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Nogar, Stephen MComprehensive Modeling and Control of Flexible Flapping Wing Micro Air Vehicles
Doctor of Philosophy, The Ohio State University, 2015, Aero/Astro Engineering
Flapping wing micro air vehicles hold significant promise due to the potential for improved aerodynamic efficiency, enhanced maneuverability and hover capability compared to fixed and rotary configurations. However, significant technical challenges exist to due the lightweight, highly integrated nature of the vehicle and coupling between the actuators, flexible wings and control system. Experimental and high fidelity analysis has demonstrated that aeroelastic effects can change the effective kinematics of the wing, reducing vehicle stability. However, many control studies for flapping wing vehicles do not consider these effects, and instead validate the control strategy with simple assumptions, including rigid wings, quasi-steady aerodynamics and no consideration of actuator dynamics. A control evaluation model that includes aeroelastic effects and actuator dynamics is developed. The structural model accounts for geometrically nonlinear behavior using an implicit condensation technique and the aerodynamic loads are found using a time accurate approach that includes quasi-steady, rotational, added mass and unsteady effects. Empirically based parameters in the model are fit using data obtained from a higher fidelity solver. The aeroelastic model and its ingredients are compared to experiments and computations using models of higher fidelity, and indicate reasonable agreement. The developed control evaluation model is implemented in a previously published, baseline controller that maintains stability using an asymmetric wingbeat, known as split-cycle, along with changing the flapping frequency and wing bias. The model-based controller determines the control inputs using a cycle-averaged, linear control design model, which assumes a rigid wing and no actuator dynamics. The introduction of unaccounted for dynamics significantly degrades the ability of the controller to track a reference trajectory, and in some cases destabilizes the vehicle. This demonstrates the importance of considering coupled aeroelastic and actuator dynamics in closed-loop control of flapping wings. A controller is developed that decouples the normal form of the vehicle dynamics, which accounts for coupling of the forces and moments acting on the vehicle and enables enhanced tuning capabilities. This controller, using the same control design model as the baseline controller, stabilizes the system despite the uncertainty between the control design and evaluation models. The controller is able to stabilize cases with significant wing flexibility and limited actuator capabilities, despite a reduction in control effectiveness. Additionally, to achieve a minimally actuated vehicle, the wing bias mechanism is removed. Using the same control design methodology, increased performance is observed compared to the baseline controller. However, due to the dependence on the split-cycle mechanism to generate a pitching moment instead of wing bias, the controller is more susceptible to instability from wing flexibility and limited actuator capacity. This work highlights the importance of coupled dynamics in the design and control of flapping wing micro air vehicles. Future enhancements to this work should focus on the reduced order structural and aerodynamics models. Applications include using the developed dynamics model to evaluate other kinematics and control schemes, ultimately enabling improved vehicle and control design.

Committee:

Jack McNamara (Advisor); Andrea Serrani (Advisor); Manoj Srinivasan (Committee Member); Junmin Wang (Committee Member); Michael Oppenheimer (Committee Member); David Doman (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

