• 한국전산유체공학회:학술대회논문집
• /
• 2006.10a
• /
• pp.66-69
• /
• 2006

In the present study, we propose a virtual boundary method for simulation of massive inextensible flexible strings immersed in viscous fluid flow. The fluid motion is governed by the Navier-Stokes equations and a momentum forcing is added in order to bring the fluid to move at the same velocity with the immersed surface. A massive inextensible flexible string model is described by another set of equations with an additional momentum forcing which is a result of the fluid viscosity and the pressure difference across the string. The momentum forcing is calculated by a feedback loop. Simulations of several numerical examples are carried out, inlcuding a hanging string which starts moving under gravity without ambient fluid, a string swimming within a uniform flow and a uniform flow over two side-by side strings. The numerical results agree well with the theoretical analysis and previous experimental observations. Preliminary results of a swimming elongated fishlike body will also be presented.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1996.11a
• /
• pp.1053-1057
• /
• 1996

The purpose of this study is to bring out the optimal design factors which effect on dynamic characteristics in the design of proportional flow control valve with fast response characteristics, and to verify the validity of the design factors In this study, force feedback type flow control valve with nozzle-flapper is studied. And, the influences which fixed orifice, nozzle diameter, and maximum displacement between nozzle and flapper effect on dynamic characteristics are analyzed. We have done simulations using the optimal design factors and simulink(Matlab) as a simulation tool, and verified the validity of our simulations by means of comparison our simulation results with an experimental results of another similar valve.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.7 no.9
• /
• pp.36-47
• /
• 1999

Three-way catalyst converter, cleaning up the exhaust gas contamination of SI engine, has the best efficiency when A/F ratio is near the stoichiometry . The feedback control using oxygen sensors in the exhaust manifold has limits caused by the system delays. So the accurate measurement of air flow rate to an engine is essential to control the fuel injection rate especially on transient condition like the rapid throttle opening and closing. To measure the rapid change of flow rates. the air flow meter for the engine requires quick response, flow reversal detection, and linearity . Tjhe proposed integration type air flow meter (IFM), composed of an ultrasonic flow meter with an integration circuit, has significantly improved the measurement accuracy of air mass inducted through the throttle body. The proposed control method estimated the air mass at the cylinder port using the measured air mass at the throttle . For the fuel dynamic model, the two constant fuel model is introduced . The control parameters from air and fuel dynamics are tuned to minimize the excursion of the air fuel ratio. As a result A/F ratio excursion can be reduced within 5% when throttle rapidly opens and closes at the various engine conditions.

• Asia pacific journal of information systems
• /
• v.13 no.4
• /
• pp.207-227
• /
• 2003

The purpose of this research is to identify if psychological temptation, site quality and sense of community influence user's flow and addiction and to identify causalities among flow, addiction, customer satisfaction and customer loyalty in online industry. Many previous researches in the area of online games have been carried out about addiction by psychologist and about the development of related technologies by scientists. There are only a few studies about the customer satisfaction from the online business perspective. However, this research is different from the previous ones in the sense that both flow and addiction are considered in the study of the relationship between customer satisfaction/loyalty and flow/addiction in the area of online industry. The empirical results of high-order factor analysis indicate that six independent variables such as design, information, feedback, impulsiveness and motivation have converge three second-order variables such psychological temptation, site quality and sense of community. Consequently, site quality and sense of community have impacts on the flow, while on the other hand, psychological temptation has impacts on the addiction. Conclusively, customer satisfaction and loyalty are positively related not with the addiction but with the flow. Besides, customer loyalty is significantly influenced by the flow and the customer satisfaction. This indicates that companies in the online game industry have to develop a strategy for the flow which is more socially and ethically allowable than the addiction.

• Journal of Electrical Engineering and Technology
• /
• v.12 no.4
• /
• pp.1357-1368
• /
• 2017

The lack of controllability over the wind causes fluctuations in the output power of the wind generators (WGs) located at the wind farms. Distribution Static Compensator (DSTATCOM) equipped with Battery Energy Storage System (BESS) can significantly smooth these fluctuations by injecting or absorbing appropriate amount of active power, thus, controlling the power flow of WGs. But because of the component aging and thermal drift, its harmonic filter parameters vary, resulting in performance degradation. In this paper, Quantitative Feedback Theory (QFT) is used as a robust control scheme in order to deactivate the effects of filter parameters variations on the wind power generation power smoothing performance. The proposed robust control strategy of the DSTATCOM is successfully applied to a microgrid, including WGs. The simulation results obviously show that the proposed control technique can effectively smooth the fluctuations in the wind turbines' (WT) output power caused by wind speed variations; taking into account the filter parameters variations (structural parameter uncertainties).

