• 대한조선학회논문집
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• 제55권5호
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• pp.438-447
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• 2018

For a fixed jacket type offshore structure directly supported by the seabed, the structural behavior of offshore structure depends on the soil properties. Soil properties affect on the stiffness of the piles and the boundary condition in the structural analysis. The structural analysis is performed using PSI (Pile-Soil Interaction) suggested in the code and design rule. PSI analysis of the jacket structure is carried out after various soil types are selected according to the soil properties like internal friction angle, undrained shear strength, unit weight and so on. Three types of soil are selected by varying strength for a clay and sand, respectively. The structural analysis of the jacket structure is performed using these soils. The results about axial and lateral reaction force and the stress and displacement on the structure are compared. As a results, the structural response is smaller as the soil becomes more stiff. In conclusion, it is confirmed that the structural response of fixed jacket type offshore platform supported by seabed is sensitive to the change of soil properties.

• 한국전산구조공학회논문집
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• 제27권4호
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• pp.223-230
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• 2014

본 논문에서는 FSI해석을 이용하여 비정형 초고층 빌딩의 풍응답 특성을 연구하였다. 해석모델은 Twist모델이며, 뒤틀림 각도와 풍가속도의 상관관계에 대해 연구 중점을 두었다. 먼저 단방향 해석을 수행하여 100년 재현주기 풍속에 대한 최대 횡 변위를 구하고, 제한조건을 만족하는 탄성계수를 산출한다. 그리고 양방향 해석을 수행, 시간이력해석을 통해 산출된 탄성계수와 임의의 밀도를 가지는 풍가속도를 예측하게 된다. 정방형 모델은 높이 400m, 변장비 1:1, 세장비 8로 설정, 뒤틀림 모델은 0도에서 90도까지 15도 간격으로, 90도에서 360도까지 90도 간격으로 비틀어 회전시켰다. 형상에 따른 풍가속도 예측 결과, 정방형 모델이 뒤틀림 모델보다 크게 산출되어 풍진동 영향에 더 민감한 것을 검증하였다.

• 한국가스학회지
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• 제12권3호
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• pp.68-74
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• 2008

폭발챔버에서 전파하는 화염과 장애물 위치 및 형태에 따른 상관관계를 조사하기 위해 폭발실험을 수행하였다. 챔버내에 장애물 설치 위치는 점화원으로부터 상부로 200 mm, 500 mm, 800 mm 높이로 변화를 주어 설치하였고, 장애물 형태는 삼각기둥, 사각기둥 및 원통형으로 변화시켰다. 전파하는 화염과 장애물 위치 및 형태에 따른 상관관계를 조사하기 위해 고속카메라를 사용하였다. 고속카메라로 얻어진 화염 이미지로부터 장애물 주위의 국부 화염속도 및 그 화염속도의 확률밀도함수가 계산되었다. 실험결과, 장애물이 800 mm에 위치하였을 때 화염속도 및 폭발압력이 가장 높게, 200 mm에서는 가장 낮게 나타났다. 이러한 결과는 폭발거동 특성이 장애물 위치에 큰 의존성을 가지는 것으로 해석될 수 있다. 또한, 장애물 형태가 삼각형이었을 때 화염속도 및 폭발압력이 가장 높게, 원형에서는 가장 낮게 나타났다.

• 한국농공학회지
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• 제23권3호
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• pp.96-104
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• 1981

In order to investigate the characteristics of the shear strength of the unsaturated cohesive soils which has mean characters of sand and clay widely used for banking, I selected soil samples from An-sung district and, against it, performed direct shear test and unconfined compression test changing grain size, compaction energy and moisture content and also performed triaxial compression test under optimum moisture content. The results are as follows; 1.As the passing percent of the No. 200 sieve increased from 23.6% to 56.1%, cohesion increased from 0. 202kg/cm2 to 0. 398kg/cm2 under the direct shear test and from 0.38 kg/cm2 to 1. 05kg/cm2 under the tria4al compression test, internal friction angle decreased from 44. 78$^{\circ}$ to 34. 34$^{\circ}$ under the direct shear test and from 31. 88$^{\circ}$ to 13. 31$^{\circ}$ under the triaxial compression test. 2.Cohesion showed it's maximum value around OMC and internal friction angle showed a tendency to increase according to the decrease of water content but it's increasing ratio was relatively slow. 3.Decreasing ratio of cohesion and internal friction angle was relatively sensitive according to the decrease of compaction energy. 4.The smaller of the vertical stress and the coarser of the grain size of samples, changing of the volume showed a tendency to increase and as the increase of water content, the shear displacement (dh) at failure shear stress ($\tau$f) showed maximum and the $\tau$f-dh curve was gentle. 5.To synthesize the results of the direct shear test and the triaxial compression test, cohesion showed higher under the triaxial compression test and internal friction angle showed a tendeney to appear higher under the direct shear test. It seems that we can get correspondent results by removing the side friction of mold with soils and adjusting the vertical stress and shearing speed under the direct shear test.

