• Title, Summary, Keyword: Terminal velocity

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Effects of Uncertainty in Graupel Terminal Velocity on Cloud Simulation (싸락눈 종단 속도의 불확실성이 구름 모의에 미치는 영향)

  • Lee, Hyunho;Baik, Jong-Jin
    • Atmosphere
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    • v.26 no.3
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    • pp.435-444
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    • 2016
  • In spite of considerable progress in the recent decades, there still remain large uncertainties in numerical cloud models. In this study, effects of uncertainty in terminal velocity of graupel on cloud simulation are investigated. For this, a two-dimensional bin microphysics cloud model is employed, and deep convective clouds are simulated under idealized environmental conditions. In the sensitivity experiments, the terminal velocity of graupel is changed to twice and half the velocity in the control experiment. In the experiment with fast graupel terminal velocity, a large amount of graupel mass is present in the lower layer. On the other hand, in the experiment with slow graupel terminal velocity, almost all graupel mass remains in the upper layer. The graupel size distribution exhibits that as graupel terminal velocity increases, in the lower layer, the number of graupel particles increases and the peak radius in the graupel mass size distribution decreases. In the experiment with fast graupel terminal velocity, the vertical velocity is decreased mainly due to a decrease in riming that leads to a decrease in latent heat release and an increase in evaporative cooling via evaporation, sublimation, and melting that leads to more stable atmosphere. This decrease in vertical velocity causes graupel particles to fall toward the ground easier. By the changes in graupel terminal velocity, the accumulated surface precipitation amount differs up to about two times. This study reveals that the terminal velocity of graupel should be estimated more accurately than it is now.

Aerodynamic Study on Pneumatic Separation of Grains(II) -The Measurement of the Terminal Velocities of Grains- (곡물(穀物)의 공기선별(空氣選別)에 관(關)한 공기동력학적(空氣動力學的) 연구(硏究)(II) -수직풍동(垂直風銅)을 이용(利用)한 곡물(穀物)의 종말속도(終末速度) 측정(測定)-)

  • Lee, C.H.;Cho, Y.J.;Kim, M.S.
    • Journal of Biosystems Engineering
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    • v.15 no.1
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    • pp.1-13
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    • 1990
  • Aerodynamic property is the most important factor in designing the pneumatic separator and handling equipment for grains and seeds. Particularly the correct information about the terminal velocities of the corresponding grains and seeds is indispensible. However, a few studies with relation to the terminal velocities of grains and seeds were conducted in this country, even though the terminal velocities of the domestic grains and seeds are required to design those equiments which can be used for the domestic grains and seeds having specific aerodynamic properties. In this study, the terminal velocities for four varieties of varley and six varieties of paddy were investigated by means of two different methods, the suspension method and the drop method in an upward current of air. For measuring the terminal velocities, the vertical wind tunnel which had been examined about the uniform air flow in the previous study was used. In addition, the effect of the size of grains and the moisture content of grain kernel on the terminal velocity was examined. The following conclusions were derived from the study : 1. The different terminal velocities of grains are resulted from the different measuring methods. The terminal velocity measured by the drop method is smaller than that by the suspension method. It is considered that the difference in the terminal velocities is caused by the difference in the projection area of grain which is faced to the air stream. 2. The terminal velocity of grain increases as the size and the moisture content of the kernel increase. 3. The linear regression equations for the terminal velocities of grains were derived in terms of the moisture content of grains by the variety of grains and the measuring method. Also, the linear regression equations for the terminal velocity, based on the weighted size of grains, were derived in terms of the moisture contents of granis.

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Calculation of Anchor's Terminal Velocity in the Water and Onshore Dropped Heights Using MDM Technique

  • Shin, Mun-Beom;Seo, Young-Kyo
    • Journal of Advanced Research in Ocean Engineering
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    • v.3 no.2
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    • pp.59-65
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    • 2017
  • When an anchor is dropped into the sea, there exists a danger of collision on the pipeline and subsea cables in the seabed. This collision could cause huge environmental disasters and serious economic losses. In order to secure the safety of subsea structures such as pipelines and subsea cables from the external impact, it is necessary to estimate the exact external force through the anchor's terminal velocity on the water. FLUENT, a computational fluid dynamic program, was used to acquire the terminal velocity and drag coefficient computation. A half-symmetry condition was used in order to reduce the computational time and a moving deforming mesh technique also adapted to present hydrostatic pressure. The results were examined with the equation based on Newton's Second Law to check the error rate. In this study, three example cases were calculated by stockless anchors of 5.25 ton, 10.5 ton, and 15.4 ton, and for the onshore experiment dropped height was back calculated with the anchor's terminal velocity in the water.

Model setup and optimization of the terminal rise velocity of microbubbles using polynomial regression analysis (다항식 회귀분석을 이용한 마이크로 버블의 종말상승속도 모델식 구축 및 운전조건 최적화)

  • Park, Gun-Il;Kim, Heung-Rae;Cho, Il Hyoung
    • Journal of the Korean Applied Science and Technology
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    • v.35 no.4
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    • pp.1393-1406
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    • 2018
  • In this study, three parameters (Pressure ($X_1$), Airflow rate ($X_2$), Operation time ($X_3$)) were experimentally designed and the predicted model and optimal conditions were established by using the terminal rise velocity of the microbubbles as the response value. The polynomial regression analysis showed that the optimum value for the terminal rise velocity at the Pressure ($X_1$) of 4.5 bar, Airflow rate ($X_2$) of 3.3 L/min and Operation time ($X_3$) of 2.2 min was 5.14 cm/min ($85.7{\mu}m/sec$). Also, the highest microbubble diameter size distribution in the range of 2 to $5{\mu}m$ and 25 to $50{\mu}m$ was confirmed by using a laser particle counting apparatus.

