• 한국정밀공학회지
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• 제23권1호
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• pp.72-79
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• 2006

The objective of this work is to simulate the etching characteristics for the optimization on the etching process of Lead-Frame. The etching characteristics such as etching factor, etching uniformity were investigated under different the actual operating conditions. The correlation between the etching characteristics and the spray ones were analyzed to simulate the etching characteristics in the etching process. To improve the etching characteristics in the etching process, effects of the various operating conditions such as pressure, distance from nozzle tip, pipe pitch, and feed speed should be understood in detail. The spray characteristics obtained by experiment using PDA system were simulated by the Monte-Carlo simulation. The etching process model was coded by Java language. It was found that the spray characteristics were correlated with the etching ones and simulation results generally agreed well with the measured results of etching characteristics in the etching process of Lead-Frame. The optimal operating parameters were successfully found under variable conditions.

• Nuclear Engineering and Technology
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• 제24권3호
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• pp.236-242
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• 1992

노심의 과온도 Delta-T보호식에 설정된 동적보정함수들의 시정수 변화에 따른 특성이 조사되었으며, 출력운전 중 제어봉집합체의 비통제된 인출사고의 경우에 있어서 위 동적보정함수들의 과온도 Delta-T보호식에 대한 영향을 시스템 코드인 NLOOP및 노심열수력 코드인 PUMA를 사용하여 연구하였다. 위 연구를 바탕으로, 과온도 Delta-T 보호식의 동적보정함수에 대한 최적화 절차가 제시되었으며, 고리 3&4 호기 친이노심의 경우에 대해 최적화된 동적보정함수를 구하였다. 그 결과, 시스템의 최소 DNBR에 가장 영향을 줄 수 있는 동적보정함수는 노심평균온도에 대한 lead-lag항으로 판명되었으며, 이때 최적화된 시정수값은 lead시간 21초, lag시간 4초로 나타났다. 이러한 동적보정함수의 최적화를 통하여 안전한계치를 변경하지 않고서도 노심의 운전영역을 개선할 수 있을 것으로 기대된다.

• 한국산학기술학회논문지
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• 제18권2호
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• pp.254-260
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• 2017

사회기반시설물은 적절한 수명관리를 통해 경제적이고 안전한 구조성능을 유지한다. 일반적으로 최적화 기법을 적용하여, 유지보수의 시점과 방법을 결정하게 되는데, 이 적용에 있어서 단일 목적함수만을 고려하기 보다는 다수의 목적함수를 동시에 고려하는 것이 보다 합리적인 의사결정을 유도한다. 최근까지 수명관리에 관련한 연구는 생애주기 비용 최소화 또는 구조성능 최대화와 관련한 목적함수를 적용하여 왔으며, 새로운 확률론적 구조성능 및 안전성 평가 기법을 이용하여 다양한 형태의 목적함수를 개발/적용하고 있다. 이러한 다수의 목적함수를 동시에 고려하는 다목적 최적화 기반 사회기반시설물 수명관리가 최근 국내외에서 많이 적용되고 있다. 하지만, 수명관리 최적화를 위한 목적함수의 개수가 증가함에 따라 신뢰성있는 결과를 얻기 위해서는 많은 계산시간이 소요되며, 특히 확률론적 계산을 위한 시뮬레이션 기법이 적용되는 목적함수의 경우 계산시간은 더욱 증가하게 된다. 또한, 목적함수의 개수 증가에 따라 계산결과의 차수가 증가하기 때문에 이를 시각화하고 나아가 의사결정에 어려움이 발생한다. 따라서, 본 논문에서는 다목적 최적화 문제의 계산된 결과를 바탕으로 한 의사결정의 효율성 향상을 위해 최소 필수 목적함수를 구별하는 목적감소 기법을 적용하여 콘크리트 교량 상판의 수명관리에 대한 연구를 수행하였으며, 최초 4개의 목적함수가 2개까지 감소되는 결과를 보여준다.

