Showing papers by "Jean-Claude Golinval published in 2009"

Modal Analysis of a Nonlinear Periodic Structure with Cyclic Symmetry

Abstract: This paper carries out modal analysis of a nonlinear periodic structure with cyclic symme- try. The nonlinear normal mode (NNM) theory is brie°y described, and a computational algorithm for the NNM computation is presented. The results obtained on a simpli¯ed model of a bladed assembly show that this system possesses a very complicated struc- ture of NNMs, including similar and nonsimilar NNMs, nonlocalized and localized NNMs, bifurcating and internally resonant NNMs. Modal interactions that occur without neces- sarily having commensurate natural frequencies in the underlying linear system are also discussed.

Energy Transfer and Dissipation in a Duffing Oscillator Coupled to a Nonlinear Attachment

Abstract: The dynamics of a two-degree-of-freedom nonlinear system consisting of a grounded Duffing oscillator coupled to an essentially nonlinear attachment is examined in the present study. The underlying Hamiltonian system is first considered, and its nonlinear normal modes are computed using numerical continuation and gathered in a frequency-energy plot. Based on these results, the damped system is then considered, and the basic mechanisms for energy transfer and dissipation are analyzed.

Influence of adhesive rough surface contact on microswitches

Abstract: Stiction is a major failure mode in microelectromechanical systems (MEMS). Undesirable stiction, which results from contact between surfaces, threatens the reliability of MEMS severely as it breaks the actuation function of MEMS switches, for example. Although it may be possible to avoid stiction by increasing restoring forces using high spring constants, it follows that the actuation voltage has also to be increased significantly, which reduces the efficiency. In our research, an electrostatic-structural analysis is performed to estimate the proper design range of the equivalent spring constant, which is the main factor of restoring force in MEMS switches. The upper limit of equivalent spring constant is evaluated based on the initial gap width, the dielectric thickness, and the expected actuation voltage. The lower limit is assessed on the value of adhesive forces between the two contacting rough surfaces. The MEMS devices studied here are assumed to work in a dry environment. In these operating conditi...

Damage Detection of Mechanical Components Using Null Subspace Analysis

Abstract: This paper presents two original applications of the Null Subspace Analysis (NSA) method for fault diagnosis in mechanical components. The method is first applied to the case-study of electro-mechanical devices at the end of the assembly line with the aim of assessing their overall quality. The advantages of the proposed method rely in its rapidity of use and its reliability. At first, a set of five good (i.e. healthy) devices and four damaged devices was considered. The components were instrumented with one triaxial accelerometer on the flank and one monoaxial accelerometer on the top. Based on the NSA method, a mapping of the space ( active components, system order ) up to a system order of 100, was realized in order to select the appropriate order and number of active components. Eventually, thanks to this mapping, the method was able to successfully detect all the faulty components using the signal from only one accelerometer in one direction. The second application is related to the quality assessment of welded joints between stripes in a steel processing plan. Six welded joints with nominal welding parameters and twenty-seven welded joints with out-of-range parameters were realized. Again, the NSA method was able to diagnose successfully the welded joints using a single signal from one accelerometer.

Modal Testing of Nonlinear Vibrating Structures Based on a Nonlinear Extension of Force Appropriation

Abstract: Modal testing and analysis is well-established for linear systems. The objective of this paper is to progress toward a practical experimental modal analysis methodology of nonlinear mechanical structures. In this context, nonlinear normal modes (NNMs) offer a solid theoretical and mathematical tool for interpreting a wide class of nonlinear dynamical phenomena, yet they have a clear and simple conceptual relation to the classical linear normal modes (LNMs). A nonlinear extension of force appropriation techniques is investigated in this study in order to isolate one single NNM during the experiments, similarly to what is carried out for ground vibration testing. With the help of time-frequency analysis, the modal curves and the corresponding backbones are then extracted from the time series. The proposed methodology is demonstrated using a numerical benchmark, which consists of a planar cantilever beam with a cubic spring at its free end.Copyright © 2009 by ASME

Static and dynamic experimental investigations of a micro-electromechanical cantilever in air and vacuum

Abstract: The dynamic response of electro-mechanically actuated micro structures is governed by nonlinear effects which directly influence their performance To date, most work in the field of micro/nano systems is done experimentally and documented theoretical research consists of nonlinear lumped-mass models as well as continuum mechanics approaches Existing and codified computational tools for micro-electromechanical systems (MEMS) more and more penetrate the market of designers and fabrication of such devices The present work is the experimental part of a bench-mark study of a selected microbeam structure investigated with aforementioned analytical and computational techniques and compared to experiments performed with a Polytec MSA400 analyzer The emphasis of this benchmark study is put on the nonlinear dynamic behavior with respect to qualitative and quantitative explanations of the electro-mechanical actuation and damping mechanisms

