• Structural Engineering and Mechanics
• /
• 제53권4호
• /
• pp.703-723
• /
• 2015

In this paper optimization of volume fraction distribution in a thick hollow cylinder with finite length made of two-dimensional functionally graded material (2D-FGM) and subjected to steady state thermal and mechanical loadings is considered. The finite element method with graded material properties within each element (graded finite elements) is used to model the structure. Volume fractions of constituent materials on a finite number of design points are taken as design variables and the volume fractions at any arbitrary point in the cylinder are obtained via cubic spline interpolation functions. The objective function selected as having the normalized effective stress equal to one at all points that leads to a uniform stress distribution in the structure. Genetic Algorithm jointed with interior penalty-function method for implementing constraints is effectively employed to find the global solution of the optimization problem. Obtained results indicates that by using the uniform distribution of normalized effective stress as objective function, considerably more efficient usage of materials can be achieved compared with the power law volume fraction distribution. Also considering uniform distribution of safety factor as design criteria instead of minimizing peak effective stress affects remarkably the optimum volume fractions.

• 산업경영시스템학회지
• /
• 제19권40호
• /
• pp.15-22
• /
• 1996

Methods to find an optimal solution that is the function of the design variables satisfying all constraints have been studied, there are still many difficulties to apply them to optimal design problems. A method to solve the above difficulties is developed by using Genetic Algorithms. but, several problems that conventional GAs are ill defined are application of penalty function that can be adapted to transform a constrained optimization problem into an unconstrained one and premature convergence of solution. Thus, we developed an modified GAs to solve this problems, and two examples are given to demonstrate the effectiveness of the methodology developed in this paper.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 추계학술대회논문집A
• /
• pp.699-704
• /
• 2000

The present paper deals with a multiobjective optimization method based on the co-evolutionary genetic strategy. The co-evolutionary strategy carries out the multiobjective optimization in such way that it optimizes individual objective function as compared with each generation's value while there are more than two genetic evolutions at the same time. In this study, the designs that are out of the given constraint map compared with other objective function value are excepted by the penalty. The proposed multiobjective genetic algorithms are distinguished from other optimization methods because it seeks for the optimized value through the simultaneous search without the help of the single-objective values which have to be obtained in advance of the multiobjective designs. The proposed strategy easily applied to well-developed genetic algorithms since it doesn't need any further formulation for the multiobjective optimization. The paper describes the co-evolutionary strategy and compares design results on the simple structural optimization problem.

• Journal of the Korean Statistical Society
• /
• 제36권1호
• /
• pp.57-76
• /
• 2007

Kriging is a nonparametric regression method used in geostatistics for estimating curves and surfaces for spatial data. It may come as a surprise that the Kriging estimator, normally derived as the best linear unbiased estimator, is also the solution of a particular variational problem. Thus, Kriging estimators can also be interpreted as generalized smoothing splines where the roughness penalty is determined by the covariance function of a spatial process. We build off the early work by Silverman (1982, 1984) and the analysis by Cox (1983, 1984), Messer (1991), Messer and Goldstein (1993) and others and develop an equivalent kernel interpretation of geostatistical estimators. Given this connection we show how a given covariance function influences the bias and variance of the Kriging estimate as well as the mean squared prediction error. Some specific asymptotic results are given in one dimension for Matern covariances that have as their limit cubic smoothing splines.

• 한국통신학회논문지
• /
• 제32권5C호
• /
• pp.530-535
• /
• 2007

변이공간영상(Disparity space image, DSI) 방법은 스테레오 영상간의 정합을 찾는 방법이다. 이 방법은 각 화소 단위로 변이값을 계산해 내는 장점이 있다. DSI 방법은 비용함수를 최소화시키는 정합을 찾는 방법이다. 이 비용함수에서 폐색영역비용 값과 정합 보상값을 경험적으로 정하여왔다. 본 논문에서는 변이공간영상 방법에서 폐색영역비용과 정합보상값이 영상 잡음과 물체와 배경간의 차이에 영향을 받는 것을 이론적으로 분석하였다.

