• Geomechanics and Engineering
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• 제25권3호
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• pp.171-178
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• 2021

Wave interaction in marine structures is an important issue where requires to be considered in view of number of bases, piles and arrangement method. In this research, effect of waves and their forces on piles with different arrangements was investigated using numerical modeling. Simulations were performed in presence of bracing elements between piles against the force of waves and also were compared with simple arrangement without bracing elements in different arrangements. Results showed that in models that were fitted with bracing elements, the displacement rate reduced about 96%, and tension tolerances increased more than 53% and abutment responses also decreased about 70%.

• Structural Engineering and Mechanics
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• 제50권2호
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• pp.241-255
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• 2014

The girder of self-anchored suspension bridge is subjected to large compression force applied by main cables. So, serious damage of the girder due to breakage of hangers may cause collapse of the whole bridge. With the time increasing, the hangers may break suddenly for their resistance capacities decrease due to corrosion. Using nonlinear static and dynamic analysis methods and adopting 3D finite element model, the responses of a concrete self-anchored suspension bridge to sudden breakage of hangers are studied in this paper. The results show that the sudden breakage of a hanger has significant effects on tensions of the hangers next to the broken hanger, bending and torsion moments of the girder, moments of the towers and reaction forces of the bearings. The results obtained from dynamic analysis method are very different from those obtained from static analysis method. The maximum tension of hanger produced by breakage of a hanger exceeds 2.2 times of its initial value, the maximum dynamic amplification factor reaches 2.54, which is larger than the value of 2.0 recommended for cable-stayed bridge in PTI codes. If two adjacent hangers on the same side of bridge break one after another, the maximum tension of other hangers exceeds 3.0 times of its initial value. If the safety factor adopted to design hanger is too small, or the hangers have been exposed to corrosion, the bridge may collapse due to breakage of two adjacent hangers.

• 한국공간구조학회논문집
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• 제8권4호
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• pp.91-100
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• 2008

본 연구에서는 sky-bridge로 연결된 고층건물의 진동제어성능을 검토하여 보았다. Sky-bridge를 이용한 진동제어의 원리는 서로 다른 동적특성을 가진 구조물이 sky-bridge를 통하여 제어력을 발휘함으로써 전체 시스템의 응답을 줄이는 것이다. 본 연구에서는 실제 건설 중인 sky-bridge로 연결된 고층건물(49층 및 42층)을 대상으로 구조물의 변위, 가속도 및 베어링반력, sky-bridge의 응력 등을 해석적인 방법으로 검토하였다. 이를 위하여 역사지진, 인공지진 및 풍동실험을 통해서 얻은 풍하중 시간이력을 사용하였다. 해석결과 sky-bridge를 사용하여 고층건물의 풍응답 및 지진응답을 효과적으로 줄일 수 있는 것을 확인하였다.

• Earthquakes and Structures
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• 제18권4호
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• pp.407-421
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• 2020

In-place analysis for offshore platforms is essentially required to make proper design for new structures and true assessment for existing structures, in addition to the structural integrity of platforms components under the maximum and minimum operating loads when subjected to the environmental conditions. In-place analysis have been executed to check that the structural member with all appurtenance's robustness have the capability to support the applied loads in either storm or operating conditions. A nonlinear finite element analysis is adopted for the platform structure above the seabed and pile-soil interaction to estimate the in-place behavior of a typical fixed offshore platform. The SACS software is utilized to calculate the dynamic characteristics of the platform model and the response of platform joints then the stresses at selected members, as well as their nodal displacements. The directions of environmental loads and water depth variations have significant effects in the results of the in-place analysis behavior. The most of bending moment responses of the piles are in the first fourth of pile penetration depth from pile head level. The axial deformations of piles in all load combinations cases of all piles are inversely proportional with penetration depth. The largest values of axial soil reaction are shown at the pile tips levels (the maximum penetration level). The most of lateral soil reactions resultant are in the first third of pile penetration depth from pile head level and approximately vanished after that penetration. The influence of the soil-structure interaction on the response of the jacket foundation predicts that the flexible foundation model is necessary to estimate the force responses demands of the offshore platform with a piled jacket-support structure well.

