• International Journal of Ocean System Engineering
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• 제3권2호
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• pp.77-89
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• 2013

The propeller performance has been investigated using a benchmark Duisburg Test Case ship with RANSE. First, the hydrodynamic characteristics of propeller in case of open water have been analyzed by a commercial CFD program and the results are compared with those of experimental data. Later, the flow around the bare hull has been solved and the frictional resistance value and form factor of the ship have been obtained and compared with those of ITTC57 formulation and experimental results for validation. The free surface effect has been ignored. A good agreement has been obtained between the results of RANSE and experiments at both stages. Then the ship - propeller interaction problem was solved by RANSE and the differences in thrust, torque and efficiency of propeller as compared with the open-water numerical results have been discussed.

• Bulletin of the Korean Chemical Society
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• 제17권2호
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• pp.143-146
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• 1996

A continuous potential pulse is applied to a silver-working electrode on a pulsed amperometric detector (PAD) for detection of free cyanide and sulfide. The moving phase is 0.1 M sodium hydroxide, 0.5 M sodium acetate and 5% (v/v) ethylenediamine mixture, and the flow rate is 0.7 mL/min. Optimized pulse conditions include a -200 mV (vs. Ag/AgCl reference electrode) detection potential(Ed) for 60 msec and 50 mV cleaning potential (Ec) for 120 msec. The silver working electrode surface is not poisoned by cyanide or sulfide, and the PAD maintains long-term stability without loss of sensitivity and reproducibility at these pulse conditions. The detection limit of cyanide and sulfide separated by ion chromatography using an anion exchange column is 0.1 ppm and 0.05 ppm, respectively.

• International Journal of Naval Architecture and Ocean Engineering
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• 제3권3호
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• pp.201-207
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• 2011

In this paper, we focused on computing the higher-harmonic components of the transmitted wave passing over a submerged circular cylinder to show that it is causing a horizontal negative drift force. As numerical models, a circular cylinder held fixed under free surface in deep water is adopted. As the submergence of a circular cylinder decreases and the incident wavelength becomes longer, the higher-harmonic components of the transmitted wave starts to increase. An increase of the higher-harmonic components of the transmitted wave makes the horizontal drift force be negative. It is also found that the higher-harmonic amplitudes averaged over the transmitted wave region become larger with the increase of wave steepness and wavelength as well as the decrease of submergence depth.

• Nuclear Engineering and Technology
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• 제54권2호
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• pp.565-578
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• 2022

Among Generation IV reactors, the sodium-cooled fast reactor (SFR) is attracting attention as a system having great potential for commercial use. Gas entrainment is a thermal-hydraulic issue related to the safety problem of the reactor core in the SFR. Typically, a dipped plate or baffles are installed under the free surface to suppress gas entrainment. However, these approaches can cause gas entrainment in other locations and require many trial-and-error and verifications. In this study, a new strategy using magnetohydrodynamics to suppress gas entrainment in the SFR is proposed. In a counter-flow model, a judgment criterion of gas entrainment occurrence was developed for both water and liquid metal. Moreover, the gas entrainment can be completely suppressed by applying a magnetic field.

• 대한조선학회지
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• 제13권2호
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• pp.13-43
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• 1976

A potential flow approach is used to develop a method and an associated computer program for floating marine structures of general configuration in wave of all water depths with arbitrary heading. It computes the total force distributions and six degrees-of-freedom motion. The hydrodynamic-force equations and derived become identical under certain assumptions to the equations commonly used by the offshore industry, and the two methods are compared in detail. The computed motions of all six degree agree quite well with model-scale and full-scale experimental data for two typical semisubmersible drilling rigs in finite-depth water. Also the presented motion computations are more accurate than a previous work by the second approach. The present computations use experimentally validated or determined values of frequency-dependent hydrodynamic coefficients with the effects of the free surface and both finite and infinite water depths. The present method generates sufficient computation accuracy to use for practical design applications.

• 한국항해항만학회지
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• 제37권1호
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• pp.1-7
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• 2013

본 연구에서는 개발된 선미부에 수직날개를 부착한 선박의 조파저항성능을 예측할 수 있는 수치해석기법의 검증에 관한 것이다. 수치해석기법은 비점성 유동장 해석기법인 랜킨소오스 패널법과 와류격자법을 사용하여 개발하였으며, 자유수면 경계조건의 비선형성은 반복해법을 사용하여 만족시켰고, 선박의 트림과 침하량을 구하는 알고리즘을 포함하고 있다. 수치해석을 위한 선체표면의 패널을 생성하기 위하여 패널절단법을 사용하였다. 4000TEU 컨테이너 운반선을 대상 선박으로 하여 선미부 6개소의 서로 다른 위치에 수직날개를 부착하여 수치해석을 수행하였으며, 수치해석기법의 타당성을 검증하기 위하여 상용 점성 유동장 해석 프로그램인 FLUENT를 사용하여 선체 주위의 점성 유동장을 계산하였고, 모형시험을 수행하여 얻은 실험 결과를 수치해석 결과와 서로 비교하였다.

