• Journal of Electrical Engineering and information Science
• /
• v.3 no.2
• /
• pp.251-260
• /
• 1998

A DSP-based robust nonlinear speed control of a permanent magnet synchronous motor(PMSM) which is robust to unknown parameter variations and speed measurement error is presented. The model reference adaptive system(MRAS) based adaptation mechanisms for the estimation of slowly varying parameters are derived using the Lyapunov stability theory. For the disturbances or quickly varying parameters. a quasi-linearized and decoupled model including the influence of parameter variations and speed measurement error on the nonlinear speed control of a PMSM is derived. Based on this model, a boundary layer integral sliding mode controller to improve the robustness and performance of the nonlinear speed control of a PMSM is designed and compared with the conventional controller. To show the validity of the proposed control scheme, simulations and experimental works are carried out and compared with the conventional control scheme.

• Journal of Korean Society for Atmospheric Environment
• /
• v.10 no.2
• /
• pp.116-123
• /
• 1994

The E- $\varepsilon$ turbulence numerical model was applied to a flow around triangular ridge in neutral boundary layer. Scale of cavity region, mean velocity, Reynolds stress and eddy diffusivity were investigated. The height of cavity region was in satifactory agreement with the wind tunnel data while the length of cavity region was underestimated. The man wind velocities outside the cavity region were well Predicted by the model, however in cavity region the mean wind velocities of wind tunnel data were larger than the model results Reynolds stress of cavity region was overestimated by the model. The eddy diffusivity of wake region was strongly modified under the influence of triangular ridge. The local minimum of the eddy diffusivity was occured in the lee of the ridge top.

• Journal of Korean Society for Atmospheric Environment
• /
• v.20 no.E2
• /
• pp.43-52
• /
• 2004

A total of 10 boundary layer sampling events over the Pacific Ocean were analyzed for the purpose of defining the sea-to-air $CH_3$I flux using a mass balance photochemical model. These events were recorded on the National Center for Atmospheric Research (NCAR) C-130 aircraft as part of the Aerosol Charac-terization Experiment (ACE 1). The latitude range, covered by these events, was 2$^{\circ}$ N to 55$^{\circ}$ S. The flux ranges were 4 to 33 nmol m$^{-2}$ day$^{-1}$ , with an average value of 11$\pm$8 nmol m$^{-2}$ day$^{-1}$ . This study also indicated that the current approach to estimate the flux was not systematically different from the sea-air exchange model.

• Proceedings of the Korean Society of Agricultural Engineers Conference
• /
• 2000.10a
• /
• pp.425-430
• /
• 2000

In the analysis of deformation in which the stiffness is greatly different between the adjacent materials, the desired results have been obtained by using the interface element method compared with those secured by the conventional method of the concept of continua. This study deals with the deformation analysis of soft foundation by the introduction of interface element. The physical conditions of interface element are divided into three categories by Mohr-Coulomb failure criterion ie. sliding, separation, and contact. Finally the accuracy of the program proposed in this paper is proved highly accurate by performing the comparison of the theoretical values numerical results of a model element with simplified boundary conditions.

• Journal of the Korean institute of surface engineering
• /
• v.24 no.4
• /
• pp.187-195
• /
• 1991

Adhesion strength of electroless-plated Ni, Ni-P and Cu deposites on alumina substrate has been studied. Grain boundary spaces produced on the substrate surface by etching treatment provided anchoring sites for enhancing the adhesion strength. Adhesion strengths of Ni-P and Ni deposit were higher than that of Cu deposit, because of higher initial nucleation rates than the latter. The electroless-plated Ni-P and Ni underlayer improved the adhesion strength of the Cu deposit. In could be attributed to the enhanced adhesion between the substrate and those underlayers as well as the satisfactory adhesion between Cu deposits and those underlayers. Heat treatment was also conducted in order to enhance the adhesion strength of Cu layer. The strength was enhanced by about 19% when the treatment was conducted at $150^{\circ}C$ for 2 hours. The enhancement was attributed to relief of internal stress and release of hydrogen.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.8 no.1
• /
• pp.65-75
• /
• 1996