• Advances in aircraft and spacecraft science
• /
• 제9권6호
• /
• pp.507-523
• /
• 2022

This study is aimed to accurately predict the vibration response of two types of functionally graded sandwich plates, one with FGM core and another with FGM face sheets. The gradation in FGM layer is quantified by exponential method. An efficient zig-zag theory is used and the zigzag impacts are established via a linear unit Heaviside step function. The present theory fulfills interlaminar transverse stress continuity at the interface and zero condition at the top and bottom surfaces of the plate for transverse shear stresses. Nine-noded C-0 FE having 8DOF/node is utilized throughout analysis. The present model is free from the obligation of any penalty function or post-processing technique and hence is computationally efficient. Numerical results have been presented on the free vibration behavior of sandwich FGM for different end conditions, lamination schemes and layer orientations. The applicability of present model is confirmed by comparing with published results. Several new results are also specified, which will serve as the benchmark for future studies.

• 대한기계학회논문집B
• /
• 제26권6호
• /
• pp.795-804
• /
• 2002

The optimal design code of an axial flow pump has been developed to determine geometric and fluid dynamic variables under hydrodynamic as well as mechanical design constraints. The design code includes the optimization of the complete radial distribution of the geometry by determining the coefficients of 2$^{nd}$ order polynomials to represent the three-dimensional geometry. The optimization problem has been formulated with a nonlinear multivariable objective function, maximizing the efficiency and stall margin, while minimizing the net positive suction head required. Calculation of the objective function is based on the mean streamline analysis and through-flow analysis using the present state-of-the-art model. The optimal solution is calculated using the penalty function method in which the genetic optimizer is employed. The optimized efficiency and design variables are presented in this paper as a function of non-dimensional specific speed in the range, 2$\leq$ $n_{s}$ $\leq$10. The results can be used in preliminary design of axial flow pumps.

• 전자공학회논문지T
• /
• 제36T권2호
• /
• pp.21-31
• /
• 1999

대규모 시스템 제어와 관련하여 몇 개의 부시스템으로 분할하여 처리하는 계층별 제어이론이 많이 연구되어 왔으며 특히 치수가 높은 대규모 비선형 시스템의 경우에 고차의 비선형 미분방정식을 동시에 적분을 해야하고 많은 계산량을 필요로 하므로 해를 구하기가 어려운 문제가 있다. 1980년대 Singh과 Hassan은 상호예측 알고리즘(two level prediction algorithm)을 제시한바 있고 이 방법은 비선형 대규모 시스템의 최적제어에 효과적이나 시스템 행렬 Q, R, S, H에 따라 제한된 최적화 구간에서만 성립되는 등 최적화 구간의 길이와 수렴성 여부가 행렬 값에 영향을 받는 알고리즘상의 단점이 있다. 본 연구에서는 수렴조건으로부터 평가함수에 구속조건(quadratic penalty term)을 부여하지 않는 새로운 개선된 알고리즘을 제시 적용하여 시스템 행렬 결정을 위한 과정 없이 수렴속도의 향상과 함께 최적의 수렴성 및 최적화 구간을 얻도록 했다. 분할된 비선형 시스템의 최적제어를 위해서는, 대수 반복연산만으로 2점 경계치 문제(two point boundary value problem)를 해결함으로써 기존의 수치 해석법에 비해 연산이 간단한 블록펄스 변환 방법을 사용해서 처리했다.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 2001년도 ICCAS
• /
• pp.44.2-44
• /
• 2001

This paper presents a new concept for controlling of under actuated robot manipulators with avoiding obstacles using switching computed torque method (SCTM). One fundamental approach of this algorithm is to use the partly stable controllers (PSCs) in order to fulfill the ultimate control objective. Here, we use genetic algorithms (GA)in order to employ the optimum control action for a given time frame with the available set of elemental controllers, depending on which links/variables are controlled, i.e. the selection of optimum switching sequence of the control actions. The proposed approach models links of the robot using evolving ellipses and then introduces a penalty scheme for the objective function of GA when it detects collisions. An under actuated robot manipulator, which has three detrees-of-freedom is taken into consideration so as to illustrate the design procedure. Simulation results show the e.ectiveness of the proposed method.

• ETRI Journal
• /
• 제41권5호
• /
• pp.619-625
• /
• 2019

In this paper, we propose an array pattern synthesis scheme using semidefinite programming (SDP) under array excitation power constraints. When an array pattern synthesis problem is formulated as an SDP problem, it is known that an additional rank-one constraint is generated inevitably and relaxed via semidefinite relaxation. If the solution to the relaxed SDP problem is not of rank one, then conventional SDP-based array pattern synthesis approaches fail to obtain optimal solutions because the additional rank-one constraint is not handled appropriately. To overcome this drawback, we adopted a bisection technique combined with a penalty function method. Numerical applications are presented to demonstrate the validity of the proposed scheme.