• 한국수자원학회논문집
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• 제51권8호
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• pp.643-654
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• 2018

수치파동수조에서 안정적인 지진해일을 조파하기 위하여 2차원 수치모델(LES-WASS-2D)에 다양한 파형의 지진해일을 고려할 수 있는 무반사 조파시스템을 도입하였다. 기존 실험에서 측정한 호안주변의 지진해일의 시 공간 파형들과 비교하여 수치계산결과가 높은 정확도를 나타내었다. 이로써 본 연구에서 적용한 수치모델이 지진해일 월파모의에 있어서 적합하다는 것을 보여주었다. 지진해일 월파모의결과로부터 지진해일 체적비와 파고와 수심비에 따른 월퍄량, 침수거리를 고찰하였다. 지진해일의 파형이 넓을수록 월파량이 선형적으로 증가하였으며, 침수거리 또한 증가하였다. 그러므로 고립파 근사이론을 지진해일의 월파 및 침수모의에 적용할 경우, 실제 지진해일보다 수리특성이 과소평가 될 우려가 크다.

• 한국해양공학회지
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• 제27권1호
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• pp.85-92
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• 2013

This paper deals with the resonant type of a WEC (wave energy converter) and the determination method of its geometric parameters which were obtained to construct the robust and optimal structure, respectively. In detail, the optimization problem is formulated with the constraints composed of the response surfaces which stand for the resonance period(heave, pitch) and the meta center height of the buoy. Use of a signal-to-noise ratio calculated from normalized multi-objective results with the weight factor can help to select the robust design level. In order to get the sample data set, the motion responses of the power buoy were analyzed using the BEM (boundary element method)-based commercial code. Also, the optimization result is compared with a robust design for a feasibility study. Finally, the power efficiency of the WEC with the optimum design variables is estimated as the captured wave ratio resulting from absorbed power which mainly related to PTO (power take off) damping. It could be said that the resultant of the WEC design is the economical optimal design which satisfy the given constraints.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2004년도 ICCAS
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• pp.176-180
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• 2004

The ST-segment that the beginning part of T wave is the important diagnostic parameter to finding myocardial ischemia. Abnormal ST appears in two types. One is the level change, and the other is the pattern change. In this paper, we describe the monitoring of abnormal ST using PC based system. Hardware of this system consists of transmitter, receiver and PC. The function of transmitter is measuring ECG in three channels which are selected manually and transmitting the data to receiver by digital radio way. Connection with receiver and PC is by RS232C, and the data received on the PC is analyzed automatically by ECG analysis algorithm and saved to file. In the algorithm part for detecting abnormal ST, ST-segments are approximated by a polynomial. This method can detect all of the deviation and pattern change of ST-segment regardless the change in the heart rate or sampling rate. To gain algorithm reliability, the method rejects distorted polynomial approximation by calculation the difference between the approximated ST-segment and original ST-segment. In pre-signal processing, the wavelet transformation separates high frequency bands including QRS complex from the original ECG. Consequently, the process improves the performance of detecting each feature points.

• Journal of electromagnetic engineering and science
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• 제8권3호
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• pp.100-109
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• 2008

The finite volume time domain(FVTD) technique faces serious limitations in simulating electromagnetic scattering at high frequencies due to requirements related to discretization. A modified FVTD method is proposed for electrically large, perfectly conducting scatterers by partially incorporating a time-domain physical optics(PO) approximation for the surface current. Dominant specular returns in the modified FVTD method are modeled using a PO approximation of the surface current allowing for a much coarser discretization at high electrical sizes compared to the original FVTD scheme. This coarse discretization can be based on the minimum surface resolution required for a satisfactory numerical evaluation of the PO integral for the scattered far-field. Non-uniform discretization and spatial accuracy can also be used in the context of the modified FVTD method. The modified FVTD method is aimed at simulating electromagnetic scattering from geometries containing long smooth illuminated sections with respect to the incident wave. The computational efficiency of the modified FVTD method for higher electrical sizes are shown by solving two-dimensional test cases involving electromagnetic scattering from a circular cylinder and a symmetric airfoil.

• Bulletin of the Korean Chemical Society
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• 제23권2호
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• pp.245-252
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• 2002

The computationally simple quantum mechanical method (VSCF-DWB-IOS) has been applied to studying the Ar-$CO_2$ vibrational predissociation phenomenon. The new methodology utilizes the vibrational self-consistent field method to determine the vibrational structure of the van der Waals complex, the distorted-wave Born approximation for dissociating process, and the infinite-order sudden approximation for the continuum dissociating product of $CO_2$. The dissociation due to the coupling of the symmetric stretching vibrational motion of $CO_2$ with the motion of the Ar van der Waals mode has been extensively investigated. The lifetimes of transient excited vibrational states, linewidths of absorption peak, and the rotational state distributions of the product, $CO_2$ have been computed. It has been found that the lifetime of the Ar-$CO_2$ in excited vibrational state is very long compared with that of triatomic van der Waals complexes and the product $CO_2$ carries a major portion of dissociation energy as a rotational energy.

