• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.8
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• pp.790-796
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• 2008

Typical solid rocket motors have a fixed propellant grain shape and nozzle throat size resulting in a fixed motor thrust. Pintle nozzle has been suggested as a means of providing variable thrust while maintaining the inherent advantage of solid rocket motors. In this study, the pintle shape effect on nozzle performance is investigated using experimental-aided Computational Fluid Dynamics(CFD). The pintle shape is modified by a principle of monotony. CFD analysis is performed using Fluent by applying the turbulent model. This analysis indicates that nozzle thrust and pintle load are influenced by change of nozzle shock pattern and flow separation due to pintle shape and there exists a high-performing pintle shape.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.2
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• pp.450-460
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• 1996

To investigate the effect of stress wave propagation for crack tip, impact responses of two-dimensional plates with oblique cracks are investigated by a numerical method. In the numerical analysis, the finite element method is used in space domain discretization and the Newmark constant acceleration algorithm is used in time integration. According to the numerical results from the impact response analysis. it is found that the stress fields are bisected at the crack surface and the parts of stress intensity are moved along the crack face. The crack tip stress fields are yaried rapidly. The magnitude of crack tip stress fields are converted to dynamic stress intensity factor. Dynamic sress intensity factor appears when the stress wave has reached at the crack tip and the aspect of change of dynamic stress intensity factor is shown to be the same as the part of the flow of stress intensity.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.4
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• pp.87-99
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• 1993

The computer program, MFPD, which is used to backcalculate the layer moduli of asphalt concrete pavement system is modified by contemplating the depth to virtual bedrock in this study. An algorithm to estimate the depth to virtual bedrock is developed through the analysis of FWD impulse load duration and the compression wave velocity of ground. For verification of the modified MFPD, FWD is fabricated and then FWD field tests and verification tests are carried out at the test sites. Plate loading tests and surface wave propagation tests are performed at FWD test sites. Laboratory tests (Marshall stability tests, unconfined compression tests) for sampled asphalt concrete specimens are also carried out. From comparison analysis, the validity and applicability of the modified MFPD are verified.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.1
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• pp.1-9
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• 1985

In-plane tension fatigue tests (R = 0.05) were carried out to investigate the initiation and propagation behaviors of micro-surface-fatigue cracks on smooth surfaces of a mild steel. Also, the investigations of saturated cyclic strain which can be obtained by the fatigue tests have been made via the cyclic strain intensity factor, .DELTA. $K_{\epsilon}$/, for the purpose of unifying two approaches of the study of fatigue; the one approach is based on the fracture mechanics concept and the other on lowcycle fatigue concept. Some of the results are as follows; The growth rate, d(2a)/dN, of small cracks cannot be represented by one straight line as a function of .DELTA.K for various of the nominal stress range, .DELTA..sigma., and is higher than that of a larger through crack. The rearrangement of the d(2a)/dN by .DELTA..epsilon..root..pi.s( = .DELTA. $K_{\epsilon}$/) with the stress range .DELTA..epsilon. in .DELTA.K replaced by .DELTA..epsilon., strain range, gives one straight line of the .DELTA. $K_{\epsilon}$-d(2a)/dN relation for various values of stress range .DELTA.$_{\epsilon}$../.X>../.

• 한국지구물리탐사학회:학술대회논문집
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• 2009.10a
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• pp.155-159
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• 2009

Crack-controlled method which utilizes the dynamic energy such as explosives and propellent gases have been applied to the development of mineral resource and oil and civil engineering. It is necessary to consider the fracture processes associated with the material properties and external forces to control crack propagation using borehole pressure. To investigate the influence of the applied borehole pressure waveform on the crack propagation in rock masses having different material properties, a no-free surface model was used, consisting of a borehole in rock with a continuous boundary. Loading rates ranging from 1 to 100MPa/${\mu}s$ with different rock mass properties was employed to investigate the loading rate dependency of fracture patterns in the rock mass.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.527-530
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• 2011

