Hover-to-Cruise Transition Control for High-Speed Level Flight of Ducted Fan UAV

2020 ◽  
Author(s):  
Zihuan Cheng ◽  
Hailong Pei
Keyword(s):  
High Speed ◽  
Transition Control ◽  
Level Flight ◽  
Ducted Fan ◽  
Speed Level

Mechanically Amplified Piezoelectric Microactuators for Laminar-Turbulent Transition Control on Airfoils

2009 ◽  
Vol 6 (4) ◽  
pp. 211-218 ◽  
Author(s):  
C. Bolzmacher ◽  
X. Riedl ◽  
J. Leuckert ◽  
M. Engert ◽  
K. Bauer ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
High Speed ◽  
Leading Edge ◽  
Transition Process ◽  
Open Loop ◽  
Film Sensor ◽  
Transition Control ◽  
Transitional Boundary Layer ◽  
Tollmien Schlichting

Drag reduction on airfoils using arrays of micro-actuators is one application of so-called Aero-MEMS. These microactuators interact with TS instabilities (Tollmien-Schlichting waves) inside a transitional boundary layer by superimposing artificially generated counterwaves in order to delay the transition process. These actuators need to exhibit a relatively large stroke at relatively high operational frequencies when operated at high Mach numbers. For this purpose, a novel micromachined mechanical amplification unit for increasing the stroke of piezoelectric microactuators up to high frequencies is proposed. The mechanical lever is provided by a sliced nickel titanium membrane. In this work, the actuator is explained in detail and wind tunnel experiments are carried out to investigate the effect of this mechanically amplified piezoelectric microactuator on thin transitional boundary layers. The experiments have been carried out in the transonic wind tunnel facility of the Berlin University of Technology on an unswept test wing with an NACA 0004 leading edge. The effectiveness of the actuator for flow control applications is determined in an open-loop setup consisting of one actuator having a relevant spanwise extension and a microstructured hot film sensor array located downstream. The aerodynamic results at Mach 0.33 are presented and discussed. It is shown that the actuator influences TS wave specific frequencies between 2.5 kHz and 7.4 kHz. The actuator amplitude is large enough to influence a transitional boundary layer significantly without bypassing the natural transition process which makes this type of micromachined actuator a candidate for high speed TS-control.

Optical Flow and Texture Variables Useful for Detecting Changes in Simulated Self Motion

1983 ◽  
Vol 27 (12) ◽  
pp. 996-1000
Author(s):  
Dean H. Owen ◽  
Lawrence J. Hettinger ◽  
Shirley B. Tobias ◽  
Lawrence Wolpert ◽  
Rik Warren
Keyword(s):  
Optical Flow ◽  
Flow Pattern ◽  
High Speed ◽  
Flight Simulator ◽  
Practical Relevance ◽  
Motion Information ◽  
Flow Acceleration ◽  
Level Flight ◽  
Texture Density ◽  
Self Motion

Several methods are presented for breaking linkages among global optical flow and texture variables in order to assess their usefulness in experiments requiring observers to distinguish change in speed or heading of simulated self motion from events representing constant speed or level flight. Results of a series of studies testing for sensitivity to flow acceleration or deceleration, flow-pattern expansion variables, and the distribution of optical texture density are presented. Theoretical implications for determining the metrics of visual self-motion information, and practical relevance for pilot and flight simulator evaluation and for low-level, high-speed flight are discussed.

Probability of Ship High-Runs from Phase-Space Data

2019 ◽  
Author(s):  
Ioannis Kontolefas ◽  
Kostas J. Spyrou
Keyword(s):  
Phase Space ◽  
Coherent Structures ◽  
High Speed ◽  
Statistical Information ◽  
Motion Patterns ◽  
Following Seas ◽  
Probability Calculation ◽  
Speed Level ◽  
Surf Riding ◽  
Space Data

A clustering scheme has been applied for capturing qualitatively different surge motion patterns in the phase space. The scheme enables the identification of “high-run” incidents as soon as such motions are triggered and while their phenomenology has not yet been well developed. A “high run” is a surf-riding–like behavior, appearing in irregular following seas. The concept of finite-time coherent sets is exploited for deriving estimates of the probability of high-runs. The method is verified by identifying independently the corresponding hyperbolic Lagrangian coherent structures; then, consistency is sought between the two approaches. An important feature of the method is that it does not rely on the use of some empirical criterion for the high-run threshold, such as one based on the exceedance of an arbitrary high-speed level. Despite its computational burden, the proposed scheme offers “objective” statistical information on a ship’s high-run tendency that can be used for benchmarking simpler (approximative) probability calculation schemes.

