• 한국항공우주학회지
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• 제35권8호
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• pp.693-698
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• 2007

로터 공기역학 모사를 위한 수치해석 기법이 제안되었다. 국부적인 유동특성변수를 4차 정확도 내삽의 MUSCL 접근방법을 유한체적 공식에 적용시킴으로써 로터 블레이드로 부터 멀리 떨어져 성긴 격자영역에서의 비 물리적인 수치 확산을 개선시켰다. 또한, 유동특성변수에 따라 각각 다른 제한자를 적용함으로써 수치적인 소산작용을 억제하고 수치적 안정성을 높였다. 대표적인 로터 공기역학 응용문제에 적용한 결과 후류포획성능이 크게 개선됨을 확인하였으나 공력소음계산 결과는 전통적인 MUSCL 기법에 비교하여 큰 개선점은 없었다.

• 한국전산유체공학회지
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• 제15권2호
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• pp.86-94
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• 2010

A thermal-hydraulic code, named CUPID, has been developed for the analysis of transient two-phase flows in nuclear reactor components. A two-fluid three-field model was used for steam-water two-phase flows. To obtain numerical solutions, the finite volume method was applied over unstructured cell-centered meshes. In steam-water two-phase flows, a phase change, i.e., evaporation or condensation, results in a great change in the flow field because of substantial density difference between liquid and vapor phases. Thus, two-phase flows are very sensitive to the local pressure distribution that determines the phase change. This in turn puts emphasis on the accurate evaluation of local pressure gradient. This paper presents a new reconstruction method to evaluate the pressure gradient at cell centers on unstructured meshes. The results of the new scheme for a simple test function, a gravity-driven cavity, and a wall boiling two-phase flow are compared with those of the previous schemes in the CUPID code.

• 전자공학회논문지
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• 제54권4호
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• pp.83-90
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• 2017

전기 임피던스 단층촬영법은 전극을 통해 주입된 전류와 측정된 전압을 기반으로, 내부 도전율 분포를 복원하는 기술로, 비교적 새로운 비파괴 영상 복원 기법이다. 본 논문에서는 이원 혼합물 유동 응용분야에서 온라인으로 적용시킬 수 있도록, 역문제의 계산시간을 줄일 뿐만 아니라 공간 해상도도 함께 향상시킬 수 있는 역문제 해법인 빠른 반복적 가우스-뉴턴 방법을 제안하였다. 제안한 방법의 영상 복원성능을 평가하기 위해 모의실험을 수행하고 그 결과를 비교분석하였다.

• 한국멀티미디어학회논문지
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• 제15권6호
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• pp.770-783
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• 2012

본 논문에서는 다중 영상에서 추출된 특징점을 사용해서 투영 공간에서의 카메라 행렬과 3차원 정점좌표를 계산하는 방법을 제안한다. 수치적인 안정성을 위해서 특징점을 정규화한 후 복원하며 얻어지는 카메라 행렬과 3차원 정점에 대해서 비정규화한다. 카메라 행렬과 3차원 정점의 초기값을 얻기 위해서 특이값 분해기법을 사용해서 투영 깊이가 적용된 측정 행렬을 분해한다. 행렬 분해 제약을 사용하여 카메라 행렬과 3차원 정점을 투영 복원한다. 투영 복원 과정에서는 비선형 반복적 최적화 방법이 사용된다. 실험 결과 제안방법은 대체로 적절한 정확성을 얻었고 오차의 편차가 크지 않았다.

• 대한전기학회논문지:시스템및제어부문D
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• 제51권5호
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• pp.212-219
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• 2002

In this paper, the epipolar geometry, genera17y used as a pin-hole camera model, is newly adapted to our proposed method that enables the affine reconstruction of the 3D object from two projected views. The proposed method models the projective projection of inherent X-ray imaging system, obviates the need to attach artifirially constructed material on the body, and requires none of the prior-knowledge regarding to intrinsic and extrinsic parameters of two X-ray imaging systems. The optimum numerical solution is obtained by applying the least mean square estimator to corresponding points on two projected X-ray planes. The performance of this proposed method is Quantitatively analyzed using computer synthesized model of Cochlear implantation electrodes. In simulated experiments, the propnsed method is insensitive to the added random noise, the scaling factor change, the center point change, and rotational angular change between two projection planes, as well as enables the stable 3D reconstruction in least square sense even in worst testing cases.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2012년도 추계학술대회 논문집
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• pp.630-635
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• 2012

