• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.2
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• pp.609-618
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• 2017

This paper presents the quantitative evaluation method for technologies acquired from the defense offset program. We firstly deduced the consideration in development by gathering the opinions of 128 experts by conducting a survey. Next, we made up an additional 49 experts for developing a performance management system of the offset program. The management system covered 4 technology fields which are defense R&D, depot maintenance, performance improvement, and manufacturing. The development procedure was composed of 4 parts: setting-up of work process, defining performance indicators, calculating weighted values of each indicator, and devising quantitative method. The results of this research could be used for enhancing the effectiveness of the offset program in 3 ways: establishing a systematic work process after acquisition of technology in offset program, establishing the positive feedback architecture by providing incentives to superior institute or company which is appointed through quantitative performance evaluating, and publicizing and promoting quantified outstanding performances for contributing to advance the offset program.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.3
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• pp.866-872
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• 2010

In this paper, we developed a digital soldering station based on PID controller, which supply stable power by controlling the current of heater of soldering iron. The proposed system designed PID controller to converge quickly to the set up temperature by user, and regain the lost of heat by external factors quickly. PID controller, designed by Ziegler-Nichols' tuning method, decides triac's trigger timing using setting temperature and present temperature to control the phase of AC 24V power that supply to the heater. Also, we give the function that shows present temperature and setting temperature of iron, and working time by graphic LCD. And during the rest time, we decided the power saving and extension of iron tip by dropping to the optimal temperature. Two experiments had implemented in $25^{\circ}C$ laboratory to confirm the performance of proposed method. The first experiment took 12sec, 13sec, 16sec, 18sec, reaching to $200^{\circ}C$, $300^{\circ}C$, $400^{\circ}C$, $480^{\circ}C$ respectively which result showed shorten of rising time than previous method. In the loading experiment of $300^{\circ}C$, $400^{\circ}C$, $480^{\circ}C$ steady state showed temperature drop of $3.8^{\circ}C$, $4.1^{\circ}C$, $4.5^{\circ}C$ which result showed the low temperature deviation than previous method.

• Journal of Korea Water Resources Association
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• v.51 no.1
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• pp.19-33
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• 2018

This study proposed a rainfall-runoff model for the purpose of real-time flood warning in urban basins. The proposed model was based on the shot noise process, which is expressed as a sum of shot noises determined independently with the peak value, decay parameter and time delay of each sub-basin. The proposed model was different from other rainfall-runoff models from the point that the runoff from each sub-basin reaches the basin outlet independently. The model parameters can be easily determined by the empirical formulas for the concentration time and storage coefficient of a basin and those of the pipe flow. The proposed model was applied to the total of three rainfall events observed at the Jungdong, Guro 1 and Daerim 2 pumping stations to evaluate its applicability. Summarizing the results is as follows. (1) The unit response function of the proposed model, different from other rainfall-runoff models, has the same shape regardless of the rainfall duration. (2) The proposed model shows a convergent shape as the calculation time interval becomes smaller. As the proposed model was proposed to be applied to urban basins, one-minute of calculation time interval would be most appropriate. (3) Application of the one-minute unit response function to the observed rainfall events showed that the simulated runoff hydrographs were very similar to those observed. This result indicates that the proposed model has a good application potential for the rainfall-runoff analysis in urban basins.

• Journal of Biomedical Engineering Research
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• v.21 no.5
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• pp.441-448
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• 2000

방출단층영상 재구성을 위한 최대우도 기대값최대화(maximum likelihood expectation maximization, MLEM) 방법은 영상 획득과정을 통계학적으로 모델링하여 영상을 재구성한다. MLEM은 일반적으로 사용하여 여과후역투사(filtered backprojection)방법에 비해 많은 장점을 가지고 있으나 반복횟수 증가에 따른 발산과 재구성 시간이 오래 걸리는 단점을 가지고 있다. 이 논문에서는 이러한 단점을 보완하기 위해 계산시간을 현저히 단축시킨 배열된부분집합 기대값최대화(ordered subsets expectation maximization. OSEM)에 Gibbs 선행치인 membrance (MM) 또는 thin plate(TP)을 첨가한 OSEM-MAP (maximum a posteriori)을 구현함으로써 알고리즘의 안정성 및 재구성된 영상의 질을 향상시키고자 g나다. 실험에서 알고리즘의 수렴시간을 가속화하기 위해 투사 데이터를 16개의 부분집합으로 분할하여 반복연산을 수행하였으며, 알고리즘의 성능을 비교하기 위해 소프트웨어 모형(원숭이 뇌 자가방사선, 수학적심장흉부)을 사용한 영상재구성 결과를 제곱오차로 비교하였다. 또한 알고리즘의 사용 가능성을 평가하기 위해 물리모형을 사용하여 PET 기기로부터 획득한 실제 투사 데이터를 사용하였다.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.74-74
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• 2016

