• Proceedings of the KIEE Conference
• /
• 2015.07a
• /
• pp.1050-1051
• /
• 2015

In industry, there are several different controllers which can be implemented for power conditioning systems (PCS) such as proportional-resonant (PR), predictive deadbeat (PD), or proportional-integral (PI) controller. But there are not any comparison studies about these controllers. To investigate the differences between the three types of the controllers, this paper presents a comparative study of PR, PI, and PD controllers in a photovoltaic (PV) PCS. These controllers are designed mathematically and simulated for the comparative analysis. The PI controller is designed in the rotating reference (dq) frame. The PR and PD controllers are implemented in the natural (abc) reference frame. The PCS is composed of a DC-DC boost converter and a full bridge inverter. The filter of the PCS is an LCL filter including a passive damping resistor. The parameters of PCS are 3 kW, 25 kHz switching frequency and 220 V-60 Hz grid voltage. The comparison results between these controllers for the grid-connected PCS are clearly shown. The simulation results demonstrate the detailed characteristics of each controller for the PV PCS in order to choose the controller for individual target properly.

• Journal of the Korean Society of Safety
• /
• v.32 no.2
• /
• pp.1-6
• /
• 2017

Modern society has been experiencing by population growth and urbanization that bring, a change of eating habits which has occurred a various types of waste in a large amount. Even though these wastes are required an immediate treatment with difficulties unsanitary handling and existing waste treatment method are by incineration, fermentation, drying and etc. however a bad smell occurs after the treatment that need's a lot of energy in processing organic wastes with high moisture contents and wasteful and inefficient problem. The strength assessment of the organic waste agitating vessel is required in terms of safety due to the differences of loading on the shaft that was treated by agitating the mixture of food waste. The damage of agitating axis is depended on steam pressure, temperature condition and the force moment that exerted by the food waste. Thus the strength assessment and stability evaluation are very important, especially to handle a hard waste. In this study the rotation capacity of agitation is about 5 tons considering general structural rolled steel pressure vessel strength and steam pressure. The purpose is to estimate the safety and strength evaluation for a agitator axis and impellers according to the rotating angle of the axis under the condition of the 3.2 ton capacity reactor.

• Journal of computational fluids engineering
• /
• v.21 no.3
• /
• pp.24-30
• /
• 2016

In the water purification plant, the mixture of water and chemical from the mixing basin enters the flocculation basin. The rotating flocculators are generally used for the efficient flocculation of dregs. In this paper, the performance of flocculators of a vertical paddle type, widely used in the typical flocculation basins, and a hydro-foil type, recently disseminated in the field, are compared with each other by use of the numerical method. Also the characteristics and the efficiency are analyzed with CFD techniques. The strain rate and the eddy viscosity are compared for two types to predict the mixing efficiency, and the maximum speed and its location are pursued from the computed data. The hydrofoil type shows that the eddy viscosity is enhanced 1.66 to 3.03 times larger than that of vertical paddle type, and also produced 1.87 to 1.95 times larger flocs for each stage. However, the rapid rotation of hydrofoil may chop the floc to small size due to the higher turbulence intensity. From the result of computation, the strong and weak points of each type have been analyzed for the decision making.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.28 no.5
• /
• pp.612-618
• /
• 2004

Stereoscopic PIV measurements were made in the wind tunnel with the actual size waterjet model. The main wind tunnel provides the vehicle velocity while the secondary wind tunnel adjusts the jet issuing velocity. Experiments were performed at the range of jet to vehicle velocity ratio (JVR), 3.75 to 8.0 and the Reynolds number of 220,000 based on the jet velocity and the hydraulic diameter of the waterjet intake duct. Wall pressure distributions were measured for various JVRs. Three dimensional velocity fields were obtained at the inlet and outlet of the intake duct. It is found that severe acceleration is occurred at the lip region while deceleration is noticeable at the ramp side. The detailed three dimensional velocity fields can be used as the accurate velocity input for the CFD simulation. It is interesting to note that there are many different types of vortices in the instantaneous velocity field. It can be considered that those vortices are generated by the corner of rectangular section of the intake and Gortler vortices due to the curved wall. However, typical secondary flow with a pair of counter rotating vortex pair is clearly seen in the ensemble averaged velocity field.

• Journal of Advanced Marine Engineering and Technology
• /
• v.31 no.8
• /
• pp.961-969
• /
• 2007

The laser material processing has replaced a conventional material processing such as a welding, cutting, drilling and surface modification and so on. LTH(Laser Transformation Hardening) is one branch of the laser surface modification process. A lot of energy is needed for the LTH process to elevate workpiece surface to temperature of the austenite transformation($A_3$), which results from utilizing a beam with a larger size and lower power intensity comparatively. The absorptivity of the laser energy with respect to material depends on the wave length of a beam. This study is related to the surface hardening for the rod-shaped carbon steel by the high power diode laser(HPDL) whose beam absorptivity is better than conventional types of lasers such as $CO_2$ or Nd:YAG laser. Because a beam proceeds on the rotating specimen the pretreated hardened-phase can be tempered and softened by the overlapping between hardened tracks. Accordingly, the longitudinal hardness measurement and observation of the micro structure was carried out for an assessment of the hardening characteristics. In addition, a hardening characteristics as a hardenability of materials was compared in the point of view of the hardness distribution and hardening depth and width.

