• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.5
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• pp.263-270
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• 2021

In this study, a reliability-based design optimization of a 130-m class fixed-type offshore platform, to be installed in the North Sea, was carried out, while considering environmental, material, and manufacturing uncertainties to enhance its structural safety and economic aspects. For the reliability analysis, and reliability-based design optimization of the structural integrity, unity check values (defined as the ratio between working and allowable stress, for axial, bending, and shear stresses), of the members of the offshore platform were considered as constraints. Weight of the supporting jacket structure was minimized to reduce the manufacturing cost of the offshore platform. Statistical characteristics of uncertainties were defined based on observed and measured data references. Reliability analysis and reliability-based design optimization of a jacket-type offshore structure were computationally burdensome due to the large number of members; therefore, we suggested a method for variable screening, based on the importance of their output responses, to reduce the dimension of the problem. Furthermore, a deterministic design optimization was carried out prior to the reliability-based design optimization, to improve overall computational efficiency. Finally, the optimal design obtained was compared with the conventional rule-based offshore platform design in terms of safety and cost.

• Wind and Structures
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• v.27 no.1
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• pp.41-57
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• 2018

Concentrated Solar Photovoltaic (CPV) is a promising alternative to conventional solar structures. These solar tracking structures need to be optimized to be competitive against other types of energy production. In particular, the selection of the structural parameters needs to be optimized with regards to the dynamic wind response. This study aims to evaluate the effect of the main structural parameters, as selected in the preliminary design phase, on the wind response and then on the weight of the steel support structure. A parametric study has been performed where parameters influencing dynamic wind response are varied. The study is performed using a semi-deterministic time-domain wind analysis method. Unsteady aerodynamic model is applied for the shape of the CPV structure collector at different configurations in conjunction with a consistent mass-spring-damper model with the corresponding degrees of freedom to describe the dynamic response of the system. It is shown that, unlike the static response analysis, the variation of the peak wind response with many structural parameters is highly nonlinear because of the dynamic wind action. A steel structural optimization process reveals that close attention to structural and site wind parameters could lead to optimal design of CPV steel support structure.

• Journal of Magnetics
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• v.21 no.4
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• pp.537-543
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• 2016

Currently, an interest in electric vehicles (EVs) exhibited by automakers, government agencies and customers make it as more attractive research. This is due to carbon dioxide emitted by conventional combustion engine that worsens the greenhouse effect nowadays. Since electric motors are the core of EVs, it is a pressing need for researchers to develop advanced electric motors. As one of the candidates, switched flux machine (SFM) is initiated in order to cope with the requirement. This paper proposes a new alternate circumferential and radial flux (AlCiRaF) of permanent magnet switched flux machines (PMSFM) for light weight electric vehicles. Firstly, AlCiRaF PMSFM is compared with the conventional PMSFM based on some design restrictions and specifications. Then the design refinements techniques are conducted by using deterministic optimization method in order to improve preliminary performance of machine. Finally the optimized machine design has achieved maximum torque and power of 47.43 Nm and 12.85 kW, respectively, slightly better than that of conventional PMSFM.

• Proceedings of the KIEE Conference
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• 1996.07a
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• pp.238-240
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• 1996

This paper presents the optimum design of the slit type linear induction motor(LIM). For the analysis of the slit type LIM, as the boundary problem, the equivalent circuit is composed from the analysis method given the slit pitch boundary condition. Using the deterministic method and the stochastic method among the optimization methods, each of the optimum design variables is derived. The analysis result by the proposed method is compared with the experimental result.

• International Journal of Aeronautical and Space Sciences
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• v.2 no.2
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• pp.95-107
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• 2001

This paper is devoted to the parameter optimization of unmanned aerial vehicle's (UAV) flight control laws. Optimization procedure is based on the ideas of mixed $H_2/H_{\infty}$ control of multi-model plants. By using this approach, some partial $H_2$-terms defining the performance of nominal and parametrically perturbed Flight Control System (FCS) responses to deterministic command signals in stochastic atmosphere as well as $H_{\infty}$-terms defining robustness of the FCS can be incorporated in the composite cost function. Special penalty function imposed on the location of closed-loop system's poles keeps the speed of response and oscillatory properties for both nominal and perturbed FCS in reasonable limits. That is the reason why this procedure may provide reasonable trade-off between the performance and robustness of FCS that are very important especially for UAV. Its practical importance is illustrated by case studies of lateral and longitudinal control of small UAV.

• Korean Journal of Computational Design and Engineering
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• v.4 no.3
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• pp.259-268
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• 1999

In order to reduce the cost of product and save the processing time, optimal nesting of two-dimensional part is an important application in number of industries like shipbuilding and garment making. There have been many studies on finding the optimal solution of two-dimensional nesting. The problem of two-dimensional nesting has a non-deterministic characteristic and there have been various attempts to solve the problem by reducing the size of problem rather than solving the problem as a whole. Heuristic method and linearlization are often used to find an optimal solution of the problem. In this paper, theoretical and practical nesting algorithm for rectangular, circular and irregular shape of two-dimensional parts is proposed. Both No-Fit-Polygon and Minkowski-Sum are used for solving the overlapping problem of two parts and the dynamic programming technique is used for reducing the number search spae in order to find an optimal solution. Also, nesting designer's expertise is complied into the proposed algorithm to supplement the heuristic method.

• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.159-161
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• 1994

This paper presents a combined algorithm of simulated annealing and determinstic method which overcomes the defects of two methods and guarantees the fast convergence to the global optimum. This optimization method is applied to optimal design of Interior Permanent Magnet Synchronous Motor. And the result of the proposed algorithm is compared with that of simulated annealing alone.

• Journal of Electrical Engineering and Technology
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• v.7 no.1
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• pp.46-50
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• 2012

The current paper presents an effective methodology for assessing the reliability of electromagnetic designs when considering uncertainties of design variables. To achieve this goal, the reliability index approach based on the first-order reliability method is adopted to deal with probabilistic constraint functions, which are expressed in terms of random design variables. The proposed method is applied to three different designs of a superconducting magnetic energy storage system that corresponds to initial, deterministic, and roust designs. The validity and efficiency of the method is investigated with reference values obtained from Monte Carlo simulation.

• Proceedings of the KIEE Conference
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• 1993.07b
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• pp.932-934
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• 1993

Optimum pole shape is designed to increase the levitation and propulsion force of magnetic levitation systems. Evolution Strategy is introduced as optimization method. Evolution Strategy is random based non-deterministic method, developed by combining Genetic Algorithm with Simulated Annealing. Trasnsrapid-06, which was developed in Germany, is referenced model to be analyze. Design variables are nodes which determine fields pole shape of a linear synchronous motor, and the model analyzed by F.E.M.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.5
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• pp.589-599
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• 2013

The concept of robust optimization is based on Taguchi's method. Especially, robustness indices of objective function pursue an insensitive and conservative design when there are variations on design variables and parameters. To accomplish the purpose, various robustness indices on the objective function have been developed. However, it can be caused limitations to develop the robustness index, because there is difference between the Taguchi's method and robust optimization. In this paper, an investigation is performed to identify the characteristics and the drawbacks of the previous studies. To achieve the purpose, evaluations are conducted by using the examples which have both a deterministic optimum and a robust optimum. Moreover, a new viewpoint as well as a robustness index using a supremum value of the objective function is proposed based on the investigation.