• Journal of IKEEE
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• v.27 no.4
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• pp.450-455
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• 2023

Among single-phase photovoltaic inverters that can avoid excessive leakage current caused by the large parasitic capacitance of photovoltaic panels, a boost converter followed by a half-bridge inverter is the simplest and has the smallest leakage current. However, due to the high DC-link voltage, the rated voltage of the switching devices is high and the switching loss is large. This paper proposes a new circuit topology which can operate as a buck-boost inverter by adding two bidirectional switches to the output side of the half-bridge inverter instead of removing the boost converter. By reducing two stages of power conversion through the high-voltage DC-link to one stage, power loss can be reduced without increasing costs and leakage current. The feasibility of the proposed circuit topology is verified by computer simulation and power loss calculation.

• The KSFM Journal of Fluid Machinery
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• v.7 no.1 s.22
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• pp.36-44
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• 2004

Three-dimensional vortical flow and separated flow topology near the casing wall in an axial flow fan having two different tip clearances have been investigated by a Reynolds-averaged Navier-Stokes (RANS) flow simulation. The simulation shows that the tip leakage vortex formed close to the leading edge of the blade tip on suction side grows in the streamwise direction. On the casing wall, a separation line is formed upstream of the leakage vortex center due to the interference between the leakage vortex and main flow. The reverse flow is observed between the separation line and the attachment line generated downstream of the trailing edge, and increased with enlarging tip clearance. The patterns of a leakage velocity vector including a leakage flow rate are also analyzed according to two tip clearances. It is noted that the understanding of the distribution of a limiting streamline on the casing wall is very important to grasp the characteristics of the vortical flow in the axial flow fan.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.427-433
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• 2004

The effects of flow interaction between mainstream and shrouded cavity leakage flow in an axial-flow compressor on aerodynamic losses are experimentally and numerically examined. A fraction of mainstream is Ingested in the downstream cavity and travelled in the shrouded cavity along the direction opposite to the mainstream. This leakage flow is caused by adverse pressure gradient along the blade passage. Then it is entrained through the upstream cavity near mid-pitch and interacts with the mainstream. As a result, the convection flow angle with respect to the blade chord is reduced i.e. underturning This underturned flow results in an increase in size of secondary flow formed near the suction side of the blade as well as its magnitude. Consequently, this causes pronounced increase in overall aerodynamic losses compared to the blading without shrouded cavity, leading to $9\%$ decrease in pressure rise through the single stage of the stators.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.1
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• pp.38-45
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• 2000

In this research, MFL technique has been studied for the inspection of storage tank floor. The reference specimens having 20%, 40%, 60% and 80% slot's are fabricated using the carbon steel plates of a 6mm and 10mm thick. Powerful permanent magnets and Hall effect sensors are used to this application. It is shown that our system is able to detect metal loss like a slot. Also, it is possible that slot diameter is measured using transverse type of Hall generator. It is demonstrated that MFL can not differentiate between the response from top side and bottom side slot. Flux leakage response from a bottom side indication is significantly lower in amplitude than that from an equivalent top side slot. It is essential to know this sensor lift-off distance because the MFL signal also changes considerably with the sensor lift-off distance.

• Journal of Power Electronics
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• v.9 no.2
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• pp.215-223
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• 2009

A design methodology for transformers including integrated and center-tapped structures for LLC resonant converters is proposed. In the LLC resonant converter, the resonant inductor in the primary side can be merged in the transformer as a leakage inductance. And, the absence of the secondary filter inductor creates low voltage stress on the secondary rectifiers and is cost-effective. A center-tapped structure of the transformer secondary side is widely used in commercial applications because of its higher efficiency and lower cost than full-bridge structures in the rectifying stages. However, this transformer structure has problems of resonance imbalance and transformer inefficiency caused by leakage inductance imbalance in the secondary side and the position of the air-gap in the transformer, respectively. In this paper, gain curves and soft-switching conditions are derived by first harmonic approximation (FHA) and operating circuit simulation. In addition, the effects of the transformer including integrated and center-tapped structures are analyzed by new FHA models and simulations to obtain an optimal design. Finally, the effects of the air-gap position are analyzed by an electromagnetic field simulator. The proposed analysis and design are verified by experimental results with a 385W LLC resonant converter.

