• Proceedings of the KSME Conference
• /
• 2001.11b
• /
• pp.640-645
• /
• 2001

The present study is to investigate the characteristics of the impulse waves discharged from the exit of the convergent and divergent pipes. An experiment is carried out using a shock tube with an open end and is compared to the computation of the axisymmetric, compressible, unsteady Euler equations, which are solved by the second-order total variation diminishing(TVD) scheme. For the computational work, some initial compression waves are assumed inside the pipe so that those are identical to the experimental ones of the shock tube. The results show that the peak pressures of the impulse waves discharged from the exit of convergent and divergent pipes decrease with an increase in the wavelength of the initial compression wave. All of the impulse waves have a strong directivity toward the pipe axis, regardless of the exit type of the pipe employed. The impulse waves discharged from the divergent pipe are stronger than those from the straight pipe, while the impulse waves of the convergent pipe are weaker than those from the straight pipe. It is believed that the convergent pipe can playa role of a passive control to reduce the peak pressure of the impulse wave. The present computations represent the experimented impulse waves with a good accuracy.

• Proceedings of the KSME Conference
• /
• 2001.11b
• /
• pp.634-639
• /
• 2001

The current study addresses experimental and computational work of impulse wave discharged from the exit of two kinds of right-angle pipe bends, which are attached to the open end of a simple shock tube. The weak normal shock wave with its magnitude of Mach number from 1.02 to 1.20 is employed to obtain the impulse wave propagating outside the exit of the pipe bends. A Schlieren optical system visualizes the impulse wave discharged from the exit of the pipe bends at an instant. The experimental data of the magnitude of the impulse wave and its propagating directivity are analyzed to characterize the impulse waves discharged from the exit of the pipe bends and compared with those discharged from a straight pipe. Computational results well predict the experimented dynamic behaviors of the impulse wave. The results obtained show that a right-angle miter bend considerably reduces the magnitude of the impulse wave and its directivity toward to the pipe axis, compared with the straight pipe and right-angle smooth bend. It is believed that the right-angle miter bend pipe can playa role of a passive control against the impulse wave.

• Journal of the Korean Society for Precision Engineering
• /
• v.32 no.9
• /
• pp.773-779
• /
• 2015

The laser Powder Bed Fusion (PBF) system is currently recognized as a leading process. Due to the various materials employed such as thermoplastic, metal and ceramic composite powder, the application's use extends to machinery, automobiles, and medical devices. The PBF system's surface quality of prototypes and processing time are significantly affected by several parameters such as laser power, laser beam size, heat temperature and laminate thickness. In order to develop a more elaborate and rapid system, this study developed a new PBF system and sintering process. It contains a 3-axis dynamic focusing scanner system that maintains a uniform laser beam size throughout the system unlike the $f{\theta}$ lens. In this study, experiments were performed to evaluate the effects of various laser scanning parameters and fabricating parameters on the fusion process, in addition to fabricating various 3D objects using a PA-12 starting material.

• Restorative Dentistry and Endodontics
• /
• v.19 no.1
• /
• pp.180-193
• /
• 1994

The purpose of this study was to observe the sealing ability and durability of All-Bond 2, Gluma Bonding System, Scotch bond 2 and Superbond D-liner which are dentin bonding agents used as desensitizing agents. The durability of the sealing ability of the materials were compared after 0, 140, 420, 840 tooth brushing strokes. 120 extracted teeth were divided into 5 groups and the agents were applied to the exposed dentin. No agents was applied on group I, the control group. Each specimen went through thermocycling from $5^{\circ}$ to $55^{\circ}C$, 200 times. Each group was devide into 4 subgroups and artificial tooth brushing strokes were done for 0, 140, 420, 840 times. Finally the specimens were stored in 0.5 % methylene blue solution for 24 hours in a incubator set at $37^{\circ}C$. The tooth were sectioned perpendicular to the long axis and the dye penetration ratio to the pulp was measured. The following results were obtained. 1. All four dentin bonding agents initially showed excellent sealing ability. 2. All-bond 2, Gluma Bonding System and Superbond D-liner showed durability of dentinal tubule sealing effect after 840 strokes(6-week) artificial tooth brushing. 3. Scotchbond 2 showed a significant decrease in sealing ability after 420 strokes(3-week) artificial tooth brushing. (P<0.05).

• Journal of the Korean Society for Precision Engineering
• /
• v.15 no.11
• /
• pp.58-66
• /
• 1998

A low power consuming laser scanning vibrometer is studied for its development. For its optical system, a laser interferometer is constructed to use the Doppler effect. In order to reduce the driving power of the scanning system, a small displacement of the scanning system is produced, which is achieved by using a magnetostrictive actuator. A sufficient rotating angle of the scanning system is obtained by using an amplified displacement from the resonant phenomena of a second order mechanical system composed of a mass and spring. The control of the magnetostrictive actuator using a Terfenol-D is performed without using a feedback system to help reduce the power consumption. The vibration analysis is made for the sinusoidal scanning input to have the space domain information from the time domain of the velocity of a vibration object. As a partial work of development of a tow power consuming laser scanning vibrometer, in this work, a scanning system which has the above features is developed and experimentally investigated. For the purpose of the optical system calibration, the vibration measurement for one axis is presented and the future works are discussed.

