• 한국구조물진단유지관리공학회 논문집
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• 제6권3호
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• pp.211-220
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• 2002

CGS(Compaction Grouting System) is widely used in reinforcement of structural foundation and ground improvement in soft ground. But the effects of ground improvement depending on the type of soil must be studied in order to adopt in various soils (granular soil and cohesive soil). In this study, characteristics of ground improvement (the increase of N value, increase in unit weight, vertical displacement on the ground surface) by CGS method was compared through two cases that were performed in granular and cohesive soil. The results show that the closer to the grout hole, the more increase in N value and this trend appear distinctly in granular soil. Unit weight of ground increase largely near by the grout hole and decrease in far from it independently of the soil type. The vertical displacement on the ground surface appeared in smaller area in case of granular soil than cohesive soil.

• 한국산업융합학회 논문집
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• 제25권4_2호
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• pp.603-609
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• 2022

Bottom hole assembly(BHA) is a key component of the drilling system, consisting of various components and tools(including the drill bit and mud motor) which operate at the bottom of the wellbore and physically drill the rock. This paper investigates the dynamic characteristics of the mud motor which is a drilling propulsion tool. And computational structural analysis is performed to calculate the von-Mises stress and the safety factor of components constituting the mud motor. In this process, the field test data of onshore drilling are used for analysis.

• Journal of Electrical Engineering and Technology
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• 제12권5호
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• pp.1842-1850
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• 2017

Reducing the noise and vibration of the BLDC motors is very essential for some special applications. In this paper, a new structural design is introduced to increase the natural frequencies of the stator in BLDC motors as increasing the natural frequencies can reduce the severe effects of the structural resonances, including high levels of noise and vibration. The design is based on placing a single hole on definite regions at the stator cross sectional area (each region contains one tooth and its upper parts in the stator yoke) in an optimum way by which the natural frequencies at different modes are shifted to the higher values. The optimum diameter and locations for the holes are extracted by the Response Surface Methodology (RSM) and the modal analyses in the iterative process are done by Finite Element Method (FEM). Moreover, the motor performance by the optimum stator structure is analyzed by FEM and compared with the prototype motor. Preventing the stator magnetic saturation and the motor cogging torque enhancement are the two constraints of the optimization problem. The optimal structural design method is applied experimentally and the validity of the design method is confirmed by the simulated and experimental results.

• 한국구조물진단유지관리공학회 논문집
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• 제16권6호
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• pp.45-55
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• 2012

가로등은 도로이용자가 안전하게 통행하기 위한 도로의 필수 시설물이지만 가로등은 도로의 부속 전기장치로 취급되어 왔다. 이러한 잘못된 인식 때문에 풍하중과 이에 대한 구조거동에 대한 연구들이 부족하여 풍하중에 충분한 안전성을 확보하지 못함에 따라 태풍 시 많은 가로등이 전도 또는 파손되는 실정이다. 본 연구에서는 가로등 안전성을 기반으로 한 기존의 설계기준을 비교 검토하여 가로등주의 설치 여건에 적합한 개선된 설계기준을 제시하였으며, 이를 바탕으로 전도의 원인이 되는 점검구의 응력집중 현상을 분석하고 응력 저감 방안을 검토하였다.

• Structural Engineering and Mechanics
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• 제31권4호
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• pp.439-451
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• 2009

The paper deals with the problem related to the modelling of riveted assemblies for crashworthiness analysis of full-scale complete aircraft structures. Comparisons between experiments and standard FE computations on high-energy accidental situations onto aluminium riveted panels show that macroscopic plastic strains are not sufficiently localised in the FE shells connected to rivet elements. The main reason is related to the structural embrittlement caused by holes, which are currently not modelled. Consequently, standard displacement FE models do not succeed in initialising and propagating the rupture in sheet metal plates and along rivet rows as observed in the experiments. However, the literature survey show that it is possible to formulate super-elements featuring defects that both give accurate singular strain fields and are compatible with standard displacement finite elements. These super-elements can be related to the displacement model of the hybrid-Trefftz principle of the finite element method, which is a kind of domain decomposition method. A feature of hybrid-Trefftz finite elements is that they are mainly used for elastic computations. It is thus proposed to investigate the possibility of formulating a hybrid displacement finite element, including the effects of a hole, dedicated to crashworthiness analysis of full-scale aeronautic structures.