• 국제초고층학회논문집
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• 제5권3호
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• pp.177-186
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• 2016

Along the subduction-zone of the western Japanese islands, large earthquakes are expected occur around the middle of this century, and long-period ground motions will reach major urban areas, shaking high-rise buildings violently. Since some old high-rise buildings were designed without considering long-period ground motions, reinforcing such buildings is an important issue. An effective method to reinforce existing high-rise buildings is installing additional dampers. However, a problem with ordinary dampers is that they require reinforcement of surrounding columns and girders to support large reaction forces generated during earthquake ground motion. To solve this problem, a deformation-dependent oil damper was developed. The most attractive feature of this damper is to reduce the damping force at the moment when the frame deformation comes close to its maximum value. Due to this feature, the reinforcement of columns, girders, and foundations are no longer required. The authors applied seismic retrofitting with a deformation-dependent oil damper to an existing 54-story office building (Shinjuku Center Building) located in Shinjuku ward, Tokyo, in 2009 to suppress vibration under the long period earthquake ground motions. The seismic responses were observed in the 2011 Tohoku Earthquake, and it is clarified that the damping ratio was higher and the response lower by 20% as compared to the building without dampers.

• 한국강구조학회 논문집
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• 제14권6호
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• pp.711-720
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• 2002

본 연구에서는 곡선교에서 주행차량에 의한 동적 응답을 보다 정밀하게 구현할 수 있는 3차원 해석 모형을 개발하였다. 원심력에 의한 차량의 롤링운동에 따른 차량의 쏠림현상을 구현하여 곡선교의 대표적인 응답특성인 편경사와 곡률반경에 따른 동적응답과 받침의 변화에 따른 동적 응답 특성을 규명하였으며, 2가지 지점조건에 대하여 주행차량에 의한 곡선교의 동적 특성을 비교 분석하였다. 또한 이와 함께 곡선교에서 어떤 파라미터가 하중 분배에 가장 효율적인가를 비교 분석하였다. 동적해석결과 받침이 외측에 배치된 경우가 중앙에 배치된 경우보다 더 유리하게 분석되었으며, 여러 가지 조건에 따라 하중분배 특성이 다르게 나타남을 알 수 있었다.

• International Journal of Automotive Technology
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• 제8권6호
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• pp.731-744
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• 2007

A method for dynamic analysis and design calculation of a Powertrain Mounting System(PMS) including Hydraulic Engine Mounts(HEM) is developed with the aim of controlling powertrain motion and reducing low-frequency vibration in pitch and bounce modes. Here the pitch mode of the powertrain is defined as the mode rotating around the crankshaft of an engine for a transversely mounted powertrain. The powertrain is modeled as a rigid body connected to rigid ground by rubber mounts and/or HEMs. A mount is simplified as a three-dimensional spring with damping elements in its Local Coordinate System(LCS). The relation between force and displacement of each mount in its LCS is usually nonlinear and is simplified as piecewise linear in five ranges in this paper. An equation for estimating displacements of the powertrain center of gravity(C.G.) under static or quasi-static load is developed using Newton's second law, and an iterative algorithm is presented to calculate the displacements. Also an equation for analyzing the dynamic response of the powertrain under ground and engine shake excitations is derived using Newton's second law. Formulae for calculating reaction forces and displacements at each mount are presented. A generic PMS with four rubber mounts or two rubber mounts and two HEMs are used to validate the dynamic analysis and design calculation methods. Calculated displacements of the powertrain C.G. under static or quasi-static loads show that a powertrain motion can meet the displacement limits by properly selecting the stiffness and coordinates of the tuning points of each mount in its LCS using the calculation methods developed in this paper. Simulation results of the dynamic responses of a powertrain C.G. and the reaction forces at mounts demonstrate that resonance peaks can be reduced effectively with HEMs designed on the basis of the proposed methods.

• 한국전문물리치료학회지
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• 제14권4호
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• pp.66-74
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• 2007

The aim of the present study was to investigate age-related differences in stepping behavior in response to sensory perturbations of postural balance. The participants for this study were 2 healthy elderly adults (mean age=76.0) and 2 younger adults (mean age=25.5). Subjects were asked to step over a 10 cm high obstacle at self-paced speed with the right limb to land on the primary target (normal step length) that is 10 cm in diameter. However, if, during movement, the light was illuminated, then the subject had to step on the secondary target (long step length). It was planned that the onset of the light would be prior to peak Fx of swing limb, between swing peak Fx and swing toe-off, and after swing toe-off. In the younger adults these secondary visual cues were provided at mean times of 240 ms (standard deviation (SD)=11), 402 ms (SD=13), and 476 ms (SD=88) following the movement onset. Corresponding mean times for the healthy elderly were 150 ms (SD=67), 352 ms (SD=39), and 562 ms (SD=115). Results showed great changes in both group and visual cue condition in Fx ground reaction forces and temporal events following the swing toe-off. Swing limb acceleration force (Fx) and stance peak Fx1 was much greater in the young adults compared to the older adults. Both young and older adults increased stance peak Fx2 in the visual cue condition compared to normal stepping. There was no difference in stance peak Fx2 between the visual cue conditions in both groups. Similarly, the time to stance peak Fx2 was much longer for the visual cue condition than for the normal stepping. It was not different between the visual cue conditions in the young adults, but in the elderly mid and late cue was much greater than early cue. In addition, time to stance peak Fx2 and swing and stance time were much longer in the older adults compared to the young adults for the visual cue conditions. These results suggest that unlike young adults, elderly adults did not flexibly modify their responses to unexpected changes in step length while stepping over obstacles.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.434-435
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• 2012

