• Title/Summary/Keyword: 빙밀도

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Analysis of Solidification Process Around a Vertical Tube Considering Density Change and Natural Convection (수직원관 주위에서 밀도차와 자연대류를 고려한 응고과정 해석)

  • 김무근;노승탁
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.1
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    • pp.142-155
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    • 1992
  • Numerical analysis is performed for the unsteady axisymmetric two dimensional phase change problem of freezing of water around a vertical tube. Heat conduction in the tube wall and solid phase, natural convection in liquid phase and volume expansion caused by density difference between solid and liquid phases are included in the numerical analysis. Existing correlation is used for estimating density-temperature relation of water, and the effect of volume expansion is reflected as fluid velocity at the interface and the free surface. As pure water has maximum density at 4.deg. C, it is found that there exists an initial temperature at which the flow direction reverses near the interface and by this effect the slope of interface becomes reversed depending on the initial temperature of water. By considering natural convection and solid-liquid density difference in the calculation, their effects on phase change process are studied and the effects of various parameters are also studied quantitatively.

A Study on the Improvement of Measuring Method for Density of Model Ice (모형빙 밀도 계측 방법 개선 연구)

  • Ha, Jung-Seok;Kang, Kuk-Jin;Cho, Seong-Rak;Jeong, Seong-Yeob;Lee, Chun-Ju
    • Journal of the Society of Naval Architects of Korea
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    • v.52 no.2
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    • pp.104-109
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    • 2015
  • The Korea Research Institute of Ships & Ocean Engineering (KRISO) has an ice tank to make a test environment similar to the real ice in the polar sea in order to carry out model tests. One of the most important task of the ice tank is to generate the model ice to have similar material properties as sea ice. The primary properties of sea ice which influence the ice performance of ice breakers and ice-strengthened vessels traveling in the polar sea are ice thickness, flexural strength, density, modulus of elasticity and crystal structure etc. Among them, since the density of model ice influences the buoyance resistance of ice for the ship model, the accurate measurement of ice density should be used to obtain the accurate analysis results from the model test. In this paper, some existing methods to measure the density of model ice are reviewed and a new one is proposed to measure it accurately and easily as possible. In this study, the measuring system including an UTM and several measuring devices was established to obtain the model ice density. Polyethylene and ice specimens are used for a series of repeatable measurement tests. From the results, it was recognized that both of the displacement method and the weight/weight methods gave the stable and favorable tendency.

A Study on Formation of Slurry Ice by using the Reversing Flow in a Bundle of Tube (역전 유동층을 이용한 관군 내에서의 슬러리아이스 생성에 관한 연구)

  • Oh, Cheol;Choi, Young-Gyu
    • Journal of Navigation and Port Research
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    • v.35 no.5
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    • pp.365-370
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    • 2011
  • The ice-thermal energy storage cooling system has been applied to relief a significant portion of the peak demand of electricity during the daytime in summer. Slurry ice type system is one kind of ice-thermal storage cooling system utilizing cheaper off-peak electricity. This study is experimented to observe an influence of experimental conditions on production characteristics of slurry ice by using reversing flow, which is putting reversing material into test section to disturb ice adhesion. At this experiment, poly propylene ball of dimeter 10 mm was used as reversing material, and ethylene glycol-water solution of 20wt% concentration was used as flow material. The experimental apparatus was constructed of the slurry ice making and storage tank(test section), the brine tank, pumps for ethylene glycol-water solution and brine circulating, a mass flow-meter, data logger for fluid temperature measuring. The experiments were carried out under various conditions, with volumetric flow rate, ball filling rate and air filling rate.

Numerical Analysis of Iceberg Impact Interaction with Ship Stiffened Plates Considering Low-temperature Characteristics of Steel (강재의 저온 특성을 고려한 선체 보강판과 빙하의 충격 상호 작용에 대한 수치 해석)

  • Nam, Woongshik
    • Journal of Ocean Engineering and Technology
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    • v.33 no.5
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    • pp.411-420
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    • 2019
  • It is essential to design crashworthy marine structures for operations in Arctic regions, especially ice-covered waters, where the structures must have sufficient capacity to resist iceberg impact. In this study, a numerical analysis of a colliding accident between an iceberg and stiffened plates was carried out employing the commercial finite element code ABAQUS/Explicit. The ice material model developed by Liu et al. (2011) was implemented in the simulations, and its availability was verified by performing some numerical simulations. The influence of the ambient temperature on the structural resistance was evaluated while the local stress, plastic strain, and strain energy density in the structure members were addressed. The present study revealed the risk of fracture in terms of steel embrittlement induced by ambient temperature. As a result, the need to consider the possibility of brittle failure in a plate-stiffener junction during operations in Arctic regions is acknowledged. Further experimental work to understand the structural behavior in a plate-stiffener junction and HAZ is required.