• 비파괴검사학회지
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• 제28권4호
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• pp.352-357
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• 2008

구조물의 안전 보장 문제에 있어 재료의 파손 이전에 미세균열을 검출하는 것은 매우 중요하다. 비선형 초음파 기법은 일반적인 초음파 기법보다 미세결함에 민감하기 때문에 이를 이용하여 비파괴적으로 구조물이나 재료의 건전성을 진단하는 방법이 주목받고 있다. 계면접촉에 의한 비선형 초음파 효과는 초음파가 내부의 미세 균열에 입사될 때 미세균열면에서 응력과 변위가 비선형 관계를 가지고, 이에 의해 파가 왜곡되어 그 결과 고조파 성분이 발생하는 현상이다. 본 연구에서는 이러한 비선형 초음파 기법의 적용가능성을 알루미늄 시편에 인위적으로 발생시킨 피로균열을 대상으로 실험적으로 검증하고자 하였다. 이를 위해 V-노치를 갖는 A16061의 피로균열 시험편을 준비하고, 균열방향으로 2차 고조파 성분의 크기를 측정하였다. 실험결과 미세균열에서 고조파 성분이 크게 발생하며 이 기법에 의한 균열깊이 측정이 일반적인 반사파의 6 dB drop법보다 정확함을 확인하였다.

• 한국소음진동공학회논문집
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• 제14권7호
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• pp.604-611
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• 2004

It is well known that wall impedance essentially determines how sound wave transmits from one place to another. The wall impedance is related with its dynamic properties : for example, the mass, stiffness, and damping characteristics. It is noteworthy, however, that the wall impedance is also function of spatial characteristics of two spaces that is separated by the wall. This is often referred that the wall is not locally reacting. In this paper, we have attempted to see how the acoustic characteristics of the two spaces is affected by various structure parameters such as density, applied tension, and a normalized length of the wall. Calculations are conducted for two different modally reacting boundary conditions by modal expansion method. The variation of the Helmholtz mode and the structural-dominated mode are analyzed as the structure parameters vary. The displacement distribution of the structure, pressure and active intensity of the inside and outside cavity are presented at the Helmholtz mode and the structure-dominated mode. It is shown that the frequency characteristics are governed by both structure-and fluid-dominated mode. The results exhibit that the density of the structure is the most sensitive design parameter on the frequency characteristics for the coupling system as we could imagine in the beginning. The Helmholtz mode frequency decrease as density increases. However. it increases as applied tension and an opening size increase. The bandwidth of the Helmholtz mode is mainly affected by density of the structure and its opening size.

• 대한원격탐사학회지
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• 제26권3호
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• pp.347-359
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• 2010

Ortho-photos provide valuable spatial and spectral information for various Geographic Information System (GIS) and mapping applications. The absence of relief displacement and the uniform scale in ortho-photos enable interested users to measure distances, compute areas, derive geographic locations, and quantify changes. Differential rectification has traditionally been used for ortho-photo generation. However, differential rectification produces serious problems (in the form of ghost images) when dealing with large scale imagery over urban areas. To avoid these artifacts, true ortho-photo generation techniques have been devised to remove ghost images through visibility analysis and occlusion detection. So far, the Z-buffer method has been one of the most popular methods for true ortho-photo generation. However, it is quite sensitive to the relationship between the cell size of the Digital Surface Model (DSM) and the Ground Sampling Distance (GSD) of the imaging sensor. Another critical issue of true ortho-photo generation using high resolution satellite imagery is the scan line search. In other words, the perspective center corresponding to each ground point should be identified since we are dealing with a line camera. This paper introduces alternative methodology for true ortho-photo generation that circumvents the drawbacks of the Z-buffer technique and the existing scan line search methods. The experiments using real data are carried out while comparing the performance of the proposed and the existing methods through qualitative and quantitative evaluations and computational efficiency. The experimental analysis proved that the proposed method provided the best success ratio of the occlusion detection and had reasonable processing time compared to all other true ortho-photo generation methods tested in this paper.

