• 한국가시화정보학회지
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• 제8권1호
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• pp.53-60
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• 2010

Experimental investigations were conducted to study the characteristics of turbulent swirling flow in an axisymmetric annuli. Swirl angle measurements were performed using a flow visualization technique using smoke and dye liquid for Re=60,00080,000. Using the two-dimensional particle image velocimetry method, we found the time-mean velocity distribution and turbulent intensities in water with swirl for Re=20,000, 30,000, and 40,000 along longitudinal sections. Neutral points occurred for equal axial velocity at y/(R-r)=0.70.75, and the highest axial velocity was recorded near y/(R-r)=0.9. Negative axial velocity was observed near the convex tube along X/(D-d)=3~23. Another experimental study was performed to investigate heat transfer characteristics of turbulent swirling flow in an axisymmetric annuli. Static pressure, and local flow temperature were measured using tangential inlet condition and the friction factors and Nusselt number were calculated for several Reynolds numbers.

• Advances in nano research
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• 제12권3호
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• pp.253-261
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• 2022

Numerical modelling of an integrated Carbon NanoTube (CNT) membrane is only achievable if probable deformations and realistic alterations from a perfect CNT membrane are taken into account. Considering the possible forms of CNTs, bending is one of the most probable deformations in these high aspect ratio nanostructures. Hence, investigation of effect associated with bent CNTs are of great interest. In the present study, molecular dynamics simulation is utilized to investigate fluid flow dynamics in deformed CNT membranes, specifically when the tube cross section is not affected. Bending in armchair (5,5) CNT was simulated using Tersoff potential, prior to flow rate investigation. Also, to study effect of inclined entry of the CNT to the membrane wall, argon flow through generated inclined CNT membranes is examined. The results show significant variation in both cases, which can be interpreted as counter-intuitive, since the cross section of the CNT was not deformed in either case. The distribution of fluid-fluid and fluid-wall interaction potential is investigated to explain the anomalous behavior of the flow rate versus bending angle.

• 한국유체기계학회 논문집
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• 제17권5호
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• pp.19-26
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• 2014

The cross flow turbine attracts more and more attention for its relatively wide operating range and simple structure. In this study, a novel type of micro cross flow turbine is developed for application to a step in an irrigational channel. The head of the turbine is only H=4.3m and the turbine inlet channel is open ducted type, which has barely been studied. The efficiency of the turbine with inlet open duct channel is relatively low. Therefore, a guide nozzle on the turbine inlet is attached to improve the performance of the turbine. The guide nozzle shapes are investigated to find the best shape for the turbine. The guide nozzle plays an important role on directing flow at the runner entry, and it also decreases the negative torque loss by reducing the pressure difference in Region 1. There is 12.5% of efficiency improvement by attaching a well shaped guide nozzle on the turbine inlet.

• 대한기계학회논문집B
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• 제26권3호
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• pp.439-447
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• 2002

The microchannel flow in miniature TCDs (thermal conductivity detectors) is investigated numerically. The solutions based on the boundary layer approximation are not very accurate in the region of the duct inlet for low Reynolds numbers. In this study, two-dimensional Navier-Stokes equations are considered to analyze the gas flow in a miniature TCD. Effects of channel size, inlet and boundary conditions on the heat transfer rate are examined. When the gas stream is not preheated, the distances for a miniature TCD to reach the conduction-dominant region for duct flow are found to be approximately two and three times the thermal entry length for duct flow with constant properties, respectively, leer constant wall temperature and constant wall heat flux boundary conditions. If the gas temperature at the channel inlet is close to the mean gas temperature in the conduction-dominant region, the entrance region is much shorter compared to other cases considered in this study.

• 정보교육학회논문지
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• 제22권3호
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• pp.335-344
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• 2018

본 연구는 초등학교 SW 교육에서 로봇의 활용이 몰입에 미치는 효과를 살펴보고, 성별의 차이를 알아보고자 하였다. 이를 위해 경기도 A 초등학교 로봇 활용 SW 교육에 참여한 초등학생 155명을 대상으로 로봇 활용 SW 교육을 실시하고, 대응 표본 t검정, 공분산분석을 통해 평균의 차이를 분석하였다. 연구 결과, 로봇 활용 SW 교육을 실시한 후 몰입이 유의하게 향상되었으나, 성별에 따른 몰입의 차이는 유의하지 않았다. 본 연구는 초등학생의 로봇 활용 SW 교육의 효과를 검증하고, 성별의 차이를 규명하여 로봇 활용 SW 교육에 대한 이해를 확장시켰다는 점에서 연구의 의의를 찾을 수 있다.

