• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.905-912
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• 2009

1-g shaking table test is conducted to evaluate the dynamic behavior of a soil-structure system under seismic loading condition. A consistent similitude law between the model and prototype is needed to predict the behavior of the prototype structure, quantitatively. The natural frequency of geomaterial decreases with the increase of shaking intensity because of the non-linear property of the geomaterial. This phenomenon affects the applicability of similitude laws in 1-g shaking table tests. In this study, a simple method is suggested to determine the frequency of the input motions in 1-g tests in order to enhance the applicability of similitude laws. Modified input frequency is calculated using the frequency ratio with consideration of the variation of the natural frequency according to the intensity of input ground acceleration. To verify the applicability of the suggested method, a series of 1-g shaking table tests were performed for three different sizes of model piles having an overburden mass on their heads by varying the acceleration and the frequency of input motion. The acceleration amplification ratio on the overburden mass, the lateral displacement at the pile head and the maximum bending moment along the pile depth were measured. The projected behaviors of the virtual prototype based on the measured values of the model tests, where the input frequencies were calculated by the new method, showed good consistency, verifying the applicability of the suggested method.

• Structural Engineering and Mechanics
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• 제29권2호
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• pp.155-169
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• 2008

A MOM-based algorithm (MOMA) has been developed for moving force identification from dynamic responses of bridge in the companion paper. This paper further evaluates and investigates the properties of the developed MOMA by experiment in laboratory. A simply supported bridge model and a few vehicle models were designed and constructed in laboratory. A series of experiments have then been conducted for moving force identification. The bending moment and acceleration responses at several measurement stations of the bridge model are simultaneously measured when the model vehicle moves across the bridge deck at different speeds. In order to compare with the existing time domain method (TDM), the best method for moving force identification to date, a carefully comparative study scheme was planned and conducted, which includes considering the effect of a few main parameters, such as basis function terms, mode number involved in the identification calculation, measurement stations, executive CPU time, Nyquist fraction of digital filter, and two different solutions to the ill-posed system equation of moving force identification. It was observed that the MOMA has many good properties same as the TDM, but its CPU execution time is just less than one tenth of the TDM, which indicates an achievement in which the MOMA can be used directly for real-time analysis of moving force identification in field.

• 한국터널지하공간학회 논문집
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• 제4권1호
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• pp.79-90
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• 2002

현재 복개 터널 라이닝의 설계는 설계상의 간편성으로 인해 복개 터널의 라이닝에 대한 구조해석적 기법인 Rigid Frame Analysis가 널리 사용되고 있으나, 이는 되메움 지반과 터널 라이닝 사이의 상호작용(Interaction) 메카니즘을 적절히 반영하지 못하게 될 뿐만 아니라, 굴착 사면의 경사, 굴착폭 및 지표면의 경사 등에 의한 영향을 고려하지 못하는 문제점이 있다. 따라서 본 연구에서는 복개 터널구조물의 합리적이고 경제적인 설계를 위한 기본연구로써, 좁은 되메움 공간에서의 토압경감과 콘크리트 라이닝과 성토체의 상호작용을 고려하기 위하여 지반공학적 모델링 기법을 이용한 수치해석을 실시하였다. 또한 복개 터널구조물의 역학적 거동 영향인자로써 굴착사면의 경사 및 콘크리트 라이닝과 굴착사면의 이격거리 등을 고려하였으며, 각 영향인자가 복개 터널구조물의 역학적 거동에 영향을 미치는 정도를 분석하였다.

