Dynamic stall at high frequency and large amplitudeusing quasi-steady aerodynamic analytic prediction method

1979 ◽  
Author(s):  
L. ERICSSON
Keyword(s):  
High Frequency ◽  
Large Amplitude ◽  
Prediction Method ◽  
Dynamic Stall ◽  
Analytic Prediction

Dynamic Stall at High Frequency and Large Amplitude

1980 ◽  
Vol 17 (3) ◽  
pp. 136-142 ◽  
Author(s):  
Lars E. Ericsson ◽  
J. Peter Reding
Keyword(s):  
High Frequency ◽  
Large Amplitude ◽  
Dynamic Stall

High-frequency vibration energy harvesting from repeated impulsive forcing utilizing intentional dynamic instability caused by strong nonlinearity

2016 ◽  
Vol 28 (4) ◽  
pp. 468-487 ◽  
Author(s):  
Kevin Remick ◽  
D Dane Quinn ◽  
D Michael McFarland ◽  
Lawrence Bergman ◽  
Alexander Vakakis
Keyword(s):  
Energy Harvesting ◽  
Mechanical System ◽  
High Frequency ◽  
Large Amplitude ◽  
Electromechanical Coupling ◽  
Dynamic Instability ◽  
Vibration Energy ◽  
Primary System ◽  
Vibration Energy Harvesting ◽  
Strongly Nonlinear

The work in this study explores the excitation of high-frequency dynamic instabilities to enhance the performance of a strongly nonlinear vibration-based energy harvesting system subject to repeated impulsive excitations. These high-fraequency instabilities arise from transient resonance captures (TRCs) in the damped dynamics of the system, leading to large-amplitude oscillations in the mechanical system. Under proper forcing conditions, these high-frequency instabilities can be sustained. The primary system is composed of a grounded, weakly damped linear oscillator, which is directly subjected to impulsive forcing. A light-weight, damped nonlinear oscillator (nonlinear energy sink, NES) is coupled to the primary system using electromechanical coupling elements and strongly nonlinear stiffness elements. The essential (nonlinearizable) stiffness nonlinearity arises from geometric and kinematic effects resulting from the traverse deflection of a piano wire coupling the two oscillators. The electromechanical coupling is composed of a neodymium magnet and inductance coil, which harvests the energy in the mechanical system and transfers it to the electrical system which, in this present case, is composed of a simple resistive element. The energy dissipated in the circuit is inferred as a measure of energy harvesting capability. The large-amplitude TRCs result in strong, nearly irreversible energy transfer from the primary system to the NES, where the harvesting elements work to convert the mechanical energy to electrical energy. The primary goal of this work is to numerically and experimentally demonstrate the efficacy of inducing sustained high-frequency dynamic instability in a system of mechanical oscillators to achieve enhanced vibration energy harvesting performance. This work is a continuation of a companion paper (Remick K, Quinn D, McFarland D, et al. (2015) Journal of Sound and Vibration Final Publication) where vibration energy harvesting of the same system subject to single impulsive excitation is studied.

Airfoil dynamic stall performance with large-amplitude motions

AIAA Journal ◽  
1985 ◽  
Vol 23 (11) ◽  
pp. 1653-1659 ◽  
Author(s):  
M. S. Francis ◽  
J. E. Keesee
Keyword(s):  
Large Amplitude ◽  
Dynamic Stall ◽  
Large Amplitude Motions

scholarly journals Exploration of High-Frequency Control of Dynamic Stall Using Large-Eddy Simulations

AIAA Journal ◽  
2018 ◽  
Vol 56 (8) ◽  
pp. 2974-2991 ◽  
Author(s):  
Miguel R. Visbal ◽  
Stuart I. Benton
Keyword(s):  
High Frequency ◽  
Frequency Control ◽  
Large Eddy Simulations ◽  
Dynamic Stall ◽  
Large Eddy

scholarly journals Large-amplitude Dithering Mitigates Glitches in Digital-to-analogue Converters

2019 ◽  
Author(s):  
Arnfinn Eielsen ◽  
John Leth ◽  
Andrew J. Fleming ◽  
Adrian Wills ◽  
Brett Ninness
Keyword(s):  
Motion Control ◽  
High Precision ◽  
High Frequency ◽  
Large Amplitude ◽  
Control Law ◽  
Control Applications ◽  
Precision Motion Control ◽  
Low Pass ◽  
Converter Topologies ◽  
Precision Motion

This paper develops and experimentally evaluates a dither-based method for improved generation of arbitrary signals in digital-to-analogue converters that exhibits glitches --- essentially converting the glitches from high-frequency to low-frequency disturbances. One major benefit of this behaviour appears in closed-loop control applications, as the glitch disturbance can be moved from outside control law bandwidth to inside control law bandwidth, enabling suppression by feedback. A behavioural model of glitches is presented and the effect of applying a dither signal is analysed in detail. Analytical and experimental results demonstrate that a dither signal with sufficiently large amplitude can mitigate the effect of glitches, when used in conjunction with a low-pass filter. Severe glitches appear in various digital-to-analogue converter topologies, including converter topologies that are used in high-precision motion control applications, such as adaptive optics and scanning force microscopy. Glitches introduce impulse-like disturbances which have a broadband frequency distribution. Low-pass filtering alone does not provide sufficient attenuation, and in applications with feedback control only frequency content within the control law bandwidth is attenuated. Hence, a high-frequency disturbance such as a glitch will not be suppressed. The use of dithering to suppress glitches is therefore beneficial in applications where errors in signal conversion are a primary concern, such as high-precision motion control or accurate reference signal generation.

Development of Prediction Method for Wind Noise Caused by Airflow Around Front Pillar

2011 ◽  
Author(s):  
Yasuhiko Okutsu ◽  
Naoki Hamamoto ◽  
Robert Powell ◽  
Long Wu
Keyword(s):  
High Frequency ◽  
Noise Level ◽  
High Speed ◽  
Prediction Method ◽  
Noise Sources ◽  
Wind Noise ◽  
Front Passenger ◽  
Passenger Seat ◽  
Simulation Results ◽  
Head Area

To control high frequency wind noise upper than 1 kHz is important to ensure the comfort for a driver and passengers when vehicles cruise at high speed. Therefore the prediction method for high frequency wind noise inside a cabin has been required for development of a vehicle. This paper describes about the prediction method for high frequency wind noise from numerical simulation results. In this study, wind noise caused by airflow around a front pillar is predicted. We have predicted wind noise by visualizing noise sources and pressure fluctuation on vehicle surfaces in recent years. Although an inferior-to-superior relationship can be predicted from these results, it was difficult to estimate quantitative interior noise level. In this research, the SEA code is examined to predict such noise level. The SEA code has confirmed showing a qualitative and almost quantitative consistency of measured and calculated SPL at the head area of a front passenger seat.

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