Nearfield acoustic holography method predicts an unmeasured sound field, therefore it depends on its prediction methods. In particular, if one has radiators or scatters, which cannot be expressed by simple geometry, then inverse boundary element method (BEM) is normally employed to reconstruct the sound field induced by sound sources with irregular profiles. The characteristics of boundary element, including the element shape, characteristic length, order of shape function and others, affect the reconstruction error. Investigating the errors by means of changing these factors will provide a guide line for selecting appropriate factors, associated with the elements of BEM. These factors are investigated by numerical simulations, and the accuracies with respect to the variant factors are compared. Novel suggestions for selecting appropriate boundary element factors are described based on the simulation results.

• 전기전자학회논문지
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• 제20권3호
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• pp.226-234
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• 2016

전기 저항 단층촬영법(ERT)은 대상체 내부 단면의 저항률 분포를 추정하고 이를 영상화하는 기술이다. ERT의 영상복원은 매우 비정치성이 강한 역문제의 일종으로 의미있는 영상을 얻기 위해서는 조정기법이 사용된다. 대표적으로 l2-norm 조정기법, l1-norm 조정기법, Total Variation 조정기법이 사용되며, 조정기법에 따라 ERT의 영상복원 성능이 달라진다. 즉, 상황에 맞는 적절한 조정기법의 사용은 ERT 영상 복원을 개선할 수 있다. 따라서, 본 논문에서는 모의실험을 통하여 상황에 따른 세 가지 조정기법의 영상복원 성능을 비교하였다.

• 한국자동차공학회논문집
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• 제23권3호
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• pp.254-262
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• 2015

This paper presents 3D collision deformation modelling methodologies using photogrammetry for reconstruction of vehicle accidents. A vehicle's deformation shape in collision provides important information on how the vehicle collided. So effective measurement(scanning) and construction of a corresponding appropriate model are essential in the analysis of collision deformation shape for obtaining much information related to collision accident. Two measurement methods were used in this study: Indirect-photogrammetry which requires relatively small amount of photos or videos, and direct-photogrammetry which requires large amount of photos directly taken for the purpose of 3D modelling. When the indirect-photogrammetry method, which was mainly used in this study, lacked enough photographic information, already secured 2D numerical deformation data was used as a compensation. This made 3D collision deformation modelling for accident reconstruction analysis possible.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 추계학술대회 논문집 학회본부
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• pp.388-390
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• 1994

We are familiar with the holography in these days. For making holography the coherent sources like LASER are used in many fields. But coherent holography has many problems. Coherent holography needs many instrument for practical use like 3-D TV case. In solving the problem we use the non-coherent source. Nowadays many methods like conoscopic holo graphy using anisotropic crystal, shadow casting and interferometric systems are suggested. In this paper we make the hologram using the triangular interferometric systems. [1],[2],[3],[4]. We explain the afocal and double-afocal system which consists of the triangular interferometric system. The holography made in one point and two point cases is imaged on CCD camera and we handle the image data digitally for the reconstruction efficiently. In reconstructing the hologram the Fraunhofer diffraction theory is used. We adopt the rectangular aperture for the convenience of calculation. In the future we must reconstruct the perfect 3-Dimensional object by optical method. For this, we have many problems like resolution problem. We must solve these problem for perfect reconstruction.

• 한국연소학회:학술대회논문집
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• 한국연소학회 제26회 KOSCO SYMPOSIUM 논문집
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• pp.57-62
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• 2003

A general procedure of obtaining reliable one-step kinetics model for hydrocarbon mixture from the fully detailed chemistry is described iin this study. One-step theoretical formulation of the induction parameter model IPM uses a theoretical reconstruction of the induction time database obtained from a detailed kinetics library. Non-dimensional induction time calculations is compared with that of detailed kinetics. The IPM was latter implemented to fluid dynamics code and applied for the numerical simulation of detonation wave propagation. The numerical results including the numerical smoked-foil record show the all the details of the detonation wave propagation characteristics at the cost around 1/100 of the detailed kinetics calculation.