting platform and the wind turbine. Therefore, it is desirable to conduct numerical simulations of a FOWT under the impact of different combinations of winds, waves and currents. In this study, a numerical code named as COUPLE-FAST has been developed to investigate the motions of a selected FOWT and the tensions in its mooring lines. The selected FOWT mainly consists of a 5MW NREL wind turbine and OC3-Hywind Spar support platform. COUPLE-FAST is made based two existing codes COUPLE and FAST. The former is an in-house code developed and being continuously expanded for the simulation of an offshore floating platform positioned by a mooring-line/tendon system. FAST is an open-source code capable of predicting both the extreme and fatigue loads of two- and three- bladed horizontal-axis wind turbines [1]. In COUPLE-FAST, COUPLE module is used to calculate the external loads on the support floating platform, mooring line forces and its motions, and FAST module to calculate the aerodynamic loads and flexible responses of the wind turbine. The displacements, velocities and accelerations predicted in COUPLE are transferred to FAST. The forces at the tower bases calculated by FAST are transferred to COUPLE. Total 25 cases with different combination of winds, waves and currents are simulated for calculating the motions of the FOWT and tensions in its mooring lines. Among many interesting observations made based on these simulations, it is confirmed that when the mean wind speed is above the rated wind speed the blade pitch control system may induce resonant interaction (also known as ?negative damping?) between the surge of the FOWT and dynamic wind loads induced by the adjustment of blade pitch angle. However, the resonant effects on surge of the FOWT in the case of turbulent winds are not as significant as in the case of steady winds of the corresponding wind speed.Item Paramagnetic resonance and optical spectra of some divalent group I-B metal pyridine complexes(Texas Tech University, 1966-08) Frazier, John PedenNot availableItem Resonance particles in heavy-ion collisions(2013-05) Wada, Masayuki; Markert, ChristinaHeavy ions are collided at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) in an effort to create a unique state of nuclear matter, where quarks and gluons can freely move over volumes larger than the typical size of a nucleon (typical scale of Quantum Chromodynamics, QCD). In this state, called a "Quark Gluon Plasma" (QGP), it is proposed Chiral symmetry is restored. The fact that Chiral symmetry is a symmetry of the Standard model and is broken at low energy (current energy scale of universe) makes the study of its possible very interesting. The analysis in this dissertation searches for signatures of chiral symmetry restoration at the phase transition between the QGP and the hadronic gas phase by using resonance particles as probes. Resonances may decay inside of hot dense matter due to their short lifetimes, and therefore their decay daughters carry away dynamical information such as the mass and decay width. Mass shift and width broadening are predicted signatures of chiral symmetry restoration. The [phi](1020) resonances reconstructed from the dielectron decay channel are investigated in this dissertation. This decay channel does not suffer scattering from the late hadronic medium due to the relatively small interaction cross section of leptons with hadrons. The disadvantage of this channel comes from the small branching ratio. Therefore, large statistics and clean Particle IDentification (PID) are necessary for this analysis. Those requirements were fulfilled with high luminosity beams at RHIC and the newly developed and installed Time Of Flight (TOF) detectors, which provide clear particle identification up to momentum of 2-3 GeV/c, as well as the large acceptance of the Solenoidal Tracker At RHIC (STAR) detector. In this dissertation, measurements of mass, width, transverse momentum spectrum, and yields of [phi][right arrow] e⁺e⁻ at mid-rapidity [mathematical symbols] from the STAR experiment in Au+Au collisions at [mathematical symbols]=200 GeV are presented and compared to a previously measured [phi] meson result from a hadronic decay channel. The possibility of medium modification which implies Chiral symmetry restoration is discussed.Item Search for new physics in the compact muon solenoid (CMS) experiment and the response of the CMS calorimeters to particles and jets(Texas Tech University, 2008-08) Gumus, Kazim Z; Akchurin, Nural; Borst, Walter; Lodhi, M. A. K.; Wigmans, RichardA Monte Carlo study of a generic search for new resonances beyond the Standard Model (SM) in the CMS experiment is presented. The resonances are axigluon, coloron, E6 