• Journal of the Korean Society for Railway
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• v.18 no.3
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• pp.194-202
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• 2015

In this paper, dynamic modeling with viscoelastic properties of a human body resting on a seat is presented to quantitatively analyze ride quality of passengers exposed to vertical vibrations. In describing the motions of a seated body, a 5 degree-of-freedom multibody model from the literature is investigated. The viscoelastic characteristics of seats used in railway vehicles are mathematically formulated with nonlinear stiffness characteristics and convolution integrals representing time delay terms. Transfer functions for the floor input are investigated and it is found that these are different in accordance with the input magnitude due to nonlinear characteristics of the seat. Measured floor input at the railway vehicle is used to analyze realistic human vibration characteristics. Frequency weighted RMS acceleration values are calculated and the effects of the seat design parameters on the frequency weighted RMS acceleration values are presented.

• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.27.3-27.3
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• 2009

인공위성이 발사체로부터 분리되면, 인공위성은 가장 먼저 태양 전지판을 전개한 후 전력을 생산한다. 전력은 인공위성의 운영에 반드시 필요하므로, 태양전지판의 성공적인 전개는 인공위성의 성공적 임무 수행의 필수 요소이다. 따라서, 태양전지판 또는 태양전지판의 전개장치 개발시에는 태양전지판이 이상없이 전개되는지를 확인할 수 있는 태양전지판 전개해석을 반드시 필요로 한다. 현재 개발중인 저궤도 지구관측위성의 경우, 3장의 태양전지판이 사용이 되며, 각 태양전지판의 전개 및 고정은 힌지 및 스트럿으로 이루어진 태양전지판 전개장치에 의하여 이루어진다. 이 논문에서는 다물체 동역학 해석프로그램인 Recurdyn을 이용하여, 상세 태양전지판 전개해석을 수행하고자 한다. 이전 연구에서는 기본적인 전개해석 모델을 수립하여, 태양전지판의 기본 전개거동을 확인할 수 있었다. 그러나, 태양전지판이 완전히 전개된 이후에 고정되는 부분의 모델링이 복잡하여, 단순하게 가정하여 전개해석을 수행하였다. 이러한 가정은 태양전지판의 전개 입장에서는 좀 더 극한상황이 되었으며, 이러한 환경하에서도 충분히 태양전지판이 잘 전개됨을 확인할 수 있었다. 이 논문에서는 간략화된 태양전지판 고정장치 및 기타 다른 부분들을 좀 더 상세모델링 하여, 전개 거동이 좀 더 실제에 가깝도록 하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.1
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• pp.31-40
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• 2021

Modern aircraft are high-performance and lightweight. Thus, the characteristics of the flexible structure appear and affect flight performance or limit it. These flexible characteristics need to be analyzed from the early stages of aircraft design. To this end, a program to analyze the dynamic and static behavior of flexible aircraft has been developed and the results are presented. Based on the multi-body dynamics simulation technique, rigid flight mechanics, structural vibrating behavior, and unsteady aerodynamics have been developed and integrated. Lastly, the level flight and the turn flight of the flexible characteristic aircraft have been analyzed using this integrated simulation program.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.10
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• pp.7071-7077
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• 2015

In recently, the demand of cover-glass is increased because smart phone, tablet pc, and electrical device has become widely used. The display of mobile device is enlarged, so it is necessary to have a high strength against the external force such as contact or falling. In fabrication process of cover-glass, a grinding process is very important process to obtain high strength of glass. Conventional grinding process using a grinding wheel is caused such as a scratch, chipping, notch, and micro-crack on a surface. In this paper, polishing system using a abrasive film was developed for a grinding of mobile cover-glass. To evaluate structural stability of the designed system, finite element model of the polishing system is generated, and multi-body dynamic analysis of abrasive film polishing machine is proposed. As a result of the analysis, stress and displacement analysis of abrasive film polishing system are performed, and using laser displacement sensor, structural stability of abrasive film polishing system is confirmed by measuring displacement.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.10B
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• pp.1937-1945
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• 1999

