Miguel M. Neves

Generalized topology design of structures with a buckling load criterion

Material based models for topology optimization of linear elastic solids with a low volume constraint generate very slender structures composed mainly of bars and beam elements. For this type of structure the value of the buckling critical load becomes one of the most important design criteria and so its control is very important for meaningful practical designs. This paper tries to address this problem, presenting an approach to introduce the possibility of critical load control into the topology optimization model.Using the material based formulation for topology design of structures, the problem of optimal structural reinforcement for a critical load criterion is formulated. The stability problem is conveniently reduced to a linearized eigenvalue problem assuming only material effective properties and macroscopic instability modes. The respective optimality criteria are presented by introducing the Lagrangian associated with the optimization problem. Based on this Lagrangian a first-order method is used as a basis for the numerical update scheme. Two numerical examples to validate the developments are presented and analysed.

Optimal design of periodic linear elastic microstructures

Abstract This paper presents two computational models to design the periodic microstructure of cellular materials for optimal elastic properties. The material equivalent mechanical properties are obtained through a homogenization model. The two formulations address the problem of finding the optimal representative microstructural element for periodic media that maximizes either the weighted sum of the equivalent strain energy density for specified multiple macroscopic strain fields, or a linear combination of the equivalent mechanical properties. Constraints on material volume fraction and material symmetries are considered. The computational models are established using finite elements and mathematical programming techniques and tested in several numerical examples.

Dynamical Response of a Multi-Laminated Periodic Bar: Analytical, Numerical and Experimental Study

This article presents a study on the use of the dynamical response of multi-laminated periodic bars to create resonance band gaps within useful frequency ranges. The objective is to control, in a passive form, the longitudinal vibration transmissibility in specific and wide enough frequency ranges of interest. This is achieved by the separation of two adjacent eigenfrequencies. A relation between the modal analysis, the harmonic analysis and the Bloch wave theory is proposed, for which no reference was found in the searched literature. As shown, the selection of appropriate material pairs is essential to obtain useful frequency ranges. The use of pairs of steel and cork agglomerate is proposed, since it allows the design of attenuators at lower frequencies through a prediction based on finite element analysis (FEA). This approach requires the storage modulus of cork for which analytical and numerical FEA models were verified and validated. A methodology to obtain experimentally the storage modulus of cork is presented. Regarding the structural improvement problem, we discuss a methodology to design periodic bars for a specific location of the first attenuations frequency range and illustrate the main results through several examples.

Exploiting Resolution-Based Representations for MaxSAT Solving

Most recent MaxSAT algorithms rely on a succession of calls to a SAT solver in order to find an optimal solution. In particular, several algorithms take advantage of the ability of SAT solvers to identify unsatisfiable subformulas. Usually, these MaxSAT algorithms perform better when small unsatisfiable subformulas are found in early iterations of the algorithm. However, this is not the case in many problem instances, since the whole formula is given to the SAT solver in each call.

Force Magnitude Reconstruction Using the Force Transmissibility Concept

This paper proposes the reconstruction of forces, based on the direct and inverse problems of transmissibility in multiple degree of freedom (MDOF) systems. The objective and novelty are to use the force transmissibility to calculate reactions given the applied loads (and vice versa). This method, relating two sets of forces, proves to be an alternative to the common inverse problem based on the measurement of FRFs and operational accelerations to determine operational forces, as it can be advantageous in some cases. This implies the a priori knowledge of the transmissibility of the structure, either experimentally or numerically. In this study a finite element model is built, describing with enough accuracy the dynamic behavior of the structure. The numerical model will play a key role in the construction of the transmissibility matrix; this will be used to evaluate either the reaction or the applied forces, using experimental data. This constitutes a hybrid methodology, which is validated experimentally. The authors present several comparisons between reconstructed and experimentally measured sets of forces. It is shown that the proposed method is able to produce good results in the reconstruction of the forces, underlining its potential for other structures and possible applications.

