• The Journal of Engineering Geology
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• v.27 no.3
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• pp.267-274
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• 2017

Behavior of rock mass depend on the mechanical properties of intact rock and geometrical property of discontinuity distributed in rock mass. In case of rock slope, particularly, location of slope failure surface and behavior after failure are changed due to discontinuities. In this study, two 3D slope stability analysis methods were developed for two different failure types which are circular failure and planar failure, considering that failure type of rock slope is dependent on scale of discontinuity which was then applied to real rock slope to review the applicability. In case of circular failure, stable condition was maintained in natural dry condition, which however became unstable when the moisture content of the surface was increased by rainfall. In case of planar failure, rock slope become more unstable comparing to dry condition which is attributable to decrease in friction angle of discontinuity surface due to rainfall. Viewing analysis result above, analysis method proved to have well incorporated the phenomenon occurred on real slope from the analysis result, demonstrating its applicability to reviewing the slope stability as well as to maintaining the slope.

• Journal of Biosystems Engineering
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• v.9 no.1
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• pp.11-21
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• 1984

This study was intended to analyze the dynamic force system which induced the shattering of paddy grains. A model to predict the shattering of paddy grains was developed, and physical quantities, such as mass distribution and rigidity of rice plant, needed for evaluating the minimum shattering forces were also measured. Under the assumption that rice plant right before harvesting is a vibratory system, the mathematical model of the vibratory system was developed and solved with the varied conditions of forcing functions. The results of the study were summarized as follows: 1. The shattering of grain occurred at the abscission layer of grain by the bending moments resulted from the impact force due to the collision of panicles of rice plant. 2. The vibratory model developed for milyang 23 rice variety was analyzed to give the natural frequencies of 7-9 Hz, which were closely related with the excitation frequencies of 4-10 Hz caused by various machine parts besides engine. Thus, avoiding the resonance should be taken into consideration in the design of the harvesting machinery. 3. It was analyzed to predict the lowest frequency that could develop the shattering when the excitation force was applied to the lower end of stem. The lowest frequency for the Milyang 23 rice variety ranged from 8.33 Hz to 11.66 Hz as the amplitude varied from 1 cm to 2.5 cm. 4. The degree of shattering depended upon the magnitude of the impact force and its application point. For Milyang 23 rice variety, the minimum impact force developing the shattering was $5g_f$ when it was applied at 1 cm above the lower end of stern and $1g_f$ when applied at 5 cm above the lower end of stem. 5. The minimum colliding velocity of the panicle, when it was on the ground that would just develop the shattering, was given as follows, $$V=\sqrt{\frac{K_t}{m_g}{\cdot}{{\phi}^2}}$$ where V : The colliding velocity of the panicle against ground to cause the shatteering of rice grain. (cm/sec) $K_t$ : The minimum spring constant for bending at the abscission layer of grain. (dyne-cm/rad) ${\phi}$ : The minimum shattering angle of grain (rad) $m_g$ : The maximum mass of grain. (g).

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.5
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• pp.456-465
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• 2015

Dual-bell nozzle can overcome the performance losses of the conventional bell-shaped nozzles which induced by off-design operations with either over-expanded or under-expanded exhaust flow and minimize the losses of the specific impulse. In United States, Rocketdyne analyzed thrust characteristics according to the shape of the expansion nozzle and NASA conducted hot firing tests with various altitudes. DLR, which is one of the research institute of the Europe, is carrying out research for the different cases of inflection angle, nozzle length and expansion ratio. MAI of Russia applied the slot nozzle to the expansion region in order to reduce the performance losses. In Asia, both the Japan and the India are researching on the dual-bell nozzle and Mitsubishi cooperation of the Japan registered its patent. In this paper, concepts and performance of dual-bell nozzle, which can compensate altitude, are investigated and trends of current research are summarized. It is necessary for Korea to research on the dual-bell nozzle for lucrative space development.

• 한국연소학회:학술대회논문집
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• 2005.10a
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• pp.328-336
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• 2005

Effects of surface defect distribution on flame instability during flame-surface interaction are experimentally investigated. To examine the chemical quenching phenomenon, we prepared thermally grown silicon oxide plates with well-defined defect density. Ion implantation was used to control the number of defects, i.e. oxygen vacancies. In an attempt to preferentially remove the oxygen atoms from silicon dioxide surface, argon ions with low energy level from 3keV to 5keV were irradiated at the incident angle of $60^{\circ}C$. Compositional and structural modification of $SiO_2$ induced by low-energy $Ar^+$ ion irradiation has been characterized by Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS). The analysis shows that as the ion energy increases, the number of structural defect also increases and non-stoichiometric condition of $SiO_x(x{\le}2)$ plates is enhanced. From the quenching distance measurements, we found out that when the surface temperature is under $300^{\circ}C$, the quenching distance decreases on account of reduced heat loss; as the surface temperature increases over $300^{\circ}C$, however, quenching distance increases despite reduced heat loss effect. Such aberrant behavior is caused by heterogeneous chemical reaction between active radicals and surface defect sites. The higher defect density, the larger quenching distance. This results means that chemical quenching is governed by radical adsorption and can be parameterized by the oxygen vacancy density on the surface.

