Letícia Fleck Fadel Miguel

Shape and size optimization of truss structures considering dynamic constraints through modern metaheuristic algorithms

Highlights? Mass optimization on shape and sizing with multiple natural frequency constraints. ? This is a highly nonlinear dynamic optimization problem. ? It is solved using recent metaheuristic algorithms: Harmony Search and Firefly. ? The results showed that both algorithms reached better results than the literature. Mass optimization on shape and sizing with multiple natural frequency constraints are highly nonlinear dynamic optimization problems. Multiple natural frequency constraints normally cause difficult dynamic sensitivity analysis and, in addition, two different types of design variables, nodal coordinates and cross-sectional areas, often lead to divergence. Thus, the choice of the appropriated method to solve this kind of problem is of paramount importance. Within this context, in this paper two of the most recent metaheuristic algorithms developed in the last decade, Harmony Search (HS) and Firefly Algorithm (FA), are used, for the first time here, to solve truss shape and sizing optimization with multiple natural frequency constraints. Since these metaheuristic algorithms are not a gradient-based search, they avoid most of the pitfalls of any gradient-based search algorithms. The effectiveness of Harmony Search and Firefly Algorithm is demonstrated through four benchmark structural optimization problems for solving shape and sizing optimization of trusses with multiple frequency constraints. The results showed that both metaheuristic algorithms reached, in a relatively low computational time, better results than the literature in three of the four examples considered, and in the other example the structure is approximately equal to the best one found, emphasizing the excellent capacity of both methods.

Multimodal size, shape, and topology optimisation of truss structures using the Firefly algorithm

This paper presents an efficient single-stage Firefly-based algorithm (FA) to simultaneously optimise the size, shape and topology of truss structures. The optimisation problem uses the minimisation of structural weight as its objective function and imposes displacement, stress and kinematic stability constraints. Unstable and singular topologies are disregarded as possible solutions by checking the positive definiteness of the stiffness matrix. Because cross-sectional areas are usually defined by discrete values in practice due to manufacturing limitations, the optimisation algorithm must assess a mixed-variable optimisation problem that includes both discrete and continuous variables at the same time. The effectiveness of the FA at solving this type of optimisation problem is demonstrated with benchmark problems, the results for which are better than those reported in the literature and obtained with lower computational costs, emphasising the capabilities of the proposed methodology. In addition, the procedure is capable of providing multiple optima and near-optimal solutions in each run, providing a set of possible designs at the end of the optimisation process.

Damage detection under ambient vibration by harmony search algorithm

Highlights? A new approach for vibration-based (SHM) procedures is presented. ? Stochastic system identification with the evolutionary harmony search algorithm. ? Numerical investigation considering noise levels and a series of damage scenarios. ? Experimental study of three cantilever beams under different damage conditions. ? The methodology has shown potential for use in the damage assessment of structures. Damage in structural systems induced by vibrations, alternating load cycles, temperature changes, corrosion, etc., constitute a serious technical problem. Smart methods of control and structural health monitoring (SHM) for large structures are, therefore, highly needed. In certain structural applications, moreover, a lack of access to the damaged area imposes an additional constraint on damage identification procedures. One method that may fulfill those requirements is dynamic nondestructive testing, which consists of monitoring changes in the structures natural frequencies, vibration modes and damping.In this paper, a new approach for vibration-based (SHM) procedures is presented, in an ambient vibration context; this method combines a time domain modal identification technique (SSI) with the evolutionary harmony search algorithm. A series of numerical examples with different damage scenarios and noise levels have been carried out under impact and ambient vibration. Thereafter, an experimental study of three cantilever beams with several different damage scenarios is conducted and the proposed methodology has shown potential for use in the damage diagnosis assessment of the remaining structural life.

