• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.4
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• pp.17-26
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• 2005

Numerical investigation has been made on the aerodynamic characteristics of supersonic air-launching rocket, as a new concept launching mechanism. Parametric study on the variations of launching velocity, incident angle and mounting location of the rocket has been performed using three dimensional Euler equations. Influential factors at separating stage of the rocket were extracted through comprehensive analyses, and, the response surface models were constructed for those factors. From the study, the aerodynamic behavior of the air-launching rocket at supersonic speed and useful guidelines for the optimal mounting location of the rocket have been obtained.

• Journal of Institute of Convergence Technology
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• v.11 no.1
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• pp.29-32
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• 2021

편대비행 항공기들은 선행항공기에서 발생시킨 후류의 영향으로 후행항공기의 공력효율이 증가하는 것으로 잘 알려져 있다. 비점성 비회전 유동장에 관한 연속방정식을 지배방정식으로 사용하는 패널법은 비교적 빠른 시간 이내에 항공기의 공력특성 변화를 계산할 수 있는 장점이 있다. 본 연구에서는 편대비행 항공기들 사이의 항공기들 사이의 흐름방향 거리는 스팬길이의 2.5배로 위치시키고, 수평상대거리는 스팬길이의 -0.4~0.3배로, 수직상대거리는 스팬길이의 -0.25, -0.15.0.15.0.25배로 변화시키며 계산을 수행했다. 연구결과 선행항공기와 후행항공기의 수평상대거리 변화의 경우 주날개들이 안쪽으로 겹침이 발생하고, 수직 상대거리가 가까울수록 더 큰 공력성능 향상을 얻을 수 있었다. 편대비행 하는 후행항공기의 공력성능 향상은 선행 항공기로부터 발생한 익단 와류의 올려흐름 영향에 기인한 것이다. 선행항공기로부터 발생한 익단와류는 후행항공기의 모멘트 특성을 변화시켜 비행안정성에 영향을 미치게 된다. 향후 연구에서는 선행항공기로부터 발생한 와의 영향이 후행항공기의 모멘트 특성에 미치는 영향을 연구 할 것이다.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.1
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• pp.1-14
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• 2023

High-Frequency Radar (HF-Radar) data of surface currents in Yeongil Bay (a semi-enclosed sea area of the East Sea) was used to investigate the between wind and horizontal surface currents The variation in horizontal and vertical flow of surface currents correlated closely to the water temperature time-series data of densely spaced (1 to 2 m) layers. During the time-series observation period, when the northeast wind prevailed over the entire Yeongil Bay area, a rapid rise in water temperature was recorded across all the layers. Moreover, currents parallel to the wind direction were clearly observed in low-frequency currents of the surface layer. Time-delayed correlation analysis between wind and surface current confirmed that if northeasterly wind blows in Yeongil Bay and continues unidirectionally, a southwestward surface current occured within a short period of time (1 to 2 hours). Convergence and divergence were calculated from the daily average values of low-frequency surface currents. A rapid rise in temperature occurred in the lower layers of water at the observation points, due to the convergence (downwelling) of the surface seawater (relatively high temperature water) associated with the northeasterly wind.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.19 no.2
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• pp.99-108
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• 2014

One year long time-series current data were obtained at two stations (K1 and K2) located in the Usan Trough in the area north of Ulleungdo in the East Sea from September 2006. The observed data reveal enhanced seafloor flows in both stations with variabilities of about 20 days which is possibly governed by the topographic Rossby wave. After February 2007, strong flow in the upper layer in St. K1 appears throughout the mooring period and this is due to the passage of the warm eddy comparing with satellite sea surface temperature data. During this period, no significant correlation between the current in the upper layer and those in two deep layers is shown indicating the eddy does not affect flows in the deep ocean. It is also observed that the flow direction rotates clockwise with depth in both stations except for the upper of the K1. This implies that the deep flow does not parallel to the isobaths exactly and it has a downwelling velocity component. The possibility of the flow from the Japan Basin to the Ulleung Basin across the Usan Trough is not evidenced from the data.

• Journal of Soil and Groundwater Environment
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• v.13 no.5
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• pp.33-46
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• 2008

A series of three-dimensional numerical simulations using a generalized multidimensional hydrodynamic dispersion numerical model is performed to simulate effectively and to evaluate quantitatively impacts of fault existence on densitydependent groundwater flow and salt transport in coastal aquifer systems. A series of steady-state numerical simulations with calibration is performed first for an actual coastal aquifer system which contains a major fault. A series of steadystate numerical simulations is then performed for a corresponding coastal aquifer system which does not have such a major fault. Finally, the results of both numerical simulations are compared with each other and analyzed. The results of the numerical simulations show that the major fault produces hydrogeologically significant heterogeneity and true anisotropy in the actual coastal aquifer system, and density-dependent groundwater flow, salt transport, and seawater intrusion patterns in the coastal aquifer systems are intensively and extensively dependent upon the existence or absence of such a major fault. Especially, the major fault may act as a pathway for groundwater flow and salt transport along the direction parallel to its plane, while it may also behave as a barrier against groundwater flow and salt transport along the direction perpendicular to its plane.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.8
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• pp.656-663
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• 2006

