• Journal of the Institute of Electronics Engineers of Korea SP
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• v.42 no.4 s.304
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• pp.13-20
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• 2005

In this paper, we propose new smoothing filters, i.e., occluding patterns that can accurately correct disparities of occluded areas in the estimated disparity map. An image is composed of several layers and each layer presents similar disparity. Furthermore, the distribution of the estimated disparities has a specific direction around the boundary of the occlusion, and this distribution presents the different direction with respect to the left- and the right-based disparity map. However, typical smoothing filters, such as mean filter and median filter, did not take into account those characteristic. So, they can decrease some error, but they cannot guarantee the accuracy of the corrected disparity. On the contrary, occluding patterns can accurately correct disparities of occluded areas because they consider both the characteristic that occlusion occurs and the characteristic that disparities of the occlusion are ranged, from estimated disparity maps with respect to the left and the right images. We made experiments on occluding patterns with some real stereo image set, and as a result, we can correct disparities of occluded areas more accurately than typical smoothing filters did.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.39 no.2
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• pp.107-115
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• 2002

In this paper, we describe a novel method to generate an intermediate scene using BDM (Bidirectional Disparity Morphing) from the parallel stereopair. Because an image is composed of several layers and each layer has a similar disparity, it is available to use the block based disparity estimation. In order to prevent the false correspondence, however, we closely investigate the corresponding block as we adaptively vary the block size according to the estimation error. Therefore, we can detect the occlusion because of larger estimation error of the occluded region. We define three occluding patterns, which ate derived from the peculiar property of the disparity map, in order to smooth the computed disparity map. The filtered disparity map using these patterns presents that the false disparities ate well corrected and the boundary between foreground and background becomes sharper. As a result, we can improve the quality of the intermediate scenes.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.699-702
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• 2004

In this study, the affect of mounting axisymmetrical supersonic inlet to airfoil, which has 65 degree swept angle was numerically investigated. The parameter for this calculation are tree stream Mach number M=2.0 and 2.5, the distance between inlet spike and airfoil lower surface $L_{sw}$/$R_{cowl}$ = 1.21-1.54 and angle of attack to the airfoil 0-4. The mass capture ratio improved 3points in M=2.0 condition and 1points in M=2.5 while the mass capture ratio without airfoil surface was 57% and 71 % for each case. These are the result from increase of density and change of velocity deflection by the shock wave structure formed between inlet and airfoil surface. On the other hand, the distortion of Mach number at cowl lip plane increased by 13% in M=2.0, 3% in M=2.5 condition. The effects of the angle attack on the mass capture ratio is greater than that of the shock wave interaction between inlet and cowl, but the effects to the distortion is smaller in the range of this calculation condition. In the condition of M=2.0 with 4 degrees of angle of attack, inlet distortion of Mach number is mainly caused by the affects of the shock wave interaction between inlet and airfoil surface, while the largest angle of the velocity vector in the radial direction at cowl lip plane is caused by the affect of angle of attack. This large velocity vector made the flow inside the cowl subsonic and caused spillage, which interfere with the boundary layer of airfoil surface.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.634-643
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• 2004

In this paper are presented a concept of a new supersonic air inlet, which is designated a Multi-Row Disk (MRD) inlet, aiming at performance improvement under off-design conditions, and results of wind tunnel tests examined performance characteristics of the MRD inlet. The MRD inlet is frequently called ‘a skeleton inlet’ because of its appearance. The performance of a conventional axisymmetric inlet with a solid center body (spike) deteriorates under off-design Mach number conditions. It is due to the fact that total pressure recovery (TPR) governed by the throat area of inlet and mass capture ratio (MCR) governed by an incidence position of an oblique shock from the spike tip into the cowl can not be controlled independently in such air inlet. The MRD inlet has the spike that is composed of a tip cone and several disks arranged downstream of it, based on the experimental fact that several deep cavities on a conical surface have little negative effect on the boundary layer growth. The overall spike length of the MRD inlet is adjustable to the given flight speed by changing space between disks so that a spillage flow can be controlled independently from controlling the throat area. It could be made clear from the result of wind tunnel tests that the MRD inlet improves TPR by 10% compared with a conventional inlet with a solid spike under off-design conditions.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.210-213
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• 2010

Recent experimental data shows that the noticeable feature of irregular roughened spots on the fuel surface occurs during the combustion test. The generation of these unexpected patterns is likely to be resulted from the disturbed boundary layer due caused by wall blowing which is intended to simulate the process of fuel vaporization. LES without chemical reaction was conducted to investigate the flow characteristics at the near-fuel surface and the behavior of turbulent structures which is evolved by the wall blowing at the Reynolds number of 23,000. Cylindrical geometry was considered to get the most reality of the calculation results because real hybrid rocket motor is circular grain configuration. It was shown that the wall blowing pushed turbulent structures upwards making them tilted and this skewed displacement, in effect, left the foot prints of the structures on the surface. This change of kinematics may explain the formation of irregular isolated spots on the fuel surface observed in the experiment.