• 산업경영시스템학회지
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• 제19권37호
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• pp.9-20
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• 1996

The writer has made efforts to solve the weaknesses of the traditional systems through reconstructing cost information systems by introducing 'logical circuit concept' instead of account. As the new designed systems also allow the basic thought of double entry, they are compatiable with the traditional ones. For this, the writer included both monetary and physical information in the systems, replaced the concept of debit & credit with the concept of inputs & outputs, and changed transfer concept between accounts based on reverse logic into flow concept between unit systems based on proceeding logic.

• 한국산학기술학회논문지
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• 제12권8호
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• pp.3374-3383
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• 2011

본 연구는 유한한 크기의 선저경사각을 갖는 2차원 쐐기형 구조물의 슬래밍 충격 현상을 수치 해석하였다. 비압축성 유체를 가정하였으며, 구조물의 입수 속도는 일정하게 유지하였다. 자유수면의 대 변형 및 동적 거동의 해석을 위해서 Geo-reconstruct(or PLIC-VOF) scheme을 사용하였다. 선저경사각이 $10^{\circ}$, $20^{\circ}$ 및 $30^{\circ}$인 경우에 대해서 해석을 수행하였으며, 각각의 선저경사각에 대하여 입수면의 격자 크기 및 입수 속도를 변화시켜 슬래밍 충격력 수치 해석 결과에 미치는 영향을 조사하였다. 수치해석 결과는 Dobrovol'skaya(1969)의 상사해(similarity solution), Wagner 방법에 기초한 점근해(asymptotic solution) 및 경계요소법(Zhao et al.(1993))에 의한 해석 결과와 비교하였다.

• Advances in aircraft and spacecraft science
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• 제6권3호
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• pp.239-256
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• 2019

This study develops a dual purpose: i) evaluating the effects of two different Mars atmosphere models (NASA Glenn and GRAM-2001) on aerodynamics of a capsule (Pathfinder) entering the Mars atmosphere, ii) verifying the feasibility of evaluating the ambient density and pressure by means of the methods by McLaughlin and Cassanto, respectively and therefore to re-build the values provided by the models. The method by McLaughlin relies on the evaluation of the capsule drag coefficient, the method by Cassanto relies on the measurement of pressure at a point on the capsule surface in aerodynamic shadow. The study has been carried out computationally by means of: i) a code integrating the equations of dynamics of the capsule for the computation of the entry trajectory, ii) a DSMC code for the solution of the flow field around the capsule in the altitude interval 50-100 km. The models show consistent differences at altitudes higher than about 40 km. It seems that the GRAM-2001 model is more reliable than the NASA Glenn model. In fact, the NASA Glenn model produces, at high altitude, temperatures that seem to be too low compared with those from the GRAM-2001 model and correspondingly very different aerodynamic conditions in terms of Mach, Reynolds and Knudsen numbers. This produces pretty different capsule drag coefficients by the two models as well as pressure on its surface, making not feasible neither the method by McLaughlin nor that by Cassanto, until a single, reliable model of the Mars atmosphere is not established. The present study verified that the implementation of the Cassanto method in Mars atmosphere should rely (such as it is currently) on pressure obtained experimentally in ground facilities.

• 대한기계학회논문집
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• 제16권10호
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• pp.1971-1978
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• 1992

본 연구에서는 원형 파이프에 원추형 디퓨져가 연결된 덕트 내의 유동장에 대 하여 Launder-Sharma의 저 레이놀즈수 k-.epsilon. 난류모델을 이용하여 수치해석을 수행하였 으며, 수치해석 방법으로는 타원형 방법을 사용하였으며, 앞으로 일반적인 단면의 곡 관이나 스크롤 내부 유동 등의 연구 수행을 감안하여 지배방정식을 일반 비직교 좌표 계로 변환하여 계산을 수행하였다.

• 한국안전학회지
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• 제32권2호
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• pp.147-152
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• 2017

The external reactor vessel cooling (ERVC) is well known strategy to mitigate a severe accident at which nuclear fuel inside the reactor vessel is molten. In order to compare the heat removal capacity of ERVC between the nuclear reactor designs quantitatively, numerical method is often used. However, the study for ERVC using computational fluid dynamics (CFD) is still quite scarce. As a validation study on the numerical prediction for ERVC using CFD, the subcooled boiling flow and natural circulation of coolant at the ULPU-V experiment was simulated. The commercially available CFD software ANSYS-CFX was used. Shear stress transport (SST) model and RPI model were used for turbulence closure and wall-boiling, respectively. The averaged flow velocities in the downcomer and the baffle entry under the reactor vessel lower plenum are in good agreement with the available experimental data and recent computational results. Steam generated from the heated wall condenses rapidly and coolant flows maintains single-phase flow until coolant boils again by flashing process due to the decrease of saturation temperature induced by higher elevation. Hence, the flow rate of coolant natural circulation does not vary significantly with the change of heat flux applied at the reactor vessel, which is also consistent with the previous literatures.