• 한국산림과학회지
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• 제87권2호
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• pp.220-229
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• 1998

이 연구(硏究)는 우리 나라 주요(主要) 낙엽(落葉) 활엽수(闊葉樹) 21종(種)에 대하여 분지부(分枝部)(branch junctions)의 상대수분통도성(相對水分通導性)(relative conductivity, RC), leaf specific conductivity(LSC), Huber value(HV), specific conductivity(SC) 등의 수분통도성(水分通道性)(hydraulic conductivity, HC), 그리고 변재부(邊材部)의 평균(平均) 도관직경(導管直經)(${\mu}m$)과 도관수(導管數)($No./mm^2$) 등을 측정(測定)하여 분지부(分枝部)의 수분통도(水分通道) 특성(特性)과 통도조직(通導組織) 특성(特性)을 종수별(樹種別)로 비교(比較)하였다. 분지부(分枝部)의 수분통도성(水分通道性)은 분기각(分技角)이 클수록 또한 분지(分技)된 가지의 직경(直經)이 작을수록 현저히 감소하였으며, 분지형(分技型)(ㅏ, Y, ${\Psi}$형(型))에 따른 분지부(分技部)의 수분통도성(水分通道性)은 Y형(型)보다는 ㅏ형(型)과 ${\Psi}$형(型)의 분지부(分技部)에서 더 작아졌다. 분지부(分技部)에 있어서 도관직경(導管直經)과 도관수(導管數)는 분지형(分技型)이나 분기각(分技角) 등의 분지형태(分技形態)에 따라 값의 차이가 있으나 인접한 줄기와 가지에 비하여 현저히 작았다.

• 한국양식학회지
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• 제13권3호
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• pp.267-275
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• 2000

이 연구는 값싸고 높은 비 표면적을 제공할 수 있는 발포스티로폼 입자를 packed column 에어레이터의 산소전달 매질로 이용 가능성을 알기 위하여 매질의 깊이와 수리학적부하량에 따른 산소 전달 특성과 효율을 조사 하였다. 이용된 발포스티로폼 입자는 직경 2.5 mm의 구형이었으며, 비표면적이 1350 $m^2$/$m^3$으로 일반적으로 이용되는 매질에 비해 약 3.7~7.0배 더 넓은 비표면적을 제공할 수 있다. 이 매질을 직경 10 cm, 높이 1 m의 내부 관찰이 용이한 아크릴 관으로 제작한 packed column 에어 레이터에 0, 4.5, 9그리고 18 cm의 매질을 채워 넣고, 수온 20, 25 및 3$0^{\circ}C$에 대해 수리학적 부하량을 2, 4 및 5.6 $m^3$/$m^2$/min로 각각 달리하여 산소전달특성을 실험한 결과(Exp. 1),모든 실험 수온에서 수리학적 부하량이 증가함에 따라 표준산소전달률이 증가하였으나 매질의 깊이는 9 cm 까지는 증가하다가 18 cm에서는 감소하였다. 표준산소전달률은 매질 깊이 9 cm에서 수리학적 부하량이 5.6 $m^3$/$m^2$/min일 때 가장 높았다. 그러나 수리학적 부하량이 증가함에 따라 펌프의 소모 전력이 증가하여, 단위소모 전력당 표준에어레이션 효율은 매질의 깊이 9 cm에서 수리학적부하량 2 $m^3$/$m^2$/min일 때 가장 높았다. 따라서 모든 수리학적 부하량에서 매질의 깊이 9 cm 일 때 표준산소전달률과 표준에어레이션 효율이 가장 좋았다. 이 매질을 직경 20 cm, 높이 2 m의 PVC관으로 제작한 packed column 에어레이터에 깊이를 0, 9, 18, 27 및 36 cm로 넣고 순환여과식 시설 내에 실험실 규모의 적용실험을 통해 에어레이터의 효율을 조사하였는데 (Exp.2), 실험 수온 27$^{\circ}C$에서, Exp. 1에서와 동일한 3개의 수리학적 부하량에서 산소 전달률을 측정한 결과, Exp. 1에서와 같이 수리학적 부하량과 매질의 깊이의 증가에 따라 산소 전달률이 증가하였으며, 매질의 깊이가 가장 깊은 36 cm에 대해, 수리학적 부하량이 2 $m^3$/$m^2$/min 일때, 2 kg 02 kg $O_2$/kW-hr의 가장 높은 표준에어레이션효율을 나타내었다. 위의 두 실험 결과에 따라 packed column 에어레이터에서 발포스티로폼 입자를 산소전달 매질로 이용하여 산소 전달률을 증가시킬 수 있다는 것을 확인할 수 있었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.929-934
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• 2001

This study aimed to examine the cause of latent hydraulic property manifestation of ground granulated blast-furnace slag(GGBFS) using different alkali activators in pH, type and quantity. According to the experimental result, the higher pH value accelerated lastly latent hydraulic property and the early stage strength of GCBFS was ranked as activators with the higher pH, in an order of NaOH, $Ca(OH)_{2}$ and $Na_{2}$$Co_{3}$. Also, NaOH had accelerated latent hydraulic property of GGBFS, which had 40~50% of the 3 and 7 days compressive strength of base mortar in case of using 10% of powder-weight. In the case of 30% of GGBFS substitution with annexing 2.5% $Ca(OH)_{2}$, the compressive strength on the 3 and 7 days of the early-age, was increased to 5~10% than that of the same admixture with no activator. With annexing 5.0% $Ca(OH)_{2}$, the strength was increased to 10~20%. Although activator NaOH was effective on the manifestation of latent hydraulic property, it caused cement mortar compressive strength decrease by enlarging pore diameter.