• Wind and Structures
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• v.14 no.4
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• pp.285-300
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• 2011

Researchers at the International Hurricane Research Center (IHRC), Florida International University (FIU), are working in stages on the construction of a large state-of-the-art Wall of Wind (WoW) facility to support research in the area of Wind Engineering. In this paper, the challenges of simulating hurricane winds for the WoW are presented and investigated based on a scale model study. Three wind profiles were simulated using airfoils, and/or adjustable planks mechanism with and without grids. Evaluations of flow characteristics were performed in order to enhance the WoW's flow simulation capabilities. Characteristics of the simulated wind fields are compared to the results obtained from a study using computational fluid dynamics (CFD) and also validated via pressure measurements on small-scale models of the Silsoe cube building. Optimal scale of the test model and its optimal distance from the WoW contraction exit are determined - which are two important aspects for testing using an open jet facility such as the WoW. The main objective of this study is to further the understanding of the WoW capabilities and the characteristics of its test section by means of intensive tests and validations at small scale in order to apply this knowledge to the design of the full-scale WoW and for future wind engineering testing.

• Wind and Structures
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• v.15 no.4
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• pp.331-343
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• 2012

Thunderstorm downbursts are responsible for numerous structural failures around the world. The wind characteristics in thunderstorm downbursts containing vortex rings differ with those in 'traditional' boundary layer winds (BLW). This paper initially performs an unsteady-state simulation of the flow structure in a downburst (modelled as a impinging jet with its diameter being $D_{jet}$) using a computational fluid dynamics (CFD) method, and then analyses the pressure distribution on a solar updraft tower (SUT) in the downburst. The pressure field shows agreement with other previous studies. An additional pair of low-pressure region and high-pressure region is observed due to a second vortex ring, besides a foregoing pair caused by a primary vortex ring. The evolutions of pressure coefficients at five orientations of two representative heights of the SUT in the downburst with time are investigated. Results show that pressure distribution changes over a wide range when the vortices are close to the SUT. Furthermore, the fluctuations of external static pressure distribution for the SUT case 1 (i.e., radial distance from a location to jet center x=$D_{jet}$) with height are more intense due to the down striking of the vortex flow compared to those for the SUT case 2 (x=$2D_{jet}$). The static wind loads at heights z/H higher than 0.3 will be negligible when the vortex ring is far away from the SUT. The inverted wind load cases will occur when vortex is passing through the SUT except on the side faces. This can induce complex dynamic response of the SUT.

• Korean Journal of Optics and Photonics
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• v.22 no.6
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• pp.283-290
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• 2011

A Raman LIDAR system has been designed and constructed for quantitative measurement of water vapor mixing ratio. The comparison with commercial microwave radiometer and global navigation satellite system(GNSS) was performed for the precipitable water vapor(PWV) profile and total PWV. The result shows that the total GNSS-PWV and LIDAR-PWV have good correlation with each other. But, there is small difference between the two methods because of maximum measurement height in LIDAR and the GNSS method. There are some significant differences between Raman and MWR when the water vapor concentration changes quickly near the boundary layer or at the edge of a cloud. Finally we have decided that MWR cannot detect spatial changes but LIDAR can measure spatial changes.

• Geophysics and Geophysical Exploration
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• v.4 no.3
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• pp.84-88
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• 2001

For the elastic migation, the velocity errors between the initial velocity model and true velocity model seriously affect the migrated images. The assumption of an initial velocity model, thus, is one of the critical factor for the successful migration. In case of applying the layered earth model as an initial velocity model, the layer boundary having large velocity contrast can not be defined well with conventional traveltime calculation algolithms and we have the difficulties for expressing the characteristics of the real subsurface. Smooth Background Model (SBM) we have applied as an initial velocity model in our study is characterized to be linearly varying the velocity with the depth, which can express the velocity variation in the subsurface properly. Thus it can properly be applied to traveltime calculation algolithms such as Vidale's method. In this study, Kirchhoff operator for prestack migration was used and the absolute amplitude obtained by modeling was applied as a weighted value to consider the true amplitude for initial model. Initial velocity model for migration was determined by using stacking velocity and we applied this model to real data.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.3A
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• pp.321-327
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• 2006

In this paper, when a H-polarized plane wave is incident on the grating consisting of uniform resistive strips, electromagnetic scattering is analyzed using the moment of methods (MoM). The current density of each resistive strip on a grounded dielectric plane is fixed by zero at both edges. To satisfy the condition at both ends of each resistive strip, the induced surface current density is expanded in a series of cosine and sine functions. The scattered electromagnetic fields are expanded in a series of floquet mode functions. The boundary conditions are applied to obtain the unknown current coefficients. According to the variation of the involving parameters such as strip width and spacing and angle of the incident field, numerical simulations are performed by applying the Fourier-Galerkin moment method. The numerical results of the normalized reflected power for resistive strips case for zero and several resistivities are obtained.