scholarly journals Identification of Unknown, Time-Varying Forces/Moments in Dynamics and Vibration Problems Using a New Approach To Deconvolution

1998 ◽  
Vol 5 (3) ◽  
pp. 181-197 ◽  
Author(s):  
C.D. Johnson
Keyword(s):  
Practical Method ◽  
General Purpose ◽  
Basis Functions ◽  
Time Varying ◽  
Force Moment ◽  
Time Variations ◽  
Vibration Problems ◽  
Real Time Identification ◽  
Weighting Coefficients ◽  
Dynamics And Vibration

In this paper an alternative approach to the classical deconvolution idea is used to obtain a new and practical method for real-time identification of unknown, time-varying forces/moments in a general class of linear (linearized) dynamics and vibration problems with multiple-inputs and multiple-measurements. This new method for force/moment identification is unique in the respect that the uncertainty in the force/moment time-variations is not characterized by random-process methods, but rather by a generalized spline-model with totally unknown weighting coefficients and completely known basis-functions. The basis-functions are custom chosen in each application to reflect, qualitatively, the known characteristics of the force/moment time-variations to be identified. The method does not involve explicit identification of the unknown weighting coefficients. General-purpose identification algorithms for both continuous-time and discrete-time measurements are developed, and a worked example including computer simulation results is presented.

Real-Time Tuning of Delayed Resonator-Based Absorbers for Spectral and Spatial Variations

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Ryan Jenkins ◽  
Nejat Olgac
Keyword(s):  
Real Time ◽  
Active Control ◽  
Design Guidelines ◽  
Spatial Variations ◽  
Time Varying ◽  
Vibration Absorption ◽  
Spatial Tuning ◽  
System Components ◽  
Hybrid Concept ◽  
Time Variations

This paper offers two interlinked contributions in the field of vibration absorption. The first involves an active tuning of an absorber for spectral and spatial variations. The second contribution is a set of generalized design guidelines for such absorber operations. “Spectral” tuning handles time-varying excitation frequencies, while “spatial” tuning treats the real-time variations in the desired location of suppression. Both objectives, however, must be achieved using active control and without physically altering the system components to ensure practicality. Spatial tuning is inspired by the concept of “noncollocated vibration absorption,” for which the absorber location is different from the point of suppression. This concept is relatively under-developed in the literature, mainly because it requires the use of part of the primary structure (PS) as the extended absorber—a delicate operation. Within this investigation, we employ the delayed resonator (DR)-based absorber, a hybrid concept with passive and active elements, to satisfy both tuning objectives. The presence of active control in the absorber necessitates an intriguing stability investigation of a time-delayed dynamics. For this subtask, we follow the well-established methods of frequency sweeping and D-subdivision. Example cases are also presented to corroborate our findings.

Identification of Time-Varying Time Constants of Thermocouple Sensors and Its Application to Temperature Measurement

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Kenneth Kar ◽  
Akshya K. Swain ◽  
Robert Raine
Keyword(s):  
Kalman Filter ◽  
Least Squares ◽  
Time Constant ◽  
Identification Problem ◽  
Basis Functions ◽  
New Technique ◽  
Ratio Test ◽  
Time Varying ◽  
Time Constants ◽  
Orthogonal Least Squares

The present study addresses the problem of estimating time-varying time constants associated with thermocouple sensors by a set of basis functions. By expanding each time-varying time constant onto a finite set of basis sequences, the time-varying identification problem reduces to a parameter estimation problem of a time-invariant system. The proposed algorithm, to be called as orthogonal least-squares with basis function expansion algorithm, combines the orthogonal least-squares algorithm with an error reduction ratio test to include significant basis functions into the model, which results in a parsimonious model structure. The performance of the method was compared with a linear Kalman filter. Simulations on engine data have demonstrated that the proposed method performs satisfactorily and is better than the Kalman filter. The new technique has been applied in a Stirling cycle compressor. The sinusoidal variations in time constant are tracked properly using the new technique, but the linear Kalman filter fails to do so. Both model validation and thermodynamic laws confirm that the new technique gives unbiased estimates and that the assumed thermocouple model is adequate.

