• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2004.04a
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• pp.269-272
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• 2004

본 논문은 비선형 시스템의 퍼지모델을 위해 정보 granules 기반 퍼지 추론 시스템의 새로운 설계 및 이의 최적화를 제시한다. 퍼지모델은 주로 경험적 방법에 의해 추출되기 때문에 보다 구체적이고 체계적인 방법에 의한 동정 및 최적화 될 필요성이 요구된다. 일반적으로, 정보 granules는 근접성, 유사성 또는 기능성 둥에 인하여 서로 결합되는 요소(특히, 수치 데이터)의 실체이다. 제안된 퍼지 모델은 정보 데이터의 특성을 살리기 위해 HCM 클러스터링 방법에 의해 전반부/후반부 구조 및 파라미터 동정을 시행한다. 두 가지 형태의 퍼지 추론 방법은 간략 추론과 선형추론에 의해 수행되며 삼각형 멤버쉽 함수를 사용한다. 구축된 정보 granule 기반 퍼지 모델은 유전자 알고리즘을 이용하여 전반부 파라미터를 최적으로 동정한다. 제안된 비선형 모델의 성능평가는 수치적인 예를 통해 비교 평가한다.

• Journal of Korean Society of Steel Construction
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• v.18 no.2
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• pp.147-160
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• 2006

GA-based fuzzy optimum design algorithm incorporated with the refined plastic hinge analysis method is presented in this study. In the refined plastic hinge analysis method, geometric nonlinearity is considered by using the stability functions of the beam-column members. Material nonlinearity is also considered by using the gradual stiffness degradation model, which considers the effects of residual stresses, moment redistribution through the occurence of plastic hinges, and the geometric imperfections of the members. In the genetic algorithm, the tournament selection method and the total weight of the steel frames. The requirements of load-carrying capacity, serviceability, ductility, and constructabil ity are used as the constraint conditions. In fuzzy optimization, for crisp objective function and fuzzy constraint s, the tolerance that is accepted is 5% of the constraints. Furthermore, a level-cut method is presented from 0 to 1 at a 0 .2 interval, with the use of the nonmembership function, to solve fuzzy-optimization problems. The values of conventional GA optimization and fuzzy GA optimization are compared in several examples of steel structures.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.151-154
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• 2001

The pneumatic vibration isolation systems have been widely used in industry and laboratories, but the full mathematical analysis and nonlinear modeling techniques have not been reported yet, even while the nonlinear features of the pneumatic vibration isolation system decide the main characteristics. For instance, the orifice in a pneumatic vibration isolator has been traditionally considered as a simple viscous damper, which was too much simplified to explain the performance of the isolation system. In this paper, the nonlinear characteristics are considered for the orifice and chamber, etc. The numerical simulation is carried out by the MATLAB/Simulink software. From the analysis result, a clear trend of the nonlinear features is shown: the vibration transmissibility changes not only due to the excitation frequency but also due to the amplitude of the vibration excitation. Therefore various design parameters are optimally chosen for the vibration isolation system. The proposed methods show good compatibility between the analysis results and the experiments.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.8
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• pp.823-830
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• 2015

Structural optimization pursues improved performance of structures. Nowadays, structural optimization is applied to the design of huge and complex structures such as an airplane. As the number of the finite elements is increased, the analysis solution becomes more accurate. However, the design cost using the finite element model is significantly increased. The component mode synthesis method that is using the substructure synthesis method is frequently employed in order to keep the accuracy and reduce the cost. A new design method for structural optimization is proposed to reduce the design cost and to consider the dynamic effect of the structure. The proposed method reduces the design cost by applying the equivalent static loads on the design domain. An example of linear dynamic response optimization is solved and the efficiency of the proposed method is demonstrated.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.222-222
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• 2011

