Partner: János Lógó

University of Technology and Economics, Budapest (HU)

Recent publications
1.Tauzowski P., Lógó J., Pintér E., Parametric Study on the Element Size Effect for Optimal Topologies, Periodica Polytechnica Civil Engineering, ISSN: 0553-6626, DOI: 10.3311/PPci.11551, Vol.62, No.1, pp.267-276, 2018
2.Błachowski B.D., Tauzowski P., Lógó J., Modal Approximation Based Optimal Design of Dynamically Loaded Plastic Structures, Periodica Polytechnica Civil Engineering, ISSN: 0553-6626, DOI: 10.3311/PPci.11016, Vol.61, No.4, pp.987-992, 2017
Abstract:

The purpose of this study is to present an optimal design procedure for elasto-plastic structures subjected to impact loading. The proposed method is based on mode approximation of the displacement field and assumption of constant acceleration of impacted structure during whole time of deformation process until the plastic displacement limit is reached. Derivation of the method begins with the application of the principle of conservation of linear momentum, followed by determination of inertial forces. The final stage of the method utilizes an optimization technique in order to find a minimum weight structure. Eventually, effectiveness and usefulness of the proposed method is demonstrated on the example of a planar truss structure subjected to dynamic loading caused by a mass impacting the structure with a given initial velocity.

Keywords:

structural dynamics, optimal design, elasto-plastic structures, short-time dynamic loading

Affiliations:
Błachowski B.D.-IPPT PAN
Tauzowski P.-IPPT PAN
Lógó J.-University of Technology and Economics, Budapest (HU)
3.Lógó J., Movahedi Rad M., Knabel J., Tauzowski P., Reliability based design of frames with limited residual strain energy capacity, , Vol.55, No.1, pp.13-20, 2011
Abstract:

The aim of this paper is to create new type of plastic limit design procedures where the influence of the limited load carrying capacity of the beam-to-column connections of elasto-plastic steel (or composite) frames under multi-parameter static loading and probabilistically given conditions are taken into consideration. In addition to the plastic limit design to control the plastic behaviour of the structure, bound on the complementary strain energy of the residual forces is also applied. If the design uncertainties (manufacturing, strength, geometrical) are taken into consideration at the computation of the complementary strain energy of the residual forces the reliability based extended plastic limit design problems can be formed. Two numerical procedures are elaborated. The formulations of the problems yield to nonlinear mathematical programming which are solved by the use of sequential quadratic algorithm.

Keywords:

reliability analysis, limit analysis, residual strain energy, Monte Carlo simulation, optimal design

Affiliations:
Lógó J.-University of Technology and Economics, Budapest (HU)
Movahedi Rad M.-University of Technology and Economics, Budapest (HU)
Knabel J.-IPPT PAN
Tauzowski P.-IPPT PAN
4.Movahedi Rad M., Lógó J., Knabel J., Tauzowski P., Reliability based limit design of frames with limited residual strain energy capacity, Proceedings in Applied Mathematics and Mechanics, ISSN: 1617-7061, DOI: 10.1002/pamm.200910323, Vol.9, pp.709-710, 2009
Abstract:

The aim of this paper is to take into consideration the influence of the limited load carrying capacity of the connections on the plastic limit state of elasto-plastic steel (or composite) framed structures under multi-parameter stochastic loading and probabilistically given conditions. In addition to the plastic limit design to control the plastic behaviour of the structure, bound on the complementary strain energy of the residual forces is also applied. This bound has significant effect for the load parameter. If the design uncertainties (manufacturing, strength, geometrical) are expressed by the calculation of the complementary strain energy of the residual forces a reliability based extended limit design problem is formed. The formulations of the problems yield to nonlinear mathematical programming which are solved by the use of sequential quadratic algorithm. The bi-level optimization procedure governed by the reliability index calculation.

Keywords:

limit analysis of frames, reliability analysis, optimization

Affiliations:
Movahedi Rad M.-University of Technology and Economics, Budapest (HU)
Lógó J.-University of Technology and Economics, Budapest (HU)
Knabel J.-IPPT PAN
Tauzowski P.-IPPT PAN

Conference papers
1.Blachowski B., Tauzowski P., Lógó J., Elasto-Plastic Topology Optimization Under Stochastic Loading Conditions, EngOpt, 6th International Conference on Engineering Optimization, 2018-09-17/09-19, Lizbona (PT), DOI: 10.1007/978-3-319-97773-7_7, pp.70-79, 2018
Abstract:

Optimal topologies obtained for structures subjected to deterministic loading can be sensitive to loading variations in terms of both magnitude and direction. Therefore, in this study we consider problem of topology optimization for structures subjected to probabilistic loading. The proposed method applies basic findings from probability theory, which allow to transform the original problem of topology optimization under single probabilistic loading into analogous problem of topology optimization under multiple deterministic loading cases. After recalling the theoretical background of the method,’ its effectiveness is demonstrated on an examples of cantilever structure subjected to horizontally oriented load with randomly varying angle of action.