Decentralized MRAC for Large-Scale Interconnected Systems With State and Input Delays by Integrators Inclusion

2017 ◽  
Vol 139 (9) ◽  
Author(s):  
Seyed Hamid Hashemipour ◽  
Nastaran Vasegh ◽  
Ali Khaki Sedigh
Keyword(s):  
Large Scale ◽  
Practical Method ◽  
Open Loop ◽  
Loop System ◽  
Input Delay ◽  
Time Varying ◽  
Delay Compensation ◽  
State And Input Delays ◽  
Input Delays ◽  
Model Reference Adaptive

This paper investigates the problem of decentralized model reference adaptive control (MRAC) for a class of large-scale systems with time-varying delays in the interconnected terms and state and input delays. The upper bounds of interconnection terms with time-varying delays and external disturbances are assumed to be completely unknown. By integrators inclusion, a dynamic input delay compensator is established for input delay compensation and it is used as a practical method for state calculation x(t + R). Also, a method is presented for a class of decentralized feedback controllers, which can evolve the closed-loop system error uniformly bounded stable. As a numerical example, the proposed technique is applied to an unstable open-loop system to show the feasibility and effectiveness of the method.

A Practical Method for the Rational Design of Ship Structures

1980 ◽  
Vol 24 (02) ◽  
pp. 101-113 ◽  
Author(s):  
Owen F. Hughes ◽  
Farrokh Mistree ◽  
Vedran Žanic
Keyword(s):  
Optimum Design ◽  
Rational Design ◽  
Cost Effective ◽  
Practical Method ◽  
General Purpose ◽  
Processing Unit ◽  
Ship Structures ◽  
Finite Element Program ◽  
Central Processing ◽  
Element Program

A practical, rationally based method is presented for the automated optimum design of ship structures. The method required the development of (a) a rapid, design-oriented finite-element program for the analysis of ship structures; (b) a comprehensive mathematical model for the evaluation of the capability of the structure; and (c) a cost-effective optimization algorithm for the solution of a large, highly constrained, nonlinear redesign problem. These developments have been incorporated into a program called SHIPOPT. The efficiency and robustness of the method is illustrated by using it to determine the optimum design of a complete cargo hold of a general-purpose cargo ship. The overall dimensions and the design loads are the same as those used in the design of the very successful SD14 series of ships. The redesign problem contains 94 variables, a nonlinear objective function, and over 500 constraints of which approximately half are non-linear. Program SHIPOPT required approximately eight minutes of central processing unit time on a CDC CYBER 171 to determine the optimum design.

Analysis of three-layer composite plates with a new higher-order layerwise formulation

2014 ◽  
Vol 21 (3) ◽  
pp. 401-404
Author(s):  
Dalal A. Maturi ◽  
Antonio J.M. Ferreira ◽  
Ashraf M. Zenkour ◽  
Daoud S. Mashat
Keyword(s):  
Composite Plates ◽  
Order Theory ◽  
Higher Order ◽  
Basis Functions ◽  
Numerical Accuracy ◽  
First Order ◽  
The Core ◽  
First Order Theory ◽  
Layer Composite ◽  
Vibration Problems

AbstractIn this paper, we combine a new higher-order layerwise formulation and collocation with radial basis functions for predicting the static deformations and free vibration behavior of three-layer composite plates. The skins are modeled via a first-order theory, while the core is modeled by a cubic expansion with the thickness coordinate. Through numerical experiments, the numerical accuracy of this strong-form technique for static and vibration problems is discussed.

scholarly journals Modal control using real-time identification for time-varying structures

2010 ◽  
Vol 11 (6) ◽  
pp. 513-520
Author(s):  
Fengyan Deng ◽  
Didier Rémond ◽  
Luc Gaudiller
Keyword(s):  
Real Time ◽  
Modal Control ◽  
Time Varying ◽  
Real Time Identification
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