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김형범,임정호,허유,Kim, Hyung-B.,Lim, Jung-H.,Huh, You 한국섬유공학회 2011 한국섬유공학회지 Vol.48 No.3
Multi-layered, prepreg or preform textile structures are often used in industrial components to achieve specific mechanical properties. Therefore a beam scanning method was developed to measure the internal structures of multi-layered preforms in a nondestructive way. The measurement system employed a low-energy X-ray beam and an X-ray detector. Specific software programs were also developed for image data processing. Trial measurements of textile specimens prepared from compound yams demonstrated the system's ability to image internal structures by detecting the layers' folded states. The method can feasibly be used for measuring the internal states of specimens with stacked textile structures.
다공성 방풍벽의 다공도가 펜스후류 속도장에 미치는 영향에 관한 연구
김형범,이상준,Kim, Hyeong-Beom,Lee, Sang-Jun 대한기계학회 1998 大韓機械學會論文集B Vol.22 No.7
Velocity fields of near turbulent was behind a porous wind fence were measured using the 2-frame PTV method in a circulating water channel. The fences used in this study had different geometric porosity(.epsilon.) of 0, 20, 40 and 65%. The fence was embedded in a thin laminar boundary layer, i.e., .delta./H ~ = 0.1. Reynolds number based on the fence height H and free stream velocity(U$\_$o/) was about 8,400. As a result, a recirculating flow region was formed behind the fence for the .epsilon.=0% and 20% wind fence. For the wind fences having porosity larger than .epsilon.=40%, it was difficult to see separation bubbles behind the fence. The .epsilon.=20% porous fence reveals the maximum velocity reduction, however, the turbulent intensity and Reynolds shear stress are much greater than those of .epsilon.=40% fence. Among the wind fence tested in this study, the porous wind fence of .epsilon.=40% porosity is the most effective for abating wind erosion.
다공성 방풍벽 뒤에 놓인 삼각 프리즘 주위 유동의 PTV 속도장 측정
김형범,이상준,Kim, Hyeong-Beom,Lee, Sang-Jun 대한기계학회 1998 大韓機械學會論文集B Vol.22 No.5
The shelter effect of a porous wind fence on a triangular prism was experimentally investigated in a circulating water channel. A porous fence of porosity .epsilon.=38.5% was installed in front of the prism model. The fence and prism model were embedded in a turbulent boundary layer. The instantaneous velocity fields around the fence and prism model were measured by using the instantaneous velocity fields around the fence and prism model were measured by using the 2-frame PTV(Particle Tracking Velocimetry) system. By installing the fence in front of the prism, the recirculation flow region decreases compared with that of no fence case. The porous fence also decreases the mean velocity, turbulent intensity and turbulent kinetic energy around the prism. Especially, at the top of the prism, the turbulent kinetic energy is about half of that without the fence.
적응형 하이브리드 기법을 이용한 2-Frame PTV 기법의 성능향상 연구
김형범,이상준,Kim, Hyoung-Bum,Lee, Sang-Joon 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.3
The performance of 2-frame PTV(particle tracking velocimetry) system was improved using an adaptive hybrid scheme. The original 2-frame PTV method based on the match probability concept employs global match parameters for the entire flow field. Since this does not reflect fully the detailed local velocity change, it sometimes reduces the recovery rate of velocity vectors and increases the number of erroneous vectors in the region where an extraordinary flow structure exists. In this study, the preliminary FFT-based PIV results are used as an input parameter to determine the local match parameters needed for the 2-frame particle tracking algorithm. A computer simulation using synthetic particle images was carried out to study the performance of the adaptive 2-frame PTV technique. The adaptive hybrid method shows the better performance with increasing the velocity vector recovery rate and decreasing the computation time, compared to the original 2-frame PTV method.
김형범(Hyoung Bum KIM),양희경(Kyung Ha MIN),민경하(Hee Kyung YANG) 한국컴퓨터게임학회 2021 한국컴퓨터게임학회논문지 Vol.34 No.3
본 연구에서는 게임 동영상의 고화질 변환이 가능한 초해상화 알고리즘을 제시한다. 본 알고리즘은 오픈 소스 형태의 GPU에서 제공하는 MMU에서 구현될 수 있도록 희소 행렬 연산을 이용해서 설게된다. 이를 위해서 일반적인 영상 해상도 향상 방법인 이중 일차 및 이중 삼차 보간 법과 심층 학습에 기반한 초해상화 모델에서 사용하는 컨볼루션 연산을 희소 행렬 연산으로 변환하는 방법을 제시한다. 이는 각 픽셀에 적용되는 필터를 행렬 곱 형태로 표현하고, 이 행렬을 희소 행렬로 표현함으로써 수행되는데, 이러한 과정을 통해서 연산의 효율성을 추구함으로써 안정적인 초해상화 알고리즘을 제공한다. 이러한 희소행렬 연산 형태로 표현되는 초해상화 알고리즘은 기존의 라이브러리를 이용해서 구현된 초해상화 알고리즘과 유사한 PSNR과 FPS를 보인다. We present a super resolution algorithm that increases the resolution of game scenes. Since game scenes are required to be rendered in real time, rendering high-resolutional game scenes in real time is very challenging. Therefore, increasing the resolution of game scenes rendered in low resolution is very promising. In order to present a fast super resolution algorithm, we implement our super resolution algorithm using a sparse matrix operation that can be accelerated through a matrix multiplication unit (MMU). Since many open source GPUs present an acceleration environment, our MMU-based approach can be implemented in many open source GPUs. As a baseline of our approach, we present a sparse matrix multiplication formula of bilinear interpolation and bicubic interpolation. We furthermore present a sparse matrix multiplication form of a convolution operation, which is necessary for deep learning-based super resolution algorithms. The filters employed in the convolution operations are converted to a series of sparse matrices, which are multiplied to complete the deep learning-based super resolution model. We demonstrate the performance of our approach by measuring peak signal-to-noise ratio (PSNR) and mean opinion score (MOS) of the result images generated by our approach and by the existing methods.
김형범(Hyoung-Bum kim),Jean Hertzberg,Robin Shandas 한국가시화정보학회 2005 한국가시화정보학회지 Vol.3 No.1
The combination of ultrasound echo images with digital particle image velocimetry (DPIV) method has resulted in a two-dimensional, two-component velocity field measurement technique appropriate for opaque flow conditions including blood flow in clinical applications. Advanced PIV processing algorithms including an iterative scheme and window offsetting were used to increase spatial resolution. The optimum concentration of the ultrasound contrast agent used for seeding was explored. Velocity validation tests in fully developed laminar pipe flow and pulsatile flow showed good agreement with both optical PIV measurements and the known analytic solution. These studies indicate that echo PIV is a promising technique for the non-invasive measurement of velocity profiles and shear stress.