• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.8
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• pp.1818-1827
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• 2004

This paper carried out numerical calculation about the directivity synthesis problem in two dimension of adaptive ultrasonic transducers. Adaptive system for directivity synthesis is constructed by multi-electrode array on the surface of only one piezoelectric ceramic plate combined with optimal algorithm. In order to realize the desired directivity that is established arbitrarily, the optimal vibrational displacement is calculated by optimal algorithm (DFP method). Secondly, the optimal voltage of electrodes which is correspond to the calculated vibrational displacement is calculated used by finite element method and DFP method. And, the vibration analysis in two dimension of piezoelectric transducer carried out by means of finite element method.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.04a
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• pp.136-141
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• 1997

Rotary compressor is one of the most useful mechanism that is widely applied in refrigeration and air-conditioning systems. That is due to character of rotary compressor -compact, simple etc.While there is a lot of strong points, there is room for improvement because it is composed of many parts which have wear problem, friction losses and leakage. In this paper, theoretical investigation about vane and slot parts at which we observe severe wear is carried out. Through the study of lubrication, the behavior of vane during one cycle can be predicted and the cause of wear at slot will be discovered. To solve the equations, fletcher-powell method is applied. The result of analysis show that vane bevell to the slot part with discharge port before rotation of shaft is 180 degree and bevell to the slot part with suction port after 180 degree. The motion of vane is divided 3 mode that depends on behavior of vane. This paper define the first mode when vane tilt to the compression chamber, the second mode when vane tilt to the suction chamber, and the third mode when vane move straightway.

• The Journal of the Acoustical Society of Korea
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• v.20 no.5
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• pp.61-68
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• 2001

In this paper, an analytical method and a difference approximation method to calculate the gradient of an objective function have been applied to the directivity optimization in an adaptive ultrasonic transducer which is combined with a point source array and an optimization algorithm (DFP method). To compare these two methods, quasi-ideal .beam with a beam width and direction specified are chosen as the desired directivity. As the numerical results, the difference approximation method shows better suppressive capacity of side lobe level, good stability in the convergence processing, faster convergence speed and excellent adaptability compared with the analytical method.

• Magazine of the Korean Society of Agricultural Engineers
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• v.38 no.2
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• pp.75-86
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• 1996

The formulas for estimating the constants of storage function model including K and TL for runoff analysis and a distributed storage function model are discussed in this study. First, the relations between parameters of the storage function model and the kinematic runoff model are theoretically examined, and then optimum constants of storage function model are obtained by the Standardized Davidson-Fletcher-Powell (SDFP) method. Through this analysis, theoretical formulas were obtained as $K = 0.63 {\alpha} KsB{^0.6}$ and $T_{L}=0.11 {\alpha} KsB{^0.6} r{^0.4} {_e}$, which are difficult to use practically because of the unclarified definition of shape factors. From a practical point of view, empirical formula were derived as $K=15.6{^0.3} {_m}$ and $T_{L}=2.1B{^0.36} {_m} {_e}/r{^0.4} {_e}$ for applied watersheds. The proposed formulas are verified for several recoded floods at a few points of watersheds. It is also found that the distributed storage function. can be applied to flood runoff analysis using the new formulas aboved mentioned.

• Structural Engineering and Mechanics
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• v.17 no.5
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• pp.611-626
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• 2004

On the basis of a structural analysis of radial gate (i.e. Tainter gate), the current paper focuses on weight minimization according to the location of the arms on a radial gate. In spite of its economical significance, there are hardly any previous studies on the optimum design of radial gate. Accordingly, the present study identifies the optimum position of the support point for a radial gate that guarantees the minimum weight satisfying the strength constraint conditions. This study also identifies the optimum position for 2 or 3 radial arms with a convex cylindrical skin plate relative to a given radius of the skin plate curvature, pivot point, water depth, ice pressure, etc. These optimum designs are then compared with previously constructed radial gates. Local genetic and hybrid-type genetic algorithms are used as the optimum tools to reduce the computing time and enhance the accuracy. The results indicate that the weights of the optimized radial gates are appreciably lower than those of previously constructed gates.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.710-710
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• 2012