• 대한조선학회논문집
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• 제29권4호
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• pp.87-97
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• 1992

극지방의 천연자원의 수송에 필수적인 빙해항행선박은 금후 우리나라의 조선산업이 지향해야 할 기술집약형 선박중 하나로서 국제경쟁에 대비하여 독자적인 연구가 요구되는 분야이다. 본 연구는 빙해항행선박 기본설계의 중요한 인자인 선수부 형상과 평탄빙에서의 쇄빙능력 사이의 상관관계를 밝히는데 목적이 있다. 통상 평탄빙(level ice)에서 선박의 전진속도를 3-4 knots로 볼 때, 탄성으로 취급되는 얼음의 재료특성을 고려하여, 파괴시킬 수 있는 얼음의 최대두께와 파괴된 얼음의 특성길이를 수치적으로 추정하는데 주안점을 두고 있다. 본 연구에서는 빙해항행 선박이 평탄빙에서 연속쇄빙을 하고 있는 상황을 탄성지지기반 위에 놓인 유한 길이의 쐐기보에 작용한 충격하중의 문제로 가정하고 굽힘모멘트에 의해 어떤 위치에서 발생한 최대인장응력이 얼음의 굽힘파괴강도에 도달한다면 그 부분에서 파단이 일어날 가능성이 가장 높다고 판단한다.

• 대한조선학회논문집
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• 제50권1호
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• pp.59-68
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• 2013

Nowadays, optimum structural design techniques based on CSR have been developed and applied to the preliminary design stage focused on minimum weight and minimum construction cost of ship structure. Optimum structural design algorithm developed before could minimize weight and cost on fixed compartment arrangement. However, to develop more efficient design technique, a designer needs to combine optimized compartment arrangement with optimized ship structural design because compartment arrangement has a large effect on structural design according to the change of still water bending moment as a consequence of compartment arrangement change. In this study, automated algorithm for compartment arrangement of an oil tanker is developed to apply preliminary structural design. The usefulness of developed algorithm is verified with Aframax oil tanker constructed by STX shipbuilding Co.Ltd..

• 대한조선학회논문집
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• 제50권4호
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• pp.217-223
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• 2013

This paper presents the wet damping estimation of the segmented hull model using the random decrement technique together with the continuous wavelet transform. The tested 16 sea states are grouped together based on the speed of the ship in order to figure out the possible influence of the ship speed on the damping ratio. The measured time histories of vertical bending moment for each tested sea state were processed with random decrement technique to derive the free decay signal, from which the damping ratios are estimated. Also, the autocorrelation functions of the filtered signal were calculated and comparison was made with the free decay signal obtained from the random decrement technique. Then the wet damping ratios for each sea state group, as well as precise wet natural frequencies, are estimated by using continuous wavelet transform. It turned out that the wet natural frequencies derived from the measured signal did not show any significant discrepancy compared with those obtained by wet hammering test, whereas the damping ratio did. It was considered that the discrepancy of the damping ratio between in calm and moving water may be attributed to the viscous effects caused by dramatically different flow pattern and relative velocity between the vibrating structure and surrounding fluid particles.

• Structural Engineering and Mechanics
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• 제12권6호
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• pp.657-668
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• 2001

Fiber reinforced cementitious composites are nowadays widely applied in civil engineering. The postcracking performance of this material depends on the interaction between a steel fiber, which is obliquely across a crack, and its surrounding matrix. While the partly debonded steel fiber is subjected to pulling out from the matrix and simultaneously subjected to transverse force, it may be modelled as a Bernoulli-Euler beam partly supported on an elastic foundation with non-linearly varying modulus. The fiber bridging the crack may be cut into two parts to simplify the problem (Leung and Li 1992). To obtain the transverse displacement at the cut end of the fiber (Fig. 1), it is convenient to directly solve the corresponding differential equation. At the first glance, it is a classical beam on foundation problem. However, the differential equation is not analytically solvable due to the non-linear distribution of the foundation stiffness. Moreover, since the second order deformation effect is included, the boundary conditions become complex and hence conventional numerical tools such as the spline or difference methods may not be sufficient. In this study, moment equilibrium is the basis for formulation of the fundamental differential equation for the beam (Timoshenko 1956). For the cantilever part of the beam, direct integration is performed. For the non-linearly supported part, a transformation is carried out to reduce the higher order differential equation into one order simultaneous equations. The Runge-Kutta technique is employed for the solution within the boundary domain. Finally, multi-dimensional optimization approaches are carefully tested and applied to find the boundary values that are of interest. The numerical solution procedure is demonstrated to be stable and convergent.

