• Journal of the Korean Institute of Intelligent Systems
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• v.14 no.5
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• pp.648-654
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• 2004

The Mass Flow Controller(MFC) has become crucial in semiconductor manufacturing equipments. It is an important element because the quality and the yield of a semiconductor process are decided by the accurate flow control of gas. Therefore, the demand for implementing the high speed and the highly accurate control of MFCs has been increasing. It is hard to find an article of the control algorithm applied to MFCs. But, it is known that commercially available MFCs adopt PID control algorithms. Particularly, when the system detects the flow by way of heat transfer, the MFC control problem includes the slow response and the nonlinearity. In this paper, MFC control algorithm with a superior performance to the conventional PID algorithm is discussed and the superiority is demonstrated through the experiment. A fuzzy controller was utilized in order to compensate the nonlinearity and the slow response, and the performance is compared with that of an MFC currently available in the market. The control system, in this paper, consists of a personal computer, the data acquisition board and the control algorithm carried out by LabWindows/CVI program on the PC. In addition, a method of estimating the actual flow from the sensor output with the slow response is presented. In conclusion, according to the result of the experiment, the proposed algorithm shows better accuracy and is faster than the conventional controller.

• Journal of Hydrogen and New Energy
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• v.20 no.5
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• pp.371-377
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• 2009

Backfire characteristics for hydrogen fueled free piston engine with uni-flow scavenging is investigated with different stroke, exhaust vlave openning timing and fuel-air equivalence ratio by using RICEM (Rapid Intake Compression Expansion Machine) for combustion research of free piston engine. As results, it is found that backfire can be occurred due to slow combustion of unhomogeneous mixture in the piston crevice volume or/and in the cylinder near piston head. And the more stroke of free piston H2 engine with uni-flow scavenging is short the more opening timing of exhaust valve have to be advanced to control backfire.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.46-47
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• 2003

Direct numerical simulations are performed for a turbulent flow subjected to a sudden change in pressure gradient. The calculations are started from a fully-developed turbulent channel flow at $Re_{\tau}=180$. The pressure gradient of the channel flow is then changed abruptly. The responses of the turbulence quantities (e.g., turbulence intensities, Reynolds shear stress, and vorticity fluctuations) and the near-wall turbulence structure to the pressure gradient change are investigated. It is found that there are two different relaxations: a fast relaxation at the early stage and a slow one at the later stage. The early response of the velocity fluctuations shows an anisotropic response of the near-wall turbulence.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.4
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• pp.324-331
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• 2004

Particle Image Velocimetry (PIV) measurements have been carried out to investigate the pulsatile flow characteristics in a triangular grooved channel. The results showed that a vortex was generated at the tip of the groove and flowed into the groove rotating inside during the acceleration phase of the main stream promoting the mixing of the fluid. Then, at the deceleration phase of the main stream, the vortex entrained fluid from the relatively slow moving main stream to grow bigger than the groove size. Finally the vortex was ejected to the main stream carrying the fluid away from the groove, resulting in the enhancement of mixing between the stagnant fluid in the groove and the main stream in the channel. It was found that the fluid mixing enhancement is maximized when the pulsatile period is the same as the time duration which the vortex takes to grow larger enough to fill the groove and to be ejected to the main stream.

• Korean Journal of Ecology and Environment
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• v.45 no.2
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• pp.200-209
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• 2012

The current of the water body is very important information for the water quality management on reservoirs. It is applied to hydraulics and water quality model for simulation. In this regard, the current characteristic of water body is the basic information that can be used to predict various conditions. However, it is very slow flowing and is affected by the reservoir operations and external factors. As such, an accurate measurement of the current is a difficult problem. In order to measure the water current, we constructed a drifter. According to the result of flow survey at Yongdam reservoir, 5m and 10 m depth layer flow was investigated from the upstream to the downstream, during a flood period. Maximum flow rate of 5 m depth is 13.8 cm $sec^{-1}$ and 10 m depth shows 4 cm $sec^{-1}$, respectively. But 2m depth shows a backward flow and maximum flow rate is 4 cm $sec^{-1}$. Density currents flow plays the role of back flow in reservoirs. Flow velocity in the reservoir was measured in the range of 1~2 cm $sec^{-1}$, at normal flow season, and the flow direction were different for each survey. This phenomenon occurs because the reservoir volume is very large, compared to the inflow and outflow volume.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.852-855
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• 2003

