• 정보저장시스템학회:학술대회논문집
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• 2005.10a
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• pp.177-178
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• 2005

The load/unload behavior of the hard disk drive slider is studied in terms of the air bearing static characteristics. The numerical continuation methods are applied to calculate suspension force - equilibrium position curve. The critical preloads of the femto size slider are analyzed. The hi-stability conditions are depicted on the skew angle - preload diagram. The perturbation method is used to check the stability of the solution branches.

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.3
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• pp.52-60
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• 2010

Combustion stability tests of 30 $ton_f$-class LRE thrust chamber with double swirl coaxial injector were carried out in domestic ground combustion test facility by means of artificial perturbation method. In these tests, thrust chambers with varying design factors like recess number of injector, baffle length, types of film cooling and chamber diameter were used and test results showed that these design factors are closely related with high frequency combustion stability. By using the oscillation decrement instead of the decay time in the combustion stability analysis of artificially perturbed LRE thrust chamber, it was confirmed that increment of damping factor results in the improvement of high frequency combustion stability of LRE thrust chamber.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.3
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• pp.31-36
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• 2006

In this study, nonlinear static aeroelastic analysis system for a high-aspect-ratio wing are developed using the transonic small disturbance (TSD) and large deflection beam theory and validated. For the coupling between fluid and structure, the transformation of displacement from the structural mesh to aerodynamic one is performed by the shape function of the beam finite element and the inverse transformation of force by work equivalent load concept. Also, for the static aeroelastic analysis of the wing the use of TSD aerodynamics are justified. The validation of the system includes one of the efficient transformation methods of force and displacement.

• Journal of Aerospace System Engineering
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• v.17 no.6
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• pp.82-93
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• 2023

In this paper, nonlinear transonic flutter analyses of a composite missile fin considering the effect of delamination are conducted. An effective modal analysis methodology is adopted and verified with the experimental modal test data for laminated composite plates with delamination. Extended version of the in-house computational aeroelastic analysis program with the transonic small-disturbance (TSD) code is used in order to predict the flutter dynamic pressure of the delaminated composite fin models. In the subsonic, transonic, and supersonic flow regions, nonlinear time-domain flutter analyses are performed for various delamination conditions, and aeroelastic characteristics due to the delamination phenomena are examined in detail.

• Korean Journal of Agricultural and Forest Meteorology
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• v.7 no.1
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• pp.28-34
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• 2005

We review three methods of separating soil respiration into root and soil microbial contribution: (1) component integration, (2) root exclusion, and (3) isotopic method. Among these methods, component integration and root exclusion are most commonly used. Root respiration contribution to soil respiration estimated by the root exclusion method is higher than those by other two methods. Trenching has little environmental disturbances in soil or on surface of site compared to other methods in root exclusion such as root removal and gap formation. Isotopic method has an advantage over other methods because of minimal soil and root disturbances, but this method is costly and requires techniques for the complex analysis. Trenching seems to be an appropriate in situ method for calculating component contributions to soil respiration with minimum disturbances in site. However, the method overestimates the contribution of microbial respiration because of root decay, and realistic results could be obtained by estimating root decay or avoiding large roots in trenched plots.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.47-51
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• 2015

하천은 인간의 활동과 산업화에 의해 많은 인위적인 교란을 받고 있다. 대표적으로 댐과 저수지는 수자원의 이용, 발전, 그리고 다양한 산업화를 위하여 건설되었다. 이는 경제발전과 함께 인간의 생명과 용수 공급 및 홍수 예방의 차원에서 많은 역할을 해오고 있다. 그러나 대부분의 댐과 저수지는 하류 하천에 서식하는 생물들에 대한 영향을 거의 고려하지 않고 건설되는 실정이다. 특히 발전방류와 같은 급격한 유량의 변화는 하류 하천에 서식하는 생물들의 서식처에 직접적으로 영향을 미치고 있다. 하류 하천에 서식하는 생물들은 인간의 인위적 교란에도 영향뿐만 아니라 유속, 수심, 기층, 영양물질, 수질, 온도 등과 같은 서식처 요소에도 영향을 받는다. 따라서 서식처 요소들에 대한 연구는 하천 생태계의 변화 또는 영향을 주는 인자에 대해 평가하고 분석하는데 유용하게 사용된다. 본 연구에서는 댐 발전방류로 인한 수온 차이가 하류 하천에 미치는 영향을 파악하였다. 발전방류로 인한 하류 하천의 수온 변화를 모의하기 위하여 미공병단에서 개발된 CE-QUAL-W2 모형을 사용하였다. 대상구간은 괴산댐 하류에 위치한 달천이며 2.5 km구간을 선정하였고, 달천 상류에 위치한 괴산댐은 빈번하게 발전방류를 발생시키고 있다. 발전방류로 인한 하류하천의 수온 변화를 살펴보기 위하여, 여름과 겨울 두 계절의 상반된 경우에 대하여 모의를 수행하였다. 괴산댐의 경우, 중층 및 하층방류를 실시하므로 상대적으로 온도 차이가 심한 발전방류가 하류 하천으로 유입이 된다. 실측된 자료를 살펴보면, 괴산댐에서 발전방류는 하류 하천과의 온도 차이가 약 $10^{\circ}C{\sim}19^{\circ}C$ 발생하는 것으로 나타났다. 본 연구를 통하여 댐 발전방류로 인한 하류 하천의 수온 변화를 분석함으로써, 댐 하류 하천에서 서식하는 생물들을 고려한 댐 운용 계획을 수립하는데 중요한 기초자료가 될 것으로 기대된다.

