• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.831-834
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• 2002

An analytic approach is attempted to predict the amplification of turbulence in compressible flows experiencing one-dimensional and axisymmetric bulk dilatation. The variations of vortex radius and vorticity are calculated, and then the amplification of turbulence is obtained from them by tracking three representative vortices. For a one-dimensionally compressed flow, the present analysis slightly underestimates the amplification of velocity fluctuations and turbulent kinetic energy, relative to that of rapid distortion theory in the solenoidal limit. For an axisymmetrically distorted flow, the amplification of velocity fluctuations and turbulent kinetic energy depend not only on the density ratio but also on the ratio of streamwise mean velocities, which represents streamwise vortex contraction/stretching. In all flows considered, the amplification of turbulence is dictated by the mean density ratio. In the axisymmetric flow, streamwise vortex stretching/contraction, however, alters the amplification slightly.

• 한국지구과학회지
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• 제30권7호
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• pp.810-823
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• 2009

지진원 상수의 정밀한 결정과 지진재해의 예측에 있어서 결정적인 요인의 하나는 부지증폭 특성에 관한 상세한 정보이다. 한반도 광대역 지진관측소의 부지증폭 특성이 0.2-20 Hz 범위 내에서 주파수의 함수로 추정되었다. 한반도 남부에서 2003년부터 2008년까지 관측된 43개의 지진에 대한 총 1275개의 지진기록이 사용되었다. 지진동 모델의 역산으로부터 추정된 28개소의 관측소에 대한 부지증폭비는 수직대 수평(H/V) 스펙트럼비로부터 얻어진 증폭비와 몇몇 관측소를 제외하고는 대체로 그 값이 일치하는 것이 발견되었다. 이 연구에서 얻어진 주파수별 부지증폭 특성은 어떤 뚜렷한 공간분포를 보이지 않았다. 또한 부지증폭 특성은 기반암 종류보다는 풍화의 정도와 크게 관련이 있는 것으로 나타났다. 주파수별 부지증폭비를 참조하여 28개소의 광대역 관측소를 4개의 그룹으로 나누었고, 그룹별 특징에 대하여 본문에 서술하였다.

• 대한기계학회논문집
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• 제17권2호
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• pp.371-379
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• 1993

The wrinkling in the electromagnetic tube compression with a mandrel is remarkably smaller than that of the process without it. To analyze this phenomenon, the critical forming parameters such as the ratio of the clearance to the shell radius, the ratio of the thickness to the shell radius, and the ratio of the applied pressure to the standard pressure are introduced tp consider the effect of the mandrel, in addition to those of the thickness of shell and applied loads. The amplification ratio is also used to observe the magnitude of amplification. The results obtained by 2-D finite element method show that the initial imperfection embedded in the radius of cylindrical shell is the dominant factor to determine the final shape of the tube compression, and that the amplification ratio tends to have smaller values with the smaller clearance ratio and also with the larger thickness and pressure ratios.

• Geomechanics and Engineering
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• 제36권4호
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• pp.367-380
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• 2024

Investigations has shown that the correct estimation of the effective amplification period is as important as the amplification value itself. It gets more important in 2D basins. This study presents a quantitative coefficient for consideration of the nonlinearity effect in terms of amplification value and the shift in its period which is missing or ineffectively considered in the previous studies. To attain this goal, by the application of a time domain fully nonlinear method, the deviation of the more common equivalent linear results from the basin nonlinear behavior under strong ground motions is investigated quantitatively. Also, despite the increase in the damping ratio, the possibility of the increase in the amplification due to the increase in motion strength is shown. To make the results useful in engineering practice, by introducing nonlinearity ratio, the effect of the nonlinearity is quantitatively estimated for two soft and stiff clayey basins with three different depths under a set of motions scaled to two target spectrum. Results show that at the 100 m depth soft clayey basin, while the nonlinearity ratio shows a 35% deviation at the basin edge part under DD1 motion level, its effect moves to the central part with 20% effect under DD3 motion level. By the increase in depth to 150 m, the results show a decrease in the overall effect of the nonlinear behavior for both clay types. At this depth, the nonlinearity ratio gives a 30% and 17% difference on a limited distance from outcrop at the soft clayey basin under DD1 and DD3 motion levels, respectively. At the 30 m depth basins, the nonlinearity ratio shows up to 25% difference for different cases. The presented ratio would be introduced as nonlinearity coefficients for consideration of the nonlinearity effects in the codes. The presented quantitative margins will help the designer to have a better understanding of the amplification period change because of nonlinearity over 2D basin surface.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2006년도 공동학술대회 논문집
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• pp.175-180
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• 2006

관측된 지진 자료의 지역적인 부지효과는 부지부근지하매질의 기하학적 형태와 물성치, 지형 등에 영향을 받고 강진운동의 중요한 특성치들을 평가할 때 큰 영향을 줄 수 있어 지진공학적인 연구에 반드시 고려되어야 할 요소이다. 본 연구에서는 Nakamura(1989)가 제시한 H/V Ratio 방법을 이용해 부지효과에 관한 연구를 수행하였다. 분석결과 부지효과는 시추공관측소에서는 아주 양호한 결과를 보여주었고 또한 상대적으로 고주파수대역에서 높은 값을 보여주었다.

