• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.52.2-52.2
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• 2020

At quasi-perpendicular shocks in the high-�� (��=Pgas/Pmag~100) intracluster medium (ICM), various microinstabilities occur by the temperature anisotropies and/or drift motions of plasma. In the downstream, the Alfvén ion cyclotron instability (AIC) due to the ion temperature anisotropy (Ti⊥>Ti║) is triggered by shock-reflected ions, the whistler instability (WI) is driven by the electron temperature anisotropy (Te⊥>Te║) as a consequence of the shock compression of magnetic fields, and the mirror instability is generated due to the ion and/or electron temperature anisotropy. At the shock foot, the modified two stream instability (MTSI) is possibly excited by the cross-field drift between ions and electrons. In the upstream, electron firehose instability (EFI) is driven by the electron temperature anisotropy or the relative drift between incoming and reflected electrons. These microinstabilities play important roles in the particle acceleration in ICM shocks, so understanding of the microinstabilities and the resultant plasma waves is essential. In this study, based on a linear stability analysis, the basic properties of the microinstabilities in ICM shocks and the ion/electron scale fluctuations are described. We then discuss the implication of our work on the electron pre-acceleration in ICM shocks.

• Steel and Composite Structures
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• v.4 no.6
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• pp.453-469
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• 2004

In this article, a genetic algorithm based optimum design method is presented for non-linear steel frames with semi-rigid connections. The design algorithm obtains the minimum weight frame by selecting suitable sections from a standard set of steel sections such as European wide flange beams (i.e., HE sections). A genetic algorithm is employed as optimization method which utilizes reproduction, crossover and mutation operators. Displacement and stress constraints of Turkish Building Code for Steel Structures (TS 648, 1980) are imposed on the frame. The algorithm requires a large number of non-linear analyses of frames. The analyses cover both the non-linear behaviour of beam-to-column connection and $P-{\Delta}$ effects of beam-column members. The Frye and Morris polynomial model is used for modelling of semi-rigid connections. Two design examples with various type of connections are presented to demonstrate the application of the algorithm. The semi-rigid connection modelling results in more economical solutions than rigid connection modelling, but it increases frame drift.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.6
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• pp.513-523
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• 2012

The objective of this research is to examine how the lateral resisting system of selected prototypes are affected by seismic zone effect and shape irregularity on its seismic performance. The lateral resisting systems are divided into the three types, diagrid, braced tube, and outrigger system. The prototype models were assumed to be located in LA, a high-seismicity region, and in Boston, a low-seismicity region. The shape irregularity was classified with rotated angle of plane, $0^{\circ}$, $1^{\circ}$, $2^{\circ}$. This study performed two parts of analyses, Linear Response and Non-Linear Response History(NLRH) analysis. The Linear Response analysis was used to check the displacement at the top and natural period of models. NLRH analysis was conducted to invest base shear and story drift ratio of buildings. As results, the displacement of roof and natural period of three structural systems increase as the building stiffness reduces due to the changes in rotation angle of the plane. Also, the base shear is diminished by the same reason. The result of NLRH, the story drift ratio, that was subject to Maximum Considered Earthquake(MCE) satisfied 0.045, a recommended limit according to Tall Building Initiative(TBI).

• Journal of IKEEE
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• v.11 no.3
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• pp.122-128
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• 2007

Sinusoidal voltage-controlled oscillators (VCOs) based on Colpitts and Hartley oscillators are presented. They consist of a LC parallel-tuned circuit connected in a negative-feedback loop with an OTA-R amplifier and two diode limiters, where the inductor is simulated one realized with temperature-stable linear operational transconductance amplifiers (OTAs) and a grounded capacitor. Prototype VCOs are built with discrete components. The Colpitts VCO exhibits less than 1% nonlinearity in its current-to-frequency transfer characteristic from 4.2 to 21.7 MHz and ${\pm}$95 ppm/$^{\circ}C$ temperature drift of frequency over 0 to $70^{\circ}C$. The total harmonic distortion (THD) is as low as 2.92% with a peak-to-peak amplitude of 0.7 V for a frequency-tuning range of 10.8-32 MHz. The Hartley VCO has the temperature drift and THD of two times higher than those of the Colpitts VCO.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.12
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• pp.3960-3969
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• 1996

A fluid flow inside a circular cylinder subject to horizontal and circular oscillation is analyzed theoretically. Under the assumption of small-amplitude oscillation, the governing equations take linear forms. The velocity field is obtained in terms of the first kind of Bessel function of order 1. It was found that a particle describes an orbit close to a circle in the central region and an arc near the side wall. We also obtained the Stokes' drift velocity induced by the traveling wave along the circumferential direction. The Eulerian streaming velocities at the edge of the bottom and side boundary layers were also obtained. It was shown that the vertical component of the steady streaming velocity on the side wall is almost proportional to the amplitude of the free surface motion.