• Journal of the Korean GEO-environmental Society
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• v.21 no.4
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• pp.19-30
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• 2020

This numerical study is to investigate the seepage characteristics of the side of the structure in the event of leakage from the structural connection part of the drainage structure installed through the enlarged levee, and to analyze the effect of piping on the stabilization of the levee by the lateral penetration behavior. To take into account lateral seepage behavior, 2D and 3D numerical analyses were performed on the same model, and the effect of lateral seepage was analyzed to assess the validity of the numerical analysis. As a result, when leakage occurs and a lateral seepage is considered with the gate located on the riverside land, the maximum pore water pressure near the leakage point of the structure has been reduced by half compared to the normal seepage state where no leakage occurred. Excessive variation in the pore pressure was shown at the lower part of the structure, especially if lateral seepage is not considered. As a water level rises to the high water level, it shows the hydraulic gradient was larger than the critical hydraulic gradient, which will be vulnerable to long-term piping. If a gate is located in the inland and side seepage is not considered, the effect of the seepage water such as hydraulic gradient and seepage velocity is underestimated compared with the case of considering side seepage. The maximum hydraulic gradient is relatively small when lateral seepage is neglected if a gate is located in the riverside land and there was might be a risk of piping or loss of material. In addition, the period exceeding the critical hydraulic gradient was interpreted as a short time zone. As a result, it is considered that the possibility of piping can be underestimated if side seepage is ignored.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.2
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• pp.110-115
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• 2010

This study was conducted to estimate the feasibility using thermal image measurement that is applicable to internal leak diagnosis for the power plant valve. Abnormal heating of valve surface associated with high temperature steam f10w toward valve outlet side in the condition of low temperature is a primary indicator of leakage problems in high temperature and pressure valves. Thermal imaging enables to see the invisible thermal radiation that may portend impending damage before their condition becomes critical. When steam flow in valve outlet side in the condition of low temperature is converted into heat transmitted through the valve body due to the internal leakage in valve. The existence of abnormally increasable leakage rate in the valve will result in abnormally high levels of heat to be generated that can be quickly identified with a thermal image avoiding energy loss or damage of valve component. From the experimental results, it was suggested that the thermal image measurement could be an effective way to precisely diagnose and evaluate internal leak situation of valve.

• The KSFM Journal of Fluid Machinery
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• v.14 no.1
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• pp.48-54
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• 2011

The effect of channel cutback on three-dimensional flow fields and aerodynamic losses downstream of a cavity squealer tip has been investigated in a turbine rotor cascade for the squealer rim height-to-chord ratio and tip gap height-to-chord ratio of $h_{st}/c$ = 5.51% and h/c = 2.0% respectively. The cutback length-to-camber ratio is changed to be $CB/c_c$ = 0.0, 0.1, 0.2 and 0.3. The results show that longer cutback delivers not only stronger secondary flow but also higher aerodynamic loss in the tip leakage vortex region, meanwhile it leads to lower aerodynamic loss in the passage vortex region. The discharge of cavity fluid through the cutback opening provides a beneficial effect in the reduction of aerodynamic loss, whereas there also exists a side effect of aerodynamic loss increase due to local wider tip gap near the trailing edge. With increasing $CB/c_c$ from 0.0 to 0.3, the aerodynamic loss coefficient mass-averaged all over the measurement plane tends to increase slightly.

• Journal of Korean Neurosurgical Society
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• v.44 no.5
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• pp.285-294
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• 2008

Objective: Jugular foramen schwannomas are uncommon pathological conditions. This article is constituted for screening these tumors in a wide perspective. Materials: One-hundred-and-ninty-nine patients published in 19 articles between 1984 to 2007 years was collected from Medline/Index Medicus. Results: The series consist of 83 male and 98 female. The mean age of 199 operated patients was 40.4 years. The lesion located on the right side in 32 patients and on the left side in 60 patients. The most common presenting clinical symptoms were hearing loss, tinnitus, disphagia, ataxia, and hoarseness. Complete tumor removal was achieved in 159 patients. In fourteen patients tumor reappeared unexpectedly. The tumor was thought to originate from the glossopharyngeal nerve in forty seven cases; vagal nerve in twenty six cases; and cranial accessory nerve in eleven cases. The most common postoperative complications were lower cranial nerve palsy and facial nerve palsy. Cerebrospinal fluid leakage, meningitis, aspiration pneumonia and mastoiditis were seen as other complications. Conclusion: This review shows that jugular foramen schwannomas still have prominently high morbidity and those complications caused by postoperative lower cranial nerve injury are life threat.

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.4
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• pp.505-508
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• 2012

A permanent magnet flux switching (PMFS) machine has a simple rotor, whilst both magnets and coils are set in the stator, resulting in easy removal of heat due to both copper loss and eddy current loss in magnets. However, the volume of magnets used in PMFS machines is usually larger than in conventional PM machines, and leakage flux does exist at the non-airgap side. To make full use of the magnets and gain higher power density, a novel 3-dimensional (3D) field PMFS machine is developed. It combines merits of the tubular linear machine, external-rotor rotary machine and axial-flux rotary machine, hence, offers high power density and peak torque capability, as well as efficient utility of magnets owing to the unique configuration of triple airgap fields.