• Nuclear Engineering and Technology
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• 제53권9호
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• pp.3026-3034
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• 2021

Multi-target X-ray tube is a new type X-ray source, and can be applied in many fields such as sensitive X-ray fluorescence analysis and medical imaging. In this work, we report an electric field modulation multi-target X-ray tube, which contains four targets (Cr, Ni, Au, Mo) coated on a Beryllium (Be) window. A four-valve electric field deflector was developed to deflect the electron beam to bombard the corresponding targets. Particle dynamics analysis software was employed to simulate the particle tracking of electron beam. The results show that the 30 keV electron beam could get a 6.7 mm displacement on the target plane by 10⁵ V/m electric field. The focus areas are about 2 mm × 5 mm and 4 mm × 2.5 mm after deflection in two directions. Thermal behavior calculated by ANSYS shows that the designed target assembly could withstand a 10 W continuous power. The optimum target thicknesses and emission spectra were obtained by Geant4 when the thickness of Be window was 300 mm and the electron beam incident angle was 0.141 rad. The results indicate that this multi-target X-ray tube could provide different X-ray sources effectively.

• 한국지반신소재학회논문집
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• 제17권4호
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• pp.81-92
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• 2018

최근 천연가스에 대한 수요가 높아지면서 이를 저장하기 위한 LNG 탱크의 건설이 증가하고 있다. LNG는 효율적인 저장을 위해 극저온의 유체로 액화되므로, LNG 탱크의 결함으로 인한 LNG 유출은 막대한 피해를 야기할 수 있다. 많은 연구자들이 다양한 LNG 유출 상황에 대하여 발생가능 한 피해 영향을 평가하였으나, 극저온의 LNG 유체가 유출될 경우 LNG 탱크를 지지하고 있는 지반에 미치는 영향에 대한 연구는 제한적이다. 따라서 본 논문에서는 LNG 탱크 및 지반의 다양한 조건을 고려하여 LNG 유출에 따른 동결 지반의 역학적, 열적 거동 변화에 대한 연구를 수행하였다. 유출 시나리오의 구현을 위해 수치해석을 수행하였으며, 상재하중, 온도 경계조건, 흙의 동결 민감성 변화에 따른 지반과 기초구조물 거동을 조사하고자 하였다. 이를 통해 LNG 유출 이후 지반의 단기 및 장기 온도변화를 평가하였으며, 지반 동결에 따른 간극 및 연직변위 변화를 분석하였다.

• 대한조선학회논문집
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• 제56권1호
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• pp.82-93
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• 2019

In this paper, the ductile fracture criteria for a marine structural steel (EH36) are presented and validated. The theoretical background of the recently developed Hosford-Coulomb (HC) fracture strain model and the DSSE fracture strain model which was developed to apply to the shell elements is described. In order to accurately estimate the flow stress in the large strain range up to the fracture, the material constants for the combined Swift-Voce constitutive equation were derived by the numerical analyses of the smooth and notched specimens made from the EH36 steel. As a result of applying the Swift-Voce flow stress to the other notched specimen model, a very accurate load - displacement curve could be derived. The material constants of the HC fracture strain and DSSE fracture strain models were independently calibrated based on the numerical analyses for the smooth and notch specimen tests. The user subroutine (VUMAT of Abaqus) was developed to verify the accuracy of the combined HC-DSSE fracture strain model. An asymmetric notch specimen was used as verification model. It was confirmed that the fracture of the asymmetric specimen can be accurately predicted when a very small solid elements are used together with the HC fracture strain model. On the other hand, the combined HC-DSSE fracture strain model can predict accurately the fracture of shell element model while the shell element size effect becomes less sensitive.