Study of imperfections in the cubic mesh of the truss-like discrete element method

In the truss-like discrete element method (DEM), masses are lumped at nodal points and interconnected by means of one-dimensional elements with arbitrary constitutive relations. In previous studies of nonhomogeneous concrete cubic samples subjected to nominally uniaxial tension, it was verified that numerical predictions of fracture using discrete element method models are feasible and yield results that present good correlation with the experimental evidence so far available, including the prediction of size and strain rate effects. In the discrete element method approach, material failure under compression is assumed to occur by indirect tension. In previous simulations of samples subjected to uniaxial compression, it was verified that the response is satisfactorily modeled up to the peak load, when a sudden collapse usually occurs, characteristic of fragile behavior. On the other hand, experimental stress versus displacement curves observed in small specimens subjected to compression typically present a softening branch, in part due to sliding with friction of the fractured parts of the specimens. A second deficiency of discrete element method models with a perfectly cubic mesh is that the best correlations with experimental results are obtained with material parameters that differ in tension and compression. This paper examines another cause of the fragile behavior of discrete element method predictions of the response of concrete elements subjected to nominally uniaxial compression, namely the regularity of the perfect cubic mesh, which is unable to capture nonlinear stability effects in the material at a microscale. It is shown herein that the introduction of small perturbations of the discrete element method regular mesh significantly improves the predicting capability of the model and in addition allows adopting a unique set of material properties, which are independent of the applied loading.

A Constitutive Criterion for the Fault: Modified Velocity-Weakening Law

Expanding on a previous article, constitutive laws for solid friction are examined jointly with available experimental results. The models are evaluated by means of numerical dynamic analysis of two sliding blocks simulating adjacent fault sections. Effective constitutive laws are determined as relations between mean values of the relevant variables on a selected area of the sliding surfaces. The material is initially assumed elastic and homogeneous and the influence of nonhomogeneity evaluated next by modeling mass density, Young’s modulus, and friction coefficient as correlated random fields. The effect of fractures in rock close to the fault is also numerically assessed. Finally, the influence of rupture of protrusions (microasperities) between the sliding surfaces is analyzed. The influence of size of the averaging interface area on the parameters of the effective constitutive law is then obtained by means of Monte Carlo simulation. When the rock regions adjacent to the fault are assumed to be linearly elastic and homogeneous or nonhomogeneous no size effect is observed. On the other hand, when the friction coefficient is characterized by a random field, a size effect is detected. Fracture occurrence in the region surrounding the fault does not cause significant alteration of the macroconstitutive law, producing only minor perturbations of the mean law determined without fracture, but it should also introduce high-frequency slave vibrations. Finally, a macroconstitutive law that takes into account the shear rupture of microasperities on the sliding surfaces is suggested. The proposed modified velocity-weakening law, constitutes a more general and flexible constitutive law.

A BACKTRACKING SEARCH ALGORITHM FOR THE SIMULTANEOUS SIZE, SHAPE AND TOPOLOGY OPTIMIZATION OF TRUSSES

THIS PAPER PRESENTS A BACKTRACKING SEARCH OPTIMIZATION ALGORITHM (BSA) TO SIMULTANEOUSLY OPTIMIZE THE SIZE, SHAPE AND TOPOLOGY OF TRUSS STRUCTURES. IT FOCUSES ON THE OPTIMIZATION OF THESE THREE AS-PECTS SINCE IT IS WELL KNOWN THAT THE MOST EFFECTIVE SCHEME OF TRUSS OPTIMIZATION IS ACHIEVED WHEN THEY ARE SIMULTANEOUSLY CONSIDERED. THE MINIMIZATION OF STRUCTURAL WEIGHT IS THE OBJECTIVE FUNCTION, IMPOSING DISPLACEMENT, STRESS, LOCAL BUCKLING AND/OR KINEMATIC STABILITY CONSTRAINTS. THE EFFECTIVENESS OF THE BSA AT SOLVING THIS TYPE OF OPTIMIZATION PROBLEM IS DEMONSTRATED BY SOLVING A SERIES OF BENCHMARK PROBLEMS COMPARING NOT ONLY THE BEST DESIGNS FOUND, BUT ALSO THE STATISTICS OF 100 INDEPENDENT RUNS OF THE ALGORITHM. THE NUMERICAL ANALYSIS SHOWED THAT THE BSA PROVIDED THE BEST DESIGN EVER FOUND FOR MOST OF THE ANALYZED PROBLEMS. MOREOVER, IN SEVERAL CASES, IT WAS ALSO ABLE TO IMPROVE THE STATISTICS OF THE INDE-PENDENT RUNS SUCH AS THE MEAN AND COEFFICIENT OF VARIATION VALUES.

