• 한국구조물진단유지관리공학회 논문집
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• 제24권3호
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• pp.26-38
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• 2020

자기 충전형 콘크리트의 배합물 설계는 전형적인 다기준의사결정의 과정이다. 본 연구에서는 실험설계법과 반응표면법을 이용하여 SCC 배합물 전산 설계가 가능하도록 재료성능 및 비용모델을 생성하고, 요구조건을 반영한 여러 성능 사이의 상대적 중요도를 산정하여 가중 다목적 설계문제로 정식화하여 수치최적해를 계산함으로써 비용효율을 고려한 SCC최적설계를 수행하였다. 실험비용과 시간을 고려하여 SCC의 수많은 요구성능 중 압축강도, 철근충전성, 재료분리저항성, 비용정보 등을 다목적 최적화의 목적함수로 설정하였다. 재료경제성을 최적재료설계프로세스에 합리적으로 반영함으로써 경제적 콘크리트배합설계를 수행할 수 있었으며, 본 연구 결과 실험점 계획에서부터 최적해 산출에 이르는 과정을 객관적인 프로세스로 구성함으로써 콘크리트 범용 최적재료설계기술 및 전산화를 기대할 수 있다.

• 한국통신학회논문지
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• 제32권5B호
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• pp.295-303
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• 2007

An algorithm is proposed to seek a local optimal solution of the network utility maximization problem in a wireless mesh network, where the architecture being considered is an infrastructure/backbone wireless mesh network. The objective is to achieve proportional fairness amongst the end-to-end flows in wireless mesh networks. In order to establish the communication constraints of the flow rates in the network utility maximization problem, we have presented necessary and sufficient conditions for the achievability of the flow rates. Since wireless mesh networks are generally considered as a type of ad hoc networks, similarly as in wireless multi-hop network, the network utility maximization problem in wireless mesh network is a nonlinear nonconvex programming problem. Besides, the gateway/bridge functionalities in mesh routers enable the integration of wireless mesh networks with various existing wireless networks. Thus, the rate optimization problem in wireless mesh networks is more complex than in wireless multi-hop networks.

• 한국해양공학회지
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• 제23권3호
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• pp.1-5
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• 2009

It is necessary to develop an efficient optimization technique to optimize engineering structures that have given design spaces, discrete design values, and several design goals. In this study, an optimum algorithm based on the genetic algorithm was applied to the multi-object problem to obtain an optimum solution that simultaneously minimizes the structural weight and construction cost of panel blocks in ship structures. The cost model was used in this study, which includes the cost of adjusting the weld-induced deformation and applying the deformation control methods, in addition to the cost of the material and the welding cost usually included in the normal cost model. By using the proposed cost model, more realistic optimum design results can be expected.

• Membrane and Water Treatment
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• 제10권1호
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• pp.75-82
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• 2019

In a highly urbanized area, land availability is limited for the installation of space consuming stormwater systems for best management practices (BMPs), leading to the consideration of underground stormwater treatment devices connected to the stormwater pipe system. The configuration of a stormwater pipe network determines the hydrological and pollutant transport characteristics of the stormwater discharged through the pipe network, and thus should be an important design consideration for effective management of stormwater quantity and quality. This article presents a multi-objective optimization approach for designing a stormwater pipe network with on-line stormwater treatment devices to achieve an optimal trade-off between the total installation cost and the annual removal efficiency of total suspended solids (TSS). The Non-dominated Sorted Genetic Algorithm-II (NSGA-II) was adapted to solve the multi-objective optimization problem. The study site used to demonstrate the developed approach was a commercial area that has an existing pipe network with eight outfalls into an adjacent stream in Yongin City, South Korea. The stormwater management model (SWMM) was calibrated based on the data obtained from a subcatchment within the study area and was further used to simulate the flow rates and TSS discharge rates through a given pipe network for the entire study area. In the simulation, an underground stormwater treatment device was assumed to be installed at each outfall and sized proportional to the average flow rate at the outfall. The total installation cost for the pipes and underground devices was estimated based on empirical formulas using the flow rates and TSS discharge rates simulated by the SWMM. In the demonstration example, the installation cost could be reduced by up to 9% while the annual TSS removal efficiency could be increased by 4% compared to the original pipe network configuration. The annual TSS removal efficiency was relatively insensitive to the total installation cost in the Pareto-optimal solutions of the pipe network design. The results suggested that the installation cost of the pipes and stormwater treatment devices can be substantially reduced without significantly compromising the pollutant removal efficiency when the pipe network is optimally designed.

