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- Type:
- Article
- Description/Abstract:
- 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.
- Creator/Author:
- Weller, Tanchum; Cohen, Kelly, and Ben-Asher, Joseph Z.
- Submitter:
- Kelly Cohen
- Date Uploaded:
- 02/08/2017
- Date Modified:
- 04/05/2017
- Date Created:
- 2003-04
- License:
- All rights reserved
-
- Type:
- Article
- Description/Abstract:
- Not available
- Creator/Author:
- Weller, Tanchum; Moulin, Boris; Cohen, Kelly; Ben-Asher, Joseph Z., and Adin, Zvi
- Submitter:
- Kelly Cohen
- Date Uploaded:
- 02/08/2017
- Date Modified:
- 04/05/2017
- Date Created:
- 2002-08
- License:
- All rights reserved
-
- Type:
- Article
- Description/Abstract:
- 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.
- Creator/Author:
- Weller, Tanchum; Cohen, Kelly; Ben-Asher, Joseph Z., and Yaffe, Ronith
- Submitter:
- Kelly Cohen
- Date Uploaded:
- 02/08/2017
- Date Modified:
- 04/05/2017
- Date Created:
- 2002-08
- License:
- All rights reserved
-
- Type:
- Article
- Description/Abstract:
- 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.
- Creator/Author:
- Weller, Tanchum; Cohen, Kelly, and Ben-Asher, Joseph Z.
- Submitter:
- Kelly Cohen
- Date Uploaded:
- 02/08/2017
- Date Modified:
- 04/05/2017
- Date Created:
- 2002-06
- License:
- All rights reserved
-
- Type:
- Article
- Description/Abstract:
- The control of exible structures employing the passivity approach has been extended to systems having noncollocated input/output pairs by introducing an observer that incorporates the nominal dynamical model of the plant. The passive observer-based control is applied to the American Control Conference benchmark problem, whereby, the control force emulates a dynamic vibration absorber attached to a virtual wall with passive control elements (spring, mass, and dashpot). The springs and mass elements of the controller are constant, whereas the damping coef cients are selected as time dependent in an attempt to choose continuously the most appropriate amount of damping in compliance with the design goals. A novel approach is introduced, whereby the passive observer-based control law is modi ed by varying the damping coef cient of the virtual dashpot by means of an adaptive fuzzy logic algorithm. This modi ed system exhibits quick settling times and desirable performance characteristics. Results from the statistical robustness analysis for the developed controller are compared to 10 other (linear) solutionsof the benchmarkproblem. The comparisonis based onrobust stability, robust performance (settling time), and control effort. The results obtained by the adaptive fuzzy logic algorithm are superior to those obtained by all other methods, and, consequently, further application of the fuzzy algorithm is advocated.
- Creator/Author:
- Weller, Tanchum; Cohen, Kelly, and Ben-Asher, Joseph Z.
- Submitter:
- Kelly Cohen
- Date Uploaded:
- 02/08/2017
- Date Modified:
- 04/05/2017
- Date Created:
- 2001-06
- License:
- All rights reserved
-
- Type:
- Article
- Description/Abstract:
- The present study deals with an AFCA (Adaptive Fuzzy Control Algorithm) for an Euler-Bernoulli approximation of a two-dimensional version of a cantilever beam-like orthogonal tetrahedral space truss. Transient disturbances, modeled as a unit impulse, excite all the modes of the beam. The resulting transverse displacement at the free end of the beam and its corresponding rate are observed by sensors placed there, and active control of the beam is provided by a collocated force actuator. A design methodology for the closed-loop control algorithm that is independent of an exact mathematical model (space-state model, F.E.M., etc.) of plant dynamics and which is based on fuzzy logic is presented. First, the behavior of the open-loop system is observed. Then, the control force applied to the system emulates the behavior of a dynamic vibration absorber which is tuned to the measured fundamental frequency. This approach not only assures inherent stability associated with passive absorbers, but also circumvents the phenomenon of modal spillover. The damping and the mass ratios of the absorber adapt themselves by using a fuzzy decision-making process. This results in relatively quick settling times, low overshoots and dying out of vibration within a few seconds. When the control force is turned off after a mere 16 seconds, almost all the vibrational energy is dissipated. In addition, the performance of the AFCA is insensitive to varying initial conditions. To demonstrate the robustness of the control system to changes in the temporal dynamics of the cantilever beam, the transient response to a considerably perturbed plant is simulated. The Young's modulus of the beam was raised as well as lowered substantially, thereby significantly perturbing the natural frequencies of vibration. The mode shapes, however, remain unchanged. For these cases, too, the AFCA provides similar settling times and rates of vibrational energy dissipation.
