1,721,009 research outputs found
Experimental Studies on Freeplay Induced Limit Cycle Oscillations and Their Major Drivers
No full textA new experimental wind tunnel test-bed has been developed for the study of limit cycle oscillations induced by control surface freeplay. A thorough examination of several factors affecting the limit cycle is presented—starting from a reference configuration, the effect of changes in inertia and stiffness, a time-varying gap size, gravitational loading, and aerodynamic preload due to an angle of attack. Both time-marching simulations and describing functions analytical methods have been used to understand the experimental measurements and study the capability of the methods to capture the physical behavior. Good agreement was found in all cases, and physical insights are gained from the mathematical models. Limitations of the analytical tools are also addressed, focusing on the important difference between the self-excited dynamics of the nonlinear system and its forced response to external excitation
Wind tunnel tests of an aeroelastic model with multiple control surface freeplay nonlinearities
No full textThe effects of multiple control surface freeplay nonlinearities on the aeroelastic behavior of a wind tunnel model of a full aircraft configuration are explored. The work follows earlier works by the authors that examined nonlinear phenomena and limit cycle oscillation due to control surface freeplay. Initially, a single nonlinearity was studied by several wind tunnel tests of components of the full configuration. The extension to multiple nonlinearities is reported here. The complete wind tunnel model is described together with the measurement system developed for the tests. Results are reported on the different LCO mechanisms that the system has and their dependency on model angle of attack and side–slip angle
Study on Interaction Between a Stability Augmentation System and an Active Flutter Suppression Controller
No full textThis work presents the research carried out using the latest update of the F-XDIA model – a wind tunnel model designed for experimentally studying active flutter suppression technologies (AFS) and freeplay induced nonlinear aeroelastic behavior of representative commercial aircraft configurations. The model was tested repeatedly during last years in the framework of an international cooperation between Politecnico di Milano and the University ofWashington. The pylon support for the wind tunnel test was modified, hosting a gimballed connection between the model and the pylon itself, allowing the rigid rotation of the model around the pitch and roll axes, separately or simultaneously. The model is unstable around the roll axis. For thisreason a Stability Augmentation System (SAS) had to be designed and implemented, and its interaction with AFS controllers is studied. The results show that the two controllers, "rigid body" stability-augmentation and AFS, have to be designed considering their interactions and that a gain scheduling w.r.t. the air speed is necessary to stabilize both rigid body motion and the aeroelastic modes. As the tests demonstrate, the model was successfully tested in the wind tunnel beyond its open-loop flutter point in the free-to-roll configuration
Design Optimization of Structures with Shape Memory Alloy Member Actuators
No full textThesis (Master's)--University of Washington, 2013A capability was developed to build a perform mass-minimization of a truss with SMA actuation to determine optimal element diameters and actuator applied temperature changes. The Nonlinear Programming/Approximation Concepts (NLP/AC) approach was used. This method is based on using a sequence of approximate optimization problems rather than optimizing with the full nonlinear analyses. Some special approximations based on new intermediate variables were used. Results are presented and analyzed
RANS-CFD Based Assessment of Corrections Applied to the Measured Characteristics of Supersonic Configurations in a Low Speed Wind Tunnel
Full text linkThesis (Master's)--University of Washington, 2022The CFD software package Star-CCM+ was used to investigate the effects of the model support system and test section walls on a double-delta wing, representative of long-range supersonic configurations, in the University of Washington's Kirsten Wind Tunnel in an effort to improve current wind tunnel test corrections. The Star-CCM+ simulation-derived support corrections were validated using past wind tunnel models and support corrections.Simulations indicated that the interference effects due to the model support system are non-negligible and must be accounted for. New model support corrections were computed using CFD and wind tunnel data.
Wall effects corrections were also evaluated via RANS CFD and results compared well to classical corrections traditionally applied by the Kirsten Wind Tunnel.
The pitching moment curve slope was underpredicted, however, with CFD simulations.
Engine nacelle form factors were also calculated with Star-CCM+ to add new nacelle internal duct drag corrections to wind tunnel data.
