• The KSFM Journal of Fluid Machinery
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• v.7 no.5 s.26
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• pp.20-28
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• 2004

Static and dynamic structural analyses of a turbine bladed-disk for a liquid rocket turbopump are performed to investigate the safety level of strength and vibration at design point. During operation, turbopump is exposed to various external loads. Therefore, the effects of them should be carefully considered and properly modeled. First, due to the high rotational speed of the turbopump, effects of centrifugal forces are considered in the structural analysis. Thermal load caused by severe temperature differences is also considered. A three dimensional finite element method (FEM) is used for linear and nonlinear structural analyses with modified Newton-Raphson iteration method. After the nonlinear solution is obtained from the structural analysis, dynamic characteristics are obtained as a function of rotational speed from the linearized eigenvalue analysis at an equilibrium position. From the analysis results, characteristics of stress distribution and vibration were thoroughly examined and investigated.

• Journal of Aerospace System Engineering
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• v.12 no.1
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• pp.17-26
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• 2018

The interaction model between variable-speed control moment gyros and a satellite has been studied based on the multi-body dynamics. Using the interaction model, we could obtain data for the design of VCMG motors and the strength design of structure. The interaction effects of flexible modules such as solar panels were included. Flexible modes are excited by the satellite's maneuver, and these modes cause perturbations in the satellite attitude. We developed a simulation program by Modelica and verified the proposed model.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.38-38
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• 2011

일반적으로 레일마모는 열차의 주행안전 및 승차감에 미치는 영향이 크고, 소음 진동의 주요원인으로 작용한다. 또한 레일마모가 발생할 경우 궤도구조의 파괴를 촉진시킴으로써 차량 및 궤도유지보수비를 크게 증가시킨다. 따라서 구간 특성 및 환경 영향 인자 등 현장에서 발생하는 마모 원인을 체계적으로 분석함으로써 마모를 저감할 수 있도록 차량운행 조건과 선로선형 및 궤도구조를 설계하는 것은 중요한 과제이다. CART(Classification And Regression Tree; 분류와 회귀나무) 분석은 패키지화된 좋은 분류 및 예측도구 기법으로 나무의 상위 분리수준에서 일반적으로 나타나는 가장 중요한 입력변수들을 사용하는 등의 입력변수를 선정하는 경우 매우 유용하다. 본 연구에서는 다변수 구간특성 및 환경인자를 고려한 검측 자료 상관관계 분석을 위한 회귀 나무기반 모델(TBM: Tree Based Model) 분석 수행을 위해 지하철 2호선 마모 데이터와 마모 데이터에 영향을 미치는 각종 다변수 구간특성 및 환경인자를 사용하였다. 2호선 지하철의 구간특성 인자 및 환경인자는 레일의 종류, 레일의 위치, 도상, 곡률반경, 캔트 슬랙 및 운행 일수 등으로 구분하였다. 레일의 종류는 ks-50kg과 ks-60kg 두 종류의 레일이 있으며, 레일의 위치는 지상과 지하로 크게 구분할 수 있다. 도상은 콘크리트 도상, 자갈 도상과 일부 구간의 방진상 콘크리트 도상으로 구분할 수 있으며, 곡률반경은 직선구간과 완화곡선 구간 및 최소 250m부터 627m까지 분포된 원 곡선 구간으로 구분할 수 있다. 캔트 간격은 최소 96cm 부터 120cm 간격으로 구분하며, 슬랙은 5~9cm에 분포하고, 운행 기간은 해당 기간 동안 유지보수 이력이 없는 구간을 선정하여 2005년부터 2006년까지 4번에 걸쳐 검측된 지하철 2호선 내선 마모데이터를 사용하였다. 총 X1부터 X7까지 총 7개의 구간특성 또는 환경특성을 영향인자로 선정하였으며, 이러한 영향인자에 의해 결정되는 종속 인자로 Y1인 직마모와 Y2인 측마모를 선정하여 이 중 실질적으로 지하철 궤도의 성능 평가에 주요 판단인자로 사용되는 측마모와 구간특성 및 환경영향인자와의 상관관계 분석을 수행하였다. 해당 마모 데이터가 검측되는 기간 동안 유지보수 이력이 없는 12272 point의 데이터를 검출하였고 CART 프로그램을 이용하여 데이터를 분석하였으며, CART 프로그램의 해석을 위해 종속변수인 직마모량은 각 검측 지점의 마모량에 해당하는 등급으로 변환하여 분석을 수행하였다. 레일의 마모에 영향을 미치는 구간특성 및 환경인자와 종속 변수로 사용된 레일의 마모량 사이의 CART를 이용한 상관관계 분석은 실제 구조물에서 영향인자간의 상관 관계와 유사하며, 추후 연구에서는 이를 바탕으로 하여 정량화된 검측 데이터를 종속변수로 하여 구간특성 또는 환경인자 등 외부 영향인자를 고려한 궤도 검측데이터와의 상관관계 분석을 수행할 계획이다.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.6
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• pp.1-9
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• 2010

