• 한국해양공학회지
• /
• 제23권1호
• /
• pp.60-66
• /
• 2009

This study presents an experimental investigation of the shallow water impact of a box type structure. The analysis was done based on the video images captured by a high speed camera, the flow field obtained by PIV (Particle Image Velocimetry), and pressure measurements in the divided region. The video images showed quite good agreement with the description given by Korobkin. The PIV measurements of the velocity field provided a clear view of the flow pattern for all three stages. The pressure was measured at the bottom of the tank with strain gauge type pressure gauges. The pressure measurements showed the characteristics of divided regions.

• 한국분무공학회지
• /
• 제9권4호
• /
• pp.83-89
• /
• 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.

• 한국결정성장학회지
• /
• 제6권3호
• /
• pp.406-414
• /
• 1996

본 연구에서는 금속타겟을 이용한 반응성 스퍼터링법을 이용하여 PZT 박막 증착후 냉각시 산소분압에 따른 박막의 상형성 거동 및 전기적 특성에 미치는 영향을 고찰하였다. 냉각시 산소분압의 감소에 따라 박막 표면의 휘발에 기인하여 표면거칠기는 증가하였고 입성장은 거의 일어나지 않았다. 산소분압이 증가할수록 각형비가 보다 우수한 hysteresis 특성을 얻을 수 있었고 산소분압이 감소함에 따라 remanent polarization과 retained polarization이 감소하였으며, 항전계의 감소가 관찰되었다. 산소분압에 따른 유전율-전압 특성 측정에서 산소분입이 감소함에 따라 internal bias field의 증가가 관찰되었으며, 유전율도 조금씩 감소하였다. Field accelerated retention 시험결과 냉각시 산소분압이 감소함에 따라 nonswitched polarization의 증가가 관찰되었고 bias time이 증가함에 따라 nonswitched polarization이 감소하였다.

• 한국전기전자재료학회논문지
• /
• 제27권3호
• /
• pp.172-177
• /
• 2014

Industrial, medical, environment and agriculture application of pulse power technology have been developing rapidly in many field. In order to make use in the form of pulses is applied to the pulse forming technique. At this time, spark gap is generally used for the pulse forming. Spark gap may be possible to simulate the shape of the electrode, to know the uniform or non-uniform electric field of the electrode structure. Further, it can be determined using Paschen's law applied pressure of the insulating gas in accordance with the voltage which is created using the value of the electric field. In this paper, we tried to found using a formula and the simulation process to determine the pressure. The value of the electric field is different according to the shape of the electrode. So, the range of pressure applied also varies. In order to withstand the 100 kV with a gap of 5 mm, the nitrogen gas must be applied to about 7 bar in the electrode structure. On the other hand, in the same conditions, Sulfur hexafluoride gas must be applied to about 2 bar. Consequently, the Sulfur hexafluoride gas has a higher insulation properties than nitrogen gas may be applied to low pressure at the same conditions.

• Wind and Structures
• /
• 제16권1호
• /
• pp.117-136
• /
• 2013

A field study of wind-induced internal pressures in a flexible and porous industrial warehouse with a single dominant opening, of various sizes for a range of moderate wind speeds and directions, is reported in this paper. Comparatively weak resonance of internal pressure for oblique windward opening situations, and hardly discernible at other wind directions, is attributed to the inherent leakage and flexibility in the envelope of the building in addition to the moderate wind speeds encountered during the tests. The measured internal pressures agree well with the theoretical predictions obtained by numerically simulating the analytical model of internal pressure for a porous and flexible building with a dominant opening. Ratios of the RMS and peak internal to opening external pressures obtained in the study are presented in a non-dimensional format along with other published full scale measurements and compared with the non-dimensional design equation proposed in recent literature.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2003년도 춘계학술대회 논문집 디스플레이 광소자분야
• /
• pp.84-87
• /
• 2003

Carbon-nitrogen (CN) nanofibers have been produced using a water cooled hot isostatic pressure (HIP) apparatus. The CN nanofibers were grown in random with the diameter of about 100-150nm and length over $10{\mu}m$. Emission properties of CN nanofibers were investigated for spacing, between anode and cathode, variation. Then turn-on fields about $1.4V/{\mu}m$. The time reliability and light emission test were carried out for above 100 hours. We suggest that CN nanofibers can be possibly applied to high brightness flat lamp because of low turn-on field and time reliability.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2001년도 추계학술대회논문집 II
• /
• pp.1078-1082
• /
• 2001

An alternative formulation of the Helmholtz integral equation is derived to express the pressure field explicitly in terms of the velocity vector of a radiating surface. This formulation, derived for arbitrary sources, is similar in form to the Rayleigh's formula for planar sources. Because the pressure field is expressed explicitly as a surface integral of the particle velocity, which can be implemented numerically using standard Gaussian quadratures, there is no need to use Boundary element method to solve a set of simultaneous equations for the surface pressure at the discretized nodes. Furthermore the non-uniqueness problem inherent in methods based on Helmholtz integral equation is avoided. Validation of this formulation is demonstrated for some simple geometries.