• 한국지반공학회논문집
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• 제33권7호
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• pp.17-28
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• 2017

본 연구에서는 건조사질토 지반에 근입된 말뚝의 동적 거동을 분석하기 위해 1g 진동대 실험을 수행하였다. 지반-말뚝 시스템의 고유 진동수를 측정한 후 고유 진동수를 기반으로 하중 진동수를 산정하고 이에 대한 거동을 분석하였다. 또한, 추가적으로 말뚝의 동적 거동에 영향을 미치는 인자를 분석하기 위하여 입력 가속도, 상부하중, 말뚝 두부 구속 조건에 따른 거동을 분석하였다. 분석결과, 하중 진동수가 지반-말뚝 시스템의 고유 진동수보다 큰 경우 상대적으로 말뚝 두부변위와 휨모멘트가 크게 발생하고 동적 p-y 곡선의 기울기가 작게 나타났다. 또한, 동적 p-y 곡선의 영향인자를 분석한 결과, 말뚝 두부구속조건은 동적 p-y 곡선의 기울기에 영향을 적게 끼침을 확인하였고, 입력가속도, 상부하중 등의 의한 관성력, 지반-말뚝 시스템의 고유 진동수와 입력 진동수의 관계 그리고 지반조건이 동적 p-y 곡선의 기울기에 큰 영향을 끼치는 것으로 확인되었다.

• 한국압력기기공학회 논문집
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• 제8권3호
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• pp.13-22
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• 2012

According to recent research on leak-rate estimates to assess rupture probabilities of nuclear piping which contains a circumferential surface/through-wall cracks due to PWSCC, i.e., xLPR (Extremely Low Probability of Rupture) program, it has been revealed that the use of crack shape with an idealized circumferential through-wall crack during actual crack growth can lead to overestimate of the leak-rate. Thus, for accurate estimation of the leak-rate during crack growth, the more realistic crack shape that can simulate the crack shape transition from surface crack to through-wall crack should be used. In this context, in the present study, the elastic crack opening displacement of slanted circumferential through-wall crack in thick-walled cylinder was proposed based on 3-dimensional elastic finite element fracture mechanics analyses. To propose the elastic crack opening displacement of slanted circumferential through-wall crack in thick-walled cylinder, the geometric variables affecting crack opening displacement, i.e., thickness of cylinder, reference inner crack length and slant crack ratio were systematically varied. In terms of loading conditions, axial tension, global bending moment and internal pressure were considered. The present results can be applied to calculate the leak-rate considering more realistic crack shape transition from surface crack to idealized through-wall crack, and can be expected to enhance current leak-rate estimation scheme, for instance, in xLPR program etc.

• 한국가스학회지
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• 제12권2호
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• pp.57-62
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• 2008

배관 엘보우의 내호면(intrados)의 과 내부에 국부적으로 두께 감육이 발생한 경우, 내압과 엘보우를 닫는 방향으로의 굽힘하중을 부가하여 파손 모드를 연구하였다. 탄소성해석 시 반력-변위 곡선이 세 그룹으로 나뉘므로 각 그룹의 한 경우씩을 해석하여 소성붕괴에 의한 파손모드의 차이를 확인하였다. 이를 위해 주요 부위에서 하중-국부적응력 곡선이 어떻게 변화하는지 결정하여, 이로부터 관찰된 파손모드와 비교하여 설명하였다. 감육폭이 $90^{\circ}$인 경우 배관은 엘보우 측면부터 소성붕괴가 시작되었으며, $360^{\circ}$인 경우 내호면으로부터 소성변형이 시작되어 서로 다른 파손모드를 보여주었다. 배관의 감육측정에 의한 건전성 평가 시 이와 같은 파손 모드의 차이점을 고려하여 평가를 실시하여야 한다.