• 한국가시화정보학회지
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• 제14권1호
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• pp.57-61
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• 2016

We report a finding of fast(exceeding 2,000 K/s) heating of polydimethylsiloxane(PDMS), one of the most commonly-used microchannel materials, under cyclic loadings at high(~MHz) frequencies. A microheater was created based on the finding. The heating mechanism utilized vibration damping of sound waves, which were generated and precisely manipulated using a conventional surface acoustic wave(SAW) microfluidic system, in PDMS. The penetration depths were measured to range from $210{\mu}m$ to $1290{\mu}m$, enough to cover most microchannel heights in microfluidic systems. The energy conversion efficiency was SAW frequency-dependent and measured to be the highest at around 30 MHz. Independent actuation of each interdigital transducer(IDT) enabled independent manipulation of SAWs, permitting spatiotemporal control of temperature on the microchip. All the advantages of this microheater facilitated a two-step continuous flow polymerase chain reaction(CFPCR) to achieve the billion-fold amplification of a 134 bp DNA amplicon in less than 3 min. In addition, a technique was developed for establishing dynamic free-form temperature gradients(TGs) in PDMS as well as in gases in contact with the PDMS.

• 한국결정성장학회지
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• 제10권3호
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• pp.177-184
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• 2000

약한 cusp 자장이 가하여진 Czochralski실리콘 단결정 성장에서 유동장의 종횡비에 따라 부력과 열모세관 현상이 용융물질의 유동과 물질(산소)전달에 미치는 영향이 수치적인 방법으로 연구되었다. 실리콘 단결정 성장이 진행됨에 따라 도가니안의 용융물질의 깊이가 즐어들어 유동장의 종횡비가 감소하고, 이에 따라 현존하는 유동장에 작용하는 자장의 상대적인 형태가 변화하므로 유동의 형태가 계속 변화한다. 유동장 내부에서 자유표면으로 접근하여 Marangoni 대류를 구성하는 용융물질의 흐름(열모세관 현상)과 함께 도가니 벽 근처의 자유표면 바로 아래에서 순환류가 발생하는데, 이 순환류의 존재로 인하여 부력의 효과가 “전반적으로”나타나지 않고 도리어 “국소적으로”나타나는 특성을 갖는다. 종횡비가 작아질수록 유동장의 대부분에서 자장의 반경방향 성분이 축방향 성분보다 우세하여 용융물질의 유동은 횡방향 성분(수평성분)이 현저해지므로 자오면에서의 온도분포는 점차 반경방향에 의존하는 특성을 갖게 된다 종횡비가 작아질수록 결정의 가장자리에서 온도구배가 작아지며 따라서 열모세관 현상포 약화된다 또 이때 결정주위의 산소의 농도가 작아지며 따라서 흡수되는 산소의 양도 작아진다.

• Journal of Biosystems Engineering
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• 제29권1호
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• pp.37-44
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• 2004

This study was conducted to develop a new drying method far reducing the drying cost and time and to investigate the drying characteristics of oak mushroom. A far infrared dryer of down draft air flow type used for this experiment can control the drying parameters, such as far infrared heater temperature and aeration velocity. The far infrared drying tests were performed at aeration velocities of 0.3 and 0.6m/s under the temperature of 90 and 100$^{\circ}C$ in for infrared heater, respectively. The results were compared and analyzed with those of an heated air drying method used as a control in terms of properties representing the drying characteristics. such as shrinkage rate, color, energy consumption amino acid components, drying rate and moisture ratio. The results obtained from this research can be summarized as follows. 1. The drying rate of far infrared drying was faster than that of heated air drying. With high temperature of far infrared heater and slow aeration velocity, the far infrared drying of down draft air flow type was superior to the heated air drying. 2. Most of far infrared drying conditions required less energy consumption than heated air drying. 3. The shrinkage rates of heated air drying and far infrared drying were decreased by 17.0% and 18.2∼19.8%, respectively. 4. The difference of color on oak mushroom surface before and after drying can be represented as $\Delta$E. $\Delta$E values of far infrared drying and heated air drying were 2.39∼4.55 and 6.77, respectively. 5. The amounts of free amino acids were higher in the far infrared than in the heated air drying. In addition the amounts of Gln and Glu generally were increased and those of Ala, Leu, and Val were decreased in order.

• 한국항공우주학회지
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• 제34권12호
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• pp.9-17
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• 2006

진동하는 에어포일에서 비정상 경계층의 거동을 조사하기 위하여 실험적 연구가 수행되었다. 가로세로비가 2.7인 NACA 0012 에어포일은 시험부에 수직으로 설치되었고, 1/4 시위에서 조화 피칭운동을 한다. 에어포일의 진동 진폭은 -6$^{\circ}$에서 +6$^{\circ}$까지 변화하며 평균 받음각은 0$^{\circ}$ 이다. 표면에 부착되는 프로브(글루온 프로브)가 경계층 표면 유동를 측정하기 위하여 이용되었다. 측정은 자유흐름속도는 1.98, 2.83, 4.03m/s에서 수행되었고, 시위길이를 근거로 한 레이놀즈수는 각각 2.3$\times$104, 3.3$\times$104, 4.8$\times$104이다. 에어포일의 무차원 진동수를 모든 경우에서 0.1로 고정하였다. 비정상 경계층에서 최소 전단력의 위치와 경계층 붕괴의 위치는 레이놀즈수 2.3$\times$104와 3.3$\times$104 사이에서 크게 다르게 나타난다.