Multilayered Infinite Medium Subject to a Moving Load: Dynamic Response and Optimization Using Coiflet Expansion

A wavelet based approach is proposed in this paper for analysis and optimization of the dynamical response of a multilayered medium subject to a moving load with respect to the material properties and thickness of supporting half-space. The investigated model consists of a load moving along a beam resting on a surface of a multilayered medium with infinite thickness and layers with different physical properties. The theoretical model is described by the Euler-Bernoulli equation for the beam and the Naviers elastodynamic equation of motion for a viscoelastic half-space. The moving load is modelled by a finite series of distributed harmonic loads. A special method based on a wavelet expansion of functions in the transform domain is adopted for calculation of displacements in the physical domain. The interaction between the beam and the multilayered medium is analyzed in order to obtain the vibration response at the surface and the critical velocities associated. The choice of the specific values of the design parameters for each layer, which minimize the vibration response of the multilayered medium, can be seen as a structural optimization problem. A first approach for using optimization techniques to explore the potential of the wavelet model is presented and briefly discussed. Results from the analysis of the vibration response are presented to illustrate the dynamic characterization obtained by using this method. Numerical examples reflecting the results of numerical optimizations with respect to a multilayered medium parameters are also presented.

An Experimental Characterization of Cork Storage Modulus for Cork-Steel Applications in Vibration Attenuation

This study presents an experimental characterization of cork storage modulus used to model the vibration response of bars built using alternate layers of cork and steel. In the experimental setup, the specimen was suspended from a fixed support by two thin lines while a shaker was suspended from a mobile support by metallic chains. The shaker was connected to the bar specimen through a force transducer imposing a dynamical deformation that propagates through the specimen. An accelerometer in the opposite extremity of the bar measures the corresponding vibration response and the cork storage modulus is then obtained from the first peak of this frequency response. The proposed methodology successfully characterized the storage modulus of the cork material used in the multilaminated periodic bars. The results obtained illustrate a satisfactory correlation between

Analysis of structural damping performance in passenger vehicles chasis.

Viscoelastic material is commonly used in the passive treatment of structural vibration of the vehicle structure, to introduce damping and reduce vibration level at resonance frequencies. The effectiveness of such damping treatment depends on design parameters such as location, area, thickness, and choice of the type of the damping material. This paper describes the experimental proceeds to evaluate two different layer damping material performances, when they are applied to a passenger vehicle chassis.

International Conference on Structural Engineering Dynamics – ICEDyn 2009

The last edition of the International Conference on Structural Engineering Dynamics, ICEDyn 2011, took place in Tavira, Algarve, south coast of Portugal, on the 20 th −22 nd of June 2011, organized by the Instituto Superior Técnico (IST), from the Technical University of Lisbon, and the Instituto de Engenharia Mecânica (IDMEC). Although it has had previous editions, it was in 2007 that it became a biennial scientific event that has grown not only in quantity, but also in quality. Its highly rated Scientific Committee is a guaranty of excellence that attracts many reputed scientists from all over the world, representatives of the industrial community and young PhD students, interacting and sharing their expertise and experience during the event. In this last edition we had the highest participation ever, with delegates from 19 countries, presenting 93 papers. From these, 46 papers have been submitted to this special issue, which has been carefully prepared. After a tough reviewing process, where most of the papers have been scrutinized by three reviewers, 12 have been rejected and 34 have been approved. These papers cover a wide spectrum of subjects that include modal updating, non-linear dynamics, damage detection, modeling of damping, etc., and reflect the excellent outcome of ICEDyn 2011. It was a pleasure and an honor to have served as Guest Editors of Shock and Vibration. Acknowledgements are due to all the authors and co-authors, to the reviewers for all their time and collaboration, to the Publication Manager Rasjel van der Holst, and to both past and present SAV Editors-in-Chief, Profs. Daniel Inman and Mehdi Ahmadian, respectively, for their interest and enthusiasm in supporting this special issue.

Analysis and Continuum Topology Optimization of Periodic Solids with Linearized Elastic Buckling Criterion

A methodology for a linearized elastic buckling analysis based on a two-scale asymptotic method for periodic materials is generalized to three-dimensional case and implemented at microscale level. The present two-scale method provides a set of uncoupled problems for the linearized elastic stability analysis at the macroscale and the microscale material levels respectively. For the microscale level problem, it is considered an infinite and periodic structured medium for a given average (at the macroscale level) strain. Using the Floquet-Bloch wave theory within the finite element method and a continuum topology optimization problem, implicitly assuming repetitive cells, the minimum critical buckling strain is obtained and maximized while the cell volume fraction is kept constant. The performance of the implemented methodology is tested for different cases. Results obtained with finite repetitive medium for periodic open cells versus closed cells keeping the same cell volume fraction are discussed.