Probability of Ship High-Runs from Phase-Space Data

2019 ◽  
Author(s):  
Ioannis Kontolefas ◽  
Kostas J. Spyrou
Keyword(s):  
Phase Space ◽  
Coherent Structures ◽  
High Speed ◽  
Statistical Information ◽  
Motion Patterns ◽  
Following Seas ◽  
Probability Calculation ◽  
Speed Level ◽  
Surf Riding ◽  
Space Data

A clustering scheme has been applied for capturing qualitatively different surge motion patterns in the phase space. The scheme enables the identification of “high-run” incidents as soon as such motions are triggered and while their phenomenology has not yet been well developed. A “high run” is a surf-riding–like behavior, appearing in irregular following seas. The concept of finite-time coherent sets is exploited for deriving estimates of the probability of high-runs. The method is verified by identifying independently the corresponding hyperbolic Lagrangian coherent structures; then, consistency is sought between the two approaches. An important feature of the method is that it does not rely on the use of some empirical criterion for the high-run threshold, such as one based on the exceedance of an arbitrary high-speed level. Despite its computational burden, the proposed scheme offers “objective” statistical information on a ship’s high-run tendency that can be used for benchmarking simpler (approximative) probability calculation schemes.

Probability of Ship High-Runs from Phase-Space Data

2020 ◽  
Vol 64 (01) ◽  
pp. 81-97
Author(s):  
Ioannis Kontolefas ◽  
Kostas J. Spyrou
Keyword(s):  
Phase Space ◽  
High Speed ◽  
Abnormal Behavior ◽  
Motion Patterns ◽  
Following Seas ◽  
Wave Celerity ◽  
Speed Level ◽  
Surf Riding ◽  
Space Data ◽  
Nonlinear Ship Motion

A clustering scheme has been applied for capturing qualitatively different surge motion patterns in the phase space. The scheme enables the identification of "high-run" incidents as soon as such motions are triggered and while their phenomenology has not yet been well developed. A "high run" is a surf-riding-like behavior, appearing in irregular following seas. The concept of finite-time coherent sets is exploited for deriving estimates of the probability of high-runs. The method is verified by identifying independently the corresponding hyperbolic Lagrangian coherent structures; then, consistency is sought between the two approaches. An important feature of the method is that it does not rely on the use of some empirical criterion for the high-run threshold, such as one based on the exceedance of an arbitrary high-speed level. Despite its computational burden, the proposed scheme offers "objective" statistical information on a ship's high-run tendency that can be used for benchmarking simpler (approximative) probability calculation schemes. 1. Introduction Current efforts to assess a ship's tendency for abnormal behavior in extreme seas are still limited from our inadequate grasp of the full variety of nonlinear ship motion phenomena that could be realized in an irregular seaway. A classification of these motion patterns would provide a sound basis for developing probabilistic calculation methods of ship operability and safety in extreme seas. A few recent research efforts in our group have been related to this target. In one case, it was endeavored to distinguish ship high-runs from ordinary surging, by engaging the concept of instantaneous wave celerity (Spyrou et al. 2014). In another, the derivation of a practical metric for the probability of high-run was pursued (Belenky et al. 2016). Also, high-run and broaching-to statistics were produced through a direct approach based on assigning prescriptive exceedance thresholds (Spyrou et al. 2016b). Moreover, the theory of surf-riding was extended for bichromatic waves, revealing some rather unexpected types of motion (Spyrou et al. 2018). Even richer phenomena could be conjectured for a multifrequency environment.

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