복잡한 지형에서 컴퓨터를 이용한 물리적 기반 수치모의는 합리적인 시간내에 연산을 완료하기 위해 대개 큰 연산장비 들을 요구한다. 더욱이 모의되는 현상이 시간단계마다 갱신되어지는 동역학적 현상에 기반된 비정상상태일 때 연산성능은 고려되어지는 가장 중요한 주제가 될 수 있다. 연산 시간을 줄이기 위한 가장 널리 이용되는 전략중의 하나는 적절한 수의 프로세서를 이용하는 병렬 기법이다. 최근 들어 연산속도를 가속화하기 위해 다수의 코어를 이용한 OpenMP 와 MPI 기법들이 병렬해석기법으로 대두되었고 그래픽 연산장치를 이용한 병렬처리 해석기법도 소개되고 있다. 본 연구에서는 중앙연산장치를 이용한 병렬 해석기법을 이용하여 제내지 침수해석의 적용성을 검토하고 그 결과을 비교하였다. 본 연구를 위해 OpenMP 병렬기법을 이용하여 확산파 침수해석 프로그램의 원시코드를 재작성하여 가상 및 실제 유역에 적용하였다. 해석결과는 분산메모리 병렬해석 기법인 MPI를 도입한 모형의 결과와 비교되었다. OpenMP를 도입한 모형과 MPI를 도입한 경우 유량 및 수심의 경우 오차 허용 한계내에 수렴되어 만족되었으나 그러나 연산 속도의 경우 두 기법간의 자료의 저장 방법 차이로 인해 차이를 나타내었다. 가상 유역에 적용된 결과로 검토된 각 기법의 증속(speedup) 효과는 MPI의 경우 4 코어를 이용하였을 때 최고 2.62 배 정도에 도달하는 것으로 나타났다. OpenMP 를 적용한 경우 2.87 배 정도로 나타나 OpenMP 를 이용하였을 때 증속효과가 조금 더 뛰어났다. 이는 두 기법의 메모리 저장방식의 차이로 인해 자료의 전송량과 전송 시간이 적은 OpenMP 를 도입한 모형에서 MPI 모형 보다 상대적으로 뛰어난 결과를 나타내었다. 실제 유역의 적용을 위해 상대적으로 우수한 증속결과를 나타낸 OpenMP를 도입한 모형을 Malpasset 댐 붕괴 유역에 적용하였다. 적용된 요소의 수는 각각 45254, 11352 개로 비교적 많은 요소를 가진 하류지역에 적용하여 병렬효과를 극대화하고자 하였다. 적용결과 두 경우 모두 병렬 해석 기법을 도입한 모형에서 유속과 침수심 등은 순차적 모형과 동일한 값을 나타내었으나 증속효과로 인한 연산시간은 순차적 모형에서 8.57 배로 나타나 병렬 모형의 상대적으로 빠른 연산속도를 판단할 있었다. 위의 적용결과를 통해 계산 요소들이 많은 2 차원 해석의 경우 기존의 단일 코어를 이용한 순차적 해석은 장시간에 걸치 연산시간으로 인해 작업효율이 낮아지는 결과를 발생시킬 수 있으며 병렬 해석을 도입할 경우 주어진 컴퓨터 자원를 효율적으로 이용가능하여 합리적인 연산시간으로 연산결과를 얻는 것이 가능하여 반복적 통계 기법/Ensemble 해석 등을 이용한 종합적 해석이 좀 더 실용적으로 이루어 질 수 있을 것이라고 판단되었다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.4
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• pp.215-222
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• 2019

The heat conduction problem with discontinuous material coefficients generally consists of the conservative equation, boundary condition, and interface condition, which should be additionally satisfied in the solution procedure. This feature often makes the development of new numerical schemes difficult as it induces a layered singularity in the solution fields; thus, a special approximation is required to capture the singular behavior. In addition to the approximation, the construction of a total system of equations is challenging. In this study, a wedge function is devised for enriching the approximation, and the interface condition itself is embedded in the moving least squares(MLS) derivative approximation to consistently satisfy the interface condition. The heat conduction problem is then discretized in a strong form using the developed derivative approximation, which is named as the interface immersed MLS difference method. This method is able to efficiently provide a numerical solution for such interface problems avoiding both numerical quadrature as well as extra difference equations related to the interface condition enforcement. Numerical experiments proved that the developed numerical method was highly accurate and computationally efficient at solving the heat conduction problem with interfacial jump as well as the problem with a geometrically induced interfacial singularity.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.2
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• pp.211-218
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• 2021

