• Title, Summary, Keyword: neutral axis

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TRIO (Triplet Ionospheric Observatory) CINEMA

  • Lee, Dong-Hun;Seon, Jong-Ho;Jin, Ho;Kim, Khan-Hyuk;Lee, Jae-Jin;Jeon, Sang-Min;Pak, Soo-Jong;Jang, Min-Hwan;Kim, Kap-Sung;Lin, R.P.;Parks, G.K.;Halekas, J.S.;Larson, D.E.;Eastwood, J.P.;Roelof, E.C.;Horbury, T.S.
    • Bulletin of the Korean Space Science Society
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    • pp.42.3-43
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    • 2009
  • Triplets of identical cubesats will be built to carry out the following scientific objectives: i) multi-observations of ionospheric ENA (Energetic Neutral Atom) imaging, ii) ionospheric signature of suprathermal electrons and ions associated with auroral acceleration as well as electron microbursts, and iii) complementary measurements of magnetic fields for particle data. Each satellite, a cubesat for ion, neutral, electron, and magnetic fields (CINEMA), is equipped with a suprathermal electron, ion, neutral (STEIN) instrument and a 3-axis magnetometer of magnetoresistive sensors. TRIO is developed by three institutes: i) two CINEMA by Kyung Hee University (KHU) under the WCU program, ii) one CINEMA by UC Berkeley under the NSF support, and iii) three magnetometers by Imperial College, respectively. Multi-spacecraft observations in the STEIN instruments will provide i) stereo ENA imaging with a wide angle in local times, which are sensitive to the evolution of ring current phase space distributions, ii) suprathermal electron measurements with narrow spacings, which reveal the differential signature of accelerated electrons driven by Alfven waves and/or double layer formation in the ionosphere between the acceleration region and the aurora, and iii) suprathermal ion precipitation when the storm-time ring current appears. In addition, multi-spacecraft magnetic field measurements in low earth orbits will allow the tracking of the phase fronts of ULF waves, FTEs, and quasi-periodic reconnection events between ground-based magnetometer data and upstream satellite data.

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Unification Model and Rayleigh Scattered Lyα in Active Galactic Nuclei

  • Chang, Seok-Jun;Lee, Hee-Won;Yang, Yujin
    • The Bulletin of The Korean Astronomical Society
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    • v.41 no.2
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    • pp.33.2-34
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    • 2016
  • The unification model of active galactic nuclei invokes the presence of a thick molecular torus that hides the broad emission line region from a line of sight toward observers with low latitude. It is expected that the illuminated side of the molecular torus may be photodissociated by strong far UV radiation from the central AGN, forming an H I region with a high neutral column density. We propose that the Rayleigh scattering optical depth of this HI region can be significant for most broad $Ly{\alpha}$ line photons with the Doppler factor not exceeding 104 km s-1. Rayleigh scattered $Ly{\alpha}$ photons can be characterized by strong linear polarization depending on their scattering optical depth. We performed Monte Carlo simulations of polarized radiative transfer of $Ly{\alpha}$ adopting simple scattering geometries relevant to the unification model of AGN. We find that for a low torus the Rayleigh scattered $Ly{\alpha}$ is polarized in the direction parallel to the symmetry axis with the polarization degree dependent on wavelength. In the case of a high torus, the core part of $Ly{\alpha}$ is polarized in the direction perpendicular to the symmetry axis whereas the wing part is parallelly polarized. We conclude that careful spectropolarimetry around $Ly{\alpha}$ can be useful in testing the AGN unification model.

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Comparative analysis among deterministic and stochastic collision damage models for oil tanker and bulk carrier reliability

  • Campanile, A.;Piscopo, V.;Scamardella, A.
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.10 no.1
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    • pp.21-36
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    • 2018
  • The incidence of collision damage models on oil tanker and bulk carrier reliability is investigated considering the IACS deterministic model against GOALDS/IMO database statistics for collision events, substantiating the probabilistic model. Statistical properties of hull girder residual strength are determined by Monte Carlo simulation, based on random generation of damage dimensions and a modified form of incremental-iterative method, to account for neutral axis rotation and equilibrium of horizontal bending moment, due to cross-section asymmetry after collision events. Reliability analysis is performed, to investigate the incidence of collision penetration depth and height statistical properties on hull girder sagging/hogging failure probabilities. Besides, the incidence of corrosion on hull girder residual strength and reliability is also discussed, focussing on gross, hull girder net and local net scantlings, respectively. The ISSC double hull oil tanker and single side bulk carrier, assumed as test cases in the ISSC 2012 report, are taken as reference ships.