• Earthquakes and Structures
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• v.8 no.3
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• pp.511-539
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• 2015

The main objective of this study is to analytically investigate the effectiveness of different strengthening solutions in upgrading the seismic performance of existing reinforced concrete (RC) buildings in Nepal. For this, four building models with different structural configurations and detailing were considered. Three possible rehabilitation solutions were studied, namely: (a) RC shear wall, (b) steel bracing, and (c) RC jacketing for all of the studied buildings. A numerical analysis was conducted with adaptive pushover and dynamic time history analysis. Seismic performance enhancement of the studied buildings was evaluated in terms of demand capacity ratio of the RC elements, capacity curve, inter-storey drift, energy dissipation capacity and moment curvature demand of the structures. Finally, the seismic safety assessment was performed based on standard drift limits, showing that retrofitting solutions significantly improved the seismic performance of existing buildings in Nepal.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2011.05a
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• pp.98-99
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• 2011

300 mm급 선형 이온원의 방전 간격에 따른 방전 및 이온빔 인출 특성 변화를 연구하였다. 방전 간격이 2 mm 에서 3 mm로 증가함에 따라 동일 방전 전압에서 방전 전류가 약 20% 증가하였으며, 이는 방전 공간 내 플라즈마 발생 증가에 의한 것임을 object oriented particle in cell 전산모사를 통해 확인하였다.

• Steel and Composite Structures
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• v.19 no.1
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• pp.59-74
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• 2015

Since there are several places located in active seismic zones in the world, serious damages and losses have happened due to major scaled earthquakes. Especially, structures having different irregularities have been severely damaged or collapsed during these seismic events. Behavior of existing structures under several loading conditions is not completely determined due to some uncertainties. This situation reveals the importance of design and analysis of structures under seismic effects. Several non-linear static procedures have been developed in recent years. Determination of the seismic safety of the existing structures and strengthening techniques are significant civil engineering problems Non-linear methods are defined in codes to determine the performance levels of structures more accurately. However, displacement based ones give more realistic results. These methods provide more reliable evaluation possibilities for existing structures with developing computer technology. In this study, non-linear performance analysis of existing and strengthened steel structures by X shaped bracing members with 3, 5 and 7 stories which have soft story irregularity is performed according to FEMA-356 and Turkish Earthquake Code-2007. Damage ratios of the structural members and global performance levels are determined as well as modal properties and story drift ratios after non-linear finite elements analysis for each structure.

• Journal of Korean Association for Spatial Structures
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• v.18 no.2
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• pp.129-135
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• 2018

Following a 5.8 magnitude earthquake on September 12, 2016 in Gyeongju Province, a magnitude 5.4 earthquake occurred in the northern region of Pohang City on November 15, 2017 in South Korea. Only 7.9 % of the building structures are earthquake-resistant, according to the recent survey conducted by the government agencies in October 2017. In this paper, the linear analysis seismic performance evaluation procedure of the existing school structures presented in the revised methodology(Seismic Performance Evaluation Procedure and Rehabilitation Manual for School Facilities) was introduced. In this paper, the linear analysis evaluation procedure presented in the revised methodology was introduced and the seismic performance index of the example structure was evaluated using the linear analysis evaluation procedure. The seismic retrofit was verified by the linear and nonlinear dynamic analyses using Perform 3D. The analysis results show that the dissipated inelastic energy is concentrated on the retrofitted shear wall and the maximum inter-story drift of the stadium model structure with damping system satisfies the requirement of the current code.

• Steel and Composite Structures
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• v.7 no.3
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• pp.201-217
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• 2007

Two combinatorial optimization algorithms, tabu search and simulated annealing, are presented for the minimum-weight design of geometrically non-linear steel plane frames. The design algorithms obtain minimum weight frames by selecting suitable sections from a standard set of steel sections such as American Institute of Steel Construction (AISC) wide-flange (W) shapes. Stress constraints of AISC Load and Resistance Factor Design (LRFD) specification, maximum and interstorey drift constraints and size constraints for columns were imposed on frames. The stress constraints of AISC Allowable Stress Design (ASD) were also mounted in the two algorithms. The comparisons between AISC-LRFD and AISC-ASD specifications were also made while tabu search and simulated annealing were used separately. The algorithms were applied to the optimum design of three frame structures. The designs obtained using tabu search were compared to those where simulated annealing was considered. The comparisons showed that the tabu search algorithm yielded better designs with AISC-LRFD code specification.