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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),Craig Lanning 한국가시화정보학회 2006 한국가시화정보학회지 Vol.4 No.1
The left ventricular filling flow is now considered as an indicator which can be used for early diagnosing of cardiovascular diseases. Because the understanding of left ventricular flow physics is critical for this purpose, the downstream flow characteristics of the artificial heart valve are investigated using particle image velocimetry (PIV) method. In this study, we investigated the wake characteristics of flows passing through three different artificial valves (St.Jude medical bileaflet mechanical valve, Bjork-Shiley monostrut mechanical valve and St.Jude medical Biocor bio valve). The downstream flow field has remarkably altered according to the different valves. SJM MHV has the flow field similar to the pulsating circular jet and BS MHV has oblique pulsating jet. SJM BHV shows the similar flow field of clinical data of normal heart.
김형범(Hyoung-Bum Kim),류청환(Chung-Hwan Ryu),최영호(Young-Ho Choi),C. Lanning 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-
The downstream flow characteristics of the artificial heart valve are investigated using particle image velocimetry (PIV) method. In this study, we investigated the wake characteristics of flows passing through three different artificial valves (St.Jude medical bileaflet mechanical valve, Bjork-Shiley monostrut mechanical valve and St.Jude medical Biocor bio valve). The downstream flow field has remarkably altered according to the different valves. SJM MHV has the flow field similar to the pulsating circular jet and BS MHV has oblique pulsating jet. SJM BHV shows the similar flow field of clinical data of normal heart.
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.
In-plane scanning PIV기법의 최적화 연구
김형범(Hyoung-Bum Kim),이상혁(Sang-Hyuk Lee),류청환(Cheong-Hwan Ryu),J. Hertzberg 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11
Conventional PIV method requires a significant angle between the illumination plane and the viewing axis. This configuration allows whole field to be viewed with minimal image distortion. In industrial situations, it is common for this requirement to be difficult to fulfill. In this paper, we describe development of a new PIV method which utilizes in-plane scanning to assemble the particle images. This is similar to the Echo PIV technique. An optimization study was performed to find parameters which minimize the measurement error: the effect of particle diameter, overlapping ratio and particle number was investigated.
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),정인영(In-Young Jeong),오재근(Jae-Geun Oh),이상혁(Sang-Hyuk Lee),Jean Hertzberg 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
PIV(Particle image velocimetry) presents the flow velocity of whole flow fields in a fraction of a second. It is a unique method to capture the flow structure in complex flow and measure the turbulent properties with good accuracy by the development of digital image processing and optics. Conventional PIV method uses two optical axis configuration during the image grabbing process. That is, the illumination plane and the recording plane must be parallel. This configuration is very natural to grab the whole field without the image distortion. In the real problem, it is often to meet the situation which this configuration is hard to be fulfilled. In this study, we developed new PIV method which only uses single optical axis to grab the particle images. This new PIV method become possible by utilizing the scanning method similar to echo PIV technique. One particle image of scanning PIV consists of scanned several line images and by repeating this scanning process, two particle images ere grabbed and processed to produce the velocity vectors.
수직벽 후방 박리영역 감소를 위한 와류 생성기의 최적화 연구
김형우(Hyoung-Woo Kim),강인수(In-Su Kang),차재은(Jae-Eun Cha),김형범(Hyoung-Bum Kim) 한국가시화정보학회 2010 한국가시화정보학회 학술발표대회 논문집 Vol.2010 No.11
We experimentally investigated the effect of vortex generator to reduce the separation bubble behind the fence. 2D vertical fence was located in a circulating water channel and the vortex generator was installed in front of the fence. The parameters including the distance between the fence and vortex generator, size of vortex generators and the thickness of boundary layer were changed as increasing Reynolds number. The averaged recirculation lengths were compared with that of uncontrolled fence flow and the optimal values of parameters which showed the reduction of reattachment length behind the fence were found.
위상평균 PTV 기법을 이용한 축류 홴 주위 유동의 속도장 측정 연구
최제호,김형범,이상준,이인섭,Choi, Jay-Ho,Kim, Hyoung-Bum,Lee, Sang-Joon,Lee, In-Seop 대한기계학회 2000 大韓機械學會論文集B Vol.24 No.1
The flow structure around a rotating axial-fan was experimentally investigated using a phase averaging velocity field measurement technique. The fan blades were divided into 4 different phases, for which 500 velocity fields were acquired for each phase angle with a 2-frame PTV system. Velocity field measurements were also carried out at two planes parallel to the axis of rotation, with offsets toward the radial direction of the fan. For accurate synchronization of the PTV system with the phase of the axial fan, two synchronization circuits were employed with a photo-detector attached to the rotating shaft. The phase averaged velocity fields show periodic variations with respect to the blade phase. The periodic formation of vortices at the blade tip is also observed in vorticity contour plots. Locations of local maximum turbulence intensities in the axial and radial directions are found to be located in an alternating pattern. These experimental results can be used to validate numerical calculations and to understand the flow characteristics of an axial fan.