• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.2 s.245
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• pp.126-135
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• 2006

The pressure drop characteristics in a rotating two-pass duct with rib turbulators are investigated in the present study. The square duct has a hydraulic diameter $(D_h)$ of 26.7 mm, and $1.5mm{\times}1.5mm$ square $90^{\circ}-rib$ turbulators are attached on the leading and trailing walls. The pitch-to-rib height ratio (p/e) is 10. The distance between the tip of the divider and the outer wall of the duct is $1.0D_h$ and the width of divider wall is 6.0mm or $0.225D_h$. The Reynolds number (Re) based on the hydraulic diameter is kept constant at 10,000 to exclude the Reynolds effect, and the rotation number (Ro) is varied from 0.0 to 0.20. The pressure drop distribution, the friction factor and thermal performance are presented for the leading, trailing and the outer surfaces. It is found that the curvature of the $180^{\circ}$-turn produces Dean vortices that cause high pressure drop in the turn. The channel rotation results in pressure drop discrepancy between leading and trailing surfaces so that non-dimensional pressure drops are higher on the trailing surface in the first-pass and on the leading and side surfaces in the second-pass. In the turning region, Dean vortices shown in the stationary case transform into one large asymmetric vortex cell, and subsequent pressure drop characteristics also change. As the rotation number increases, the pressure drop discrepancy enlarges.

• The Journal of Engineering Geology
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• v.26 no.1
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• pp.23-32
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• 2016

This study evaluates landslide susceptibility using statistical analysis by SVM (support vector machine) and the illite index of clay minerals extracted from ASTER(advanced spaceborne thermal emission and reflection radiometer) imagery which can be use to create mineralogical mapping. Landslide locations in the study area were identified from aerial photographs and field surveys. A GIS spatial database was compiled containing topographic maps (slope, aspect, curvature, distance to stream, and distance to road), maps of soil properties (thickness, material, topography, and drainage), maps of timber properties (diameter, age, and density), and an ASTER satellite imagery (illite index). The landslide susceptibility map was constructed through factor correlation using SVM to analyze the spatial database. Comparison of area under the curve values showed that using the illite index model provided landslide susceptibility maps that were 76.46% accurate, which compared favorably with 74.09% accuracy achieved without them.

• Journal of Korean Neurosurgical Society
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• v.54 no.3
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• pp.207-210
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• 2013

Objective : To compare spinopelvic parameters in young adult patients with spondylolysis to those in age-matched patients without spondylolysis and investigate the clinical impact of sagittal spinopelvic parameters in patients with L5 spondylolysis. Methods : From 2009 to 2012, a total of 198 young adult male patients with spondylolysis were identified. Eighty age-matched patients without spondylolysis were also selected. Standing lateral films that included both hip joints were obtained for each subject. Pelvic incidence (PI), sacral slope (SS), pelvic tilt, lumbar lordosis angle, sacral inclination, lumbosacral angle, and sacral table angle were measured in both groups. A comparative study of the spinopelvic parameters of these two groups was performed using SPSS 15.0 (SPSS Inc., Chicago, IL, USA). Results : Among the aforementioned spinopelvic parameters, PI, SS and STA were significantly different between patients with spondylolysis and those without spondylolysis. PI and SS were higher in the spondylolysis group than in the control group, but STA was lower in the spondylolysis group than in the control group. Conclusion : PI and SS were higher in the spondylolysis group than in the control group, but STA was lower in the spondylolysis group than in the control group. Patients with spondylolysis have low STA at birth, which remains constant during growth; a low STA translates into high SS. As a result, PI is also increased in accordance with SS. Therefore, we suggest that STA is an important etiologic factor in young adult patients with L5 spondylolysis.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.15 no.9
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• pp.785-795
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• 1990

For the far field radiation pattern of a microstrip array antenna which is conformed to a cylindrical surface and forms an arc array, an approximate analysis method using FOURIER TRANSFORM is presented. In this method, the conformal array antenna is projected on the effective aperture plane and assumed to be an aperiodic array with nonlinear phase tilt. The effective aperture plane includes four end-points of each arc on the cylindrical surface. When the effective aperture ratio which is normalized to the planar type is from 1.0 to 0.9, it is confirmed that this approximate method is valid. To the array on the effective aperture plane, it is assumed that the phase tilt is due to the distance between aperture plne and curvature surface. Specially, when the radius of arc is more than 5 times to its length, the FOURIER TRANSFORM METHOD could be used with only varying scale factors. The results of calculating by approximate method are good agreement with the results of COORDINATE TRANSFORM METHOD and experimentally measured value in the range of -40dB. And, the difference of half power angle is less than 5 degrees when the effective aperture ratio moer than 0.9.

• Journal of Korea Water Resources Association
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• v.38 no.7 s.156
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• pp.527-535
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• 2005

The computation of normal depth is very important for the design of channel and the analysis of water flow. Drainage pipe generally has the shape of curvature like circular or U-type, which is different from artificial triangular or rectangular channel. In this case, the computation of normal depth or the derivation of equations is very difficult because the change of hydraulic radius and area versus depth is not simple. If the ratio of the area to the diameter, or the hydraulic radius to the diameter of pipe is expressed as the water depth to the diameter of pipe by power law, however, the process of computing normal depth becomes relatively simple, and explicit equations can be obtained. In the present study, developed are the explicit normal depth equations for circular and U-type pipes, and the normal depth equation associated with Hagen (Manning) equation and friction factor equation of smooth turbulent flow by power law is also proposed because of its wide usage in engineering design.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.48 no.4
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• pp.474-482
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• 2015