Most of shear wall structures require openings in shear walls and thus shear walls are linked by floor slabs or coupling beams resulting in the coupled shear wall structures. When these structures are subjected to seismic excitations, excessive shear forces are induced in coupling beams. Accordingly, brittle failure of coupling beams may occur or shear walls may yield first. To avoid this problem, damping devices can be installed in coupling beams. It can increase the vibration control effect and improve the seismic resistance performance of the coupled shear wall structure by avoiding stress concentration and the brittle failure of coupling beams. Based on this background research, an LRB (lead rubber bearing) was introduced in the middle of the coupling beam in this study and the authors investigated the seismic response control effect and stress distribution of the proposed system. To this end, a modeling technique that can effectively predict the structural behavior of coupled shear wall structures has been proposed. With this proposed technique, time history analyses of the example coupled shear wall structure subjected to seismic excitation were performed and the vibration control effects of the seismic responses were investigated.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.2
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• pp.170-178
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• 2011

In this paper, a research was performed to develop a wireless measurement system for bridge monitoring using MEMS sensor and bluetooth wireless communication module. First, in order to prove the suitability of MEMS sensor for the bridge measurement, its ranges of measuring acceleration and of frequency response were experimented. Also, the quality of wireless communication was tested by an experiment on long-distance communication for the knowledge of maximum communication distance, and also by an experiment on the data transmit-receive capability both inside and outside of a steel box bridge. Later, placing the wireless acceleration sensor system that had been developed in our lab on a bridge in public service, we acquired vibration data from the bridge under traffic load and analyzed its dynamic characteristics in realtime. For the analysis of the data, NExT & ERA algorithm were employed. The result of analysis was compared to the FE analysis of the same bridge, and the comparison made it possible to evaluate the performance of wireless acceleration sensor system. As a result, it was proven that the wireless acceleration sensor system developed with the use of MEMS sensor and bluetooth wireless communication module could be effectively applied to the measurement of structure whose vibration feature was low frequency like a bridge.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.120-129
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• 2023

To evaluate the vertical loads on railway bridges, conventional load tests are typically conducted. However, these tests often entail significant costs and procedural challenges. Railway conditions involve nearly identical load profiles due to standardized rail systems, which may appear straightforward in terms of load conditions. Nevertheless, this study aims to validate load tests conducted under operational train conditions by comparing the results with those obtained from conventional load tests. Additionally, static and dynamic structural behaviors are extracted from the measurement data for evaluation. To ensure the reliability of load testing, this research demonstrates feasibility through comparisons of existing measurement data with sensor attachment locations, train speeds, responses between different rail lines, tendency analysis, selection of impact coefficients, and analysis of natural frequencies. This study applies to the Dongho Railway Bridge and verifies the applicability of the proposed method. Ten operational trains and 44 sensors were deployed on the bridge to measure deformations and deflections during load test intervals, which were then compared with theoretical values. The analysis results indicate good symmetry and overlap of loads, as well as a favorable comparison between static and dynamic load test results. The maximum measured impact coefficient (0.092) was found to be lower than the theoretical impact coefficient (0.327), and the impact influence from live loads was deemed acceptable. The measured natural frequencies approximated the theoretical values, with an average of 2.393Hz compared to the calculated value of 2.415Hz. Based on these results, this paper demonstrates that for evaluating vertical loads, it is possible to measure deformations and deflections of truss railway bridges through load tests under operational train conditions without traffic control, enabling the calculation of response factors for stress adjustments.