Plasma enhanced chemical vapor deposition (PECVD) silicon dioxide thin films have many applications in semiconductor manufacturing such as inter-level dielectric and gate dielectric metal oxide semiconductor field effect transistors (MOSFETs). Fundamental chemical reaction for the formation of SiO2 includes SiH4 and O2, but mixture of SiH4 and N2O is preferable because of lower hydrogen concentration in the deposited film [1]. It is also known that binding energy of N-N is higher than that of N-O, so the particle generation by molecular reaction can be reduced by reducing reactive nitrogen during the deposition process. However, nitrous oxide (N2O) gives rise to nitric oxide (NO) on reaction with oxygen atoms, which in turn reacts with ozone. NO became a greenhouse gas which is naturally occurred regulating of stratospheric ozone. In fact, it takes global warming effect about 300 times higher than carbon dioxide (CO2). Industries regard that N2O is inevitable for their device fabrication; however, it is worthwhile to develop a marginable nitrous oxide free process for university lab classes considering educational and environmental purpose. In this paper, we developed environmental friendly and material cost efficient SiO2 deposition process by substituting N2O with O2 targeting university hands-on laboratory course. Experiment was performed by two level statistical design of experiment (DOE) with three process parameters including RF power, susceptor temperature, and oxygen gas flow. Responses of interests to optimize the process were deposition rate, film uniformity, surface roughness, and electrical dielectric property. We observed some power like particle formation on wafer in some experiment, and we postulate that the thermal and electrical energy to dissociate gas molecule was relatively lower than other runs. However, we were able to find a marginable process region with less than 3% uniformity requirement in our process optimization goal. Surface roughness measured by atomic force microscopy (AFM) presented some evidence of the agglomeration of silane related particles, and the result was still satisfactory for the purpose of this research. This newly developed SiO2 deposition process is currently under verification with repeated experimental run on 4 inches wafer, and it will be adopted to Semiconductor Material and Process course offered in the Department of Electronic Engineering at Myongji University from spring semester in 2012.

• The Journal of Advanced Prosthodontics
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• 제5권4호
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• pp.402-408
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• 2013

PURPOSE. The aim of this study was to evaluate the surface properties and in vitro bioactivity to osteoblasts of magnesium and magnesium-hydroxyapatite coated titanium. MATERIALS AND METHODS. Themagnesium (Mg) and magnesium-hydroxyapatite (Mg-HA) coatings on titanium (Ti) substrates were prepared by radio frequency (RF) and direct current (DC) magnetron sputtering.The samples were divided into non-coated smooth Ti (Ti-S group), Mg coatinggroup (Ti-Mg group), and Mg-HA coating group (Ti-MgHA group).The surface properties were evaluated using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The surface roughness was evaluated by atomic force microscopy (AFM). Cell adhesion, cell proliferation and alkaline phosphatase (ALP) activity were evaluated using MC3T3-E1 cells. Reverse transcription polymerase chain reaction (RT-PCR) analysis was performed. RESULTS. Cross-sectional SEM images showed that Mg and Mg-HA depositionson titanium substrates were performed successfully. The surface roughness appeared to be similaramong the three groups. Ti-MgHA and Ti-Mg group had improved cellular responses with regard to the proliferation, alkaline phosphatase (ALP) activity, and bone-associated markers, such as bone sialoprotein (BSP) and osteocalcin (OCN) mRNA compared to those of Ti-S group. However, the differences between Ti-Mg group and Ti-MgHA group were not significant, in spite of the tendency of higher proliferation, ALP activity and BSP expression in Ti-MgHA group. CONCLUSION. Mg and Mg-HAcoatings could stimulate the differentiation into osteoblastic MC3T3-E1 cells, potentially contributing to rapid osseointegration.