• Nuclear Engineering and Technology
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• 제47권3호
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• pp.380-387
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• 2015

A lead slowing-down spectrometer (LSDS) system is a promising nondestructive assay technique that enables a quantitative measurement of the isotopic contents of major fissile isotopes in spent nuclear fuel and its pyroprocessing counterparts, such as $^{235}U$, $^{239}Pu$, $^{241}Pu$, and, potentially, minor actinides. The LSDS system currently under development at the Korea Atomic Energy Research Institute (Daejeon, Korea) is planned to utilize a high-flux ($>10^{12}n/cm^2{\cdot}s$) neutron source comprised of a high-energy (30 MeV)/high-current (~2 A) electron beam and a heavy metal target, which results in a very intense and complex radiation field for the facility, thus demanding structural shielding to guarantee the safety. Optimization of the structural shielding design was conducted using MCNPX for neutron dose rate evaluation of several representative hypothetical designs. In order to satisfy the construction cost and neutron attenuation capability of the facility, while simultaneously achieving the aimed dose rate limit (< $0.06{\mu}Sv/h$), a few shielding materials [high-density polyethylene (HDPE)eBorax, $B_4C$, and $Li_2CO_3$] were considered for the main neutron absorber layer, which is encapsulated within the double-sided concrete wall. The MCNP simulation indicated that HDPE-Borax is the most efficient among the aforementioned candidate materials, and the combined thickness of the shielding layers should exceed 100 cm to satisfy the dose limit on the outside surface of the shielding wall of the facility when limiting the thickness of the HDPE-Borax intermediate layer to below 5 cm. However, the shielding wall must include the instrumentation and installation holes for the LSDS system. The radiation leakage through the holes was substantially mitigated by adopting a zigzag-shape with concrete covers on both sides. The suggested optimized design of the shielding structure satisfies the dose rate limit and can be used for the construction of a facility in the near future.

• Journal of Welding and Joining
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• 제30권6호
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• pp.113-119
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• 2012

Ultrasonic bonding is the novel packaging method for flip-chip with high yield and low-temperature bonding. The bonding module is a core part of the bonding machine, which can transfer the ultrasonic energy into the bonding spot. In this paper, we propose topology optimization technique which can make new design of boding modules due to the constraints on resonance frequency and mode shapes. The designed bonding module using topology optimization was fabricated in order to evaluate the bonding performance and reliable operation during the continuous bonding process. The actual production models based on the proposed design satisfied the target frequency range and ultrasonic power. The bonding test was performed using flip-chip with lead-free Sn-based bumps, the results confirmed that the bonding strength was sufficient with the designed bonding modules. Also the performance degradation of the bonding module was not observed after the 300-hour continuous process with bonding conditions.

• Industrial Engineering and Management Systems
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• 제6권2호
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• pp.136-145
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• 2007

The selection of suppliers and the determination of order quantities to be placed with those suppliers are important decisions in a supply chain. In this research, a non-linear mixed integer programming model is presented to select suppliers and determine the order quantities. The model considers the purchasing cost which takes into account quantity discount, the cost of transportation, the fixed cost for establishing suppliers, the cost for holding inventory, and the cost of receiving poor quality parts. The capacity constraints for suppliers, quality and lead-time requirements for the parts are also taken into account in the model. Since the purchasing cost, which is a decreasing step function of order quantities, introduces discontinuities to the non-linear objective function, it is not easy to employ traditional optimization methods. Thus, a heuristic algorithm, called particle swarm optimization (PSO), is used to find the (near) optimal solution. However, PSO usually generates initial solutions randomly. To improve the PSO solution quality, a heuristic procedure is proposed to find an initial solution based on the average unit cost including transportation, purchasing, inventory, and poor quality part cost. The results show that PSO with the proposed initial solution heuristic provides better solutions than those with PSO algorithm only.

