1,720,967 research outputs found
Parameter identification studies using SIDPAC with Fenrir’s 1st flight data set
Full text linkThis document summarizes the process of identifying unknown dynamic systems from measured flight test
data. Several available system identification tools were evaluated based on accuracy and robustness. Among
them,SIDPAC developed by NASA was chosen. The objective of this study is to lay out the
procedures to identify unknown systems from flight test data and to provide recommendations for following
flight tests. Data from the Fenrir’s flight was used.NASA NRA, "Lightweight Adaptive Aeroelastic Wing for Enhanced Performance Across the Flight Envelope," NRA NNX14AL36A, Mr. John Bosworth Technical Monitor.Dongchan, Lee; Danowsky, Brian. (2015). Parameter identification studies using SIDPAC with Fenrir’s 1st flight data set. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/174384
Classical Control Design Feasibility Study with BFF Models
Full text linkThis working paper documents an initial control feasibility study to determine if classical control techniques
could be utilized to favorably augment the stability of the BFF vehicle. This study focused on the lower
speed models which have stable, or slightly unstable aeroelastic dynamics. Future studies will explore the
higher speed models with highly unstable aeroelastic modes. The final control solution will incorporate
stability augmentation with aeroelastic suppression, including flutter suppression to stabilize the vehicle
beyond the flutter boundary. The principal goal is a defined strategy, process and supporting software tools
to develop a full envelope controller for flexible aeroelastic vehicles with significant rigid body and flexible
coupling. Focus will be on blended wing-body vehicle designs like the BFF and X-56A. The purpose of
this study is a background feasibility investigation.NASA NRA, "Lightweight Adaptive Aeroelastic Wing for Enhanced Performance Across the Flight Envelope," NRA NNX14AL36A, Mr. John Bosworth Technical Monitor.Lee, Dongchan; Danowsky, Brian. (2014). Classical Control Design Feasibility Study with BFF Models. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/174378
Investigation of suitable flight test inputs for system identification of low frequency dynamics for the mini MUTT
Full text linkThe purpose of this document is to investigate suitable excitations for flight test to identify rigid body
dynamic characteristics. It is understood that the stiff wing mini MUTT (Fenrir) will be flown soon for identification
of rigid body dynamic characteristic. The flight test data will further be used to identify unknown system
parameters offline. The model system considered in this study is the BFF model at 40 kts as this is the
lowest flight condition available and displays the least amount of coupling between rigid body and flexible
dynamics. It is noted that this model still displays coupling between the pitch dynamics and the 1st
symmetric wing bending mode. The objective is to focus on low frequency dynamics as it is expected that
the stiff wing mini MUTT (Fenrir) should display similar low frequency dynamics.
Different input sequences for the elevator and aileron control inputs, are investigated. The sensors
investigated are the roll and pitch rates at the aircraft center body IMU.NASA NRA, "Lightweight Adaptive Aeroelastic Wing for Enhanced Performance Across the Flight Envelope," NRA NNX14AL36A, Mr. John Bosworth Technical Monitor.Dongchan, Lee; Danowsky, Brian. (2015). Investigation of suitable flight test inputs for system identification of low frequency dynamics for the mini MUTT. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/174382
Formulation of a complete structural uncertainty model for robust flutter prediction
Full text linkFlutter is a dynamic instability that aerodynamic vehicles encounter in atmospheric flight. The interaction between structural elastic, structural inertial and aerodynamic forces may cause the flexible vehicle to undergo divergent oscillations, at which point flutter is encountered. Undesirable effects of this behavior include difficult controllability, structural fatigue and even catastrophic structural failure. This point of instability is dependant on many factors including the structural properties, structural geometry, aerodynamic shape and the flight condition. Since these factors may influence the flutter point in a sensitive manner investigation of uncertainty in these properties is warranted. A modern method to investigate system uncertainty is with the use of robust stability, namely [mu] analysis. These modern technologies are used to analyze the uncertainty in structural properties (mass and stiffness properties) of a wing in flight and the effect these uncertainties have on the flutter point. Recent use of these robust stability techniques on the flutter problem have focused on uncertainty in the natural structural modal frequencies. The uncertainties in the modal frequencies are also typically assumed independent. Uncertainties in the natural structural mode shapes have not been explored in complete detail. By including uncertainty in the structural mode shapes the robust flutter margins will be much less conservative. A complete structural uncertainty model for robust flutter prediction is constructed. Robust flutter margins are found for a fictitious wing with uncertainties in wing mass and stiffness properties, using the structured singular value ([mu]). Since the robust flutter margins include uncertainty in the structural mode shapes, as well as the structural mode frequencies, they are least conservative estimates. The uncertainties in many structural properties on the wing are investigated and the effect that they have on the flutter point is determined. The formulation presented herein can be applied to a wide array of problems concerning the sensitivity of the flutter solution.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Modal Identification from Sköll flight tests
Full text linkModal identification was performed on flight test data using the Curve Fitting Frequency Domain
Decomposition (CFDD) method. The emphasis is to identify aeroelastic modes rather than rigid body
modes. Consequently, the aeroelastic short period mode was identified in addition to several higher
frequency aeroelastic modes. All of the modes identified reflect complex-valued aeroelastic modes, as
opposed to real-valued dry structural modes. The following flights were used for identification: Sköll Flight 3: 20 m/s flight condition; Sköll Flight 4: 30 m/s flight condition.NASA NRA, "Lightweight Adaptive Aeroelastic Wing for Enhanced Performance Across the Flight Envelope," NRA NNX14AL36A, Mr. John Bosworth Technical Monitor.Danowsky, Brian. (2015). Modal Identification from Sköll flight tests. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/174387
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
System identification studies with the stiff wing mini MUTT Fenrir – Flight 20
Full text linkA successful flight test with the stiff wing mini MUTT, named Fenrir, was conducted on 27 May
2015. The purpose of this flight was to gather preliminary data for system identification focused on low
frequency rigid body dynamics. No augmentation was used during the 1st flight on this day, which is
formally flight 20. This working paper analyzes flight 20 only. 3-2-1-1 pitch excitations were sent to
individual symmetric surface pairs coincident with normal pilot inputs.
For reference, a preliminary model of the stiff wing Fenrir (developed by D. K. Schmidt) at a flight
condition of 65 ft/s (19.8 m/s) indicates a short period mode at 9.02 rad/s with a damping ratio of 0.658 and
a phugoid mode at 0.569 rad/s with a damping ratio of -0.0251. It is expected that the actual aircraft
dynamics will differ but these dynamic parameters provide a good baseline for ballpark values for
comparison to the flight test data.
Analysis of these data were performed in both the frequency and time domains. Short period system
parameters were identified using two approaches: 1) frequency domain equation error, and 2) subspace
system identification in the time domain.NASA NRA, "Lightweight Adaptive Aeroelastic Wing for Enhanced Performance Across the Flight Envelope," NRA NNX14AL36A, Mr. John Bosworth Technical Monitor.Danowsky, Brian. (2015). System identification studies with the stiff wing mini MUTT Fenrir – Flight 20. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/174386
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