• Bulletin of the Korean Chemical Society
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• 제23권2호
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• pp.229-240
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• 2002

Quantum mechanical calculation is performed for the $O(^1D)$ + HCl ${\rightarrow}$OH + Cl reaction using Reactive Infinite Order Sudden Approximation. Shifting approximation is also employed for the l ${\neq}$ 0 partial wave contributions. Various dynamical quantities are calculated and compared with available experimental results and quasiclassical trajectory results. Vibrational distributions agree well with experimental results i.e. product states mostly populated at $v_f$ = 3, 4. Our results also show small peak at $v_f$ = 0, which indicates bimodal vibrational distribution. The results show two significant broad peaks in ${\gamma}_i$ dependence of the cross section, one is at ${\gamma}_i$ = $15^{\circ}-35^{\circ}$ and the another is at ${\gamma}_i$= $55^{\circ}-75^{\circ}$ which can be explained as steric effects. At smaller gi, the distribution is peaked only at higher state ($v_f$ = 3, 4) while at the larger gi, both lower state ($v_f$ = 0) and higher state ($v_f$ = 3, 4) are significantly populated. Such two competing contributions (smaller and larger ${\gamma}_i$) result in the bimodal distribution. From these points we suggest two mechanisms underlying in current reaction system: one is that reaction occurs in a direct way, while the another is that reaction occurs in a indirect way.

• 대한전자공학회논문지SP
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• 제40권1호
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• pp.130-138
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• 2003

Stripmap-mode 합성개구레이더의 고전적인 영상 복원기술은 Range-Doppler 알고리즘이다. 하지만 고해상도 Spotlight-mode 합성개구레이더 시스템에서는 Range-Doppler 알고리즘을 적용했을 때 성능이 상당히 나빠지므로 Spotlight-mode에 맞는 별도의 Inversion 알고리즘이 연구되어왔다. 본 논문에서는 Spotlight-mode 합성개구레이더에서 Raw-data를 처리하기 위한 알고리즘 연구를 통해 기존의 평면파 근사 방법을 이용하고 있는 Polar format 알고리즘과 근사 방법을 사용하지 않는 Wavefront Reconstruction 기법에 대한 성능분석을 시도하였다. 이 때 Source 신호의 Carrier 주파수, 합성 개구면 Size, 그리고 표적물의 위치에 따라 두 Inversion기법의 결과 영상을 비교함으로써 Wavefront Reconstruction 기법의 우수성을 입증하였다. Spotlight-mode 합성 개구 레이더 시스템을 시뮬레이션하여 Raw-data를 생성시키고 각 알고리즘에 적용하여 역변환을 통해 영상화된 표적물의 형태로 성능을 비교 분석하였다.

• 한국해안해양공학회지
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• 제19권2호
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• pp.170-178
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• 2007

대부분의 포물형 수치모형은 경계 외측의 수심이 해안방향으로 변하지 않는 Snell 법칙을 적용할 수 있는 조건으로 국한한다. 여기에는 기존의 Kirby 방법이 있으며 본 논문에서는 이를 수정한 방법 그리고 Dirichlet 경계조건에 대해 자세히 기술하고 이에 대한 수치실험 결과를 제시하였다. 일정 수심 위에 존재하는 원형 천퇴에 대한 수치실험 결과 계산영역 좌우에 가상 수치 조정구역을 두고 본 Dirichlet 경계조건을 적용한 경우가 파고비의 분포가 가장 작게 왜곡되는 것으로 나타났다.

• Journal of Magnetics
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• 제21권1호
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• pp.6-11
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• 2016

The magnetic anisotropy energy (MAE) and the saturation magnetization $B_s$ of (110) $Fe_nCo_n$ heterostructures with n = 1, 2, and 3 are investigated in first-principles within the density functional theory by using the precise full-potential linearized augmented plane wave (FLAPW) method. We compare the results employing two different exchange correlation potentials, that is, the local density approximation (LDA) and the generalized gradient approximation (GGA), and include the spin-orbit coupling interaction of the valence states in the second variational way. The MAE is found to be enhanced significantly compared to those of bulk Fe and Co and the magnetic easy axis is in-plane in agreement with experiment. Also the MAE exhibits the in-plane angle dependence with a two-fold anisotropy showing that the $[1{\overline{I}}0]$ direction is the most favored spin direction. We found that as the periodicity increases, (i) the saturation magnetization $B_s$ decreases due to the reduced magnetic moment of Fe far from the interface, (ii) the strength of in-plane preference of spin direction increases yielding enhancement of MAE, and (iii) the volume anisotropy coefficient decreases because the volume increase outdo the MAE enhancement.

• 한국해안해양공학회지
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• 제6권3호
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• pp.216-225
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• 1994

Berkhoff등(1982)의 수리실험 결과를 사용하여 PCGM파 포물형근사식(PA) 수치모형의 정밀도와 계산효율을 비교하였다. 두 모형 결과는 수리실험의 실측치와 잘 부합되었으나 비교적 도고가 큰 천퇴 뒷편의 일부 단면에서는 PCGM모형 결과에 비해 PA모형 결과가 실험치에 가까운 것으로 나타났다. PA모형은 천해역의 넓은 지역에 대한 파랑변형을 예측하는 데 유용한 모형이나 반사파를 무시할 수 있는 경우에만 적용 가능하다. 한편 완경사 파랑식으로부터 직접 차분화하여 반사파를 고려할 수 있는 PCGM모형의 계산효율을 증대시킬 필요가 있다. PA모형 결과를 PCGM모형의 초기 입력조건으로 사용함으로써 약 40%의 계산시간 감소를 가져왔다.