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- Type:
- Article
- 摘抄:
- For feedback control using low-dimensional proper orthogonal decomposition (POD) models, the mode amplitudes of the POD mode coefficients need to be estimated based on sensor readings. This paper is aimed at suppressing the von Kairman vortex street in the wake of a circular cylinder using a low-dimensional approach based on POD. We compare sensor placement methods based on the spatial distribution of the POD modes to arbitrary ad hoc methods. Flow field data were obtained from Navier-Stokes simulation as well as particle image velocimetry (PIV) measurements. A low-dimensional POD was applied to the snapshot ensembles from the experiment and simulation. Linear stochastic estimation was used to map the sensor readings of the velocity field on the POD mode coefficients. We studied 53 sensor placement configurations, 32 of which were based on POD eigenfunctions and the others using ad hoc methods. The effectiveness of the sensor configurations was investigated at Re = 100 for the computational fluid dynamic data, and for a Reynolds number range of 82-99 for the water tunnel PIV data. Results show that a five-sensor configuration can keep the root mean square estimation error, for the amplitudes of the first two modes to within 4% for simulation data and within 10% for the PIV data. This level of error is acceptable for a moderately robust controller The POD-based design was found to be simpler. more effective, and robust compared to the ad hoc methods examined.
- 作者:
- Sick, Aaron; Wetlesen, Dave; Cohen, Kelly; Siegel, Stefan, and Cameron, Jeff
- 提交者:
- Kelly Cohen
- 上传日期:
- 02/10/2017
- 更改日期:
- 04/05/2017
- 创建:
- 2004-12
- 证书:
- All rights reserved
-
- Type:
- Image
- 摘抄:
- Oxycomanthus bennetti
- 作者:
- Meyer, David L.
- 提交者:
- David L. Meyer
- 上传日期:
- 02/09/2017
- 更改日期:
- 02/09/2017
- 创建:
- 2017-02-09
- 证书:
- Attribution-NonCommercial 4.0 International
-
- Type:
- Image
- 摘抄:
- Oxycomanthus bennetti
- 作者:
- Meyer, David L.
- 提交者:
- David L. Meyer
- 上传日期:
- 02/09/2017
- 更改日期:
- 02/09/2017
- 创建:
- 2017-02-09
- 证书:
- Attribution-NonCommercial 4.0 International
-
- Type:
- Generic Work
- 摘抄:
- Underwater images of comatulid crinoids from the Palau Islands, Micronesia
- 作者:
- Meyer, David L.
- 提交者:
- David L. Meyer
- 上传日期:
- 10/27/2017
- 更改日期:
- 11/02/2017
- 证书:
- All rights reserved
-
- Type:
- Article
- 摘抄:
- Not available
- 作者:
- Cohen, Kelly; Siegel, Stefan; McLaughlin, Thomas, and Gillies, Eric
- 提交者:
- Kelly Cohen
- 上传日期:
- 02/08/2017
- 更改日期:
- 04/05/2017
- 创建:
- 2003-03
- 证书:
- All rights reserved
-
- Type:
- Article
- 摘抄:
- Closed-loop control strategies were studied experimentally at low Reynolds and incompressible Mach numbers using periodic excitation to vector a turbulent jet. Vectoring was achieved by attaching a short, wide-angle diffuser at the jet exit and introducing periodic excitation from a slot covering one quadrant of the circumference of the round turbulent jet. Closed-loop control methods were applied to transition quickly and smoothly between different jet de ection angles. The frequency response of the zero-mass- ux piezoelectric actuatorwas at to about 0.5 kHz, but the jet responds up to 30–50 Hz only. This is still an order of magnitude faster than conventional thrust vectoring mechanism. System identi cation procedures were applied to approximate the system’s transfer function. A linear controller was designed that enabled fast and smooth transitions between stationary de ection angles and maintained desired jet vectoring angles under varying system conditions. The linear controller was tested over the entire range of available de ection angles, and its performance is evaluated and discussed.
- 作者:
- Cohen, Kelly; Rapoport, D.; Seifer, A., and Fono, I.