Flapping Wings; Control; Aeroelasticity; Dynamics

TIAN, BINYUCOMPUTATIONAL AEROELASTIC ANALYSIS OF AIRCRAFT WINGS INCLUDING GEOMETRY NONLINEARITY
PhD, University of Cincinnati, 2003, Engineering : Aerospace Engineering
Because the flutter phenomenon of aircraft wings is usually associated with large deformations/deflections, the structural solution based on linear theory for the aircraft wings might give inaccurate or totally unphysical solutions. This is due to the equilibrium state of the structure is referred to the initial configuration, which can be very different with actual configuration at a given time when the wing deflection is large. So the changing geometry of the structure has to be taken into account in order to accurately describe the fluid/structure interactions at the onset of flutter, or in the post-flutter regime. The objective of the present study is to show the ability of solving fluid structural interaction problems more realistically by including the geometric nonlinearity of the structure so that the aeroelastic analysis can be extended into the onset of flutter, or in the post flutter regime. A nonlinear Finite Element Analysis software is developed based on second Piola-Kirchhoff stress and Green-Lagrange strain. The second Piola-Kirchhoff stress and Green-Lagrange strain is a pair of energetically conjugated tensors that can accommodate arbitrary large structural deformations and deflection, to study the flutter phenomenon. Since both of these tensors are objective tensors, i.e., the rigid-body motion has no contribution to their components, the movement of the body, including maneuvers and deformation, can be included. The nonlinear Finite Element Analysis software developed in this study is verified with ANSYS, NASTRAN, ABAQUS, and IDEAS for the linear static, nonlinear static, linear dynamic and nonlinear dynamic structural solutions. To solve the flow problems by Euler/Navier equations, the current nonlinear structural software is then embedded into ENSAERO, which is an aeroelastic analysis software package developed at NASA Ames Research Center. The coupling of the two software, both nonlinear in their own field, is achieved by domain decomposition method first purposed by Guru swamy. The improved diagonal form of Beam and Warming Scheme is used to solve the Euler/Navier Stokes equations. Total Lagrange Scheme is used for the structural solutions. The Newmark time integration scheme is used for the sub-iterations of the structural solutions within each time step to ensure the accuracy. The interaction of the structural dynamic and fluid flow is achieved by the fluid-structure interface, which also pre-exist in ENSAERO. For the accuracy of the flow field solutions, the algebraic adaptive moving grid is used to make the fluid flow boundary conform to the deforming wing geometry at every time step. Certain criteria are enforced to the adaptive grid scheme to make sure that the accuracy of the flow solutions is achieved. To the best knowledge of the author, it is the first time that a nonlinear Finite Element Analysis code is coupled with Euler and Navier Stokes equations directly. A procedure has been set for the aeroelastic analysis process. The aeroelastic analysis results have been obtained for fight wing in the transonic regime for various cases. The influence dynamic pressure on flutter has been checked for a range of Mach number. Even though the current analysis matches the general aeroelastic characteristic, the numerical value not match very well with previous studies and needs farther investigations. The flutter aeroelastic analysis results have also been plotted at several time points. The influences of the deforming wing geometry can be well seen in those plots. The movement of shock changes the aerodynamic load distribution on the wing. The effect of viscous on aeroelastic analysis is also discussed. Also compared are the flutter solutions with, or without i the structural nonlinearity. As can be seen, linear structural solution goes to infinite, which can not be true in reality. The nonlinear solution is more realistic and can be used to understand the fluid and structure interaction behavior, to control, or prevent disastrous events.

Committee:

Dr. Kirti N. Ghia (Advisor)

Subjects:

Applied Mechanics

Keywords:

aeroelasticity; FEA; CFD fluid mechanics; solid mechanics

Pesich, Justin MSteady Aeroelastic Response Prediction and Validation for Automobile Hoods
Master of Science, The Ohio State University, 2017, Aero/Astro Engineering
This thesis describes a strategy to predict steady aeroelastic response of an automobile hood at high speeds using coupled fluid dynamic and structural codes. The pursuit of improved fuel economy through weight reduction, reduced manufacturing costs, and improved crash safety can result in increased compliance in automobile structures. However, with compliance comes an increased susceptibility to aerodynamic and vibratory loads. The hood in particular withstands considerable aerodynamic force at highway speeds, creating the potential for significant aeroelastic response that may adversely impact customer satisfaction and perception of vehicle quality. The goal of this thesis is to develop and couple high fidelity fluid and structural computational models to improve the understanding of fluid-structure interactions between automobile hoods and the surrounding internal and external flow. Computational analysis is carried out using coupled CFD-FEM solvers with detailed models of the automobile topology and structural components. The experimental work consists of wind tunnel tests using a full-scale production vehicle. Comparisons between the numerical and experimental results yield important insights into required modeling fidelity, coupling, and challenges in validation for the aeroelastic response of automobile hoods. Three separate vehicle configurations are considered. The first configuration resembles an initial design model or “styling” model which neglects the internal flow through the front fascia and has a simplified underbody and wheels. The second configuration is a “complete” model including all vehicle components. The last configuration is an adaptation of the complete model employing a simplified engine compartment and underbody. One motive for the last configuration is the complete model was found to have inadequate mesh cell quality to implement into the coupled simulation framework, but a model with reduced complexity is satisfactory. Furthermore, these configurations are used to study the importance of the internal flow. The degree of the mutual interaction between the fluid and structure is also considered. Investigations of computational uncertainty indicate low sensitivity of simulation results to small changes in fluid modeling. In addition, an examination of measurement compliance showed large margins of experimental uncertainty.