Experimental Study for Ice Formation around Two Horizontal Circular Tubes (수평 2열 원통관 주위의 동결형상에 관한 연구)

  • Yoon, J.I.;Kim, J.D.;Toyofumi, Kato;Oh, H.K.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.7 no.1
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    • pp.89-97
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    • 1995
  • Experimental study was performed for free convection and ice formation around two horizontal circular tubes which were placed vertically. Temperature and velocity distributions were visualized with real time holographic interferometry technique and tracer method. When water was cooled, super cooled region was formed around cooling pipe. It was found that flow induced by free convection always directed downwards when the coolant temperature was low, while it directed upwards when the coolant temperature was comparably high though it directed downwards initially. Flow phenomena with free convection were investigated in detail with varying cooling rate and length between cooling pipes. And growing process of dense ice was also investigated. Dendritic ice is suddenly formed within a supercooled region, and a dense ice layer begins to develop from the cooling wall.

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Late Quaternary Sedimentary Processes in the Northern Continental Margin of the South Shetland Islands, Antarctica (남극 남쉐틀랜드 군도 북부 대륙주변부의 후기 제 4기 퇴적작용)

  • 윤석훈;윤호일;강천윤
    • The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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    • v.9 no.1
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    • pp.1-12
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    • 2004
  • Sedimentary facies and high-resolution echo facies were analyzed to elucidate sedimentation pattern of the late Quaternary glacial-marine deposits in the northern continental margin of the South Shetland Islands. Six sedimentary facies are classified, based on grain texture and sedimentary structures in gravity cores. The high-resolution (3.5 ㎑) echo characters are classified into 6 echo facies on the basis of clarity, continuity, and shape of bottom and subbottom echoes together with seafloor topography. Distribution of the echo and sedimentary facies suggest that there was a significant change in sedimentation pattern between the Last Glacial Maximum (LGM) and subsequent glacier-retreating period. When the grounded glaciers extended to the present shelfbreak during LGM, coarse-grained subglacial tills were widespread in the shelf area, and deep troughs in the shelf were carved beneath the fast-flowing ice steam. As the glacial margin retreated landward after LGM, dense meltwater plumes released from the retreating ice-front were funneled along the glacier-carved troughs, and accumulated channel- or cannyon-fill deposits in the shelf and the upper to mid slope. At that time, slope sediments seem to have been reworked by slope failures and unsteady contour currents, and further transported by fine-grained turbidity currents along the South Shetland Trench. After the glacial retreat, sediments in the shelf and slope areas have been mainly introduced by persistent (hemi) pelagic settling, and fine-grained turbidity currents frequently occur along the axis of the South Shetland Trench.

Analysis of cooling phenomenon of water with the supercooled (과냉각을 동반한 순수물의 냉각현상 해석)

  • Chu, Mi-Seon;Yun, Jeong-In;Kim, Jae-Dol;Kamata, Yoshinobu;Kato, Toyofumi
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.7
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    • pp.862-872
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    • 1997
  • Ice formation in a horizontal circular cylinder has been studied numerically. From the numerical analysis results, it was found that there were three types of freezing pattern and that freezing phenomenon was affected largely by density inversion and cooling rate. The type of freezing pattern largely depends on the secondary flow which is generated by density inversion. When supercooling energy is released before the development of the secondary flow, the annular ice layer grows. If the energy is released when the secondary flow is considerably developed and the supercooled region is removed to the upper half part of the cylinder, an asymmetric ice layer grows. And if the energy is released after perfect development of the secondary flow, instantaneous dendritic ice formation over the full region occurs. Furthermore, this secondary flow was found to have an effect on heat transfer characteristics. The heat transfer rate becomes small at the instant when the secondary flow is generated, but becomes large with the development of the flow. It's concluded that for the facilitation of heat transfer it is desirable to keep water in liquid phase until the secondary flow is perfectly developed. This study gave an instruction of performance improvement of capsule type ice storage tank.