All CFD derived corrections were applied to past uncorrected wind tunnel data, compared to data with KWT's standard corrections, and to Star-CCM+ simulations of the models in freestream conditions. The CFD derived corrections appear to improve the resulting "free flight" wind tunnel data for the wing alone case. More work is necessary, however, for full configurations and CFD-based corrections should be validated with follow-on dedicated "Tare and Interference" (T\&I) testing
Investigation of Aspects of Aeroservoelastic State-Space Modeling on Active Flutter Suppression LQR Control Synthesis
Full text linkThesis (Master's)--University of Washington, 2018Whether motivated by cost or performance, the shift to structurally lighter aircraft has increased the demand for new developments in aeroservoelasticity. The William E. Boeing Department of Aeronautics and Astronautics has invested significant resources to meet this demand, involving wind tunnel models and modifications, and software development. A major step in aeroservoelastic analysis is the generation of the required state-space models. This thesis describes the development of a MATLAB code with such a capability. The code is intended to be modified and used by the department for future research. This in-house capability allows for greater flexibility and transparency for future users. Two numerical experiments were run using the new code. The focus was the effect of actuator model's order and the range of reduced frequencies used to generate rational function approximation in the form of a Roger series. It was determined that the order of actuation models and the range of reduced frequencies used in a Roger Approximation had little to no effect on Linear-Quadratic Regulator synthesis and performance for Active Flutter Suppression of a wing/flap system investigated in this work
Frequency Response Simulations and Tests of an Aeroservoelastic Wind Tunnel Model
Full text linkThesis (Master's)--University of Washington, 2019The development of active controls has the potential to provide weight savings, cost savings, and safety enhancements for many types of aircraft. With the creation of an aeroservoelastic wind tunnel model and testbed, the William E. Boeing Department of Aeronautics and Astronautics now has the capability to test active controls on representative flexible aircraft configurations. Simulations of the aeroservoelastic model, validated by experimental data, advance the field of active controls by establishing reference test cases that are ready for testing alternative active control laws. This thesis focuses on frequency response simulations that use inputs from a NASTRAN Finite Element Model to create a state-space representation that aids in modern control law design for Active Flutter Suppression. Two analytical-numerical methods for finding the frequency response of the model are used and compared to one another as well as to experimental data to produce a full aeroservoelastic wind tunnel model test case
Aeroelasticity of Nonlinear Tail / Rudder Systems with Freeplay
Full text linkThesis (Master's)--University of Washington, 2015This thesis details the development of a linear/nonlinear three degree of freedom aeroelastic system designed and manufactured at the University of Washington (UW). Describing function analysis was carried out in the frequency domain. Time domain simulations were carried out to account for all types of motion. Nonlinear aeroelastic behavior may lead to limit cycles which can be captured in the frequency domain using describing function approximation and numerically using Runga-Kutta integration. Linear and nonlinear aeroelastic tests were conducted in the UW 3x3 low-speed wind tunnel to determine the linear flutter speed and frequency of the system as well as its nonlinear behavior when freeplay is introduced. The test data is presented along with the results of the MATLAB-based simulations. The correlation between test and numerical results is very high
Contributions to Physics-Based Aeroservoelastic Uncertainty Analysis
Full text linkThesis (Ph.D.)--University of Washington, 2016-06The thesis presents the development of a new fully-integrated, MATLAB based simulation capability for aeroservoelastic (ASE) uncertainty analysis that accounts for uncertainties in all disciplines as well as discipline interactions. This new capability allows probabilistic studies of complex configuration at a scope and with depth not known before. Several statistical tools and methods have been integrated into the capability to guide the tasks such as parameter prioritization, uncertainty reduction, and risk mitigation. The first task of the thesis focuses on aeroservoelastic uncertainty assessment considering control component uncertainty. The simulation has shown that attention has to be paid, if notch filters are used in the aeroservoelastic loop, to the variability and uncertainties of the aircraft involved. The second task introduces two innovative methodologies to characterize the unsteady aerodynamic uncertainty. One is a physically based aerodynamic influence coefficients element by element correction uncertainty scheme and the other is an alternative approach focusing on rational function approximation matrix uncertainties to evaluate the relative impact of uncertainty in aerodynamic stiffness, damping, inertia, or lag terms. Finally, the capability has been applied to obtain the gust load response statistics accounting for uncertainties in both aircraft and gust profiles. The gust response analysis shows a significant increase of the critical loads when system’s uncertainties are included. The work is expected to make a contribution to the understanding of the propagation of uncertainty and the resulting reliability of realistic integrated aeroservoelastic system inherent in real modern aircraft. This work will motivate more research in the aeroservoelastic uncertainty area regarding both methods development in general and reliability studies of different configurations of interest. The mathematical derivations which serve as the foundation of the capability are also well documented
Simulation of Gust Generator-Induced Wind Tunnel Flow Fields
No full textThesis (Master's)--University of Washington, 2020A mathematical/numerical investigation was carried out of the flow characteristics of wind tunnel test section flow influenced by a gust generation system. The University of Washington's 3'x3' Low-Speed wind tunnel was modeled using high-fidelity Computational Fluid Dynamics (CFD) simulations and using easy-to-program and inexpensive-to-run vortex lattice methods (VLM). Steady and unsteady CFD flow simulations were completed to study the nature of the flow field created by the gust generator in the wind tunnel. The gust generator induced gust angle-of-attack and the velocity of the flow field at various locations in the test section were determined and the aerodynamic effect on a test wing was also studied. In the time marching vortex lattice method developed, accounting for the effect of the walls of the wind tunnel on the forces felt by the test object was done via a system of mirror images. The VLM simulations were compared to classical Theodorsen solutions and to the CFD simulations to gauge the accuracy of the VLM simulations. In the presence of wind tunnel walls, the VLM simulations overestimated the forces felt by the test object when compared to the force predictions of the CFD simulations, but overall captured the time behavior well. Knowing the magnitude of difference between CFD and VLM results, VLM simulations can still be a useful tools, fast and inexpensive, for the design of wind tunnel gust generation systems and the positioning of wind tunnel models relative to them
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