Yazar "Nigdeli, Sinan Melih" seçeneğine göre listele

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    Advanced energy-based analyses of trusses employing hybrid metaheuristics
    (Wiley, 2019) Bekdas, Gebrail; Kayabekir, Aylin Ece; Nigdeli, Sinan Melih; Toklu, Yusuf Cengiz
    Total potential optimization using metaheuristic algorithm (TPO/MA) is an alternative method in structural analyses, and it is a black-box application for nonlinear analyses. In the study, an advanced TPO/MA using hybridization of several metaheuristic algorithms is investigated to solve large-scale structural analyses problems. The new generation algorithms considered in the study are flower pollination algorithm (FPA), teaching learning-based optimization, and Jaya algorithm (JA). Also, the proposed methods are compared with methodologies using classic and previously used algorithms such as differential evaluation, particle swarm optimization, and harmony search. Numerical investigations were carried out for structures with four to 150 degrees of freedoms (design variables). It has been seen that in several runs, JA gets trapped into local solutions. For that reason, four different hybrid algorithms using fundamentals of JA and phases of other algorithms, namely, JA using Levy flights, JA using Levy flights and linear distribution, JA with consequent student phase, and JA with probabilistic student phase (JA1SP), are developed. It is observed that among the variants tried, JA1SP is seen to be more effective on approaching to the global optimum without getting trapped in a local solution.
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    Analysis of Plane-Stress Systems via Total Potential Optimization Method Considering Nonlinear Behavior
    (Asce-Amer Soc Civil Engineers, 2020) Toklu, Yusuf Cengiz; Kayabekir, Aylin Ece; Bekdas, Gebrail; Nigdeli, Sinan Melih; Yucel, Melda
    As an alternative structural analysis method, total potential optimization using metaheuristic algorithms (TPO/MAs) has been demonstrated to be very effective, especially in nonlinear cases, for trusses and trusslike systems such as tensegric structures and cable networks. A recent study showed that TPO/MAs also can be applied successfully to plane-stress problems with linear constitutive equations. The present study enlarged the application area of TPO/MAs to the analysis of plates for plane-stress cases with nonlinear stress-strain equations. A relevant formulation was developed and used to solve five problems. Because TPO/MAs can be applied by using different metaheuristic algorithms, a number of them, some hybrid, were used, and they were compared among themselves and with finite-element solutions. The final example was a tunnel problem with 150 nodes, i.e., with 265 unknowns. This problem also was solved via hybrid algorithms. Several proposals for future research are listed. (c) 2020 American Society of Civil Engineers.
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    A metaheuristic-based method for analysis of tensegrity structures
    (Wiley, 2024) Bekdas, Gebrail; Ocak, Ayla; Nigdeli, Sinan Melih; Toklu, Yusuf Cengiz
    Tensegrity systems are construction system that offers solutions for lighter designs compared with a standard truss system consisting of tension and compression elements. Due to their structure, they are recommended in the design of space structures due to the use of lighter and easy-to-assemble structural elements such as cables, ropes, and similar to provide the desired durability. In this study, energy minimization was carried out to solve the structural element displacements. It is expected to reduce the total potential energy of the system with minimization. By minimizing the total potential energy of the tensegrity system models, the displacement of each building element is found for the equilibrium condition. Tensegrity models were analyzed by minimizing energy via the adaptive harmony search (AHS) algorithm. In this research, two distinct tensegrity structure specimens were employed. One comprised a cantilever beam, while the other adopted a cyclic model, forming eight equal octagons from eight nodes at both the base and the top. Additionally, an examination was conducted on a two-layer iteration of the cyclic model. The method is robust for both space and planar tensegrity structures, allowing the determination of deformed shapes under various loads without design assumptions. The TPO/MA method demonstrates superiority in handling nonlinear and barely stable systems, as evidenced by examples illustrating its efficacy in maintaining structural form under increasing loads and challenging conditions.
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    Tranfer function amplitude minimization for structures with tuned mass dampers considering soil-structure interaction
    (Elsevier Sci Ltd, 2019) Bekdas, Gebrail; Kayabekir, Aylin Ece; Nigdeli, Sinan Melih; Toklu, Yusuf Cengiz
    The optimum tuned mass damper (TMD) parameters rely on the superstructure's natural frequency, which, in turn, depends on the soil condition under the structure. Thus, the consideration of soil conditions in determination of the optimum TMD parameters is necessary. In this study, a methodology is proposed for the determination of TMD parameters considering soil-structure interaction. The objective function in the study is the acceleration transfer function. For the stochastic optimization problem, several metaheuristic algorithms, namely harmony search, flower pollination algorithm, teaching, learning based optimization, Jaya algorithm and two new versions of it are employed. Numerical experiments on methodology are presented for a 40-story structure considering soil-structure interaction. It is shown through applications that, especially for soft soils, the use of TMDs is an effective way to damp structural vibrations resulting from seismic sources and consideration of the base stiffness is effective on the optimum TMD parameters. Comparisons among the results obtained through different metaheuristic algorithms are also given.