• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.10
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• pp.787-794
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• 2003

The effect of inclination angle on natural convection heat transfer has been studied for water layers. The range of the Raleigh number was from the subcritical value to 1.4${\times}$10$^{7}$ , and the range of the inclination angle, $\theta$, measured from the horizontal was 0$\leq$$\theta$$\leq$180$^{\circ}$. For horizontal water layers, present results agreed well with the results of previous investigators and also showed significant departures from the results of air layers in the turbulent regime. Inclined cylindrical water layers showed secondary maxima in heat transfer, whereas rectangular air layers showed continuous decline of Nusselt number.

• Journal of Navigation and Port Research
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• v.33 no.2
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• pp.105-110
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• 2009

Shipwaves am have harmful effects on ships working on the sea, in a harbour or navigational channel and caused beach erosion, seawall destruction. This study aims to investigate describe the characteristics of the wave pattern generated by an individual model ship tested at different velocities and hull forms for a given water depth and to investigate the variations at a given distance from the sailing line under the same conditions. As a result, the angles a's by model ship tests are smaller than those by real ship ones. Wave heights decreases with an increasing the mid-ship cross sectional area $A_s$. The maximum wave height and period increase rapidly in the subcritical speed, and beyond the critical speed the height and period decrease with increasing depth Froude number. And the period keeps constant with the distance from the sailing line.

• Proceedings of the KIEE Conference
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• 2000.07d
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• pp.2342-2344
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• 2000

Many years ago, most of thermal power plants built in this country were of subcritical pressure, of medium or small size, of constant pressure operation, of drum type steam generator. But, nowadays, almost all of them were of high efficiency, of supercritical pressure, of great capacity(about 500MW), of sliding pressure operation, of once through type steam generator. Presently built once through boiler introduces turbine bypass systems to variable pressure operation which eliminates unexpected materials in boiler tube during startup, minimizes fuel loss by short startup period, eventually improves total efficiency and power system stability

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.597-600
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• 2010

Cold flow injection test was conducted to investigate the characteristics of cryogenic liquid nitrogen jet at sub to supercritical condition. Single jet injector element was installed in high pressure chamber to investigate the effect of ambient pressure around the jet, injector geometry and flow conditions. Experimental results showed obvious differences between jet characteristics under subcritical and supercritical condition. Effect of injector inlet shape also was investigated.

• Structural Engineering and Mechanics
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• v.14 no.2
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• pp.209-221
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• 2002

In this paper a fracture criterion is proposed for cracked cylindrical samples of high-strength prestressing steels of different yield strength. The surface crack is assumed to be semi-elliptical, a geometry very adequate to model sharp defects produced by any subcritical mechanism of cracking: mechanical fatigue, stress-corrosion cracking, hydrogen embrittlement or corrosion fatigue. Two fracture criteria with different meanings are considered: a global (energetic) criterion based on the energy release rate G, and a local (stress) criterion based on the stress intensity factor $K_I$. The advantages and disadvantages of both criteria for engineering design are discussed in this paper on the basis of many experimental results of fracture tests on cracked wires of high-strength prestressing steels of different yield strength and with different degrees of strength anisotropy.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.274-277
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• 2004

The most important mode of subcritical crack growth is primary water stress corrosion crack, which was the reported mechanism from the root cause analysis of the crack in the bimetallic welds. Stress corrosion crack growth evaluations was carried out for several flaw shapes of both axial and circumferential flaws, using the steady-state stresses including residual stresses. This evaluation considered the possibility of additional flaws in the primary loops of nuclear power plant, even though no such flaws have been identified by Ultrasonic Test. Consequently, Results show that the predicted flaw sizes will determine acceptability for continued service and maintenance.

• Proceedings of the KSR Conference
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• 2003.05a
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• pp.91-96
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• 2003

In this report, numerical investigations have demonstrated, that the displacement underneath a moving loa야ng reach a maximum value, if the speed of the load is equal to propagation velocity of the maximum wave. The load speed for which the maximum displacement occurs is called critical speed. The critical speed divides the velocities in a subcritical and a super-critical region. By means of calculations the dynamic behaviour of the slab track-soil is investigated. For concrete slab track dynamic wheel load are given in dependence of relevant excitation mechanism and speed of the train. These loads can be used for the dimensioning of the track as well as for the prognosis of the vibrations at the track and the surrounding soil.

• Journal of ILASS-Korea
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• v.9 no.4
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• pp.83-89
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• 2004

Vaporization characteristics of a liquid heptane droplet in high-pressure and temperature flow field are numerically studied. Variable thermodynamic and transport properties and high-pressure effects are taken into account in order to consider real gas effects. Droplet Vaporization in convective environments was investigated on the basis of droplet vaporization in quiescent and convective environment. In quiescent environments, droplet lifetime is directly proportional to pressure at the subcritical temperature range but it is inversely proportional to pressure at the supercritical temperature range. In convective environment, droplet deformation becomes stronger by increasing Reynolds number due to increase of velocity while droplet deformation is relatively weak at a higher pressure for the same Reynolds number cases.

• Nuclear Engineering and Technology
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• v.25 no.3
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• pp.480-496
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• 1993

원자력발전 핵연료주기에서 고려하여야 할 중요한 요소의 하나는 사용후핵연료에서 비롯되는 고준위 방사성핵종이다. 고준위 방사성핵종의 처분 방법으로서 심지층처분방식은 가장 손쉬운 방법이기는 하나 매우 장시간의 감시가 필요하며, 특히 자연환경으로의 누출가능성이 커서 이의 대안으로서 외국 몇 나라에서는 소위 소멸처리(Transmutation)방법에 대한 연구를 활발히 하고 있다. 현시점에서 소멸처리 방법으로 가장 타당성이 있는 것으로 여겨지는 것은 원자로를 이용하는 것과 가속기 구동 미임계 시스템 (Accelerator-Driven Subcritical System)을 이용하는 방법이다. 본 기고문에서는 이들 방법을 중심으로 다양한 소멸처리 방법의 소개와 기술적인 문제점(특히 핵 특성관점에서)에 대한 고찰 그리고 향후 연구과제 등에 대하여 기술하고자 한다. 비록 소멸처리 시스템의 현실화를 위해서는 해결되어야 할 과제가 많이 남아 있지만, 기술적인 가능성과 방사능의 소멸이란 면을 고려할 때 소멸처리시스템은 궁극적인 방사성핵종 처리기술로서 연구·개발할 충분한 가치가 있는 것으로 판단된다.

• Journal of the Korean Society of Safety
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• v.8 no.2
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• pp.51-57
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• 1993

This study was done by ultrasonic testing. The proves used in this study were 5Z10$\times$10A70. The useful fatigue life of structural components is determined by the sum of the elapsed load cycles required to initiate a fatigue crack and to propagate the crack from subcritical size to critical dimensions. Thus, to predict the service life of many steel structures and to establish safe inspection intervals, an understanding of the Fatigue Crack Initiation and Fatigue Crack Propagation behavior in the steel is required. In the present study, the Fatigue Crack Initiation Life in SPS 5A steel was investigated by testing specimens having widely varying notch acuities. The variation in the notch acuity covered the range from notch root raidus 0.5mm to 2.5mm, and Fatigue Crack Initiation Life data were obtained in that range.