Committee:

Jack McNamara (Advisor)

Subjects:

Aerospace Engineering

Keywords:

aeroelasticity; fluid structure interaction; aerodynamics; automobiles; hood lift; hood vibration; validation

Miller, Brent AdamLoosely Coupled Time Integration of Fluid-Thermal-Structural Interactions in Hypersonic Flows
Doctor of Philosophy, The Ohio State University, 2015, Aero/Astro Engineering
The development of reusable hypersonic cruise vehicles requires analysis capability that can capture the coupled, highly-nonlinear interactions between the fluid flow, structural mechanics, and heat transfer. This analysis must also be performed over significant portions of the flight trajectory due to the long-term thermal evolution of the vehicle. The fluid and structural physics operate at significantly smaller time scales than the thermal evolution, requiring time marching that can capture the small time scales for time records that encapsulate the longer time scale of the thermal response. This leads to extreme computational times and motivates research that seeks to maximize efficiency of the time integrations for the coupled problem. The goal of this dissertation is to develop time integration procedures that significantly improve computational efficiency while also maintaining time accuracy and stability for fluid-thermal-structural analysis. This is achieved using carefully designed loosely coupled schemes for the fluid, thermal, and structural solvers. Here, different time integrators are used for the solvers of each physical field, and boundary conditions are exchanged at most once per time step. Coupling schemes for both time-accurate and quasi-steady flow models are considered. Computational efficiency and time accuracy are improved through the use of both extrapolating predictors and interpolation during the exchange of boundary conditions; the latter of which enables the use of different sized time steps between the solvers, known as subcycling. The developed coupling procedures are compared to several other schemes, including a basic one that does not use the predictors, and a subiteration-based strongly coupled scheme. Response predictions of multiple configurations of a panel in two dimensional high-speed flow are performed. Using second order implicit time integrators for the individual solvers, the predictor and strongly coupled schemes are demonstrated to retain the second order accuracy with and without subcycling, while the others reduced to first order. Simulations of two panel configurations are performed to investigate the performance of the coupling schemes in predicting stable and dynamically unstable responses. From the stable response analysis, the predictor-based schemes are found to be the least computationally expensive compared to the strongly coupled and basic loosely coupled schemes. In the second configuration, the panel is predicted to undergo snap-through and ultimately a dynamically unstable limit cycle response with each scheme. The predictor schemes are shown to provide a 3-10 times reduction in computational cost compared to the other schemes. Finally, a 30 second response of the panel with a flutter instability using time-accurate CFD is performed and compared to the response using quasi-steady surrogate and analytical aerothermodynamic models. The unsteady CFD and surrogate based responses have excellent agreement throughout the response, with differences under 1%. The time to flutter predicted from the analytical models is 15% higher than that predicted by the CFD and surrogate models. However, the flutter response shows good agreement between the three responses, indicating that the quasi-steady flow assumption can accurately capture the coupled dynamics.

Committee:

Jack McNamara (Advisor); Thomas Eason, III (Committee Member); Datta Gaitonde (Committee Member); Sandip Mazumder (Committee Member); Stephen Spottswood (Committee Member); Manoj Srinivasan (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

Hypersonic; FTSI; fluid-thermal-structural interactions; aeroelasticity; aerothermoelasticity; time integration; loosely coupled

Li, SihaoEffect of aeroelasticity in tow tank strain gauge measurements on a NACA 0015 airfoil
Master of Science (MS), Ohio University, 1993, Mechanical Engineering (Engineering)

Effect of aeroelasticity in tow tank strain gauge measurements on a NACA 0015 airfoil

Committee:

Gary Graham (Advisor)

Subjects:

Engineering, Mechanical

Keywords:

Effect of aeroelasticity; Tow tank strain gauge measurements; NACA 0015 airfoil

Kecskemety, Krista MarieAssessing the Influence of Wake Dynamics on the Performance and Aeroelastic Behavior of Wind Turbines
Doctor of Philosophy, The Ohio State University, 2012, Aero/Astro Engineering
While wind turbine farms are currently rapidly expanding, there are numerous technological challenges that must be overcome before wind energy represents a significant contributor to energy generation in the United States. One of the primary challenges is accurately accounting for the aerodynamic environment. This dissertation is focused on improving the aerodynamic modeling through the incorporation of wake effects. A comprehensive verification and validation of the NREL FAST code, which has been enhanced to include a Free Vortex Wake (FVW) model was conducted. The verification and validation is carried out through a comparison of wake geometry, blade lift distribution, wind turbine power and force and moment coefficients using a combination of Computational Fluid Dynamics (CFD) and experimental data. The results are also compared against Blade Element Momentum Theory (BEM), and results from an extensive experimental campaign by NREL on the prediction capabilities of wind turbine modeling tools. Results indicate that the enhanced aeroelastic code generally provides improved predictions. However, in several notable cases the predictions are only marginally improved, or even worse, than those generated using Blade Element Momentum Theory aerodynamics. After verification and validation of the model, the impact of including the free vortex wake model in the presence of turbulent flow was also examined. The inclusion of turbulence created large differences between BEM and FVW in predictions of rotor loading and power, however the amplitude of the turbulence did not have a large impact on the difference between the FVW and BEM. In addition to loading and power predictions, the structural response (tip deflections and root bending moments) of the wind turbine is investigated in the presence of turbulent inflow. The results indicate that the turbulence intensity and spectral model have a significant effect on the importance of the wake dynamics in modeling the tip deflections and root moments. From the dissertation results, it is concluded that modeling of the aerodynamic environment remains incomplete, even after inclusion of wake effects. One important aspect identified for future improvements is modeling of the unsteady aerodynamic lift characteristics of the rotor.

Committee:

Jack McNamara, PhD (Advisor); Jen-Ping Chen, PhD (Committee Member); Mo-How Herman Shen, PhD (Committee Member); Mei Zhuang, PhD (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

Wind Turbine; Vortex Wake; Aeroelasticity

Swaim, Robert LeeActive control of booster elasticity /
Doctor of Philosophy, The Ohio State University, 1966, Graduate School

Committee:

Not Provided (Other)

Subjects:

Engineering

Keywords:

Aeroelasticity

Fellows, Mark TAeroelastic Stability and Control of Rectangular Plates with Compliant Boundary Supports
Master of Science, Miami University, 2014, Computational Science and Engineering
A proposed design to reduce airframe noise emissions by attaching a flexible fairing between the flap and trailing edge of airplane wings has inspired new research into aeroelastic phenomena in plates and plate-membranes. These flexible plates are susceptible to aeroelastic instabilities which are influenced by aerodynamic loading, axial loading, and boundary conditions. In this research, the aeroelastic behavior of a rectangular plate is considered. The structural system is modeled using the Rayleigh-Ritz method and the piston theory is used to approximate the aerodynamic loading. The effects of the boundary support stiffness, dynamic pressure, and static in-plane loading on the flutter and buckling instability boundaries are explored. Control strategies employing a robust pole placement method, a unique control gain method, and the linear quadratic regulator method are used to improve the open loop stability boundary, allowing for an increase in the operational envelope of the aeroelastic plate system.

Committee:

Amit Shukla, PhD (Advisor); Kumar Singh, PhD (Advisor); Timothy Cameron, PhD (Committee Member)

Subjects:

Aerospace Engineering; Mechanical Engineering

Keywords:

aeroelasticity; rectangular plate; control; flutter; buckling;