The convective heat transfer on the outer surface of tube arrays perpendicular to the flow direction was experimentally investigated. The test sections which include the aligned and staggered arrangements were made and the local heat transfer coefficients on the outer surface of the tube were measured after the flow has been fully developed. The results showed that the local heat transfer coefficients of the staggered arrangement, which has transverse pitch of 0.075 m and longitudinal pitch of 0.08 m, were about 15% greater than that of the aligned arrangement. Also, the overall mean Nusselt number of the former was greater than that of the latter. It is verified that the results obtained by using the simulation show the same tendency with those of experiment.

• Tunnel and Underground Space
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• v.13 no.1
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• pp.52-63
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• 2003

Discontinuities such as faults, fractures and joints in rock mass play the dominant role in the mechanical and hydraulic properties of the rock mass. The key factors that influence on the flow of groundwater are hydraulic and geometric characteristics of discontinuities and their connectivity. In this study, a program that analyzes groundwater flow in the 3D discontinuity network was developed on the assumption that the discontinuity characteristics such as density, trace length, orientation and aperture have particular distribution functions. This program generates discontinuities in a three-dimensional space and analyzes their connectivity and groundwater flow. Due to the limited computing capacity In this study, REV was not exactly determined, but it was inferred to be greater than 25$\times$25$\times$25 ㎥. By calculating the extent of aperture that influences on the groundwater flow, it was found that the discontinuities with the aperture smaller than 30% of the mean aperture had little influence on the groundwater flow. In addition, there was little difference in the equivalent hydraulic conductivity for the the two cases when considering and not considering the boundary effect. It was because the groundwater flow was mostly influenced by the discontinuities with large aperture. Among the parameters considered in this study, the length, aperture, and orientation of discontinuities had the greatest influence on the equivalent hydraulic conductivity of rock mass in their order. In case of existence of a fault in rock mass, elements of the equivalent hydraulic conductivity tensor parallel to the fault fairly increased in their magnitude but those perpendicular to the fault were increased in a very small amount at the first stage and then converged.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.7
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• pp.539-549
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• 2017

In this paper, experimental studies on the shroud separation were performed to investigate characteristics of the shroud separation at mach 3. Shroud separation tests were carried out in the vertical free-jet wind tunnel that is capable of testing separable structures. A shroud model was miniaturized to meet test objectives and test section dimensions of the wind tunnel. Pneumatic Locking and separation mechanisms were designed considering external force due to free stream. High speed cameras were used to record the shroud motion and unsteady shock patterns over the deploying shrouds during the shroud separation process. Also, unsteady pressures on the nose surface were measured by using the pressure sensors. Through the tests, the measurement data necessary for researches on the shroud separation technology were obtained. Shroud separation behaviors and characteristics of unsteady pressure on the nose surface for each external flow conditions were analyzed.

• Korean Journal of Applied Biomechanics
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• v.18 no.1
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• pp.203-212
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• 2008

The purpose of this study is to propose appropriate model for 3 staged Didimsae movement to Jajinmori rhythm and to provide information for ideal foot step movements. For the locational change of body center, the height of body center is lowered at the moment of forward step and during forward intersection of the feet, forward direction linear motion is converted to vertical motion to maintain stability. Speed change of body center reduces flow of body on step forward moment and controls rapid forward movement for stabled movement and position when preventing fast forward horizontal direction movement of centroid speed while knee joint and foot joint are vertically risen for heel bone contacts the ground. For angle changes of joints, in order to prevent hyperextension of lower leg, hip joint is extended and knee joint is curved to secure stability of movement for smooth curves and extension. When centroid of foot joint is moved from top of the feet to whole foot sole and when left foot makes dorsal curve, stabled movement is accomplished.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.11
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• pp.971-978
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• 2016

Recent trends in miniaturization and lightness in portable electronics parts have driven developments in subminiature screws. This study aims to investigate the thread rolling process of a subminiature screw with an outer diameter and pitch of 1.0 and 0.25 mm, respectively. Finite element (FE) analyses were performed for the thread rolling process of symmetric and asymmetric screw threads. Through FE analyses, various process parameters, such as the horizontal and vertical die gap and the rolling stroke, were investigated in terms of the forming accuracy. The material flow characteristics in the thread rolling process of the symmetric and asymmetric screws were also discussed, and the relevant process parameters were determined accordingly. These simulation results were then reflected on real thread rolling processes, from which the symmetric and asymmetric screws could be formed successfully with allowable dimensional accuracy.