High vibration sensors: Modelling, design and integration

Abstract: Since many years, the University of Liege is involved in micro-electronics and micro-electromechanical systems modelling, design and integration. Recently, the University of Liege had received the opportunity to build a brand new infrastructure (clean rooms - ISO 7) with specific equipments for packaging and MEMS characterisation. This new facility (clean rooms and equipments) enables the University to be very well positioned in the nano/micro-electronics modelling, analysis and packaging world and is now able to answer specific research and related industrial needs. In this paper we consider the design of a vibration sensor in its significantly vibrating surroundings and investigate in its dynamical behaviour. Environmental vibrations affect the sensor part of the MEMS device and influence the choice of the “best” packaging methods for the application. Within the framework of packaging, we consider a simple test application ensuring best interconnection technology. Dynamical investigations include a preliminary analysis of the packaging and a separate finite-element analysis of the MEMS device (inside the package), testing the device under the condition of a harsh environment (high vibration spectral level). Computations are proposed in combination with experimental observations.

Dimensionality Reduction Using Linear and Nonlinear Transformation

Abstract: With a clear trend toward very large experimental data sets, dimensionality reduction has become an important step of structural health monitoring. The objective of this article is to support that the proper orthogonal decomposition and its nonlinear generalizations are a meaningful addition to the dynamicist's toolbox in this context. The techniques are demonstrated using two application examples, namely, reduced-order modeling and damage detection under varying environmental conditions. Keywords: dimensionality reduction; feature extraction; proper orthogonal decomposition; principal component analysis; nonlinear generalizations of proper orthogonal decomposition; autoassociative neural networks; clustering techniques

Modal analysis of a nonlinear structure with cyclic symmetry

Abstract: When resorting to numerical algorithms, we show that nonlinear normal mode (NNM) computation is possible with limited implementation effort, which paves the way to a practical method for determining the NNMs of nonlinear mechanical systems. The proposed method relies on two main techniques, namely a shooting procedure and a method for the continuation of NNM motions. In addition, sensitivity analysis is used to reduce the computational burden of the algorithm. A simplified discrete model of a nonlinear bladed disk is considered to demonstrate the developments.

Damping Material Characterization and Modeling: An Industrial Case-Study

Abstract: Turbojet engines contain potential nonlinearity sources such as geometric nonlinearities due to the slenderness and the length of modern blades, contacts between the blades and the shrouds, friction in the connections, and material nonlinearities. This paper focuses on the damping material which can be found in some stator stages of low-pressure compression parts. This material makes the shroud and all the blades of the stage interdependent, providing damping and fluid vein airtightness. The objective is to propose a characterization and a numerical modeling methodology that could easily be integrated within an industrial process. Nonlinearity characterization tests, based on the Restoring Force Surface method, are presented as well as viscoelastic characterization. Finally the proposed viscoelastic modeling, based on the Modal Strain Energy method, is validated against experimental data.Copyright © 2009 by ASME

Dual Approach for Electromechanical Coupling in MEMS

Abstract: In this paper we present an approach for the computation of coupled electromechanical problems in micro-electromechanical systems based on a vector potential formulation of the electrostatic problem. This formulation is the dual of the scalar potential approach commonly used in the literature. We present an analytic derivation of the force computed using this dual method based on the virtual work principle, and compare the primal and dual approaches on the finite element solution of simple two-dimensional test-cases.Copyright © 2009 by ASME

Qualification procedure of luminaires in the event of an impact to the pole

Abstract: The objective of the study is to develop a testing specification on an electrodynamic shaker which ensures the qualification of a parking lighting device, whose pole is impacted by a car. The methodology is based on both a numerical approach and an experimental approach using an electrodynamic shaker. The first step of the analysis consists in modeling the structure and the excitation by means of a finite element approach. The calculation of the dynamic response of the "pole/lighting device" system to impact loading is repeated for different geometries of the pole. The second step is to consider each dynamic response at the fixing point of the lighting device on the pole as input for a base-excited single degree of freedom system. The theory developed for such a system allows to define severity criteria like the Shock Response Spectrum (SRS) which is the most representative criterion in the case of an impact. The severity of the vibration environment of the lighting device is then obtained by considering the envelope of the different computed SRS. Finally, different test specifications leading to equivalent SRS are proposed and the device is tested on an electrodynamic shaker. The developed methodology was applied to the NEMO lighting device (Schreder).