• Journal of Mechanical Science and Technology
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• 제18권9호
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• pp.1590-1603
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• 2004

In this study the optimization of plate-fin type heat sink with vortex generator for the thermal stability is performed numerically. The optimum solutions in the heat sink are obtained when the temperature rise and the pressure drop are minimized simultaneously. Thermal performance of heat sink is influenced by the heat sink shape such as the base-part fin width, lower-part fin width, and basement thickness. To acquire the optimal design variables automatically, CFD and mathematical optimization are integrated. The flow and thermal fields are predicted using the finite volume method. The optimization is carried out by means of the sequential quadratic programming (SQP) method which is widely used for the constrained nonlinear optimization problem. The results show that the optimal design variables are as follows; B$_1$=2.584 mm, B$_2$=1.741 mm, and t=7.914 mm when the temperature rise is less than 40 K. Comparing with the initial design, the temperature rise is reduced by 4.2 K, while the pressure drop is increased by 9.43 Pa. The relationship between the pressure drop and the temperature rise is also presented to select the heat sink shape for the designers.

• Advances in aircraft and spacecraft science
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• 제4권4호
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• pp.467-486
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• 2017

A method for decoupling reliability based design optimization problem into a set of deterministic optimization and performing a reliability analysis is described. The inner reliability analysis and the outer optimization are performed separately in a sequential manner. Since the outer optimizer must perform a large number of iterations to find the optimized shape and size of structure, the computational cost is very high. Therefore, during the course of this research, new multilevel reliability optimization methods are developed that divide the design domain into two sub-spaces to be employed in an iterative procedure: one of the shape design variables, and the other of the size design variables. In each iteration, the probability constraints are converted into equivalent deterministic constraints using reliability analysis and then implemented in the deterministic optimization problem. The framework is first tested on a short column with cross-sectional properties as design variables, the applied loads and the yield stress as random variables. In addition, two cases of curvilinearly stiffened panels subjected to uniform shear and compression in-plane loads, and two cases of curvilinearly stiffened panels subjected to shear and compression loads that vary in linear and quadratic manner are presented.

• Journal of Mechanical Science and Technology
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• 제15권9호
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• pp.1257-1267
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• 2001

For efficient mechanical system optimization, a new two-point approximation method is presented. Unlike the conventional two-point approximation methods such as TPEA, TANA, TANA-1, TANA-2 and TANA-3, this introduces the shifting level into each exponential intervening variable to avoid the lack of definition of the conventional exponential intervening variables due to zero-or negative-valued design variables. Then a new quadratic approximation whose Hessian matrix has only diagonal elements of different values is proposed in terms of these shifted exponential intervening variables. These diagonal elements are determined in a closed form that corrects the typical error in the approximate gradient of the TANA series due to the lack of definition of exponential type intervening variables and their incomplete second-order terms. Also, a correction coefficient is multiplied to the pre-determined quadratic term to match the value of approximate function with that of the previous point. Finally, in order to show the numerical performance of the proposed method, a sequential approximate optimizer is developed and applied to solve six typical design problems. These optimization results are compared with those of TANA-3. These comparisons show that the proposed method gives more efficient and reliable results than TANA-3.

• Structural Engineering and Mechanics
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• 제62권4호
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• pp.465-475
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• 2017

Photovoltaic (PV) panels are used in high-rise buildings to convert solar energy to electricity. Due to the considerable energy consumption of high-rise buildings, applying PV technology is of great significance to energy saving. In the application of PV panels, one of the most important construction issues is the connection of the PV panel with the main structures. One major difficulty of the connection design is that the PV panel connection consists of two separate components with coupling and indeterminate dimension. In this paper, the gap element is employed in these two separated but coupled components, i.e., hook and catch. Topology optimization is applied to optimize and design the cross-section of the PV panel connection. Pareto optimization is conducted to operate the optimization subject to multiple load scenarios. The initial design for the topology optimization is determined by the common design specified by the Technical Code for Glass Curtain Wall Engineering (JGJ 102-2003). Gravity and wind load scenarios are considered for the optimization and numerical analysis. Post analysis is conducted for the optimal design obtained by the topology optimization due to the manufactory requirements. Generally, compared with the conventional design, the optimized connector reduces material use with improved structural characteristics.