Barnes, Caleb J.Unsteady Physics and Aeroelastic Response of Streamwise Vortex-Surface Interactions
Doctor of Philosophy (PhD), Wright State University, 2015, Engineering PhD
Streamwise vortex-surface interactions can occur in aviation intentionally in the context of formation flight as an energy saving mechanism, unintentionally in wake crossings when aircraft fly in close proximity, and as a consequence of aircraft design through the interaction of fluid dynamics between different aerodynamic surfaces. The bulk of past work on streamwise vortex-surface interactions has focused on steady inviscid analysis for optimizing aerodynamic loads in the context of formation flight or experimental analysis on fin buffeting problems. A fundamental understanding of the viscous and unsteady effects that may occur is both important and currently lacking in the literature. This dissertation seeks to fill this need by using a high-fidelity implicit large-eddy simulation approach coupled with geometrically non-linear finite elements to identify and analyze important physics that may occur. Simple, canonical configurations are employed in order help disentangle the many interrelated factors of a very complex problem. Analysis of a tandem wing configuration elucidated mutual induction between the incident vortex from the leader wing and tip vortex of the follower wing that resulted in a broad taxonomy of flow structure, wake evolution, and unsteady behaviors for several lateral impingement locations. Interaction of an isolated streamwise vortex with a wing revealed a robust helical instability develops when a strong vortex impinges directly with the leading-edge. This spiraling behavior was found to occur as a result of the upstream influence of adverse pressure gradients provided by the wing that drive the vortex into its linearly unstable regime allowing for the growth of shortwave perturbations. Stability can be augmented through vertical positioning of the vortex. A negative offset can enhance stability by providing a stronger adverse pressure gradient while a positive offset exploits a favorable gradient and removes the upstream instability altogether. The effects of wing compliance were revealed through full aeroleastic simulations. Essentially static, vortex-induced bending deformations reposition the vortex and drive it further into its unstable regime. Static and dynamic components of the aeroelastic response were systematically isolated where the static deformations were shown to provide the greatest influence. Dynamic effects provide some influence to the incident vortex behavior but these are secondary to the static behavior.

Committee:

George Huang, Ph.D. (Advisor); Joseph Shang, Ph.D. (Committee Member); Zifeng Yang, Ph.D. (Committee Member); Miguel Visbal, Ph.D. (Committee Member); Aaron Altman, Ph.D. (Committee Member)

Subjects:

Aerospace Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

formation flight; streamwise vortex interaction; fluid structure interaction; aeroelasticity; unsteady fluid dynamics; vortex dynamics; vortex surface interaction

Riley, Matthew E.Quantification of Model-Form, Predictive, and Parametric Uncertainties in Simulation-Based Design
Doctor of Philosophy (PhD), Wright State University, 2011, Engineering PhD
Traditional uncertainty quantification techniques in simulation-based analysis and design focus upon on the quantification of parametric uncertainties-inherent natural variations of the input variables. This is done by developing a representation of the uncertainties in the parameters and then efficiently propagating this information through the modeling process to develop distributions or metrics regarding the output responses of interest. However, in problems with complex or newer modeling methodologies, the variabilities induced by the modeling process itself-known collectively as model-form and predictive uncertainty-can become a significant, if not greater source of uncertainty to the problem. As such, for efficient and accurate uncertainty measurements, it is necessary to consider the effects of these two additional forms of uncertainty along with the inherent parametric uncertainty. However, current methods utilized for parametric uncertainty quantification are not necessarily viable or applicable to quantify model-form or predictive uncertainties. Additionally, the quantification of these two additional forms of uncertainty can require the introduction of additional data into the problem-such as experimental data-which might not be available for particular designs and configurations, especially in the early design-stage. As such, methods must be developed for the efficient quantification of uncertainties from all sources, as well as from all permutations of sources to handle problems where a full array of input data is unavailable. This work develops and applies methods for the quantification of these uncertainties with specific application to the simulation-based analysis of aeroelastic structures.