• Structural Engineering and Mechanics
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• 제69권5호
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• pp.537-545
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• 2019

Stress analysis of bottom-hole rock has to be considered with much care to further understand rock fragmentation mechanism and high penetration rate. This original study establishes a fully coupled simulation model and explores the effects of overburden pressure, horizontal in-situ stresses, drilling mud pressure, pore pressure and temperature on the stress distribution in bottom-hole rock. The research finds that in air drilling, as the well depth increases, the more easily the bottom-hole rock is to be broken. Moreover, the mud pressure has a great effect on the bottom-hole rock. The bigger the mud pressure is, the more difficult to break the bottom-hole rock is. Furthermore, the maximum principal stress of the bottom-hole increases as the mud pressure, well depth and temperature difference increase. The bottom-hole rock can be divided into three main regions according to the stress state, namely a) three directions tensile area, b) two directions compression areas and c) three directions compression area, which are classified as a) easy, b) normal and c) hard, respectively, for the corresponding fragmentation degree of difficulty. The main contribution of this paper is that it presents for the first time a thorough study of the effect of related factors, including stress distribution and temperature, on the bottom-hole rock fracture rather than the well wall, using a thermo-poroelastoplasticity model.

• 천문학회보
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• 제38권2호
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• pp.42.2-42.2
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• 2013

We investigate the cosmic evolution of the black hole mass-bulge luminosity relation with a sample of 52 moderate-luminosity AGNs at $z{\simeq}0.36$ and $z{\simeq}0.57$, corresponding to look-back times of 4 and 6 Gyrs. By employing robust multi-component spectral and structural decomposition methods to the obtained high-quality Keck spectra and high-resolution HST images, black hole masses ($M_{BH}$) are estimated from the Hbeta broad emission line with the 5100A nuclear luminosity, and bulge luminosities ($L_{bul}$) are derived from the surface photometry. Based on these consistent measurements, we constrain the redshift evolution of the $M_{BH}-L_{bul}$ relation by performing the Monte Carlo simulations designed to account for selection effects. We provide implications of our results in terms of the black hole-galaxy co-evolution and discuss possible bulge growth mechanisms.

• Structural Engineering and Mechanics
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• 제51권1호
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• pp.111-130
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• 2014

The aim of this study is to investigate the effects of the beam aspect ratio(L/h), hole diameter, hole location and stacking layer sequence ($[0/45/-45/90]_s$, $[45/0/-45/90]_s$ and $[90/45/-45/0]_s$) on natural frequencies of glass/epoxy perforated beams under room and high (40, 60, 80, and $100^{\circ}C$) temperatures for the common clamped-free boundary conditions (cantilever beam). The first three out of plane bending free vibration of symmetric laminated beams is studied by Timoshenko's first order shear deformation theory. For the numerical analyses, ANSYS 13.0 software package is utilized. The results show that the hole diameter, stacking layer sequence and hole location have important effect especially on the second and third mode natural frequency values for the short beams and the high temperatures affects the natural frequency values significantly. The results are presented in tabular and graphical form.

• 한국구조물진단유지관리공학회 논문집
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• 제21권1호
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• pp.100-108
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• 2017

최근에 도시화와 산업화 및 교통망의 지속적인 확보로 인하여 발파공사를 시행하는 공사장이 증가하고 있다. 발파공사는 주변 주민들의 주거환경과 인접시설물들의 안전에 큰 영향을 미치므로 이에 대한 대책이 필요하다. 본 연구에서는 발파피해를 줄이기 위한 방법 중에서 발파공내의 발파메커니즘을 규명하고 개선하였다. 일반적인 공법에서 발생하는 천공경과 폭약경 사이의 차이로 인한 공간에서 디커플링효과를 규명하고, 이 공간의 매질을 변화시킴으로서 발파 시 진동발생의 규모를 규명하였다. 발파시험은 도로, 철도, 산업단지에서 실시하고, 발파진동을 측정하였다. 측정된 진동속도를 회귀분석하여 발파진동추정식을 산정하고 이를 이용하여 이격거리를 산정하였다. 공내 매질이 공기보다는 물처럼 비중이 큰 경우에 충격력은 크나 폭발 지연시간이 짧아 진동전달거리가 작아 이격거리를 크게 확보할 수 있다.

• 한국강구조학회 논문집
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• 제11권3호통권40호
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• pp.301-309
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• 1999

본 연구의 목적은 소성영역에서의 철골 부재내에 존재하는 존재응력을 추정하는 법을 개발하기 위함이다. 여기에선 선행 실험 연구를 근거로 하여 응력집중 현상에 기인한 국부 소성화를 고려하여 보정계수법이 제안되었다. 구멍주위의 응력 분포를 파악하기 위하여 유한요소 해석을 수행하였고, 그 결과를 탄 소성역에서의 구멍내기법에 의한 결과와 비교하였다. 보정계수법을 적용한 결과, 본 연구에서 제안된 방법은 실재 초기 존재응력값과 약 2% 정도의 오차를 가진 매우 좋은 결과치를 나타냈다.