- Creator/Author:
- Abramovich, Haim; Weller, T.; Cohen, Kelly, and Levitas, Joseph
- Submitter:
- Kelly Cohen
- Date Uploaded:
- 02/08/2017
- Date Modified:
- 04/05/2017
- Date Created:
- 1997-03
- License:
- All rights reserved
-
- Type:
- Article
- Description/Abstract:
- The present study deals with an AFCA (Adaptive Fuzzy Control Algorithm) for an Euler-Bemoulli approximation of a two-dimensional version of a cantilever beam-like orthogonal tetrahedral space truss. Transient disturbances, modeled as a unit impulse, excite all the modes of the beam. The resulting transverse displacement at the free end of the beam and its corresponding rate are observed by sensors placed there, and active control of the beam is provided by a collocated force actuator. A design methodology, based on fuzzy logic which assumes no a priori knowledge of plant dynamics, for the closed-loop control algorithm results in relatively quick settling times, low overshoots and dying out of vibration within a few seconds. The control algorithm is enhanced and made much faster by eliminating the need of repeatedly solving the set of differential equations of motion of an emulated dynamic vibration absorber. When the control force is turned off after a mere 15 seconds, almost all the vibrational energy is dissipated as the beam returns to its undisturbed state throughout its length. In addition, the performance of the AFCA is insensitive to varying initial conditions. To examine the robustness of the control system to changes in the temporal dynamics of the cantilever beam, the transient disturbance response to a considerably perturbed plant is simulated. The Young's modulus of the beam was raised as well as lowered by 60%, substantially perturbing the natural frequencies of vibration compared to the nominal plant. The AFCA provided similar settling times and rates of vibrational energy dissipation, satisfying the aim of plant model independence.
- Creator/Author:
- Abramovich, Haim; Weller, Tanchum; Cohen, Kelly, and Levitas, Joseph
- Submitter:
- Kelly Cohen
- Date Uploaded:
- 02/08/2017
- Date Modified:
- 04/05/2017
- Date Created:
- 1996-03
- License:
- All rights reserved
-
- Type:
- Article
- Description/Abstract:
- For a Timoshenko beam model the equations of motion, representing the anisotropic continuum model of a two-dimensional, latticed, large space structure, are extended to include coupling between the extensional, shear and bending modes. This analytical model, applied to a 20-bay, orthogonal, tetrahedral, cantilevered truss structure, is used to determine the transient response when subjected to a unit impulse. It is demonstrated that for beam-like structures having a fixed bending stiffness and beam mass an increase in diagonal stiffness, on account of the stiffness of the vertical girder, leads to a rise in the transverse shear rigidity. This results in higher natural frequencies and a reduction in peak displacement. In addition, in an asymmetrical truss configuration, coupling between the extensional and shear modes raises the maximum peak displacement compared to that obtained for a symmetric truss. The model is modified to investigate the introduction of passive damping in the form of several dynamic vibration absorbers. For a fixed absorber mass budget, a simple yet efficient absorber parameter optimization procedure, based on the classical steady state criteria of a 2-DOF system, is developed to design several absorbers each tuned to a different modal frequency. It is found that inclusion of transverse shear rigidity, as a design parameter in damping augmentation studies, reduces settling time for predetermined maximum peak displacements.
- Creator/Author:
- Weller, T. and Cohen, Kelly
- Submitter:
- Kelly Cohen
- Date Uploaded:
- 02/08/2017
- Date Modified:
- 04/05/2017
- Date Created:
- 1994-08
- License:
- All rights reserved
-
- Type:
- Article
- Description/Abstract:
- Breakthroughs in genetic fuzzy systems, most notably the development of the Genetic Fuzzy Tree methodology, have allowed fuzzy logic based Artificial Intelligences to be developed that can be applied to incredibly complex problems. The ability to have extreme performance and computational efficiency as well as to be robust to uncertainties and randomness, adaptable to changing scenarios, verified and validated to follow safety specifications and operating doctrines via formal methods, and easily designed and implemented are just some of the strengths that this type of control brings. Within this white paper, the authors introduce ALPHA, an Artificial Intelligence that controls flights of Unmanned Combat Aerial Vehicles in aerial combat missions within an extreme-fidelity simulation environment. To this day, this represents the most complex application of a fuzzy-logic based Artificial Intelligence to an Unmanned Combat Aerial Vehicle control problem. While development is on-going, the version of ALPHA presented withinwas assessed by Colonel (retired)Gene Lee who described ALPHA as “the most aggressive, responsive, dynamic and credible AI (he’s) seen-to-date.” The quality of these preliminary results in a problem that is not only complex and rife with uncertainties but also contains an intelligent and unrestricted hostile force has significant implications for this type of Artificial Intelligence. This work adds immensely to the body of evidence that this methodology is an ideal solution to a very wide array of problems.
- Creator/Author:
- Schumacher, Corey; Cohen, Kelly; Ernest, Nicholas; Carroll, David; Lee, Gene, and Clark, Matthew
- Submitter:
- Kelly Cohen
- Date Uploaded:
- 02/08/2017
- Date Modified:
- 04/05/2017
- Date Created:
- 2016-03
- License:
- All rights reserved
-
- Type:
- Article
- Description/Abstract:
- This work presents a methodology for real-time estimation of wildland fire growth, utilizing afire growth model based on a set of partial differential equations for prediction, and harnessing concepts of space-time Kalman filtering and Proper Orthogonal Decomposition techniques towards low dimensional estimation of potentially large spatio-temporal states. The estimation framework is discussed in its criticality towards potential applications such as forest fire surveillance with unmanned systems equipped with onboard sensor suites. The effectiveness of the estimation process is evaluated numerically over fire growth data simulated using a well-established fire growth model described by coupled partial differential equations. The methodology is shown to be fairly accurate in estimating spatio-temporal process states through noise-ridden measurements for real-time deploy ability.
- Creator/Author:
- Sharma, Balaji R.; Cohen, Kelly, and Kumar, Manish
- Submitter:
- Kelly Cohen
- Date Uploaded:
- 02/08/2017
- Date Modified:
- 04/05/2017
- Date Created:
- 2013-10
- License:
- All rights reserved