• Journal of Mechanical Science and Technology
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• 제14권5호
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• pp.547-552
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• 2000

The objective of this paper is to present a modified fractional step method of keeping a constant mass flow rate in spatially periodic flows, because original fractional step methods do not precisely keep the mass flow rate constant in time. In the modified method, the mean and fluctuating pseudo-pressure gradients are separately obtained at each time step. This method is successfully applied to channel and pipe flows and shown to be suitable for maintaining a constant mass flow rate in time.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2002년도 추계학술대회 논문집
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• pp.35-38
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• 2002

Variations of temperature and velocity fields in a Hele-Shaw Convection Cell (HSC) were measured using a holographic interferometry and PIV technique with varying Rayleigh number. Experimental results show a steady flow pattern at low Rayleigh numbers and a time-dependent periodic flow at high Rayleigh numbers. Two different measurement methods of holographic interferometry, double-exposure method and real-time method, were employed to measure the temperature field variations of HSC convective flow. In the double-exposure method, unwanted waves can be eliminated and reconstruction images are clear, but transient flow structure cannot be observed clearly. On the other hand, transient flow can be observed and reconstructed well using the real-time method. PIV results show that flow inside the HSC is periodic and the oscillating state is well matched with the temperature field results. The holographic interferometry and PIV techniques employed in this study are useful for analyzing the unsteady convective thermal fluid flows.

• 지질공학
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• 제27권1호
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• pp.59-66
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• 2017

최근들어 발생하는 강우는 지금까지의 강우특성과 비교하여 여름철에 단기간 집중적으로 내리는 형태로 바뀌고 있다. 2011년 강원도 춘천지역에서는 이러한 집중강우로 인해 많은 산사태가 발생하였으며, 이로 인해 재산피해와 인명피해를 야기시켰다. 본 연구의 목적은 강우에 의한 산사태 물질의 이동에 대한 특성을 분석하기 위해서 현장 자료와 수치해석 자료를 활용하여 시간에 따른 특성의 변화 및 강우량에 따른 특성의 변화를 분석하는 것이다. 본 연구에서는 항복응력 값의 변화를 통해서 강우량을 재현하였으며, 이를 통해서 어떠한 거동 특성을 보이는지 해석하였다. 그 결과 많은 강우에 의해 항복응력 값이 낮아지는 경우가 빠른 속도의 이동형태를 보이고 동시에 넓은 지역에 걸쳐 확산되는 특성을 확인하였으며, 이러한 결과는 현장에서 확인된 토석류의 흔적과 매우 유사하다는 것을 확인하였다. 본 연구를 통해서 산사태 발생 당시의 토석류 최대 속도 및 최대 두께 등을 파악하는 것이 가능하다.

• 대한기계학회논문집
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• 제18권7호
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• pp.1840-1850
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• 1994

Enhancement of numerical algorithms for low speed compressible flow will be considered. Contemporary time-marching algorithm has been widely accepted and applied as the method of choice for transonic, supersonic and hypersonic flows. In the low Mach number regime, time-marching algorithms do not fare as well. When the velocity is small, eigenvalues of the system of compressible equations differ widely so that the system becomes very stiff and the convergence becomes very slow. This characteristic can lead to difficulties in computations of many practical engineering problems. In the present approach, the time-derivative preconditioning method will be used to control the eigenvalue stiffness and to extend computational capabilities over a wide range of flow conditions (from very low Mach number to supersonic flow). Computational capabilities of the above algorithm will be demonstrated through computation of a variety of practical engineering problems.

• 한국시뮬레이션학회논문지
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• 제8권4호
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• pp.73-87
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• 1999

Order Review/Release (ORR) System is the linkage between planning system and actual production. Reduction of the waiting time on the machines, work in process and lead time variation may be achieved by adopting ORR strategies. But researchers on the ORR do not agree on the effectiveness of ORR. Some say that the overall system flow time may be increased if ORR is adopted, but others say that ORR can reduce work in process, flow time and variation of flow time. The objective of this research is to clarify under what environments order release strategy is effective. Simulation study was conducted in a hypothetical job shop. The experimental results show that dispatching rule is much more important than ORR is in controlling the shop floor. But the results indicate that ORR can reduce mean shop flow time, average work in process and variation of shop flow time under such environments where utilization level is high and planned order is weekly released to the order pool. And the results also show that the effect of plan smoothing on the ORR is insignificant, which is inconsistent with the results of the previous researches.

