• Nuclear Engineering and Technology
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• 제55권2호
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• pp.756-768
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• 2023

Neutron transport calculations are extremely challenging due to the high computational cost of large and complex problems. A multilevel octree grid algorithm (MLTG) of discrete ordinates method was developed to improve the modeling accuracy and simulation efficiency on 3-D Cartesian grids. The Balakovo-3 VVER-1000 neutron dosimetry benchmark is calculated to verify and validate this numerical technique. A simplified S₂ synthetic acceleration is used in the MLTG calculation method to improve the convergence of the source iterations. For the triangularly arranged fuel pins, we adopt a source projection algorithm to generate pin-by-pin source distributions of hexagonal assemblies. MLTG provides accurate geometric modeling and flexible fixed source description at a lower cost than traditional Cartesian grids. The total number of meshes is reduced to 1.9 million from the initial 9.5 million for the Balakovo-3 model. The numerical comparisons show that the MLTG results are in satisfactory agreement with the conventional S_N method and experimental data, within the root-mean-square errors of about 4% and 10%, respectively. Compared to uniform fine meshing, approximately 70% of the computational cost can be saved using the MLTG algorithm for the Balakovo-3 computational model.

• 한국의학물리학회:학술대회논문집
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• 한국의학물리학회 2003년도 제27회 추계학술대회
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• pp.41-41
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• 2003

Purpose: Even if the wedge filter is widely used for the radiation therapy to modify the photon beam intensity, the wedged photon beam dose calculation is not so easy. Radiation therapy planning systems (RTPS) have been used the empirical or semi-analytical methods such as attenuation method using wedge filter parameters or wedge filter factor obtained from measurement. However, these methods can cause serious error in penumbra region as well as in edge region. In this study, we propose the dose calculation algorithm for wedged field to minimize the error especially in the outer beam region. Materials and Method: Modified intensity by wedge filter was calculated using tissue-maximum ratio (TMR) and scatter-maximum ratio (SMR) of wedged field. Profiles of wedged and non-wedged direction was also used. The result of new dose calculation was compared with measurement and the result from attenuation method. Results: Proposed algorithm showed the good agreement with measurement in the high dose-gradient region as well as in the inner beam region. The error was decreased comparing to attenuation method. Conclusion: Although necessary beam data for the RTPS commissioning was increased, new algorithm would guarantee the improved dose calculation accuracy for wedged field. In future, this algorithm could be adopted in RTPS.

• 전자공학회논문지S
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• 제35S권12호
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• pp.69-76
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• 1998

본 논문에서는 ICP (Iterative Closest Point) 알고리즘을 이용한 영상등록에서의 회전 성분 신뢰도를 추정할 수 있는 행렬을 유도하 였다. ICP 알고리즘 결과의 신뢰도는 영상등록을 하려는 입력 물체의 모양에 따라 다르다. 보통 원통과 같은 어떤 축에 대한 회전체보 다는 더 복잡하고 두드러진 특징이 많은 물체일수록 신뢰도가 높은 결과를 얻게 된다. 본 논문에서는 ICP 알고리즘으로 구한 값의 신뢰도를 점으로 표현되는 입력물체에서의 각 점의 위치와 법선 벡터에 대한 식으로 나타내었다. 입력물체에 잡음이 들어갔을 때, 이로 인한 ICP 결과의 오차를 제시한 신뢰도를 이용해 추정하였다. 마지막으로 타원체 합성영상에 대한 신뢰도와 잡음이 들어갔을 때의 ICP 결과의 오차를 컴퓨터 모의실험으로 비교 분석하여 이론치와 부합되는 것을 보였다.

• 한국전산유체공학회지
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• 제17권1호
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• pp.44-53
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• 2012

Immersed boundary method(IBM) is a numerical scheme proposed to simulate flow field around complex objectives using simple Cartesian grid system. In the previous studies, the IBM has mostly been implemented to fractional step method based Navier-Stokes solvers. In this study, we implement the IBM to an incompressible Navier-Stokes solver which uses SIMPLE algorithm. The weight coefficients of the bi-linear and quadratic interpolation equations were formulated by using only geometric information of boundary to reconstruct velocities near IB. Flow around 2D circular cylinder at Re=40 and 100 was solved by using these formulations. It was found that the pressure buildup was not observed even when the bi-linear interpolation was adopted. The use of quadratic interpolation made the predicted aerodynamic forces in good agreement with those of previous studies. For an analysis of moving boundary, we smulated an oscillating circular cylinder with Re=100 and KC(Keulegan-Carpenter) number of 5. The predicted flow fields were compared with experimental data and they also showed good agreements.