• Structural Engineering and Mechanics
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• 제46권1호
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• pp.19-37
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• 2013

The optimum design of base isolation system considering model parameter uncertainty is usually performed by using the unconditional response of structure obtained by the total probability theory, as the performance index. Though, the probabilistic approach is powerful, it cannot be applied when the maximum possible ranges of variations are known and can be only modelled as uncertain but bounded type. In such cases, the interval analysis method is a viable alternative. The present study focuses on the bounded optimization of base isolation system to mitigate the seismic vibration effect of structures characterized by bounded type system parameters. With this intention in view, the conditional stochastic response quantities are obtained in random vibration framework using the state space formulation. Subsequently, with the aid of matrix perturbation theory using first order Taylor series expansion of dynamic response function and its interval extension, the vibration control problem is transformed to appropriate deterministic optimization problems correspond to a lower bound and upper bound optimum solutions. A lead rubber bearing isolating a multi-storeyed building frame is considered for numerical study to elucidate the proposed bounded optimization procedure and the optimum performance of the isolation system.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2006년도 정기 학술대회 논문집
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• pp.299-306
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• 2006

Using a level set method and topological derivatives, a topological shape optimization method that is independent of an initial design is developed for linearly elastic structures. In the level set method, the initial domain is kept fixed and its boundary is represented by an implicit moving boundary embedded in the level set function, which facilitates to handle complicated topological shape changes. The 'Hamilton-Jacobi (H-J)' equation and computationally robust numerical technique of 'up-wind scheme' lead the initial implicit boundary to an optimal one according to the normal velocity field while minimizing the objective function of compliance and satisfying the constraint of allowable volume. Based on the asymptotic regularization concept, the topological derivative is considered as the limit of shape derivative as the radius of hole approaches to zero. The required velocity field to update the H -J equation is determined from the descent direction of Lagrangian derived from optimality conditions. It turns out that the initial holes is not required to get the optimal result since the developed method can create holes whenever and wherever necessary using indicators obtained from the topological derivatives. It is demonstrated that the proper choice of control parameters for nucleation is crucial for efficient optimization process.

• 한국군사과학기술학회지
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• 제25권2호
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• pp.125-134
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• 2022

Recently, there are an increased the number of reports on the misuse or malicious use of an UAS. Thus, many researchers are studying on defense schemes for UAS by developing or improving C-UAS sensor technology. However, the wrong placement of sensors may lead to a defense failure since the proper placement of sensors is critical for UAS defense. In this study, a multi-object optimization model for C-UAS sensor placement in an air base is proposed. To address the issue, we define two objective functions: the intersection ratio of interested area and the minimum detection range and try to find the optimized placement of sensors that maximizes the two functions. C-UAS placement model is designed using a NSGA-II algorithm, and through experiments and analyses the possibility of its optimization is verified.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제18권7호
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• pp.2027-2046
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• 2024

Reconfigurable Intelligent Surface (RIS) is an innovative technique to precisely control the phase of incident signals with the help of low-cost passive reflective elements. It shows excellent potential in the sixth generation of mobile communication systems, which not only extends wireless coverage but also boosts channel capacity. Considering that multipath propagation and a high number of antennas are involved in RIS in assisted mega multiple-input multiple-output (MIMO) systems, it suffers from severe channel fading and multipath effects, which in turn lead to signal instability and degradation of transmission performance. To overcome this obstacle, this essay suggests an improved gradient optimization algorithm to dynamically and optimally adjust the phase of the reflective elements to counteract channel fading and multipath effects as a strategy. In order to overcome the optimization problem of falling into local minima, this paper proposes an adaptive learning rate algorithm based on Adagrad improvement, which searches for the global optimal solution more efficiently and improves the robustness of the optimization algorithm. The suggested technique helps to enhance the estimate of channel efficiency of RIS-assisted large MIMO systems, according to simulation results.