안전한 수질의 용수를 안정적으로 공급하기 위해 대단위 농업단지를 중심으로 농업용 관수로 건설이 고려되고 있는 환경에서 보다 경제적으로 관수로를 건설하기 위한 연구가 수행되었다. 관수로의 최적 관경설계는 전통적으로 비선형성을 고려하여야 하므로 수리학적 해석모형과 추계학적 탐색기법을 이용한 연구가 수행되었다. 그러나 본 연구에서는 비선형성을 가진 최적 관경시스템의 선형화를 시도한 후, 농지이용에 따른 대표작물에 대한 설계용수량을 사용한 농업용 관수로 관경 최적화를 시도하였다. 제안된 모형을 이용하여 농지의 크기, 작물의 형태, 동수경사선의 기울기에 따라 적합한 관경을 산정하였으며, 그 결과를 이용한 설계 표준화를 시도하였다. 표준화된 설계지침을 이용하면 향후 보다 편리하게 농업용 관수로를 설계할 수 있을 것으로 판단된다. 또한 실제 관수로에의 적용성을 입증하기 위해 실제 건설되는 농업단지의 설계에 제안된 모형을 이용하고, 시행착오법으로 산정된 결과와 비교하여 그 경제성을 입증하였다.

• Journal of Industrial Convergence
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• v.16 no.2
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• pp.33-39
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• 2018

This paper describes the design method of the linear PID controller and proposed the design method in the future. The first PID design method is to ensure phase margin and gain margin. This method guarantees stability by designing in the frequency domain. The second method is an internal model control method. This method is to design the PID controller using the parameters of the internal model after identifying the internal model for the control model. Therefore, this method has a strong disturbance characteristic. Finally, a proposed Cascade and smith-Predictor controller. The combination of the cascade controller and the smith-predator of this method is a controller structure that has two advantages: robust control and optimal control. This method can obtain the performance evaluation index as the optimal controller design method. This PID controller design method becomes the basis of the nonlinear method and is being continuously studied.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1391-1407
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• 1990

In this paper, optimization procedures are presented considering the static and dynamic constraints for laminated composite plate and hybrid laminated composite plate subject to concentrated load on center of the plates. Design variables for this problem are ply angle or ply thickness. Deflection, natural frequency and specific damping capacity are considered as constraints. Using a recursive linear programming method, the nonlinear optimization problems are solved. By introducing the design scaling factor, the number of iterations is reduced significantly. Composite plates could be designed optimally combined with FEM analysis under various conditions. In the optimization procedure, verification for both analysis and design of the laminated composite plates are compared with the results of the others. Various design results are presented for the laminated composite plates and hybrid laminated composite plates.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.1
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• pp.1-10
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• 2011

An optimization method is proposed for preform and billet shape designs in the forging process by using the Equivalent Static Loads (ESLs). The preform shape is an important factor in the forging process because the quality of the final forging is significantly influenced by it. The ESLSO is used to determine the shape of the preform. In the ESLSO, nonlinear dynamic loads are transformed to the ESLs and linear response optimization is performed using the ESLs. The design is updated in linear response optimization and nonlinear analysis is performed with the updated design. The examples in this paper show that optimization using the ESLs is useful and the design results are satisfactory. Consequently, the optimal preform and billet shapes which produce the desired final shape have been obtained. Nonlinear analysis and linear response optimization of the forging process are performed using the commercial software LS-DYNA and NASTRAN, respectively.

• Journal of Korean Society of Steel Construction
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• v.12 no.3 s.46
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• pp.317-328
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• 2000

The objective of the research is to develop an algorithm for the optimum design of two-dimensional braced steel frames using an advanced analysis, which considers both material and geometric nonlinearties. Since both nonlinearties are considered in analysis process, Optimum design algorithm which does not require to calculate K-factor is presented. A multi-level discrete optimization technique with two parameters that uses the information of structural system and separate member has been developed. The structural analysis is performed by the relined plastic-hinge method which is based on zero-length plastic hinge theory. Optimization problem are formulated by AISC-LRFD code. The feasibility, validity and efficiency of the developed algorithm is demonstrated by the results of the braced steel frame.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.5
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• pp.438-447
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• 2008

This study is focused on reliability based design optimization (RBDO) using moving least squares. A response surface is used to derive a limit-state equation for reliability based design optimization. Response surface method (RSM) with least square method (LSM) or Kriging will be used as a response surface. RSM is fast to make the response surface. On the other hand, RSM has disadvantage to make the response surface of nonlinear equation. Kriging can make the response surface in nonlinear equation precisely but needs considerable amount of computations. The moving least square method (MLSM) is made of both methods (RSM with LSM+Kriging). Numerical results by MLSM are compared with those by LMS in Rosenbrock function and six-hump carmel back function. The RBDO of engine duct of smart UAV is pursued in this paper. It is proved that RBDO is useful tool for aerospace structural optimal design problems.