Assessment of modern metaheuristic algorithms - HS, ABC and FA - in shape and size optimisation of structures with different types of constraints

Shape and size optimisation of structures combining different types of constraints normally causes difficult sensitivity analysis. Thus, choosing the appropriate method to solve this kind of problem is of paramount importance. There are many metaheuristic methods and new ones continue being developed. An assessment of these algorithms may help to choose one. In this paper, three recent metaheuristic algorithms, harmony search HS, artificial bee colony ABC and firefly algorithm FA, are evaluated. The effectiveness of these methods are demonstrated by solving seven benchmark structural optimisation problems. Additionally, the optimisation of a realistic transmission tower is performed, which may serve as benchmark to validate new optimisation methods. A parametric study was also carried out and the statistical results were presented. The results showed that the three algorithms reached, in a relatively low computational time, better results than most literature, emphasising their excellent ability. Comparisons among the algorithms could be established.

Optimization of location and forces of friction dampers

Damper optimization is a new area which has been investigated in recent years. There are various methods employed in optimization, among which are highlighted the classic and the most recent that are functioning with reliability, efficiency and speed for optimum results. This paper proposes a method for simultaneous optimization of placement and forces of friction dampers using the Firefly Algorithm, which is a recent meta-heuristic algorithm inspired in the behavior of fireflies. Herein, three different optimization objective are presented: i) minimize the maximum displacement at the top of the structure; ii) minimize the maximum interstory drift; iii) minimize the maximum acceleration at the top of the structure. The three objective functions were evaluated in two civil structures (a nine-story building and a sixteen-story building) subjected to two real seismic records. The first seismic record is El Centro, which took place in the southeastern California on the boarder of the United States and Mexico in 1940. The second one is the earthquake that occurred in Caucete, province of San Juan, Argentina, in 1977. The results showed that the proposed method was able to optimize the friction dampers, reducing considerably the response of the structures.

Influence of the Width of the Loading Strip in the Brazilian Tensile Test of Concrete and Other Brittle Materials

AbstractDifficulties presented by the direct tensile test of nonhomogeneous, brittle materials were circumvented by the proposal of an indirect tensile test for concrete, known in the literature as the Brazilian test, which found applications in the technology of concrete, rocks, ceramics and other materials. Relationships between the predictions of the Brazilian test and the results of both the direct tensile test and the unconfined compression test have been proposed on the basis of experimental evidence. On the other hand, developments in numerical fracture analysis allowed for the examination of the fracture process in the test, including the consideration of scale and rate effects. The discrete element method was used to determine the nonlinear response of brittle solids and to predict the response of simulated concrete samples subjected to indirect tensile tests. This paper extends this approach to more precisely quantify the role of factors such as the width and stiffness of the strips inserted bet...

Dynamic response of a 190m-high transmission tower for a large river crossing

AbstractThe construction of a double circuit 500 kV transmission line (TL) in the Brazilian Amazon region is currently in progress. In addition to its length within the rain forest, the TL had to overcome large river crossings and environ- mental constrains. Among them, the crossing of the Trombetas River is one of the most important, with a total length of more than 5100 m. The proposed design includes two 190 m high towers necessary to attain spans as long as 1600 m. Additionally, the towers had to be supported by concrete columns, 10 m above ground level, due to the annual flood- ing of the river bed. These structures demand a detailed assessment, since the design required long-span conductors and tall structures that are outside the range normally considered in codes. In this context, the present article describes the dynamic analysis of the complete TL segment for this crossing, with emphasis on the response of the 190 m-high main structure which is subjected to Extended Pressure Systems and Thunders...