전 세계적인 LNG 수요 증가에 따라 LNG 운반선의 대형화 및 극한 환경의 항로 선택이 불가피해지고 있다. 이러한 상황에서 LNG의 슬로싱 현상에 따른 화물창의 구조적 안정성 여부가 큰 이슈거리로 떠오르고 있다. 슬로싱 현상에 의한 구조 안전성을 평가하는 가장 이상적인 방법은 유체 영역과 탱크의 복합적인 상호 작용을 완벽하게 구현하는 것이다. 하지만 과도한 계산 시간과 결과의 정확성이 확보되지 못한 상황에서 LNG 운반선 화물창의 안전성 평가에 적용하기에는 문제가 있다. 많은 연구 단체에서는 불규칙적인 슬로싱 압력 신호를 삼각파 등의 형태로 이상화하여 구조해석에 적용하고 있지만 이 또한 유체의 압축성 및 비선형성을 고려하는데 한계를 드러내고 있다. 본 연구에서는 슬로싱 하중을 받는 구조의 안전성을 평가함에 있어 쌍방향(2-way) FSI(Fluid-Structure Interaction)의 과도한 해석 시간 및 수렴의 어려움을 보안하고 유체의 비선형성을 고려할 수 있는 단 방향(1-way) FSI 기법을 이용하는 절차를 제안하고자 한다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.1
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• pp.87-94
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• 2003

A geometric non-linear finite element formulation of CRTS reflector subjected to displacement loads, corresponding to the successional assembly steps of the reflector, is presented in order to determine the initial static equilibrium state based on the displacement incremental method. Parametric analyses of the influence of cables and mechanical properties of the reflector on the shape error between reference and equilibrium surfaces have been studied. These results of the present study are compared with the others using Galerkin mothod and NASS 98 program to demonstrate the feasibility.

• Journal of the Society of Naval Architects of Korea
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• v.35 no.4
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• pp.46-54
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• 1998

In this paper, the erect of notch geometries on dynamic stress concentration was investigated by using the dynamic photoelasticity and the drop weight loading system Dynamic stress fields arisen by elastic wave through the loading system around various types of notch geometries were captured by using $10^6/sec$ frame rate Cranz-Shardin camera system with 12 photographic frames. We found that dynamic stress concentrations around the notch tip and comer were highly dependent on the change in notch geometries. The elders of dynamic stress singularity ware determined with respect to varying geometries of notches and we explained dynamic stress concentration in terms of the orders of dynamic stress singularity.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.1
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• pp.75-82
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• 1999

일반 해양 구조물이나 해저면에 설치되는 해저 관로는 외력에 의한 변형이 발생된다. 구조물 형상이 복잡하거나, 구성 요소의 개수가 많을 경우 응력해석 시 많은 초기값이 필요하고 해석 시간 또는 장 시간 소요된다. 해양 구조물에 작용하는 대표적인 외력은 파도, 조류, 바람이고 이런 외력은 구조물의 사용 기간(operation life)동안 계속적으로 작용하기 때문에 구조물의 변형율은 항상 허용치 안에서 발생되도록 설계되어야 한다. 허용 변형은 탄성범위 내에 존재해야 하며, 비교적 큰 변형을 일으키는 구조물이나 해저파이프라인의 응력해석을 수치적으로 접근하는 방법을 고찰하였다. 평행상태의 하중 벡터값만 직각 좌표계에서 인트린직(intrinsic) 좌료로 변환시킬 때 변형이 발생함으로, 본 논문에서 소개하는 이차 요소(quadratic element)방법을 사용할 경우 수치해석 시 많은 장점이 있다는 것을 보여준다. 본 방법을 도입함으로써 비교적 큰 변형이 발생되는 구조물 해석 시 일반 수치해석 방법과 그 결과는 같으나 해석 시간을 단축시킬 수 있다는 장점이 있다. 응력 해석 시 국부 강도 행열(element stiffness matrix)은 방향과 무관하며 이차요소 방법을 사용하여 각 요소 벡터를 발생시켰다. 해저관로 일점 상승 시 관로에 작용하는 변형과 상승력에 따른 휨 모멘트를 산출하여 일반적으로 사용되는 선형이론과 비교하였다.

• Journal of the Society of Naval Architects of Korea
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• v.35 no.1
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• pp.61-71
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• 1998

This paper describes a dynamic fracture behaviors of structural elements under elastic or elasto-plastic stress waves in two dimensional space. The governing equation of this problem has the type of hyperbolic partial differential equation, which consists of the equation of motions and incremental elasto-plastic constitutive equations. To solve this problem we introduce Zwas' method which is based on the finite difference method. Additionally, in order to deal with the dynamic behavior of elasto-plastic problems, an elasto-plastic loading path in the stress space is proposed to model the plastic yield phenomenon. Based on the result of this computation, the dynamic stress intensity factor at the crack tip of an elastic material is calculated, and the time history of a plastic zone of a elasto-plastic material is to be shown.