• 한국결정학회지
• /
• 제11권4호
• /
• pp.200-206
• /
• 2000

In a 200 mm Cz-Si crystal, a macroscopic fluctuation in pulling rate was intentionally introduced then the variations of the pulling rate and the formation behaviors of grow-in defects were compared. The diameters of the OSF-ring and the FPD area were affected by the fluctuation in the region above 1100℃. The COP density depended on the diameter of the OSF-ring. ΔOi and BMD were affected by the fluctuation in the region near 1000Δ. As the result, when a macroscopic fluctuation in pulling rate is introduced, the quality of crystal in the region of 150 mm from the growth interface should be reviewed carefully because it can be affected by the fluctuation.

• International Journal of Fluid Machinery and Systems
• /
• 제10권3호
• /
• pp.307-317
• /
• 2017

In liquid-propellant rockets, POGO instability can occur, in which a fluctuation of propellant supply to the engine, a thrust fluctuation, and a structural vibration are coupled. For the prediction of this instability, it is required to provide dynamic characteristics of the pump represented as the transfer matrix correlating the upstream and downstream pressure and flow rate fluctuations. In the present study, the flow rate fluctuation is evaluated from the fluctuation of pressure difference at the different locations assuming that the fluctuation is caused by the inertia of the flow rate fluctuation. The experiments were performed in some flow conditions, and it was shown that the tendencies of dynamic characteristics are related to excitation frequencies, cavitation numbers and flow rate coefficients.

• 상하수도학회지
• /
• 제21권4호
• /
• pp.485-491
• /
• 2007

The fluctuation of inlet flow to a water treatment plant makes a serious problem that it can change the filtration rate abruptly, and ultimately occur the breakthrough of the detained particles inside filter media. Also, since it takes very short time (about 10 minutes) for the surface wave occurred from the fluctuation of inlet flow to reach the filtration process, it is impossible to control the filtration rate stably. Therefore, this study was conducted to evaluate the effect of daily flow-rate fluctuation on the performance of sand filtration process, and to suggest the dual media composition for coping with that effect. Comparative column tests have been carried out for various dual media (sand and anthracite) compositions. From the results of column tests, dual media, especially in the case of sand 45cm/anthracite 30cm, is more effective to cope with the effect of flow-rate fluctuation on the performance of filtration than single media (only sand). In addition, irrespective of dual media composition, managing ability to cope with that fluctuation tends to be weak at the end of allowable filtration duration time,

• Architectural research
• /
• 제8권1호
• /
• pp.69-76
• /
• 2006

The purpose of this study is to suggest policies to improve the price escalation system in a construction contract through a Policy Delphi technique. The Delphi, including two times questionnaires and a group discussion, was conducted by joining 14 experts. Also, the escalation provisions of various countries were examined. Results of the Delphi showed that the minimum fluctuation rate for price escalation was desirable at a level of 3%. To compute the fluctuation rate, calculating the price fluctuation of overall articles was more desirable than using price indices. A bidding date was more reasonable as the initial date of change in price. Losses caused by price change should be shared between contractor and owner; therefore a deduction rate should be introduced in price escalation. Meanwhile, overhead and profit should be adjusted in proportion to the fluctuation rate; but advance payment or the delayed construction amount should be deducted from the adjusted amount.

• International Journal of Fluid Machinery and Systems
• /
• 제7권2호
• /
• pp.42-53
• /
• 2014

Phase resonance in Francis type hydraulic turbine is studied. The phase resonance is a phenomenon that the pressure fluctuation in the penstock of hydraulic turbine installation can become very large when the pressure waves from each guide vane caused by the interaction with the runner vane reach the penstock with the same phase. Experimental and numerical studies have been carried out using a centrifugal fan. In the present study, comparisons between the pump mode and the turbine mode operations are made. The experimental and numerical results show that the rotational direction of the rotor does not affect characteristics of the pressure fluctuation but the propagation direction of the rotorstator interaction mode plays an important role. Flow rate fluctuations through the stator are examined numerically. It has been found that the blade passing flow rate fluctuation component can be evaluated by the difference of the fluctuating pressure at the inlet and the outlet of the stator. The amplitude of the blade passage component of the pressure fluctuation is greater at the stator inlet than the one at the stator outlet. The rotor-stator interaction mode component is almost identical at the inlet and the outlet of the stator. It was demonstrated that the pressure fluctuation in the volute and connecting pipe normalized by the flow rate fluctuation becomes the same for pump and turbine mode operations, and depends on the rotational direction on the interaction mode.