구형펄스모형(Rectangular Pulse Model)에서 반영하지 못하는 강우의 군집특성을 잘 반영하는 NSRPM(Neyman-Scott Rectangular Pulse Model) 강우생성 모형은 수자원 분야에 널리 쓰이고 있다. 일반적으로 NSRPM의 5개의 매개변수를 추정하는 최적화기법으로 DFP(Davidon-Fletcher-Powell)과 유전자알고리즘(Genetic Algorithm)을 사용하고 있다. 그러나 DFP는 주어진 초기 값에 따라 민감하며 각 반복 단계마다 헤시안행렬(Hessian Matrix)을 계산하여야 하며 추정된 전체의 해가 국지해에 수렴 할 수 있는 단점이 있다. 유전자 알고리즘을 DFP와 다르게 헤시안 행렬을 사용하지 않고 최적화를 할 수 있다는 장점이 있으나 시간이 오래 걸리는 단점이 있다. 이에 본 연구에서는 이러한 단점을 보완, 강화 하기위해서 최적화 기법으로 반복 단계마다 미분계산이 필요하지 않고 빠른 속도로 계산이 가능한 Nelder-Mead 알고리즘 이용하여 NSRPM매개변수를 추정하고 정확도를 비교하였다. 표 1은 각 기법을 이용하여 추정된 매개변수를 이용하여 생성한 강우의 통계특성과 관측된 통계특성의 상대오차를 나타낸 것이다. 괄호 안 숫자는 중첩되지 않는 누적시간을 나타낸다. 상대오차는 다음과 같다(식 1). 분석결과 Nelder-Mead 기법이 1시간의 평균, 공분산과 6시간 분산 등 전체적으로 GA, DFP보다 높은 정확도를 보였다.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.327-327
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• 2018

돌발홍수, 집중호우 등 강우가 발생 원인되는 자연재해에 효과적으로 대응하기 위한 연구가 활발히 이루어지고 있으나 강우의 시공간 변동성과 발생과정의 복잡한 물리과정으로 인해 강우 추정에 한계를 가진다. 일반적으로 강우 추정은 물리적, 추계학적 모형을 이용하며 추계학적 모형의 점과정(point process)을 이용하여 강우를 생산한다. 추계학적 강우 모형은 관측 강우의 시간 스케일, 강우발생 빈도, 강우 강도 등 강우 구조의 특성을 반영 할 수 있다는 장점을 가지고 있으나 생산되는 강우의 구조가 추정되는 매개변수에 크게 의존한다는 점에서 실제 강우에 적합한 매개변수 추정이 중요하다. 본 연구에서는 낙동강 유역내에 있는 20개의 강우관측 지점을 대상으로 1973년-2017년까지의 강우 관측자료를 수집하였으며 추계학적 강우생성 모형으로 점과정을 이용하는 추계학적 강우생성 모형인 NSRPM(Neymann-Scott rectangular pulse model)을 선정하였다. NSRPM모형의 매개변수를 추정하기위한 최적기법으로 DFP(Davidon-Fletcher-Powell), GA(genetic algorithm), Nelder-Mead, DE(differential evolution)를 이용하여 추정된 매개변수의 적합성을 분석하고 지역특성을 고려한 매개변수 추정 기법을 제시하였다. 추정된 모형의 매개변수를 분석한 결과 DE와 Nelder-Mead 기법이 높은 적합성을 보였으며 DFP, GA기법이 상대적으로 낮은 적합도를 보였다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.14 no.3
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• pp.267-276
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• 2001

On the basis of structural analysis of the radial gate(that is, Tainter gate), this paper focuses on the optimization of the moment distribution according to the location of the arm of the radial gate. In spite of its importance from economical view point, we could hardly find the study on the optimum design of radial gate. Accordingly, the present study identifies the optimum section modulus for a radial arm along with the optimum position for 2 of 3 radial arms with a convex cylindrical skin plate relative to a given radius of the skin plate curvature, pivot point, water depth, ice pressure, etc. These optimum measurements are then compared with previously constructed radial gates. The results indicate that the optimum section modulus vague for a radial arm was appreciably smaller than the previously constructed examples.