• Journal of the Korean earth science society
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• v.21 no.4
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• pp.423-436
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• 2000

The lithofacies, biofacies, and paleosol development of the Jindong Formation, the Geoncheonri Formation, and the lacustrine deposits of Mt. Hwangryeong at Pusan, which occur in the southeastern part of the Gyeongsang Basin, were analyzed in comparative sedimentology and in stratigraphy. The common features of these lacustrine deposits are: 1) clastic deposits are prevailing, 2) deltaic deposits are not associated, 3) mudflat deposits are common, and 4) stromatolites are absent. The distinct differences among these deposits are: 1) in the Jindong Formation, the mudflat deposits are predominant, pedogenic calcretes are commonly present, and dinosaur tracks frequently occur, compared with other two lacustrine deposits, and 2) in the Geoncheonri Formation, invertebrate fossils are relatively common and storm deposits are not recognized, compared with other deposits, and 3) evaporite mineral casts and tuffaceous turbidite deposits are common in the Mt. Hwangryeong lacustrine deposits. In stratigraphy, the Geoncheonri Formation is correlated with the lower part of the Jindong Formation, and the Mt. Hwangryeong lacutsrine deposits are deemed to overlie the Jindong Formation. On the basis of comparative sedimentology and stratigraphic relationship among these lacustrine deposits, general paleoenvironements of the southeastern part of the Gyeongsang Basin from the late Hayang time to the early Yucheon time are interpreted as follows. During the late Hayang time, tectonic and volcanic activities were generally inacitive in the Gyeongsang Basin, and lacustrine environments expanded since the paleoclimatic condition became less arid compared with the middle Hayang time. In general, however, paleoclimate during the late Hayang time was still arid, and wetting and drying periods were alternated. The occasional occurrences of severe droughts were also characteristic of the late Hayang time. Mudflats existed in wide area in the southeastern part of the Gyeongsang Basin during the late Hayang time, and sedimentation rate was accordingly low. The sedimentation rate became relatively high during the latest Hayang time and the early Yucheon time since tectonic and volcanic activities had been active. Generally arid climate continued for the early Yucheon time, enough for evaporite minerals to precipate occasionally.

• Journal of the Korean Society for Railway
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• v.16 no.5
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• pp.394-401
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• 2013

Here we report the results of an experimental laboratory test to verify the applicability to railway bridges of a PSC I girder of which the upper flange thickness was increased to improve sectional performance. The thicker this flange is, the further upward the neutral axis is moved. If in this way the span length can be increased to 40m long, the bridge may be constructed with four girders instead of five. Therefore, construction cost could be lowered by reducing the weight of the long span structure due to increased sectional efficiency. It was also necessary to be certain that the dynamic performance of this relatively flexible structure would be applicable to railway bridges. Therefore numerical analysis, as well as static and dynamic tests, was carried out for a full-size PSC I girder. Based on these results, it was verified that the performance of the PSC I railway bridge satisfied the performance criteria of the design code.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.4
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• pp.497-503
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• 2012

The aim of this study was to optimize S-tube shape of heat exchanger in term of reducing the size of tube bundle and improving the mechanical properties such as the thermal stress and resonance. The geometric parameters such as offset length, the straight distance between one end and other end of tube, the tube length in straight portion and fillet radius was assessed as a valid parameters. The structural analysis was performed to estimate the structural characteristics. Main effect analysis was performed to investigate the main effect for the various geometric parameters. The response surface methodology was employed to establish mathematical approximation models as a function of the geometric parameters of the S-tube. Also, The optimization was performed to optimize geometric parameters of S-tube using the regression equations and optimization tool. The optimized tube shape has been proposed. Those could be used in the heat exchanger design used in high temperature.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.9 no.2
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• pp.43-54
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• 1989

In this paper, measured and calculated responses are compared in order to give how the static and dynamic responses occurred in steel railway bridges due to train loads could be calculated appropriately. From this, it is investigated how the impact factors are varied by changing the train speed above 100km/h Field measurement is carried out by the steel strain gages and displacement transducers at the main design points, and then the static and dynamic response, fundamental frequencies, damping ratios and impact factors of the bridges are obtained. Static analysis is done using the computer program developed according to three dimensional matrix structural analysis in which the trains and bridges are modelled as 1,2 and 3 dimensions. Dynamic analysis is done according to 2 approaches, the moving force and mass problem. In moving force problem, the solutions are obtained by the modesuperposition-method and in moving mass problem by the direct integration method. From this study, it is known that in order to obtain the static response in the railway bridges, the bridge could be modelled by 1 or 2 dimension as in the highway bridge, however the response ratio(measured/calculaled) is high comparing to the highway bridges. By the way, the dynamic response should be obtained by the moving mass problem. And by comparing the measured and code specified impact factors, it is known that the factors specified in the present railway bridge code are very safe under the present service speed below 100km/h. However, because the factors become very high under the speed above 100km/h, especially in the simple plate girder bridge, it is thought that the code specification on impact factor should be discussed enough under the rapid transit system.