Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 32 for “"Limit cycle oscillations"”.
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Suppression of limit cycle oscillations in an aeroelastic system using robust and adaptive control
… the purpose of control. First the existence of limit cycle oscillations and domain of stability (attraction) of prototypical aeroelastic wing sections with pitch structural nonlinearity using the describing function method is determined. The model includes unsteady aerodynamics based on …
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Robust and Adaptive Nonlinear Control of Limit Cycle Oscillations in UAVs Using Synthetic Jet Actuators
<p>Limit cycle oscillations (LCO), also known as utter, cause significant challenges in fight control of unmanned aerial vehicles (UAVs), and could potentially lead to structural damage and catastrophic failures. LCO can be described as vibrational motions in the pitching and plunging displacements …
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Numerical Study in Wind Energy Extraction from Controlled Limit-Cycle Oscillations in Modified Glauert Airfoil
… Glauert (MG) airfoil experiencing aeroelastic limit cycle oscillation (LCO) from which energy may be extracted. Synthetic jet actuators (SJA)s are used along with the unique geometry of the MG airfoil to control flow separation and amplify the LCO and energy generation potential of the system. …
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Fast prediction of transonic aeroelasticity using computational fluid dynamics
… include the transonic flutter dip and limit cycle oscillations. An intensive research effort is underway to account for aerodynamic nonlinearity at a practical computational cost.To achieve this a large reduction in the numbers of degrees of freedoms is required and leads to the …
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Robust Nonlinear Estimation and Control Applications using Synthetic Jet Actuators
<p>Limit cycle oscillations (LCO), also known as utter, cause significant challenges in flight control of small unmanned aerial vehicles (SUAVs), and could potentially lead to structural damage and catastrophic failures. LCO can be described as vibrational motions in the rocking, pitching and …
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Suppression of Limit Cycles in Digital Filters
The injection of randan dither to suppress limit cycle oscillations in second-order direct form digital filter sections is discussed. Three types of dither signal are used: uniformly distributed random dither, binary randan dither and bandstop dither. All the limit cycles in the second-order filter …
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An Experimental Study of Synthetic Jet Actuators with Application in Airfoil LCO Control
… for eliminating aeroelastic phenomenon such as Limit Cycle Oscillations (LCO). One of the biggest challenges involved in the design of UAVs operating in unsteady atmosphere conditions is the susceptibility of the airframe to aeroelastic instabilities, such as flutter or LCO. Suppression of such …
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Synchronization in Coupled Opto-thermal Silicon MEMS Limit Cycle Oscillators
… oscillators exhibit nonlinear phenomena such as limit cycle oscillations, self-synchronization, and frequency entrainment to an external drive. In this work, we chart the behavior of silicon MEMS oscillators that are nominally 40 µm long and 205 nm thick, mechanically coupled, and opto-thermally …
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Structure-preserving Numerical Methods for Engineering Applications
… from engineering applications, which include limit cycle oscillations of an aeroelastic system, dynamics of a neutrally buoyant underwater vehicle, and optimization for spherical shape correlation and matching.
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Aerodynamic Parameter Identification of a Venus Lander
… model used is incapable of replicating the limit cycle oscillations with stochastic peak amplitudes observed during the test.
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Modeling Analysis and Control of Nonlinear Aeroelastic Systems
… Examples of structural aspects include but not limited to large deformations (geometric nonlinearities), concentrated masses or elements (inertial nonlinearities) and freeplay. In some systems, and depending on the parameters, the nonlinearities can cause multiple solutions. Determining the …
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Identification of Thermoacoustic Dynamics Exhibiting Limit Cycle Behavior
… of thermoacoustic dynamics that exhibit limit cycle behavior is needed to gain a better intuitive feel of the system, to design complex control strategies, and to validate modeling efforts. Limit cycle oscillations arise in thermoacoustic systems due to the coupling between a nonlinear …
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Unsteady Nonlinear Aerodynamic Modeling and Applications
… like the flutter of fixed wings and ensuing limit cycle oscillations can be exploited for harvesting energy. In this dissertation, we focus on modeling the unsteady nonlinear aerodynamic response and present various applications where unsteady aerodynamics are very relevant. The dissertation …
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Optimization of a Plate Beam System for Energy Harvesting Using a Piezoelectric Material
… over its surface. It is assumed that sustained limit cycle oscillations of this system will occur at the flutter velocity. This research creates an optimization framework to obtain the best values of parameters that will result in the minimum flutter velocity for the system. Minimization of …
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Parametric Viscous Analysis of Gust Interaction with Stationary and Elastically Mounted Airfoil
… with emphasis on the wing section transition to limit cycle oscillations (LCO).</p>
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Nonlinear Analysis and Control of Aeroelastic Systems
Presence of nonlinearities may lead to limit cycle oscillations (LCOs) in aeroelastic systems. LCOs can result in fatigue in wings leading to catastrophic failures. Existence of LCOs for velocities less than the linear flutter velocity has been observed during flight and wind tunnel tests, making …
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Modelling the human cochlea
… level, harmonic and intermodulation distortion, limit cycle oscillations that travel along the cochlear membranes, and the mutual suppression of nearby linear instabilities.
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Design of tracking systems incorporating multivariable plants
… of the latter plants, the novel concepts of limit tracking (i.e. the tracking exhibited by plants with moreoutputs than inputs) is introduced and an associatedmethodology for the design of self-selecting controllers isproposed. Such controllers involve the selection of differentset-point …
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Model reduction for nonlinear dynamical systems with parametric uncertainties
… class of such systems -- one which exhibits limit cycle oscillations (LCOs) and Hopf-bifurcations. Highfidelity simulations for systems with LCOs are computationally intensive, precluding probabilistic analyses of these systems with uncertainties in the input parameters. In this thesis, we …
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Numerical Simulations of Interactions Among Aerodynamics, Structural Dynamics, and Control Systems
… the roadbed can easily suppress the wind-excited oscillations. The governing equations for a proposed passive system were developed. The wing structure is modelled with finite elements. The deflections are expressed as an expansion in terms of the free-vibration modes. The time-dependent …
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