• 한국콘텐츠학회논문지
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• 제15권7호
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• pp.21-29
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• 2015

본 논문은 목적이 네 개 이상인 고도 다목적 문제(many-objective problem)에서의 의사 결정을 위한 새로운 이중(two-tier) 최적화 접근법을 제안한다. 목적의 개수가 증가할수록, 특히 네 개 이상부터는, 전체해(solution) 중에서 파레도 최적해(Parero-optimal solution)가 차지하는 비율이 기하급수적으로 증가한다. 그래서 일반 다목적 문제와는 달리, 의사 결정을 하는데 단순히 파레토 최적 해만을 찾는 것으로는 충분하지 않고, 찾은 파레토 최적 해들 중에서도 상대적으로 좀 더 선호하는 해들을 가려내는 것이 필요하다. 제안하는 접근법에서는 추가적인 최적화 단계를 추가함으로써 사용자의 선호도를 균형있게 반영하는 방향으로 파레토 최적해들을 찾는다. 이러한 2차 최적화는 관련된 2차 목적들을 수반하게 되는데, 2차 목적으로는 광역평가값과 혼잡 거리를 사용하였다. 광역평가값과 혼잡 거리는 각각 사용자의 선호도와 다양성을 대변하는 척도이다. 제안한 접근법의 우수성을 보이기 위해서는 잘 알려진 검증 함수들을 활용하는데, 같은 함수에 대해 제안한 접근법을 적용한 경우와 적용하지 않은 경우의 결과를 비교한다. 제안한 접근법을 적용함으로써 기존보다 사용자의 선호도를 잘 반영하면서 동시에 우수하고 다양한 의사 선택이 가능하다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.869-874
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• 2005

This paper proposes the Pareto artificial life algorithm for a multi-objective function optimization problem. The artificial life algorithm for a single objective function optimization problem is improved through incorporating the new method to estimate the fitness value fur a solution and the Pareto list to memorize and to improve the Pareto optimal set. The proposed algorithm is applied to the optimum design of a Journal bearing which has two objective functions. The Pareto front and the optimal solution set for the application are reported to present the possible solutions to a decision maker or a designer.

• Structural Engineering and Mechanics
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• 제43권6호
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• pp.795-821
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• 2012

The size and topology of geometrically nonlinear dome structures are optimized thereby minimizing both its entire weight & joint (node) displacements and maximizing load-carrying capacity. Design constraints are implemented from provisions of American Petroleum Institute specification (API RP2A-LRFD). In accordance with the proposed design constraints, the member responses computed by use of arc-length technique as a nonlinear structural analysis method are checked at each load increment. Thus, a penalization process utilized for inclusion of unfeasible designations to genetic search is correspondingly neglected. In order to solve this complex design optimization problem with multiple objective functions, Non-dominated Sorting Genetic Algorithm II (NSGA II) approach is employed as a multi-objective optimization tool. Furthermore, the flexibility of proposed optimization is enhanced thereby integrating an automatic dome generating tool. Thus, it is possible to generate three distinct sphere-shaped dome configurations with varying topologies. It is demonstrated that the inclusion of brace (diagonal) members into the geometrical configuration of dome structure provides a weight-saving dome designation with higher load-carrying capacity. The proposed optimization approach is recommended for the design optimization of geometrically nonlinear dome structures.

• Structural Engineering and Mechanics
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• 제34권5호
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• pp.597-609
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• 2010

A problem formulation and solution methodology for design optimization of laminated thin-walled composite beams of generic section is presented. Objective functions and constraint equations are given in the form of beam stiffness. For two different problems one for open section and the other for closed section, the objective function considered is bending stiffness about x-axis. Depending upon the case, one can consider bending, torsional and axial stiffnesses. The different search and optimization algorithm, known as Evolution Strategies (ES) has been applied to find the optimal fibre orientation of composite laminates. A multi-level optimization approach is also implemented by narrowing down the size of search space for individual design variables in each successive level of optimization process. The numerical results presented demonstrate the computational advantage of the proposed method "Evolution strategies" which become pronounced to solve optimization of thin-walled composite beams of generic section.

• Structural Engineering and Mechanics
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• 제70권3호
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• pp.367-380
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• 2019

The paper concerns topology and geometry optimization of statically determinate beams with arbitrary number of supports. The optimization problem is treated as a bi-criteria one, with the objectives of minimizing the absolute maximum bending moment and the maximum deflection for a uniform gravity load. The problem is formulated and solved using the Pareto optimality concept and the lexicographic ordering of the objectives. The non-dominated sorting genetic algorithm NSGA-II and the local search method are used for the optimization in the Pareto sense, whereas the genetic algorithm and the exhaustive search method for the lexicographic optimization. Trade-offs between objectives are examined and sets of Pareto-optimal solutions are provided for different topologies. Lexicographically optimal beams are found assuming that the maximum moment is a more important criterion. Exact formulas for locations and values of the maximum deflection are given for all lexicographically optimal beams of any topology and any number of supports. Topologies with lexicographically optimal geometries are classified into equivalence classes, and specific features of these classes are discussed. A qualitative principle of the division of topologies equivalent in terms of the maximum moment into topologies better and worse in terms of the maximum deflection is found.

• 한국생산제조학회지
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• 제21권6호
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• pp.954-960
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• 2012

Nowadays, rapidly changing and unstable global economic environments request a lot of roles to engineers. In this situation, product should be designed to make more profit by cost down and to satisfy distinguished performance comparing to other competitive ones. In this research, the optimization design of the industrial robot casting will be done. The weight and deflection have to be reduced as objective functions and stress has to be constrained under some constant value. To reduce time cost, CCD (Central Composite Design) will be used to make experimental design. And RSM (Response Surface Methodology) will be taken to make regression model for objective functions and constraint function. Finally, optimization will be done with Genetic Algorithm. In this problem, the objective functions are multiple, so NSGA-II which is brilliant and efficient for such a problem will be used. For the solution quality check, the diversity between Pareto solutions will be also checked.