Committee:

Ramana Grandhi, PhD (Advisor); Erwin Johnson, PhD (Committee Member); Raymond Kolonay, PhD (Committee Member); Donald Kunz, PhD (Committee Member); Ravi Penmetsa, PhD (Committee Member); Joseph Slater, PhD (Committee Member)

Subjects:

Aerospace Engineering; Mechanical Engineering; Statistics

Keywords:

Uncertainty Quantification; Stochastic Models; Model-form Uncertainty; Bayesian Statistics; Aeroelasticity

Leger, Timothy JamesDevelopment of an Unsteady Aeroelastic Solver for the Analysis of Modern Turbomachinery Designs
Doctor of Philosophy (PhD), Wright State University, 2010, Engineering PhD

Developers of aircraft gas turbine engines continually strive for greater efficiency and higher thrust-to-weight ratio designs. To meet these goals, advanced designs generally feature thin, low aspect airfoils, which offer increased performance but are highly susceptible to flow-induced vibrations. As a result, High Cycle Fatigue (HCF) has become a universal problem throughout the gas turbine industry and unsteady aeroelastic computational models are needed to predict and prevent these problems in modern turbomachinery designs. This research presents the development of a 3D unsteady aeroelastic solver for turbomachinery applications. To accomplish this, a well established turbomachinery Computational Fluid Dynamics (CFD) code called Corsair is loosely coupled to the commercial Computational Structural Solver (CSD) Ansys® through the use of a Fluid Structure Interaction (FSI) module.

Significant modifications are made to Corsair to handle the integration of the FSI module and improve overall performance. To properly account for fluid grid deformations dictated by the FSI module, temporal based coordinate transformation metrics are incorporated into Corsair. Wall functions with user specified surface roughness are also added to reduce fluid grid density requirements near solid surfaces. To increase overall performance and ease of future modifications to the source code, Corsair is rewritten in Fortran 90 with an emphasis on reducing memory usage and improving source code readability and structure. As part of this effort, the shared memory data structure of Corsair is replaced with a distributed model. Domain decomposition of individual grids in the radial direction is also incorporated into Corsair for additional parallelization, along with a utility to automate this process in an optimal manner based on user input. This additional parallelization helps offset the inability to use the fine grain mp-threads parallelization in the original code on non-distributed memory architectures such as the PC Beowulf cluster used for this research. Conversion routines and utilities are created to handle differences in grid formats between Corsair and the FSI module.

The resulting aeroelastic solver is tested using two simplified configurations. First, the well understood case of a flexible cylinder in cross flow is studied with the natural frequency of the cylinder set to the shedding frequency of the Von Karman streets. The cylinder is self excited and thus demonstrates the correct exchange of energy between the fluid and structural models. The second test case is based on the fourth standard configuration and demonstrates the ability of the solver to predict the dominant vibrational modes of an aeroelastic turbomachinery blade. For this case, a single blade from the fourth standard configuration is subjected to a step function from zero loading to the converged flow solution loading in order to excite the structural modes of the blade. These modes are then compared to those obtained from an in vacuo Ansys® analysis with good agreement between the two.

Committee:

Mitch Wolff, PhD (Advisor); Scott Thomas, PhD (Committee Member); Joseph Shang, PhD (Committee Member); Gary Lamont, PhD (Committee Member); David Johnston, PhD (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

FSI; Turbomachinery; CFD; Aeroelasticity

McDonough, LauraReceptance Based Control of Aeroelastic Systems for Flutter Suppression
Master of Science, Miami University, 2012, Computational Science and Engineering
The field of aeroelasticity deals with mutual interaction between inertial, elastic, and aerodynamic properties of a flexible system. Aeroelastic instabilities, such as flutter, can lead to fatigue and potential failure of an aerospace structure. Active control strategies may be needed to avoid such instabilities to achieve increased flight performance. In this research, receptance based active control schemes are developed for flutter suppression and flutter-boundary extension. In principle, this method utilizes receptance frequency response functions extracted from embedded sensors and actuators of the aircraft, representing the true aeroelastic interaction, for control force computations. Hence, it circumvents potential modeling errors associated with structural and aerodynamic parameters, which are used in traditional state-space based aeroelastic control. In this study, receptance based single input, multiple input and output state feedback control is developed. Several aspects of control design including actuator dynamics, optimization and robustness are demonstrated through numerical simulations and computational studies.

Committee:

Kumar Singh (Advisor); Timothy Cameron, Ph.D (Committee Member); Raymond Kolonay, Ph.D (Advisor)

Subjects:

Aerospace Engineering; Mechanical Engineering

Keywords:

Aeroelasticity; control; aircraft; active control; receptance method; single input; multiple input; output; control design