• Steel and Composite Structures
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• 제37권4호
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• pp.391-404
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• 2020

Human-induced vibration could present a serious serviceability problem for large-span and/or lightweight floors using the high-strength material. This paper presents the results of heel-drop, jumping, and walking tests on a large-span composite steel rebar truss-reinforced concrete (CSBTRC) floor. The effects of human activities on the floor vibration behavior were investigated considering the parameters of peak acceleration, root-mean-square acceleration, maximum transient vibration value (MTVV), fundamental frequency, and damping ratio. The measured field test data were validated with the finite element and theoretical analysis results. A comprehensive comparison between the test results and current design codes was carried out. Based on the classical plate theory, a rational and simplified formula for determining the fundamental frequency for the CSBTRC floor is derived. Secondly, appropriate coefficients (β_rp) correlating the MTVV with peak acceleration are suggested for heel-drop, jumping, and walking excitations. Lastly, the linear oscillator model (LOM) is adopted to establish the governing equations for the human-structure interaction (HSI). The dynamic characteristics of the LOM (sprung mass, equivalent stiffness, and equivalent damping ratio) are determined by comparing the theoretical and experimental acceleration responses. The HSI effect will increase the acceleration response.

• 건축역사연구
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• 제5권2호
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• pp.83-95
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• 1996

Computerized visual database construction of architectural precedents has just begun in some research institutes in the world. In Korea the first visual database has shown its testl version by S architectural design firm in september 1996. In this article the author discusses the historical contexts and the recent computerization cases, the traits, the uses and the limits of architectural visual database system of precedents. The forms and contents of data fields in two cases are compared with a focus on the description of architectural traits of each data entry. Compared to the KIA format, the S database has better performance for architectural design reference because it collects more pictures and drawings and larger texts for the field of architectural chracteristics. But this latter also is constrained by its capacity of memory and so lacks the reciprocity of the DOORS in the Graduate School of Design, Harvard University. A visual database system which has more flexible allocation of memory and respondent with the users is yet to be prepared. But this system also should be maintained by some experts in architectural history, theory and criticism, because their knowledge is essential for selection of precedents and revision of the data description. A full-fledged electronic visual database in architecture will not only save much effort for the architect, but also will change the architects' design behavior. Nevertheless this does not mean the automatic promotion of architects' creativity.

• 대한전자공학회논문지SP
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• 제40권5호
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• pp.322-331
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• 2003

HDTV(high-definition television)와 개인용 컴퓨터와 같은 다양한 매체의 발전에 따라 비월주사(interlaced scanning) 방식의 신호와 순차주사(progressive scanning) 방식의 신호 상호간의 변환에 대한 요구가 점점 늘어나고 있으며, 특히 비월주사 방식을 순차주사 방식으로 바꾸어주는 순차주사화(deinterlacing)가 활발히 연구되고 있다. 이러한 추세에 따라 본 논문에서는 부화소 단위의 움직임 정보를 이용한 순차주사화 알고리즘을 제안한다 이를 위해 움직임 추정과정에서 발생하는 부정확한 부화소 단위의 움직임 정보에 대하여 모델링하였다. 또한 집합이론(set-theory)에 근거하여 어떠한 사전 정보 없이 정규화값(regularization parameter)을 결정하여 영상들간의 부정확한 움직임에 의해 발생하는 에러를 최소화하였다. 본 논문에서 제안된 알고리즘은 실험을 통하여 검증 할 수 있었다.

• 대한기계학회논문집B
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• 제31권3호
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• pp.306-312
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• 2007

This paper describes the flow characteristics of circular multiple jet investigated by hot-wire anemometry. The nozzle arrays were classified into two cases; 6- or 7-nozzle located circumferentially in equal interval without or with a central jet. The flow field was measured according to the number of nozzles when the Reynolds number based on the nozzle exit is about $10^4$. Mean velocity, Reynolds shear stress and turbulent kinetic energy were investigated in the downstream of jets. The Tollmien's theory holds for downstream only when a nozzle locates at the center. Jet interaction is influenced due to with or without a center nozzle. In addition, the two-dimensional numerical computation was conducted for 3-nozzle case to obtain the general flow structure near the nozzle exit, which verifies the formation of the recirculation region with captive vortices, that is, the evidence of the interaction between jets.

• 대한의용생체공학회:의공학회지
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• 제23권4호
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• pp.329-332
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• 2002

일반적으로 금지뉴런의 효과는 신경망을 안정시킨다고 알려져 있다. 본 연구에서는 확률적 평균 필드 이론에 근거한 신경망 모델에서 느린 금지뉴런의 역할을 살펴보았다. 흥분뉴런과 빠른 금지뉴런으로 구성된 신경망에 느린 금지뉴런을 더하면, 느린 금지 뉴런이 없는 모델에서보다 매우 낮은 역치에서 안정적인 동시적 활동이 유도된다는 것을 발견하였다. 이 역치는 대뇌 피질 신경의 생리학적 역치와 일치하며. 느린 금지 뉴런만이 신경망에 낮은 발화율과 낮은 역치를 유지시키는 네거티브 피드백을 줄 수 있다.

