• Nuclear Engineering and Technology
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• 제53권6호
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• pp.1878-1886
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• 2021

For industrial package (IP)-type transport containers for radioactive materials, a free drop test should be conducted under regulatory conditions. Owing to various uncertainties observed during the drop test, errors in drop angles inevitably occur. In IP-type metal transport containers in which the container directly impacts onto a rigid target without any shock absorbing materials, the error in the drop angle due to a slight misalignment makes a significant difference from the ideal drop. In particular, in a vertical drop, the error in the drop angle causes a strong secondary impact. In this paper, a numerical method is proposed to estimate the error in the drop angle occurring during the test. To determine this error, an optimization method accompanying a computational drop analysis is proposed, and a surrogate model is introduced to ensure calculation efficiency. Effectiveness of the proposed method is validated by performing the verification and comparison between the test and the analysis applied with the drop angle error.

• 한국통신학회논문지
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• 제29권2B호
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• pp.203-209
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• 2004

OBS 네크워크에서 contention으로 인한 burst의 drop은 TCP의 성능에 중요한 영향을 끼치는 요소이나, 기존의 drop policy에서는 이를 고려하지 않으며 TCP에 대한 연구로는 burst의 assembling이 주를 이루고 있다. 본 논문에서는 OBS 네트워크에서 TCP의 재전송 문제를 drop policy와 연계하여 TCP의 성능을 향상시키고자 한다. 본 논문에서 제안하는 drop policy는 burst의 재전송 횟수가 drop을 결정하는데 있어서 priority로 작용하는 Retransmission Count-based DP(RC-based DP)이다. RC-based DP 모델과 general DP 모델의 성능을 ns-2를 이용한 시뮬레이션을 통해 평가하며, 이 때 시간의 변화에 따른 TCP throughput, 목적지에서 수신한 최고 Sequence 번호, 패킷의 drop rate을 비교 분석한다.

• 한국자동차공학회논문집
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• 제10권2호
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• pp.87-95
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• 2002

The aim of this article is to perform the numerical simulation far drop drag and breakup processes in air-assisted sprays using the Taylor analogy breakup (TAB) model with a modified drop drag model, in which a random method is newly used to consider the variation of the drop's frontal area. The predicted results for drop trajectory and Salter mean diameter (SMD) were compared with experimental data and the simulation results using the earlier published models such as TAH model, surface wave instability (Wave) model, and Wave model with original drop drag model. In addition, the effects of the breakup model constant, Ck, on prediction of spray behaviors were discussed. The results shows that the TAB model with the modified drop drag model is in better agreement with experimental data than the other models, indicating the present model is acceptable for predicting the drop breakup process in air-assisted sprays. At higher Weber numbers, the smaller Ck shows the best fitting to experimental data. It should be noted that more elaborated studies is required in order to determine the breakup model constant in the suggested model in the study.

• 한국분무공학회지
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• 제5권3호
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• pp.37-44
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• 2000

High velocity, gas-assisted liquid drop trajectories were investigated under well-controlled experimental conditions at elevated gas densities and room temperature. A monodisperse stream of drops which are generated by a vibrating-orifice drop generator were injected into a transverse high velocity gas stream. The gas density and air jet velocity were adjusted independently to keep the Weber numbers constant. The Weber numbers studied were 72, 148, 270, 532. The range of experimental conditions included studied the three drop breakup regimes previously referred as bag, stretching/thinning and catastrophic breakup regimes. High-magnification photography and conventional spray field photographs were taken to study the microscopic breakup mechanisms and the drop trajectories in high velocity gas flow fields, respectively. The parent drop trajectories were affected by the gas density and the gas jet velocities and do not show similarity with respect to the either Weber or the Reynolds number, as expected.

• Journal of Biosystems Engineering
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• 제21권1호
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• pp.44-51
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• 1996

The purpose of this paper is to obtain the basic data for design of pressure cooling system. Static pressure drop, as a function of superficial velocity, was measured for different stacking methods and stacking heights of some fruits and vegetables. At given superficial velocity, sphericity and void fraction had a much greater influence on static pressure drop than average diameter of spherical fruits such as apple, peach, tomato and kiwi fruit. Among cylindrical vegetables such as cucumber, carrot, radish and chinese cabbage, cucumber showed different pattern of static pressure drop because of its bended shape, radish showed less static pressure drop than other vegetables because its large sizes of voids. When cucumber and spinach were stacked vertically and horizontally to air flow, a much greater static pressure drop was shown in vertical than in horizontal type, therefore static pressure drop was affected not only by void fraction but also by void shape. Also, in packed-beds of fruits and vegetables, static pressure drop could be estimated very well by Ramsins equation.