• Transactions of the Korean hydrogen and new energy society
• /
• v.18 no.3
• /
• pp.292-300
• /
• 2007

A dynamic system model of a proton exchange membrane fuel cell(PEMFC) has been developed. The PEMFC of this study has large active area with water cooling in order to simulate the performance of the commercially viable PEMFC system for the transportation. A PEMFC stack model is a transient thermal model which is respond to the dynamic change of the coolant temperature and the flow rate. The dynamic cooling system model has been developed to determine the coolant flow rate and the coolant temperature. Prior to the system level study, thermal management criteria have been set up and brought to the control command of the cooling system. Since the system model is designed to evaluate the effect of thermal management on the system performance, it is attempted to determine the proper control algorithm of the cooling system so that the PEMFC system is working on the thermal management criteria. As a result of simulation, feedback controlled cooling system consumes less power and produce more power comparing with that of conventionally controlled cooling system.

• Journal of Ocean Engineering and Technology
• /
• v.18 no.5
• /
• pp.15-21
• /
• 2004

An edge tone is the discrete tone or narrow-band sound produced by an oscillating free shear layer, impinging on a rigid surface. In this paper, we present a 2-D edge tone to predict the frequency characteristics of the discrete oscillations of a jet-edge feedback cycle, using the finite difference lattice Boltzmann method (FDLBM). We use a modified version of the lattice BGK compressible fluid model, adding an additional term and allowing for longer time increments, compared to a conventional FDLBM, and also use a boundary fitted coordinates system. The jet is chosen long enough in order to guarantee the parabolic velocity profile of the jet at the outlet, and the edge consists of a wedge with an angle of ${\alpha}$ = 23. At a stand-off distance, the edge is inserted along the centerline of the jet, and a sinuous instability wave, with real frequency, is assumed to be created in the vicinity of the nozzle and propagates towards the downstream. We have succeeded in capturing very small pressure fluctuations, resulting from periodical oscillations of a jet around the edge. The pressure fluctuations propagate with the speed of sound. Its interaction with the wedge produces an non-rotational feedback field, which, near the nozzle exit, is a periodic transverse flow, producing the singularities at the nozzle lips.

• The Journal of the Korea Contents Association
• /
• v.19 no.10
• /
• pp.522-534
• /
• 2019

The purpose of this study is to investigate the interaction factors(learning motivation, concrete feedback, learner's control) and affordance factors (aesthetics, playfulness, stability) that influence flow in e - learning. This study collected 236 survey data from e-learning users. The data was analyzed the statistical relationships among the variables using the SPSS21 and AMOS21. The measurement model was reliable and valid, and the structual model was good. The result shows that interaction factors (concrete feedback, learner's control) and affordance factor (playfulness) influence on flow. Flow has a significant effect on satisfaction. Especially the effect of playfulness on flow is meaningful. Playfulness is one of the most important factors leading to the flow state of humans. The contribution of this study is to find the factors influencing flow in the interaction between learners and computer in e-learning. It can be used to provide an entertainment experience that can enhance the satisfaction of consumers in the Internet environment by finding the antecedents that affect the flow in computer - human interaction.

• 한국전산유체공학회:학술대회논문집
• /
• 2005.10a
• /
• pp.235-238
• /
• 2005

The unsteady supersonic flow over two- and three-Dimensional cavities has been analyzed by the integration of unsteady Reynolds-Averaged Navier-Stokes(RANS) with the k - w turbulence model. The unsteady flow is characterized by the periodicity due to the mutual relation between the shear layer and the internal flow in cavities. Numerical method is upwind TVD scheme based on the flux vector split with the Van Leer limiters, and time accuracy is used explicit 4th stage Runge-Kutta scheme. Cavity flows are Comparison of two- and three-dimensional. The cavity has a L/D ratio of 3 for two-dimensional case. and same L/D and W/D ratio is 1 for three-dimensional case. The Mach and Reynolds numbers are held constant at 1.5 and 450000 respectively. For the three-dimensional case, the flow field is observed to oscillate in the 'shear layer mode' with a feedback mechanism that follow Rossiter's formula. On the other hand, the self-sustained oscillating flow transitions to a 'wake mode' for the two-dimensional simulation, with more violent fluctuations inside the cavity.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.36 no.12
• /
• pp.1217-1222
• /
• 2012

A wall flow sensor has been used for feedback flow control and wall shear stress measurement. In this study, we developed a new wall flow sensor by combining the PIV algorithm and the micro image sensor used in an optical mouse. The feasibility of the wall flow sensor was investigated by using simulated fluid flow experiments. Compared with the quadrature signal from imaging devices, the accuracy of the wall flow velocity measurement was improved and the dynamic range increased. In addition, the depth information of particles was also measured by using the defocusing imaging technique.