• 상하수도학회지
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• 제27권4호
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• pp.495-502
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• 2013

Hydraulic dead-zone and particle removal efficiency in the base frame of a constructed wetland was evaluated with computational fluid dynamics (CFD). The fraction of hydraulic dead-zone was estimated to be 1.2-2.1 % (v/v) and it was attributed to the artificial islands developed in the constructed wetland. Solids deposition rate could be increased with higher hydraulic retention time (HRT, ranged from 2.2 to 4.2 hr) of the wetland and larger particle size (ranged from 10 to $50{\mu}m$) in the influent. Experimental results showed that the volume concentration of the particles smaller than $10{\mu}m$ in diameter was varied from $1.99{\times}10^3{\mu}m^3/ml$ (HRT 12.8 hr) to $3.92{\times}10^3{\mu}m^3/ml$(HRT 2.2 hr) in the influent of the constructed wetland. With the effluent volume concentration data, removal efficiency of those particles was calculated to be 71.2 and 24.7 % when the HRT was 12.8 and 2.2 hr, respectively. Similar trend with the HRT variation could be identified with CFD analysis.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2000년도 제31회 춘계학술대회
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• pp.62-67
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• 2000

This paper was undertaken to do morphological analysis of wear debris for slipper-Pad of hydraulic rotary acuator. The lubricating wear test was performed under different experimental conditions using the wear test device and wear specimens of the pin on disk type was rubbed in paraffinic base oil by three kinds of lubricating materials, varying applied load, sliding distance. The four shape parameters(50% volumetric diameter, aspect, roundness and reflectivity) are used for morphological analysis of wear debris. The results showed that the four shape parameters of wear debris depend on a kind of the lubricating condition. It was capable of presuming wear volume for slipper-pad of hydraulic rotary acuator on driving time.

• 한국산업융합학회 논문집
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• 제5권1호
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• pp.21-26
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• 2002

Response time of actuator in a hydraulic system may be important and necessary to avoid failures and to improve the efficiency of operation. Flow restricting devices can result in a decrease in the peak pressure, but may change the response time. The response time has an important effect on both operator and operator perceived smoothness. The response time should correspond to how fast a system responds to a given disturbance at the system boundary, Occasionally the appropriate response time is not easily determined. This study is on the characteristics of response time in the hydraulic system.

• 한국자동차공학회논문집
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• 제10권1호
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• pp.133-142
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• 2002

To improve the hydraulic control performance of ABS, it is necessary to establish an efficient control algorithm. And also it is necessary to ova]Hate a hydraulic modulator with solenoid valve quantitatively. In this paper, FEM and permeance method are used to analyze dynamic characteristics of outlet valve. In return, mathmatical modeling of a hydraulic modulator and operating pressure is presented, and the model parameters of an outlet valve are moving plunger, spring constant and orifice diameter. This study shows the way to improve the dynamic characteristic of an ABS outlet valve heavily depending on operating pressure. It is recommended that operating pressure should be justified at the first step toward the design to get the optimal design of an outlet valve.

• 동력기계공학회지
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• 제13권4호
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• pp.31-37
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• 2009

The purpose of this numerical study was to investigate performance characteristics for cooling tower axial fans with sweep. Performance data for the fans with various sweep angles were obtained in terms of the setting angle at a constant flow rate. Viscous flow calculations were carried out to obtain Performance data of the total pressure rise and hydraulic efficiency. A solution of the Ffowcs Williams-Hawkings equations was used to calculate the sound pressure level at three times fan diameter away from the fan. The calculated performance data well represented performance characteristics of the cooling tower axial fan. The total pressure rise and hydraulic efficiency at the same setting angle decreased with sweep angle. Sound pressure level slightly decreased for the fan with a sweep angle of 10 degree. No significant effect of the sweep geometry was found on the sound pressure level.

• Water Engineering Research
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• 제4권3호
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• pp.127-139
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• 2003

This paper presents the hydraulic analysis of the oxygen transfer through the air entrainment and the relationships between the efficiency of the oxygen transfer and the hydraulic parameters in the riparian riffles. Field survey on the pool-riffle formation of the river reach and the measurements of the oxygen transfer in the riffles were performed. Air entrainment occurred more frequently in the edged gravels rather than in the round and edgeless ones, and it was formed mainly from behind the trailing edges of the gravels. Oxygen transfer was found to be proportional to the flow velocity, the flow discharge, and the Froude number, but to be not closely related to the particle diameter. Average value of oxygen transfer in the riffles of study area was about 0.085, which shows good efficiency compared with results of smooth chute. Variation of the water level, which increases in proportion to the flow velocity and the flow discharge, seems to make the air entrainment more active, but has not been verified quantitatively. Relationships between the air entrainment and the variation of the water level must be considered in the further study.

• 한국정밀공학회지
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• 제16권7호
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• pp.24-31
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• 1999

Bulging is a forming method to shape of die cavity by using hydraulic pressure in tube or vessel. Bulging machine and die were developed in order to produce vessel for keeping warm. Bulging machine is a double type with two horizontal cylinders for bulging of two pieces at the same time. The developed die system has one bulging die and two drawing dies for necking at the both ends of tube. The diameter of tube expands by hydraulic pressure in tube. at the same time, thrust at the both ends of tube. pushes tube in the direction of expansion to obtain high expanding rate with no crack. In this study, the bulging properties were investigated to solve tube crack and necking in manufacturing vessel by the combination method of bulging and drawing. As a result, high expanding rate of tube radius without crack, precision necking and high productivity were obtained.