• 기술경영경제학회:학술대회논문집
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• 기술경영경제학회 1999년도 제16회 동계학술발표회 논문집
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• pp.296-327
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• 1999

Nowadays, there is a huge need of an extensive study to understand features and behavior modes of consumers who have an indefinite potential of purchase and to make EC a bullish market, Recently, the flow construct has been proposed as important for understanding consumer behavior on the cyber space. The purpose of this study is threefold. To investigate (1) the effect of the flow experience when navigating Internet shopping-mall sites and Internet on purchase intention and relational factors of this (2) the difference in the flow experiences between during the time of navigating Internet and during the time of navigating Internet shopping-mall sites. (3) the difference in purchase intention and relational factors of this between an experiential flow and a purposeful flow. The results show that (1) increase of the purchase intention on EC (or relational factors of this) in proportion to the degree of cognition of users' flow experience (2) By the separate motive of searching Internet shopping-mall sites, the flow experiences during the time of navigating Internet lead to different results (3) Although the difference in the purchase intention on EC between subjects is nonsignificant, it suggests that we need to focus on the fact that the correlation between the purchase intention on EC and the purposeful flow experience on Internet shopping-mall sites is greater than any other correlation. In the end of this study, The theoretical and practical implications of the study, limitations of the study, and future research implications are discussed.

• 산업기술연구
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• 제6권
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• pp.19-31
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• 1986

The residence time distribution of liquid flow in a 4.0cm diameter column packed with porous $Al_2O_3$ spheres of 0.37cm diameter were measured with pulse injections of a tracer under cocurrent trickling flow conditions. The mean residence time of liquid flow and liquid hold-up calculated by the transient curve of tracer were unaffected by gas flow rates under experimental ranges of liquid flow rates from 2.4 to $4.5(kg/m^2\;sec)$ and gas flow rates from 0 to $0.13(kg/m^2\;sec)$. The axial dispersion coefficient of liquid stream and apparent diffusivity of tracer in a micropore of solid particle were estimated from the response curve of tracer. The calculated Peclet No. were increased in ranges of 68-to 82 with a increasing of liquid mass velocity, and the external effective contacting efficiency between liquid and solid which can be expressed. by $(D_i)_{app}/D_i$ varied in ranges of 0.54 to 0.68 depending on the liquid flow rates. The gas to liquid(water) volumetric mass transfer coefficient were determined from desorption experiments with oxygen at $25^{\circ}C$ and 1 atm. The measured mass transfer coefficients were increased with liquid flow rates and the effect of gas flow rates on the mass transfer coefficient was insignificant.

• 정보통신설비학회논문지
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• 제8권4호
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• pp.170-181
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• 2009

When a slow-moving vehicle occupies one of the lanes of a multi-lane highway, it often causes queuing behind, unlike one is caused by an actual stoppage on that lane. This happens when the traffic flow rate upstream from the slow vehicle exceeds a certain critical value. This phenomena is called as the Moving Bottleneck, defined by Gazis and Herman (1992), Newell (1998) [3], and Munoz and Daganzo (2002), who conducted the flow estimates of upstream and downstream and considered slow-moving vehicle speed and the flow ratio exceeding slow vehicle and the microscopic traffic flow characteristics of moving bottleneck. But, a study of delay on moving bottleneck was not conducted until now. So this study provides a average delay time model related to upstream flow and the speed of slow vehicle. We have chosen the two-lane highway and homogeneous traffic flow. A slow-moving vehicle occupies one of the two lanes. Average delay time value is a result of AIMSUN[9], the microscopic traffic flow simulator. We developed a multiple regression model based on that value. Average delay time has a high value when the speed of slow vehicle is decreased and traffic flow is increased. Conclusively, the model is formulated by the negative exponential function.

• Journal of Advanced Marine Engineering and Technology
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• 제21권5호
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• pp.491-502
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• 1997

This paper describes a theoretical and exprimental investigation of the pressure - time histories of some basic internal combustion engine exhaust systems. The program package is utilized the method of characteristics to solve the general equations of one - dimensional unsteady gas flow. This analysis is then combined with boundary models, based on quasi - steady flow approach, to give a complete treatment of the flow behavior in the exhaust system. Using a rotary valve exhaust simulator, experimental pressure - time histories were obtained. The predictions are com¬pared with measured results and show a high degree of correlation in amplitude and phasing.

• Journal of Biosystems Engineering
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• 제23권3호
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• pp.211-218
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• 1998

A variable flow-controlled boom sprayer was developed and evaluated. Field tests were conducted to evaluate the adoptability of the sprayerr with optimal conditions. Negative response time was obtained from the field test because pump and PTO were interlocked with the speed of sprayer. Another reason for the negative value was due to the definition of the response time. With constant on-time control, the system was unstable at the conditions of small tolerance and long control interval. The performances of the spray system were stable and accurate. The stable and synchronous responses were achieved with a variable on-time control. The flow control system with an optimal condition (1.0 sec of control interval, 2 of damping ratio, 1% of tolerance) provided the proper performance for uniform spraying. A standard operating procedure of the flow compensating boom sprayer for the ground speed variation was presented and recommended.