• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.10a
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• pp.319-320
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• 2009

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.4
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• pp.213-221
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• 2013

This paper introduces a mesh continuation scheme for a one-dimensional inverse medium problem to reconstruct the spatial distribution of elastic wave velocities in heterogeneous semi-infinite solid domains. To formulate the inverse problem, perfectly-matched-layers(PMLs) are introduced as wave-absorbing boundaries that surround the finite computational domain truncated from the originally semi-infinite extent. To tackle the inverse problem in the PML-truncated domain, a partial-differential-equations(PDE)-constrained optimization approach is utilized, where a least-squares misfit between calculated and measured surface responses is minimized under the constraint of PML-endowed wave equations. The optimization problem iteratively solves for the unknown wave velocities with their updates calculated by Fletcher-Reeves conjugate gradient algorithms. The optimization is performed using a mesh continuation scheme through which the wave velocity profile is reconstructed in successively denser mesh conditions. Numerical results showed the robust performance of the mesh continuation scheme in reconstructing target wave velocity profile in a layered heterogeneous solid domain.

• Journal of KSNVE
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• v.26 no.5
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• pp.22-25
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• 2016

• The Journal of Engineering Geology
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• v.13 no.1
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• pp.129-137
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• 2003

We interpreted the seismic signal characteristics from crosswell seismic tomography in the underground cavity like abandoned mines. The first arrival time delay and amplitude attenuation showed clearly at the low velocity zone of cavity and fracture. Also ray density decreased by detour of raypath. As a result of the amplitude spectrum analysis of fresh rock and low velocity zone, there were no noticeable differences of the amplitude up to about 1000Hz frequency, but indicated that the one passed around cavity decreased about 7dB at 2000Hz, and 20dB at 3000Hz. It was possible to compare the signal characteristics between two media by extracting the signal data from the fresh rock zone and the underground cavity through the seismic crosswell tomography.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.247-250
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• 2009

본 연구에서는 반복하중을 받는 구리 나노와이어에서 나타나는 초탄성 거동을 분자동역학 전산모사를 통해 해석하였다. 나노스케일에서는 표면적 대 부피비가 매우 크기 때문에 표면효과가 지배적으로 나타난다. 이로 인해 벌크상태에서는 보이지 않던 새로운 성질들이 나노크기에서 나타나는데, 이러한 효과로 인해 나노와이어의 경우에는 초탄성 거동을 보인다. 초탄성 거동은 나노와이어의 결정학적 방향의 재배열에 의한 것으로써, 하중을 받는 동안 나노와이어의 결정 구조는 변하지 않으며, 쌍정의 발생 및 쌍정계면의 전파에 의해 결정학적 방향이 재배열된다. 재배열에 의해 부분적으로 변형되었던 나노와이어는 하중을 제거하거나 하중의 방향이 바뀜에 따라 원래의 상태를 회복하는 거동을 보이게 된다. 본 연구에서는 분자 동역학 전산 모사를 통해 <100>/{100} 구리 나노와이어가 반복적인 압축-인장 거동 하에서 초탄성을 보이게 됨을 확인하였으며, 반복 하중 싸이클을 증가시키는 전산모사를 통해 나노와이어의 초탄성이 영구적으로 유지됨을 확인하였다.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.600-606
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• 2006

실제 지반은 경계가 없는 무한상태로 존재하기 때문에 지반구조물의 동적거동을 유한요소법을 이용하여 해석할 시 모델의 영역을 성립하는 것은 특별한 고려가 필요하다. 유한요소법에서의 동적해석은 파동의 전달을 포함하기 때문에 모델의 경계에서 인공적인 경계조건이 필요하다. 인공적인 경계 조건은 유한요소내의 지반상태를 무한상태로 변형시킬 수 있어야 하며, 경계에 도달하는 응력 파동을 모델내로 반사시키지 않고 흡수 할 수 있어야 한다. 본 논문에서는 간단한 점 탄성 반무한 불연속 요소를 이용하여 지반구조물의 동적해석을 수행하는 방법을 보여준다. 반무한 요소의 실행은 OpenSees라는 유한요소 해석프로그램을 이용하여 수행되었으며, 예를 통하여 불연속 요소가 경계에 도달하는 응력 파동을 충분히 흡수하여 유한요소 모델을 반무한 상태로 전환 시킬 수 있다는 것을 보여준다.