• 한국대기환경학회지
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• 제12권4호
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• pp.459-472
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• 1996

An experimental investigation on the wind flow over smooth bell-shaped two-dimensional hills with hill slopes (the ratio of height to half width) of 0.3 and 0.5 is performed in an atmospheric boundary-layer wind tunnel. Two categories of the models are used in the present investigation; six two-dimensional single-hills, and four continuous double-hills. The measurements of the flow field and surface static-pressure distribution are carried out over the Reynolds number (based on the hill height) of 1.9 $\times 10^4, 3.3 \times 10^4, and 5.6 \times 10^4$. The velocity profiles and turbulence characteristics are measured by the pitot-tube and X-type hot-wire anemometer, respectively. The undisturbed boundary-layer profile on the bottom surface of the wind tunnel is reasonably consistent with the power-law profile with $\alpha = 7.0 (1/\alpha$ is the power-law exponent) and shows good spanwise uniformities. The profiles of turbulent intensity are found to be consistent along the centerline of the wind tunnel. The measured non-dimensional speed-up profiles at the hill crest show good agreements with the predictions of Jackson and Hunt's linear theory. The flow separation occurs in the hill slope of 0.5, and the oil-ink dot method is used to find the reattachment points in the leeside of the hill. The measured reattachment points are compared with the numerical predictions. Comparisons of the mean velocity profiles and surface pressure distributions between the numerical predictions and the experimental results show good agreements.

• Structural Engineering and Mechanics
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• 제27권2호
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• pp.199-222
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• 2007

Composite laminated structures supported on elastic foundations are being increasingly used in a great variety of engineering applications. Composites exhibit larger dispersion in their material properties compared to the conventional materials due to large number of parameters associated with their manufacturing and fabrication processes. And also the dispersion in elastic foundation stiffness parameter is inherent due to inaccurate modeling and determination of elastic foundation properties in practice. For a better modeling of the material properties and foundation, these are treated as random variables. This paper deals with effects of randomness in material properties and foundation stiffness parameters on the free vibration response of laminated composite plate resting on an elastic foundation. A $C^0$ finite element method has been used for arriving at an eigen value problem. Higher order shear deformation theory has been used to model the displacement field. A mean centered first order perturbation technique has been employed to handle randomness in system properties for obtaining the stochastic characteristic of frequency response. It is observed that small amount of variations in random material properties and foundation stiffness parameters significantly affect the free vibration response of the laminated composite plate. The results have been compared with those available in the literature and an independent Monte Carlo simulation.

• 한국농공학회논문집
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• 제54권3호
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• pp.55-63
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• 2012

Soil properties are not random values which is represented by mean and standard deviation but show spatial correlation. Especially, soils are highly variable in their properties and rarely homogeneous. Thus, the accuracy and reliability of probabilistic analysis results is decreased when using only one random variable as design parameter. In this paper, to consider spatial variability of soil property, one-dimensional random fields of coefficient of consolidation ($C_v$) were generated based on a Karhunen-Loeve expansion. A Latin hypercube Monte Calro simulation coupled with finite difference method for Terzaghi's one dimensional consolidation theory was then used to probabilistic analysis. The results show that the failure probability is smaller when consider spatial variability of $C_v$ than not considered and the failure probability increased when the autocorrelation distance increased. Thus, the uncertainty of soil can be overestimated when spatial variability of soil property is not considered, and therefore, to perform a more accurate probabilistic analysis, spatial variability of soil property needed to be considered.

• Nuclear Engineering and Technology
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• 제51권4호
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• pp.1008-1016
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• 2019

In the SG (steam generator) of PWR (pressurized water reactor) for a nuclear plant, hundreds of U-shaped tubes are used for the heat exchanger system. They interact with primary pressurized cooling water flow, generating flow-induced vibration in the secondary flow region. A simplified U-tube model is proposed in this study to apply for experiment and its counterpart computation. Using the commercial code, ANSYS-CFX, we first verified the Moody chart, comparing the straight pipe theory with the results derived from CFD (computational fluid dynamics) analysis. Considering the virtual mass of fluid, we computed the major modes with the low natural frequencies through the comparison with impact hammer test, and then investigated the effect of pump flow in the frequency domain using FFT (fast Fourier transform) analysis of the experimental data. Using two-way fluid-structure interaction module in the CFD code, we studied the influence on mean flow rate to generate the displacement data. A feasible CFD method has been setup in this research that could be applied potentially in the field of nuclear thermal-hydraulics.

• 항공우주시스템공학회지
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• 제15권1호
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• pp.63-71
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• 2021

한국해군은 1978년에 하푼 유도탄을 최초 도입 후 단계적인 획득을 통하여 현재까지 운용하고 있다. 하푼 유도탄을 장기 운용함에 따라 성능보장을 위한 적극적인 후속 군수지원이 필요하며, 유도탄 검사는 유도탄 상태를 확인하기 위한 기본 활동이다. 본 연구는 장기간 운용 중인 하푼 유도탄의 기존 검사주기가 적절한지 확인하기 위하여 수행되었으며, 연구 방법은 해군의 야전운용자료를 바탕으로 Martinez 이론과 비모수적 MCF 기법을 활용하여 운용 기간에 따른 구간별 검사주기를 분석하여 제시하였다.