A pilot plant, which is simplified the hot water heating control system of a large scale residential building, is used to investigate the effects of control methods and operating conditions on the system performance and to compare control characteristics. Digital variable structure controller(DVSC) and digital PI controller are implemented to control the speed of the circulating pump for the pilot plant using PC. For the DVSC, a control algorithm is suggested, which using a nonlinear sliding surface and a PID sliding surface outside and inside of output error boundary layer, respectively. Smith predictor algorithm is used for the compensation of long dead time. The suggested DVSC yields improved control performance compared with existing DVSC using linear sliding surface only. the system responses with the suggested DVSC shows good responses without overshoot for various operating conditions and robust under external disturbances compared with digital PI controller.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.7 no.1
• /
• pp.20-29
• /
• 1995

A theoretical model for film condensation of a vapor including a relatively lighter noncondensable gas on a horizontal tube has been formulated on the basis of the conservation laws and other fundamental physical principles. The model is applied to the prediction of the condensation heat transfer characteristics for the Freon vapor in the presence of air on a horizontal tube. Calculated results for the mean heat transfer coefficient, which is shown to depend strongly on the bulk concentration of air, are in good agreement with the available experimental results for a range of operating conditions. The distributions of physical quantities along the surface of tube are also calculated, such as the boundary layer thickness and local heat transfer coefficient. The present model is readily reduced to the Nusselt model as the bulk concentration of air decreases to zero. Therefore, the transition from the condensation of pure vapor to that of vapor-air mixture occurs continuously not abruptly.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.7 no.1
• /
• pp.13-19
• /
• 1995

An experimental investigation has been made for flow in a circular cylinder with a rotating bottom disk. Flow system considered in this paper is a characteristic model of interior flows of an electric washing machine. Flows in a tub of an electric washing machine are driven by a rotating bottom disk called a pulsator. The simple and characteristic model was composed of a circular cylinder with impulsively rotating endwall disk and a viscous fluid in it. Rotational motion of the pulsator is periodic and alternative in rotation direction. The flow field in the interior region is governed by a horizontal boundary layer forms on the impulsively rotating disk. Experimental approach was accomplished by adopting an image processing technique for velocity measurements. Comprehensive details of the flow structure are presented. Also a meridional circulation is obtained by tracking image particles suspended in the fluid. Flow structure and data are successfully procured for this complex rotating flow field.

• Journal of the Society of Naval Architects of Korea
• /
• v.41 no.1
• /
• pp.47-54
• /
• 2004

The friction drag reduction of a ship is of prime importance for the design and production of high-valued/high-tech ship. Thus, this study carried out the development of reliable numerical tools to identify the friction drag reduction mechanism for turbulent boundary layer on the ship surface and to deduce the optimum reduction technique by numerical experiment. The developed LES and DNS numerical tools were applied to simulate the turbulent channel flow These results were very well matched with previous results not only qualitatively but also quantitatively. The parallelization using MPI (Message Passing Interface) technique implemented in the developed code to speed up the simulation and to obtain the accurate results from the fine grid system was testified its computational efficiency.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.3 no.4
• /
• pp.16-24
• /
• 1966

The LASER Amplifier is treated in the manner of a Fabry-Perot Resonator with an active media, five layers are considered: air, reflector, active medium(ruby), reflector and air. One dimensional scalar wave equations are derived using the method of boundary value probrems in which it is assumed that incident coherent radiation falls normally on the surface wall. All equations are treated from the transient analysis point of view using the Laplace transform nethods, and are arranged steady state region as an amplifier and transient region as a self excited oscillator. Also some remarks are given on the design problem of LASER amplifier in connection with the transient terms involved.