Keywords:

Topology optimization, Stochastic load, Elastoplastic FE analysis

Affiliations:
Blachowski B.-IPPT PAN
Tauzowski P.-IPPT PAN
Lógó J.-University of Technology and Economics, Budapest (HU)

Conference abstracts
1.Blachowski B., Tauzowski P., Logo J., Topology optimization of elastoplastic structures: Stress intensity driven formulation and functor-oriented implementation, CST2018, The Thirteenth International Conference on Computational Structures Technology 2018, 2018-09-04/09-06, Sitges, Barcelona (ES), No.0090, pp.1-3, 2018
Abstract:

This study is devoted to a practical method for topology optimization of elastoplastic structures subjected to stress constraints. Instead of the classical compliance minimization problem the aim of this work is to find a minimum weight structure, which is able to carry given load and the corresponding stresses do not exceed an allowable limit. The general form of the problem is based on the classical limit design formulations of plasticity. The proposed method finds optimal structure in an iterative way using only stress intensity distribution and doesn’t require computing of any gradients or sensitivities.
Our method starts with determining representative stresses in every quadrilateral finite element. At first an elastoplastic analysis is performed to obtain stress values in four Gaussian points, then by the use of von Misses criterion and these stress values the resultant stress is calculated. Next, having obtained stress intensity distribution within the structure we apply penalization to avoid stress concentration issues. Finally, the material is removed proportionally to the stress intensities of individual finite elements. The above mentioned procedure is repeated until limit load capacity is achieved for a given loading vector. The checkerboard problem is solved by means of design filter. Two benchmark problems have been selected as illustrative examples. They are: cantilever and simply supported beam. For these examples parametric studies on different length to height ratios and support patterns are conducted. Additionally, the results of topology optimization for different values of filter radius and penalty parameter are presented.
Finally, efficient computer implementation based on functor-oriented programming is discussed. It is demonstrated how Functor and Template-based programming can be utilized to create versatile Finite Element environment. Within this environment computation of all element matrices and loading vectors can be called in the same way, this in turn allows for implementation of effective aggregation procedure.

Keywords:

topology optimization, minimum-weight design, functor-oriented programming, stress constraints

Affiliations:
Blachowski B.-IPPT PAN
Tauzowski P.-IPPT PAN
Logo J.-University of Technology and Economics, Budapest (HU)
2.Tauzowski P., Blachowski B., Lógó J., Functor-Oriented Finite Element Programming with Application to Structural Topology Optimization, SolMech 2018, 41st SOLID MECHANICS CONFERENCE, 2018-08-27/08-31, Warszawa (PL), No.P076, pp.490-491, 2018
Abstract:

The subject of this study is an efficient approach to the development of a finite element framework, which is intended to be used for solving a variety of problems in computational solid mechanics. One of such problems, recently becoming an active field of research, is topology optimization of structures made of elastic-plastic materials. For finding the optimal topology of real, practical and complex structures the knowledge of a number of numerical algorithms is required, to mention a few: modification of finite element meshes, aggregation of tangent stiffness matrices, or direct and iterative solvers. The classical computer implementation of the original Classical Optimality Criteria method (COC) of the topology optimization problem given by Bendsoe and Sigmund is relatively simple and contains 99 lines of code in the MATLAB language. However, it assumes that there exists only a single loading case, single displacement (compliance) constraint, the material is linearly elastic and the optimal topology can be found using the so-called Solid Isotropic Material with Penalization (SIMP) algorithm, which is based on the original COC method. In reality, engineers face a slightly different problem. They need to find the topology of a minimum weight structure subjected to multiple loading cases, made of an elasto-plastic material, and with a limit on stresses. The above mentioned SIMP approach may not lead to an optimal solution.

Keywords:

functor-oriented programming, topology optimization, elastoplastic FE analysis

Affiliations:
Tauzowski P.-IPPT PAN
Blachowski B.-IPPT PAN
Lógó J.-University of Technology and Economics, Budapest (HU)