• 한국농공학회지
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• 제36권2호
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• pp.88-95
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• 1994

This paper is to evaluate the applicability of neural networks to the estimation of evapotranspiration. Two neural networks were developed to forecast daily evapotranspiration of the rice crop with back-propagation and counter-propagation algorithm. The neural network trained by back-propagation algorithm with delta learning rule is a three-layer network with input, hidden, and output layers. The other network with counter-propagation algorithm is a four-layer network with input, normalizing, competitive, and output layers. Training neural networks was conducted using daily actual evapotranspiration of rice crop and daily climatic data such as mean temperature, sunshine hours, solar radiation, relative humidity, and pan evaporation. During the training, neural network parameters were calibrated. The trained networks were applied to a set of field data not used in the training. The created response of the back-propagation network was in good agreement with desired values and showed better performances than the counter-propagation network did. Evaluating the neural network performance indicates that the back-propagation neural network may be applied to the estimation of evapotranspiration of the rice crop. This study does not provide with a conclusive statement as to the ability of a neural network to evapotranspiration estimating. More detailed study is required for better understanding and evaluating the behavior of neural networks.

• KIEE International Transactions on Power Engineering
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• 제2A권4호
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• pp.131-135
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• 2002

This paper describes a new ultra-fast contingency screening algorithm for on-line TSA without time simulation. All machines are represented in a classical model and the stability index is defined as the ratio between acceleration power during a fault and deceleration power after clearing the fault. Critical clustering of machines is done based on the stability index, and the power-angle curve of the critical machines is drawn assuming that the angles of the critical machines increase uniformly, while those of the non-critical ones remain constant. Finally, the critical clearing time (CCT) is computed using the power-angle curve. The proposed algorithm is tested on the KEPCO system comprised of 900-bus and 230-machines. The CCT values computed with the screening algorithm are in good agreement with those computed using the detailed model and the SIME method. The computation time for screening about 270 contingencies is 17 seconds with 1.2 GHz PC.

• 한국지능시스템학회논문지
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• 제15권5호
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• pp.615-620
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• 2005

Sensor networks are usually composed of tens or thousands of tiny devices with limited resources. Because of their limited resources, there will often be some faulty nodes within the network. As nodes in some certain regions rely on each other to route the information gathered by different sensors to a base station (sink), the network should be able to detect a non-operational node in order to determine new paths for routing the information. Failure detection, which identifies the faulty nodes, is rather necessary in sensor networks and a very important research issue. The detection of a non-operational node can be performed using Consensus Algorithm with the purpose of achieving agreement about a node which is supposed to be faulty (non-operational). In this work, we discuss the application of a Consensus Algorithm to sensor node called 'mote'. Our experimental results show that it works efficiently for identifying faulty nodes in sensor networks.

• 한국통신학회논문지
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• 제18권7호
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• pp.1028-1035
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• 1993

Signed Regressor 적응 알고리즘은 한 비트 양자화를 이용하여 탭 입력이 +1또는 -1이 되도록 양자화한다. 따라서 이미 널리 사용되고 있는 Least Mean Square (LMS) 알고리즘에 비하여 계산량 측면에서 효율적이다. 그러나 SR 알고리즘의 동작특성은 입력신호의 특성에 매우 종속적이며, 효율성을 위하여 성능을 약간 희생한다. 본 논문에서는 이 SR 알고리즘의 동작특성에 대하여 통계적 분석을 하였다. 이를 위해, 사용되는 신호가 평균이 제로인 가우시안 신호라는 가정과 이러한 분석에 이미 널리 통용되어 사용되는 독립가정을 이용하여, SR 알고리즘의 평균 및 평균자승 특성을 나타내는 일련의 비선형 관계식을 유도하였다. 그리고 유도된 이론적 결과가 실험적 결과와 매우 일치함을 보였다.

• 대한전기학회논문지
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• 제40권6호
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• pp.582-589
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• 1991

We used Cd Se as the semiconductor to analyze the Poly-TFT. Cd Se TFT is fabricated by the vacuum evaporation method and the characteristics curves of the current-voltage are obtained using the results of measurement of Cd Se TFT devices. Employing least square method and Rosenbrock algorithm, we can extract the device parameters(grain boundary mobility, trap density). The current-voltage relations calculated by extracted parameters are in good agreement with experimental results.

• 한국전산응용수학회:학술대회논문집
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• 한국전산응용수학회 2003년도 KSCAM 학술발표회 프로그램 및 초록집
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• pp.5.3-5
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• 2003

The boundary of a typical period-2 component in the degree-3 bifurcation set is formulated by a parametrization of its image which is the unit circle under the multiplier map, Some properties on the geometry of the boundary are investigated including the root point, the cusp, the component center and the length as well as the area bounded by the boundary curve. An algorithm drawing the boundary curve with Mathematica codes is proposed and its implementation exhibits a good agreement with the analysis presented here.