Rimantas Belevičius

Global optimization of trusses with a modified genetic algorithm

Abstract In this paper, a technology enabling the optimization of the topology of truss or frame structures with genetic algorithms is presented. It has been shown that due to a huge number of possible variants the global solution of similar problems with exhaustive search algorithms is feasible only for systems possessing small numbers of d.o.f. s (usually until 10 nodes). These problems can be solved in a reasonable time by genetic algorithms. The modified genetic algorithm for optimization of topology of truss systems is suggested, where the repair of the genotype, instead of some constraint is used. The solution of numerical examples with original software illustrates the efficiency of proposed technology; the global solutions are obtained in all cases.

MULTILEVEL OPTIMIZATION OF GRILLAGES

Abstract The mathematical models and solution algorithms for optimization of grillage-type foundations are presented. Optimization of grillage is based on optimization of separate beams comprising grillage. Minimising of maximum in absolute value vertical reactive force, bending moment, and reaction-bending moment together is sought in a separate beam. All these problems are non-linear, therefore are solved iteratively changing in each iteration the structure shape to a better neighbouring shape. Solution of this requires three steps: finite element analysis, analytical sensitivity analysis, and optimal re-design via linear mathematical programming. The main problem related to the proposed technique is to guarantee the global minimum solution. Engineering algorithm is suggested for avoidance of local minimum solutions: optimization procedure starts from quasi-optimal initial pile placement scheme, which is designed by a special expert system.

Parallel global optimization of foundation schemes in civil engineering

The important problem in civil engineering is obtaining optimal pile placement schemes for grillage-type foundations. The standard technique for solution of problem is application of local optimization methods, starting from initial guess obtained by means of engineering heuristics. We propose a new technology based on the use of global optimization algorithms, which are implemented as the “black-boxes”. In the real world applications the problems of interest involve till 500 design parameters. Therefore such problems can not be solved using one processor due to the huge CPU and computer memory requirements. We propose a parallel version of global optimization algorithm. The results of computational experiments for a number of practical problems are presented. Efficiency of suggested parallel algorithms is investigated and results for different clusters of workstations are presented.

One Application of the Parallelization Tool of Master–Slave Algorithms

The paper analyzes the performance of parallel global optimization algorithm, which is used to optimize grillage-type foundations. The parallel algorithm is obtained by using the automatic parallelization tool. We describe briefly the layer structure of the Master–Slave Template library and present a detailed mathematical formulation of the application problem. Experiments are done on the homogeneous computer cluster of 7 IBM machines RS6000. The results of experiments are presented.

Elastic Constants of Composite Materials by an Inverse Determination Method Based on A Hybrid Genetic Algorithm

A numerical method combining finite element analysis and a hybrid genetic algorithm is proposed to inversely determine the elastic constants from the vibration testing data. As verified from composite material specimens, the repeatability and accuracy of the proposed inverse determination method are con- firmed, and it also proves that the concept of effective elastic constants is workable. Moreover, three different sets of assumptions to reduce the five independent elastic constants to four do not make clear difference on the obtained results by the proposed method. In addition, to obtain robust values of the five elastic constants for a transversely isotropic material, it is recommended to use the out-of-plane Poissons ratio instead of the out-of-plane shear modulus as the fifth one.

OPTIMAL PLACEMENT OF PILES IN REAL GRILLAGES: EXPERIMENTAL COMPARISON OF OPTIMIZATION ALGORITHMS

The aim of the article is to choose algorithms suited for optimal placement of piles in real grillages by performing experimental comparison of different global optimization algorithms. The comparison includes several algorithms: random search, metaheuristics (simulated annealing and genetic algorithm) and local optimization combined with random search. The algorithms are compared using the results of optimization of pile placement schemes of 10 practical grillages of small-to-medium scale with data obtained from several design bureaus. The best results have been achieved with simulated annealing and nonlinear optimization algorithm NEWUOA combined with heuristic random search. http://dx.doi.org/10.5755/j01.itc.40.2.427

Identification of material properties of composite materials

Abstract Present paper describes the facilities of composite material properties identification technique using specimen vibration tests, genetic algorithms, finite elements analysis and specimen shape optimization. In identification process the elastic constants in a numerical model is updated so that the output from the numerical code fits the results from vibration testing. Main problem analysed in this paper is that Poissons ratio is the worst determined elastic characteristic due to its low influence on specimen eigenfrequencies. It is shown that it is possible to increase its influence by choosing specific test specimen characteristics (side aspect ratio, orthotropy angle, etc.) via optimization routine. In this paper are presented test results of some experiments wherein glass‐epoxy and carbon‐epoxy material properties were identified.

OPTIMISATION OF GRILLAGE-TYPE FOUNDATIONS

The mathematical models for optimisation of grillage-type foundations are presented. Minimising ofmaximum in absolute value vertical reactive force, bending moment, and reaction-bending momenttogether is sought employing methods of finite elements, analytical sensitivity analysis, andmathematical programming. Present models and computer code are implemented in the softwareMatrixFrame. Solutions of a number of problems demonstrate the validity of proposed algorithms.

Analysis and sensitivity analysis by computer algebra for a third-order plate finite element

Abstract It is shown that even a complicated 50 degree of freedom laminated plate element can be dealt with analytically without numerical integration. In addition to saving computer time, this has many advantages. The different aspects of the element behaviour, i.e. material dependence, orientational dependence and element geometry are separated by using the basic element matrices of the finite element method. This allows for simple sensitivity analysis in optimal design solutions and also simplifies the solution of material non-linear problems.

Some insights on the optimal schemes of tall guyed masts

AbstractThe article presents the technique for simultaneous topology, shape and sizing optimisation of tall guyed masts under wind loadings and self-weight using simulated annealing. The objective function is the mass of the mast structure including guys, while the set of design parameters may consist of up to 10 parameters of different nature. The constraints are assessed according to Eurocodes and include the local and global stability constraints, limitations on the slenderness in mast elements, and strength constraints. The proposed optimisation technique covers three independent parts: the optimisation algorithm, meshing pre-processor that yields computational scheme of mast depending on the design parameters, and finite element program evaluating the objective function and constraints via penalisation technique. As an example the results of optimisation of a typical 60 m tall guyed telecommunication mast with different antenna areas are presented. On the basis of these results, the authors try ascer...