• 한국결정학회지
• /
• 제11권3호
• /
• pp.157-161
• /
• 2000

In a 200nm Cz-Si crystal, a macroscopic fluctuation in pulling rate was intentionally introduced an then the variations of the pulling rate and the position of OSF-ring were compared each other. The formation behavior of OSF-ring in the effective volume, defined as the region between the growth interface position -α and the growth interface position +α, is most affected by the pulling rate fluctuation. To understand the correct effect of a macroscopic pulling rate fluctuation, its cumulative effect in the effective volume should be considered. A new concept of modeling for it was proposed here.

• 대한토목학회논문집
• /
• 제35권1호
• /
• pp.217-227
• /
• 2015

본 연구는 건설투자 GDP (Gross Domestic Product) 디플레이터 방식의 물가조정이 이루어진 제주특별자치도 내 하수관거정비 BTL(Build-Transfer-Lease)사업에 대하여 물가변동률 적용에 문제점을 파악하기 위하여 실시되었다. 분석 결과, GDP 디플레이터 방식의 기준지수는 고정값을 사용하며 매분기별 물가변동률이 반영되기 때문에 지수조정률 방식보다 물가변동률이 높게 나타나는 것으로 조사되었다. 그러나 GDP 디플레이터 지수가 총사업비에 일괄적으로 적용되기 때문에 현실적인 물가를 반영하지 못함으로써 정확도가 떨어지는 단점이 있는 것으로 조사되었다. 또한 GDP 디플레이터 방식의 기준지수가 고정값을 사용하기 때문에 기준이 되는 시점(정부고시일)이 물가조정에 매우 크게 영향을 미치는 것으로 조사되었다.

• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2006년도 제33회 KOSCO SYMPOSIUM 논문집
• /
• pp.27-35
• /
• 2006

It has been observed in experiments that combustion instability of low frequency (${\sim}$ 10Hz) results form the modulation of equivalence ratio at fuel injection hole when a pressure fluctuation propagates upwards along the channel of the burner under an unchoked fuel flow condition. In this study, a commercial program was used to determine how the fuel flow rate changed with respect to the pressure, velocity of the fuel flow and the mass fraction in a choked and an unchoked condition. The calculation focus on the upstream of the dump plane to know how the forced pressure with the fuel injection conditions affects the modulation of the equivalence ratio. Therefore, it is found that pressure fluctuation leads to oscillation of mass flow rate and then results in equivalence ratio modulation under the unchoked fuel flow condition.

• 한국압력기기공학회 논문집
• /
• 제19권2호
• /
• pp.155-162
• /
• 2023

In nuclear power plants, the flow rate information is a major indicator of the performance of rotating equipment such as pumps, and is a very important one required for facility operation and maintenance. To measure a flow rate, various types of methods have been developed and used. Among them, the differential pressure type using orifice and the direct doppler type using ultrasonic waves are the most commonly used. However, these flow rate measurement methods have limitations in installation, conditions and status of the measuring part, etc. To solve this problem, we have studied a new technique for measuring flow rate from scratch. In this paper, we have devised a technique to estimate the flow rate using an average moving velocity of large-scale eddy in turbulence that occurs in the piping flow field. The velocity of the large-scale eddy can be measured using the pressure fluctuation signals on the inner surface of the pipe. To estimate the flow rate, at first a cross-correlation function is applied to the two pressure fluctuation signals located at different positions in the down stream for calculating the time delay between the moving eddies. In order to validate the proposed flow rate estimation method, CFD analyses for the internal turbulence flow in pipe are conducted with a fixed flow condition, where the pressure fluctuation signals on the pipe inner surface are simulated. And then the average flow velocity of the large scale eddy is to be estimated. The estimated flow velocity is turned out to be similar to the fixed (known) flow rate.

• 상하수도학회지
• /
• 제22권2호
• /
• pp.239-243
• /
• 2008

The fluctuation of inlet flow to a water treatment plant makes a serious problem that it can change the outlet flow-rate from each process abruptly, and ultimately occur the detachment of the attached particles inside each unit process. Also, since it takes very short time for the surface wave occurred from the fluctuation of inlet flow to reach the latter processes, it is impossible for operators to cope with that stably. Therefore this study was conducted to suggest the methodology for accurately predicting the travel time of surface wave occurred from the fluctuation of inlet flow to reach the latter process. Through the experiment, which was carried out for the full-scale water treatment plants(capacity : 2,000m3/d), it could be confirmed that the flow rate fluctuation from equalization tank produce the surface wave. And the wave transfer velocity is a function of the hydraulic radius and the length of each open type tanks which are comprised in the latter processes.