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Magnetopause Waves Controlling the Dynamics of Earth’s Magnetosphere
황경주 한국우주과학회 2015 Journal of Astronomy and Space Sciences Vol.32 No.1
Earth’s magnetopause separating the fast and often turbulent magnetosheath and the relatively stagnant magnetosphereprovides various forms of free energy that generate low-frequency surface waves. The source mechanism of this energyincludes current-driven kinetic physical processes such as magnetic reconnection on the dayside magnetopause andflux transfer events drifting along the magnetopause, and velocity shear-driven (Kelvin-Helmholtz instability) or density/pressure gradient-driven (Rayleigh-Taylor instability) magnetohydro-dynamics (MHD) instabilities. The solar wind externalperturbations (impulsive transient pressure pulses or quasi-periodic dynamic pressure variations) act as seed fluctuationsfor the magnetopause waves and trigger ULF pulsations inside the magnetosphere via global modes or mode conversion atthe magnetopause. The magnetopause waves thus play an important role in the solar wind-magnetosphere coupling, whichis the key to space weather. This paper presents recent findings regarding the generation of surface waves (e.g., Kelvin-Helmholtz waves) at the Earth’s magnetopause and analytic and observational studies accountable for the linking of themagnetopause waves and inner magnetospheric ULF pulsations, and the impacts of magnetopause waves on the dynamicsof the magnetopause and on the inner magnetosphere.
볼트 유격을 고려한 융합적 노드 접합 시스템의 축강성에 대한 구조 해석적 평가
황경주 국제차세대융합기술학회 2020 차세대융합기술학회논문지 Vol.4 No.2
단층 그리드 대공간 철골 지붕 구조물은 접합 시스템의 구조적인 능력이 전체구조물의 안정성에 크게 영 향을 미치는 건축시스템이다. 시공성을 높이기 위해 볼트 접합 시스템이 많이 적용되었으나 볼트 유격의 크기에 따른 접합 시스템의 구조적인 거동과 최대 내력은 파악하기 어려웠다. 특히 접합 시스템의 축강성에 대한 파악은 압축력에 근거한 멤브레인 응력이 중요하게 작용하는 쉘구조의 특성상 상당히 중요하다. 효과적인 구조거동 및 최 대내력등을 파악하기 위해 4개의 대표적인 접합 시스템을 선정하여 비선형 수치해석을 수행하였다. 볼트 유격의 크기가 고려된 수치해석을 통해서 볼트 유격의 차이가 가져오는 구조거동의 차이와 축하중의 최대치의 차이를 발 견하였으며 효과적인 볼트 접합 시스템의 유형에 대해서도 평가하였으며 2면의 전단면을 갖는 접합시스템이 높은 축강성을 갖는 것으로 평가되었다. Single-layered grid space steel roof structure is an architectural system in which the structural ability of the nodal connection system greatly influences the stability of the entire structure. Many bolt connection systems have been suggested to enhance for better construct ability, but the structural behavior and maximum resistance of the connection system according to the size of bolt clearance play were difficult to identify. In particular, the identification of axial stiffness of the connection system is very important due to the characteristics of shell structures in which membrane stresses based on compressive force effect significantly. To identify effective structural behavior and maximum bearing force, four representative nodal connection systems were selected and nonlinear numerical analysis was performed. The numerical analysis considering the size of the bolt clearance were performed to investigate structural behavior and maximum values of the axis force. In addition, the type of effective nodal connection system were evaluated.