• Journal of electromagnetic engineering and science
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• 제3권1호
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• pp.62-66
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• 2003

Novel coupled line phase shifters and its equivalent phase delay line for compact broadband phased array antennas are proposed. These phase control circuits are designed to be less complex, small size and to use a less number of active devices. The phase shifter is able to control a 120$^{\circ}$ phase shift continuously, and the phase delay line for a reference phase has a fixed 60$^{\circ}$ shifted phase. Both have the low phase error of less than $\pm$3.5$^{\circ}$ and the low gain variations of less than 1 ㏈ within the 300 MHz bandwidth. These proposed circuits are adequate to form the efficient beam-forming networks with compactness, broadband, less complexity, and low cost.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 1997년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Fall 1997
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• pp.241-248
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• 1997

The super-structure in a soil-structure interaction analysis is commonly idealized as lumped parameter system. In this study, the complex shear wall structure is modeled using three different kinds of modeling techniques : 1) full FEM comparatively as an exact solution, 2)equivalent shear spring model assuming mainly shear deformations of the wall, 3) equivalent beam-stick model made by independent static analysis. Dynamic characteristics due to three different modeling methods are compared and investigated before performing structural response analysis. The beam-stick model in comparison to shear spring model gives closer dynamic responses when compared with the full FEM, even though it requires additional unit load static analyses.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2002년도 봄 학술발표회 논문집
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• pp.233-240
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• 2002

In this paper, the effects of vehicle loads on flat slab system are investigated on the basis of the previous studies for beam-girder parking structural system. The influence surfaces of flat slab for typical design section are developed for the purpose of obtaining maximum member forces under vehicle loads. In addition, the equivalent vehicle load factors for flat slab parking structures are suggested using artificial neural network. The network responses are compared with the results by numerical analyses to verify the validation of Levenberg-Marquardt algorithm adopted as training method in this paper. Many parameter studies fur the flat slab structural system show dominant vehicle load effects at the center positive moments in both column and middle strips, like the beam-girder parking structural system.

• Structural Engineering and Mechanics
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• 제64권2호
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• pp.259-270
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• 2017

The stochastic vibration response of the sandwich beam with the nonlinear adjustable visco-elastomer core and supported mass under stochastic support motion excitations is studied. The nonlinear dynamic properties of the visco-elastomer core are considered. The nonlinear partial differential equations for the horizontal and vertical coupling motions of the sandwich beam are derived. An analytical solution method for the stochastic vibration response of the nonlinear sandwich beam is developed. The nonlinear partial differential equations are converted into the nonlinear ordinary differential equations representing the nonlinear stochastic multi-degree-of-freedom system by using the Galerkin method. The nonlinear stochastic system is converted further into the equivalent quasi-linear system by using the statistic linearization method. The frequency-response function, response spectral density and mean square response expressions of the nonlinear sandwich beam are obtained. Numerical results are given to illustrate new stochastic vibration response characteristics and response reduction capability of the sandwich beam with the nonlinear visco-elastomer core and supported mass under stochastic support motion excitations. The influences of geometric and physical parameters on the stochastic response of the nonlinear sandwich beam are discussed, and the numerical results of the nonlinear sandwich beam are compared with those of the sandwich beam with linear visco-elastomer core.

• 한국정밀공학회지
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• 제16권9호
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• pp.9-17
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• 1999

This investigation is the result of the structural analysis by finite element method for optimal design of the cross beam with circular holes of the electric car-body. in order to install the air pipe and electric wire pipe that correspond signal between electric machines for the control system and to reduce the weight of the electric car-body, several circular areas from a cross beam should be taken off. What we want to perform is the optimal design of a cross beam with circular holes to posses equal stress in comparison with no hole cross beam. first, no hole cross beam as basic modal be chosen, executing the analysis, reviewing the distribution of stress and displacement at each location. several parameter should be adopted from the cross beam geometry like the location and shape of the hole to affect the maximum stress and displacement. So the analysis was executed by finite element analysis for finding optimal design parameter to the change of the location and shape of the circular hole. finally, the optimal design of the cross beam with circular holes was obtained and the maximum equivalent stress was compared with no hole cross beam at each location.