In paper, we propose a 3D polygonal mesh simplification technique based on vertex clustering. The proposed method differentiates the size of each cluster according to the local property of a 3D object. We determine the size of clusters by considering the normal vector of triangles and the vertex distribution. The subdivisions of cluster are represented by octree. In this paper, we use the Harsdorff distance between the original mesh and the simplified one as a meaningful error value. Because proposed method adaptively determine the size of cluster according to the local property of the mesh, it has smaller error as compared with the previous methods and represent the small regions on detail. Also it can generate a multiresolution model and selectively refine the local regions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.8
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• pp.1-7
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• 2003

The numerical simulation of flow-filed around a square cylinder near a wall with $\varepsilon$-SST turbulence model is carried out in this study. The newly suggested $\varepsilon$-SST turbulence model that modifies the original SST turbulence model is proved to yield more accurate results than the other 2-equation turbulence models in large separation region around a bluff body. Therefore, $\varepsilon$-SST turbulence model can be effectively applied for predicting the flow-fields with large separation. And it is found that vortex shedding is suppressed below the critical gap height, the Strouhal number is affected by the gap height and the wall boundary layer thickness.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.6
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• pp.877-883
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• 1987

A new improved inviscid separation model to calculate the mean flow past circular cylinders is proposed. The wake region is modeled by a pair of vortex sheets which emerge from the separation points and are allowed to move freely with the local stream. The vortex strength assumes a constant value for some initial distance which is related to the pressure drag and gradually decreases to zero as the sheet moves farther away from the body. This vorticity distribution automatically takes care of the length parameter which has been one of the deficiencies in the existing models. The procedure is tested against various experimental data and the agreement is quite good for both sub and super-critical regimes. The comparison with an existing model is also given.

• Journal of the Korean Society of Hazard Mitigation
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• v.6 no.3 s.22
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• pp.17-28
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• 2006

Structural health monitoring is important to maintain the safety and serviceability of the structures. The displacement in the structure should be precisely and frequently monitored because it is a direct assessment index indicating its stiffness. However, no practical method has been developed to monitor such displacement precisely, particularly for high-rise buildings and long span bridges because they cannot be easily accessible. To overcome such difficult accessibility, we propose to use a LIDAR system that remotely samples the surface of an object using laser pulses and generates the coordinates of numerous points on the surface. In this study, using terrestrial LiDAR, we develop a novel displacement measuring model for structural health monitoring and perform an indoor experiment to prove its performance.

• Journal of the Korean Society for Railway
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• v.10 no.5
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• pp.492-498
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• 2007

For the running safety assessment of Saemaul train passing through curves, an analysis model for multibody system has been developed. By using this model and ADAMS/Rail, sensitivity analyses depending on the variation of parameters related to the derailment coefficients have been conducted. At low speed, the derailment coefficient and the unload ratio of right wheel showed higher than left wheel, while those of left wheel showed higher than right wheel at high speed. According to decrease of curve radius, the derailment coefficient and the unload ratio were increased. When the length of transition curve was increased, the derailment coefficient was increased but there was no change on the unload ratio. According to the increase of cant, the derailment coefficient and the unload rate were increased.

• Journal of the Korean Society for Railway
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• v.15 no.4
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• pp.343-351
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• 2012

With the cooperation of many research institutes and railway companies, the next generation high speed train is under development for many years. To confirm the safety requirement of the developed high speed train, multibody dynamic analysis is implemented. Through this analysis, railway derailment and lateral guiding force simulation was evaluated according to UIC code 518 OR for international railway vehicle. Test results were compared by limit value of safety criteria. Safety evaluation results, according to international standards, would provide basic reference data of ensuring safety speed and track radius curve. The safety of the train at the maximum speed is verified by numerical analysis results.