• 유체기계공업학회:학술대회논문집
• /
• 2005.12a
• /
• pp.776-781
• /
• 2005

Cavitation is the most serious problem caused in developing high-speed turbopump, and use of an inducer is often made to avoid cavitation in main impeller. Thus, the inducer always operates under the worst condition of cavitation. If it could be possible to control and suppress cavitation in the inducer by some new device, it would also be possible to suppress cavitation occurring in all types of pumps. The purpose of our present study is to develop a new effective method of controlling and suppressing cavitation in an inducer using shallow grooves, named as "J-Groove", J-Groove is installed on the casing wall near the blade tip to use the pressure difference between high pressure region and low pressure region in the axial direction at the inlet of the inducer. The results show that proper combination of backward-swept inducer with J-Groove improves suction performance of turbopump remarkably in the range of partial flow rate as well as designed flow rate. The rotating backflow cavitation occurring in the range of low flow rate and the cavitation surge occurring in the vicinity of the best efficiency point can be almost fully suppressed by installing J-Groove.

• Tribology and Lubricants
• /
• v.30 no.2
• /
• pp.116-123
• /
• 2014

The objective of this study is to model and simulate the nonlinear lubrication performance of the sliding part between the piston and cylinder wall in a hydrostatic swash-plate-type axial piston pump. A numerical algorithm is developed that facilitates simultaneous calculation of the rotating body motion and fluid film pressure to observe the fluid film geometry and power loss. It is assumed that solid asperity contact, so-called mixed lubrication in this study, invariably occurs in the swash-plate-type axial piston pump, which produces a higher lateral moment on the pistons than other types of hydrostatic machines. Two comparative mixed lubrication models, rigid and elastic, are used to determine the reaction force and sliding friction. The rigid model does not allow any elastic deformation in the partial lubrication area. The patch shapes, reactive forces, and virtual local elastic deformation in the partial lubrication area are obtained in the elastic contact model using a simple Hertz contact theory. The calculation results show that a higher reaction force and friction loss are obtained in the rigid model, indicating that solid deformation is a significant factor on the lubrication characteristics of the reciprocating piston part.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.17 no.2 s.119
• /
• pp.105-113
• /
• 2007

In this study, three-dimensional rotordynamic analyses have been conducted using equivalent beam, hybrid and full three-dimensional models. The present computational method is based on the general finite element method with rotating gyroscopic effects of the rotor system. General purpose commercial finite element code, SAMCEF which includes practical rotordynamics module with various types of rotor analysis tools and bearing elements is applied. For the purpose of numerical verification, comparison study for a benchmark rotor model with support bearings is performed first. Detailed finite element models based on three different modeling concepts are constructed and then computational analyses are conducted for the realistic and complex three-dimensional rotor system. The results for rotor stability and mass unbalance response are presented and compared with the experimental vibration test data conducted herein.

• Laser Solutions
• /
• v.11 no.4
• /
• pp.7-12
• /
• 2008

Laser Transformation Hardening(LTH) is one branch of the laser surface modification processes. A lot of energy is needed for the LTH process to elevate workpiece surface to temperature of the austenite transformation($A_3$), which results from utilizing a beam with a larger size and lower power density comparatively. This study is related to the surface hardening for the rod-shaped carbon steel by the high power diode laser whose beam absorptivity is better than conventional types of lasers such as $CO_2$ or Nd:YAG laser. Because a beam proceeds on the rotating specimen, the pretreated hardened-phase can be tempered and softened by the overlapping between hardened tracks. Accordingly, the longitudinal hardness measurement and observation of the micro structure was carried out for an assessment of the hardening characteristics. In addition, a hardening characteristics as a hardenability of materials was compared in the point of view of the hardness distribution and hardening depth and width.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.48 no.3
• /
• pp.192-199
• /
• 1999

During start up and shut down, the generator is rotating at a low speed and copper dusts cause arcing between the turns in the slot. Shorted turns occurred primarily by the movement of these copper dusts between individual windings in the generator rotor. Detection of shorted turns was performed in five gas turbine generators in two combined cycle power plants. Two types of permanent and temporary flux probes were used in this paper. These flux probes have been used to develop a methodology for detecting shorted turns in an operating generator's rotor. The flux probes sense the rotor winding slot leakage flux and produce a voltage proportional to the rate of change of the flux. This pattern of flux variation is the signature unique to each rotor winding. An appropriate waveform analysis technique canidentify the pole location, the slot number, and the number of shorted turns within each slot. Shorted turns in field winding of gas turbine generator(125.7 MVA) were detected to twelve turns on al total 190 turns.