Aerospace Engineering Theses and Dissertations
http://hdl.handle.net/1903/2737
Mon, 16 Dec 2019 02:44:17 GMT2019-12-16T02:44:17ZTransient Dynamics of Helicopter Rotor Wakes Using a Time-Accurate Free-Vortex Method
http://hdl.handle.net/1903/25270
Transient Dynamics of Helicopter Rotor Wakes Using a Time-Accurate Free-Vortex Method
Bhagwat, Mahendra J.
A second-order accurate predictor-corrector type algorithm has been developed to
obtain a time-accurate solution of the vortical wake generated by a helicopter rotor.
The rotor blade flapping solution was fully integrated with the wake geometry solution
using the same time-marching algorithm. The analysis was used to predict the locations
of wake vortex filaments under transient flight conditions, where the rotor wake
may not be periodic at the rotational frequency. Applications of this analysis include
prediction of the rotor induced velocity field and blade airloads during transient flight
and maneuvers.
The stability of the rotor wake structure is important from the perspective of free-vortex
wake models. The wake stability was examined using a linearized stability
analysis, and the rotor wake was shown to be physically unstable. Therefore, the
stability of the numerical algorithm is an important consideration in developing robust wake methodologies. Both the stability and accuracy of the numerical wake solutions
algorithms was rigorously examined. The straight-line vortex segmentation used in
the present analysis was shown to be second-order accurate. The overall numerical
solution was also demonstrated to converge with a second-order accuracy. A technique
for increasing the order of accuracy for high resolution solutions is also described.
Along with a formal (mathematical) verification of solution accuracy, the numerical
solution for the rotor wake problem was compared with experimental results for
both steady-state and transient operating conditions. The steady-state wake model was
shown to give good predictions of rotor wake geometry, induced inflow distribution
as well as performance trends. Under transient conditions, such as those following a
pitch input during a maneuver, the time-accurate wake model was shown to correctly
model the dynamic response of rotor wake. In axial descent passing through the vortex
ring state, the present analysis was shown to properly model the associated power
losses as shown by experimental results. The present analysis was also shown to give
improved predictions of wake distortions during simulated maneuvering flight with
various imposed angular rates of the rotor.
Mon, 01 Jan 2001 00:00:00 GMThttp://hdl.handle.net/1903/252702001-01-01T00:00:00ZModeling, Estimation, and Control of Actuator Dynamics for Remotely Operated Underwater Vehicles
http://hdl.handle.net/1903/25194
Modeling, Estimation, and Control of Actuator Dynamics for Remotely Operated Underwater Vehicles
Boehm, Jordan
Modeling and control of remotely operated underwater vehicles is a challenging problem that depends greatly on how the dynamics of their thrusters are compensated. In this thesis a novel method for characterizing thruster dynamics using a six-axis load cell is presented. Multiple dynamic models are characterized with this test setup. Model-based control design strategies are used to compensate for nonlinearities in the dynamics, which include input dead zones and coupling with fluid dynamics. Multiple estimation methods are presented to construct an estimate of fluid velocity which is handled as an unmeasured state. The different models, controllers, and estimators are comparatively evaluated in closed-loop experiments using the six-axis load cell to measure thrust tracking performance. Full vehicle simulations using the experimentally characterized models provide additional opportunities for comparison of control and estimation strategies. The potential tracking control benefits from the variety of presented thruster dynamics compensation strategies are evaluated for a remotely operated underwater vehicle with multiple thrusters.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/1903/251942019-01-01T00:00:00ZOptimization of Expanding Turning Vanes by Bezier Curve Parameterization
http://hdl.handle.net/1903/25189
Optimization of Expanding Turning Vanes by Bezier Curve Parameterization
Schirf, Collin
The development of a new process for optimizing wind tunnel turning vanes for use in expanding corners is described. This process uses MATLAB tools to operate the infinite airfoil cascade solver MISES in order to take advantage of the powerful optimization tools already present in MATLAB. Airfoils are defined using four Bezier curves of fifth order to limit the number of design variables and take advantage of simple smoothness constraints. A parameter sweep is performed to verify the tool's operation and gain insight into the impacts of airfoil thickness, airfoil camber, cascade solidity, and expansion ratio before several optimization cases using various MATLAB optimization functions were used to show the ability of the optimizer to reduce total pressure loss and flow separation in turning vane cascades. Optimizer outputs were shown to reduce total pressure losses by up to 18% and separation magnitude by up to 53% over initial designs. Comparison with STAR-CCM+ models verified applicability of MISES cases to more accurate wind tunnel flows.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/1903/251892019-01-01T00:00:00ZFlowfield Estimation and Vortex Stabilization near an Actuated Airfoil
http://hdl.handle.net/1903/25187
Flowfield Estimation and Vortex Stabilization near an Actuated Airfoil
Gomez Berdugo, Daniel Fernando
Feedback control of unsteady flow structures is a challenging problem that is of interest for the creation of agile bio-inspired micro aerial vehicles. This thesis presents two separate results in the estimation and control of unsteady flow structures: the application of a principled estimation method that generates full flowfield estimates using data obtained from a limited number of pressure sensors, and the analysis of a nonlinear control system consisting of a single vortex in a freestream near an actuated cylinder and an airfoil. The estimation method is based on Dynamic Mode Decompositions (DMD), a data-driven algorithm that approximates a time series of data as a sum of modes that evolve linearly. DMD is used here to create a linear system that approximates the flow dynamics and pressure sensor output from Particle Image Velocimetry (PIV) and pressure measurements of the flowfield around the airfoil. A DMD Kalman Filter (DMD-KF) uses the pressure measurements to estimate the evolution of this linear system, and thus produce an approximation of the flowfield from the pressure data alone. The DMD-KF is implemented for experimental data from two different setups: a pitching cambered ellipse airfoil and a surging NACA 0012 airfoil. Filter performance is evaluated using the original flowfield PIV data, and compared with a DMD reconstruction. For control analysis, heaving and/or surging are used as input to stabilize the vortex position relative to the body. The closed-loop system utilizes a linear state-feedback control law. Conditions on the control gains to stabilize any of the equilibrium points are determined analytically for the cylinder case and numerically for the airfoil. Simulations of the open- and closed-loop systems illustrate the bifurcations that arise from varying the vortex strength, bound circulation and/or control gains.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/1903/251872019-01-01T00:00:00Z