• Journal of Welding and Joining
• /
• v.22 no.2
• /
• pp.59-68
• /
• 2004

Plasma transferred arc welding (PTAW) has been taken into consideration for repairing Ni-based superalloy components used gas turbine blades. Various cracks has been generally reported to be found in the base metal heat affected zone(HAZ) along grain boundary. Thus, hot cracking susceptibility of Ni-based superalloys was evaluated according to heat treatments. Hot ductility test was conducted on specimens with solution treated at 112$0^{\circ}C$ for 2 hours and aging treated at 845$^{\circ}C$ for 24hours after solution treatment. The results of the hot ductility test appeared that solution treated specimens were the highest ductility recovery rate among three conditions. The loss of ductility at high temperature in Ni-based superalloy was mainly controlled by the degree of pain boundary wetting due to constitutional liquation of MC carbide precipitates. Meanwhile, the highest ductility recovery rate in solution-treated alloys seems to be lack of M23C6, which can be dissolved during heating and then result in the local enrichment of Cr in the vicinity of the grain boundary.

• Journal of Power Electronics
• /
• v.13 no.4
• /
• pp.609-618
• /
• 2013

This paper proposes a primary side constant power control scheme for TRIAC dimmer compatible LED drivers. The LED driver is a Flyback converter operated in boundary conduction mode (BCM) to minimize the switching loss. With the proposed control scheme, the input power of the Flyback converter can be controlled by the TRIAC dimming angle, which is not affected by AC input voltage variations. Since the output voltage is almost constant for LED loads, the output current can be changed by controlling the input power with a given conversion efficiency. The isolated feedback circuit is eliminated with the proposed primary side control scheme, which dramatically simplifies the whole circuit. In addition, the input current automatically follows the input voltage due to the BCM operation, and the resistive input characteristic can be achieved which is attractive for TRIAC dimming applications. Experimental results from a 15W prototype verify the theoretical analysis.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2015.08a
• /
• pp.104-104
• /
• 2015

Due to the demand of the cold neutron flux in the neutron science and beam utilization technology, the cold neutron source (CNS) has been constructed and operating in the nuclear research reactor all over the world. The majority of the heat load removal scheme in the CNS is two-phase thermosiphon using the liquid hydrogen as a moderator. The CNS moderates thermal neutrons through a cryogenic moderator, liquid hydrogen, into cold neutrons with the generation of the nuclear heat load. The liquid hydrogen in a moderator cell is evaporated for the removal of the generated heat load from the neutron moderation and flows upward into a heat exchanger, where the hydrogen gas is liquefied by the cryogenic helium gas supplied from a helium refrigeration system. The liquefied hydrogen flows down to the moderator cell. To keep the required liquid hydrogen stable in the moderator cell, the CNS consists of an in-pool assembly (IPA) connected with the hydrogen system to handle the required hydrogen gas, the vacuum system to create the thermal insulation, and the helium refrigeration system to provide the cooling capacity. If one of systems is running out of order, the operating research reactor shall be tripped because the integrity of the CNS-IPA is not secured under the full power operation of the reactor. To prevent unscheduled reactor shutdown during a long time because the research reactor has been operating with the multi-purposes, the introduction of the standby cooling system (STS) can be a solution. In this presentation, the design considerations are considered how to design the STS satisfied with the following objectives: (a) to keep the moderator cell less than 350 K during the full power operation of the reactor under loss of the vacuum, loss of the cooling power, loss of common electrical power, or loss of instrument air cases; (b) to circulate smoothly helium gas in the STS circulation loop; (c) to re-start-up the reactor within 1 hour after its trip to avoid the Xenon build-up because more than certain concentration of Xenon makes that the reactor cannot start-up again; (d) to minimize the possibility of the hydrogen-oxygen reaction in the hydrogen boundary.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.19 no.9
• /
• pp.876-883
• /
• 2009

The radiation of sound from a rectangular plate with a guided edge condition is investigated. By taking this particular boundary condition into account, simple analytical forms of the average radiation efficiency and radiation power based on the modal approach can be found, where the cross-modal terms can average out for all possible point excitation locations. Design variables of the plate such as thickness, aspect ratio, and damping that are closely related to the sound radiation are mainly discussed. The radiation power of the guided plate is found to be governed by the piston mode as well as the critical frequency. While both the radiation efficiency and the radiation power seem to be influenced by thickness and a large aspect ratio, damping loss factor seems less important to the radiation power. It is also shown that no clear corner and edge mode regions may be found for the guided case, unlike the pinned.