• Journal of IKEEE
• /
• v.24 no.4
• /
• pp.954-960
• /
• 2020

This paper proposes a speed variable proportional resonant current control method for a single-phase permanent magnet synchronous motor(PMSM). Due to the electromagnetic characteristics of a single-phase PMSM, negative and zero torques are generated in the part corresponding to the phase difference between the stator current and the back electromotive force. In addition, overcurrent limitation is required because of the low stator resistance and inductance in sensorless operation. When using the vector control for current control of single-phase PMSM under these conditions, processes of coordinate transformation, inverse coordinate transformation, and generation of virtual dq-axis components are required. However, the proposed variable speed proportional resonant current control method does not need the coordinate transformation used for AC motors. In this paper, we have confirmed stable maneuverability by using variable proportional resonant current control algorithm, and proposed sensorless control based on a mathematical model of a single-phase PMSM without a position sensor when reaching a constant speed. The usefulness of the current control method was verified through several experiments.

• ETRI Journal
• /
• v.26 no.6
• /
• pp.597-604
• /
• 2004

In stereoscopic television, there is a trade-off between visual comfort and 3-dimensional (3D) impact with respect to the baseline-stretch of a 3DTV camera. It is necessary to adjust the baseline-stretch at an appropriate the distance depending on the contents of a scene if we want to obtain a subjectively optimal quality of an image. However, it is very hard to obtain a small baseline-stretch using commercially available cameras of broadcasting quality where the sizes of the lens and CCD module are large. In order to overcome this limitation, we attempt to freely control the baseline-stretch of a stereoscopic camera by synthesizing the virtual views at the desired location of interval between two cameras. This proposed technique is based on the stereo matching and view synthesis techniques. We first obtain a dense disparity map using a hierarchical stereo matching with the edge-adaptive multiple shifted windows. Then, we synthesize the virtual views using the disparity map. Simulation results with various stereoscopic images demonstrate the effectiveness of the proposed technique.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.20 no.2
• /
• pp.115-121
• /
• 2015

Stand-alone inverter supplies constant voltage to loads. However, when a three-phase stand-alone inverter supplies unbalanced load, the generated output voltages also become unbalanced. The nonlinear characteristics of inverter dead time cause a more serious distortion in the output voltage. With unbalanced load, voltage distortion caused by dead time differs from voltage distortion under balanced load. Phase voltages in the stationary reference frame include unbalanced odd harmonics and then, d-q axis voltages in the synchronous reference frame have even harmonics with different magnitude, which are mitigated by the proposed multiple resonant controller. This study analyzes the voltage distortion caused by unbalanced load and dead time, and proposes a novel dead time compensation method. The proposed control method is tested on a 10-kW stand-alone inverter system, and shows that total harmonic distortion (THD) is reduced to 1.5% from 4.3%.

• 제어로봇시스템학회:학술대회논문집
• /
• 2005.06a
• /
• pp.580-585
• /
• 2005

A QRT(Quad-Rotor Type) hovering robot system is developed for quick detection and observation of the circumstances under calamity environment such as indoor fire spots. The UAV(Unmanned Aerial Vehicle) is equipped with four propellers driven by each electric motor, an embedded controller using a DSP, INS(Inertial Navigation System) using 3-axis rate gyros, a CCD camera with wireless communication transmitter for observation, and an ultrasonic range sensor for height control. The developed hovering robot shows stable flying performances under the adoption of RIC(Robust Internal-loop Compensator) based disturbance compensation and the vision based localization method. The UAV can also avoid obstacles using eight IR and four ultrasonic range sensors. The VTOL(Vertical Take-Off and Landing) flying object flies into indoor fire spots and sends the images captured by the CCD camera to the operator. This kind of small-sized UAV can be widely used in various calamity observation fields without danger of human beings under harmful environment.

• Journal of Power Electronics
• /
• v.10 no.3
• /
• pp.313-319
• /
• 2010

This paper proposes a new compensation algorithm for the current measurement errors in a DFIG (Doubly Fed Induction Generator). Generally, current measurement path with current sensors and analog devices has non-ideal factors like offset and scaling errors. As a result, the dq-axis currents of the synchronous reference frame have one and two times ripple components of the slip frequency. In this paper, the main concept of the proposed algorithm is implemented by integrating the 3-phase rotor currents into the stationary reference frame to compensate for the measured current ripples in a DFIG. The proposed algorithm has several beneficial features: easy implementation, less computation time, and robustness with regard to variations in the electrical parameters. The effectiveness of the proposed algorithm is verified by several experiments.