• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.7
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• pp.853-858
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• 2003

The suitable estimation of the filter width in the dynamic eddy viscosity model were investigated in high Reynolds number channel flow. In this study, the improvement on matters by optimizing the test filter shape was attempted through the numerical experiment. The way that select optimum test filter width is recommended. Some test filters, one is based on a discrete representation of the top-hat filter and another are based on a high-order filtering operation, are evaluated in simulations of the turbulent channel flow at Reynolds number 1020, based on friction velocity and channel half width. It appears that the estimation of test filter width practically can decrease the dissipative nature of dynamic eddy viscosity model with explicit test filter. It shows that the value of the filter width ratio used in the dynamic procedure must match the properties of the test filter actually used in the calculation.

• Journal of Broadcast Engineering
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• v.24 no.6
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• pp.1035-1052
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• 2019

Recently, as the demand for immersive videos increases, efficient video processing techniques for omnidirectional immersive video is actively developed by MPEG-I. While the omnidirectional video provides a larger degree of freedom for a free viewpoint, the size of the video increases significantly. Furthermore, in order to compress 6 degree-of-freedom (6 DoF) videos that support motion parallax, it is required to develop a codec to yield better coding efficiency. In this paper, we develop a 6 DoF codec using Versatile Video Coding (VVC) as the next generation video coding standard. To the authors' best knowledge, this is the first VVC-based 6 DoF video codec toward the future ISO/IEC 23090 Part 7 (Metadata for Immersive Media (Video)) MPEG-I standardization. The experiments were conducted on the seven test video sequences specified in Common Test Condition (CTC) in two operation modes of TMIV (Test Model for Immersive Media) software. It is demonstrated that the proposed codec improves coding performance around 33.8% BD-rate reduction in the MIV (Metadata for Immersive Video) mode and 30.2% BD-rate reduction in the MIV view mode as compared to the state-of-the-art TMIV reference software. We also show the performance comparisons using Immersive Video PSNR (IV-PSNR) and Mean Structural Similarity (MSSIM).

• Fire Science and Engineering
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• v.34 no.1
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• pp.135-141
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• 2020

The first case of Middle East Respiratory Syndrome (MERS) was reported in Korea in 2015, after a Korean man from Bahrain tested positive for the infection. After first eruption, there were numbers of secondary infectees and whole country were frightened. At the time, isolated ambulances were available but few, and there was no specific way to prevent contamination during transfer. Therefore, Seoul National University Hospital and the University of Seoul developed isolation units and air filters. Four years after the MERS outbreak, this study measured the differential pressure inside and outside the small isolation units based on the differential pressure and air flow derived from simulation and testing, and proposed minimum values for virus leakage and internal sealing. A performance evaluation and testing method for the transfer equipment is proposed. The critical function of the small isolated transport equipment was defined and selected as an evaluation item; performance evaluation was carried out by simulating a real-world case. The results provide the proper pressure configuration of positive and negative pressure inside the segregation feeder; the clear criteria for the HEPA filter; and the performance criteria for the segregation feeder and air purifier.