• Ocean Systems Engineering
• /
• v.2 no.2
• /
• pp.147-158
• /
• 2012

A time-domain simulation of a land-based Oscillating Water Column (OWC) with various irregular waves as a form of PM spectrum is performed by using a two-dimensional fully nonlinear numerical wave tank (NWT) based on the potential theory, mixed Eulerian-Lagrangian (MEL) approach, and boundary element method. The nonlinear free-surface condition inside the OWC chamber was specially devised to describe both the pneumatic effect of the time-varying pressure and the viscous energy loss due to water column motions. The quadratic models for pneumatic pressure and viscous loss are applied to the air and free surface inside the chamber, and their numerical results are compared with those with equivalent linear ones. Various wave spectra are applied to the OWC system to predict the efficiency of wave-energy take-off for various wave conditions. The cases of regular and irregular waves are also compared.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1999.11a
• /
• pp.350-353
• /
• 1999

This Paper Presents the optimized design of micro-heaters using 501(Si-on-insulator) substrate and oxide-filled trench structure In order to justify a lumped model approximation and thermal boundary assumptions, two-dimensional FDM(finite difference among which conduction is the dominant heat dissipation path. Compared with no-trenchs on the SOI structure, the micro-heaters with trench structures has properties of low heater loss and good thermal isolation. The simulation results show that the heater loss decreases as the number. width and distance of trenchs increases.

• Journal of Drive and Control
• /
• v.11 no.2
• /
• pp.30-35
• /
• 2014

The pumps of electro-hydrostatic actuators operate most frequently in boundary lubrication speed range, as they compensate for the position control errors as a control element. When conventional swash plate type piston pumps are applied to electro-hydrostatic actuators, the frictional power losses as well as the wear rate of sliding components, such as piston shoes can increase drastically under the boundary friction condition. In this paper, the power losses of the piston shoes were investigated which were engendered by a frictional solid-to-solid contact and leakage flow rate of their hydrostatic bearing. In order to reduce them, DLC-coating was applied to the swash plate and the ball joint of pistons along with its effects were demonstrated. In addition, it was also shown that the wear rate of the piston shoes could be markedly reduced using the DLC-coated swash plate.

• Journal of Drive and Control
• /
• v.12 no.4
• /
• pp.48-53
• /
• 2015

This paper deals with the flow characteristics of a reed valve analyzed using computational dynamics(CFD) for optimal design. The seat sizes of the valve are modeled asØ6[mm] and Ø8[mm] to compare the flow characteristics. The inlet boundary condition is entered at 10[kPa], 15[kPa], 20[kPa], and 30[kPa] and the outlet boundary condition is set to the atmospheric pressure. The flow coefficient(C) and pressure loss coefficient(K) are calculated from the results of flow analysis. From the analysis results, it was confirmed that the flow coefficient of a reed valve having a seat size of Ø6[mm] is greater than that having a seat size of Ø8[mm], and the coefficient of pressure loss of a valve with a seat size of Ø6[mm] is lower than the Ø8[mm] size valve.

• Journal of the Korean Society for Precision Engineering
• /
• v.34 no.4
• /
• pp.287-292
• /
• 2017

A gas turbine is the main equipment used in a combined heat and power plant. It generates a high sound pressure noise level. To reduce the noise level, an enclosure is installed around the turbine. The sound insulation performance of the enclosure affects the amount of external noise reduction. In this study, a sound transmission loss analysis is performed using the boundary element method to predict sound insulation performance according to the numbers and shapes of the supporter. Radiated noise analysis is also performed for the main external points of the enclosure using ray-acoustics. The results of these analyses are presented and a design plan is proposed that reduces the sound pressure noise level of the enclosure.

• Journal of the Society of Naval Architects of Korea
• /
• v.42 no.1 s.139
• /
• pp.1-9
• /
• 2005

Waterjet propulsion is widely used to thrust high speed marine vessels in excess of 30-35 knots by virtue of the high propulsive efficiency, good maneuverability, and less cavitation. From the aspect of power loss, approximately $7-9\%$ of the total power is lost in intake duct due to the flow separation, nonuniformity, etc. Thus, detail understanding of flow phenomena occurring within intake duct is essential to reduce the power loss, as well as noise and vibration. The present work solved 30 incompressible RANS equations to provide complicated viscous flow features of intake duct. The numerical results were compared with experiments and good agreements were obtained for three jet velocity ratios.