The Bending and Twisting Analysis of SMA/Composite Beams (SMA 선이 삽입된 복합재 보의 굽힘 및 비틀림 해석)

  • Park, Bum-Sik;Kim, Cheol
    • Proceedings of the Korean Society For Composite Materials Conference
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    • pp.151-154
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    • 2001
  • Shape memory alloy (SMA) has demonstrated its potentials for various smart structure applications. SMA wires undergo a reversible phase transformation from martensite to austenite as temperature increases. This transformation leads to shape recovery and associated recovery strains. If SMA actuators are embedded off the neutral surface and are oriented in arbitrary angles with respect to a beam axis, then the beam bends and twists due to the coupling effects of recovery strains activated. In this study, the bending and twisting of a SMA/Composite beam were controlled by both electric resistive heating and passive elastic tailoring. 3-dimensional finite element formulations were derived and validated to analyze the responses of the SMA/Composite beam. Numerical results show that the shape of the SMA/Composite beam can be controlled by judicious choices of control temperatures, SMA angles, and elastic tailoring.

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Earthquake-Resistance of Slender Shear Wall with No Boundary Confinement (단부 횡보강이 없는 세장한 전단벽의 내진성능)

  • 박홍근;강수민;조봉호;홍성걸
    • Journal of the Korea Concrete Institute
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    • v.12 no.5
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    • pp.47-57
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    • 2000
  • Experimental and numerical studies were done to investigate seismic performance of slender shear walls with no boundary confinement that are principal structural members of high0rise bearing wall buildings. 1/3 scale specimens that model the plastic region of long slender shear walls subjected to combined axial load and bending moment were tested to investigate strength, ductility, capacity of energy dissipation, and strain distribution, The experimental results show that the slender shear walls fail due to early crushing in the compressive boundary, and then have very low ductility. The measured maximum compressive strain is 0.0021, much less than 0.004 being commonly used for estimation of ductility. This result indicates that the maximum compressive strain is not a fixed value but is affected by moment gradient along the shear wall height and distance from the neutral axis to the extreme compressive fiber.

An Experimental Study on Flexural Strength of Composite Beam with Reduced Top Flange of Steel (상부플랜지를 감소시킨 합성보의 휨내력에 관한 실험적 연구)

  • Moon, Chan-II;Jeong, Jae-Hun;Kim, Jin-Moo;Joo, Kyong-Jae
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.4 no.3
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    • pp.153-160
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    • 2000
  • In simply supported composite beams, the neutral axis of the composite cross section usually is located the top flange of the steel I-shape, so that the top flange does not impart much strength to the member. This suggests that omitting the top flange entirely could be a means to lower the cost of the beam without greatly reducing the strength. The purpose of this investigation is to research flexural strength and behavior of the composite beams with reduced top flange of steel. Five specimens with H and inverted T steel section were tested. As the test results, comparison of the experimental to computed full-plastic moment, and variations of flexural strength with reduced top flange were analyzed.

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A Fatigue Analysis of Prestressed Concrete Composite Girders with Time Dependent Effects (시간에 따른 영향을 고려한 프리스트레스트 콘크리트 합성 거더의 피로해석)

  • 김지상;오병환
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.126-130
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    • 1992
  • Recently, fatigue problem become a critical issue in the design of prestressed concrete bridges due to the increase of traffic volumes and use of high-strength materials. Most existing studies are mainly concerned with the fatigue behavior of component materials only such as concrete, reinforcing bars, and prestressing steels and few studies exist that deals with the fatigue behavior of bridge members. An improved analytic formulation for both uncracked and cracked prestressed concrete composite section with cyclic creep effect is developed to take into account the change of neutral axis with crack propagation. The procedure also enables to investigate serviceability limit states, deflection and crack width. The present study allows more realistic analysis and design of prestressed concrete composite girder bridges under fatigue loadings.

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A Comparitive Study on the Ultimate Tendon Stress of Unbonded Tendon According to Various Codes (규격별 비부착 긴장재의 극한응력식에 대한 비교 연구)

  • 유성원;서정인
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.501-506
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    • 2002
  • The unbonded prestressed concrete(PSC) members exhibit very different structural behavior from that of bonded PSC members because of having different tendon stress increment. Recently, AASHTO changed the provision of ultimate tendon stress with unbonded tendons, because some researches tried to improve the provision of ultimate tendon stress with unbonded tendons. The purpose of the present study is to compare various Codes with the ultimate failure stresses of prestressing(PS) steels for the unbonded PSC members. To this end, Some national Codes have been collected and analyzed. A series of major influencing variables have been included in the analysis. It was found that the span-depth ratio, neutral axis depth-effective depth ratio, concrete compressive strength, effective prestress, and prestressing steel ratio have great influence on the ultimate failure stress of PS steel in unbonded PSC members. The Comparison indicates that existing formulas including ACI and domestic Code's equations shows some unwarranties. The present study allows more realistic analysis and design of prestressed concrete structures with internal unbonded tendons.

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