• Journal of the Korean Geotechnical Society
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• v.38 no.5
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• pp.5-17
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• 2022

A pile is a type of medium for constructing superstructures in weak geotechnical conditions. A pretensioned spun high-strength concrete (PHC) pile is composed of high-strength concrete with a specified strength greater than 80 MPa. Therefore, it has advantages in resistance to axial and bending moments and quality control and management since it is manufactured in a factory. However, the skin friction of a pile, which accounts for a large portion of the pile bearing capacity, is only approximated using empirical equations or standard penetration test (SPT) N-values. Particularly, there are some poor research results on the pile-soil interface under the seismic loads in Korea. Additionally, some studies do not consider geoenvironmental elements, such as groundwater pH values. This study performs sets of cyclic simple shear tests using submerged concrete specimens for 1 month to consider pH values of groundwater and clay specimens composed of kaolinite to generate a pile-soil interface. 0.2 and 0.4 MPa of normal stress conditions are considered in the case of pH values. The disturbed state concept is employed to express the dynamic behavior of the interface, and the disturbed function parameters are newly suggested. Consequently, the largest disturbance increase under basic conditions is observed, and an early approach to the failure under low normal stress conditions is presented. The disturbance function parameters are also suggested to express this disposition quantitatively.

• Korean Journal of Organic Agriculture
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• v.15 no.2
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• pp.219-228
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• 2007

강원도 고랭지는 채소 재배지로 그 이용 면적이 매년 급속히 증가하고 있다. 금한 경사와 집중적으로 발생하는 장마철의 폭우는 토양 유실은 물론이고 토양 비옥도의 심각한 저하를 초래할 위험이 경작의 강도와 범위가 넓어짐에 따라 더욱더 증가하고 있다. 또한 험한 지형에 따른 기계화 영농의 어려움과 이에 수반하는 노동력의 낭비로 문제점을 제기한다. 채소 작물 재배를 위해 많이 사용하는 요소 비료, 황산암모늄 비료와 함께 특별히 수지(resin)를 피막 처리한 복합비료를 가지고 배추의 생장과 토양에 미치는 영향을 조사하였다. 수지 피막처리는 각각 7, 10, 15%의 비율로 혼합했다. 배추의 수량은 실험에 사용된 비료간에 큰 차이가 없었다. 요소와 황산암모늄은 기본 시비와 함께 2차례 추비를 하였고 수지 피막 복합 비료는 단 한번 초기에 시비하였다. 따라서 이 경우 노동력 절감과 토양 환경 교란의 최소화를 달성할 수 있었으므로 완효성의 수지 피막 처리 비료가 바람직한 것으로 나타났다. 토양에 미치는 효과는 비료의 종류간에 별다른 차이가 없었으나 인산$(P_2O_5)$의 토양내 축적 현상이 t지 피막 처리 복합 비료 시용 구에서 뚜렷하게 조사되었다. 일반적으로 화학 비료의 시용은 토양 반응(pH)의 저하를 초래하였다.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.3
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• pp.35-47
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• 1996

A surface panel method treating a boundary-value problem of the Dirichlet type is presented to design a three dimensional body with free surface corresponding to a prescribed pressure distribution. An integral equation is derived from Green's theorem, giving a relation between total potential of known strength and the unknown local flux. Upon discretization, a system of linear simultaneous equations is formed including free surface boundary condition and is solved for an assumed geometry. The pseudo local flux, present due to the incorrect positioning of the assumed geometry, plays a role f the geometry corrector, with which the new geometry is computed for the next iteration. Sample designs for submerged spheroids and Wigley hull and carried out to demonstrate the stable convergence, the effectiveness and the robustness of the method. For the calculation of the wave resistance, normal dipoles and Rankine sources are distributed on the body surface and Rankine sources on the free surface. The free surface boundary condition is linearized with respect to the oncoming flow. Four-points upwind finite difference scheme is used to compute the free surface boundary condition. A hyperboloidal panel is adopted to represent the hull surface, which can compensate the defects of the low-order panel method. The design of a 5500TEU container carrier is performed with respect to reduction of the wave resistance. To reduce the wave resistance, calculated pressure on the hull surface is modified to have the lower fluctuation, and is applied as a Dirichlet type dynamic boundary condition on the hull surface. The designed hull form is verified to have the lower wave resistance than the initial one not only by computation but by experiment.

• Journal of the Korean Society for Marine Environment & Energy
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• v.9 no.2
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• pp.79-84
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• 2006

The present study deals with the flow over a flat plate with repeated roughness elements of 2-dimensional rectangular shape, which can be applied into the study on the natural geographical roughness and the turbulent flow on roughened solid surface. Experiment was performed using PIV technique in the circulating water channel. Results showed that the flow over roughness elements was characterized by the high shear flow emanating from top of roughness element and the recirculating region formed at the trough of two roughness elements. In general, the ratio between the spacing and the height of roughness elements plays a crucial role in developing the flow pattern near wall surface.