• 한국해안해양공학회지
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• 제14권1호
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• pp.86-93
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• 2002

항만부진등 해석에 사용되는 유한요소의 적정 크기를 검토하기 위해 완전개방 직사각형 항만에 대해서 다양한 크기의 요소를 사용한 수치실험을 실시하였다. 수치실험 결과, 공진주기와 증폭비의 허용 오차율을 모두 2%로 하는 경우 파장당 9개, 1%로 하는 경우 12개의 요소가 필요한 것으로 나타났다. 또한, 요소 수의 증가에 따라 공진주기의 오차율은 선형적으로, 증폭비의 오차는 진동하면서 감소하였으며, 요소 수를 9개보다 적게 하는 경우 증폭비의 오차가 상대적으로 크게 증가하였다

• Nuclear Engineering and Technology
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• 제55권10호
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• pp.3549-3558
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• 2023

The jet pump can be used in a test device of a nuclear reactor for high flow amplification as it reduces inlet flow requirement and thereby size of the process components. In the present work, a miniature jet pump was designed to meet high flow amplification greater than 3. Subsequently, experiments were carried out using a test setup for design validation and performance evaluation of the jet pump for different parameters. It was observed that a minimum pressure of 0.6 bar (g) was required for the secondary fluid inside the jet pump to ensure cavitation free performance at high amplification. Spacing between the nozzle tip and the mixing chamber entry point had significant effect on the performance of the jet pump. Variation in primary flow, temperature and area ratio also affected the performance. It was observed that at high flow amplification, the analytical solution differed significantly from experimental results due to very large velocities encountered in the miniature size jet pump.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2007년도 정기 학술대회 논문집
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• pp.777-782
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• 2007

Displacement amplification factor can be used to estimate inelastic displacement demands from elastic displacement demands, The simple formula for displacement amplification factor considering hysteretic behavior of structural system and earthquake characteristics is proposed. And the effects of several parameters such as displacement ductility, strain hardening ratio, period, characteristics of earthquakes and hysteretic models for the displacement amplification factor are evaluated. Accuracy of the proposed formula is evaluated by comparing the displacement amplification factors estimated by existing and proposed formula with those calculated from inelastic time history analysis. The displacement amplification factors by proposed formulas provide a good agreement with those calculated by inelastic time history analysis.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제53권11호
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• pp.647-657
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• 2004

Helical magneto-cumulative generator(HMCG)s are very useful devices in suppling pulsed high current to inductance loads. To apply fast high voltage pulses to high impedance loads, high current outputs of HMCGs are required to be conditioned to higher voltages by using various pulse components such as opening/closing switches and pulse transformer. In this paper, stepping with the trends of requirements for ever-increasing energy in pulsed power applications coupling methods is investigated to obtain higher output energy by connecting several HMCGs in series or parallel way. The coil dimension of HMCGs used in series or parallel connections was 50 mm in diameter and 150 mm in length. The coil was fabricated by using enamel-coated copper wire of 1 mm in diameter. The highest energy amplification ratio and peak voltage of load were achieved from the serially connected four-barrel HMCG system. They were 68 and 34 kV, respectively, when the initial energy of 0.36 kJ was supplied into that system with the load of 0.4 μH. Within the tested range of inductance ratio, energy amplification ratio was found to be highly dependent on the inductance ratio of serial- and parallel-connected HMCG systems to load, which to be optimal around 500 was turned out. The experimental results showed that the output energy and voltage of load are controlled by connecting HMCGs in series or parallel.

• 한국지구과학회지
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• 제36권7호
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• pp.632-642
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• 2015

지반진동은 지진원, 지각감쇠 및 지반의 증폭특성 등 3가지 주요 인자로 구성되어 있다. 이 중 지반 증폭특성은 지진원 및 지각감쇠를 신뢰성 있게 평가하기 위해 반드시 고려하여야 한다. 본 연구의 목적은 수평/수직(H/V) 스펙트럼비를 이용하여 각 관측소의 지반증폭 특성을 평가하는 것이다. 주파수 영역에서 H/V 스펙트럼 비를 구하는 방법은 Nakamura(1989)에 의해 처음으로 제시되었으며, 초기에는 상시미동의 표면파 특성을 이해하기 위해 사용되어 왔다. 최근에 와서 강진동의 전단파 에너지 등으로 확장되면서 지반 증폭특성 연구에 많이 이용되고 있다. 본 연구는 예당저수지 인근에 4개의 관측소에서 관측된 6개의 가속도 지반진동을 이용하여 H/V 스펙트럼 비를 분석하였고 각 지반진동의 S파, Coda파 및 배경잡음 각각으로부터 분석된 지반증폭 특성을 상호 비교하였다. 분석결과, 4개 관측소는 각각의 우월 주파수 대역(YDS: ~11 Hz, YDU: ~4 Hz, YDD: ~7 Hz)에서 관측소 고유의 증폭특성을 보여준다. 본 연구의 도출 결과와 다른 방법을 통해 구한 결과의 비교 평가는 국내 지반의 동적특성 및 지반분류 연구에 유익한 정보가 될 것으로 판단된다.