• 수산해양교육연구
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• 제28권5호
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• pp.1273-1279
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• 2016

Flow boiling pressure drop in multi channels was experimently investigated. The multi channel has a width and depth of 0.45 and 0.2mm respectively, and comprises 15 parallel channels. The measured total pressure drop is expressed by the sum of the frictional pressure drop and acceleration pressure drop. In order to predict the total pressure drop, it is required to obtain the correct frictional pressure drop. The existing correlations to predict the frictional pressure were compared with measured frictional pressure drop. The new correlation was developed in the form of the Chisholm correlation. It was related to Chisholm Constant B as a function of Martinelli parameter. The new correlation predicted the experimental data within a mean absolute error of 5.5%.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2003년도 가을 학술발표논문집 Vol.30 No.2 (3)
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• pp.1-3
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• 2003

OBS망에서 버스트의 충돌로 인한 버스트의 drop은 TCP의 성능에 중요한 영향을 끼치나, 기존의 drop policy에서는 이를 고려하지 않으며 TCP에 대한 연구로는 버스트의 assembling이 주를 이루고 있다. 본 논문에서는 OBS망에서 TCP의 재전송 문제를 drop policy와 연계하여 그 성능을 향상시키고자 한다. 본 논문에서 제안하는 drop policy는 버스트의 재전송 횟수가 더 작은 버스트를 drop시키는 TCP 기반 DP이다. TCP 기반 DP 모델과 일반적인 DP 모델의 성능을 ns­2를 이용한 시뮬레이션을 통해 평가하며, 이 때 시간의 변화에 따른 TCP throughput과 패킷의 drop rate을 비교 분석한다.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2019년도 춘계학술발표대회
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• pp.464-466
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• 2019

CNN 은 합성곱 연산을 사용하는 인공신경망의 한 종류이다. 이러한 인공 신경망에서는 훈련 데이터에 대한 과도한 학습으로 인해 시험 데이터에 제대로 반응하지 못하는 오버피팅이 발생할 우려가 있다. 이를 해결하기 위해 DropOut 과 DropConnect 를 사용할 수 있다. 본 논문에서는 DropOut 과 DropConnect 를 통한 학습 정도를 실험을 통해서 비교해보고, 인공 신경망에서 이 방법의 효과를 살펴본다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.17-18
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• 2003

Drop deformation in a cylindrical contraction geometry, characterized here by the formation of a thread of drop fluid in the contraction, is predicted using a Volume-of-Fluid numerical technique. The predicted drop shape is found to closely follow the observed deformation. A capillary instability in the developing drop thread in the contraction was predicted, in agreement with experimental observation.

• 한국세라믹학회지
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• 제33권12호
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• pp.1325-1330
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• 1996

Sessile drop method에 의해서 표면장력을 간단히 구하는 수치계산법을 계산프로그램과 같이 소개하였다. 이방법에 의하면 표명장력의 계산에 필요한 data는 sessile drop 표면상의 임의의 한 점에서의 좌표(X.Z)와 그 점에서의 접선의 각도${\theta}$, 그리고 밀도${\rho}$가 전부이다. 따라서 sessile drop의 형상으로부터 가장 정밀한 측정이 가능한 임의의점을 선정하여 그 점의 좌표, 접선의 각도를 측정하면 되므로 종래의 방법보다 정확한 값을 얻을 수 있다. 또한 4개의 data를 입력하는 것만으로 계산결과가 단시간에 나오므로 계산과정이 대단히 간단하다. Sessile drop의 크기, 접선의 각도, 밀도 등에 제한이 없으므로 응용범위가 넓다. 하나의 sessile drop에서 수개의 점으로부터 구한 각 표면장력의 값을 상호 비교하면 측정치 및 계산결과에 대하여 신뢰성을 높일 수 있다. 또한 이 수치계산법을 응용하면 pendant drop method에의 응용, 그외 sessile drop의 체적, 표면적, 접촉각의 계산 등에도 이용할 수 있다.