• Coupled systems mechanics
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• 제7권4호
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• pp.407-420
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• 2018

In solid-liquid two phase flow, the knowledge of how descending solid particles affected by the presence of downstream wall is important. This work studies at what interstitial distance the velocity of a vertically descending sphere is affected by a downstream wall as a consequence of wall-modified hydrodynamic forces through a validated dynamic model. This interstitial distance-the hydrodynamic coupling distance ${\delta}_c-is$ found to decay monotonically with the approach Stokes number St which compares the particle inertia to viscous drag characterized by the quasi-steady Stokes' drag. The scaling relation ${\delta}_c-St-1$ decays monotonically as literature below the value of St equal to 10. However, the faster diminishing rate is found above the threshold value from St=10-40. Furthermore, an empirical relation of ${\delta}_c-St$ shows dependence on the drop height which clearly indicates the non-negligible effect of unsteady hydrodynamic force components, namely the added mass force and the history force. Finally, we attempt a fitting relation which embedded the particle acceleration effect in the dependence of fitting constants on the diameter-scaled drop height.

• Ocean Systems Engineering
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• 제8권2호
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• pp.167-182
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• 2018

RTI (Rayleigh-Taylor instability) is investigated by a multi-liquid MPS (Moving Particle Semi-implicit) method for both viscous and inviscid flows for various density differences, initial-disturbance amplitudes, viscosities, and surface tensions. The MPS simulation can be continued up to the late stage of high nonlinearity with complicated patterns and its initial developments agree well with the linear theoretical results. According to the relevant linear theory, the difference between inviscid and viscous fluids is the rising velocity at which upward-mushroom-like RTI flow with vortex formation is generated. However, with the developed MPS program, significant differences in both growing patters and developing speeds are observed. Also, more dispersion can be observed in the inviscid case. With larger Atwood (AT) number, stronger RTI flows are developed earlier, as expected, with higher potential-energy differences. With larger initial disturbances, quite different patterns of RTI-development are observed compared to the small-initial-disturbance case. If AT number is small, the surface tension tends to delay and suppress the RTI development when it is sufficiently large. Interestingly, at high AT number, the RTI-suppressions by increased surface tension become less effective.

• 한국분무공학회지
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• 제16권2호
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• pp.76-81
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• 2011

A fuel injection system which is operated with a real vehicle driving simulation was developed as an alternative to a vehicle test for the fuel injectors. The sensor signals that are supplied to the ECU were measured and recorded as a data file for a vehicle driven in FTP-75 mode in a chassis dynamometer. The imperative sensor signals of the throttle position, vehicle speed, engine speed, crank position, cam position, intake air flow, and cooling water and intake air temperature were reconstructed using FPGA DAQ boards and a PXI computer. The scanning results showed good agreement with the input signals that were reconstructed. The ECU HILS system operated successfully to drive six fuel injectors, which injected fuel in the same pattern as if they were mounted in the vehicle driven in FTP-75 mode. Also, the fuel injection system developed in this research shows the possibility of application in evaluating the characteristics of fuel injection rate for injectors according to properties of injected fuel with the real driving mode of vehicles.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1999년도 제14차 학술회의논문집
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• pp.288-291
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• 1999

The PID (Proportional-Integral-Derivative) controller is widely used in the industries for more than fifty years with the well known Ziegler-Nichols tuning method and others varieties. However, most of the PID controller being used in the real practice still require trial and error adjustment for each process after the tuning method is done, which is consuming of time and needs the operator experiences to obtain the best results for the controller parameter. In order to reduce the inconvenience in the controller tuning, this paper presents a design of an automatic PID controller parameter analyzer being used as a support instrument in the industrial process control. This analyzer is designed based on the tuning formula of Dahlin to synthesize the PID controller parameter. Using this analyzer, the time to be spent in the trial and error procedures and its complexity can be neglected. Experimental results using PID controller parameter synthesized from this analyzer to the liquid level control plant model and the fluid flow control plant model show that the responses of the controlled systems can be efficiently controlled without any difficulty in mathemathical computation.

• 설비공학논문집
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• 제6권4호
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• pp.399-405
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• 1994

Beacuse of the energy resources exhaustion, the aggravating environmental air pollution and the smoke phenomena etc., the importance of clean gas fuel compared with liquid fuel is highly considered in recent years. The combustion system which consists of porous media is actively studied as a new method for solving above problems. Therefore, excess enthalpy combustion using porous media was interested by many researchers and investigated through numerical and experimental analysis. In this study, the simplified combustor has the unique combustion characteristics of mixture gas preheated effect using radiative and convective heat energy by changing the flow passage of unburned gas with solenoid valves and has the intensive excess enthalpy phenomena As the result of according to reduce equivalence ratio, flame temperature was remarkably higher than adiabatic flame temperature. This show the ability of super-lean combustion.