Gas-Assisted Injection Molding(GAIM) process, that can be used to provide a hollow shape in a molding, is a variant of the conventional injection molding process. GAIM has many advantages such as reduction of material, sink mark. warpage. and lower injection pressure. Thus, GAIM has been widely applied in the industry to make moldings with a hollow channel such as handles, TV frames and so on. On the other hand, GAIM has some disadvantages such as slow cooling time and flow marks. In the disadvantages, hot gas core causes slow cooling of a molding and the overflow. which is to prevent flow mark. is waste of materials. To solve these problems, we developed a new GAIM system that we called RGIM(Reverse Gas Injection Molding). The RGIM has two special units; one is the overflow buffer, which is used for reduction of a material, and the other tile air unit, which is used for faster cooling of a molding. We conducted an experiment and simulation to verify the efficiency of the RGIM system. Through experiments and simulation, we confirmed the effectively operating of the RGIM system and extracted the optimum process conditions.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.148-153
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• 2017

During natural ageing of HTPB propellant undergoes a series of slow physico-chemical degradation reactions. By using accelerated ageing conditions it is possible to simulate the material behaviour at different time-temperature conditions especially focused on the in-service conditions. Ageing behaviour of HTPB propellant were investigated using HFC(Micro-Heat Flow Calorimeter) is universal technique for measuring the rate of slow chemical and physical processes in long-term storage.

• Advances in aircraft and spacecraft science
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• v.3 no.3
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• pp.271-298
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• 2016

In this paper, we study a problem of passive suppression of helicopter Ground Resonance (GR) using a single degree freedom Nonlinear Energy Sink (NES), GR is a dynamic instability involving the coupling of the blades motion in the rotational plane (i.e. the lag motion) and the helicopter fuselage motion. A reduced linear system reproducing GR instability is used. It is obtained using successively Coleman transformation and binormal transformation. The analysis of the steadystate responses of this model is performed when a NES is attached on the helicopter fuselage. The NES involves an essential cubic restoring force and a linear damping force. The analysis is achieved applying complexification-averaging method. The resulting slow-flow model is finally analyzed using multiple scale approach. Four steady-state responses corresponding to complete suppression, partial suppression through strongly modulated response, partial suppression through periodic response and no suppression of the GR are highlighted. An algorithm based on simple criterions is developed to predict these steady-state response regimes. Numerical simulations of the complete system confirm this analysis of the slow-flow dynamics. A parametric analysis of the influence of the NES damping coefficient and the rotor speed on the response regime is finally proposed.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.5
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• pp.59-65
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• 2018

During natural aging, hydroxyl-terminated polybutadiene(HTPB) propellant undergoes a series of slow physico-chemical degradation reactions. By using accelerated ageing conditions it is possible to simulate the material behavior at different time-temperatures focusing on in-service conditions. Aging behaviors of HTPB propellant are investigated using HFC(heat flow calorimeter), a universal technique for measuring the rate of slow chemical and physical processes in long-term storage.

• Nuclear Engineering and Technology
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• v.34 no.4
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• pp.382-395
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• 2002

An experimental study on transient critical heat flux (CHF) under flow coastdown has been performed for the water flow in a non-uniformly heated vertical annulus under low flow and a wide range of pressure conditions. The objectives of this study are to systematically investigate the effect of the flow transient on the CHF and to compare the transient CHF with steady-state CHF The transient CHF experiments have been performed for three kinds of flow transient modes based on the coastdown data of a nuclear power plant reactor coolant pump. At the same inlet subcooling, system pressure and heat flux, the effect of the initial mass flux on the critical mass flux can be negligible. However, the effect of the initial mass flux on the time-to- CHF becomes large as the heat flux decreases. The critical mass flux has the largest value for slow flow reduction rate. There is a pressure effect on the ratio of the transient CHF data to steady-state CHF data. Except under low system pressure conditions, the flow transient CHF was revealed to be conservative compared with the steady-state CHF data. Bowling CHF correlation and thermal hydraulic system code MARS show promising results for the prediction of CHF occurrence .