• Journal of Aerospace System Engineering
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• v.16 no.5
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• pp.78-85
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• 2022

Multicopter-type unmanned aerial vehicles (UAV) are increasingly for cargo transportation to mountainous and island regions, image information acquisition in disaster areas, and emergency rescue transport. In order to successfully perform these tasks, the aircraft structure must be able to safely support the loads induced by flight conditions while ensuring the vibration and aeroelastic stability of the prop-rotor. This study introduced a structural analysis model of a 40kg payload multicopter with an engine-generator hybrid power system. The deformation and stress distribution are investigated depending on the load conditions. In addition, the vibration characteristics and aeroelastic stability of the prop-rotor were also presented to flight speed and aircraft pitch angle. The maximum thrust generated by the prop-rotor and the landing load applied to the multicopter under normal and emergency landing conditions were reviewed., It confirmed that the structure could support without failure. In addition, it confirmed that the damping characteristics of each primary locate in the constant region according to the aircraft's flight speed and the prop-rotors rotating speed.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.3
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• pp.271-278
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• 2004

Numerical analysis of wind effects on civil engineering structures was performed. Aerodynamic effect often becomes a governing factor and aeroelastic stability boundary becomes a prime criterion which should be confirmed during the structural design stage of bridges because the long-span suspension bridges are prone to the aeroelastic instabilities caused by wind. If the wind velocity exceeds the critical velocity that the bridge can withstand, then the bridge fails due to the phenomenon of flutter. Navier-Stokes equations were used for the aeroelastic analysis of bridge girder section. The aeroelastic simulation is carried out to study the aeroelastic stability of bridges using both Computational Fluid Dynamic (CFD) and Computational Structural Dynamic (CSD) schemes. Critical flutter velocities were computed for bridges with different stiffness. It was confirmed that the critical flutter velocity of bridge girder section was sensitive to the change of structural stiffness.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.5 s.45
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• pp.11-19
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• 2005

Seismic design of a building is usually performed by using the linear static procedure. However, the actual behavior of the building subjected to earthquake is inelastic and dynamic in nature. Therefore, inelastic dynamic analysis is required to evaluate the safety of the structure designed by the current design codes. For the validation, a RC special moment resisting frame building was chosen and designed by IBC 2003 representing new codes. Maximum plastic rotation and dissipated energy of some selected members were calculated for examining if the inelastic behavior of the building follows the intention of the code, and drift demand were calculated as well for checking if the building well satisfies the design drift limit. In addition, the effect of including internal moment resisting frames (non lateral resisting system) on analyses results was investigated. As a result of this study, the building designed by IBC 2003 showed the inelastic behavior intended in the code and satisfied the design drift limit. Furthermore, the internal moment resisting frames should be included in the analytical model as they affect the results of seismic analyses significantly.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.6
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• pp.683-690
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• 2007

Topology optimization techniques have been developed as a very efficient design tool and utilized for design engineering processes in many industrial sections during the past decade. And topology optimization has become the focus into structural optimization design up to now. Recently, thermally actuated compliant mechanisms have a wide range of applications. In this research, the thermo-elastic problem is a coupled problem which has to consider heat transfer analysis and structural analysis. Hence, the thermo-elastic problem has to deal with heat transfer material properties and structural material properties at the same time. The numerical examples are presented. From the results, it was shown that in terms of the displacement after optimization. Moreover, this paper compared thermo-system, elastic-system with thermo-elastic system and was shown a good result of topology optimization while thermo-elastic system was used.