- 提交者:
- Kelly Cohen
- 上传日期:
- 02/08/2017
- 更改日期:
- 04/05/2017
- 创建:
- 2003-08
- 证书:
- All rights reserved
-
- Type:
- Article
- 摘抄:
- In this study a general approach is introduced for the design of a robust control law for suppression of structure borne vibration. This control law is based on a passive design in the form of dynamic vibration absorbers. Passive absorbers minimize vibration at a speci c frequency, but their performance is improved by introducing adaptive tuning of the absorber. An adaptive dynamic vibration absorber is tuned to the forcing frequency, using classical methods. The tuning ratio is time varying and adapts itself to variations in the forcing frequency. However, the uniqueness of the approach in this study is that the damping parameter of the absorber is continuously varied by means of a fuzzy-logic control algorithm to provide a lower sound pressure level. The inputs of the fuzzy control law are the displacement and velocity of the main structure. The effectiveness of the control algorithm for active vibration control is demonstrated using MATLAB® simulations of a single-degree-of-freedom plant. This methodology provides superior performance in the presence of signi cant mistuning compared to a more conventional approach.
- 作者:
- Weller, Tanchum; Cohen, Kelly, and Ben-Asher, Joseph Z.
- 提交者:
- Kelly Cohen
- 上传日期:
- 02/08/2017
- 更改日期:
- 04/05/2017
- 创建:
- 2003-04
- 证书:
- All rights reserved
-
- Type:
- Article
- 摘抄:
- Not available
- 作者:
- Weller, Tanchum; Moulin, Boris; Cohen, Kelly; Ben-Asher, Joseph Z., and Adin, Zvi
- 提交者:
- Kelly Cohen
- 上传日期:
- 02/08/2017
- 更改日期:
- 04/05/2017
- 创建:
- 2002-08
- 证书:
- All rights reserved
-
- Type:
- Article
- 摘抄:
- The present investigation deals with the application of an Adaptive Fuzzy Control Algorithm for active vibration control of an experimental flexible beam. The two-dimensional model of the experimental cantilever beam, given by an orthogonal tetrahedral space truss, represents a slender cantilever aluminum (7075-T6) beam of rectangular cross-section (1145 × 60 × 1.95 mm3). A variety of transient disturbances are introduced to excite the first four modes of the beam. The resulting transverse displacements are observed by a single sheet (50 × 50 mm2) of piezoceramic material placed at the clamped end of the beam. Active control of the beam is provided by one, two or three identical sheets of piezoceramic material collocated with the sensor. The control moments applied by the piezoceramic actuator are made to emulate the behavior of a discrete dynamic vibration absorber. The virtual absorber is tuned to the fundamental frequency using classical methods and the tuning ratios are time-invariant. However, the uniqueness of this approach is that the damping parameters of the emulated absorber are continuously varied by means of a fuzzy logic control algorithm to provide near minimum-time suppression of vibration. It is demonstrated that application of this methodology allows for its real-time implementation and provides relatively quick settling times in the closed-loop.
- 作者:
- Weller, Tanchum; Cohen, Kelly; Ben-Asher, Joseph Z., and Yaffe, Ronith
- 提交者:
- Kelly Cohen
- 上传日期:
- 02/08/2017
- 更改日期:
- 04/05/2017
- 创建:
- 2002-08
- 证书:
- All rights reserved
-
- Type:
- Article
- 摘抄:
- This study deals with the development and application of an active control law for the vibration suppression of beam-like flexible structures experiencing transient disturbances. Collocated pairs of sensors/actuators provide active control of the structure. A design methodology for the closed-loop control algorithm based on fuzzy logic is proposed. First, the behavior of the open-loop system is observed. Then, the number and locations of collocated actuator/sensor pairs are selected. The proposed control law, which is based on the principles of passivity, commands the actuator to emulate the behavior of a dynamic vibration absorber. The absorber is tuned to a targeted frequency, whereas the damping coefficient of the dashpot is varied in a closed loop using a fuzzy logic based algorithm. This approach not only ensures inherent stability associated with passive absorbers, but also circumvents the phenomenon of modal spillover. The developed controller is applied to the AFWAL/FIB 10 bar truss. Simulated results using MATLAB© show that the closed-loop system exhibits fairly quick settling times and desirable performance, as well as robustness characteristics. To demonstrate the robustness of the control system to changes in the temporal dynamics of the flexible structure, the transient response to a considerably perturbed plant is simulated. The modal frequencies of the 10 bar truss were raised as well as lowered substantially, thereby significantly perturbing the natural frequencies of vibration. For these cases, too, the developed control law provides adequate settling times and rates of vibrational energy dissipation.
- 作者:
- Weller, Tanchum; Cohen, Kelly, and Ben-Asher, Joseph Z.
- 提交者:
- Kelly Cohen
- 上传日期:
- 02/08/2017
- 更改日期:
- 04/05/2017
- 创建:
- 2002-06
- 证书:
- All rights reserved