• Journal of Advanced Marine Engineering and Technology
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• 제25권3호
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• pp.631-635
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• 2001

The major problems associated with the manufacturing processes of the microaccelerometer based on the tunneling current concept is the residual stress. This paper deals with finite element analysis of residual stress causing pop up phenomenon which are induced in micromachining processes for a microaccelerometers sensor using silicon on insulator(SOI) wafer. After heating the tunnel gap up to $100^{\circ}C$and get it through cooling process and the additional beam up to $80^{\circ}C$get it through the cooling process. We learn the residual stress of each shape and compare the results with each other, after heating the tunnel gap up to $400^{\circ}Cduring$ the Pt deposition process. The equivalent stresses produced during the heating process of focused ion beam(FIB) cut was also to be about $0.02~0.25Pa/^{\circ}C$and cooling process the gradient of residual stresses of about $8.4\{times}10^2Pa/{\mu}m$ still at cantilever beam and connected part of paddle. We want to seek after the real cause of this pop up phenomenon and diminish this by change manufacturing processes of microaccelerometer sensors.

• 한국구조물진단유지관리공학회 논문집
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• 제8권4호
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• pp.239-246
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• 2004

충격하중에 대한 양단 고정보의 거동을 강 소성 모델을 이용하여 파악 하였다. 또한 손상을 발생시키는 정 역학적 붕괴하중과 이상임펄스에 대한 하중최대치 비와 임펄스 비를 이용하여 손상곡선을 작성하였다. 작성된 손상곡선으로부터 충격하중의 하중 최대치와 임펄스는 구조물의 안전에 중요 변수가 됨을 보였으며 또한 하중최대치 비와 임펄스 비로 작성된 손상곡선은 하중작용시간과 하중의 형태 그리고 구조물의 동적 특성이 함께 고려된 기준으로, 등가 동하중에 초점을 맞추어 일괄적으로 구조물의 안전성을 판단할 수 있는 방법이다.

• Structural Engineering and Mechanics
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• 제2권1호
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• pp.95-112
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• 1994

This paper describes the formulation and application of a dynamic model for a conventional rail track subjected to arbitary loading functions that simulate wheel/rail impact forces. The rail track is idealized as a periodic elastically coupled beam system resting on a Winkler foundation. Modal parameters of the track structure are first obtained from the natural vibration characteristics of the beam system, which is discretized into a periodic assembly of a specially-constructed track element and a single beam element characterized by their exact dynamic stiffness matrices. An equivalent frequency-dependent spring coefficient representing the resilient, flexural and inertial characteristics of the rail support components is introduced to reduce the degrees of freedom of the track element. The forced vibration equations of motion of the track subjected to a series of loading functions are then formulated by using beam bending theories and are reduced to second order ordinary differential equations through the use of mode summation with non-proportional modal damping. Numerical examples for the dynamic responses of a typical track are presented, and the solutions resulting from different rail/tie beam theories are compared.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.859-862
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• 2002

The Core Support Barrel (CSB) is a major component of Reactor Internals, and is designed to support and protect the Reactor Core. In this study, Reactor Core, Core Shroud and CSB were simplified to coaxial cylinders and then the offset of Reactor Core & Core Shroud to the dynamic characteristic of CSB was analyzed. For the beam modes, natural frequencies of the cantilevered cylinder are compared with those of the cantilevered beam. And it was found out that shear modulus must be used correctly to convert the shell model to the equivalent beam model. From the dynamic characteristics of the beam model, it was found out that natural frequencies are proportional to the length of Reactor Core & Core Shroud and inversely proportional to the mass. From the comparison with the dynamic characteristics of a beam model and a lumped-mass model it was found out that the size of lumped-mass must be determined considering both the length and the mass of Reactor Core & Core Shroud.

• Structural Engineering and Mechanics
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• 제90권5호
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• pp.505-515
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• 2024

In this study, obtaining theoretical stress-strain curves and determining the parameters defining the equivalent rectangular stress block were aimed for 3 and 4-layered rectangular Reinforced Concrete (RC) cross-sections subjected to flexure. For these aims, the analytical stress-strain model proposed by Hognestad was chosen for the concrete grades (20 MPa≤fck≤60 MPa) used in this study. The tensile strength of the concrete was neglected and the thickness of the concrete layers in the compression zone of the concrete cross-section was taken as equal. In addition, while concrete strength was kept constant within each layer, concrete strengths belonging to separate layers were increased from the neutral axis towards the outer face of the compression zone of the concrete cross-section. After the equivalent rectangular stress block parameters were determined by numerical iterations, variations of these parameters depending on concrete strength in layers and layer numbers were obtained. Finally, some analytical equations have been proposed to predict the equivalent stress block parameters for the 3 and 4-layered RC cross-sections and validities of these proposed equations were shown by different metrics in this study.