Grounding Line of Campbell Glacier in Ross Sea Derived from High-Resolution Digital Elevation Model (고해상도 DEM을 활용한 로스해 Campbell 빙하의 지반접지선 추정)

  • Kim, Seung Hee;Kim, Duk-jin;Kim, Hyun-Cheol
    • Korean Journal of Remote Sensing
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    • v.34 no.3
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    • pp.545-552
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    • 2018
  • Grounding line is used as evidence of the mass balance showing the vulnerability of Antarctic glaciers and ice shelves. In this research, we utilized a high resolution digital elevation model of glacier surface derived by recently launched satellites to estimate the position of grounding line of Campbell Glacier in East Antarctica. TanDEM-X and TerraSAR-X data in single-pass interferometry mode were acquired on June 21, 2013 and September 10, 2016 and CryoSat-2 radar altimeter data were acquired within 15 days from the acquisition date of TanDEM-X. The datasets were combined to generate a high resolution digital elevation model which was used to estimate the grounding line position. During the 3 years of observation, there weren't any significant changes in grounding line position. Since the average density of ice used in estimating grounding line is not accurately known, the variations of the grounding line was analyzed with respect to the density of ice. There was a spatial difference from the grounding line estimated by DDInSAR whereas the estimated grounding line using the characteristics of the surface of the optical satellite images agreed well when the ice column density was about $880kg/m^3$. Although the reliability of the results depends on the vertical accuracy of the bathymetry in this study, the hydrostatic ice thickness has greater influence on the grounding line estimation.

An Experimental Study on the Heat Transfer Characteristics during Outward Melting Process of Ice in a Vertical Cylinder(comparison of thermal performance on the flow direction of working fluid) (수직원통형 빙축열조내 얼음의 외향용융과정시 전열특성에 관한 실험적 연구(작동 유체의 유입 방향에 따른 비교))

  • Kim, D.H.;Kim, D.C.;Kim, I.K.;Kim, Y.K.;Yim, C.S.
    • Solar Energy
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    • v.16 no.2
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    • pp.113-122
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    • 1996
  • This study presents experimental results of heat transfer characteristics of P.C.M. during outward melting process in a vertical cylinder. The experiment was carried out in six conditions, i. e., three different inlet temperature($7^{\circ}C,\;4^{\circ}C\;and\;1^{\circ}C$) and two directions of working fluid(upward and downward). Melting P.C.M. produced a bell-shaped phase change interface. When the inlet temperature was $7^{\circ}C$, the lower region remained at $4^{\circ}C$ until the temperature of upper region reached $4^{\circ}C$. This was due to the state of maximum density of the lower region. When the direction of the working fluid in the case of $7^{\circ}C$, inlet temperature, was upward, the rate of melting and the total melting energy were higher than when it's direction was downward. But the rate of melting and the total melting energy appeared higher value as it's direction was downward when the inlet temperature is $4^{\circ}C$ and $1^{\circ}C$.

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Distribution Characteristics of the Incised Meander Cutoff in Gyeonggi and Gangwon Provinces, Central Korea (경기${\cdot}$강원 지역 감입곡류 하천의 곡류절단면 분포 특성)

  • Lee Gwang-Ryul;Yoon Soon-Ock
    • Journal of the Korean Geographical Society
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    • v.39 no.6 s.105
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    • pp.845-862
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    • 2004
  • The aim of this study is to investigate distribution characteristics of incised meander cutoff in Gyeonggi and Gangwon Provinces of Central Korea. The density of meander cutoff is highest in the mountain rivers including Naerin and Dongdae flowing on Jeongseon-gun and Inje-gun of Gangwon Province. Most of meander cutoff process has been occurred repeatedly during the Quaternary period, especially concentrated in the period of climatic change between glacial and interglacial stages. In the aspect of the lithology, the density of cutoff is highest in sedimentary rock, but lowest in igneous rock. As for geological structure, its frequency is high at $11{\sim}20km$ westerly away from the Taebaek Mountains, at subsequent channel, lower part of resequent channel, and channels crossing the fault line. The relation between distance from the Taebaek Mountains and altitude is very obvious at the western side of the Taebaek Mountains. The values of altitude, height from riverbed, and stream order are highest at sedimentary rock and lowest at volcanic rock.