• Journal of Satellite, Information and Communications
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• v.10 no.2
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• pp.90-94
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• 2015

We stuidied liauid crystal alignment treatment using solution process for making thin oxide layer in liquid crystal display. It is the one of very effient and popular process in making thin oxide layer in electronical industrial fields. Particularly, this process has highly potential value in liquid crystal display industrial fields because it cause automatically induced alignment process without tranditional alignment process in liquid crystal alignment process. We made several different kinds of mol density solutions using strontium oxide solution. And those solutions were treated for solidification layers using annealing process for 2 hours. And we stuided pretilt angle properties of these alignment layers of strontium oxide for clarifying the relationship of liquid crystal molecules and thin strontium oxide layer. And we also tested the existence of strontium oxide thin layer on substrate using XPS measurement. We expected the hig gain of electro-optical properties in liquid crystal display using strontium oxide thin layer because it has high K property material than the other metal-based oxide layers. In this results, we measured 1.447 to 1.613 thresholds volts as 0.1 mol to 0.4 mol density in 0.1 mol density steps. This is significant better characteristics than conventional liquid crystal display as higher than 1.85 thresholds volts. And it make possible to making next-generation liquid crystal display which present low-power consumption and wide gray scale in liquid crystal display.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.3
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• pp.115-121
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• 2017

The efficiency of railway track cleaning vehicle for eliminating fine particulate matter (PM10 and PM2.5) in a subway tunnel depends strongly on the structure of the air blowing and suction system installed under the train. To increase the efficiency of underbody suction system, this paper proposes a novel method to use the Coanda effect for the air blower and dust suction module. In particular, through Computational Fluid Dynamics (CFD) analysis, the flow control device induced by the Coanda effect enables an increase in the overall flow velocity and to stabilize the flow distribution of the suction module at a control angle of $90^{\circ}$. In addition, the flow velocity drop at the edge of the air knife-type blower can be improved by placing small inserts at the edge of the blower. Those 4 modular designs of the dust suction system can help remove the dust accumulated on the track and tunnel by optimizing the blowing and suction flows.

• Korean Journal of Optics and Photonics
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• v.15 no.2
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• pp.171-176
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• 2004

A light deflector integrated laser diode(LD) was fabricated and the characteristics of LD and ourput beam deflection as a function of deflector injection current were measured. To integrate the deflector with LD, a passive waveguide was integrated with the LD and a triangular-type light deflector was fabricated on the upper clad of the passive waveguide section. Light deflection from the fabricated light deflector is controlled by the effective refractive index variation induced by carrier injection. To characterize the effect of the deflector injection current, threshold current, slope efficiency, and output beam spectrum were measured as a function of deflector injection current. From these measured data, the increment in the threshold current and the decrement of the slope efficiency were observed. However, the output beam spectrum was not affected by the deflector. The Beam Propagation Method(BPM) was used to simulate the proposed device and the light deflection was measured by the far-field pattern of the output beam as a function of the deflector injection current. In the fabricated deflector integrated LD, the deflection angle of 1.9$^{\circ}$ at the injection current of 15 ㎃ was obtained.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.1
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• pp.1-8
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• 1999

In the present paper an attempt has been made to simulate the secondary injection-primary flow interaction in the conical rocket nozzle and to derive the performance of secondary injection thrust vector control(SITVC) system. Complex three-dimensional flowfield induced by the secondary injection is numerically analyzed by solving unsteady three-dimensional Euler equation with Beam and Warming's implicit approximate factorization method. Emphasized in the present study is the effect of secondary injection such as secondary mass flow rates and the momentum of secondary/primary nozzle flow mass rates upon the gross system performance parameters such as thrust ratio, specific impulse ratio and deflection angle. The results obtained in terms of system performance parameters show that lower secondary mass flow rate is advantageous for to reduce secondary specific impulse loss. It is further found that the nozzle with secondary jet injected downstream and interacting with fast primary flow is preferable for efficient and stable SITVC over the wide range of use with the penalty of side specific impulse loss.

• The KSFM Journal of Fluid Machinery
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• v.4 no.3 s.12
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• pp.7-13
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• 2001

The present study investigates convective heat/mass transfer and flow characteristics inside a cooling passage of rotating gas-turbine blades. The rotating duct has staggered ribs with $70^{\circ}$ attack angle, which are attached on leading and trailing surfaces. Naphthalene sublimation technique is employed to determine detailed local heat transfer coefficients using the heat and mass transfer analogy. Additional numerical calculations are conducted to analyze the flow patterns in the cooling passage. The present experiments employ two-surface heating conditions in the rotating duct because the exposed surfaces to hot gas stream are pressure and suction side surfaces in the middle passages of an actual gas-turbine blade. Secondary flows are generated by Coriolis and centrifugal forces in the spanwise and streamwise directions. The ribs attached on the walls disturb the mainflow resulting in recirculation and secondary flows near the ribbed wall. The local heat transfer and flow patterns in the passage are changed significantly according to rib configurations and duct rotation speeds. Therefore, the geometry and arrangement of the ribs are important for the advantageous cooling performance. The experimental results show that the ribs enhance the heat transfer more than $70\%$ from that of the smooth duct. The duct rotation generates the heat transfer discrepancy between the leading and trailing walls due to the secondary flows induced by the Coriolis force. The overal heat transfer pattern on the leading and trailing walls for the first and second passes are depended on the rotating speed, but the local heat transfer trend is affected mainly by the rib arrangements.

• Journal of Ocean Engineering and Technology
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• v.24 no.4
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• pp.23-31
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• 2010

The flow around a remotely-operated vehicle (ROV) has been investigated numerically to improve the resistant performance by modifying the hull form of the ROV. In the case of the base hull form considered in this study, form drag rather than friction drag was the dominant component of total drag. Subsequently, the surfaces that were most susceptible to local pressure effects were modified to give them a more streamlined shape. Eleven different hull forms were chosen to undergo surface modification for drag reduction. In addition, four different boat-tail appendages with different slant angles were installed at the stern to reduce the wake vortices that are induced by the local regions of very low pressure. Consequently, a total of 11 different hull forms for drag reduction were considered. The final hull form, which combined the hull for which surface modification resulted in the lowest drag with a boat-tail appendage with a 15-degree slant angle, resulted in a drag reduction of 20%.