diquark, excited quark, W', Z', and the Randall-Sundrum graviton which decay to dijets. The dijet resonance cross section that the CMS can expect to discover at a 5 sigma significance or to exclude at 95% confidence level for integrated luminosities of 100 pb−1, 1 fb−1, and 10 fb−1 is evaluated. It is shown that a 5 sigma discovery of a multi-TeV dijet resonance is possible for an axigluon, excited quark, and E6 diquark. However, a 5 sigma discovery can not be projected with confidence for a W', Z' and the Randall-Sundrum graviton. On the other hand, 95% CL exclusion mass regions can be measured for all resonances at high luminosities. In the second part of this dissertation, the analyses of the 2006 test beam data from the combined electromagnetic and hadronic barrel calorimeters are presented. The CMS barrel calorimeters’ response to a variety of beam particles in a wide momenta range (1 to 350 GeV/c) is measured. Furthermore, using these beam data, the expected performance of the barrel calorimeters to jets is predicted.Item Two-particle correlations of identified particles in heavy ion collisions at STAR(2016-08) Bhattarai, Prabhat; Markert, Christina; Ray, Robert L. (Robert Landon); Bohm, Arno; Walker, Stephen; Onyisi, PeterThe study of quarks and their interactions through gluons has been an active area of research since their discovery. For two decades the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory has been dedicated to studying the interactions between quarks by producing nuclear matter in an extremely dense and hot environment. It has been hypothesized that colliding beams of atomic nuclei near the speed of light creates the hot and dense environment in which all quarks in the nuclei de-confine to form a short-lived state of matter called a Quark Gluon Plasma (QGP). Because of the short lifetime of QGP, it is impossible to observe it directly and, the only way to study such matter is through the final state particles. Two-particle correlation, which is defined using Pearson's normalized covariance, is one of the techniques to study the early interactions via the final state particles. A broad survey has been made to study the two-particle correlations of identified-charged hadrons (pi, K and p) in various ranges of momentum for the hadrons produced in √sNN=200 GeV Au+Au collisions at the STAR experiment at RHIC. A total of 2123 two-dimensional independent structures made by correlation coefficients in relative angular space in (eta, phi) for different combinations of identified hadrons have been studied. Correlations between any two identified particles contrasts to all-particle correlations giving an opportunity to study the contribution of each particle species in the hadronization processes. As a new feature, same-side anti-correlations are observed in both like-sign and unlike-sign pairs in certain yT bins and in certain identified particles. A significant feature of the final state distribution of particles is an azimuthal anisotropy which is defined as the second Fourier component; the amplitude is proportional to parameter v2. We report the measure of azimuthal anisotropy of identified hadrons for the first time and test for the factorization used in conventional analysis. The data presented here constitute a comprehensive measurement of the light-flavor, di-hadron density as function of collision centrality, transverse momentum and 2D relative angles in longitudinal (beam direction) and azimuthal directions.Item Vibrations of non-homogeneous media and the prediction of mechanical resonance in human tibia(Texas Tech University, 2000-08) Miller, Allen CharlesAn analysis of longitudinal and transverse vibration in thin rods and Euler-Bernoulli beams is presented in which consitutive and geometric properties are allowed to vary with spatial coordinates. The specific form of cross-sectional areas and material properties that are adopted are used to model the mechanical resonances of the human tibia. Three specific models are presented. The transeverse vibrations in a beam with linear cross-sectional taper are addressed. This model is considered with both free-free and torsion spring-mass boundary conditions. A second model for transverse vibration in a beam with three piecewise linearly tapered segments is also analyzed. This model is considered with free-free boundary conditions. A model for longitudinal vibration in a beam with general cross-sectional areas and Young's modulus with free-free boundary conditions is also presented. For each of these beams, parameters are chosen to model data from the human tibia. The low-order frequencies of vibrations are computed and a comparison of other results in the literature is made.