• Wind and Structures
• /
• 제16권4호
• /
• pp.301-322
• /
• 2013

Recent major post-hurricane damage assessments in the United States have reported that the most common damages result from the loss of building roof coverings and subsequent wind driven rain intrusion. In an effort to look further into this problem, this paper presents a full-scale (Wall of Wind --WoW--) investigation of external and underneath wind pressures on roof tiles installed on a low-rise building model with various gable roofs. The optimal dimensions for the low-rise building that was tested with the WOW are 2.74 m (9 ft) long, 2.13 m (7 ft) wide, and 2.13 m (7 ft) high. The building is tested with interchangeable gable roofs at three different slopes (2:12; 5:12 and 7:12). The field tiles of these gable roofs are considered with three different tile profiles namely high (HP), medium (MP), and low profiles (LP) in accordance with Florida practice. For the ridge, two different types namely rounded and three-sided tiles were considered. The effect of weather block on the "underneath" pressure that develops between the tiles and the roof deck was also examined. These tests revealed the following: high pressure coefficients for the ridge tile compared to the field tiles, including those located at the corners; considerably higher pressure on the gable end ridge tiles compared to ridge tiles at the middle of the ridge line; and marginally higher pressure on barrel type tiles compared to the three-sided ridge tiles. The weather blocking of clay tiles, while useful in preventing water intrusion, it doesn't have significant effect on the wind loads of the field tiles. The case with weather blocking produces positive mean underneath pressure on the field tiles on the windward side thus reducing the net pressures on the windward surface of the roof. On the leeward side, reductions in net pressure to a non-significant level were observed due to the opposite direction of the internal and external pressures. The effect of the weather blocking on the external pressure on the ridge tile was negligible.

• 한국농공학회지
• /
• 제17권2호
• /
• pp.3758-3762
• /
• 1975

In order to find out the optimum size of nozzle of the power sprayer in the paddy field, four different sized hole of nozzles were tested on its discharge volume per unit time and its effective covering distance. 1. The discharge rate of each nozzle is proportional to square root of the transmitted internal pressure of liquid, and the discharge coefficient ranges from 0.82 to 0.86 at the pressure of 20 to 30 kg/$\textrm{cm}^2$. 2. The effective covering distance is increased as the size of the hole is larded and also the pressure is increased under under the limited pressure. Generally, the effective covering distance is not greatly increased at the pressure of above 25kg/$\textrm{cm}^2$. The distance from the nozzle to the spot where the largest amount of droplets are dropped is about 14.5m for 3.05mm nozzle and 16m for 4.05mm nozzle in the pressure range from 20 to 25kg/$\textrm{cm}^2$. 3. From the above results it is concluded that the 3mm nozzle with the power sprayers, which are now being supplied to the farmers, can be used for disease and insect control on the paddy field of which block size is 30m${\times}$100m, and operators need not to enter the field for spraying. For the 40m${\times}$100m block, 4mm nozzle should be used with large size of pump which discharge capacity is 60l/min or more.

• Wind and Structures
• /
• 제5권2_3_4호
• /
• pp.337-346
• /
• 2002

Wind tunnel pressure measurements and numerical simulations based on the Reynolds Stress Model (RSM) are compared with full and model scale data in the flow area of impingement, separation and wake for $60^{\circ}$ and $90^{\circ}$ wind azimuth angles. The phase averaged fluctuating pressures simulated by the RSM model are combined with modelling of the small scale, random pressure field to produce the total, instantaneous pressures. Time averaged, rsm and peak pressure coefficients are consequently calculated. This numerical approach predicts slightly better the pressure field on the roof of the TTU (Texas Tech University) building when compared to the wind tunnel experimental results. However, it shows a deviation from both experimental data sets in the impingement and wake regions. The limitations of the RSM model in resolving the intermittent flow field associated with the corner vortex formation are discussed. Also, correlations between the largest roof suctions and the corner vortex "switching phenomena" are observed. It is inferred that the intermittency and short duration of this vortex switching might be related to both the wind tunnel and numerical simulation under-prediction of the peak roof suctions for oblique wind directions.