• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.201-210
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• 2009

A volume capturing method using unstructured grid system for numerical analysis of multiphase flows is introduced in the present paper. This method uses an interface capturing method (CICSAM) in a volume of fluid(VOF) scheme for phase interface capturing. The novelty of CICSAM lies in the adaptive combination of high resolution discretization scheme which ensures the preservation of the sharpness and shape of the interface while retaining boundedness of the field, and no explicit interface reconstruction which is perceived to be difficult to implement on unstructured grid system. Several typical test cases for multiphase flows are presented, which are simulated by an in-house solution code(PowerCFD). This code employs an unstructured cell-centered method based on a conservative pressure-based finite-volume method with CICSAM. It is found that the present method simulates efficiently and accurately complex free surface flows such as multiphase flows.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.4
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• pp.369-375
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• 2011

Design is important in the IT, digital appliance, and auto industries. Aesthetic and art images are being applied for better quality of the products. Most image patterns are complex and much lead-time is required to implement them to the product design process. A precise reverse engineering method generating 2.5D engraving models from 2D artistic images is proposed through the image processing, NURBS interpolation and 2.5D reconstruction methods. To generate 2.5D TechArt models from the art images, boundary points of the images are extracted by using the adaptive median filter and the novel MBF (modified boundary follower) algorithm. Accurate NURBS interpolation of the points generates TechArt CAD models. Performance of the developed system has been confirmed through the quick turnaround 2.5D engraving simulation linked with the commercial CAD/CAM system.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.11
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• pp.144-153
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• 2007

In order to generate the input data for rapid prototyping, a new approach which is based on the implicit surface interpolation method is presented. In the method a surface is reconstructed by creating smooth implicit surface from unorganized cloud of points through which the surface should pass. In the method an implicit surface is defined by the adaptive local shape functions including quadratic polynomial function, cubic polynomial function and RBF(Radial Basis Function). By the reconstruction of a surface, various types of error in raw STL file including degenerated triangles, undesirable holes with complex shapes and overlaps between triangles can be eliminated automatically. In order to get the slicing data for rapid prototyping an efficient intersection algorithm between implicit surface and plane is developed. For the direct usage for rapid prototyping, a robust transformation algorithm for the generation of complete STL data of solid type is also suggested.

• Proceedings of the KOSOMBE Conference
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• v.1997 no.05
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• pp.230-234
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• 1997

The matching pursuit (MP) algorithm developed by S. Mallat and Z. Zhang is applied to magnetic resonance (MR) imaging. Since matching pursuit is a greedy algorithm to find waveforms which are the best match for an object-signal, the signal can be decomposed with a few iterations. In this paper, we propose an application of the MP algorithm to the MR imaging to reduce imaging time. Inner products of residual signals and selected waveforms in the MP algorithm are derived from the MR signals by excitation of RF pulses which are fourier transforms of selected waveforms. Results from computer simulations demonstrate that the imaging time is reduced by using the MP algorithm and further a progressive reconstruction can be achieved.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.8
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• pp.1094-1101
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• 1993

We show that image compression possibilities of BDPCM which reduces information and increases correlation with signal-blurring. Under the same quantization steps, signal flow at the coder is analyzed and complete signal reconstruction properties are shown. Dynamic range characteristics of the differences by the conventional DPCM predictor are analyzed. In order to improve the median filter reduces impulse noise with blurring, adaptive filtering for the differences is proposed. By means of the difference range, transmission impulse noises are detected and corrected by the filtering. Therefore, low bit rate image codec with noise eliminations is proposed.

• Proceedings of the Korea Society for Simulation Conference
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• 2001.10a
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• pp.223-230
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• 2001

This paper proposes a new contour detection method and adaptive reconstruction scheme for the cylindrical organs, such as blood vessels or arteries. Furthermore, we present java-based navigation controller which has been built to examine the inside of cylindrical objects. Tn the preprocessing procedure, a few preprocessing image filters are applied in order to remove unwanted artifacts from the medical images and to estimate threshold values for the object of interest. We define a context-free grammar, which is proper fur properties of contours of cylindrical objects. In the next procedure, we extract contours using advanced radial gradient method and represent contours as context-free grammar derivation trees. We build polygons between two contours efficiently by traversing the derivations trees of the contours. We fly through the reconstructed virtual models using java-based navigation controller and VRML viewer.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.1 s.244
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• pp.8-15
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• 2006

A Sparse Point Representation(SPR) based on interpolation wavelets is presented. The SPR is implemented for the purpose of CFD data compression. Unlike conventional wavelet transformation, the SPR relieves computing workload in the similar fashion of lifting scheme that includes splitting and prediction procedures in sequence. However, SPR skips update procedure that is major part of lifting scheme. Data compression can be achieved by proper thresholding method. The advantage of the SPR method is that, by keeping even point physical values, low frequency filtering procedure is omitted and its related unphysical thresholing mechanism can be avoided in reconstruction process. Extra singular feature detection algorithm is implemented for preserving singular features such as shock and vortices. Several numerical tests show the adequacy of SPR for the CFD data. It is also shown that it can be easily extended to nonlinear adaptive wavelets for enhanced feature capturing.

• Proceedings of the Korea Contents Association Conference
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• 2005.11a
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• pp.622-626
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• 2005

Voxel Coloring is one of the well known methods to reconstruct three dimensional shape from calibrated two dimensional multiple-view images. This paper proposes an advanced Voxel Coloring to complement drawbacks of previous color consistency tests. We propose an adaptive threshold using double threshold and an weight component to test color consistency. From the reconstruction experiment, we have verified that our proposed method outperforms the previous one.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2002.11a
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• pp.49-55
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• 2002

기존의 영상 획득 시스템들이 어느 정도의 엘리어싱을 허용하도록 제작되어왔음에도 불구하고, 고해상도 영상에 대한 요구는 점점 더 증가하고 있다. 본 논문에서는 부정확한 부화소 단위의 위치추정 오류를 고려한 고해상도 재구성 알고리즘을 제안한다. 부정확한 부화소 위치 추정 오류로 인해 생기는 불량위치문제(ill-posedness)를 해결하기 위해 정규화된 반복 연산법을 적용하였다. 특히 여러장의 저해상도 영상들을 개별적으로 고려하기에 적합한 다중채널 영상 재구성 방법을 도입하였다. 각 저해상도 영상에서 발생하는 움직임 추정오류는 서로 다른 경향성을 나타내므로, 정규화 파라미터들은 각 채널에 맞게 결정되어야 한다. 이를 위채 정규화 파라미터들을 자동으로 결정하는 방법을 제안한다. 제안한 알고리즘은 움직임 추정 오류에 매우 안정하며, 원 영상과 잡음에 대한 사전정보를 필요로 하지 않는다. 또한 주관적인 측면과 객관적인 측면에서 모두 우수한 결과를 실험적으로 보인다.

• Journal of Institute of Control, Robotics and Systems
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• v.12 no.11
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• pp.1081-1087
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• 2006

Generally, biped walking is difficult to control because a biped robot is a nonlinear system with various uncertainties. In this paper, we propose a hybrid sliding-mode control method using a WNN uncertainty observer for stable walking of the 5-link biped robot with model uncertainties and the external disturbance. In our control system, the sliding mode control is used as main controller for the stable walking and a wavelet neural network(WNN) is used as an uncertainty observe. to estimate uncertainties of a biped robot model, and the error compensator is designed to compensate the reconstruction error of the WNN. The weights of WNN are trained by adaptation laws that are induced from the Lyapunov stability theorem. Finally, the effectiveness of the proposed control system is verified through computer simulations.