This paper addressed the problems of controlling the coupled pitch-roll motions in a marine vessel exposed to the regular waves in the longitudinal and transversal directions. Stabilization of the pitch and roll motions can be regarded as the essential task to ensure the safety of a ship's navigation. One of the important features in the pitch-roll motions is the resonance phenomena, which result in unexpected large responses in terms of pitch and roll modes in some specific conditions. Besides, owing to its inherent characteristics of coupled combination and nonlinearity of restoring terms, the vessel shows various dynamical behaviors according to the system parameters, especially in the pitch responses. Above all, it can be seen that suppression of pitch rate remains the most significant challenge to overcome for ship maneuvering safety studies. To secure the stable upright condition, a quasi-sliding mode control scheme is employed to reduce the undesirable pitch and roll responses as well as chattering elimination. The Lyapunov theory is adopted to guarantee the closed stability of the pitch-roll system. Numerical simulations demonstrate the effectiveness of the control scheme. Finally, the control goals of state convergences and chattering reduction are effectively realized through the proposed control synthesis.

• Journal of Navigation and Port Research
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• v.46 no.6
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• pp.491-500
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• 2022

It has been noted that an accurate estimation of wind loads on offshore structures such as an FLNG (Liquefied Natural Gas Floating P roduction Storage Offloading Units, LNG FPSOs) with a large topside plays an important role in the safety design of hull and mooring system. Therefore, the present study aims to develop a computational model for estimating the wind load acting on an FLNG. In particular, it is the sequel to the previous research by the author. The numerical computation model in the present study was modified based on the previous research. Numerical analysis for estimating wind loads was performed in two conditions for an interval of wind direction (α), 15° over the range of 0° to 360°. One condition is uniform wind speed and the other is the NPD model reflecting the wind speed profile. At first, the effect of sand-grain roughness on the speed profile of the NPD model was studied. Based on the developed NPD model, mesh convergence tests were carried out for 3 wind headings, i.e. head, quartering, and beam. Finally, wind loads on 6-degrees of freedom were numerically estimated and compared by two boundary conditions, uniform speed, and the NPD model. In the present study, a commercial RANS-based viscous solver, STAR-CCM+ (ver. 17.02) was adopted. In summary, wind loads in surge and yaw from the wind speed profile boundary condition were increased by 20.35% and 34.27% at most. Particularly, the interval mean of sway (45° < α <135°, 225° < α < 315°) and roll (60° < α < 135°, 225° < α < 270°) increased by 15.60% and 10.89% against the uniform wind speed (10m/s) boundary condition.

• Smart Media Journal
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• v.11 no.2
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• pp.77-83
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• 2022

The neuromorphic architecture uses a spiking neural network (SNN) model to derive more accurate results as more spike values are accumulated through inference experiments. When the inference result converges to a specific value, even if the inference experiment is further performed, the change in the result is smaller and power consumption may increase. In particular, in an AI-based IoT environment, power consumption can be a big problem. Therefore, in this paper, we propose a technique to reduce the power consumption of AI-based IoT by reducing the inference time by adjusting the inference image exposure time in the neuromorphic architecture environment. The proposed technique calculates the next inferred image exposure time by reflecting the change in inference accuracy. In addition, the rate of reflection of the change in inference accuracy can be adjusted with a coefficient value, and an optimal coefficient value is found through a comparison experiment of various coefficient values. In the proposed technique, the inference image exposure time corresponding to the target accuracy is greater than that of the linear technique, but the overall power consumption is less than that of the linear technique. As a result of measuring and evaluating the performance of the proposed method, it is confirmed that the inference experiment applying the proposed method can reduce the final exposure time by about 90% compared to the inference experiment applying the linear method.

• The Journal of Korean Institute of Next Generation Computing
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• v.13 no.4
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• pp.29-39
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• 2017

Various electronic warfare situations drive the need to develop an integrated electronic warfare simulator that can perform electronic warfare modeling and simulation on radar threats. In this paper, we analyze the components of a simulation system to reversely model the radar threats that emit electromagnetic signals based on the parameters of the electronic information, and propose a method to gradually maintain the reverse extrapolation model of RF threats. In the experiment, we will evaluate the effectiveness of the incremental model update and also assess the integration method of reverse extrapolation models. The individual model of RF threats are constructed by using decision tree, naive Bayesian classifier, artificial neural network, and clustering algorithms through Euclidean distance and cosine similarity measurement, respectively. Experimental results show that the accuracy of reverse extrapolation models improves, while the size of the threat sample increases. In addition, we use voting, weighted voting, and the Dempster-Shafer algorithm to integrate the results of the five different models of RF threats. As a result, the final decision of reverse extrapolation through the Dempster-Shafer algorithm shows the best performance in its accuracy.