Effect of Wall Proximity on Air Bubbles Rising in Liquid (액체중을 상승하는 공기포의 괸벽영향)

  • Kang, Joon Mo
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.1 no.1
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    • pp.17-25
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    • 1977
  • The purpose of this paper is to clarify the effect of wall proximity on the terminal velocity of single air bubbles in vertical tubes. As an initial step, experiments were conducted to determine the terminal velocity, shape, and path of single air bubbles rising freely in water. The terminal velocity of air bubbles rising through water was measured in cylindrical tubes, rectangular tubes, and parallel plates respectively. The results of effect wall of cylindrical tubes were shown as a dimensionless plot, and may also be used to arrive at a decision regarding the minimum size of tube.

Ignition Temperature and Residence Time of Suspended Magnesium Particles (마그네슘 부유 분진의 입자 체류시간과 발화온도)

  • Han, Ou-Sup
    • Journal of the Korean Institute of Gas
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    • v.19 no.3
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    • pp.25-31
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    • 2015
  • Effects of residence time on the MIT(Minimum Ignition Temperature) in suspended Mg particles are examined by using MIT experimental data and calculation results of terminal velocity. With increasing of the average particle diameter, we were able to identify that MIT of Mg dusts increased and the calculated residence time of particle decreased exponentially. Also, the influence on terminal velocity due to temperature increase increased slightly with increasing of average particle diameter.

Evaluation of Changesin the Physical Characteristics of Raindrops Under a Canopy in Central Korea (나무 아래 빗방울(雨滴)의 물리적 특성변화 분석)

  • Kim, Jin Kwan;Kim, Min Seok;Yang, Dong Yoon;Lim, Young Shin
    • Journal of The Geomorphological Association of Korea
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    • v.23 no.3
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    • pp.105-122
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    • 2016
  • To evaluate the changes in the physical characteristics of open rainfall related to canopy effects and rainfall intensity in Korea, the terminal velocity of raindrops and drop size distributions(DSD) were continuously measured by an optical-laser disdrometer in an open site(Op) and in two forest stands(Th1: Larix leptolepis, Th2: Pinus koraiensis) during five rainfall events in 2008. The terminal velocity, DSD and two forms of kinetic energy(KE, $Jm^{-2}$ $mm^{-1}$; KER, $Jm^{-2}$ $h^{-1}$) of open rainfall drops were determined and were compared with those of throughfall drops under two different canopy heights. The effects of the canopy and rainfall intensity, together with wind speed, on the changes in drop size and kinetic energy of throughfall were evaluated. Throughfall drops were larger than open rainfall drops. The distribution of terminal velocities for the drop sizes measured at Th2 was lower than that at Op; however, at Th1 the distribution was similar to that at Op. The total kinetic energy of throughfall at Th1 and Th2 was higher than the total kinetic energy of open rainfall, and the kinetic energy distribution for the drop sizes wassimilar to the drop size distribution. The observed throughfall-KER at Th1 was lower than an estimate previously produced using a model. The overestimation from the modeled value at Th1 was likely to be due to overestimated values of a square root transformation of fall height and its coefficient in the model because the distributions of terminal velocity for the drop size measured at Th1 were similar to those of open rainfall.

A Study of the Characteristics Times of Polymer Solutions Using the PIV System (PIV 시스템을 이용한 폴리머 용액의 특성시간에 관한 실험적 연구)

  • Lee, Jae-Su;Jeon, Chan-Yeal;Park, Jong-Ho
    • Proceedings of the KSME Conference
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    • pp.1552-1557
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    • 2004
  • Characteristics diffusion time of viscoelastic fluids are determined experimental results of terminal velocity by using the falling ball viscometer. The characteristics diffusion time of viscoelastic fluids are determined with help of the sphere device which is installed to return the dropped sphere from the bottom of the test cylinder without disturbing the working fluids. Terminal velocity of th sphere the reason why experimental of characteristics diffusion time that it is have an effect on the time interval of the measuring. Viscous of the fluid the temperature changed in order to have an effect on temperature and terminal velocity of the ball it becomes larger the possibility of knowing. A result of visualization for flow phenomena of around the sphere uses the PIV and the density of the polymer solution which it appears 2000wppm is to a case which is the right and left becomes symmetry to be it will be able to confirm and according to the time interval, to observed velocity vector of same at first drop the sphere.

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THE WIND VELOCITIES DRIVEN BY ALFVEN WAVES IN 31 CYG (Alfven Wave에 의한 31 Cyg의 Wind 속도)

  • 김경미;최규홍
    • Journal of Astronomy and Space Sciences
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    • v.8 no.1
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    • pp.63-72
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    • 1991
  • 31Cyg는 Aur형의 장주기 쌍성으로, 확장된 대기를 갖는 초거성과 뜨거운 주계열성으로 이루어져 있다. 초거성의 wind는 질량 손실률이 크고, 차갑고, 낮은 terminal velocity를 갖는데, 일반적으로 Alfven wave가 wind mechanism으로 받어들여지고 있다. 이 논문에서는 31 Cyg에 대해 Alfven wave에 의한 모델을 적용하여 운동방정식을 직접 적분하였는데, 그 terminal velocity가 50∼80km/s로 관측값과 잘 들어 맞았다. 그리고 그 결과를 Kuin과 Ahmad(1989)의 경험적인 모델과 비교하였다.

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