This study aims to investigate the patterns and incidence rates of morphological deformities during artificial fingerling production of blackhead seabream (BSB, Acanthopagrus schlegeli) juveniles by visual and soft X-ray observations of BSB juveniles (n=881) collected from four industrial hatcheries. Using both methods, we observed seven types of external deformity ($11.2{\pm}4.4%$) and eight types of skeletal deformity ($53.4{\pm}5.1%$). Lordosis occurred in all hatcheries with the highest frequency and the mean frequency was $13.1{\pm}4.4%$ (24.5% in total abnormal) by soft X-ray. Although they had a similar standard length (SL), juveniles with lordosis had a significantly lower condition factor and body weight than normally developed juveniles (P<0.05); normal distribution curves of histogram of body proportions, i.e., body height (BH)/head length (HL) and trunk (=SL-HL)/BH, indicated differences between normally developed juveniles and those with lordosis. In addition, 59% of juveniles with lordosis had vertebral curvature of less than $20^{\circ}$, generally at the $17^{th}$ vertebrae. It is expected that the above results will be used as basic data necessary for determining the cause of lordosis and for developing techniques to prevent this symptom in the fingering production industry of BSB juveniles.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.4
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• pp.382-388
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• 2010

In this work the replacement material for magnesium alloy was investigated and an optimized design was suggested for the horizontal fin of a fighter's external fuel tank. For the replacement of magnesium alloy, Aluminum alloy, AL 2034-T351, was selected by considering material properties and its procurement. The strength and fracture toughness properties of AL 2034-T351 are stronger than those of magnesium alloy, but the specific weight of AL 2034-T351 is heavier than that of magnesium alloy by 65%. To meet the allowable limit of C.G. shift in the tank, the design of horizontal fin was optimized by reducing the original shape by 20% and resizing the maximum thickness to 7 mm. From the results of the static and dynamic stress analysis for improving the safety factor of the joint section and the joint hole, the radius of curvature in the aft joint section of the new fin was designed as 8.5mm.

• Journal of The Korean Astronomical Society
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• v.45 no.5
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• pp.127-138
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• 2012

We explore how wave-particle interactions affect diffusive shock acceleration (DSA) at astrophysical shocks by performing time-dependent kinetic simulations, in which phenomenological models for magnetic field amplification (MFA), Alfv$\acute{e}$nic drift, thermal leakage injection, Bohm-like diffusion, and a free escape boundary are implemented. If the injection fraction of cosmic-ray (CR) particles is ${\xi}$ > $2{\times}10^{-4}$, for the shock parameters relevant for young supernova remnants, DSA is efficient enough to develop a significant shock precursor due to CR feedback, and magnetic field can be amplified up to a factor of 20 via CR streaming instability in the upstream region. If scattering centers drift with Alfv$\acute{e}$n speed in the amplified magnetic field, the CR energy spectrum can be steepened significantly and the acceleration efficiency is reduced. Nonlinear DSA with self-consistent MFA and Alfv$\acute{e}$nic drift predicts that the postshock CR pressure saturates roughly at ~10 % of the shock ram pressure for strong shocks with a sonic Mach number ranging $20{\leq}M_s{\leq}100$. Since the amplified magnetic field follows the flow modification in the precursor, the low energy end of the particle spectrum is softened much more than the high energy end. As a result, the concave curvature in the energy spectra does not disappear entirely even with the help of Alfv$\acute{e}$nic drift. For shocks with a moderate Alfv$\acute{e}$n Mach number ($M_A$ < 10), the accelerated CR spectrum can become as steep as $E^{-2.1}$ - $E^{-2.3}$, which is more consistent with the observed CR spectrum and gamma-ray photon spectrum of several young supernova remnants.

• International Journal of Ocean System Engineering
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• v.1 no.2
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• pp.95-101
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• 2011

Perforated plates with cutouts (or holes) are widely used in structural members. These cutouts provide stress concentration in plates. Extensive studies have been carried out on stress concentration in perforated plates, which consider cutout shapes, boundary conditions, bluntness of cutouts, and more. This study presents stress concentration analyses of perforated plates with not only various cutouts and bluntness but also different cutout orientations. Especially, the effect of cutout orientation on stress concentration is emphasized since structural members have become more complicated recently. To obtain stress concentration patterns, a finite element program, ANSYS, is used. For the designated goal, three parameters are considered as follows: the shapes of polygonal cutouts (circle, triangle, and square), bluntness (a counter measure of radius ratio, r/R), and rotation of cutouts (${\theta}$). From the analyses, it is shown that, in general, as bluntness increases, the stress concentration increases, regardless of the shape and rotation. A more important finding is that the stress concentration increases as the cutouts become more oriented from the baseline, which is the positive horizontal axis (+x). This fact demonstrates that the orientation is also a relatively significant design factor to reduce stress concentration. In detail, in the case of the triangle cutout, orienting one side of the triangle cutout to be perpendicular to the applied tensile forces is preferable. Similarly, in the case of the square cutout, it is more advantageous to orient two sides of square cutout to be perpendicular to the applied tensile force. Therefore, at the design stage, determining the direction of a major tensile force is required. Then, by aligning those polygon cutouts properly, we can reduce stress concentration.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.5
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• pp.1191-1197
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• 1994

The purpose of this study is to examine morphometric characteristics in a channel bend reach. The new shape factor is suggested that channel deformation rate of cross section (${\Delta}A_s$) showed the variation of concentrated location of force due to the current and the variation of erosional section in alluvial channel. In the downstream direction the meaning of decreasing "${\Delta}A_s$" is the stability of channel bed. This study was analyzed morphological characteristics of cross section-width of channel ($W_s$), width to the thalweg ($W_{th}$), maximum depth ($D_{th}$)-on the Guem River, and typical cross sections in channel bend were proposed. The channel migration rate (M) for the study river was represented that the zones of curvature ratio (R/W) with 2~4 were larger 12% than other zones.