ORBi Open Repository and Bibliography
In may 2007, the ULg's Administrative Board (joined in June 2007 by the FUSAGx) decided to create an institutional repository and defined a strong institutional self-archiving policy to increase the visibility, accessibility and impact of the University's publications (Board's decision).
This decision led to the official launch, in November 2008, of the ORBi platform including both the Academic Bibliography and the Institutional Repository of the Wallonia-Europe University Academy.
Nonlinear generalization of Den Hartog's equal peak method for nonlinear primary systems - Habib, Giuseppe; Detroux, Thibaut; Kerschen, Gaëtan
This study addresses the mitigation of one problem nonlinear resonance of a mechanical system. In view of the narrow bandwidth of the classical linear tuned vibration absorber, a new nonlinear absorber, termed the nonlinear tuned vibration absorber (NLTVA), is introduced in this paper. One unconventional aspect of the NLTVA is that the mathematical form of its restoring force is tailored according to the nonlinear restoring force of the primary system. The NLTVA parameters are then determined using a nonlinear generalization of Den Hartog's equal-peak method. The mitigation of the resonant vibrations of a Duffing oscillator is considered to illustrate the...
Identification of a Time-varying Beam Using Hilbert Vibration Decomposition - Bertha, Mathieu; Golinval, Jean-Claude
The present work is concerned by modal identification of time-varying systems. For this purpose, a method based on instantaneous frequency identification and synchronous demodulation is used to extract modal components from recorded signals. The proposed method of iterated sifting process is based on the Hilbert Vibration Decomposition (HVD) technique which is used to extract the instantaneous dominant vibrating component at each iteration. A source separation preprocessing step is introduced to treat multiple degree-of-freedom systems in an optimal way. Sources are used as reference signals to get a single instantaneous frequency of each mode for the demodulation on all the channels....
Comparison of parameterization schemes for solving the discrete material optimization problem of composite structures - Duysinx, Pierre; Guillermo Alonso, Maria; Tong, Gao; Bruyneel, Michaël
Optimal design of composite structures can be formulated as an optimal selection of material in a list of different laminates. Based on the seminal work by Stegmann and Lund, the optimal problem can be stated as a topology optimization problem with multiple materials. The research work carries out a large investigation of different interpolation and penalization schemes for the optimal material selection problem. Besides the classical Design Material Optimization (DMO) scheme and the recent Shape Function with Penalization (SFP) scheme by Bruyneel, the research introduces a generalization of the SFP approach using a bi-value coding parameterization (BCP) by Gao, Zhang...
Comparison of parameterization schemes for solving the discrete material optimization problem of composite structures - Duysinx, Pierre; Guillermo Alonso, Maria; Gao, Tong; Remouchamps, Alain; Bruyneel, Michaël
In the context of weight reduction challenges in aerospace, automotive, and energy engineering problems, composite materials are gaining a revived interested. Because of the problem complexity and the large number of design variables, their design of composite structures is greatly facilitated by using optimization techniques.
While several formulations have been proposed for composite structure design, Stegmann and Lund  have showed that composite optimization can take advantage of the topology optimization approach. The fundamental idea of the Discrete Material Optimization (DMO) approach is 1/ to formulate the composite optimization problem as an optimal material selection problem in which the different...
A stochastic framework for subspace identification of a strongly nonlinear aerospace structure - Noël, Jean-Philippe; Schoukens, Johan; Kerschen, Gaëtan
The present study exploits the maximum likelihood identification framework for deriving statistically-optimal models of nonlinear mechanical systems. The identification problem is formulated in the frequency domain, and model parameters are calculated by minimising a weighted least-squares cost function. Initial values of the model parameters are obtained by means of a nonlinear subspace algorithm. The complete identification methodology is first demonstrated on a Duffing oscillator, prior to being applied to a full-scale aerospace structure.
Non-Local Incremental-Secant Mean-Field-Homogenization of Damage-Enhanced Elasto-Plastic Composites - Wu, Ling; Noels, Ludovic; Adam, Laurent; Doghri, Issam
An anisotropic gradient–enhanced continuum damage model is herein embedded in a mean–field homogenization (MFH) process for elasto-plastic composites.
The homogenization procedure is based on the newly developed incremental secant mean-field homogenization formulation, for which the residual stress and strain states reached in the phases upon a fictitious elastic unloading are considered as starting point to apply the secant method. The mean stress fields in the phases are then computed using isotropic secant tensors, which are naturally used to define the Linear Comparison–Composite
The resulting multi– scale model is then applied to study the damage process at the meso–scale of laminates, and...
Computational homogenization of cellular materials capturing micro-buckling, macro-localization and size effects - Nguyen, Van Dung
The objective of this thesis is to develop an efficient multi-scale finite element framework to capture the macroscopic localization due to the micro-buckling of cell walls and the size effect phenomena arising in structures made of cellular materials.
Under the compression loading, the buckling phenomenon (so--called micro--buckling) of the slender components (cell walls, cell faces) of cellular solids can occur. Even if the tangent operator of the material of which the micro--structure is made, is still elliptic, the presence of the micro--buckling can lead to the loss of ellipticity of the resulting homogenized tangent operator. In that case, localization bands...
Subspace and nonlinear-normal-modes-based identification of a beam with softening-hardening behaviour - Grappasonni, Chiara; Noël, Jean-Philippe; Kerschen, Gaëtan
The capability to reproduce and predict with high accuracy the behaviour of a real system is a fundamental task of numerical models. In nonlinear structural dynamics, additional parameters compared to classical linear modelling, which include the nonlinear coefficient and the mathematical form of the nonlinearity, need to be identified to bring the numerical predictions in good agreement with the experimental observations. In this context, the present paper presents a method for the identification of an experimental cantilever beam with a geometrically nonlinear thin beam clamped with a prestress, hence giving rise to a softening-hardening nonlinearity. A novel nonlinear subspace identification...
Numerical and Experimental Investigation of Slot-Blowing Air Over a Cylinder - Runge, William; Buysschaert, Frank; Hayez, Jules; Carlier, François; Antoine, Hubert; Hendrick, Patrick; Dimitriadis, Grigorios; Degrez, Gérard
Tangential slot blowing around a cylinder in the Coanda effect has been proposed as a mechanism for yaw control in a novel coaxial helicopter. The proposed design has been investigated computationally, using the unsteady k-ω SST solver in NUMECA, as well as experimentally in the wind tunnel at the Université de Liège. While the concept in general is promising, it has been shown that there are some potential problems, including pitch-yaw coupling and some unsteady flow conditions. These problems exist under varied circumstances, and, exist at least in part due to the complicated flow-field in this problem, even in 2-dimensions.
Dry galloping on bridge cables: roughness and shape effects on an inclined circular cylinder - Benidir, Adel; Flamand, Olivier; Gaillet, Laurent; Dimitriadis, Grigorios
Dry galloping of stays in cable-stayed bridges is a phenomenon that is still of interest to the scientific community. Over the course of the current three-year research project numerous experiments will be carried out to investigate the effect of turbulence and inclination angle on dry galloping. The novel aspect of this study consists of an in-depth investigation into the effect of non uniformity of the pipe surrounding the stay cables on the dry galloping excitation mechanism. Previous studies reported that dry galloping is caused by the appearance of a negative pressure bubble on one side of the circular cylinder at...