• Structural Engineering and Mechanics
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• 제76권6호
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• pp.799-821
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• 2020

The optimum design of truss structures is one of the significant categories in structural optimization that has widely been applied by researchers. In the present study, new mathematical programming called Consistent Approximation (CONAP) method is utilized for the simultaneous optimization of the size and shape of truss structures. The CONAP algorithm has already been introduced to optimize some structures and functions. In the CONAP algorithm, some important parameters are designed by employing design sensitivities to enhance the capability of the method and its consistency in various optimum design problems, especially structural optimization. The cross-sectional area of the bar elements and the nodal coordinates of the truss are assumed to be the size and shape design variables, respectively. The displacement, allowable stress and the Euler buckling stress are taken as the design constraints for the problem. In the proposed method, the primary optimization problem is replaced with a sequence of explicit sub-problems. Each sub-problem is efficiently solved using the sequential quadratic programming (SQP) algorithm. Several truss structures are designed by employing the CONAP method to illustrate the efficiency of the algorithm for simultaneous shape and size optimization. The optimal solutions are compared with some of the mathematical programming algorithms, the approximation methods and metaheuristic algorithms those reported in the literature. Results demonstrate that the accuracy of the optimization is improved and the convergence rate speeds up.

• 한국CDE학회논문집
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• 제12권5호
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• pp.376-381
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• 2007

The geometric configuration in the weight-reduced structure is very required to be started from the conceptual design with low cost, high performance and quality. In this point, a structural-topological shape concerned with conceptual design of structure is important. The method used in this paper combines three optimization techniques, where the shape and physical dimensions of the structure and material distribution are hierachically optimized, with the maximum rigidity of structure and lightweight.

• 한국CDE학회논문집
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• 제11권4호
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• pp.265-272
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• 2006

For the design and analysis of 3D object featuring complexity and irregularity in shape, sectional digital images measured by an industrial CT scanner are employed to generate a finite element model with uniform voxels. The voxel model plays a key role in developing an integrated reverse engineering system including geometric modeling, simulation and optimization. Design examples applied to topology optimization show that the proposed approach can provide a remarkable reduction in time cost at the conceptual and detail design stages.

• 한국강구조학회 논문집
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• 제12권5호통권48호
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• pp.503-513
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• 2000

본 연구에서는 구조물의 최적설계문제를 다를 때 나타나는 퍼지성을 고려하는 동시에 대립되는 기준들을 다루기 위해 중요도를 적용 유전자알고리즘 및 퍼지이론에 의한 이산형의 다목적 함수를 갖는 트러스구조물의 최적화를 시도하는 다목적 이산화 최적화 프로그램을 개발하였다. 그리고 개발된 프로그램을 적용하여 10부재철골트러스에 대한 설계 예를 들어 비교 고찰하였다. 본 연구를 통해 평면트러스구조물에대한 응력해석 및 최적설계가 일률적으로 처리될 수 있는 통합 시스템화된 퍼지-유전자알고리즘에 의한 다목적최적 구조설계가 가능하게 되었다. 특히 일반최적설계에서 처리되지 않는 불확실한 제약조건에 대한 경우에 대하여도 피지이론을 도입함으로써 가능하게 되어 보다 구조물의 합리적인 최적설계가 가능하게 되었다.

• 한국전산유체공학회지
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• 제5권2호
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• pp.55-63
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• 2000

In this paper, the numerical study has been done for the improvement of the superdetonative ram accelerator performance and for the design optimization of the system. The objective function to optimize the premixture composition is the ram tube length, required to accelerate projectile from initial velocity V/sub 0/ to target velocity V/sub e/. The premixture is composed of H₂, O₂, N₂ and the mole numbers of these species are selected as design variables. RSM(Response Surface Methodology) which is widely used for the complex optimization problems is selected as the optimization technique. In particular, to improve the non-linearity of the response and to consider the accuracy and the efficiency of the solution, design space stretching technique has been applied. Separate sub-optimization routine is introduced to determine the stretching position and clustering parameters which construct the optimum regression model. Two step optimization technique has been applied to obtain the optimal system. With the application of stretching technique, we can perform system optimization with a small number of experimental points, and construct precise regression model for highly non-linear domain. The error compared with analysis result is only 0.01% and it is demonstrated that present method can be applied to more practical design optimization problems with many design variables.

• 대한기계학회논문집A
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• 제27권8호
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• pp.1353-1362
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• 2003

This paper considers a simultaneous optimization problem of structure and control systems. The problem is generally formulated as a non-convex optimization problem for the design parameters of mechanical structure and controller. Therefore, it is not easy to obtain the global solutions for practical problems. In this paper, we parameterize all design parameters of the mechanical structure such that the parameters work in the control system as decentralized static output feedback gains. Using this parameterization, we have formulated a simultaneous optimization problem in which the design specification is defined by the Η$_2$and Η$\_$$\infty$/ norms of the closed loop transfer function. So as to lead to a convex problem we approximate the nonlinear terms of design parameters to the linear terms. Then, we propose a convex optimization method that is based on linear matrix inequality (LMI). Using this method, we can surely obtain suboptimal solution for the design specification. A numerical example is given to illustrate the effectiveness of the proposed method.