Arnaud Deraemaeker

Mixing Rules for the Piezoelectric Properties of Macro Fiber Composites

This article focuses on the modeling of structures equipped with Macro Fiber Composite (MFC) transducers. Based on the uniform field method under the plane stress assumption, we derive analytical mixing rules in order to evaluate equivalent properties for d31 and d33 MFC transducers. In particular, mixing rules are derived for the longitudinal and transverse piezoelectric coefficients of MFCs. These mixing rules are validated using finite element computations and experimental results available from the literature.

Reduced bases for model updating in structural dynamics based on Constitutive Relation Error

Abstract This paper deals with the application of a model reduction method to the updating of models of industrial structures with many degrees of freedom. The updating method is based on the concept of constitutive relation error. This is an iterative method in which each iteration consists of a first step in which the most important errors in the model are localized and a second step in which these errors are corrected. The reduction method follows a classical approach in which we introduce a truncated modal basis to which the static responses associated with different excitations are added. The efficiency of the method is illustrated on one example of a finite element model containing 10,000 degrees of freedom. In the first part, we update the mass and stiffness properties of the model based on eigenmodes and eigenfrequencies. In the second part, the damping properties are updated based on the frequency response functions of the structure.

Dispersion and pollution of meshless solutions for the Helmholtz equation

It is well known today that the standard finite element method (FEM) is unreliable to compute approximate solutions of the Helmholtz equation for high wavenumbers due to the pollution effect, consisting mainly of the dispersion, i.e. the numerical wavelength is longer than the exact one. Unless highly refined meshes are used, FEM solutions lead to unacceptable solutions in terms of precision, while the use of very refined meshed increases the cost in terms of computational times. The paper presents an application of the element-free Galerkin method (EFGM) and focuses on the dispersion analysis in 2D. It shows that it is possible to choose the parameters of the method in order to minimize the dispersion and to get extremely good results in comparison with the stabilized FEM. Moreover, the present meshless formulation is not restricted to regular distribution of nodes and a simple but real-life problem is investigated in order to show the improvement in the accuracy of the numerical results w.r. FEM results.

Active damping of chatter in machine tools: demonstration with a “hardware-in-the-loop” simulator

Abstract The motivation of the work is twofold: (a) understand the physics behind regenerative chatter and the influence of structural damping and (b) demonstrate an active damping technique based on collocated actuator/sensor pairs. A numerical stability analysis is performed using the root locus method and it is shown that, along with the structural poles, eigenvalues due to the delay parameter may contribute to instability. Since experimental demonstration of chatter in real machines is difficult, an alternative way of demonstration via a mechatronic simulator is presented, using the ‘hardware-in-the-loop’ concept. The mathematical model of the regenerative cutting process in turning is simulated in a computer and this is interfaced to a beam, representing the structural dynamics of the machine, via a displacement sensor and force actuator. In this way, a hardware and a software loop are combined. In a second step, an additional control loop is added, consisting of an accelerometer sensor and a collocated inertial actuator. Numerical and experimental stability lobe diagrams are compared, with and without active damping.

Monitoring of the ultrasonic P-wave velocity in early-age concrete with embedded piezoelectric transducers

This note deals with the use of embedded piezoelectric transducers to monitor the ultrasonic P-wave velocity evolution during the setting and hardening phases of concrete subsequent to casting time. The main advantage of the technique is the possibility of overcoming the limitations of traditional methods which prevent the application of specific mechanical boundary conditions during the measurement. The embedded transducers are based on the ‘smart aggregates’ concept previously developed at the University of Houston, Texas. Two piezoelectric transducers are embedded in a prismatic mold and the evolution of the P-wave velocity is recorded for the first 24 h in concrete after the casting time. The results are very promising and show a good agreement with classical ultrasonic tests using external transducers. (Some figures may appear in colour only in the online journal)

Vibration Isolation of Precision Payloads: A Six-Axis Electromagnetic Relaxation Isolator

This paper describes a passive six-axis vibration isolation system for space applications. The system consists of a Stewart platform with cubic architecture; each leg is equipped with an electromagnetic transducer connected to a RL circuit. The system behaves like a relaxation isolator and its transmissibility exhibits an asymptotic decay rate of ―40 dB/decade. The performances are very similar to that of an active isolator based on a skyhook controller.

Model validation in the presence of uncertain experimental data

In this paper, we discuss the application of the constitutive relation error (CRE) to model updating and validation in the context of uncertain measurements. First, a parallel is drawn between the CRE method and a general theory for inverse problems proposed by Tarantola. Then, an extension of the classical CRE method considering uncertain measurements is proposed. It is shown that the proposed mechanics‐based approach for model validation is very effective in filtering noise in the experimental data. The method is applied to an industrial structure, the SYLDA5, which is a satellite support for Ariane5. The results demonstrate the robustness of the method in actual industrial situations.

Validation and Updating of Industrial Models Based on the Constitutive Relation Error

The validation and updating of models of industrial structures based on the concept of constitutive relation error is treated. The method is extended to the problem of the detection of defective sensors. The capabilities of the method are illustrated on the structure of the SYLDA5 double launching system of the European space launcher Ariane 5. The results obtained are encouraging and demonstrate the efficiency of the method for updating models of industrial structures.

New trends in vibration based structural health monitoring

This book is a collection of articles covering the six lecture courses given at the CISM School on this topic in 2008. It features contributions by established international experts and offers a coherent and comprehensive overview of the state-of-the art research in the field, thus addressing both postgraduate students and researchers in aerospace, mechanical and civil engineering.

Piezoelectric vibration damping using resonant shunt circuits: an exact solution

The objective of this paper is to propose an exact closed-form solution to the optimization of piezoelectric materials shunted with inductive-resistive passive electrical circuits. Realizing that Den Hartogʼs method which imposes fixed points of equal height in the receptance transfer function is approximate, the parameters of the piezoelectric tuned vibration absorber are calculated through the direct minimization of the maxima of the receptance. The method is applied to a one-degree-of-freedom primary oscillator considering various values of the electromechanical coupling coefficients.