Tamara Nestorović

Experimental model identification and vibration control of a smart cantilever beam using piezoelectric actuators and sensors

Mechanical lightweight structures often tend to unwanted vibrations due to disturbances. Passive methods for increasing the structural damping are often inadequate for the vibration suppression, since they include additional mass in the form of damping materials, additional stiffening designs or mass damper. In this paper the concept of an active vibration control for piezoelectric light weight structures is introduced and presented through several subsequent steps: model identification, controller design, simulation, experimental verification and implementation on a particular object—piezoelectric smart cantilever beam. Special attention is paid to experimental testing and verification of the results obtained through simulations. The efficiency of the modeling procedure through the subspace-based system identification along with the efficiency of the designed optimal controller are proven based on the experimental verification, which results in vibration suppression to a very high extent not only in comparison with the uncontrolled case, but also in comparison with previously achieved results. The experimental work demonstrates a very good agreement between simulations and experimental results.

On finite and practical stability of time delayed systems: Lyapunov-Krassovski approach, delay dependent criteria

This paper gives sufficient conditions for the practical and finite time stability of linear continuous time delay systems of the form X(t)=A0X(t)+A1X(t−τ). When we consider finite time stability, these new, delay independent conditions are derived using the approach based on Lyapunov-Krassovski functionals. In this case these functionals need not to have: a) properties of positivity in whole state space and b) negative derivatives along system trajectories. When we consider practical stability, before mentioned concept of stability, it is combined and supported by classical Lyapunov technique to guarantee attractivity properties of system behavior.

A new approach to the stability of time-delay systems in the sense of Non-Lyapunov delay-independent and delay-dependent criteria

In this article the sufficient conditions for the practical and finite-time stability of the linear continuous systems with the time-delay are presented. The new delay-independent stability conditions are derived using Lyapunov-like functions for the finite-time systems. For these functions it is not necessary to have properties of positivity in the whole state space as well as negative derivatives along the system trajectories. The proposed approach is supported and combined with classical Lyapunov technique to guarantee actractivity of the system.

Nonlinear Kalman Filters for Model Calibration of Soil Parameters for Geomechanical Modeling in Mechanized Tunneling

AbstractThis work shows that nonlinear Kalman filters can be applied very effectively for the calibration of geomaterial parameters for geomechanical modeling in mechanized tunneling, using tunneling-induced settlements and horizontal displacements. The data curves measured along tunnel excavation steps, which exhibit a nonlinear relationship with respect to soil parameters and are prone to measurement inaccuracies, are utilized in combination with finite element modeling to estimate the underlying soil parameters, using a sequential inference framework: the nonlinear Kalman filtering. The paper shows the comparative performance of the two types of nonlinear Kalman filters that are effective for the identification of soil parameters in terms of convergence speed and accuracy: the extended Kalman filter (EKF) and the sigma-point Kalman filter (SPKF). The effectiveness of the two Kalman filters for inverse analysis is demonstrated through computer simulations for identifying a number of important constituti...

Robust nonfragile observer-based H2/H∞ controller

A robust nonfragile observer-based controller for a linear time-invariant system with structured uncertainty is introduced. The H ∞ robust stability of the closed-loop system is guaranteed by use of the Lyapunov theorem in the presence of undesirable disturbance. For the sake of addressing the fragility problem, independent sets of time-dependent gain-uncertainties are assumed to be existing for the controller and the observer elements. In order to satisfy the arbitrary H2-normed constraints for the control system and to enable automatic determination of the optimal H 2 / H ∞ bound of the performance functions in disturbance rejection control, additional necessary and sufficient conditions are presented in a linear matrix equality/inequality framework. The H 2 / H ∞ observer-based controller is then transformed into an optimization problem of coupled set of linear matrix equalities/inequality that can be solved iteratively by use of numerical software such as Scilab. Finally, concerning the evaluation of the performance of the controller, the control system is implemented in real time on a mechanical system, aiming at vibration suppression. The plant under study is a multi-input single-output clamped-free piezo-laminated smart beam. The nominal mathematical reduced-order model of the beam with piezo-actuators is used to design the proposed controller and then the control system is implemented experimentally on the full-order real-time system. The results show that the closed-loop system has a robust performance in rejecting the disturbance in the presence of the structured uncertainty and in the presence of the unmodeled dynamics.

Semi-Analytical Modeling and Vibration Control of a Geometrically Nonlinear Plate

This paper presents the dynamic modeling of a piezolaminated plate considering geometrical nonlinearities. The piezo-actuator and piezo-sensor are connected via proportional derivative feedback control law. The Hamilton’s principle is used to extract the strong form of the equation of motion with the reflection of the higher order strain terms by means of the strain–displacement relationship of the von Karman type. Then the nonlinear partial differential equation (PDE) obtained is converted to a nonlinear algebraic equation by employing the combination of harmonic balance method and single-mode Galerkin’s technique. Finally, the vibration suppression performance and sensitivity of the dynamic response is evaluated for various control parameters and magnitudes of external disturbance.

A new approach to the stability of discrete descriptor time delay systems in the sense of non-lyapunov delay independent conditions

This paper gives sufficient conditions for the practical and finite time stability of linear singular continuous time delay systems of the form E x(k +1) = A0x(k ) + A1x(k - 1). When we consider finite time stability concept, these new, delay independent conditions are derived using approach based on Lyapunov - like functions and their properties on sub-space of consistent initial conditions. .

Modelling and analysis of piezoelectric smart structures for vibration and noise control

The paper presents an overall numerical approach for the simulation and design of smart lightweight structures in order to control vibration and noise. The design process requires an overall virtual computer model, which includes the passive mechanical structure, the acoustic fluid, the active materials, such as piezoelectric patch actuators glued to the structure, as well as the controller. Based on the finite element method such an overall model is presented in the paper. An acoustic box is used to verify the computational approach by comparing simulated and measured results.

A new approach to stability of singular time delay systems in the sense of non-Lyapunov delay independent conditions

This paper provides sufficient conditions for both practical stability and finite time stability of linear singular continuous time delay systems which can be mathematically described as Eẋ(t) = A0x(t) + A1x(t − τ). Considering a finite time stability concept, new delay independent conditions have been derived using the approach based on the Lyapunov-like functions and their properties on the subspace of consistent initial conditions. These functions do not need to have the properties of positivity in the whole state space and negative derivatives along the system trajectories. When the practical stability has been analyzed the above mentioned approach was combined and supported by the classical Lyapunov technique to guarantee the attractivity property of the system behavior.

Piezoceramic Smart Aggregates for Active Monitoring of Reinforced Concrete Structures

Active structural health monitoring of reinforced concrete civil engineering structures using piezoceramic smart aggregates represent nondestructive evaluation techniques which is characterized by high reliability, wide frequency range, low cost, ease of use, and multifunctionality. Procedure of damage detection is based on wave propagation and used basic piezoelectric effects for smart aggregate actuators and sensors. Represented active monitoring method can detect damage that is not visible with the naked eye, damage that is in inaccessible parts of structures, and damage that cannot be caught by visual inspections. Also, during the measurement, a construction can be undisturbed used which is very important for bridges or industrial production halls. Structural health monitoring is performed by a one-dimensional and two-dimensional damage index formed using wavelet signal analysis and based on energy changes of output sensor signals. In this paper, piezoelectric smart aggregates for structural health monitoring, damage detection, and localization purpose of reinforced concrete civil engineering structures are represented.