• Progress in Superconductivity
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• 제5권2호
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• pp.132-135
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• 2004

We fabricated YBCO thick films by using a screen printing method with $Y_2$BaCuO$_{5}$(Y211) and BaCO$_3$ powders on Cu-substrate in $N_2$ atmosphere. Cu-sheathed YBCO thick film process is more simple and economic than YBCO coated conductor methods. The heat treatment is performed in the range of 860 - 875 $^{\circ}C$ for 5 min in the tube furnace of $N_2$ atmosphere. The flow rate of $N_2$ gas is fixed 60 $m\ell$/min. Microstructure and phases of thick films were investigated by optical microscope, X-ray diffraction(XRD) and SEM. At heat-treatment temperature, the thick films were partially melted by liquid reaction between CuO of oxidized copper substrate and the powders screen-printed on Cu-sheath. During the heat-treatment procedure, YBCO superconducting grains nucleate.e.

• 상하수도학회지
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• 제21권6호
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• pp.709-715
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• 2007

The dewaterability of a sludge can be characterized by two ways: the residual moisture content in the sludge cake after dewatering process, and the filtration of the sludge. Time to filter (TTF) represents filtration processes that are special cases of the flow through a solid matrix concept. TTF characterizes a resistance to filtration. The sludge resistance, in turn, can be subdivided into resistances associated with the solid phase and the liquid phase to evaluate the effect of each of the two phases on sludge dewaterability. In order to determine the dewatering characteristics of the water sludge samples, TTF and zeta potential were measured. For these studies cationic polymer was chosen for water sludge dewatering experiments. The zeta potential of thickener sludges neared from minus values to zero values till 4 days after sampling. The dewaterability of thickener sludges using cationic polymer was deteriorated according to the increase of detention time. As the detention time was increased from 4 to 10 days, the optimal dose of the polymer was increased from 4 to 8mg/L. Therefore, the optimal detention time plays an important part for the dewaterability of a sludge.

• 한국결정성장학회지
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• 제5권2호
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• pp.100-108
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• 1995

SOI구조를 얻기 위한 방법의 한가지인 ZMR공정에 있어서 열전달은 계면의 위치와 모양을 결정하는 중요한 역할을 한다. 본 연구에서는 SOI구조를 얻기 위한 ZMR공정중의 열전달 공정을 모사할 수 있는 의사정상상태 2차원 ZMR모델을 수립하였다. 본 모델은 복사, 전도 그리고 대류 열전달을 포함하며, 고/액 계면의 위치를 결정한다. 모델로부터 구한 수치해는 실리콘 기판의 용융부에서의 유동장, 전체 SOR구조에서의 온도장 그리고 실리콘 박막과 기판에서의 고/액 계면의 위치를 포함한다. 여러 공정 변수들의 변화에 따른 온도장과 계면의 형상과 폭의 변화를 알아보았다.

• 한국해양공학회지
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• 제32권4호
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• pp.228-236
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• 2018

The performance of a porous swash bulkhead for the reduction of the resonant liquid motion in a swaying rectangular tank was investigated based on the assumption of linear potential theory. The Galerkin method (Porter and Evans, 1995) was used to solve the potential flow model by adding a viscous frictional damping term to the free-surface condition. By comparing the experimental results and the analytical solutions, we verified that the frictional damping coefficient was 0.4. Darcy's law was used to consider the energy dissipation at a porous bulkhead. The tool that was developed with a built-in frictional damping coefficient of 0.4 was confirmed by small-scale experiments. Using this tool, the free-surface elevation, hydrodynamic force (added mass, damping coefficient) on a wall, and the horizontal load on a bulkhead were assessed for various combinations of porosity and submergence depth. It was found that the vertical porous bulkhead can suppress sloshing motions significantly when properly designed and by selecting the appropriate porosity(${\approx}0.1$) and submergence depth.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2001년도 봄 학술발표회 논문집
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• pp.65-72
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• 2001

Since Pyoungtaek thermal power plant began using natural gas in 1986, the annual using volume has rapidly increased and reached 12.7 million tons in 1999. When the natural gas is cooled to a temperature of approximately -162$^{\circ}$C at atmospheric pressure, it condenses to a liquid called liquefied natural gas(LNG). LNG has a special characters such as odorless, colorless, non-corrosive, and non-toxic. So, LNG storage tank, tanker ship, transfer pipelines are required the special storage and transportation systems and technology. The presently operating LNG terminals are Pyongtaek and Inchon terminals. A total of 19 above-ground LNG storage tanks(100 thousand ㎘ grade) are currently in operation with a sendout capacity of 4,360tons/hour. To meet the growing domestic demand of LNG supply, the Inchon receiving terminal is expanding(six in-ground tank) and constructing a third LNG terminal at Tongyong. In this paper, case study on seepage analysis and countermeasure against increasing the seepage volume of in-ground LNG storage tank excavation work is reported. The results of an additional seepage analysis are presented to verify the design seepage volume of assumption section and seepage volume after curtain-grouting in the slurry wall.